Polarity modification of graphitic carbon nitride (g-C3N4) for mitigation of shuttle effect in lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries are one of the most promising next-generation energy-storage systems due to their high energy density (2600 Wh kg-1). Nevertheless, the shuttle effect caused by the dissolution of lithium-polysulfides interrupt the commercial application of Li-S batteries. Recently, researches have recognized the importance of strong chemical interaction between polar materials and polysulfides to improve the performance of Li-S batteries. In general, many researches were focused on the incorporation of sulfur into nonpolar carbon-based materials which cannot suppress the shuttle effect through weak interaction. Recent investigations have revealed a notable propensity for polar polysulfides to selectively adhere to the surface of quaternary nitrogen atoms positioned adjacent to carbon atoms. Nevertheless, pristine graphitic carbon nitride (GCN) exhibits comparatively subpar adsorption performance concerning lithium polysulfides (LiPSs) surrounding C-N bonds. In-depth investigations should thus be directed toward the strategic design of GCN with improved adsorption of lithium polysulfides. Herein, we synthesize boron-doped and nitrogen-deficient g-C3N4 (BCN4-x) as an electrode slurry additive by simple calcination method with g-C3N4 and sodium borohydride in an argon atmosphere. Without significant electrode weight and volume increase, BCN4-x has an effective adsorption of lithium-polysulfides. In a Li-S battery, BCN4-x delivered the initial capacity of 1238.94 mAh g-1 and maintained 71.33% of the capacity for 100 cycles at 0.5 C-rate. Moreover, it recovered 97.17% of capacity after rate-capability test.