From ‘core-shell’ to composite mixed cathode materials for rechargeable lithium batteries by mechanochemical process

Solid state mechanical activation method was applied for surface modification of LiMn₂O₄ by Li-M-O (M = Co, Co+Ni) and for preparation of composite mixed LiMn₂O₄/LiCoO₂ cathode materials. Pristine LiMn₂O₄ was ground with correspondent precursors (for coating) or with LiCoO₂ (for composites) in high-energy planetary mills and then heat treated at different temperatures. As prepared materials were studied by XRD, ⁷Li MAS NMR spectroscopy, XPS, SEM and electrochemical cycling. It has been shown that both ‘core-shell’ and composite materials prepared by mechanochemical process are characterized by superior electrochemical performance due to smaller particles and chemical modification of LiMn₂O₄.     

Electrochemical activities of yttrium doped spinel LiMn2O4

It was found for the first time that the catalysis of yttrium doping of spinel LiMn₂O₄ can enhance the electrochemical activities of manganese, leading to both improvement of electrochemical capacity and reactivity with the electrolyte of manganese. A proper amount of doping was 0.5%, and such yttrium-doped sample, Li(Y_0.005Mn_0.995)₂O₄, had an initial capacity of 130 mAh g⁻¹ over that of the undoped one with the capacity retention to reach 92.3% exceeding that of the undoped one at 100th cycle.     

A novel approach to synthesize lithium ion battery spinel cathode materials

Spinel LiMn₂O₄ and LiMg_0.2Mn_1.8O₄ have been synthesized by a soft chemistry method using citric acid as the chelating agent and acryl amide as the gelling agent. This technique offers better homogeneity, preferred surface morphology, reduced heat treatment conditions, sub-micron-sized particles, and better crystallinity. The synthesized spinel materials are characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and charge–discharge studies.     

Preparation of TiO2-coated LiMn2O4 by carrier transfer method

The TiO₂-coated LiMn₂O₄ has been prepared by a carrier transfer method and investigated. This novel synthetic method involved the transfer of TiO₂ into the surface of LiMn₂O₄ with Vulcan XC-72 active carbon powders as a dispersant. The X-ray diffraction shows that spinel structure of materials does not change after the coating of TiO₂. The electrochemical performance tests show that the initial discharge capacity of TiO₂-modified LiMn₂O₄ is 111.5 mA h g⁻¹, which is better than that of pristine LiMn₂O₄ (103.8 mA h g⁻¹). The cyclic performance is significantly improved after surface modification. The TiO₂-modified LiMn₂O₄ by a carrier transfer method exhibits better discharge capability and lower resistance.     

Improvement of electrochemical performance of all-solid-state lithium secondary batteries by surface modification of LiMn2O4 positive electrode

To improve the electrochemical performance of an all-solid-state In/80Li₂S⋅20P₂S₅ (electrolyte)/LiMn₂O₄ cell, a lithium-titanate thin film was used to coat LiMn₂O₄. The interfacial resistance between LiMn₂O₄ and the electrolyte (measured after initial charging) decreased when the LiMn₂O₄ particles were coated with lithium-titanate. A cell with lithium-titanate-coated LiMn₂O₄ had a higher capacity than a cell with noncoated LiMn₂O₄ for current densities in the range 0.064 to 2.6 mA cm^− 2. Additionally, a cell with coated LiMn₂O₄ retained 96% of the 10th-cycle reversible capacity at a current density of 0.064 mA cm^− 2 after 50 cycles.     

Effect of ultrasonic irradiation on structure and electrochemical properties of LiMn2O4 thin films cathode material for Li-ion micro-batteries

Two kinds of spinel LiMn₂O₄ thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn₂O₄ thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn₂O₄ thin films of USG at the current density of 50 μAh/cm² between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm²-μm for USG thin films and 51.7 μAh/cm²-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn₂O₄ thin films with better electrode performance for lithium ion micro-batteries.     

Hydrothermal synthesis of spinel Li1+x Mn2O4 as cathode material for rechargeable lithium battery

Abstract

The hydrothermal synthesis of Li-Mn spinel oxide (Li_1+xMn₂O₄) was undertaken in order to develop high quality, low cost cathode material for a rechargeable lithium battery. In our experiments, γ-MnOOH, LiOH · H₂O and H₂O₂ were used as starting materials to synthesize Li-Mn spinel oxide under hydrothermal conditions of 180-230°C and about 1.0-2.8 MPa. The chemical composition and particle size of the Li_1+xMn₂O₄ is easily controlled in the hydrothermal reaction. The Li_1+xMn₂O₄ produced was characterized by X-ray diffraction, with the spinel phase having a Li/Mn ratio of 0.50-0.60. There is convincing evidence, as a result of this work, that our synthesis process is most suitable for producing high quality cathode material that can be used in a rechargeable lithium battery.     

Enhanced electrochemical performance of La- and Zn-co-doped LiMn2O4 spinel as the cathode material for lithium-ion batteries

We report on the nanoparticle uptake into MCF10A neoT and PC-3 cells using flow cytometry, confocal microscopy, SQUID magnetometry, and transmission electron microscopy. The aim was to evaluate the influence of the nanoparticles?? surface charge on the uptake efficiency. The surface of the superparamagnetic, silica-coated, maghemite nanoparticles was modified using amino functionalization for the positive surface charge (CNPs), and carboxyl functionalization for the negative surface charge (ANPs). The CNPs and ANPs exhibited no significant cytotoxicity in concentrations up to 500???g/cm³ in 24?h. The CNPs, bound to a plasma membrane, were intensely phagocytosed, while the ANPs entered cells through fluid-phase endocytosis in a lower internalization degree. The ANPs and CNPs were shown to be co-localized with a specific lysosomal marker, thus confirming their presence in lysosomes. We showed that tailoring the surface charge of the nanoparticles has a great impact on their internalization.     

Al掺杂的尖晶石型LiMn2O4的结构和电子性质

采用基于密度泛函理论的第一性原理方法, 在广义梯度近似(GGA)和GGA+U方法下对尖晶石型LiMn₂O₄及其Al掺杂 的尖晶石型LiAl_0.125Mn_1.875O₄晶体的结构和电子性质进行了计算. 结果表明: 采用GGA方法得到尖晶石型LiMn₂O₄是立方晶系结构, 其中的Mn离子为+3.5价, 无法解释它的Jahn-Teller 畸变. 给出的LiMn₂O₄能带结构特征也与实验结果不符. 而采用GGA+U方法得到在低温下的LiMn₂O₄和其掺杂 体系LiAl_0.125Mn_1.875O₄的晶体都是正交结构, 与实验一致. 也能明确地确定Mn的两种价态Mn³⁺/Mn⁴⁺的分布并且能够说明Mn³⁺O₆的z方向有明显的Jahn-Teller 畸变, 而Mn⁴⁺O₆则没有畸变. LiMn₂O₄的能带结构与实验比较也能够符合. 采用GGA+U方法对Al掺杂体系的LiAl_0.125Mn_1.875O₄的研究表明, 用Al替换一个Mn不会明显地改变晶体的电子性质, 但可以有效地消除Al³⁺O₆ 八面体的Jahn-Teller畸变, 从而改善正极材料LiMn₂O₄的性能, 这与电化学实验的观察结果相一致.     

Direct micron-sized LiMn2O4 particle coating on LiCoO2 cathode material using surfactant

Micron-sized LiMn₂O₄ particles were easily coated on LiCoO₂ cathodes using an amphoteric gelatin surfactant at pH4–5. The coated LiCoO₂ material showed a significantly higher thermal stability during charging and capacity retention on cycling at 4.6 V, compared to the bare LiCoO₂.     

同步辐射XAFS研究高比能LiMn2O4材料的局域结构

用EXAFS和XANES技术研究了高温固相反应法合成尖晶石结构的LiMn2O4中Mn原子的局域结构受到焙烧温度的影响.XANES结果表明,B1峰和B2峰强度分别与Mn3+,Mn4+的含量高低相关,焙烧温度愈高,B1峰的强度愈大.EXAFS给出的结构参数结果进一步表明,LiMn2O4(673K)的Mn-O第一配位和MnMn第二配位的无序度σ1(0.0059nm)和σ2(0.0092nm)分别小于及大于LiMn2O4(973K)的σ1(0.0066nm)和σ2(0.0081nm),LiMn2O4(1073K) 关键词： XAFS 局域结构 尖晶石LiMn2O4     

Effect of fluorine in Li1.27Cr0.2Mn0.53O2 cathode for secondary lithium batteries

Fluorine substituted Li_1.27Cr_0.2Mn_0.53O₂ electrode, prepared by sol–gel method, was investigated in the present work. Thermal analysis was done on this cathode material and found to be thermally stable with a loss of weight near 300 °C. Influence of fluorine substitution on the structural and electrochemical properties of the Li_1.27Cr_0.2Mn_0.53O₂ electrode was studied by X-ray diffraction (XRD) and field emission scanning electron microscope. XRD pattern of the fluorine-doped Li_1.27Cr_0.2Mn_0.53O₂ cathode material quenched at 900 °C indicates a phase pure material. The charge–discharge profile of the prepared cathode material showed that the fluorine substitution for oxygen in the cathode material resulted in improved capacity retention. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Li4Ti2.5Cr2.5O12 as anode material for lithium battery

Chromium-substituted Li₄Ti₅O₁₂ has been investigated as a negative electrode for future lithium batteries. It has been synthesized by a solid-state method followed by quenching leading to a micron-sized material. The minimum formation temperature of Li₄Ti_2.5Cr_2.5O₁₂ was found to be around 600 °C using thermogravimetric and differential thermal analysis. X-ray diffraction, scanning electron microscopy, cyclic voltammetry (CV), impedance spectroscopy, and charge–discharge cycling were used to evaluate the synthesized Li₄Ti_2.5Cr_2.5O₁₂. The particle size of the powder was around 2–4 μm. CV studies reveal a shift in the deintercalation potential by about 40 mV, i.e., from 1.54 V for Li₄Ti₅O₁₂ to 1.5 V for Li₄Ti_2.5Cr_2.5O₁₂. High-rate cyclability was exhibited by Li₄Ti_2.5Cr_2.5O₁₂ (up to 5  C) compared to the parent compound. The conduction mechanism of the compound was examined in terms of the dielectric constant and dissipation factor. The relaxation time has been evaluated and was found to be 0.07 ms. The mobility was found to be 5.133 × 10⁻⁶ cm² V⁻¹ s⁻¹.     

Silver-coated LiVPO4F composite with improved electrochemical performance as cathode material for lithium-ion batteries

Nano-structured LiVPO₄F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO₄F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO₄F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO₄F material exhibits high discharge capacity, good cycle performance (108.5 mAh g⁻¹ after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g⁻¹ for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (R_ct) of LiVPO₄F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO₄F for lithium-ion batteries cathode material.     

Characterization and electrochemical performance of the spinel LiMn2O4 prepared from -MnO2

The preparation and characterization of the spinel LiMn₂O₄ obtained by solid state reaction from quasi-amorphous -MnO₂ is reported. A well-defined highly pure spinel was characterized from X-ray diffractograms. The average manganese valence of -MnO₂ and spinel samples was found to be 3.89±0.01 and 3.59±0.01, respectively. The electrochemical performance of the spinel was evaluated through cyclic voltammetry and chronopotentiometry. The voltammetric profiles obtained at 1 mV/s for the LiMn₂O₄ electrode in 1 M LiClO₄ dissolved in a 2:1 mixture of ethylene carbonate and dimethyl carbonate showed typical peaks for the lithium insertion/extraction reactions. The charge capacity of this electrode was found to be 110 mA h g⁻¹ for the first charge/discharge cycles.     

Preparation and characterization of Li2CoMn3O8 thin film cathodes for high energy lithium batteries

An ion layer gas reaction (ILGAR) dip-coating process for the deposition of homogeneous spinel structured Li₂CoMn₃O₈ thin layers has been developed. Thin film cathodes for use in high-energy density lithium batteries with thicknesses of about 200 nm have been prepared. The films were found to be X-ray amorphous after preparation. After annealing at 700°C in air for 2 h, the spinel structure of Li₂CoMn₃O₈ was observed by X-ray diffraction analysis. The composition of the surface was studied by XPS, which indicated enhanced Li and Mn concentrations as a result of the rinsing process and different solubilities of the precursor salts. The electrochemical behavior was investigated by separating the annealed electrode sample from a conventional organic lithium ion-conducting electrolyte by a layer of LiPON solid electrolyte and using elemental lithium as counter electrode. A capacity of 110.8 mAh/g was observed which is related to the valence changes of Mn and Co in the spinel structure.     

表面效应对锂离子电池正极材料LiMn2O4性能的影响

应用基于自旋极化和广义梯度近似(generalized gradient approximation,GGA)的密度泛函理论计算,研究了锂离子电池正极材料LiMn₂O₄ (001)表面原子和电子结构.发现表面和亚表面附近的原子在垂直于(001)面的方向上具有非常大的弛豫,这对LiMn₂O₄材料在锂离子电池中应用时发现的表面Mn的溶解现象有很大关联.由于表面效应,在LiMn₂O₄ (001) 表面只有三价Mn³⁺离子存在,而这些三价锰离子非常活跃,在该材料电极/电解液界面很容易发生歧化反应,从而加速了Mn的溶解.其他计算结果也和实验观察相符合. 关键词： 锂二次电池 表面弛豫 从头算     

熔融盐法合成锂离子电池正极材料纳米LiNiO2

采用熔融盐法,在较低的温度和较短的时间制备了符合理论化学计量比的纳米LiNiO₂.研究表明,经过空气中的低温预烧,可以使制备的纯相纳米LiNiO₂具有更加优良的结晶性能和更佳的电化学特性.添加预烧步骤前后所得最终产物的初始容量分别为151和148 mAh ·g^-1,经过100周的循环,容量衰减到55和118 mAh ·g^-1,容量保持率分别为36.4%和79.7%.原因在于预烧后再进行煅烧降低了阳离子无序度,减少了混杂 关键词： 2')" href="#">LiNiO₂ 熔融盐法 锂离子电池 电化学性能     

Synthesis and characterization of Cr8O21 as cathode material for rechargeable lithium batteries

Pure phase Cr₈O₂₁ with excellent electrochemical properties has been synthesized by sintering anhydrous chromium trioxide (CrO₃) at low temperature in flowing oxygen. Cyclic voltammetry (CV) and X-ray diffraction (XRD) characterizations indicate that the inner tetra-chromate groups of Cr₈O₂₁ are damaged and Cr₈O₂₁ is changed to another layer-structured material when lithium is inserted into the host.     

First principles study on Mn-doped LiFePO4 as cathode material for rechargeable lithium batteries

The electronic structure and diffusion energy barriers of Li ions in pure and Mn-doped LiFePO4 have been studied using density functional theory(DFT).The results demonstrate clearly that Fe-O covalent bond is weaker than P-O covalent bond.Pure LiFePO4 has band gap of 0.56 eV and diffusion energy barrier of 2.57 eV for Li ions,while the dopant has small band gap of 0.25 eV and low diffusion energy barrier of 2.31 eV,which indicates that the electronic and ionic conductivity of LiFePO4 have been improved owing to doping.