Electrocatalysis of sulfur and polysulfides in Li-S batteries

Li-S batteries have attracted considerable attention because of their high energy density; however, the poor electrochemical reaction kinetics of sulfur and polysulfides limit their high-power output. Besides, the capacity fade caused by the shuttle effect hinders the commercialization of Li-S batteries. To solve these problems, electrocatalysts have been proposed to promote the conversion of polysulfides and inhibit their diffusion. It has been demonstrated that the electrochemical performance can be greatly improved when electrocatalysts are introduced into Li-S batteries, but their mechanisms still require further clarification. For a more in-depth understanding of electrocatalysis in the sulfur electrode, this review summarizes the role of electrocatalysis from three aspects. First, the phase transition of sulfur species and the effect of electrocatalysts on the conversion of sulfur species are systematically summarized. Second, the research methods of electrocatalysts in Li-S batteries are introduced from computational chemistry and electrochemical detection methods. Third, according to the current development of electrocatalysts, strategies for improving electrocatalyst efficiency are summarized based on the intrinsic electrocatalytic activity of the active sites and the number of active sites. Finally, according to current electrocatalyst research, perspectives and future research efforts are proposed to facilitate the design and application of high-performance electrocatalysts for the sulfur electrodes of Li-S batteries.