Stabilizing Effect of a Hybrid Surface Coating on a Ni-Rich NCM Cathode Material in All-Solid-State Batteries

Bulk-type all-solid-state batteries (SSBs) are receiving much attention as next-generation energy storage technology with potentially improved safety and higher power and energy densities (over a wider operating temperature range) compared to conventional Li-ion batteries (LIBs). However, practical implementation of SSBs faces a number of hurdles, such as issues related to interfacial stability between the solid electrolyte (SE) and other active and inactive electrode constituents. One approach to effectively prevent or mitigate side reactions at the positive electrode is through surface coating of the cathode material with a dielectric material. In this article, we report on the preparation of Li2CO3- and Li2CO3/LiNbO3-coated NCM622 (60% Ni) for application in pelletized SSB cells using β-Li3PS4 as the SE. Specifically, we demonstrate that in contrast to state-of-the-art LIBs, the presence of surface carbonate contaminants helps improve the cell cyclability, and the combination of carbonate and niobate species in a kind of hybrid or solid-solution coating is particularly beneficial for achieving stable performance of Ni-rich NCM composite cathodes of practical loading (91% capacity retention after 100 cycles at a C/10 rate and 25 °C). This is in part because of the formation of robust interfaces in the cathode layer, strongly suppressing CO2 evolution (because of decomposition of the relevant carbonate species) and the accompanied SO2 formation and release during cycling operation.