Symposium ES04—Solid-State Electrochemical Energy Storage

The all-solid-state lithium battery offers an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Among the lithium ion conductors proposed for the solid electrolytes, the sulphide LGPS (Li₁₀GeP₂S₁₂) type system is a candidate because of its extreme high bulk ionic conductivity of over 10^-2S cm^-1at room temperature. To provide the electrolytes suitable for practical usage of the solid-state battery, electrochemical and chemical stabilities are important parameters besides the ionic conductivity. Composition varieties of the LGPS type materials provide suitable combinations of the electrodes and the electrolyte. Based on the host compositions ofLi₁₀GeP₂S₁₂, various cation and anion substitutions were examined, and their structures, conduction mechanism and chemical/electrochemical stability will be discussed.

In the period 1967-1975, substituted beta aluminas [MAl₁₁O₁₇] were the subject of extensive study. These studies identified several key parameters that control the ionic conductivity of such ions as Na⁺, Ag⁺, Cu⁺, Li⁺, K⁺, Tl⁺and NO⁺. These parameters include the ionic size, the lattice spacing (diffusion path size), the defect concentration, defect type and diffusion mechanism. Later, similar studies on the WO₃, MoO₃, TiO₂ and VOPO₄ materials, all of which exist in several different structures with varying molar volumes, show the criticality of matching the diffusion path size to the mobile cation. The learnings from these studies will be described.

Solid state batteries with alkali metal anodes promise to deliver higher energy densities than conventional Li-ion batteries. However, alkali metal dendrite growth, even at modest rates and even when paired with dense, well-sintered solid electrolytes, leads to short circuits and cell failure. We have investigated the effect of cycling conditions on the formation of dendrites under controlled applied pressure. The results reveal the significance of plating/stripping current densities on cell failure. These results and their implications for the operation of a failure free all-solid-state battery will be discussed.

Sulfur-based glasses have reemerged as promising candidates for use as solid electrolytes in Li-based batteries. Nevertheless, due to their amorphous structure, the ion migration mechanisms that underlie their high Li-ion conductivity remain poorly understood. The present study employs ab initio molecular dynamics to reveal the local structure and migration mechanisms in the prototype Li-ion conducting glass, 0.75 Li₂S- 0.25 P₂S₅. A computational model of the amorphous structure was generated, and is shown to closely match the measured neutron weighted pair distribution. The structure data indicates that Li-ions experience a range of coordination environments, with typical Li-S coordination numbers between 3 to 5. Lithium is observed to migrate via correlated, 'string-like' events involving multiple adjacent cations. Furthermore, these migration events involve the dynamic participation of the PS₄anions, which undergo simultaneous rotation and translational displacements. This behavior contrasts with that of the Li₃PS₄ crystalline analogue, were rotations and translations of the anions during migration events are severely limited. These observations provide direct evidence of the importance of anion dynamics on cation mobility in fast ion conductors.

Since the inception of scanning tunneling microscopy [1], electrochemists have sought to take advantage of scanned probe microscopy techniques to manipulate the spatial position of a probe with high resolution to facilitate simultaneous high resolution topographical, conductometric, and amperometric/voltammetric imaging of surface and interfaces. Lately, scanning ion conductance microscopy (SICM) [2], has emerged as a versatile non-contact imaging tool and been employed for a variety of applications. SICM has been used to investigate the surface topography of both synthetic and biological membranes, ion transport through porous materials, dynamic properties of living cells, and suspended artificial black lipid membranes. In addition, integration of complementary techniques with SICM has led to many exciting new applications, including scanning near-field optical microscopy and patch-clamping [3]. Powerful as it is, SICM remains insensitive to electrochemical properties, or, in other word, SICM is inherently chemically-blind and has no chemical specificity.
To obtain spatially-resolved electrochemical information, scanning electrochemical microscopy (SECM), also known as the chemical microscope, has been developed. SECM has been widely employed to examine localized electrochemical properties and reactivity of various materials/interfaces, such as electrode surfaces and interfaces, membranes [4], and biological systems. Despite its many applications, SECM, however, lacks reliable probe-sample distance control, and the probe is usually kept at a constant height during conventional SECM scanning. As a result, any variation in surface topography will result in changes in probe-sample distance, and thus leading to convolution to the measured faradaic current, which will complicate the subsequent data interpretation [4].
To address the above-mentioned issues for SICM and SECM, hybrid SICM-SECM techniques have been developed, in which the SICM compartment provides the accurate probe-sample distance control, while the SECM compartment measures the faradaic current for electrochemical information collection.
In this work, we demonstrate the use of an AFM (Park NX10) in combination with an ammeter for concurrent topography imaging and electrochemical mapping. The SICM-SECM probe utilized here consisted of a Au crescent electrode (AuE) on the peripheral of a nanopipette. High resolution probe-substrate distance control was obtained by the ion current feedback from SICM, while simultaneous electrochemical signal collection was achieved via the AuE from SECM. As a proof-of-concept experiment, a Au/Pyrex pattern standard sample was imaged with the SICM-SECM technique. The Au bar and the Pyrex substrate were clearly resolved from the SICM topography image, with the bar height and pitch width closely matching the actual values. In terms of the electrochemical property mapping, higher Faradaic current was seen when the probe was scanned over Au bar as a result of redox cycling, while lower Faradaic current was observed when the probe was over Pyrex substrate due to hindered diffusion. The capability of the SICM-SECM technique described here holds promise of many exciting applications in the field of electrochemistry, material science and battery research.

[1] Binnig, G., Rohrer, H., Gerber, C. and Weibel, E., Tunneling through a controllable vacuum gap. Appl. Phys. Lett., 1982, 40, 178-180..
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[3] Shi, W., Zeng, Y., Zhou, L., Xiao, Y., Cummins, T.R. and Baker, L.A., Membrane patches as ion channel probes for scanning ion conductance microscopy. Faraday discussions, 2016, 193, 81-97.
[4] Shi, W. and Baker, L.A., Imaging heterogeneity and transport of degraded Nafion membranes. RSC Adv., 2015, 5, 99284-99290.

Basic understanding of ionic conductivity is critical to the development of new technologically strategic solid electrolytes. Ionic conduction is fundamentally rooted in transforming vibrational thermal energy into diffusive atomic motion. While methods such as molecular dynamics (MD) can simulate the process accurately computationally, understanding of the process remains rooted in models employing either a harmonic vibrational or quasi-liquid model of the mobile ion. We propose to develop a model of ionic conductivity through the lens of anharmonic lattice dynamics. As a prototypical case we consider superionic AgI, with Ag conductivity > 1 S/cm at 150°C and activation energy of ~0.1 eV. While the Raman spectrum of this material has been studied for decades, using Raman crystallography at low wavenumbers we reveal a novel picture of vibrational motion in superionic AgI: The Raman spectrum in the superionic phase at 170°C is dominated by two first-order modes of symmetry E_g and T_2g and a central peak arising from motion with no restoring force. The mode symmetries confirm the accepted structural model of Ag occupying tetrahedral sites and indicate that mobile Ag participates in these modes. The very low phonon lifetimes (~100 fs) of the observed modes and pronounced central peak indicate the presence of strong anharmonicity. The vibrational power spectrum from MD simulations indicates that Ag motion contributes strongly to the observed central peak, and that both I and Ag display strong motion at the frequencies of the observed modes. From these results we hypothesize that anharmonic nuclear motion of both the mobile ion and host lattice is an important factor in ionic conductivity, and possible mechanisms will be discussed.

The ion transport kinetics in solid electrolytes is believed to be highly sensitive to the topological characteristics of ion conduction pathways. The conduction mechanisms usually involve concurrent ionic diffusion along a variety of mesoscopic features of internal microstructures such as bulk grain, structural domains, and associated boundaries as well as their network. In addition, inhomogeneous elastic interactions within the electrolyte microstructures are non-trivially coupled with ionic diffusion mechanisms. Due to the complexity of these structural features of the solid electrolytes during operation, it is significantly challenging to experimentally characterize the microstructure-ionic diffusion property relationship. For better mechanistic understanding of relevant conduction mechanisms, it is necessary to thoroughly explore the impacts of individual microstructural factors on the overall kinetic properties and performances. In this talk, we will present our development of an efficient mesoscopic computational method for extracting the effective diffusivity of the solid electrolyte containing arbitrarily distributed microstructural inhomogeneities (e.g., differently oriented multiple grains, several structural variants of phase domains, and grain/domain boundaries) and their elastic interactions with Li conduction. Using three-dimensional digital microstructures generated by phase-field simulations as well as the fundamental diffusivity tensors of reference phases and boundaries derived from atomistic calculations as inputs, the developed method enables us to efficiently compute the effective ionic diffusivity tensor of the entire system. We will then discuss the applications of this framework to investigating the relationship between relevant individual microstructural features and effective diffusivity of highly conductive solid electrolytes (e.g., LLTO and LLZO) focusing on the impacts of topological features of grains, internal mesoscopic structures of high- and low-temperature phase domains, and grain/phase boundary networks.


This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The correlation between the pre-exponential factor and the activation energy in the Arrhenius equation, variously known as compensation law or Meyer-Neldel rule, is ubiquitous in almost all physical/chemical systems whose kinetic is thermally activated. In this talk, we focus specifically on the origin of Meyer-Neldel rule observed in solid-state Li-ion conductors by systematically investigating the ionic conductivity in the model system Li₃PO₄-Li₃VO₄-Li₄GeO₄. We found that the activation energies and pre-exponential factors exhibit a strong correlation as expected from Meyer-Neldel rule. However, the series of compound with and without partial lithium occupancy were shown to fall into two distinct lines with similar slopes but different intercepts. By combining the microscopic model of diffusion with multi-excitation entropy theory, we were able to relate the slope to the inverse of the energy scale associated with phonon in the systems and the intercept to the Gibbs free energy of defect formation. Compiled data of pre-exponential factor and activation energy for commonly studied Li-ion conductors shows that this correlation is very general, implying an unfavorable trade-off between high pre-exponential factor and low activation energy needed to achieve high ionic conductivity. Understanding the circumstances under which this correlation can be violated might provide a new opportunity to further increase the ionic conductivity in Li-ion conductors.

Solid-state batteries are garnering significant interest for their potential to double energy density compared to conventional Li-ion technology. By supplanting liquid Li-ion electrolytes with solid-state electrolyte, physical stabilization of the Li interface during cycling may be achieved. Replacing graphitic anodes with Li metal would push energy density to > 1000 Wh/L at the cell level. However, despite all the progress made in developing fast-ion conducting and stable solid-state electrolytes, relatively little is known about the mechanical and physical properties of metallic Li. The purpose of this paper is to provide a perspective on the significance of Li mechanical properties. How to engineer battery packs with cells that change thickness +/- 10% with every cycle? How can relatively soft Li penetrate hard ceramic electrolytes? How to address Li flow under pressure? These are some of the answers that should be addressed as solid-state battery technology matures. This paper will present recent efforts to characterize the elastic, plastic, and creep properties of Li metal. The implications of some of these findings may impact approaches to design solid-state batteries using Li metal anodes.

The most widely studied sulfide-based solid electrolytes are P2S5-Li2S glasses and their analogs, which show conductivity as high as 10-3 S/cm. However, due to the volatibility of P2S5, the atmospheric pressure synthesis method of P2S5-Li2S was limited to the high energy plenary milling, as a result, scientists started to investigate the ionic conductive glasses based on SiS2 1, because the utilize of SiS2 as a glass former allow more flexibility in synthesis technique.
In 1985, Kennedy et al. first reported on Li2S-SiS2 based sulfide and their analogs with LiI and LiBr, which exhibited high lithium ion conductivity on the order of 10-4 S/cm at room temperature 2. Kondo et al, developed a Li3PO4-dooped Li2S-SiS2 glassy system, which exhibited superior electrochemical properties such as stability in contact with lithium 3. Tatsumisago et al. have reported a variety of oxy-sulfide glasses in the systems Li2S-SiS2-LixMOy with high conductivity and stability against crystallization 4. However, to the best of our knowledge, none of the studies have investigated the critical current density and the cyclibility of the glass solid electrolyte material when cycling pure lithium metal, and those important properties of the SiS2 based glasses as a solid electrolyte is still unknown.
In this work, we demonstrate three glass systems with SiS2 as a glass former. First, Li2S-SiS2-P2S5 glass system was synthesized by mechanical milling and the mix glass former effect was investigated, the material were characterized using XRD, Raman and NMR, and tested in symmetric cells with lithium metal as electrodes. Next, to improve the glass stability in contact with lithium, Li2S-SiS2-P2O5 glass was made and tested in symmetric cells for electrochemical impedance spectroscopy and cycling, to address the high solid-solid interfacial resistance and short-circuiting dendrite problems, we demonstrate a simple strategy to engineer the lithium-GSE interface by forming an in-situ interlayer via a heat treatment. Then, LiI doped Li2S-SiS2-P2S5 was made by melt-quenching technique and superior electrochemical properties were observed. These results provide a promising group of glass with SiS2 as glass former that can be applied to lithium metal battery and other energy storage application as solid-state electrolytes.

1. Kennedy JH. Ionically conductive glasses based on SiS2. Mater Chem Phys. 1989;23(1-2):29-50. doi:10.1016/0254-0584(89)90015-1.
2. Sahami S, Shea SW, Kennedy JH. Preparation and Conductivity Measurements of SiS2-Li2S-LiBr Lithium Ion Conductive Glasses. J Electrochem Soc. 1985:985-986.
3. Aotani N, Iwamoto K, Takada K, Kondo S. Synthesis and electrochemical properties of lithium ion conductive glass, Li3PO4-Li2S-SiS2. Solid State Ionics. 1994;68(1-2):35-39. doi:10.1016/0167-2738(94)90232-1.
4. Hayashi A, Yamashita H, Tatsumisago M, Minami T. Characterization of Li2S-SiS2-LixMOy(M=Si, P, Ge) amorphous solid electrolytes prepared by melt-quenching and mechanical milling. Solid State Ionics. 2002;148(3-4):381-389. doi:10.1016/S0167-2738(02)00077-2.

Sodium based thio-phosphate glasses exhibit extraordinarily high ionic conductivities, and have received a lot of attention as potential electrolyte materials in solid state batteries. However due to the poor chemical and electrochemical stability of sulfide materials efforts have been made to improve these properties though the incorporation of oxygen. The short-range order (SRO) structures of glasses in the Na₄P₂S _(7-x)O_(x), 0 ≤ x ≤ 7 system were investigated on samples prepared by melt quench technique. The short range order (SRO) structure of the glasses were characterized using FT-IR, Raman and ³¹P Magic Angle Spinning NMR (MAS NMR) spectroscopies to identify the role of oxygen in the glass structure. Evidence suggests that the addition of oxygen causes a disproportionation reaction to occur in the structure though the formation of mixed oxy-sulfide tetrahedra. These units allow for greater uptake of sodium ion to the system leading to a large change in the physical properties, most notably in ionic conductivity.

All solid state batteries in principle allow for a reduction of the net weight and volume of the battery, greater energy output, and better ion transport while affording small self-discharge, minimal wear and tear, and a more uniform output voltage [1]. Materials that can reversibly store Li/Li⁺ to create capacity are potentially good anode materials, among which lithium metal offers a particularly high theoretical specific capacity, though lithium metal in contact with liquid electrolytes often leads to formation of high surface area metallic lithium structures upon repeated charge and discharge [2]. Solid electrolytes can be made compatible with lithium metal and allow to almost suppress lithium deposits rendering them a viable alternative, including advantages in terms of mechanical stability, operational safety and simplicity of cell design [3]. Solvent-free electrolytes require further improvement of achievable lithium ion conductivities at ambient temperatures, e.g. via design of nanostructures that facilitate directional pathways for Li⁺ ion transport [4]. Polyrotaxane and ethylene oxide (EO) based polymer electrolytes exhibiting impressive ionic conductivities and excellent oxidation stability at potentials higher than 5.5 V vs. Li/Li⁺ will be discussed, highlighting interesting characteristics in terms of specific capacity, cycle life and Coulombic efficiency. In addition, Polysulfonamide based single ion conducting blend polymers that other than dual ion conducting electrolytes offer excellent transference numbers will be considered. The polymer blend electrolyte has superior oxidative stability and long-term stability against lithium metal, hence enabling operation in Li(Ni_1/3Mn_1/3CO_1/3)O₂/ lithium metal cells at 20 °C and 60 °C, respectively [5]. Moreover, considerable improvements of sulfidic-based ceramic electrolytes will be discussed in view of challenges associated with materials processing and reproducibility aspects, in this way providing a reasonable basis for systematic exploration of electrode/electrolyte interfaces.

[1] Kim, J. G.; Son, B.; Mukherjee, S.; Schuppert, N.; Bates, A.; Kwon, O.; Choi, M. J.; Chung, H. Y.; Park, S., J. Power Sources 2015, 282, 299-322.
[2] Ryou, M.H.; Lee, Y. M.; Lee, Y.; Winter, M.; Bieker, P., Adv. Funct. Mater. 2015, 25, 834-841.
[3] Long, L.; Wang, S.; Xiao, M.; Meng, Y., J. Mater. Chem. A 2016, 26, 10038-10069.
[4] Imholt, L.; Dörr, T. S.; Zhang, P.; Ibing, L.; Cekic-Laskovic, I.; Winter, M.; Brunklaus, G., J. Power Sources 2018, https://doi.org/10.1016/j.jpowsour.2018.08.077
[5] Borzutzki, K.; Thienenkamp, J.; Diehl, M.; Winter, M; Brunklaus, G., J. Mater. Chem. A 2018, in press

I will start by giving an overview of active research activities in my research group located at University of Maryland Energy Research Center, including wood materials toward sustainability, 3000K high temperature materials and processing (Science 2018), wood nanotechnologies (Nature 2018), beyond-Li ion batteries (solid state, Na-ion). Then I will focus on our recent development on garnet-based solid-state Li-metal batteries including interface engineering to improve the wetting between Li metal anode and Garnet solid-state electrolyte (Nature Materials 2016; Advanced Materials 2017; Science Advances 2017); Garnet based 3D Li ion conductive framework (bilayer, trilayer) toward high energy density Li-S batteries (EES 2017); Garnet nanofiber based flexible, hybrid electrolyte with a high Li ion conductivity (PNAS 2016), and In-situ neutron depth profiling technique in understanding Li-garnet and CNT-garnet interfaces (JACS 2016).

Solid electrolytes have been successfully developed for use in high temperature energy devices, e.g., Yttria stabilized zirconia (YSZ) as oxide ion conductors in solid oxide fuel cells operating at ~800^oC, and sodium b”-alumina solid electrolyte in Na-S and Na-Metal chloride (Zebra) batteries operating at 300-400^oC. Excellent performance and lifetimes have been demonstrated in these devices. The b”-alumina solid electrolyte separator enabled successful implementation of molten anode and cathodes in Na-S cells, and with a molten salt electrolyte for the Zebra batteries, without the issues of any (Na) dendrites during cycling. Development of room temperature Li⁺-conducting solid electrolytes has been the topic of intense research in the last few years, mainly guided by the potential to replace the flammable organic electrolytes in current Li-ion cells for enhanced safety. Additionally, these solid electrolytes can improve energy characteristics beyond the current Li-ion cells with the use of Li anode and high voltage cathodes. A noteworthy success was reported by Bates et al with a new solid electrolyte, LiPON (Lithium Phosphorus Oxynitride), which has a moderate ionic conductivity of 10^-6 S/cm at 25^oC, but impressive interfacial stability against Li and cathodes.¹ One difficulty with this material is its method of synthesis, i.e., reactive sputtering directly on cathode layers, which is not amenable for scale up. At JPL, we utilized this electrolyte in the development of micro-batteries with Li/LiCoO₂ cells and demonstrated excellent cycle life at ambient temperatures² and also at high temperature with cells fabricated by Front Edge Technologies.
The search for new Li⁺-solid electrolytes has proceeded more rapidly in recent years, with improved conductivity of some of the recent systems, approaching and even surpassing that of liquid electrolytes. Room temperature conductivities of around 1 mS cm⁻¹ have been shown in lithium garnet oxides.^3,4 These systems typically require co-sintering to obtain good contact between the electrode and electrolyte, which is important for battery performance. More recently, new sulfide superionic conducting materials have emerged with higher conductivities and with mechanical properties amenable for better physical contact with electrodes. These include Li₁₀ GeP₂S₁₂ (LGPS), with a conductivity of 12 mS/cm at 25^oC,⁵ and Li₇P₃S₁₁, a glass-ceramic with a conductivity of 27 mS/cm at 25^oC.⁶ The challenges associated with these high conductivity solid electrolytes are; i) Poor interfacial stability of almost all the solid electrolytes towards Li or cathode materials, which warrants intermediate buffering layers (e.g., Al₂O₃) and ii) Need to have sufficient solid electrolyte as part of cathode, i.e., composite cathode, for a good utilization of cathodes of nominal thickness. Often, a hybrid system is preferred, where the solid electrolyte is utilized to protect Li anode and is used in conjunction with a conventional liquid electrolyte. In this paper, we will review the status of this technology and also present the results of our studies on the interfacial stability of some of these solid electrolytes towards Li anode and various cathodes.
References:
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Lithium solid electrolytes are expected to improve next-generation energy storage technology on the basis of energy density, safety, cost, amongst other parameters. However, there has been limited success in growing oxide-based solid electrolytes, such as Li_7-3xAl_xLa₃Zr₂O₁₂ (LLZO), into thin films between 200 nm and 5 µm in thickness using scalable solution-based techniques. Several vacuum-based^1,2 and sol-gel-derived^3,4 methods have shown promise in making thin garnet-based solid electrolyte films with relatively high ionic conductivity (~10^-6 - 10^-5 S/cm at room temperature), yet lithium loss during the post annealing can alter the phase as well as significantly affect the lithium ion conductivity. Only a recent report⁵ has overcome this issue by using an alternative ceramic processing strategy establishing lithium reservoirs directly in lithium garnet-based films (through Li₃N multilayers) that allow for lithiated and fast-conducting cubic solid state battery electrolytes at unusually low processing temperatures using pulsed laser deposition. Still, the exploration of scalable fabrication techniques is of special importance to develop thin films of garnet-based solid electrolytes with high ionic conductivity. Here, we present a new solution based on spray pyrolysis for growing garnet-based thin films. We show that the crystallization and the phase transformation can be modulated to lower temperatures ( <750 °C) by tuning the concentration of cations and the boiling point of the solvents used in the spray solution. Also, by altering the chemistry of the spray solution and the post-annealing conditions, we show that the surface roughness can be modulated while still maintaining dense and continuous membranes of LLZO. Our results highlight a new opportunity for manufacturing garnet-based solid electrolytes with tunable electrochemical surface areas. The insights from this work are expected to serve as fundamental guidelines for future optimization toward solution-based processing of thin film superionic garnet-based materials for next-generation lithium metal batteries.

Acknowledgements:
This research was supported by Samsung Electronics and a portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

References:
R.J. Chen, M. Huang, W.Z. Huang, Y. Shen, Y.H. Lin, and C.W. Nan. Sol–gel derived Li–La–Zr–O thin films as solid electrolytes for lithium-ion batteries. Journal of Materials Chemistry A, 2014, 2(33), 13277-13282.
M. Bitzer, T. Van Gestel, and S. Uhlenbruck. Sol-gel synthesis of thin solid Li₇La₃Zr₂O₁₂ electrolyte films for Li-ion batteries. Thin Solid Films, 2016, 615,128-134.
I. Garbayo, M. Struzik, W.J. Bowman, R. Pfenninger, E. Stilp, and J.L.M. Rupp. Glass-Type Polyamorphism in Li-Garnet Thin Film Solid State Battery Conductors. Advanced Energy Materials, 2018, 8(12), 1702265.
M. Rawlence, A.N. Filippin, A. Wäckerlin, T.Y. Lin, E. Cuervo-Reyes, A. Remhof, C. Battaglia, J.L.M. Rupp, and S. Buecheler. Effect of Gallium Substitution on Lithium-Ion Conductivity and Phase Evolution in Sputtered Li_7–3xGa_xLa₃Zr₂O₁₂ Thin Films. ACS Applied Materials & Interfaces, 2018, 10(16), 13720-13728.
R. Pfenninger, M. Struzik, I. Garbayo, E. Stilp and J.L.M. Rupp. A Low Ride on Processing Temperature for a Fast Li Conduction in Garnet Solid State Battery Films. Nature Energy, 2019, in press.

While microfabrication techniques have been used extensively to form the complex circuitry of modern microelectronic devices, its application in the fabrication of electrochemical energy storage (EES) systems has not been considered traditionally. However, the microfabrication approach can open new routes for minimizing the dimensions of EES devices and for directly incorporating them with integrated circuits, sensors, MEMS devices, and various other Internet-of-Things components. In particular, the photopatterning of mechanically robust solid electrolytes offers several potential advantages, such as the spatial control with micron and sub-micron resolution in complex designs, ease of co-packaging with other integrated circuits, and high-throughput wafer-scale fabrication of EES arrays.

This presentation will review our work on the fabrication and characterization of a photopatternable, ionically conducting solid electrolyte. Electrolyte materials consist of the epoxy-based photopatternable polymer matrix that confines an ionic liquid, thus providing an appropriate source of ions and measurable ionic conductivity of 0.4 mS cm^-1. This ionogel solid electrolyte possesses excellent mechanical integrity, demonstrates good electrochemical stability, and can be photopatterned with micrometer-scale resolution. To validate its electrochemical performance and on-chip integration, fabrication of all-solid-state micro-supercapacitor devices was demonstrated using microfabrication methods that are fully compatible with current semiconductor processing. The interdigitated electrode designs were optimized to minimize the ion transport distance, compensating for the modest ionic conductivity of our solid electrolyte. The resulting TiC-derived-carbon micro-supercapacitor devices with 15-μm electrode spacings demonstrate a high areal capacitance and long-term electrochemical stability. In addition, the potential range and total capacitance of micro-supercapacitor devices can easily be tailored through modifying the device arrangements in series or parallel configurations.

Solid state batteries (SSBs) can be fabricated using thin film processing techniques like those which dominate major high-tech markets such as semiconductors, displays and optoelectronics. In particular this approach – profoundly divergent from today’s Li ion battery mainstream – enables controlled patterning of electrode and electrolyte shapes and connectivity that opens the door to simultaneous high energy and high power, 3D nano/micro configurations exploiting conformal high aspect ratio geometries, and flexible form factors for integrating SSBs into multifunctional systems. We have made substantial progress in realizing these benefits in conformal 3D vertical interdigitated nanobattery arrays, forming SSB layers in high aspect ratio nano/micro pores, affording the opportunity to project performance. We are also pursuing a contrasting lateral design that promises similar benefits. We compare the vertical and lateral designs in terms of projected performance and associated synthesis and fabrication challenges, and we highlight key scientific challenges at the levels of nanoscale interfaces and mesoscale architectures.

Ceramic sulfide solid electrolyte can show high lithium conductivity, while the voltage stability was reported as an issue in many previous literatures. We show in this talk a new way to improve the voltage stability of sulfide solid electrolyte materials by microstructure and battery designs. The improved battery performance and voltage stability are shown by electrochemical test. A combination of first principle simulation and transmission electron microscopy imaging techniques are used to understand the principle behind the phenomenon.

Specifically, sulfide Li-Si-P-S has been synthesized, characterized and tested to show an improved voltage stability window up to 3.1 V and qasi-stable voltage window up to 5V due to the microstructure modification. This is far beyond the limited voltage stability of these sulfides around 1.7 – 2.1 V as predicted by previous DFT simulation. We further from a combined thermodynamic modeling and DFT simulation understand the principle behind this promising result. A new design principle and theory is proposed and discussed systematically for tuning the voltage stability of solid electrolyte, giving the guidelines for the design of advanced sulfide electrolytes. All-solid-state battery using 5V cathode materials based on sulfide solid electrolyte is demonstrated in our experiment.

References: Advanced sulfide solid electrolyte by core-shell structural design, Nature Communications, (9), 4037 (2018)

Producing battery materials by thin film deposition techniques provides many benefits for future solid state batteries (SSB) and opens up new possibilities for on chip energy storage in microelectronics applications operating in harsh environments and with high power demands. We have recently demonstrated that a fully 3D thin film based SSB can be produced by atomic layer deposition (ALD) into an array of nanopores etched into an inert substrate, with potential to scale capacity to rival that of modern lithium ion batteries. Such extreme 3D architectures apply certain constraints to the selection of materials and deposition techniques, and effectively limits us to using ALD, not to mention limiting the ways in which we wire these 3D TFSSB to the rest of the device.

Experiments on an alternative TFSSB architecture, simpler and more efficient in many regards, are presented which relaxes many of these constraints, while retaining the same capacity scaling performance. In this architecture, the battery layers are deposited in a planar way using magnetron sputtering, and the processing is repeated to produce multiple layers of TFSSB in the same space. Once electrode connections are completed, this multibattery architecture alleviates many of the concerns raised from the previous 3D battery, while presenting other issues (e.g., annealing steps required to produce the desirable phase in the cathode).

We will describe and compare our measurements on these two distinctly different approaches to 3D battery architectures for high power-energy solid state electrochemical energy storage, considering such aspects as mesoscale synthesis, performance scaling, flexibility in form factor, and integration into multifunctional systems.

Solid-State batteries have experienced a recent explosion in research and development, owing to their potential to improve safety and enable higher energy density electrode chemistries. However, it has been widely recognized that all solid-state interfaces present unique challenges compared to traditional liquid electrolytes, including reduction of high interfacial impedances (which can evolve during cycling), accommodation of mechanical stresses due to solid-solid interfacial contact with active materials, and (electro)chemical instabilities that can arise from localized gradients in ionic and electronic concentrations.
To address these challenge, our group focuses on gaining new fundamental insights into the coupled phenomena occurring at interfaces, and applied this knowledge to rationally design interfacial chemistry to address the root cause of performance limitations. The key enabling technology that will be discussed in this talk for surface modification is Atomic Layer Deposition (ALD). This is a gas-phase deposition process capable of conformally coating high aspect-ratio structures with sub-nanometer control in thickness. This atomic-scale modification of surfaces allows for precise control of interactions at heterogeneous interfaces, including (electro)chemical stability, interfacial kinetics, wettability, and mechanical load transfer.
In this talk, examples will be presented in both bulk solid-state battery interfaces, and thin film electrolytes deposited by ALD. By studying interfacial chemistry across length scales ranging from atoms to millimeters, we have been able to systematically identify the mechanisms of interfacial degradation, and answer the question of why a particular interface exhibits the observed electrochemical behavior. At bulk length scales, the coupled chemical/electrochemical/morphological evolution of a range of solid electrolytes will be discussed, including metal oxides, sulfides, and polymers [1,2]. To modify these surfaces, ALD of solid lithium electrolytes is demonstrated [3,4], which enables tunability of surface chemistry, defect structure, morphology, and stability. These ALD electrolytes are demonstrated in both high power density thin-film battery architectures, and as interfacial layers at bulk solid electrolyte-electrode interfaces. Through this interdisciplinary approach of fundamental chemistry and applied engineering, strategies to address future interfacial challenges will be addressed.

1. A. Sharafi, E. Kazyak, A. L. Davis, S. Yu, T Thompson, D. J. Siegel, N. P. Dasgupta, J. Sakamoto, Chem. Mater. 29, 7961 (2017)
2. A. Gupta, E. Kazyak, N. Craig, J. Christensen, N. P. Dasgupta, and J. Sakamoto, J. Electrochem. Soc. 165, A2801 (2018)
2. E. Kazyak, K.-H. Chen, K. N. Wood, A. L. Davis, T. Thompson, A.R. Bielinski, A. J. Sanchez, X. Wang, C. Wang, J. Sakamoto, N. P. Dasgupta, Chem. Mater. 29, 3785 (2017)
4. E. Kazyak, K.-H. Chen, A. L. Davis, S. Yu, A. J. Sanchez, J. Lasso, A. R. Bielinski, T. Thompson, J. Sakamoto, D. J. Siegel, N. P. Dasgupta, J. Mater. Chem. A 6, 19425 (2018)

The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes, especially in the lithium thiophosphates. While current lithium electrolytes provide fast-ionic conduction to fundamentally study solid-state batteries, their ionic conductivities are not sufficient for thick electrode configurations, which will really allow high energy densities to be achieved.¹ In this presentation, we show how an understanding of the structure-transport properties of the lithium argyrodites Li₆PS₅X can help tailor the ionic conductivity. We show that an anion site-disorder between S^2- and X^- is beneficial for the activation barrier² and that an induction of the site disorder in Li₆PS₅I leads to a significant improvement of the conductivity.³ Having achieved the fastest lithium argyrodite so far with = 18 mS/cm, solid-state batteries with thick electrode configurations (150 – 350 ) can be built. Due to the optimized solid electrolyte, the solid-state battery can be cycled even at 1C with no capacity fade over 150 cycles. This work shows that optimizing solid electrolytes helps to achieve stable cycling at high rates in solid-state batteries with thick electrodes. Further, we will show how tuning the lattice polarizability in ionic conductors affects the ionic transport due to a softening of the lattice. Our work shows that the idea of “the softer, the better” needs to be revisited.^2,4,5 Lastly, we show how volume changes, induced by electrochemical (de-)intercalation, affect the performance in solid state batteries providing an understanding of the underlying mechanochemical influences in solid-state batteries.^6,7 (1) Janek, J.; Zeier, W. G. A Solid Future for Battery Development. Nat. Energy 2016, 16141.
(2) Kraft, M. A.; Culver, S. P.; Calderon, M.; Böcher, F.; Krauskopf, T.; Senyshyn, A.; Dietrich, C.; Zevalkink, A.; Janek, J.; Zeier, W. G. Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li₆PS₅X (X = Cl, Br, I). J. Am. Chem. Soc. 2017, 139, 10909–10918.
(3) Kraft, M. A.; Ohno, S.; Zinkevich, T.; Koerver, R.; Culver, S. P.; Senyshyn, A.; Indris, S.; Morgan, B. J.; Zeier, W. G. Inducing High Ionic Conductivity in the Lithium Superionic Argyrodites Li_6+xP_1-xGe_xS₅I for All-Solid-State Batteries. J. Am. Chem. Soc. 2018, 140, 16330–16339.
(4) Krauskopf, T.; Muy, S.; Culver, S. P.; Ohno, S.; Delaire, O.; Shao-Horn, Y.; Zeier, W. G. Comparing the Descriptors for Investigating the Influence of Lattice Dynamics on Ionic Transport Using the Superionic Conductor Na₃PS_4-XSe_x. J. Am. Chem. Soc. 2018, 140, 14464–14473.
(5) Krauskopf, T.; Pompe, C.; Kraft, M.; Zeier, W. G. Influence of Lattice Dynamics on Na+-Transport in the Solid Electrolyte Na₃PS_4−xSe_x. Chem. Mater. 2017, 29, 8859–8869.
(6) Zhang, W.; Schröder, D.; Arlt, T.; Manke, I.; Koerver, R.; Pinedo, R.; Weber, D. A.; Sann, J.; Zeier, W. G.; Janek, J. (Electro)Chemical Expansion during Cycling: Monitoring the Pressure Changes in Operating Solid-State Lithium Batteries. J. Mater. Chem. A 2017, 5, 9929–9936.
(7) Koerver, R.; Zhang, W.; de Biasi, L.; Schweidler, S.; Kondrakov, A.; Kolling, S.; Brezesinski, T.; Hartmann, P.; Zeier, W.; Janek, J. Chemo-Mechanical Expansion of Lithium Electrode Materials – On the Route to Mechanically Optimized All-Solid-State Batteries. Energy Environ. Sci. 2018, 11, 2142–2158.

Driven by solid-state lithium batteries with both high safety and high energy density, solid electrolyte materials with high lithium-ion conductivity have experienced a rapid development in the past years. Various solid electrolytes such as oxides, sulfides, polymers, and composites are being extensively investigated. Among them, composite solid electrolytes with inorganic fillers embedded into polymer matrix have attracted ever-increasing attention for all-solid-state lithium metal batteries due to their high ionic conductivity, flexibility, and excellent scalability for battery manufacturing. In this talk, we focus mainly on recent progresses on polymer-based composite solid electrolytes with high lithium-ion conductivity, with special emphasis on the challenges of the applications of solid electrolytes in lithium batteries. Several kinds of high-performance composite solid electrolytes will be introduced. The interfacial stability and compatibility between the composite electrolytes and electrodes, and the relation between the properties of the composite electrolytes and the performance of solid-state batteries will be discussed.

All-solid-state batteries are expected to outperform conventional lithium-ion batteries with respect to energy density and fast charging capabilities anytime soon [1], representing a promising energy storage concept for future mobility solutions. However, many experimental studies [2-4] dampen the expectations on cell performance for multiple reasons, ranging from volumetric strain to insufficient ionic or electronic percolation paths in composite electrodes.
We take the first step to an elaborate electrode layout, designed to develop advanced and reliable composite electrodes. To fundamentally understand the role of percolation throughout composites, we combine percolation theory and microstructural modeling and apply it to all-solid-state battery electrodes. In identifying ionic and electronic conduction networks of generated composite cathode models, we provide a holistic approach, studying the impacts of porosity, active material particle size, composition and electrode thickness on the effective conduction.
Our 3D model microstructures consist of spherical active material particles and convex polyhedra that represent solid electrolyte particles. The identification of conduction clusters by the Hoshen-Kopelman-Algorithm [5] allows for the quantification of the utilization of active material and the active interface area, indicating ionic and electronic limitations on effective conductivity: While small active material particles enhance effective electronic conductivity due to their higher surface area available for inter-particle connection, an impact of electrode thickness is exclusively observed in thin electrodes, where the suppression of percolation effects implies favorable electrode properties. We find that porosity has crucial effects on conduction clusters and strongly propose future experimental studies to measure or calculate porosity for the sake of comparability.
Based on microstructural modeling, we provide explanations for the limited performance of all-solid-state battery cells in various studies and are able to identify ideal compositions at given porosities, particle size and shape. Accordingly, we suggest guidelines for elaborate composite electrode architecture, assuring sufficient ionic and electronic percolation.

[1] Janek, J.; Zeier, W. G. Nat. Energy 2016, 1, 1-4.
[2] Nam, Y. J.; Oh, D. Y.; Jung, S. H.; Jung, Y. S. J. Power Sources 2018, 375, 93-101.
[3] Zhang, W.; Weber, D. A.; Weigand, H.; Arlt, T.; Manke, I.; Schröder, D.; Koerver, R.; Leichtweiss, T.; Hartmann, P.; Zeier, W. G.; Janek. J. ACS Appl. Mat. Int. 2017, 9, 17835-17845.
[4] Strauss, F.; Bartsch, T.; de Biasi, L.; Kim, A.-Y.; Janek, J.; Hartmann, P.; Brezesinski, T.
ACS Energ. Lett. 2018, 3, 992-996.
[5] Hoshen, J. and Kopelman, R. Phys. Rev. B 1976, 14, 3438-3445.

Ceramic-polymer composite electrolytes (CPEs) are being explored to achieve both high ionic conductivity and mechanical flexibility. Here, we show that, by incorporating mixed-sized fillers of Li₇La₃Zr₂O₁₂ (LLZO) doped with Nb/Al, the room temperature ionic conductivity of a polyvinylidene fluoride (PVDF)-LiClO₄-based composite can be as high as 2.6e-4 S/cm which is one order of magnitude higher than that with nano- or micro-meter sized LLZO particles as fillers. The CPE also shows a high lithium-ion transference number, a stable and low Li/CPE interfacial resistance, and good mechanical properties favorable for all-solid-state lithium-ion battery applications. XPS and Raman analysis demonstrate that the LLZO fillers of all sizes interact with PVDF and LiClO₄. High packing density (i.e., lower porosity) and long conducting pathways are believed responsible for the excellent performance of the composite electrolyte filled with mixed-sized ionically conducting ceramic particles.

We report a highly ion conductive gel polymer electrolytes for supercapacitor, composed of poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl] ethyl methacrylate)-poly(oxyethylene methacryalate) (PBE) copolymer and 1-Ethyl-3-methylimidazolium dicyanmide ionic liquid. When incorporated with EMIM DCA, selective interaction between ether groups and EMIM DCA induced micro-structured morphology, observed by (TEM). Structured morphology effectively suppressed aggregation of EMIM DCA and provide ion transport pathway, which led to fast diffusion of mobile ions. The PBE/EMIM DCA electrolytes showed gel-like morphology, which is suitable to fabricate solid-state, leakage-free supercapacitor. The best performance of supercapacitor using PBE/EMIM DCA electrolytes exhibited higher capacitance (125.1 F g^-1) than that of reference PVA/H₃PO₄ electrolyte (39.5 F g^-1) due to its high ion conductivity and good affinity with electrode.

Development of practical high-energy-density lithium metal batteries (LMBs) remains a grand challenge due to uneven lithium deposition and uncontrollable lithium dendrite growth. Herein, to further stabilize lithium electrodeposition, polymeric ionic liquid (PIL), poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (P(DADMA-TFSI)) with TFSI^- as the anions, is introduced in the cross-linked polyhedral oligomeric silsesquioxane (POSS)-poly(ethylene glycol) (PEG) solid polymer electrolyte to form an interpenetrating polymer network (IPN) in order to homogenize the anion concentration and reduce the local space charge-associated large electric field during the cycling process. Galvanostatic cycling and polarization measurements of symmetrical lithium cells show that introducing proper amount of PIL could improve the lithium dendrite resistance at relatively low current density, and reduce anion depletion velocity and extend Sand's time when polarized at high current density, indicating the improved lithium electrodeposition stability. Calculations from the Chazalviel model reveal that the improvement derives from elevated ionic conductivity and ionic concentration when PIL is introduced. The results demonstrated here represent a facile way for stabilizing lithium electrodeposition in high-performance LMBs.


References
[1] X.-B. Cheng, et al, Chem. Rev., 117, 10403-10473 (2017)
[2] M.D. Tikekar, et al, Science Advances, 2, e1600320 (2016)
[3] Q. Pan, et al, Adv. Mater., 27, 5995-6001 (2015)
[4] Q. Pan, et al, Adv. Energy Mater., 1701231 (2017)

Solid state electrolytes have garnered significant interest in recent years due to their potential to enable high energy-density Li-metal batteries. Because solid electrolytes have the potential to physically stabilize the Li-metal/electrolyte interface, significant emphasis has been placed on understanding the kinetics and stability of the Li/electrolyte interface. As significant progress is made in stabilizing the Li/electrolyte interface at higher current densities, there is an increasing need to develop and improve compatible cathodes for all solid-state architectures. Currently, achieving a combination of facile ion and electron transport through the cathode thickness is emerging as a challenge toward high-rate cycling. It has been proposed that a method of improving charge transport in the cathode is introducing a mixed electronic and ionic conductor (MEIC) which can reduce the amount of net conductive additive required. This study focuses on the perovskite Li_0.33La_0.57TiO₃ (LLTO) as a model MEIC system. The physical and charge transport properties for LLTO are measured in the oxidized and reduced state. Furthermore, the effects of p_O2 and grain size on the transport properties are examined. Overall, this work will motivate the further study and development of MEIC materials in the context of solid-state batteries and may improve the potential for high-rate cathodes for solid-state architectures.

Solid-state lithium metal battery attracts lots of interest for its high theoretical capacity and less flammability. Poly (ethylene oxide)-based solid polymer electrolyte (SPE) has been proved to be successful in lithium metal battery. However, one challenge is the comparatively low lithium ion transference number which restrains the battery working at high current rate. Herein, a novel SPE combined poly (ethylene oxide) and poly (propylene carbonate) and with semi-interpenetration network structure is reported. The synthesis of the SPE is based on the crosslinking of octakis(3-glycidyloxypropyldimethylsiloxy) octasilsesquioxane and amine-terminated polyethylene glycol while adding linear poly (propylene carbonate) with controlled concentration. The optimized SPE could be stably cycled for over 300 hours at current density of 1.5 mA cm^-2 during the galvanostatic symmetrical cell plating/stripping experiment. Lithium ion transference number could reach 0.38 which is almost double to the single network SPE. Scanning electrical microscope (SEM) revealed that the involvement of poly (propylene carbonate) could effectively suppress the lithium dendrite growth. X-ray photoelectron spectrum (XPS) found Li₂S₂O₃ from solid electrolyte interface (SEI). Full battery fabricated the semi-interpenetration network SPE sandwiched by lithium metal and LiFePO4 cathode delivered high specific capacity of over 160 mAh g^-1 at C/10 and over 95 mAh g^-1 at 2C and excellent Coulombic efficiency. This work is doomed to enlighten the development of SPE from the aspects of both materials (polycarbonate) and structure (interpenetration network).

Hazards associated with the utilization of organic liquid electrolyte has created a growing concern while the number of lithium rechargeable battery (LRB) applications has been increasing over the last two decades. Glassy solid-state electrolytes (GSSEs) have been considered as a safer alternative credited to its promising thermal stability and physical durability. In addition to this, the elimination of fire and explosion risks provides the chance to adopt high-energy-density metallic lithium as anode material, leading to drastic improvements in overall energy density of LRBs. However, few papers have been reported on lithium oxythio-silicophosphate (LiPSiSO) GSSE, and the compositional dependence on structural, thermal and electrochemical properties are not clear yet.

In our research, LiPSiSO GSSE materials were synthesized via melt-quench method, and the structural and thermal properties were characterized using differential scanning calorimetry, Raman, infrared, nuclear magnetic resonance spectroscopies. The electrochemical properties have been tested via electrochemical impedance spectroscopy and direct-current cycling methods, for which powderized LiPSiSO GSSE was pressed into thin pellets (~1mm). The experimental results showed the structural, thermal and electrochemical properties of our GSSE are highly composition dependent. This insight allows for the correlation among those properties, and helps optimize the performance of LiPSiSO GSSEs by composition adjustment during synthesis.

Current lithium-ion batteries contain flammable organic-based electrolyte with limited voltage stability. A promising solid state electrolyte has been proposed to improve safety and limited voltage stability of the current lithium-ion battery. A global research activity is underway to develop a safe solid-state electrolyte with high conductivity and high voltage stability to replace the organic liquid electrolyte.

The polymer-salt complex electrolytes have been investigated in the past. However, this class of electrolyte exhibits low ionic conductivity (~10^-6 - 10^-7 S cm^-1) at room temperature due to their high degree of crystallinity at low temperatures and a high degree of ion-pairing that limits salt solubity. These issues have been addressed by adding plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), etc., or using inorganic fillers. In this research, we have studied PEO based polymer electrolyte with inorganic filler, Li₇La₃Zr₂O₁₂ (LLZO), which is also a Li-ion conductor. We have shown that the ionic conductivity of PEO-LLZO composite electrolyte increases by one order of magnitude upon adding LLZO (20 wt%) and EC (20 wt%) and lowering the activation energy from 0.6 eV to 0.4 eV with high (5V) voltage stability. The results of a detailed study of electrochemical properties of PEO-LLZO composite electrolytes using electrochemical impedance spectroscopy, linear sweep voltammetry, and chronoamperometry will be presented.

High capacity all-solid-state Li-ion battery anodes were prepared using an industrially scalable solution coating processes. Employing commercially available polyacrylonitrile as a mixed conducting binder, we have demonstrated stable cycling, high capacity electrodes with large mass loadings of tin active material. This is, to our knowledge, the first time a high capacity lithium-alloying material has been utilized in a slurry-coated sheet-style all-solid-state Li-ion battery anode. Optimization of this new electrode architecture resulted in a sheet-style anode capable of retaining an electrode specific capacity of 643.5 mAh/g after 100 charge-discharge cycles at a 0.1C rate. We believe that this work represents a step forward for slurry-coated electrodes and that the continued development of these high capacity sheet-style anodes will be critical to the commercialization of the all-solid-state Li-ion battery.

Modern lithium batteries use liquid electrolytes as the source for lithium ions in batteries and electrochromic devices. However, liquid electrolytes present its own set unique problems. Lithium ion batteries are prone to runaway thermal reactions and a loss of performance due to dendritic growth in the electrodes. Lithium phosphorous oxy-nitride (LiPON) is a solid-state material with good lithium ion conductivity that should address some of these challenges.
In this work, we investigate the growth of LiPON films using pulsed-laser deposition (PLD) on pristine and copper-coated soda-lime glass. The goal of this work is to optimize the growth parameters for the development of highly conductive LiPON films that can be used in both solid-state lithium ion batteries and electrochromic devices.
A lithium phosphate (Li₃PO₄) target was ablated in a nitrogen atmosphere using a Quantel Q-Smart 850 laser with a neodymium-doped yttrium aluminum garnet (Nd: YAG) crystal and a laser fluence of 20 J/cm². Two sets of films were deposited at room temperature and at 400°C. For each set of films the nitrogen pressure was varied from 10^-3 mbar to 10^-1 mbar. The target to substrate distance was held constant at 5.5 cm and the thickness of the films was controlled by the number of shots on the target.
The films were studied both as-deposited and with a post deposition anneal of 30 minutes. We characterized the films using a number of techniques including x-ray diffraction, electron microscopy, Raman spectroscopy and electrical measurements. The detailed results will be presented.

A high demand of energy storage devices has boosted researchers for fabricating ultra-efficient capacitor with better energy density and cycling stability. Supercapacitor made up of organic and inorganic nanostructured electrode showing better performance in terms of flexibility, light weight, and electrochemical stability. The supercapacitior made up of composite nanostructured electrode operates at higher voltage and exhibits excellent retention behavior with a very little loss of capacity even after few thousands of charge and discharge cycles. The composite electrode shows excellent flexibility without changing any sheet resistance even after few tens of bending mode. FESEM images reveals the formation of high dense nanostructure of different size with diameter vary from few tens to few hundreds of nanometer. The asymmetric supercapacitor shows energy density, power density of 0.47 mW h/g, and 35.2 mW/g respectively. This device exhibits a high areal Csp of more than 6F/g. These energy storage unit holds a great potential for the use in future flexible electronic device.

Wearable energy sources are in urgent demand due to the rapid development of wearable electronics. Supercapacitors possess a high power density and long cycle lifetime, thus developing flexible high-performance supercapacitors is a promising route to meet the demand for wearable energy sources. The realization of high-performance flexible supercapacitors strongly relies on the electrical properties and mechanical integrity of the constitutive materials and their ingenious assembly into free-standing and binderless skeleton. Pseudocapacitive metal (e.g., nickel, cobalt, and manganese) hydroxides/oxides provide multiple oxidation states for reversible Faradaic reactions which have been extensively pursued to realize efficient supercapacitors devices. However, the faradaic nature of bulk pseudoactive material with limited diffusion length restrains the capacitance contribution within the surface and/or near the surface of the material. Thus, a method to control the structure of the material should be found to improve the charge and ion-transfer efficiency of the flexible pseudoactive material. Core–shell structure with different pseudocapacitive materials can provide more electroactive sites, higher electrical conductivity, faster ion-electron transport, which might lead to unprecedented electrochemical performance. Herein, we design and fabricate a new and hierarchically core-shell structured hybrid of electroactive material coating (NiMn-glucose-LDH) on in situ grown NiCo₂S₄ nanotube arrays on a flexible carbon fiber cloth (CFC), denoted as NiMn-G-LDH@NiCo₂S₄. Highly conductive NiCo₂S₄ nanotube arrays grown on a flexible CFC, which can serve not only as a superior pseudocapacitive material but also as a three-dimensional (3D) conductive scaffold for loading additional electroactive materials. Glucose intercalated NiMn LDH (NiMn-G-LDH) could significantly improve the ion diffusion coefficient with the expansion of the interlayer distance. Inheriting the merits of NiMn-G-LDH and NiCo₂S₄ nanotube, the free-standing NiMn-G-LDH@NiCo₂S₄ hybrid could synchronously achieve the excellent rate performance and cycle stability. The electrochemical investigation shows that the NiMn-G-LDH@NiCo₂S₄ have a significantly enhanced specific capacitance (1,793 Fg^-1 at 1Ag^-1) , rate capability (~70% retention at 20 A g^-1) and cycling performance (keep ~82% after 1000 cycles) that far exceed those of the reported individual NiCo₂S₄ and NiMn LDH electrodes.

Polymer-mineral composite solid electrolytes have been prepared using lithium ion-exchanged natural bentonite and mineral derived NASICON materials as solid electrolyte fillers in the polyethylene oxide (PEO) polymer containing LiTFSI salt. The mineral based solid electrolyte fillers not only increase ionic conductivity but also improve thermal and mechanical stability. The flexible and mechanical sturdy polymer-mineral composite solid electrolyte films can be used in the all-solid-state batteries.

Flexible and wearable supercapacitor (SC) has drawn a great attention for the potential in powering smart and wearable electronics. Particularly, 1D fiber-shaped flexible devices can be directly knitted or sewn into conventional textiles. Here, an electrodeposition strategy is devised to purposefully fabricate nickel/cobalt composite oxides and polypyrrole (PPy) decorated stainless steel yarns (SSY) as the the positive and negative electrodes, respectively. The nickel/cobalt composite oxides based SSY positive electrode showed the highest volumetric capacitance of about 166.5 F/cm³ at the current density of 0.4 A/cm³. Asymmetric all-solid-state supercapacitors (AASs) were then successfully developed and assembled by wrapping a PPy coated negative electrode on the as-prepared positive electrode in conjunction with the PVA/KOH gel electrolyte, showing competitive flexibility and electrochemical properties owing to the flexible SSY substrate and the highly pseudocapacitive materials. The as-obtained AASs exhibited a wide voltage window of 0-1.5 V, and the highest volumetric capacitance was nearly 13.88 F/cm³ at the current density of 20 mA/cm³, and the maximum energy density was 2.95 mWh/cm³ at a power density of 17.68 mW/cm³. Furthermore, the highly flexible AASs were then directly sewn into a conventional textile fabric, exhibiting great electrochemical stability under 6,000 charging/discharging cycles. Collectively, the work uses the highly pseudocapacitive materials and facile methods fabricated flexible AASs with enhanced electrochemical properties, which showed a decent potential in designing and exploring the next-generation wearable and portable SC devices.

Solidifying the components of a Li-ion battery consisting of a high energy capacity oxide cathode (e.g. NMC, NCA), a Li metal anode, and a sulfide-based glass ceramic solid electrolyte (SE), is a pathway to overcome the challenges of liquid electrolyte cells, namely dendrite growth and safety concerns without compromising high energy density. Even though the conductivity of a few sulfide solid electrolytes (SSEs) surpasses that of liquid electrolytes, multiple interfacial phenomena at both the cathode and anode interfaces play a crucial role in affecting efficient battery performance. Such phenomena include solid-electrolyte interphase (SEI) formation and mechanical deformation; the SEI forms due to poor chemical and electrochemical stability of SSEs while mechanical deformation arises from volume changes experienced by the cathode during cycling and also the rigid nature of SSEs. In the past several decades, tremendous effort has been made to study the SEI for SSEs, however, the properties of cathodic and anodic SEIs and their effects on long-term All Solid State Battery (ASSB) cycling are still not well-understood. In this work, we use multi-modal characterization and computation modeling tools to understand and elucidate the reaction mechanisms at the solid-solid interfaces. Interfacial engineering through coating of active electrode materials can be an effective method to enable ASSB at room temperature.

The lithium for many batteries comes packed in the cathode, so little is needed to seed the lithium anode and form the current collector. For this we grow the lithium films by vacuum thermal evaporation. This presentation will describe conditions and control of the film growth and the resulting morphology and properties of the films deposited onto a variety of solid electrolytes. Initial studies will also address how the lithium properties, structure and its interfaces evolve as functions of the rate and depth of the cycling.

Acknowledgement: The research was supported by the Advanced Battery Materials Research and Battery500 Consortium programs of Vehicles Technology Office within the US DOE’s Office of Energy Efficiency and Renewable Energy; and by the IONICS program of the Advanced Research Program Agency for Energy (ARPA-E).

Solid state electrolytes have the potential to enable safe, high energy-density Li metal batteries by serving as a physical barrier against unstable Li plating. Because of the tendency for Li filaments to propagate through the solid electrolyte and short circuit the cell at high current densities, significant emphasis has been placed on studying the kinetics and mechanics of the plated Li-electrolyte interface. However, as the mechanics of the Li-metal/solid-electrolyte interface are drastically different from conventional Li-ion batteries, there is a continued need to understand the behavior of both Li metal stripping and plating. The present work evaluates the electrochemical behavior at the interfaces under dynamic stack pressure conditions. Using a novel mechanical testing apparatus in an inert environment, symmetric Li-electrolyte cells are studied under dynamic loading and electrochemical cycling conditions. Li₇La₃Zr₂O₁₂ (LLZO) garnet electrolytes are used as a model system, given the ability to achieve low interface resistances (~10Ω cm²) and stably plate Li at relatively high current densities. Using a combination of AC and DC methods, it is demonstrated that deviation from Ohmic behavior during constant current cycling occurs at a “critical stack-pressure” and is a result of surface roughening primarily at the Li stripping electrode. Changes in the interfacial resistance on the Li stripping electrode suggest the presence of Kirkendall voids which form when there is insufficient stack pressure to replenish the supply of Li being dissolved at the interface. The results further motivate the need to understand the coupled electrochemo-mechanical behavior of the Li-metal/solid-electrolyte interface and identifies stack pressure as an important design parameter for future solid-state batteries.

The realization of a low-cost, safe, reversible, high-areal capacity lithium metal electrode for solid-state batteries has remained elusive despite ongoing advances in anode protection using ion-conducting ceramics and glasses as well as organic and inorganic passivating layers. Here, I will outline a framework to understand the successes and failures of these differentiated materials platforms on the basis of their mechanical properties, transport properties, and partial molar volume considerations for solid-ion conductors relative to the lithium anode. Within this framework, I will also highlight an unexpected opportunity for suppressing lithium metal dendrites using soft solid-ion conductors. I will then detail the extent to which these predictions deliver on their promise, from early-stage discovery science and in-depth synchrotron hard x-ray techniques to platform maturation from coin cells to pouch cells.

Lithium dendrite growth is one of the grand challenges in the design of high energy rechargeable lithium-ion batteries. "Dendrites" are undesired elongated metallic nanostructures that form on the anode during fast charging. Upon battery cycling, they grow towards the cathode causing short-circuits and other catastrophic failures (including fires) in portable electronic devices and electric vehicles. A computational framework based on the Phase Field Method has been developed to couple lithium electrodeposition kinetics on the anode with the inherent mechanical behavior of metallic lithium. The framework provides a means to provide detailed insight on the time-dependent, spatially heterogeneous electrical, chemical, and mechanical driving forces during electrodeposition that are otherwise difficult to visualize through experiments. The different mechanisms observed during classical electrodeposition and those previously unidentified are predicted and rationalized through this framework as a stepping stone to design safer, high energy density devices.

Li-ion batteries are currently the most energy-dense battery technology. If the intercalation anode (e.g. graphite) can be completely removed and Li ions stored in the intercalation cathode can be reduced into a thin film of Li metal anode during recharge, the energy density of the state-of-the-art Li-ion battery will be nearly doubled. However, the formation of Li metal anode in liquid electrolytes has been plagued by the dendrite penetration and low cycling efficiency for decades [1,2]. While solid electrolytes in principle could solve both problems, recent studies revealed that Li metal dendrites can easily penetrate the garnet Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte at current densities lower than 1 mA cm^-2 [3-12]. This relatively low critical current density (CCD) prohibits the battery using solid electrolyte from fast charging, therefore will significantly limit the application, especially for electric vehicles. Accurately understanding the mechanisms of CCD has become an urgent need for designing high-rate, dendrite-proof solid electrolytes.
In this study, we first analyzed 16 sets of reported experimental data, and discovered for the first time a linear relationship between the CCD, J_c, and the ratio of the total conductivity σ_total and the thickness of the solid electrolyte pellet L, i.e. J_c ∝ σ_total/L. This linear relationship resembles the proved limiting current in liquid electrolytes, i.e. J_lim ∝ D_app/L [1], suggesting that the solid electrolyte may also have a limiting current, even though prevailing understandings prefer that the near unity transference number ensures an infinitely high limiting current. Inspired by the electrochemical methods used in studying lithium electrodeposition in liquid electrolytes, further investigations of the transport properties of LLZO solid electrolytes led to the discovery of the limiting current in the I-V curve, which is consistent with the CCD discovered from the standard constant current cycling. Quantitative explanations and a simple mathematical model were provided to better understand the mechanisms of the CCD.

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[9] Y. Suzuki, K. Kami, K. Watanabe, A. Watanabe, N. Saito, T. Ohnishi, K. Takada, R. Sudo, N. Imanishi, Solid State Ionics 2015, 278, 172.
[10] Y. Ren, Y. Shen, Y. Lin, C.-W. Nan, Electrochemistry Communications 2015, 57, 27.
[11] N. J. Taylor, S. Stangeland-Molo, C. G. Haslam, A. Sharafi, T. Thompson, M. Wang, R. Garcia-Mendez, J. Sakamoto, J Power Sources 2018, 396, 314.
[12] L. Cheng, W. Chen, M. Kunz, K. Persson, N. Tamura, G. Chen, M. Doeff, ACS Applied Materials & Interfaces 2015, 7, 2073.

Room temperature metallic anodes possess potential to enable batteries with enormous capacity. Lithium metal is known as the “holy grail” of anode materials, as it has the highest theoretical capacity, lowest density, and most negative electrochemical potential of known anode materials for rechargeable batteries. However, dendrites of lithium form during repeated cycling, posing a significant safety hazard. Sodium has similar safety concerns and a much larger sized ion than lithium (1.02 Å versus 0.59 Å), leading to generally comparatively worse kinetic performance. Despite their issues, sodium metal anodes have recently received increased attention due to sodium's natural abundance and relatively low cost. A comprehensive understanding of both lithium’s and sodium’s mechanical properties is vital in designing solid-state electrolytes to mitigate dendritic growth. Through nanoindentation and bulk tensile testing, we explore the mechanical properties of the metallic sodium and lithium anode.

Solid electrolytes are advocated for next-generation lithium batteries given their conformity against lithium metal anodes. Intuitively the mechanical stiffness of the solid electrolytes should discourage irregular lithium deposition. However, often lithium dendrites are found to form in solid electrolytes. We find that the solid electrolytes defy the conventional wisdom of electroplating. An irregular lithium dendrite leads to a misfit strain which alters both the reaction kinetics and transport in the solid electrolyte. These competing mechanisms give rise to an interfacial instability, which marks the onset of dendrite formation. Here in we discuss the regimes to promote uniform deposition.

To meet the future demands of future hybrid, plug-in hybrid, and all electric vehicles, advances in energy storage for transportation is indispensable. Additionally, energy diversification is vital to tailor electrification requirements to optimize the cost, range and size of the application. Recently, post Li-ion batteries, such as Li-O₂, multivalent and anion batteries, have garnered much attention. The lithium-metal/sulfur (Li-S) battery is an exciting system due to its high theoretical capacity (1673 mAh/g) and the potential of low cost.¹ However, realizing Li-S batteries relies on solving key challenges such as dissolution and shuttling of polysulfides, low sulfur utilization at high-areal loading levels, lithium metal dendrite formation, and continuous electrolyte decomposition on the Li metal surface.
The potential benefits of solid-state electrolytes, such as polymer electrolytes, gel electrolytes and ion-conducting ceramics electrolytes, are wide-operating windows, active material dissolution prevention and metal dendrite inhibition. However, low ionic conductivity and interfacial stability require continued development to achieve a viable energy storage system. Recently, ionic conductivities rivaling liquid based-systems have been observed for the sulfide-based, glass-ceramic L₁₀GeP₂S₁₂ (LGPS),² encouraging continued research into solid-state batteries using sulfide-based solid-electrolytes. Tatsumisago et al.³ illustrated and impressive initial cycling results using lithium-indium alloy anode, a lithium iodide/lithium sulfide solid-solution cathode, and a solid sulfide electrolyte: over 1000 mAh/g at 2C cycling for over 2000 cycles. Inspired by the results, developing all solid Li-S (AS-LiS) batteries presents hope for a high-energy density battery.
The major road-block to enabling AS-LiS batteries lies is the capability to utilize lithium metal. Researchers have recently observed the decomposition of sulfide electrolytes in contact with lithium metal, as well as the tendency for the active metal to plate within the electrolyte layer and create electrical shorts. ^4,5 Here, we will discuss protection strategies to inhibit undesired reactions at the anode-electrolyte interface; including lithium metal surface modification, and additives for the solid-electrolyte separator layer as potential solutions. Realizing lithium metal for solid-state batteries will provide the energy needed for future mobility.
[1] Manthiram, A. et al. Chem. Rev. 2014, 114, 11751-11787.
[2] Kanno, R. et al. Nat. Mater. 2011, 10, 682-686.
[3] Tatsumisago, M. et al. Adv. Sustainable Syst. 2017, 1700017, 1-6.
[4] Sakamoto, J. et al. Electrochimica Acta 2017, 237, 144-151.
[5] Janek et al. Solid-State Ionics 2016, 286, 24-33.

Solid-state batteries (SSBs) have been regarded as promising next-generation Li-ion batteries (LIBs), and promising solid electrolytes (SEs) with higher Li-ion conductivities have been found. However, the high interfacial resistance of Li-ion transport at the electrode-SE interface remains a crucial bottleneck. Although interposing a buffer layer into the interface has been used to remedy this problem in practice [1], the fundamental mechanism is still under considerable debate.
We have been exploring the atomistic understanding of this interfacial resistance mechanism with DFT-based calculation approaches [2,3]. So far we have devised some systematic ways for the solid-solid interfaces and discussed possible origins such as the space-charge layer and the reaction layer. However, the sufficient sampling of the solid-solid interface configurations is too cumbersome for deducing any significant statistical and general features of the interfacial Li-ion transport. Hence, we utilized the CALYPSO structure prediction method [4,5] as a calculation technique for the interface structure search, to be combined with mismatch treatment, lateral shift etc.
Here as representative model systems, we applied the above DFT-based calculation techniques to LiCoO₂ (LCO), β-Li₃PS₄ (LPS), and LiNbO₃ (LNO) acting as a cathode, a sulfide electrolyte, and a buffer layer, respectively, For the LCO/LPS interfaces, we sampled over 20000 configurations and found several stable disordered structures involving cation and anion exchange, leading to the formation of a reaction layer. On the other hand, Li-ion sites that can be preferentially depleted upon charging always exist around the cathode-SE interfaces irrespective of the interfacial order/disorder. Therefore, we conclude that the dynamic Li-ion depletion is likely to be a major cause that prevents successive Li-ion transport, leading to the resistance. Through investigating the buffer layer effects and the interfacial electronic states, we also deduced a probable origin for the interfacial Li depletion and a mean to suppress this problematic behavior. In the talk, we will also discuss the related works on anodes and SEI interfaces.
References:
[1] K. Takada, Acta Mater., 61, 759-770 (2013).
[2] J. Haruyama, K. Takada, Y. Tateyama et al., Chem. Mater. 26, 4248-4255 (2014).
[3] J. Haruyama, Y. Tateyama et al., ACS Appl. Mater. Interfaces 9, 286-292 (2017).
[4] Y. Ma et al., Phys. Rev. B 82, 094116 (2010).
[5] B. Gao, Y. Ma et al., Appl. Surf. Sci. 393, 422 (2016).

The major bottleneck for the all-solid-state batteries lies at the high interfacial resistance, which is due to two main factors, physical contact and chemical effect, both will be evaluated via modeling in this talk. First, we devise a model, incorporating atomic electrochemical potentials, thermodynamic stability of bulk electrolyte phases, and point defect formation energies to yield quantitative profiles of the electrostatic potential, lithium chemical potential, and electronic energy levels. This model complements direct microscopic and macroscopic simulations by rigorously and simultaneously determining the potential drop, electrostatic dipole, and space-charge layer at the interface. The application of this model to the Li/LiPON/LixCoO2 system leads to the important discovery that the space-charge layer varies with the state of charge (i.e. Li concentration in LixCoO2). This new physics insight unifies the seemingly contradictory experimental observations and leads to new device design rules to promote interfacial ion transport in future solid-state-battereis. Secondly, we combined contact mechanics with 1D Newman battery model to capture the effect of imperfect electrode/electrolyte interfacial contacts, which can be formed during cell fabrication and worsened due to cycling of solid-state-battereis. Constant current discharging processes at different rates and contact areas were simulated to correlate the capacity drop with the contact area loss. Furthermore, the model suggested how much pressures should be applied to recover the capacity drop due to contact area loss.

Next generation of energy storage and sensors may largely benefit from fast Li⁺ ceramic electrolyte conductors to allow for safe and efficient batteries and real-time monitoring anthropogenic CO₂. Recently, Li-solid state conductors based on Li-garnet structures received attention due to their fast transfer properties and safe operation over a wide temperature range. Through this presentation basic theory and history of Li-garnets will first be introduced and critically reflected towards new device opportunities demonstrating that these electrolytes may be the start of an era to not only store energy or sense the environment but also to emulate environmental data and information based on simple electrochemistry device architecture twists.
In the first part we focus on the fundamental investigation of the electro-chemo-mechanic characteristics and design of disordered to crystallizing Li-garnet structure types and their description. Understanding the fundamental transport in solid state and asking the provocative question: how do Li-amorphous to crystalline structures conduct?
New insights on degree of glassy to crystalline Li-garnet thin films are presented based on model experiments of the structure types. Here, the thermodynamic stability range of maximum Li-conduction, phase, nucleation and growth of nanostructure is discussed using high resolution TEM studies, near order Raman investigations on the Li-bands and electrochemical transport measurements.
In a second part, we focus on new processing opportunities to Lithiate thin film structures in crystalline state and to assure cubic and fast conducting garnet structures for thin film form. For this we will review the field of thin film processing and structure-property for garnet type films and reflect our recent new processing routes based on vacuum and wet-chemical techniques.
The insights provide novel aspects of glass and ceramic thin film processing and material structure designs for both the Li-garnet structures (bulk to films) and their interfaces to electrodes, which we either functionalize to store energy for next generation solid state batteries or ... make new applications such as Li-operated CO₂ sensor tracker chips which we present in a final part.

Polymer-Lithium Lanthanum Zirconium oxide (LLZO) composites have gained traction as a promising candidate to be used as electrolytes for solid state batteries. They can exhibit high ionic conductivity and suitable mechanical properties owing to the complementary characteristics of the ceramic and polymer respectively. However, without intervention, the polymer-ceramic interface is highly resistive. Thus, to achieve facile ion transport across the polymer-ceramic interface it is necessary to minimize the interfacial resistance. We hypothesize that two important factors which limit the interfacial kinetics between the two electrolytes are: 1) surface impurities on the LLZO electrolyte and 2) a large disparity in charge carrier concentration the polymer electrolyte (Polyethylene oxide (PEO)-LiTFSI) and LLZO.

Firstly, we studied the effect of the LLZO heat treatment (HT) temperature on the interfacial impedance between LLZO and PEO-LiTFSI (27:1 [EO]:[Li] ratio) using a trilaminar PEO-LiTFSI/LLZO/PEO-LiTFSI cell configuration. We determined that the interfacial impedance decreased exponentially with increasing LLZO HT temperature. Secondly, we believe that by increasing the Li-ion concentration we would facilitate charge transfer at PEO-LiTFSI/LLZO interface. For this we studied the effect of Li salt concentration in the polymer electrolyte on the interfacial impedance, observing that the interfacial impedance decreases with increasing salt concentration. We achieved an interfacial impedance value of ~390 Ohms.cm² at the optimal [EO]:[Li] salt concentration.

With the results from the two studies, we believe we can further lower the interfacial impedances, achieve facile Li ion transport across the PEO-LiTFSI/LLZO interface and thereby, enable the development of composite electrolytes with high room temperature ionic conductivities.

While the demand for batteries with a high energy density is rapidly growing, the current commercially available Li-ion battery chemistry is approaching a theoretical limit.¹ To overcome this issue, Li-S batteries exploiting the conversion reaction between sulfur and Li₂S have been attracting significant attention as a promising candidate for next-generation batteries.^2,3 The history of the development of conventional Li-S batteries has involved the fight against the notorious shuttle effect caused by polysulfides dissolved in the liquid electrolyte. However, employing solid electrolytes as a separator can mitigate the occurrence of this polysulfide shuttle. Indeed, solid-state Li-S batteries composed of Li-ion conducting thiophosphates (e.g. Li₆PS₅Cl), exhibit no evidence of the shuttle effect.

Nevertheless, there are still several major challenges hindering the development of batteries exhibiting a high capacity and good capacity retention. In this study, the mechanisms of short-term and long-term capacity fade within solid-state Li-S batteries employing Li₆PS₅Cl are investigated. The cause of a crucial capacity loss observed after the initial discharge is elucidated and overcome using a facile cathode processing method, thereby resulting in a specific capacity of over 1000 mAhg_sulfur^-1. The degradation processes affecting the battery performance during long-term cycling are also investigated. Using the results from our investigations toward the optimization of the aforementioned battery architecture, we were able to achieve a specific capacity of 700 mAhg_sulfur^-1 after 100 cycles. A deeper understanding of the underlying chemistry influencing crucial degradation mechanisms will enable further enhancements of both the capacity and cyclability of solid-state Li-S batteries.


References:
(1) Janek, J.; Zeier, W. G. A Solid Future for Battery Development. Nature Energy 2016, 1 (9), 16141.
(2) Suzuki, K.; Mashimo, N.; Ikeda, Y.; Yokoi, T.; Hirayama, M.; Kanno, R. High Cycle Capability of All-Solid-State Lithium-Sulfur Batteries Using Composite Electrodes by Liquid-Phase and Mechanical Mixing. ACS Applied Energy Materials 2018, 1 (6), 2373-2377.
(3) Yang, C.; Zhang, L.; Liu, B.; Xu, S.; Hamann, T.; McOwen, D.; Dai, J.; Luo, W.; Gong, Y.; Wachsman, E. D.; et al. Continuous Plating/Stripping Behavior of Solid-State Lithium Metal Anode in a 3D Ion-Conductive Framework. Proceedings of the National Academy of Sciences 2018, 115 (15) 3770-3775.

Although lithium-ion (Li-ion) battery is one of the most successful energy storage devices, especially for electric vehicle (EV) applications, it retains a thermal runaway risk that stems from the presence of flammable liquid electrolytes made of organic solvents. To overcome this challenge, significant research efforts have been recently devoted on the development of new ceramic electrolytes that can replace the flammable liquid electrolyte and yield an all-solid-state Li-ion batteries. Among various solid electrolytes investigated, Li_6.7La₃Zr_1.7Ta_0.3O₁₂ (LLZT) with garnet structure and Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) in NASICON family showed great promises due to their stabilities in air, high-voltage stability, good mechanical properties, and reasonable Li-ion conductivity (10^-4 – 10^-5 S/cm).

Despite the significant progress in discovering new ceramic electrolytes with promising Li-ion conductivity, a ceramic-based solid-state battery is not commercially available today. The main barrier for a scale-up of solid-state batteries as practical power sources is the instability of electrode-ceramic electrolyte interface and the consequent premature cell-failure. In particular, the fabrication processes of solid-state batteries involve high-temperature heat-treatment to obtain good adhesions between ceramic components. During the sintering process, unwanted elemental inter-diffusion between the electrodes and electrolytes can occur and form secondary phases at interfaces, which often impede the transportation of Li-ions at the interfaces.

In this presentation, we will report our recent systematic study on the interface stability between solid-state electrolytes (e.g., LLZT or LATP) and conventional cathodes in Li-ion batteries including various chemical compositions and crystal structures (e.g., LiCoO₂, LiNiO₂, LiNi_1/3Co_1/3Mn_1/3O₂, LiNi_0.5Mn_1.5O₄, and LiFePO₄). First, we investigated high-temperature phase stabilities between solid-electrolyte and cathode composites, characterized by X-ray diffractometer (XRD) and Rietveld refinement in a temperature range of 500 – 900^oC in air. By identifying crystalline phases at each temperature, we can find (1) on-set temperatures of unwanted side-reactions between solid-electrolytes and cathodes, (2) types of secondary phases and their evolutions depending on temperature, and (3) fundamental reaction mechanisms between different types of solid electrolytes and cathode materials.

In addition to the thermodynamic stabilities at interfaces, we will present the effect of interface stability and microstructure on the electrochemical performances at cathode/solid-electrolyte interfaces. From electrochemical impedance spectroscopy (EIS) and adhesion test combined with scanning electron microscopy (EIS), increasing a sintering temperature offers a trade-off between good adhesion of cathodes and interface stability, which significantly impacts the electrochemical performances of solid-state Li-ion batteries. Therefore, by exploring the phase stability – microstructure – electrochemical performances relationship, we can find the optimal sintering conditions of cathode/solid-electrolyte interfaces.

The results from our systematic study will be essential in determining processing parameters of solid-state Li-ion batteries. Moreover, understanding the fundamental reaction mechanisms between solid-electrolytes and cathode materials will be a prerequisite for a design new solid electrolyte – cathode interfaces in future studies.

The demand for vehicle electrification has created the impetus to develop energy storage technology beyond Li-ion. One approach involves the use solid electrolytes to enable metallic Li anodes, pushing energy densities to 1200 Wh/l. However, the ability to plate Li metal at relatively high current densities (> 3 mA/cm²), has not been demonstrated using solid electrolytes. Moreover, it was reported [1] that in polycrystalline solid electrolyte such as Li_6.25Al_0.25La₃Zr₂O₁₂ (LLZO), Li preferentially deposits intergranularly. We hypothesize that the maximum Li plating rate (or critical current density – CCD) is strongly correlated to the existence of microstructural defects, such as grain boundaries, as initiation points for Li metal propagation. In this work, the role that grain boundaries play in initiating Li metal propagation was studied. DC measurements as a function of current density and evolution of the AC impedance spectra were analyzed to characterize the effects of Li metal penetration above the CCD. The results obtained from this work provide a more comprehensive understanding of the role that microstructural defects, specifically grain boundaries, play in controlling Li plating rates. The knowledge gained will help engineer solid electrolyte microstructures to enable all-solid state batteries using metallic Li anodes.

[1] Cheng, E. J., Sharafi, A., & Sakamoto, J. (2017). Intergranular Li metal propagation through polycrystalline Li 6.25 Al 0.25 La 3 Zr 2 O 12 ceramic electrolyte. Electrochimica Acta, 223, 85-91.

Interest in solid-state electrolytes has grown rapidly in recent years owing to the desire to utilize Li metal anode for improved specific energy density and the inherent safety advantage of a non-flammable solid state electrolyte. A practical solid electrolyte for energy storage must be a fast ion conductor, have negligible electronic conductivity, high relative density and adequate chemical and electrochemical stability with electrodes. For ease of manufacturing and potentially higher power capability we have focused research on oxide ceramic electrolytes. This work will cover our work on the synthesis and characterization of NASICON, perovskite, garnet and newly emergent structural families including how to stabilize the most conductive phase and maximize the ionic conductivity through substitutional chemistry. We will discuss materials synthesis, ionic/electronic conductivity, mechanical properties, Li/water stability and the results will be compared and contrasted for varied structural families of Li-ion solid electrolyte conductors.

Creating new, high conductivity, zero-crossover solid state separators is central to the advance of emerging solid state and other high energy density batteries. In particular, we sodium ion conductors could enable new classes of low cost, high performance systems. Here, we focus on recent progress advancing sodium ion conductors based on materials such as NaSICON or β”-alumina, which typically require elevated temperatures (~250-350°C) for optimal ionic conductivity. Lowering the usable temperature of these materials makes them much more practical for applications such as solid-state batteries. NaSICON ceramics, in particular, are recognized for potential as room temperature sodium ion conductors, and here we highlight our efforts to tailor the composition and structure of NaSICON-based solid state separators for use in ambient or near-ambient applications. We not only explore how variations in NaSICON chemistry can affect conductivity, but also how processing these materials into hybrid architectures and composite materials promises improvements in separator conductance and overall separator performance. We specifically discuss material design, processing, and characterization of separator properties, focusing not only on ionic conductivity, but also on challenges to mechanical behavior and chemical stability of these materials that affect battery safety and long term performance. These emerging solid state separators offer great promise toward a new class of robust and reliable energy storage technologies.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

The concept of all-solid-state Li-ion batteries has gained broad attention in recent years as it has the potential to overcome the energy density and safety limitations of the nowadays widely used Li-ion batteries based on liquid electrolytes. Thin film manufacturing opens up the possibility of further enhancing volumetric and gravimetric energy densities by reducing the amount of inactive materials, lower the costs of production, and enable new applications, like on-chip batteries.

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) electrolyte is a promising ionic superconductor for the development of all-solid-state thin-film batteries. While high ionic conductivities (above 1 mS/cm at RT)¹ have been demonstrated for bulk material in pellet form, processing LLZO in the form of thin films still poses some challenges. Ionic conductivities reported so far lag behind by some orders of magnitude,² and density and conformability are difficult to achieve at the limited sintering temperatures required.

In our work we investigated LLZO thin films deposited by co-sputtering from LLZO, Li₂O and Al₂O₃ targets, and subsequently annealed under a controlled oxidizing atmosphere at a limited temperature of 700°C. Prepared samples were investigated using in-situ grazing-incidence X-ray diffractometry, to assess the crystalline phase and its stability. Scanning electron microscopy and focused-ion-beam time-of-flight secondary ion mass spectrometry were used to analyze the density and the distribution of the substitutional element in the film. The ionic conductivity was measured by in-plane impedance spectroscopy.

In this contribution we will present successful approaches to increase the ionic conductivity of LLZO thin films above 10^-5 S/cm and achieve higher density, uniformity and surface stability, which are key attributes necessary for the implementation of a LLZO-based thin-film battery with a metallic Li anode. In particular, we will discuss how we tackled common challenges in the fabrication of thin-film ceramic Li-ion electrolytes: the stabilization of highly conductive phases at room temperature, the compensation of Li losses during annealing, the densification of the films at relatively low temperatures, and the mitigation of moisture-induced surface degradation.

¹ E. Yi, W. Wang, J. Kieffer, and R. M. Laine, “Key Parameters Governing the Densification of Cubic-Li₇La₃Zr₂O₁₂ Li⁺ Conductors,” Journal of Power Sources, vol. 352, pp. 156–164, Jun. 2017.
² M. Rawlence et al., “Effect of Gallium Substitution on Lithium-Ion Conductivity and Phase Evolution in Sputtered Li_7–3xGa_xLa₃Zr₂O₁₂ Thin Films,” ACS Applied Materials & Interfaces, vol. 10, no. 16, pp. 13720–13728, Apr. 2018.

Lithium conducting garnets such as the lithium lanthanum zirconates (LLZO) are promising solid electrolytes for future lithium ion batteries owing to their beneficial confluence of high ionic conductivity, electrochemical stability / compatibility with metallic lithium, thermal stability, and relative stability under ambient conditions. Conventional synthesis via solid-state reaction is the most common method to obtain phase-pure crystalline LLZO, but generally results in coarse powders with and wide particle size distribution, also requiring long times (often in excess of 12 h) and high processing temperatures (often above 900-1000 °C). Attempts to use more 'advanced' synthesis routes such as sol-gel, combustion, or thin film deposition generally suffer from high reagent cost, high equipment cost, poor scalability of the process, or a combination of these. Further, many of the attractive features of these synthesis methods are offset by poor electrochemical performance. Molten salt synthesis (MSS) has recently been shown to be an alternative synthetic route to obtain garnets with both fine particle size and high ionic conductivity. Acting as high temperature solvents, molten salts present a large design space wherein the properties of the salt melt can be finely tuned to present desirable properties in the as-synthesized material. Further, modifying the basicity of the salt melt enables sometimes substantial reduction in the formation temperature of complex oxides, which is expected to drastically lower the energy cost of synthesis of lithium conducting garnets. However, the increased complexity of chemistry in molten salts presents a non-trivial challenge, requiring finer tuning of both the molten salt medium and precursors to take full advantage of the benefits offered by MSS to obtain pure material. In particular, relative solubility of reagents as well as the stability of LLZO in a given salt melt have substantial implications on crystal chemistry, phase purity, and performance. The work described herein explores a wide range of salt media including 'neutral' media (e.g. molten halides) and 'basic' media (e.g. molten oxosalts), as well as the effect of certain additives, in the synthesis of lithium conducting garnets. Design principles for formation of doped and co-doped LLZO are discussed, wherein salt and reagent composition have direct effects on the formation temperature, particle size, particle size distribution, and electrochemical performance of the as-synthesized material. Depending on the choice of salt medium, powders consisting of single-crystals of LLZO with tunable particle size between 0.5 to 20 µm can be obtained at temperatures as low as 500 °C, while maintaining high ionic conductivity, demonstrating the versatility of the MSS approach for this crucial class of ionic conducting materials.

Types I and II Si and Ge clathrate materials have recently been studied for their electrochemical properties as anodes for lithium-ion batteries due to their unique cage structures and ability to incorporate extrinsic guest atoms. First-principles density functional theory (DFT) calculations were performed to investigate the type I Si and Ge clathrate compounds with and without the guest Ba atoms to understand the optimal structural configurations of small degrees of lithiation and Li diffusion paths inside the clathrates. The studied structures include Si₄₆, Li_xBa_ySi₄₆, Li_xBa_yA_l6Si₄₀ and Li_xBa₈Ge₄₃. The results showed that Li insertion into framework or Ba vacancies could stabilize the clathrate structures. Substitution of Si network atoms by Al lowered the formation energies of the lithiated compounds and mitigated the calculated volume increase upon lithiation. The results also showed that it is energetically feasible for multiple guest atoms to be placed in the Si₂₄ cages. For Ba-doped Ge clathrates, it was found that Li insertion into the three framework vacancies in Ba₈Ge₄₃ is energetically favorable, with a calculated lithiation voltage of 0.77 V versus Li/Li+. However, the high energy barrier (1.6 eV) for Li diffusion between vacancies and around Ba guest atoms suggests that framework vacancies are unlikely to significantly contribute to lithiation processes unless the Ba guest atoms are absent. The results from this study can elucidate the preferred structural configurations for Li in type I, Ba-doped Si and Ge clathrates and also be informative for efforts related to understanding the structures obtained after electrochemical insertion of Li into the clathrates.

All solid-state batteries are considered as one of the primary battery configurations that offers cost-effective and efficient energy storage. Recently, several solid electrolyte materials have demonstrated ionic conductivities that are equivalent to that of organic liquid electrolytes. Low ion conductivities that were previously believed to be the major issue impeding the use of solid electrolytes are no longer the bottleneck. Rather, their interfaces are frequently found to limit the performance of all solid-state batteries. These interfaces include both internal interfaces such as grain boundaries and the interfaces between two electrolytes if the solid electrolyte is a composite or a multilayered material. The associated challenges now include electronic conductivity, mechanical integrity, chemical, and electrochemical instabilities that result in limited current densities, inadequate cyclability, and dendrite growth. These phenomena, however, are challenging to characterize and understand since they are often spatially confined and embedded. Owing to its atomic-level spatial resolution for both imaging and spectroscopy, scanning transmission electron microscopy (STEM) is now a primary technique for addressing the challenges in such studies. In this talk, I will focus on introducing how we use state-of-the-art atomic-resolution STEM and electron energy loss spectroscopy (EELS) to understand the complex phenomena at interfaces in all solid-state batteries. I will also introduce emerging STEM techniques, such as 4D-STEM based differential phase contrast (DPC) imaging and vibrational spectroscopy, and discuss how these methods can benefit research of solid-state ionic materials. I will touch on the importance of understanding synthesis mechanisms regarding interfaces by highlighting examples of our recent work aimed at elucidating synthesis and processing mechanisms of solid electrolytes using in situ electron microscopy and neutron scattering. This work was sponsored by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, the Materials Sciences and Engineering Division, and was performed at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is an Office of Science User Facility.

Lithium sulfide (Li₂S) nanocrystals (NCs) are critical materials used to make solid-state electrolytes and cathodes for emerging battery technologies. Li₂S is typically produced by high temperature carbothermal reduction that creates powders, which then require extensive ball milling to produce the nano-sized materials desirable for battery applications. We have recently developed a solution-based synthesis of Li₂S nanocrystals by contacting metalorganic solutions with hydrogen sulfide at ambient temperature, employing bubble columns for scalable production. Additional benefits include complete abatement of H₂S and recovery of the valuable H₂ stored within. Control of nanocrystal size and uniformity is demonstrated through choice of solvent and manipulation of processing conditions such as precursor concentration and solvent evaporation rate. X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM) were used to quantify crystallinity, particle size distribution (PSD), and morphology, respectively. These complementary techniques confirmed the production of anhydrous, phase-pure Li₂S nanocrystals with tunable size (5-40 nm) and narrow PSDs. Mild annealing conditions were identified that provide the purity required for battery applications, while retaining the original PSD. These materials were used to synthesize simple cathodes and solid-state electrolytes to validate their electrochemical properties. Li₂S cathodes fabricated using small NCs (<10 nm) achieved capacities approaching the theoretical limit (1166 mAh/g), exhibiting good rate capability and promising stability. Control of size is also expected to provide many benefits for solid-state electrolyte production including reduced thermal budgets, improved ionic conductivity, and minimized interfacial resistance. Studies are underway to fabricate Li₂S-P₂S₅ based electrolytes, where it has already been shown that the use of NCs dramatically shortens the ball mixing time required to create the glassy phase relative to commercial powders. We will report on the electrochemical performance of these electrolytes and the integration of these materials in solid- state architectures.

Some of lithium-ion conducting solid electrolytes with rather high ionic conductivity exhibit high sensitivity to air. It is well known that sulfide-based ones hydrolize. Even oxide-based ones, garnet-type lithium ion conductors react with air, resulting in formation of LiOH and Li₂CO₃ on their surface and deterioration of conductivity. Among them, NASICON-type solid electrolytes, such as Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), have been supposed to be stable in air.
In this study, we have found that unusual temperature-dependent ionic conductivity of LATP: ionic conductivity showed negative activation energy from 0 to −15°C on cooling. Detailed studies using high-frequency electrochemical impedance spectroscopy and synchrotron X-ray diffraction confirmed that the unusual temperature-dependence is due to the change in grain boundary resistance, while bulk (inner grain) resistance exhibits monotonic temperature dependence. In addition, this unusual temperature dependence of the grain boundary resistance disappeared after the specimen was annealed in inert atmosphere.
Based on all results, it is proposed that the atmosphere dependent grain boundary resistance was due to the depletion layer formed on the surface and along the grain boundary.
This work conclude that even NASICON-type solid electrolytes is not stable in air.

According to consulting firm, Wood Mackenzie Power & Renewables, more than $500 million was invested in solid-state battery technology in 2018; double that of all previous years combined [1]. At the moment, it may be argued that sulfide solid-state electrolytes (SSEs) have the best combination of performance and manufacturability. Accordingly, ongoing work at General Motors Global R&D is concerned with the development of processing technology for sulfide SSE separators and evaluating how different processing methods affect SSE separator performance. In this presentation, we will compare the properties and performance of sulfide SSE separators made by cold pressing versus melt casting.

The manufacture of prototype bulk all-solid-state Li-ion batteries by a conventional slurry casting method has already been demonstrated [2]. However, the promise of doubling energy density with solid-state technology will only be realized with a Li metal anode. Unfortunately, the slurry cast/cold pressed separators used in all-solid-state Li-ion batteries may have upwards of 10 - 15 % porosity since they are analogous to green-tape ceramics. It has been shown that Li deposits penetrate porous cold compacted sulfide SSE separators, which results in cell failure by shorting [3,4]. Consequently, robust charging of bulk all-solid-state Li metal batteries is limited to elevated temperature and/or low C-rate.

LiI dopants have been shown to improve the resistance of cold-compacted sulfide SSE separators towards Li penetration [4]. However, Porz et al. suggest that dense sulfide glass SSE may fully block Li deposits [5]. The data presented here are the first to show, at a device scale, that dense sulfide glass SSE separators are effective at blocking the penetration of Li metal deposits. Monolithic glass wafers 4-5 cm² in diameter and 400-500 microns thick with a nominal composition of (Li₂S)₆₀(SiS₂)₂₈(P₂S₅)₁₂ were made by melt casting. This glass composition was chosen as a compromise between glass formability and stability versus Li metal; the SiS₂ co-former reduced melt volatility while the P₂S₅ co-former increased the glass’ stability versus Li metal. Symmetric Li | SSE | Li cells were made to measure separator ionic conductivity and critical current density (CCD), the current density at which shorting failure is evident. The resulting melt cast glass had an ionic conductivity of 1.8 mS/cm and a CCD of 1,800 μA/cm² at room temperature. For comparison, porous separators formed by cold compaction of the same glass powder have an ionic conductivity of 0.81 mS/cm and a CCD of only 400 μA/cm² at room temperature. The lower conductivity of the cold compacted separator suggests that percolation and interparticle impedance of sulfide glass electrolytes is significant. Consistent with previous findings, the primary cause of shorting for the cold compacted separator was deposition of Li metal through interparticle porosity. On the other hand, the primary cause of shorting for the melt cast glass wafer was stack pressure induced macrocracking and subsequent Li deposition through the crack. Our work suggests that dense sulfide SSE separators may prove appropriate for Li metal batteries so long as Li/SSE interfacial contact can be maintained at low stack pressures.

References:
[1] M. Jaffe, The Colorado Sun, Jan. 2, 2019.
[2] S. Ito et al., J. Power Sources, 248 (2014): 943 – 950.
[3] C. R. Stoldt and S.-H. Lee, Transducers, 2013.
[4] F. Han et al., Adv. En. Mater., 2018, 1703644.
[5] L. Porz, et al., Adv. En. Mater., 2017, 7, 1701003.

Solid state batteries are attractive for next-generation energy storage as they could provide better safety and higher energy density. There are two major categories of solid electrolytes: ceramic electrolytes and polymer electrolyte. While ceramic electrolytes have high ionic conductivity, they have large interfacial resistance with electrode materials. On the other side, polymer electrolyte has low ionic conductivity, but compatible with state-of-the-art manufacturing process. An attractive approach is to combine polymer and ceramic electrolyte together to combine advantages of both. In this talk, I will discuss recent work in my group to enhancing performance of composite electrolyte-based solid state batteries, which includes 1) vertically aligned ceramic electrolyte in PEO Polymer electrolyte, which enhances ionic conductivity by more than a factor of 3, and reasonable conductivity of 1.7 x 10^-4 S/cm is achieved in PEO/LAGP system. The corresponding LiFePO4/Li cell can be cycled for over 400 cycles with high capacity retention. 2) stabilization of PEO with 4V layered oxide cathode. By optimizing surface coating and electrolyte composition, the cycle life is significantly improved compared to bare layered oxides.

References:
Zhai, H et al., A Flexible Solid Composite Electrolyte with Vertically Aligned and Connected Ion-Conducting Nanoparticles for Lithium Batteries, Nano Letters, 17(5), 3182–3187 (2017).