Synthesis and electrochemical characterization of xLi(Ni0.8Co0.15Mg0.05)O2–(1−x)Li[Li1/3Mn2/3]O2 (0.0 ≤ x ≤ 1.0) cathodes for Li rechargeable batteries

Using solution based processing route, we have successfully synthesized xLi(Ni_0.8Co_0.15Mg_0.05)O₂–(1?x)Li[Li_1/3Mn_2/3]O₂ (0.0 ≤ x ≤ 1.0) cathode materials for lithium rechargeable batteries. The phase formation behavior of these cathode materials is characterized by X-ray diffraction measurements. The Galvanostatic charge–discharge characteristic of these cathodes is reported in various cut-off voltage limits. When these composite cathodes are charged to 4.8 V, electrochemical extraction of lithium takes place from active (Li[Ni_0.8Co_0.15Mg_0.05]O₂) as well as inactive (Li[Li_1/3Mn_2/3]O₂) components. Good cycleability of these cathodes is obtained when cycled in the cut-off voltage limits of 4.6–3.0 V. The cycleability of these cathodes are deteriorated when charged above 4.8 V and deep discharged up to 1.2 V followed by repeated cycling in these voltage limits. Based on the analyses of impedance spectra at various charge and discharge states, the probable reasons for such findings are discussed.     

Thermal and electrical relaxation studies in Li(4+x)TixNb1−xP3O12 (0.0 ≤ x ≤ 1.0) phosphate glasses

A new superionic conducting transparent phosphate glasses with composition Li_(4+x)Ti_xNb_1?xP₃O₁₂ (0 ≤ x ≤ 1.0) were prepared by rapid melt quenching. As quenched samples were characterized by X-ray powder diffraction, differential scanning calorimetric and Fourier transform infrared spectroscopy studies. These glasses were found to have high thermal stability parameter and Li₄NbP₃O₁₂ has been found to have high glass forming ability. Electrical properties of the present glasses were studied by impedance and dielectric spectroscopy in the frequency range 10 Hz–3 MHz in the temperature range 323–523 K. Arrhenius behavior has been observed for all the glass in conductivity, dielectric loss and conductivity relaxation and their activation energies are explained and reported.     

Structural and magnetic properties of TbxY3−xFe5O12 (0 ≤ x ≤ 0.8) thin film prepared via sol–gel method

Terbium-doped yttrium iron garnet (Tb_xY_3−x Fe₅O₁₂; x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles thin films have been prepared onto quartz substrate by sol–gel method followed by spin coating process. Annealing of the films was processed at 900 °C in air for 2 h. The structures were investigated by using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FE-SEM). The magnetic properties were studied by a vibrating sample magnetometer (VSM). The XRD patterns of the films were consistent with a single phase garnet structure. The lattice parameter was initially increased with Tb³⁺ concentration due to the larger size of the Tb³⁺ ion compared to Y³⁺ ion, but a decrease in lattice parameter was observed at higher Tb³⁺ concentration due to the effect of film’s thickness. FE-SEM micrographs reveal that the particles were highly agglomerated. The grain’s sizes for all films were in the range of 40–59 nm. The magnetic measurements at room temperature (25 °C) show that the saturation magnetization (M_s) of the films was reduced with the increase in Tb³⁺ ions, which due to the antiparallel alignment between Tb³⁺ ions and Fe³⁺ ions. The films illustrate normal shapes of hysteresis loops except Tb_0.2Y_2.8Fe₅O₁₂ and Tb_0.4Y_2.6Fe₅O₁₂ films exhibiting two steps increments before being saturated. The coercivity values (H_c) demonstrate non linear dependency with the terbium concentration (x).     

The oxygen deficient cubic perovskite SrFe1−xScxO3−δ (x ≤ 0.5; 0.1 ≤ δ ≤ 0.5): Structural features and physical properties

Solid state synthesis method has been used to stabilize oxygen deficient perovskite phases SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5). The good homogeneity of samples is confirmed by energy dispersive spectroscopy (EDS) analysis performed with a transmission electronic microscope (TEM). By combining X-ray and electronic diffraction (ED), it is demonstrated that the cationic substitution on the B site of the perovskite induces a decrease of the oxygen content but without inducing long range ordering phenomenon. On this basis, X-ray patterns of compounds were indexed in the cubic Pm3m space group. The oxidation states of iron evidenced by Mössbauer spectroscopy, are in good agreement with the oxygen stoichiometries determined by cerimetric titration. In the SrFe_1?xSc_xO_3?δ series, the Fe³⁺/Fe⁴⁺ origin of the electronic conductivity is clearly evidenced. The limit compound SrFe_0.5Sc_0.5O_2.5 is highly resistive and characterized by a cluster glass-like behaviour. Finally, negative magnetoresistivity properties are revealed for the x = 0.1 and x = 0.2 samples, reaching ?10% around the magnetic transition temperature in a 7T magnetic field.     

Structural variations and cation distributions in Mn3−xCoxO4 (0 ≤ x ≤ 3) dense ceramics using neutron diffraction data

Single phase ceramics of cobalt manganese oxide spinels Mn_3?xCo_xO₄ were structurally characterized by neutron powder diffraction over the whole solid solution range. For x < 1.75, ceramics obtained at room temperature by conventional sintering techniques are tetragonal, while for x ≥ 1.75 ceramics sintered by Spark Plasma Sintering are of cubic symmetry. The unit cells, metal–metal and metal–oxygen average bonds decrease regularly with increasing cobalt content. Rietveld refinements using neutron data show that cobalt is first preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site for increasing x values. Structural methods (bond valence sum computations and calculations based on Poix's work in oxide spinels) applied to our ceramics using element repartitions and [M–O] distances determined after neutron data refinements allowed us to specify the cation distributions in all phases. Mn²⁺ and/or Co²⁺ occupy the tetrahedral site while Mn³⁺, Co²⁺, Co^III (cobalt in low-spin state) and Mn⁴⁺ occupy the octahedral site. The electronic conduction mechanisms in our highly densified ceramics of pure cobalt and manganese oxide spinels are explained by the hopping of polarons between adjacent Mn³⁺/Mn⁴⁺ and Co²⁺/Co^III on the octahedral sites.     

Co1−xFe2+xO4 (x = 0.1, 0.2) anode materials for rechargeable lithium-ion batteries

A cobalt-poor or iron rich bicomponent mixture of Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ anode materials have been successfully prepared using simple, cost-effective, and scalable urea-assisted auto-combustion synthesis. The threshold limit of lower cobalt stoichiometry in CoFe₂O₄ that leads to impressive electrochemical performance was identified. The electrochemical performance shows that the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode exhibits high capacity and rate capability in comparison to a Co_0.8Fe_2.2O₄/Fe₂O₃ electrode, and the obtained data is comparable with that reported for cobalt-rich CoFe₂O₄. The better rate performance of the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode is ascribed to its unique stoichiometry, which intimately prefers the combination of Fe₂O₃ with Co_1−xFe_2+xO₄ and the high electrical conductivity. Further, the high reversible capacity in Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ electrodes is most likely attributed to the synergistic electrochemical activity of both the nanostructured materials (Co_1−xFe_2+xO₄ and Fe₂O₃), reaching beyond the well-established mechanisms of charge storage in these two phases.     

Investigation of the LiCo1−xMgxPO4 (0 ≤ x ≤ 0.1)–graphitic carbon foam composites

LiCo_1−xMg_xPO₄–graphitic carbon foam (LCMP–GCF with 0 ≤ x ≤ 0.1) composites are prepared by Pechini-assisted sol-gel method and annealed with the 2-steps annealing process (T = 300 °C for 5 min in flowing air, then at T = 730 °C for t = 12 h in flowing nitrogen). The XRD analysis, performed on powders reveals LiCoPO₄ as major crystalline phase, Co₂P and Co₂P₂O₇ as secondary phases. The morphological investigation revealed the formation and growth of microcrystalline “islands” which consist of acicular crystallites with different dimensions (typically 5–50 μm). By addition of Mg-ions, CV-curves of LCMP–GCF composites show a decrease of the surface between anodic and cathodic sweeps by cycling and a stark contribution of faradaic processes due to the graphitic structured foam. The electrochemical measurements, at a discharge rate of C/10 at room temperature, show the decrease of the discharge specific capacity from 100 mAh g⁻¹ for x = 0.0 to ∼35 mAh g⁻¹ for 0.025 ≤ x ≤ 0.05, then an increase to 69 mAh g⁻¹ for x = 0.1. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity at high Mg-ions content into the LiCoPO₄ phase (x ≥ 0.025).     

Thermal and kinetic parameters of 30Li2O–55B2O3–5ZnO–xTiO2–(10−x)V2O5 (0 ≤ x ≤ 10) glasses

Journal of Thermal Analysis and Calorimetry - In the present investigation, the effects of titanium and vanadium concentration on the thermal properties have been studied for...     

A single crystal X-ray and powder neutron diffraction study on NASICON-type Li1+xAlxTi2−x(PO4)3 (0 ≤ x ≤ 0.5) crystals: Implications on ionic conductivity

Single crystals of NASICON-type material Li_1+xTi_2−xAl_x(PO₄)₃ (LATP) with 0 ≤ x ≤ 0.5 were successfully grown using long-term sintering techniques. Sample material was studied by chemical analysis, single crystal X-ray and neutron diffraction. The Ti⁴⁺ replacement scales very well with the Al³⁺ and Li⁺ incorporation. The additional Li⁺ thereby enters the M3 cavity of the NASICON framework at x, y, z ∼ (0.07, 0.34, 0.09) and is regarded to be responsible for the enhanced Li⁺ conduction of LATP as compared to Al-free LTP. Variations in structural parameters, associated with the Ti⁴⁺ substitution with Al³⁺ + Li⁺ will be discussed in detail in this paper.     

Structural and magnetic properties of the Zn0.8−4xHoxOy (0.05 ≤ x ≤ 0.10) compounds prepared by solid state reactions

Zn_0.8−4xHo_xO_y (0.05 ≤ x ≤ 0.10) diluted magnetic semiconductors were prepared by the solid state reaction method. We have studied the structural properties of the samples by using the XRD, SEM, and EDX techniques. The SEM results clearly demonstrate that Ho³⁺ ions are quite well substituted for Zn²⁺ in the ZnO lattice, and the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra of the samples, it has been concluded that the substitution of Ho causes no change in the hexagonal wurtzite structure of ZnO. According to our M–H and M–T measurements paramagnetism has been observed for all the samples from our attainable lowest temperature of 10 K to 300 K. Furthermore, the trend of the AC-susceptibility (χ) versus temperature curves, measured under an AC-magnetic field of 10 Oe, also support our conclusion about the paramagnetic contribution in the Zn_0.8−4xHo_xO_y compounds explored in this study. In order to clearly see the paramagnetic contribution, and whether there is also a ferromagnetic or antiferromagnetic contribution or not the inverse susceptibility (1/χ) against temperature curves are also plotted. Those curves indicate that, the substitution of Ho into the ZnO compound causes, in addition to the paramagnetism, a weaker antiferromagnetic (AFM) interaction.     

Comparison of magnetocaloric properties of the Mn2−xFexP0.5As0.5 (x = 1.0 and 0.7) compounds

The Mn_2−xFe_xP_0.5As_0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase transitions, which are accompanied by a magnetic entropy change. For x = 1 the PM–FM transition is of the first order one with a weak (2–3 K) thermal hysteresis in the vicinity of T_C = 275 K. The Mn_1.3Fe_0.7P_0.5As_0.5 compound possesses two magnetic transitions: the second-order PM–FM transition at T_C = 190 K, followed by the FM–AFM transition at T_N = 90 K, leading to normal and inverse magnetocaloric effects, respectively. The maximum values of magnetic entropy change are equal to 17 J kg⁻¹ K⁻¹ in MnFeP_0.5As_0.5 and 5 J kg⁻¹ K⁻¹ in Mn_1.3Fe_0.7P_0.5As_0.5 for a field change of 5 T. The magnetic entropy changes were calculated using both the isofield magnetization curves versus temperature and the isothermal magnetization curves versus applied magnetic field. The magnetocaloric effect in MnFeAs_0.5P_0.5 is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius–Clapeyron equation.     

Synthesis of Li3Ni x V2−x (PO4)3/C cathode materials and their electrochemical performance for lithium ion batteries

Li₃Ni _x V_2?x (PO₄)₃/C (x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li₃Ni_0.04?V_1.96(PO₄)₃/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g^?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li₃V₂(PO₄)₃ have also been effectively improved through Ni doping.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

Synthèse et caractérisation de strontium–calcium–lanthane apatites Sr7−xCaxLa3(PO4)3(SiO4)3F2 0 ≤ x ≤ 2

Apatites with the chemical formula Sr_7−xCa_xLa₃(PO₄)₃(SiO₄)₃F₂, where x = 0, 1 and 2, were prepared by mechanochemical synthesis using a planetary mill. However, the obtained apatites were carbonated. For comparison, the compound with x = 0 was synthesized by a solid-state reaction at 1300 °C. To determine the influence of the synthesis method on the distribution of the lanthanum between the two cationic sites, a refinement by the Rietveld method was carried out on the latter compound, obtained by the two synthesis methods. This study shows that lanthanum was preferentially located in the sites Me(1) when mechanochemical synthesis was used, while it has a marked preference for the sites Me(2) when heat treatment was used. In addition, the electrical properties of the compound were investigated by impedance spectroscopy. The main result is that the Arrhenius plot presents a change in slope. This break has been related to the nature of the Sr/La–F bond.     

Thermal behaviour,surface properties and vibrational spectroscopic studies of the synthesized Co3xNi3−3x(PO4)2·8H2O (0 ≤ x ≤ 1)

Co_3xNi_3−3x(PO₄)₂·8H₂O (x = 1, 0.8, 0.6, 0.4, 0.2, and 0) were synthesized via simple wet chemical reaction and energy saving route method. The final decomposition products of hydrates are corresponding anhydrous tri(cobalt nickel) diphosphates. The metal and water contents of the synthesized hydrates were confirmed by AAS and TG/DTG/DTA techniques, respectively. The observed metal and water contents agree well with the formula of the title compounds. The crystal structures and lattice parameters as well as crystallite sizes of the studied compounds were determined using XRD data. The results from XRD and TG/DTG/DTA techniques confirmed that Co_3xNi_3−3x(PO₄)₂·8H₂O at all ratios were the single phase. The FTIR spectra of studied compounds were recorded and assigned. The thermal behaviours of single and binary tri(cobalt nickel) diphosphate octahydrates were studied for the first time. The morphologies of the studied compounds were investigated by using the SEM technique. The micrographs of all studied compounds exhibited the thin plated morphology. The surface area and the pore size data of anhydrous forms were measured by N₂ adsorption at −190 °C according to the BET method. The anhydrous forms of binary metal phosphate at x = 0.8, Co_2.4Ni_0.6(PO₄)₂, exhibits the highest surface area and expects to improve the catalytic activity.     

Approaching compositional limits of perovskite – type oxides and oxynitrides by synthesis of Mg0.25Ca0.65Y0.1Ti(O,N)3, Ca1–xYxZr(O,N)3 (0.1 ≤ x ≤ 0.4), and Sr1–xLaxZr(O,N)3 (0.1 ≤ x ≤ 0.4)

Partial substitution of cations and anions in perovskite-type materials is a powerful way to tune the desired properties. The systematic variation of the cations size, the partial exchange of O²⁻ for N³⁻ and their effect on the size of the optical band gap and the thermal stability was investigated here. The anionic substitution resulted in the formation of the orthorhombic perovskite-type oxynitrides Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃, Ca_1-xY_xZr(O,N)₃, and Sr_1–xLa_xZr(O,N)₃. A two-step synthesis protocol was applied: i) (nano-crystalline) oxide precursors were synthesized by a Pechini method followed by ii) ammonolysis in flowing NH₃ at T = 773 K (Ti) and T = 1273 K (Zr), respectively. High-temperature synthesis of such oxide precursors by solid–state reaction generally resulted in phase separation of the different A-site cations. Changes of the crystal structures were investigated by Rietveld refinements of the powder XRD data, thermal stability by DSC/TG measurements in oxygen atmosphere, oxygen and nitrogen contents by O/N analysis using hot gas extraction technique, and optical band gaps by photoluminescence spectroscopy. By moving from Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ via Ca_1–xY_xZr(O,N)₃ to Sr_1–xLa_xZr(O,N)₃, the degree of tilting of the octahedral network is reduced, as observed by an increase in the B–X–B angles caused by the simultaneously increasing effective ionic radius of the A-site cation(s). In general, increasing substitution levels on the A-site (Y³⁺ and La³⁺) are accompanied by an enhanced replacement of O²⁻ by N³⁻. In all three systems, this anionic substitution resulted in a reduction of the optical band gap by approximately 1 eV (Ti) and up to 2.1 eV (Zr) compared to the respective oxides. For Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ an optical band gap of 2.2 eV was observed, appropriate for a solar water splitting photocatalyst. The Zr-based oxynitrides required a by a factor of 2 higher nitrogen contents to significantly reduce the optical band gap and the measured values of 2.9 eV–3.2 eV are larger compared to the Ti-based oxynitride. Bulk thermal stability was revealed up to T = 881 K. In general, the thermal stability decreased with increasing substitution levels due to an increasing deviation from the ideal anionic composition as demonstrated by O/N analysis.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.