Spinel Framework Research Articles

Structure and stability of Li-Mn-Ni composite oxides as lithium ion sieve precursors in acidic medium

A series of spinel Li-Mn-Ni composite oxides with theoretical chemical formula of LiNixMn2−xO4 (0≤x≤1.0) were synthesized by liquid phase method. Their structure and morphology were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively. The stability of these Ni-substituted spinel oxides prepared at different temperatures was investigated in acidic medium as well. The results show that Ni can be brought into the spinel framework completely to form well-crystallized product when x≤0.5 and the optimized synthesis temperature is 800 °C. LiNi0.4Mn1.6O4 prepared at 800 °C can maintain the spinel structure and morphology with Li extraction ratio of 30.37%, Mn extraction ratio of 8.78% and Ni extraction ratio of 1.82% during acid treatment. The incorporated Ni not only inhibits the dissolution of Mn, but also reduces the extraction of Li due to the lattice contraction.

Epitaxial growth and electrochemical properties of Li4Ti5O12 thin-film lithium battery anodes

Epitaxial Li(4)Ti(5)O(12) thin-films were successfully synthesized on SrTiO(3) single-crystal substrates with (111), (110), and (100) lattice plane orientations using pulsed laser deposition (PLD). Thin-film X-ray diffraction (XRD) revealed that the Li(4)Ti(5)O(12) films had the same orientation as the SrTiO(3) substrates: Li(4)Ti(5)O(12) (111) on SrTiO(3) (111), Li(4)Ti(5)O(12) (110) on SrTiO(3) (110), and Li(4)Ti(5)O(12) (100) on SrTiO(3) (100). These epitaxial films contained island structures, and the morphology of the (111), (110), and (100) films, observed by field emission scanning electron microscopy (FE-SEM), exhibited angular, needle-like, and circular shapes, respectively. The electrochemical properties of 20 nm thick Li(4)Ti(5)O(12) (111) and (110) films were investigated by cyclic voltammetry. Reversible intercalation proceeded through both lattice planes due to the three-dimensional diffusion pathway of lithium in the spinel framework. Reduction peaks in the first cathodic scan appeared at different positions from those in subsequent scans, suggesting a surface reconstruction at the Li(4)Ti(5)O(12) surface due to interfacial reactions.

On the Correlation between Nanoscale Structure and Magnetic Properties in Ordered Mesoporous Cobalt Ferrite (CoFe2O4) Thin Films

In this work, we report the synthesis of periodic nanoporous cobalt ferrite (CFO) that exhibits tunable room temperature ferrimagnetism. The porous cubic CFO frameworks are fabricated by coassembly of inorganic precursors with a large amphiphilic diblock copolymer, referred to as KLE. The inverse spinel framework boasts an ordered open network of pores averaging 14 nm in diameter. The domain sizes of the crystallites are tunable from 6 to 15 nm, a control which comes at little cost to the ordering of the mesostructure. Increases in crystalline domain size directly correlate with increases in room temperature coercivity. In addition, these materials show a strong preference for out-of-plane oriented magnetization, which is unique in a thin film system. The preference is explained by in-plane tensile strain, combined with relaxation of the out-of-plane strain through flexing of the mesopores. It is envisioned that the pores of this ferrimagnet could facilitate the formation of a diverse range of exchange coupled composite materials.

Electrochemical Insertion of Li and Na Ions into Nanocrystalline Fe3O4 and α‐Fe2O3 for Rechargeable Batteries

powders with different particle sizes on average (400, 100, and ) were prepared and characterized by X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and electrochemical methods. To examine the electrochemical activity of in relation to the particle size effect, galvanostatic cycling tests in aprotic electrolytes containing lithium or sodium ions were conducted. The electrochemical activity was significantly enhanced as the mean particle size decreased. The nanocrystallized prepared by precipitation method delivered of the rechargeable capacity in the voltage range of in a lithium-ion containing electrolyte, whereas the 400 and powders showed 10 and of the rechargeable capacity, respectively. An ex situ X-ray diffraction study for the electrochemically cycled samples suggested the partly reversible Fe ion migration from the tetrahedral sites to the octahedral sites with a retained spinel framework structure. The nanocrystallized as well as were highly electrochemically active in the sodium salt electrolyte. The rechargeable capacity of 160 or with excellent capacity retention was obtained for nanocrystalline or , respectively.

Spinel LiMn2−xNixO4 cathode materials for high energy density lithium ion rechargeable batteries

The practical limitations of fully lithium ion insertion and extraction into LiMn2O4 cathode structure without any structural instability make it unsuitable in commercial Li-ion rechargeable batteries. In this work, we showed that those partially substituted by Ni, i.e., LiMn2−xNixO4 (0≤x≤0.5), prepared by sol-gel technique, could be used as a potential candidate for high energy density and high voltage Li-ion battery applications with superior rate capabilities. The improved structural stability of the cathode was probed by x-ray diffraction and micro-Raman spectroscopy. The density-functional theoretical calculations were employed to identify the minimum energy needed for Li+ diffusion pathway and activation energy in the spinel framework with different Ni ion concentrations. Our results showed significant enhancement in the properties with 25at.% of Ni solid-solution doping in LiMn2O4 host and the experimental results are in line with the theoretical computations.

Effect of Thermal Treatment on the Electronic Conductivity Properties of Cobalt Spinel Phases Synthesized by Electro-Oxidation in Ternary Alkaline Electrolyte (KOH, LiOH, NaOH)

A thermal treatment of Co3O4 type spinel phases, synthesized by electrooxidation of CoO powder in a mixed alkaline electrolyte (KOH, LiOH, NaOH), is shown to have an important influence on the electronic conductivity properties of the materials. The initial spinel phase contains hydrogen, lithium, cobalt vacancies, and especially Co4+ ions within the structure, leading to an electronic conductivity significantly larger than that of stoichiometric Co3O4. The thermal treatment, followed by in situ X-ray diffraction, TGA-MS and electronic conductivity measurements, induces a water release, coupled with an increase of the Co/O atomic ratio and a structural reorganization. The resulting cationic redistribution within the spinel framework entails an increase of the Co4+ amount in the [Co2O4] network and therefore of the electronic conductivity (by 3 orders of magnitude).

Hollow Single-Crystal Spinel Nanocubes: The Case of Zinc Cobalt Oxide Grown by a Unique Kirkendall Effect

Small hollow nanocubes of the ternary spinel Zn x Co 1- x Co 2O 4 of ca. 18 nm dimension were prepared via a facile hydrothermal route. A growth mechanism is suggested in which solid single-crystal Co 3O 4 nanocubes are gradually converted to hollow single-crystal Zn x Co 1- x Co 2O 4 nanocubes with preservation of the spinel framework through differential diffusion of Zn (2+) and Co (2+) ions. With the cation exchange, the chemical composition and thus physical properties can be tailored.

Preparation of macrospherical magnesia-rich magnesium aluminate spinel catalysts for methanolysis of soybean oil

In order to fully exploit the green characteristics of solid base catalysts they should be fabricated into macrostructured rather than powder form. Magnesia-rich magnesium aluminate spinel ( MgO · MgAl 2 O 4 ) framework catalysts with tunable basicity have been prepared by using γ ‐ Al 2 O 3 macrospheres (0.5–1.0 mm in diameter) as a hard template. The process involves in situ growth of magnesium–aluminum layered double hydroxides (MgAl-LDHs) in the channels of the γ ‐ Al 2 O 3 macrospheres by the urea hydrolysis method, followed by calcination, tuning of the basicity through etching of excess aluminum with aqueous alkali and a final calcination step. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), elemental analysis and low temperature N 2 adsorption–desorption studies demonstrate that the composite MgO · MgAl 2 O 4 materials are composed of nanosized rod-like particles aggregated into a spherical framework. Catalytic reactivity was investigated by using methanolysis of soybean oil as probe reaction. The MgO · MgAl 2 O 4 composite shows a higher biodiesel yield compared to an MgO / MgAl 2 O 4 / γ ‐ Al 2 O 3 material with the same loading of magnesium prepared by a conventional impregnation method. The enhanced catalytic activity of the former material can be ascribed to its higher basicity, specific surface area, pore volume and pore size.

Cathode materials: A personal perspective

A thermodynamically stable rechargeable battery has a voltage limited by the window of the electrolyte. An aqueous electrolyte has a window of 1.2 eV, which prevents achieving the high energy density desired for many applications. A non-aqueous electrolyte with a window of 5 eV requires Li + rather than H + as the working ion. Early experiments with Li x TiS 2 cathodes showed competitive capacity and rate capability, but problems with a lithium anode made the voltage of a safe cell based on a sulfide cathode too low to be competitive with a nickel/metal-hydride battery. Transition-metal oxides can give voltages of 4.5 V versus Li +/Li 0. However, the challenge with oxides has been to obtain a competitive capacity and rate capability while retaining a high voltage with low-cost, environmentally friendly cathode materials. Comparisons will be made between layered Li 1− x MO 2, spinels Li 1− x [M 2]O 4, and olivines Li 1− x MPO 4 having 0 < x < 1. Although higher capacities can be obtained with layered Li 1− x MO 2 compounds, which have enabled the wireless revolution, their metastability makes them unlikely to be used in power applications. The spinel and olivine framework structures have been shown to be capable of charge/discharge rates of over 10 C with a suitable temperature range for plug-in hybrid vehicles.

Synthesis and characterization of nanosized lithium manganate and its derivatives

Abstract Spinel lithium manganese oxide, LiMn2O4 and its derivatives are prepared by the sol–gel method. The lattice constant of the pure material is calculated as 8.23 A. Different transition metal cations of chromium, iron, cobalt, nickel, copper and zinc (0.05 and 0.15 M) are doped in place of manganese in the LiMn2O4. X-ray powder diffraction data show that the spinel framework preserved its integrity upon doping. Formation of a single phase and the purity of the samples are confirmed by X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The crystallite size of the samples is calculated by use of the Scherrer formula and is found to be within a range of 43–66 nm. The electrical conductivity of the samples is determined over a temperature range of 200–300 K by means of four-point probe method. An increasing trend of conductivity with increase in temperature is noted for all the samples. The parent compound LiMn2O4 has a conductivity value of 3.47 × 10−4 ohm−1 cm−1 at room temperature. This value increases on doping with the above-mentioned transition metal cations.

Synthesis and electrochemical characterization of Li 1.05RE xCr yMn 2− x− yO 4 spinel as cathode material for rechargeable Li-battery

The spinel phases of Li 1.05RE x Cr y Mn 2− x− y O 4 (RE = Sc, Ce, Pr, Tb; 0 ≤ x ≤ 0.05; 0 ≤ y ≤ 0.1) were prepared by a soft chemical method. The structural and electrochemical properties of Li 1.05RE x Cr y Mn 2− x− y O 4 were investigated by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and charge–discharge experiments. Rare earth element-Sc and transition metal-Cr as co-substituents stabilize the spinel framework and improve charge–discharge performance. For Li 1.05Sc 0.01Cr 0.03Mn 1.96O 4, the capacity of the cell maintained 95% of the initial capacity at the 80th cycle. The rare earth elements of the variable valent metals such as Ce 3+/4+, Pr 3+/4+, Tb 3+/4+ with transition metal Cr 3+ as co-substituent do not stable framework of spinel or improve the cycling performance. Cyclic voltammetry (CV) were measured to provide clues for the improved cycling performance of cathode electrodes.

Preparation and characterization of Li 4/3Ti 5/3O 4 thin films by solution deposition

Li 4/3Ti 5/3O 4 thin films were prepared by the solution deposition technique. The structural and electrochemical properties of the thin film were studied by X-ray diffraction, cyclic voltammetry, galvanostatic charge–discharge experiments, and electrochemical impedance spectroscopy. The thin film prepared by this method is of pure phase with a spinel framework structure. The thin film delivers a capacity of 57 μA h cm − 2 μm − 1 and possesses excellent cycling behavior with a 0.08% capacity loss per cycle after being cycled 50 times. The average chemical diffusion coefficient of lithium ion in the thin film is 4.5 × 10 − 11 cm 2 s − 1 .

Aberration-Corrected STEM for Understanding of the Catalytic Mechanisms and Development of New Catalysts

Aberration-corrected Z-contrast (HAADF) STEM has proven an invaluable tool for catalysis research due to its superior resolution and high sensitivity. ORNL’s 300 kV VG Microscopes’ HB603U STEM with Nion aberration corrector was shown to resolve lattice spacings as small as 0.78 A [1] and routinely allows us to image single atoms inside the materials and on their surfaces as well . The ability to simultaneously collect EELS spectra provides additional possibilities for characterization. All these aspects have proven instrumental for the studies of catalytic activity and degradation in Cr-doped transition aluminas, which are widely used for dehydrogenation of alkanes [2]. Even though structural difference between γ-Al2O3 and η-Al2O3 is minimal and only amounts to different distribution of cation vacancies within spinel framework, Cr-doped η-Al2O3 catalysts can last several years, while Cr/γ-Al2O3 catalysts degrade in weeks [3]. Our STEM studies revealed that Cr dopant is distributed differently in these two systems. On γ-Al2O3, Cr is segregated into extended “patches” of Cr2O3 (Fig. 1). On η-Al2O3, on the other hand, no segregation was observed. Contrast in the STEM images was mostly uniform, with the thinnest areas of the alumina flakes sometimes displaying faint spots (Fig.2a)). The spots have similar intensity (Figs. 2b)-d)) of about the right level for Cr. EELS studies (Fig. 2e)) also indicate uniform distribution of dopant on η-Al2O3 surface. Our first-principles calculations suggest that catalytic processes primarily happen on isolated CrOx species, and preserving a high density of these active sites is necessary to retain activity. Due to a unique surface reconstruction resulting from its specific distribution of cation vacancies, γ-Al2O3 (110C) surface can accommodate growth of extended Cr2O3 “patches’, while on η-Al2O3 Cr remains isolated, resulting in much slower degradation.

Local structure of manganese oxides and lithium intercalates

The aim of this work is to determine the vibrational properties of manganese oxide frameworks and their lithium intercalates used as positive electrode material in Li-ion batteries. Raman and FTIR spectroscopies yield reliable description of material structure in which distortion of the basal MnO6 octahedra may be expected. Lattice dynamics are studied using either a classical group theoretical analysis or a local environment model. The local arrangement in MnO2 structures is investigated for pyrolusite, ramsdellite and the Li0.33MnO2 phase. The phase evolution as a function of the degree of lithium intercalation or deintercalation is reported and analysed in series of manganospinels Li1–x+δMn2–δO4 with 0≤x≤1 and 0≤δ≤0.33. The trigonal distortion of MnO6 octahedra is evidenced by insertion of lithium ions into the [B2]O4 spinel framework. A comparison with tetragonal Li2Mn2O4 and Li6.5Mn5O12 spinels shows the influence of the Jahn-Teller effect on the Raman features for this class of materials. The local structure was characterized as a function of the mean oxidation state of manganese cations.

XPS and Raman spectroscopic characterization of LiMn2O4 spinels

AbstractSurface analysis of lithium manganese oxides synthesized by the melt–impregnation method has been made by x‐ray photoelectron spectroscopy. These results revealed the change in the average oxidation state of Mn cations upon lithium substitution in Li1+δMn2−δO4 spinels. Studies of the local structure characterized by Raman scattering show the MnO bonding evolution as a function of the replacement of manganese cations. Modification in the trigonal distortion of MnO6 octahedra is evidenced by insertion of lithium ions into the octahedral holes of the [B2]O4 spinel framework. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Topotactic Two-Phase Reactions of Li [ Ni1 / 2Mn3 / 2 ] O 4 ( P4332 ) in Nonaqueous Lithium Cells

was prepared by a two-step solid state reaction and characterized by X-ray diffraction (XRD), infrared (IR)-Raman, and electron diffraction (ED). having characteristic eight absorption bands in 400-800 cm−1 in IR spectrum, extra lines in XRD, and extra spots in ED was analyzed in terms of a superlattice structure. Analytical results on the structural data indicated that (cubic: was a superlattice structure based on a spinel framework structure having a space group of (or in which nickel ions were located at the octahedral 4(b) sites, manganese ions were at the octahedral 12(d) sites, and lithium ions were at the 8(c) sites in a cubic-close packed oxygen array consisting of the 8(c) and 24(e) sites. Well-defined was examined in nonaqueous lithium cells and showed that the cell exhibited extremely flat operating voltage of about 4.7 V with rechargeable capacity of 135 mAh/g based on the sample weight. The reaction mechanism of was examined and shown that the reaction at ca. 4.7 V consisted of two cubic/cubic two-phase reactions, i.e., was reduced to via Results on the detailed reversible potential measurements indicated that the flat voltage at ca. 4.7 V consisted of two voltages of 4.718 and 4.739 V. The reaction of to is also examined and showed that the reaction proceeded in a cubic /tetragonal two-phase reaction with the reversible potential of 2.795 V. From these results, characteristic features of topotactic two-phase reactions of were discussed by comparing with the results on © 2004 The Electrochemical Society. All rights reserved.

Characterization of Al-doped spinel LiMn 2O 4 thin film cathode electrodes prepared by Liquid Source Misted Chemical Deposition (LSMCD) technique

A novel process called Liquid Source Misted Chemical Deposition (LSMCD) was used to synthesize Al-doped LiMn 2O 4 cathode films for Lithium microbatteries. The cathode films were characterized by XRD, SEM, cyclic volatmmetry, and charge/discharge test. LiMn 1.8Al 0.2O 4 film crystallized at 800 °C in rapid thermal annealing (RTA) for 5 min under oxygen atmosphere exhibited more improved electrochemical rechargeability than spinel LiMn 2O 4 film because the substitution of Al 3+ for Mn 3+ increased MnO bonding strength in the spinel framework and suppressed the two-phase behavior of the unsubstituted spinel during the intercalation/deintercalation that is the origin of the failure mechanism in the 4 V region. As a result, LiMn 1.8Al 0.2O 4 film showed an initial discharge capacity of 52 μAh/cm 2 μm and no capacity fade over 100 cycles.

Microwave synthesis of cathode material Li x Mn2O4 for lithium-ion battery

LiMn2O4 was synthesized rapidly by microwave heating. The product phases of the microwave synthesis and conventional solid-state synthesis were comparatively invesitigated. The capacity of microwave synthesis product decreases relatively slow. The lithium ion can be inserted into and extracted from the spinel framework structure fluently after cycling. But the capacity of the conventional solid-state synthesis product is more remarkably lowered. The spinel framework structure was destroyed which hindered the lithium ion from inserting and extracting. The influential factors of the process parameters are discussed such as heat preservation time, pre-heating at 400°C for 24h and coupled agent.

Inhibition of Jahn−Teller Cooperative Distortion in LiMn2O4 Spinel by Ga3+ Doping

Ga-doped Li−Mn-spinels Li1.02GaxMn1.98-xO4 with 0.00 ≤ x ≤ 0.20 are investigated to verify the lattice capability to allocate the Ga3+ ions on both tetrahedral and octahedral sites and to determine the lowest amount of dopant that prevents the occurrence of the Jahn−Teller (J−T) transition observed near room temperature in LiMn2O4. XRPD, NMR, and EPR spectra and static magnetic susceptibility and conductivity data are related to the site occupancy, the Mn valence state and the homogeneous distribution of the dopant. The electronic and magnetic features of the spinel framework are strongly dependent on substitution in its cationic sublattice: dopant amounts as low as 1% significantly modify the temperature of the conductivity drop associated with the J−T distortion. Ga3+ ions substitute chiefly in the octahedral sites, Mn4+ ions occupy regular and distorted octahedral sites and, at the same time, the value of lattice parameter remains unchanged. Mn2+ ions are present in the tetrahedral site and Li+ increa...

Nano-crystalline LiNi 0.5Mn 1.5O 4 synthesized by emulsion drying method

LiNi 0.5Mn 1.5O 4 spinel has been prepared by an emulsion drying method which can intermix cations very homogeneously at the atomic scale. When the emulsion-dried precursor was fired at 750 °C for 24 h, the observed particle of the LiNi 0.5Mn 1.5O 4 was nano-crystallite, being about 50 nm in diameter. The Rietveld refinement result clearly exhibited that the cubic spinel phase was successfully formed without any secondary phases, indicating that Li and transition metal cations occupied the 8 a and 16 d sites of the Fd3m structure, respectively. Li deintercalation from the spinel framework brings about a shift in the XRD peak toward higher angles and a peak splitting in the composition range δ=0–0.2 in Li δ Ni 0.5Mn 1.5O 4, implying that the host structure is progressively oxidized from Ni 2+ to Ni 4+ and accompanied by a two phase reaction. The sample calcined at 750 °C for 24 h showed the best cyclability upon cycling due probably to better crystallinity and a smaller particle size. We suggest that this material can be used as a 4.5 V cathode material for Li-ion battery.