Meaning
Voltage loss resulting from the depletion of reactants at the electrode surface characterizes the internal resistance associated with ion movement. When diffusion overpotential occurs, the cell potential deviates from its equilibrium value because the chemical species cannot arrive or depart fast enough. This effect becomes more pronounced at high discharge rates.
Efficiency decreases as heat builds up.
Concentration Gradient
Ion transport depends on the difference in molarity between the bulk electrolyte and the interface. The concentration gradient of diffusion overpotential represents the physical driving force that moves lithium ions toward the active sites. If the gradient becomes too steep, the voltage drops sharply.
Power delivery suffers.
Rate Limitation
Physical barriers like the separator or the tortuosity of the electrode pores slow down the movement of particles. Within the rate limitation of diffusion overpotential, the thickness of the electrode layer acts as a constraint. Thinner coatings allow for faster ion travel.
Fast charging depends on minimizing these transport delays.
Thermal Sensitivity
Viscosity of the liquid electrolyte changes as the environment cools, making ion movement more difficult. The thermal sensitivity of diffusion overpotential explains why battery performance degrades in cold weather. Kinetic energy is lower.
Increasing the temperature lowers the resistance and restores the voltage profile. Warm cells exhibit much lower losses during rapid acceleration. Heating the pack before a high power event is a common strategy to mitigate this specific voltage drop.
