Showing papers in "Ionics in 2007"

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

Abstract: The stoichiometry range and lithium ion conductivity of Li5+xBaxLa3−xTa2O12 (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 Li5+xBaxLa3−xTa2O12 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 Li5+xBaxLa3−xTa2O12. The impedance plots of Li5+xBaxLa3−xTa2O12 samples obtained at 33 °C indicated a minimum grain-boundary resistance (Rgb) contribution to the total resistance (Rb + Rgb) 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 Li5+xBaxLa3−xTa2O12. Scanning electron microscope investigations revealed that Li6.25Ba1.25La1.75Ta2O12 is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li6.25Ba1.25La1.75Ta2O12 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 electrical properties of pure and NaBr doped poly (vinyl alcohol) (PVA) polymer electrolyte films for solid state battery applications

Abstract: A sodium ion conducting polymer electrolyte based on poly (vinyl alcohol) (PVA) complexed with sodium bromide (NaBr) was prepared using solution cast technique. Several experimental techniques such as XRD, FTIR, SEM, temperature-dependant conductivity and transference number measurements have been performed. XRD and FTIR studies confirm the complexation of salt with the polymer. Surface morphology was studied using Scanning Electron Microscopy. DC conductivity was measured in the temperature range of 303–373 K, and the conductivity was found to increase with the increase of dopant concentration as well as temperature. Transference number data suggests that the charge transport in this polymer electrolyte system is mainly due to ions. Using these polymer electrolyte films, electrochemical cells were fabricated with configuration Na/(PVA:NaBr)/V2O5 and Na/(PVA:NaBr)/(I2+C+electrolyte) and their discharge characteristics like open circuit voltage (OCV), short circuit current (SCC), power density, energy density were evaluated and compared.

Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

Abstract: We present a review of the structural properties of LiFePO4. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries.

Effects of dopant on the electrochemical properties of Li4Ti5O12 anode materials

Abstract: The effects of dopant on the electrochemical properties of spinel-type Li3.97M0.1Ti4.94O12 (M = Mn, Ni, Co) and Li(4-x/3)CrxTi(5-2x/3)O12(x = 0.1, 0.3, 0.6, 0.9, 1.5) were systematically investigated. Charge-discharge cycling were performed at a constant current density of 0.5 mA/cm2 between the cut-off voltages of 3.0 and 1.0 V, the experimental results showed that Cr3+ dopant improved the reversible capacity and cycling stability over the pristine Li4Ti5O12. The substitution of the Mn3+ and Ni3+ slightly decreased the capacity of the Li4Ti5O12. Dopants such as Co3+ to some extent worsened the electrochemical performance of the Li4Ti5O12.

Impedance spectroscopy studies of poly (methyl methacrylate)-lithium salts polymer electrolyte systems

Abstract: In the present work, five systems of samples have been prepared by the solution casting technique. These are the plasticized poly(methyl methacrylate) (PMMA-EC) system, the LiCF3SO3 salted-poly(methyl methacrylate) (PMMA-LiCF3SO3) system, the LiBF4 salted-poly(methyl methacrylate) (PMMA-LiBF4) system, the LiCF3SO3 salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiCF3SO3) system, and the LiBF4 salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiBF4) system. The conductivities of the films from each system are characterized by impedance spectroscopy. The room temperature conductivity in the pure PMMA sample and (PMMA-EC) system is 8.57 × 10−13 and 2.71 × 10−11 S cm−1, respectively. The room conductivity for the highest conducting sample in the (PMMA-LiCF3SO3), (PMMA-LiBF4), ([PMMA-EC]-LiCF3SO3), and ([PMMA-EC]-LiBF4) systems is 3.97 × 10−6, 3.66 × 10−7, 3.40 × 10−5, and 4.07 × 10−7 S cm−1, respectively. The increase in conductivity is due to the increase in number of mobile ions, and decrease in conductivity is attributed to ion association. The increase and decrease in the number of ions can be implied from the dielectric constant, ɛr-frequency plots. The conductivity–temperature studies are carried out in the temperature range between 303 and 373 K. The results show that the conductivity is increased when the temperature is increased and obeys Arrhenius rule. The plots of loss tangent against temperature at a fixed frequency have showed a peak at 333 K for the ([PMMA-EC]-LiBF4) system and a peak at 363 K for the ([PMM-EC]-LiCF3SO3) system. This peak could be attributed to β-relaxation, as the measurements were not carried out up to glass transition temperature, T g. It may be inferred that the plasticizer EC has dissociated more LiCF3SO3 than LiBF4 and shifted the loss tangent peak to a higher temperature.

Electrical, optical, and structural characterization of polymer blend (PVC/PMMA) electrolyte films

Abstract: Ion-conducting solid polymer blend electrolytes based on polyvinyl chloride (PVC)/poly methyl methacrylate (PMMA) complexed with sodium perchlorate (NaClO4) were prepared in various concentrations by solution cast technique. The features of complexation of the electrolytes were studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. DC conductivity of the films was measured in the temperature range 303–398 K. Transference number measurements were carried out to investigate the nature of charge transport in the polymer blend electrolyte system. The electrical conductivity increased with increasing dopant concentration, which is attributed to the formation of charge transfer complexes. The polymer complexes exhibited Arrhenius type dependence of conductivity with temperature. In the temperature range studied, two regions with different activation energies were observed. Transference number data showed that the charge transport in this system is predominantly due to ions. Optical properties like absorption edge, direct band gap, and indirect band gap were estimated for pure and doped films from their optical absorption spectra in the wavelength region 200–600 nm. It was found that the energy gap and band edge values shifted to lower energies on doping with NaClO4 salt.

Structural and electrical studies of sodium iodide doped poly(vinyl alcohol) polymer electrolyte films for their application in electrochemical cells

Abstract: Solid polymer electrolyte films based on poly(vinyl alcohol) (PVA) complexed with sodium iodide (NaI) were prepared using solution cast technique. The structural properties of pure and complexed PVA polymer electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD results revealed that the amorphous domains of PVA polymer matrix was increased with the increase in NaI salt concentration. The variation of film morphology was examined by scanning electron microscopy (SEM) studies. Fourier transform infrared spectral studies for pure and complexed PVA films revealed the vibrational changes that occurred due to the effect of dopant salt in the polymer. Direct current conductivity was measured in the temperature range of 303–373 K, and the conductivity was found to increase with the increase in dopant concentration as well as temperature. Measurement of transference number was carried out to investigate the nature of charge transport in these polymer electrolyte films using Wagner’s polarization technique. Transport number data showed that the charge transport in these polymer electrolyte systems was predominantly due to ions. Using these polymer electrolytes, solid-state electrochemical cells were fabricated. Various cell parameters like open-circuit voltage, short circuit current, power density, and energy density were determined.

Structural investigation on PEO-based polymer electrolytes dispersed with Al2O3 nanoparticles

Abstract: Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF3SO3) dispersed with various concentrations of aluminum oxide (Al2O3) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T g) whereas the degree of crystallization (X c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm−1; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only.

Vibrational and impedance spectroscopic analysis of poly(vinyl alcohol)-based solid polymer electrolytes

Abstract: Solid polymer electrolytes based on poly(vinyl alcohol) (PVA) doped with NH4Br have been prepared by the solution-casting method. The complex formation between the polymer and the salt has been confirmed by Fourier transform infrared spectroscopy. The highest conductivity at 303 K has been found to be of the order of 10−4 Scm−1 for 25 mol% NH4Br-doped PVA system. The ionic transference number of polymer electrolyte has been estimated by Wagner’s polarization method, and the results reveal that the conducting species are predominantly ions.

Dielectric spectra of LiTFSI-doped chitosan/PEO blends

Abstract: Solid-polymer-blend electrolyte consisting of chitosan and polyethylene oxide (PEO) in a 1:1 weight ratio and doped with lithium trifluoromethanesulfonimide (LiTFSI) salt was prepared by solution cast technique. The highest conducting film with conductivity value of 1.40 × 10-6 S cm−1 at room temperature consists of 30 wt% LiTFSI. The temperature dependence for the highest conducting film obeyed Arrhenius relationship. From loss tangent–frequency plots at different temperatures, the frequency f max at which the plot is a maximum was obtained. From this, ln f max vs 103/T was plotted. The activation energy value obtained from the log σ vs 103/T plot and ln f max vs 103/T plot is about the same, suggesting that the processes of conductivity and relaxation for the charge carriers are the same.

Dielectric and conduction mechanism studies of PVA-orthophosphoric acid polymer electrolyte

Abstract: Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The conductivity is observed to increase from 10−9 to 10−4 S cm−1 as a result of orthophosphoric acid (H3PO4) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt% H3PO4. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H3PO4 is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity σac = Aωs was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph of s vs T from which the conduction mechanism for sample PVA-17 wt% H3PO4 was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the sample PVA-33 wt% H3PO4 by way of the correlated barrier height (CBH) model.

Electrochemical cell performance studies on all-solid-state battery using nano-composite polymer electrolyte membrane

Abstract: All-solid-state proton-conducting polymeric batteries have been fabricated in the cell configurations: Zn + ZnSO4·7H2O (anode) || polyethylene oxide (PEO):NH4HSO4 + SiO2 || MnO2 + C (cathode) and Zn + ZnSO4·7H2O (anode) || PEO:NH4HSO4 + SiO2 || PbO2 + V2O5 + C (cathode). Nano-composite proton-conducting polymeric membrane in wt.% composition, 92PEO: 8 NH4HSO4 + 3 SiO2, synthesized by solution cast technique, has been used as electrolyte. Dispersal of nanosized (8 nm) fumed-SiO2 particles resulted into an enhancement in the room temperature conductivity of polymer electrolyte host, 92PEO: 8 NH4HSO4 (wt.%), approximately by an order of magnitude with the substantial increase in the mechanical strength of the films. Details on the electrolyte film casting and ion transport characterization studies have been discussed elsewhere in the literature. However, a brief mention has been made for reference. An open circuit voltage in the range 1.5–1.8 V, obtained for both the batteries, is in very good agreement with the value reported. The cell performance has been studied under varying load conditions.

Hydrothermal synthesis of FeS2 for lithium batteries

Abstract: Nanocrystalline FeS2 cathode material of lithium cell was synthesized from cheap materials of FeSO4, Na2S2O3, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized, about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative effect on the electrochemical performance of the material. The synthetic FeS2 showed a significant improvement of electrochemical performance for Li/FeS2 cells.

Hydrogen separation from syngas using high-temperature proton conductors

Abstract: Hydrogen pumps using high-temperature proton conductors have been examined as a candidate means of hydrogen separation from syngas. Durability to CO2 is a main concern for the alkali-earth-containing perovskites and was tested for a few typical compositions. Ce-excluded and cerate–zirconate solid solution electrolytes, SrZr0.9Y0.1O3-α, and BaCe0.6Zr0.3Nd0.1O3-α were stable in CO2-containing atmospheres, whereas they showed poor overpotential characteristics when platinum electrodes were used. It is demonstrated that the hydrogen pumping properties can be much improved for the case of SrZr0.9Y0.1O3-α by the use of palladium anode and SrCe0.95Yb0.05O3-α interlayer for the cathode.

High performance PEO-based polymer electrolytes and their application in rechargeable lithium polymer batteries

Abstract: Solvent-free, lithium-ion-conducting, composite polymer electrolytes have been prepared by a double dispersion of an anion trapping compound, i.e., calyx(6)pyrrole, CP and a ceramic filler, i.e., super acid zirconia, S-ZrO2 in a poly(ethylene oxide)-lithium bis(oxalate) borate, PEO–LiBOB matrix. The characterization, based on differential thermal analysis and electrochemical analysis, showed that while the addition of the S-ZrO2 has scarce influence on the transport properties of the composite electrolyte, the unique combination of the anion-trapping compound, CP, with the large anion lithium salt, LiBOB, greatly enhances the value of the lithium transference number without depressing the overall ionic conductivity. These unique properties make polymer electrolytes, such as PEO20LiBOB(CP)0.125, of practical interest, as in fact confirmed by tests carried out on lithium battery prototypes.

Electrochemical solid state gas sensors: An overview

Abstract: Gas sensors has been currently in great demand because of serious concern over environmental pollution and public health considerations resulting from tremendous growth of industrialisation. Concurrently, there have been continuous efforts to obtain sensors with improved performance. The performance of any solid-state electrochemical gas sensor has been always rated on its response time, thermodynamic stability, operating temperature, gas sensing ability, sensitivity and gas concentration range, which is to be sensed. This article reviews the factors contributing towards a gradual development of electrochemical solid-state gas sensors in terms of a continuous tailoring of its two basic components, i.e. solid electrolyte and reference electrode.

Dependence of NO2 sensitivity on thickness of oxide-sensing electrodes for mixed-potential-type sensor using stabilized zirconia

Abstract: The effect of thickness of oxide-sensing electrode (SE) on NO2 sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer of Cr2O3–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4-μm-thick SE even at a high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization curves, and the gas-phase NO2 decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO2 decomposition on the oxide–SE matrix played an important role in determining the NO2 sensitivity of the present sensors.

Low temperature processing of dense samarium-doped CeO2 ceramics: sintering and intermediate temperature ionic conductivity

Abstract: Samarium-doped Ceria powders for solid electrolyte ceramics were synthesized by a combustion process. Cerium nitrate and samarium nitrate were used as the starting materials, and glycine was used as fuel. Decomposition of unburned nitrogen and carbon residues was investigated by simultaneous thermogravimetry analysis and differential thermal analysis experiments. The X-ray diffraction results showed that the single-phase fluorite structure forms at a relatively low calcination temperature of 800 °C. X-rays patterns of the SDC powders revealed that the crystallite size of the powders increases with increasing calcination temperature. The sintering behavior results showed that more than 96% of the relative density is obtained for powders sintered at 1,100 °C for 8 h. The alternating current impedance spectroscopy results showed that the SDC15 sample sintered at 1,100 °C has ionic conductivity of 0.015 Scm−1at 650 °C in air. The present work results have indicated that glycine–nitrate route is a relatively low-temperature preparation technique to synthesize SDC powders with a high sinterability and a good ionic conductivity.

Solid polymeric electrolyte of PVC–ENR–LiClO4

Abstract: The ionic conductivity of PVC–ENR–LiClO4 (PVC, polyvinyl chloride; ENR, epoxidized natural rubber) as a function of LiClO4 concentration, ENR concentration, temperature, and radiation dose of electron beam cross-linking has been studied. The electrolyte samples were prepared by solution casting technique. Their ionic conductivities were measured using the impedance spectroscopy technique. It was observed that the relationship between the concentration of salt, as well as temperature, and conductivity were linear. The electrolyte conductivity increases with ENR concentration. This relationship was discussed using the number of charge carrier theory. The conductivity–temperature behaviour of the electrolyte is Arrhenian. The conductivity also varies with the radiation dose of the electron beam cross-linking. The highest room temperature conductivity of the electrolyte of 8.5 × 10−7 S/cm was obtained at 30% by weight of LiClO4. The activation energy, E a and pre-exponential factor, σ o, are 1.4 × 10−2 eV and 1.5 × 10−11 S/cm, respectively.

A study on LiBOB-based nanocomposite gel polymer electrolytes (NCGPE) for Lithium-ion batteries

Abstract: Lithium bis(oxalato)borate (LiBOB) salt-based nanocomposite gel polymer blend electrolyte (PVdF/PVC) membranes have been prepared by solution casting technique for various concentrations of TiO2. The effect of anatase structure of nanosized titanium dioxide in the plasticized PVC/PVdF + LiBOB matrix has been observed in the 2:1 salt filler ratio in the impedance measurements that the conductivity is increased one order of magnitude higher than the filler-free electrolyte (1:0 salt:filler ratio). The phase morphology of this electrolyte membrane represents the appearance of the free volume sites for ionic migration.

Two-phase reaction mechanism during chemical lithium insertion into α-MoO3

Abstract: The phase transition during chemical lithium insertion into α-MoO3 was investigated by chemical analysis, X-ray diffraction (XRD) and electrochemical characterisation. The samples have been prepared by reaction of various amounts of water-free lithium iodide with fine-particulate orthorhombic molybdenum trioxide in n-hexane (non-aqueous media), which yielded materials with different Li/Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO3 has been changed after the chemical lithiation. The phase transition ranged from 0.25 < x < 0.5 in Li x MoO3 upon chemical lithium insertion into α-MoO3. The XRD lines of lithium inserted phase Li x MoO3 grew at the expense of the XRD lines of the pristine α-MoO3 as lithium ions were chemically inserted until the disappearance of lines related to α-MoO3. The electrochemical performance of the lithiated samples is improved in comparison with the starting material (non-lithiated α-MoO3).

An investigation of the proton conductivities of hydrated poly(vinyl alcohol)/boric acid complex electrolytes

Abstract: Proton-conducting polymer complex electrolytes were prepared by incorporation of boric acid, H3BO3 into poly(vinylalcohol), PVA, to form hydrated PVAxH3BO3 where x denotes the number of moles of boric acid per polymer repeat unit. The dried materials were characterized via Fourier transform infrared spectroscopy, thermogravimetry, and X-ray diffraction. The proton conductivity of the hydrated complex electrolytes was measured by AC impedance spectroscopy. PVA2H3BO3 with RH ∼25% was found to be optimum composition that exhibited proton conductivity of 1.3 × 10−3 S/cm at 80 °C.

Preparation and electrical characterization of (PVC+KBrO3) polymer electrolytes for solid state battery applications

Abstract: This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate (KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied by X-ray diffraction and Fourier transform infrared spectroscopy.

Synthesis of Yb-doped Ba(Ce,Zr)O3 ceramic powders by sol–gel method

Abstract: This study was aimed to synthesize a ceramic electrolyte of BaCe0.76Zr0.19Yb0.05O2.975 using acetate and chloride precursors. The transparent sol was stable for more than 10 months but only 3 months for the gel. The dried gel was characterized using thermogravimetric analysis/differential scanning calorimetry, particle analyzer, X-ray diffraction (XRD), and scanning electron microscopy/dispersive X-ray (SEM/EDX) analysis. Thermal behavior analysis showed three steps of weight losses. All the processes were exothermic reactions as shown by derivative thermogravimetric analysis signal. Two groups of particle size were observed in the particle size distribution for the sample in the form of sol and powders ranging from 100 to 1,100 nm. A high purity single-phase sample with orthorhombic structure was identified by XRD. The theoretical density estimated from the unit cell parameters was 6.40 g cm−3. SEM of the powdered sample showed homogeneous distribution of particles and the grains size were in the range of 0.7–1.3 μm. EDX data revealed that the residue of small amount of chloride (≈0.25%) was still present in the final product of the compound.

The effects of ceramic fillers on the PMMA-based polymer electrolyte systems

Abstract: The effects of ceramics fillers on the polymethylmethacrylate (PMMA)-based solid polymer electrolytes have been studied using ac impedance spectroscopy and infrared spectroscopy. The polymer film samples were prepared using solution cast technique, tetrahydrofuran (THF) used as a solvent, and ethylene carbonate (EC) has been used as plasticizer. Lithium triflate salt (LiCF3SO3) has been incorporated into the polymer electrolyte systems. Two types of ceramic fillers, i.e., SiO2 and Al2O3, were then implemented into the polymer electrolyte systems. The solutions were stirred for several hours before it is poured into petri dishes for drying under ambient air. After the film has formed, it was transferred into desiccator for further drying before the test. From the observation done by impedance spectroscopy, the room temperature conductivity for the highest conducting film from the (PMMA–EC–LiCF3SO3) system is 1.36 × 10−5 S cm−1. On addition of the SiO2 filler and Al2O3 filler, the conductivity are expected to increase in the order of ∼10−4 S cm−1. Infrared spectroscopy indicates complexation between the polymer and the plasticizer, the polymer and the salts, the plasticizer and the salts, and the polymer and the fillers. The interactions have been observed in the C=O band, C–O–C band, and the O–CH3 band.

Electrical and electrochemical behaviour of several life x co1?-x po4 solid solutions as cathode materials for lithium ion batteries

Abstract: Several olivine phosphates were investigated in the last years as cathode materials for secondary lithium ion batteries. Among these compounds, LiFe x Co1 − x PO4 solid solutions might be interesting candidates because they should combine the high potential value of Co3+/Co2+ (higher than 4.5 V vs Li+/Li) with the relatively high charge–discharge rate of LiFePO4. Solid solutions were prepared by solid-state route and characterised by X-ray powder diffraction, cyclic voltammetry, impedance spectroscopy and the Hebb–Wagner method. The results show that also low amount of iron induces high electronic conductivity in the solid solutions.

Sulfur composite cathode materials: comparative characterization of polyacrylonitrile precursor

Abstract: The electrochemical behavior of the sulfur composite cathode material for rechargeable lithium batteries and the characteristic of the polyacrylonitrile precursor were investigated. The samples of different polyacrylonitrile precursors were characterized by thermogravimetric analysis, nuclear magnetic response, Fourier transform infrared spectrometer, and differential scanning calorimetry. The electrochemical performance of the sulfur composite cathode material made from the polyacrylonitrile precursor was also tested. The analysis showed that the molecular weight distribution and the impurity of the polyacrylonitrile precursor affected the electrochemical performance of the sulfur composite cathode material made from the precursor. The polyacrylonitrile precursor with the narrower distribution of the molecular weight and the higher structural purity of the polyacrylonitrile precursor led the better electrochemical performance of the sulfur composite cathode material made from the precursor.

Synthesis of nanosized Si composite anode material for Li-ion batteries

Abstract: A simple method was proposed to prepare nanosized Si composite anode materials for lithium-ion (Li-ion) batteries. The preparation started with the shock-type ball milling of silicon in liquid media of polyacrylonitrile (PAN)/dimethylformamide (DMF) solution, forming slurry where the nano-Si particles were uniformly dispersed, followed by the drying of the slurry to remove DMF. The nanosized Si composite anode material was obtained after the pyrolysis of the mixture at 300 °C where the pyrolyzed PAN provided a conductive matrix to relieve the morphological change of Si during cycling. As-prepared composite presented good cyclability for lithium storage. The proposed process paves an effective way to prepare high performance Si, Sn, Sb and their alloys based composite anode materials for Li-ion batteries.

Ionic conduction and effect of cation doping in Tl4HgI6

Abstract: The ionic conduction properties of undoped and doped Tl4HgI6 were investigated using electrical conductivity, dielectrics, differential scanning calorimetry, and X-ray diffraction techniques. The heavy Tl+-ions diffusion was activated at high temperature, whereas low conductivity at the lower temperature suggested electronic contribution in undoped Tl4HgI6. The partial replacement of heavy Tl+ ion by suitable cations (Ag+ and Cu+) enhanced the conductivity by several orders of magnitude, whereas diminution in conductivity results with increasing dopants’ concentration in Tl4HgI6. These results can be interpreted in terms of a lattice contraction and vacancy–vacancy interaction (leading to the cluster formation), respectively. The dielectric values of undoped Tl4HgI6 system gradually increasing with temperature, followed by a sharp change, were observed around 385 K and can be explained on the basis of increasing number of space charge polarization and ions jump orientation effects. The activation energy of undoped and doped Tl4HgI6 systems were calculated, and it was found that ionic conductivity activation energy for 5 mol% of cation dopants is much lower than that of undoped one, and also 10 mol% doped Tl4HgI6 systems.

Synthesis and characterization of electron beam evaporated LiCoO2 thin films

Abstract: LiCoO2 thin films were prepared by electron beam evaporation technique using LiCoO2 target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10−4 mbar. The films prepared at substrate temperature Ts 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–eg absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains.