Synergistic electronic and crystal structure regulation of Na 2+2 x Fe 2− x (SO 4 ) 3 via Zr doping for high-performance sodium-ion batteries

Zr doping was applied to synergistically optimize the electronic and crystal structure of Na 2+2 x Fe 2− x (SO 4 ) 3 . This strategy resulted in a high specific capacity of 96.4 mAh g −1 at 0.1C with 85% retention after 10 000 cycles at 30C.