Test And Simulation Of Thermal Characteristics Of Single And Module Of Power Battery

As the power source of electric vehicle,the thermal safety of lithium battery has always been concerned.In the actual operation of electric vehicles,the battery modules inevitably discharge for a long time or at a high rate.If the heat generated by the battery cannot be transferred out in time,it will cause the temperature of the single battery in the module to rise continuously and aggravate the temperature difference of each single battery in the module.In addition,the performance of the single battery is obviously affected by the temperature,so in the long run,the performance of the internal single battery will be inconsistent,which will seriously reduce the cycle life of the battery;the accumulation of heat will cause the thermal runaway of the single battery in the battery module,which may cause safety problems such as combustion and explosion of the battery module.Therefore,the research of high efficiency.heat conduction structure in the power battery module has become the most important.The main research contents and conclusions are as follows:1.The basic heat generation model is built by the heat generation rate of D.Bernardi lithium battery.The heat radiation,heat conduction and convection heat transfer in the working process of lithium battery are studied,and the basic physical parameters and geometric parameters to be measured are determined.The effects of current and ambient temperature on the performance of the battery in the actual heat generation process were studied through the battery disassembly test,internal resistance test,temperature rise test and capacity and energy test.The experimental results show that the internal resistance and discharge capacity of the same type of battery are inconsistent under the same working condition;the temperature difference between the positive and negative electrodes and the middle part of the battery is within 2.1?.When the test current exceeds 3a,the temperature will exceed 50?;the fluctuation range of internal resistance will be kept within 15?3 0m?;In the process of charge and discharge cycle,the discharge capacity and energy of the battery show signs of decline;When the discharge capacity is in the range of 0?0.8,the voltage temperature coefficient of the test battery is greater than 0.In the mirror image test,it is found that the short circuit and needling behavior lead to the phenomenon of graphite and positive active substances'disengaging,which seriously destroys the electrode material structure of the battery and causes serious damage to the battery.2.According to the heat generation mechanism,a simplified model of lithium battery is established,and the temperature rise characteristics of different constant current discharge and different ambient temperature under constant natural convection coefficient are analyzed by simulation,and compared with the test data.The UDF model of variable convection coefficient is built,and the simulation temperature error of 6 A discharge at 30? is optimized.The results show that when the natural convection coefficient is set as a constant,the error rate of the simulation results is less than 5%,but the error rate is more than 9.48%,the worst is 23.88%.After optimization,the temperature accuracy of 6A discharge at 25? is improved to 2.9%.3.In view of the existing battery box model,the calculation module of this paper is established,and the staggered arrangement mode of single battery is determined.The heat dissipation performance of battery pack is studied from four factors:inlet flow,coolant temperature,contact angle,channel height and channel contact angle.According to the problem of large temperature difference,the optimization strategy of variable contact angle structure is proposed.The results show that increasing the coolant inlet flow rate and reducing the coolant temperature can effectively reduce the battery temperature,but it will increase the system load;increasing the contact angle and the channel height have a certain impact on the heat dissipation performance,but the decline will gradually decrease with the increase of the value;using the variable contact angle can reduce the battery temperature difference,and the reduction can reach 24.05%.