Effect of Temperature on Reversible and Irreversible Processes during Lithium Intercalation in Graphite

Effect of temperature on reversible and irreversible processes during lithium intercalation in graphite from 1 M LiClO₄ solution in PC–DME is studied by galvanostatic cycling, cyclic voltammetry, and impedance spectroscopy. Reducing temperature diminishes both reversible and irreversible capacities. Conditions for the passive-film formation on graphite are discussed. If several first cycles are run at a negative temperature, the overall charge spent irreversibly decreases if the temperature is then elevated. The lower the initial-cycling temperature, the smaller the overall irreversible capacity.     

Decreasing Irreversible Capacity of Graphite Electrodes in Lithium-Ion Batteries by Direct Contact of Graphite with Metallic Lithium

The feasibility of reducing the irreversible capacity of negative graphite electrodes in lithium-ion batteries by a direct contact of such electrodes with lithium in the electrolyte is studied. It is shown that the dynamics of the formation of the passive film on graphite and the degree of the decrease in the irreversible capacity depend on the ratio between weights of graphite and lithium in contact. This method of reducing the irreversible capacity does not diminish the reversible capacity of graphite during the cycling. The irreversible capacity of the initial graphite cycled in 1 M LiPF₆ in a mixture of propylene carbonate and diethyl carbonate at a current density of 20 mA g^–1 is 550–1150 mA h g^–1. The reversible capacity of electrodes cycled in the same conditions reaches 290 mA h g^–1.     

A New Tin Graphite Intercalation Compound for Lithium Ion Batteries

IntroductionLithium ion batteries have attracted a great interestbecause of their commercial applications in portable de-vices[1,2].Great efforts have been made to improve theenergy density of new anode materials.For example,Sn-based compounds,such as SnO…     

碳纳米管和石墨在电化学嵌锂过程中的协同效应

锂电子电池;负极材料;碳纳米管和石墨在电化学嵌锂过程中的协同效应     

Electrochemical Intercalation of Lithium into Graphite in Acetonitrile Solutions: The Effect of the Anion Nature

Effect of the anion nature on the cathodic intercalation of lithium into graphite is studied. The duration of a discharge process and the capacity of Li _x C₆ electrodes increase in the row Cl^– HSO₄ ^– < ClO₄ ^– < SCN^–. The highest negative potential of an Li _x C₆ electrode is reached when lithiating in an LiSCN non-aqueous solution. X-ray diffraction and microstructure analyses confirm the presence in the electrode's upper layers of predominantly layered compounds Li _x C₆A _y , where A is anion. In deep layers, the principal intercalation product is Li _x C₆.     

锂在高有序热解石墨(HOPG)电极中的扩散系数

用循环伏安、交流阻抗和电位阶跃法研究了平板高有序热解石墨(HOPG)电极在1mol/LLiPF₆和体积比为1∶1的EC/DMC溶液中的电化学行为.结果表明,石墨的嵌锂反应仅发生在边界面上.随着嵌锂量的增加,表面SEI膜的电阻和嵌入反应的极化电阻减小.用交流阻抗谱和电位阶跃方法测定的锂在高有序热解石墨中的扩散系数一致,并随充电程度的增加而显著减小.在电极电位(vs.Li/Li⁺) 0.2～0.05V区间,扩散系数由10^-11cm²/s下降到10^-12cm²/s.     

粒度对石墨负极材料嵌锂性能的影响

研究了不同粒径（13～80 μm）石墨材料作为锂离子电池负极材料的嵌锂性能.结果表明，石墨粒度大小对嵌锂性能有明显影响，石墨的不可逆容量随着粒径的减小而逐渐增大，当粒径从80 μm减小到13 μm时，其不可逆容量增大了10％.而对可逆容量来说，随着粒径的减小，可逆容量逐渐增大;当粒径减小到20 μm时，可逆容量达到最大;再进一步减小石墨颗粒的粒径，可逆容量则随之减小.这表明石墨颗粒过大或过小都不利于锂离子的可逆脱嵌，只有合适的粒度才能最大限度地可逆脱嵌锂离子.根据不同粒度石墨的比表面的变化趋势，阐述了嵌锂性能随粒度变化的原因.     

锂嵌碳的磁共振研究

本文综述了十数年来电子自旋共振(ESR)和7Li核磁共振(7Li-NMR)技术用于锂嵌碳研究的进展.ESR研究发现锂嵌碳材料中存在两种电子自旋.一种来自碳材料中的载流子电子,称为Pauli自旋.从Pauli自旋的ESR强度可推算给定锂嵌碳样品的电子态密度曲线,并进而计算能带模型机理对该样品嵌锂容量的贡献.另一种来自局域化自旋,即Curie自旋,其与嵌锂位置的关系尚不清楚.7Li-NMR测试已发现几个不同的谱峰,其峰位和强度随碳样品性质和嵌锂深度而异.一般认为,45±5×10-6(即ppm,下同)处的NMR谱线源于深度嵌锂(在LixC6中x=0.5～1)石墨化结构中的Li+,属于Knight位移;而明显小于45×10-6的谱峰则可能是来自碳材料中石墨化微结构中低浓度Li+的Knight位移,也可能是于无序微结构中共价结合的Li的化学位移.ESR与7Li-NMR在研究锂嵌碳方面有很强的互补性,联合应用此两技术可望对深入认识锂嵌碳材料的构效关系作出新贡献.     

Intercalation of Sodium and Lithium into Graphite as a First Stage in an Electrochemical Method for Producing Carbon Nanotubes

A cyclic voltammetry method is used to show that the process of reduction of sodium (and, possibly, lithium) out of melts of corresponding chlorides on the molybdenum, glassy-carbon, and graphite electrodes is complicated by the process of dissolution of the corresponding alkali metal in the melt. A notion called “reversibility of material balance” is introduced. The notion reflects the ratio of the amount of substance that undergoes oxidation in the anodic half-cycle of a voltammetric curve to the amount of substance that is deposited in the cathodic half-cycle of the curve. The adsorption of sodium and lithium on glassy carbon and graphite plays an important role in the process of reduction, leading to an increase in the reversibility of the process. This is pronounced especially strongly at potential scan rates below 1 V s^?1. The sodium intercalation into graphite leads to a decrease in the reversibility of the process of reduction, the more so at potential scan rates below 0.03 V s^?1. However, the intercalation of lithium (probably because of its small atomic radius) does not exert practically any influence on the reversibility of process at the above potential scan rates.     

Electrochemical Intercalation of Lithium Ions into Electrolytic Vanadium Pentoxide

The discharge of thin films of Li _x V₂O₅ is described by a mathematical diffusion model. The chemical diffusion coefficient for lithium ions, estimated with the model, is equal to (1.01–2.5) × 10^–11 cm²/s. As the film thickness increases, the discharge capacity at a current of 20 A/cm² tends to the calculated limiting of 3.12 C/cm². The optimum thickness of the film electrode calculated for a discharge current of 20 A/cm² is 33.4 m and agrees satisfactorily with the experimental value.     

Electrochemical Intercalation of Lithium into Carbon: A Relaxation Study

Basic kinetic parameters of electrochemical intercalation of lithium into thin carbon films are determined by relaxation methods of current and potential steps. The overall electrode polarization is theoretically and experimentally divided into kinetic and diffusion constituents. The former is connected with the hindered ion transfer in a surface solid-electrolyte layer. The latter is due to the slow diffusion of lithium inside the carbon matrix. Concentration dependences of parameters of a solid-electrolyte layer and those of the diffusion coefficient for lithium in carbon are determined at lithium concentrations in the electrode varied from 2 to 16 M. The kinetic current is dependent on polarization in the interval 0.01 to 2.5 V, the dependence being identical to that for a lithium electrode.     

Lithium Intercalation into Nanostructured Films Based on Oxides of Tin and Titanium

The lithium intercalation into nanostructured films of mixed tin and titanium oxides is studied. X-ray diffraction and Moessbauer spectroscopy analyses reveal that films consist of a rutile solid solution (Sn, Ti)O₂ and an amorphous tin oxide enriched with Sn²⁺ ions. The films specific capacity during the first cathodic polarization in a 1 M lithium imide solution in dioxolane is 200–700 mA h/g, of which nearly one half is the irreversible capacity. During the second cycle, the latter is 15% of that in the first cycle. As the films are thin (<1 m), their capacity does not depend on the current density at 1–80 mA/g. During the electrode cycling, the capacity decreases by 2 mA h/g each cycle. The effective lithium diffusion coefficient, determined by a pulsed galvanostatic method, is 10^–11 cm²/s; it slightly increases with the film lithiation. During the first cycle, the amorphous phase of oxides is reduced to tin metal, the solid solution (Sn, Ti)O₂ decomposes, SnO₂ disperses to become an x-ray amorphous phase, and TiO₂ precipitates as a rutile phase. Lithium reversibly incorporates into the tin metal, yielding Li _y Sn, and into a disperse SnO₂ phase, yielding Li _x SnO₂.     

Lithium Intercalation into Titanium Dioxide Films from a Propylene Carbonate Solution

Intercalation of lithium from an LiClO₄ propylene carbonate solution into thin-film TiO₂ (rutile) electrodes produced by thermal oxidation of a titanium substrate are studied using cyclic voltammetry and impedance measurements at 0.01 to 10⁵ Hz. An equivalent circuit adequately modeling the impedance spectra of TiO₂- and Li _x TiO₂ electrodes throughout the frequency range studied is proposed. The electrochemical characteristics of film electrodes, the reversibility of intercalation-deintercalation process, the effect of surface passivation on the lithium transfer rate, and the dependence of electric, kinetic, and diffusion parameters on the electrode potential (composition) are discussed. The diffusion coefficient of lithium in Li _x TiO₂ is 10^–12 cm²/s, as estimated by the impedance method.     

Studying the Initial Stage of Nucleation and Growth of a New Phase during Cathodic Intercalation of Lithium into Aluminum

Kinetics of cathodic intercalation of lithium into aluminum from a 0.5 M LiCl solution in dimethylformamide at the stage of nucleation and growth of intermetallic compound -LiAl is studied by one- and two-pulse potentiostatic methods. If the length of the first potential pulse is short, the current at the beginning of the second pulse is proportional to the overvoltage squared. The experimental data point to a lamellar-spiral growth of -LiAl crystals at the initial stage of their development and to a change in the balance between different growth mechanisms as a function of the overvoltage and surface coverage by -LiAl.     

Electrochemical Intercalation of Lithium into Intermetallic Bismuth Compounds with Indium in Nonaqueous Solutions

Phase conversions and kinetics of electrochemical intercalation of lithium from dimethylformamide solutions of LiCl into bulk electrodes of bismuth, indium and their intermetallic compounds InBi and In₂Bi are studied using chronopotentiometry and chronoamperometry methods. The intercalation is controlled by non-steady-state lithium diffusion in the solid electrode. In the lithium–intermetallic compound systems, both components of alloys take part in the formation of compounds with lithium. Considerable volume changes, which occur during the intercalation, may lead to disintegration of lithium-containing phase constituents with a high lithium content. The extremum shape of cathodic chronoamperograms may be due successive and/or parallel reactions in which various lithium-containing compounds form. Some of these reactions are limited by solid-phase diffusion, while others involve the formation and diffusion-controlled growth of three-dimensional nuclei of a new phase.     

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.     

Phase Formation and Kinetics of Electrochemical Intercalation of Lithium into Intermetallic Compounds MgCd and MgCd3

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd₃ out of propylene carbonate solutions of LiBF₄ is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li₃Cd on MgCd or LiCd and Li₃Cd on MgCd₃. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd₃–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd₃is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd₃ are linear in semilogarithmic coordinates.     

正交相MoO3的制备、表征及其电化学嵌锂性质

用化学沉淀-水热法在较低的温度下制备了片状正交相MoO3,由XRD、FT-IR、XPS和SEM表征了产物的相态、结构、成分和形貌。电化学测试表明,在0.1mA.cm-2的电流密度和1.2~3.5V电压范围,其初始放电容量为663mA.h.g-1,有望成为理想的锂离子插层材料。