Polarity Modification of Graphitic Carbon Nitride for the Mitigation of the Shuttle Effect in Lithium–Sulfur Batteries

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 polysulfide (LiPS) interrupts the commercial application of Li–S batteries. Graphitic carbon nitride (GCN), with an enriched density of pyridinic-N sites for LiPS adsorption, has been explored as an effective adsorption material to inhibit the migration of polysulfides. However, the inferior conductivity of GCN imposes limitations on sulfur utilization in Li–S batteries. Herein, the boron-doped, nitrogen-defect GCN (BCN4–x) is designed as a slurry additive to synergistically enhance the adsorption strength of LiPS and the conductivity of GCN. Boron doping in GCN enhances positive polarization, improving the conductivity of GCN. Additionally, B-doping induces nitrogen defects and cyano groups, increasing the polarity of the GCN. Based on UV–Vis absorbance, BCN4–x exhibits a stronger affinity for LiPS compared to GCN. Moreover, compared to pristine GCN, BCN4–x achieved 20% higher capacity retention (71.33% after 100 cycles at 0.5 C) and 1.7 times greater rate performance (803.01 mAh g–1 at 1.0 C) in Li–S batteries due to a synergistic effect.