Effect of composition change of metals in transition metal sites on electrochemical behavior of layered Li[Co1 −2x(Li1 / 3Mn2 / 3)x(Ni1 / 2Mn1 / 2)x]O2 solid solutions

Five compositions of Li[Co_1 −2x(Li_1 / 3Mn_2 / 3)_x(Ni_1 / 2Mn_1 / 2)_x]O₂ solid solutions ( x = 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized using a sol–gel method with three end members of LiCoO₂, Li₂MnO₃(Li[Li_1 / 3Mn_2 / 3]O₂), and Li[Ni_0.5Mn_0.5]O₂. The compositions of metals in transition metal sites were changed to see the effect of them on electrochemical behavior of the solid solutions. All the samples were nano-sized semi-spherical shaped particles with a layered structure. The reduction of cobalt content (the increase of other metals) in the sites increases the lattice parameters, a and c, resulting in the shift of Raman and XRD peak positions. The discharge capacity fading turned serious at higher Co contents, but it was significantly diminished with the decrease of Co content. At lower Co contents, the capacity increased with cycle numbers. The most stable voltage profile was obtained from the composition of Li[Li_1 / 15Co_3 / 5Ni_1 / 10Mn_7 / 30]O₂ (x = 0.2).     

Synthesis and electrochemical characterization of M2Mn3O8 (M = Ca,Cu) compounds and derivatives

M₂Mn₃O₈ (M = Ca²⁺, Cu²⁺) compounds were synthesized and characterized in lithium cells. The M²⁺ cations, which reside in the van der Waals gaps between adjacent sheets of Mn₃O₈⁴⁻, may be replaced chemically (by ion-exchange) or electrochemically with Li. More than 7 Li⁺/Cu₂Mn₃O₈ may be inserted electrochemically, with concomitant reduction of Cu²⁺ to Cu metal, but less Li can be inserted into Ca₂Mn₃O₈. In the case of Cu²⁺, this process is partially reversible when the cell is charged above 3.5 V vs. Li, but intercalation of Cu⁺ rather than Cu²⁺ and Li⁺/Cu⁺ exchange occurs during the subsequent discharge. If the cell potential is kept below 3.4 V, the Li in excess of 4 Li⁺/Cu₂Mn₃O₈ can be cycled reversibly. The unusual mobility of + 2 cations in a layered structure has important implications both for the design of cathodes for Li batteries and for new systems that could be based on M²⁺ intercalation compounds.     

Hydrothermal phase formation of orthorhombic LiMnO2 and its derivatives as lithium intercalation compounds

Different from a conventional solid state reaction, a hydrothermal reaction mechanism is very difficult to illuminate and sometimes it remains undisclosed. Making an attempt to understand the hydrothermal phase formation process of o-LiMnO₂ obtained between the reaction of spinel type Mn₃O₄ precursor and LiOH aqueous solution, the possible reaction route was postulated and experimentally testified. Firstly, the selective dissolution of Mn²⁺ from the tetrahedral site of [Mn^II]^tet_4a[Mn^III₂]^oct_8dO₄, which is considered as to be an ionic exchange reaction with Li⁺, and an additional Li⁺ intercalation into the host structure of precursor would give rise to the formation of meta-stable Li₂Mn₂O₄ ([Li^I]^tet_4a[Li^I]^oct_8c[Mn^III₂]^oct_8dO₄). Secondly, the phase would be simultaneously transformed to thermodynamically stable o-LiMnO₂ phase under hydrothermal state during hydrothermal reaction. Through the above reaction process, the solid solution range of o-LiCo_xMn_1−xO₂ was as large as x ≤ 0.14, and that of o-LiFe_xMn_1−xO₂ was x ≤ 0.05. Co doped o-LiMnO₂ has higher capacity and good cyclability upon cycling, being substantially more stable to cycle than the unsubstituted and Fe doped materials.     

The study of novel multi-doped spinel Li1.15Mn1.96Co0.03Gd0.01O4 + δ as cathode material for Li-ion rechargeable batteries

Novel spinel Li_1.15Mn_1.96Co_0.03Gd_0.01O_4 + δ was synthesized by high temperature solid-state reaction method. The product was identified as well-defined spinel phase by X-ray diffraction (XRD); the SEM images illustrated that the particle distribution was well-proportioned. The initial special capacity was 126.5 and 128.1 mAh g^? 1 at 25 and 50 °C. The fading rate was 0.017% and 0.098% per cycle under 0.5 °C at 25 and 50 °C, respectively. The results showed that Li_1.15Mn_1.96Co_0.03Gd_0.01O_4 + δ displayed excellent capacity and cycleability.     

Layered lithium chromium manganese oxide compounds for high capacity electrode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ cathode materials were prepared by the sol-gel process. The structural characterization was carried out by fitting the XRD data by the Rietveld method. The results of X-ray diffraction show that the crystal structure is similar to that of thelayered lithium transition metal oxides (R3-m space group). The particle morphology and size were observed by SEM, and the elemental content was determined by ICP. The electrochemical performance of the cathode was evaluated in the voltage range of 2.0 ∼ 4.9 V with a current density of 7.947 mA/g. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of around 280 mAh/g in cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ was found to be a promising cathode material. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

The studies on structural and thermal properties of delithiated LixNi1/3Co1/3Mn1/3O2 (0 < x ≤ 1) as a cathode material in lithium ion batteries

The structural and thermal properties of the delithiated Li_xNi_1/3Co_1/3Mn_1/3O₂ (0 < x ≤ 1) material have been investigated by using diffraction and thermoanalytical techniques such as XRD and TG-DSC methods. XRD result shows that the delithiated materials maintain the O3-type structure with defined stoichiometric number at the range of 0.24 < x ≤ 1, exhibiting good crystal structural stability. The cobalt and nickel ions in the delithiated materials change their valence state (i.e. Co³⁺ to Co⁴⁺ and Ni³⁺ to Ni⁴⁺) when x < 0.49; the irreversible changes of the transformation may affect the first cycle of charge–discharge efficiency of the materials. A comparison of the results of TG-DSC with TPD-MS shows that the irreversible change of oxygen species during the delithiation process of Li_xNi_1/3Co_1/3Mn_1/3O₂ have great influence on the structural and thermal stability and reversibility of the materials.     

Investigation on the microscopic features of layered oxide Li[Ni1 / 3Co1 / 3Mn1 / 3]O2 and their influences on the cathode properties

Three kinds of samples of Li[Ni_1 / 3Co_1 / 3Mn_1 / 3]O₂ were prepared respectively from direct solid-state reaction method, combustion method and co-precipitation route and their microscopic structural features have been investigated using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), magnetic susceptibility measurement and X-ray photoelectron spectroscopy (XPS). The microscopic features such as uniform distribution of transition metal ions at 3b-site and the site-exchange ratio between lithium and nickel were found to be significantly dependent on the synthetic routes. The electrochemical properties of three samples were monitored using 2016 coin-cell by galvanostatic charge–discharge cycling test and cyclic voltammetry, which showed that the microscopic structural features are deeply related with the electrochemical performance. The obtained results also suggested that the combustion method may become a much simple alternative synthetic route to the complicate co-precipitation method.     

Spectroscopic studies of the structural properties of Ni substituted spinel LiMn2O4

Microstructure and local structure of spinel LiNi_xMn_2 − xO₄ (x = 0, 0.1 and 0.2) were studied using X-ray diffraction (XRD) and a combination of X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and Raman scattering with the aim of getting a clear picture of the local structure of the materials responsible for the structural stability of LiNi_xMn_2 − xO₄. XRD study showed that Ni substitution caused the changes of the materials’ microstructure from the view of the lattice parameter, mean crystallite size, and microstrain. XPS and XANES studies showed the Ni oxidation state in LiNi_xMn_2 − xO₄ was larger than + 2, and the Mn oxidation state increased with Ni substitution. The decrease of the intensity of the 1s → 4p_z shakedown transition on the XANES spectra indicated that Ni substitution suppressed the tetragonal distortion of the [MnO₆] octahedron. The Mn(Ni)–O bond in LiNi_xMn_2 − xO₄, which is stronger than the Mn–O bond in LiMn₂O₄ was responsible for the blue shift of the A_1g Raman mode and could enhance the structural stability of the [Mn(Ni)O₆] octahedron.     

Structural reinvestigation of Li3FeN2: Evidence of cationic disorder through XRD,solid-state NMR and Mössbauer spectroscopy

A significant cationic disorder is evidenced on Li₃FeN₂ prepared through solid-state reaction under controlled atmosphere. This derivative anti fluorite type structure (orthorhombic, space group Ibam, a=4.870(1) Å, b=9.652(1) Å and c=4.789(1) Å), solved first through single crystal X-ray diffraction [7], is usually described by Li⁺ and Fe⁺³ ordered distribution in tetrahedral sites formed by the nitrogen network, leading to [FeN_4/2]³⁻ edge-sharing tetrahedral chains. From ⁷Li/⁶Li Nuclear Magnetic Resonance spectroscopy, ⁵⁷Fe Mössbauer spectroscopy and powder X-ray and neutron diffraction, we demonstrate that about 4% of lithium sites are filled by iron and about 11% of iron sites are occupied by Li, which can explain the discrepancy within the Gudat's model observed on larger scale solid-state synthesis samples.     

Correlation between Li+ adsorption capacity and the preparation conditions of spinel lithium manganese precursor

Spinel lithium manganese oxides can be used as Li⁺ adsorbent with topotactical extraction of lithium. In this paper, the solid state methods were introduced to prepare spinel lithium manganese precursors with Li₂CO₃ and LiOH·H₂O as different Li sources. The Li⁺ uptake was studied to clarify the correction between Li⁺ adsorption capacity and the preparation conditions of precursors, including different Li sources, Li/Mn mole ratios and heating time. The results indicated that the Li⁺-extracted materials prepared with LiOH·H₂O and MnCO₃ usually have higher Li⁺ adsorption capacity than Li₂CO₃ and MnCO₃, and an ascending trend was found in Li⁺ uptake with increasing Li/Mn mole ratio in the preparation of the precursor, but it is not proportional. The Mn₂O₃ impurities could be the primary reason for decreasing Li⁺ adsorption capacity. Furthermore, it is concluded that the Li⁺-extracted materials obtained from spinel manganese oxides synthesized with Li/Mn = 1.0 can serve as selective Li⁺ absorbents due to its high selectivity and large adsorption capacity.     

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li6CaLa2Ta2O12 and Li6BaLa2Ta2O12

High-purity specimens of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li₆CaLa₂Ta₂O₁₂ and a = 13.001(4) Å for Li₆BaLa₂Ta₂O₁₂. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li⁺ ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ samples exhibit the conductivity σ = 2.2 × 10^? 6 S cm^? 1 at 27 °C (E_a = 0.50 eV) and σ = 1.3 × 10^? 5 S cm^? 1 at 25 °C (E_a = 0.44 eV), respectively.     

Sonochemical synthesis,characterization, thermal and semiconducting behavior of nano-sized azidopentaamminecobalt(III) complexes containing anion,CrO42− or Cr2O72−

New nano-sized cobalt(III) coordination complexes, [Co(NH₃)₅N₃]CrO₄ (1N) and [Co(NH₃)₅N₃]Cr₂O₇ (2N) were synthesized using an innovative sonochemical methodology based on reaction between [Co(NH₃)₅N₃]Cl₂ and potassium salt of CrO₄²⁻ or Cr₂O₇²⁻ in aqueous medium. These complexes were also compared with their respective bulks which were synthesized under identical conditions in the absence of sonicaion. All the complexes were characterized by elemental analysis and spectroscopic techniques (UV–visible and IR). Morphology and particle size of nano-sized complexes was determined by SEM and Zeta-sizer respectively. TGA was used for comparative thermal stability and XRD to identify the phase difference between nano structures and bulk complexes. Furthermore, the electrical property was investigated and all complexes were found to be electrical semiconducting materials and 2N shows better result than others. The single crystals X-ray structure study of new [Co(NH₃)₅N₃]Cr₂O₇ revealed the presence of discrete ions, [Co(NH₃)₅N₃]²⁺ and Cr₂O₇²⁻, crystallizes in monoclinic, space group P_c, with R = 0.0636 in the solid state.     

Electrochemical and magnetic properties of Li4 / 3Mn2 / 3O2–LiCoO2 solid solution

The compounds Li_(4−x)/3Mn_2(1−x)/3Co_xO₂ (0 < x < 0.5) were prepared by the sol–gel technique. X-ray diffraction patterns of these compounds were identified as α-NaFeO₂ type layered structure, though some super-structure lines, related to the ordered array of Li and transition metal ions in the transition metal layer, were observed. The magnetic susceptibility exhibited an antiferromagnetic transition around 40 K for x < 0.2, however the specimens with x > 0.3 had no magnetic transition. The magnetic percolation may explain these magnetic variations. The electrochemical performances were evaluated for the compound of x = 0.5, and it was seen that the electrochemical properties were sensitive to the potential window. Additionally, it was also found that the discharge capacity strongly depended on the preparation temperature; it took a maximum value at the preparation temperature of 900 °C. The discharge capacity is sensitive not only to the cation mixing degree but also to the particle size.     

Development and application of combinatorial electrostatic atomization system “M-ist Combi”: High-throughput preparation of electrode materials

We introduce a newly developed combinatorial electrostatic atomization system, “M-ist Combi,” and demonstrate the effectiveness of the system by establishing a pseudo-ternary Li–Ni–Co oxide phase diagram. After heating the starting materials with compositions in the range of 0.4 ≤ Li / (Li + Ni + Co) ≤ 0.6 at 973 K for 3 h, the diffraction of all of the products was indexed as single-phase with layer-type hexagonal structures such as LiCoO₂ and LiNiO₂. As the substitution quantity of Co to the Ni site increased, the value of 2θ shifted to a high-angle. By combining the M-ist Combi system with combinatorial XRD apparatus, we successfully completed the high-throughput sample preparation and phase identification of over 150 samples in one day.     

Electrochemical properties of spinel-type manganese oxide/porous carbon nanocomposite powders in 1 M KOH aqueous solution

Spinel-type manganese oxide/porous carbon (Mn₃O₄/C) nanocomposite powders have been simply prepared by a thermal decomposition of manganese gluconate dihydrate under an Ar gas flow at above 600 °C. The structure and texture of the Mn₃O₄/C nanocomposite powders are investigated by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) equipped scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), selected area-electron diffraction (SA-ED), thermogravimetric and differential thermal analysis (TG-DTA) and adsorption/desorption of N₂ gas at ?196 °C. The electrochemical properties of the nanocomposite powders in 1 M KOH aqueous solution are studied, focusing on the relationship between their structures and electrochemical capacitance.In the nanocomposite powders, Mn₃O₄ nano particles approximately 5 nm in size are dispersed in a porous carbon matrix. The nanocomposite powders prepared at 800 °C exhibit a high specific capacitance calculated from cyclic voltammogram of 350 and 600 F g^?1 at a sweep rate of 1 and 0.1 mV s^?1, respectively. The influence of the heating temperature on the structure and the electrochemical properties of nanocomposite powders is also discussed.     

X-ray photoelectron spectroscopy of LiM0.05Mn1.95O4 (M = Ni,Fe and Ti)

LiMn₂O₄ and LiM_0.05Mn_1.95O₄ (M = Ni, Fe and Ti) were synthesized by using solid-state reactions and their surface stoichiometries were confirmed by XPS data. The crystal and electronic structures were investigated by using X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). XRD data suggested that LiM_0.05Mn_1.95O₄ possesses nearly no any variations in lattice parameters compared with LiMn₂O₄ for slight substitution of Ni, Fe and Ti; the substituted Ni, Fe and Ti ions were located on the 16d octahedral sites in the spinel crystal lattice. The XPS results suggested that Fe and Ti ions were at + 3 and + 4 oxidation states, respectively; while Ni ions are mixed with + 2 and + 3 oxidation states. The normal oxidation state of Mn ions in the above four materials is almost the same and calculated as + 3.55 according to the splitting energies of Mn3s states.     

Synthesis and characterization of spinel type high-power cathode materials Li MxMn2−x O4 (M=Ni,Co, Cr)

The transition metal-doped spinel cathode materials, LiM_0.5Mn_1.5O₄ (M=Ni. Co, Cr) were prepared by solid-state reaction. The structure and morphology of the samples were investigated by X-ray diffraction, Rietveld refinement and scanning electron microscopy (SEM). The diffraction peaks of all the samples corresponded to a single phase of cubic spinel structure with a space group Fd3m. Field-emission SEM shows octahedron like shapes and the primary particles size was between 500 nm and 2 μm. Oxidation states of Ni, Co and Cr were found to be 2+, 2+ and 3+ as revealed by X-ray photoelectron spectroscopy. During discharging, LiNi_0.5Mn_1.5O₄ and LiCo_0.5Mn_1.5O₄ sample shows more than 130 mAh/g between 3.5 and 5.2 V at a current density of 0.65 mA/cm² and well developed plateau around 5 V, respectively.     

7Li and 51V NMR study on Li+ ionic diffusion in lithium intercalated LixV2O5

Li_xV₂O₅ (0.4 < x < 1.4) prepared by solid-state reaction were studied by ⁷Li and ⁵¹V NMR spectroscopy. ⁷Li NMR spectra showed a narrowing of the line width in relation to Li⁺ionic diffusion. Analysis of Li_xV₂O₅ using a Debye-type relaxation model showed a low activation energy ∼0.07 eV in the sample of x = 0.4 below room temperature, and revealed a Li⁺ionic diffusion with larger activation energy ∼0.5 eV above 450 K in lithium-rich samples. The latter is ascribed to the existence of a multi-phase system comprising stable ɛ- and γ-phases, resulting from complicated phase transitions at high temperature. These shapes and shifts enable the classification of the β-, ɛ-, δ-, and γ-phases. The ionic diffusion of Li⁺ ions is discussed in relation to the complicated phase transitions.     

Fabrication and luminescent properties of Al2O3:Cr3 + microspheres via a microwave solvothermal route followed by heat treatment

AlOOH:Cr^3 + powders were synthesized via a microwave solvothermal route at 433 K for 30 min and were used as the precursor and template for the preparation of γ-Al₂O₃:Cr^3 + by thermal transformation at 773 K for 2 h in air. The obtained γ-Al₂O₃ based powders were microspheres with an average diameter about 1.9 μm. Photoluminescence (PL) spectra showed that the Al₂O₃:Cr^3 + particles presented a symmetric broad R band at 696 nm without appreciable splitting when excited at 462 nm. It is shown that the 0.04 mol% of doping concentration of Cr^3 + ions in γ-Al₂O₃:Cr^3 + is optimum. According to Dexter's theory, the critical distance between Cr^3 + ions for energy transfer was determined to be 47.54 Å. Based on the corresponding PL spectrum, full width at half maximum (FWHM) of Al₂O₃:Cr^3 + (0.04 mol%) was calculated to be 3.35 nm.