Revealing the Role of the Cathode Electrolyte Interface on Solid-State Batteries

Interfaces play crucial, but still poorly understood roles in the performance of secondary solid-state batteries (SSBs). Using crystallographically oriented and highly faceted thick cathodes, we directly assess the impact of cathode crystallography and morphology on long-term performance of SSBs. The controlled interface crystallography, area, and microstructure of these cathodes enables understanding interface instabilities unknown (hidden) in conventional thin film and composite solid-state electrodes. A generic and direct correlation between cell performance and interface stability is revealed for a variety of both lithium and sodium-based cathodes and solid electrolytes. Our findings highlight that minimizing interfacial area, rather than its expansion as is the case in conventional composite cathode, is key to both understanding the nature of interface instabilities and improving cell performance. Our findings also point to the use of dense and thick cathodes as a new path for increasing the energy density and stability of SSBs.