ZIF-8 derived hollow carbon to trap polysulfides for high performance lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) have a high theoretical energy density and are low cost. However, the undesirable shuttle effect with the solid discharge product, Li₂S, greatly impedes their market penetration. Conductive carbon materials with functional elements are beneficial in controlling the shuttle effect and can reactivate the Li₂S, leading to improved long term cycling performance of LSBs. Herein, we report zinc (Zn) and nitrogen (N) co-doped ZIF-8 derived hollow carbon (ZHC) as a promising separator coating for LSBs to control the shuttle effect. The hollow area in the ZHC is identified to be around 250 nm with a carbonized outer surface thickness of approximately 50 nm. The presence of Zn and N in the nanohollow carbon structure helps to mitigate polysulfide (PS) diffusion in LSBs. Furthermore, the hollow interior of the carbon acts as a PS pocket to physically capture the PS and in addition Zn and N chemically attract the PS through polar–polar and metal sulfide interactions. The ZHC with its unique architecture and functional groups shows a promising performance with an initial specific capacity (S.cap) of 842 mA h g⁻¹ at 4.80 mg cm⁻² and cycling stability until 400 cycles, which is considerably higher in comparison with the cycling performance of parent ZIF-8.