Thermal Characteristic Analysis of Rectangular and Large-Capacity Lithium-Ion Power Batteries

Operating temperature and thermal uniformity have great effect on the performance, cycle life and safety of lithium-ion power batteries. In order to investigate the surface temperature change and distribution of a large-capacity and rectangular LiFePO4/C power battery, this paper conducts experiments on charging and discharging a battery module and cell at different current rates and various ambient temperatures. Results of thermalcouple-measurement show that temperature rising rates at different temperatures during charge and discharge change in accordance with the variation tendency of the resistance at different state of charge (SOC) and oprating temperatures. Under elevated ambient temperatures, the temperature excurtion and maximum temperature difference of the module are all smaller. Under the same ambient temperature, battery temperature at the end moment of discharge increases and the temperature uniformity of the module deteriorate at higher discharging rate. Temperature excurtion over the same time period is in a relationship of a standard quadratic function with the discharge current. Results of the thermal infrared imaging tests show that the maximum surface temperature differences at different discharging currents of 20A, 40A, and 80A are all above 5°C under natral convection heat transfer. The temperature of the lower part is higher than that of the upper part, while that of the central area is the highest. In a comprehensive charging and discharging scheme, the tendency of maximum surface temperature difference changes in accordance with that of the average surface temperature.