Rapid evaluation of charge/discharge properties for lithium manganese oxide particles at elevated temperatures

A microelectrode technique was applied to investigate the electrochemical properties of LiMn₂O₄ particles at elevated temperatures. Cyclic voltammograms of LiMn₂O₄ were measured after the particles were exposed to the electrolytes. This technique results in rapid and precise evaluation of the redox behavior of the materials. A significant capacity fading was observed in 1 M LiPF₆/EC+PC electrolytic solution, which indicates that both LiMn₂O₄ and LiPF₆ participate in the reaction to produce an inert material on the particle surface. Next, the capacity fading for two different BET surface area particles were compared using 1 M LiPF₆/EC+PC at 50 °C. The reaction was found not to be controlled by the surface area. Finally, a Li_1.1Mn_1.9O₄ particle was employed. The fading in discharge was ca. 10% for 50 cycles even at 50 °C, which means that the partial substitution of Mn in LiMn₂O₄ by Li substantially enhanced the capacity stability. Electronic Publication     

Influence of sequential lithium insertions on the physical properties of spinel manganese oxide

We present first principles studies based on density functional theory (DFT) to investigate the lithium intercalation process in spinel manganese oxide compound. The lattice volume change, energetics, and insertion voltage were systematically examined upon sequential lithium insertions into the lattice. The charge transfer mechanism upon lithium intercalation was studied by analyzing the calculated spectra of density of states. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

High-temperature X-ray diffraction study of crystallization and phase segregation on spinel-type lithium manganese oxides

To study crystallization process of spinel-type Li_1+xMn_2−xO₄, in-situ high-temperature X-ray diffraction technique (HT-XRD) was utilized for the mixture consisting of Li₂CO₃ and Mn₂O₃ as starting material in the temperature range of 25-700 °C. In-situ HT-XRD analysis directly revealed that crystallization process of Li_1+xMn_2−xO₄ was significantly affected by the difference in the Li/Mn molar ratio in the precursor. Single phase of stoichiometric LiMn₂O₄ formed at 700 °C. The formation of single phase of spinel was achieved at the lower temperature than the stoichiometric sample as Li/Mn molar ratio in the precursor increased. Lattice parameter of the stoichiometric LiMn₂O₄ at 25 °C was 8.24 Å and expanded to 8.31 Å at 700 °C, which corresponds to the approximately 3% expansion in the unit cell volume. From the slope of the lattice parameter change as a function of temperatures, linear thermal expansion coefficient of the stoichiometric LiMn₂O₄ was calculated to be 1.2×10⁻⁵ °C⁻¹ in this temperature range. When the Li/Mn molar ratio in Li_1+xMn_2−xO₄ increased (x > 0.1), the spinel phase segregated into the Li_1+yMn_2−yO₄ (x > y) and Li₂MnO₃ during heating, which involved the oxygen loss from the materials. During the cooling process from 700 °C, and the segregated phase merged into Li_1+xMn_2−xO₄ with oxygen incorporation. Such trend directly observed by in-situ HT-XRD was supported by thermal gravimetric analysis as reversible weight (oxygen) loss/gain at higher temperature (500-700 °C).     

Solar photocatalytic activities of porous Nb-doped TiO2 microspheres prepared by ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis method was used to prepare Nb-doped TiO₂ porous microspheres with an average diameter of 500 nm for solar photocatalytic applications. The effect of Nb-doping on morphology, structure, surface area, as well as spectral absorption properties of TiO₂ microspheres was investigated with SEM, TEM, XRD, Raman spectra, BET, and UV-Vis absorption spectra. The Nb-doping decreased the grain size of TiO₂ porous microsphere, and influenced its surface area and pore size distribution dependent on the doping concentration, but changed negligibly the morphology and size of TiO₂ microspheres. Moreover, the Nb-doping was observed to extend the spectral absorption of TiO₂ into visible spectrum, and the absorption onset was red-shifted for about 88 nm at a doping level of 5% compared to pristine TiO₂ microspheres. Under solar or visible irradiation, Nb-doped TiO₂ microspheres showed higher photocatalytic activity for methylene blue degradation compared with TiO₂ microspheres, which could be ascribed to the extended light absorption range and the suppression of electron-hole pair recombination.     

Fabrication of minimal capital-intensive scratch-resistant and hydrophobic tungsten oxide film on stainless steel through spray pyrolysis

In this contribution, a pure and robust tungsten oxide (WO₃) film was accomplished on stainless steel (SS) substrate at 400°C through a minimal capital intensive, simplistic spray pyrolysis method by utilizing a precursor comprising tungsten hexachloride and 2-methoxyethanol. Thermal analysis revealed the precursor's thermal decomposition and crystallization at ~230°C and 255°C, respectively. The fabricated polycrystalline (monoclinic crystal structured) film was uniform and dense in nature, exhibiting surface porosity and average surface roughness of 4.7 % and 15.9 nm, respectively. The average grain size and thickness of film were 360 ± 70 nm and ~3.6 μm, respectively. W, O elemental presence with a close atomic ratio of 1:3 on the film's surface was acquired along with 91 % lattice oxygen. Regardless of applied normal load in the range of 5 to 15 N, an increment of ~22 % in scratch hardness was gained in WO₃-coated SS compared to uncoated one. Hydrophilic natured WO₃ film (water contact angle, WCA, of ~31°) was efficaciously transformed into hydrophobic (WCA, 136°) by chemical modification with octadecyltrichlorosilane to create a self-assembled monolayer on the surface of the film. The hydrophobicity of octadecyltrichlorosilane (OTS)-treated film was found to be preserved even after 100 days.     

Synthesis of iron oxide cubes/reduced graphene oxide composite and its enhanced lithium storage performance

Fe₃O₄ is considered as a promising electrode material for lithium-ion batteries(LIBs) due to its low cost and high theoretical capacity(928 mAh/g).Nevertheless,the huge volume expansion and poor conductivity seriously hamper its practical applications.In this study,we use a facile hydrothermal reaction together with a post heat treatment to construct the three-dimensional heterostructured composite(Fe₃O₄/rGO) inwhich reduced graphene oxide sheets wraped the Fe₃O₄ submicron cubes as the conductive network.The electric conduction and electrode kinetics of lithium ion insertion/extraction reaction of the composite is enhanced due to the assist of conductive rGO,and thus the Listorage performance is obviously improved.The composite exhibits a reversible charge capacity of772.1 mAh/g at the current density of 0.1 A/g,and the capacity retention reaches 70.3% after400 cycles at0.5 A/g,demonstrating obviously higher specific capacity and rate capability over the Fe₃O₄ submicron cubes without rGO,and much superior cycling stability to the parent Fe_2 O_3 submicron cubes without rGO.On the other hand,as a synergic conductive carbon support,the flexible rGO plays an important role in buffering the large volume change during the repeated discharge/charge cycling.     

Synthesis and characterization of alumina- and zirconia-based powders obtained by the ultrasonic spray pyrolysis

The ultrasonic spray pyrolysis (USP) technique was used for synthesis of alumina- and zirconia-based powders. The starting agents were aqueous solutions, atomized by the ultrasonic spray generator and pyrolized in the furnace under the open-air conditions. The powders prepared by USP were in the form of solid and hollow aggregates (spheres) consisted of nanosize amorphous grains as determined by the microscopy and the X-ray diffraction techniques. The alumina-based powders were consolidated by the pulse plasma sintering resulting in single-phase materials. Different behavior of solid and hollow particles during the isostatic sintering is found; a higher degree of deformation of spheres is observed in the second case.     

Enhanced electrochemical performance of submicron LiCoO<Subscript>2</Subscript> synthesized by polymer pyrolysis method

Submicron LiCoO₂ was synthesized by a polymer pyrolysis method using LiOH and Co(NO₃)₂ as the precursor compounds. Experimental results demonstrated that the powders calcined at 800 °C for 12 h appear as well-crystallized, uniform submicron particles with diameter of about 200 nm. As a result, the as-prepared LiCoO₂ electrode displayed excellent electrochemical properties, with an initial discharge capacity of 145.5 mAh/g and capacity retention of 86.1% after 50 cycles when cycled at 50 mA/g between 3.5 and 4.25 V. When cycled between 3.5 and 4.5 V, the discharge capacity increased to 177.9 mAh/g with capacity retention of 85.6% after 50 cycles.     

铝基化合物改性富锂锰三元正极材料的高温性能

通过多相复合分别制备了Al₂O₃、AlF₃、AlPO₄改性的富锂锰三元正极材料(Li_1.2Ni_0.133Co_0.133Mn_0.533O₂,LR)。采用X射线光电子能谱、透射电镜和电化学交流阻抗等对复合材料的成分结构、高温下的电化学性能及作用机理进行了研究。结果表明:Al₂O₃改性的Li_1.2Ni_0.133Co_0.133Mn_0.533O₂(LRO)性能最佳,包覆层薄且均匀;在50℃高温下,LRO的200圈平均放电比容量为189.5 mAh·g^-1,容量保持率为81.5%,比原材料分别提高61.5 mAh·g^-1、49.8%;100圈循环后的电荷转移电阻为443.1 Ω,仅为原材料一半,表现出较优的电化学性能。     

铝基化合物改性富锂锰三元正极材料的高温性能

通过多相复合分别制备了Al₂O₃、AlF₃、AlPO₄改性的富锂锰三元正极材料(Li_1.2Ni_0.133Co_0.133Mn_0.533O₂,LR)。采用X射线光电子能谱、透射电镜和电化学交流阻抗等对复合材料的成分结构、高温下的电化学性能及作用机理进行了研究。结果表明：Al₂O₃改性的Li_1.2Ni_0.133Co_0.133Mn_0.533O₂(LRO)性能最佳,包覆层薄且均匀;在50℃高温下,LRO的200圈平均放电比容量为189.5mAh·g^-1,容量保持率为81.5%,比原材料分别提高61.5 mAh·g^-1、49.8%;100圈循环后的电荷转移电阻为443.1 Ω,仅为原材料一半,表现出较优的电化学性能。     

铝基化合物改性富锂锰三元正极材料的高温性能

通过多相复合分别制备了Al₂O₃、AlF₃、AlPO₄改性的富锂锰三元正极材料(Li_1.2Ni_0.133Co_0.133Mn_0.533O₂,LR)。采用X射线光电子能谱、透射电镜和电化学交流阻抗等对复合材料的成分结构、高温下的电化学性能及作用机理进行了研究。结果表明：Al₂O₃改性的Li_1.2Ni_0.133Co_0.133Mn_0.533O₂(LRO)性能最佳,包覆层薄且均匀;在50℃高温下,LRO的200圈平均放电比容量为189.5mAh·g^-1,容量保持率为81.5%,比原材料分别提高61.5 mAh·g^-1、49.8%;100圈循环后的电荷转移电阻为443.1 Ω,仅为原材料一半,表现出较优的电化学性能。     

Influence of substrate temperature on the structural and optical properties of crystalline ZnO films obtained by pulsed spray pyrolysis

In this work, we report on the structural and optical properties of ZnO films deposited by pulsed spray pyrolysis at relatively low temperatures, compatible with a large variety of substrates and processing technologies. Crystalline ZnO films were deposited onto glass substrates using zinc acetate dihydrate dissolved in distilled water with concentration of 0.2 M. The temperature of the substrate was varied in the range T_s = 473–673 K with ΔТ = 50 K. Effect of T_s were investigated by scanning electron microscopy, x‐ray diffraction and energy dispersive x‐ray, and optical spectroscopies. Also, the influence of T_s on the grain size, phase composition, texture quality, coherent scattering domain size, crystal lattice parameters, chemical composition, transmission coefficient, and the bang gap of the ZnO films were studied. X‐ray diffraction analysis revealed that films were polycrystalline with hexagonal phase and showed as preferential orientation (101) at T_s < 573 K and (100) and (002) at T_s > 573 K. Scanning electron microscopy (SEM) measurements showed that the substrate temperature has a strong effect on morphology of the films. Energy dispersive analysis revealed that ZnO films consisted of the non‐stoichiometric compounds. Optical measurements showed ZnO films to be highly transparent in the visible region, and optical band gap is shifting from 3.18 eV to 3.30 eV. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and electrochemical properties of Co3O4-coated layered manganese oxide by a novel coating method

Potassium type birnessite (K-bir) was synthesized by O₂ oxidizing Mn²⁺ in aqueous solution of KOH. Co₃O₄-coated K-bir (Co-K-bir) was prepared by employing a novel coating method, in which the remaining OH⁻ ions on the particle surface of the as-precipitated K-bir reacted with Co²⁺ ions in aqueous solution, forming CoOOH coverage; the coating layer of CoOOH was subsequently annealed at 300 °C to transform into Co₃O₄. All the K-bir and Co-K-birs were investigated by scanning electron microscopy, transmission electron microscopy, inductive coupled plasma–atomic emission spectroscopy, Brunauer–Emmett–Teller specific area, and laser particle size analyzing techniques. Their electrochemical properties were also studied by discharging–charging at constant current. The results show that the covering layers of Co₃O₄ are incompact, and their average thickness are about 0.65–0.78 μm. Compared to the as-prepared and the annealed K-bir, the Co₃O₄-coated samples have higher initial discharge capacities and show distinctly improved cycleability performance.     

锰源对尖晶石LiMn2O4高温性能的影响

为考察不同锰源对所制备尖晶石LiMn₂O₄(LMO)电化学性能的影响(特别是高温性能),采用沉淀法制备前驱体,通过不同煅烧温度制备得到最常用的锰氧化物(MnO₂、Mn₂O₃和Mn₃O₄)为锰源,经相同条件制备得到LMO正极材料,通过考察所得LMO形貌及电化学性能来研究锰源与LMO电化学性能的关系。研究结果表明,相同的前驱体在不同煅烧温度下可以得到不同的锰氧化物,且各自具有不同的形貌结构。由这些锰氧化物都可以得到高纯度的LMO,但产物形貌结构以及材料中的八面体晶体含量和尺寸不同。由Mn₂O₃制备得到的LMO材料中的八面体晶体含量最多,且尺寸最均匀,在3种LMO中容量性能、倍率性能和循环性能最好：0.2C(1C=148 mA·g^-1)下首次放电比容量为131.8 mAh·g^-1;3C下还有100.4 mAh·g^-1的放电比容量。其...     

锰源对尖晶石LiMn2O4高温性能的影响

为考察不同锰源对所制备尖晶石LiMn₂O₄(LMO)电化学性能的影响(特别是高温性能),采用沉淀法制备前驱体,通过不同煅烧温度制备得到最常用的锰氧化物(MnO₂、Mn₂O₃和Mn₃O₄)为锰源,经相同条件制备得到LMO正极材料,通过考察所得LMO形貌及电化学性能来研究锰源与LMO电化学性能的关系。研究结果表明,相同的前驱体在不同煅烧温度下可以得到不同的锰氧化物,且各自具有不同的形貌结构。由这些锰氧化物都可以得到高纯度的LMO,但产物形貌结构以及材料中的八面体晶体含量和尺寸不同。由Mn₂O₃制备得到的LMO材料中的八面体晶体含量最多,且尺寸最均匀,在3种LMO中容量性能、倍率性能和循环性能最好：0.2C(1C=148 mA·g^-1)下首次放电比容量为131.8 mAh·g^-1;3C下还有100.4 mAh·g^-1的放电比容量。其对应半电池在0.5C下循环100次后,放电比容量还有116.0 mAh·g^-1,容量保持率为93.9%,电化学储能性能远远优于其他2种LMO。即使是在高温55 ℃下,由Mn₂O₃得到的LMO也表现出明显优于其他2种材料的高倍率性能和抗衰减性能。     

Synthesis and characterization of LiCo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> powder by a novel CAM microwave-assisted sol–gel method for Li ion battery

LiMn₂O₄-based spinels are of great interest as positive electrode materials for lithium ion batteries. LiCo _x Mn_2−x O₄ (x = 0.0, 0.1, 0.2, 0.3, and 0.4) spinel phases have been synthesized by novel citric acid-modified microwave-assisted sol–gel method. The structural properties of the synthesized products have been investigated by X-ray powder diffraction and scanning electron microscopy. To improve the recharge capacity of Li/LiCo _x Mn_2−x O₄ cells, the electrochemical features of LiCo _x Mn_2−x O₄ compounds have been evaluated as positive electrode materials. The structural properties of Co-doped oxides are very similar to LiMn₂O₄ electrode. Techniques like cyclic voltammetry, charge–discharge and cycle life are also used to characterize the LiCo _x Mn_2−x O₄ (x = 0.0, 0.1, 0.2, 0.3, and 0.4) electrodes.     

Cyclic voltammetric study on the catalysis of electrodeposited manganese oxide on the electrochemical oxygen reduction reaction (ORR) in room temperature ionic liquids (RTILs) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF<Subscript>4</Subscript>) on glassy carbon clectrode

For the first time, the electrochemical oxygen reduction reaction (ORR), was investigated using cyclic voltammetry (CV) on the electrodeposited manganese oxide (MnO _x )-modified glassy carbon (MnO _x -GC) electrode in the room temperature ionic liquids (RTILs) of EMIBF₄, i.e. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄). The results demonstrated that, after being modified by MnO _x on a GC electrode, the reduction peak current of oxygen was increased to some extent, while the oxidation peak current, corresponding to the oxidation of superoxide anion, i.e., O₂⁻ was attenuated in some degree, suggesting that MnO _x could catalyze ORR in RTILs of EMIBF₄, which is consistent with the results obtained in aqueous solution. To accelerate the electron transfer rate, multi-walled carbon nanotubes (MWCNTs) was modified the GC electrode, and then MnO _x was electrodeposited onto the MWCNTs-modified GC electrode to give rise to a MnO _x /MWCNTs-modified GC electrode, consequently, the improved standard rate constant, k_s, originated from the modified MWCNTs, along with the modification of electrodeposited MnO _x , showed us a satisfactory electrocatalysis for ORR in RTILs of EMIBF₄. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 3, pp. 340–345. The article is published in the original.