Sulfur/Iodine/Graphene Composites as a Cathode Material for Lithium–Sulfur Battery

Lithium–sulfur battery (LSB) is one of the most promising energy storage devices because of its high specific capacity, energy density, and low cost. However, the sluggish redox reaction due to the low conductivity of discharge products is the major challenge that still impedes its application. In this work, iodine is introduced into sulfur/graphene composite via an facile in situ chemical reaction method, forming a sulfur/iodine/graphene (S/I2/G) composite cathode material for LSB. During cycling, the generated intermediate I radicals can induce the formation of the oligomer as Li-permeable protective layer, which attaches to the cathode surface and can efficiently suppress the diffusion loss of polysulfides. Also, the introduced I2 can promote the oxidation of Li2S/Li2S2 to Li2Sn (n = 4–8), thus decreasing the deposition of Li2S/Li2S2 on the electrode surface, reducing the overpotential and improving the active material's utilization. The optimized S/I2/G cathode (S:I2 = 1:0.1) material delivers better electrochemical performance as compared with that of the material without iodine. Even with a high mass loading of 6.0 mg cm−2, the cathode still shows a low capacity decay rate of 0.13% per cycle and high Coulombic efficiency of 97.9% over 500 cycles. This work may offer a feasible design for developing high-loading cathode of LSB.