Achieving Stable High‐Voltage Cycling of P2‐Na 2/3 Ni 1/3 Mn 2/3 O 2 Cathode via Gradient Fluoride‐Based Interfacial Modulation

P2‐Na 2/3 Ni 1/3 Mn 2/3 O 2 is a promising cathode for sodium‐ion batteries, but it suffers irreversible phase transition, lattice oxygen release, and parasitic interfacial side reactions under high‐voltage cycling, leading to severe capacity and voltage fading. Herein, a multifunctional gradient fluoride‐based interfacial layer is fabricated via LiF‐CaF 2 molten‐salt treatment combined with air quenching, which integrates outer fluoride coating and near‐surface Li + /Ca 2+ /F − gradient co‐doping. The fluoride coating physically isolates the cathodes from electrolyte, thereby inhibiting interfacial side reaction and promoting the formation of a robust cathode‐electrolyte interface (CEI) layer. The Li + /Ca 2+ /F − gradient co‐doping introduces high‐energy Ca─O and TM─F bonds to inhibits irreversible phase transition and synergistically suppresses lattice oxygen involvement in redox compensation to improve oxygen redox reversibility. Consequently, the modified P2‐Na 2/3 Ni 1/3 Mn 2/3 O 2 (LCF‐2) achieves stable cycling at 4.5 V, delivering a high capacity retention rate of 90.3% after 200 cycles at 2C with negligible discharge potential decay. Additionally, the full cell coupled with hard carbon achieves a high initial energy density of 237.96 Wh kg −1 (based on cathode mass) at 2C, demonstrating great application potential. This work offers an effective strategy for stabilizing high‐voltage P2‐type cathodes.