Co/Co3O4@NC-CNTs modified separator of Li-S battery achieving the synergistic effect of adsorption-directional migration-catalysis via built-in electric field.

Abstract

The shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur conversion kinetics have seriously hindered the commercial application of lithium-sulfur (Li-S) batteries. Currently, the adsorption and catalysis processes are emphasized; however, the diffusion process is often neglected. The delayed diffusion of the adsorbed LiPSs significantly reduce battery performance. Herein, the directional migration of S_n^2- was realized by adjusting the characteristics of heterostructure materials. The heterostructure consists of Co with a high Fermi level and excellent catalytic activity and Co₃O₄ with a low Fermi level and strong adsorption ability. This configuration regulated the direction of the built-in electric field (BIEF) at the heterogeneous interface, which promoted the migration of S_n^2- from Co₃O₄ to Co side and realised a continuous "adsorption-directional migration-catalysis" mechanism. Experimental and theoretical results indicated that the Co/Co₃O₄ heterostructure modified by nitrogen-doped carbon nanotubes (Co/Co₃O₄@NC-CNTs), as the separator of Li-S batteries, not only enhanced the adsorption of LiPSs but also accelerated the kinetic conversion process. Consequently, the battery modified by the Co/Co₃O₄@NC-CNTs separator exhibited a high initial specific capacity of 1423 mAh g^-1 at 0.2C, and maintained 735.5 mAh g^-1 at a current density of 1C after 400 cycles.