Research progress on safety of lithium ion battery electrolyte

锂离子电池的能量密度及其安全问题是限制其在电动汽车应用中的主要障碍。随着能量密度的不断提升,当务之急是有效解决锂离子电池的安全性问题。锂离子电池安全问题本质上与当前电解液中使用的高挥发性、易燃的有机溶剂有关。因此,本文主要从电解液的燃烧性角度,介绍了电解液在锂离子电池材料安全性方面的研究现状,包括阻燃添加剂、不燃性氟代有机溶剂、高浓度电解液及固液混合电解质的应用等,分析其对安全性能提升的机理,并对电解液的发展方向进行了展望。     

A review on thermal management techniques for lithium-ion battery

随着新能源汽车的广泛使用,动力锂离子电池的热安全性问题日益突出。本文以Bernardi生热机理为基础,耦合不同物理量,分别从电化学-热耦合模型、电-热耦合模型和热滥用模型来介绍单体电池的热特性。由于电池能量密度的增加与行驶工况复杂程度的提高,动力锂离子电池容易发生热量堆积,甚至造成热失控,对此,文中梳理了商用动力电池包的常用冷却方式。最后,根据对影响电池模组安全性的热失控蔓延机理及实测结果,介绍了阻断单体及基本模块热失控传播的有效方法。     

Progress in lithium ion battery simulation model

基于锂离子电池的仿真对新能源汽车动力电池的生产与应用的重要性,本文对锂离子电池模型的分类以及近年来的发展进行了分析,包括对集中质量模型、一维模型、二维模型、三维模型的研究,以及包含多个维度子模型的多物理场耦合模型的研究,并总结了当前模型的不足之处和未来需要发展的方向。     

The technical route exploration of lithium ion battery with high safety and high energy density

发展高比能动力锂离子电池是新能源汽车,特别是纯电动汽车实现长续航里程的关键手段之一,然而,随着电池能量密度的不断提高,电池的循环寿命和安全性能就会受到影响。本文以能量密度300W·h/Kg单体电池为对象,从材料体系的选择、电芯结构设计以及系统安全防护措施等多维度展开论述,探究了高安全高比能动力锂离子电池系统技术路线。     

Investigation on the root cause of the decreased performances in the overcharged lithium iron phosphate battery

The overcharge of the lithium iron phosphate (LiFePO₄) batteries usually leads to the sharp capacity fading and safety issues, especially under low temperature environment. Thus, investigating their root cause originated from the electrode materials is critical for the safety performance optimization and market promotion of the LiFePO₄ batteries. In this work, the electrochemical/thermal behaviors of 18650 LiFePO₄ batteries are investigated after overcharge under room and low temperature of 25°C and ?20°C, respectively. The results demonstrate a decreased electrochemical performance and faster heating rate of the overcharged battery, particularly under harsh working environments such as high discharge rate and low temperature. Coupling with the analyses of the internal resistance, the crystal structure, and microstructure of the electrodes, the root cause is attributed to the damage of the crystal structure and microstructure, which reduce the electron/Li⁺ migrating capability and electrolyte diffusion/transfer efficiency.     

Application of lithium ion phosphate battery in 110 kV substation DC power system

本项目选用了两种不同的电池管理模式对磷酸铁锂电池组进行管理,并将组装好的两套电池组应用于110 kV变电站直流系统的日常运行.运行结果表明,磷酸铁锂电池可以在变电站替代铅酸蓄电池使用,并且可以浮充运行;运行过程中,单体电池的电压会由于电池充电态的变化下降或上升;单体电池的内阻呈现先下降再上升的变化;电池组的放电容量随着运行时间的延长出现每年3%左右的衰减(浮充电压为3.6 V);合适的电池管理模式能将电池组内单体电池的电压差保持在较小的范围,有利于电池组长寿命的运行.     

A review on recycling technology of spent lithium iron phosphate battery

纯电动客车用电池以磷酸铁锂电池为主,电池寿命结束后将产生大量的废旧电池,如何处理废旧电池是人们关心的重要问题。基于此,本文介绍了国家目前对于废旧电池回收的相关政策以及废旧LiFePO₄电池的主要有价成分。详细介绍了废旧LiFePO₄材料的多种回收、再利用方法,包括化学沉淀法回收、高温固相修复技术、高温固相再生技术、生物浸出技术以及机械活化处理回收技术等;并分别介绍了高温热解处理、有机溶剂萃取回收、超临界CO₂回收的电解液回收处理技术以及负极材料的分选回收技术、石墨修复改性技术。沉淀法回收产物为含锂、铁的工业原料,该类方法易于实现规模化应用,但是会产生大量酸碱废液;高温固相修复、再生方法工艺流程短,除杂将会是该工艺规模化应用的难点。对不同类型的回收材料提出不同回收处理方法,为废旧磷酸铁锂电池的回收提供参考。     

Identification of spatial temperature gradient in large format lithium battery using a multilayer thermal model

The spatial resolving of temperature gradient is a key but challenging issue for the loading performance, aging evaluation, and safety guarantee of large format lithium battery, while the internal temperature cannot be measured directly in field. Notable temperature difference of large format battery emerges in heavy load applications. This paper tries to solve spatial-distributed temperature gradient by proposing a novel method. The multilayer thermal model and the real-time method based on this model are firstly proposed to noninvasively identify the spatial temperature gradient of the battery. And the thermal conduction resistance of the battery along aging are estimated by the extended lumped-parameter model and forgetting factor recursive least square algorithm, while the convection resistance and heat capacity can be estimated by the lumped parameter model and least square algorithm. The relation between the temperature sensor number and total thermal nodes is then derived by the experiment. Finally, the proposed method is systematically verified through the simulation and experiment. Both the spatial distribution and the highest node of the battery temperature are obtained with promising accuracy and robustness. And it can be implemented in battery management systems for various online applications such as electric vehicles and hybrid electric vehicles.     

Transmission electron microscopy of lithium ion battery materials

理解材料的构-效关系是功能材料领域的永恒话题,在锂离子电池材料的研究中亦是如此。因此可以看到如X射线衍射、中子衍射、核磁共振、X射线电子能谱等结构表征手段被应用于锂离子电池材料的研究中。但是因上述方法对于微观局域结构并不敏感,而给出平均的结构信息。材料的性能往往随微观结构的不同而天差地别,因此获取锂离子电池材料的微观结构信息十分重要。透射电子显微镜具有原子尺度的空间分辨能力,可以获取原子尺度上的结构扭曲和电子结构变化,在锂离子电池材料的研究中起到了至关重要的作用。本文从电子显微学和锂离子电池材料的关系入手,从基本原理和实验方法出发,为相关领域科研人员提供便利。     

Modeling of steady‐state and transient thermal performance of a Li‐ion cell with an axial fluidic channel for cooling

Thermal management of Li‐ion cells is an important technological problem for energy conversion and storage. Effective dissipation of heat generated during the operation of a Li‐ion cell is critical to ensure safety and performance. In this paper, thermal performance of a cylindrical Li‐ion cell with an axial channel for coolant flow is analyzed. Analytical expressions are derived for steady‐state and transient temperature fields in the cell. The analytical models are in excellent agreement with finite‐element simulation results. The dependence of the temperature field on various geometrical and thermal characteristics of the cell is analyzed. It is shown that coolant flow through even a very small diameter axial channel results in significant thermal benefit. The trade‐off between thermal benefit and reduction in cell volume, and hence capacity due to the axial channel, is analyzed. The effect of axial cooling on geometrical design of the cell, and transient thermal performance during a discharge process, is also analyzed. Results presented in this paper are expected to aid in the development of effective cooling techniques for Li‐ion cells based on axial cooling. Copyright © 2014 John Wiley & Sons, Ltd.     

In situ observation of lithium dendrite on the electrode in a lithium-ion battery

锂离子电池尽管已成为便携式电子设备的主流电源,也是电动汽车、混合动力汽车等电源的主要选择之一,但依然存在使用过程中因形成锂枝晶而发生内短路的安全隐患。本文设计了一个宏微观实验研究商业用锂离子电池电极材料的充放电循环性能。在常温小电流充放电条件下,实时原位地观测锂枝晶的产生、生长、消融以及死锂残留等过程。实验结果揭示了锂枝晶不仅仅只是大电流过充或低温充电状态下的产物,常温常态小电流充电条件下依然能够生成锂枝晶。实验发现：锂枝晶出现在充电后期,随后直线伸长,尖端区域形貌保持不变;放电时,锂枝晶逐渐消融,尖端区域形貌依然不变,放电结束后电极上有死锂残留。     

Research status of iron based fluoride cathode materials for lithium ion battery

随着新能源技术的不断发展,对锂离子电池的能量密度要求越来越高。氟化铁（FeF₃）和氟化亚铁（FeF₂）因具有较小的分子量、多电子转化反应及高电压等优点正成为极具发展潜力的高比能锂电正极材料,但是导电性差、转化反应使得材料需要较大过电势,这制约了其实际应用。本文首先介绍了FeF₃和FeF₂的基本性质及储锂机制,随后具体论述了两者的电化学性能改进措施,主要包括对FeF₃和FeF₂进行晶体结构扩展和元素替换而出现的很多铁基氟化物新相（氟化铁的水合物Fe_xF_y·mH₂O、氟氧化铁FeOF）,纳米多孔结构的设计,碳纳米复合材料构建的研究,并简要展望了未来的发展方向。     

Patent analysis of lithium ion power battery recycling technology

锂离子动力电池的回收是当前储能产业关注的焦点之一,为了解锂离子动力电池的回收现状,以CNABS和DWPI专利数据库中的检索结果为分析样本,对锂离子动力电池回收技术的专利申请量趋势、全球分布区域、国内外主要申请人、全球重点技术分布以及国内重点技术进行全面分析,结果表明,虽然锂离子动力电池回收技术是目前全球尤其是中国争相布局的产业对象,但目前各个企业的专利申请量均较小且技术布局零散,总体来说锂离子动力电池回收技术仍处于摸索阶段,产业前景不明,本文以期给锂离子动力电池回收技术未来的布局和发展提供一定的借鉴。     

The capacity matchup design and its effects on the performances of LTO lithium ion battery

本研究以三元NCM为正极材料,钛酸锂LTO为负极材料制作了软包装锂离子电池,并通过固定正极容量,变化负极容量的方式设计4种不同的N/P比电池,并对不同N/P比钛酸锂电池的电池容量、高温存储和循环性能进行了研究,结果显示N/P比设计对正负极材料克容量发挥,电池容量发挥,高温存储和循环性能均具有较大影响。提高N/P比可以提高电池初始放电容量,提高正极克容量发挥。但提高N/P比会使得正极电极电位提高,特别是在接近满充电状态时,电解液易在正极侧发生氧化反应。而低的N/P比可以保证正极具有低的电极电位,从而降低在进行高温存储和循环测试时电池内部的副反应,有利于改善电池高温存储性能和循环性能。对能量密度要求不高时,为了保证长寿命循环和良好的高温性能,可以适当降低N/P比到0.85~0.9之间。     

Analysis and improvement of high temperature floating charge performance for high voltage lithium ion batteries

为研究高电压体系锂离子电池浮充性能的影响因素,对浮充失效电池的产气成分、正负极材料的结构变化、金属溶出情况、隔膜形貌及Gurley值变化等进行了深入分析研究,结果表明：电池在长时间高温浮充过程中,正极材料发生相变,金属元素溶出,同时释放O₂造成电解液的氧化分解;高温高电压状态下负极SEI膜也会破坏,并发生不断的重整及修复反应,这些反应产物沉积到负极表面及隔膜孔隙内,导致靠近负极侧的隔膜孔隙堵塞甚至贯穿,即引起正负极微短路,释放出大量气体。通过提高正极材料的结构稳定性、优化电解液形成稳定的CEI和SEI,改善增加隔膜的穿刺强度都能明显改善电池的高温浮充性能。     

Research progress of novel binders for silicon-based anode in lithium ion battery

硅基材料由于具有超高的理论比容量,安全的嵌锂工作电位和廉价易得等诸多优点,是下一代高比能量电池体系最理想的负极材料。尽管硅基材料的研究已经进行很长时间,但是硅基材料嵌锂时巨大的体积膨胀,循环性能较差等问题一直难以得到有效解决。开发高性能硅基负极黏结剂是解决硅基材料应用问题的重要途径之一,具有“刚柔并济”结构特性的黏结剂分子能够有效抑制硅基材料结构膨胀粉化,保持电极导电网络的完整性,从而有效提升其循环性能。本文综述了硅基负极黏结剂的特性要求,新型硅基负极黏结剂的研究进展,并对该领域未来潜在的研究方向进行了展望：复合体系聚合物黏结剂的开发;特殊空间构型黏结剂的开发;新型导电黏结剂的开发;自支撑无黏结剂硅基负极的开发。     

A review on lithium iron phosphate cathode materials

目前全球高动力锂离子电池系统的发展主要集中在锂锰电池,锂钴镍锰电池以及锂铁电池,其中磷酸亚铁锂材料具有高电容量,高放电功率,极佳的长循环寿命以及良好的热稳定性与高温性能等优点,已成为动力锂离子电池首选的高安全性正极材料.然而,磷酸亚铁锂材料在工业化量产时,必须解决电池芯加工性差及材料一致性不佳等问题,作者曾结合多项新颖观念与技术于磷酸亚铁锂材料制做过程,在粉体表面涂布碳层,在晶体内部掺杂金属,分别改善材料电导率与锂离子扩散速度以及有效地控制碳含量,粉体比表面积,碳层均匀性,粒径大小与分布,制备出高质量磷酸亚铁锂产品.该文将回顾并探讨上述研发工作的一些重要结果.     

Recent progress on evolution of safety performance of lithium-ion battery during aging process

安全性是制约锂离子电池规模应用的重要技术问题。锂离子电池的安全性能不仅仅与材料体系、电芯设计相关,还会随着使用过程而发生变化。锂离子电池安全性能在全生命周期内的演变规律需要重点展开研究,以保障电池在使用过程中的安全性。本文对锂离子电池全生命周期安全性演变问题的国内外研究进展进行了综述,分析了国内外关于电池安全性能在循环老化和储存老化两种工况下的演变规律的研究,总结了电池老化衰减机理与安全性能变化之间的关系,指出负极析锂是影响电池全生命周期安全性能的重要因素,最后对锂离子电池全生命周期安全性演变研究进行了展望。     

Electrical‐thermal behaviors of a cylindrical graphite‐NCA Li‐ion battery responding to external short circuit operation

Large amount of heat generated during an external short circuit (ESC) process may cause battery safety events. An experimental platform is established to explore the battery electrothermal characteristics during ESC faults. For 18650‐type nickel cobalt aluminum (NCA) batteries, ESC fault tests of different initial state of charge (SOC) values, different external resistances, or different ambient temperatures are carried out. The test case of a smaller external resistance is characterized by a shorter ESC duration with a faster cell temperature rise, whereas the case of a larger external resistance will last for a longer duration, discharge more electricity, and terminate in a slightly higher temperature. The tested batteries of high initial SOCs generally have higher temperature rise rates, smoother changes at the output current/voltage curves, but a smaller discharged capacity. The batteries of low initial SOCs can be overdischarged by the ESC operations. At low temperatures, say 0°C, the ESC process outputs much less electricity than the process at high temperatures, eg, 30°C. The initial low temperature has little effect on reducing the battery overheat due to ESC operations. The battery thermal behavior is of hysteresis property; analysis of heat generations reveals the subsequent increase of battery surface temperature after the completion of ESC discharge is due to the battery material abusive reaction heats. It is found from analytical and numerical analyses that there can have approximately 30°C temperature difference between the battery core and its surface during ESC operations. The interruption of ESC operation is very probably caused by the high battery core temperature, which leads to the destruction of solid‐electrolyte interface (SEI) film.     

Studies on the standard of lithium ion battery separator

隔膜是保障电池安全、影响电池性能发挥的重要材料。随着隔膜产业在中国的快速发展,我国的隔膜产能已经排进了世界前列。产品系列化、产品质量标准化、检测标准规范化是我国隔膜产业做大、做强的必要环节。分析了国内涉及隔膜的相关标准情况,并主要针对隔膜的检测方法及参考的标准做解读。