Highly Conductive Metal-based Flowable Electrodes

Elad Halfon, Energy Program, Mechanical Engineering, Technion, Haifa, Israel
Matthew Suss, Energy Program, Mechanical Engineering, Technion, Haifa, Israel

Metal deposition Redox Flow Batteries (RFBs) hold promise for grid-scale energy storage applications as they provide advantages such as geographical and operational flexibility, low material costs, high efficiency and improved energy density. The use of metal deposition introduces the danger of dendritic growth. Metal dendrites continuously grow as charging-discharging cycles continue, and eventually reach the separator causing a critical failure. The use of suspension electrodes composed of particles has been investigated as a mean to boost flexibility by decoupling energy from power as well as avoid dendritic growth. The use of flowable electrodes architecture provides a more homogeneous deposition which is obtained on the surface of constantly moving particles. Avoiding the danger of dendritic static deposition while simultaneously enabling energy storage outside of the electrode chamber.

While the benefits of flowable electrodes are easy to grasp, they generally suffer from sluggish electron transport through the discontinuous solid particulate phase. Efforts to analyze the reasons for measured low conductivities is ongoing, with the goal of approaching the conductivity achieved by static electrodes. Lately, fluidized bed electrodes have been also introduced, substantially increasing solid loading in the flow electrode to values above that attained by slurries. Although conductivity improved, it was still measured to be orders of magnitude lower than the bulk conductivity of the electrode material and does not reach the desired values.

Here, we explored the electric conductivity of a suspension formed with 20µm copper particles under various operating parameters using 4-electrode EIS. We achieved unprecedented measured values of up to 1000 S/m. Conductivity was a strong function of velocity, as shown in Figure 1. We will discuss the mechanisms underpinning the observed high electric conductivity and the potential applications of such flowable electrodes in energy storage systems.