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 Sx ; 2<x≤8) from the cathode to the anode, as proven by using an H-type glass cell divided by a g-C3 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 Sx 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 Sx as a result of the g-C3 N4 /GS interlayer.