Achieving Highly Reversible Mn2+/MnO2 Conversion Reaction in Electrolytic Zn-MnO2 Batteries via Electrochemical-Chemical Process Regulation

Abstract

Despite the widespread interest in electrolytic Zn-MnO₂ batteries with excellent output voltage and high theoretical capacity, the spontaneous disproportionation reaction of free Mn³⁺ along with the disorderly deposited inactive MnO₂ results in the low Mn²⁺/MnO₂ conversion reversibility, which seriously affects their cycling stability. Here, we propose a novel aqueous SiO₂ colloidal electrolyte with FeSO₄ mediator (denoted as SF electrolyte) based on a bidirectional electrochemical-chemical model to achieve dual regulation of the MnO₂ deposition/dissolution process. During the charging process, the SiO₂ colloidal particles located at the carbon felt interface and the electrolyte bulk phase simultaneously provide sufficient disproportionation sites for the diffused Mn³⁺ to guide the orderly rapid deposition of MnO₂. Meanwhile, the introduction of Fe²⁺ mediators during the discharge process can sufficiently react with MnO₂ on the SiO₂ particles in the electrolyte, thereby further enabling the efficient conversion of Mn²⁺/MnO₂. Consequently, electrolytic Zn-MnO₂ battery with SF electrolyte can stably run for 550 cycles at 10 mAh cm⁻² and achieve superior reversibility at a high area capacity of 20 mAh cm⁻². This work demonstrates the feasibility of colloidal electrolytes in modulating electrochemical-chemical processes to stabilize electrolytic Zn-MnO₂ batteries.