Sulfur Composite Cathode for Lithium-Sulfur Batteries

Elemental sulfur, as a cathode material of the rechargeable Li-S battery, has a high theoretical gravimetric energy density of 1675 mAh/g, moreover, it is inexpensive, abundant on earth, and environmentally benign. So it is considered to be the most promising cathode materials for the next generation batteries. However, Li-S is facing many problems that constrain its widespread application. The main obstacles are its poor conductivity, volume expanding. Moreover, sulfur can be reduced the polysulfide ions and dissolved into electrolyze in the discharge process and therefore causes the loss of active materials. In this review, the charge-discharge mechanism and two capacity fading reasons of Li-S battery are summarized. One is the dissolution of polysulfide ions, which is the so called "redox shuttle" between the sulfur cathode and Li anode. The other is the formation of insoluble lithium sulfide( Li2S) and lithium disulfide( Li2S2) which can cause the sluggish electrochemical reaction during charge and discharge processes. After that, we introduce some recent progress of novel sulfur composites as cathode materials for lithium sulfur battery. These composites can be divided into three categories( such as sulfur/carbon, sulfur/polymer and sulfur/oxide composite materials) and are discussed. In the end, we have concluded the characters of those sulfur composites, and analyzed the prospect of Li-S battery in the future.