Tuning the electrochemical activity of Li–Se batteries by redox mediator additives

Abstract

A lithium–selenium (Li–Se) battery is considered as a promising next-generation energy storage system due to its ultrahigh volumetric energy density. However, the capacity attenuation due to the dissolution and shuttle effect of polyselenides is urgent to be addressed. Herein, 1,4-benzenedithiol (1,4-BDT) and benzeneselenol (PhSeH) are proposed as redox mediator additives in the electrolyte. They both change the multi-step reaction of Se and accelerate the redox kinetics, thus suppressing the shuttle effect of polyselenides and improving the cycling stability and rate performance. The Li–Se cell with 1,4-BDT exhibits steady 450 cycles at 1 C with capacity decay only 0.058% per cycle. Differently, the Li–Se cell with PhSeH features fast kinetics, which shows 91.4% capacity retention after 450 cycles at a high rate of 5 C. Due to the difference of molecular structures between 1,4-BDT and PhSeH, the cyclic oligomers formed in the Li–Se cell with 1,4-BDT diminish the solubility of polyselenides enhancing the cycling stability, while the chain-like diphenyl selenides generated in the Li–Se cell with PhSeH promote kinetics performance through a single-phase reaction. This work provides an effective redox regulation strategy that will stimulate interest in exploration of organic mediators for rechargeable batteries.