Constructing in-situ SOCl2-induced protective layer on Li anode for high-performance Li–O2 batteries containing LiI redox mediator

Li–O2 batteries have attracted wide attention on account of the ever-increasing demand of high energy density systems. However, their practical application is still facing many critical problems, especially the slurry reaction rate/serious side reactions on cathodes and the fast growth of Li dendrites/passivating layers on anodes. Therefore, we design an in-situ formed coating layer on Li metal anode by introducing thionyl chloride (SOCl2) additives into the Li–O2 system with a redox mediator (RM), LiI. The robust and uniform SOCl2-derived layer can effectively prevent the attack of O2/O2–, which inhibits the surface passivation of Li metal anode and greatly supresses the infinite dendrite growth. Additionally, the SOCl2 additive also contributes to a certain specific capacity of the Li–O2 cells at full discharge/charge conditions. Moreover, the SOCl2-derived coating layer can almost completely stop the diffusion of the soluble I-based RM on Li metal anode to eliminate contiunous side reactions between them. The symmetrical batteries containing SOCl2 display lower overpotentials and longer cycling life than those of cells without SOCl2. More importantly, the SOCl2 based Li–O2 batteries with LiI exhibit the extra-high capacity (31000 mAh g−1), ultra-small voltage polarization (∼1.4 V), and extended operation life (190 cycles).