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

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.