聚合物热裂解碳材料结构对电化学性能的影响

近年来 ,对各种碳材料如天然石墨、焦炭、碳纤维、非石墨碳、裂解碳、掺杂型碳等用于锂离子二次电池的负极已进行了广泛的研究[17].随着碳材料来源和制备方法的不同 ,其形态和结构差异很大 ,这些宏观和微观结构的变化对锂离子电池碳负极的电化学性能有很大影响 .也就是说锂离子在碳负极材料中的嵌入与脱出能力与碳负极的种类 (石墨碳或非石墨碳 )、形态 (如结晶或非结晶碳 )及比表面积、Ｈ/Ｃ原子比率、粒径大小及其分布、聚集态以及微晶尺寸ｄ0 0 2 、Ｌａ、Ｌｃ 等物理参数均有密切关系 .由于碳材料本身结构的复杂性及其形态的多样性 ,目…     

锂离子电池高容量合金复合负极材料的研究新进展

随着锂离子电池的应用范围向薄膜电池、储能和动力电池等方面扩展,对电池的能量密度和使用寿命提出了更高的要求,电极材料是决定这些性能的关键.目前商业化的锂离子电池负极材料主要是中间相炭微球和改性石墨.它们的比容量,尤其是体积比容量不够高.     

尖晶石LiNi0.5Mn1.5O4正极材料首周充放电过程的结构与动力学研究

以NaOH为沉淀剂,采用共沉淀法制备尖晶石LiNi_0.5Mn_1.5O₄正极材料,使用X-射线衍射（XRD）、傅里叶转换红外光谱（FTIR）和扫描电镜（SEM）分析材料结构与表面形貌. 结果表明,该材料属于空间群的无序尖晶石LiNi_0.5Mn_1.5O₄材料,由八面体粒子团聚成3 ~ 6 μm的大粒子. 恒电流充放电结果显示,材料在0.1C倍率下首周放电比容量为121.5 mAh·g^-1,经过150周充放电后,材料比容量无明显衰减,其容量保持率为99%. 用PITT和原位XRD联用技术研究了充放电过程中材料的结构与锂离子扩散系数之间的关系. PITT法测得材料中锂离子的扩散系数为10^-10 ~ 10^-11 cm²·s^-1.     

一维棒状ZnO的制备及电化学嵌锂性能研究

目前,商业化锂离子电池一般采用石墨作为负极材料,因其电位与金属锂电极的电位很接近,所以当电池反复循环和过充时,石墨表面易析出金属锂,会因形成枝晶而短路。在温度过高时还容易引起热失控。同时,锂离子电池的容量在很大程度上取决于负极的锂嵌入量,而且石墨材料容量相对较低     

锂离子电池高容量合金复合负极材料的研究新进展

随着锂离子电池的应用范围向薄膜电池、储能和动力电池等方面扩展，对电池的能量密度和使用寿命提出了更高的要求，电极材料是决定这些性能的关键。目前商业化的锂离子电池负极材料主要是中间相炭微球和改性石墨。它们的比容量，尤其是体积比容量不够高。而且，由于它们的嵌锂电位接近金属锂，快速充电时容易在电极表面析出锂并产生锂枝晶，有安全隐患。因此，寻求新的高性能负极材料一直是锂离子电池研究的重要方向。     

锡基复合氧化物的高能球磨法制备及其电化学性能

随着锂离子电池的发展,人们越来越多地要求可充锂离子电池电极材料具有更高的容量.许多研究小组正致力于寻找和开发能够取代现有碳材料(理论最大比容量为372 mAh·g-1)的新型负极材料[1].锡氧化物基材料由于其高的储锂容量和低的锂离子脱嵌平台电压倍受人们关注,有望作为新一代锂离子电池负极材料[2～5].通过在线X-射线研究,Courtney等[4,5]提出了这类材料作为锂离子电池负极材料的两步反应机理:在首次放电过程中,锡氧化物被不可逆地还原成金属锡,同时生成氧化锂;随后,金属锡与锂发生可逆的合金化与去合金化反应,用反应式表示如下:     

锡基非晶态材料的化学合成及其嵌锂性能的初步研究

锂离子电池是近年来化学电源领域研究与发展的热点．为了进一步提高电池的能量密度，开发高容量嵌锂材料是锂离子电池技术发展的关健．目前，广泛应用的嵌锂负极多采用石墨结构碳素材料，其充放电容量已接近ＬｉＣ６的理论比容量３７２ｍＡ·ｈ／ｇ．与此同时，采用其它类...     

基于非锂金属负极的锂离子全电池

可充电锂离子电池对于电子产品特别是手持设备的发展至关重要,其关键作用同样体现在飞速发展的电动汽车领域。此外,对电力系统的调配(削峰填谷)和新能源发电的并网也是很好的选择。但是传统锂离子电池较低的能量密度常被人诟病。传统石墨负极材料的替代物(如金属氧化物、钛基、锡基、硅基、合金等材料)能有效提高锂离子电池的容量和倍率性能,但目前缺乏充分的全电池实验数据予以证实,也鲜有新型负极材料成功用于商业化的锂离子全电池。由此可见,新型负极材料在锂离子全电池中的研究现状及其商业化应用前景等问题亟需面对和斟酌,也应受到锂离子电池研究者的广泛关注。因此,本文从负极材料首圈容量可逆/不可逆的特点着手,对基于非锂金属负极(如石墨、钛酸锂、二氧化钛、氧化锗、氧化铁、锡基、硅基等)的锂离子全电池的最新研究进行了论述。     

锂离子电池用钴基氧化物的结构设计及本征活性调控的研究进展

锂离子电池的商业石墨负极材料的容量已经接近理论值,限制了动力电池的发展,开发容量高、稳定性好、循环寿命长和倍率性能优良的新型负极材料显得尤为重要。钴基氧化物材料由于其具有较高的比容量,是锂离子电池的理想负极材料之一。本文分别从结构设计和化学成分调控2个方面,结合本课题组近年来的研究及国内外重要文献综述了钴基氧化物作为锂离子电池负极材料的研究进展。在结构设计方面,通过构建一维结构、二维结构、三维结构、空心结构、碳材料支撑结构以及异质结构来增加钴基氧化物的反应活性位点数量;而在化学成分调控方面则通过引入无定型结构、非金属杂原子掺杂、金属杂原子掺杂、构筑高熵氧化物来提高钴基氧化物的本征活性,从而提高钴基氧化物的锂离子电池性能。最后,对钴基氧化物在锂离子电池领域未来的发展进行了展望。     

锂离子电池Sn30Co30C40三元合金负极材料的制备与性能研究

随着人们对高比能量锂离子电池需求的逐步增加,Sn基合金成为目前高比容量负极材料的研究热点.以低成本的金属氧化物、活性炭为原料经碳热还原法首先合成出中间产物CoSn2,再将Co、石墨引入,经高能球磨制备了Sn30Co30C40三元合金负极材料.材料呈现微米级颗粒形貌,其内部是由均匀分散于无定形碳中10 nm左右CoSn晶粒所组成.材料的比容量为550 mAh/g左右,首次效率为80%左右,循环稳定性好、倍率性能优越,是一种非常有发展前景的高比容量锂离子电池负极材料.     

Development and experimental verification of a mathematical model of lithium ion battery

A model of the lithium ion battery is developed which takes into account intercalation and extraction of lithium ions in the active mass of negative and positive electrodes, the dependences of equilibrium electrode potentials on the concentration of intercalated lithium, the ion transfer in pores of electrodes and the separator, the kinetics of electrode reactions, and the electric double layer charging. As the active material for the negative electrode, UAMS graphite material is used. Lithium-nickel-cobalt oxide serves as the positive electrode. The porous structure of electrodes is studied by the method of standard contact porosimetry. Sufficiently high porosity values found for both electrodes (50% for anode and 27% for cathode) made it possible to consider the interface as regards the internal pore surface found from porosimetry data rather than as regards their external surface as in the previous studies. A comparison of calculated and experimental discharge curves demonstrates their closeness, which points to the correctness of the model. By the fitting procedure, the coefficients of solid-state diffusion of lithium ions and the rate constants for reactions on both electrodes are found.     

锂在碳素材料中的扩散过程研究

本文利用间歇电量滴定法(GITT)研究了锂在苯碳黑和树脂裂解碳等碳素材料中嵌入时的扩散过程, 结果表明, 锂在不同碳素材料的石墨微晶区中的扩散过程基本相似, 扩散系数在10^-^9cm^2/s数量级, 而在碳素材料的非石墨化区中的扩散则与碳素材料的结构有很大关系。     

The Diffusion Coefficient of Lithium Ions into Highly Oriented Pyrolytic Graphite

The diffusion coefficient of lithium in graphite is an important parameter for the use of graphite because it relates to the ability of charge and discharge rate of lithium battery. It remains a problem that there are often obvious differences among the diffusion coefficients obtained using different methods, even in one paper^[1,2]. This difference may attribute to the complicate properties of intercalation process, as well as some uncertain parameters of the porous structure electrode. In order to measure the diffusion coefficient of lithium in carbon more precisely, a well crystallized material Highly Oriented Pyrolytic Graphite (HOPG) was used as the material of working electrode in this study.     

Analysis of the FePO4 to LiFePO4 phase transition

The electrochemical phase transformation of carbon coated nanophase (60–70 nm) FePO₄ to LiFePO₄ was investigated by use of the Avrami–Johnson–Mehl–Eroofev equation. The analysis at three temperatures showed an Avrami exponent equal to one. Based upon reinterpretation and in agreement with recent microstructural evidence, a two-dimensional growth mechanism for the phase transformation is proposed in which the new phase grows in a direction perpendicular to the direction of lithium ion transport. Furthermore, the relatively low value of the activation energy for the phase transformation of 13 kJ/mol suggests that the phase transition is controlled by lithium ion diffusion along the phase boundary.     

Two-cation competition in ionic-liquid-modified electrolytes for lithium ion batteries

It is a common observation that when ionic liquids are added to electrolytes the performances of lithium ion cells become poor, while the thermal safeties of the electrolytes might be improved. In this study, this behavior is investigated based on the kinetics of ionic diffusion. As a model ionic liquid, we chose butyldimethylimidazolium hexafluorophosphate (BDMIPF(6)). The common solvent was propylene carbonate (PC), and lithium hexafluorophosphate (LiPF(6)) was selected as the lithium conducting salt. Ionic diffusion coefficients are estimated by using a pulsed field gradient NMR technique. From a basic study on the model electrolytes (BDMIPF(6) in PC, LiPF(6) in PC, and BDMIPF(6) + LiPF(6) in PC), it was found that the BDMI(+) from BDMIPF(6) shows larger diffusion coefficients than the Li(+) from LiPF(6). However, the anionic (PF(6)(-)) diffusion coefficients present little difference between the model electrolytes. The higher diffusion coefficient of BDMI(+) than that of Li(+) suggests that the poor C-rate performance of lithium ion cells containing ionic liquids as an electrolyte component can be attributed to the two-cation competition between Li(+) and BDMI(+).     

REDOX POTENTIALS AND DIFFUSION OF LITHIUM IN LAMELLAR COMPOUNDS

Abstract

Themodynamic and dynamic properties of intercalation products of lithium into MoS₂ are strongly determined by the coordination of lithium in the interlaminar spaces. Lithium redox potentials as well as lithium diffusion coefficients in MoS₂ pure, exfoliated, as well as in compounds where lithium is co-intercalated with the polymeric electron pair donors, poly(ethylene oxide) and poly-acrylonitrile, and discrete species, OH^? ions and secondary amines, were analyzed comparatively. Reduction potentials in pure or exfoliated MoS₂ are always much lower than those observed in lithium-donor co-intercalates. Thus, donors appear to effectively stabilize higher lithium oxidation states. The donors also influence lithium migration properties, with lithium diffusion coefficients in general higher than in pure MoS₂. Lithium diffusion activation energy in pure MoS₂ is constant in a relatively large lithium concentration range, while for co-intercalates it often depends on lithium intercalation degree. These more complex diffusion mechanisms probably arise from changes in the donor conformation in the interlaminar spaces, which affect the lithium first coordination sphere.     

Generalized Einstein relations from a three-temperature theory of gaseous ion transport

Generalized Einstein relations between mobility and diffusion coefficients are derived within the framework of a recently developed three-temperature kinetic theory of gaseous ion transport. A previously assumed connection between diffusion and differential mobility is firmly established within low-order approximations of the kinetic theory. Equations are obtained for the approximate calculation of the unobservable parallel and perpendicular ion temperatures, and for two higher moments of the ion velocity distribution function that appear as correction terms in the generalized Einstein relations. The present theory is tested on inverse-power potentials and on several alkali ion-noble gas systems, and is compared to two previous semi-empirical generalized Einstein relations. Simple procedures are recommended for the estimation of the parameters and correction terms that occur, to permit approximate calculation of gaseous ion diffusion coefficients from mobility data without the need of a computer or specific knowledge of the ion-neutral interaction potential.     

Mutual diffusion coefficients of heptane isomers in nitrogen: a molecular dynamics study

The accurate knowledge of transport properties of pure and mixture fluids is essential for the design of various chemical and mechanical systems that include fluxes of mass, momentum, and energy. In this study we determine the mutual diffusion coefficients of mixtures composed of heptane isomers and nitrogen using molecular dynamics (MD) simulations with fully atomistic intermolecular potential parameters, in conjunction with the Green-Kubo formula. The computed results were compared with the values obtained using the Chapman-Enskog (C-E) equation with Lennard-Jones (LJ) potential parameters derived from the correlations of state values: MD simulations predict a maximum difference of 6% among isomers while the C-E equation presents that of 3% in the mutual diffusion coefficients in the temperature range 500-1000 K. The comparison of two approaches implies that the corresponding state principle can be applied to the models, which are only weakly affected by the anisotropy of the interaction potentials and the large uncertainty will be included in its application for complex polyatomic molecules. The MD simulations successfully address the pure effects of molecular structure among isomers on mutual diffusion coefficients by revealing that the differences of the total mutual diffusion coefficients for the six mixtures are caused mainly by heptane isomers. The cross interaction potential parameters, collision diameter σ(12), and potential energy well depth ?(12) of heptane isomers and nitrogen mixtures were also computed from the mutual diffusion coefficients.     

Probing Degradation in Lithium Ion Batteries with On-Chip Electrochemistry Mass Spectrometry**

The rapid uptake of lithium ion batteries (LIBs) for large scale electric vehicle and energy storage applications requires a deeper understanding of the degradation mechanisms. Capacity fade is due to the complex interplay between phase transitions, electrolyte decomposition and transition metal dissolution; many of these poorly understood parasitic reactions evolve gases as a side product. Here we present an on-chip electrochemistry mass spectrometry method that enables ultra-sensitive, fully quantified and time resolved detection of volatile species evolving from an operating LIB. The technique's electrochemical performance and mass transport is described by a finite element model and then experimentally used to demonstrate the variety of new insights into LIB performance. We show the versatility of the technique, including (a) observation of oxygen evolving from a LiNiMnCoO₂ cathode and (b) the solid electrolyte interphase formation reaction on graphite in a variety of electrolytes, enabling the deconvolution of lithium inventory loss (c) the first direct evidence, by virtue of the improved time resolution of our technique, that carbon dioxide reduction to ethylene takes place in a lithium ion battery. The emerging insight will guide and validate battery lifetime models, as well as inform the design of longer lasting batteries.     

In situ NMR diffusion coefficients assessment of lithium ion conductor using electrochemical priors and Arrhenius constraint——A computational study

In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is proposed to estimate the diffusion sensitivity factors of pulsed-field gradient using prior information of the electrochemical performance and Arrhenius constraint.The model postulates that the active lithium nuclei participating electrochemical reaction are relevant to the NMR signal intensity,when discharge rate or temperature condition is varying.The electrochemical data and the NMR signal strength show a highly fit with the proposed model according our simulation and experiments.Furthermore,the diffusion time is constrained by temperature based on Arrhenius equation of reaction rates dependence.An experimental calculation of Li_4Ti_5O_(12)(LTO)/carbon nanotubes(CNTs) with the electrolyte evaluating at 20 ℃ is presented,which the b factor is estimated by the discharge rate.