Enhanced Cycling Performance for Lithium-Sulfur Batteries by a Laminated 2D g-C3N4/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-C3N4/graphene sheet composite (g-C3N4/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-C3N4/GS interlayer significantly suppresses diffusion of the dissolved polysulfide species (Li2Sx; 2<= 8) from the cathode to the anode, as proven by using an H-type glass cell divided by a g-C3N4/GS-coated separator. The S/KB cathode with the g-C3N4/GS interlayer (S/KB@C3N4/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@C3N4/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-C3N4/GS interlayer to Li2Sx can be attributed to a coefficient chemical binding effect of g-C3N4 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 Li2Sx as a result of the g-C3N4/GS interlayer.