Mechanics-Coupled Interface Kinetics in Solid-State Batteries

Abstract

Solid-state batteries (SSBs) utilizing lithium metal anode are promising candidates for next-generation energy storage systems, offering high energy density and enhanced safety. However, imperfect electrochemical contact at the lithium-solid electrolyte (SE) interface results in transport limitations and high interfacial resistance, posing a critical bottleneck on rate performance. Solid-solid point contacts at the interface lead to stress hotspots and current-focusing, resulting in localized lithium deposition, filament growth and mechanical fracture of the SE. The application of external pressures potentially enables enhanced electrochemical contact at such solid-solid interfaces. Under these circumstances, non-uniform stresses arising due to the heterogeneous nature of interface morphology and surface defects play a critical role in the onset of interface instability. In this work, we present a mechanistic description of stress-coupled reaction kinetics governing the evolution of solid-solid interfaces in SSBs. We demonstrate how the energetic contribution of interfacial stresses alters the open circuit potential and exchange current density, which further affects the Butler-Vomer kinetics and morphological stability of the lithium-SE interface. Through our analysis, we illustrate the strong dependence of mechanical stress contributions to reaction current on the material characteristics of the electrode-SE pair and delineate interface stability regimes for different formulations of mechanics-coupled reaction kinetics interactions.