| Due to the advantages of high energy efficiency and less pollution emissions,electric vehicles are becoming one of the mainstreams for future vehicles. To improvethe charge and discharge performance of the battery pack is an urgent issue.Rapid development of the lithium ion battery provides great space for electricvehicles, but the performance of lithium ion batteries is sensitive to temperaturechange. Battery packs which have high capacity and power are particularly evident.Further data indicates that the best operating temperature for lithium ion battery packsis20℃to60℃, and the maximum temperature difference within the packs shouldnot exceed6℃. Working under ideal conditions, the life of the battery pack will beeffectively extended and the performance will also be fully exploited. As is shownabove, we should take effective measures to control the temperature of battery packs,especially when they are discharging.From two dimensional and three dimensional simulation of one single lithiumion battery, the effects of discharge currents and heat transfer coefficients to thetemperature distribution in the battery are analyzed. The results show that increasingof the discharge currents and decreasing of the heat transfer coefficients make themaximum temperature high, which may lead to thermal runaway. In two dimensionalmodel, when the discharge current is10A and the heat transfer coefficient is0W/m2·K, the maximum temperature within the battery reached77.75℃at the end ofthe discharge.Based on the simulation of one single battery, we simulate the effect of watercooling and air cooling. By making three dimensional model, the detailed temperaturedistribution in the battery pack in control of air cooling and water cooling is made.Taking the maximum temperature and the maximum temperature difference asevaluation criteria, the cooling effect of water cooling is better than that of air cooling,but they are both not so good.The article proposed a novel cooling method—material composed of aluminumfoam and kerosene acts as temperature buffer medium to control the temperature inthe battery pack. By three dimensional numerical simulation, we make completecomparison of composite material cooling、air cooling and water cooling, the temperature distribution of the battery pack is carried out under each coolingcondition. The simulation results show that even in conditions of large currentdischarge, the composite material can also control the maximum temperature and themaximum temperature difference within the appropriate range ideally. When thebattery in the pack discharges in10A to the end, the composite material cansuccessfully maintain the maximum temperature of the pack below65℃. On theother hand, when using water cooling, the pack’s maximum temperature reachesnearly70℃, the temperature inside the pack under air cooling even becomes nearly80℃which is prone to thermal runaway. The composite material can also control themaximum temperature difference of the battery pack very well. When the battery inthe pack discharges in5A to the end, the maximum temperature difference within thepack can be stabilized in range of0.29℃to0.35℃, even if the discharge currentreaches10A, the temperature difference is also between1.2℃and1.3℃. Insummary, the temperature controlling effect of composite material is much better thanthat of traditional water cooling and air cooling. |
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