Unveiling the role of water in enhancing the performance of zinc-ion batteries using dimethyl sulfoxide electrolyte and the manganese dioxide cathode

Abstract

Due to its excellent reversibility and stability, dimethyl sulfoxide (DMSO) electrolyte is seen to be a promising nonaqueous electrolyte. Compared to aqueous Zn–MnO₂ systems, ZIBs having DMSO electrolyte, and the manganese dioxide (MnO₂) cathode display inferior rates and capacity performances. However, it is found that the addition of water can improve the performance of DMSO-based ZIBs, even a small amount of water. In this work, the effect of water on the performance of DMSO-based ZIBs is thoroughly investigated. Herein, the layer-type MnO₂ (δ type, birnessite) is used as the main cathode material. Ex situ/operando X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption spectroscopy (XAS) results suggest that the existence of water in DMSO electrolytes can lead to changes occurring in the Zn²⁺ intercalated phase. Zn-birnessite when replaced by super-hydrated Zn-buserite provides a much improved solid-phase diffusion of Zn²⁺ and surface kinetics. The optimized battery yields the highest capacity of 224 mA h g⁻¹ and can cycle over 2500 cycles. This discovery extends the understanding of wet nonaqueous electrolyte chemistry and paves the way towards the practical application of ZIBs.