Cobalt‐Doped FeS2 Nanospheres with Complete Solid Solubility as a High‐Performance Anode Material for Sodium‐Ion Batteries

Abstract

Considering that the high capacity, long‐term cycle life, and high‐rate capability of anode materials for sodium‐ion batteries (SIBs) is a bottleneck currently, a series of Co‐doped FeS 2 solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na‐storage properties were investigated. The optimized Co 0.5 Fe 0.5 S 2 (Fe0.5) has discharge capacities of 0.220 Ah g−1 after 5000 cycles at 2 A g−1 and 0.172 Ah g−1 even at 20 A g−1 with compatible ether‐based electrolyte in a voltage window of 0.8–2.9 V. The Fe0.5 sample transforms to layered NaxCo 0.5 Fe 0.5 S 2 by initial activation, and the layered structure is maintained during following cycles. The redox reactions of NaxCo 0.5 Fe 0.5 S 2 are dominated by pseudocapacitive behavior, leading to fast Na+ insertion/extraction and durable cycle life. A Na 3 V 2(PO 4)3/Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g−1.