Covalent Sulfur Embedding in Inherent N, P Co-doped Biological Carbon for Ultrastable and High Rate Lithium-Sulfur Batteries
Lithium-sulfur (Li-S) batteries are attracting extensive interest owing to their low cost and potential for high-density energy storage. However, the widespread application is severely plagued by poor cycling stability, inferior rate capability and low Coulombic efficiency, which is largely attributed to the shuttling effect of soluble polysulfides. Herein, we report an architecture of N, P co-doped biological carbon-based covalent sulfur composite (NP@BCCSC) as cathode for highly robust Li-S batteries. The NP@BCCSC can not only buffer volume expansion of sulfur during charge/discharge process, but also afford a strong absorption to soluble polysulfides, which can effectively suppress shuttling effect. As cathode for Li-S battery, the NP@BCCSC with sulfur content of 20.1% exhibits a reversible capacity of 1190 mA h g-1 (All specific capacities are calculated based on mass of sulfur) at a current density of 500 mA g-1 after 500 cycles with an average Coulombic efficiency of approximately 100%. Moreover, the NP@BCCSC offers a highly robust cycling stability (an ultralow capacity fading rate of 0.0024% per cycle during 15000 consecutive cycles) and an excellent rate capability (high specific capacity of 920 mA h g-1 even at current density of 10000 mA g-1), indicating great potential for future energy storage systems.