Crystallinity Tailoring of TiNb2O7 Coating Enables Enhanced Interfacial Stability and Electrochemical Performance of NCM811 Cathode for Sulfide-Based All-Solid-State Lithium Batteries

Elemental interdiffusion and interfacial side reactions between sulfide solid-state electrolytes (SSEs) and nickel-rich layered oxide cathodes inevitably form high-impedance, ion-insulating phases at cathode/electrolyte (C/E) interface, which severely degrades the electrochemical performance of all-solid-state lithium batteries (ASSLBs). Herein, we propose a crystallinity-tailored TiNb 2 O 7 (TNO) coating strategy for LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathodes and the long-term interfacial stability of NCM811/SSE interfaces. The ion-conductive yet electron-insulating TNO coating not only guarantees rapid Li + migration across the C/E interface but also effectively suppresses the oxidative decomposition of SSEs at high voltage. More importantly, compared with the high-crystallinity TNO coating, the low-crystallinity counterpart exhibits superior structural adaptability, which can well accommodate the volume changes of NCM811 during Li + insertion/extraction. This unique structural advantage endows the TNO coating with durable protective capability for NCM811 cathodes, especially under high-current-density cycling conditions. Benefiting from the above synergistic effects, the NCM811 cathode modified with low-crystallinity TNO coating synthesized at 500°C (NCM811@T500) delivers a high specific discharge capacity of 150.9 mAh g − 1 after 100 cycles at 0.069 mA cm − 2 and 25°C. This work provides a novel crystallinity-regulation strategy for cathode surface modification, and offers valuable insights into the rational design of high-performance protective coatings for nickel-rich cathodes in sulfide-based ASSLBs.