不同外热部位下18650型锂离子电池热失控研究

On the thermal runaway mechanism of 18650 lithium-ion batteries at the different external thermal positions

为探究不同外热部位对18650型锂离子电池热失控特性的影响,通过自主设计的试验平台对电荷量为100%的18650型锂离子电池开展不同外热部位下热失控试验,探讨不同部位外热源对电池热失控行为过程、热失控响应时间、温度特性、电池破裂部位的影响。结果表明:在相同热源功率条件下,外热源位置对电池热失控过程中初爆与二次燃爆间的时间间隔存在影响,顶部加热时安全阀打开瞬间便发生二次燃爆,底部和中部加热工况下,时间间隔分别延迟至18 s和40 s;中部加热时池体温升速率最慢,为0.873℃/s,分别为顶部和底部加热时的77.5%和77.8%;中部加热时热失控响应时间最长达290 s,顶部和底部加热时分别缩短12.4%和30.0%;顶部和底部加热时,热失控破裂部位集中于顶部"褶皱处"和底部防爆阀,但在中部加热工况下,电池发生破裂部位的随机性增加,其外壳破坏程度也有增加。

The paper intends to investigate the effectiveness of the different external heat positions on the thermal runaway features of 18650 lithium-ion battery and provides necessary supports for the cell thermal prevention. For the given purpose,a lithium-ion battery thermal runaway experiment platform with the related testing methods has been developed,in which we have observed and determined the phenomena of the thermal runaway behavior through a proper camera,through which we have obtained the temperature of the surface and the flame of the battery through the thermocouples. At the same time,we have also analyzed the parameters of the time interval between the primary and the secondary explosion,as well as between the thermal runaway response time and the rupture positions. The experimental results prove that the position of the external thermos source may have an effect on the time interval in the thermal runaway process with the same heat power. When the top of the battery is heated,the secondary explosion would like to come up close to the moment when the safety vent is going to open. In the meantime,the time interval might be delayed from 18 s to 40 s,respectively,so that the bottom and the middle of the battery get to be enough heated.Besides,the temperature rising rate of the batteries can last for 0. 873 ℃/s till the heating source may get to the middle point,that is,a delay of 22. 5% and 22. 2% before the heating source goes up and spread to the top and the bottom,correspondingly.Furthermore,the maximum response time of the thermal runaway should be 290 s till the middle of the battery is heated. However,in case when the top and bottom of the battery are heated to reduce the response time by 12. 4% and 30. 0%,respectively,and,if the heat source is coming up at the top or at the bottom,the thermal runaway rupture may take place at the top positions of " fold" and/or at the bottom safety vent. Such randomness of the rupture positions may increase the damage degree of the shell in case the heating source is in the middle. Thus,it can be concluded that the effectiveness of the different external heat positions can be expected discovered and clarified on the thermal runaway specifications and the structural fragile parts of the cell.The partial thermal prevention function of the cell can also be purposefully enhanced in accordance with the position instructions of the external heating source in storage,transportation and application.