N, S, Se-Codoped dual carbon encapsulation and Se substitution in pyrite-type FeS2 for high-rate and long-life sodium-ion batteries

The use of metal sulfides as anodes in sodium-ion batteries (SIBs) faces significant challenges due to slow reaction kinetics and extensive shuttling of sodium polysulfides (NaPSs). In response, a selenium-substituted iron disulfide encapsulated in a nitrogen-sulfur-selenium-codoped dual carbon framework (Se-FeS2@NSSC) has been engineered for high-performance SIBs. Selenium substitution within the FeS2 lattice improves electrical conductivity, facilitates favorable redox kinetics that reducing the possibility of NaPSs generation. Moreover, the dual NSSC encapsulation promotes Na+/electron transport and efficiently manages volume expansion during electrochemical processes. Strong interfacial interaction (Fe-S-C bonding) between Se-FeS2 and NSSC further suppress NaPSs shuttling, significantly alleviating the cell failure and thus prolonging its lifespan. Consequently, SeFeS2@NSSC demonstrates a top-notch performance, achieving a notable capacity of 725 mAh g(-1) at 0.5 A g(-1), unparalleled rate capability (355.1 mAh g(-1) at 30 A g(-1)), and sustained cyclic stability (89.6 % capacity is retained after 1250 cycles). Theoretical analyses underscore the critical role of selenium in diminishing bulk stress-strain energies, lowering energy barriers for Na+ diffusion, and decreasing Gibbs free energy for conversion reactions, thereby markedly bolstering electrochemical kinetics and overall performance of SeFeS2@NSSC. The insights gleaned from this research foster advancements in developing next-generation anodes with high capacity and durability, representing a promising response to the existing hurdles in SIBs technology.