Microstructure and Pressure Driven Electrodeposition Stability in Solid-State Batteries

Interfacial deposition stability at the lithium metal-solid electrolyte interface in all solid-state batteries (ASSB) is governed by the stress-transport-electrochemistry coupling in conjunction with the polycrystalline/amorphous solid electrolyte architecture. In this work, we delineate the optimal solid electrolyte microstructure comprising of grains, grain boundary and voids possessing desirable ionic conductivity and elastic modulus for superior transport and strength. An analytical formalism is provided to discern the impact of external “stack” pressure induced mechanical stress on electrodeposition stability; stress magnitude obtained are in the megapascal range considerably diminishing the stress-kinetics effects. For experimental stack pressures ranging up to 10 MPa, the impact of stress on reaction kinetics is negligibly small and electrolyte transport overpotentials dictate electrodeposition stability. We detail the deposition stability phase map as a function of solid electrolyte to Li metal shear modulus and molar volume ratios under varying operating conditions including external pressure, surface roughness, applied current density and ambient temperature. High current density operation with stable deposition can be ensured with ample external pressure, high temperature and low surface roughness operation for low shear modulus ratio of the solid electrolyte to Li metal.