Recent progress on thermal runaway propagation of lithium-ion battery

简述了电动汽车锂离子动力电池热失控蔓延机理、建模与抑制技术的最新研究进展。为了满足汽车高能量的要求,需要动力电池进行串并联成组来提供动力。电池组成组安全问题成为电动汽车大规模应用的重要技术问题。电池组中的某一个电池单体发生热失控后产生大量热,导致周围电池单体受热产生热失控。因而,电池组成组安全问题的重要关注点是电池组内的热失控蔓延问题。本文对锂离子电池热失控蔓延问题的国内外研究进展进行了综述,分析了对于不同种类锂离子动力电池影响其热失控蔓延特性的主要因素。总结了文献中的热失控蔓延建模方法,并指出了已有方法的不足。从电池系统热安全管理的角度,阐述并分析了热失控蔓延防控技术的研究成果与方向。最后对锂离子电池热失控蔓延研究进行了展望。     

Influence of cycling on the heat-release and thermal runaway of the lithium ion battery under adiabatic condition

随着锂离子电池能量、寿命的提升,对安全性需求也越来越高,温度对电池的寿命和安全有着重要影响。以钴酸锂/中间相碳微球体系电池为研究对象,采用加速量热仪研究了不同工作电流、不同循环老化周期电池的产热特性和热失控行为,电池的发热量随着充放电倍率的增加而增大。通过比较不同循环老化周期电池的产热速率,发现容量衰减速度与直流内阻、产热量之间存在很强的关联性。从热失控行为研究发现,自放热起始温度为105.4℃,随后发生连续自放热,直到温度达到149.7℃热失控起始温度,发生内短路,最终导致电池热失控。循环后电池的热失控过程中自放热和热失控起始温度稍有变化,热失控时间大大缩短。     

Thermal runaway due to symmetry breaking in parallel‐connected battery cells

A battery energy system consists of networks of cells. This paper considers the coupling among the cells that are connected in parallel. Cells are designed to react uniformly in response to charging and discharging. We study the possible occurrence of symmetry breaking when small perturbation leads to further deviation from uniform responses. By including coupling among the cells to the existing battery models, we formulate a dynamical system governing the rate of change of thermal and electrical quantities of the cells. Limited numerical solution using fourth‐order Runge–Kutta method was carried out, and stability criteria are obtained from algebraic analysis. The results show that a much more stringent effort in thermal management is required to prevent thermal runaway initiated by cells interacting with each other due to asymmetric perturbations. The increased heat transfer between the two cells serves to offset the undesirable effect of the parallel connection, but the stabilizing effect could be greatly compromised if the cell incorporates three parallel units as in some commercial Li‐ion battery cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal runaway fire characteristics of lithium ion batteries with high specific energy NCM811

通过NCM811高比能锂离子电池在低氧环境、电滥用、热滥用和机械滥用工况下热失控实验研究,获取该电池的热失控特性及关键参数,为进一步的热失控早期预警和火灾扑救研究提供了技术支持。     

Venting process of lithium-ion power battery during thermal runaway under medium state of charge

以电动汽车用方壳型镍钴锰（NCM）锂离子动力电池为研究对象,以氮气为惰性保护,采用高速摄影的方法,在密闭容器内开展了电池热失控产物喷发过程的试验研究。检测压力突变表明,中等荷电状态下的电池热失控后的喷发过程出现了2次剧烈喷射,分别导致了喷发物射流区温度的突然降低和快速升高。借助辅助光源,捕捉到了热失控产物首次喷发演变过程的高速影像,进一步分析发现,首次喷发经历了初期的带状和锥形喷发,然后进入较长时间的无定形喷发和后期的倒锥形喷发;同时,在影像中还观察到了气-液-固三相共存的特征。     

薄膜锂离子电池负极材料的研究进展

全固态薄膜锂离子电池是锂离子电池的最新研究领域,其能量密度高、厚度薄、循环寿命长、可靠度高。薄膜化的负极材料是锂离子电池的重要组成部分,负极薄膜材料制备方法的研究取得了较大的进展,未来研究重点是低成本、低能耗、高综合电化学性能的负极薄膜材料以及可批量生产的薄膜制备技术。对薄膜化的硅负极材料、金属或合金薄膜材料、氧化物薄膜材料和复合薄膜材料近几年来的研究状况进行了综述,并对其发展前景进行了展望。     

Thermal runaway behavior and features of LiFePO4/graphite aged batteries under overcharge

In this paper, the overcharge tests of 25 Ah LiFePO₄/graphite batteries are conducted in an open environment and the overcharge-to-thermal-runaway characteristics are studied. The effects of current rates (C-rates: 2C, 1C, 0.5C, and 0.3C) and states of health (SOHs: 100%, 80%, 70%, and 60%) on thermal runaway features are discussed in detail. The overcharge process can be summarized into five stages based on the experimental phenomena (C-rate ≥ 1 and SOH ≥ 80%): expansion, fast venting after safety valve rupture, slow venting, intense jet smoke, and explosion, while the battery cannot explode at lower C-rates and SOHs. The maximum pressure increases with the increase in C-rate or SOH. There are five obvious inflection points in the voltage curve during overcharge process. The V₁ (point B) of aged battery, corresponding to lithium plating on the anode, changes little with C-rates. It is slightly lower than that of the new battery. A sharp drop in voltage (point E) is probably due to the internal short circuit (ISC), caused by the local melting and rupture of the separator. It takes more than 2 minutes from the moment of ISC to thermal runaway regardless of the SOH, indicating that there are a few minutes to take safety measures if the voltage is an indication parameter. The onset temperature of thermal runaway decreases first and then increases as the SOH decreases from 100% to 60% during 1C constant overcharge tests. These results can provide guidance for the thermal management of the whole battery life cycle and the reuse of retired batteries.     

Safety test and evaluation method of lithium ion battery

对锂离子电池的机械滥用、热滥用和电滥用安全性测试与评价方法的原理进行了分析,对具有代表性的锂离子电池安全测试标准GB/T 31467.3/31485和SAE J2464/UN 38.3的相关试验方法进行了对比分析。应用X射线三维CT技术,测试了安全性试验前后锂离子电池内部结构的变化,对X射线三维CT应用于锂离子电池安全性测试分析的前景进行了展望。为锂离子电池安全失效模式分析指明了方向。     

Research of leaked toxics from Li-ion battery electrical heat triggering thermal runaway

为探究锂离子电池电热触发热失控过程,本工作在研究和建立电热触发锂离子电池热失控方法的基础上,对不同荷电状态下18650锂离子电池进行电热触发热失控,分析了电热触发18650锂离子电池热失控现象,对热失控过程中泄露的气体进行采集与分析。研究结果表明,电热方法可以触发18650锂离子的热失控,该热失控过程中会产生有毒气体,同时伴随浓烟和高温,防护不当将对人体和环境造成伤害。     

Research on early warning system of lithium ion battery energy storage power station

研究锂离子电池储能电站消防预警技术对于储能系统的安全运行具有重要意义。本文通过对电池热失控及热扩散特征识别展开讨论,由于锂离子电池发生热失控时会伴随着可燃气体缓慢释放,如果能够提取电池热失控早期气体参数并对其进行研究分析,可以在此基础上建立电池系统的热失控预警机制。本文采用加热方式和过充方式诱发电池热失控气体提取试验,通过采气试验进行气体成分含量分析,确定了将一氧化碳和温度作为典型的侦测依据来实现锂电池热失控的早期预警。并将这种电池热失控早期预警判断应用到了储能电站消防预警系统中,同时结合多级预警及防护机制和安全联动策略做了深入研究,确定了锂离子电池储能电站消防预警系统的设计架构,从系统部件、联动通信、人员安全3个方面对系统设计做了简要说明,在保证快速有效的检测出电池热失控状态的同时快速联动消防设施,极大提高了储能系统运行的可靠性。     

两种石墨烯修饰的复合热界面材料的制备及热性能的研究

采用化学氧化还原法制备的石墨烯和化学气相沉积法制备的三维网状石墨烯共同作为导热填料改性环氧树脂,研究导热填料质量分数的变化对环氧树脂热导率的影响,并进一步测定复合热界面材料的热导率在高温下的稳定性。结果表明:当石墨烯-三维网状石墨烯的质量分数为0.2(石墨烯和三维网状石墨烯的比例为1∶9)时,可使环氧树脂的热导率提高2 400%;三维网状石墨烯的三维网状结构和石墨烯的表面官能团对复合热界面材料的热性能具有显著地影响;三维网状石墨烯为声子提供了快速传输通道,而石墨烯的表面官能团能促进环氧树脂与石墨烯之间形成良好的接触,降低界面热阻,在石墨烯和三维网状石墨烯的协同作用下可提高热界面材料的热导率。此外,可以通过优化导热填料的尺寸,提高复合热界面材料热导率的稳定性。     

Overview of research on thermal safety of lithium-ion batteries

随着锂离子电池在生活和工作中的普及,锂离子电池的安全事故逐年增加,锂离子电池的安全研究逐渐引起学术界的关注。研究锂离子电池的热安全性,可以有效分析锂离子电池发生起火和爆炸的内在原因,指导锂离子电池安全性研究的开展。本文介绍了锂离子电池工作过程中产热的来源和影响因素,以及锂离子电池热失控发生时的内部反应和反应对应的温度,并对电池热失控时的热特性参数进行了总结。     

锂离子电池模组热失控传播的结构因素影响分析

为优化锂离子电池模组的结构设计,通过热失控数值分析,结合COMSOL MULTIPHYSICS软件搭建了圆柱电池模组的三维热失控传播模型,研究不同排列结构和电池间隙下的热失控传播特性。结果表明：插排结构能有效降低热失控传播速率;增加模组中电池间隙,电池的热失控触发时间后移;在模组热失控后期,扩散速率加快。     

锂离子电池热安全防控技术的研究进展

在众多储能技术中,锂离子电池以其能量密度大、能量转换效率高、循环寿命长、应用范围广、对环境友好等优势,成为当前最具应用前景的电力系统电池储能技术之一。但现有锂离子电池体系无法从本质上保证其安全性,在使用过程中具有发生热失控乃至燃烧、爆炸等安全事故的风险。本文就锂离子电池的热失控机理、电池本体的安全设计、安全预警、电池组热失控起火的阻燃装置以及消防安全的研究进展进行了综述。     

Experimental study on fire extinguishing of large-capacity lithium-ion batteries by various fire extinguishing agents

为研究不同灭火介质对大容量动力锂离子电池火灾的有效性,搭建了适用于多种灭火介质的灭火测试平台。在灭火测试平台上以功率为300 W的电热管作为外热源引发单电池热失控,通过改变灭火介质,研究了不同灭火介质的灭火行为及灭火效率。研究结果表明,对于38 A·h单体动力电池火灾,ABC干粉、七氟丙烷（HFC）、水、全氟己酮和CO₂灭火剂均能快速熄灭电池明火,但CO₂灭火剂灭火后电池出现了复燃;电池灭火过程中,不同的灭火剂在抑制电池温度上升表现出明显差异,其中,抑制温升效果优劣依次为水、全氟己酮、HFC、ABC干粉和CO₂。本研究的结果可为工程应用及电池灭火规范制定提供实验支撑。     

Interpretation of the electrode binder standard for lithium ion battery

电极黏结剂是锂离子电池的重要辅助功能材料之一,虽然本身没有容量,但却是维持电极完整性的关键,决定了电极涂层的附着力和电极的柔韧性,并会影响到电极浆料的流变特性等工艺性能。本文主要分析了与电极黏结剂相关的国内标准,对锂离子电池电极黏结剂的相关特性和测试方法进行了介绍,并对未来电极黏结剂标准的制定提出了建议。     

Progress of inorganic solid electrolyte for lithium ion batteries

目前,商品化的锂离子电池电解液主要以碳酸乙烯酯、碳酸二甲酯和碳酸甲乙酯等有机溶剂为溶剂,在电池使用过程中,存在电解液分解、锂枝晶生成和漏液等问题,从而影响电池的稳定性和安全性。无机固态锂电池电解质具有热稳定性高、电化学性能稳定、与高电压正极材料相容性好、安全性高及环境友好等优点,是目前储能领域研究的一个热点。研究和开发具有高离子电导率的无机固态电解质是促进其在电池中应用的关键和难点,本文综述了几类目前研究较多的LiPON型、钙钛矿型、石榴石型、LISICON型电解质,重点关注了其在离子电导率方面的研究及应用进展。     

Using high‐HFP‐content cathode binder for mitigation of heat generation of lithium‐ion battery

We investigate the effects of thermally sensitive binder (TSB) on the temperature increase of lithium‐ion battery (LIB) coin cell subjected to severe mechanical abuse. The TSB is poly(vinylidenefluoride‐co‐hexafluoropropylene) (PVDF‐HFP), similar to conventional poly(vinylidenefluoride) (PVDF) binder but with a significant hexafluoropropylene (HFP) content. The testing data show that by using TSB, the peak temperature increase of nail‐penetrated LIB coin cell can be reduced by 20% to 40%, attributed to the softening of TSB that begins from ~80°C. The cycling performance of the LIB cells is also characterized. This research sheds light on the development of thermal‐runaway mitigation techniques.     

Thermal behavior of lithium batteries used in electric vehicles using phase change materials

Electric vehicles equipped with lithium-ion batteries face a huge challenge, and the fact that battery life is very much affected by the temperature conditions of their operating environment, the heat reduces battery life cycle and time and increases the likelihood of thermal degradation and explosion. This problem has forced engineers to cool the battery. The methods used to cool the battery includes a cool water method (passing water or a dielectric fluid from the battery pack), cooling air (blowing air into the battery compartment by the fan), using a refrigeration system (such as cooling screens), and the use of phase-change material (PCM). In this research after reviewing and referring to valid authorities, it was found that PCMs are superior to all three other cooling systems because the air-conditioning system is not very desirable due to the high-temperature gradient between the battery cells. Also, cooling and refrigeration systems with refrigerant gases will also cost a very high cost on the electric car. The results of the studies showed that the cooling the battery using the PCM creates a similar temperature profile between the batteries in the battery pack, the temperature gradient is much smaller than the air cooler and cool water, and the final cost will be much lower. Also, it performs more efficiently in high-speed road dynamics and increases the battery life of an electric car or electric hybrid.     

Fundamental scientific aspects of lithium ion batteries (XV) ——Summary and outlook

自摇椅式可充放锂电池概念由Armand M等人在1972年提出,锂离子电池的基础研究历经43年,在材料体系、电化学反应机理、热力学、动力学、结构演化、表界面反应、安全性、力学行为等方面不断取得更为深入广泛的认识,并最终推动锂离子电池技术发展和成功实现了商业化。锂离子电池面临着电池性能需要全面提升、应用领域需进一步拓宽的强劲需求,因此要求基础研究能够提供创新的、更好的技术解决方案,对锂离子电池材料复杂的构效关系能精确认识,对于电池在制造和服役过程中的失效机制有全面的理解,对各种控制策略的效果能提供可靠的科学依据。同时,锂离子电池的发展也在促进着固态电化学、固态离子学、能源材料、能源物理、纳米科学等交叉基础学科的发展。作为“锂离子电池基础科学问题”讲座的最后一篇文章,本文对锂离子电池基础研究的科学问题,存在的难点、发展趋势进行了总结。