Simulation-supported analysis of pH impacts on the voltage efficiency of aqueous zinc manganese dioxide batteries

Rechargeable aqueous zinc manganese dioxide batteries (AZMBs) are a promising technology for stationary energy storage due to their low cost, high safety, and environmental compatibility. However, their practical deployment remains limited by poor cycle life, capacity fading and reduced energy efficiency. A major factor contributing to these limitations is the proton-coupled nature of the cathode reaction, which generates local pH gradients that promote parasitic phenomena such as formation of irreversible manganese oxides, salt precipitation, and zinc (Zn) corrosion. In addition, these local pH gradients lead to irreversible voltage losses that directly reduce the usable energy. While experimental measurement of these gradients is challenging, modeling provides a spatially and temporally resolved view of pH dynamics. To address this, we introduce a physics-based framework that links ion transport, electrolyte speciation, and electrode kinetics to quantitatively resolve pH-driven polarization and voltage losses. This approach enables a mechanistic assessment of how pH dynamics govern voltage efficiency and identifies pH-driven overpotentials as a dominant and previously underestimated loss mechanism in AZMBs. These findings provide new and fundamental guidelines for electrolyte design and operating conditions, paving the way toward more efficient, durable and marketable AZMBs.