Polar Ultrathin Self-Doping Carbon Nitride Nanosheets with Intrinsic Polysulfide Adsorption for High Performance Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li−S) batteries are promising for next-generation electrochemical energy storage due to their high energy density and low cost. Here, we introduce light-weight polar carbon self-doping C3N4 nanosheets (C−CNN) as sulfur host for the fabrication of high performance Li−S batteries. The role of carbon doping in boosting the electrical conductivity of C−CNN is revealed by electrochemical impedance spectroscopy and electrical conductivity measurements. The strong chemical interactions between C−CNN and polysulfides are investigated by adsorption and post-mortem X-ray photoelectron spectroscopy analysis. Benefiting from the high surface area, enhanced electrical conductivity and high content of active N species (56.7 at %) in C−CNN, the strong chemical interactions between C−CNN and polysulfides can be fully exploited to minimize the shuttle effect and achieve long cycle life of Li−S batteries. As a result, the C−CNN/S cathode delivers a high specific capacity of 1050 mAh g−1, good rate capability and excellent cycling stability with a low capacity decay of 0.07 % per cycle at 1 C over 500 cycles, showing better performance than nitrogen-doped graphene. A performance comparison with the literature also shows that C−CNN is one of the most promising nitrogen-containing carbon materials for long cycle life Li−S batteries.