Nitrogen-Doped Porous Carbon with High Degree of Graphitization Derived from Silk Cocoon for Lithium-Sulfur Batteries

Abstract

Lithium/sulfur batteries (Li/S) are receiving significant attention due to its high theoretical specific capacity (1675 mA·h/g) and high theoretical specific energy (2600 W·h/kg), and inexpensive sulfur. However, the practical applications of Li/S batteries are still greatly hindered because of the low coulombic efficiency, poor cycle life and rate capability. To enhance the inherent insulating property of sulfur and insoluble discharge products and alleviate the shuttling effect of soluble polysulfides, here, a new type of nitrogen-doped porous carbon (NPC) derived from renewable silk cocoon has been successfully prepared via simultaneously activation and graphitization using metal salts FeCl3 and ZnCl2. Interestingly, the as-prepared NPC exhibits an extremely high degree of graphitization and possesses a high specific surface area of 1058 m2 g-1 and a large pore volume of 0.9026 cm3 g-1. The NPC/S composite with encapsulated sulfur content of 63% was prepared by a facile melt-diffusion method. The NPC/S electrode delivered a high initial discharge capacity of 1499 mAh g- 1 at 80 mA g-1 and coulombic efficiency of over 98%. Especially, the NPC/S composite still show excellent cycle life when the rate recover to 800 mA g-1 after cycling at various rates from 80 to 2560 mA g-1. Taking into account the low-cost of renewable biomass carbon resource and facile strategy, this work is an effective approach to increase the utilization of sulfur and improve the electrochemical performance of Li/S batteries.