Study On Thermal Management Performance Of Lithiumion Battery Based On Phase Change Cooling

In recent years,the world has begun to promote new energy.In its many applications,electric vehicles are undoubtedly the most important.As the power source of electric vehicles,the importance of power battery is self-evident.The temperature of the power battery greatly affects the performance,safety and life of the battery.Too high or too low temperature will adversely affect the battery.Therefore,battery thermal management technology has become an important research direction in the field of power batteries.Phase change cooling technology is different from air cooling,liquid cooling and other battery thermal management technologies.It absorbs or releases the latent heat of phase change through the phase change process of phase change materials.It has the advantages of strong temperature control ability,low energy consumption and small size.Based on phase change cooling,this thesis optimizes and designs eight different battery thermal management system models for lithium iron phosphate square batteries with a capacity of 10 Ah(battery size : 82 mm × 11 mm × 138 mm).According to its symmetry and thermal conductivity,the battery thermal management system model is reasonably simplified.On this basis,with the help of COMSOL multi-physics simulation software,the influence of discharge rate,fin thickness,fin spacing,phase change material thickness,fin extension height and wind speed on the heat dissipation performance of the battery is numerically analyzed.The simulation results show that the phase change material composite fin structure can effectively control the temperature rise of the battery,and the three structures have the same ability to control the highest temperature.Under 3C discharge,the maximum temperature is reduced by2.6 °C when the fin is extended by 15 mm and combined with air cooling.Combined with factors such as cost and system volume,this thesis selects the phase change material thickness of 10 mm,the fin thickness of 0.5 mm,the fin spacing of 2.5 mm,and the fin extension height of 15 mm as the basic structural parameters of the battery thermal management system.Applying the basic structural parameters to the battery pack system model,the unsteady heat transfer characteristics of the battery pack are numerically simulated under the conditions of unilateral air cooling,bilateral unidirectional air cooling and bilateral opposite air cooling.Compared with the other two air cooling methods,the bilateral opposite air cooling has obvious advantages in the temperature control ability of the highest temperature and the control ability of the temperature uniformity : the highest temperature is reduced by 1.2 °C,and the maximum temperature difference is reduced by 66 %.By optimizing the fin extension height,the temperature uniformity between the batteries can be effectively improved.The maximum temperature difference after optimization is less than 0.1 °C,and the maximum temperature difference under the disconnected,staggered and truncated structures is reduced by71 %,92 % and 87 %,respectively.In the study of battery thermal runaway,this thesis compares the ability of fin connection,fin disconnection,fin interleaving,and fin truncation structure to block thermal runaway propagation.The simulation results show that the ability of fin interleaving and fin disconnection to block thermal runaway propagation is stronger.Under the condition of insufficient phase change materials,the optimized three fin forms can effectively protect adjacent batteries from thermal runaway.In the battery pack,fin disconnection can effectively protect adjacent batteries from thermal runaway.In summary,the disconnected fin structure combined with bilateral opposite air cooling and non-uniform fin extension height not only has good thermal management performance,but also can effectively prevent the spatial propagation of thermal runaway.