A carbon quantum dot-decorated g-C 3 N 4 composite as a sulfur hosting material for lithium-sulfur batteries.

Although lithium-sulfur (Li-S) batteries have attracted strong consideration regarding their fundamental mechanism and energy applications, the inferior cycling performance and low reaction rate caused by the "shuttling effect" and the sluggish reaction kinetics of lithium polysulfides (LiPSs) impede their practical application. In this work, graphitic C 3 N 4 (g-C 3 N 4 ) assembled with highly-dispersed nitrogen-containing carbon quantum dots (CQDs) is designed as a cooperative catalyst to accelerate the reaction kinetics of LiPS conversion, the precipitation of Li 2 S during discharging, and insoluble Li 2 S decomposition during the charging process. Meanwhile, the introduction of CQDs improves the conductivity of the g-C 3 N 4 substrate, showing great significance for the construction of high-performance electrocatalysts. As a result, the as-obtained composite shows efficient adsorption and electrochemical conversion of LiPSs, and the Li-S batteries assembled with CQDs/g-C 3 N 4 exhibit an initial specific capacity of 1300.0 mA h g -1 at the current density of 0.1C and retain 582.3 mA h g -1 after 200 cycles. The electrode with the modified composite displays a greater capacity contribution of Li 2 S precipitation (175.7 mA h g -1 ), indicating an enhanced catalytic activity of g-C 3 N 4 decorated by CQDs. The rational design of CQDs/g-C 3 N 4 as a sulfur host could be an effective strategy for developing high performance Li-S batteries.