Acidity‐Aided Surface Modification Strategy to Enhance In Situ MnO₂ Deposition for High Performance Zn‐MnO₂ Battery Prototypes

Abstract

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.