Collaborative Research: Understanding the Role of Directional Porosity in Transport and Mechanical Properties of Hierarchical Sintered Metal Oxide Electrodes

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Solid state batteries provide power for countless applications, and their manufacture and application has significant impact on the US economy, health and prosperity. The electrodes in these batteries are conventionally made of composites where each material plays a role: an electroactive material stores and delivers energy, conductive additives carry electrons, and polymer binders hold the components together and provide mechanical robustness. If instead a single multifunctional material phase could be used as the electrode, the energy storage and power capacity of these battery materials would be greatly increased. Porous ceramic thin film materials have been developed for this application, but little is known about the transport properties of ions through these ceramics during electrochemical reactions, their mechanical properties, or the tradeoffs between these multifunctional roles and resulting properties. This award supports fundamental research to understand the properties of electrodes comprised of a single sintered porous thin film as the active material. This research has the potential to provide a new paradigm for multifunctional hierarchical materials which would fundamentally change the way these materials are designed and processed. This work will provide a framework for understanding electrochemically active and ion-conducting porous ceramics, which have application not only in batteries, but also in other devices such as solid oxide fuel cells and electrochemical sensors.In this collaborative research program, the researchers will test the hypothesis that concentration polarization and ion transport limits the electrochemical current density of sintered multifunctional electrodes. To tune the mechanical properties of electrodes and to achieve tunable, low tortuosity in sintered electrodes, a novel ice-templating processing approach is used to produce electrodes of ordered structure, and directional pores with tunable dimensions. This will enable systematic investigation of the impact of tunable directional porosity on both ionic transport and mechanical properties. The detailed impact of microstructure of the ice-templated electrodes on resulting mechanical properties, especially compressive strength, will be studied. In addition, the coupling between mechanical and electrochemical properties will be investigated. Higher bridge density between ceramic lamellae is hypothesized to improve mechanical strength, but at the expense of increased tortuosity and restricted transport. This work investigates the tradeoffs between transport and mechanical properties as a result of ceramic processing, with the objective of understanding the processing-microstructure-property relationships for high-performance electrode materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.