Particulate modification of lithium-ion battery anode materials and electrolytes

Lithium-ion batteries (LIBs) are considered a rechargeable and commercial energy storage device for electronic equipment such as smartphone and electric vehicles. Despite the prospective future of LIBs, unsatisfied electrochemical properties like reversible capacity, cycle ability and coulombic efficiency still hinder their development. High volume expansion rate, uncontrolled Li dendrite growth and unsatisfied solid electrolyte interphase also occur when LIBs are applied in long-time usage. Numerous modification methods such as exploring high-capacity anode/cathode materials, constructing artificial solid electrolyte interphase and improved conductive binders can be adopted to enhance the performances. Among them, particulate modification for LIBs anode and electrolytes is receiving tremendous attraction in the recent work. The method is composed of changing the morphology and particle size of the active materials, also introduce nano-size additives to the main structure. This review emphasizes on introducing and discussing the modification in following aspects: particulate modification on carbon group IVA element anodes, introduction of additives like transition metal oxide nanoparticles into anode and electrolyte materials, dissipate the influence of Li dendrite growth and ameliorate the performances of solid electrolyte interface. This review hopes to be denoted for the future development of LIBs with the comprehensive understanding on the particulate modification.     

Crushing of particles in idealised granular assemblies

Four idealised assemblies of equally sized spherical particles are subjected to a range of macroscopic compressive principal stresses and the contact forces on individual particles are determined. For each set of contact forces the stress fields within individual particles are studied. A failure criterion for brittle materials is imposed and indicates that crushing (or rupture) occurs when the maximum contact force reaches a threshold particle strength value, irrespective of the presence and magnitude of other lesser contact forces acting on the particle and the material properties of the particle. Combining the crushing mechanism with an assembly instability mechanism enables failure surfaces to be drawn in the three-dimensional stress space. A simple spatial averaging technique has been applied to the failure surfaces to remove the effects of assembly anisotropies. Sections of the failure surfaces on π planes have similarities to those commonly used in sand modelling.     

Particle size effect on heat transfer performance in an oscillating heat pipe

The effect of Al₂O₃ particles on the heat transfer performance of an oscillating heat pipe (OHP) was investigated experimentally. Water was used as the base fluid for the OHP. Four size particles with average diameters of 50 nm, 80 nm, 2.2 μm, and 20 μm were studied, respectively. Experimental results show that the Al₂O₃ particles added in the OHP significantly affect the heat transfer performance and it depends on the particle size. When the OHP was charged with water and 80 nm Al₂O₃ particles, the OHP can achieve the best heat transfer performance among four particles investigated herein. In addition, it is found that all particles added in the OHP can improve the startup performance of the OHP even with 20 μm Al₂O₃ particles.     

Lattice–Boltzmann simulations for analysing the detachment of micron-sized spherical particles from surfaces with large-scale roughness structures

Fully resolved numerical simulations of a micron-sized spherical particle residing on a surface with large-scale roughness are performed by using the Lattice–Boltzmann method. The aim is to investigate the influence of surface roughness on the detachment of fine drug particles from larger carrier particles for transporting fine drug particles in a DPI (dry powder inhaler). Often the carrier surface is modified by mechanical treatments for modifying the surface roughness in order to reduce the adhesion force of drug particles. Therefore, drug particle removal from the carrier surface is equivalent to the detachment of a sphere from a rough plane surface. Here a sphere with a diameter of 5 μm at a particle Reynolds number of 1.0, 3.5 and 10 are considered. The surface roughness is described as regularly spaced semi-cylindrical asperities (with the axes oriented normal to the flow direction) on a smooth surface. The influence of asperity distance and size ratio (i.e. the radius of the semi-cylinder to the particle radius, R_c/R_d) on particle adhesion and detachment are studied. The asperity distance is varied in the range 1.2 < L/R_d < 2 and the semi-cylinder radius between 0.5 < R_c/R_d < 0.75. The required particle resolution and domain size are appropriately selected based on numerical studies, and a parametric analysis is performed to investigate the relationship between the contact distance (i.e. half the distance between the particle contact points on two neighbouring semi-cylinders), the asperity distance, the size ratio, and the height of the particle centroid from the plane wall. The drag, lift and torque acting on the spherical particle are measured for different particle Reynolds numbers, asperity distances and sizes or diameters. The detachment of particles from rough surfaces can occur through lift-off, sliding and rolling, and the corresponding detachment models are constructed for the case of rough surfaces. These studies will be the basis for developing Lagrangian detachment models that eventually should allow the optimisation of dry powder inhaler performance through computational fluid dynamics.     

孤立波与半无限复合材料体耦合作用研究

基于一维颗粒链中产生的高度非线性孤立波,研究孤立波与半无限复合材料体的耦合作用。根据赫兹定律推导了一维颗粒链中颗粒间相互作用的运动微分方程,建立了颗粒链与半无限复合材料体的接触模型。对于颗粒与复合材料的接触,采用已有文献中修正后的赫兹定律,研究了高度非线性孤立波与半无限复合材料体的耦合力学作用机理,推导了颗粒链与半无限复合材料体的相互耦合运动微分方程组,通过数值计算,得到了各颗粒的内力、速度、位移曲线。分析了材料属性对回弹孤立波出现的时间、幅值的影响。结果表明:随着纤维方向弹性模量的增大,次级回弹波出现的时间和波幅都逐渐增大,随着垂直纤维方向弹性模量的增大,次级回弹波出现的时间先减小后增大,次级回弹波的幅值逐渐减小直至消失。     

A nonlocal species concentration theory for diffusion and phase changes in electrode particles of lithium ion batteries

A nonlocal species concentration theory for diffusion and phase changes is introduced from a nonlocal free energy density. It can be applied, say, to electrode materials of lithium ion batteries. This theory incorporates two second-order partial differential equations involving second-order spatial derivatives of species concentration and an additional variable called nonlocal species concentration. Nonlocal species concentration theory can be interpreted as an extension of the Cahn–Hilliard theory. In principle, nonlocal effects beyond an infinitesimal neighborhood are taken into account. In this theory, the nonlocal free energy density is split into the penalty energy density and the variance energy density. The thickness of the interface between two phases in phase segregated states of a material is controlled by a normalized penalty energy coefficient and a characteristic interface length scale. We implemented the theory in COMSOL Multiphysics\(^{\circledR }\) for a spherically symmetric boundary value problem of lithium insertion into a \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\) cathode material particle of a lithium ion battery. The two above-mentioned material parameters controlling the interface are determined for \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\), and the interface evolution is studied. Comparison to the Cahn–Hilliard theory shows that nonlocal species concentration theory is superior when simulating problems where the dimensions of the microstructure such as phase boundaries are of the same order of magnitude as the problem size. This is typically the case in nanosized particles of phase-separating electrode materials. For example, the nonlocality of nonlocal species concentration theory turns out to make the interface of the local concentration field thinner than in Cahn–Hilliard theory.     

Effect of particle size distribution on micro- and macromechanical response of granular packings under compression

The role of particle size heterogeneity on micro- and macromechanical properties of assemblies of spherical particles was studied using DEM simulations. The response to an imposed load of a granular material composed of non-uniformly sized spheres subjected to uniaxial confined compression was investigated. A range of geometrical and micro-mechanical properties of granular packings (e.g., void fraction, contact force distribution, average coordination number and degree of mobilisation of friction at contacts between particles) were examined, and provided a more accurate interpretation of the macroscopic behaviour of mixtures than has previously been available. The macromechanical study included stress transmission, stiffness and angle of internal friction of the granular assemblies.The degree of polydispersity showed slight effect on both, the void fraction and the elastic properties of the system. The tendency for increase in the lateral-to-vertical pressure ratios was observed with an increasing degree of particle size heterogeneity; however, the different pressure ratios calculated for samples with various degrees of polydispersity lay within the range of data scatter.     

DEM analysis of the effect of electrostatic interaction on particle mixing for carrier-based dry powder inhaler formulations

Particle interactions play a significant role in controlling the performance of dry powder inhalers (DPIs), which mainly arise through van der Waals potentials, electrostatic interactions, and capillary forces. Our aim is to investigate the influence of electrostatic charge on the performance of DPIs as a basis for improving the formulation of the particle ingredients. The mixing process of carrier and active pharmaceutical ingredient (API) particles in a vibrating container is investigated using a discrete element method (DEM). The number of API particles attaching to the carrier particle (i.e., contact number) increases with increasing charge and decreases with increasing container size. The contact number decreases with increasing vibrational velocity amplitude and frequency. Moreover, a mechanism governed by the electrostatic force is proposed for the mixing process. This mechanism is different from that previously proposed for the mixing process governed by van der Waals forces, indicating that long-range and short-range adhesive forces can result in different mixing behaviours.     

Effect of drum structure on particle mixing behavior based on DEM method

The optimization of the drum structure is beneficial to improve the particle motion and mixing in rotary drums. In this work, two kinds of drum structures, Lacy cylinder drum (LC) and Lacy-lifters cylinder drum (LLC), are developed on the basic of cylinder drum to enhance the heat transfer area. The particle motion and mixing process are simulated by DEM method. Based on the grid independence and model validation, the contact number between particles and wall, particle velocity profile, thickness of active layer, particle exchange coefficient, particle concentration profile and mixing index are demonstrated. The influences of the drum structure and the operation parameters are further evaluated. The results show that the contact number between particles and wall is improved in LC and LLC compared to cylinder drum. The particle velocity in LC is higher than that in cylinder drum at high rotating speed, and the particle velocity of the particle falling region is significantly improved in LLC. Compared to cylinder drum and LC, the thickness of active layer in LLC is smaller, while the local particle mixing quality is proved to be the best in the active region. In addition, the particle exchange coefficients between static region and active region in the three drums are compared and LLC is found tending to weaken the particle flow. Besides, the fluctuations of particle concentration in the active region, static region, and boundary region are weakened in LLC, and the equilibrium state is reached earlier. In addition, the overall particle mixing performance in cylinder drum, LC and LLC is analyzed. The particle mixing performance in cylinder drum is the worst, while the difference in mixing quality of LC and LLC depends on the operation conditions.     

Pozzolanic reactivity of silico-aluminous fly ash

For some years it has been possible to control the particle size of fly ashes, by-products of thermal power stations. Incorporating these very fine particles （obtained by grinding and/or pneumatic selection） improves the physical-mechanical characteristics of mortars and concretes. In this study, we measured the lime consumption of the various fractions （granulometric and densimetric） and identified by X-ray diffraction the neoformed phases by the pozzolanic reaction, to show that it is not sufficient to simply define the pozzolanicity of products based on lime consumption since it does not take into account the nature of the phases formed. The size of the particles used in the test samples also has a determining effect on the quantity of lime consumed. Before comparing results, it is necessary to ensure that the size of the particles （of the global ash and its constituents） be the same. Two distinct neoformed ohases appear： CSH in the largest granular fractions （d〉 40 μm） and C3AH6 in the smaller fractions.     

Influence of intrinsic parameters on the particle size of magnetic spinel nanoparticles synthesized by wet chemical methods

The synthesis of magnetic spinel ferrites at the nanoscale is a field of intense study, because the mesoscopic properties enable their novel applications. Spinel nanoparticles have a promising role because of their extraordinary properties compared with those of micro and macro scale particles. Several colloidal chemical synthetic procedures have been developed to produce monodisperse nanoparticles of spinel ferrites and other materials using sol–gel, co-precipitation, hydrothermal, and microemulsion techniques. To improve the synthesis method and conditions, quality and productivity of these nanoparticles, understanding the effect of extrinsic (pH, temperature, and molecular concentration) and intrinsic parameters (site preferences, latent heat, lattice parameters, electronic configuration, and bonding energy) on the particle size during synthesis is crucial. In this review, we discuss the effect of the intrinsic parameters on particle size of spinel ferrites to provide an insight to control their particle size more precisely.     

Effects of deformed volume, volume fraction and particle size on the deformation behaviour of W/Cu composites

Tungsten/copper (W/Cu) particle reinforced composites were used to investigate the scaling effects on the deformation and fracture behaviour. The effects of the volume fraction and the particle size of the reinforcement (tungsten particles) were studied. W/Cu-80/20, 70/30 and 60/40 wt.% each with tungsten particle size of 10 μm and 30 μm were tested under compression and shear loading. Cylindrical compression specimens with different volumes (D_S = H) were investigated with strain rates between 0.001 s⁻¹ and about 5750 s⁻¹ at temperatures from 20 °C to 800 °C. Axis-symmetric hat-shaped shear specimens with different shear zone widths were examined at different strain rates as well. A clear dependence of the flow stress on the deformed volume and the particle size was found under compression and shear loading. Metallographic investigation was carried out to show a relation between the deformation of the tungsten particles and the global deformation of the specimens. The size of the deformed zone under either compression or shear loading has shown a clear size effect on the fracture of the hat-shaped specimens.The quasi-static flow curves were described with the material law from Swift. The parameters of the material law were presented as a function of the temperature and the specimen size. The mechanical behaviour of the composite materials were numerically computed for an idealized axis-symmetric hat-shaped specimen to verify the determined material law.     

Coupling Effect of State-of-Health and State-of-Charge on the Mechanical Integrity of Lithium-Ion Batteries

Two governing factors that influence the electrochemical behaviors of lithium-ion batteries (LIBs), namely, state of charge (SOC) and state of health (SOH), are constantly interchanged, thus hindering the understanding of the mechanical integrity of LIBs. This study investigates the electrochemical failure of LIBs with various SOHs and SOCs subjected to abusive mechanical loading. Comprehensive experiments on LiNi_0.8CoO₁₅Al_0.05O₂ (NCA) LIB show that SOH reduction leads to structural stiffness and that the change trend varies with SOC value. Low SOH, however, may mitigate this phenomenon. Electrochemical failure strain at short circuit has no relationship with SOC or SOH, whereas failure stress increases with the increase of SOC value. Experiments on three types of batteries, namely, NCA, LiCoO₂ (LCO), and LiFePO₄ (LFP) batteries, indicate that their mechanical behaviors share similar SOH-dependency properties. SOH also significantly influences failure stress, temperature increase, and stiffness, whereas its effect on failure strain is minimal. Results may provide valuable insights for the fundamental understanding of the electrochemically and mechanically coupled integrity of LIBs and establish a solid foundation for LIB crash-safety design in electric vehicles.     

Neighborhood Relationships of Widely Distributed and Irregularly Shaped Particles in Partially Dewatered Filter Cakes

A more thorough understanding of the properties of bulk material structures in solid–liquid separation processes is essential to understand better and optimize industrially established processes, such as cake filtration, whose process outcome is mainly dependent on the properties of the bulk material structure. Here, changes of bulk properties like porosity and permeability can originate from local variations in particle size, especially for non-spherical particles. In this study, we mix self-similar fractions of crushed, irregularly shaped Al₂O₃ particles (20 to 90 µm and 55 to 300 µm) to bimodal distributions. These mixtures vary in volume fraction of fines (0, 20, 30, 40, 50, 60 and 100 vol.%). The self-similarity of both systems serves the improved parameter correlation in the case of multimodal distributed particle systems. We use nondestructive 3D X-ray microscopy to capture the filter cake microstructure directly after mechanical dewatering, whereby we give particular attention to packing structure and particle–particle relationships (porosity, coordination number, particle size and corresponding hydraulic isolated liquid areas). Our results reveal widely varying distributions of local porosity and particle contact points. An average coordination number (here 5.84 to 6.04) is no longer a sufficient measure to describe the significant bulk porosity variation (in our case, 40 and 49%). Therefore, the explanation of the correlation is provided on a discrete particle level. While individual particles?<?90 µm had only two or three contacts, others?>?100 µm took up to 25. Due to this higher local coordination number, the liquid load of corresponding particles (liquid volume/particle volume) after mechanical dewatering increases from 0.48 to 1.47.

     

Effect of coal particle swarm properties on the fluidization characteristics and coal beneficiation in a dense-phase gas–solid fluidized bed

This paper analyzes the influence of different coal mass fraction in an air dense medium fluidized bed (ADMFB). The effect of the low density particles layer on heavy sedimentation increased with increasing material layer thickness. The thickness of the low density particles layer also affected the final settling time of the high density particles. Increasing the thickness of the low density particles layer by Δh provoked an increase in the settling of high density particles that was related to their diameter (Δh/D). The pressure gradient across the bed was lower than that observed for the control experiment, which had only the dense material, owing to a decrease in the pressure gradient in Zones 1 and 5 (at the top and bottom of the bed, respectively). Introducing different coal sizes resulted in different fluidization environments, particle accumulation layers, and changes to the surrounding zone. However, the influence of the coal particles on the local bed characteristics was related to its concentration. The feeding mass fraction of 6–13 mm size and 13–25 mm size coal should be limited to10% and 13%, respectively. The ranges of possible deviation were found to be 0.08–0.15 and 0.07–0.10 for the respective samples.     

Diffusion induced stresses in buckling battery electrodes

Highly networked nanostructured battery electrode materials offer the possibility of achieving both rapid battery charge–discharge rates and high storage capacity. Recently, lithium ion battery (LIB) electrodes based on a 2-D honeycomb architecture were shown to undergo remarkable and reversible morphological changes during the lithiation process. Charge–discharge rates in 3-D composite electrode have also been shown to benefit from sandwiching the electrolytically active material between highly conductive ion and electron transport pathways to reduce electrical resistance and solid-state diffusion lengths. In the present work we simulate and analyze the observed morphological changes in honeycomb electrodes, with and without the presence of conductive pathways, during the lithiation–delithiation process. Diffusion induced stresses are analyzed for such structures undergoing elastic–plastic deformation during cycling. The results show that such a periodic, nanostructured electrode geometry allows for the presence of buckling-like deformation modes, which effectively reduce the resulting mechanical stresses that lead to electrode failure.     

Preparation and characterization of LiAlxCoyNi1-x-yO2 particles

Lithium-aluminum-cobalt-nickel oxide (LiAlxCoyNi1-x-yO2) particles, generally used as cathode of lithium battery, were prepared by chemical coprecipitation from an aqueous solution of LiOH, AI(NO3)3, Co(NO3)2 and Ni(NO3)2 with NH4OH. XRD, SEM and FTIR were used to examine the effect of nickel content on the product. FHR patterns showed that increase in nickel content decreased the absorption strength of the peak of spinel structure of the product, attributed to the occupation by nickel in the aluminum sites. Particle size and electrical properties of the lithium-aluminum-cobalt-nickel oxide (abbreviated as LACNO) particles were also determined.     

基于统一相场理论的锂电池电极颗粒断裂模拟研究

锂电池充放电过程中, 锂离子的脱出和嵌入会引发电极颗粒的不均匀体积变化和机械应力. 上述锂离子扩散过程诱发的应力与电极颗粒的尺寸大小、截面形状和冲放电速率有关, 可能会导致电极颗粒出现裂缝起裂、扩展甚至断裂等力学失效, 对锂离子电池的容量和循环寿命等性能产生不利影响. 为准确模拟并预测电极颗粒的力学失效过程, 在笔者前期提出的统一相场理论框架内进一步考虑化学扩散、力学变形和裂缝演化等耦合过程, 建立化学–力学耦合相场内聚裂缝模型, 发展相应的多场有限元数值实现算法, 并应用于二维柱状和三维球体锂电池电极颗粒的力学失效分析. 由于同时涵括了基于强度的起裂准则、基于能量的扩展准则以及基于变分原理的裂缝路径判据, 这一模型不仅适用于带初始缺陷电极颗粒的开裂行为模拟, 而且适用于无初始缺陷电极颗粒的损伤破坏全过程分析. 数值计算结果表明, 相场内聚裂缝模型能够模拟锂离子扩散引发的电极颗粒裂缝起裂、扩展、汇聚等复杂演化过程, 可为锂离子电池电极颗粒的力学失效预测和优化设计提供有益的参考.      

轮胎磨损颗粒物形貌及产生机理的实验研究

采用自行设计的磨损试验机采集轮胎-路面摩擦副产生的轮胎磨损颗粒物,通过光学显微镜和扫描电子显微镜(SEM)分析和讨论了不同负载、速度和胎压工况影响下磨损颗粒物的表面形貌、粒度及磨损胎面形貌,建立了磨损颗粒物与胎面磨损形态的关系.结果表明:轮胎磨损颗粒物的粒度和数量类似正态分布,粒度主要集中在100~300μm.轮胎磨损颗粒物的主要产生机理是胎面疲劳剥落,形式主要为片状剥落和卷曲磨损共存,卷曲磨损会导致更多的磨损颗粒物脱离.载荷可使两种磨损形式的主导地位发生转变.接触界面应力提高会使团絮状胎面磨损颗粒物增多,速度增大会明显减小磨损颗粒物粒度.对小于10μm颗粒物来说,工况对其数量影响的主次顺序依次为速度、胎压和载荷.本研究可以为减少因轮胎磨损而导致的磨屑次生危害提供可供借鉴的理论指导.     

Numerical simulation study on particle breakage behavior of granular materials in confined compression tests

In order to study the fragmentation law, the confined compression experiment of granular assemblies has been conducted to explore the particle breakage characteristic by DEM approach in this work. It is shown that contact and contact force during the loading process gradually transform from anisotropy to isotropy. Meanwhile, two particle failure modes caused by different contact force states are analyzed, which are single-through-crack failure and multi-short-crack failure. Considering the vertical distribution of the number of cracks and the four characteristic stress distributions (the stress related to the maximum contact force, the major principal stress, the deviatoric stress and the mean stress), it is pointed out that the stress based on the maximum contact force and the major principal stress can reflect the distribution of cracks accurately. In addition, the size effect of particle crushing indicates that small size particles are prone to break. The lateral pressure coefficient of four size particles during the loading process is analyzed to explain the reason for the size effect of particle breakage.