Promoting the reversibility of electrolytic MnO₂-Zn battery with high areal capacity by VOSO₄ mediator

Abstract

Electrolytic MnO2-Zn batteries possess high energy density due to the high reduction potential and capacity of the cathode Mn2+/MnO2. However, the low reversibility of the Mn2+/MnO2 conversion results in a limited lifespan. In this study, we propose the utilization of VOSO4 as a redox mediator in the MnO2-Zn battery to facilitate the dissolution of MnO2. Through various techniques such as electrochemical measurements, ex-situ UV-visible spectroscopy, X-ray diffraction, and scanning electron microscopes, we validate the interaction between VO2+ and MnO2, which effectively mitigates the accumulation of MnO2. The introduction of the redox mediator results in exceptional redox reversibility and outstanding cycling stability of the MnO2/VOSO4-Zn battery at high areal capacities, with 900 cycles at 5 mAh cm-2 and 500 cycles at 10 mAh cm-2. Notably, even in the flow battery device, the battery exhibits a stable cycling performance over 300 cycles at 20 mAh cm-2. These research findings shed light on the potential large-scale application of electrolytic MnO2-Zn batteries.

High-energy and durable aqueous Zn batteries enabled by multi-electron transfer reactions

“…Studies have identified the root causes of capacity degradation in Zn-Mn batteries based on the MnO 2 /Mn 2+ reaction during cycling. As a result, the increased pH value and Mn 3+ concentration in the electrolyte and the accumulation of inactive MnO 2 (designed as "dead MnO 2 ") near the CEI severely hinder ion diffusion and reaction efficiency of MnO 2 /Mn 2+ [53][54][55][56] . Therefore, efforts are currently focused on preventing the disproportionation of Mn 3+ , eliminating "dead MnO 2 ", and enhancing the applications for Zn-Mn batteries [15] .…”

Recent development in addressing challenges and implementing strategies for manganese dioxide cathodes in aqueous zinc ion batteries

“…In this process, hydrogen ions are the only ions inserted/extracted into the cathode material, while Zn 2+ is primarily converted to ZHS and does not participate directly in the charging/discharging reactions. The energy density and cycle life of batteries are influenced by the types and amounts of conversion-type cathodes and the category and structure of substrates [79] . Note that the crystal phase and electrolyte differences in manganese oxide necessitate a thorough and precise analysis of the reaction mechanism.…”

Influence of Defects and Surfaces on the Electrochemical Performance of MnO2 Cathodes in Rechargeable Alkaline Zn/MnO2 Batteries: A First-Principles Study

“…In mild-acid Zn/MnO 2 batteries, the electrolyte is typically made of an aqueous solution of ZnSO 4 , Zn(CF 3 SO 3 ) 2 , Zn(CH 3 COO) 2 , or other zinc salts. In mild-acid electrolytes, the discharge on MnO 2 is carried out either via a one-electron insertion–extraction mechanism or via a two-electron dissolution–precipitation mechanism. − The discharging process of rechargeable mild-acid Zn/MnO 2 batteries utilizing the dissolution–precipitation mechanism involves the reductive dissolution of MnO 2 with the formation of solvated Mn 2+ ions. − In alkaline rechargeable Zn/MnO 2 batteries, the initial discharge reaction is dominated by the insertion of hydrogen ions into the solid structure of MnO 2 cathode material. ,, The second-electron discharge reaction is carried out via a dissolution–precipitation mechanism that produces Mn 2+ (OH) 2 . ,, In a simplified form, the first-electron discharge of MnO 2 in alkaline Zn/MnO 2 batteries can be written as normalM normaln normalO 2 ( s ) + x H + + x e − → normalM normaln normalO 2 − x false( normalO normalH false) x ( s ) …”