| Nowadays,the main problems facing global sustainable development are resource shortage and environmental pollution.Compared with traditional fuel oil automobiles,electric vehicles have become the main direction of the transformation of the global automotive industry due to their dual advantages of zero emission and high energy utilization efficiency.As one of the key components of electric vehicles,the performance of power batteries directly determines the performance and safety of electric vehicles.Among all kinds of power batteries,lithium-ion batteries have a higher performance ratio and become one of the most promising power sources for electric vehicles.However,during the charging and discharging cycle,a large amount of heat is generated inside the lithium-ion battery,and the safety risks such as overheating,burning and even explosion increase with the increase of battery temperature.Therefore,it is necessary to design an effective battery thermal management system to control the temperature rise of the battery and improve the temperature uniformity between the batteries.In this paper,the laminated lithium iron phosphate battery is used as the research object,and the combination of experiment and numerical simulation is adopted.Under the condition of ambient temperature of 25℃ and natural convection,firstly,the temperature characteristics of single cell under constant current discharge of 1C,2C and 3C were experimentally studied by using infrared imaging technology(Among 1C=22 A,2C=44 A,3C=66 A).And then,according to the hybrid pulse power characterization test method,the variation of internal resistance of the battery with the depth of discharge under different pulse rates was measured.Based on the experimental conditions and results,a thermal model of the single cell was established,and the reliability of the model was verified.On this basis,taking the maximum temperature and the maximum temperature difference of the battery pack as the evaluation indexes of the thermal management effect of the battery pack,the six thermal management methods of the battery pack,such as air natural convection cooling without fins,composite cooling of fins and air cooling,composite cooling of fins and phase change materials,were numerically simulated,and the effects of fin thickness,fin extension length and fin material were analyzed.The results show that:(1)With the progress of the discharge,there is a transfer phenomenon in the high-temperature region of the battery surface,which is concentrated in the upper part of the cell near the positive electrode at the initial stage of the discharge and then transferred to the middle of the cell.At the later stage of the discharge,it is located in the middle of the cell and expands outwards in a ring.The simulated temperature contours are more consistent with the experimental infrared images and have the same high-temperature region transfer phenomenon.The maximum deviation of the surface maximum temperatures of the battery between the simulated values and the experimental values at 3C discharge is only 1.4℃.(2)Compared with the air natural convection cooling method without fins,the maximum temperature of the battery pack can be reduced by 15.6℃ at 1C discharge after the fins are added.The fin installation has achieved a better cooling effect.(3)The fin natural convection cooling method has simpler system than other cooling methods,and is a preferred thermal management method at low discharge rates(1C,2C).In the case of high discharge rate,the structure of this thermal management method needs to be optimized.(4)Under high discharge rate(3C),increasing the fin thickness can further reduce the maximum temperature of the battery pack.In this paper,the copper fin structure with 3 mm thickness and the aluminum fin structure with 4 mm thickness under forced air cooling or composite cooling with phase change materials can meet the cooling requirements of the battery pack.After changing the fin material to aluminum,the total mass of the overall structure of the battery pack is reduced by about 41% under the composite cooling method of fins and phase change materials.If the quality requirements of the battery pack thermal management system are high,the slotted fins or aluminum fins can be considered.(5)In different thermal management methods,it is found that the fin forced convection cooling method is very effective for reducing the maximum temperature of the battery pack,while filling the phase change materials into the fins can greatly improve the temperature uniformity between the batteries. |
