Balancing particle properties for practical lithium-ion batteries

As a state-of-the-art secondary battery, lithium-ion batteries (LIBs) have dominated the consumer electronics market since Sony unveiled the commercial secondary battery with LiCoO₂ as the negative electrode material in the early 1990s. The key to the efficient operation of LIBs lies in the effective contact between the Li-ion-rich electrolyte and the active material particles in the electrode. The particle properties of the electrode materials affect the lithium ion diffusion path, diffusion resistance, contact area with the active material, the electrochemical performance and the energy density of batteries. To achieve satisfied comprehensive performance and of LIBs, it is not only necessary to focus on the modification of materials, but also to balance the properties of electrode material particles. Therefore, in this review, we analyze the influence of particle properties on the battery performance from three perspectives: particle size, particle size distribution, and particle shape. A deep understanding of the effect and mechanism of particles on electrodes and batteries will help develop and manufacture practical LIBs.     

全固态锂电池界面的机械失效模型综述

全固态锂电池具有高能量密度和高安全性能等优点,有望替代传统锂电池成为下一代可移动储备．然而,全固态结构也给这种新型电池的应用带来全新的挑战,阻碍其商业化的进程,其中很重要的一个挑战就是机械不稳定性．首先,尽管固态电解质具有较高刚度与强度,理论上应该可以阻挡锂枝晶的穿透,但在其使用过程中仍能观察到锂枝晶的生长,这与高刚度电解质可抵制锂枝晶生长的理论相悖．其次,与液态电解质相比,固态电解质刚度大,在电极活性材料充放电时不能始终保持与活性材料的有效接触,可能导致活性颗粒和电解质的界面分层．因此,解释这些现象并提供解决策略对促进全固态锂电池的广泛应用至关重要．本文旨在总结近年来关于全固态锂电池不同界面处机械失效的力化耦合模型,主要包括以下两个方面：(1) 锂金属负极与固态电解质界面处锂枝晶的形成与生长;(2) 活性颗粒锂化/脱锂化引起的界面分层和破裂．本文从理论模型的角度总结了全固态锂离子电池中不同界面上的机械失效行为,旨在为全固态锂离子电池的模型建立与结构优化提供借鉴思路．     

A theory and a simulation capability for the growth of a solid electrolyte interphase layer at an anode particle in a Li-ion battery

A major mechanism for electrochemical aging of Li-ion batteries is the growth of a solid electrolyte interphase (SEI) layer on the surface of anode particles, which leads to capacity fade and also results in a rise in cell resistance. We have formulated a continuum theory for the growth of an SEI layer—a theory which accounts for the generation of the attendant growth stresses. The theory has been numerically implemented in a finite-element program. This simulation capability for SEI growth is coupled with our previously published chemo-mechanical simulation capability for intercalation of Li-ions in electrode particles. Using this new combined capability we have simulated the formation and growth of an SEI layer during cyclic lithiation and delithiation of an anode particle, and predicted the evolution of the growth stresses in the SEI layer. The evolution of the stress state within the SEI layer and at the SEI/anode-particle interface for spherical- and spheroidal-shaped graphite particles is studied. This knowledge of the local interfacial stresses provides a good estimate for the propensity of potential delamination of an SEI layer from an anode particle.     

Atomic-scale simulations for lithium dendrite growth driven by strain gradient

Dendrite formation is a major obstacle, e.g., capacity loss and short circuit, to the next-generation high-energy-density lithium (Li)-metal batteries. The development of successful Li dendrite mitigation strategies is impeded by an insufficient understanding in Li dendrite growth mechanisms. The Li-plating-induced internal stress in Li-metal and its effects on dendrite growth have been widely studied, but the underlying microcosmic mechanism is elusive. In the present study, the role of the plating-induced stress in dendrite formation is analyzed through first-principles calculations and ab initio molecular dynamic (AIMD) simulations. It is shown that the deposited Li forms a stable atomic nanofilm structure on the copper (Cu) substrate, and the adsorption energy of Li atoms increases from the Li-Cu interface to the deposited Li surface, leading to more aggregated Li atoms at the interface. Compared with the pristine Li-metal, the deposited Li in the early stage becomes compacted and suffers the in-plane compressive stress. Interestingly, there is a giant strain gradient distribution from the Li-Cu interface to the deposited Li surface, making the deposited atoms adjacent to the Cu surface tend to press upwards with perturbation and causing the dendrite growth. This provides an insight into the atomicscale origin of Li dendrite growth, and may be useful for suppressing the Li dendrite in Li-metal-based rechargeable batteries.     

Particles in composite polymer electrolyte for solid-state lithium batteries: A review

Solid-state lithium batteries (SSLBs) have been identified as one kind of the most promising energy conversion and storage devices because of their safety, high energy density, and long cycling life. The development of solid-state electrolyte is vital to commercialize SSLBs. Composite polymer electrolyte (CPE), derived by compositing inorganic particles into solid polymer electrolyte has become the most practical species for SSLBs because it inherits the advantages of polymer electrolyte and simultaneously achieves enhanced ionic conductivity and mechanical properties. The characteristics of inorganic particles and their interaction with polymers strongly impact the performance of CPE, improving its ionic conductivity, mechanical properties, thermal and electrochemical stability, as well as interface compatibility with both electrodes. In this review, the effects of particle characteristics including its species, size, proportion, morphology on the ionic conductivity and mechanical properties of CPE are reviewed. Meanwhile, some novel composite strategies are also introduced including surface modification, hybridization, and alignment of particles in polymer matrices, as well as some new preparation methods of CPE. The interactions between particles and other components in CPE including polymer matrices or lithium salt are particularly focused herein to reveal the lithium conductive mechanism. Finally, a perspective on the direction of future CPE development for SSLBs is presented.     

A finite strain model of stress, diffusion, plastic flow, and electrochemical reactions in a lithium-ion half-cell

We formulate the continuum field equations and constitutive equations that govern deformation, stress, and electric current flow in a Li-ion half-cell. The model considers mass transport through the system, deformation and stress in the anode and cathode, electrostatic fields, as well as the electrochemical reactions at the electrode/electrolyte interfaces. It extends existing analyses by accounting for the effects of finite strains and plastic flow in the electrodes, and by exploring in detail the role of stress in the electrochemical reactions at the electrode-electrolyte interfaces. In particular, we find that that stress directly influences the rest potential at the interface, so that a term involving stress must be added to the Nernst equation if the stress in the solid is significant. The model is used to predict the variation of stress and electric potential in a model 1-D half-cell, consisting of a thin film of Si on a rigid substrate, a fluid electrolyte layer, and a solid Li cathode. The predicted cycles of stress and potential are shown to be in good agreement with experimental observations.     

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.     

Effect of prestress on the stability of electrode–electrolyte interfaces during charging in lithium batteries

We formulate a model of the growth of electrode–electrolyte interfaces in lithium batteries in the presence of an elastic prestress. The model accounts for the kinetics of Li⁺ transport through a solid electrolyte and, within the interface, for the kinetics of Li⁺ adsorption by the anode, electrostatics, and the elastic field. We specifically account for the effect of the elastic field through an asymptotic analysis of a nearly flat interface between two semi-infinite elastic bodies. We use the model as a basis for assessing the effect of prestress on the stability of planar growth and the potential of prestress as a means of suppressing the formation of deleterious dendrites. We present a linear stability analysis that results in explicit analytical expressions for the dependence of growth rates, and of the critical unstable wavelength for the interfacial roughening, on the state of prestress and on fundamental parameters such as surface diffusivities, surface energy, deposition kinetics, and elastic moduli. Finally, we examine the model in the light of experimental observations concerned with the effect of applied pressure on a lithium/dioxolane-dimethoxy ethane electrolyte systems. With reasonable choices of parameters and some calibration, the model accounts for the observation that a modest applied pressure indeed results in a substantial reduction in the roughening of the lithium surface during cycling.     

高熵合金的力学性能及变形行为研究进展

高熵合金是近年来提出的一种新的合金设计理念,打破了一般合金中以1种或2种元素为主,辅以极少量其他元素来改善合金性能的传统思想,由多种元素以等原子或近似等原子比混合后形成具有独特原子结构特征的单一固溶体合金.高熵合金的多主元特性使其在变形过程中表现出多重机制(包括位错机制、形变孪生、相变等)的协同,因而高熵合金已经展示了优异的力学性能,如高强、高硬、高塑性、抗高温软化、抗辐照、耐磨等,被认为是最具有应用潜力的新型高性能金属结构材料,已经成为国际固体力学和材料科学领域研究的热点.本文首先介绍了高熵合金独特的结构特征, 即具有短程有序结构和严重的晶格畸变;随后对近年来针对不同类型高熵合金(包括具有面心立方相、体心立方相、密排六方相、多相以及亚稳态高熵合金)力学性能、变形行为方面的研究成果,特别是强韧化机制以及相关的原子尺度模拟, 进行了较为系统的综述;最后强调了高熵合金未来研究中所面临的一些主要问题和挑战,并对其研究进行了展望.      

表面改性技术在微动摩擦学领域中的应用

对近年来国内外在采用表面改性技术改善材料的抗微动损伤性能方面的研究和进展作了简要的综述。分析了各种表面改性层在微动摩擦学中的应用和作用机制。指出采用多种表面改性手段，如表面机械强化，表面化学处理及表面涂覆等可不同程度地提高材料的抗微动损伤性能，延长零件的服役寿命。     

轻质夹层材料的制备和振动声学性能

轻质夹层材料被广泛地用来制备动车组车体和飞机的机身,其结构设计面临着一系列挑战:即同时要求质量轻、力学强度高、散热性能好、动力学性能和隔声性能可调等多功能特性.针对动车组高速运行和飞机飞行过程中经常面临的振动及噪声问题,以及如何在现有的材料和结构基础上进一步减轻重量并获得更优良的综合性能是材料制备、固体力学、流体力学、声学、智能材料和结构、优化设计等诸多领域工作者面临的共同挑战.结合近年来围绕"超轻多孔结构创新构型的多功能化基础研究"国家基础研究计划项目所开展的一系列工作,综述了有关轻质三明治材料及结构振动和声学特性的国内外研究进展及现状,以及相应的主被动控制技术;针对目前存在的问题,讨论并展望了有关轻质材料和结构动力学性能及隔声性能的研究发展趋势.     

A review on wall slip in high solid dispersions

High solid dispersions are soft materials made of colloidal or non-colloidal particles dispersed at high volume fractions in a liquid matrix. They include hard sphere glasses, colloidal pastes, concentrated emulsions, foams, and vesicles. These materials are prone to exhibit different kinds of flow heterogeneities: shear banding, wall slip, and fracture. While wall slip is often considered as a nuisance by experimentalists, it appears to be a fundamental component to the way that high solid dispersions respond to mechanical deformation. Moreover, the ability of soft materials to slip onto surfaces allows them to move readily and efficiently in many natural phenomena and industrial processes. This review surveys recent developments and current research in the field. Topics like wall slip detection and control, microscopic modeling for rigid and soft particles materials, and the relation between wall slip and other flow heterogeneities are discussed. We also identify important open issues for future research.     

PERSPECTIVES IN MECHANICS OF HETEROGENEOUS SOLIDS

The Microand Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives,trends,and directions in mechanics of heterogeneous materials in January 2010.The international journal,Acta Mechanica Solida Sinica,is devoted to all fields of solid mechanics and relevant disciplines in science,technology,and engineering,with a balanced coverage on analytical,experimental,numerical and applied investigations.On the occasion of the 30 th anniversary of Acta Mechanica Solida Sinica,its editor-in-chief,Professor Q.S.Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids,with a particular emphasis on the recent research development results of Chinese scientists.Their reviews are organized into five research areas as reported in different sections of this paper.§I firstly brings in focus on microand nano-mechanics,with regards to several selective topics,including multiscale coupled models and computational methods,nanocrystal superlattices,surface effects,micromechanical damage mechanics,and microstructural evolution of metals and shape memory alloys.§II shows discussions on multifield coupled mechanical phenomena,e.g.,multi-fields actuations of liquid crystal polymer networks,mechanical behavior of materials under radiations,and micromechanics of heterogeneous materials.In §III,we mainly address the multiscale mechanics of biological nanocomposites,biological adhesive surface mechanics,wetting and dewetting phenomena on microstructured solid surfaces.The phononic crystals and manipulation of elastic waves were elaborated in §IV.Finally,we conclude with a series of perspectives on solid mechanics.This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development.     

Prediction of turbulent gas–solids flow in curved ducts using the Eulerian–Lagrangian method

The flow of particulate two‐phase flow mixtures occur in several components of solid fuel combustion systems, such as the pressurised fluidised bed combustors (PFBC) and suspension‐fired coal boilers. A detailed understanding of the mixture characteristics in the conveying component can aid in refining and optimising its design. In this study, the flow of an isothermal, dilute two‐phase particulate mixture has been examined in a high curvature duct, which can be representative of that transporting the gas–solid mixture from the hot clean‐up section to the gas turbine combustor in a PFBC plant. The numerical study has been approached by utilising the Eulerian–Lagrangian methodology for describing the characteristics of the fluid and particulate phases. By assuming that the mixture is dilute and the particles are spherical, the governing particle momentum equations have been solved with appropriately prescribed boundary conditions. Turbulence effects on the particle dispersion were represented by a statistical model that accounts for both the turbulent eddy lifetime and the particle transit time scales. For the turbulent flow condition examined it was observed that mixtures with small particle diameters had low interphase slip velocities and low impaction probability with the pipe walls. Increasing the particle diameters (>50 μm) resulted in higher interphase slip velocities and, as expected, their impaction probability with the pipe walls was significantly increased. The particle dispersion is significant for the smaller sizes, whereas the larger particles are relatively insensitive to the gas turbulence. The main particle impaction region, and locations most prone to erosion damage, is estimated to be within an outer duct length of two to six times the duct diameter, when the duct radius of curvature to the duct diameter ratio is equal to unity. Copyright © 1999 John Wiley & Sons, Ltd.     

润滑油极压抗磨添加剂的复合效应及其与固体润滑剂和表面改性层的协同作用

随着现代科学技术的进步，机器设备正日益向高速、重载和高精度的方向发展，因此，如何改善材料的摩擦磨损性能和机器零件的润滑状态，以延长机器设备的使用寿命，已经受到摩擦学工作者的广泛关注，在基础润滑油中加入各种添加剂是改善其润滑性能的重要方法，而对材料表面进行改性处理则是改善其摩擦磨损性能的有效方法。若将这两种方法配合使用，可能获得更好的实用效果，然而有关的研究工作还很不深入和系统。基于这种情况，对润滑油极压抗磨添加剂的复合效应及其分别与固体润滑剂和表面改性层的协同作用研究的现状进行了综合介绍与评述，并且提出了当前值得重视的一些研究内容。     

固体跨尺度压痕标度律的研究与展望

压痕标度律是对通过压痕试验方法测定固体材料力学性能参量问题所给出的一般性结论, 具有重要的理论意义, 是探寻材料力学性能潜在规律的方法论研究. 本综述论文系统而简要地介绍如下主要内容: 采用传统理论对传统固体材料压痕标度律的研究回顾; 采用跨尺度力学理论对先进固体材料的跨尺度压痕标度律的研究回顾. 总结并得到了如下主要结论: 传统固体材料压痕标度律可由一空间曲面完整描绘, 若进一步已知某类无量纲独立参量的取值范围, 则该空间曲面可退化为系列平面曲线族; 先进固体材料(新材料)的跨尺度压痕标度律可由一个三维函数关系完整描绘, 若存在某类独立无量纲参量取值范围已知, 则该三维函数关系将退化为系列空间曲面族. 压痕标度律的未来研究发展仍将重点集中在建立新材料的跨尺度压痕标度律上, 以试图从根本上解决新材料力学性能标准规范难以建立的理论问题. 除此之外也将重点关注建立各类功能新材料的多尺度及跨尺度压痕标度律规律.      

Rapid determination of iron oxide content in magnetically modified particulate materials

Magnetically responsive composite materials have been used in interesting applications in various areas of bioscience, biotechnology, and environmental technology. In this work, a simple method to determine the amount of magnetic iron oxide nano- and microparticles attached to magnetically-modified particulate diamagnetic materials has been developed using a commercially available magnetic permeability meter. The procedure is fast and enables dry particulate magnetically modified materials to be analysed without any modification or pretreatment. We show that the magnetic permeability can be measured for materials containing up to 20% magnetic iron oxide. The magnetic permeability measurements are highly reproducible.     

单晶硅表面改性及其微观摩擦学性能研究进展

评述了单晶硅表面改性及其微观摩擦磨损性能研究现状和进展,就单晶硅微观机械性能和摩擦磨损性能、单晶硅表面沉积薄膜和氧化层的微观机械和摩擦学性能及硅材料表面离子注入和表面纳米化等相关研究进行了归纳总结;指出应当继续深化硅材料表面改性技术及改性层微观摩擦学性能的研究,特别是应当加强硅材料表面离子注入及表面纳米化的研究,从而满足MEMs／NEMs等高技术领域的应用和发展需要．     

Micromechanical modeling of packing and size effects in particulate composites

This paper is devoted to the introduction of packing and size effects in micromechanical predictions of the overall elastic moduli of particulate composite materials. Whereas micromechanical models derived from the classical ‘point approach’ are known to be unable to model such effects, it is shown that the so-called ‘morphologically representative pattern-based approach’ (MRP-based approach) offers new means of taking some geometrical parameters into account such as the mean distance between nearest-neighbor particles or their size, so as to predict the dependence of the overall moduli on these parameters, at least in a relative way. Moreover, when internal lengths, such as the thickness of interphase shells of coated particles, are introduced, absolute size effects can be predicted as well. Illustrative applications are reported in view of comparisons between such new treatments and the predictions of some classical models which are shown to coincide with the ones derived from MRP-based models in definite limiting cases only.     

Mathematical analysis of SOFC based on co-ionic conducting electrolyte

In co-ionic conducting solid oxide fuel cell (SOFC), both oxygen ion (O2) and proton (H+) can transport through the electrolyte, generating steam in both the an-ode and cathode. Thus the mass transport phenomenon in the electrodes is quite different from that in conventional SOFC with oxygen ion conducting electrolyte (O-SOFC) or with proton conducting electrolyte (H-SOFC). The generation of steam in both electrodes also affects the concentration over-potential loss and further the SOFC performance. However, no detailed modeling study on SOFCs with co-ionic electrolyte has been reported yet. In this paper, a new mathematical model for SOFC based on co-ionic electrolyte was developed to predict its actual performance considering three major kinds of overpotentials. Ohm’s law and the Butler-Volmer formula were used to model the ion conduction and electrochemical reactions, respectively. The dusty gas model (DGM) was employed to simulate the mass transport processes in the porous electrodes. Parametric simulations were performed to investigate the effects of proton transfer number (tH) and current density (jtotal) on the cell performance. It is interesting to find that the co-ionic conducting SOFC could perform better than O-SOFC and H-SOFC by choosing an appropriate proton transfer number. In addition, the co-ionic SOFC shows smaller difference between the anode and cathode concentration overpotentials than O-SOFC and H-SOFC at certain t H values. The results could help material selection for enhancing SOFC performance.