Design And Performance Study Of Heat Dissipation Scheme For Battery Thermal Management Based On Composite Phase Change Materials

With the global research and development of new energy vehicles and attention to environmental protection,electric vehicles have achieved unprecedented development in recent years.As the only energy supplier of pure electric vehicles,the safety performance of power battery pack directly affects the safety and performance of electric vehicles during use.The current electric vehicle power battery pack is mainly lithium ion battery pack,and the performance of the lithium battery is greatly affected by temperature.When the temperature of the lithium battery is too high,the electrolyte transfer speed of the lithium battery and the reaction rate of the electrode will accelerate,which will destroy the normal chemical equilibrium inside the lithium battery,and some unfavorable side reactions will occur.Especially when the temperature of the lithium battery exceeds 45 ℃,the performance degradation of the internal materials of the lithium battery will be aggravated,which will greatly affect the performance and service life of the lithium battery.In severe cases,the thermal runaway of the lithium battery pack will occur,leading to safety accidents such as spontaneous combustion of the lithium battery.Aiming at higher temperatures that will affect the performance of electric vehicle power battery packs and cause safety accidents,with the support of project of National Scientific Fund,the design and performance research of battery thermal management scheme based on composite phase change material are carried out to reasonably control the temperature of electric vehicle power battery pack during application.The main research contents are as follows:1.Analyzing the heat generation mechanism of lithium battery in the working process from the working principle and internal structure of lithium battery,and the composition and calculation method of heat are introduced in detail.2.The PW/EG/LDPE composite phase change material was prepared by the melt blending method,and the relationship between the ratio of EG and LDPE and the thermal conductivity and leakage rate of the composite phase change material was studied.The performance of the prepared composite phase change material was characterized to explore its physical properties,and the composite phase change material with high thermal conductivity and low leakage has been developed.3.By Combining the prepared composite phase change material with a heat sink,it was found that the heat sink greatly improved the thermal conductivity of the composite phase change material,and effectively reduced the leakage rate of the composite phase change material.The cooling method was applied to the battery thermal management,and the charging and discharging experiments were carried out.The actual temperature control effect of the cooling method on the lithium battery was compared and analyzed.4.A double-layer composite phase change material was researched and prepared,and a large number of experiments and comparative analyses were conducted to find out the appropriate material ratio of PA,MA and LA,finally,the ternary low fusion eutectic phase change matrix was prepared.The inner layer composite phase change material was obtained by applying melt blending method to the above-mentioned phase change matrix,EG and LDPE,and the PW/EG/LDPE composite phase change material was used as the outer layer composite phase change material.Two layers of composite phase change material with different phase change temperatures was prepared and applied to the battery thermal management,the heat dissipation effect was verified by charging and discharging experiments.5.In this paper,a heat-conducting silica gel was prepared and coated on the contact surface between the lithium battery and the composite phase change material,so as to squeeze out the air between them and enhance the heat transfer efficiency of the interface,which is convenient to transfer the heat generated by lithium battery to the composite phase change material faster.Through the comparison of charging and discharging experiments,it was shown that the heat-conducting silica gel can effectively prolong the action time of the composite phase change material.6.Software simulation analyses have been made to verify the cooling effect of the above cooling schemes,the simulation results show that the combined temperature control scheme of composite phase change material and heat sink and the double-layer composite phase change material temperature control scheme can control the working temperature of lithium battery in a safe and reasonable temperature range under the discharge rate of 1C,2C and 3C,it is indicated that the two heat dissipation schemes have good temperature control effects for the heat dissipation of the lithium battery,basically consistent with the experimental results.