Synthesis and structure refinement studies of LiNiVO4 electrode material for lithium rechargeable batteries

The lithium nickel vanadate (LiNiVO₄) cathode material has been synthesized by using sol-gel method. The thermal behavior of the material has been examined by thermogravimetric and differential thermal analysis (TG/DTA). The structure of LiNiVO₄ compound has been studied by the Rietveld refined x-ray diffraction (XRD) technique. The Brunauer–Emmett–Teller (BET) surface area of 0.79 m² g^?1 was estimated with N₂ absorption characteristics. The synthesized powder morphology was observed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) studies of synthesized LiNiVO₄ powder indicate that the oxidation states of nickel and vanadate are +2 and +5, respectively. The electrochemical properties were monitored using 2032 coin cells by cyclic voltammetry and EIS, which showed that the microscopic structural features were deeply related with the electrochemical performance.     

Structural,dielectric, and conductivity studies of yttrium-doped LiNiPO<Subscript>4</Subscript> cathode materials

Olivine-structured pure LiNiPO₄ and yttrium-doped LiNiPO₄ have been synthesized by a Pechini-type polymerizable precursor method. Compound formation temperature is confirmed from thermogravimetry to differential thermal analysis. Powder X-ray diffraction pattern confirmed the formation of phase pure LiNiPO₄ compound with an orthorhombic structure with fine crystallite size. Presence of preferred local cation environment is understood from Fourier transform infrared spectroscopy (FTIR) studies. XRD and FTIR studies show that doped yttrium ion entered in the lattice of LiNiPO_4. It has been found that the ionic conductivity of LiNiPO₄ is enhanced by around two orders of magnitude by doping yttrium. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample.     

Structural,electrical and dielectric studies of nanocrystalline LiMnPO4 particles

Olivine-structured LiMnPO₄ nanoparticles were prepared by microwave-assisted solvothermal method. The as obtained LiMnPO₄ sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and impedance spectroscopy techniques. The XRD pattern confirms the formation of LiMnPO₄ phase with an orthorhombic structure. The electrical conductivity of the sample at room temperature is found to be 1.2654?×?10^?7 S cm^?1. Dielectric spectra show an increase in dielectric constant with increase of temperature. The dielectric loss spectra reveal the predomination of DC conduction in the sample. The modulus studies indicate the non-Debye nature of the sample which corresponds to the distribution of elements in the sample. Galvanostatic battery testing showed that LiMnPO₄ nanoparticles displayed good cycleability in 30 cycles.     

Electrical characterization of PVA-based nanocomposite electrolyte nanofibre mats doped with a multiwalled carbon nanotube

An attempt has been made to prepare and characterise ammonium thiocyanate (NH₄SCN) salt and a multiwall carbon nanotube (MWNT)-doped polyvinyl alcohol-based nanofibre mats using an electrospinning process. The X-ray diffraction result shows an improvement in the amorphous nature of composite electrolyte fibre mats with increasing concentrations of the MWNT filler. The DSC behaviour of these nanofibre mat exhibits better thermal response upon dispersal of the filler. Composite electrolyte nanofibre mat doped with 6 wt% MWNT shows optimum conductivity, viz., 5.8?×?10^?4 Scm^?1. The temperature dependence of the bulk electrical conductivity displays a combination of Arrhenius and Vogel–Tammam–Fulcher nature. Dielectric loss studies have also been used to understand the conduction process in the system. Jonscher power law seems to be obeyed during ac conductivity measurements of the fibre mats.     

Effect of Ni(II) substitution on phase stabilization electrical properties of BICo(III)VOX.20 oxide-ion conductor

The BICO_0.20–xNI_xVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10^?4?S^?cm^?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔE_LT. However, the local minimum high-temperature conductivity, σ₆₀₀?°C?~?2.26?×?10^?2?S^?cm^?1 for x?=?0.10, coupled with a local maximum value of ΔE_HT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.     

CO(III)–NI(II) double substituted bismuth vanadate: synthesis,phase stabilization,and structural and electrical characterization

Samples of Co–Ni double substituted bismuth vanadate, BICO_0.20?x NI _x VOX (Bi₄Co_0.20???x ^(III)Ni _x ^(II)V_1.8O_{10.8???(x/2)???δ} ;0?≤?x?≤?0.20) were synthesized by standard solid state reactions. The influence of Ni substitution for Co on phase stabilization and oxide-ion performance have been investigated using X-ray powder diffraction, differential thermal analysis, and AC impedance spectroscopy. The high conducting γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380 °C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (～2.56?×?10^?4 S cm^?1 at 300 °C) was observed for the composition with x?=?0.13. However, a good agreement was generally found between the values of electrical conductivity and corresponding activation energies of conduction.     

Study on phase stabilization and electrical performance of BICO0.20−xNIxVOX solid electrolyte

BICO_0.20?xNI_xVOX solid electrolyte in the composition range 0 ≤ x ≤ 0.20 was synthesized by standard solid-state reactions. The influence of Ni substitution for Co on the relationship between the phase stabilization and electrical performance was investigated by means of X-ray powder diffraction (XRPD), differential thermal analysis (DTA) and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.13 whose thermal stability increases with Ni content. On the other hand, complex plane plots of impedance suggested a major contribution of polycrystalline grain interiors to the overall electrical conductivity and the fastest oxygen-vacancy diffusion in the perovskite vanadate layers at x = 0.13. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. However, a maximum ionic conductivity at lower temperatures (～2.56 × 10^?4 S cm^?1 at 300 °C) was observed for the composition with x = 0.13.     

Correlation between phase structure and electrical conduction in BISNVOX system for intermediate temperature solid oxide fuel cells (IT-SOFC)

Samples of Sn⁴⁺-substituted bismuth vanadate, formulated as Bi₄Sn _x V_{2? x} O_{11?( x /2)? δ} in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ? β, β ? γ and γ′ ? γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ? β and β ? γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ? γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10^?5 S cm^?1 at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.     

Structural and electrochemical investigation of Zn-doped LiCoO2 powders

A commercial cathode material (LiCoO₂) was modified by doping with Zn to improve its performance in lithium battery. The structure and morphology of the doped cathode material were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM). The synthesized samples were characterized using X-ray photoelectron spectra (XPS), used to investigate the elementary states on the system. The electrical conductivity variations of doped powders were measured in the temperature range between 30 and 150?°C. The 3?mol% Zn-doped LiCoO₂ sample shows the highest reversibility capacity (178?mA?h g^?1) after 30 cycles in the voltage window 3.0?C4.5?V.     

Studies on structural and electrical properties of Mg<Subscript>0. 5+y</Subscript> (Zr<Subscript>2-y</Subscript>Fe<Subscript>y</Subscript>) <Subscript>2</Subscript> (PO<Subscript>4</Subscript>) <Subscript>3</Subscript> ceramic electrolytes

The sample of Mg_{0. 5+y} (Zr_1-y Fe_y) ₂ (PO₄) ₃ (0.0 ≤y ≤0.5) was synthesized using the sol-gel method. The structures of the samples were investigated using X-ray diffraction and Fourier transform infrared spectroscopy measurement. XRD studies showed that samples had a monoclinic structure which was iso-structured with the parent compound, Mg_0.5Zr (PO₄) ₃. The complex impedance spectroscopy was carried out in the frequency range 1–6 MHz and temperature range 303 to 773 K to study the electrical properties of the electrolytes. The substitutions of Fe³⁺ with Zr⁴⁺ in the Mg_0.5Zr (PO₄) ₃ structure was introduced as an extrainterstitial Mg²⁺ ion in the modified structured. The compound of Mg_0.5+y (Zr_1-y Fe_y)₂(PO₄)₃ with y?=?0.4 gives a maximum conductivity value of 1.25?×?10^?5 S cm^?1 at room temperature and 7.18?×?10^?5 S cm^?1 at 773 K. Charge carrier concentration, mobile ion concentration, and ion hopping rate are calculated by fitting the conductance spectra to power law variation, σ _ac (ω)?=?σ _o ? +?Aω ^α . The charge carrier concentration and mobile ion concentration increases with increase of Fe³⁺ inclusion. This implies the increase in conductivity of the compounds was due to extra interstitial Mg²⁺ ions.     

Synthesis and impedance analysis of proton-conducting polymer electrolyte PVA:NH4F

An attempt has been made to prepare a new proton-conducting polymer electrolyte based on poly(vinyl alcohol) doped with ammonium fluoride (NH₄F) by solution casting technique. The complex formation between polymer and dissociated salt has been confirmed by X-ray diffraction and Fourier transform infrared spectroscopy studies. The highest ionic conductivity has been found to be 6.9?×?10^?6?Scm^?1 at ambient temperature (303 K) for 85PVA:15NH₄F polymer electrolyte. The conductance spectra contain a low frequency plateau region and high frequency dispersion region. The dielectric spectra exhibit the low frequency dispersion, which is due to space charge accumulation at the electrode–electrolyte interface. The modulus spectra indicate non-Debye nature of the material. The highest ionic conductivity polymer electrolyte 85PVA:15NH₄F has low activation energy 0.2 eV among the prepared polymer electrolytes.     

Structural and Dielectric Properties of Polythiophene/Chrom(III) Acetylacetonate Composites

The dielectric and morphological properties of polythiophene (PT) filled with various mass fractions of chrom(III) acetylacetonate (Cr(acac)₃), synthesized via chemical oxidative polymerization, are described. Significant shifts of the absorption peak of the C-S bond in the Fourier transform infrared (FT-IR) spectra indicated that the metal cations mostly interacted with sulfur atoms. Thermal analyses performed by differential scanning calorimetry (DSC) indicated that the cold crystallization temperature (T_cc) of PT decreased with increasing doping level. Microstructural differences were observed between PT and its composites in scanning electron microscopy (SEM) images. Dielectric measurements showed that the conductivity of the PT significantly increased with increasing doping level, from ?10^?7 S/m to ?10^?4 S/m at 10 kHz and 300 K.     

Influence of calcium substitution on the phase transition and ionic conductivity in BICAVOX oxide ion conductor

Samples of Bi₄Ca _x V_{2? x} O_{11?(3 x /2)?δ} in the composition range 0.07 ≤ x ≤ 0.30 were prepared by conventional solid state reactions. The stability of different phases as a function of composition was analysed by X-ray powder diffraction, FT-IR spectra, differential thermal analysis and AC impedance spectroscopy. For the compositions x ≤ 0.10, monoclinic α-phase structure is retained at room temperature. For x = 0.13, orthorhombic β-phase is observed, whereas for x ≥ 0.17, high O^2?conducting tetragonal γ-phase is stabilised. However, the highest ionic conductivity σ_300°C = 3.27 × 10^?4 S cm^?1 was observed for x = 0.17. This higher value of conductivity of the substituted compound as compared to the parent compound can be attributed to the increased oxygen ion vacancies generated as a result of cation doping. AC impedance spectroscopy reveals the fact that this ionic conductivity is mainly due to the grain contribution.     

Effect of Cu–Al double substitution on the electrical properties of Bi4V2O11

Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ, 0.02 ≤ x ≤ 0.08, were synthesized by standard solid-state reaction route. Structural and electrical properties of samples are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) and alternating current (AC) impedance spectroscopy. The tetragonal γ′ phase structure is preserved to room temperature with compound x = 0.02. The stabilization of β orthorhombic phase is observed for compositions 0.04 ≤ x ≤ 0.05. As the Al content increases, the monoclinic α phase is evidenced for materials 0.06 ≤ x ≤ 0.08. The electrical investigation of Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ system has been performed in the frequency range from 20 Hz to 1 MHz using AC impedance spectroscopy. The impedance spectra indicate the two semicircle arcs associated with the bulk and grain boundary resistances at temperature below ～450 ^○C. The conductivity generally changes when Al is substituted. The highest conductivity at 300 ^○C (σ = 2.55 × 10^?4 S cm^?1) is shown for x = 0.02.     

Influence of nanocrystalline phases on the electrical properties of lithium titanate phosphate glass ceramics mixed with Ga2O3 nanocrystals

Several glass ceramic compositions dispersed with Ga₂O₃ nanocrystals, in the series samples (100???x)[0.4Li₂O–0.1TiO₂–0.5P₂O₅]?+?xGa₂O₃ with x?=?0, 2, 4, 6, 8, and 10?mol% of Ga₂O₃ were synthesized via high-energy ball milling technique and labeled as lithium gallium titanate phosphate glass (LTPG _x ) (x is the mol% of Ga₂O₃ nanocrystals). The compositions have been selected on the basis of thermal stability data obtained from differential thermal analysis. X-ray diffraction studies indicate nanocrystalline phase formation in the controlled crystallized glasses. The variation of electrical conductivity was explained in the light of growth of nanocrystalline phases. The best bulk conductivity (σ?=?7.03?×?10^?4?S?cm^?1, at 303?K) was achieved by the sample containing 8?mol% of Ga₂O₃ nanocrystals content, labeled as LTPG₈ sample. The activation energy for conduction (E_{a σ} ) is obtained from the temperature dependent of conductivity data, which is fitted to Arrhenius equation. The single super curve in the scaling spectra suggested the temperature-independent relaxation phenomenon.     

EPR study of the impurity paramagnetic centres in (CaO−Ga2O3−GeO2) glasses

The X-band EPR spectra of Cr³⁺, Mn²⁺, and Fe³⁺ impurity ions in glasses of (CaO?Ga₂O₃?GeO₂) system are investigated in the 77÷300 K temperature range. The experimental data analysis yields the following results: (i) Impurity chromium ions are incorporated into the (CaO?Ga₂O₃?GeO₂) glasses network in Cr³⁺ (3d³,⁴F_3/2) paramagnetic valence state only and occupy the strong distorted oxygen coordinated octahedral sites. (ii) For all activated and non-activated (CaO?Ga₂O₃?GeO₂) glasses the iron impurity is present at concentration roughly 0.01 wt.%. Isotropic EPR signals atg _eff=4.29 andg _eff=2.00 are assigned to Fe³⁺ (3d⁵,⁶S_5/2) ions in the sites with strong rhombic distortion and in the sites with nearly cubic symmetry respectively. (iii) The manganese EPR spectrum in (CaO?Ga₂O₃?GeO₂) glasses is weakly dependent on temperature, doping procedure as well as manganese concentration. EPR spectra of impurity manganese ions in glasses with Ca₃Ga₂Ge₃O₁₂ and Ca₃Ga₂Ge₄O₁₄ compositions are virtually identical and belong to Mn²⁺ (3d⁵,⁶S_5/2) ions. Impurity manganese ions are incorporated into the (CaO?Ga₂O₃?GeO₂) glass network as isolated Mn²⁺ centres and clusters of Mn²⁺ ions.     

Dielectric characteristics and thermal behaviour of terbium fumarate heptahydrate crystals

Dielectric properties, ac conductivity and thermal characteristics of terbium fumarate heptahydrate crystals grown by gel diffusion method have been carried out. The real part of dielectric constant, dielectric loss and ac conductivity of the material have been measured as a function of temperature and frequency of the applied electric field. Dielectric constant, dielectric loss and ac conductivity of the title compound were systematically investigated, showing a hump at about 85 °C, which could be attributed to water molecules in the crystal boundary. The dielectric anomaly exhibited by the material has been correlated with its thermal behaviour. The ac conductivity of the material obeys the Jonscher's power law relation; σ(ω) = σ_o + Aω^s, with the temperature dependent power exponent s < 1. The ac conductivity of the compound has been found to increase with the increase in frequency. The material is suggested to show protonic conduction. The non-isothermal kinetics was used to evaluate the activation energy for the dehydration step of thermal decomposition of terbium fumarate heptahydrate by using the Coats–Redfern integral method.     

Microwave-sintered Pr<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>, and Gd<Superscript>3+</Superscript> triple-doped ceria electrolyte material for IT-SOFC applications

The Pr³⁺, Sm³⁺, and Gd³⁺ triple-doped ceria Ce_0.76Pr_0.08Sm_0.08Gd_0.08O_2-δ material as solid electrolyte for IT-SOFC has been successfully synthesized by sol–gel auto-combustion route. The effect of microwave sintering (1300 °C for 15, 30, and 60 min, named as PSG-MS15, PSG-MS30, and PSG-MS60, respectively) on structural, electrical, and thermal properties of prepared electrolyte material has been studied. Powder X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and Raman analysis revealed the single phase, microstructure, elemental confirmation, and structural oxygen vacancy formation of all the samples. Impedance spectroscopy analysis revealed the highest total ionic conductivity, i.e., 3.47 × 10^?2 S cm^?1 at 600 °C with minimum activation energy of 0.69 eV, in PSG-MS30 sample when compared to PSG-MS15 and PSG-MS60. The thermal expansion measurements have been carried out for PSG-MS30 specimen. The highest total ionic conductivity with minimum activation energy and moderate thermal expansion coefficient of PSG-MS30 sample makes the possibility of its use as solid electrolyte in IT-SOFC applications.     

Electrical conductivity and dielectric relaxation behavior of AgFeP2O7 compound

In the present study, AgFeP₂O₇ was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. Not only were the impedance spectroscopy measurements of our compound carried out from 209 Hz to 5 MHz over the temperature range of 553 K–698 K but its AC conductivity as well as the dielectric relaxation were evaluated. Impedance measurements show AgFeP₂O₇ an ionic conductor being the conductivity 1.04?×?10^–?5(Ω^–?1cm^–?1) at 573 K. The conductivity and modulus formalisms provide nearly the same activation energies for electrical relaxation of mobile ions revealing that transport properties in this material appear to be due to an ionic hopping mechanism dominated by the motion of the Ag⁺ ions along tunnels presented in the structure of the investigated material.     

Preparation and characterization of biodegradable poly(ε-caprolactone)-based gel polymer electrolyte films

Biodegradable polymer electrolyte films based on poly(ε-caprolactone) (PCL) in conjunction with lithium tetrafluoroborate (LiBF₄) salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid were prepared by solution cast technique. The structural, morphological, thermal, and electrical properties of these films were examined using X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), and impedance spectroscopy. The XRD and OM results reveal that the pure PCL possesses a semi-crystalline nature and its degree of crystallinity decreases with the addition of LiBF₄ salt and EMIMBF₄ ionic liquid. DSC analysis indicates that the melting temperature and enthalpy are apparently lower for the 40 wt% EMIMBF₄ gel polymer electrolyte as compared with the others. The ambient temperature electrical conductivity increases with increasing EMIMBF₄ concentration and reaches a high value of ～2.83?×?10^?4 S cm^?1 for the 85 PCL:15 LiBF₄ + 40 wt% EMIMBF₄ gel polymer electrolyte. The dielectric constant and ionic conductivity follow the same trend with increasing EMIMBF₄ concentration. The dominant conducting species in the 40 wt% EMIMBF₄ gel polymer electrolyte determined by Wagner’s polarization technique are ions. The ionic conductivity of this polymer electrolyte (～2.83?×?10^?4 S cm^?1) should be high enough for practical applications.