Order-disorder transition in the complex lithium spinel Li2CoTi3O8

Li₂CoTi₃O₈ has an ordered Li₂BB′₃O₈ spinel structure, space group P4₃32, at room temperature with 3:1 ordering of Ti and Li on the octahedral sites, and Li, Co disordered over the tetrahedral site. Rietveld refinement of variable temperature neutron powder diffraction data has shown an order-disorder phase transition in Li₂CoTi₃O₈ which commences at ∼500 °C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at ∼915 °C. The fraction of Ti on the 12-fold octahedral site exhibits a small decrease with increasing temperature, which may suggest that the disordering involves all three cations. Above 930 °C, the structure, space group Fd3¯m, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site, although Co still exhibits a preference for tetrahedral coordination. A labelling scheme for ordered and partially ordered 3:1 spinels is devised which focuses on the occupancy of the Li,B cations.     

Li and Li MAS NMR Studies on Fast Ionic Conducting Spinel-Type Li2MgCl4, Li2-xCuxMgCl4, Li2-xNaxMgCl4, and Li2ZnCl4

⁶Li and ⁷Li MAS NMR spectra including 1D-EXSY (exchange spectroscopy) and inversion recovery experiments of fast ionic conducting Li₂MgCl₄, Li_2-xCu_xMgCl₄, Li_2-xNa_xMgCl₄, and Li₂ZnCl₄ have been recorded and discussed with respect to the dynamics and local structure of the lithium ions. The chemical shifts, intensities, and half-widths of the Li MAS NMR signals of the inverse spinel-type solid solutions Li_2-xM^I_xMgCl₄ (M^I=Cu, Na) with the copper ions solely at tetrahedral sites and sodium ions at octahedral sites and the normal spinel-type zinc compound, respectively, confirm the assignment of the low-field signal to Li^tet of inverse spinel-type Li₂MgCl₄ and the high-field signal to Lioct as proposed by Nagel et al. (2000). In contrast to spinel-type Li_2-2xMg_1+xCl₄ solid solutions with clustering of the vacancies and Mg²⁺ ions, the Cu⁺ and Na⁺ ions are randomly distributed on the tetrahedral and octahedral sites, respectively. The activation energies due to the various dynamic processes of the lithium ions in inverse spinel-type chlorides obtained by the NMR experiments are E_a=6.6-6.9 and ΔG^*>79 KJ mol⁻¹ (in addition to 23, 29, and 75 kJmol-1 obtained by other techniques), respectively. The largest activation energy of >79 KJ mol⁻¹ corresponds to hopping exchange processes of Li ions between the tetrahedral 8a sites and the octahedral 16d sites. The smallest value of 6.6-6.9 KJ mol⁻¹, which was derived from the temperature dependence of both the spin-lattice relaxation times T₁ and the correlation times τ_C of Li^tet, reveals a dynamic process for the Li^tet ions inside the tetrahedral voids of the structure, probably between fourfold 32e split sites around the tetrahedral 8a site.     

Etude par RMN de la mobilité du lithium dans trois oxydes à structure pseudo-bidimensionnelle: Li8SnO6, Li7NbO6 et Li6In2O6

The lithium ion mobility in three solid electrolytes (Li₈SnO₆, Li₇NbO₆, and Li₆In₂O₆) has been studied by NMR at several resonance frequencies from 170 to 500°K. The ⁷Li quadrupolar lineshape evolution shows the predominant influence on the conductivity mechanism of the vacancies in the octahedral sites of the oxygen close packing. In Li₈SnO₆, which has no vacancies, the lithium ions situated in the tetrahedral sites have the highest mobility. Spin-lattice relaxation times are in good agreement with the hypothesis of a Li₇NbO₆ 2D conductivity. The values of the activation energy, increasing from Li₇NbO₆ to Li₆In₂O₆ and to Li₈SnO₆, are found to be three times lower than those obtained from conductivity measurements.     

Chemical Synthesis and Properties of Spinel Li1−xCo2O4−δ

Spinel Li_1−xCo₂O_4−δ samples with 0.44≤(1−x)≤1 have been synthesized by chemically extracting lithium with the oxidizer NO₂BF₄ in acetonitrile medium from the LT-LiCoO₂ synthesized at 400°C. Rietveld analysis of the X-ray diffraction data reveals that the Li_1−xCo₂O_4−δ samples adopt the normal cubic spinel structure with a cation distribution of (Li_1−x)_8a[Co₂]_16dO_4−δ. Redox iodometric titration data indicate that the LT-LiCoO₂ tends to lose oxygen on extracting lithium and the spinel Li_1−xCo₂O_4−δ samples are oxygen-deficient. Both infrared spectroscopic and magnetic susceptibility data suggest that the LiCo₂O_4−δ spinel is metallic with itinerant electrons. The tendency to lose oxygen on extracting lithium from the LT-LiCoO₂ and the observed metallic behavior of the spinel LiCo₂O_4−δ are explained on the basis of a qualitative band diagram.     

Preparation of Li4Ti5O12 Microspheres with a Pure Cr2O3 Coating Layer and its Effect for Lithium Storage

The pure Cr₂O₃ coated Li₄Ti₅O₁₂ microspheres were prepared by a facile and cheap solutionbased method with basic chromium(III) nitrate solution (pH=11.9). And their Li-storage properties were investigated as anode materials for lithium rechargeable batteries. The pure Cr₂O₃ works as an adhesive interface to strengthen the connections between Li₄Ti₅O₁₂ particles, providing more electric conduction channels, and reduce the inter-particle resistance. Moreover, LixCr₂O₃, formed by the lithiation of Cr₂O₃, can further stabilize Li₇Ti₅O₁₂ with high electric conductivity on the surface of particles. While in the acid chromium solution (pH=3.2) modification, besides Cr₂O₃, Li₂CrO₄ and TiO₂ phases were also found in the final product. Li₂CrO₄ is toxic and the presence of TiO₂ is not welcome to improve the electrochemical performance of Li₄Ti₅O₁₂ microspheres. The reversible capacity of 1% Cr₂O₃-coated sample with the basic chromium solution modification was 180 mAh/g at 0.1 C, and 134 mAh/g at 10 C. Moreover, it was even as high as 127 mAh/g at 5 C after 600 cycles. At-20℃, its reversible specific capacity was still as high as 118 mAh/g.     

A combined X-ray and neutron Rietveld study of the chemically lithiated electrode materials Li2.7V3O8 and Li4.8V3O8

The lithium insertion in the positive electrode material Li_1+αV₃O₈ (α close to 0.1-0.2) includes a phenomenon near 2.6 V (voltage vs. the Li metal electrode), the mechanism being a two-phase process with the transformation from ca. Li_2.9V₃O₈ to ca. Li₄V₃O₈. Near 2.4 V down to 2 V, Li is inserted in a single phase up to ca. Li₅V₃O₈. Chemical Li insertions have been performed in a Li_1.1V₃O₈ precursor prepared at 350 °C and the structures of the products Li_2.7V₃O₈ (before the 2.6 V phenomenon) and Li_4.8V₃O₈ (near the expected maximum) have been studied by a combined Rietveld refinement of X-ray and neutron diffraction data. The structure of Li_4.8V₃O₈ is an ordered derivative of the rock-salt type, with all the Li and V ions in slightly distorted octahedral sites. Li_2.7V₃O₈ has a poor crystallization state and, although the expected V₃O₈ layers are obtained, only a part of the Li sites have been reliably determined. Between adjacent V₃O₈ layers, several unidentified sites are likely weakly occupied, thus giving a markedly disordered character for the structure of the compound formed just before the transition at 2.6 V. The atomic shifts at the transition are briefly discussed.     

Magnetic and Mössbauer studies on α-Fe2O3Li2O system

A study has been made of the structural and thermal phase behavior of the mixed system αFe₂O₃xLi₂O with a view toward investigating the changes occurring in the properties of different compositions due to substitution of diamagnetic Li⁺ for Fe³⁺ at B sites in the inverse spinel lattice. This also indicates whether the addition of Li₂O, over and above that (x = 0.2) required for the formation of the spinel LiFe₅O₈, enters the substitutional or interstitial sites. Characterization by X-ray powder diffraction, initial magnetic susceptibility, magnetic hysteresis, Mössbauer spectroscopy, and differential thermal analysis clearly indicates that Li⁺ does not enter the spinel lattice, but forms a biphasic system LiFe₅O₈ and LiFeO₂, which are not miscible.     

The structure of Li3.4Si0.7S0.3O4 by powder neutron diffraction

The structure of Li_4?2xSi_1?xS_xO₄ (x ≈ 0.32) has been determined from neutron powder diffraction studies at room temperature, 350, and 700°C. This compound, which is a member of the series of ionic-conducting solid solutions formed between Li₄SiO₄ and Li₂SO₄, is isostructural with Li₃PO₄. The space group is Pmnb, with a = 6.1701(1), b = 10.6550(2), c = 5.0175(1)Å at room temperature. The distribution of lithium ions suggests the occurrence of a defect cluster in which the inclusion of an interstitial lithium ion causes displacements of the adjacent lithium ions of the normal Li₃PO₄ structure. There appears to be little variation of the structure with temperature.     

Li2MTiO4 (M=Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li2NiTiO4

We describe the synthesis and characterization of a new series of oxides, Li₂MTiO₄ (M=Mn, Fe, Co, Ni) that crystallize in the rocksalt structure. For M=Ni, we have also obtained a low-temperature modification that adopts a Li₂SnO₃-type structure. All the phases, excepting M=Ni, undergo oxidative deinsertion of lithium in air/O₂ at elevated temperatures (>150°C), yielding LiMTiO₄ (M=Mn, Fe) spinels and a spinel-like Li_1+xCoTiO₄ as final products.     

Structural and magnetic properties of Nd18Li8Co4−xFexO39−y and Nd18Li8Co4−xTixO39−y

Nd₁₈Li₈Co₃FeO_39−y, Nd₁₈Li₈CoFe₃O_39−y and Nd₁₈Li₈Co₃TiO_39−y have been synthesised and characterised by neutron powder diffraction, magnetometry and Mössbauer spectroscopy. Their cubic structure (Pm3?n, a∼11.9 Å) is based on intersecting <1 1 1> chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd-O framework. Each compound has an incomplete oxide sublattice (y∼1), with vacancies located around the octahedral sites that lie at the points of chain intersection. These sites are fully occupied by a disordered arrangement of transition-metal cations but only 75% of the remaining octahedral sites are occupied. The trigonal-prismatic sites are fully occupied by lithium except in the case of Nd₁₈Li₈CoFe₃O_39−y where some iron is present. Antiferromagnetic interactions are present on the Nd sublattice in each composition, but a spin glass forms below 5 K when a high concentration of spins is also present on the octahedral sites.     

Effects of Metal Ion Sources on Synthesis and Electrochemical Performance of Spinel LiMn2O4 Using Tartaric Acid Gel Process

The effect of lithium and manganese ions on the synthesis, phase purity, and electrochemical properties of tartaric acid gel processed lithium manganese oxide spinel were investigated. The poor bonding between both lithium and manganese ions with tartaric acid was shown by the FT-IR analysis when lithium nitrate and/or manganese nitrate were used as sources. Li₂MnO₃ and Mn₂O₃ impurities formed in addition to lithium manganese oxides when nitrate salts were used as the sources. When acetate salts were used as sources for the lithium and manganese ions, single-phase LiMn₂O₄ was obtained. These results indicate that homogeneous bonding between acetate salt and tartaric acid was formed. The capacity of single-phase LiMn₂O₄ calcined at 500°C was 117 mAh/g which was much higher than those containing Mn₂O₃ and Li₂MnO₃ impurity compounds. Thus, sources of lithium and manganese ions play an important role in the synthesis and electrochemical behaviors of lithium manganese oxide spinel.     

A neutron diffraction study of the d and d lithium garnets Li3Nd3W2O12 and Li5La3Sb2O12

The garnets Li₃Nd₃W₂O₁₂ and Li₅La₃Sb₂O₁₂ have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950 °C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group with lattice parameters a=12.46869(9) Å (Li₃Nd₃W₂O₁₂) and a=12.8518(3) Å (Li₅La₃Sb₂O₁₂). Li₃Nd₃W₂O₁₂ contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li₅La₃Sb₂O₁₂ contains partial occupation of lithium over two crystallographic sites. The conventional tetrahedrally coordinated 24d site is 79.3(8)% occupied. The remaining lithium is found in oxide octahedra which are linked via a shared face to the tetrahedron. This lithium shows positional disorder and is split over two positions within the octahedron and occupies 43.6(4)% of the octahedra. Comparison of these compounds with related d⁰ and d¹⁰ phases shows that replacement of a d⁰ cation with d¹⁰ cation of the same charge leads to an increase in the lattice parameter due to polarisation effects.     

Phase relationships of the lithium halide spinels Li2MCl4-Li2MBr4 with M = Mn,Fe, Cd

The sections Li₂MCl_4?4xBr_4x of the quaternary systems LiCl-LiBr-MCl₂-MBr₂ with M = Mn, Cd, and Fe were studied by high-temperature X-ray diffraction patterns and DTA and DSC measurements. In the quasibinary lithium manganese halide system complete series of solid solutions exist between the inverse spinels Li₂MnCl₄ and Li₂MnBr₄. Li₂MnBr₄ and solid solutions with x > 0.54 undergo phase transitions to tetragonal spinels at lower temperatures. In the nonquasibinary system with M = Cd, only at temperatures near 400°C a complete series of mixed crystals is formed. At lower temperatures the system is mainly two-phase with rock salt-type Li_1?yCd_0.5yCl_1?xBr_x and cadmium chloride-type Cd_1?yLi_2yCl_2?2xBr_2x solid solutions in equilibrium. The lithium iron halide system is similar to that of cadmium, but spinel-type Li₂FeBr₄ does not exist at any temperature. The manganese and cadmium halide spinels and spinel solid solutions undergo phase transitions to NaCl defect structures at elevated temperatures.     

Thermodynamic properties and cation distribution of the ZnFe2O4Fe3O4 spinel solid solutions at 900°C

The thermodynamic properties of the Fe₃O₄ZnFe₂O₄ spinel solid solution were determined at 900°C by the use of the solid electrolyte galvanic cell Fe₂O₃ + Fe₃O₄|O^2?|Fe₂O₃ + Zn_xFe_3?xO₄The activity values obtained exhibit slight negative deviation from the ideal solution model. An analysis of the free energy of mixing of the spinel solid solution provided information on the distribution of cations between the tetrahedral and octahedral sites of the spinel lattice. This is the basis for the estimation of the free energy of formation of pure zinc ferrite from oxides. ΔG⁰_ZnFe2O4 = ?2740 ? 1.6 T cal mole^?1     

Ge4+、Sn4+掺杂尖晶石LiMn2O4的合成与电化学表征

使用Ge⁴⁺、Sn⁴⁺作为掺杂离子, 通过高温固相法制备四价阳离子掺杂改性的尖晶石LiMn₂O₄材料. X射线衍射(XRD)和扫描电子显微镜(SEM)分析表明, Ge⁴⁺离子取代尖晶石中Mn⁴⁺离子形成了LiMn_2-xGe_xO₄ (x=0.02,0.04, 0.06)固溶体; 而Sn⁴⁺离子则以SnO₂的形式存在于尖晶石LiMn₂O₄的颗粒表面. Ge⁴⁺离子掺入到尖晶石LiMn₂O₄材料中, 抑制了锂离子在尖晶石中的有序化排列, 提高了尖晶石LiMn₂O₄的结构稳定性; 而在尖晶石颗粒表面的SnO₂可以减少电解液中酸的含量, 抑制酸对LiMn₂O₄活性材料的侵蚀. 恒电流充放电测试表明, 两种离子改性后材料的容量保持率均有较大幅度的提升, 有利于促进尖晶石型LiMn₂O₄锂离子电池正极材料的商业化生产.     

Etude structurale de la forme ordonnée de LiAl5O8

A single crystal of ordered LiAl₅O₈ has been prepared by image furnace melting and its structure has been determined; 400 X-ray reflections were collected on an automatic counter diffractometer (MoKα radiation). The structure is of the spinel type. The space group is P4₃32 (or P4₁32); the lattice parameter is a = 7.908(2), Å, Z = 4. The value of R is 0.022. The distribution of cations shows the absence of Li⁺ ions in tetrahedral cation sites and 1–3 imperfect ordering of Li⁺ and Al₃₊ in octahedral cation sites of spinel.     

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。     

A study of the spinel materials LiTi2O4 and Li43Ti53O4 by photoelectron spectroscopy

HeI-excited valence-band ultraviolet photoelectron spectra and MgKα-excited Ti-2p X-ray photoelectron spectra are reported for the spinel materials LiTi₂O₄ and $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4$. The presence of a Fermi edge in the ultraviolet photoelectron spectrum of LiTi₂O₄ confirms the metallic nature of this material, although the measured density of states at the Fermi energy is much lower than that expected from an independent-electron interpretation of the magnetic susceptibility. This difference is attributed to a strong interaction of the conduction electrons with the lattice vibrations. The localization of conduction electrons that occurs in the final state in the Ti-2p X-ray photoelectron spectrum of LiTi₂O₄ is attributed to a Coulomb interaction with a core hole.     

Neutron and X-ray powder diffraction study of LixRuO2 and LixIrO2: The crystal structure of Li0.9RuO2

Compounds formed by the insertion of lithium into the rutile structure hosts RuO₂ and IrO₂ were studied by X-ray and neutron powder diffraction techniques. Compositions in the range Li_xMO₂, M = Ru or Ir, 0 < x < 1 are two-phase materials consisting of unreacted host, x = 0, and limiting compositions x = 0.9 in both cases. Preparation of compounds with x > 1 was unsuccessful. Li_0.9RuO₂ and Li_0.9IrO₂ have orthorhombic cells with a = 5.062(3), b = 4.967(4), c = 2.771(4) and a = 4.962(4), b = 4.758(4), c = 3.108(6), respectively. Compared to the host rutile (tetragonal) cells those of the insertion compounds are greatly expanded along [100] and [010], ～0.5 Å for both, and contracted along [001], by ～0.3 Å for Li_0.9RuO₂ and 0.05 Å for Li_0.9IrO₂. The space group for both insertion phases appears to be Pnnm, a subgroup of the rutile space group $\text{P4}{}_2\text{mnm}$. The structure of Li_0.9RuO₂ was solved from neutron diffraction data. Lithium exists as Li⁺ in octahedral sites. The LiO coordination is highly regular with two bonds at 2.05(1) Å and four at 2.08(2) Å. The overall structure is essentially an ordered NiAs-type very similar to but more regular than the previously reported LiMoO₂. Attempts to solve the structure of Li_0.9IrO₂ from both X-ray and neutron powder data were unsuccessful due, presumably, to severe preferred orientation.     

X-ray diffraction and Mössbauer spectroscopy studies of LiFe0.5Ti1.5O4 – A new primitive cubic ordered spinel

LiFe_0.5Ti_1.5O₄ was synthesized by solid-state reaction carried out at 900 °C in flowing argon atmosphere, followed by rapid quenching of the reaction product to room temperature. The compound has been characterized by X-ray powder diffraction (XRD) and ⁵⁷Fe Mössbauer effect spectroscopy (MES). It crystallizes in the space group P4₃32, a = 8.4048(1) Å. Results from Rietveld structural refinement indicated 1:3 cation ordering on the octahedral sites: Li occupies the octahedral (4b) sites, Ti occupies the octahedral (12d) sites, while the tetrahedral (8c) sites have mixed (Fe/Li) occupancy. A small, about 5%, inversion of Fe on the (4b) sites has been detected. The MES data is consistent with cation distribution and oxidation state of Fe, determined from the structural data.The title compound is thermally unstable in air atmosphere. At 800 °C it transforms to a mixture of two Fe³⁺ containing phases – a face centred cubic spinel Li_(1+y)/2Fe_(5−3y)/2Ti_yO₄ and a Li_(z−1)/2Fe_(7−3z)/2Ti_zO₅ – pseudobrookite. The major product of thermal treatment at 1000 °C is a ramsdellite type lithium titanium iron(III) oxide, accompanied by traces of rutile and pseudobrookite.