Discharge and Thermal Distribution Characteristics of Electric Vehicle Battery Pack in Closed Circuit System

Abstract

This paper presents an experimental study of the depth of discharge (DOD) and temperature distribution characteristics at different locations of the lithium-ion battery (LIB) pack in the closed circuit system. Three different discharge power setups i.e., 600 W, 800 W, and 1000 W are prepared for investigating the depth of discharge and temperature characteristics of commercial LIB. Voltage measurement was implemented to achieve the DOD curve, while thermocouple measurement was used to identify real-time temperature at four different locations of the LIB. As a result, internal resistance and discharging time tend to be increased, while the voltage and current decline linearly from 0% to 80% of LIB capacity. Discharge power greatly affected the four variables when the process continued to the 10% cut-off voltage. Furthermore, the heat generation of the LIB caused a rise in temperature on its surface. The highest temperature was identified on the LIB cell surface followed by an air gap, internal surface casing, and external surface casing temperature. Among all locations, the real-time temperature on the LIB surface operated close to the upper limit of optimum temperature. Due to that reason, increasing of discharge power should be maintained to extend battery cycle life as well as to prevent battery failure. The high-temperature difference between the LIB surface and air gap during the discharging process indicated that there is required heat transfer enhancement.