Boosting the Sodium Storage Capacity of Floral Spherical Tungsten Disulfide/Nitrogen-Doped Carbon Composites Anode Through Sodium Alginate Binder

Abstract

Tungsten disulfide (WS2) becomes one of the potential anode materials for sodium-ion batteries (SIBs) thanks to its large theoretical specific capacity and interlayer distance. However, the rapid capacity fading and poor rate capability of WS2 constrain its practical application. This study reveals that the unsatisfactory performance is ascribed to the WS2 gradually converted into a conversion reaction between sodium polysulfides (NaPSs) as cycling proceeds, accompanied by pulverization and aggregation of morphological structures. Hence, based on the above mechanism, it is constructed that a porous hierarchical WS2/N-doped carbon (WS2/NC) composites with robust structural stability, fast Na+ diffusion kinetics and exceptional electrical conductivity. Moreover, multifunctional sodium alginate (SA) is used as a unique binder to capture NaPSs and inhibit its shuttling, thereby further boosting the specific capacity, cycling life and rate capability of WS2/NC composites. Consequently, the WS2/NC electrode with SA binder shows a superior specific capacity of 483 mAh g−1 after 800 cycles at 2 A g−1, and a remarkable rate performance up to a capacity of 395 mAh g−1 at 10 A g−1. This study not only uncovers an interesting capacity fading mechanism of WS2 but also effectively improves its performance through multiple combination strategies, which offers a reference for the study of other metal sulfide anodes.

Keywords: Tungsten disulfide, Nitrogen-doped carbon, Sodium alginate, Capacity fading mechanism, sodium-ion batteries