Building a cycle- stable sulphur cathode by tailoring its redox reaction into a solid- phase conversion mechanism

Sulphur has been actively investigated as a high capacity, naturally abundant and low cost cathode for next generation rechargeable lithium batteries. However, the poor cyclability and low capacity utilization of sulphur materials remain a great challenge for battery applications. To overcome this problem, we proposed a new strategy to convert the redox chemistry of sulphur cathodes from the dissolution-deposition mechanism to a solid-phase conversion (SPC) reaction by in situ formation of a thin and compact solid electrolyte interface (SEI) on the sulphur surface through a prompt nucleophilic reaction of soluble polysulfide intermediates with carbonate molecules specially designed as a co-solvent in the electrolyte. The such-formed SEI film can effectively block the penetration of the electrolyte but allows Li+ transport for electrochemical conversion, thus completely suppressing the generation and dissolution of polysulfide intermediates without sacrificing the two-electron redox capacity of sulphur. As a result, the S/C cathode in a VC/DME + DOL co-solvent electrolyte demonstrated a stable cycling capacity of approximate to 1100 mA h g(-1) and a high capacity retention of 88% over 400 cycles with a coulombic efficiency of approximate to 100%, showing a prospect for battery application. More significantly, the strategy and method developed in this work may provide a new insight for future development of structurally and electrochemically stable sulphur cathodes for building practically viable Li-S batteries.