High-Speed voltammetry of Mn-doped LiCoO2 using a microelectrode technique

The microelectrode technique was applied to investigate the electrochemical properties of LiCo_{1- x} Mn _x O₂ (x=0, 0.01, 0.05, 0.2, or 0.5) synthesized using the citrate process. From the X-ray diffraction measurements, an expansion of the c-axis and a decrease in the crystal size of the materials were observed on substitution of Mn into LiCoO₂. In the electrochemical measurements, the high-speed cyclic voltammogram for the Mn-substituted materials gave one set of peaks at 3.9 V vs. Li/Li⁺. The apparent chemical diffusion constant (D _app) of LiCo_0.8Mn_0.2O₂ obtained from the potential step experiment was 6.4 × 10⁻⁸ cm²/s, which is larger than that of LiCoO₂. The increase in D _app is attributable to the expansion of the c-axis and/or the decrease in the crystal size. In addition, the increase in Mn substitution up to 20% lead to an improvement in the kinetic reversibility and the cycle stability of LiCoO₂. Received: 7 June 1999 / Accepted: 25 June 1999     

烧结温度对锂离子电池正极材料LiCoO2结构与电化学性能的影响

锂钴氧化物;烧结温度对锂离子电池正极材料LiCoO2结构与电化学性能的影响     

Formation of solid solution and its effect on lithium insertion schemes for advanced lithium-ion batteries: X-ray absorption spectroscopy and X-ray diffraction of LiCoO2, LiCo1/2Ni1/2O2 and LiNiO2

The X-ray absorption spectra (XAS) of LiCoO₂, LiCo_1/2Ni_1/2O₂ and LiNiO₂ were examined together with X-ray diffraction (XRD). Co and Ni K-edge XANES spectra of LiCo_1/2Ni_1/2O₂ are quite similar to that of LiCoO₂ or LiNiO₂, suggesting that electronic states of Co and Ni in LiCo_1/2Ni_1/2O₂ are Co³⁺ and Ni³⁺. Analytical results of Co and Ni K-edge EXAFS oscillations on the first coordination shell of nickel and cobalt ions in LiCo_1/2Ni_1/2O₂ indicate that the local environment around the targeted species is the same as that in LiCoO₂ or LiNiO₂. Since there is no doubt about the crystal and electronic structures of LiCoO₂ and LiNiO₂, the results indicate that LiCo_1/2Ni_1/2O₂ consists of low-spin states of Co³⁺ and Ni³⁺ distributed at equivalent positions in triangular lattice of sites forming homogeneous transition metal oxide layers. Thus, XAS complements XRD in describing solid solution LiCo_1/2Ni_1/2O₂ of LiCoO₂ and LiNiO₂. The electrochemical behaviors of LiCoO₂, LiCo_1/2Ni_1/2O₂ and LiNiO₂ are also restated and the effects of the formation of solid solution on the change in lattice dimension during topotactic electrochemical reactions are discussed.     

Synthesis and Electrochemical Property of Calcium Doped LiNi0.8Co0.2O2 Solid Solution

Today, batteries with high capacity, good cyclability, long life and environmental goodness are much required to meet some pressing demands of our modern society. In principle, lithium ion cells can satisfy these requirements1. But the properties of the cathode materials have limited the further development of the lithium ion cells. The studied cathode materials before were mainly LiCoO2, LiMn2O4, LiNiO2. The LiCoO2 has disadvantages including cost and environmental risk although it is…     

Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO₂ cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface-enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO₂ layer (Au@SiO₂). We observe a surface-enhanced Raman signal of Li₂CO₃ at 1090 cm⁻¹ during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li₂CO₃ as a component of the SEI on LiCoO₂ composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.     

锂离子电池正极材料Li[Li0.167Mn0.583Ni0.25]O2的合成与性能研究

应用低热固相法制备镍锰复合正极材料Li[Li0.167Mn0.583Ni0.25]O2.XRD、FESEM和恒电流充放电测试表明,该材料结晶良好,可标定为α-NaFeO2型结构(空间群R3-m),颗粒粒径约为60~100 nm,粒度均匀细小.在2.5~4.4 V之间以0.5 C(100 mA/g)做充放电循环时,可逆比容量在120 mAh/g以上,循环性能非常稳定.如将截止电压升高到4.6 V,则比容量大大提高,最高可达234 mAh/g.上述充放电测试都出现了比容量随循环次数上升的现象.主要原因可归结为材料中Mn(Ⅳ)向Mn(Ⅲ)的转变,但在不同的电压范围内导致该转变的起因并不相同.     

脉冲激光沉积掺杂二氧化硅的钴酸锂正极薄膜材料

采用脉冲激光溅射的方法成功制备了掺杂二氧化硅的钴酸锂薄膜电极。结合SEM, XRD,HRTEM,SAED,EDX,充放电,以及循环伏安等手段对其形貌,结构与电化学性能进行了研究。结果表明,掺杂了二氧化硅的钴酸锂电极薄膜在电化学反应的过程中具有结构刚性,放电平台稳定,极化较小等优点,因此可能成为一种优良的二次锂离子正极材料。     

LiCoO2中锂离子固相扩散系数随循环次数的变化

The solid diffusion coefficient of lithium-ion in LiCoO₂ cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. By SEM, XRD and FTIR techniques, the structure of LiCoO₂ was studied before and after charge-discharge cycles, and the relationship between solid diffusion coefficient and crystal structure was further discussed. CITT results show that the value of Li⁺ solid diffusion coefficient of LiCoO₂ is about 10^-12 cm²·s^-1. During the whole charge-discharge cycles, the Li⁺ solid diffusion coefficient decreased within the voltage of 4.0～4.3 V, which is attributed to the change of the structure of LiCoO₂.     

In-situ imaging of Li-ion migration at interfaces in an all solid Li-ion battery

We investigated the migration of Li ions at an interface between a Li_xTi₅O₁₂ (LTO) and a solid electrolyte in an all-solid Li-ion battery. The optical reflection of LTO changes with variations in the Li content because the band structures of LTO vary with the changes in the Li content. This enables us to observe Li-ion migration in the interface between the LTO and the solid electrolyte using an optical microscope. To observe the LTO particles optically, they were coated on an indium tin oxide on a glass substrate. Variations in Li migration caused by charging/discharging were clearly observed through the changes in the reflection of the LTO. LTO changed between an insulator Li₄Ti₅O₁₂ of the spinel structure and a conductor Li₇Ti₅O₁₂ of the rock-salt structure according to the changes in the Li content. The spinel LTO has a bandgap energy of approximately 2 eV. When electron–hole pairs were generated, electric strains were produced. Surface force microscopy detected the strains and imaged the distribution of lithiation/delithiation of LTO. Interfacial conduction between a sputtered LTO and Li₃PO₄ particles was imaged with high spatial resolution.     

双包覆法改善高压钴酸锂正极材料的电化学性能

通过结合固相和液相包覆在Al掺杂LiCoO₂表面共包覆了钛酸锂(Li₄Ti₅O₁₂)和聚吡咯(PPy)。这种双包覆方法不仅稳定了高电压下LiCoO₂的表面,还增强了材料的离子和电子电导率。电化学测试表明,当活性物质、导电剂和黏结剂的质量比为80∶10∶10时,在0.5C(1C=180 mA·g^-1)电流下,循环300周后的容量保持率为76.9%,且在5C电流密度下可逆比容量为150 mAh·g^-1;由于双包覆后LiCoO₂电子电导率大幅提高,当活性物质、导电剂和黏结剂的质量比为90∶3∶7时,在0.5C电流下,循环200周后的容量保持率为82.8%,且在5C电流密度下可逆比容量为130 mAh·g^-1。X射线光电子能谱测试表明,包覆层可以在循环中保持稳定且能抑制LiCoO₂材料在高电压下的表面副反应。     

Lithium AlPO<Subscript>4</Subscript> composite polymer battery with nanostructured LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode

The borate ester plasticized AlPO₄ composite solid polymer electrolytes (SPE) have been synthesized and studied as candidates for lithium polymer battery (LPB) application. The electrochemical and thermal properties of SPE were shown to be suitable for practical LPB. Nanostructured LiMn₂O₄ with spherical particles was synthesized via ultrasonic spray pyrolysis technique and has shown a superior performance to the one prepared via conventional methods as cathode for LPB. Furthermore, the AlPO₄ addition to the polymer electrolyte has improved the polymer battery performance. Based on the AC impedance spectroscopy data, the performance improvement was suggested as being due to the cathode/polymer electrolyte interface stabilization in the presence of AlPO₄. The Li/composite polymer electrolyte/nanostructured LiMn₂O₄ electrochemical cell showed stable cyclability during the various current density tests, and its performance was found to be quite acceptable for practical utilities at ambient temperature and showed remarkable improvements at 60 °C compared with the solid state reaction counterpart.     

Co0.2/Ce1-xZrxO2催化剂的制备、表征及其催化碳烟燃烧反应性能

 采用微孔扩散-共沉淀法制备了不同 Ce/Zr 摩尔比的 Ce1-xZrxO2 (x = 0, 0.2, 0.4, 0.5) 固溶体, 并以此为载体用超声波助分散等体积浸渍法制备了 Co0.2/Ce1-xZrxO2 催化剂, 考察了催化剂中 Ce/Zr 比对其催化柴油车尾气碳烟颗粒物燃烧反应性能的影响. 结果表明, 在催化剂与碳烟颗粒松散接触条件下, Co0.2/Ce1-xZrxO2 催化剂催化碳烟颗粒物燃烧的活性非常高. 其中 Co0.2/Ce0.8Zr0.2O2 催化剂活性最高, T10, T50, T90 和 SmCO2 分别为 316 oC, 385 oC, 413 oC 和 99.9%. 这与目前文献报道的松散接触条件下活性最高的担载 Pt 催化剂相近. 应用 X 射线衍射、透射电镜、扫描电镜、紫外-可见漫反射和傅里叶变换红外光谱技术对 Ce1-xZrxO2 固溶体及 Co0.2/Ce1-xZrxO2 催化剂进行了表征. 结果表明, Ce1-xZrxO2 固溶体由纳米级小颗粒组成 (平均粒径在 10 nm 左右). 适量的 Ce/Zr 比有利于改善立方尖晶石型 Co3O4 在 Ce1-xZrxO2 固溶体表面的分散, 从而提高催化剂活性. 程序升温还原结果表明, Co0.2/Ce0.8Zr0.2O2 催化剂具有最优的低温还原特性, 与它具有最高的催化活性相一致.     

Products of lithium interaction with nanostructured oxides SnO2-TiO2 and mechanism of charge-discharge of electrodes in a lithium-ion battery

Products of lithium interaction with thin-film nanostructured SnO₂-TiO₂ (ST) oxides are studied with the aid of x-ray diffraction analysis and Moessbauer spectroscopy on the ¹¹⁹Sn nuclei. Electrochemical properties of a series of the ST electrodes with different concentrations of TiO₂ varied from 0 to 20 mol % are also examined. It is concluded that the specific feature of the charge-discharge mechanism of the ST electrodes is a significant participation of oxygen in reversible reactions during insertion and extraction of lithium as compared with an alloying mechanism of operation of tin-containing anodes. The leading role in this is played by titanium oxide. Remaining stable towards reduction by lithium, it facilitates the holding of the neighboring layers of SnO₂ in a nanodisperse state and in an oxidized state. The effect of a decrease in the capacity degradation in modified TiO₂ electrodes, which is discovered in this work, is attributed to the hampering of the growth of nanocrystallites of β-Sn by interlayers of tin and titanium oxides mentioned above.     

Cobalt Element Effect of Ternary Mesoporous Cerium Lanthanum Solid Solution for the Catalytic Conversion of Methanol and CO2 into Dimethyl Carbonate

A citric acid ligand assisted self-assembly method is used for the synthesis of ternary mesoporous cerium lanthanum solid solution doped with metal elements (Co, Zr, Mg). Their textural property was characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption, X-ray photoelectron spectroscopy and TPD techniques, and so on. The results of catalytic testing for synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ indicated that the DMC yield reached 316 mmol/g on Ce-La-Co solid solution when the reaction temperature was 413 K and the reaction pressure was 8.0 MPa. It was found that Co had synergistic effect with La and Ce, doping of Co on the mesoporous Ce-La solid solution was helpful to increase the surface area of the catalyst, promote CO₂ adsorption and activation, and improve the redox performance of solid solution catalyst. The conversion of Co²⁺ to Co³⁺ resulted in the continuous redox cycle between Ce⁴⁺ and Ce³⁺, and the oxygen vacancy content of the catalyst was increased. Studies have shown that the catalytic performance of Ce-La-Co solid solution is positively correlated with oxygen vacancy content. On this basis, the reaction mechanism of DMC synthesis from CO₂ and CH₃OH on the catalyst was speculated.     

Superstructure in the Metastable Intermediate‐Phase Li2/3FePO4 Accelerating the Lithium Battery Cathode Reaction

LiFePO₄ is an important cathode material for lithium‐ion batteries. Regardless of the biphasic reaction between the insulating end members, Li_xFePO₄, x≈0 and x≈1, optimization of the nanostructured architecture has substantially improved the power density of positive LiFePO₄ electrode. The charge transport that occurs in the interphase region across the biphasic boundary is the primary stage of solid‐state electrochemical reactions in which the Li concentrations and the valence state of Fe deviate significantly from the equilibrium end members. Complex interactions among Li ions and charges at the Fe sites have made understanding stability and transport properties of the intermediate domains difficult. Long‐range ordering at metastable intermediate eutectic composition of Li_2/3FePO₄ has now been discovered and its superstructure determined, which reflected predominant polaron crystallization at the Fe sites followed by Li⁺ redistribution to optimize the Li? Fe interactions.     

温度对LiCoO2中锂离子嵌脱过程的影响

摘要 运用EIS研究了LiCoO2正极在1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中0~30℃范围内阻抗谱特征、SEI膜阻抗、电子电阻和电荷传递电阻等随温度的变化。结果表明,LiCoO2正极的EIS谱特征与温度有关,随温度的升高其低频区域在1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中分别于10和20℃出现反映锂离子固态扩散的斜线。LiCoO2正极在 1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中,锂离子迁移通过SEI膜的离子跳跃能垒平均值分别为37.74和26.55KJ/mol;电子电导率的热激活化能平均值分别为39.08和53.81KJ/mol;嵌入反应活化能平均值分别为68.97和73.73KJ/mol。