Development of Organic Positive Electrodes for Rechargeable Aqueous Zinc-Ion Batteries for Stationary Energy Storage Systems

The rising concern towards the amount of anthropogenic carbon emissions and their effects on the environment has motivated the transition away from fossil fuels. The implementation of renewable energy sources has promoted the decarbonization of the power sector, but the variability of wind and solar energy necessitates the parallel deployment of high-performance energy storage infrastructure to ensure a reliable on-demand supply of green electricity to the grid. To this end, aqueous rechargeable zinc-ion batteries (ZIBs) are a promising new option for stationary energy storage owing to their high safety and low cost, when compared to established storage technologies like lithium-ion batteries. However, ZIBs are still limited by several technological challenges that hinder their uptake for commercial energy storage installations. In particular, the positive electrode materials, mostly comprised of metal oxides, are restraining the energy density and stability of the batteries and are yet under investigation. Low cost, long cycle life, and natural abundance are required properties of materials used in batteries for stationary energy storage. The search for materials with these properties has motivated the investigation of alternatives to metal oxides. One group of materials attracting considerable research attention is organic compounds which offer advantages like their natural abundance and high theoretical capacities. In this work, we developed an organic positive electrode for ZIBs using carbonyl groups as redox-active centers to provide energy storage capacity at round-trip energy efficiencies that are higher than the conventionally utilized manganese oxide electrodes. Furthermore, we investigated the effects of the conductive carbon additive on the deliverable capacity of the battery and elucidated the charge storage mechanism of this positive electrode material through detailed characterization. The results indicated that both Zn2+ and H+ are involved in the energy storage process of this organic electrode material. In addition to studying the energy storage process, degradation mechanisms were identified through nuclear magnetic resonance (NMR) and mass spectroscopy (MS). Both dissolution of the reduced form of the active material from the electrode and the formation of unwanted decomposition products are important contributors to the capacity fade of the battery. The technological and scientific insights provided in this presentation will thereby contribute towards the development of high-performance and naturally abundant electrode materials for the next generation of ZIBs to enable clean energy grid storage.