Electrochemical behaviors of Li[Li(1−x)/3Mn(2−x)/3Nix/3Cox/3]O2 cathode series (0 < x < 1) synthesized by sucrose combustion process for high capacity lithium ion batteries

A mixed cathode material between Li₂MnO₃ and Li[Mn_1/3Ni_1/3Co_1/3]O₂ for high capacity lithium secondary batteries was introduced in this study. It was prepared using the sucrose combustion process because this is a simple process. The oxidation states of Mn, Co and Ni ions in the pristine Li[Li_(1−x)/3Mn_(2−x)/3Ni_x/3Co_x/3]O₂ compounds were confirmed to be tetravalent, trivalent and divalent, respectively, via XANES measurements. Electrochemical charge/discharge studies showed that the highest first discharge capacity of 224 mAh/g was obtained in composition of x = 0.5 at a 0.2 C rate. The oxidation state of the Co and Ni ions in the Li[Li_1/6Mn_1/2Ni_1/6Co_1/6]O₂ changed to higher oxidation states, but that of the Mn ions did not change.     

Synthesis of xLi2MnO3·(1 − x)LiMO2 (M = Cr, Mn, Co, Ni) nanocomposites and their electrochemical properties

A series of 0.4Li₂MnO₃·0.6LiMO₂ (M = Ni_1/3Co_1/3Mn_1/3 and Ni_1/3Cr_1/3Mn_1/3) cathode materials are prepared by a co-precipitation method with subsequent quenching. Crystal structures of samples are investigated by X-ray diffraction and electron diffraction, which show a co-existence of rhombohedral and monoclinic structures indicating nanocomposite characteristics of the sample of 0.4Li₂MnO₃·0.6Li Ni_1/3Cr_1/3Mn_1/3O₂. The average particle size distributions of the powders are analyzed to be an order 400 and 100 nm. The 0.4Li₂MnO₃·0.6LiMO₂ (M = Ni_1/3Co_1/3Mn_1/3 and Ni_1/3Cr_1/3Mn_1/3) electrodes, which consist of a well balanced partial phases of rhombohedral and monoclinic can deliver a high reversible capacity of 220-230 mAh/g during an extended cycling.     

Low temperature synthesis of nanocrystalline Li4Mn5O12 by a hydrothermal method

A mild hydrothermal method using Li-birnessite (Li_xMnO₂·nH₂O) ultrafine fiber as the precursor has been adopted to prepare Li₄Mn₅O₁₂, which is of interest as an electrode material for 3 V rechargeable lithium ion batteries. X-ray diffraction data reveal that the obtained powders have a pure spinel structure with a lattice constant of 8.135 Å. The scanning electron microscopy image of the obtained powders shows the particles are cubic-shaped whose average size is about 40-50 nm. The results from inductively coupled plasma-atomic emission spectroscope and wet chemical analysis indicate that a Li/Mn ratio of 0.796, and an average valence of 3.96 of Mn ion have been achieved in the as-prepared products. The thermogravimetric and differential thermal analysis data also agree with the previous reports on Li₄Mn₅O₁₂, suggesting that near stoichiometry of Li₄Mn₅O₁₂ has been synthesized by this procedure at the rather low temperature 110°C.     

Enhanced electrochemical properties of nano-Li3PO4 coated on the LiMn2O4 cathode material for lithium ion battery at 55 °C

The electrochemical performance of LiMn₂O₄ is improved by the surface coating of nano-Li₃PO₄ via ball milling and high-temperature heating. The Li₃PO₄-coated LiMn₂O₄ powders are characterized by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). At 55 °C, capacity retention of 85% after 100 cycles was obtained for Li/Li₃PO₄-coated LiMn₂O₄ electrode at 1C rate, while that of pristine sample was only 65.6%. The Li/Li₃PO₄-coated LiMn₂O₄ electrode also showed improved rate capability especially at high C rates. At 5C-rates, the delivered capacities of pristine and Li₃PO₄-coated LiMn₂O₄ electrodes were 80.7 mAh/g and 112.4 mAh/g, respectively. The electrochemical impedance spectroscopy (EIS) indicates that the charge transfer resistance for Li/Li₃PO₄-coated LiMn₂O₄ cell was reduced compared to Li/LiMn₂O₄ cell.     

Crystallization and microstructure of glasses in the system Na2O/MnO/SiO2/Fe2O3

Glasses with the compositions (100 − x)(0.16Na₂O/0.10MnO/0.74SiO₂)/xFe₂O₃, (x = 5-30) and 16Na₂O/10MnO/(74 − y)SiO₂/yFe₂O₃ (y = 5-30) were studied using X-ray diffraction and scanning electron microscopy. The effect of the chemical composition and the thermal history on the phase formation and the resulting microstructure was investigated. During cooling, the precipitation of ferrimagnetic solid solutions Fe₃O₄/Mn₃O₄ was observed. These crystals show dendritic or platelet shape, whereby the platelets are ferromagnetic and the dendrites - mainly paramagnetic. The tendency towards crystallization can be suppressed by increasing the Na₂O-concentration. In contrast to glasses without manganese oxide, the precipitation of hematite is not observed. Therefore, the addition of reducing agents is not required, in order to crystallize large volume concentrations of the ferrimagnetic phase.     

Synthesis of layered Li1.2+x[Ni0.25Mn0.75]0.8−xO2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li⁺ content on electrochemistry of Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO₂ structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li⁺ is possibly incorporated in structure of layered Li_1.2Ni_0.2Mn_0.6O₂ (x = 0), accompanying oxidization of Ni²⁺ to Ni³⁺ to form Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni³⁺ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) in this work delivered the highest discharge capacity of 219 mAh g⁻¹ between 4.8 and 2.0 V. Increasing Li content (x value in Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂) reduced charge–discharge capacities, but significantly enhancing cycleability.     

Synthesis and electrochemical characterization of LixCoO2 for lithium-ion batteries

The cathode material Li_xCoO₂ was synthesized by preliminary mechanochemical activation of precursor oxide mixture powders, followed by thermal treatment at 800 °C for 5 h. The effects of the molar ratio of Li/Co on the electrochemical behavior were examined. The Li_xCoO₂ at Li/Co=1.07 showed superior cycling stability to the Li/Co=1.0 sample. This is attributed to the disappearance of a phase transition related to monoclinic distortion and the relatively lowered transport resistance in Li/Co=1.07 sample.     

Effect of chromium substitution on structure and magnetic properties of Bi2Fe4O9

Orthorhombic Bi₂Fe_4 − xCr_xO₉ (x = 0.0, 0.25, and 0.75) nanoplatelets were synthesized by a simple hydrothermal method. The structure, morphology, and magnetic properties of the obtained powders have been characterized. Calculation of the lattice parameters of Bi₂Fe_4 − xCr_xO₉, as well as bond lengths and angles, was carried out by X-ray diffraction Rietveld refinement. The volumes of the metal-oxygen tetrahedra and octahedra were calculated to be sequentially increasing as the Cr doping level increases. The samples undergo an antiferromagnetic transition at 250 ± 5 K. The magnetic moments of the samples increase with higher Cr doping level. The 3d electron spin state for Fe³⁺ in the as-prepared samples is different, which is possibly due to the distortion of Fe-O tetrahedra and octahedra in the crystal structure after chromium substitution.     

Electrochemical studies on cathode blends of LiMn2O4 and Li[Li1/15Ni1/5Co2/5Mn1/3O2]

Composite cathodes were prepared by blending LiMn₂O₄ spinel and Li[Li_1/15Ni_1/5Co_2/5Mn_1/3O₂] layer by simple mixing/ball milling followed by calcination at 800 °C. The prepared blend materials were subjected to XRD and charge–discharge studies. The cycling results revealed that the discharge capacity and cycleability of LiMn₂O₄ can be considerably increased upon blending the material with layered Li[Li_1/15Ni_1/5Co_2/5Mn_1/3O₂].     

Mixed cation effect in xR2O-(40 − x)Na2O-50B2O3-10Bi2O3 (R = Li, K) glasses

Mass density, glass transition temperature and ionic conductivity are measured in xLi₂O-(40 − x)Na₂O-50B₂O₃-10Bi₂O₃ and xK₂O-(40 − x)Na₂O-50B₂O₃-10Bi₂O₃ glass systems with 0 ≤ x ≤ 40 mol%. The strength of the mixed alkali effect in T_g, dc electrical conductivity and activation energy has been determined in each glass system. The magnitudes of the mixed alkali effect in T_g for the mixed Li/Na glass system are much smaller than those in the mixed K/Na glasses. The impact of mixed alkali effect on dc electrical conductivity in mixed Li/Na glass system is more pronounced than in the K/Na glass system. The results are explained based on dynamic structure model.     

Lithium insertion into manganese spinels

Lithium has been inserted chemically and electrochemically into Mn₃O₄ and Li[Mn₂]O₄ at room temperature. From X-ray diffraction, it is shown that the [Mn₂]O₄ subarray of the A[B₂]X₄ spinels remains unperturbed and that the electrons compensating for the Li⁺-ion charge reduce Mn³⁺ to Mn²⁺ in Mn₃O₄ and Mn⁴⁺ to Mn³⁺ in Li[Mn₂]O₄. In Li_xMn₃O₄, the tetragonal distortion due to a cooperative Jahn-Teller distortion by octahedral-site Mn³⁺ ions decreases with x from $\text{c}\text{a}\text{= 1.157}$ for x = 0 to $\text{c}\text{a}\text{= 1.054}$ for x = 1. The system Li_1+x[Mn₂]O₄, is cubic at x = 0 and tetragonal ($\text{c}\text{a}\text{= 1.161}$) at x = 1.2. Electrochemical data reveal a two-phase region in the Li_1+xMn₂O₄ system and a maximum x_m = 1.25. X-ray diffraction confirms the coexistence of a cubic and a tetragonal phase in the compositional range 0.1 ≤ x ≤ 0.8. The X-ray data also show that the inserted Li⁺ ions occupy the interstitial octahedral positions of the spinel structure. However, in Li_xMn₃O₄ the tetrahedral-site Mn²⁺ions are displaced from the A positions to the interstitial octahedral positions, as in Li_xFe₃O₄, whereas the tetrahedral-site Li⁺ ions in Li[Mn₂]O₄ remain on the A sites.     

Preparation and mobile ion transport studies of Ta and Nb doped Li6Zr2O7 Li-fast ion conductors

Pure and doped Li_6−x(Zr_2−xM_x)O₇, M = Nb and Ta; x = 0, 0.15 compounds have been prepared by the urea combustion method followed by annealing at 950 °C for 8 h. The samples are characterized by X-ray diffraction and impedance spectroscopy. Ionic conductivities, σ_ionic, were determined in the temperature range of 60-360 °C by impedance spectroscopy. We observe that the Ta doped Li₆Zr₂O₇ has a measurable σ_ionic at ∼160 °C, and at 300 °C exhibits a conductivity value of 1 × 10⁻³ S/cm. The temperature dependence of the conductivity in the range 100-360 °C obeys an Arrhenius relation, yielding an activation energy of E_a = 0.95 eV (for M = Ta and x = 0.15).The bond valence approach has been used to visualise Li⁺ ion migration pathways and the conductivity mechanism in these compounds. The lowest energy pathway is found to extend along the [0 1 2] direction. The Bond valence analysis also indicates a significantly anisotropic Li-ion conductivity in compounds with Li₆Zr₂O₇ type structure, predicting activation energies of 1.1 and 0.9 eV for the low energy pathway in undoped and doped Li₆Zr₂O₇.     

Synthesis and Li ion conductivity of Li2O-Nb2O5-P2O5 glasses and glass-ceramics

Glasses with the compositions of xLi₂O-(70 − x)Nb₂O₅-30P₂O₅, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li⁺ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li⁺ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li₂O content, and the glass of 60Li₂O-10Nb₂O₅-30P₂O₅ shows the value of σ = 2.35 × 10⁻⁶ S/cm at room temperature and the activation energy (E_a) of 0.48 eV for Li⁺ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li₃PO₄ and NbPO₅ are formed in the crystallization of the glasses and the crystallization results in the decrease in Li⁺ ion conductivity in all samples, indicating that any high Li⁺ ion conducting crystalline phases have not been formed in the present glasses. 60Li₂O-10Nb₂O₅-30P₂O₅ glass shows a bulk nanocrystallization (Li₃PO₄ nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10⁻⁷ S/cm at room temperature and E_a = 0.49 eV.     

Systeme Li0,5Ga2,5−xCrxO4 (0 ⩽ x ⩽ 2) : Correlations entre structure cristalline,proprietes optiques et spectre vibrationnel

The order-disorder transitions P4₃32 → Fd3m and F4?3m → Fd3m in the system Li_0,5Ga_2,5?xCr_xO₄ occur respectively for x = 1,25 and x = 1,75. The absorption spectra (d.r.s) disclose Cr³⁺ ions in Td symetry from x = 0,75 to x = 2 (ligand-field parameters of Cr³⁺ in A sites : Dq = 700 cm^?1, B = 500 cm^?1). Structure of Li_0,5Ga_0,875Cr_1,625 is established by means of X-ray and neutronic diffraction : Li⁺_0,24Ga³⁺_0,74Cr³⁺_0,02 [Li⁺_0,26Ga³⁺_0,135Cr³⁺_1,605] O^2?₄. Infrared and Raman spectra of ⁶Li_0,5Ga_2,5O₄ and ⁷Li_0,5Ga_2,5O₄ are reported. The IR spectra of ordered spinels (0 ? x ? 0,5 ; 1,75 < x ? 2) are discussed and partly assigned with the help of ⁶Li ? ⁷Li isotopic shifts.     

Electrochemical extraction of lithium from LiMn2O4

Lithium has been removed electrochemically at 15 μA/cm² from LiMn₂O₄ (spinel) to yield single phase Li_1?xMn₂O₄ for 0 < × ? 0.60. The electrochemical curve suggests that beyond x = 0.60 an electrochemical process other than lithium extraction occurs. Powder X-ray-diffraction spectra indicate that during the extraction process the [Mn₂]O₄ framework of the spinel structure remains intact. Previous results have shown that 1.2 Li⁺ ions can also be inserted into LiMn₂O₄, which suggests that lithium may be cycled in and out of the [Mn₂]O₄ framework of the spinel structure over a wide range of x, at least from Li_0.4Mn₂O₄ to Li₂Mn₂O₄. Discussion of the mechanism of formation of λ-MnO₂ in an acidic environment is extended.     

Synthesis and characterisation of the garnet-related Li ion conductor, Li5Nd3Sb2O12

In this paper the synthesis, conductivity, and structure of the garnet-related Li ion conductor, Li₅Nd₃Sb₂O₁₂, are reported. As for the related Li₅La₃M₂O₁₂ (M = Nb, Ta) materials, this phase shows high Li ion conductivity, with a conductivity at 300 °C of 9.2 × 10⁻³ S cm⁻¹. Structural studies using neutron diffraction indicate a cubic unit cell, space group Ia-3d, with Li located in two partially occupied sites. One of the sites is the traditional garnet structure tetrahedral site, while the other Li site is considerably more distorted. Although the latter is nominally a six coordinate site, a close inspection suggests that the coordination could be described as distorted tetrahedral, with the remaining two bonds being significantly longer (≈2.6 Å).     

Synthesis and electrochemical behavior of layered Li(Ni0.5−xCo2xMn0.5−x)O2 (x = 0 and 0.025) materials prepared by solid-state reaction method

Layered Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ (x=0 and 0.025) materials were prepared by conventional solid state reaction method combined with high energy ball milling (HEBM). The Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ electrodes delivered discharge capacity of 142-185 mAh/g depending on upper cut-off voltage limit with excellent cycleability. The charge/discharge and differential capacity versus voltage studies show that only one phase reaction occurs and no phase transition takes place during the electrochemical cycling.     

Fluorine-doped LiNi0.5Mn1.5O4 for 5 V cathode materials of lithium-ion battery

Fluorine-doped 5 V cathode materials LiNi_0.5Mn_1.5O_4−xF_x (0.05 ≤ x ≤ 0.2) have been prepared by sol-gel and post-annealing treatment method. The results from X-ray diffraction and scanning electron microscopy (SEM) indicate that the spinel structure changes little after fluorine doping, but the particle size varies with fluorine doping and the preparation conditions. The electrochemical measurements show that stable cycling performance can be obtained when the fluorine amount x is higher than 0.1, but the specific capacity is decreased and 4 V plateau capacity resulting from a conversion of Mn⁴⁺/Mn³⁺ remains. Moreover, influence of the particle size on the reversible capacity of the electrode, especially on the kinetic property, has been examined.     

Synthesis and crystal structure of a novel lithium bismuth phosphate, Li2Bi14.67(PO4)6O14

A lithium bismuth phosphate, Li₂Bi_14.67(PO₄)₆O₁₄, has been synthesized for the first time by the solid-state method. The crystal structure was determined by single crystal X-ray diffraction at 150 K. Li₂Bi_14.67(PO₄)₆O₁₄ crystallizes in the monoclinic system C2/c (No. 15), with a = 30.8189(4) Å, b = 5.2691(3) Å, c = 24.5302(3) Å, β = 122.84(2)°, V = 3346.81(1) Å³ and Z = 2. The structure along the b axis consists of layers of [Bi₂O₂] units as the basic building block. These are separated by isolated PO₄ and LiO₄ tetrahedra. The oxygen co-ordination around two of the phosphorus atoms is disordered. Solid-state ⁷Li NMR studies confirm the presence of lithium in the structure. The material shows ionic conductivity of the order of 10⁻⁵ S cm⁻¹ at 600 °C.     

Phase transformation of lithium tungsten bronzes, LixWO3, at room temperature ambient conditions

Samples of Li_xWO₃ with x = 0.05-0.7 were synthesized at 700 °C for 7 days using appropriate amounts of Li₂WO₄, WO₃ and WO₂ in evacuated sealed silica tubes. The products reveal different phases of perovskite tungsten bronze (PTB). An interesting phenomenon observed for the PTB phases is the gradual change in colours when they are exposed at room temperature ambient conditions (in air). This effect has been investigated using X-ray powder diffraction, infrared absorption and optical reflectivity methods for the powdered samples before and after 30 and 90 days in air. The spectra of the samples with x = 0.25-0.5 are dominated by a peak with maximum around 16,000 cm⁻¹ in the Kubelka Munk spectra which is related to the cubic Li_xWO₃ phase. The peak intensity increases with increasing x. After 30 days of exposure in air this peak disappeared for x < 0.5 samples due to a diffusion of Li from Li_xWO₃. X-ray and IR data show a gradual transformation into the lower symmetric phases (PTB_cubic ⇒ PTB_tetragonal ⇒ PTB_orthorhombic ⇒ PTB_monoclinic). The results suggest that Li is attracted by O₂ to the surface forming Li₂O which further reacts with H₂O and CO₂ in air. The in air altered samples regain their original colour when reheated at 500 °C in vacuum.