Lithium-sulphur (Li-S) cells are attractive electrochemical energy storage systems because of the high theoretical capacity of 1675 mAh g^-1of sulphur. But low active material utilization, poor cycle life and low rate performance hinder their practicality, which arising from the highly insulating nature of sulphur, the high solubility/diffusivity of lithium polysulphides in the organic electrolyte and volumetric expansion of sulphur during lithiation.

Carbon materials with high specific surface area and the porous structure are beneficial for uniform loading and distribution of sulphur in the structure to improve the reaction of sulphur in the cathode. It is important to maintain the electrical conductivity network of carbon providing envelope for lithium sulphide reduction and oxidation within a liquid solvent electrolyte without loss of fluidity, while minimising shuttling away of sulphur and avoiding or controlling the deposition of insoluble sulphides which can block the conducting paths. In addition, porous space could accommodate the volume variation of sulphur. Therefore, sulphur-carbon composites, using porous carbon have become a key research topic in Li-S batteries. Herein, the design and preparation of a series of unique carbon materials, based on metal organic framework (MOF)-derived hierarchical porous carbon, graphene-wrapped microporous carbon composite, few-layer graphene foam and carbon nanotube forest, have been demonstrated for sulphur loading to fabricate cathode structures for Li-S batteries. The improved electrochemical performance provides novel approaches to designing and fabricating long cycle life cathodes in Li-S cells.

Reference

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