Air stable and fast-charging cathode material for all climate sodium-ion batteries

The off-stoichiometric compound Na3.12Fe2.44(P2O7)2 (NFPO) is a highly promising, cost-effective, and structurally robust cathode material for sodium-ion batteries (SIBs). However, the slowing Na-ion migration kinetics and poor interface stability have seriously limited its rate capability and air stability. In this work, we successfully synthesis a sodium titanium pyrophosphate (NaTiP2O7 donated as NTPO) coating NFPO (denoted as NFPO-NTPO) cathode material via a liquid phase coating method for SIBs. After optimizing NTPO content, at 0.1C, NFPO-NTPO-4 % cathode achieves a reversible specific capacity of 108.4 mAh g- 1. Remarkably, it maintains 88.39 % capacity at 10C comparing to 0.1C and stabilizes over 3000 cycles with 92.66 % retention rate. Moreover, it retains 88.89 % capacity after 5000 cycles at 20C, even after 28 days of air exposure. The NFPO-Ti cathode, alongside the complete battery system, exhibits remarkable electrochemical performance across a broad temperature range spanning from -40 to 60 degree celsius.