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

Abstract

The NASICON-type Na 3 MnTi(PO 4 ) 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 3.5 V 0.5 Mn 0.5 Cr 0.5 Ti 0.5 (PO 4 ) 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.