A computational model of particle hydrodynamics and charge transfer for the carbon slurry in electrochemical supercapacitors

Slurries of porous carbon particles are being used as flowable electrodes in electrochemical supercapacitors such as electrochemical flow capacitors (EFCs) and flow-electrode capacitive deionization (FCDI). In these devices, the activated carbon beads absorb ions from the aqueous electrolyte and meanwhile store electronic charges by forming a dynamic, topology-varying percolation network. Our objective is to study how the hydrodynamic interactions of the carbon particles affect transfer of electrons and the charging/discharging process. In our computational model, the hydrodynamics of particles is simulated using a Stokesian dynamics approach that incorporates the presence of a no-slip wall representing the stationary electrode. The flow is driven by a specified shear. A generalized electrical circuit is introduced to represent the percolation network whose topology is constantly disrupted by random particle-particle and particle-wall contact and separation. The model parameters are either based on previous experimental setups or estimated from relevant studies. We explored three cases where the hydrodynamic time scale is either much smaller than, or comparable to, or much larger than the characteristic charging time scale.