Role of Surface Diffusion Mechanism in Void Formation and Instability at Solid/Solid Electrochemical Interfaces

Solid-state batteries (SSBs) with alkali metal anodes, especially lithium anodes, offer the potential for substantial improvements in energy density, safety, and operational lifespan compared to conventional lithium-ion batteries. However, forming voids at the solid-solid interface is one of the fundamental bottlenecks in developing stable interfaces in SSBs. Disparity between reaction kinetics and metal atom transport near the solid-solid interface leads to nucleation of voids during electro-dissolution. In this work, we have analyzed the role of disparate modes of surface diffusion mechanisms on the lithium metal surface and how those impact the final morphology of the lithium metal surface during lithium stripping. We have developed a mesoscale model that considers all the surface diffusion mechanisms, reaction kinetics, and ionic diffusion inside the inorganic solid electrolyte. We revealed that specific surface diffusion modes influence the nature of non-uniform growth and morphological evolution of voids. We identify distinct stability regimes driven by surface diffusion, transport, and kinetic interactions at the lithium metal and solid electrolyte interface.