随着电动汽车的逐渐普及，频繁发生的锂离子电池起火爆炸等安全事故威胁人身财产安全。热失控是锂离子电池安全事故的根源，而内短路是诱发电池热失控的关键环节，其机理复杂，是国际公认的研究难题。本研究从锂离子电池单体出发，围绕锂离子电池内短路机理及失效动力学展开研究。首先，通过锂枝晶生长原位观测与铁枝晶诱导实验，证实了金属枝晶存在诱发内短路的可能性，并建立了可预测锂枝晶形貌的锂枝晶生长动力学模型。进一步地，进行了大量内短路失效的等效测试，阐明了不同等效测试方法的有效性与适用场合，开发了将相变材料和记忆合金相融合的等效测试新方法。最后，揭示了由于隔膜收缩熔化导致的内短路区域扩展是热失控演化过程中的关键环节，预测了内短路诱发热失控的边界条件。首先，针对由于金属枝晶导致的锂离子电池内短路机理尚未明确的问题，通过铁枝晶诱导与锂枝晶观测实验，证明了锂枝晶和铁枝晶引发内短路的可能性，并发现由金属枝晶造成的正极-负极类型内短路具有短路阻值较高、危险性较低的特征。建立了基于蒙特卡洛动力学的锂枝晶生长模型，预测锂枝晶生长特性，并揭示了不同充电条件与电池内部缺陷对锂枝晶生长的影响机制。其次，针对锂离子电池内短路失效的等效测试方法尚不完善的问题，提出了基于添加无盐电解液电池电化学阻抗谱的内短路阻值辨识方法，并从热特征、电特征、真实性、可控性、重复性、操作性的六维指标评价了相变材料、记忆合金、等效电阻与针刺等四种现存测试方法的有效性。进一步地，探究了高精度针刺方法对于短路阻值的控制性，开发了将记忆合金和相变材料相融合的等效测试新方法，该方法重复性好，适用于软包电池与方壳电池，为储能电池内短路测试标准的建立提供了技术支撑。最后，针对内短路诱发锂离子电池热失控机理不清晰的问题，阐明了四种类型内短路的危险性及其失效机理，揭示了隔膜收缩熔化导致的内短路区域扩展是诱发热失控的关键环节。建立了单层极片电池的内短路-热失控三维模型，分析短路阻值、局部散热条件等因素对内短路诱发热失控的影响；进一步建立了单体电池的内短路-热失控三维模型，预测了内短路诱发热失控的边界条件。
With the gradual market penetration of electric vehicles, accidents such as lithium-ion battery fire and explosion threaten the safety of people and property. Thermal runaway is the root cause of the safety accidents in lithium-ion batteries, whereas internal short circuit (ISC) is the key factor of thermal runaway recognized as a universally acknowleged hard problem for research.This thesis studies the ISC mechanism and failure dynamics in lithium-ion batteries. Firstly, the existence of ISC induced by metal dendrite is proved by in-situ observation of controlled lithium and iron dendrite. A dynamic model for predicting the morphology of lithium dendrite is established. Furthermore, a large number of ISC failure equivalent tests are carried out to decalre the effectiveness and applicability of different test methods. A novel ISC failure equivalent test method based on the fusion of phase change materials and shape memory alloys is developed. Finally, the key process that judges the critical condition of thermal runaway is the expansion of ISC region caused by the separator melting. A 3D electrochemical-thermal coupled model of ISC is established to evaluate the boundary conditions of ISC-induced thermal runaway.Firstly, the ISC caused by metal dendrite is investigated. In-situ ovservation experiments confirms the existence of ISC caused by lithium dendrite. The cathode-anode type ISC caused by iron dendrite has the high resistance and low risk, based on the experiment results of battery cycling with iron particles inside. A dynamic dendrite growth model using the Kinetic Monte Carlo method is established to predict the dendrite morphology and reveal the influence of different charging conditions and internal defects on the lithium dendrite morphology during growing.Secondly, the efficiency of existent ISC failure equivalent test methods is compared. A novel method using the electrochemical impedance spectroscopy for cells with salt free electrolyte is proposed to measure the ISC resistance. Four existing ISC failure equivalent test methods including those use phase change material, shape memory alloy, equivalent resistance and nail penetration are evaluated by six indexes including thermal characteristics, electrical characteristics, authenticity, controllability, repeatability and operability. A fusion method that combines the shape memory alloy and the phase change material has the utmost advantages over the other methods, and is proposed in this thesis. Correlated work supports the establishment of an ISC test standard for energy storage batteries.Finally, the failure mechanism of ISC is revealed based on experiments and modeling. The hazard of the four types of ISC is clarified. That the expansion of ISC region caused by separator melting is the key process that judges the critical condition of battery thermal runaway. A 3D electrochemical-thermal coupled model of ISC at single-layer level is established to analyze the influence of the ISC type, ISC resistance, local heat dissipation conditions and other factors. Furthermore, the 3D electrochemical-thermal coupled model helps quantify the cirtical conditions when ISC will transforms into thermal runaway.
