Deposition of thin δ-MnO2 functional layers on carbon foam/sulfur composites for synergistically inhibiting polysulfides shuttling and increasing sulfur utilization

Abstract

Practical application of LiS battery is greatly impeded by the critical challenges of large volume expansion, intrinsic insulation problem of active materials, and serious polysulfides shuttling. Thus, it is still quite essential for us to search an efficient strategy to synergistically overcome these problems. Herein, we design and in-situ deposit a functional δ-MnO2 layer onto the outside surface of porous carbon foam/sulfur composites to synergetic inhibit the polysulfides shuttling and increase sulfur utilization, finally improve the electrochemical performance of LiS batteries. As verified by UV–vis and XPS results, the strong chemical interaction between the MnO2 layer and polysulfide intermediates is characterized to be an internal disproportionation reaction by transferring the absorbed long-chain polysulfides into insoluble polythionate complex. Also, the unique structure possesses high conductivity and good volume expansion tolerance, further guaranteeing the electrode a good cycling stability, rate performance and low self-discharge behavior. The MnO2 coated carbon foam/S electrode displays a remarkable capacity of 1547 mA g−1 at 0.1 C, and achieves a reversible capacity of 629 mA g−1 after 300 cycles at 1 C. Even with sulfur loading of 2.6 and 4.3 mg cm−2, the designed electrodes still deliver an initial discharge capacity of 1106 and 963 mA g−1 at 0.2 C.