Unraveling the Zn2+ and H+ ions storage co-insertion kinetics of MnO@rGO composites for high-rate aqueous Zn-ion batteries

Abstract

Manganese oxides are regarded as promising candidates for rechargeable aqueous zinc-ion batteries (AZIBs) due to their high capacity, high operating voltage, low cost, and environmental friendliness. However, irreversible Mn dissolution, sluggish Zn²⁺ diffusion kinetics, and poor electronic conductivity severely hinder their long-term cycling stability and rate performance. To address these issues, we adopt a composite strategy by introducing conductive reduced graphene oxide (rGO). The MnO@rGO electrode delivers a high specific capacity of 318 mAh g⁻¹ at 0.5 A g⁻¹ and an enhanced rate capability of 117 mAh g⁻¹ at 1 A g⁻¹. Notably, the MnO@rGO exhibits an enhanced cycling stability with stable capacity retention during prolonged charge-discharge cycling. Comprehensive electrochemical analyses, including in situ electrochemical impedance spectroscopy with distribution of relaxation time analysis, capacitive contribution evaluation, and the galvanostatic intermittent titration technique, are conducted to investigate the co-insertion mechanism of Zn²⁺ and H⁺ ions, confirming enhanced reaction kinetics. This study provides an approach to designing advanced cathode materials for AZIBs and contributes to the development of electrochemical performance analysis for next-generation AZIBs systems.