Functional Carbon-Based Zn Host Assisted with Ultra-Thin Hydrophilic ZnO Layer for Practical Aqueous Zn-Metal Batteries

Eco-friendly aqueous Zn-metal batteries (AZMBs) is considered a promising candidate for grid-scale energy storage system owing to its high theoretical capacity (5,854 mAh cm^-3), low standard reduction potential (–0.76 V vs. Standard Hydrogen Electrode), and high compatibility with aqueous electrolyte. However, the inevitable dendritic Zn growth and side-reactions (hydrogen evolution reaction (HER) and Zn corrosion) during continuous cell operation block the practical utilization of AZMBs. Hence, we effectively ameliorate the growth of Zn dendrite and the side reactions of Zn-metal anode by developing the zincophilic porous carbon host (top layer) and ultra-thin ZnO layer (bottom layer) originating from native-oxide of metallic Zn. The functional carbon host provides many zincophilic Zn nucleation/growth sites due to its large specific surface area and oxygen doping effect, which inhibits Zn dendrite growth and volume expansion, as well as inhibits sides reactions due to its low HER properties stemming from hydrophobicity of carbon. Also, the hydrophilic ultra-thin ZnO layer (~10 nm) facilitates hygroscopicity of the aqueous electrolyte to the host to prevent “top accumulation” of Zn deposits on the carbon host, compensating low wettability of hydrophobic carbon host. Thus, the resonance between these two layers layer stably maintains low overpotential (~50 mV) even at ultra-high current density and high capacity (10 mA cm^-2 and 5 mAh cm^-2, respectively) during repetitive Zn plating/stripping. Furthermore, when combined with a MnO₂ cathode, the full-cell exhibits superior cyclability over 1,000 cycles at a low negative-to-positive electrode capacity ratio (~7.3), approaching practical AZMBs.<br/><br/>ACKNOWLEDGEMENTS<br/>This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2022R1A2C3003319).