Symposium S.EN05—Low-Cost Aqueous Rechargeable Battery Technologies

The addition of Mn²⁺ additives in the electrolyte of aqueous zinc-ion batteries (ZIBs), in general, has shown to greatly improve the cyclability of the cathode, very recently. Despite a growing number of studies on this issue with respect to manganese-based cathodes, a complete understanding on the role of Mn²⁺ additive towards the electrochemical reaction in ZIBs has not yet been reached. In such a scenario, we studied the electrochemical activity of one such manganese-based cathode, ZnMn₂O₄ (ZMO) with zinc in a ZIB. Zinc manganate, as a ZIB cathode, is an intriguing choice due to its high theoretical capacity and voltage. We compared the electrochemical reaction of this ZMO nanorods cathode obtained through a simple co-precipitation process in the presence of a 0.1 M MnSO₄ (MS) solution as a full-time electrolyte, as an additive in zinc sulfate (ZMS) electrolyte (1 M ZnSO₄ + 0.1 M MnSO₄) and in its absence or a full-time zinc sulfate (ZS) electrolyte (1 M ZnSO₄), respectively. Systematic investigations including ex situ X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies revealed the reasons for the superior stability and high reversibility of ZMO in the ZMS electrolyte medium. The exceptional performance was facilitated by the the electrochemical equilibrium between Zn²⁺ and Mn²⁺ ions via a stable Zn²⁺ (de)insertion in the bulk, a reversible electro-deposition/dissolution of MnO_x from the Mn²⁺ additive in the electrolyte onto(from) the surface of the cathode and the reversible Zn-insertion into the formed surface MnO₂ layer. This finding is significant as it is contrary to the conventional understanding that the addition of Mn²⁺ merely tends to prevent manganese dissolution thereby facilitating a stable cycle-life performance of the cathode in ZIBs.

Recently, aqueous rechargeable zinc-ion batteries (ARZIBs) have attracted great attention as compared to commercial lithium-ion batteries due to their unique advantages of high intrinsic safety (non-flammable water-based electrolyte) and low cost. [1-3] Over the past few decades, much progress has been focused on the exploration of suitable cathode materials. Among them, vanadium dioxide (B) has been considered as a potential cathode for ARZIBs owing to its unique double layers of V₄O₁₀ type with tunnels, which can facilitate rapid zinc-ions de/insertion processes. [4] However, the reported VO₂ (B) displays a high initial capacity but noticeable capacity fading and especially declines drastically at a high current rate. Compositing VO₂ (B) with an electrically conductive matrix has recently been introduced as an effective way to improve the power capability. However, it can only improve the external electric conductivity and the usage of expensive carbon (graphene) negates the cost advantage of vanadium oxides. Therefore, it is of great importance to construct novel VO₂ (B) electrode materials with excellent electrochemical performance.
Herein, we report an alternative approach to designing and engineering a hierarchical porous Ni-doped vanadium dioxide (B) nanobelts for ARZIBs. The as-synthesized samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The existence of Ni dopant was confirmed by the X-ray absorption near-edge structure studies (XANES) and X-ray photoelectron spectroscopy analysis. Electrochemical studies indicate that the Ni-doped VO₂ nanobelts electrode exhibits superior cycling stability and ultrahigh rate capability with long cycle life, which is significantly higher than that of the undoped VO₂ (B). This can be attributed to the utilization of Ni dopant to electrical wiring the electroactive material, the intrinsic conductivity of VO₂ can be effectively increased. In-operando XRD measurements coupled with ex-situ TEM micrographs taken at specific potentials were exploited to gain a further understanding into the structural evolution upon cycling and ions storage mechanism. The results of the study can potentially open the doors for the widespread application of constructing other elemental doping materials as cathodes with high rate capability and long cycle life for aqueous rechargeable batteries.

References:
[1] Fang G, Zhou J, Pan A, et al. Recent advances in aqueous zinc-ion batteries[J]. ACS Energy Letters, 2018, 3(10): 2480-2501.
[2] Pan H, Shao Y, Yan P, et al. Reversible aqueous zinc/manganese oxide energy storage from conversion reactions. Nature Energy, 2016, 1(5): 16039.
[3] Li H, Ma L, Han C, et al. Advanced rechargeable zinc-based batteries: Recent progress and future perspectives[J]. Nano Energy, 2019.
[4] Mai L, Wei Q, An Q, et al. Nanoscroll buffered hybrid nanostructural VO2 (B) cathodes for high rate and long life lithium storage. Advanced Materials, 2013, 25(21): 2969-2973.

Prussian blue analogue (PBA)-type metal hexacyanoferrates have been considered as significant cathode materials for aqueous rechargeable zinc batteries (ZBs) due to the open face centered cubic framework, multiple active sites, and environmental benign. However, these PBA-type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), inferior rate capability (1A g^-1), and low operating voltage (ca. 1.2 V). This is because the redox active sites of multivalent iron (Fe(III/II)), which dominates its electrochemical activities, can only be very limited activated and thus utilized. The limited activity is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded six cyanogroup per unit, and the inferior conductivity. In this paper, surprisingly, we found high-voltage-scanning can effectively activate the C-coordinated Fe (redox active sites) in FeHCF cathode in ZBs. The activation spurred the increase of capacity at a high operating voltage plateau of ca. 1.5 V. Thanks to this activation, the Zn-FeHCF hybrid-ion battery achieved a record-breaking cycling performance of 5000 (82% capacity retention) and 10000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at super-high current density of 8 A g^-1 (ca. 97 C). To the best of our knowledge, this is the best cycling performance among all the Zn-PBA batteries up to now. As for the mechanism, the reversible distortion and recovering of crystalline structure caused by the (de)insertion of zinc and lithium ions was revealed. The developed strategy of applying a high-voltage-scan to trigger a greatly enhanced overall electrochemical performance of FeHCF can be easily extended to other PBA materials and other battery systems. We believe this work represents a substantial advance on PBA electrode materials and may essentially promote application of PBA materials.

The emerging zinc ion rechargeable batteries show high potential in the fast expanding market of electrochemical energy storage devices owing to their intrinsic safety and low cost, as they use aqueous electrolytes and zinc anodes that are stable and come from abundant sources, while current popular lithium ion batteries employ flammable organic electrolytes. Therefore, it would be very appealing to utilize zinc ion batteries in environments where safety is very crucial, such as ocean or space systems. However, it is challenging to use zinc ion battery in extremely cold environments due to its aqueous electrolyte. Herein we have prepared new flexible quasi-solid-state zinc ion battery consisting of anti-freezing gum-based electrolyte, high-capacity ammonium vanadate cathode and zinc foil anode, for subzero temperature applications. High concentration zinc salts are used to depress the freezing point and maintain the ionic conductivity of the quasi-solid-state electrolyte. The as-prepared battery cells exhibit a reversible capacity of 275mAh/g at 0.2 A/g at room temperature and 170mAh/g at 0 degreeC. When cycled at 0.5 A/g, the cell delivers an initial discharge specific capacity of 155mAh/g and maintains 119mAh/g after 100 cycles at 0 degreeC, and at -20 degreeC it shows an initial discharge capacity of 122mAh/g and a final capacity of 93mAh/g after 100 cycles. The capacity retention becomes higher when cycled at higher rate. As such, the high-performance quasi-solid-state zinc ion batteries with good mechanical flexibility can find potential wide applications in wearable devices and cold environments.

Arguably, aqueous rechargeable Zn-ion Batteries (ARZIBs) are currently the most efficient energy storage device (ESD) for eco-friendly grid-scale applications, as associated with organic batteries such as lithium and sodium-ion batteries. However, for the long-standing storage requests the present cathode materials used in the ARZIBs are not sufficient; due to the poor rate capability and fast capacity fading issues. In the present study, a stable and robust Na2V6O16.3H2O (NVO) Cathode is introduced for ARZIBs, which found to satisfy the above-said uncertainties by delivering superior electrochemical Zn storing capability. In situ synchrotron X-ray diffraction technique is used to establish the Zn storage mechanism in NVO cathode during the Zn (de)insertion stage. The constructed ARZIBs using NVO cathode and metallic Zinc anode in the presence of low-cost ZnSO4 electrolyte delivers high specific energy of 90 Wh kg-1 at a specific power of 15.8 KW kg-1, and superior cycling stability (80% capacity retention after 1000 cycles) at 40C (1c=361 mAh g-1), illuminating the material rewards for an eco-friendly ambiances.

Research interest in aqueous rechargeable zinc-ion batteries (ARZIBs) is growing enormously because of their low-cost and eco-friendly cell components. However, designing high-performance cathode materials towards practical application of ARZIBs remains a great challenge. In this contribution, ground-breaking work on the potassium-pillared V₂O₅.nH₂O (K_0.5V₂O₅.nH₂O) nanorod with exposed layer structure as high-performance cathode for ARZIB is presented. The storage mechanism of the K_0.5V₂O₅.nH₂O cathode in ARZIB is systematically elucidated using a combined of in operando synchrotron X-ray diffraction, ex situ synchrotron X-ray absorption spectroscopy, ex situ TEM analyses, and first-principle calculations. The K_0.5V₂O₅.nH₂O cathode exhibits a remarkable discharge capacity of 439 and 286 mAh g⁻¹ at current densities of 50 and 3000 mA g⁻¹, respectively. Furthermore, it recovers 96% of the capacity after 1500 cycles at 8000 mA g⁻¹. Impressively, the Zn/K_0.5V₂O₅.nH₂O battery offers a specific energy of 121 Wh kg⁻¹ at a high specific power of 6480 W kg⁻¹. The superior performance of the cathode is attributed to its unique exposed layer structure with high surface energy, high conductivity, and low migration barrier. This study provides an insight for designing high-performance cathode materials for ARZIBs and other electrochemical systems.

Batteries play significant role in powering modern electronic devices. Li-ion batteries are widely used in such applications. However, there are several factors such as scarcity of Li metal, major safety issues, cost and life cycle that can affect the long-term applicability of Li-batteries. Recently, aqueous Zn-ion batteries have caught research attention due to their characteristic properties such as intrinsic safety, low cost and high theoretical volumetric capacity desired for safer energy storage system. Due to high molecular weight of Zn metal, the active weight utilization of Zn anode plays major role in designing commercial batteries. Inefficient use of Zn ions from anodes can result in inferior battery performance. The active utilization of Zn anodes can be improved by decreasing the unwanted weight from Zn anodes and increasing electrochemically active surface area. In this study, we used additive manufacturing assisted technique to fabricate 3D Zn anodes. Our results suggest, that 3D Zn anode show higher rate capability at high charge-discharge current as compared to commercial Zn foil. The higher performance owes to the porous surface area of designed 3D Zn anode and can be used for high-performance battery application.

Rechargeable aqueous Zn/MnO₂ batteries are promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fade. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways in Zn/MnO₂. In this talk, I will discuss our latest work on discerning the reaction mechanisms of rechargeable Zn/MnO₂ batteries. We find that both H⁺/Zn²⁺ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions at ∼1.26 V, we successfully demonstrated high power and long life that are superior to most of the reported Zinc-ion Batteries or even some lithium-ion batteries.

Rechargeable aqueous Zn batteries are being actively explored due to the high natural abundance and safety associated with Zn, along with the intrinsic nonflammability and the high ionic conductivity of the aqueous electrolyte. While the individual cell voltage is lower than lithium systems, the benefits may be significant for some application where low cost and nonflammability are key considerations.
Several cathode systems are under exploration for zinc based batteries. The most frequently explored cathode materials are oxides based on the transition metals manganese or vanadium where both layered and tunneled structural motifs have been utilized. The discharge mechanisms can be complex where there can be a combination of H⁺ insertion and Zn²⁺ insertion. Further, the mechanisms can be highly electrolyte dependent.
This presentation will discuss exploration of cathode materials used in Zn based aqueous batteries and their electrochemistry. Characterization methods used for the analysis include cyclic voltammetry, galvanostatic discharge, scanning electrochemical microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy mapping, and x-ray micro- fluorescence spectroscopy will be highlighted.

Since after a new concept of mild acidic aqueous rechargeable zinc-ion batteries (ARZIBs) was introduced in 2011, the technology has been establishing gradually. ARZIBs have proven to be the most eco-friendly energy storage systems (ESSs) as they use zinc as the negative electrode (with a notable large theoretical capacity value of 820 mAh g⁻¹). Zinc is widely available in the Earth's crust and forms a non-toxic, low-cost aqueous electrolyte, thus ensuring low principal investment and high reliability and safety. Till to date, both manganese and vanadium oxides are widely utilized as cathode for this technology and well documented. However, all these oxides have their drawbacks accompanied with their life stability through long-term cycling, particularly at low current rates. The reason is: electrolyte pH change due to metal dissolution during electrochemical reaction, resulting a reversible parasitic reaction which seriously affects the cycling life of a cathode, depending on type of electrolyte being employed. Thus a most reversible product of zinc basic sulfate (ZBS, Zn₄(OH)₆SO₄.nH₂O), an insulating material, formed/dissolved on the cathode-electrolyte interface due to change of electrolyte pH resulting from metal dissolution, when ZnSO₄ utilized as an electrolyte. Irrespective of the cathode used, this side reaction related to ZBS formation is observed in most of the reported ARZIBs. As the reason, most of the reported studies demonstrate long cyclability in metal oxides-based electrodes at very high current drains. In other words, the application of high current drain increases cycle life-span as much as it can before the electrode demonstrates capacity fading due to metal dissolution.
Through Operando analyses, this work establishes the parasitic reaction during electrochemical reaction and document its consequence on the cycle life of the aqueous battery. This will be discussed in detail.

In this work we seek to reduce cost and increase cycle life of a grid scale system by de-emphasizing the requirements for shelf life and short circuit prevention. We show a reconfiguration of the zinc-bromine system creates a system that may “live forever by dying everyday” by eliminating much of the balance-of-plant and exploiting the physical properties of the bromine and zinc. This "solution" also creates new questions. In a system that can safely short circuit at any point, what defines state of charge and state of health? At what point is the battery now "dead"? Is this actually a useful system? The system will be illustrated and current answers to these questions will be discussed.

I will present how quinone based organic materials can be designed to address the short cycle life challenges in aqueous batteries -- the structural and chemical instability of anode electrode plays a critical role. Quinone-based organic crystals can store multiple protons with high reversibility, which makes them promising candidates for the anode materials for aqueous batteries. However, the understanding of molecular structures and packing motifs on proton storage and proton-induced phase transition process is currently lacking. Recently we utilized the synchrotron-based X-ray surface scattering technique to probe the tetrachloro-p-benzoquinone (TCBQ) single crystal surface structure change during H⁺ insertion in operando. TCBQ underwent a two-phase reaction during the proton insertion process as the crystal planes of protonated TCBQ (H₂TCBQ) formed step-by-step on the crystal surface. Quinone-based polymers have also demonstrated superior performance in aqueous Na⁺, Ca²⁺, and Zn²⁺ batteries. We will also present mechanistic studies using in-situ techniques such as EQCM-D, FT-IR, and optical imaging that provide insights on how to optimize ion-solvent-polymer interactions in aqueous batteries to further improve cycle life.

Surface modification of nanoparticles with organic molecules and metal cations is a powerful tool to direct their assembly and catalytic properties. The composition of the inorganic cores determines the ability of nanoparticle to be modified. We will discuss the effect of surface modification and purification on catalytic and photocatalytic properties of the metal and semiconducting nanoparticles. We will also demonstrate that functional materials can be obtained using templated synthesis. The sequential infiltration synthesis which involves diffusion-controlled penetration and subsequent chemisorption of inorganic precursor molecules inside polar domains of the block-copolymer template is proposed as an efficient chemo-physical approach to design highly porous all inorganic single and multi-component nanostructures. We will show that this approach can be efficiently used for the fabrication of films with a low refractive index that enables the design of single-layer and broad-band graded-index anti-reflective coatings (ARCs). The fine-tuning of the refractive index can be achieved via control over the characteristics of the block copolymer templates, and the number of infiltration cycles. We will show that modification of the block-copolymer template with cations of different elements prior to the gas-phase infiltration cycles enables the fabrication of multicomponent structures consisting of highly accessible thermally stable functional centers randomly distributed in the highly porous host matrix.

The Nickel-Zinc battery has an energy density that fits in the gap between Lead-Acid and Li-Ion batteries. Given its non-flammability, environmental friendliness, and relatively low cost, it is an attractive candidate for grid-scale storage and industrial motive applications. With tailored electrodes for optimized rate capability, Nickel-Zinc is also suitable for applications like data center storage and heavy trucking. This presentation will give an overview of this rechargeable alkaline chemistry with an emphasis on large format designs (cell capacity > 120Ah) for a variety of applications. It will cover the strengths and weaknesses of this technology when compared to Lead-Acid and Li-ion. Data will show improved deep cycle performance and superior recharge capability over Lead-Acid. Long term float charge test results will also be discussed, as well as the safety of the chemistry and how this impacts sizing, cost, and management of large-scale energy storage systems.
The presentation will also discuss recent advancements in manufacturability of both positive and negative electrodes that enables high rate production of large format Nickel-Zinc batteries. Manufacturing equipment traditionally used by the Lead-Acid industry has been shown to be suitable in the production of the electrodes used in Nickel-Zinc batteries. This will have a significant impact on manufacturing rate and cost and will allow Ni-Zn to be even more competitive in terms of price.

For energy storage to become ubiquitous in the electric grid, safe, reliable low-cost electrochemical storage technologies manufactured at high volumes with low capital expenditures are needed. Alkaline batteries based on high capacity multi-electron conversion electrodes from low cost, abundant and safe materials, such as a Zn/MnO₂ are a promising technology. These batteries have a theoretical specific energy rivaling that of Li-ion systems (Zn @820 mAh/g and MnO₂ @617 mAh/g, with ~400 Wh/L) and costs reducible to <$50/kWh, when produced at scale (S. Banerjee et al.). While recent advances by Yadav et al. have demonstrated highly reversible Bi- and Cu-stabilized MnO₂ electrodes that can achieve the full 2e^- capacity of MnO₂ in alkaline electrolyte, the ability to pair this electrode with Zn over 5000+ cycles, which equates to ~10-15 years of battery life, remains a difficult challenge.

Zn anodes suffer from irreversible shape change, the redistribution of active material, and passivation over repeated charge and discharge, limiting their achievable capacity and lifetime. Pre-saturating the electrolyte with zincate [Zn(OH)₄^2-], which minimizes dissolution of Zn from the anode and reduces the rate of hydrogen evolution, has recently been shown to enhance cycle life for ~10-35% depth-of-discharge (DOD) Zn anodes by ~100-200% (M. Lim et al.); however, Zn(OH)₄^2- saturated electrolyte is incompatible with high DOD MnO₂, and exacerbates the formation of electrochemically inactive phases, such as ZnMn₂O₄ at the cathode. Hence, using zincate-blocking separators, able to entrap the zincate within the anode and effectively isolate the MnO₂ cathode from Zn(OH)₄^2- crossover, while maintaining hydroxide/cation conductivity, is one approach to improve the reversible cycling of a Zn/MnO₂ cell at high DOD of both MnO₂ and Zn.

Previously, our group has shown that a ceramic Na-ion super ionic conductor (NaSICON) membrane, which completely inhibits Zn(OH)₄^2- crossover, increased cycle life in limited DOD batteries; however, its poor conductivity severely limited the rate capabilities and DOD of MnO₂ (Duay et al.). More recently we have developed a series of permselective polymeric separators (Kolesnichenko et al.) and screened them using our newly-developed anodic stripping voltammetry crossover assay (Duay et al.) to identify those with Zn(OH)₄^2- blocking ability. A primary discharge of MnO₂ was used to demonstrate that a sustained 2^nd e^- discharge plateau, indicative of the absence of zinc species at the cathode, was observed only for Zn/MnO₂ batteries that utilized our selective polymeric separators. Finally, application of these polymeric separators in rechargeable Zn/MnO₂ batteries increased cycle life with higher coulombic efficiencies. Various aspects involved in improving the cycle life of Zn anodes at increased DOD, and of the application of our polymeric separators in isolating the MnO₂ cathode from soluble zincate and their ability to enable higher DOD cycling in Zn, will be discussed.

This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program 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-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Zinc (Zn) and manganese dioxide (MnO₂) are key components of primary alkaline batteries which have dominated the market for decades. They have been demonstrated as promising electrochemical energy storage materials due to the high energy density, low cost, and outstanding safety characteristics. Transforming this non-rechargeable technology into a rechargeable system would enable it as a revolutionary low-cost solution for grid-scale energy storage. However, the poor reversibility of the traditional Zn and MnO₂ materials, especially at high depth of discharge, has limited the achievable energy density and cycle life of this rechargeable battery system.
Recent developments in rechargeable Zn/MnO₂ batteries achieved by the City University of New York Energy Institute (CUNY-EI) in partnership with Urban Electric Power, Inc. (UEP) has presented unique characteristics that could potentially disrupt existing technologies to access a $50BN market. In this talk, the challenges in developing and commercializing rechargeable Zn/MnO₂ batteries for energy storage will be presented, from initial concept through the technical breakthroughs needed to commercialize and manufacture.

Market price points for grid-scale energy storage range from $10− $200 per kWh depending on the application. These cost targets are not possible using lithium-ion technology. Fire safety is also a concern and prohibits lithium-ion in some locations. Lead-acid, Ni-MH, and Ni-Cd currently serve as alternatives, but are too expensive, bulky, and/or contain very toxic materials. Recent research from The City College of New York shows a rechargeable alkaline Mn-Zn battery that is very low cost, very safe fire, contains no toxic materials, and has moderately high energy density. Here we review what is currently known about the materials chemistry of this Mn-Zn battery and show new results of in-operando micro-XRD and XRD-imaging chemistry of the Mn electrode. New materials evolution pathways are identified using the in-operando data.

The silver (Ag)-zinc (Zn) system has the highest theoretical specific (Wh/kg) and volumetric energy density (Wh/L) amongst all rechargeable batteries with the added benefit of safety and non-flammability compared to lithium-ion or lithium metal batteries, which makes it a good and ideal candidate for portable applications like hearing-aids, ear buds and other wearable devices. However, historically, the Ag-Zn battery has suffered from poor rechargeability and low energy utilization. At ZPower, we have tailored the chemistry and engineered a new Ag-Zn battery system, which is highly energy dense and rechargeable, thus making it possible to use it portable applications and giving more power to the consumer to allow them to contribute to a greener future.

As aforementioned, enhancing the capacity of the active materials is paramount for high energy density, which we achieved by developing proprietary additives and approaches. For divalent silver oxide (AgO) cathode, we developed an optimal method of processing the raw materials and novel proprietary conductive coatings for AgO, which allowed integrity control of material properties, faster charge, high capacity utilization and retention for many cycles. The optimal process was verified by experimenting processed AgO cathode under different fast charge rate, where the results showed that it improved the charge capabilities. The role of these coatings was further studied through charge algorithm cycling, where we found that it reduced AgO cathode’s impedance compared to the control tests and maintained its active surface area. More importantly, we found that the morphology of the proprietary conductive coatings played a crucial role in efficiently utilizing the AgO cathode’s capacity.

For the Zn anode, where it has a theoretical specific capacity of 820 mAh/g; however, Zn has a long history of poor rechargeability due to problems like shape change (zinc redistribution), dendrite formation and passivation. In the past, previous researchers tried altering the Zn formulation to increase utilization; however, these attempts were not fruitful. We have engineered a new Zn anode that can access 94% of its theoretical capacity in a single primary discharge and 56% of its theoretical capacity rechargeably for over 300 cycles. We achieved this breakthrough by developing proprietary additives and methods that localize the Zn to the current collector and prevent dendrite formation. We showed that with incorporating these additives into Zn anode, it further helped mitigating shorting for 400 + cycles.

Realizing a next-generation battery that meets or exceeds the system energy density of lithium batteries while capturing attributes beyond the reach of lithium batteries requires a balancing act. The elements that comprise aqueous, safer-than-lithium batteries need to be reasonably naturally abundant, can be acquired through low-risk supply chains, are nontoxic, and can be fabricated, modified, and assembled using green protocols. Zinc checks all those boxes and now that monolithic spongy zinc negative electrodes open new performance terrain—rechargeably cycled at high rate, to deep utilization of the metal—a broad class of rechargeable zinc-based aqueous batteries is finally possible. We perform the systems analysis to show that zinc anodes versus either MnO₂ cathodes or air cathodes satisfy energy storage at low cost while meeting the sustainability sought for batteries beyond lithium.

Rechargeable aqueous Zn/MnO₂ batteries are promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fade. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways in Zn/MnO₂. In this talk, I will discuss our latest work on discerning the reaction mechanisms of rechargeable Zn/MnO₂ batteries. We find that both H⁺/Zn²⁺ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions at ∼1.26 V, we successfully demonstrated high power and long life that are superior to most of the reported Zinc-ion Batteries or even some lithium-ion batteries.

Rechargeable aqueous Zn batteries are being actively explored due to the high natural abundance and safety associated with Zn, along with the intrinsic nonflammability and the high ionic conductivity of the aqueous electrolyte. While the individual cell voltage is lower than lithium systems, the benefits may be significant for some application where low cost and nonflammability are key considerations.
Several cathode systems are under exploration for zinc based batteries. The most frequently explored cathode materials are oxides based on the transition metals manganese or vanadium where both layered and tunneled structural motifs have been utilized. The discharge mechanisms can be complex where there can be a combination of H⁺ insertion and Zn²⁺ insertion. Further, the mechanisms can be highly electrolyte dependent.
This presentation will discuss exploration of cathode materials used in Zn based aqueous batteries and their electrochemistry. Characterization methods used for the analysis include cyclic voltammetry, galvanostatic discharge, scanning electrochemical microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy mapping, and x-ray micro- fluorescence spectroscopy will be highlighted.

The Nickel-Zinc battery has an energy density that fits in the gap between Lead-Acid and Li-Ion batteries. Given its non-flammability, environmental friendliness, and relatively low cost, it is an attractive candidate for grid-scale storage and industrial motive applications. With tailored electrodes for optimized rate capability, Nickel-Zinc is also suitable for applications like data center storage and heavy trucking. This presentation will give an overview of this rechargeable alkaline chemistry with an emphasis on large format designs (cell capacity > 120Ah) for a variety of applications. It will cover the strengths and weaknesses of this technology when compared to Lead-Acid and Li-ion. Data will show improved deep cycle performance and superior recharge capability over Lead-Acid. Long term float charge test results will also be discussed, as well as the safety of the chemistry and how this impacts sizing, cost, and management of large-scale energy storage systems.
The presentation will also discuss recent advancements in manufacturability of both positive and negative electrodes that enables high rate production of large format Nickel-Zinc batteries. Manufacturing equipment traditionally used by the Lead-Acid industry has been shown to be suitable in the production of the electrodes used in Nickel-Zinc batteries. This will have a significant impact on manufacturing rate and cost and will allow Ni-Zn to be even more competitive in terms of price.

The silver (Ag)-zinc (Zn) system has the highest theoretical specific (Wh/kg) and volumetric energy density (Wh/L) amongst all rechargeable batteries with the added benefit of safety and non-flammability compared to lithium-ion or lithium metal batteries, which makes it a good and ideal candidate for portable applications like hearing-aids, ear buds and other wearable devices. However, historically, the Ag-Zn battery has suffered from poor rechargeability and low energy utilization. At ZPower, we have tailored the chemistry and engineered a new Ag-Zn battery system, which is highly energy dense and rechargeable, thus making it possible to use it portable applications and giving more power to the consumer to allow them to contribute to a greener future.

As aforementioned, enhancing the capacity of the active materials is paramount for high energy density, which we achieved by developing proprietary additives and approaches. For divalent silver oxide (AgO) cathode, we developed an optimal method of processing the raw materials and novel proprietary conductive coatings for AgO, which allowed integrity control of material properties, faster charge, high capacity utilization and retention for many cycles. The optimal process was verified by experimenting processed AgO cathode under different fast charge rate, where the results showed that it improved the charge capabilities. The role of these coatings was further studied through charge algorithm cycling, where we found that it reduced AgO cathode’s impedance compared to the control tests and maintained its active surface area. More importantly, we found that the morphology of the proprietary conductive coatings played a crucial role in efficiently utilizing the AgO cathode’s capacity.

For the Zn anode, where it has a theoretical specific capacity of 820 mAh/g; however, Zn has a long history of poor rechargeability due to problems like shape change (zinc redistribution), dendrite formation and passivation. In the past, previous researchers tried altering the Zn formulation to increase utilization; however, these attempts were not fruitful. We have engineered a new Zn anode that can access 94% of its theoretical capacity in a single primary discharge and 56% of its theoretical capacity rechargeably for over 300 cycles. We achieved this breakthrough by developing proprietary additives and methods that localize the Zn to the current collector and prevent dendrite formation. We showed that with incorporating these additives into Zn anode, it further helped mitigating shorting for 400 + cycles.

For energy storage to become ubiquitous in the electric grid, safe, reliable low-cost electrochemical storage technologies manufactured at high volumes with low capital expenditures are needed. Alkaline batteries based on high capacity multi-electron conversion electrodes from low cost, abundant and safe materials, such as a Zn/MnO₂ are a promising technology. These batteries have a theoretical specific energy rivaling that of Li-ion systems (Zn @820 mAh/g and MnO₂ @617 mAh/g, with ~400 Wh/L) and costs reducible to <$50/kWh, when produced at scale (S. Banerjee et al.). While recent advances by Yadav et al. have demonstrated highly reversible Bi- and Cu-stabilized MnO₂ electrodes that can achieve the full 2e^- capacity of MnO₂ in alkaline electrolyte, the ability to pair this electrode with Zn over 5000+ cycles, which equates to ~10-15 years of battery life, remains a difficult challenge.

Zn anodes suffer from irreversible shape change, the redistribution of active material, and passivation over repeated charge and discharge, limiting their achievable capacity and lifetime. Pre-saturating the electrolyte with zincate [Zn(OH)₄^2-], which minimizes dissolution of Zn from the anode and reduces the rate of hydrogen evolution, has recently been shown to enhance cycle life for ~10-35% depth-of-discharge (DOD) Zn anodes by ~100-200% (M. Lim et al.); however, Zn(OH)₄^2- saturated electrolyte is incompatible with high DOD MnO₂, and exacerbates the formation of electrochemically inactive phases, such as ZnMn₂O₄ at the cathode. Hence, using zincate-blocking separators, able to entrap the zincate within the anode and effectively isolate the MnO₂ cathode from Zn(OH)₄^2- crossover, while maintaining hydroxide/cation conductivity, is one approach to improve the reversible cycling of a Zn/MnO₂ cell at high DOD of both MnO₂ and Zn.

Previously, our group has shown that a ceramic Na-ion super ionic conductor (NaSICON) membrane, which completely inhibits Zn(OH)₄^2- crossover, increased cycle life in limited DOD batteries; however, its poor conductivity severely limited the rate capabilities and DOD of MnO₂ (Duay et al.). More recently we have developed a series of permselective polymeric separators (Kolesnichenko et al.) and screened them using our newly-developed anodic stripping voltammetry crossover assay (Duay et al.) to identify those with Zn(OH)₄^2- blocking ability. A primary discharge of MnO₂ was used to demonstrate that a sustained 2^nd e^- discharge plateau, indicative of the absence of zinc species at the cathode, was observed only for Zn/MnO₂ batteries that utilized our selective polymeric separators. Finally, application of these polymeric separators in rechargeable Zn/MnO₂ batteries increased cycle life with higher coulombic efficiencies. Various aspects involved in improving the cycle life of Zn anodes at increased DOD, and of the application of our polymeric separators in isolating the MnO₂ cathode from soluble zincate and their ability to enable higher DOD cycling in Zn, will be discussed.

This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program 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-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Zinc (Zn) and manganese dioxide (MnO₂) are key components of primary alkaline batteries which have dominated the market for decades. They have been demonstrated as promising electrochemical energy storage materials due to the high energy density, low cost, and outstanding safety characteristics. Transforming this non-rechargeable technology into a rechargeable system would enable it as a revolutionary low-cost solution for grid-scale energy storage. However, the poor reversibility of the traditional Zn and MnO₂ materials, especially at high depth of discharge, has limited the achievable energy density and cycle life of this rechargeable battery system.
Recent developments in rechargeable Zn/MnO₂ batteries achieved by the City University of New York Energy Institute (CUNY-EI) in partnership with Urban Electric Power, Inc. (UEP) has presented unique characteristics that could potentially disrupt existing technologies to access a $50BN market. In this talk, the challenges in developing and commercializing rechargeable Zn/MnO₂ batteries for energy storage will be presented, from initial concept through the technical breakthroughs needed to commercialize and manufacture.

Market price points for grid-scale energy storage range from $10− $200 per kWh depending on the application. These cost targets are not possible using lithium-ion technology. Fire safety is also a concern and prohibits lithium-ion in some locations. Lead-acid, Ni-MH, and Ni-Cd currently serve as alternatives, but are too expensive, bulky, and/or contain very toxic materials. Recent research from The City College of New York shows a rechargeable alkaline Mn-Zn battery that is very low cost, very safe fire, contains no toxic materials, and has moderately high energy density. Here we review what is currently known about the materials chemistry of this Mn-Zn battery and show new results of in-operando micro-XRD and XRD-imaging chemistry of the Mn electrode. New materials evolution pathways are identified using the in-operando data.

Realizing a next-generation battery that meets or exceeds the system energy density of lithium batteries while capturing attributes beyond the reach of lithium batteries requires a balancing act. The elements that comprise aqueous, safer-than-lithium batteries need to be reasonably naturally abundant, can be acquired through low-risk supply chains, are nontoxic, and can be fabricated, modified, and assembled using green protocols. Zinc checks all those boxes and now that monolithic spongy zinc negative electrodes open new performance terrain—rechargeably cycled at high rate, to deep utilization of the metal—a broad class of rechargeable zinc-based aqueous batteries is finally possible. We perform the systems analysis to show that zinc anodes versus either MnO₂ cathodes or air cathodes satisfy energy storage at low cost while meeting the sustainability sought for batteries beyond lithium.

Since after a new concept of mild acidic aqueous rechargeable zinc-ion batteries (ARZIBs) was introduced in 2011, the technology has been establishing gradually. ARZIBs have proven to be the most eco-friendly energy storage systems (ESSs) as they use zinc as the negative electrode (with a notable large theoretical capacity value of 820 mAh g⁻¹). Zinc is widely available in the Earth's crust and forms a non-toxic, low-cost aqueous electrolyte, thus ensuring low principal investment and high reliability and safety. Till to date, both manganese and vanadium oxides are widely utilized as cathode for this technology and well documented. However, all these oxides have their drawbacks accompanied with their life stability through long-term cycling, particularly at low current rates. The reason is: electrolyte pH change due to metal dissolution during electrochemical reaction, resulting a reversible parasitic reaction which seriously affects the cycling life of a cathode, depending on type of electrolyte being employed. Thus a most reversible product of zinc basic sulfate (ZBS, Zn₄(OH)₆SO₄.nH₂O), an insulating material, formed/dissolved on the cathode-electrolyte interface due to change of electrolyte pH resulting from metal dissolution, when ZnSO₄ utilized as an electrolyte. Irrespective of the cathode used, this side reaction related to ZBS formation is observed in most of the reported ARZIBs. As the reason, most of the reported studies demonstrate long cyclability in metal oxides-based electrodes at very high current drains. In other words, the application of high current drain increases cycle life-span as much as it can before the electrode demonstrates capacity fading due to metal dissolution.
Through Operando analyses, this work establishes the parasitic reaction during electrochemical reaction and document its consequence on the cycle life of the aqueous battery. This will be discussed in detail.

The addition of Mn²⁺ additives in the electrolyte of aqueous zinc-ion batteries (ZIBs), in general, has shown to greatly improve the cyclability of the cathode, very recently. Despite a growing number of studies on this issue with respect to manganese-based cathodes, a complete understanding on the role of Mn²⁺ additive towards the electrochemical reaction in ZIBs has not yet been reached. In such a scenario, we studied the electrochemical activity of one such manganese-based cathode, ZnMn₂O₄ (ZMO) with zinc in a ZIB. Zinc manganate, as a ZIB cathode, is an intriguing choice due to its high theoretical capacity and voltage. We compared the electrochemical reaction of this ZMO nanorods cathode obtained through a simple co-precipitation process in the presence of a 0.1 M MnSO₄ (MS) solution as a full-time electrolyte, as an additive in zinc sulfate (ZMS) electrolyte (1 M ZnSO₄ + 0.1 M MnSO₄) and in its absence or a full-time zinc sulfate (ZS) electrolyte (1 M ZnSO₄), respectively. Systematic investigations including ex situ X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies revealed the reasons for the superior stability and high reversibility of ZMO in the ZMS electrolyte medium. The exceptional performance was facilitated by the the electrochemical equilibrium between Zn²⁺ and Mn²⁺ ions via a stable Zn²⁺ (de)insertion in the bulk, a reversible electro-deposition/dissolution of MnO_x from the Mn²⁺ additive in the electrolyte onto(from) the surface of the cathode and the reversible Zn-insertion into the formed surface MnO₂ layer. This finding is significant as it is contrary to the conventional understanding that the addition of Mn²⁺ merely tends to prevent manganese dissolution thereby facilitating a stable cycle-life performance of the cathode in ZIBs.

Recently, aqueous rechargeable zinc-ion batteries (ARZIBs) have attracted great attention as compared to commercial lithium-ion batteries due to their unique advantages of high intrinsic safety (non-flammable water-based electrolyte) and low cost. [1-3] Over the past few decades, much progress has been focused on the exploration of suitable cathode materials. Among them, vanadium dioxide (B) has been considered as a potential cathode for ARZIBs owing to its unique double layers of V₄O₁₀ type with tunnels, which can facilitate rapid zinc-ions de/insertion processes. [4] However, the reported VO₂ (B) displays a high initial capacity but noticeable capacity fading and especially declines drastically at a high current rate. Compositing VO₂ (B) with an electrically conductive matrix has recently been introduced as an effective way to improve the power capability. However, it can only improve the external electric conductivity and the usage of expensive carbon (graphene) negates the cost advantage of vanadium oxides. Therefore, it is of great importance to construct novel VO₂ (B) electrode materials with excellent electrochemical performance.
Herein, we report an alternative approach to designing and engineering a hierarchical porous Ni-doped vanadium dioxide (B) nanobelts for ARZIBs. The as-synthesized samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The existence of Ni dopant was confirmed by the X-ray absorption near-edge structure studies (XANES) and X-ray photoelectron spectroscopy analysis. Electrochemical studies indicate that the Ni-doped VO₂ nanobelts electrode exhibits superior cycling stability and ultrahigh rate capability with long cycle life, which is significantly higher than that of the undoped VO₂ (B). This can be attributed to the utilization of Ni dopant to electrical wiring the electroactive material, the intrinsic conductivity of VO₂ can be effectively increased. In-operando XRD measurements coupled with ex-situ TEM micrographs taken at specific potentials were exploited to gain a further understanding into the structural evolution upon cycling and ions storage mechanism. The results of the study can potentially open the doors for the widespread application of constructing other elemental doping materials as cathodes with high rate capability and long cycle life for aqueous rechargeable batteries.

References:
[1] Fang G, Zhou J, Pan A, et al. Recent advances in aqueous zinc-ion batteries[J]. ACS Energy Letters, 2018, 3(10): 2480-2501.
[2] Pan H, Shao Y, Yan P, et al. Reversible aqueous zinc/manganese oxide energy storage from conversion reactions. Nature Energy, 2016, 1(5): 16039.
[3] Li H, Ma L, Han C, et al. Advanced rechargeable zinc-based batteries: Recent progress and future perspectives[J]. Nano Energy, 2019.
[4] Mai L, Wei Q, An Q, et al. Nanoscroll buffered hybrid nanostructural VO2 (B) cathodes for high rate and long life lithium storage. Advanced Materials, 2013, 25(21): 2969-2973.

Prussian blue analogue (PBA)-type metal hexacyanoferrates have been considered as significant cathode materials for aqueous rechargeable zinc batteries (ZBs) due to the open face centered cubic framework, multiple active sites, and environmental benign. However, these PBA-type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), inferior rate capability (1A g^-1), and low operating voltage (ca. 1.2 V). This is because the redox active sites of multivalent iron (Fe(III/II)), which dominates its electrochemical activities, can only be very limited activated and thus utilized. The limited activity is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded six cyanogroup per unit, and the inferior conductivity. In this paper, surprisingly, we found high-voltage-scanning can effectively activate the C-coordinated Fe (redox active sites) in FeHCF cathode in ZBs. The activation spurred the increase of capacity at a high operating voltage plateau of ca. 1.5 V. Thanks to this activation, the Zn-FeHCF hybrid-ion battery achieved a record-breaking cycling performance of 5000 (82% capacity retention) and 10000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at super-high current density of 8 A g^-1 (ca. 97 C). To the best of our knowledge, this is the best cycling performance among all the Zn-PBA batteries up to now. As for the mechanism, the reversible distortion and recovering of crystalline structure caused by the (de)insertion of zinc and lithium ions was revealed. The developed strategy of applying a high-voltage-scan to trigger a greatly enhanced overall electrochemical performance of FeHCF can be easily extended to other PBA materials and other battery systems. We believe this work represents a substantial advance on PBA electrode materials and may essentially promote application of PBA materials.

In this work we seek to reduce cost and increase cycle life of a grid scale system by de-emphasizing the requirements for shelf life and short circuit prevention. We show a reconfiguration of the zinc-bromine system creates a system that may “live forever by dying everyday” by eliminating much of the balance-of-plant and exploiting the physical properties of the bromine and zinc. This "solution" also creates new questions. In a system that can safely short circuit at any point, what defines state of charge and state of health? At what point is the battery now "dead"? Is this actually a useful system? The system will be illustrated and current answers to these questions will be discussed.

I will present how quinone based organic materials can be designed to address the short cycle life challenges in aqueous batteries -- the structural and chemical instability of anode electrode plays a critical role. Quinone-based organic crystals can store multiple protons with high reversibility, which makes them promising candidates for the anode materials for aqueous batteries. However, the understanding of molecular structures and packing motifs on proton storage and proton-induced phase transition process is currently lacking. Recently we utilized the synchrotron-based X-ray surface scattering technique to probe the tetrachloro-p-benzoquinone (TCBQ) single crystal surface structure change during H⁺ insertion in operando. TCBQ underwent a two-phase reaction during the proton insertion process as the crystal planes of protonated TCBQ (H₂TCBQ) formed step-by-step on the crystal surface. Quinone-based polymers have also demonstrated superior performance in aqueous Na⁺, Ca²⁺, and Zn²⁺ batteries. We will also present mechanistic studies using in-situ techniques such as EQCM-D, FT-IR, and optical imaging that provide insights on how to optimize ion-solvent-polymer interactions in aqueous batteries to further improve cycle life.

The emerging zinc ion rechargeable batteries show high potential in the fast expanding market of electrochemical energy storage devices owing to their intrinsic safety and low cost, as they use aqueous electrolytes and zinc anodes that are stable and come from abundant sources, while current popular lithium ion batteries employ flammable organic electrolytes. Therefore, it would be very appealing to utilize zinc ion batteries in environments where safety is very crucial, such as ocean or space systems. However, it is challenging to use zinc ion battery in extremely cold environments due to its aqueous electrolyte. Herein we have prepared new flexible quasi-solid-state zinc ion battery consisting of anti-freezing gum-based electrolyte, high-capacity ammonium vanadate cathode and zinc foil anode, for subzero temperature applications. High concentration zinc salts are used to depress the freezing point and maintain the ionic conductivity of the quasi-solid-state electrolyte. The as-prepared battery cells exhibit a reversible capacity of 275mAh/g at 0.2 A/g at room temperature and 170mAh/g at 0 degreeC. When cycled at 0.5 A/g, the cell delivers an initial discharge specific capacity of 155mAh/g and maintains 119mAh/g after 100 cycles at 0 degreeC, and at -20 degreeC it shows an initial discharge capacity of 122mAh/g and a final capacity of 93mAh/g after 100 cycles. The capacity retention becomes higher when cycled at higher rate. As such, the high-performance quasi-solid-state zinc ion batteries with good mechanical flexibility can find potential wide applications in wearable devices and cold environments.

Surface modification of nanoparticles with organic molecules and metal cations is a powerful tool to direct their assembly and catalytic properties. The composition of the inorganic cores determines the ability of nanoparticle to be modified. We will discuss the effect of surface modification and purification on catalytic and photocatalytic properties of the metal and semiconducting nanoparticles. We will also demonstrate that functional materials can be obtained using templated synthesis. The sequential infiltration synthesis which involves diffusion-controlled penetration and subsequent chemisorption of inorganic precursor molecules inside polar domains of the block-copolymer template is proposed as an efficient chemo-physical approach to design highly porous all inorganic single and multi-component nanostructures. We will show that this approach can be efficiently used for the fabrication of films with a low refractive index that enables the design of single-layer and broad-band graded-index anti-reflective coatings (ARCs). The fine-tuning of the refractive index can be achieved via control over the characteristics of the block copolymer templates, and the number of infiltration cycles. We will show that modification of the block-copolymer template with cations of different elements prior to the gas-phase infiltration cycles enables the fabrication of multicomponent structures consisting of highly accessible thermally stable functional centers randomly distributed in the highly porous host matrix.