层状正极材料LiNi0.5Co0.25Mn0.25O2的结构及电化学行为

采用溶胶-凝胶方法制备了正极材料LiNi_0.5Co_0.25Mn_0.25O₂。XRD、XPS测试结果表明：LiNi_0.5Co_0.25Mn_0.25O₂中阳离子排列有序度较高，层状结构明显；Co、Mn分别以+3、+4价形式存在，Ni以+2、+3价形式存在，且Ni²⁺与Ni³⁺的含量之比约为1∶1。SEM测试结果表明：正极材料LiNi_0.5Co_0.25Mn_0.25O₂结晶粒径较均匀。充放电测试结果表明：与LiCoO₂相比，尽管LiNi_0.5Co_0.25Mn_0.25O₂的放电电压平台较低，但放电容量较高；在恒流充电模式下，当充电截止电压由4.35 V升高至4.75 V时，首次放电容量由179 mAh·g^-1增至201 mAh·g^-1，50次循环后，容量保持率由74.95%增至78.48%；在先恒流再恒压的充电模式下，电池首次放电容量为212 mAh·g^-1，50次循环后，容量保持率提高到87.71%。循环伏安测试表明：在2.80～4.80 V扫描范围内，该正极材料发生Ni²⁺/Ni³⁺，Co³⁺/Co⁴⁺两对电化学反应。EIS测试表明：随着充电截止电压的增大，该正极材料的传荷电阻变小。     

锂离子电池正极材料层状LiNi1/2Mn1/2O2的制备与表征

用一种简单的共沉淀法制备出了层状LiNi_1/2Mn_1/2O₂材料，并且用XRD、SEM、循环充放电、循环伏安(CV)和电化学阻抗谱(EIS)等方法对材料进行了表征测试。首先，用共沉淀法制备氢氧化镍和氢氧化锰的混合物;然后，对共沉淀溶液进行预氧化来制备前驱体;最后，用预氧化的前驱体合成了LiNi_1/2Mn_1/2O₂材料。SEM和XRD测试结果分别表明:LiNi_1/2Mn_1/2O₂材料是粒径范围在100～200 nm之间的球形粒子，并且具有非常好的层状结构。循环充放电表明:在空气中900 ℃下合成时间为9 h的材料，在充放电截止电压为2.8～4.6 V的情况下，经过40次循环，材料的容量可以稳定地保持在140 mAh·g^-1左右。循环伏安曲线表明:在锂的初始脱嵌和入嵌过程中存在不可逆相变。电化学阻抗谱测试表明LiNi_1/2Mn_1/2O₂具有很好的锂离子扩散能力。     

高温固相法合成LiNi1/3Mn1/3Co1/3O2及其性能研究

采用高温固相法合成出层状锂离子电池正极材料LiNi_1/3Mn_1/3Co_1/3O₂。通过XRD、ICP、SEM和电化学测试手段对产物的结构、组成、形貌及电化学性能进行了研究。XRD结果表明此方法合成的LiNi_1/3Mn_1/3Co_1/3O₂具有标准的α-NaFeO₂型层状结构，SEM照片显示颗粒粒径大约在500 nm左右，粒径分布较窄。以20 mA·g^-1电流密度放电，充放电电压在2.8～4.4 V之间，其首次放电比容量为170 mAh·g^-1，40次循环容量保持率为85.3%。进一步加入石墨导电剂后，同样条件下首次放电比容量变为179 mAh·g^-1，50次循环容量保持率为89.6%。容量衰减主要发生在前10次循环。XRD和SEM测试表明循环初期容量衰减的原因是由材料本体结构变化和界面反应共同作用的结果。     

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.     

正极材料LiNi0.5Mn1.5O4的合成及性能

采用低温固相法制备镍锰复合草酸盐，煅烧后生成的镍锰复合氧化物与Li₃CO₃混合，在空气中于700 ℃反应12 h，得到LiNi_0.5Mn_1.5O₄。通过XRD，SEM和恒电流充放电测试对样品进行了表征。XRD结果表明：复合草酸盐经390 ℃煅烧3 h，生成了多相氧化物；合成的LiNi_0.5Mn_1.5O₄为纯相，具有立方尖晶石结构。电化学测试结果表明，合成的样品在室温和高温(55 ℃)下，具有较好的电化学性能；大电流充放电时，具有良好的循环性能。     

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。     

离子电池正极材料LiNi0.5Mn0.5O2的合成

采用共沉淀法制备锂离子电池正极材料LiNi_0.5Mn_0.5O₂，前驱体制备过程中金属离子氢氧化物的形貌、粒径分布和最终合成材料的性能息息相关。本文讨论了共沉淀反应过程中沉淀体系、pH值、搅拌速度和氨水浓度对沉淀产物形貌的影响。同时还考察了烧结制度对材料电化学性能的影响。结果表明，在优化条件下制备的正极材料LiNi_0.5Mn_0.5O₂首次放电容量高达178 mAh·g^-1，50个循环后放电容量稳定保持在165 mAh·g^-1(电压范围2.8～4.5 V，电流密度30 mA·g^-1)。     

以α型氢氧化物前驱体制备LiNi0.8Co0.15Al0.05O2及其电化学性能

本文采用球形Al/Co部分取代α型Ni(OH)₂为前驱体成功制备了锂离子电池正极材料LiNi_0.8Co_0.15Al_0.05O₂。首先采用氢氧化钠与碳酸钠为沉淀剂合成出Al/Co部分取代α型Ni(OH)₂,然后将之与LiOH·H₂O混合,最后在氧气气氛中不同温度下热处理8 h,即可得到球形LiNi_0.8Co_0.15Al_0.05O₂材料。X射线衍射结果表明,LiNi_0.8Co_0.15Al_0.05O₂材料为α-NaFeO₂相。扫描电镜结果表明,材料颗粒形貌为球形。热重分析结果表明合成LiNi_0.8Co_0.15Al_0.05O₂的主反应温度在700～750 ℃之间。振实密度测试结果表明, 750 ℃下制备的LiNi_0.8Co_0.15Al_0.05O₂材料可达2.2 g·cm^-3。恒流充放电结果表明,该材料在0.5 mA·cm^-2电流密度下,在3.0～4.3 V间的首次充电容量可达210.3 mAh·g^-1,首次放电容量为179.7 mAh·g^-1,充放电效率为85.4%。与采用以β-Ni_0.85Co_0.15(OH)₂为前驱体合成的LiNi_0.85Co_0.15O₂和Al掺杂的LiNi_0.8Co_0.15Al_0.05O₂相比,尽管其首次放电容量与放电效率都有所降低,但循环性能有所提高,50周期后容量仍为初始容量的89.5％。研究表明,以球形Al/Co部分取代α型Ni(OH)₂作为前驱体为球形氧化镍钴铝锂材料的制备提供了一条新的途径。     

流变相法制备LiNi0.5Mn1.5O4锂离子电池正极材料及其电化学性质

LiNi_0.5Mn_1.5O₄ was prepared by rheological method using CH₃COOLi, Ni(CH₃COO)₂ and Mn(CH₃COO)₂ as raw materials. XRD and SEM results show that LiNi_0.5Mn_1.5O₄ synthesized at 850 ℃ has cubic spinel structure with clearly defined shape and particle size of 0.2～0.4 μm. Electrochemical tests show that the LiNi_0.5Mn_1.5O₄ presents a plateau near 4.7 V and delivers the maximum discharge capacity of 140.5 mAh·g^-1. After 100 cycles, the capacity loss per cycle was only 0.015% discharged at 0.2C and the capacity retention was more than 76.3% discharged at 2.0C at room temperature and the capacity loss per cycle was only 0.32% discharged at 0.2C at 55 ℃.     

嵌入化合物LixMn2O4的水热浸渍合成研究

本文用水热浸渍二步法合成了尖晶石型Li_xMn₂O₄微粉，并对其采用XRD，SEM， ICP， XPS和IR等进行测试。结果表明产物为单相立方晶体，粒子尺寸范围0.15-0.5 μm, Li_xMn₂O₄中X为0.96，其中锰为Mn³⁺和Mn⁴⁺混合价态存在。该液相合成Li_xMn₂O₄材料的方法尚未见报道。     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Li2O-TiO2-SiO2-P2O5和Li2O-TiO2-Al2O3-P2O5体系锂离子固体电解质的制备及性能研究

一些具有NASICON型网格结构的固体电解质具有高的电导率和好的稳定性,NASICON的意思是Na Super Ionic Conductor[1]。当NaZr2(PO4)3中P5 被Si4 部分取代时便可以得到具有NASICON结构的Na1 xZr2SixP3-xO12体系,其具有高的钠离子电导率。然而有相同结构的Li1 xZr2SixP3-xO12体系的离子电导率却很低,这是因为Li 半径太小,而NASICON三维网格结构的离子通道太大,两者不匹配而使电导率下降[2]。但当LiZr2(PO4)3中Zr4 被离子半径小些的Ti4 取代,所得LiTi2(PO4)3的通道就与Li 半径相匹配,适合于锂离子的迁移,从而使其电导率…     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

g-C_3N_4/CaTi_2O_5复合材料制备及其光催化性能

利用类石墨氮化碳(g-C_3N_4)和亚稳相钙钛氧化物(CaTi_2O_5)固相法制备C_3N_4/CaTi_2O_5复合材料。利用X射线衍射(XRD)、金相显微镜、扫描电子显微镜(SEM)及附带能谱分析仪(EDS)和N2吸附-脱附对样品的显微结构和比表面积进行检测分析,并用紫外-可见吸收光度计(UV-Vis)测试了样品的光吸收性能,研究C_3N_4与CaTi_2O_5物质的量之比(nC_3N_4/nCaTi_2O_5)对C_3N_4/CaTi_2O_5复合样品的物相结构和微观形貌的影响,同时考察C_3N_4/CaTi_2O_5复合样品在可见光照射下光催化降解罗丹明染料效果。实验结果表明:相比纯C_3N_4和CaTi_2O_5样品,C_3N_4/CaTi_2O_5复合样品在可见光下具有较高的光催化性能,随着nC_3N_4/nCaTi_2O_5增加,样品的光催化降解率随之增加而后降低,当nC_3N_4/nCaTi_2O_5=1∶1时,样品的光催化降解率达到最大值99.5%,并且循环重复利用5次后,样品的光催化剂降解率仍几乎保持不变。复合样品光催化性能提高主要归因于复合能级结构有效地抑制了电子和空穴复合所致。     

Magnetic diphase nanostructure of ZnFe2O4/γ-Fe2O3

Magnetic diphase nanostructures of ZnFe₂O₄/γ-Fe₂O₃ were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe₂O₄/γ-Fe₂O₃ was formed, in which the presence of ZnFe₂O₄ enhanced the thermal stability of γ-Fe₂O₃. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe₂O₃. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe₂O₃ content.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

A new 2212-type stair like structure: Bi14Sr21Fe12O61, m=5 member of the generic [Bi2Sr3Fe2O9]m[Bi4Sr6Fe2O16] family

A new oxide, Bi₁₄Sr₂₁Fe₁₂O_61, with a layered structure derived from the 2212 modulated type structure Bi₂Sr₃Fe₂O₉, was isolated. It crystallizes in the I2 space group, with the following parameters: a=16.58(3) Å, b=5.496(1) Å, c=35.27(2) Å and β=90.62°. The single crystal X-ray structure determination, coupled with electron microscopy, shows that this ferrite is the m=5 member of the [Bi₂Sr₃Fe₂O₉]_m[Bi₄Sr₆Fe₂O₁₆] collapsed family. This new collapsed structure can be described as slices of 2212 structure of five bismuth polyhedra thick along , shifted with respect to each other and interconnected by means of [Bi₄Sr₆Fe₂O₁₆] slices. The latter are the place of numerous defects like iron or strontium for bismuth substitution; they can be correlated to intergrowth defects with other members of the family.     

Raman scattering investigations on lanthanum-doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

The ferroelectric ceramics of Bi₄Ti₃O₁₂, SrBi₄Ti₄O₁₅, and lanthanum-doped Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅ were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅. The structure of the Bi₂O₂ layers and TiO₆ octahedra of the intergrowth was found to be different from those of Bi₄Ti₃O₁₂ and SrBi₄Ti₄O₁₅. La³⁺ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi₂O₂ layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi₂O₂ slabs.     

Crystal growth, structural characterization and magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6

Single crystals of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ were synthesized by high temperature flux growth in molten K₂CO₃ and structurally characterized by single crystal X-ray diffraction. While Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca₃Co_1.34Rh_0.66O₆a=9.161(1) Å, c=10.601(2) Å; Ca₃FeRhO₆a=9.1884(3) Å, c=10.7750(4) Å; Ca₃CuRhO₆ adopts a monoclinic distortion of the K₄CdCl₆ structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca₃CuRhO₆ examined were twinned by pseudo-merohedry. Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO₆ octahedra and MO₆ trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are discussed.