Carbon Coated Fe‐Based Sulphate Nanoparticles within Continuous Conductive Network for Low‐Cost and High‐Performance Symmetrical Sodium‐Ion Batteries

Abstract Fe‐based sulfate materials have attracted much attention in the cathode of sodium‐ion batteries (SIBs) due to their low cost and high operating voltage, as well as possessing application prospects comparable to hard carbon in the anode based on Fe⁰/Fe²⁺/Fe³⁺ redox properties. However, the poor conductivity and the tendency to agglomerate have limited their further application. Herein, the study constructs a dual‐conductive structure that the Na_2.31Fe_1.72(SO₄)₃ particles with amorphous carbon in situ‐coated embedded in ketjen black (KB) conducting carbon networks (NFS/KB) via a solid phase ball‐milling strategy, which effectively enhanced inherent conductivity and electron transfer efficiency among particles of the Fe‐based sulphate. The NFS/KB can provide a reversible capacity of 92 mAh g⁻¹ at 0.1 C and stable cycling stability at high current (85% retention after 500 cycles at 20 C) as cathode of SIBs. Surprisingly, as anode of SIBs, the NFS/KB delivers a rate performance (149 mAh g⁻¹ at 10 C) that is superior to that of hard carbon. Notably, further application of the material to symmetric SIBs also achieves favorable results. This work effectively enhances the performance of Fe‐based sulphate materials in SIBs with a low‐cost carbon modification method, providing a new approach for the low‐cost symmetric SIBs.