Understanding and Improving Zinc Anodes for High-Energy Rechargeable Alkaline Batteries
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Batteries with aqueous electrolytes generally feature better intrinsic safety, higher ionic conductivity and lower cost compared with flammable organic electrolytes. Metallic zinc as a rechargeable anode material for aqueous batteries has gained tremendous attention with merits of intrinsic safety, low cost, and high theoretical volumetric capacity (5,854 mAh cm-3). Among zinc-based batteries, Zn-air batteries are promising with high theoretical gravimetric and volumetric energy densities (1,093 Wh kg-1 and 6,134 Wh L-1, respectively). Rechargeable zinc anode has achieved big progress in neutral electrolytes, yet developed slowly in alkaline electrolytes, which are kinetically favorable for air cathodes. Passivation, dissolution, hydrogen evolution reaction (HER), and dendrite formation are four reasons for irreversibility of zinc anodes in alkaline electrolytes. This thesis comprises three parts: material, mechanism, and device. From the aspect of material, four types of zinc anodes were designed and synthesized to overcome above issues and improve their reversibility. These anodes include graphene oxide-modified (Zn@GO), lasagna-inspired (ZnO@GO), sealed (ZnO@TiNxOy), and hydrogen-evolution-suppressing (ZnO@TiO2) anodes, which improve the deep cycling performance when cycled at lean electrolyte. From the aspect of mechanism, the underlying mechanism of the spatial control of zinc deposition on zinc alloy anodes has been elucidated for the first time. The spatially controlled Zn deposition was visualized for the first time by operando optical microscopy. From the aspect of device, it was discovered that the testing device material has a clear effect on the hydrogen evolution. Specifically, stainless-steel coin cell cases, as widely used devices in research laboratories, accelerate the HER. Plastic devices were successfully constructed to minimize the HER. Future research on rechargeable Zn-air batteries is discussed.