Tailoring the LiNbO₃ coating of Ni-rich cathode materials for stable and high-performance all-solid-state batteries

The research and development of advanced nanocoatings for high-capacity cathode materials is currently a hot topic in the field of solid-state batteries (SSBs). Protective surface coatings prevent direct contact between the cathode material and solid electrolyte, thereby inhibiting detrimental interfacial decomposition reactions. This is particularly important when using lithium thiophosphate superionic solid electrolytes, as these materials exhibit a narrow electrochemical stability window, and therefore, are prone to degradation during battery operation. Herein we show that the cycling performance of LiNbO₃-coated Ni-rich LiNi_xCo_yMn_zO₂ cathode materials is strongly dependent on the sample history and (coating) synthesis conditions. We demonstrate that post-treatment in a pure oxygen atmosphere at 350 ℃ results in the formation of a surface layer with a unique microstructure, consisting of LiNbO₃ nanoparticles distributed in a carbonate matrix. If tested at 45 ℃ and C/5 rate in pellet-stack SSB full cells with Li₄Ti₅O₁₂ and Li₆PS₅Cl as anode material and solid electrolyte, respectively, around 80% of the initial specific discharge capacity is retained after 200 cycles (~ 160 mAh·g⁻¹, ~ 1.7 mAh·cm⁻²). Our results highlight the importance of tailoring the coating chemistry to the electrode material(s) for practical SSB applications.