Optimization Of Thermal Management Performance Of Phase Change Cooled Lithium Ion Batteries Under High And Low Temperature Environment

In this paper,based on the thermal management technology of phase change cooled lithium ion batteries,the effects of improving the thermal conductivity of phase change materials and optimizing the arrangement of single batteries on the thermal management performance of lithium batteries at high and low temperatures were studied.Firstly,the effects of carbon nanotubes/paraffin on the thermal management performance of lithium-ion batteries at high and low temperatures were investigated by using carbon nanotubes/paraffin composite phase change materials and adding fins.Then,taking lithium-ion battery pack as the research object,the influence of single battery layout optimization on the thermal management performance of battery pack was analyzed,and the amount of phase change material was further reduced on the basis of ensuring the temperature control performance.The following conclusions were drawn:Firstly,different mass fractions of carbon nanotubes/paraffin composite phase change materials were prepared and their thermal management performance based on single cell was studied.The test results show that the thermal conductivity of the composite phase change material with 1% carbon nanotubes content is improved by27.3%,and the thermal conductivity of the composite phase change material is improved.Compound phase change cooling at 35℃ can control the temperature of the battery below 45℃ during 3C high current discharge to ensure the safe operation of the battery.At-15℃,the discharge power of the battery coated with PCM increases by 19.2%compared with that of the bare battery,and the time required for the battery temperature to drop from 50℃ to 20℃ is about 37.3% longer.At the same time,the composite phase change material can only improve the discharge power by 14.5% under the 4% content,indicating that the increase of thermal conductivity also enhances the heat loss process in the material,resulting in the decline of thermal insulation performance.Secondly,with metal fins as high thermal conductivity structure,a joint temperature control and thermal management device of phase change material and fins based on single battery was designed.The influence of fin extension length and opening Angle on the heat dissipation of the battery was analyzed,and the temperature control ability of the device under high and low temperature environment was investigated.The results show that at 35℃,the discharge temperature decreases by about 5%,the initial time of phase transition is prolonged by 40%,and the duration is increased by nearly 1.8 times.It shows that the addition of fins not only improves the heat transfer and heat dissipation rate of phase change cooling,but also greatly improves the utilization rate of phase change materials.At-15℃,the discharge temperature of the battery is always lower than that without fins,indicating that the presence of fins weakens the thermal insulation ability of PCM and poor thermal management performance at low temperature.Finally,the temperature control ability of phase change cooling system is improved by optimizing the arrangement.The change of temperature field of the phase change cooling system based on battery pack at different cell spacing was investigated by numerical simulation,and the arrangement of battery pack and the amount of phase change material were optimized.It is found that the thermal management performance of phase change cooling can be effectively improved by orderly reducing the cell spacing from the center to the outer edge of the battery pack.At 35℃,25℃ and-15℃,the temperature differences within the optimized arrangement were reduced by 12.5%,17.5%and 30.0%,respectively.After reducing the amount of PCM by about 12%,the same temperature control effect can be achieved by optimizing the arrangement of single cells in the group.It indicates that optimizing the spacing of single cells not only improves the thermal management performance of battery pack,achieves the goal of reducing system cost,but also meets the temperature control requirements of battery at different operating temperatures,providing a reference for the subsequent design of phase change cooling system.