(455g) Slurry Electrodes Unlock Dynamic Control over Capacitive Currents for Multi-Duration Energy Storage

Cost forecasts heavily suggest that energy arbitrage alone does not allow long-duration energy storage to remain profitable, necessitating storage deployments that provide a suite of storage services across varying power draws and timescales. Existing solutions struggle to intensify and decouple the timescales, power draw rates, and operational flexibility required of grid-scale storage into a single technology. Though traditional flow batteries decouple capacity and power by separating design of the electrochemical cell and reactant storage tank, they employ porous electrodes with static reactive surface area, inherently coupling operational and electrochemical timescales. This limits the extent they can draw current from higher-power density capacitive double layer discharge due to saturation at steady-state – in effect forcing congruency between electrochemical and operational timescales.

Slurry electrodes, which employ suspended conductive particles to form percolated networks supporting charge transport, allow advection of the electrochemical interface; this enables orthogonal control over the timescale and current draw the electrochemical interface experiences relative to the electrochemical cell. Where previous studies explored the transition between capacitive and faradaic behavior of slurry electrode cells, here, we explore control over this transition and its implications on the power density of the slurry electrode cell.

Leveraging a 1D transient PDE model, we find the extent of capacitive discharge can be controlled by tuning current draw at the cell and the residence time of the slurry electrode. We also find that this region of capacitive discharge can drastically increase sustained power draw and offer dimensionless design criteria to exploit this operating regime. Finally, we demonstrate a half cell slurry electrode operating continuously at power draws 5 times higher than the faradaically-limited pseudo steady-state rate – realizing the goal of an electrochemical cell that can be tuned to operate across a range of power draw rates.