基于应力场的锂离子电池正极多尺度失效研究

锂离子电池已广泛应用于动力和储能领域, 电池寿命是影响其进一步发展的关键因素。循环充放电过程中的电化学-力学多场耦合作用会导致正极材料发生机械损伤累积, 降低电极材料的结构稳定性并形成多尺度损伤, 从而缩短电池循环充放电寿命。本文通过总结团队在三元正极材料多尺度失效行为方面的研究成果, 系统介绍了不同尺度下实验与模拟相结合的电极材料损伤分析方法, 旨在为不同尺度下选取损伤分析方法提供参考。基于电化学循环实验表征、扩展有限元分析法(XFEM)、线性匹配法(LMM)等研究手段, 深入分析了电极材料在多尺度下的力学损伤机理。研究工作为电极材料的多尺度失效行为分析及结构改性提供了重要指导。     

基于电化学-力耦合模型的锂离子电池充电过程中石墨颗粒的应力模拟

在锂离子电池的充放电过程中,随着电极颗粒中锂的嵌入和脱出,颗粒会发生膨胀和收缩而导致应力的产生,应力过大时会发生电极材料的脱落、破裂,致使电池内阻增加、循环性能下降、容量衰减,最终导致电池失效。该文对正负极椭球颗粒建立三维电化学-力耦合模型,计算了充电过程中电极颗粒的锂浓度分布以及负极石墨颗粒的应力分布。结果表明:两个颗粒接触的部位应力较大,且过大的应力会削弱锂离子的脱嵌能力,导致两个负极颗粒接触的部位锂浓度较低而两个正极颗粒接触的部位锂浓度较高。此外,颗粒表面径向应力为零,径向应力最大值出现在颗粒中心,最大切向应力出现在两个颗粒接触的表面。     

MCrAlY金属黏结层高温失效行为研究进展

随着航空发动机与燃气轮机涡轮进口温度的不断提高,MCrAlY(M=Ni,Co或NiCo)包覆型涂层因具有抗高温氧化以及高的热膨胀系数等优点,成为广泛应用的热障涂层金属黏结层材料。然而,高温服役环境下热障涂层中金属黏结层与陶瓷面层界面应力分布状态愈加复杂,黏结层界面失效导致陶瓷面层的剥落,限制了其在热防护涂层领域的发展。本文简述了黏结层的发展进程,重点阐述高温相转变、热应力和生长应力增加以及S元素扩散等因素导致的黏结层界面的失效行为,分析黏结层界面失效机理,归纳总结了国内外针对金属黏结层界面失效的改进研究工作,并在此基础上提出采用稀土及纳米颗粒协同强化MCrAlY材料,为未来热障涂层体系的优化设计提供了研究方向。     

原位拉曼光谱在碱金属离子电池炭负极材料研究中的应用（英文）

拉曼散射仪是一种基于激光物理学的快速、无损、高分辨率的通用表征工具,已被证明是研究温度、应力、电化学反应等诱导的结构相变的一种有力工具。碱金属电池的原位拉曼表征可以追踪充放电过程中的电极材料变化和界面反应。炭材料因其良好的可逆性、优异的稳定性、低电化学平台和低成本,成为应用最广泛的锂离子电池负极材料。本文详细总结了原位拉曼谱图在碱金属离子电池炭负极材料研究中的应用,着重整理归纳了原位拉曼谱图在分析Li~+/Na~+/K~+在石墨、硬碳等炭材料储能机理中的应用,分析了尺寸效应、应力、掺杂、溶剂化共插层等对碱金属离子电池炭负极材料储能的影响。原位拉曼与原子力显微镜(AFM),X射线衍射(XRD)等高分辨率的原位表征联用以达到分析储能机理的目的,将会在储能领域中表现出广阔的应用前景。     

面向可充电电池的锂金属负极的枝晶生长:理论基础、影响因素和抑制方法

在全球能源与环境问题日趋紧迫的大背景下,可再生能源的获取与利用途径及高效安全的储能技术的研发一直是工业界和科学界关注的热点之一。锂离子二次电池作为能量存储器件,拥有高比能量、长循环寿命等优点,近十几年来其研究取得了长足进展,并在各类便携式电子设备和电动交通工具中获得了广泛应用。然而,随着各种高性能设备的不断涌现,商业化的锂离子电池越来越难以满足其在能量密度、循环稳定性和安全性等方面的要求。为了进一步提高锂离子电池的能量密度,需要开发出高比容量的负极材料(硅、锡和锂等)以取代传统石墨负极。硅、锡等新式负极材料通过与锂离子反应形成含锂化合物的原理来存储与释放锂离子,完成电池的一个充放电过程。这个过程往往伴随着负极材料体积的剧烈变化,经历较长时间循环使用后会导致负极材料的粉化甚至从集流体上剥离,引起电池容量迅速衰减甚至失效。而锂负极通过锂在负极上的溶解和沉积来完成电池的充放电过程,该过程不存在反应相变所导致的体积变化。另外,锂金属负极材料具有极高的质量比容量(3 860mAh/g)、低密度(0.59g/cm3)和低的还原电位(-3.04V,相比于氢标准电极),被认为是一种理想的可充电电池负极材料。然而,锂的枝晶生长、锂金属电池低的库伦效率和锂的无主体沉积引起的体积膨胀等一些关键问题长期以来制约着锂负极的商业应用。锂的每次沉积都会产生枝晶,在充放电循环中,锂枝晶会导致电池内部短路甚至发生爆炸,带来严重的安全问题。除此之外,锂枝晶还会增加负极表面积,新暴露的锂金属会与电解液反应生成固态电解质膜(Solid electrolyte interface,SEI),这会损耗活性材料以及降低电池的库伦效率。为了解决以上问题,研究者们对锂金属电极进行了许多探索,尤其是在锂枝晶生长的机理及其抑制方法方面。一些理论模型如扩散模型、SEI保护模型、电荷诱导生长模型和薄膜生长模型等,以及与这些模型相对应的一些抑制方法如均匀锂离子流法、SEI膜保护法、稳定沉积主体法和静电屏蔽保护法等被提出。这些抑制方法能够在一定程度上缓解锂枝晶的生长问题,但都未能达到商业化应用的要求。本文总结了近几年研究人员针对锂离子电池锂金属负极的一些重要研究,系统地介绍了业内较为认同的枝晶生长模型和影响因素,并着重叙述了抑制枝晶生长的方法及成效,最后就锂金属负极将来的研究方向给出一些建议。     

影响热障涂层失效因素的研究现状及展望

热障涂层(TBCs)具有良好的隔热性能,是燃气轮机高温部件的关键材料,在高温服役过程中,涂层脱落会导致部件工作失效,因此为获得长寿命热障涂层,涂层的脱落失效机理是急需深入研究的问题。综述了热应力、α-Al_2O_3生长、外应力、热生长氧化层(TGO)起伏及孔隙率等缺陷对涂层应力发展的影响,探讨了微裂纹的产生、扩展及脱落的失效过程,最后展望了研究热障涂层失效及提高涂层寿命的努力方向和前景。     

层状锂钴镍锰氧化物交流阻抗谱的研究

用交流阻抗法研究了锂离子电池结构、充电状态以及温度对层状锂钴镍锰氧化物反应动力学的影响.结果表明：与未卷绕的2032电池相比,卷绕的18650电池在高频出现了感抗.根据不同电位下的阻抗谱可以推断层状锂钴镍锰氧化物的脱锂过程分为三个阶段,2.0～2.7V为克服晶格结构作用力阶段,2.7～3.65V为锂离子多层钝化膜的形成过程,3.65～4.25V为多层钝化膜与溶液界面的双电层形成过程.温度的升高加快了电荷传递速度和锂离子扩散速度,计算得到电荷传递活化能和锂离子扩散活化能分别为20.48、48.67kJ/mol,且后者是电化学反应的控制步骤.     

热浸镀铝球墨铸铁失效机理研究

采用VK-9710型激光共聚焦显微镜对热浸镀铝球墨铸铁试样的三点弯曲失效过程进行原位观察,分析镀层和基体的裂纹萌生和扩展机理。结果表明:对于纯Al浸镀球墨铸铁,在拉应力作用下,铁铝合金镀层率先萌生裂纹,诱导临近基体中铁素体撕裂与石墨球剥离,裂纹近似垂直于拉应力方向并沿着临近石墨球最短途径扩展;压应力导致表面纯Al层剥离和铁铝合金层破碎,镀层失效对球墨铸铁基体基本无影响。对于Al-3.7Si-1.0RE浸镀球墨铸铁,拉应力作用下的失效机理与纯Al浸镀相似;压应力作用下纯Al层和铁铝合金层与基体脱开,表现为铁素体基体失效。     

锂离子电池硅基负极黏合剂的研究进展

硅（Si）基负极因具有超高的理论比容量(4200 mAh/g),有望替代石墨电极(理论比容量372 mAh/g)成为新一代的高容量锂离子电池负极。但Si负极在电池循环过程中所引起的巨大体积膨胀,会导致Si颗粒的粉碎、电接触失效及其它副反应,最终导致电池容量的快速衰减以及循环稳定性变差。黏合剂是锂离子电池负极的重要组成部分之一,虽然含量很少,但在稳定电极循环中起着关键作用。文中主要对Si基负极电池黏合剂的溶剂类型及聚合结构（包括线型、交联以及共轭导电聚合物）进行了分类,并在黏合机理、优点、局限性以及性能等方面进行了阐述,最后对亟待深入研究的方向和发展前景进行了展望。     

层状锂钴镍锰氧化物交流阻抗谱的研究

用交流阻抗法研究了锂离子电池结构、充电状态以及温度对层状锂钴镍锰氧化物反应动力学的影响．结果表明:与未卷绕的2032电池相比,卷绕的18650电池在高频出现了感抗．根据不同电位下的阻抗谱可以推断层状锂钴镍锰氧化物的脱锂过程分为三个阶段,2．0-2．7V为克服晶格结构作用力阶段,2．7-3．65V为锂离子多层钝化膜的形成过程,3．65-4．25V为多层钝化膜与溶液界面的双电层形成过程．温度的升高加快了电荷传递速度和锂离子扩散速度,计算得到电荷传递活化能和锂离子扩散活化能分别为20．48、48.67kJ／mol,且后者是电化学反应的控制步骤．     

静电纺丝聚芳醚砜酮纤维膜穿刺强度研究

静电纺丝纤维膜因为具有高孔隙率、大的比表面积和良好的电解液润湿性而被广泛地应用于锂离子电池隔膜的研究,但对于锂离子电池安全性能至关重要的隔膜穿刺强度的研究还比较匮乏。本工作采用静电纺丝技术制备得到PPESK纤维膜,并采用热处理提高纤维膜的力学性能,然后通过穿刺实验测得一系列不同厚度热处理PPESK纤维膜的穿刺强度,并建立起穿刺强度与纤维膜厚度之间的线性关系。通过对穿刺破坏区域的微观分析,探究热处理PPESK纤维膜穿刺破坏机理,结果表明:各向同性的热处理PPESK纤维膜穿刺过程是由纤维受挤压产生弯曲、变形和断裂造成的破坏,破坏区域呈近似圆形穿刺孔,而PP微孔膜的破坏区域则是由脆性断裂造成的长条形裂缝,相比之下热处理PPESK纤维膜的穿刺破坏过程更加缓和,可以降低锂枝晶刺穿隔膜带来的风险,但是热处理PPESK纤维膜的穿刺强度还有待增强。     

Diffusion of lithium ions and diffusion-induced stresses in a phase separating electrode under galvanostatic and potentiostatic operations: Phase field simulations

Phase separation in an electrode of a lithium ion battery, which is a phenomenon where an active electrode material is separated into Li-rich and Li-poor phases, exists widely in many active materials and has significant impacts on the diffusion of lithium ions and diffusion-induced stresses. A phase field model is developed to study the phase separation. Firstly, the influences of various energies, such as the free energy of uniform Li-ion concentration, gradient energy and elastic energy, on phase separation are discussed. Secondly, the impacts of charge operation, e.g. galvanostatic and potentiostatic, on Li-ion diffusion and diffusion-induced stresses in a planar phase separating electrode are investigated. Calculations are also made for single phase electrodes based on Fick’s law for comparison. The obtained simulation results show that the Li-ion diffusion in a phase separating electrode depends significantly on the phase separating profile and movement of phase boundary, but it is not sensitive to charge operation. The diffusion-induced stresses also separate into high and low stress regions. Finally, based on the diffusion process and diffusion-induced stress, it is suggested that phase separation should be avoided for the sake of fast charging and mechanical reliability.     

Dynamic mechanical integrity of cylindrical lithium-ion battery cell upon crushing

Lithium-ion batteries are currently widely used in various industries, including automotive industry. Thus, the study of battery mechanical integrity subject to dynamic loading is critical for vehicle safety, which still remains rare. In this paper, first of all, by taking the advantage of previous efforts on quasi-static mechanical experiments on lithium-ion batteries, a new battery mechanical integrity criteria is suggested based on the mechanical strength theory. Further, by considering the strain rate and inertia effect of the battery structural and material, the dynamic mechanical behavior of lithium-ion battery is investigated. Different mechanical failure behaviors are obtained through the combination of numerical simulation and the suggested battery mechanical integrity criteria. Finally, parametric studies are carried out to further comprehensively reveal the battery dynamic mechanical integrity behavior. Results may shed lights on the lithium-ion battery dynamic mechanical behavior and safety research.     

Synthesis of anode active material particles for lithium-ion batteries by surface modification via chemical vapor deposition and their electrochemical characteristics

The high capacity and optimal cycle characteristics of silicon render it essential in lithium-ion batteries. We have attempted to realize a composite material by coating individual silicon (Si) particles of μm-order diameter with a silicon oxide film to serve as an active material in the anode of a lithium-ion battery and thus improve its charge-discharge characteristics. The particles were coated using an inductively coupled plasma-chemical vapor deposition (ICP-CVD) process that realized a homogeneously coated silicon oxide film on each Si particle. The film was synthesized using tetraethyl orthosilicate (TEOS) with hydrogen (H₂) gas used as a reducing agent to deoxidize the silicon dioxide. This enabled the control of the silicon oxidation number in the layers produced by adjusting the H₂ flow during the silicon oxide deposition by ICP-CVD. The silicon oxide covering the Si particles included both silicon monoxide and suboxide, which served to improve the charge-discharge characteristics. We succeeded in realizing an active material using Si, which is abundant in nature, for the anode of a lithium-ion battery with highly charged, improved cycle properties.     

Research Progresses of Liquid Electrolytes in Lithium-Ion Batteries

In recent years, the rapid development of modern society is calling for advanced energy storage to meet the growing demands of energy supply and generation. As one of the most promising energy storage systems, secondary batteries are attracting much attention. The electrolyte is an important part of the secondary battery, and its composition is closely related to the electrochemical performance of the secondary batteries. Lithium-ion battery electrolyte is mainly composed of solvents, additives, and lithium salts, which are prepared according to specific proportions under certain conditions and according to the needs of characteristics. This review analyzes the advantages and current problems of the liquid electrolytes in lithium-ion batteries (LIBs) from the mechanism of action and failure mechanism, summarizes the research progress of solvents, lithium salts, and additives, analyzes the future trends and requirements of lithium-ion battery electrolytes, and points out the emerging opportunities in advanced lithium-ion battery electrolytes development.     

A statistical analysis of the mechanical and electronic-transport properties of stochastic porous fibrous materials

Computer simulations are used to analyze mechanical and electronic-transport properties and their degradation in stochastic porous fibrous materials. Such materials are currently being used for electrochemical substrates in advanced battery technologies such as the nickel/metal-hydride and lithium-ion technologies. It is found that due a structural damage, material mechanical and electron-transport properties degrade during loading at a progressively higher rate leading ultimately to a complete loss of the material ability to support mechanical load or to conduct electrical current. A statistical sensitivity analysis is also developed which could be used in the design and fabrication of stochastic porous fibrous materials in order to ensure that a desired minimum level of the failure strength is attained at a sufficiently high probability.     

Structural and mechanical characterization of lithium-ion battery electrodes via DEM simulations

Electrode structural stability and mechanical integrity is of major importance regarding not only lithium-ion battery performance but also safety aspects. The goal of this study is to design a simulation procedure to reproduce the microstructural and mechanical properties of such lithium-ion battery electrodes. Taking into consideration the particulate state of these electrodes, a discrete element method (DEM) approach is proposed, which comprises a procedure to reproduce real electrode structures and the application of a proper contact model to capture the bulk mechanics. This is accomplished by considering particle interactions as well as the performance of the binder. Three different electrodes are manufactured with the aim of calibrating and validating the Hertzian-bond contact model. Experimental nanoindentation measurements prove to be in good agreement with the simulation outcome, concluding that the method constitutes a valuable physical and mechanical basis for further applications.     

3Ah高镍/硅氧碳软包电池循环容量衰减分析EI北大核心CSCD

随着电动汽车的发展,对电池能量密度提出了更高的要求,具有高能量密度的高镍/硅氧碳软包电池成为长续航电动汽车的首选,但是高镍/硅氧碳电池在实际使用中存在容量快速衰减的问题。采用无损电化学分析和事后拆解分析对循环过程中电池容量和内阻的变化进行检测,通过对比电池循环前后正负极结构、材料形貌和表面成分的变化,揭示高镍/硅氧碳电池循环失效机制。结果表明:电池容量衰减呈现平稳期、快速衰减期和急速衰减期3个阶段。循环后电池极化更加严重,电池极化内阻、负极表面膜阻抗和电荷转移阻抗明显增加。通过微分曲线分析结合拆解分析发现,高镍正极材料衰减较少,硅氧碳负极材料衰减和活性锂离子损失较多。硅氧颗粒膨胀开裂,负极活性物质损失,负极表面膜连续生长消耗过多的活性锂为电池容量快速衰减的主要原因。     

Diffusion-induced stress and delamination of layered electrode plates with composition-gradient

Diffusion-induced stress can result in failure of layered electrodes in lithium-ion batteries during the process of fast lithiation and delithiation. Recent studies have demonstrated that the electro-chemo-mechanical properties of compositions-gradient nanoparticles are superior to those of homogeneous ones. In light of this aspect, we develop a theoretical model to probe the effects of composition-gradient on the stress evolution in layered electrodes. Our analysis concludes that, compared with the corresponding homogeneous structure, symmetrical negative-exponent gradient active plates or positive-exponent gradient bilayer electrodes can significantly reduce the maximum compressive stress and the stress drop at the electrode–collector interface, while the energy release rate of interface delamination is slightly weakened by it. These results, again, show that the composition-gradient could improve the mechanical performance of electrodes in lithium-ion batteries, and are instrumental to the design of electrode structures.