Enhanced Cycling Performance for Lithium-Sulfur Batteries by a Laminated 2D g-C₃ N₄ /Graphene Cathode Interlayer

Decay in electrochemical performance resulting from the "shuttle effect" of dissolved lithium polysulfides is one of the biggest obstacles for the realization of practical applications of lithium-sulfur (Li-S) batteries. To meet this challenge, a 2D g-C₃ N₄ /graphene sheet composite (g-C₃ N₄ /GS) was fabricated as an interlayer for a sulfur/carbon (S/KB) cathode. It forms a laminated structure of channels to trap polysulfides by physical and chemical interactions. The thin g-C₃ N₄ /GS interlayer significantly suppresses diffusion of the dissolved polysulfide species (Li₂ S_x ; 23 N₄ /GS-coated separator. The S/KB cathode with the g-C₃ N₄ /GS interlayer (S/KB@C₃ N₄ /GS) delivers a discharge capacity of 1191.7 mAh g^-1 at 0.1 C after 100 cycles, an increase of more than 90 % compared with an S/KB cathode alone (625.8 mAh g^-1 ). The S/KB@C₃ N₄ /GS cathode shows good cycling life, delivering a discharge capacity as high as 612.4 mAh g^-1 for 1 C after 1000 cycles. According to XPS results, the anchoring of the g-C₃ N₄ /GS interlayer to Li₂ S_x can be attributed to a coefficient chemical binding effect of g-C₃ N₄ and graphene on long-chain polysulfides. Generally, the improvement in electrochemical performance originates from a coefficient of the enhanced Li⁺ diffusion coefficient, increased charge transfer, and the weakening of the shuttle effect of the dissolved Li₂ S_x as a result of the g-C₃ N₄ /GS interlayer.