锂离子电池负极材料Li_(4-x)K_xTi_5O_(12)结构和电化学性能

采用固相反应的方法制备了尖晶石型Li4Ti5O12和K掺杂Li4-xKxTi5O12(x=0.02,0.04,0.06)。通过XRD、SEM、BET等对制备材料进行了分析。结果表明,K掺杂没有影响立方尖晶石型Li4Ti5O12的合成,同时也没有改变Li4Ti5O12的电化学反应过程。K掺杂Li4-xKxTi5O12具有比Li4Ti5O12小的颗粒粒径和比Li4Ti5O12大的比表面积、孔容积。适量的K掺杂能够明显改善Li4Ti5O12的电化学性能,尤其是倍率性能,但是过多的K掺杂却不利于材料电化学性能的提高。研究表明,Li3.96K0.04Ti5O12体现了相对较好的倍率性能和循环稳定性。0.5C下,首次放电比容量为161mAh·g-1,3.0和5.0C下,容量保持分别为138和121mAh·g-1。3.0C下,200次循环后容量保持为137mAh·g-1。     

尖晶石对β／β″—Al2O3膜相组成和离子导电性的影响

以wag／P”－AI。O。为固体电解质的CO。、SO。、NO。等气体传感器的研究已有很多报道［‘－‘］，多采用的是个AI。O。结构的电解质。AI刀。和p”－AI刃。的结构具有一定的相似性，但后者具有更高的迁移离子浓度和更开放的晶体结构，表现出更好的离子导电性‘’‘．由于卢”－AI。O。为介稳结构，需要加入如Li。O、MgO等作为稳定剂才能稳定存在．以Li对稳定的产”－al。O。烧结较容易，P”－AI。O。相转化率高，但以MsO为稳定剂制备的”－AI刃。其显微结构和抗吸湿性能更为优越．LJLi对和MgO共同稳定的产”－AI。O。可以…     

Cu-Ni-Al尖晶石催化甲醇重整制氢:Al含量的影响

采用固相球磨法制备了Al含量不等的Cu-Ni-Al三元尖晶石固溶体催化剂，通过BET、XRD、H₂-TPR、XPS表征和催化性能评价，研究了Al含量对Cu-Ni-Al尖晶石的物化性质和甲醇制氢缓释催化性能的影响。结果表明，恒定Cu：Ni（molar ratio）=0.95：0.05，增加Al含量时（Al=2、3、4），所得催化剂的比表面积和孔体积都明显增大，且尖晶石晶胞常数和晶粒尺寸均减小，催化剂也变得难以还原。进一步研究发现，随着Al含量增加，尖晶石Ni²⁺含量略微增加，但尖晶石Cu²⁺含量大幅降低，因此，尖晶石结构中Cu²⁺和Ni²⁺的总量降低，表明Ni²⁺的存在抑制了Cu²⁺进入尖晶石结构。表面分析结果证实，Al含量增加导致催化剂表面由富Cu转变为富Al，表层尖晶石Cu²⁺含量降低，但仍高于体相含量。评价结果显示，随着Al含量增加，反应初始活性增大，CO选择性降低，但Al过量太多时催化稳定性降低，综合来说，Al=3的催化剂表现出较好的催化性能。结果表明，对于Cu-Ni-Al尖晶石缓释催化剂，存在最佳Al含量，对催化稳定性起到关键作用。     

LiMn2O4表面包覆Li4Ti5O12的制备及倍率特性

采用固相法合成了尖晶石型LiMn₂O₄，并通过溶胶-凝胶法制备了不同物质的量的百分比含量Li₄Ti₅O₁₂包覆的正极材料。X-射线衍射和扫描电镜结果表明，Li₄Ti₅O₁₂微粒包覆在LiMn₂O₄的表面没有产生晶体结构的变化。实验电池在室温下，以1C，2C和5C倍率作充放电循环测试；结果表明，与未包覆的LiMn₂O₄相比，表面包覆Li₄Ti₅O₁₂微粒的正极材料在高倍率下具有更好的循环稳定性。     

Activity promotion of anti-sintering AuMgGa2O4 using ceria in the water gas shift reaction and catalytic combustion reactions

Heterogeneous gold nanocatalysts have both inspired researchers with their unique catalytic performance and frustrated them due to the contradictions observed in their activities and stabilities. A recent breakthrough has shown that gold nanoparticles (NPs) can retain their catalytically active size over a MgGa₂O₄ spinel support upon sintering at high temperatures. Herein, we report the catalytic activity of anti-sintering Au

MgGa₂O₄ for use in water gas shift reaction (WGSR) and catalytic combustion reactions, and the promoting effect of ceria. Upon adding ceria to 800°C-aged Au

MgGa₂O₄, the CO conversion in the WGSR was increased from ～1.5% to ～34.0% at 450°C, and the “light-off” temperatures (T₅₀) for methane combustion and CO oxidation were decreased by ～80 and ～100°C, respectively. Characterizations using XRD, HAADF-STEM, EDS mapping, H₂-TPR, XPS, and DRIFTs confirmed the proximate contact of Au with ceria and their significant synergistic effect, which thereby combined the benefits of ceria toward the dissociation of H₂O or O₂ and the Au NPs toward activating CO or CH₄. These results show that this stepwise stabilization-activation strategy is efficient for rationally constructing stable and active gold nanocatalysts, which may open up possibilities for the wide application of gold nanocatalysts at elevated temperatures.     

Doping Effect on the Grain Growth of Spinel LiMn2O4 Prepared by Sol-Gel Methods

The cathode-active materials, Li1+yMxMn2-xO4 (M = Al, Co, Ni, Zn, y = 0.02, x = 0.02) powder, were synthesized by sol-gel method using LiOH, Mn(NO3)2 as the starting materials, citric acid as a carrier and Al(NO3)3·9H2O or Co(NO3)2·6H2O or Ni(NO3)2·6H2O or Zn(NO3)2·6H2O as dopants. The influence of different doping elements on the structural properties of the as-prepared samples was investigated by X-ray diffraction (XRD), infrared (IR) spectroscopy and scanning electron microscopy (SEM). X-ray diffraction patterns of the prepared samples were identified as the spinel structure with space group Fd3m. The grain size increases gradually as the sintering temperature rises and corresponding activation energies for the grain growth have been estimated using Arrhenius’ empirical relation.     

Heat of Formation for LiMyMn2−yO4 (M=Co,Cr, Li,Mg, Ni) Spinel Solid Solution

The enthalpy of formation for LiM_yMn_2–yO₄ (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn₂O₄ at 876 K was evaluated to be H_f⁰=–1404.2±6.4 kJ mol^–1. The partial substitution of Co and Ni for Mn decreased the absolute H_f⁰ value, while that of Cr and Mg for Mn increased the absolute H_f⁰ value. In the case of the partial substitution of Li for Mn, no marked change in H_f⁰ could be observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

X-ray study of some spinels containing gallium and manganese

The ternary oxides CrMnGaO₄, NiMnGaO₄, CuMnGaO₄ and ZnMnGaO₄, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga³⁺ [Mn²⁺ Cr³⁺] O ₄ ^2? . Ga³⁺ [Cu²⁺ Mn³⁺] O ₄ ^2? , Mn²⁺ [Ga³⁺ Ni³⁺] O ₄ ^2? and Zn²⁺ [Mn³⁺ Ga³⁺] O ₄ ^2? .     

Synthesis of lithium-manganese oxide spinel in hydrothermal conditions

Abstract

Lithium-manganese oxide spinel LiMn₂O₄ was synthesized in hydrothermal conditions (400°C, 20 MPa) in the course of thermovaporous treatment mixtures of MnO₂ and LiOH/or Li₂CO₃. The conditions of synthesis of the spinel as monophase product were determined. The obtained product has been characterized by means of various physical and chemical methods. The spinel has been used for manufacturing cathodes of rechargeable lithium cells. The cells discharged in the potential range 2.8-3.5 V. The specific capacity was 100-140mAh/g.     

Influence of intrinsic parameters on the particle size of magnetic spinel nanoparticles synthesized by wet chemical methods

The synthesis of magnetic spinel ferrites at the nanoscale is a field of intense study, because the mesoscopic properties enable their novel applications. Spinel nanoparticles have a promising role because of their extraordinary properties compared with those of micro and macro scale particles. Several colloidal chemical synthetic procedures have been developed to produce monodisperse nanoparticles of spinel ferrites and other materials using sol–gel, co-precipitation, hydrothermal, and microemulsion techniques. To improve the synthesis method and conditions, quality and productivity of these nanoparticles, understanding the effect of extrinsic (pH, temperature, and molecular concentration) and intrinsic parameters (site preferences, latent heat, lattice parameters, electronic configuration, and bonding energy) on the particle size during synthesis is crucial. In this review, we discuss the effect of the intrinsic parameters on particle size of spinel ferrites to provide an insight to control their particle size more precisely.