Meaning
Electrochemical transport properties quantify the ease with which ions move through a liquid medium within a battery cell. Electrolyte diffusivity determines the maximum current the cell can provide during rapid discharge. This coefficient is expressed in square centimetres per second.
Concentration Gradient
Variations in the density of salt throughout the solvent drive the movement of ions toward the reactive surfaces. The electrolyte diffusivity dictates how quickly the system can return to equilibrium after a high-load event. If the ions move too slowly the cell experiences polarization which drops the operating voltage.
Proper formulation of the organic solvents ensures that the liquid remains fluid enough for efficient transport.
Temperature Dependency
Cold environments greatly reduce the kinetic energy of the molecules and slow the ionic motion. Lower electrolyte diffusivity at sub-zero temperatures is the primary cause of reduced power availability in electric vehicles during winter. Thermal management systems keep the pack within a range where the transport remains optimal.
At higher temperatures the viscosity decreases and the ions move with less friction. Heated enclosures are used to bypass this limitation.
Rate Limitation
Fast charging protocols are often restricted by the speed at which ions can reach the anode. Electrolyte diffusivity sets the ceiling for how much energy can be pumped into the battery in a short window. If the charge rate exceeds the transport capacity lithium plating may occur on the surface of the negative electrode.
This leads to permanent capacity loss and potential safety hazards.
