Self-assembled 3D CoSe-based sulfur host enables high-efficient and durable electrocatalytic conversion of polysulfides for flexible lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries are considered as promising candidates for next-generation energy storage systems. However, the commercial applications are severely limited by the sluggish kinetics and shuttling effect. Herein, we have designed an integrated free-standing functional CoSe-CNF-GO-MXene (CCGM) sulfur host with a “point-line-plane” 3D porous structure for Li-S batteries. The two-dimensional (2D) graphene, MXene and one-dimensional (1D) nanocellulose fibers combined with zero-dimensional (0D) transition metal selenide (CoSe) shows good electrical conductivity and enhanced catalytic performance, respectively. Additionally, the rationally designed porous structure (from 0D to 3D) demonstrates well-connected ion/electron transport channels, conferring the good kinetic performance. Electrochemical tests show that CoSe catalytic materials with moderate adsorption energies can catalyse both precipitation and dissolution processes of Li2S, enabling fast conversion kinetics. The density functional theory (DFT) calculations show that the synergistic effect of CoSe, Ti3C2Tx, and graphene can improve the chemisorption and catalytic performance. As a result, the 3D porous S@CCGM cathode exhibits a high initial discharge capacity of 1205.1 mAh g−1 at 0.2C and good long-term cycling performance with a low decay rate of 0.055 % per cycle at 1C. Furthermore, the gel electrolyte Li-S pouch cell successfully passes the 0–180° bending test, nailing test, and cutting test. Such design offers a new perspective for the commercialization of safe and flexible electrochemical energy-storage devices especially in Li-S batteries.