Two C-S bonds derived from carbons with different IG/ID values promote high sulfur loads and stable capacity storage

Abstract

Carbon materials are always used as sulfur carriers in lithium-sulfur batteries. However, storage mechanism of carbon materials with different graphitization degree is different. Carbons with lower graphitization degree (IG/ID value) usually possess many defects and poor electrical conductivities. Carbon materials with high graphitization degree always possess less contact sites. Both two carbon materials are conducive to achieve sulfur loads. However, sulfur-loading capacities of two materials are different. In this paper, two carbon materials with different graphitization degrees are combined to form composite carbon materials. Studies show that composite carbon electrodes with suitable IG/ID values possess good sulfur-loading capacities (80%) because of high conductivity and defect contents. Two kinds of C-S bonds are produced after loading sulfur and both of them are conducive to stable production of polysulfides. One C-S bond is conducive to diffusion of lithium ions on electrode surface and the other C-S bond is conducive to rapid conversion of polysulfides. Under the performance of two C-S bonds, high capacity storage and good cycling stability can be achieved by electrodes under high sulfur-loading conditions.