Boosting the sodium storage capacity of floral spherical tungsten disulfide/nitrogen-doped carbon composites anode...

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. This study employs pure WS₂ as a case to reveal its unique sodium storage process by ex-situ XPS, which involves the conversion reactions between sodium polysulfide (NaPSs). Furthermore, the pulverization and aggregation of morphological structures triggered by the conversion reaction as well as the shuttling effect of NaPSs can lead to a rapid capacity decay of pure WS₂. Based on the above phenomenon, the dual optimization strategy is proposed to improve electrochemical properties of the electrode material. On the one hand, the porous hierarchical WS₂/nitrogen-doped carbon (WS₂/NC) composites are constructed to strengthen the structural stability and Na⁺ diffusion kinetics; On the other hand, the multifunctional sodium alginate (SA) as a unique binder is used to inhibit NaPSs shuttling, reducing the loss of the active substance and the damage to metallic Na. Consequently, the WS₂/NC electrode with SA binder shows a superior gravimetric/areal capacity of 483 mAh g^-1/0.51 mAh cm^-2 after 800 cycles at 2 A g^-1, and a remarkable rate performance up to a gravimetric/areal capacity of 395 mAh g^-1/0.46 mAh cm^-2 at 10 A g^-1. This study not only uncovers an interesting capacity fading mechanism of WS₂ but also effectively improves its performance through the dual optimization strategy, which offers a reference for the performance enhancement of other metal sulfide anodes.