Electrochemical-thermal analysis of 18650 Lithium Iron Phosphate cell

A pseudo two dimensional electrochemical coupled with lumped thermal model has been developed to analyze the electrochemical and thermal behavior of the commercial 18650 Lithium Iron Phosphate battery. The cell was cut to obtain the physical dimension of the current collector, electrodes, separator, casing thickness, gasket, etc. The layer structure of the spiral wound, cylindrical casing, gasket and heat shrink wrapping were modeled to understand better the temperature distribution across the cell. Natural convection and radiation were used to reflect the heat dissipation on the side surface. Experimental study was carried out to validate the simulation results. The simulation results suggested that the cell temperature and total heat generation rate have a positive correlation with the It-rates and these were inline with the experimental results. Reaction heat was the main heat source and it contributed about 80-85% of the total heat generated during charging and discharging of the cell. Based on the simulation results, the final temperature of the cell surface was elevated to 59 °C using 10It of charging. The effect of electrical contact resistance between the connectors and terminals of the cell was also investigated. It was found that the electrical contact resistance caused a large temperature gradient across the cell. These effects are important and should be considered in the design of EV battery pack and thermal management system to reduce the maximum temperature and maintain the temperature uniformity of the cells.