Accelerated polysulfide conversion on hierarchical porous vanadium-nitrogen-carbon for advanced lithium-sulfur batteries.

With high theoretical specific density, low cost, and non-toxicity, Li-S batteries are regarded as a promising candidate for next-generation energy storage systems. However, the shuttling of soluble Li polysulfides (LiPSs) results in self-discharge and rapid capacity degradation. Herein, nitrogen-doped hierarchical porous carbon with embedded highly dispersed vanadium (v)-N sites (V-N-C) is developed as a high-performance Li-S battery cathode for the first time. The metal-organic polymer supramolecule structure formed by the electrostatic/hydrogen bond interaction of chitosan-VO strongly stabilizes V to generate a high density of V-N/C sites. During the discharge/charge process, the unique V-N/C active sites can serve as efficient catalysts to accelerate the redox kinetics of LiPSs, while the hierarchical porous carbon structure of V-N-C benefits the diffusion/transfer of Li/e and suppresses the shuttling of LiPSs. As a result, the S/V-N-C composite delivers a high specific capacity of 1111.2 mA h g at 0.5C and maintains 573.6 mA h g at 5C with a low capacity decay rate of 0.087% per cycle (over 500 cycles at 1C). The rate performance of the developed V-N-C cathode in Li-S batteries is superior to that of most of the reported M-N-C and carbon material/metal compound composite electrodes.