Investigation On Thermal Management Technology Of Lithium Battery Pack With Composite Phase Change Material

As core component of new energy electric vehicles and power source of automobiles,lithium-ion batteries are currently attracting worldwide attention.Temperature is crucial in affecting the performance,lifetime and safety of battery.Reasonable and efficient thermal management system can make the battery temperature within a reasonable range,thus improving the battery performance and extending the lifetime of battery.So the research on thermal management system is of great significance.Thermal management systems based on phase change materials have good application prospects because of high latent heat.Li-ion battery cooling experiment system is built to explore the temperature rise and temperature uniformity of battery at various discharge rates and thermal management systems.The experimental results show that the higher the discharge rate is,the higher the temperature rise of Li-ion battery is.Compared with the air cooling and the pure paraffin cooling,the thermal management of composite PCM can more effectively reduce the surface temperature of battery,especially at high discharge rate.With the increase of discharge rate,the temperature difference of battery pack and single battery all increase.Compared with the pure paraffin cooling,the foam-PCM composite could bring the battery pack a better temperature uniformity.According to the experimental phenomena and the experimental data,numerical simulation is adopted to investigate the effect of composite PCM thickness on the surface temperature,thereby optimizing the structure of thermal management system.The battery and composite phase change material combination model corresponding to the experiment is established and is verified with the experimental results.The numerical results indicate that the variation of thickness of composite PCM has little effect on the surface temperature of battery and effective thermal management time at lower discharge rate.However,at higher discharge rate,the decrease in thickness of the composite PCM brings a detrimental effect on the surface temperature of battery and effective thermal management time,whereas the increase in thickness of the composite PCM has less beneficial effect on the surface temperature of battery and effective thermal management time.During the continuous charge-discharge process,phase change materials would melt completely and lose cooling capacity,but adding the active cooling to passive thermal management system can speed up the solidification of PCM to restore its cooling capacity.The tube and composite phase change material combination model is constructed.The numerical results indicate that,due to the natural convection,the liquid phase change material below the tube solidifies faster than the composite phase change material in other positions.When the volume of tube accounts for 6%of the total volume,the solidification rate of the composite PCM with 20 tubes is 14.2%larger than that of the composite PCM with 10 tubes and far more than that of the composite PCM with 5 tubes.Under the condition of 20 tubes,the solidification rate of the composite PCM with tube volume accounting for 6%is the least,however,the solidification rate of the composite PCM with tube volume accounting for 14%is 3%larger than that of composite PCM with 10%tube volume.Under the condition of 20 tubes and 10%tube volume,the solidification rate of the composite PCM with combination arrangement of double and single row is equal to that of composite PCM with single row,moreover,the solidification rate of the composite PCM with combination arrangement of cross and single row is 11%larger than the two former cases.