Uncovering the solid-phase conversion mechanism via a new range of organosulfur polymer composite cathodes for lithium-sulfur batteries

Abstract

The sulfur cathodes operating via solid phase conversion of sulfur have natural advantages in suppressing polysulfide dissolution and lowering the electrolyte dosage, and thus realizing significant improvements in both cycle life and energy density. To realize an ideal solid-phase conversion of sulfur, a deep understanding of the regulation path of reaction mechanism and a corresponding intentional material and/or cathode design are highly essential. Herein, via covalently fixing of sulfur onto the triallyl isocyanurate, a series of S-triallyl isocyanurate organosulfur polymer composites (STIs) are developed. Relationship between the structure and the electrochemical conversion behavior of STIs is systematically investigated. It is found that the structure of STIs varies with the synthetic temperature, and correspondingly the electrochemical redox of sulfur can be controlled from conventional “solid–liquid–solid” conversion to the “solid–solid” one. Among the STI series, the STI-5 composite realizes an ideal solid-phase conversion and demonstrates great potential for building a Li–S battery with high-energy density and long-cycle-life: it realizes stable cycling over 1000 cycles in carbonate electrolyte, with a degradation rate of 0.053% per cycle; the corresponding pouch cell shows almost no capacity decay for 125 cycles under the conditions of high sulfur loading (4.5 mg cm−2) and lean electrolyte (8 μL mgs−1). In addition, the tailoring strategy of STI can also apply to other precursors with allyl functional groups to develop new organosulfur polymers for “solid–solid” sulfur cathodes. The vulcanized triallyl phosphate (STP) and triallylamine (STA) both show great lithium storage potential. This strategy successfully develops a new family of organosulfur polymers as cathodes for Li–S batteries via solid-phase conversion of sulfur, and brings insights to the mechanism study in Li–S batteries.