Acidity-Aided Surface Modification Strategy to Enhance In Situ MnO 2 Deposition for High Performance Zn-MnO 2 Battery Prototypes.

Zn-MnO 2 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-MnO 2 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 MnO 2 /Mn 2+ reaction crucial for high voltage operation. The electrolyte, characterized by being relatively lean in Mn 2+ 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-MnO 2 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-MnO 2 batteries, that minimizes additional processing and assembly costs.