Ultrathin Sb₂S₃ nanosheet anodes for exceptional pseudocapacitive contribution to multi-battery charge storage

Few-layer 2D Sb₂S₃ (2D-SS) nanosheets are synthesized using a simple and scalable exfoliation method assisted by Li intercalation, which are employed as bifunctional anodes for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs) for the first time. The 2D-SS nanosheets present a well-defined layered structure with an ultrathin thickness of 3.8 nm and a lateral size as large as several tens of micrometers, giving rise to an extremely large aspect ratio and surface area, compared to their bulk form before exfoliation. These ameliorating features of 2D-SS nanosheets offer fast high-rate transportation of Li⁺/Na⁺ ions through the short diffusion paths and abundant active sites. The 2D-SS electrode delivers a steady cyclic stability and an outstanding rate capability of 607 mA h g⁻¹ at 2.0 A g⁻¹ in LIBs, while exhibiting a decent capacity of ~680 mA h g⁻¹ at 0.05 A g⁻¹ in SIBs. Remarkably, the 2D-SS anodes present comparable or even better pseudocapacitive behaviors in SIBs than in LIBs, and the anomaly is explained by the better diffusion characteristics of Na atoms than Li atoms along with improved structural integrity after Na adsorption according to the first-principles calculations. Both the Li and Na atoms exhibit higher mobilities on the exfoliated 2D-SS nanosheets than on the bulk counterpart, responsible for the enhanced pseudocapacitive behaviors of the 2D-SS electrode. These new findings will help rationally design high-performance bifunctional anodes for next-generation alkali metal ion batteries.