Delocalized Electron System Enables Stable NASICON Cathode for Sodium-Ion Batteries

The NASICON-type Na₃MnTi(PO₄)₃ is a promising sodium-ion battery cathode material due to its considerable theoretical specific capacity. However, its practical implementation is hindered by inferior kinetics and a stepwise phase transition. Here, we show a multi-d-electron approach for synthesizing a novel NASICON-type material, Na_3.5V_0.5Mn_0.5Cr_0.5Ti_0.5(PO₄)₃, with a delocalized electron system that facilitates electrochemical kinetics and a stable single-phase reaction mechanism with minimal volume change (1.8%). This effectively breaks the performance trade-off among high-rate capability (98.9 mAh g^-1 at 40 C), long-term cycling (88.3% after 10,000 cycles at 40 C), and operation over a temperature range of -40 to 50 °C. Importantly, the pouch-type full cell demonstrates its practical feasibility by achieving 85.2% capacity retention after 500 cycles. This study sheds new light on delocalized electron-driven reaction dynamics and the modulation of phase transitions to realize a high-performance NASICON cathode for sodium-ion batteries.