2D spinel ZnCo2O4 microsheet-coated functional separator for promoted redox kinetics and inhibited polysulfide dissolution

Abstract

Lithium-sulfur (Li-S) batteries are receiving increasing attention as one of the potential next-generation batteries, owing to their high energy densities and low cost. However, practical Li-S batteries with high energy densities are extremely hindered by the sulfur loss, low Coulombic efficiency, and short cycling life originating from the polysulfide (LiPS) shuttle. In this study, two-dimensional (2D) ZnCo2O4 microsheets fabricated by a facile hydrothermal process are employed to modify the separator, for improving the electrochemical performances of Li-S cells. The resulting 2D ZnCo2O4-coated separator features a coating thickness of approximately 10 mu m, high ionic conductivity of 1.8 mS/cm, and low mass loading of 0.2 mg/cm(2). This 2D ZnCo2O4-coated separator effectively inhibits LiPS shuttle by a strong chemical interaction with LiPS as well as promotes the redox kinetics by ZnCO2O4-coated layers, as determined by X-ray photoelectron spectroscopy analysis, self-discharge, time-dependent permeation test, Li symmetric cell test, and Li2S nucleation analyses. Consequently, the Li-S batteries based on the 2D ZnCo2O4-coated separator exhibit a high initial discharge capacity of 1292.2 mAh/g at 0.1 C. Moreover, they exhibit excellent long cycle stability at 1 and 2 C with capacity retention of 84% and 86% even after 800 cycles, corresponding to a capacity fading rate of 0.020% and 0.016% per cycle, respectively. Effectively, these Li-S cells with a high sulfur loading at 5.3 mg/cm(2) and low electrolyte concentration of 9 mu L/mg deliver a high discharge capacity of 4.99 mAh/cm(2) after 200 cycles at 0.1 C. (C) 2020 Published by ELSEVIER B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.