Promising battery systems for renewable energy sources are ones that will provide resilient, flexible power while reducing the carbon emissions, oil demands, and recurring costs of fossil fuel. To this end, the electrochemical flow capacitor (EFC) is an innovative energy storage technology comprised of a slurry active material stored externally from the electrochemical flow cell. This spatial decoupling absent from conventional batteries allows low-cost scaling of EFCs as the price of the overall package asymptotes towards slurry raw material costs. Energy-dense slurries require electrically conductive particles to form a charge-carrying network in an electrolyte solution. Previous work has focused on carbon black because it is inexpensive, has a high surface-area-to-volume ratio, and has excellent electrical conductivity. Unfortunately, carbon black suspensions under flow become undesirably viscous, leading to unacceptable pumping costs for EFC operations. Mitigating high viscosities, however, comes at a trade-off with improving energy storage efficiency as the slurry electrical conductivity and specific capacitance also increase with carbon black content, as described by electrosorption. We hypothesize that by engineering the nanoscale forces of carbon black within suspension, we can design suspension electrodes with better rheological and electrochemical performance. Carbon black particles were functionalized by acid oxidation, presenting a surface chemistry that exhibits a strong, repulsive surface charge and confers colloidal stability. Changes to the size and the surface charge density of the primary agglomerates were derived from dynamic light scattering and zeta potential measurements, respectively. Chemical composition of the surface was obtained through X-ray photoelectron spectroscopy, complemented with Fourier-transform infrared spectroscopy. The active surface was further characterized with porosity and BET surface area measurements through gas sorption. Simultaneous shear stress and impedance measurements of homogenized Carbon black slurries with varying salt concentrations were acquired from a custom-built, cup and bob flow cell. We will develop structure-property relationships for several Carbon black slurries by linking flow-induced microstructural evolutions to observed rheoelectric performances. We anticipate the presence of an optimal position between low viscosity and high conductivity that maximizes the performance to cost ratio of carbon black slurry electrodes.
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