LiClO4 In Propylene Carbonate Research Articles

Effect of stabilizer on structural, optical and electrochemical properties of sol–gel derived spin coated TiO2 films

Thin films of TiO2 were prepared using two different sol–gel routes. The two routes employed diethanolamine (DEA) and acetylacetone as stabilizing agents with titanium isopropoxide (Ti(OPri)4) in ethanol as the deposition solution. The densification at 500 °C achieved the nanophase TiO2 films, which were investigated by performing structural, optical and electrochemical studies. Ion storage capacity and transmission measurements showed superior response of the films derived from DEA. Between the films obtained from the two routes, the appearance of the rutile phase at lower temperature for the film synthesized using DEA was predicted on the basis of the thermal analysis of the corresponding xerogel. The nanocrystalline nature of the films was evident from the X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The films deposited from both the stabilizers exhibited electrochromism in 1 M LiClO4-propylene carbonate electrolyte on cathodic polarization.

Casteel−Amis Equation: Its Extension from Univariate to Multivariate and Its Use as a Two-Parameter Function

The report describes the background of the empirical Casteel−Amis equation and its application to fitting experimental data of conductivity as a function of salt content in electrolytes. It further summarizes the attempts since its publication to extend the equation from a univariate to a multivariate function to include additional variables such as temperature and solvent composition, focusing on that to extend it to a bivariate function of salt content and solvent composition with examples from the solutions of LiPF6, LiBF4, LiBOB, Et4NPF6, and Et4NBF4 in propylene carbonate (PC) + diethyl carbonate and in PC + ethylene carbonate and LiClO4 in PC + acetonitrile. In addition, I discuss, along with experimental data and functional analysis, the validity of using this equation as a two-parameter function in relation to the range of salt content.

Influence of cointercalated HF on the electrochemical behavior of highly fluorinated graphite

Highly fluorinated graphite was prepared at room temperature using high oxidation state transition metal complex fluoride (K2PdF6, K2MnF6, K2NiF6 or KAgF4) and elemental fluorine under pressure ((5.9–11.8) ×105 Pa) in anhydrous liquid HF (aHF). The composition of the fluorinated graphite samples ranged from C1.1F to C1.9F containing small amounts of HF. IR absorption spectra revealed that stage 1 phase of CxF contained several different phases with planar (sp2) and puckered (sp3) graphene layers. Electrochemical discharge of the fluorinated graphite showed that profile of discharge potential and discharge capacity varied depending on the amount of cointercalated HF. The CxF samples with less amounts of HF and HF2δ− had relatively flat discharge potentials and large discharge capacities. The discharge capacity reached 500–600 mAh/g in 1 mol/dm3 LiClO4–propylene carbonate solution at 25 °C. Chemical diffusion coefficients of Li+ ion in the intermediate discharge products were (4.4–13) ×10−12 cm2/s from impedance measurement.

Lithium Intercalation into Titanium Dioxide Films from a Propylene Carbonate Solution

Intercalation of lithium from an LiClO4 propylene carbonate solution into thin-film TiO2 (rutile) electrodes produced by thermal oxidation of a titanium substrate are studied using cyclic voltammetry and impedance measurements at 0.01 to 105 Hz. An equivalent circuit adequately modeling the impedance spectra of TiO2- and Li x TiO2 electrodes throughout the frequency range studied is proposed. The electrochemical characteristics of film electrodes, the reversibility of intercalation-deintercalation process, the effect of surface passivation on the lithium transfer rate, and the dependence of electric, kinetic, and diffusion parameters on the electrode potential (composition) are discussed. The diffusion coefficient of lithium in Li x TiO2 is 10–12 cm2/s, as estimated by the impedance method.

Transient natural convection induced by electrodeposition of Li + ions onto a lithium metal vertical cathode in propylene carbonate

Transient natural convection caused by Li+ electrodeposition at constant current along a vertical Li metal cathode immersed in a 0.5 M LiClO4–PC (propylene carbonate) electrolyte was compared with that by Cu2+ ion electrodeposition in aqueous CuSO4 solution. The concentration profile of the Li+ ions was measured in situ by holographic interferometry. The interference fringes start to shift with time at a higher current density. The concentration boundary layer thickness for Li+ ions was successfully determined. With the progress of electrodeposition, the density difference between the electrolyte at the cathode surface and the bulk electrolyte increased to induce upward natural convection of the electrolyte. The electrolyte velocity was measured by monitoring the movement of tracer particles. The measured transient behavior of the ionic mass and momentum transfer rates normalized with respect to the steady-state value was numerically analyzed. Transient natural convection along a vertical cathode due to Li metal electrodeposition can be reasonably explained by boundary layer theory, similar to the case of Cu electrodeposition in aqueous CuSO4 solution.

A study on polyurethane/acrylate crosslinked gel polymer electrolytes

Abstract2,4‐Toluene diisocyanate, poly(propylene glycol), poly(ethylene glycol) (PEG) and 2‐hydroxyethyl methacrylate were used to synthesize PEG–UA (urethane acrylate) monomer. The crosslinked polymer and gel polymer electrolytes were prepared in dioxane by free radical polymerization. The swelling behaviour, thermal degradation properties, morphology and ionic conductivity of the gel polymer electrolytes were investigated. With decrease in the proportion of dioxane used, the synthesized polymer's network density increased, its affinity with a solution of 1 M LiClO4 in propylene carbonate (PC) decreased, and more microgel which diffused in the network. At the same time, the conductivity increased and reached 4 × 10−4 S cm−1 at 25 °C. Copyright © 2003 Society of Chemical Industry

Influence of electrolyte additives on safety and cycle life of rechargeable lithium cells

The influence of electrolyte additives on the safety and cycle life of 4V-class lithium cells is examined. The electrolyte solution employed was 1 M LiClO4-propylene carbonate, the most widely used electrolyte in lithium battery research. The additives studied were ten organic aromatic compounds including biphenyl, cyclohexylbenzene and hydrogenated diphenyleneoxide. For safety, focus was given to the overcharging tolerance of the lithium cells. Biphenyl is well-known as an overcharge protection additive. The purpose of this work was to find additives with a higher oxidation potential and longer charge–discharge cycle life than biphenyl. The oxidation potentials and currents of the additives were measured to determine whether or not these compounds work as overcharge protection additives. Charge–discharge cycling efficiencies were examined for lithium metal anodes. The results showed that cyclohexylbenzene and hydrogenated diphenyleneoxide have a higher oxidation potential and a higher lithium cycling efficiency than biphenyl.

MnO2-polypyrrole conducting polymer composite electrodes for electrochemical redox supercapacitors

Redox supercapacitors using electrochemically synthesised MnO2-polypyrrole composite electrodes have been fabricated with different electrolytes, namely polymer electrolyte film (polyvinyl alcohol, PVA-H3PO4 aqueous blend), aprotic liquid electrolyte (LiClO4-propylene carbonate, PC) and polymeric gel electrolyte [poly methyl methacrylate, (PMMA)-Ethylene carbonate (EC)-Propylene carbonate (PC)-NaClO4]. The capacitors have been characterised using galvanostatic charge-discharge methods. The cell with aqueous PVA-H3PO4 shows non-capacitive behaviour owing to some reversible chemical reaction of MnO2 with water while the MnO2-polypyrrole composite is found to be a suitable electrode material for redox supercapacitors with aprotic (non-aqueous) electrolytes. The solid state supercapacitor based on MnO2-polypyrrole composite electrodes with gel electrolyte gives stable values of capacitance of 10.0–18.0 mF cm−2 for different discharge current densities.

High-temperature combustion synthesis and electrochemical characterization of LiNiO2, LiCoO2 and LiMn2O4 for lithium-ion secondary batteries

Lithium nickelate (Li0.88Ni1.12O2), lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) were synthesized by fast self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. The electrochemical behaviour of these oxides was investigated with regard to potential use as cathode materials in lithium-ion secondary batteries. The cyclic voltammograms of these cathode materials recorded in 1 M LiClO4 in propylene carbonate at scan rates of 0.1 and 0.01 mV s–1 showed a single set of redox peaks. Charge-discharge capacities of these materials were calculated from the cyclic voltammograms at different scan rates. The highest discharge capacity was observed in the case of Li0.88Ni1.12O2. In all the cases, at a very slow scan rate (0.01 mV s–1) the capacity of the charging (oxidation) process was higher than the discharging (reduction) process. A strong influence of current density on the charge-discharge capacity was observed during galvanostatic cycling of Li0.88Ni1.12O2 and LiMn2O4 cathode materials. LiMn2O4 can be used as cathode material even at higher current densities (1.0 mA cm–2), whereas in the case of Li0.88Ni1.12O2 a useful capacity was found only at lower current density (0.2 mA cm–2). For the fast estimation of the cycling behaviour of LiMn2O4, a screening method was used employing a simple technique for immobilizing microparticles on an electrode surface.

A FTIR and Raman study of spontaneous reactions occurring at the LiNi yCo (1− y) O 2 electrode/non-aqueous electrolyte interface

Spontaneous reactions occurring at the surface of LiNi y Co (1− y) O 2-based electrodes during contact with non-aqueous organic electrolytes have been investigated by FTIR and Raman spectroscopy. It is found that several types of compounds and/or functional groups are formed on the electrode surface and that these compounds appear to be dependent on the type of electrolyte used. Thus, for a LiClO 4-propylene carbonate (PC) electrolyte, the main reaction is formation of Li-carbonate, whereas in the case of LiPF 6-ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte formation of P-, O- and F-containing compounds dominate. Spectroscopic data also show a variation of the LiNi (1− y) Co y O 2 crystalline structure during storage in an electrolyte which probably is due to a spontaneous deintercalation of the Li ions. An analysis of the newly formed species is presented and possible reaction mechanisms are discussed.

Effects of ion beam bombardment on electrochromic tungsten oxide films studied by X-ray photoelectron spectroscopy and Rutherford back-scattering

The effect of ion bombardment on thermally evaporated and magnetron sputtered tungsten oxide films were investigated using X-ray photoelectron spectroscopy (XPS). Results show that irrespective of the porosity and crystallinity of the film samples formed with different techniques and conditions, ion bombardment induced preferential sputtering of oxygen, resulting in a decrease of oxygen/tungsten (O/W) ratio with increasing sputtering time. Samples experienced electrochromic switching cycles also show the same effect, except that a higher O/W ratio is detected because the tungsten oxide film reacts with the LiClO 4-propylene carbonate electrolyte. Angle-resolved XPS experiments further confirm preferential sputtering of oxygen, suggesting that ion beam sputtering used in XPS for pre-cleaning and depth profile analysis of tungsten oxide must be used with caution. Rutherford back-scattering gives more reliable composition data of tungsten oxide, since it does not involve any sputtering process.

Lithium Transport Through Sputter Deposited Lithium Cobalt Dioxide Thin Film Electrode

Lithium transport through lithium cobalt dioxide thin film electrode prepared by rf-magnetron sputtering was investigated in IM solution of LiClO4 in propylene carbonate using cyclic voltammetry, galvanostatic intermittent titration technique (GITT) and potentiostatic current transient technique. The cathodic and anodic current transients exhibited the non-Fickian behaviour of lithium transport when the applied potential steps encountered potential plateaus near 3.91 V Li/Li+' determined from GITT. It is suggested that the occurrence of this abnormal behaviour during lithium intercalation and deintercalation is accompanied by a ‘diffusion-controlled’ α/β phase transformation and ‘cell-impedance-controlled’ phase transformation, respectively. Lithium transport through the electrode comprising two phases of α and β has been theoretically considered by a numerical analysis of the phase transformation.

Preparation of conductive polyaniline/chlorosulfonated polyethylene composites viain situ emulsion polymerization and study of their properties

The conductive composites of polyaniline (PAn) and chlorosulfonated polyethylene (CSPE) were prepared by polymerization of aniline in the presence of CSPE, using a direct, one-step in situ emulsion polymerization method. The polymerization of aniline was performed in an emulsion comprising water and xylene containing CSPE in the presence of dodecylbenzene sulfonic acid, which acts both as a surfactant and a dopant for PAn. The composites can be processed by either melt method (MP) or solution method (SP). Conductivity of the composites obtained by different processing methods shows different percolation thresholds: 14 wt % for MP samples and 22 wt % for SP samples. At the same content of PAn, the conductivity of MP composites is higher than that of SP composites. The relationships between mechanical properties and PAn content obtained by the two different processing methods were also investigated. When PAn content of MP samples is between 12 and 18 wt %, the composites behave like a thermoplastic elastomer with tensile strength at 6–8 MPa, ultimate elongation > 400% and permanent set < 30%. The conductivity of composites obtained by SP method after secondary doping with m-cresol is about 6 orders of magnitude higher than the original at below 18 wt % PAn content and the percolation threshold for conductivity is lowered to 3 wt % PAn content. The composite shows no electrochromic activity in acidic solution of LiClO4 in propylene carbonate, but after secondary doping exhibits electrochromic activity even in neutral electrolyte. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 845–850, 2000

高温酸化膜の蒸発現象を利用したエレクトロクロミック薄膜の作成

A simple evaporation technique have been proposed for the fabrication of all-solid-state electrochromic devices, and applied to high-temperature-oxidation of transition metals such as tungsten, manganese and tantalum. A wire coil of such a transition metal was heated by direct current flow in a vacuum chamber under less than 5.3 Pa, and metal oxide films were deposited on ITO glass substrates. The tungsten oxide films were found to be amorphous with slightly blue surfaces. The manganese oxide films showed less transparent, but the tantalum oxide films were transparent. Columnar morphology was observed for all these films. Electrochromic behavior of the as-deposited oxide films was examined with an applied voltage of 2V in 1M LiClO4 propylene carbonate electrolyte. It was confirmed that the tungsten oxide films show a cathodic type, and the manganese oxide films show an anodic type of electrochromic behavior. Technical points to be improved are summarized in terms of experimental results.

Synthesis of ternary Li-Mn-O phase at a temperature of 260 °C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li x MnO2 (x = 0.30.6), has been synthesized by heating a mixture (Li/Mn ratio = 0.30.8) of electrolytic manganese dioxide (EMD) and LiNO3 in air at moderate temperature, 260 ∘C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO4-propylene carbonate electrolyte solution. About 0.3 Li in Li x MnO2 (x = 0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5 V and 2.8 V vs Li/Li+. The Li x MnO2 synthesized by heating at Li/Mn ratio = 0.5 demonstrated higher discharge capacity, about 250 mAh (g of oxide)−1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.

Electrochemical Lithium Intercalation into Nb2O5Cathode for 2 V Class-Secondary Lithium Batteries

ABSTRACTNb2O5powder was prepared by heating niobium hydroxide in the temperature range from 600 to 1000°C. The crystal system of Nb2O5compounds depended on the heating temperatures,i.e., hexagonal, orthorhombic and monoclinic Nb2O5compounds were obtained at 600, 800 and 1000°C, respectively. Electrochemical lithium intercalation into the three Nb2O compounds was investigated in a cell with an LiClO4-propylene carbonate electrolytic solution for the application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of 2 V class-lithium battery, which will play important role in power supply for IC memory backup developed recently. The thermodynamics and kinetics of the lithium intercalation into the Nb2O5cathode have been investigated. The thermodynamic parameters, such as standard free energies, lithium partial molar entropy, interaction energies between ions, the crystal lattice parameters, and the kinetic parameters, such as chemical and self diffusion constants, have been obtained as a function ofx-value in LiNb2O5.

Intrinsic Asymmetry, Hysteresis, and Conformational Relaxation during Redox Switching in Polypyrrole: A Coulovoltametric Study

Theoretical coulovoltammograms associated with the evolution of anodic charges when a polypyrrole film, which was previously compacted at a strong negative potential in a 0.1 M LiClO4 propylene carbonate solution, was submitted to anodic potential sweeps were compared with experimental responses. The electrochemically stimulated conformational relaxation (ESCR) model provides a good description of either the influence of the negative potential limit, the sweep rate, the temperature, or the electrolyte concentration on the rate of electrochemical oxidation, this being initiated through conformational relaxation processes and completed under counterions diffusion control. An analysis of both anodic and cathodic experimental branches, together with theoretical conformational relaxation curves, allows to detect four different structural rearrangement processes affecting electrochemical responses: the well-known conformational relaxation effect observed only in anodic branches, a hysteresis effect on cathodic...

A Study of The Li|LixV2O4 Cell

ABSTRACTThe studies of the Li | 1M LiClO4 in propylene carbonate | LixV2O4 cell were carried out. The results of the electrochemical and X-ray investigations indicated that the cathode reaction in this cell proceeds as an intercalation process. Cycling test shows the reversibility of this cell along 35 charge/discharge cycles. However X-ray diffraction of the electrode material shows partial oxidizing of the LixV2O4 phase yielding γ-LiV2O5. The kinetic parameters of this process such as the chemical diffusion coefficient and mobility of lithium in the LixV2O4 were calculated.

TiO 2 electrochromic thin films by reactive direct current magnetron sputtering

TiO 2 electrochromic thin films have been prepared by reactive dc magnetron sputtering under various conditions and their electrochromic properties have been investigated by using 1 M LiClO4 in propylene carbonate as an electrolyte. Total pressure was found to be the most important parameter to control the electrochromic properties of sputtered TiO2 films. The sample deposited under high pressure conditions (8–10 Pa) showed good electrochromic properties; its visible transmittance changed from 14% (colored state) to 81% (bleached state) and the coloration efficiency was 29 cm2/C.

Preparation of polyaniline-poly (p-styrenesulfonic acid) composite by post-polymerization and application as positive active material for a rechargeable lithium battery

Polyaniline (PANI)-poly (p-styrenesulfonic acid) (PSS) composite was prepared by thermal post-polymerization of PANI-p-styrenesulfonic acid (SSA) composite. A PANI–SSA composite was prepared by mixing PANI/N-methyl-2-pyrrolidinone solution with SSA aqueous solution. The PANI–SSA composite film was prepared by casting the composite onto an ITO glass plate. The cast film was converted to PANI-PSS film by heating at 100°C for 3h (post-polymerization process). The PANI–PSS modified ITO electrode showed electrochemical responses based on the redox reaction of PANI–PSS composite in the organic electrolyte solution, for example, propylene carbonate containing 1moldm−3 LiClO4. The PANI–PSS composite was a cation -doping polymer composite. The composite was also modified on a porous carbon material (Reticulated Vitreous CarbonTM, RVC, Energy Research and Generation, Inc.). The PANI–PSS modified RVC electrode showed similar electrochemical behaviour as the PANI–PSS modified ITO electrode. Model secondary lithium cells, Li|1moldm−3 LiClO4-propylene carbonate|PANI–PSS modified RVC electrode, were constructed and charge–discharge cycling tests were carried out. The cell showed about 60% coulombic efficiency under high current density cycling conditions (3.8Ag−1, per gram of PANI–PSS modified RVC electrode).