Study On Thermal State Of Lithium-ion Power Battery

Under the dual effects of the energy crisis and environment protection, most of the car companies in the world are working on electric vehicles, as a representative of new energy vehicles. Now lithium-ion power batteries have been widely used in electric vehicles. Temperature plays an important role in battery performance, safety and cycle life. A battery thermal management system is necessary to ensure that the temperature of battery is uniformity and in a normal range. So the study on thermal state of lithium-ion power battery has great significance on development of power battery technology.By simulation and experiment, this paper built an accurate thermal model of a 18650 LiFePO4 single cell, and studied influence factors on the thermal fields of module batteries with air cooling. Provide certain ideas and basis for power battery pack cooling organization and structure design. The research of this paper has the following aspects:(1) Theoretically analyze thermal characteristics of lithium-ion battery. During the research about heat generation mechanism, a heat generation rate formula was established by using Joule’s low and thermodynamics. Analyze heat transfer model of lithium-ion battery by heat transfer theory.(2) Study on thermal characteristics of single cell by experiment. A battery charging and discharging experiment platform was built to study the influences of temperature and SOC on ohm resistance, polarize resistance and voltage temperature coefficient of battery. This paper measured the temperature of the single cell under different conditions, and analyzed the influence of environment temperature and current on battery conformance.(3) Study on thermal state of single cell by simulation. Using resistance and other experimental data, this paper fitted a heat generation rate function about battery temperature and SOC. Using this function, this paper simulated the thermal fields of single cell under different conditions, then comparatively analyzed the simulation results and test results.(4) Study on thermal state of module battery by simulation. Using the thermal model of single cell, which was verified by test, this paper made some simulation research about different influence factors on the thermal fields of module battery with air cooling.