Physicochemical properties of LiAl x Mn2 − x O4 and LiAl0.05Mn1.95O4 − y F y cathode material by the citric acid-assisted sol–gel method

LiAl _x Mn_2 − x O₄ and LiAl_0.05Mn_1.95O_4 − y F _y spinel have been successfully synthesized by citric acid-assisted sol–gel method. The structure and physicochemical properties of this as-prepared powder were investigated by electronic conductivity test, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test in detail. The electronic conductivity decreases with increasing of the content of doped Al. XRD patterns show that the diffraction of LiAl_0.05Mn_1.95O_4 − y F _y samples is similar, with all the peaks indexable in the Fd3m space group, and a little impurity appears in the LiAl_0.05Mn_1.95O_3.8F_0.2 sample. SEM reveals that all LiAl_0.05Mn_1.95O_4 − y F _y powders have the uniform, nearly cubic structure morphology with narrow size distribution which is less than 500 nm. Galvanostatic charge–discharge test indicates that LiAl_0.05Mn_1.95O₄ has the highest discharge capacity and electrochemical performance among all LiAl _x Mn_2 − x O₄ samples after 50 cycles, and the initial discharge capacity of LiAl_0.05Mn_1.95O_4 − y F _y (y = 0, 0.02, 0.05, 0.1) is 123.9, 124.6, 124.9, and 125.0 mAh g⁻¹, respectively, and their capacity retention ratios are 94.2%, 94.9%, 91.7%, and 89.9% after 50 cycles, respectively. EIS indicates that LiAl_0.05Mn_1.95O_3.98F_0.02 have smaller charge transfer resistance than that of LiAl_0.05Mn_1.95O₄ corresponding to the extraction of Li⁺ ions.     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

Ionic conductivity and structural properties of MnO-doped Bi4V2O11 system

Bi₄V₂O₁₁ exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher conductivity by the partial substitution of metallic cations for vanadium in Bi₄V₂O₁₁. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn²⁺-doped compounds Bi₄V_2−x Mn _x O_{11− δ} (0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi₄V_2−x Mn _x O_{11− δ} samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

Local structure and electrochemistry of LiNi y Mn y Co1 − 2y O2 electrode materials for Li-ion batteries

A series of LiNi _x Mn _y Co _z O₂ (x = y, z = 1 − 2y) oxides have been synthesized by “chimie douce” and investigated as positive electrodes in rechargeable lithium batteries. Layered LiNi _y Mn _y Co_1 − 2y O₂ materials with high homogeneity and crystallinity were synthesized using the wet-chemical method assisted by carboxylic acid as the polymeric agent. The long range and local structural properties are investigated with experiments including X-ray diffraction, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy. The evolution of the structure is discussed as a function of the cobalt content that confers layer-like behavior on the framework. Electrochemical performance of LiNi _y Mn _y Co_1 − 2y O₂ oxides is tested in cells using nonaqueous 1 M LiPF₆ dissolved in ethylene carbonate–diethyl carbonate. Charge–discharge profiles are investigated as a function of the rate capability and the voltage window. A relation is found between the gravimetric capacity and the cation disorder of the positive electrode as indicated by structural analysis. Fast lithium extraction attributed to the larger interslab space has been observed in the cobalt-rich oxides. Paper presented at the 11th Euro-Conference on Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007.     

Synthesis and electrical characterisation of different doped magnesium titanates

The synthesis and characterization are reported for the cubic spinel titanate Mg_(2−x)Ni_xTiO₄ (x≤0.25) and Mg_(2−x)Mn_xTiO₄ (x≤1). Single phase samples were observed for Mg_(2−x)Ni_xTiO₄ and with x≤0.4 for Mg_(2−x)Mn_xTiO₄. AC measurements were carried out on four different compositions (x=0.01, 0.03, 0.04 and 0.15) in the Mg_(2−x)Ni_xTiO₄ series and for Mg_1.9Mn_0.1TiO₄. For all these compounds, increasing conductivity with temperature and Arrhenius conductivity dependence are observed, the activation energy is around 0.28 eV for the Ni compounds and is 0.184 eV for Mg_1.9Mn_0.1TiO₄. The DC conductivity was recorded over a range of oxygen partial pressures (10⁻¹⁹ to 1 atm) at 930 °C. The Mg_(2−x)Ni_xTiO₄ compounds show a n-type behaviour whereas the Mg_(2−x)Mn_xTiO₄ show a p-type behaviour at high p(O₂) and n-type at low p(O₂). The stability under reduced conditions was checked and discussed for the different synthesized compounds. Paper presented at the 5th Euroconference onSolid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Enhanced cycling properties of transition metal molybdates, Li x M2(MoO4)3 {0?≤ x

K. M. Begam  M. S. Michael  S. R. S. Prabaharan 《Ionics》2007,13(6):467-471

Broadband infrared luminescence from transparent glass–ceramics containing Ni<Superscript>2+</Superscript>-doped <Emphasis Type="BoldItalic">β</Emphasis> -Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals

Transparent Ni²⁺-doped β-Ga₂O₃ glass–ceramics were synthesized. The nanocrystal phase in the glass–ceramics was identified to be β-Ga₂O₃ and its size was about 3.6 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-cast glass to the octahedral sites in the glass–ceramics. The broadband infrared emission centering at 1270 nm with full width at half maximum (FWHM) of more than 250 nm was observed. The fluorescence lifetime was about 1.1 μs at room temperature. The observed infrared emission could be attributed to the ³ T _2g (³ F )→³ A _2g (³ F ) transition of octahedral Ni²⁺ ions. It is suggested that the Ni²⁺-doped transparent β-Ga₂O₃ glass–ceramics with broad bandwidth and long lifetime have a potential as a broadband amplification medium. PACS 42.70.-a; 42.70.Ce; 81.40.Tv     

Vibrational studies of spinel LixMn2O4 (0.3≤x≤1.0) cathodes

We report on the vibrational properties of spinel LiMn₂O₄ and its electrochemically delithiated forms Li_xMn₂O₄. Raman scattering and infrared absorption spectra have been studied as a function of the delithiation content in the wavenumber range 50–700 cm⁻¹. Results show that lithium ions can be extracted at room temperature to obtain Li_x[Mn₂]O₄ (0.3≤x≤1.0) without disrupting the [Mn₂]O₄ array. The normal modes of the spinel LiMn₂O₄ have been discussed in the O _h ⁷ symmetry and vibrations due to lithium ions with their oxygen neighbors have been identified at ca. 400 cm⁻¹. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Synthesis and pseudocapacitive investigation of LiCr x Mn2-x O4 cathode material for aqueous hybrid supercapacitor

A series of Cr-substituted LiMn₂O₄ samples (LiCr _x Mn_2-x O₄, 0?≤?x?≤?0.3) were synthesized by a urea-assisted combustion method to enhance pseudocapacitive properties of LiMn₂O₄ material in aqueous electrolyte. Their structure and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LiCr _x Mn_2-x O₄ and activated carbon (AC) electrode were used as the cathode and anode in hybrid supercapacitors, respectively, which capacitive properties were determined by cyclic voltammetry (CV), galvanostatic charge/discharge test, and electrochemical impedance spectroscopy (EIS) in Li₂SO₄ solution. The results revealed that the partial substitution of Mn³⁺ by Cr³⁺ decreased initial capacity, but it prevented capacity fading. In the working voltage of 0–1.4 V, the AC/LiCr_0.1Mn_1.9O₄ capacitor delivered an initial specific capacitance of 41.6 F g^?1 (based on the total active mass of two electrodes) at a current density of 100 mA g^?1 in 1 M Li₂SO₄ solution. After 1,000 cycles, its capacity loss was only 1.7 %.     

Capacity fading of LiCr0.1Mn1.9O4/MPCF cells at elevated temperature

Capacity fading of LiCr_0.1Mn_1.9O₄ /MPCF (mesophase pitch-based carbon fiber) cells was investigated at elevated temperature (55 °C). The cells showed very fast capacity fading, keeping only 60% of capacity retention at the 100th cycle at 55 °C. The cycled electrodes and the electrolyte were analyzed using electrochemical test, inductively coupled plasma, and X-ray diffraction. Results of the analyses indicated that LiCr_0.1Mn_1.9O₄ exhibited good effects on restraint of Mn dissolution and stabilization of structure at 55 °C. The cycled LiCr_0.1Mn_1.9O₄ electrode and the cycled MPCF electrode presented good electrochemical performance again with fresh electrolyte. Therefore, it was proposed that the cycling fading of LiCr_0.1Mn_1.9O₄/MPCF cells was mainly caused by decomposition of electrolyte upon LiCr_0.1Mn_1.9O₄ electrode during cycling. It was found that the decomposition of electrolyte led to the formation of a surface layer comprised of Li₂CO₃, Li _x PF _y , CH₃OCO₂Li or (CH₂OCO₂Li)₂, polymeric ether etc. The formation of this film consumed active lithium ions, leading to fast capacity fading of LiCr_0.1Mn_1.9O₄/MPCF cell at elevated temperature.     

Electrochemical behavior of Li intercalation processes into a Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 cathode

Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO₂ structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂. Indeed, Li[Ni_0.50Mn_0.50]O₂ compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni_0.17Li_0.22Mn_0.61]O₂ and Li[Ni_0.25Li_0.17Mn₀.₅₈]O₂ compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni²⁺ and about Ni³⁺, while the oxidation state of Mn ion sustains Mn⁴⁺ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂, in which Ni ion changes between Ni²⁺ and NI⁴⁺. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Lithium ion conductivity of Li5+xBaxLa3?xTa2O12 (x?=?0–2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li_5+x Ba _x La_3−x Ta₂O₁₂ (x = 0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data of Li_5+x Ba _x La_3−x Ta₂O₁₂ indicated that single phase oxides with garnet-like structure exist over the compositional range 0 ≤ x ≤ 1.25; while for x = 1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice parameter increases with increasing x and reaches a maximum at x = 1.25 then decreases slightly with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. The impedance plots of Li_5+x Ba _x La_3−x Ta₂O₁₂ samples obtained at 33 °C indicated a minimum grain-boundary resistance (R _gb) contribution to the total resistance (R _b + R _gb) at x = 1.0. The total (bulk + grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches a maximum at x = 1.25 and then decreases with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. Scanning electron microscope investigations revealed that Li_6.25Ba_1.25La_1.75Ta₂O₁₂ is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li_6.25Ba_1.25La_1.75Ta₂O₁₂ exhibits the highest total (bulk + grain boundary) and bulk ionic conductivity of 5.0 × 10⁻⁵ and 7.4 × 10⁻⁵ S/cm at 33 °C, respectively.     

Structural and electrochemical effects of cobalt doping on lithium manganese oxide spinel

Pure LiMn₂O₄ and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCo_xMn_2−xO₄, were prepared. The effect of extended cycling on the crystal structure was investigated. A capacity decrease with increasing cobalt content was observed in the potential range about 4100 mV vs. Li/Li⁺. Cycling behavior is significantly improved, compared to LiMn₂O₄. LiCo_xMn_2−xO₄ is discharged in a single phase reaction in the upper potential range around 4100 mV vs. Li/Li⁺, whereas pure LiMn₂O₄ shows a two phase behavior. LiMn₂O₄ shows a significant broadening of peaks in plots of differential capacity and change in shape of the voltage profile upon extended cycling. LiCo_xMn_2−xO₄ shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared to spinels with lithium substitution, Li_1+xMn_2−xO₄. In contrast to Li_1+xMn_2-xO₄, LiCo_xMn_2-xO₄ is discharged in a two step process in the range of 0 ≤ × ≤ 0,5. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

X-ray photoelectron spectroscopy study of the electronic structure of La<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3+δ</Subscript> solid solutions

The electronic structure of La_1–x Ga _x MnO_3+δ. solid solutions is studied by X-ray photoelectron spectroscopy (XPS). The valence state of the manganese is estimated by various methods: by analyzing the difference in the binding energies of the Mn2p_3/2 and O1s electronic levels, analyzing exchange splitting in the spectrum of Mn3s, and from the dependence of the binding energy of the XPS spectrum of Mn2p_3/2 on the calcium concentration. The state of oxidation of the manganese in the compositions containing calcium lies between Mn³⁺ and Mn⁴⁺. The efficacies of these methods are compared. A correlation is found between the type of crystalline structure of La_1–x Ga _x MnO_3+δ. (0 ≤ x < 1) and the binding energy of the Mn2p_3/2 peak. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 419–427, May–June, 2009.     

The NASICON solid solution Li1−x La x /3Zr2(PO4)3: optimization of the sintering process and ionic conductivity measurements

The Li_1−x La _{x /3}Zr₂(PO₄)₃ NASICON-type compounds (0 ≤ x ≤ 1) have been synthesized in powder form by a sol-gel method and sintered for ionic conductivity measurements. In order to improve the compactness of the ceramic without decomposition of the compound, several sintering processes have been tested for one member of the solid solution (x = 0.6): the use of sintering aids (ZnO, B₂O₃, TiO₂ and LiNO₃), a ball-milling of the synthesized powder, a flash heating, high isostatic pressure, and spark plasma sintering. Finally, a satisfactory compactness of 85% is obtained compared to the referenced value (63%) obtained by uniaxial and isostatic pressing. The ionic conductivity study was performed by impedance spectroscopy. It shows that, despite the formation of vacancies, the substitution Li⁺→ 1/3 La³⁺ + 2/3 □ has unfortunately no influence on the conduction for 0 ≤ x ≤ 0.7 since the ionic conductivity remains identical to the LiZr₂(PO₄)₃ one. For higher x values, the ionic conductivity strongly decreases.     

<Superscript>29</Superscript>Si MAS-NMR study of oxide conductors derived from the apatite-type La<Subscript>9.33</Subscript>Si<Subscript>6</Subscript>O<Subscript>26</Subscript> compound

The preparation of (La_9.33−2x/3Sr _x □_0.67−x/3)Si₆O₂₄O₂ (0 ≤ x ≤ 2) samples with different amounts of cation vacancies is reported. Structure and unit-cell parameters were deduced by Rietveld analysis of XRD patterns. Structural features that enhance oxygen conductivity in Sr-doped apatites are discussed. Up to three components were detected in ²⁹Si MAS-NMR spectra which change with the amount and distribution of cation vacancies. In general, oxygen conductivity increases with the amount of vacancies at La1 (6h) sites, passing through a maximum for x = 0.4. In the case of activation energy, a minimum is detected near x = 1.2, indicating that entropic and enthalpic change in different ways. The presence of cation vacancies should enhance oxygen hopping along c-axis; however, the analysis of the frequency dependence of conductivity suggests that oxygen motions are produced along three axes.     

Structural, transport and electrochemical properties of LiNi1 − yCoyMn0.1O2 and Al, Mg and Cu-substituted LiNi0.65Co0.25Mn0.1O2 oxides

LiNi_{1 - y − z}Co_yMn_zO₂ (y = 0.25, 0.35, 0.5, 0.6; z = 0.1, 0.2), LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂, LiNi_0.65Co_0.25Mn_0.08Al_0.02O₂, LiNi_0.65Co_0.25Mn_0.08Mg_0.02O₂ and LiNi_0.65Co_0.25Mn_0.08Al_0.01Mg_0.01O₂ cathode materials were synthesized by a soft chemistry EDTA-based method. Structural and transport properties of pristine and delithiated materials (Li_xNi_0.65Co_0.25Mn_0.1O₂, Li_xNi_0.55Co_0.35Mn_0.1O₂ and LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ oxides) are presented. In the considered group of oxides there is no correlation between electrical conductivity and the a parameter (M-M distance in the octahedra layers). The results of electrochemical performance of cathode materials are presented. The best stability during first 10 cycles was obtained for Li/Li_xNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ cell due to enhanced kinetics of intercalation process.     

Band structure and dominating electron-scattering mechanisms in Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis>−<Emphasis Type="Italic">y</Emphasis></Subscript>Mn<Subscript>x</Subscript>Fe<Subscript>y</Subscript>Se

Magnetic and kinetic properties as well as transmission and absorption spectra of Hg _1−x−y Mn _x Fe _ySe (0.09 ≤ x ≤ 0.099 and 0.001 ≤ y ≤ 0.01) crystals are investigated at H ≈ 0.5–6 kOe in the temperature range T = 77–300 K. The band parameters are determined on the basis of experimental data. It is found that in the crystals under study at T ≈ 300 K, electron scattering by polar optical phonons dominates, direct optical band-to-band transitions occur, and replacement of a part of Mn atoms by Fe for x + y = 0.1 results in an increase in E_g ^op with Fe content. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 35–39, March, 2007.