(60ay) Vacancies on 2D Layered W2N3 As Efficient Active Site for Li2Sx Catalytic Conversion in Lithium-Sulfur Battery

Advanced energy-storage technologies are becoming more and more critical with the social demand for energy. Among them, Lithium-sulfur battery (Li-S battery) is a kind of attractive energy-storage technology alternative for next-generation, benefits from the advantages of high theoretical capacity (1672 mAh g^-1), high energy density (2500 Wh kg^-1) and abundant sulfur raw material and so on. However, several technical challenges inhibit further development of Li-S battery. Mainly, the electrical insulating properties of sulfur and its discharge products (Li₂S₂ and Li₂S) led to a slow charge/discharge performance and a low capacity. The large volume change (80 %) of S after lithiation resulted in the structural instability. The lithium polysulfides (Li₂S_n, where 3<n<8) formed during battery charge and discharge. The electrolyte soluble Li₂S_n causes a shuttle effect, which further causes fast capacity fading during battery cycling. It is highly essential to reduce the inherent shuttle effect of polysulfide for Li-S battery performance improvement.

The modification of separators in the Li-S battery has been considered to be a promising strategy to inhibit polysulfide shutting and further improve battery performance. The recent works are mainly focused on carbon materials, metal oxides/sulfides, and their composites to be the interlayer between the cathode and separator, which physically and chemically decrease the polysulfide diffusion to the anode surface. However, the dissolution and diffusion of polysulfide in the organic electrolytes cannot be prevented entirely thermodynamically. The lithium polysulfide conversion is still restricted by its intrinsically sluggish kinetics and the low conductivity of oxides/sulfides. Herein, a two-dimensional (2D) layered W₂N₃ nanosheet is obtained and the nitrogen vacancies are manifested to be active for polysulfide catalytic conversion. Significantly, the nitrogen-vacancy-engineered 2D W₂N₃ exhibits outstanding lithium-sulfur performance, which shows a high reversible discharge capacity of 1062 mAh g^-1at 1.0 C and a capacity fading rate of 0.053 % per cycle after 1000 cycles. The mechanism of electrocatalysis in Li-S is further theoretically and experimentally demonstrated, which provides new insights and opportunities to develop advanced Li–S batteries with highly efficient electrocatalysts for lithium polysulfide conversion.