Selectively etched inhomogeneous metal-organic framework-derived CoS/N-codoped hierarchical hollow carbon for long-cycling lithium sulfur batteries

Abstract

Owing to high theoretical energy density and potentially low cost, lithium sulfur (Li–S) batteries have become a viable alternative for use in future energy storage devices. However, practical applications of this battery type are limited by the significant volume change of S and the undesired shuttle effect of polysulfides during cycling, ultimately causing rapid capacity decay. Herein, we developed a novel method to fabricate a N-doped hollow carbon composite (CoS/HNC) embedded with well-dispersed CoS nanoparticles (NPs) through inheritable carbonization of functionalized hollow metal-organic frameworks (MOFs). Specifically, the hollow UiO-66-NH2 is created by a sequence involving (1) use of non-uniform nucleation-growth approach to generate inhomogeneous UiO-66-NH2 that has more defects in the core, and (2) selective etching of the less stable core to obtain hollow structure. The CoS/HNC composite has advantages associated with not only hollow nanostructure that buffers the volume expansion of S species during cycling, but also CoS that prevents the shuttle effect. More importantly, both experimental and calculated results reveal that CoS/HNC could catalyze the reduction of LiPSs more effectively and CoS/HNC heterostructure enables the short-chain polysulfide that obtained from the catalytic conversion of soluble long-chain polysulfide by CoS NPs to be deposited on HNC. This process avoids passivation of the catalytic site and ensures continuity of the catalytic conversion. Benefiting from integration of its intriguing composition and morphology advantages, an as-prepared CoS/HNC–S cathode exhibits significantly improved electrochemical performance and cycling stability associated with a low capacity decay of 0.05% per cycle over 800 cycles at 1 C.