Development of Rechargeable Mildly Acidic Aqueous MnO2-Zn Batteries

Abstract

Rechargeable mildly acidic aqueous manganese dioxide-zinc (MnO₂-Zn) batteries are promising candidates for safe and low-cost grid-scale energy storage. However, their widespread application is hindered by the rapid capacity fade of the MnO₂ cathode and the uncontrollable dendritic growth on the Zn anode. This thesis aims to address these challenges by elucidating the underlying degradation mechanisms and developing effective stabilization strategies for both electrodes.

For the MnO2 cathode, a combination of operando and ex-situ characterizations reveals a mixed reaction mechanism governed by concurrent proton insertion and MnO₂ dissolution/deposition, with the contributions quantified as 59% and 43%. The irreversible formation of Zn-Mn-O phases is identified as the root cause of capacity decay. To mitigate this, two novel additive-based strategies are developed: a Bi₂O₃ electrode additive and a TiOSO₄ electrolyte additive, which suppresses the phase formation and enables long-term cycling. 10% of Bi₂O₃ addition can deliver a capacity retention of 92.7% for 1000 cycles at 1000 mA g^-1, and 0.5% TiOSO₄ addition exhibits a high capacity of 230 mAh g^-1 for over 1500 cycles under a current of 1200 mA g^-1.

For the Zn anode, two complementary approaches are pursued. First, a cationic poly(ionic liquid) interfacial layer is designed to homogenize the surface charge distribution via electrostatic shielding, which facilitates uniform Zn deposition and extends the symmetric cell lifespan to over 2000 hours. Second, a methyl acetate-based hybrid electrolyte is formulated, which is found to regulate the nucleation process, modify the Zn²⁺ solvation sheath and promote a preferential Zn(002) crystallographic orientation. 70% methyl acetate-based electrolyte achieves outstanding performance with 4000-hour Zn-Zn cyclability and 99.9% coulombic efficiency in Cu-Zn cell.

Overall, the fundamental insights and practical strategies presented in this work provide a comprehensive framework for the rational design of highly stable aqueous MnO₂-Zn batteries, significantly advancing their prospects for practical energy storage applications.

Date of Award	2 Mar 2026
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Patrick SIT (Supervisor) & Denis YU (External Co-Supervisor)