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

Na_2.5Fe_1.71Zr_0.02(SO₄)₃ with a synergistically optimized electronic and crystal structure is designed for high-performance sodium ion batteries. The orbital interaction induced by Zr doping significantly improves its intrinsic conductivity. Additionally, the longer Na-O bonds after Zr doping accelerate the Na⁺ transfer kinetics. Ultimately, Na_2.5Fe_1.71Zr_0.02(SO₄)₃ exhibits a high specific capacity of 96.4 mAh g^-1 at 0.1C with 85% retention after 10 000 cycles at 30C.