Enhancing the Capacity and Stability of a Tungsten Disulfide Anode in a Lithium-Ion Battery Using Excess Sulfur.

Tungsten disulfide (WS2) is a transition metal disulfide and a promising anode material due to its layered structure, making it favorable for attaining lithium-ion batteries with rate capability and thermal/mechanical stability. Although WS2 has a rich redox chemistry and a large density, which can increase the specific capacity and volumetric energy density, it still has an inferior specific capacity and poor long-term stability for practical use due to its insufficient space for the accommodation of lithium ions and large volume change during cycling. Herein, to overcome the chronic limitations of WS2-based anodes, we propose a micron-sized tungsten disulfide/reduced graphene oxide composite by employing excess sulfur (Sx-WS2/r-GO). In particular, the excess sulfur modifies the polarity of r-GO by chemically binding on the r-GO sheet during WS2 formation, leading to an increase in the adsorption strength due to WS2. Moreover, the excess sulfur increases the lattice parameter of WS2 and decreases the crystallinity degree, securing additional sites for the accommodation of lithium ions. Therefore, the excess sulfur can increase the specific capacity and impede the separation of the pulverized WS2 nanoparticles, hence mitigating structural decay during cycling. As a result, the Sx-WS2/r-GO anode exhibits an enhanced specific capacity of 1426 mAh g-1 at 0.4 A g-1 and a high cyclic performance, with 87.9% capacity retention after 4000 cycles at a high current density (2.0 A g-1).