High Energy Density Battery Electrodes with Low and Anisotropic Tortuosity

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The high inactive materials content (e.g., separators, current collectors, conductive additives, binder and packaging) of current nonaqueous battery designs contributes directly to high battery cost and reduces specific energy and energy density. Area specific capacity, which is perhaps the most objective measure of design performance, cannot be increased arbitrarily by increasing electrode thickness and/or density, due to kinetic limitations. In the limit of high density and large thickness, salt depletion within the electrolyte-filled porosity typically becomes rate-limiting. In order to reach higher usable energy at practical C-rates from thick, dense electrodes, it is essential to tailor the topology of the pore structure to reduce tortuosity anisotropy. Here we report on the fabrication, characterization of tortuosity, and electrochemical testing of thick, dense electrodes made by the freeze-casting of aqueous suspensions followed by drying/sintering. This shaping technique allows design of oriented and interconnected structures that have tortuosity anisotropy, low absolute tortuosity, and high ionic transport. We report on the characterization of tortuosity of directionally fabricated electrodes with similar porosity while varying the solidification rate that resulted in different microstructural features. The electrochemical performance of the fabricated electrodes in half cells exhibits high areal capacity. Hybrid pulse power characterization (HPPC) and dynamic stress tests (DST) were also performed.