Wet chemical synthesis and photocatalytic activity of potassium niobate K6Nb10.8O30 powders

The nanometer potassium niobate powders with tungsten bronze (TB)-type structure were synthesized by a wet chemical method and characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). X-ray photoelectron spectroscopy (XPS) analysis confirmed the niobium with mixed valence states exists in the crystal structure of the photocatalyst, which may be advantage for increasing the photocatalytic activity. The band gap of K₆Nb_10.8O₃₀ powders was estimated to be about 2.92 eV and shows a markedly blue-shift as compared to that of the sample obtained by the solid-state reaction. The photocatalytic activity of the samples was evaluated by degradation of acid red G under UV irradiation and the photocatalytic reaction follows first-order kinetics. The photocatalytic activity of the as-prepared sample is much higher than that of sample synthesized by solid-state reaction, and slightly higher than that of P25-TiO₂.     

Effects of Ni-ion doping on electrochemical characteristics of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by a spray-drying method

Spinel LiMn_2−x Ni _x O₄ compounds doped with a range of Ni (x=0–0.06) were synthesized by a spray-drying method. The structure and morphology characteristics of the powders were studied in detail by means of X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. The XRD data reveal that all the samples have well-defined spinel structure, but, with the increase in Ni content, the doped lithium manganese spinels have smaller lattice constant. The undoped and doped spinel LiMn₂O₄ particles are fine, narrowly distributed, and well crystallized. The electrochemical characteristics of the samples are measured in the coin-type cells in a potential range of 3.2–4.35 V vs Li/Li⁺. All cyclic voltammogram curves exhibit two pairs of redox reaction peaks, but, among them, there are some differences about the peak split. With the increase in the Ni content, the specific capacities of the samples decrease slightly, but their cyclic ability increases.     

Li2CO3、NiO和电解MnO2合成高容量LiNi0.5Mn1.5O4及其表征

Well-developed crystalline LiNi_0.5Mn_1.5O₄ was prepared by solid-state reaction using Li₂CO₃, NiO and electrolytic MnO₂ at high heating and cooling rate. X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images showed that LiNi_0.5Mn_1.5O₄ synthesized at 900 ℃ and 950 ℃ had cubic spinel structure with clearly defined shape. LiNi_0.5Mn_1.5O₄ spinel phase decomposed at 1 000 ℃ accompanying with structural and morphological degradation. TG measurement revealed that the weight loss during heating process could be mostly gained in cooling process, and the upward tendency of weight loss during heating process decreased, while that of irreversible weight loss rapidly increased with the increase of temperature. LiNi_0.5Mn_1.5O₄ powders prepared at 900 ℃ for 12 h delivered the maximum discharge capacity of 134 mAh·g^-1 with good cyclic performance at 2/7 C. In addition, by adjusting the calcination time at 900 ℃, the capacity and cycling performance of LiNi_0.5Mn_1.5O₄ were further enhanced.     

LiFePO4：水热合成及性能研究

LiFePO4是继尖晶石型LiMn2O4[1]之后的一种新型锂离子电池正极材料,其具有结构稳定,工作电位适中(3.45VvsLi/Li )、可逆容量高、无毒价廉等优点,被认为是极具发展潜力的锂离子电池正极材料[2]。有关LiFePO4的结构[3]和性能[4]研究引人关注。目前,LiFePO4主要是采用高温固相法[5]来合成,尽管简单方便,但由于该传统方法的局限性,很难得到纯度高、粒径小、电性能好的LiFePO4。因此人们尝试用微波加热[6]、溶胶-凝胶[7]、共沉淀[8]等制备方法,希望得到理想的LiFePO4材料,但是采用水热法制备LiFePO4鲜见报道。本文采用水热法制备了纯…     

锂离子电池正极材料LiMn2O4的合成与晶体结构（英）

Spinel LiMn₂O₄ powders were prepared using two-step synthesis method consisting of solid-state reaction method and citrate modified sol-gel method. The effects of the calcination temperature and the Li/Mn ratio of raw materials were studied on the physicochemical and electrochemical properties of the spinel LiMn₂O₄ powders, such as crystallinity, lattice constant and density. The title compound was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polycrystalline LiMn₂O₄ powers calcined at 750 ℃ were found to be composed of very uniformly-sized microcrystal with an average particle size of 300 nm. The improvement in electrochemical properties was mainly attributed to the process of re-grinding by absolute alcohol.     

异质双碳源对LiMn0.8Fe0.2PO4复合材料电化学性能的影响

采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn_0.8Fe_0.2PO₄/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn_0.8Fe_0.2PO₄/C复合材料进行了X射线衍射(XRD)、比表面积测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g^-1,达到其理论比容量的 87%;在 5C 下最大的放电比容量为 133 mAh·g^-1;在 2C 倍率下经过 300 次循环后比容量维持在 127 mAh·g^-1,衰减率仅为1.9%,表现出了优良的循环稳定性。     

Synthesis,characterization and lithium-intercalation properties of rod-like CaMoO<Subscript>4</Subscript> nanocrystals

Rod-like CaMoO₄ nanocrystals were synthesized via a template-based rheological phase reaction route as a novel method. The physical characterization was carried out by thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elected-area electron diffraction (SAED). A structure-directed role of hexamethylene tetramine (HMTA) was observed during the formation of CaMoO₄ nanocrystals. The electrochemical performance of CaMoO₄ as anode for lithium ion batteries has also been investigated by galvanostatic cycling and AC impedance spectroscopy. CaMoO₄/Li cell can deliver superior capacity than theoretical value in the initial cycle, and the much improved capacity was attributed to the contribution of oxygen besides the reduction of molybdenum during lithium insertion. Furthermore, a charge capacity of 276 and 438 mAh/g was retained after 50 cycles in the range of 0.01–2.50 V vs Li at a current density of 100 and 200 mA/g, respectively. The particle size and morphological properties were found to play an important role in fast lithium insertion/extraction performance and cycling stability at high rate.     

Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> powders by the complex polymerization method: synthesis,characterization and morphology

Lanthanum-modified bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂, BLTO) powders were prepared by the complex polymerization method. The structure and morphology of BLTO powders were investigated by X-ray diffraction and scanning electron microscopy. The complexation of citric acid with the metallic cations was detected by Fourier transformed infrared (FT-IR). The thermal analyses of obtained gels were investigated by differential thermal gravimetric (DTG). The pure and normally stoichiometric phase of BLTO powders could be obtained at relatively low temperature of 550–700 °C even if the bismuth content is not excess in the starting precursors, while the secondary phase could be detected at lower and higher calcination temperatures. The shape of the BLTO grains is similarly to platelet in Bi-layer structure and stoichiometry BLTO was detected by the analysis of energy dispersive spectrometry.     

Synthesis and tunable thermal expansion property of Al2−δScδW3O12

A series of solid solutions of Al_2−δSc_δW₃O₁₂ (δ = 0-2) were successfully synthesized by the solid-state reaction with aluminum oxide, scandium oxide and tungsten trioxide as raw materials. The phase composition and structure of the products were analyzed by X-ray powder diffraction and scanning electron microscopy, while the linear thermal expansion coefficients were measured by thermo dilatometer. The results indicate that Al_2−δSc_δW₃O₁₂ with high purity can be successfully prepared by the solid-state method. All samples of different δ values crystallize in the same orthorhombic structure with space group of Pnca. The lattice constants and cell volume increase linearly with increasing Sc content. The average linear thermal expansion coefficients of Al_2−δSc_δW₃O₁₂ measured by thermo dilatometer indicate that the thermal expansion coefficients of the solid solutions could be adjusted to the desired values, such as positive, near zero or negative by simply changing the δ value.     

Synthesis and characterization of La2Mo2O9 obtained from freeze-dried precursors

La₂Mo₂O₉ ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La₂Mo₂O₉ from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries.     

纳米CuFe2O4-rGO复合材料的制备及电化学性能

采用溶剂热法成功制备了纳米CuFe₂O₄-rGO复合材料。通过X射线衍射（XRD）,扫描电子显微镜（SEM）、透射电子显微镜（TEM）和电化学工作站对样品的结构、形貌及电容特性进行表征。结果表明,CuFe₂O₄纳米粒子均匀地分散在石墨烯片层间,其中CuFe₂O₄-20% rGO复合材料具有最优的电化学性能,当电流密度1 A·g^-1时,其比电容为1 952.5 F·g^-1,当电流密度为1 A·g^-1时,CuFe₂O₄-20% rGO复合材料经1 000次充放电后的比电容保持率为86.17%。     

纳米CuFe_2O_4-rGO复合材料的制备及电化学性能

采用溶剂热法成功制备了纳米CuFe_2O_4-rGO复合材料。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电化学工作站对样品的结构、形貌及电容特性进行表征。结果表明,CuFe_2O_4纳米粒子均匀地分散在石墨烯片层间,其中CuFe_2O_4-20%rGO复合材料具有最优的电化学性能,当电流密度1 A·g~(-1)时,其比电容为1 952.5 F·g~(-1),当电流密度为1 A·g~(-1)时,CuFe_2O_4-20%rGO复合材料经1 000次充放电后的比电容保持率为86.17%。     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

EDTA-甘氨酸法制备SmBaCo2O5+δ阴极材料及其性能

采用EDTA-甘氨酸法(EGP)合成了中温固体氧化物燃料电池(IT-SOFC)的阴极材料SmBaCo2O5+δ(SBCO).通过热重-差热分析(TG-DTA),X射线衍射(XRD),透射电镜(TEM),扫描电镜(SEM),直流四极法及交流阻抗技术分析材料的性能.结果表明,初始粉体在850°C煅烧5 h形成钙钛矿结构单相.EGP制备的SBCO粉体颗粒细小、分散性好、粒径分布均匀,其与Sm0.2Ce0.8O1.9(SDC)电解质材料具有良好的高温化学相容性.SBCO的电导率在500-800°C时达到668-382 S cm-1.以SDC为电解质,SBCO为阴极制备对称半电池,其界面结合良好,颗粒连接充分,形成好的三相界面,具有高的阴极催化活性,750°C时阴极极化电阻为0.0688Ωcm2,远低于固相法(SSR)的值,活化能(Ea)为122.21 kJ mol-1.     

前处理时间对Co_3O_4形貌及光催化性能的影响

以Co Cl2、Na2CO3为原料,以油酸钠(SOA)为表面活性剂,采用水热-热分解法合成了纯相尖晶石结构的Co3O4粉体。利用TG-DTA、XRD和SEM等手段跟踪反应过程,研究了不同水热时间对产物形貌和结构的影响,并根据实验结果分析了可能的反应机理及结构对光催化性能的影响。实验结果表明:制备前驱体的水热时间是影响产物形貌的关键因素,并且终产物的结构形貌很大程度上决定了其光催化性能。     

前处理时间对Co3O4形貌及光催化性能的影响

以CoCl₂、Na₂CO₃为原料, 以油酸钠(SOA)为表面活性剂, 采用水热-热分解法合成了纯相尖晶石结构的Co₃O₄粉体。利用TG-DTA, XRD和SEM等手段跟踪反应过程, 研究了不同水热时间对产物形貌和结构的影响, 并根据实验结果分析了可能的反应机理及结构对光催化性能的影响。实验结果表明:制备前驱体的水热时间是影响产物形貌的关键因素, 并且终产物的结构形貌很大程度上决定了其光催化性能。     

Ge4+、Sn4+掺杂尖晶石LiMn2O4的合成与电化学表征

使用Ge⁴⁺、Sn⁴⁺作为掺杂离子, 通过高温固相法制备四价阳离子掺杂改性的尖晶石LiMn₂O₄材料. X射线衍射(XRD)和扫描电子显微镜(SEM)分析表明, Ge⁴⁺离子取代尖晶石中Mn⁴⁺离子形成了LiMn_2-xGe_xO₄ (x=0.02,0.04, 0.06)固溶体; 而Sn⁴⁺离子则以SnO₂的形式存在于尖晶石LiMn₂O₄的颗粒表面. Ge⁴⁺离子掺入到尖晶石LiMn₂O₄材料中, 抑制了锂离子在尖晶石中的有序化排列, 提高了尖晶石LiMn₂O₄的结构稳定性; 而在尖晶石颗粒表面的SnO₂可以减少电解液中酸的含量, 抑制酸对LiMn₂O₄活性材料的侵蚀. 恒电流充放电测试表明, 两种离子改性后材料的容量保持率均有较大幅度的提升, 有利于促进尖晶石型LiMn₂O₄锂离子电池正极材料的商业化生产.     

片状MoS2/MoS1.5Se0.5纳米复合材料的制备及其摩擦学性能研究

将钼粉与升华硫和硒粉的混合粉末按一定化学计量比混合,通过固相反应法成功制备出了均匀的片状纳米颗粒。分别使用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)以及透射电子显微镜(TEM)对该纳米粉体进行结构表征和分析,发现该粉体为MoS2/MoS1.5Se0.5混合晶相,晶粒尺寸在300~600 nm,厚度约为5 nm的片状结构。将该MoS2/MoS1.5Se0.5纳米片作为润滑油添加剂添加到基础油中,使用UMT-2型摩擦磨损试验机对其摩擦学性能进行测试,并对摩擦机理进行了解释,结果表明MoS2/MoS1.5Se0.5纳米片作为润滑油添加剂具有良好的减摩抗磨性能。     

Comparison of different soft chemical routes synthesis of nanocrystalline LiMn2O4 and their influence on its physicochemical properties

A comparative study of nanocrystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as solution and sol-gel methods using lithium and manganese acetates are the precursors under different calcination temperatures. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using thermal analysis (TGA/DTA), FTIR, X-ray diffraction studies, SEM, specific surface area (BET) and electrical conductivity measurements. The results show that pure LiMn₂O₄ can be prepared from acetate precursors as starting materials at a low temperature of 600°C from solution route and 500°C from sol-gel method. The charge-discharge characteristics and the cycling behavior of Li/1M LiBF₄-EC/DEC electrolyte / LiMn₂O₄cells revealed that LiMn₂O₄ calcined at higher temperatures showed a high initial capacity, while the LiMn₂O₄calcined at lower temperatures exhibited a good cycling behavior.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and LiCoO<Subscript>2</Subscript> composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn₂O₄/(1 ? x) LiCoO₂(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn₂O₄ and LiCoO₂ partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ～100 mAh/g.