Meaning
Voltage loss arising from the development of ion gradients within the liquid medium of a battery cell. During high-current operations, electrolyte concentration polarization reduces the terminal voltage as the salt concentration at the electrode surface deviates from the bulk value. This effect represents the kinetic limit of ion transport through the porous separator and the electrode structure.
It defines the boundary where further increases in current no longer yield higher power due to the depletion of active ions.
Diffusion Limitation
Ion movement relies on a concentration gradient to drive flow from the bulk electrolyte to the reaction site. As electrolyte concentration polarization increases, the salt concentration on the anode side may drop toward zero while the cathode side becomes saturated. This starvation of ions at the surface forces the cell potential to drop sharply.
Thick electrodes are particularly susceptible to this failure mode because the path length for diffusion is longer.
Viscosity Influence
Temperature changes the rate at which ions can move through the solvent. Cold environments exacerbate electrolyte concentration polarization by increasing the viscosity of the electrolyte and slowing the diffusion coefficient. A cell that performs well at room temperature may fail to deliver its rated capacity at sub-zero temperatures for this reason.
Selecting salts with higher mobility can extend the operational window of the chemistry.
Voltage Recovery
Removal of the external load allows the salt concentration to equalize across the cell. This relaxation phase demonstrates how electrolyte concentration polarization is a transient loss. If a measurement is taken too soon after a high-load event, the resulting data will show a lower open-circuit voltage than the true state of charge.
The time required for this gradient to dissipate depends on the porosity and tortuosity of the electrode. Researchers monitor the voltage decay curve to extract the diffusion coefficient of the lithium ions in the specific electrolyte blend used in the cell.
