“One stone two birds” design for hollow spherical Na4Fe3(PO4)2P2O7/C cathode enabled high-performance sodium-ion batteries from iron rust

Sodium-ion battery (SIB) is considered as a revolutionary technology toward large-scale energy storage applications. Developing cost-effective cathode material as well as economical synthesis procedure is a key challenge for its commercialization. Herein, we develop a facile and economic strategy to simultaneously remove rust from the surface of carbon steel and achieve porous and hollow spherical Na₄Fe₃(PO₄)₂P₂O₇/C (HS-NFPP/C). Benefiting from the desirable structure that fastens the electronic/ionic transportation and effectively accommodates the volume expansion/contraction during discharge/charge process, the as-prepared cathode exhibits outstanding rate capability and ultralong cycle life. An extraordinarily high-power density of 32.3 kW kg⁻¹ with an ultrahigh capacity retention of 89.7% after 10 000 cycles are achieved. More significantly, the 3 Ah HC||HS-NFPP/C full battery manifests impressive cycling stability. Therefore, this work provides an economical and sustainable approach for the massive production of high-performance Na₄Fe₃(PO₄)₂P₂O₇ cathode, which can be potentially commercialized toward SIB applications.