Active site construction to boost electrochemical property for Li–S batteries: a review

Lithium–sulfur (Li–S) batteries, as a research hotspot, are expected to address the need for energy storage systems with high energy density. However, the slow reaction kinetics of polysulfides due to the loss of electrical contact of soluble polysulfides and further shuttle effect hinder the further progression of Li–S batteries. This paper reviews the recent efficient approach to remedy the above issues: active site construction in the electrode materials or separators. The active site construction includes the increasing surface area, inducing molecular and single-atom catalysts, inducing heteroatomic doping, vacancies, or functional group. The high specific surface area can provide more sites for loading sulfur and also the more active sites for adsorption. Many porous materials are designed to provide more transfer paths for ions. Molecular and single-atom catalysts use some catalysts such as Fe–N–C or single metal atoms in various matrixes, representing the high catalytic activity. Defects can improve the electronic conductivity to quicken lithium ions diffusion in electrode materials, but also render more active sites to enhance catalytic activity and adsorption of electrode materials, accelerating the conversion of long-chain polysulfides to the next short-chain polysulfides and final products Li2S2/Li2S. The common active site construction and characterization methods of diversiform materials, for example, carbon materials, metal oxides, metal sulfides, and some other metal-free materials, are reviewed in this paper.