Partially substituted lithium manganese oxides as 3 V cathode materials for secondary lithium batteries

Low temperature synthesis and electrochemical properties of partially substituted lithium manganese oxides are reported. We demonstrate various metallic cations (Cu²⁺, Ni²⁺, Fe³⁺, Co³⁺) can be incorporated in the 3 V layered cathodic material Li_0.45MnO_2.1. New compounds Li_0.45Mn_0.88Fe_0.12O_2.1, Li_0.45Mn_0.84Ni_0.16O_2.05, Li_0.45Mn_0.79Cu_0.21O_2.3, Li_0.45Mn_0.85Co_0.15O_2.3 are prepared. These 3 V cathode materials are characterized by the same shape of discharge-charge profiles but different values of the specific capacity, between 90 mAh g⁻¹ and 180 mAh g⁻¹. The best results in terms of capacity and cycle life are obtained with the selected content of 0.15 Co per mole of oxide, as the optimum composition. The high kinetics of Li⁺ transport in Li_0.45Mn_0.85Co_0.15O_2.3 compared to that in the Co-free material is consistent with a substitution of Mn(III) by Co(III) in MnO₂ sheets.     

Electrochemical and structural investigations of the reaction of lithium with tin-based composite oxide glasses

Tin-based composite oxide materials have received considerable attention as potential anode materials for rechargeable lithium batteries. In this contribution we present the results of our investigations of the SnOB₂O₃P₂O₅ system. We have investigated its electrochemical properties and especially its cycling performance. A focus of our interest was to explain the structural changes which occur during lithium cycling and their strong dependence on the preparation method. A part of the SnO component was converted into a very stable metallic phase. In addition, a decrease was observed in capacity owing to the formation of isolated and inactive tin grains. We also report on structural changes in the B₂O₃P₂O₅ matrix. Received: 2 October 1997  / Accepted: 3 July 1998     

Battery performance of nanostructured lithium manganese oxide synthesized by ultrasonic spray pyrolysis at elevated temperature

Nanostructured lithium manganese oxide with spherical particles was synthesized via ultrasonic spray pyrolysis technique. The material shows a pronounced stability upon prolonged cycling at room temperature at high charge–discharge rates up to 10C. The electrochemical performance of the cell at elevated temperature was remarkably improved by addition of AlPO₄ to the electrolyte. The AC impedance spectroscopy study showed the interface stabilization by the AlPO₄ additives and the suppression of the interface impedance development upon prolonged cycling.     

The effect of chromium substitution on the phase transition of lithium manganese spinel oxides

The phase transition of chromium substituted lithium manganese spinel oxide, LiCr_yMn_2−yO₄ was investigated by low-temperature powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and electrical resistivity measurements. The sample prepared at 820 °C resulted in lowering the transition temperature T_t with Cr composition y, whereas T_t of the sample prepared at 750 °C remained constant for 0≤y≤0.17 in LiCr_yMn_2−yO₄. This would be caused by a difference in distribution of the substituted Cr³⁺ ion in octahedral site depending on the preparation temperature. The phase transition was suppressed with increasing the amount of Cr content.     

Recent advances in the study of layered lithium transition metal oxides and their application as intercalation electrodes

A review is presented on the extensive work carried out during the last 30 years on layered oxides structurally related to LiCoO₂ and LiNiO₂. The studies considered here range from the structural and chemical characterization of the layered solids to the detailed evaluation of their aptitude towards lithium deintercalation-intercalation reactions, which form the basis of their successful application in rechargeable battery technology. The different challenges remaining in this area, such as the development of advanced preparation procedures and the optimization of the electrochemical performance by controlled changes in composition, structure, and particle morphology, are discussed. Received: 15 May 1998 / Accepted: 24 July 1998     

X-ray diffraction study on phase transition of orthorhombic LiMnO2 in electrochemical conversions

Orthorhombic LiMnO₂ was synthesized by hydrothermal reaction. Phase transition during electrochemical process has been investigated using the high-resolution X-ray diffraction. Contrary to numerous earlier reports, phase analysis of the orthorhombic LiMnO₂ electrode cycled for three times evidences the irreversible structure transition from orthorhombic LiMnO₂ (Pmnm) to spinel LiMn₂O₄ (Fd3m) and rock salt Li_0.5Mn_0.5O (Fm \( \overline{3} \) m). Here, the spinel structure with a cell parameter a?=?8.241 (1) Å has a large cationic disorder on lithium and manganese sites, i.e., about 9% of the Li positions are occupied by Mn and vice versa. For Li_0.5Mn_0.5O, the cell parameter is a?=?4.121 (3) Å, and both Li⁺ and Mn³⁺ cations occupy the octahedral 4a sites with mole ratio 1:1. The quantity of Li_0.5Mn_0.5O phase is greatly dependent on cycling rate, namely, the higher the current density is, the larger the quantity of formed-rock salt structure is.     

Low-temperature and high-pressure structural behaviour of NaBi(MoO4)2—an X-ray diffraction study

NaBi(MoO₄)₂ has been characterized by single-crystal and powder X-ray diffraction in the temperature and pressure ranges 13-297 K and 0-25 GPa, respectively. The domain structure developing below proves that NaBi(MoO₄)₂ undergoes a ferroelastic phase transition associated with tetragonal I4₁/a to monoclinic I2/a symmetry change. The character of the unit cell evolution as a function of temperature indicates a continuous transition with the spontaneous strain as an order parameter. The structural distortion, due to small displacements of Bi³⁺ and Na⁺ ions, develops slowly. Therefore the overall changes, as measured in single-crystal diffraction at 110 and 13 K, appear to be subtle. High-pressure powder X-ray diffraction shows that the elastic behaviour is anisotropic, the linear compressibility along the a- and c-axes of the tetragonal unit cell being β_a=2.75(10)×10^-3 and , respectively. The cell contraction, stronger along the c-axis, causes the distances between the MoO₄ layers to be shortened. Consequently, the cation migration in the channels formed by MoO₄ tetrahedra becomes hindered, and any symmetry lowering phase transition is not observed up to 25 GPa. The zero-pressure bulk modulus is , and its pressure derivative .     

Formation of solid solution and its effect on lithium insertion schemes for advanced lithium-ion batteries: X-ray absorption spectroscopy and X-ray diffraction of LiCoO2, LiCo1/2Ni1/2O2 and LiNiO2

The X-ray absorption spectra (XAS) of LiCoO₂, LiCo_1/2Ni_1/2O₂ and LiNiO₂ were examined together with X-ray diffraction (XRD). Co and Ni K-edge XANES spectra of LiCo_1/2Ni_1/2O₂ are quite similar to that of LiCoO₂ or LiNiO₂, suggesting that electronic states of Co and Ni in LiCo_1/2Ni_1/2O₂ are Co³⁺ and Ni³⁺. Analytical results of Co and Ni K-edge EXAFS oscillations on the first coordination shell of nickel and cobalt ions in LiCo_1/2Ni_1/2O₂ indicate that the local environment around the targeted species is the same as that in LiCoO₂ or LiNiO₂. Since there is no doubt about the crystal and electronic structures of LiCoO₂ and LiNiO₂, the results indicate that LiCo_1/2Ni_1/2O₂ consists of low-spin states of Co³⁺ and Ni³⁺ distributed at equivalent positions in triangular lattice of sites forming homogeneous transition metal oxide layers. Thus, XAS complements XRD in describing solid solution LiCo_1/2Ni_1/2O₂ of LiCoO₂ and LiNiO₂. The electrochemical behaviors of LiCoO₂, LiCo_1/2Ni_1/2O₂ and LiNiO₂ are also restated and the effects of the formation of solid solution on the change in lattice dimension during topotactic electrochemical reactions are discussed.     

Rapid evaluation of charge/discharge properties for lithium manganese oxide particles at elevated temperatures

A microelectrode technique was applied to investigate the electrochemical properties of LiMn₂O₄ particles at elevated temperatures. Cyclic voltammograms of LiMn₂O₄ were measured after the particles were exposed to the electrolytes. This technique results in rapid and precise evaluation of the redox behavior of the materials. A significant capacity fading was observed in 1 M LiPF₆/EC+PC electrolytic solution, which indicates that both LiMn₂O₄ and LiPF₆ participate in the reaction to produce an inert material on the particle surface. Next, the capacity fading for two different BET surface area particles were compared using 1 M LiPF₆/EC+PC at 50 °C. The reaction was found not to be controlled by the surface area. Finally, a Li_1.1Mn_1.9O₄ particle was employed. The fading in discharge was ca. 10% for 50 cycles even at 50 °C, which means that the partial substitution of Mn in LiMn₂O₄ by Li substantially enhanced the capacity stability. Electronic Publication     

Site occupancy determination for manganese in some spinel-type oxides by Kβ X-ray fluorescence spectra

Site occupancy of cations in spinel-type oxides is sometimes extremely difficult to solve by the conventional crystallographic analysis based on diffraction methods. The present report describes successful determination for manganese spinels by analyzing Kβ X-ray fluorescence spectra, which are essentially sensitive to chemical environments such as oxidation and/or coordination numbers. Instead of looking at peak positions and/or shapes of the spectra, the intensity ratios of Kβ′ satellite and Kβ₅ lines were investigated in detail. It has been found that the spectra are apparently classified depending on the manganese site occupancy whether tetrahedral A or octahedral B. Applications to some spinel-type oxides, for which the manganese states have not yet been fully solved so far, were also discussed.     

Voltammetric and X-ray diffraction analysis of the early stages of the thermal crystallization of mixed Cu,Mn oxides

Mixed Cu,Mn, Cu,Mn,Al, Cu,Mg,Mn, and Cu,Mg,Mn,Al oxides were obtained by calcination of amorphous basic carbonate (Cu,Mn oxides) or hydrotalcite-like precursors at 300–800 °C. The product composition was characterized by chemical analysis, XRD, and voltammetry of the microparticles. The XRD amorphous portion was detected indirectly by XRD and directly by voltammetry. Tenorite (CuO) and spinels were the main crystalline components of the oxide mixtures. The presence of Al shifted the onset of the crystallization of XRD-detectable tenorite and spinel to temperatures higher by 100–200 °C, and the presence of Mg shifted tenorite crystallization by 100 °C, but voltammetry was able to detect these phases even in XRD-amorphous or nanocrystalline calcines. Voltammetry is hence suitable for analysis of poorly crystalline oxides that can be used in heterogeneous catalysis.     

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.     

Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa

We have studied CaWO₄ under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO₄ beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure–volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of the fergusonite phase and a different transition pressure. These facts suggest that deviatoric stresses influence on the high-pressure structural behavior of CaWO₄ as previously found in related compounds. The reported experiments also provide information on the pressure dependence of interatomic bond distances, shedding light on the transition mechanisms.     

Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

Relationship between transport properties and phase transformations in mixed-conducting oxides

To elucidate the relationship between transport properties and phase transformations in mixed-conducting oxides, Sr_0.9Ca_0.1Co_0.89Fe_0.11O_3−δ (SCCFO) and SrCoO_3−δ (SCO) were chosen as the model materials and have been investigated in detail. Oxygen permeation measurements verified that both oxides are well permeable to oxygen at elevated temperatures, e.g., at 900 °C during a cooling procedure, oxygen permeation rates as large as 1.5 and 2.0 mL/min/cm² could be obtained with disk-shaped SCCFO and SCO membranes of thickness 1.5 mm, respectively. But when cooled to critical temperatures, the oxygen permeability of these kinds of oxides diminished sharply, which could be recovered by increasing the temperature again to certain values. Abrupt changes on electrical conductivity were also observed for both oxides around the same region of temperature as that of oxygen permeability. As indicated by high-temperature X-ray diffraction and thermal analysis, the SCCFO and SCO systems undergo phase transformation between a low-temperature orthorhombic brownmillerite structure (B) or a hexagonal 2H-type structure (H) and a high-temperature cubic perovskite structure (C), respectively. The present results suggest the observed abrupt changes in transport properties versus temperature are attributed to such phase transformation, which may be directly associated with the order-disorder transition of oxygen vacancies. Moreover, compared to the B/C transformation that mainly involves an order-disorder transition on the oxygen sublattice, the H/C one necessarily also involves the cooperative long-range reorganization on the cation sublattice. Therefore it occurs at a higher temperature and absorbs more heat quantity than those of B/C transformation.     

Structural disorder along the lithium diffusion pathway in cubically stabilized lithium manganese spinel: I. Synchrotron X-ray studies

Electron density distribution, EXAFS, and transmission electron microscope studies on stoichiometric Li(Mg_1/6Mn_11/6)O₄ have revealed that: (1) the structure is essentially of spinel-type with slight diffuse scattering, (2) the Li atoms are not all located at the ideal 8a site of the spinel structure, but are partially tetrahedrally distributed along the 8a-16c tie line, (3) the O atoms also exhibit a statistical distribution about their ideal positions and (4) the Mn 3d electrons are squeezed out toward the open space of the coordinating octahedra with D_3d distortion. The present results indicate the possible existence of many metastable Li positions in the structure, suggestive of complicated Li atom hopping routes in conjunction with a local distortion of neighboring atoms at least up to the second shell.     

Simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction

The simultaneous SAXS/WAXD technique is shown to provide an unambiguous method for following structural changes taking place during the programmed heating of a range of multiphase polymeric materials. Results are given for polyethylene, block copolyurethanes and block copolyesters containing liquid crystalline hard segments. UK Thermal methods Group Award Lecture     

Nano-sized lithium manganese oxide dispersed on carbon nanotubes for energy storage applications

Nano-sized lithium manganese oxide (LMO) dispersed on carbon nanotubes (CNT) has been synthesized successfully via a microwave-assisted hydrothermal reaction at 200 °C for 30 min using MnO₂-coated CNT and an aqueous LiOH solution. The initial specific capacity is 99.4 mAh/g at a 1.6 C-rate, and is maintained at 99.1 mAh/g even at a 16 C-rate. The initial specific capacity is also maintained up to the 50th cycle to give 97% capacity retention. The LMO/CNT nanocomposite shows excellent power performance and good structural reversibility as an electrode material in energy storage systems, such as lithium-ion batteries and electrochemical capacitors. This synthetic strategy opens a new avenue for the effective and facile synthesis of lithium transition metal oxide/CNT nanocomposite.