Two-phase reaction mechanism during chemical lithium insertion into α-MoO<Subscript>3</Subscript>

The phase transition during chemical lithium insertion into α-MoO₃ was investigated by chemical analysis, X-ray diffraction (XRD) and electrochemical characterisation. The samples have been prepared by reaction of various amounts of water-free lithium iodide with fine-particulate orthorhombic molybdenum trioxide in n-hexane (non-aqueous media), which yielded materials with different Li/Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO₃ has been changed after the chemical lithiation. The phase transition ranged from 0.25 < x < 0.5 in Li _x MoO₃ upon chemical lithium insertion into α-MoO₃. The XRD lines of lithium inserted phase Li _x MoO₃ grew at the expense of the XRD lines of the pristine α-MoO₃ as lithium ions were chemically inserted until the disappearance of lines related to α-MoO₃. The electrochemical performance of the lithiated samples is improved in comparison with the starting material (non-lithiated α-MoO₃).     

The first in situ 7Li NMR study of the reversible lithium insertion mechanism in disorganised carbons

We study a disordered carbon designed to be used as negative electrode in a secondary lithium battery. We perform in situ magnetic resonance, i.e. we run several electrochemical cycles inside the magnet while recording NMR spectra. We obtain simultaneous ⁷Li NMR and electrochemistry data and may thus analyse: the detailed chronology of the events, the Knight shift, the line width, the relaxation time T₁. This experimental work allows us to evidence a quasi metallic lithium, less diffusive than in metal and in graphite. The quasi metallic lithium is responsible for the very good reversible capacity, at a very low voltage. We indicate a model for the insertion/extraction of lithium in the fibers. The disordered carbon under study exhibits better qualities than graphite's for secondary battery applications. Only one drawback remains: a 0.5 V hysteresis; NMR shows that it occurs when the lasts quasi metal lithium are to be extracted. We evaluate the energy barrier.     

Improvement of the lithium insertion properties of Li1.1V3O8

Two Li_1.1V₃O₈ samples have been prepared by heating a sol–gel precursor at 350 °C and 650 °C, i.e. below and above the melting point, respectively. Their electrochemical lithium insertion behavior was investigated after different grinding treatments. This work shows the importance of grain morphology (size, size distribution and shape) and texture (agglomeration of smaller particles or not) on both initial capacity and cyclability. It also shows that the dissolution of a small quantity of V^III in the electrolyte occurs during the last process at 2.4 V, depending on the morphology of the compound studied. Such results were taken advantage of to optimize the morphology and texture of Li_1.1V₃O₈ in order to obtain enhanced performance.     

Sn3InSb4合金嵌Li性能的第一性原理研究

采用第一性原理超软赝势平面波方法计算了Sn₃InSb₄的嵌Li性能,得到各种嵌Li相的嵌Li形成能、理论质量比容量、体积膨胀率、能带结构、态密度和差分电荷密度等.从能量角度分析,Li在嵌入时,优先占据晶胞的四面体间隙位置,然后逐步挤出处于节点位置的Sn原子和In原子.在嵌Li过程中,材料表现出较大的体积膨胀率(11.74%-43.40%),这是导致Sn₃InSb₄作为Li离子电极材料循环性能差的重要原因.态密度计算表明,体系的导电性能首先随嵌Li量的增加而增加,当所有的间隙位置被Li填满,发生Sn的替换反应时,富Li态合金相的导电性反而下降.     

A better understanding of the irreversible lithium insertion mechanisms in disordered carbons

It is now well established that high lithium storage capacities can be received from disordered carbons. However, compared to graphite, they generally demonstrate high hysteresis and irreversibility, and sometimes a poor cycleability, which strongly limit their practical application. Our work is an attempt for better understanding the phenomena occurring during the first reduction (discharge) of nanostructured carbons, with the expectation that this could give rise to future improvement of the electrochemical performance. The irreversible capacity is generally supposed to be related with the specific surface area, but many deviations to this law are observed. We found that a better linear relationship exists considering the active surface area (ASA). Furthermore, deactivating the surface by a pyrolytic carbon deposit allows the irreversible capacity to be noticeably reduced. The electrochemical properties of this new C/C composite are investigated by galvanostatic cycling.     

锂离子电池硅基负极材料嵌锂行为的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算不同数量的锂离子引起的硅材料晶体结构的变化以及在嵌锂过程中形成Li_xSi(x=1、2、2.4、4.4)合金相的形成能与电子结构.采用LST/QST方法计算过渡态,模拟合金体相中的锂离子迁移过程.计算结果表明,随着嵌锂数量的增加,硅晶胞的体积在不断增大;Li_xSi合金相的形成能为负值,表明在嵌锂过程中锂离子和硅原子可以自发形成这些合金相,其中Li₇Si₃合金最容易形成;随着嵌锂量的增加,锂离子在费米能级处s轨道提供的电子数逐渐增加,锂硅合金在费米能级处的电子数量呈增大趋势,表明锂硅合金的导电性越来越优;常温下Li₂Si体相中很难直接形成锂离子空位,但锂离子空位的迁移过程很容易发生.     

Large-scale production of Cu3P nanocrystals for ultrahigh-rate supercapacitor

Ionics - The fast development of supercapacitors inspires a growing interest in inexpensive super-capacitive electrode material with high performance. Herein, we develop a Rone step method for...     

锂离子电池负极材料CuSn的Li嵌入性质的研究

使用基于混合基表示的第一原理赝势法，研究了锂离子电池非碳类负极材料CuSn的Li嵌入时的形成能以及相应的电子结构.还给出了Li嵌入时的体积变化，能带结构、电子态密度以及电荷密度分布等性质, 并讨论了CuSn作为负极材料的特点.计算发现，Cu-Sn化合物在闪锌矿结构时，Li嵌入主体材料时的嵌入形成能大致在3.5eV附近. 关键词： 锂离子电池 负极材料 CuSn 电子结构     

Thermodynamic study of lithium insertion in V6O13 and Li1+xV3O8

The enthalpies of Li⁺ insertion into two V oxides of interest as cathodes for secondary Li batteries, i.e. V₆O₁₃ and Li_1+xV₃O₈ have been directly measured by solution calorimetry. By comparing the integral molar enthalpies ΔH⁰/x with the corresponding ΔG⁰/x values, ΔS⁰/x higher than expected have been found for Li_1+xV₃O₈. This has been correlated to a reorganization of its distorted structure induced by the initial Li⁺ insertion. Two other cathode materials, having the same variation of the potential with Li⁺ content, i.e. MoO₃ and (Mo_0.3V_0.7)₂O₅, show even higher ΔS⁰/x values. The entropic values stemming from structural reorganizations add to the configurational entropies of inserted ions in determining the initial profile of E as a function of Li⁺.     

Raman study on electrochemical lithium insertion into multiwalled carbon nanotubes

We have carried out in situ Raman studies during the electrochemical insertion of lithium ions (Li⁺) into pristine and thermally treated multiwalled carbon nanotubes (MWNTs). We found an improved structural integrity as well as the removal of defects in the thermally treated tubes. The different Li⁺ insertion behaviors above 0.5 V in as‐grown and thermally treated tubes could be explained by the presence of defects on the outer surface of the tubes. No change of Raman spectra from 2.8 to 0.8 V is characterized by the coverage of Li⁺ on the outer surface of tubes, whereas the upshift of G band and the absence of a separated G band below 0.75 V indicate the formation of diluted graphite intercalation below the stage‐2 phase (LiC₁₂). Copyright © 2008 John Wiley & Sons, Ltd.     

锂电池失效分析与研究进展

锂电池在使用或储存过程中会出现一定概率的失效,包括容量衰减(跳水)、循环寿命短、内阻增大、电压异常、析锂、产气、漏液、短路、变形、热失控等,严重降低了锂电池的使用性能、一致性、可靠性、安全性.对锂电池失效进行准确诊断并探究其失效机理是锂电池失效分析的主要任务,对锂电池性能提升和技术发展具有深远意义.为了全面且深入地介绍锂电池失效分析,本文从锂电池失效分析的定义、失效表现、失效原因、分析内容、分析流程、困难点等方面进行了简述,希望能为推动中国锂电池失效分析技术的发展起到积极作用.     

Structure and lithium ionic conduction mechanism in La4/3−yLi3yTi2O6

The solid solutions La_4/3−yLi_3yTi₂O₆ (y=0.09∼0.33) have been studied by complex impedance spectroscopy, X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) methods. The ionic conductivity shows a maximum value at around y=0.21, and keeps high values at high y concentrations. The XRD patterns show a single phase for all concentration. The crystal structure is orthorhombic with space groupPmmm for y=0.09∼0.15 and tetragonal with space groupP4/mmm for y=0.17∼0.33. The⁷Li static NMR spectra show a main central peak with a Lorenzian shape for y=0.09∼0.21. The central peak is divided into two parts for y=0.23∼0.33. The narrow intense peak is a mobile component due to mobile ions, and a small broad central peak is due to less mobile lithium ions which contribute to immobile component. The⁷Li MAS NMR spectra show negative chemical shifts which decrease with increasing y concentration. In this paper, we discuss the conduction mechanism and the structure from the analysis of conductivity, lattice parameters, occupation, atomic positions and the⁷Li static/MAS NMR spectra.     

Hyperfeinstrukturanomalie und Kernquadrupolwechselwirkungskonstanten des angeregten 3d 94s 4p 4 P 3/2-Terms im Cu I-Spektram von Cu63 und Cu65

Zeitschrift für Physik A Hadrons and nuclei - The hyperfine structure of the excited 3d 9 4s 4p 4 P 3/2-term of the Cu I-spectrum was investigated in a level-crossing experiment using an...     

Level-crossing-Untersuchung der Hyperfeinstruktur des 3d 10 4p 2 P 3/2-Terms von Cu63 und Cu65

The level-crossing technic has been used to investigate the hyperfinestructur of the 3d ¹⁰ 4p ² P _3/2-term in Copper I by scattering the resonance line λ=3248 Å on an atomic beam of separated isotop Cu⁶³ respectively Cu⁶⁵ in an external magnetic field. From the level-crossing signals values for the magnetic dipol interaction constantsA and for the electric quadrupol interaction constantsB are deduced to beeA(Cu⁶³)=(194,72±0,15) Mc/secB(Cu⁶³)=?(28,8±0,6) Mc/secA(Cu⁶⁵)=(208,57±0,15) Mc/secB(Cu⁶⁵)=?(25,9±0,6) Mc/sec. With theA-value of the 3d ¹⁰ 4p²P_1/2-term from optical measurements the ratioA(² P _3/2)∶A(² P _1/2)≈0,4 is about twice greater than for an unperturbetalkali-like²P-term. From the width of the level-crossing signals a mean lifetime of the 3d¹⁰ 4p²P_3/2-term τ=(7,0±0,2) · 10^?9 sec is deduced.     

石墨嵌锂的结构转变和弹性性质计算研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了锂离子电池石墨负极在嵌Li过程中形成石墨嵌层化合物LixC6(0≤x≤1)的形成能、嵌锂平台、晶体结构、电子结构和弹性性质的变化规律。结果表明,随着嵌Li量x增加,LixC6的体系总量能逐渐降低,形成能逐渐增大,嵌Li反应逐渐变得困难;计算得到石墨的嵌Li电位逐渐降低,这与实验测得的充放电曲线具有良好的一致性。石墨嵌Li导致碳层发生滑移,晶胞体积逐渐增大,当x为1时晶胞体积增大约12.75%。随着x增加,LixC的费米能态密度几乎呈现增大趋势,有利于增强电子导电性。随着x增加,平行于碳平面的杨氏模量Ea和Eb都呈现小幅下降趋势,而垂直于碳平面的杨氏模量Ec呈现大幅度增加趋势,导致石墨刚性逐渐增大,结构稳定性变差。     

石墨嵌锂的结构转变和弹性性质计算研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了锂离子电池石墨负极在嵌Li过程中形成石墨嵌层化合物Li_xC_6(0≤x≤1)的形成能、嵌锂平台、晶体结构、电子结构和弹性性质的变化规律.结果表明,随着嵌Li量x增加,Li_xC_6的体系总量能逐渐降低,形成能逐渐增大,嵌Li反应逐渐变得困难;计算得到石墨的嵌Li电位逐渐降低,这与实验测得的充放电曲线具有良好的一致性.石墨嵌Li导致碳层发生滑移,晶胞体积逐渐增大,当x为1时晶胞体积增大约12.75%.随着x增加,Li_xC_6的费米能态密度几乎呈现增大趋势,有利于增强电子导电性.随着x增加,平行于碳平面的杨氏模量Ea和Eb都呈现小幅下降趋势,而垂直于碳平面的杨氏模量Ec呈现大幅度增加趋势,导致石墨刚性逐渐增大,结构稳定性变差.     

Physical investigation of the mechanisms of lithium insertion in sulfides as anode materials for lithium-ion batteries

Electrochemical and chemical lithium insertion (vian-butyllithium) were carried out on a family of spinel phases of the Cu₂S-In₂S₃-SnS₂ system. Electrochemical measurements have revealed great reversible capacities and the possible use of these materials as negative electrodes in lithium-ion batteries.¹¹⁹Sn Mössbauer spectroscopy,⁷Li NMR and S K edge EXAFS spectroscopy were carried out to characterize the mechanisms of lithium insertion. This study has shown the formation of lithium-metal alloys finely dispersed in an amorphous lithium sulfide matrix at low potentials. A model is proposed to explain the great capacities observed in these materials.     

Doping mechanism of optical-damage-resistant ions in lithium niobate crystals

The doping mechanism of optical-damage-resistant ions (Mg²⁺, Zn²⁺, In³⁺, Sc³⁺, Hf⁴⁺, and Zr⁴⁺) in the lithium niobate crystallographic frame is quantitatively studied from the chemical bond viewpoint. Calculated results show that optical-damage-resistant ions have a strong interaction with the lithium niobate matrix, which is quantitatively evaluated by the deviation between normal and calculated valence states and the global instability index. All optical-damage-resistant ions first substitute Nb_Li and then Li ions, they change their dopant occupancies from Li to Nb sites at the same global instability index value 0.1055. On the basis of such a quantitative interaction, the doping mechanism of these ions is finally derived. Furthermore, a criterion in searching for new optical-damage-resistant ions is also proposed.     

Ion transport mechanism in solid electrolyte films on lithium

The rate of Li⁺ ion transport in an insulating solid electrolyte film on the Li metal surface versus electric field (<10⁷ V/cm) and temperature (in the range 238–343 K) is studied. The dependences found in this work are shown to reflect structural disorder in the electrolyte film material. Disorder causes a spread in the site-to-site hopping length and time.