Transformation of Two-Dimensional Iron Sulfide Nanosheets from FeS 2 to FeS as High-Rate Anodes for Pseudocapacitive Sodium Storage

Exploration of advanced anodes is significant for fabricating high-performance sodium ion batteries (SIBs). Two-dimensional (2D) transition-metal sulfide nanosheets have attracted great interest owing to their fascinating electrochemical performance. In this work, pyrite FeS 2 nanosheets (FeS 2 NSs) and their conversion to hexagonal FeS nanosheets with carbon coating (FeS/C NS) are designed as robust and high-rate anodes of SIBs. Transformation from the FeS 2 NS to FeS/C NS by one-step annealing is investigated. Benefitting from the surface carbon coating and 2D morphology with large lateral size and thin thickness, the FeS/C NS possesses enhanced electron conductivity and ion diffusion coefficients, has a short ion diffusion distance and abundant active sites, and exhibits accelerated reaction kinetics. Consequently, the FeS/C NS shows significantly improved cycling stability and rate capability relative to the FeS 2 and FeS counterparts. The FeS/C NS anode maintains a stable reversible capacity of 388 mA h g –1 after 300 cycles at 1 A g –1 . Impressive capacities of 438 and 391 mA h g –1 can be yielded, respectively, at high current densities of 5 and 10 A g –1, thereby exhibiting superior high rate capability.