【作者】 李坤；

【导师】 王敬；

【作者基本信息】 北京理工大学 ， 环境科学与工程， 2016， 硕士

【摘要】 本文以26Ah软包型三元锂离子动力电池为研究对象,在对锂离子电池本征热特性的研究基础之上,进行动力电池在热滥用方面的探索和研究。首先,在绝热环境和恒温环境条件下,研究了锂离子动力电池在充放电过程中的热特性。对绝热环境和恒温环境下动力电池在不同倍率充放电过程中温升进行测量,从而对过程中的产热量和产热速率进行定量计算,并进一步比较不同环境温度和充放电倍率对电池热特性的影响。除了常规充放电循环,还进行了电池在过充电条件下的热特性研究。其次,对电池不同滥用条件下发生热失控的临界状态进行分析,主要针对动力电池在不同荷电状态以及不同生命周期下的电池在发生热失控时的临界点温度和电压突降点,并进一步计算了热失控反应的表观活化能。最后,基于有限元方法,利用ANSYS建模软件建立了动力电池在不同倍率下放电过程中的二维热模型,并模拟和预测了电池在不同充放电条件下的温度场分布。研究主要结果如下:(1)在扩展加速量热仪(EV ARC)的绝热环境下,首先测得26Ah软包型单体电池的比热容值为1242 J kg-1 K-1,根据所测得的比热容值,采用电化学量热法定量测得锂离子电池在不同充放电倍率下的产热量。同时,利用温度箱的恒温条件测试电池表面温度分布,结果表明电池表面表面最高温度位于电池几何中心位置。另一方面,锂离子电池在放电倍率较小时,电池表面的温度分布差异不明显梯度不大;而随着放电电流增大,电池温度梯度也随之增大。(2)在EV ARC绝热环境下,研究电池在5.2A、13A、26A及52A电流下充电过程至过充热失控时的热行为,同时分析过充电过程中不同阶段的热特性规律。结果表明,在电池过充至4.2V进入第二阶段后,电池温升速率开始不断增大,电池内部正负极材料发生反应并不断产生气体。直至电池过充到达5V左右温升速率接近10℃/min,进入快速发热阶段,此时电池将在短时间内发生热失控。(3)结合HPPC测试和交流阻抗测试两种方法,利用EV ARC来研究不同循环周期下动力电池的电化学行为和热失控行为并进一步考察电池的热稳定性和安全性。结果表明,电池经过常温下1000周循环后容量下降至83%,直流内阻随循环次数增加而增大。从热失控曲线来看,随着循环次数的增加,电池自产热温度呈现总体下降,这说明了不断循环老化的电池SEI膜热稳定逐渐变差。同时,通过锂离子电池自产热的表观活化能计算得出,荷电状态越高,电池热失控反应的表观活化能越低,进而反映了荷电状态对电池热失控反应产生了显著的影响。(4)利用有限元软件模拟出电池温度分布情况。通过在恒温箱内不同环境温度下测试电池恒流放电结果,与模型结果进行验证,在此基础上进一步对电池温度特性进行分析,并得出以下结论。从模型得出的结果以及红外热成像结果表明,电池表面最高温度集中在电池中心位置,越靠近边缘温度逐渐减小。在位于电池表面中心位置,该点温度随着时间呈现非线性变化,同时随着放电电流增大,温升幅度也越大。更多还原

【Abstract】 A soft pack 26 Ah lithium-ion battery was studied in this paper. Based on the research of intrinsic thermal characteristics for lithium ion battery, the thermal runaway behavior of battery was studied. Firstly, the thermal characteristics of the lithium-ion battery was studied under adiabatic environment during charging and discharging. Thus heat production and heat production rate was quantitatively calculated and further compared impacts on different temperature and charge-discharge rates of the battery thermal characteristics. In addition to conventional charge and discharge cycles, the research on thermal characteristics of the battery was conducted under overcharge conditions. Secondly, the critical state of thermal runaway was analyzed under different conditions, mainly in different charge states and different life cycles. The critical point temperature and voltage sags point of the battery was confirmed when thermal runaway occurred. Finally, based on the finite element method a three-dimensional thermal model during discharge at different rates was established using ANSYS modeling software. The model simulated and predicted the battery temperature distribution under different charge and discharge conditions. The main results are draw as follows:1. In the Extended Volume Accelerating Rate Calorimeter, specific heat capacity of 26 Ah soft pack type battery was measured. Its value is 1242 J kg-1 K-1. Therefore, the heat production during charging and discharging at different rates can be measured by electrochemical measurement for lithium-ion battery. Meanwhile, temperature distribution of the tested cell was measured in constant temperature tank, the results showed that the maximum surface temperature of the battery cell is located in the geometric center. On the other hand, when the discharge rate is small, the surface temperature gradient of the battery was not significant. With the increase in the discharge current, battery temperature gradient increased.2. In the EV ARC, research on overcharge process in different currents was to study thermal behavior of thermal runaway. The results showed that in the second stage during overcharging, temperature rate of battery began to increase, and positive and negative materials inside the battery reacted and continued to produce gas. When the battery charge reached to 5V, the temperature rate was into nearly 10 ℃/ min. Then it began to rapidly heat and the battery thermal runaway would occur in a short time.3. The combination of HPPC test and AC impedance test was used to study the different cycle power battery electrochemical behavior and thermal runaway behavior. The results showed that, discharge capacity decreased to 83% after 1000 cycles, the DC resistance increased with increasing cycles number. From thermal runaway curve, with the increase of the cycle number, the battery production for the heating temperature showed an overall decline, indicating that the continuous cycle of aging batteries make SEI film gradually deteriorated. Meanwhile, the apparent activation energy of lithium-ion battery was calculated. The higher state of charge, the activation energy is lower apparently. It reflected the state of charge of the battery had a significant impact on thermal runaway reaction.4. Finite element method was used to simulate the battery temperature distribution. Meanwhile discharge process was tested at different ambient temperatures to validate the model. The temperature characteristics of the battery further was analyzed and the following conclusions are draw. From the results obtained by the models and infrared thermal imaging results, maximum surface temperature of the battery cells concentrated in a central location, closer to the edge temperature decreases. Located in a central location at the cell surface, the temperature changes nonlinearly with time. With the discharge current increases, the greater the temperature rise.更多还原