Acidity-aided surface modification strategy to enhance In situ MnO₂ deposition for high performance Zn-MnO₂ battery prototypes

Zn–MnO₂ batteries offer cost-effective, eco-friendly, and efficient solutions for large-scale energy storage applications. However, challenges, like irreversible cathode reactions, prolonged cyclability, and electrolyte stability during high-voltage operations limit their broader application. This study provides insight into the charge–discharge process through in situ deposition of active β-MnO₂ nanoflakes on a carbon-based current collector. The study elucidates the effect of pH and electrolyte concentration on chemical conversion reactions with Zn, in particular focus on their impact on the two-electron MnO₂/Mn²⁺ reaction crucial for high voltage operation. The electrolyte, characterized by being relatively lean in Mn²⁺ and with a targeted low pH, enables extended cycling. This research achieves greater cycling durability by integrating a carbon-based cathode current collector with high density of structural defects in combination with cell architectures suitable for large-scale energy storage. A flooded stack-type Zn–MnO₂ battery prototype employing the optimized electrolyte demonstrates a high discharge voltage (≈2 V) at a substantial discharge current rate of 10 mA cm⁻². The battery exhibits an impressive areal capacity of ≈2 mAh cm⁻², maintaining ≈100% capacity retention over 400 cycles. This research establishes a promising practical, and cost-effective cathode-free design for Zn–MnO₂ batteries, that minimizes additional processing and assembly costs.