Meaning
Voltage losses arising from concentration gradients of lithium ions within the liquid electrolyte represent a primary limitation to fast charging in battery cells. High current densities induce liquid phase polarization by depleting lithium ions near the active material surface while accumulating them near the opposite electrode. This spatial imbalance generates an additional overpotential that shifts the cell voltage toward the safety cutoff limit.
Concentration Gradient
Electrolyte properties like salt diffusion coefficient and transference number determine the severity of this polarization. When the salt diffusion coefficient is low, the concentration gradient across the electrode thickness grows steeper. This behavior reduces the effective ionic conductivity of the liquid phase in the innermost pores.
Diffusion Limitation
Cell design parameters like tortuosity and thickness directly influence the onset of these gradients. High mass loading electrodes create long pore pathways that hinder salt relaxation during discharge. Consequently, the liquid phase polarization can become the dominant component of total cell resistance during sustained power delivery.
Operational Consequence
Mitigating this transport resistance is essential for electric vehicle battery packs that must recharge in under fifteen minutes. Engineering teams select low-viscosity solvents or decrease the thickness of the coating to prevent this polarization from triggering early cutoffs. If the gradient becomes too severe during charging, the negative electrode potential can drop below zero volts versus lithium, causing metallic lithium to deposit on the graphite surface and compromising cell safety.
