Quantifying Solid Electrolyte Interphase Growth and Lithium Plating Thresholds
Quantifying solid electrolyte interphase growth and lithium plating thresholds requires parsing passivating solvent consumption from kinetic overpotentials.
Solid State Diffusion Coefficient
Meaning
Physical transport parameters quantify the rate at which lithium ions move through the solid electrode host material during charging and discharging. This rate parameter, referred to as the solid state diffusion coefficient, is a critical determinant of the power density of a lithium-ion cell. Sourcing managers evaluate this parameter when comparing the fast-charging performance of cells from different suppliers.
Transport Physics
Solid-state ion transport is a thermally activated process. The solid state diffusion coefficient determines how quickly lithium ions can migrate within the crystal lattice of the cathode and anode materials. This rate of migration slows down as the temperature drops, which causes a rapid increase in concentration polarization.
At low temperatures, this transport bottleneck can lead to a severe reduction in available capacity. Consequently, cells designed for cold climates must incorporate materials with higher intrinsic diffusion rates or have thinner electrodes to minimize the diffusion path.
Characterization Method
Electrochemical techniques are utilized to measure the transport rate of lithium ions in the solid phase. The most common methods include galvanic intermittent titration technique and potentiometric intermittent titration technique. These measurements allow engineers to calculate the solid state diffusion coefficient as a function of the cell’s state of charge.
Material Selection
High diffusion rates are essential for high-power applications. Battery manufacturers adjust particle sizes and surface coatings to reduce diffusion lengths and increase the effective rate of ion transport. Sourcing teams use these diffusion metrics to select the appropriate cell chemistry for electric vehicle applications.
This selection process ensures that the chosen battery pack can meet the power demand during acceleration.