锂离子电池中的物理问题及其研究进展

锂离子电池作为一种性能优越的新型可充放电池已经或将要在移动通信、手提式计算机和电动汽车等诸多领域获得广泛的应用 .然而与锂离子电池相关的物理问题却往往被人们忽视 .例如 ,如何从本质上来提高正极材料的体相电子电导率 ,而不是在正极活性物质中添加炭黑之类的电子导电材料 .文章将着重针对与锂离子电池相关的物理问题 ,介绍近年来的主要进展 ,以期待对锂离子电池有更深入的了解 .     

基于扩展单粒子模型的锂离子电池参数识别策略

为了精确识别电动汽车锂离子动力电池的关键状态参数,基于多孔电极理论和浓度理论,建立了一种考虑液相动力学行为的锂离子电池扩展单粒子模型.相较于传统单粒子模型,该模型增加了对负电极表面固体电解质界面膜参数的描述,并考虑了温度和液相浓度变化对锂离子电池关键参数的耦合影响.基于所建立的扩展单粒子模型,提出一种简化的参数灵敏度分析方法和有效的锂电池参数识别策略,用以确定特定工况下的高灵敏度待识别参数,进而利用遗传算法实现参数的优化求解.最后,通过对比分析本文模型和传统单粒子模型的仿真输出电压和相同工况下电池的实验输出电压验证了提出模型和参数识别方法的有效性和可行性,为电池管理系统的健康状态估计提供了理论基础.     

电动汽车与锂离子电池

文章简要介绍了混合动力汽车、插电式混合动力汽车、纯电动汽车和锂离子动力电池及其关键材料。发展电动汽车可以大幅度降低人们对石油的依赖和改善城市空气质量。锂离子电池性能优越,为电动汽车的发展提供了支撑。近期,新一代锂离子动力电池正极材料即将走向应用,可使电动汽车里程增加一倍,材料选择和电池设计及制造工艺与电池储存能量、寿命、安全等密切相关,尊道而重德,可做出“好”电池。     

基于电化学模型的锂离子电池多尺度建模及其简化方法

锂离子电池的精确建模和状态估计对于电动汽车电池管理系统非常重要,准二维(P2D)电化学模型由于计算复杂,难以直接应用于电池管理的参数在线估计和实时控制中.本文基于多孔电极理论和浓度理论,提出一种考虑锂离子液相动力学的简化准二维(SP2D)模型.忽略锂离子孔壁流量沿电极厚度方向的变化求解SP2D模型所描述的锂离子电池锂浓度分布,基于锂离子电池电化学平均动力学行为求解固相和液相电势变化,推导出电池电压计算的简化表达式;采用恒流、脉冲以及城市循环工况放电电流对比分析了严格P2D模型与SP2D模型的终端电压和浓度分布.结果表明:SP2D模型在保持较高计算精度的同时,可显著提高计算效率.     

基于电池热特性及产热行为的新型锂离子电池评价

建立了一种新的基于锂离子电池热特性及产热行为的电池性能评价方法. 通过测量一系列不同容量及电极材料的18650电池在不同充放电时间及电流下其充放电能量的变化,建立了一个包含焦耳热与极化热影响因子的表达电池在充放电过程中的能量损失的模型. 利用这种模型,计算出电池总内阻R以及极化参数′,并且对R及′在不同温度下的变化情况进行了研究,建立一个对不同电池和不同温度都适用的普适性模型.     

轴向压缩下圆柱形动力锂离子电池的性能

动力电池的安全问题制约了电动汽车的推广和发展,轴向压缩是锂离子电池的一种重要的破坏工况。通过实验方法,研究了18650锂离子电池在轴向压缩载荷下的安全性能,探讨了荷电状态分别为60%、80%、100%时电池的载荷、电压、温度的变化特征,分析了轴向压缩载荷下电池的失效过程。研究表明:轴向压缩过程中电压均出现特有的台阶式下降,极限载荷和温度骤升几乎同时发生;电池正极的凹槽结构诱导电池在靠近正极的侧面破裂。对比轴向压缩实验和径向平板压缩实验发现,动力电池轴向压缩热失控程度弱于径向平板压缩。     

锂电池液冷结构设计与仿真分析

锂离子电池近年来被广泛应用于电动汽车之中,其对温度具有很高的灵敏度,温度过高会使得电池组电化学性能严重下降。采用双进双出的微通道液冷板换热器对电池进行热管理,为了优化液冷板的冷却性能分析了入口Re数、冷却液温度、流道宽度和流道进出口位置对电池组热性能的影响。结果表明,在单体电池以3C电流倍率放电时该结构能够有效地将电池组温差控制在5℃以内。增大入口Re数、流道宽度对电池组温度变化影响较小;改变流道宽度与进出口位置能够有效改善电池组的温度均匀性。     

后锂电池时代新型电池的开发与展望

石油、天然气等化石能源的枯竭及人类生存环境的进一步恶化,迫使人们寻求和开发清洁可再生能源和高效绿色的储能装置.传统的锂离子电池等已难以满足将来电动汽车等大规模使用的电器对于大容量蓄电装置的要求.文章综述了日本产业技术综合研究所周豪慎教授课题组近年来的研究成果,介绍了组合型电解液的概念及原理,并重点讨论了锂-铜电池和锂-空气电池等基于组合型电解液的后锂离子电池的设计方法和电化学性能.文章指出,组合电解液技术将是开发高能量电化学储能装置的重要思路和有效方法.     

锂离子电池放电循环的发热特性研究

锂离子电池发热特性的研究对于发展电池热管理系统具有重要意义.本文采用数值方法对锂电池放电过程中的微观发热特性进行了研究,并对锂电池放电循环过程中固体电解质(SEI)膜和欧姆热的变化规律进行了分析,研究结果表明:锂电池以高倍率(5C)放电时,SEI膜产生的热量是锂电池发热的重要部分;随着放电循环的进行,锂电池负极颗粒表面SEI膜以线性规律增厚,导致电池SEI膜电阻不断增大;锂电池放电环境温度越高,锂电池负极SEI膜增厚越快,容量衰退越快。     

基于反激式直流变换器的电池均衡系统仿真研究

针对电动汽车锂离子电池组在工作过程中出现的能量不一致现象,设计了一种基于反激式直流变换器的主动均衡电路,包括电源转换、信号采集、驱动电路以及均衡器4个模块。研究了均衡系统的拓扑结构和工作原理以及控制策略,阐述了反激式直流变换器与锂离子电池的建模方法,针对电池组8种典型的非均衡工况,进行了混合策略下的5 kHZ高频仿真实验,实验用电池SOC从44.3%到55.7%均有涉及,仿真与实验结果误差均在10%以内,验证了PSIM仿真电路与同轴多绕组变压器与电池建模方法以及混合控制策略的正确性。     

Analysis of the Properties of Fractional Heat Conduction in Porous Electrodes of Lithium-Ion Batteries

Research on the heat transfer characteristics of lithium-ion batteries is of great significance to the thermal management system of electric vehicles. The electrodes of lithium-ion batteries are composed of porous materials, and thus the heat conduction of the battery is not a standard form of diffusion. The traditional heat conduction model is not suitable for lithium-ion batteries. In this paper, a fractional heat conduction model is used to study the heat transfer properties of lithium-ion batteries. Firstly, the heat conduction model of the battery is established based on the fractional calculus theory. Then, the temperature characteristic test was carried out to collect the temperature of the battery in various operating environments. Finally, the temperature calculated by the fractional heat conduction model was compared with the measured temperature. The results show that the accuracy of fractional heat conduction model is higher than that of traditional heat conduction model. The fractional heat conduction model can well simulate the transient temperature field of the battery. The fractional heat conduction model can be used to monitor the temperature of the battery, so as to ensure the safety and stability of the battery performance.     

A heatproof separator for lithium-ion battery based on nylon66 nanofibers

The safety of lithium-ion battery is closely related to the anti-shrink and heatproof stability of the separator. In this paper, electrospun nylon66 (PA66) nanofiber-based membrane is used as lithium-ion battery separator, showing good thermodynamics properties via thermogravimetric analysis (TG), thermal shrinkage experiment, and tension test. Furthermore, electrospun nylon66 separator based battery exhibits better safety than the battery applying Celgard commerce separator under the condition of high temperature and severe vibration. Meanwhile, the electrochemical properties of both batteries are nearly identical. These facts prove that the electrospun nylon66 separator is an ideal separator candidate for power lithium-ion battery of electric vehicles. In addition, the nylon66 separator annealed in the air has higher tensile strength and better property of elongation than the unannealed one.     

Design and management of lithium-ion batteries:A perspective from modeling,simulation,and optimization

Although the lithium-ion batteries(LIBs) have been increasingly applied in consumer electronics, electric vehicles,and smart grid, they still face great challenges from the continuously improving requirements of energy density, power density, service life, and safety. To solve these issues, various studies have been conducted surrounding the battery design and management methods in recent decades. In the hope of providing some inspirations to the research in this field, the state of the art of design and management methods for LIBs are reviewed here from the perspective of process systems engineering. First, different types of battery models are summarized extensively, including electrical model and multi-physics coupled model, and the parameter identification methods are introduced correspondingly. Next, the model based battery design methods are reviewed briefly on three different scales, namely, electrode scale, cell scale, and pack scale. Then, the battery model based battery management methods, especially the state estimation methods with different model types are thoroughly compared. The key science and technology challenges for the development of battery systems engineering are clarified finally.     

Thermal transport in lithium-ion battery: A micro perspective for thermal management

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.     

Analysis on the capacity degradation mechanism of a series lithium-ion power battery pack based on inconsistency of capacity

The lithium-ion battery has been widely used as an energy source. Charge rate, discharge rate, and operating tem- perature are very important factors for the capacity degradations of power batteries and battery packs. Firstly, in this paper we make use of an accelerated life test and a statistical analysis method to establish the capacity accelerated degradation model under three constant stress parameters according to the degradation data, which are charge rate, discharge rate, and operating temperature, and then we propose a capacity degradation model according to the current residual capacity of a Li-ion cell under dynamic stress parameters. Secondly, we analyze the charge and discharge process of a series power battery pack and interpret the correlation between the capacity degradations of the battery pack and its charge/discharge rate. According to this cycling condition, we establish a capacity degradation model of a series power battery pack under inconsistent capacity of cells, and analyze the degradation mechanism with capacity variance and operating temperature difference. The comparative analysis of test results shows that the inconsistent operating temperatures of cells in the series power battery pack are the main cause of its degradation; when the difference between inconsistent temperatures is narrowed by 5 ℃, the cycle life can be improved by more than 50%. Therefore, it effectively improves the cycle life of the series battery pack to reasonably assemble the batteries according to their capacities and to narrow the differences in operating temperature among cells.     

A review of recent developments in the surface modification of LiMn2O4 as cathode material of power lithium-ion battery

LiMn₂O₄ (LMO) is a very attractive choice as cathode material for power lithium-ion batteries due to its economical and environmental advantages. However, LiMn₂O₄ in the 4-V region suffers from a poor cycling behavior. Recent research results confirm that modification by coating is an important method to achieve improved electrochemical performance of LMO, and the latest progress was reviewed in the paper. The surface treatment of LMO by coating oxides and nonoxide systems could decrease the surface area to retard the side reactions between the electrode and electrolyte and to further diminish the Mn dissolution during cycling test. At present, LiMn₂O₄ is the mainstreaming cathode material of power lithium-ion battery, and, especially the modified LMO, is the trend of development of power lithium-ion battery cathode material in the long term.     

A dynamic capacity fading model with thermal evolution considering variable electrode thickness for lithium-ion batteries

Capacity is one of the key parameters to characterize the performances of lithium-ion batteries. Heat generation analysis is essential to evaluate the safety of batteries. To figure out the effects of electrode thickness on capacity fade and thermal behaviors, a capacity fading model is proposed considering reaction kinetics and mass transfer processes on solid electrolyte interface (SEI) layers coupled with thermal evolution. Simulations are conducted on seven LiFePO₄ batteries with variable electrode thicknesses. Results show that, with the increase of electrode thickness, the capacity losses of batteries deteriorate, and the total heat generation aggravates. For the battery with thick electrode, both the polarization overpotential and the gradient of lithium ion concentrations on particle surfaces of active materials increase on the edges, and then decrease perpendicularly to the cathodes. Under the adiabatic conditions, the temperature of battery (with anode 68 μm and cathode 140 μm) is increased to over 130 °C at the sixth cycle. The temperature of batteries declines when discharging in the beginning and then rises, which is noticeable for the batteries with thin electrodes. The proposed model and the simulation results would provide deep insights into both design and operation of batteries.     

锂离子动力电池高倍率充放电过程中弛豫行为的仿真

基于电化学热耦合模型研究了动力锂离子电池高倍率充放电过程中的弛豫行为, 分析对比了不同充放电机制对电池弛豫行为的影响. 研究发现: 充放电过程中, 欧姆极化是造成电压骤变的主要原因; 而恒流-恒压的充电模式能够缓慢消除欧姆极化, 避免电池电压的骤变; 利用恒流恒压对电池进行充电能够充进更多的电量, 有利于电池性能的完全发挥; 固相锂离子浓度的弛豫时间比液相锂离子浓度的弛豫时间长, 并且在放电后期, 固相扩散的特征时间与液相扩散特征时间的比值不断增大, 固相扩散造成的极化在整个放电过程不可忽略.     

基于电化学-热耦合模型研究隔膜孔隙结构对锂离子电池性能的影响机制

隔膜孔隙结构对锂离子电池性能具有重要的影响,本文提出了可准确描述充放电过程中锂离子电池内部复杂物理化学现象的电化学-热耦合模型,发现该模型较文献中模型的计算结果更接近实验测试数据.利用该模型探讨了隔膜孔隙率与扭曲率分别对锂离子电池性能的影响规律,发现减小孔隙率或增大扭曲率,电池输出电压、最大放电容量和平均输出功率均不断降低,电池表面温度和温升速度均不断升高;当孔隙率减小或扭曲率增大到一定程度时,放电初期电池输出电压均会出现先下降后回升的现象,且孔隙率越小或扭曲率越大,其下降的幅度越大、速度越快,回升所需时间也越长;要确保其不低于截止电压,隔膜扭曲率必须小于临界扭曲率(其下降至最低点刚好等于截止电压时的隔膜扭曲率).综合分析了放电过程中电池内部各电化学参量和产热量的动态分布规律,发现隔膜孔隙率和扭曲率主要影响放电末期电极膜片内部电化学反应以及其他放电时刻电解液中有效Li~+扩散(传导)系数.     

双相多孔锂离子电池液/固界面的声反射与声透射

采用传递矩阵法,同步联立改进的Biot理论,对含液固界面的双相多孔锂离子电池的超声反射与透射系数进行理论求解。考虑锂离子的摇摆特性对电极力学性能的影响,计算了对应状态下液/固界面的双相多孔锂离子电池声反射及透射系数的角度谱与频率谱。同时,构建了不同荷电状态时含单元锂离子电池的频域仿真模型,以萃取对应的超声反射及透射角度谱及频率谱,并与理论计算结果对比吻合良好。随后,以多单元锂离子电池为例,在不同的荷电状态下,分析了反射与透射系数随斜入射角度、入射波频率的变化关系,并分别指出了其角度谱及频率谱特征点随荷电状态的变化特征,为锂离子电池运行状态的超声无损测量提供了理论基础。