Large scale flow battery energy storage has long been considered as a potential candidate for smart grid batteries because of their design flexibility, safety and high current densities. However, one limitation of flow batteries for certain applications is their relatively low power density, which is fundamentally due to limited solubility of active species in the electrolyte which leads to the formation of precipitates at high concentration and/or high temperature. To overcome energy density limitations several methods/improvements have been reported in the battery research literature, including: polymer based flow batteries, new active materials, ionic liquids, and hybrid flow batteries with multiple redox couples.

Semi-solid flow batteries, first reported using lithium-ion chemistry by Duduta et. al¹ use high energy density lithium storage compounds within a suspension/slurry in a redox flow battery. This system also relies on a nanoscale conducting network of carbon particles to provide electronic contact between the active material particles and increase active material participation in the flow channel. Their reported energy density was an order of magnitude greater than conventional flow batteries; however, the carbon network resulted in a highly viscous electrolyte requiring high pumping energy. This poster will describe carbon-free redox flow couples with solid electroactive materials in electrolyte suspensions. LiCoO₂ (LCO) and Li₄Ti₅O₁₂ (LTO) were used as the active cathode and anode active materials, respectively.² The use of solid active materials and lithium-ion battery materials and electrolytes expands both the voltage range and volumetric energy density of the electrolyte. Without carbon the dispersions with sub-micron LTO and LCO particles have reduced viscosity compared to semi-solid flow batteries due to the absence of carbon conducting additives. The lack of carbon results in dramatic decreases in power density due to lower active material participation. The impacts of active material loading on electrochemical and rheological behavior in multiple cell designs will be described.

1. Duduta, M., Ho, B., Wood, V. C., Limthongkul, P., Brunini, V. E., Carter, W. C., & Chiang, Y. M. (2011). Semi‐Solid lithium rechargeable flow battery. Advanced Energy Materials, 1(4), 511-516.

2. Qi, Z., Liu, A. L., & Koenig, G. M. (2017). Carbon-free Solid Dispersion LiCoO2 Redox Couple Characterization and Electrochemical Evaluation for All Solid Dispersion Redox Flow Batteries. Electrochimica Acta.