New solid-state synthesis routine and mechanism for LiFePO4 using LiF as lithium precursor

Li₂CO₃ and LiOH·H₂O are widely used as Li-precursors to prepare LiFePO₄ in solid-phase reactions. However, impurities are often found in the final product unless the sintering temperature is increased to 800 °C. Here, we report that lithium fluoride (LiF) can also be used as Li-precursor for solid-phase synthesis of LiFePO₄ and very pure olivine phase was obtained even with sintering at a relatively low temperature (600 °C). Consequently, the product has smaller particle size (about 500 nm), which is beneficial for Li-extraction/insertion in view of kinetics. As for cathode material for Li-ion batteries, LiFePO₄ obtained from LiF shows high Li-storage capacity of 151 mAh g⁻¹ at small current density of 10 mA g⁻¹ (1/15 C) and maintains capacity of 54.8 mAh g⁻¹ at 1500 mA g⁻¹ (10 C). The solid-state reaction mechanisms using LiF and Li₂CO₃ precursors are compared based on XRD and TG-DSC.     

球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_(1.0)Na_(0.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_(0.77)Mn O_(2.05)新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 m Ah·g~(-1)和215.8 m Ah·g~(-1),库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 m Ah·g~(-1)和106.2 m Ah·g~(-1)。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li_2Mn O_3组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni~(2+)、Co~(3+)、Mn~(4+)所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

La0.6Sr1.4MnO4 layered perovskite anode material for intermediate temperature solid oxide fuel cells

La_0.6Sr_1.4MnO₄ (LSMO₄) layered perovskite with K₂NiF₄ structure was prepared and evaluated as anode material for La_0.8Sr_0.2Ga_0.83Mg_0.17O_3 − δ (LSGM) electrolyte supported intermediate temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction results show that LSMO₄ is redox stability. Thermal expansion coefficient of LSMO₄ is close to that of LSGM electrolyte. By adopting LSMO₄ as anode and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF) as cathode, maxium power densities of 146.6, 110.9 mW cm^− 2 with H₂ fuel at 850, 800 °C and 47.3 mW cm^− 2 with CH₄ fuel at 800 °C were obtained, respectively. Further, the cell demonstrated a reasonably stable performance under 180 mA cm^− 2 for over 40 h with H₂ fuel at 800 °C.     

球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_1.0Na_0.2Ni_0.13Co_0.13Mn_0.54O₂正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_0.77MnO_2.05新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 mAh·g^-1和215.8 mAh·g^-1,库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 mAh·g^-1和106.2 mAh·g^-1。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li₂MnO₃组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni²⁺、Co³⁺、Mn⁴⁺所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

The direct decomposition of NO over the La2CuO4 nanofiber catalyst

The NO catalytic direct decomposition was studied over La₂CuO₄ nanofibers, which were synthesized by using single walled carbon nanotubes (CNTs) as templates under hydrothermal condition. The composition and BET specific surface area of the La₂CuO₄ nanofiber were La₂Cu_0.88²⁺Cu_0.12⁺O_3.94 and 105.0 m²/g, respectively. 100% NO conversion (turnover frequency-(TOF): 0.17 g_NO/g_catalyst s) was obtained over such nanofiber catalyst at temperatures above 300 °C with the products being only N₂ and O₂. In 60 h on stream testing, either at 300 °C or at 800 °C, the nanofiber catalyst still showed high NO conversion efficiency (at 300 °C, 98%, TOF: 0.17 g_NO/g_catalyst s; at 800 °C, 96%, TOF: 0.16 g_NO/g_catalyst s). The O₂ and NO temperature programmed desorption (TPD) results indicated that the desorption of oxygen over the nanofibers occurred at 80-190 and 720-900 °C; while NO desorption happened at temperatures of 210-330 °C. NO and O₂ did not competitively adsorb on the nanofiber catalyst. For outstanding the advantage of the nanostate catalyst, the usual La₂CuO₄ bulk powder was also prepared and studied for comparison.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Investigation of the quasi-ternary system LaMnO3-LaCoO3-“LaCuO3”—I: the series La(Mn0.5Co0.5)1−xCuxO3−δ

The La(Mn_0.5Co_0.5)_1−xCu_xO_3−δ series with x=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1 was synthesized by the Pechini method to obtain insight into the phase formation in the quasi-ternary LaMnO₃-LaCoO₃-“LaCuO₃” system caused by the instability of LaCuO₃ under ambient conditions. After sintering at 1100°C some remarkable results were obtained: LaMn_0.3Co_0.3Cu_0.4O_3−δ crystallized as a single phase in the orthorhombic perovskite structure typical of LaCuO₃. Among the synthesized compositions this compound showed the highest electrical conductivity in air at 800°C (155 S cm⁻¹) and also the highest thermal expansion coefficient (α_30−800°C=15.4×10⁻⁶ K⁻¹). The LaCuO_3−δ composition also crystallized as a single phase but in a monoclinic structure although previous investigations have shown that other phases are preferably formed after sintering at 1100°C. The electrical conductivity and thermal expansion coefficient were the lowest within the series of compositions, i.e. 9.4 S cm⁻¹ and 11.9×10⁻⁶ K⁻¹, respectively.     

Hydrogen production from water decomposition by redox of Fe2O3 modified with single- or double-metal additives

Iron oxide modified with single- or double-metal additives (Cr, Ni, Zr, Ag, Mo, Mo-Cr, Mo-Ni, Mo-Zr and Mo-Ag), which can store and supply pure hydrogen by reduction of iron oxide with hydrogen and subsequent oxidation of reduced iron oxide with steam (Fe₃O₄ (initial Fe₂O₃)+4H₂↔3Fe+4H₂O), were prepared by impregnation. Effects of various metal additives in the samples on hydrogen production were investigated by the above-repeated redox. All the samples with Mo additive exhibited a better redox performance than those without Mo, and the Mo-Zr additive in iron oxide was the best effective one enhancing hydrogen production from water decomposition. For Fe₂O₃-Mo-Zr, the average H₂ production temperature could be significantly decreased to 276 °C, the average H₂ formation rate could be increased to 360.9-461.1 μmol min⁻¹ Fe-g⁻¹ at operating temperature of 300 °C and the average storage capacity was up to 4.73 wt% in four cycles, an amount close to the IEA target.     

镁二次电池正极材料纳米Fe3S4的电化学性能

首次将尖晶石相的纳米Fe₃S₄材料用作镁二次电池的正极材料。采用水热法一步合成了具有纳米结构的Fe₃S₄材料, 并采用XRD、SEM测试手段对产物的物相、形貌进行了表征。实验结果表明, 在160 ℃能够合成纯相的Fe₃S₄材料, 该材料具有银耳状纳米结构。电化学测试结果显示, 水热法合成的纳米Fe₃S₄材料能够在镁二次电池体系中进行有效的可逆充放电, 放电平台电压为0.9 V, 首次放电容量高达267 mAh·g^-1, 50次循环后衰减至110 mAh·g^-1。电化学交流阻抗测试结果表明镁离子能够在Fe₃S₄晶格中扩散。     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Snx[BPO4]1−x composites as negative electrodes for lithium ion cells: Comparison with amorphous SnB0.6P0.4O2.9 and effect of composition

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB_0.6P_0.4O_2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn_0.72[BPO₄]_0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO₄ matrix. The electrochemical responses of ATCO and Sn_0.72[BPO₄]_0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g⁻¹, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by ¹¹⁹Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn^II composite oxide and shows that in the case of Sn_0.72[BPO₄]_0.28, the surface of the tin clusters is mainly formed by Sn^II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn⁰. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn⁰ and Sn^II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn_x[BPO₄]_1−x composite materials (0.17<x<0.91). The cell using the compound Sn_0.72[BPO₄]_0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g⁻¹ at C/5 rate).     

A Facile synthesis of flower-like Co3O4 porous spheres for the lithium-ion battery electrode

The porous hierarchical spherical Co₃O₄ assembled by nanosheets have been successfully fabricated. The porosity and the particle size of the product can be controlled by simply altering calcination temperature. SEM, TEM and SAED were performed to confirm that mesoporous Co₃O₄ nanostructures are built-up by numerous nanoparticles with random attachment. The BET specific surface area and pore size of the product calcined at 280 °C are 72.5 m² g⁻¹ and 4.6 nm, respectively. Our experiments further demonstrated that electrochemical performances of the synthesized products working as an anode material of lithium-ion battery are strongly dependent on the porosity.     

掺F影响LiNi0.8Co0.1Mn0.1O2结构和性能的微观机制

以氟化锂为氟源,通过高温固相法合成了F掺杂的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2。采用X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)和电化学测试等手段研究F影响LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2结构和性能的微观机制。结果表明:适量F掺杂可以提高正极材料的放电比容量,改善其倍率性、循环性和热稳定性。当F掺杂量(物质的量分数)为1.5%时,材料的综合电化学性能最优,初始放电比容量(0.2C)和50周循环容量保持率(1C)分别由原始的174.0 mAh·g~(-1)(78.7%)提高到178.6 mAh·g~(-1)(85.7%)。LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2材料性能的改善可归因于F能够增强过渡金属层、锂层与氧层之间的结合力,提高材料的结构稳定性。此外,F掺杂还有利于降低电化学反应中的界面电阻和电荷转移阻抗。     

Electrocatalytic oxidation behavior of guanosine at graphene, chitosan and Fe3O4 nanoparticles modified glassy carbon electrode and its determination

A graphene, chitosan and Fe₃O₄ nanoparticles (nano-Fe₃O₄) modified glassy carbon electrode (graphene-chitosan/nano-Fe₃O₄/GCE) was fabricated. The modified electrode was characterized by scanning electron microscope and electrochemical impedance spectroscopy. The electrochemical oxidation behavior of guanosine was investigated in pH 7.0 phosphate buffer solution by cyclic voltammetry and differential pulse voltammetry. The experimental results indicated that the modified electrode exhibited an electrocatalytic and adsorptive activities towards the oxidation of guanosine. The transfer electron number (n), transfer proton number (m) and electrochemically effective surface area (A) were calculated. Under the optimized conditions, the oxidation peak current was proportional to guanosine concentration in the range of 2.0 × 10⁻⁶ to 3.5 × 10⁻⁴ mol L⁻¹ with the correlation coefficient of 0.9939 and the detection limit of 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). Moreover, the modified electrode showed good ability to discriminate the electrochemical oxidation response of guanosine, guanine and adenosine. The proposed method was further applied to determine guanosine in spiked urine samples and traditional Chinese medicines with satisfactory results.     

镁二次电池正极材料纳米Fe3S4的电化学性能研究

首次将尖晶石相的纳米Fe₃S₄材料用作镁二次电池的正极材料。采用水热法一步合成了具有纳米结构的Fe₃S₄材料, 并采用XRD、SEM测试手段对产物的物相、形貌进行了表征。实验结果表明, 在160 ℃能够合成纯相的Fe₃S₄材料, 该材料具有银耳状纳米结构。电化学测试结果显示, 水热法合成的纳米Fe₃S₄材料能够在镁二次电池体系中进行有效的可逆充放电, 放电平台电压为0.9 V, 首次放电容量高达267 mAh· g^-1, 50次循环后衰减至110 mAh· g^-1。电化学交流阻抗测试结果表明镁离子能够在Fe₃S₄晶格中扩散。     

高能量密度LiMn0.6Fe0.4PO4/C的制备及其电化学性能

以Mn(NO_3)_2、Fe(NO_3)_3·9H_2O、NH_4H_2PO_4、LiOH·H_2O为原材料,采用改进的溶胶凝胶法制备了具有高能量密度的Li Mn_(0.6)Fe_(0.4)PO_4/C材料。该方法通过金属和多种配体配位构筑的框架,把得到的一次纳米颗粒构筑为类球形的二次颗粒,即发挥了纳米材料优异的电化学性能,又提高了材料的压实密度,电池的能量密度可提升约30%。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、交流阻抗谱(EIS)、振实密度、粒度以及电化学测试等表征手段对材料的晶体结构、形貌和电化学性能进行了较系统的研究,结果表明此方法制备的LiMn_(0.6)Fe_(0.4)PO_4/C材料不仅具有较高的振实密度和电压平台,还具有优异的电化学性能:振实密度为1.3 g·cm~(-3),且在1C倍率下,放电中值电压为3.85 V,100次循环后,比容量仍有142.3 mAh·g~(-1),容量保持率为99.4%。     

Kinetic analysis of the thermal stability of lithium silicates (Li4SiO4 and Li2SiO3)

The kinetics describing the thermal decomposition of Li₄SiO₄ and Li₂SiO₃ have been analysed. While Li₄SiO₄ decomposed on Li₂SiO₃ by lithium sublimation, Li₂SiO₃ was highly stable at the temperatures studied. Li₄SiO₄ began to decompose between 900 and 1000 °C. However, at 1100 °C or higher temperatures, Li₄SiO₄ melted, and the kinetic data of its decomposition varied. The activation energy of both processes was estimated according to the Arrhenius kinetic theory. The energy values obtained were −408 and −250 kJ mol⁻¹ for the solid and liquid phases, respectively. At the same time, the Li₄SiO₄ decomposition process was described mathematically as a function of a diffusion-controlled reaction into a spherical system. The activation energy for this process was estimated to be −331 kJ mol⁻¹. On the other hand, Li₂SiO₃ was not decomposed at high temperatures, but it presented a very high preferential orientation after the heat treatments.     

多元醇法合成具有不同长径比的棒状LiFePO4/C材料

以三价铁盐为铁源,采用多元醇还原法在低温下制备出了具有不同长径比的棒状LiFePO₄材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、循环伏安(CV)、交流阻抗谱(EIS)和恒电流充放电测试等手段分析了不同回流反应时间下制备出的前驱体和最终的LiFePO₄/C 样品. 结果表明：回流反应时间对LiFePO₄的形貌和特性有明显的影响. 通过把回流反应时间从4 h延长至16 h,材料的形貌由不规则的短棒状颗粒变为规则的长棒状颗粒,且棒的直径明显变小. 当回流反应时间为10 h 时,样品复合了多种形貌,有利于电子的传输,在低倍率下具有优秀的性能,0.1C放电比容量为163 mAh·g^-1;当回流反应时间为16 h 时,样品具有最大的长径比,有利于锂离子的扩散,在高倍率下具有良好的性能,1C、3C、5C、10C、20C倍率下放电比容量分别为135、125、118、110、98 mAh·g^-1,循环性能良好,几乎无衰减.     

High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5

Phase transitions in MgAl₂O₄ were examined at 21-27 GPa and 1400-2500 °C using a multianvil apparatus. A mixture of MgO and Al₂O₃ corundum that are high-pressure dissociation products of MgAl₂O₄ spinel combines into calcium-ferrite type MgAl₂O₄ at 26-27 GPa and 1400-2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al₂O₃ corundum and a new phase with Mg₂Al₂O₅ composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg₂Al₂O₅ phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å³, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O₆ octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O₆ octahedra. The structure is related with that of ludwigite (Mg, Fe²⁺)₂(Fe³⁺, Al)(BO₃)O₂. The molar volume of the Mg₂Al₂O₅ phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al₂O₃ corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl₂O₄ among various A²⁺B³⁺₂O₄ compounds.     

Structure and conductivity of strontium-doped cerium orthovanadates Ce1−xSrxVO4 (0≤x≤0.175)

A-site substituted cerium orthovanadates, Ce_1−xSr_xVO₄, were synthesised by solid-state reactions. It was found that the solid solution limit in Ce_1−xSr_xVO₄ is at x=0.175. The crystal structure was analysed by X-ray diffraction and it exhibits a tetragonal zircon structure of space group I4₁/amd (1 4 1) with a=7.3670 (3) and c=6.4894 (1) Å for Ce_0.825Sr_0.175VO₄. The UV-vis absorption spectra indicated that the compounds have band gaps at room temperature in the range 4.5-4.6 eV. Conductivity measurements were performed for the first time up to the strontium solid solution limit in air and in dry 5% H₂/Ar with conductivity values at 600 °C ranging from 0.3 to 30 mS cm⁻¹ in air to 30-45 mS cm⁻¹ in reduced atmosphere. Sample Ce_0.825Sr_0.175VO₄ is redox stable at a temperature below 600 °C although the conductivity is not high enough to be used as an electrode for solid oxide fuel cells.