Stable Nickel-Rich Layered Oxide Cathodes Enabled by Conformal AlF₃ Nanoshell for High-Voltage All-Solid-State...

Chloride-based solid-state electrolytes (SSEs) emerge as promising catholytes for all-solid-state batteries (ASSBs) because of their high ionic conductivity and good oxidative stability. However, their integration with nickel-rich layered oxides, such as LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), remains hindered by poor interfacial stability, leading to continuous performance degradation, particularly at high operation voltages. Herein, we demonstrate that the surface modification of NCM811 particles through the construction of conformal AlF₃ nanoshells enables stable battery operation at voltages up to 4.8 V with chloride-based SSE Li₃InCl₆. Notably, a solution-based route is developed to first form a uniform (NH₄)₃AlF₆ precursor nanoshell, which was subsequently converted into the AlF₃ surface layer by sintering, thereby overcoming the long-standing synthetic challenge in building AlF₃ coatings. We found that this AlF₃ surface layer not only enhances the structural robustness of NCM811 against surface degradation during the electrochemical cycling, but also effectively suppresses oxidative decomposition of the interfacial Li₃InCl₆ electrolyte, thereby enabling a significantly enhanced high-voltage stability (up to 4.8 V), excellent rate capability (3 C), and prolonged cyclability (≥1000 cycles). This work elucidates the critical role of surface chemistry in governing interfacial and structural evolution in chloride-based ASSBs and provides a generalizable pathway for designing reliable high-energy storage devices.