Effect of annealing on the morphology evolution and densification of LiMn2O4 film from chitosan-containing solution

Dense LiMn₂O₄ films deposited on a Pt-coated silicon substrate were obtained by annealing the deposited Li–Mn–O-chitosan films under a two-stage heat-treatment procedure. It was demonstrated that the heat-treatment at 300 °C plays an important role in the subsequent densification of LiMn₂O₄ films. This is attributed to the formation and rearrangement of the nano-sized LiMn₂O₄ crystallites. The surface morphology of the calcined Li–Mn–O-chitosan films was highly related to the annealing temperature. Ridge-like bumps formed on the surface of the films after being heated at 200 °C for 1 h. With calcination at 400 °C or higher, the surface morphology turned into a wrinkle-like microstructure. This morphology transformation is ascribed to the flowing characteristics of the Li–Mn–O-chitosan films during heat-treatment and subsequent thermal decomposition of the precursor at higher temperatures. Moreover, the electrochemical tests showed that the 700 °C-annealed LiMn₂O₄ film possesses the highest discharge capacity of 56.3 μA h/(cm² μm) and best capacity retention of 90.7% after 50 charge/discharge cycles of all annealed films.     

LiMn2O4 thin films derived by rapid thermal annealing and their performance as cathode materials for Li ion battery

1. Introduction Thin-film lithium-ion batteries have received considerable attention [1-4] because of their many possible applications, such as smart cards, CMOS-based integrated circuits, and microdevices [5-7]. Among the several thin films that can be used as cathode material for thin-film lithium-ion batter- ies, LiMn2O4 is one of the most studied cathode ma- terials [8-9] because of its relatively high-voltage plateau, nontoxicity, and good rechargeability. LiMn2O4 thin films have been…     

Structure and electrochemical properties of Li(Ni0.5Mn0.5)1-xTixO2 prepared by one-step solid state reaction

The layered compound Li(Ni_0.5Mn_0.5)_1-xTi_xO₂ powders were prepared with Ni(OH)₂, MnCO₃, Li₂CO₃ and TiO₂ by one-step solid state reaction. The effect of doping Ti on the structure and electrochemical properties was studied. The XRD results indicate that the powders with 0≤x≤0.05 have good layered structure and trace of impurity appears in the samples with x≥0.1. The SEM photographs show that the particle size distributes homogeneously and the sample with x=0.15 has larger particle size than other samples. The charge-discharge tests show that Li(Ni_0.5Mn_0.5)_0.95Ti_0.05O₂ synthesized at 800 °C for 36 h exhibits good electrochemical properties. It firstly delivers 173 mA·h/g and maintains 90% of the initial discharge capacity after 30 cycles. The cyclic voltammetry and differential capacity vs voltage curves show that the major oxidation and reduction peaks are around 3.95 V and 3.75 V, respectively, assigned to Ni²⁺/Ni⁴⁺ oxidation-reduction process. A weak peak around 4.5 V is found during the oxidation process in the first cycle, which can be regarded as the main reason of the large drop of discharge capacity in the initial cycle.     

Effect of calcination temperature on characteristics of LiNi1/3Co1/3Mn1/3O2 cathode for lithium ion batteries

LiNi1/3Co1/3Mn1/3O2 was synthesized by sol-gel method and effect of calcination temperature on characteristics of LiNi1/3Co1/3Mn1/3O2 cathode was investigated. The structure and characteristics of LiNi1/3Co1/3Mn1/3O2 were determined by XRD, SEM and electrochemical measurements. The results show that the compound LiNi1/3Co1/3Mn1/3O2 has layered structure with hexagonal lattice. With the increase of calcination temperature, the basicity of the material decreases, and the size of primary particle rises. The LiNi1/3Co1/3Mn1/3O2 calcined at 900 ℃ for 12 h shows excellent electrochemical performances with large reversible specific capacity of 157.5 mA-h/g in the voltage range of 2.75-4.30 V and good capacity retention of 94.03% after 20 charge/discharge cycles. Capacity of LiNi1/3Co1/3Mn1/3O2 increases with enhancement of charge voltage limit, and specific discharge capacities of 179.4 mA.h/g, 203.1 mA.h/g are observed when the charge voltages limit are fixed at 4.50 V and 4.70 V, respectively.     

Preparation and electrochemical performance of nanosized Co3O4 via hydrothermal method

The hydrotalcite-type cobalt compounds were prepared through oxidation of Co（OH）2 gel using NH4OH as precipitating agent and H2O2 as oxidant. These hydrotalcite-type cobalt compounds were transformed into Co3O4 through hydrothermal decomposition with nanostructural deformation. The precursor and product were characterized by Fourier-transform infrared（FT-IR） spectrum, X-ray diffractometry（XRD） and transmission electron microscopy（TEM）. The electrochemical performances of as-prepared nanosized Co3O4 as anode materials in lithium-ion batteries were tested by charge-discharge test in the voltage range of 0-3.0 V. The influence of morphology of Co3O4 particle on the capacity and cycling performance was studied. The results show that the shape and size of the final product can be controlled by altering cobalt sources. The irregular cubic Co3O4 with the average particle size of about 10 nm shows the best electrochemical performance. After 10 charge-discharge cycles, the specific charge capacity retains 555 mA.h/g.     

Li^＋ extraction/insertion reaction with Mg2Mn0.5Ti0.5O4 inverse spinel in the aqueous phase

An inverse spinel-type metal oxide, magnesium-manganese-titanium oxide (Mg2Mn0.5Ti0.5O4), were prepared using the coprecipitation/thermal crystallization method. The extraction/insertion reaction with this material was investigated by X-ray, saturation capacity of exchange, pH titration, and distribution coefficient (Kd) measurement The acid treatments of Mg2Mn0.5Ti0.5O4 caused Mg2 extractions of more than 81%, whereas the dissolutions of Mn4 and Ti4 were less than 10%. The experimental results proved that the acid-treated sample has a capacity of exchange 56 mg·g-1 for Li in the solution. The chemical analysis showed that the Li extraction/insertion progressed mainly by ion-exchange mechanism and surface adsorption.     

封孔处理等离子喷涂Cr2O3涂层耐蚀性的电化学表征

用等离子喷涂工艺在Q235钢基体上制备Cr₂O₃陶瓷涂层,并采用磷酸铝和环氧树脂对其进行封孔处理。利用图像分析法和电化学方法对封孔前后涂层的孔隙率进行了测试,采用弱极化技术和电化学阻抗谱技术对封孔前后涂层的耐蚀性能进行了研究。结果表明,封孔处理提高了涂层的耐蚀性能,环氧树脂封孔涂层的耐蚀性能更优异;陶瓷涂层在腐蚀介质中耐蚀性能主要取决于涂层的孔隙率。     

Structure and hydrogen storage properties of MgH2 catalysed with La2O3

The catalytic effect of the addition of lanthanum oxide (La₂O₃), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH₂ prepared by ball milling has been studied. The addition of La₂O₃ reduces the formation during milling of the metastable orthorhombic γ-MgH₂ phase. The desorption rate of samples with 1 and 2 mol% La₂O₃ comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La₂O₃. The presence of LaH₃ after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La₂O₃ gives a lower hysteresis factor compared with sample with 2 mol%.     

Characteristics and properties of surface coated nano-TiO2

Nano-TiO₂ was coated with Al₂O₃, SiO₂ and silane coupling agent by chemical liquid deposition. The coating was characterized by Raman spectroscopy, XRD, TEM and FT-IR. The coating content and anti-ultraviolet capacity of nano-TiO₂ were measured by XRF and UV-vis spectrometer. The results show that dense coatings containing 5% Al₂O₃ or SiO₂ can be obtained by mixing slurry at pH 10, adding coating reagent and neutralization reagent into the slurry for 60 min at 85–95 °C, and finally aging for 120 min. Noncrystal SiO₂ was coated on the surface of nano-TiO₂ to form silica gel polymer with a Ti—O—Si bond, while aluminum compound exists in the form of AlOOH and part Al(OH)₃. The integrated dense film can shield photocatalysis effectively. The inorganic coating film can increase the wettability for xylene and stability in water. The surface modification of nano-TiO₂ will not impair its ability for anti-ultraviolet radiation, and more short band ultraviolet radiation can be absorbed. In addition, the optimal coating amount of silane coupling agent should be less than 3% and the best wettability for xylene can be reached when the amount is 1.2%.     

保护渣对铝钛系夹杂物溶解的吸收规律

以CaO-SiO₂-Al₂O₃-Na₂O-CaF₂-MgO为基础渣系,采用旋转动力学方法研究了不同碱度、BaO质量分数(0~15%)、B₂O₃质量分数(0~15%)对连铸保护渣吸收Al₂O₃或TiO₂速率的影响以及吸收前后矿相变化。结果表明,保护渣吸收TiO₂的速率要远大于吸收Al₂O₃的速率;添加BaO或B₂O₃后均能提高保护渣吸收Al₂O₃和TiO₂的能力;保护渣主要物相为钙镁黄长石(2CaO·MgO·2SiO₂)、钙铝黄长石(2CaO·Al₂O₃·2SiO₂)、枪晶石(3CaO·2SiO₂·CaF₂)及玻璃相(Na₂O·Al₂O₃·SiO₂);添加BaO后,钙镁黄长石转变为重硅酸钡钙镁(2CaO·MgO·2SiO₂·BaO),并抑制黄长石和枪晶石晶体长大;当添加B₂O₃的质量分数不低于10%,保护渣形成的物相为玻璃相。试验条件下,不同碱度的保护渣和添加B₂O₃的保护渣中TiO₂仍以TiO₂形式存在,而在添加BaO的保护渣中,TiO₂形成钙钛矿。     

Characteristics of an electrochemical reduction of Ta2O5 for the preparation of metallic tantalum in a LiCl–Li2O molten salt

The electrochemical reduction of Ta₂O₅ in a LiCl–Li₂O molten salt system has been carried out in an electrolytic cell with an integrated cathode assembly. During the electrochemical run, Ta₂O₅ reacts chemically with Li₂O to form LiTaO₃. The chronopotentiometry method was used to prepare the metallic tantalum from Ta₂O₅. The electrolysis of Li₂O and the reduction of Ta₂O₅ and/or LiTaO₃ take place simultaneously at the cathode part of an electrolysis cell. The recycle of Li₂O by an O²⁻ diffusion occurs in the cell. The results suggest that the metallic tantalum is prepared successfully by an electrochemical reduction in the LiCl–Li₂O molten salt.     

阳极氧化钽酸锂薄膜在NaOH溶液中的腐蚀行为研究

通过阳极氧化法在高纯钽片表面制备了钽酸锂复合薄膜,采用浸泡失重法和电化学测试法考察了镀膜前后样品在10% (质量分数) NaOH溶液中的腐蚀行为。利用X射线衍射仪、扫描电子显微镜及能谱仪分别对薄膜的物相组成、表面及截面形貌、膜层厚度进行了测试分析。结果表明,阳极氧化后得到的复合薄膜由钽酸锂和氧化钽组成;该薄膜与基体之间结合良好,厚度约3 μm;镀膜后样品的质量腐蚀速率至少减少了6倍,腐蚀电流密度下降了2个数量级,腐蚀96 h后样品表面没有明显变化。而对比的纯钽样品却发生了严重的腐蚀反应,生成了很多长条状和多棱柱状的腐蚀产物Na₃TaO₄、Na₂Ta₂O₆和Na₈Ta₆O₁₉。     

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

A novel molybdenum diphosphate, Mo_1.3O(P₂O₇), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO₆ octahedra, P₂O₇ groups and also from MoO₄, Mo₂O₄ and Mo₃O₈ units containing Mo₂ and Mo₃ clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located.     

Synthesis and characterization of LiGaxMn2−xO4 (0 ≤ x ≤ 0.05) by triethanolamine-assisted sol–gel method

Spinel LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) cathode materials with phase-pure particles and nano-sized distribution were synthesized by sol–gel method using triethanolamine as the chelating agent. The effects of heat treatment on the physicochemical properties of the spinel LiGa_xMn_2−xO₄ powders were examined with thermogravimetric and differential thermal analysis (TG/DTA), powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). The LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) electrodes were characterized electrochemically by charge/discharge experiments under a current rate of 0.5C at 55 °C. Although the Ga-doped spinel electrode showed smaller initial discharge capacity, it exhibited better cycling performance than the undoped-LiMn₂O₄ electrode. The dQ/dV versus potential plots at 55 °C revealed that the improvement in cycling performance of the Ga-doped spinel electrode is attributed to stabilization of the spinel structure by the presence of gallium ion.     

含B2O3钙铝基连铸保护渣剪切变稀特性

为兼顾钙铝基连铸保护渣在结晶器弯月面上下方不同剪切速率区域的冶金功能,从非牛顿流体特性角度出发,研究了CaO-Al₂O₃-Li₂O-B₂O₃保护渣的剪切变稀特性。结果表明,在剪切稀化温度区间内,随着温度的降低,保护渣剪切变稀特性逐渐增强。在钙铝基保护渣中,B₂O₃对剪切变稀特性具有明显的抑制作用,该作用与其在硅酸系保护渣中的作用明显相反。在1 300 ℃下,B₂O₃质量分数由4%提高至6%时,保护渣剪切变稀特性逐渐减弱。当B₂O₃质量分数提高至8%时,保护渣转变为牛顿流体,剪切变稀特性消失。     

Cr/Al/B/diamond体系中金刚石表面的热爆反应涂层

采用Cr/Al/B/diamond粉体为原料,并添加少量Cr₂O₃或B₂O₃以诱发热爆反应。结果表明:在高纯Ar保护下,热爆反应后的试样粉末化严重,易将结合剂与金刚石颗粒分离。添加Cr₂O₃的原料体系发生热爆反应后,结合剂中的主相为Cr₂AlB₂,金刚石表面会形成含Cr₃C₂和Al的复合涂层,涂层的晶粒大小为0.5～7.0 μm。当金刚石质量分数为10%和20%时,试样中的金刚石颗粒表面涂覆良好,其起始和终止氧化温度都显著高于未涂覆金刚石的;而在金刚石质量分数较高时,其表面涂覆效果略差。添加B₂O₃的原料体系发生热爆反应后,金刚石表面的涂覆效果不佳,只有半数或以下数量的金刚石颗粒被涂覆。      

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

Synthesis and structure of a potassium nitridoditungstenate (K6W2N4O3), a potassium digermanate (K6Ge2O7) and a rubidium digermanate (Rb6Ge2O7)

Light yellow single crystals of potassium nitridoditungstate (K₆W₂N₄O₃) and pale single crystals of potassium digermanate (K₆Ge₂O₇) were obtained by the reaction of the metal oxides WO₃ (molar ratio, 1 : 15.7) or GeO₂ (molar ratio, 1 : 2) in alkali metal amide melts in an autoclave at 530–600 °C for 6–8 days. Colourless single crystals of rubidium digermanate (Rb₆Ge₂O₇) were prepared by the reaction of GeO₂ with rubidium amide (molar ratio, 1 : 2) in ammonia at 350 °C in a high-pressure autoclave (H. Jacobs and D. Schmidt, in E. Kaldis (ed.), High-pressure Ammonolysis in Solid State Chemistry, Current Topics in Materials Science, Vol. 8, North Holland, Amsterdam, 1981, p. 379) (p(NH₃) = 5.5 kbar) for 10 days. In all three cases other nitrogen-containing products were present.

The structures of the title compounds were determined on the basis of single-crystal data. They are isotypic or structurally closely related to each other: K₆W₂N₄O₃: P2₁/n, a = 6.720(2) Å, b = 9.473(1) Å, c = 9.581(2) Å, β = 91.99(2)°, Z = 2, R/R_w = 0.040/0.048, N(I) > 3σ(I) 2057, N(Var.) = 71. K₆Ge₂O₇: Pn, a = 6.529(2) Å, b = 9.079(4) Å, c = 9.162(6)Å, β = 91.85(4)°, Z = 2, R/R_w = 0.022/0.024, N(I) 3σ(I) = 1486, N(Var.) = 135. Rb₆Ge₂O₇: P2₁/n, a = 6.839(4) Å, b = 9.437(6) Å, c = 9.460(6) Å, β = 91.53(5)°, Z = 2, R/R_w = 0.061/0.074, N(I) 3σ(I) = 1055, N(Var.) = 71.     

Synthese und kristallstruktur von KCr0,8Al0,2Mo2O8

Single crystals of KCr_0.8Al_0.2Mo₂O₈ were prepared and investigated by the X-ray diffractometer technique. It shows a structure type related to trigonal KAIMo₂O₈, monoclinic NaCrMo₂O₈ or orthorhombic KInMo₂O₈, space group C_2h⁶—C2/c; a=17.445 Å, b=5.649 Å, c=8.997 Å, β=119.37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ is characterized by isolated MoO₄ tetrahedra, isolated (Cr/Al)O₆ octahedra and a distorted square antiprism around K⁺. The crystal structure is discussed with respect to those of related compounds.

Zusammenfassung

Einkristalle von KCr_0.8Al_0.2Mo₂O₈ wurden synthetisiert und mit Vierkreisdiffraktometertechnik röntgenographisch untersucht. Sie zeigen einen mit trigonal-KA1Mo₂O₈, monoklin-NaCrMo₂O₈ oder orthorhombisch-KlnMo₂O₈ verwandten Strukturtyp, Raumgruppe C_2h⁶—C2/c; a=17,445 Å, b=5,649 Å, c=8,997 Å, β=119,37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ zeichnet sich durch isolierte MoO₄-Tetraeder, isolierte (Cr/Al)O₆-Oktaeder und ein verzerrtes quadratisches Antiprisma um K⁺ aus. Die Kristallstruktur wird mit solchen verwandter Verbindungen diskutiert.