Research On Battery Thermal Management Based On GA/PW Composite Phase Change Materials

At present,environmental pollution and energy problems are becoming more and more serious.New energy vehicles are in line with the development strategy of energy conservation and emission reduction,and electric vehicles are the most reliable and promising development direction.Lithium-ion batteries have many excellent performances as an important part of electric vehicles.However,lithium-ion batteries will release a lot of heat during their work.If they are not discharged in time,accumulation in the battery will result in a decrease in battery performance and a shortened life.The phase change material is applied to the battery thermal management to have a better heat dissipation effect on the battery,and as a passive cooling,the battery energy can be saved.This paper firstly deals with the problem that paraffin wax has low thermal conductivity and easy to leak after melting.For this purpose,graphene aerogel(GA)/paraffin wax(PW)composite phase change material is prepared and then applied to the battery,research the thermal management effects in high and low temperature environments.The main contents and conclusions are as follows:The GA was prepared by the dispersion of graphene oxide(GO)at concentrations of3mg/ml,4mg/ml and 5mg/ml respectively.Then the PW was used to form the GA/PW composite phase change material,and its properties were tested and analyzed.The thermal conductivity of composite phase change materials with GO concentrations of 3 mg/ml,4mg/ml,and 5 mg/ml were 0.29,0.35,and 0.4 W/(m?K);GA and PW were well compatible,and the coverage rate was more than 98%;there is no chemical reaction between the two,and the phase change temperature and latent heat value change little.The heat generation mechanism of the battery and its heat transfer model with the phase change material were analyzed.The thermal property parameters of the battery were calculated,and the simulation model was built and verified.The maximum temperature of natural convection cooling at 3C rate discharge reaches 328.6K.The maximum temperature of the GA/PW composite phase change material prepared by 5mg/ml GO and pure PW was326.9K and 325.9K respectively at 4C rate.The phase change material having a thickness of 6mm is suitable.At 4C rate discharge,the control of the phase change material cooling on the maximum temperature of the battery pack is similar to the effect of using the forced air-cooled with wind speed of 5m/s alone,and has better temperature uniformity.The phase change materialis coupled with air-cooled for heat dissipation.After comparison and optimization,it is arranged as two ventilation holes,the distance from the battery surface is 1.5mm,and the distance between the two ventilation holes is 15 mm,the battery temperature can be controlled below 323 K at 2m/s wind speed.Then the corresponding stepped air cooling control scheme is designed at different ambient temperatures.The heating method of the battery pack in low temperature environment was studied.The PI metal heating film was selected as the heating element,and the heating film was arranged on the left and right sides of the battery.The heating power shouled be 5W to meet the maximum temperature difference.The low temperature heating strategy was studied.The maximum temperature difference can be controlled within 5K by variable power heating.According to the above design,the battery pack integrated thermal management system control strategy is designed.