Mechanism of internal thermal runaway propagation in blade batteries

Blade batteries are extensively used in electric vehicles,but unavoidable thermal runaway is an inherent threat to their safe use.This study experimentally investigated the mechanism underlying thermal runaway propagation within a blade battery by using a nail to trigger thermal runaway and thermocouples to track its propagation inside a cell.The results showed that the internal thermal runaway could propagate for up to 272 s,which is comparable to that of a traditional battery module.The velocity of the thermal runaway propagation fluctuated between 1 and 8 mm s^(-1),depending on both the electrolyte content and high-temperature gas diffusion.In the early stages of thermal runaway,the electrolyte participated in the reaction,which intensified the thermal runaway and accelerated its propagation.As the battery temperature increased,the electrolyte evaporated,which attenuated the acceleration effect.Gas diffusion affected thermal runaway propagation through both heat transfer and mass transfer.The experimental results indicated that gas diffusion accelerated the velocity of thermal runaway propagation by 36.84%.We used a 1D mathematical model and confirmed that convective heat transfer induced by gas diffusion increased the velocity of thermal runaway propagation by 5.46%-17.06%.Finally,the temperature rate curve was analyzed,and a three-stage mechanism for internal thermal runaway propagation was proposed.In Stage I,convective heat transfer from electrolyte evaporation locally increased the temperature to 100℃.In Stage II,solid heat transfer locally increases the temperature to trigger thermal runaway.In StageⅢ,thermal runaway sharply increases the local temperature.The proposed mechanism sheds light on the internal thermal runaway propagation of blade batteries and offers valuable insights into safety considerations for future design.

Internal short circuit evaluation and corresponding failure mode analysis for lithium-ion batteries

Internal short circuit(ISC)is the major failure problem for the safe application of lithium-ion batteries,especially for the batteries with high energy density.However,how to quantify the hazard aroused by the ISC,and what kinds of ISC will lead to thermal runaway are still unclear.This paper investigates the thermal-electrical coupled behaviors of ISC,using batteries with Li(Ni_(1/3)CO_(1/3)Mn_(1/3))O_(2) cathode and composite separator.The electrochemical impedance spectroscopy of customized battery that has no LiPF6 salt is utilized to standardize the resistance of ISC.Furthermore,this paper compares the thermal-electrical coupled behaviors of the above four types of ISC at different states-of-charge.There is an area expansion phenomenon for the aluminum-anode type of ISC.The expansion effect of the failure area directly links to the melting and collapse of separator,and plays an important role in further evolution of thermal runaway.This work provides guidance to the development of the ISC models,detection algorithms,and correlated countermeasures.

Internal failure of anode materials for lithium batteriesd——A critical review

Prevention of mechanical and finally electrochemical failures of lithium batteries is a critical aspect to be considered during their design and performance, especially for those with high specific capacities. Internal failure is observed as one of the most serious factors, including loss of electrode materials, structure deformation and dendrite growth. It usually incubates from atomic/molecular level and progressively aggravates along with lithiation. Understanding the internal failure is of great importance for developing solutions of failure prevention and advanced anode materials. In this research, different internal failure processes of anode materials for lithium batteries are discussed. The progress on observation technologies of the anode failure is further summarized in order to understand their mechanisms of internal failure. On top of them, this review aims to summarize innovative methods to investigate the anode failure mechanisms and to gain new insights to develop advanced and stable anodes for lithium batteries.

High‑Performance Silicon‑Rich Microparticle Anodes for Lithium‑Ion Batteries Enabled by Internal Stress Mitigation

Si is a promising anode material for Li ion batteries because of its high specific capacity,abundant reserve,and low cost.However,its rate performance and cycling stability are poor due to the severe particle pulverization during the lithiation/delithiation process.The high stress induced by the Li concentration gradient and anisotropic deformation is the main reason for the fracture of Si particles.Here we present a new stress mitigation strategy by uniformly distributing small amounts of Sn and Sb in Si micron-sized particles,which reduces the Li concentration gradient and realizes an isotropic lithiation/delithiation process.The Si8.5Sn0.5Sb microparticles(mean particle size:8.22μm)show over 6000-fold and tenfold improvements in electronic conductivity and Li diffusivity than Si particles,respectively.The discharge capacities of the Si_(8.5)Sn_(0.5)Sb microparticle anode after 100 cycles at 1.0 and 3.0 A g^(-1)are 1.62 and 1.19 Ah g^(-1),respectively,corresponding to a retention rate of 94.2%and 99.6%,respectively,relative to the capacity of the first cycle after activation.Multicomponent microparticle anodes containing Si,Sn,Sb,Ge and Ag prepared using the same method yields an ultra-low capacity decay rate of 0.02%per cycle for 1000 cycles at 1 A g^(-1),corroborating the proposed mechanism.The stress regulation mechanism enabled by the industry-compatible fabrication methods opens up enormous opportunities for low-cost and high-energy-density Li-ion batteries.

Thermal runaway evolution of a 280 Ah lithium-ion battery with LiFePO_(4) as the cathode for different heat transfer modes constructed by mechanical abuse

Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored.This work analyzes the thermal runaway evolution of high-capacity LiFePO_(4) batteries under different internal heat transfer modes,which are controlled by different penetration modes.Two penetration cases involving complete penetration and incomplete penetration were detected during the test,and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism.A theoretical model of microcircuits and internal heat conduction is also established.The results indicated three thermal runaway evolution processes for high-capacity batteries,which corresponded to the experimental results of thermal equilibrium,single thermal runaway,and two thermal runaway events.The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole.By controlling the heat dissipation conditions,the time interval between two thermal runaway events can be delayed from 558 to 1417 s,accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.

Functional Optical Fiber Sensors Detecting Imperceptible Physical/Chemical Changes for Smart Batteries

The battery technology progress has been a contradictory process in which performance improvement and hidden risks coexist.Now the battery is still a“black box”,thus requiring a deep understanding of its internal state.The battery should“sense its internal physical/chemical conditions”,which puts strict requirements on embedded sensing parts.This paper summarizes the application of advanced optical fiber sensors in lithium-ion batteries and energy storage technologies that may be mass deployed,focuses on the insights of advanced optical fiber sensors into the processes of one-dimensional nano-micro-level battery material structural phase transition,electrolyte degradation,electrode-electrolyte interface dynamics to three-dimensional macro-safety evolution.The paper contributes to understanding how to use optical fiber sensors to achieve“real”and“embedded”monitoring.Through the inherent advantages of the advanced optical fiber sensor,it helps clarify the battery internal state and reaction mechanism,aiding in the establishment of more detailed models.These advancements can promote the development of smart batteries,with significant importance lying in essentially promoting the improvement of system consistency.Furthermore,with the help of smart batteries in the future,the importance of consistency can be weakened or even eliminated.The application of advanced optical fiber sensors helps comprehensively improve the battery quality,reliability,and life.

Fast internal preheating of 4680 lithium-ion batteries in cold environments

Lithium-ion batteries are expected to operate within a narrow temperature window around room temperature for optimal performance and lifetime.Therefore,in cold environments,electric vehicle battery packs must be extensively preheated prior to charge or discharge.However,conventional preheating is accomplished externally,which is slow and thus significantly increases charging times.Recently,internal heating has been demonstrated as a potential solution to quickly and uniformly preheat a lithium-ion pouch cell.However,internal heating has not been evaluated in other battery formats such as cylindrical batteries.In this work,we present a numerical model of a 4680 battery with internal heaters for fast preheating in cold environments.The effects that the number of heater layers,heating duration,resting duration,environmental temperature,and boundary heat transfer coefficient have on the temperature heterogeneity of the battery were investigated.The results show that internal heating alone reduces the temperature variation within the battery by a factor of 5 compared to external heating,and by a factor of 20 when combining internal and external heating.This study further proves that internal preheating of lithium-ion batteries is a promising thermal management strategy,and provides guidance on potential design considerations and heating protocols to implement internal heating.

Salt-washing Improvement of the Electrochemical Properties of Zeolite-sulfur Cathode for Lithium-sulfur Batteries

We displayed that the low-cost natural zeolite with molecular sieve structure can be used as the carrier of sulfur in lithium-sulfur batteries.Meanwhile,a simple salt-washing method was implemented on zeolite for dredging the internal microchannel to improve the ability of adsorption,ion exchange and sulfur loading.The experimental results show that the first specific discharge capacities of zeolite/S and salt-washed zeolite/S cathode under 0.2 C current density are 950.7 and1116.8 mAh/g,respectively,and corresponding discharge capacities remain at 350.6 and 604.2 mAh/g after 300 cycles.The first specific discharge capacity of salt-washed zeolite/S composite is 17.5%higher than that sample without salt-washing,and the corresponding ionic conductivity is improved.

Data-driven short circuit resistance estimation in battery safety issues

Developing precise and fast methods for short circuit detection is crucial for preventing or mitigating the risk of safety issues of lithium-ion batteries(LIBs).In this paper,we developed a Convolutional Neural Networks(CNN)based model that can quickly and precisely predict the short circuit resistance of LIB cells during various working conditions.Cycling tests of cells with an external short circuit(ESC)are produced to obtain the database and generate the training/testing samples.The samples are sequences of voltage,current,charging capacity,charging energy,total charging capacity,total charging energy with a length of 120 s and frequency of 1 Hz,and their corresponding short circuit resistances.A big database with~6×10^(5)samples are generated,covering various short circuit resistances(47~470Ω),current loading modes(Constant current-constant voltage(CC-CV)and drive cycle),and electrochemical states(cycle numbers from 1 to 300).Results show that the average relative absolute error of five random sample splits is 6.75%±2.8%.Further parametric analysis indicates the accuracy estimation benefits from the appropriate model setups:the optimized input sequence length(~120 s),feature selection(at least one total capacity-related variable),and rational model design,using multiple layers with different kernel sizes.This work highlights the capabilities of machine learning algorithms and data-driven methodologies in real-time safety risk prediction for batteries.

Separator Dependency on Cycling Stability of Lithium Metal Batteries Under Practical Conditions

Development of practical lithium(Li)metal batteries(LMBs)remains challenging despite promises of Li metal anodes(LMAs),owing to Li dendrite formation and highly reactive surface nature.Polyolefin separators used in LMBs may undergo severe mechanical and chemical deterioration when contacting with LMAs.To identify the best polyolefin separator for LMBs,this study investigated the separator-deterministic cycling stability of LMBs under practical conditions,and redefined the key influencing factors,including pore structure,mechanical stability,and chemical affinity,using 12 different commercial separators,including polyethylene(PE),polypropylene(PP),and coated separators.At extreme compression triggered by LMA swelling,isotropic stress release by balancing the machine direction and transverse direction tensile strengths was found to be crucial for mitigating cell short-circuiting.Instead of PP separators,a PE separator that possesses a high elastic modulus and a highly connected pore structure can uniformly regulate LMA swelling.The ceramic coating reinforced short-circuiting resistance,while the cycling efficiency degraded rapidly owing to the detrimental interactions between ceramics and LMAs.This study identified the design principle of separators for practical LMBs with respect to mechanical stability and chemical affinity toward LMAs by elucidating the impacts of separator modification on the cycling performance.

Experimental study on thermal characteristics of LiFePO_4 power batteries

As an important high-energy chemical power source, lithium-ion power batteries come up to application problems of thermal performance, such as extended temperature range and high power charge ＆ discharge. LiFeP04 battery is applied and developed well recently, its charge and discharge experiment at different temperatures and hybrid pulse power characterization （HPPC） test are analyzed, and the optimal temperature range of LiFeP04 battery is put forward. In order to provide experimental suggestion of power battery application and its thermal management, internal resistance, influencing factor of electromotive force and entropy change state of charge （SOC）, battery thermal characteristic of different charge ＆ discharge rates are summarized.

Research of Pure Electric Ferry System and Its Short-Circuit Protection and Calculation

System control and safety reliability are important links of the marine DC (Direct Current) power system. The simulationmodel is built by Matlab/Simulink, the battery and super-capacitor are supplied to the system through a three-phase interleaved DC/DCconverter, the fuse and disconnector switch combination are used as the protection device, and the short-circuit point is set betweeneach branch and the DC distribution board, performing short-circuit simulation. This paper also proposes a short-circuit calculationmethod for super-capacitors based on the simplified model of series RC (Resistors & Capacitors), and verifies its correctness throughsimulation data. The results show that the introduction of a three-phase interleaved DC/DC converter reduces the current ripple andmakes the system control more convenient;short-circuit calculation and simulation have determined the short-circuit withstandcapability of the DC distribution board, and verified the feasibility of the fuse selection method and the short-circuit calculation methodof the super-capacitor. This provides reliable verification for the application and calculation of the actual project.

基于SVR和电化学阻抗谱的锂电池内部温度在线估计

准确实时地监测锂电池内部温度对于预防电池热失控至关重要。然而,目前尚缺乏有效的在线监测电池内部温度的方法。基于小型化阻抗测试系统,对锂离子电池在不同温度和荷电状态(SOC)下进行阻抗测试实验,研究电池温度和SOC对阻抗的影响,寻找与温度强相关而与SOC弱相关的特征频率。在此基础上,提出了一种基于支持向量回归(SVR)算法的锂电池内部温度估计算法,无需额外传感器,实现对电池内部温度的无损准确估计。

针刺诱发电池热失控的研究进展综述

针刺测试是研究锂离子电池热失效机理和热失控特性的重要方法之一。本文汇总了目前广泛采用的针刺测试设置,并研究了不同变量对热失控演化的影响,包括针刺的深度、速度、位置以及针的材料和直径等,对针刺破坏下锂离子电池内短路及热失控行为进行机理性探索与分析。结果发现,针刺的深度与电池热失控行为的严重程度成正比,针刺的速度对电池热失控没有明显影响,针刺发生在活性材料较密集或电极附近时电池热失控更严重。针的材料和直径对电池热失控行为具有双重影响,需要结合实际情况对产热和散热情况分别进行分析。最后通过总结不同因素对电池热失控的影响,对减缓锂离子电池热失控以及更新其安全测试程序提出了新的见解,为后续的创新型研究工作提供思路。

基于主动方波激励检测锂离子电池早期内短路

锂离子电池内部短路(ISC)的早期检测对于避免潜在安全风险至关重要。现有的故障检测方法在检测早期短路时准确性较差,且需要大量的数据。以18650型锂离子电池为研究对象,通过在电池充电过程中施加微小的电流激励信号,借助极化压升与激励压升,发现锂离子电池在短路时压升异常规律。该方法在荷电状态(SOC)较低时效果更明显,对120Ω以内的短路检测有效,且适用范围可根据采样精度调配,可用于锂离子电池的常规短路检测。

受限空间锂离子电池热失控热传递仿真研究

为探究锂离子电池在航空运输等受限空间条件下的热失控热传递来源及占比,以正极材料钴酸锂(LCO)的18650型锂离子电池(100%荷电状态)为研究对象。通过ANSYS Fluent软件建立锂离子电池热失控热传递模型,将第1节电池及其热失控产生的热解气体作为热源,通过辐射传热和对流换热对第2节电池进行加热至热失控。研究结果表明:第2节电池达到热失控温度时,电池内部副反应产热占总能量的30.01%;第1节电池热失控产生的气体燃烧为第2节电池热失控提供能量,且占总能量的5.64%;第2节电池达到最高温度时,电池内部产热占比87.39%,气体燃烧提供的能量占比为1.76%;热解气体的燃烧虽然加速第2节电池的热失控进程,但提供的能量所占比例较小。

基于电压曲线诊断锂离子电池的故障

锂离子电池在电动汽车中应用广泛,电池的不一致性故障与内短路故障是电动汽车的严重安全隐患。采用绝对中位差方法来放大电池组故障电池的电压特性;再利用非局部均值滤波算法进行滤波,得到平滑的故障电压特征;最后,通过动态时间归整(DTW)算法计算特征值曲线之间的相似度距离,实现故障电池自动定位。使用运行车辆电压数据进行验证,发现该诊断方法对两类故障车辆均具有良好的检测效果:一是故障电池DTW距离长期偏离其他电池的不一致性故障车辆;二是故障电池DTW距离短期偏离其他电池的内部短路故障车辆。与余弦相似度进行对比,验证所提方法的准确性更高。

进出口锂离子电池质量安全标准与海关监管优化对策

锂离子电池是拉动我国进出口贸易的“新三样”之一。目前,国际上对锂离子电池的运输和进出口标准不一。缘于锂离子电池自身性质的不稳定性以及企业尚未普遍形成将锂离子电池作为危险品运输的意识,导致锂离子电池在运输过程中事故频发。此外,部分企业在锂离子电池进出口过程中存在不符合标准、不规范申报的情况。因此,海关作为执法部门,应对锂离子电池及其包装实施有效的鉴定和监管,制定行业标准,严防安全漏洞,确保锂离子电池进出口环节安全。

锂离子电池内部信号监测技术概述

锂离子电池在便携式电子产品、储能电站和电动汽车等领域得到了广泛的应用。然而,在电池容量不断上升的同时,锂离子电池的热失控风险也在增加,进而带来安全问题。现有的电池管理系统通过监测电池表面温度以及端电压来判断电池的健康状况。但是研究发现由于电池组件的多层结构和较差的导热性,电池内部温度、气体等很难散发到外部,导致对电池表面温度等外部信号的监测存在时效性差的问题。因此人们尝试直接监测电池内部温度、压力、应变和气体等信号的变化情况,实现及时预警电池热失控,增强锂离子电池在不同应用场景下的安全性。本文在理解热失控机制的基础上,概述了可以监测电池内部信号的方法。总结了锂离子电池在发生热失控时涉及的一系列放热反应,及在这些反应过程中电池内部温度、压力和气体等信号的变化情况。对于能够直接监测电池内部信号的技术,主要介绍了电化学阻抗分析和内置传感器监测,为以后优化监测方法提供参考信息。其中,将传感器植入到电池内部在实际应用中具有良好的前景。为了进一步提高锂离子电池系统的安全性,本文还对未来可能的研究方向进行了展望。

储能用锂离子电池安全评价标准现状

锂离子电池装机量不断增加,锂离子电池安全问题可能诱发储能系统的事故。为更好地开展储能用锂离子电池标准制修订工作,促进储能用锂离子电池产业高质量发展,调研产业发展概况,分析国内外储能用锂离子电池安全标准化现状。目前,国际电工委员会(IEC)、美国保险商实验室(UL)和国内相关标准化机构均已制定基础准入标准,但存在部分标准考核不全面,缺乏适用性的问题,此外,缺少安全等级评价相关标准。后续标准制修订时,应以有效评估储能用锂离子电池的安全性为目的,注重锂离子电池多方面的考核,以此助推储能产业高质量发展。