UNS: Mechanistic Approach to Design Robust Composite Polymer Cathodes for Potassium-Air Batteries

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PI: Vishnu-Baba SundaresanProposal Number: 1512405Rechargeable batteries support the development of sustainable energy systems by storing electricity generated by renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. However, lithium ion batteries now in use have relatively low energy storage capacity. Metal-air batteries offer the potential for much higher energy storage capacity than lithium-ion batteries because they store electrical charge by a different process that uses oxygen in air to help transfer electrons. But this process can also increase charging times. Of the metal-air batteries, the potassium-air system is among the fastest, but is prone to failure. The goal of this project is develop a fundamental understanding of the mechanism of failure, and then use this understanding to develop a new cathode design based on conducting polymers that provides better control of oxygen atom transport. In this way, potassium-air battery systems can move forward towards eventual commercial application. As part of this research, graduate and undergraduate students will be given the skills to further develop metal-air battery systems. The principal investigators will also organize workshops on energy storage materials and smart materials to promote STEM education among middle and high school age students in greater Columbus, Ohio area. Metal-air batteries offer the potential for high electrochemical energy storage capacity that exceeds that of comparable metal ion batteries. Of the metal-air batteries, the potassium-air system uses a one-electron redox process between oxygen and superoxide to improve upon the low rates of oxygen reduction/evolution associated with other metal-air battery systems. However, the fundamental limitation of potassium-air batteries is the crossover of molecular oxygen from the cathode to potassium anode, leading to the formation of potassium superoxide on the anode surface. This process causes self-discharge and reduces the availability of metal that can participate in energy storage. The goal of the proposed research is to investigate the feasibility of a composite cathode formed from conducting polymers and carbon support materials to regulate the oxygen reduction reaction in the cathode and prevent the diffusion of molecular oxygen to the anode. The conducting polymer is a functionally graded, nanostructured polypyrrole membrane with an optimized density of redox sites, and the carbon support material is reduced graphene oxide. An electropolymerization process will be used to make the membrane so that the porosity of the cathode gradually decreases across the thickness of the membrane. It is hypothesized that the graded porous structure will block molecular oxygen crossover, thereby enhancing the performance lifetime of the potassium-air battery. The proposed research plan will develop a mechanistic understanding of charge storage of the conducting polymers within the composite cathode that accounts for mechanical stress, diffusion of gases, and electrochemical reduction reactions during faradaic processes. As part of this plan, the chemo-mechanical coefficients that relate volumetric stress generated in conducting polymers and well as their application for increasing the energy density and specific power of potassium-air batteries will be quantified. The research plan has four specific tasks: 1) electrochemical synthesis of the functionally graded, nanostructured polypyrrole membrane; 2) characterization of this membrane as the cathode for a potassium-air electrochemical cell; 3) construction of potassium-air battery containing the conducting polymer composite cathode, and 4) battery performance measurements (capacity, power, cycling). The research outcomes will advance a more generic and mechanistic understanding of energy storage and conversion in conducting polymers for metal-air battery systems, and concepts derived from the research will be introduced into an energy storage materials course.