Investigation On Battery Thermal Management Of Electric Vehicle Based On Phase Change Heat Transfer Technology

With the advantage of low energy consumption and no exhaust emissions,electric vehicles show obvious benefit in terms of energy saving and mitigation of urban environmental pollution.However,there are still many problems with the safety and ease of use of electric vehicles,making them not widely used commercially.The Li-ion batteries currently used in electric vehicles are very sensitive to temperature.Too high or too low temperatures will cause battery performance to decline,causing accidents such as short circuits,fires,and even explosions.Therefore,battery thermal management system(BTMS)of electric vehicle power batteries is necessary.Firstly,the structure,heat generation and heat transfer characteristics of current commercial Li-ion-ion batteries are studied in this paper,then a numerical model of Li-ion battery heating and heat transfer was built and the software of COMSOL was used to simulate different Li-ion battery cells and modules to study their temperature distribution characteristics.In addition,the effect of temperature on Li-ion batteries is studied in detail in this article,including the effects of high and low temperature on the internal resistance of Li-ion batteries,and the impact on the life and safety of Li-ion batteries.This paper mainly uses the phase change heat transfer technology to conduct thermal management research of Li-ion batteries.Firstly,an ultra-thin aluminum flat heat pipe battery thermal management system was designed for high-power Li-ion batteries.The preparation process of ultra-thin aluminum flat heat pipes was studied,and the performance test and characterization of ultra-thin aluminum flat heat pipes were performed.The battery pack's thermal management device of aluminum flat heat pipe was tested experimentally with battery packs.The results show that the ultra-thin aluminum flat heat pipe can effectively control the battery temperature.Phase change material is a kind of material with high temperature endothermic and low temperature exothermic heat storage characteristics.In this paper,composite phase change materials with different paraffin and expanded graphite ratios were prepared.Then,the thermal conductivity and latent heat of the composite phase change materials were tested.A composite phase change material with a good comprehensive performance was developed,and the microstructure of the composite phase change material was analyzed under an electron microscope.In addition,chlorinated paraffin was added as a flame retardant in the composite phase change material group to improve its safety.Secondly,use the prepared composite phase change material to conduct battery thermal management experiments,verify the thermal management performance of the composite phase change material under different charge and discharge conditions.Finally,according to the cold start requirements of power batteries under extremely low temperature conditions,conduct Based on the test of the thermal insulation performance of the composite phase change material and the preheating test of the battery under low temperature conditions.The results show that the composite phase change material can effectively control the pack temperature of the battery,reduce the impact of high and low temperature,and can play a thermal insulation effect at low temperatures.A sodium alginate(SA)film with a higher water content above 99% is fortified by adding polyethylene(PE)fibers.The phase change from water to gas retains a large amount of latent heat.As a result,a BTMS using water evaporation(WE)coupled with air-cooling(AC)for a tube–shell Li-ion batteries pack was designed and its performances are evaluated by experiments and numerical simulation.When an automatic refilling system is used,the issue of film drought will be well addressed.The water can be continuously supplied,realizing high effectiveness and excellent performance of the system.The effectiveness of WE coupled with AC in controlling the temperature rise at 1C,1.5C and 1.8C is validated.By using this method,the temperature is controlled below 32 ? at 1.8 C within the discharge time of 1000 s.