Li4Ti5O12/(Ag+C)电极材料的固相合成及电化学性能

以Li₂CO₃,TiO₂为原料,葡萄糖为碳源,采用固相煅烧工艺合成了亚微米级的Li₄Ti₅O₁₂/C复合负极材料。并将之与AgNO₃复合,采用固相方法制备出了Ag表面修饰的Li₄Ti₅O₁₂/(Ag+C)复合材料。采用XRD、SEM和TEM测试方法对材料的微结构进行了表征。结果表明,C的存在对Ag单质在Li₄Ti₅O₁₂/C颗粒表面的大量形成起到了积极的促进作用,从而很大程度地提高了Li₄Ti₅O₁₂/C的电导率,因此有效地改善了其电化学性能。在1C倍率下,Li₄Ti₅O₁₂/(Ag+C)复合材料的首次放电容量达到了164 mAh·g^-1。     

Phase relations of the Cr2O3TiO2 system

The phase relations of the system Cr₂O₃TiO₂ were determined at temperatures between 1400 and 1765°C in air. Discrete homologous series of Cr₂Ti_n?2O_2n?1, with n = 6, 7, 8, were found to be stable as single phases in the range of certain temperatures, while a continuous solid solution existed in the composition of n > 8 below 1425°C. This presence and its stable region of a new compound of Cr₂TiO₅ corresponding to n = 3 are revealed in the present paper. Cr₂Ti₂O₇, the so-called E phase, existed in wide homogeneity range, corresponding to the composition of approximately 3 < n < 5. High-temperature phases (called n and n′ phases in the present work) existed above 1425°C and seemed to be closely related to each other from the viewpoint of the structure except that some X-ray diffraction lines of n phase were strongly diffused. Both rutile and chromia had limited solid solubilities. In the present paper, phase relations between Cr₂O₃ and TiO₂ are summarized in a phase diagram.     

Structural characterization and physical properties of the system La1.33LixCrxTi2−xO6

New phases which arise from partial substitution of Ti⁴⁺ by Cr³⁺ and Li⁺ of the compound La_2/3TiO₃ have been obtained, giving rise to the series La_1.33Li_xCr_xTi_2−xO₆ (x=0.66, 0.55 and 0.44). These phases adopt a perovskite-type structure as deduced from their structural characterization. Rietveld's analyses of neutron diffraction data show that it is orthorhombic (S.G. Pbnm) with ordered domains. Conductivity has been examined by complex impedance spectroscopy and it increases with increasing lithium and chromium content. These materials behave as mixed conductors with low activation energies. Magnetic susceptibility variation with temperature shows antiferromagnetic interactions at the lowest temperatures.     

Li4Ti5O12/CMK-3复合材料的制备及其作为锂离子电池负极材料的性能

将LiNO₃和Ti(OC₄H₉)₄填填充在有序介孔碳CMK-3 孔道中, 然后烧结合成了Li₄Ti₅O₁₂/CMK-3复合材料. 利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射(XRD)对其结构和微观形貌进行了表征. 利用差热-热重分析(TG-DTA)测试复合材料中Li₄Ti₅O₁₂的含量. 利用充放电测试、循环伏安和电化学阻抗技术考察了复合材料作为锂离子电池负极材料的性能. 发现Li₄Ti₅O₁₂分布在CMK-3孔道中及其周围, 复合材料的高倍率充放电性能显著优于商品Li₄Ti₅O₁₂, 复合材料中Li₄Ti₅O₁₂的比容量明显高于除去CMK-3的样品(在1C倍率时比容量为117.8 mAh·g^-1), 其0.5C、1C和5C倍率的放电比容量分别为160、143 和131 mAh·g^-1, 库仑效率接近100%, 5C倍率时循环100次的容量损失率只有0.62%. 本研究结果表明CMK-3明显提高了Li₄Ti₅O₁₂的高倍率充放电性能, 可能是CMK-3特殊的孔道结构和良好的导电性减小了Li₄Ti₅O₁₂的粒径并提高了其电导率.     

Nanosized Spinel Li4Ti5O12 Anode Material Prepared by Gel-polymer Method using Furfuryl Alcohol as Polymerizable Solvent

Nanosized Li₄Ti₅O₁₂ powders are synthesized by a polymerization-based method using ti-tanium butoxide and lithium nitrate as precursors and furfuryl alcohol as a polymerizable solvent. The prepared samples are characterized by X-ray diffraction, scanning electron mi-croscopy, transmission electron microscopy and Braunauer-Emmett-Teller (BET) analysis. The electrochemical performances of these Li₄Ti₅O₁₂ powders are also studied. The effect of different surfactants including citric acid, polyvinylpyrrolidone, and cetyltrimethyl am-monium bromide on the structure and properties is also investigated. It is found that pure spinel phase of Li₄Ti₅O₁₂ is obtained at an annealing temperature of 700 oC or higher. The use of surfactants can improve the powder morphology of nanosized particles with less ag-glomeration. With suitable annealing temperature and the addition of surfactant, Li₄Ti₅O₁₂ powders with high BET surface area and favorable electrochemical performance can be ob-tained.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

Preparation and Structure of Cerium Titanates Ce2TiO5, Ce2TiO7, and Ce4Ti9O24

Compounds Ce₂TiO₅, Ce₂Ti₂O₇, and Ce₄Ti₉O₂₄ were prepared by heating appropriate mixtures of solids containing Ce⁴⁺ and Ti³⁺ or Ti which were placed in a platinum-silica-ampoule combination at T = 1250°C (3d) under vacuum. The new compounds were characterized by powder patterns. We obtained Ce₂TiO₅ which is isotypic to La₂TiO₅ and crystallizes in the Y₂TiO₅-type (space group Pnma) with a = 10.877(6) Å, b = 3.893(1) Å, c = 11.389(8) Å, Z = 4. Ce₂Ti₂O₇ is isotypic to La₂Ti₂O₇ and crystallizes in the monoclinic Ca₂Nb₂O₇ type (space group P 2₁) with a = 7.776(6) Å, b = 5.515(4) Å, c = 12.999(6) Å, β = 98.36(5), Z = 4. The compound Ce₄Ti₉O₂₄ crystallizes orthorhombic with a = 14.082(4) Å, b = 35.419(8) Å, c = 14.516(4) Å, Z = 16. The new cerium titanate Ce₄Ti₉O₂₄ is isotypic to Nd₄Ti₉O₂₄ (space group Fddd (No. 70)) which represents a novel type of structure.     

LiMn2O4表面包覆Li4Ti5O12的制备及倍率特性

采用固相法合成了尖晶石型LiMn₂O₄，并通过溶胶-凝胶法制备了不同物质的量的百分比含量Li₄Ti₅O₁₂包覆的正极材料。X-射线衍射和扫描电镜结果表明，Li₄Ti₅O₁₂微粒包覆在LiMn₂O₄的表面没有产生晶体结构的变化。实验电池在室温下，以1C，2C和5C倍率作充放电循环测试；结果表明，与未包覆的LiMn₂O₄相比，表面包覆Li₄Ti₅O₁₂微粒的正极材料在高倍率下具有更好的循环稳定性。     

Electrochemical reaction mechanism of porous Zn2Ti3O8 as a high-performance pseudocapacitive anode for Li-ion batteries

Zn₂Ti₃O₈, as a new type of anode material for lithium-ion batteries, is attracting enormous attention because of its low cost and excellent safety. Though decent capacities have been reported, the electrochemical reaction mechanism of Zn₂Ti₃O₈ has rarely been studied. In this work, a porous Zn₂Ti₃O₈ anode with considerably high capacity (421 mAh/g at 100 mA/g and 209 mAh/g at 5000 mA/g after 1500 cycles) was reported, which is even higher than ever reported titanium-based anodes materials including Li₄Ti₅O₁₂, TiO₂ and Li₂ZnTi₃O₈. Here, for the first time, the accurate theoretical capacity of Zn₂Ti₃O₈ was confirmed to be 266.4 mAh/g. It was also found that both intercalation reaction and pseudocapacitance contribute to the actual capacity of Zn₂Ti₃O₈, making it possibly higher than the theoretical value. Most importantly, the porous structure of Zn₂Ti₃O₈ not only promotes the intercalation reaction, but also induces high pseudocapacitance capacity (225.4 mAh/g), which boosts the reversible capacity. Therefore, it is the outstanding pseudocapacitance capacity of porous Zn₂Ti₃O₈ that accounts for high actual capacity exceeding the theoretical one. This work elucidates the superiorities of porous structure and provides an example in designing high-performance electrodes for lithium-ion batteries.     

Effects of carbon coating from sucrose and PVDF on electrochemical performance of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C composites in different potential ranges

The carbon coated nanoflower-like Li₄Ti₅O₁₂/C composites were prepared via hydrothermal method followed by surface modification using sucrose or polyvinylidene fluoride (PVDF) as carbon sources. X-ray diffraction, SEM, TEM, Raman spectroscopy, TGA, and the electrochemical measurements were used for the materials characterization. Such modification leads to the formation of a high-conductive carbon coating. In the case of polyvinylidene fluoride use, fluorination of Li₄Ti₅O₁₂ surface takes place also. As a result, electrochemical performance of the obtained composites is improved. In the potential range of 1–3 V, Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C_PVDF, and Li₄Ti₅O₁₂/C_sucrose exhibit, respectively, the discharge capacities of 142.5, 154.3, and 170.4 mAh/g at a current of 20 mA/g and 57.2, 82.1, and 89.3mAh/g at a current of 3200 mA/g. When cycled in a potential range of 0.01–3 V, the discharge capacity of Li₄Ti₅O₁₂/C_PVDF increases up to 252 mAh/g at 20 mA/g.     

The compound Cr2TiO5 in the system Cr2O3TiO2

The compound Cr₂TiO₅ could be synthesized as a stoichiometric single phase above 1660°C in air. Application of selected area electron diffraction, high resolution electron microscopy and powder X-ray diffraction studies showed that Cr₂TiO₅ is isomorphous with CrFeTiO₅, with V₃O₅ type structure. It is monoclinic, a = 7.020(1)Å, b = 5.025(1)Å, c = 9.945(2)Å and β = 111.43(2)°. It was found that Cr₂TiO₅ is unstable relative to a mixture of Cr₂O₃ (ss) and a so-called “E” phase, below 1660°C.     

Reduction of the titanium niobium oxides. I. TiNb2O7 and Ti2Nb10O29

Reduction of the titanium-niobium oxides follows a common pattern. TiO₂ is eliminated, to form a new phase richer in titanium than the original compound, and Nb(iv) replaces Ti(iv) in the original block structure, which is thereby enriched in niobium. With TiNb₂O₇, the second phase is a TiO₂NbO₂ solid solution, with the rutile structure, initially with a high titanium content, in equilibrium with a solid solution of composition Me₃O₇, isostructural with TiNb₂O₇. At log p_O2 (atm) about ?9.0 this reaches the limiting composition Ti_0.72Nb_2.28O₇, in equilibrium with Ti_0.56Nb_0.44O₂. The Me₃O₇ block structure then transforms into the Me₁₂O₂₉ block structure (Ti₂Nb₁₀O₂₉Nb₁₂O₂₉ solid solution), which rapidly increases in niobium content as reduction continues. Reduction of Ti₂Nb₁₀O₂₉ at oxygen fugacities above log p_O2 (atm) = ?9.0 forms the Me₃O₇ phase as the titanium-rich phase. At log p_O2 = ?9.0, and a composition about Ti_1.6Nb_10.4O₂₉, the rutile solid solution takes over as second phase. The niobium/titanium ratio in both phases rises as reduction proceeds, and the last vestiges of the Me₁₂O₂₉ phase, in equilibrium with the final product, Ti_0.17Nb_0.67O₂, are almost denuded of titanium.     

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.     

Phase equilibria in the system V2O3Ti2O3TiO2 at 1473°K

The phase equilibria in the V₂O₃Ti₂O₃TiO₂ system have been determined at 1473°K by the quench method, using both sealed tubes and controlled gaseous buffers. For the latter, $\text{CO}{}_2\text{H}{}_2$ mixtures were used to vary the oxygen fugacity between 10^?10.50 and 10^?16.73 atm. Under these conditions the equilibrium phases are: a sesquioxide solid solution between V₂O₃ and Ti₂O₃ with complete solid solubility and an upper stoichiometry limit of (V, Ti)₂O_3.02; an M₃O₅ series which has the V₃O₅ type structure between V₂TiO₅ and V_0.69Ti_2.31O₅ and the monoclinic pseudobrookite structure between V_0.42Ti_2.58O₅ and Ti₃O₅; series of Magneli phases, V₂Ti_n?2O_2n?1Ti_nO_2n?1, n = 4–8; and reduced rutile phases (V, Ti)O_2?x, where the lower limit for x is a function of the $\text{V}\text{(V + Ti)}$ ratio. The extent of the different solid solution areas and the location of the oxygen isobars have been determined.     

Li4Ti5O12/(Cu+C)复合材料的制备及电化学性能

以Li₄Ti₅O₁₂,Cu(CH₃COO)₂·H₂O和C₆H₁₂O₆为前驱体,化学沉积与热分解结合合成锂离子电池负极材料Li₄Ti₅O₁₂/(Cu+C)。采用X-射线衍射(XRD)、扫描电子显微镜(SEM)、恒流充放电、循环伏安和电化学阻抗方法表征样品的结构、形貌和电化学性能。结果表明,Li₄Ti₅O₁₂表面包覆的Cu与C提高了Li₄Ti₅O₁₂电极材料的导电率,其循环性能和倍率性能得到有效地改善。在0.5C、1C和3C倍率下,经过50次充放电循环,放电比容量分别为168.2、160、140.6 mAh·g^-1,其容量保持率分别为88.7%、84.4%、71.2%。电化学阻抗测试表明,表面包覆的Cu与C使其电荷转移阻抗大幅度减少。     

The crystal structures of the lithium-inserted metal oxides Li0.5TiO2 anatase,LiTi2O4 spinel,and Li2Ti2O4

The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined. The tetragonal anatase form of TiO₂ becomes orthorhombic on ambient-temperature lithium insertion to Li_0.5TiO₂ due to the formation of TiTi bonds. The lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen. Cubic LiTi₂O₄ formed by heating Li_0.5TiO₂ anatase has a normal spinel structure with Li in the tetrahedral sites. In Li₂Ti₂O₄ formed by reacting LiTi₂O₄ spinel with n-BuLi at ambient temperature, the titanium remains in the spinel positions but the lithium is displaced, filling all the available octahedral sites.     

Phase relations in the pseudobinary system TiO2Ga2O3

Phase relations and microstructures in the TiO₂-rich part of the TiO₂Ga₂O₃ pseudobinary system have been determined at temperatures between 1373 and 1623°K using X-ray diffraction and electron and optical microscopy. The phases occurring in the system are TiO₂ (rutile), β-Ga₂O₃, a series of oxides Ga₄Ti_m?4O_2m?2 (m odd) which exist above 1463°K, and Ga₂TiO₅, which exists above 1598°K. The width of the phase region occupied by the Ga₄Ti_m?4O_2m?2 phases varies with temperature. At 1473°K it is narrow, and has limits of Ga₄Ti₂₅O₅₆ to Ga₄Ti₂₁O₄₈ while at higher temperatures it broadens to limits of from Ga₄Ti₂₇O₆₀ to Ga₄Ti₁₁O₂₈ at 1623°K. These phases are often disordered and crystals frequently contain partially ordered intergrowths of oxides with various values of m. On the TiO₂-rich side of the phase region there is a continuous change in texture from rutile to the end members of the Ga₄Ti_m?4O_2m?2 structures. The findings are summarized on a phase diagram.     

Crystal structures of lazulite-type oxidephosphates TiTi3O3(PO4)3 and M4Ti27O24(PO4)24 (M=Ti, Cr, Fe)

Single crystals of the oxidephosphates Ti^IIITi^IV₃O₃(PO₄)₃ (black), Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (red-brown, transparent), and Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [Ti^IIITi^IV₃O₃(PO₄)₃: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R₁=0.029, wR₂=0.084, 6055 independent reflections, 301 variables; Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R₁=0.037, wR₂=0.097, 1524 independent reflections, 111 variables; Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R₁=0.049, wR₂=0.140, 1240 independent reflections, 112 variables). For Ti^IIITi^IVO₃(PO₄)₃ a well-ordered structure built from dimers [Ti^III,IV₂O₉] and [Ti^IV,IV₂O₉] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr₄Ti₂₇O₂₄(PO₄)₂₄ and Fe₄Ti₂₇O₂₄(PO₄)₂₄, consisting of dimers [M^IIITi^IVO₉] and [Ti^IV,IV₂O₉], monomeric [Ti^IVO₆] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs Ti^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates M^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (M^III: Cr, Fe). The UV/vis spectrum of Cr₄Ti₂₇O₂₄(PO₄)₂₄ reveals a rather small ligand-field splitting Δ_o=14,370 cm⁻¹ and a very low nephelauxetic ratio β=0.72 for the chromophores [Cr^IIIO₆] within the dimers [Cr^IIITi^IVO₉].     

锂离子电池负极材料Li_(4-x)K_xTi_5O_(12)结构和电化学性能

采用固相反应的方法制备了尖晶石型Li4Ti5O12和K掺杂Li4-xKxTi5O12(x=0.02,0.04,0.06)。通过XRD、SEM、BET等对制备材料进行了分析。结果表明,K掺杂没有影响立方尖晶石型Li4Ti5O12的合成,同时也没有改变Li4Ti5O12的电化学反应过程。K掺杂Li4-xKxTi5O12具有比Li4Ti5O12小的颗粒粒径和比Li4Ti5O12大的比表面积、孔容积。适量的K掺杂能够明显改善Li4Ti5O12的电化学性能,尤其是倍率性能,但是过多的K掺杂却不利于材料电化学性能的提高。研究表明,Li3.96K0.04Ti5O12体现了相对较好的倍率性能和循环稳定性。0.5C下,首次放电比容量为161mAh·g-1,3.0和5.0C下,容量保持分别为138和121mAh·g-1。3.0C下,200次循环后容量保持为137mAh·g-1。     

Crystallography and phase relations of MeOM2O3TiO2 systems (Me = Fe,Mg, Ni; M = Al,Cr, Fe)

Subsolidus phase relations of ternary oxide systems containing divalent Fe, Mg, or Ni, trivalent Al, Cr, or Fe, and tetravalent Ti are characterized by solid solutions at metal/oxygen ratios $\text{3}\text{4}$, $\text{2}\text{3}$, and $\text{3}\text{5}$. At low temperatures only compounds with cubic or hexagonal close-packed oxygen and uniform oxygen coordination remain stable in the crystal structures NaCl, spinel, ilmenite-α-Al₂O₃, TiO₂. The pseudobrookite phases FeTi₂O₅, MgTi₂O₅, Al₂TiO₅, Fe₂TiO₅, the V₃O₅ structure phase Cr₂TiO₅, and the Andersson phases Cr₂Ti_n?2O_2n?1 (n = 4,6,7,8,9) decompose. Additional phases with close-packed oxygen as predicted by a simple structure model for metal/oxygen ratios $\text{7}\text{12}$, $\text{5}\text{6}$, and $\text{11}\text{12}$ do not form but presumably are important for nonstoichiometric solid solutions. Most differences between systems containing transition metals and the MgOAl₂O₃TiO₂ system can be attributed to crystal field effects.