Studies on improving stability of aqueous Zn-ion batteries by understanding interfacial reactions

Abstract

With the increasing demand for renewable energy sources, the necessity of energy storage systems is increased to compensate for the irregular energy generation for efficient energy storage and supply. Energy storage systems require high power density, stability, safety, and economic feasibility for grid-scale applications. In this regard, aqueous batteries are spotlighted as a next-generation system. Among the candidates, I studied rechargeable aqueous zinc-ion batteries in this dissertation. I tried to understand the overall reaction mechanisms based on the interphase reactions among the positive electrodes, negative electrodes, and electrolyte solutions. All these approaches aimed to improve the cycling performance of zinc-ion batteries. In chapter 2, I adopted naphthalenediimide as an organic cathode. The dissolution of active materials, commonly observed in inorganic electrodes, was suppressed, and the reaction processes between the naphthalenediimide cathode and aqueous electrolyte solution were identified (Chapter 2). I demonstrated that protons in the aqueous electrolyte solution were inserted/deinserted into the naphthalenediimide cathode along with the zinc ions during the charging and discharging process. However, the protons-involved process caused undesired deformation of the organic cathodes, revealing that the mitigation of proton-related reactions is necessitated. In chapter 3 and 4, I focused on the interphacial reactions between the zinc anode and electrolyte solutions. I employed glutaric acid as the organic additive, which in situ formed the zinc glutarate layer protecting the anode surface and suppressed the zinc corrosion, hydrogen evolution reaction, and precipitation of zinc hydroxyl sulfate. Using zinc-iodide semiredox flow cells, I successfully demonstrated the improved cyclability with the glutaric acid additive,underpinning the vital steering of the interfacial reactions in the rechargeable zinc-ion aqueous batteries.