Revealing unprecedented cathode interface behavior in all-solid-state batteries with oxychloride solid electrolytes

All-solid-state lithium batteries (ASSLBs) are highly desirable for their sustainability, enhanced safety, and increased energy densities. The compatibility between cathodes and solid electrolytes (SEs) is critical for ASSLB electrochemical performance. While the conventional LiCoO2 (LCO) cathode shows structural stability, limitations in the energy density and materials cost prompt exploration of Ni-rich, Co-poor cathodes like lithium nickel cobalt manganese oxide (NCM). However, Ni-rich NCM faces challenges with typical solid electrolytes (e.g., sulfides or oxides), hindering high-energy-density ASSLBs. Our study reveals a unique cathode/electrolyte interface behavior with lithium tantalum oxychloride (LTOC) superionic conductors, favoring Co-less, Ni-rich NCM over LCO. The Ta/Co interaction is identified as a failure mechanism for LTOC/LCO, while a kinetically stabilized interface is achieved with lean-Co cathodes. Beyond the cathode material composition, our study also establishes a correlation between the temperature used for battery testing and both interface reactivity and cell performance. This research provides crucial insights into the innovative design of high-performance ASSLBs based on the promising LTOC oxychloride SEs. The superionic conductor, lithium tantalum oxychloride (LTOC), exhibits unprecedented stability with Co-lean and Ni-rich cathodes, while lowering the working temperature proves effective in regulating the Co-rich cathode interface with LTOC.