Stabilizing the Cathode/Electrolyte Interface Using a Dry-Processed Lithium Titanate Coating for All-Solid-State Batteries

Considering the high theoretical energy density and improved safety, thiophosphate-based all-solid-state batteries (ASSBs) have become one of the most promising candidates for next-generation energy storage systems. However, the intrinsic electrochemical instability of thiophosphate-based solid electrolytes in contact with oxide-based cathodes results in rapid capacity fading and has driven the need of protective cathode coatings. In this work, for the first time, a fumed lithium titanate (LTO) powder-based coating has been applied to Ni-rich oxide-based cathode active material (CAM) using a newly developed dry-coating process. The LTO cathode coating has been tested in thiophosphate-based ASSBs. It exhibits a significantly improved C-rate performance along with superior long-term cycling stability. The improved electrochemical performance is attributed to a reduced interfacial resistance between coated cathode and solid electrolyte as deduced from in-depth electrochemical impedance spectroscopy analysis. These results open up a new, facile dry-coating route to fabricate effective protective CAM coatings to enable long-life ASSBs. This nondestructive coating process with no post-heat-treatment approach is expected to simplify the coating process for a wide range of coatings and cathode materials, resulting in much improved cathode/electrolyte interfacial stability and electrochemical performance of ASSBs.