高容量商用方形锂离子电池外部短路行为

外部短路是锂离子电池应用中的主要失效模式之一。外部短路会导致锂离子电池在较短的时间内产生较大的短路电流,带来热失控风险。当前锂离子电池外部短路的研究主要集中在小容量的电池上,但是不同容量的电池会在短路持续时间、短路温升以及温升滞后等行为上产生明显的差异。本文以51 Ah三元(NCM622)商用方形锂离子电池为研究对象,探究了锂离子电池在不同电阻下的短路行为,并关注了温度特征。研究表明,锂离子电池短路放电容量、短路电流对最高温度具有决定作用。高容量方形锂离子电池产热速率与导热速率的不平衡导致锂离子电池短路过程温升的滞后性。对短路后的电池进行拆解,电池内部发生了正极对隔膜的热粘接以及正极析铜现象,外部短路对锂离子电池产生了不可逆的破坏。基于锂离子电池在短路过程中电压、电流、温度的变化,提出锂离子电池短路机制。

Effect of temperature on soil-water characteristics and hysteresis of compacted Gaomiaozi bentonite

Laboratory tests under different constraint conditions were carried out to obtain the soil-water retention curves(SWRCs) of highly-compacted confined/unconfined Gaomiaozi(GMZ) bentonite at 20,40 and 80 ℃,respectively. The effect of temperature on the soil-water characteristics of the highly-compacted GMZ bentonite was analyzed. The results show that the water retention capacity of the highly-compacted GMZ bentonite decreases as the temperature increases under unconfined and confined conditions. At a certain temperature,the constraint conditions have little influence on the water retention capacity of the compacted bentonite at high suction,but the water retention capacity of the confined specimen is lower than that of the unconfined specimen at low suction. Under unconfined conditions,the hysteretic behaviour of the compacted bentonite decreases with increasing temperature. At high suction(>4 MPa) ,the hysteretic behaviour of the unconfined bentonite tends to increase with the decrease of the suction. In summary,the hysteretic behaviour of the compacted bentonite is not significant.

循环加载下复合推进剂的能量耗散

在空空导弹的挂载飞行阶段,弹体高频振动导致的固体推进剂温升极大地损害了固体火箭发动机的性能。为深入探究固体推进剂的能量耗散及其影响因素,针对某复合推进剂进行了不同应变幅值下的多频率疲劳测试,并利用非接触式红外辐射装置同步采集了循环加载下推进剂试件的表面温度,讨论了频率、应变幅值两个因素对复合推进剂能量耗散的影响。结果发现,复合推进剂由于自身的黏滞性,在外部激励下产生了剧烈的疲劳生热行为,其能量耗散密度随着加载幅值和频率的增大而提高,能量耗散带来的试件表面温度呈现出先增大后稳定的规律。根据能量耗散和温度场方程,建立了复合推进剂疲劳过程中的温升计算模型,利用有限元仿真对不同加载条件下推进剂的滞后温升进行了较好的预测。