Sandwich-like NOCC@S₈/rGO composite as cathode for high energy lithium-sulfur batteries

Lithium-sulfur (Li–S) battery delivers its energy density far higher than currently commercialized lithium ion batteries, but challenges remain before it can be applied in large scale. One of the main issues is the dissolubility of intermediates, lithium polysulfides (LiPSs), of sulfur cathode. To address this issue, we report a novel composite as sulfur cathode that can highly immobilize the LiPSs and thus significantly improve the cyclic stability of Li–S battery. This composite is fabricated by successively loading S and N,O-carboxymethyl chitosan (NOCC) on graphene oxide (GO) and subsequent hydrothermal reduction, presenting a sandwich-like structure (NOCC@S₈/rGO). Electrochemical measurements indicate that the as-fabricated NOCC@S₈/rGO as cathode of Li–S battery exhibits a small capacity decay of 0.068% per cycle at 0.5C over 500 cycles and a significantly improved rate capability. Such superior cyclic stability and rate capability are attributed to the support to S species from rGO and the strong interaction of NOCC with LiPSs via Li–N bonds, as demonstrated by physical characterization and theoretical calculations. Considering the easy availability and environmental friendliness of NOCC, the reported composite is a promising cathode material for Li–S battery to be applied in large scale.