Engineering a superionic conductor surface enables fast Na⁺ transport kinetics for high-stable layered oxide cathode

Unstable cathode/electrolyte interphase and severe interfacial side reaction have long been identified as the main cause for the failure of layered oxide cathode during fast charging and long-term cycling for rechargeable sodium-ion batteries. Here, we report a superionic conductor (Na₃V₂(PO₄)₃, NVP) bonding surface strategy for O3-type layered NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathode to suppress electrolyte corrosion and near-surface structure deconstruction, especially at high operating potential. The strong bonding affinity at the NVP/NFM contact interface stabilizes the crystal structure by inhibiting surface parasitic reactions and transition metal dissolution, thus significantly improving the phase change reversibility at high desodiation state and prolonging the lifespan of NFM cathode. Due to the high-electron-conductivity of NFM, the redox activity of NVP is also enhanced to provide additional capacity. Therefore, benefiting from the fast ion transport kinetics and electrochemical Na⁺-storage activity of NVP, the composite NFM@NVP electrode displays a high initial coulombic efficiency of 95.5 % at 0.1 C and excellent rate capability (100 mAh g^-1 at 20 C) within high cutoff voltage of 4.2 V. The optimized cathode also delivers preeminent cyclic stability with ∼80 % capacity retention after 500 cycles at 2 C. This work sheds light on a facile and universal strategy on improving interphase stability to develop fast-charging and sustainable batteries.