Polarization-Driven Saturation in Thick Lithium-Ion Electrodes

While thick electrodes may achieve good utilization at low charge and discharge rates (c-rates) used for diurnal grid storage, the widespread commercialization of thick electrodes across the electric vehicle and stationary storage industries is limited by their performance at higher c-rates. In thick electrodes, highly polarized concentration gradients form across the electrode to drive lithium ion transport through the thickness of the electrode, resulting in large overpotentials that limit capacity utilization at higher rates. It is well understood that depletion at one side of this concentration gradient results in a limiting current for the cell; our models show that for high-power thick electrode systems, salt accumulation at the other side of the concentration gradient can exceed the solubility of conventional carbonate electrolytes used in lithium-ion batteries. Both saturation and depletion phenomena are important to consider when defining the c-rates of operation as we move towards thicker electrodes, and analytical expressions for limiting currents in both scenarios are derived from first principles to facilitate the design of other electrode-electrolyte systems.