Thermal Management And Electrochemical Thermal Analysis For Lithium-Ion Battery

With global environmental problems becoming serious,such as the energy shortage,environmental pollution,and the greenhouse effects,the development of electric vehicles which have no pollution and low energy consumption,has become a new development direction for the automotive industry all over the world.Lithium-ion battery is widely used as the power battery for electric vehicles because it has no pollution,high cell voltage,high capacity density,no memory effect and long cycling life.The thermal safety problem has been one of the key issues that restrict the development of power battery.Developing a real-time and efficient thermal management system to ensure both the battery pack temperature in the best operating range(25?-40?)and the maximum temperature difference between the cells less than 5? are very important.Considering the cost and the compact space requirements of electric vehicle,the air-cooled battery pack system has been the first choice.In addition,the battery pack is composed of a large number of battery cells in series and in parallel.The discharge and heat generation characteristics of battery cell affect the discharge and heat generation characteristics of the battery pack.Focusing on the thermal safety issues of lithium-ion batteries,the main research contents of this paper are carried out separately from the parallel air-cooled thermal management system and battery cell.Firstly,the cooling effect of a parallel air-cooled thermal management system containing 40 cylindrical lithium-ion battery cells is studied.The effects of inflow air velocity and temperature on the maximum temperature and temperature difference between cells are investigated at 3C discharge rate.The results show that the maximum temperature decreases with the increase of the inflow velocity and has a linear correlation with the incoming flow temperature.The maximum temperature difference of the battery module decreases with the increase of the inflow velocity and is independent of the inflow temperature.In addition,this paper improves the structure of the primary model from three aspects:cell distance S,deviation angle ?,and plenums' plate angle ?.A more compact model with a more uniform and reasonable temperature field distribution is obtained.On the second part of this paper,based on the reaction principle of charge and discharge of lithium-ion batteries,an electrochemical-thermal coupling numerical model is established.A cylindrical lithium iron phosphate 26650 battery cell is chosen as the research object,and the effects of discharge rate,ambient temperature,and convective heat transfer coefficient on the discharge performance and heat generation performance are discussed.The results show that the cell discharge voltage and the depth of discharge decrease when the discharge rate increases.The cell temperature rise increases approximately linearly at the same discharge rate.When the ambient temperature is increased,both the cell discharge voltage and the depth of discharge increase.The cell temperature rise decreases approximately linearly with the increase of the ambient temperature.In the low temperature environment,both the cell discharge voltage and discharge depth decrease with the increase of the heat transfer coefficient.However,when the convective heat transfer coefficient is changed in the high temperature environment,the cell discharge voltage and discharge depth unchanged.Both in the low temperature environment and high temperature environment,the cell temperature rise decreases with the increase of the heat transfer coefficient.