Mechanistic Role of Thermal Gradients on Lithium Plating in Li-Ion Batteries

Abstract

Unwanted lithium deposition on the surface of graphite particles tends to occur during charging of Li-ion batteries at low temperatures, high rates, and high states of charge. However, the intricacies of the coupled thermal-electrochemical interactions that govern Li plating behavior are yet to be fully uncovered. Thermal inhomogeneity naturally develops during the high rate operation of large-format cells, particularly when active cooling systems are employed; hence, a deeper investigation of the relationship between thermal gradients and Li plating is merited. This study employs a microstructure-aware modeling approach to probe the influences of both in-plane and inter-electrode thermal gradients on Li plating. Both types of thermal gradient were found to cause inhomogeneous current distribution within the electrodes. While inter-electrode gradients resulted in a variation in the Li plating onset point and severity, the Li plating induced by in-plane gradients was nearly the same as for isothermal cases at the same mean temperature. The sensitivity of charging performance to mean temperature and thermal gradient magnitude was analyzed across a range of practical conditions. Electrochemical experiments were performed under applied external thermal gradients to study the effect on plating and cell lifespan in various cell formats, and the electrode degradation was characterized post-mortem. By gaining a fundamental understanding of the Li plating phenomenon, this study aims to assist in the design of electrode structures and cell formats that will reduce the propensity for this mode of degradation.