Flowable Electrodes: A Review of the Material Aspects of Capacitive Suspension Electrodes for Grid Energy Storage and Desalination Applications

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In the past couple of years flowable electrodes have emerged as a possible avenue for achieving high charge capacity in large scale infrastructure applications across the globe (grid energy storage [1-4] and water desalination[5-6]). Flowable electrodes or suspension electrodes are a new type of electrode system where the active materials is directly combined with an electrolytic medium. The electrolyte is gravimetrically the majority component and aids in the physical transport of the active material for charge storage (ion adsorption). The ability to continuously flow (replenish) active (solid) material through a polarization cell allows for continuous charge storage. At Drexel, our focus has been on the development of capacitive suspension electrode (CSE) systems that utilize electrostatic charge storage mechanisms as means for charge storage. A key difference between suspension (flowing) electrodes and film electrodes is the thickness of the electrodes. Suspension electrodes, targeted for large scale applications, are at least an order magnitude thicker than film electrodes. Thus, as the capacitance decreases with electrode thickness the energy density (E=1/2CV2) also suffers [7]. To address this challenge, we have examined an array of active materials (metal oxides/highly porous carbon spheres) and electrolytes (redox-active, aqueous, organic) in order to understand the key aspects that govern efficient charge and ion transport in suspension electrodes. This poster will review the fundamental physical and kinetic considerations that must be examined in order to achieve high performing flowable electrodes. Furthermore, we will highlight the key material differences when developing active materials for flowable electrodes for grid energy storage applications and desalination applications.