Synthesis of pompon-like ZnO microspheres as host materials and the catalytic effects of nonconductive metal oxides for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries have attracted tremendous attention as promising next-generation battery systems because of their high theoretical specific capacity and cost-competitiveness. Nevertheless, the commercialization of sulfur-based cathodes has been limited by substantial problems such as the insulating property of S8/Li2S, low active material utilization, and inevitable dissolution of lithium polysulfides into organic electrolytes. Among the materials used to solve these problems, metal oxide materials have attracted attention because of their strong chemical/physical interactions with polysulfides and catalytic effect. However, most studies include strategies to add electron networks or synthesize metal oxides into nanosize because of the nonconductive properties of metal oxides. Herein, to demonstrate the intrinsic effect of metal oxides, pompon-like ZnO microspheres (p-ZnO) are employed by a hydrothermal method and subsequent calcination for a sulfur host (p-ZnO/S) for the first time. The composite of p-ZnO/S significantly enhanced the sulfur utilization and rate capability without additional efforts to improve the electrical conductivity. In addition, the decrease of reaction resistance and charge-transfer resistance was shown in electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) results. Furthermore, the catalytic effect is described by analyzing the lithium ion diffusion coefficient and verifying the chemical composition change on the cathode surface during the sulfur redox reaction.