The Study On Thermal Characteristics Of The Charge/Discharge Processes In High Capacity Li-ion Power Batteries

With the energy crisis and global climate warming, Lithium-ion power batteries with long cycle life, high energy density, high operating voltage quickly become the research focus, but the major handicap of lithium-ion power batteries is the thermal safety.Understanding the heating mechanism of lithium-ion power batteries and the factors that affect the heating mechanism of lithium-ion power batteries are the key to solve the problem.First of all, the impact of different factors on the thermal characteristics of lithium-ion power batteries are discussed through charging and discharging experiment of lithium-ion power batteries, as well as the impact of ohmic resistance and polarization resistance on thermal characteristics of lithium-ion power batteries are analyzed by measuring ohmic resistance and polarization resistance. It is indicated that charge-discharge rate, ambient temperature and state of charge are important factors influencing the thermal performance of the Lithium-ion power batteries. The heat flux and temperature of battery are higher when the charge-discharge rate is higher, the lower ambient temperature is lower and the state of charge is lower. The ohmic resistance and polarization resistance are measured in this research. It is showed that, with the increase of discharge rate, the percentage of ohmic heat in total heat increases and the percentage of polarization heat and heat of reaction in total heat decreases respectively. The lower ambient temperature is, the greater total internal resistance of the battery is, so the heat power is high, and the higher temperature is high. Meanwhile, entropy change is only the function of SOC, regardless of the temperature of the battery in this SOC.Secondly, a new heat source model is suggested by analyzing experimental date and combining the heating mechanism of lithium-ion power batteries. Simulation results show that this model can reflect the temperature distribution in battery. Meanwhile, this model is used to simulate battery temperature when battery works in harsh environment, Results indicated that increasing the convective heat transfer coefficient can help to reduce the battery temperature.