热失控小知识.doc

11.13.20171. The high gravimetric and volumetric energy densities of Li-ion cells provide clear advantages over other battery chemistries such as NiMH or lead-acid, but their active materials and electrolytes pose ongoing safety challenges for these applications.锂离子电池的高重量和体积能量密度与其他电池化学品如镍氢电池或铅酸电池相比具有明显的优势，但其活性材料和电解质对这些应用构成持续的安全挑战。2. Frequent incidents with Li-ion battery fires highlight these safety concerns in personal electronics, transportation vehicles, and even large commercial aircraft. To guard against such accidents, a robust thermal management system is necessary to protect the battery pack under all circumstances, especially when the monitoring or active cooling system fails to detect a cell failure.频繁发生的锂离子电池事故突显了个人电子，交通车辆甚至大型商用飞机的安全隐患。 为防止此类事故发生，在任何情况下都需要强大的热管理系统来保护电池组，特别是在监控或主动冷却系统未能检测到电池故障时。3. These Li-ion fires were caused by thermal runaway, a chemical phenomenon during which the anode, cathode, and electrolyte irreversibly react, generating large amounts of heat that escalate the cell temperature and internal pressure, often with combustion of gases.这些锂离子火是由热失控引起的，这种化学现象是阳极，阴极和电解质发生不可逆反应的过程，产生大量热量，使电池温度和内部压力升高，常常伴随着气体的燃烧。4. Several scenarios and factors can trigger thermal runaway. Overheating of the cell can lead directly to thermal runaway by triggering a series of exothermic chemical reactions. Overcharging can lead to lithium metal plating on the anode and destabilization of the cathode crystal structure due to excessive delithiation. Mechanical damage, crush, or penetration of a cell can cause a short circuit, leading to rapid heating and thermal runaway. Foreign debris that enters the cell during manufacturing can also cause an internal short circuit, leading to localized heating and subsequent thermal runaway.几种情况和因素可能引发热失控。1. 电池过热通过触发一系列放热化学反应可能会直接导致热失控。2. 过度充电会导致阳极上的锂金属镀层和由于过度脱锂而导致的阴极晶体结构的不稳定。3. 电池的机械损坏，挤压或渗透可能导致短路，导致快速加热和热失控。4. 在制造过程中进入电池的异物也会引起内部短路，导致局部发热和随后的热失控。5. Due to all of these potential hazards, numerous safety mechanisms are often built into Li-ion cells. A safety vent provides pressure relief to prevent electrolyte oxidation and gas generation from reaching dangerous pressures that could burst the cell can. A positive temperature coefficient device (PTC) acts as a current limiter if a cell overheats, preventing high current due to an external short circuit. A current interrupt device (CID) acts like a mechanical switch inside the cell to isolate one of the electrical terminals if internal pressure becomes too high. Porous separators have been designed to shut down all ionic diffusion through the electrolyte if the cell is overheated, mitigating internal short circuits.由于所有这些潜在的危险，锂离子电池通常内置许多安全机制。 1. 一个安全通风口提供压力释放，以防止电解质氧化和气体产生达到可能爆裂的电池罐的危险压力。 2. 如果电池过热，则正温度系数器件（PTC）可用作限流器，防止由于外部短路而导致的高电流。3. 电流中断装置（CID）就像电池内部的机械开关一样，如果内部压力变得太高，就会隔离其中一个电端子。 4. 如果电池过热，多孔分离器被设计成通过电解质关闭所有的离子扩散，从而减轻内部短路。6.The failure of a single cell can generate sufficient heat to trigger the surrounding cells into thermal runaway, leading to propagation, the largest danger of thermal runaway. While the energy release of a single cell event can reasonably be contained, if the liberated heat raises the temperatures of neighboring cells in a pack, it becomes likely that a cascade of propagating cells will result in fire and complete pack destruction.单个电池的故障可以产生足够的热量来触发周围的电池热失控，导致传播，最大的热失控危险。虽然单个细胞事件的能量释放可以被合理地包含，但是如果释放的热量升高了包装中的相邻细胞的温度，则可能是一连串的传播细胞将导致着火和完全破坏包装。7. Single cells are known to reach 700 in open air during thermal runaway, giving rise to significant heat transfer via conduction (either through cells in direct contact or through external current collectors), convection, and radiation. Additionally, the venting of vaporized electrolyte and its combustion can contribute an even larger amount of heat, and the flow of these hot gases and combustion make thermal runaway propagation a largely unpredictable process.已知单电池在露天达到700会引起热失控，引起显着的热传导（通过直接接触的电池或通过外部集电器）通过传导、对流和辐射。另外，气化电解质的排放及其燃烧可以贡献更大量的热量，并且这些热气体和燃烧物的流动使热失控传播成为很大程度上不可预测的过程。8. PCC is a composite of wax and graphite that absorbs heat during battery operation or abuse conditions, while maintaining good temperature uniformity across the pack.PCC是蜡和石墨的复合材料，可在电池工作或滥用条件下吸收热量，同时保持整个电池组良好的温度均匀性。9. A common safety feature of cylindrical format Li-ion cells is a current interrupt device, or CID. The CID is a pressure-activated disk assembly inside the cell can. When internal pressure reaches a certain threshold, still below the burst pressure of the cell vent, the CID breaks the electrical connection to the can positive terminal, so that no more current can flow through the cell. After the CID activates, the negative and positive terminals are isolated, so the cell will appear as 0 V even though it still contains some nonzero state of charge.圆柱形锂离子电池的常见安全特性是电流中断装置或CID。 CID是电池罐内的压力激活磁盘组件。 当内部压力达到一定阈值时，仍低于电池通气孔的爆破压力时，CID断开与罐正极端子的电连接，从而不再有电流流过电池。 在