In Situ PVDF-Derived LiF-Rich Interphase Enables Air-Stable, High-Voltage Layered Ni-Rich Oxide Cathodes

High-nickel layered cathode materials (LiNi_xMn_yCo_zO₂, x + y + z = 1, x ≥ 0.8) have garnered significant attention for next-generation lithium-ion batteries due to their outstanding energy density. However, increasing the nickel content leads to deteriorated air stability and poor cycling performance at high cutoff voltages, primarily due to interfacial chemical instability and electrochemical degradation. Herein, we report a facile and effective surface modification strategy for LiNi_0.83Co_0.12Mn_0.05O₂ (NCM811), leveraging surface residual alkaline lithium compounds as a lithium source to enable in situ transformation and the concurrent formation of a LiF-rich protective layer. The modified material, referred to as PT-NCM811, exhibits markedly reduced surface impurities after 7 days of air exposure, demonstrating excellent air stability. Furthermore, in a baseline ester-based electrolyte without any additives, PT-NCM811 delivers a capacity retention of 79.2% after 200 cycles at 0.5 C under a high cutoff voltage of 4.4 V vs Li⁺/Li, substantially outperforming the pristine NCM811 counterpart. This work offers a promising avenue for interfacial engineering of high-nickel cathodes and paves the way toward their practical deployment in high-energy-density lithium-ion batteries.