Investigating The Electro-Mechano-Chemical Coupling Phenomena of an Electrolyte in All Solid-State Battery

Lithium-ion technology's energy density is constrained by negative electrode intercalation. The integration of lithium metal into solid-state batteries shows promise for a substantial enhancement of energy density. It would increase energy density from 372 mAh/g to 3862 mAh/g. However, several challenges persist, including cycling pressure, dendrite growth, and volumetric electrode variations that can lead to detachment and cracks in the electrodes, ultimately causing premature battery degradation.<br/>This study primarily focuses on understanding the intricate relationships between electrochemical and mechanical properties within solid-state batteries. The chosen material is the argyrodite (Li₆PS₅Cl), which exhibits high ionic conductivity (10^-3cm^-1), comparable to that of liquid electrolytes. This material can be easily compacted through cold pressing due to its favorable mechanical properties. According to literature results, the material has a relatively low Young's modulus [E] 25-40 GPa [1,2], classifying it as a soft material, in contrast to oxide families.<br/>The material's intrinsic properties (such as Young's modulus, hardness, viscoelasticity, etc.) were investigated using nanoindentation. In order to overcome the reactivity issues related to air and humidity, we have designed a specific device, inspired by Hikima [2] to conduct nanoindentation test in ambient atmosphere. Young's modulus values for the pure material were around 16 GPa which is lower than literature. The inconsistency in these results is attributed to the shaping process which introduces factors like porosity and surface inhomogeneity, necessitating refinement.<br/>On the other hand we shown that the material has small elastic range, corresponding to its reversible deformation. It becomes evident that expanding the material's elastic range is imperative to accommodate electrode volumetric variations. We studied mechanical properties of argyrodite by a) modifying the particle size to manipulate macrostructural defects, and b) modifying the material's stoichiometry Li_6+xPS_5-x-yO_yZ by introducing elements like (F, Cl, Br, I). This modification is intended to affect the strength of chemical bonds, consequently influencing the Young's modulus.<br/>Simultaneously, on a macroscopic scale, a testing cell is developed to monitor pressure variations during cycling. The Li₄Ti₅O₁₂ / Li₆PS₅Cl | Li₆PS₅Cl | Li₆PS₅Cl / NMC811 (single or polycrystalline) system is the primary focus. The nearly negligible volumetric variation of LTO allows for the examination of pressure changes specifically at the positive electrode. Using this system, we were able to monitor the impact of electrolyte particle size on the pressure variation. Moreover, a composite with polymer is studied to accommodate volume variation and reduce pressure variation at macroscale.<br/>The ultimate goal of this research is to enhance our understanding of the intricate mechanisms involved in the electro-mechano-chemical coupling and the degradation processes within solid-state batteries.<br/>[1] Ai, Q. et al High-Spatial-Resolution Quantitative Chemomechanical Mapping of Organic Composite Cathodes for Sulfide-Based Solid-State Batteries. <i>ACS Energy Lett. </i><b>2023</b>, <i>8 </i>(2), 1107–1113.<br/>[2] Papakyriakou, M. et al. Mechanical Behavior of Inorganic Lithium-Conducting Solid Electrolytes. <i>J. Power Sources </i><b>2021</b>, <i>516</i>, 230672.<br/>[3] McGrogan et al. - <b>2017 </b>- Compliant Yet Brittle Mechanical Behavior of Li s