Hollow-structured cobalt sulfoselenide as cathode host to enhance the kinetics and improve the energy density of lithium-sulfur batteries

Abstract

Lithium-sulfur batteries are a promising next-generation battery system due to their high energy density, low cost, and environmental friendliness. However, the shuttle effect and resulting low redox kinetics are significant issues that currently hinder their development. The addition of catalysts to accelerate the redox process is a common strategy. Metal sulfide catalysts, in particular, have been widely studied due to their good affinity for sulfur and sulfides. Although metal sulfide show good adsorption performance for lithium polysulfides, their low conductivity does not significantly improve the kinetic performance of the battery. Additionally, the high molecular weight of the inactive sulfide leads to the low actual energy density of the battery. Thus, this study constructed the hollow structural cobalt sulfoselenide by replacing partial elemental sulfur in cobalt sulfide (Co3S4) with the higher metallicity element selenium (Se). This was done to increase catalytic activity and reduce the amount of inactive substances, ultimately leading to an increase in actual energy density. This strategy systematically investigated the electrical conductivity, catalytic activity, and inhibition of the shuttle effect of Co3S2Se2. It was found that cobalt sulfoselenide with a 1:1 ratio of sulfur to selenium exhibited higher catalytic activity than pure cobalt sulfide. Additionally, the hollow structure of cobalt sulfoselenide showed greater performance enhancement than bulk cobalt sulfoselenide. In the assembled lithium-sulfur battery, the initial specific capacity of 1294.7 mAh/g at 0.1C was obtained, and the capacity retention was 77.5 % after 100 cycles. On this basis, the structure–activity relationship between selenium-sulfur ratio and electrochemical properties will provide ideas for the design of microscopic cathode structures.