Modelling the voltammetric study of intercalation in a host structure: application to lithium intercalation in RuO2

Intercalation process kinetics have been studied theoretically for the case of potential sweep voltammetry. The influence of the thickness (or the particle radius) of the “host” material and the potential sweep rate has been determined between the limits of thin film diffusion and semi-infinite diffusion for a reversible process. Experimental data have been obtained with the cell: RuO₂/LiClO₄-PEO/Li. The theoretical results have been used to calculate the diffusion coefficient of lithium in the “host” structure RuO₂ at 80°C, giving an approximate value of 1.6 × 10^?11 cm² s^?1     

Lithium insertion into layered quaternary chalcogenides: CdIn2S2Se2

CdIn₂S₂Se₂, a new quaternary chalcogenide having a typical layered structure, has been characterized and its electrochemical behaviour in a room temperature lithium cell investigated. Thermogravimetric analyses and differential scanning calorimetry measurements, discharge experiments and micropolarization tests as well as X-ray investigations have been carried out and the results discussed. A quasi-plateau and an extended plateau are observed during the discharge of the (−) Li/1M LiClO₄PC/CdIn₂S₂Se₂ (+) cell to a 1.0 V cut-off, and up to 6 lithium equivalents per mole are inserted at 0.3 mA cm⁻². Lithium inserted in the region of the first plateau (around 1.35 V versus Li/L⁺) is not readily available and possibly produces a structural rearrangement of the cathode material, whereas fast kinetics and good reversibility occur in correspondence of the second plateau at about 1.20 V versus Li/Li⁺. A new amorphous phase has been observed after a deep discharge.     

Determination of the interaction using FTIR within the components of GPE based on the synthesized grafted polymer

An oxyethylene chain (–CH₂–CH₂–O–) grafted polymer (P(MMA–MAh)–PEGME) was synthesized by reacting poly(ethylene glycol) monomethyl ether (PEGME) with the copolymer of poly(methyl metacrylate–maleic anhydride) (P(MMA–MAh)) and endcapping the residual carboxylic acid with methanol. Rectorite modified with dodecyl benzyl dimethyl ammonium chloride (OREC) was used as a filler additive to modify gel polymer electrolytes (GPE) that consisted of P(MMA–MAh)–PEGME used as polymer matrix, propylene carbonate (PC) as plasticizer and LiClO₄ as lithium ion producer. Characterization of interaction of the polar group of C=O or C–O–C in PC and grafted polymer with Li⁺ and OH group on OREC surface has been thoroughly examined using Fourier transform infrared (FTIR), respectively. The quantitative analysis of FTIR shows that the absorptivity coefficients (a) of polymer/LiClO₄, PC/LiClO₄, PC/OREC and polymer/OREC are 0.705, 0.113, 0.430 and 0.500, respectively, which means that the Li⁺ or OH bonded polar group of C=O and C–O–C is more sensitive than free C=O and C–O–C in FTIR spectra. The limited values of bonded C=O and C–O–C equivalent fraction of polymer/LiClO₄, PC/LiClO₄, PC/OREC and polymer/OREC are 33%, 94%, 60% and 22%, respectively, which implies that the interaction within the components is reversible and the intensity of interaction is ordered as PC/LiClO₄, PC/OREC, polymer/OREC and polymer/LiClO₄.     

Lattice and ion dynamics in gel electrolytes based on poly(acrylonitrile) by6Li-7Li NMR

Two composite gel electrolytes prepared from mixtures of poly(acrylonitrile) (PAN), propylene carbonate (PC), ethylene carbonate (EC) and LiClO₄ have been studied with differential scanning calorimetry (DSC) and⁷Li-⁶Li NMR. The data allow estimation of ionic conductivities, local (short range) diffusivities, and lattice dynamics. Furthermore, they point to an unexpected behavior of the Li-rich sample that hints to a complex LiClO₄-PAN phase diagram. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, September 11–18,1994     

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO₄. Ionic conductivities higher than 10^?5 ω^?1 cm^?1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO₄ 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO₂ battery with a linear high molecular weight P(EO)₈-LiClO₄ as electrolyte.     

Electrical properties of LiBSe ternary system

Amorphous products were obtained in the LiBSe ternary system by quenching melts of Li₂Se, B and Se mixture prepared at 100°C in sealed silica tubes. The vitreous region was slightly lower selenium composition than that of the Li₂SeB₂Se₃ tie-line. The amorphous products were lithium ionic conductors and most of them showed contributions to their total conductivity. The amorphous product of composition Li₂₅B₃₆Se₃₉ has the least electronic contribution to its total conductivity of 6.0 × 10⁻⁶ S/cm at room temperature. A new crystalline compound and crystalline LiBH₄ were also obtained in LiBSe ternary. Both of them were lithium ionic conductors having conductivities of about 1 × 10⁻⁶ S/cm at room temperature.     

Etudes electrique et Raman des verres des systemes B2O3M2OM3PO4 (M=Li,Na)

New glasses with alkali carriers have been prepared in the system B₂O₃M₂OM₃PO₄ (M = Li, Na). The variation of the ionic conductivity has been discussed. Raman spectroscopy allows to characterize the behavior of the orthophosphate M₃PO₄ with respect to the boron-oxygen glass matrix.     

Studies of lithium intercalation in heat-treated products obtained from molybdic acid

Several characteristics of the lithium intercalation in molybdenum trioxide hydrate, MoO₃.2/3H₂O, have been studied. The non-stoichiometric molybdenum trioxide, MoO_2.8, was obtained by dehydration and annealing treatment of molydic acid MoO₃.1H₂O. These cathode materials were tested in a lithium battery of the type Li/LiClO₄-PC/MoO_m and the electrochemical performance has been evaluated during the discharge/charge of the galvanic lithium cells.     

New secondary batteries for room temperature applications using a vitreous electrolyte

In order to obtain room temperature high energy secondary batteries, a B₂S₃Li₂SLiI vitreous electrolyte has been used. Lithium or a lithium-aluminium alloy have been tested as negative electrode in symmetrical cells and then utilized in four different types of experimental Li (or LiAl) /glass/TiS₂ batteries. The best results have been obtained with a composite TiS₂-liquid electrolyte positive electrode.     

A neutron powder diffraction study of the lithium insertion compound LiMoO2 from 4–440K

The structure of the lithium inserted rutile-based compound LiMoO₂ has been determined from neutron powder diffraction data by use of the Rietveld profile technique. The inserted Li is incorporated into the MoO₂ lattice in octahedral sites with an average Li0 distance of 2.12 Å. The Mo atoms also occupy octahedral sites with an average MoO distance of 2.12 ǎ, and form Mo-Mo pairs with a separation of 2.46 Å. LiMoO₂ can best be regarded as having a distorted NiAs-type structure rather than one of rutile-type. No changes in structure were observed in the temperature range 4–400K.     

Redox mechanism and cycling behaviour of nonylbenzo-hexaquinone electrodes in Li cells

Nonylbenzo-hexaquinone (NBHQ), a quinonoid polymer of low molecular weight, has been reinvestigated as a cathode material for Li cells. Its reduction mechanism gives rise at first, in a 3-electron process, to an irreversible species involving the formation of radical anions. Successively, a direct two-electron reduction of other quinone groups occurs. This second step, which involves 4 e in quasi-thermodynamic conditions, is reversible and allows cells of the type Li/LiClO₄-PC,DME/NBHQ,C to be cycled for more than 500 cycles at the C/2 rate between 3.5 and 2.0 V. The average energy density during this cycling was 160 Wh/kg, based on the weight of the cathode material (additives included).     

导电聚合物聚醚聚氨酯的结构与导电性能的正电子湮没研究

用正电子湮设方法研究了高分子固体电解质聚醚聚氨酯（ＰＥＵ）在与ＬｉＣlＯ₄络合前后的结构变化及导电性能．实验结果表明，当ＰＥＵ与ＬｉＣlＯ₄络合后，正电子素（o－Ｐｓ）的寿命及其强度均减少，而中间寿命分量的湮没参数基本不变．这表明Ｌｉ杂质主要扩散在无序的非晶区．掺杂前后样品的温度实验表明，在玻璃化转变温度Ｔ_g之下，络合前后的自由体积分数的变化很小，这与自由体积理论预言的结果一致．在Ｔ_g之上，络合后的自由体积空洞的浓度和自由体积分数均减小．此外，ＰＥＵ－ＬｉＣlＯ₄络合物的电导率随温度和Ｌｉ杂质浓度的变化可以用自由体积理论解释． 关键词：     

Ordering behaviors of the F.C.C. and B.C.C. phase alloys in the InMg,LiMg and AlZn systems

Expressions of the band-structure energy and the electrostatic energy characterized by the usual long-range and short-range order parameters are given to a binary alloy of simple metals with the f.c.c.-type or b.c.c.-type structure.The ordering energy and the local ordering energy are calculated for the InMg, LiMg and AlZn systems. The numerical results explain successfully the facts that the InMg system has the Ll₀-type and Ll₂-type ordered phases, each of which exists over a wide range of concentration and that the LiMg system has a local order with a negative short-range order parameter, while the AlZn system has that with the positive one. A lattice distortion in the Ll₀-type ordered structure of InMg is also discussed.     

Chemical synthesis of nano-porous ruthenium oxide (RuO2) thin films for supercapacitor application

Ruthenium oxide (RuO₂) thin films have been prepared using single step chemical method containing Ru(III) Cl₃ solution in an aqueous medium at low temperature. The structural, morphological and optical properties have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorption technique. The XRD study revealed the formation of amorphous RuO₂ thin film. The surface examination by SEM showed formation of nano-porous material on the substrate. The TEM study revealed the formation of nanostructured material. The optical absorption studies showed the presence of direct band transition with band gap equal to 2.2 eV. The RuO₂ has proved its applicability in supercapacitor showing 50 F/g specific capacitance in 0.5 M H₂SO₄ at 20 mV/s scan rate.     

Low-temperature zirconia oxygen gauges based on RuO2 electrode

A low temperature oxygen gauge based on zirconia electrolyte has been developed. It makes use of RuO₂ as electrode material in place of platinum in conventional gauges. The low interfacial impedance of the RuO₂ electrode makes it possible to keep the cell resistance below 10⁶ ω even at low temperatures. Nernst's law tests indicate that this cell can give theoretical outputs down to 498 K campared to 923 K for gauges with platinum electrodes. Faraday's law tests confirm its good performance over a wide range of oxygen concentrations. High electronic conductivity, single oxide phase, slight non-stoichiometry and good adherence are responsible for the good performance of RuO₂ as electrode. An activation energy of 90.95 kJ/mole observed for the interface shows that the vacancy movement in the electrolyte is the rate controlling step. The evaporation of RuO₂ as RuO₄ gives rise to flow dependent output. This can be overcame by operating the cells at low temperatures though at the cost of speedy response. The low operating tempratures lead to a compact gauge with good stability.     

Lithium conducting solid polymer electrolytes based on polyacrylonitrile copolymers: Ion solvation and transport properties

The systems poly(butadiene-co-acrylonitrile) (PBAN) - lithium salts have been studied by means of X-ray and IR spectroscopy, optical microscopy and ac- and dc-conductivity measurements. X-ray and microscopy studies have confirmed that PBAN dissolves LiClO₄ up to [CN]/[Li] ≈ 2: 1. IR spectra of the samples with LiAsF₆, LiCF₃SO₃ and LiClO₄ have indicated the coordination between Li⁺ and the polar CN groups of PBAN. So, PBAN was found to be a suitable polymer matrix for SPE. The polymer films exhibited predominant ionic conductivity. Measurements of conductivity and Li transport numbers versus temperature over a wide range of salt concentrations revealed the existence of two concentration regions (within the limits of salt solubility) corresponding to liquid-like and glass-like ion transport mechanisms. New solid polymer electrolyte with lithium single-ion conductivity of 10⁻³ S cm⁻¹ at 25 – 95 °C was obtained. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Lithium intercalation in sputtered MoO3 films

Molybdenum trioxide films have been prepared by RF-sputtering using an oxygen-argon mixture containing sputter gas and a molybdenum target. Samples were deposited at different oxygen flow rates in the range from 1.5 to 8 cm³/min onto ITO-covered thick glass plate or nickel foil substrates. Lithium intercalation of RF-sputtered films has been tested in Li/1M LiClO₄-PC-PMMA/MoO₃ galvanic cells. We report the electrochemical properties of various lithium-intercalated MoO₃ films. Influence of both the growth conditions and the nature of the film substrate have been investigated on the discharge behavior of cells and on the kinetics of intercalation. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.     

Hexagonal nanorods of tungsten trioxide: Synthesis, structure, electrochemical properties and activity as supporting material in electrocatalysis

Tungsten trioxide, unhydrated with hexagonal structure (h-WO₃), has been prepared by hydrothermal method at a temperature of 180 °C in acidified sodium tungstate solution. Thus prepared h-WO₃ has been characterized by X-ray diffraction (XRD) method and using electrochemical techniques. The morphology has been examined by scanning and transmission electron microscopies (SEM and TEM) and it is consistent with existence of nanorods of 50-70 nm diameter and up to 5 μm length. Cyclic voltammetric characterization of thin films of h-WO₃ nanorods has revealed reversible redox behaviour with charge-discharge cycling corresponding to the reversible lithium intercalation/deintercalation into the crystal lattice of the h-WO₃ nanorods. In propylene carbonate containing LiClO₄, two successive redox processes of hexagonal WO₃ nanorods are observed at the scan rate of 50 mV/s. Such behaviour shall be attributed to the presence of at least two W atoms of different surroundings in the lattice structure of h-WO₃ nanorods. On the other hand, in aqueous LiClO₄ solution, only one redox process is observed at the scan rate of 10 mV/s. The above observations can be explained in terms of differences in the diffusion of ions inside two types of channel cavities existing in the structure of the h-WO₃ nanorods. Moreover, the material can be applied as active support for the catalytic bi-metallic Pt-Ru nanoparticles during electrooxidation of ethanol in acid medium (0.5 mol dm⁻³ H₂SO₄).     

Ultrahigh Electron Emissive Carbon Nanotubes with Nano-sized RuO2 Particles Deposition

Multi-wall carbon nanotubes (MWNTs) have a great commercial potential as electron field emitters, but suffer from fundamental problems such as stability and brightness. By depositing the MWNTs with nano-sized ruthenium dioxide (RuO₂) particles, a new high performance emitter has been developed. When compared to MWNTs, the MWNTs impregnated with 1–2 nm sized RuO₂ have superior and more efficient electrical characteristics. MWNTs supported by a silicon substrate showed a reduction in the onset voltage from 5.4 to 4 V/μm after RuO₂ impregnation. The long-term stability of the impregnated MWNTs is also demonstrated with only a 20% increase in applied voltage required after 700 h operation at 40 mA/cm².     

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

The measurement of diffusion parameters like activation energies and translational jump rates of small cations plays a key role in materials science. Especially the in-depth investigation of Li diffusion in ionic conductors is of great interest, because suitable ionic conductors are needed for, e.g., the development of new secondary ion battery systems. As the standard tracer method is not applicable to study Li diffusion due to the lack of a suitable radioactive isotope, Li diffusion is alternatively probed by solid state NMR techniques. With the different NMR methods being available, diffusion processes can be studied on different length- and timescales. In the present paper we use two-time spin-alignment echo (SAE) NMR for the direct, i.e., model independent, measurement of extremely small translational Li jump rates. To this end, different crystalline and glassy ion conductors like Li_xTiS₂, Li₄SiO₄ as well as LiNbO₃ served as model substances to reveal the special features of this technique. SAE-NMR, which was originally developed for deuterons, has also been applied in a few cases to spin-3/2 nuclei, like ⁷Li, before. The corresponding correlation functions yield not only information about diffusion parameters but also about geometric properties of the diffusion pathways, making SAE-NMR a powerful method which complements well-established NMR techniques.