Regulating manganese dioxide polymorphism by epitaxial electrodeposition for reversible aqueous Zn metal batteries

Abstract

The practical deployment of the high-energy Mn2+/MnO2 deposition chemistry in aqueous zinc metal batteries is fundamentally challenged by sluggish reaction kinetics due to the low electron conductivity of the deposit MnO2. Herein, we report a direct epitaxial growth strategy to bypass this kinetic and thermodynamic limitation, enabling the stable electrodeposition of the thermodynamically favored, highly conductive γ-MnO2 at ambient temperature. This is achieved by pre-establishing γ-MnO2 seed layers at elevated temperature, which templates the phase-pure growth of subsequent MnO2 deposition via a coherent homointerface. The resulting epitaxial γ-MnO2 exhibits high conductivity, reduced structural symmetry, weakened Mn-O interaction, and a well-defined nanorod architecture, collectively contributing to accelerated reaction kinetics. The Zn||γ-MnO2 cells demonstrate promising electrochemical performance with high-rate capability (86.2% at 30 mA cm-2), high areal capacity (20 mAh cm-2), and prolonged cyclability (>3000 cycles). This work further underscores interfacial phase design as a pivotal strategy for regulating polymorphic electrodeposition in advanced batteries.