Dual redox catalysis of VN/nitrogen-doped graphene nanocomposites for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as one of the promising candidates for the next-generation energy storage system owing to their high capacity and energy density. However, the durable operation for the batteries is blocked by the shuttle behavior of soluble lithium polysulfides and the sluggish kinetics in the redox process. Here, VN nanoparticles on nitrogen-doped graphene (VN/NG) composite is synthesized by simple calcining method to modify the separators, which can not only chemically trap polysulfides, but also catalyze the conversion reaction between the polysulfides and the insoluble Li2S during the charge/discharge process. The catalytic effects of VN/NG are verified by the calculated activation energy (Ea), which is smaller than the counterpart with NG toward both directions of redox. Because of the synergistic adsorption-catalysis of VN/NG, the cells with VN/NG-modified separators deliver a superior rate performance (791 mAh g−1 at 5C) and cycling stability (863 mAh g−1 after 300 cycles with a low decaying rate of 0.068% per loop at 1C). This work provides a simple preparation strategy and fundamental understanding of the bifunctional catalyst for high-performance Li-S batteries.