Doped-Graphene in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is a kind of rechargeable batteries with lithium as negative electrode and sulfur as positive electrode. It has a high theoretical specific capacity of 1675 mA.h/g and a specific energy density of 2600 W.h/kg. Theoretically, Li-S batteries can boost capacity fivefold over the current lithium-ion batteries, enabling it as a candidate of the most promising lithium-ion batteries. Due to the insulativity of sulfur and the easy dissolution of sulfur as active material to form polysulfide ions as electrochemical reaction intermediate material in the electrolyte during the process of charging and discharging, the poor cycle stability and high self-discharge of Li-S batteries result in the realizable energy density achieved far below the theoretical value. In this review, we target heteroatom-doped graphene, which has been widely used in Li-S batteries because of its retained excellent conductivity of graphene as well as strong adsorption to lithium polysulfide (LiPS) derived from a certain amount of defects and active sites of doped graphene. The adsorption can effectively alleviate the "shuttle effect" in the charge and discharge process and improve the cycling stability and cycling rate performance of Li-S batteries. This paper reviews current research state of heteroatom-doped graphene(such as N, P, S, B) in the Li-S batteries in terms of single-atom doping and diatomic doping. The advantages and mechanism of nitrogen-doped, nitrogen-sulfur co-doped and other doped graphene applied to Li-S batteries are analyzed utterly. Finally, the effect of battery performance is classified based on doping amount, doping form, doping location, and so on. The development direction and prospect of heteroatom-doped graphene are also predicted and forecast.