bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Li Insertion in Lamellar (Birnessite) and Tunnel Manganese Oxides (Todorokite)
Authors: Duncan M. J. , Leroux F. , Nazar L. F. 
Published: April 2011

ABSTRACTA comparison of Li insertion in manganese oxide phases with a tunnel (todorokite) framework, its two-dimensional layered precursor (birnessite/buserite), and Li-exchanged materials are presented. The results outline the effect of the MnO6 octahedral arrangement and framework composition on the electrochemical response. The interlayer cations in the lamellar materials are exchangeable for Li, giving rise to a lithiated birnessite that displays a sustainable capacity of 125 mAh/g. For todorokite, molten salt exchange using LiNO3 results in displacement of water from the tunnels, and incorporation of additional Li into the structure. Some of this Li is extractable during charge, resulting in a reversible capacity of 172 mAh/g in the voltage window 4.2–2.0V.
X-ray Absorption and NMR Studies of LiNiCoO2 Cathodes Prepared by a Participate Sol-Gel Process
Authors: Rostov S. , Wang Y. , denBoer M. L. , Greenbaum S. , Change C. C. , Kumta Prashant N. 
Published: April 2011

AbstractWe have synthesized lithiated nickel oxide-based cathode materials containing stoichiometric and excess lithium using a new low temperature colloidal paniculate sol-gel process. The process yields a xerogel precursor that transforms to the crystalline oxide at 800 °C in 2h. We studied the Li environment with nuclear magnetic resonance (NMR) and that of the transition metal ions with x-ray absorption spectroscopy. We measured samples of LiNi1−xCoxO2, with x = 0 and 0.25. The effect on each composition of the incorporation of 5 mol % Li was also examined. The precursor material appears to have no Ni3+, as indicated x-ray absorption measurements, and is highly disordered, showing little sign of interatomic correlations beyond the nearest neighbor in extended x-ray absorption fine structure (EXAFS) spectra. The 7Li NMR line widths and spin-lattice relaxation (T1) behavior are dominated by strong interactions with the paramagnetic Ni3+. The presence of 5 % excess Li causes almost no change in NMR line width or T1 in the mixed (Ni/Co) cathode, but does produce an almost 30% reduction in line width for the pure LiNiO2, implying that Co stabilizes the structure. The near-edge x-ray absorption measurements show the local Ni environment is relatively unaffected by Co substitution, a result confirmed by EXAFS analysis. The heat-treated samples are highly ordered, and both the near-edge and extended analysis imply Co substitutes primarily for Ni2+, not Ni3+. The Jahn-Teller distortion is apparent in both the stoichiometric and Li-excess materials.
On the Electroanalytical Characterization of LixCoO2, LixNiO2 and LiMn2O4 (Spinel) Electrodes in Repeated Lithium Intercalation-Deintercalation Processes
Authors: Aurbach D. , Levi M. D. , Levi E. , Markovsky B. , Salitra G. , Teller H. , Heider U. , Heider L. 
Published: April 2011

ABSTRACTThis paper reports on electroanalytical studies of the intercalation-deintercalation of lithium into lithiated transition metal oxides which are used as cathodes for Li ion batteries. These include LixCoO2 LixNiO2 and LixMn2O4 spinel. The basic electroanalytical response of these systems in LiAsF6 1M/EC-DMC solutions was obtained from the simultaneous use of slow and fast scan cyclic voltammetry (SSCV), potentiostatic intermittent titration (PITT) (from which D vs. E was calculated), and impedance spectroscopy (EIS). Surface sensitive FTIR spectroscopy and XRD were also used for surface and 3D characterization, respectively. A large and important denominator was found in the electrochemical behavior of lithium intercalation-deintercalation into these transition metal oxides and graphite. The use of the electroanalytical response of these systems as a tool for the study of stabilization and failure mechanisms of these materials as cathodes in rechargeable Li batteries is demonstrated and discussed.
Influence of Water and Other Contaminants in Electrolyte Solutions on Lithium Electrodeposition
Authors: Fujieda T. , Koike S. , Higuchi S. 
Published: April 2011

ABSTRACTElectrochemistry of a nickel electrode in propylene carbonate [PC] containing LiClO4, LiCF3SO3, LiPF6 was studied through a micro electrode (φ =25 μ m) techniques in the wide potential range between +4.5 and -0.2 V vs. Li/Li+. Common pronounced peaks were observed in the potential range positive to lithium electrodeposition on nickel in all electrolyte solutions examined. Thus, these peaks can be attributed to reactions related to Li+ or commonly contained contaminants such as water and acids. In particular, the peak which appeared at the most negative potential seemed to be underpotential deposition (UPD) of lithium.To prove this hypothesis a nickel electrode in highly dried PC (water content : 3 – 8 ppm) intentionally contaminated with a small amount of water and CF3COOH was examined via cyclic voltammetry. Changing the content of water and acid (and its ratio) in PC resulted in a variety of voltammograms and one of them was identical to the one observed in PC containing lithium electrolytes. These facts preclude the existence of UPD of lithium on nickel in the electrolyte solutions. Instead, the existence of NiOH on nickel and its redox reaction mechanism have been postulated. The mechanism is consistent with the experimental facts : a nickel electrode passivates in PC with a small amount of water, and a small amount of acid, CF3COOH, can prevent passivation. The vicinity of the electrode surface may be exposed to an alkaline atmosphere owing to the reduction product of water. This seems to be the cause of troubles we run into with the electrodes at cathodic potentials
Passive-Film Formation on Metal Substrates in IM LiPF6/EC-DMC Solutions
Authors: Guidotti Ronald A. , Nelson Gerald C. 
Published: April 2011

ABSTRACTThe initial irreversible capacity loss in lithium-ion cells has been attributed to passive-film formation on the carbon and graphite anodes during the first intercalation. We have examined the nature of these passive films on select metal substrates. We studied film formation on Cu, 304 stainless steel, and Mo cycled in a 1M LiPF6/ethylene carbonate (EC)-dimethyl carbonate (DMC) solution (1:1 v/v) over a potential range of 3 V to below 0 V. Film formation occurs readily on each of the metals and involves both solvent and salt species. The composition, thickness, and distribution of the films depends strongly on the substrate. The redox processes that occur during film formation and the potential for Li plating are highly dependent on the substrate composition.
Pyrrole Copolymers with Enhanced Ion Diffusion Rates for Lithium Batteries
Authors: Calvert Paul , Gardlund Zack , Huntoon Trey , Hall H. K. , Padias Anne 
Published: April 2011

ABSTRACTCopolymers of pyrrole with a polyether-substituted pyrrole were tested as cathodes for lithium batteries. The charge and discharge characteristics showed that anion transport was much faster in the copolymer than in polypyrrole. As a result these electrodes store and release much more charge at higher current densities but are similar to polypyrrole at low currents. Pulse and relaxation measurements of the ion diffusion showed that this difference was due to a ten-fold increase in the anion diffusion coefficient.
New 7Li-NMR Evidence for Lithium Insertion in Disordered Carbon
Authors: Wang S. , Matsui H. , Matsumura Y. , Yamabe T. 
Published: April 2011

ABSTRACTIn fully-charged carbon materials, we tried to determine the nature of the interaction between Li species and carbon using variable temperature measurements of the Li Knight shift Only one interaction between the Li species and graphite carbon was observed from room temperature to -10°C. However, while only one average interaction between the Li species and the disordered carbon was observed at room temperature, three kinds of interactions were observed at low temperature. These results provide direct evidence for the model which explains why the discharge capacity of the carbon electrode with a disordered structure as an anode can exceed the theoretical capacity of a graphite anode in lithium ion rechargeable batteries.
Commercial Cokes and Graphites as Anode Materials for Lithium - Ion Cells
Authors: Derwin David J. , Kinoshita Kim , Tran Tri D. , Zaleski Peter 
Published: April 2011

AbstractSeveral types of carbonaceous materials from Superior Graphite Co. were investigated for lithium ion intercalation. These commercially available cokes, graphitized cokes and graphites have a wide range of physical and chemical properties. The coke materials were investigated in propylene carbonate based electrolytes and the graphitic materials were studied in ethylene carbonate / dimethyl solutions to prevent exfoliation. The reversible capacities of disordered cokes are below 230 mAh / g and those for many highly ordered synthetic (artificial) and natural graphites approached 372 mAh / g (LiC6). The irreversible capacity losses vary between 15 to as much as 200 % of reversible capacities for various types of carbon. Heat treated cokes with the average particle size of 10 microns showed marked improvements in reversible capacity for lithium intercalation. The electrochemical characteristics are correlated with data obtained from scanning electron microscopy (SEM), high resolution transmission electron microscopy (TAM), X - ray diffraction (XRD) and BET surface area analysis. The electrochemical performance, availability, cost and manufacturability of these commercial carbons will be discussed.
Electrochemical Properties of Nitrogen-Substituted Carbon and Organofluorine Compounds
Authors: Nakajima T. , Koh M. , Dan K. 
Published: April 2011

ABSTRACTThe CxN samples(C14N-C62N) prepared with a nickel catalyst had the higher crystallinity and less pyridine-type nitrogens existing at the edge of graphene layers than CxN prepared in the absence of a catalyst. With increase in the deposition temperature of CxN, the cy-cleability for electrochemical intercalation-deintercalation of lithium ions was improved and the profile of the charge-discharge curve approached that of graphite due to increase in the crystallinity and decrease in the incorporated nitrogens. CxN-coated graphites demonstrated gradual increase in the potential at the last stage of lithium ion deintercalation process.The effect of fluoroester-mixing in 1 M LiClO4-EC/DEC was also investigated at a low temperature. It was found that CHF2COOCH3 with a low molecular weight and a small number of fluorine atoms was effective as a mixing agent.
Effects of Processing Conditions on the Physical and Electrochemical Properties of Carbon Aerogel Composites
Authors: Tran T. D. , Lenz D. , Kinoshita K. , Droege M. 
Published: April 2011

ABSTRACTThe carbon aerogel/carbon paper composites have physical properties similar to those of monolithic carbon aerogels but do not require supercritical extraction during fabrication. The resorcinol-formaldehyde based carbon aerogel phase is intertwined between the fibers of a commercial carbon paper. The resulting composites have variable densities (0.4–0.6 g/cc), high surface areas (300–600 m2/g), and controllable pore sizes and pore distribution. The effects of the resorcinol-formaldehyde concentrations (50–70% w/v) and the pyrolysis temperature (600–1050°C) were studied in an attempt to tailor the aerogel microstructure and properties. The composite physical properties and structure were analyzed by transmission electron microscopy and multipoint-BET analyses and related to electrochemical capacitive data in 5M KOH. These thin carbon aerogel/carbon paper composite electrodes are used in experiments with electrochemical double-layer capacitors and capacitive deionization.
Reactions of Lithium with Small Graphene Fragments: Semi-Empirical Quantum Chemical Calculations
Authors: Radosavljević Marko , Papanek Peter , Fischer John E. 
Published: April 2011

AbstractSemi-empirical and ab initio calculations [1], as well as inelastic neutron spec-troscopy [2], demonstrate that Li can bind to protonated “edge carbons” to create a moiety analogous to the organolithium monomer C2H2Li2. This provides a possible additional channel for Li uptake in high capacity Li-ion battery anodes based on low-T pyrolyzed soft carbons. Here we show that similar reactivity is exhibited by polyaro-matic hydrocarbons with the protons removed (taken as surrogates for the structural units in hard carbons). In the deprotonated PAH'es the Li serves to saturate dangling bonds, maintaining sp2 hybridization, whereas Li added to PAH'es creates sp3 carbons at the edges. In both cases this extra reactivity occurs in parallel with the usual intercalation. These findings have implications for further development in Li-ion rechargeable battery technology.
Electrical Properties of Novel Anodic Films Formed in Nonaqueous Electrolyte Solutions
Authors: Mizutani F. , Takeuchi S. , Nishiwaki T. , Sato N. , Ue M. 
Published: April 2011

ABSTRACTAn aluminum alloy (Al - 1.0% Si - 0.5% Cu) was anodized in nonaqueous electrolyte solutions containing propylene carbonate (PC), ethylene glycol (EG), or γ-butyrolactone (GBL) as a solvent. MIM (metal-insulator-metal) elements using these anodic films were made to evaluate their electrical properties. Leakage current of the anodic films formed in the nonaqueous solutions was lower than those formed in aqueous electrolyte solutions. These novel films are useful as a high insulating film used for a gate insulator in thin film transistor liquid crystal displays (TFT-LCD).
Electromagnetic Properties of Soils
Authors: Sant Amarina J. C. , Klein K. A. 
Published: April 2011

ABSTRACTElectromagnetic waves can be used to characterize geomaterials and to monitor geo-processes. Permittivity, conductivity, and magnetic permeability measurements provide complementary information. Furthermore, events at different frequencies, such as the various polarization mechanisms, suggest multiple internal scales within materials. Three laboratory studies are presented: characterization of kaolinite-water mixtures with permittivity data, monitoring soil-cement hydration with conductivity measurements, and characterization of kaolinite-iron mixtures with magnetic permeability data. Laboratory techniques face inherent limitations, in particular, low frequency permittivity measurements of highly conductive specimens are not feasible. Likewise, field techniques are restricted by the compromise between the desired resolution and the achievable skin depth.
Resistometric Mapping using a Scanning Tunneling Microscope
Authors: Lang C I , Tapson J 
Published: April 2011

ABSTRACTWe present a method whereby spatial variations in the resistivity of bulk conductive specimens may be detected on the same scale as the microstructural variations from which they arise. This technique, a new development of scanning tunneling potentiometry, offers significant benefits for microstructural characterization and for investigation of microstructure/resistivity relationships in metallic materials.
Time Domain Response of Electrical Ceramics Micro to Megaseconds
Authors: Modine F. A. 
Published: April 2011

ABSTRACTThe electrical properties of ceramics can be measured in either the time domain or in the frequency domain. But for electrically nonlinear ceramics such as varistors, time-domain measurements provide insights that are different and more relevant to material performance as well as being more physically incisive. This article focuses specifically on the electrical properties of ZnO varistors, but much of it is of relevance for other materials, in particular those materials with grain-boundary barriers and disordered ceramics or glasses. The interpretation of electrical measurements in the time domain is profoundly influenced by such practical matters as source impedance and waveform characteristics. Experimental results are presented for both high and low source impedance relative to that of a test varistor, and the difference in experimental difficulty and ease of interpretation is described. Time-domain measurements of capacitance and of the inductive response of varistors to large, fast electrical pulses are presented and their implications for varistor theory are given. Experimental evidence is given of short- and long-term memory in varistors. These memory phenomena are ascribed respectively to the life time of holes that become trapped in barriers and to polarization currents originating from deep electron traps. Polarization current measurements are presented for a wide range of time and temperature. The power-law time dependence and “universal” behavior of these currents is discussed. The exponent that describes the power law behavior is seen to change with temperature, and the change is interpreted as a double transition from diffusive to dispersive transport that originates with current from two different electron traps.
Non-Debye and CPA Behaviors of Ionic Materials
Authors: Wang J. C 
Published: April 2011

ABSTRACTNon-Debye and constant-phase-angle (CPA) behaviors associated with the bulk and interfacial processes involving ionic materials are discussed in terms of complex impedance, admittance, and dielectric spectra. The yielding of a CPA and/or a broad non-Debye dielectric loss peak in a spectrum from fractal, pore, and ion-hopping models are compared and reviewed. The observed wide frequency ranges of the CPA behavior suggest that the fractal and pore models, which require a wide range of special structures down to very fine scales, may not be realistic. The ion-hopping model treats the bulk and interfacial processes as a chemical reaction having a thermally-activated Arrhenius form. Because of thermal fluctuations, the activation energies for ion hopping (e.g., in a potential double-well) have a double-exponential distribution which yields a non-Debye dielectric loss peak and a CPA spectrum over a wide frequency range above the loss peak. The distribution also has a special temperature dependence which may explain the invariance of dielectric spectral shapes with temperature, an observation by Joscher. The construction of CPA elements (in a generalized Warburg impedance form) using three distinct types of resistor-capacitor networks are presented and used to aid the discussion.
Measurement of Stratified Distributions of Dielectric Properties and Dependent Physical Parameters
Authors: Mamishev A. V. , Du Y. , Lesieutre B. C. , Zahn M. 
Published: April 2011

ABSTRACTRecent advances in ω-k (frequency-wavenumber) interdigital dielectrometry are described. Using this technology, information about the microstructure of dielectric materials is obtained by applying to the sensor-dielectric interface a spatially periodic electric potential swept in frequency from 0.005 Hz to 10,000 Hz. The penetration depth of the electric field is proportional to the spatial wavelength of the electric potential. Application of multi-wavelength electrode arrangements allows measurement of stratified distributions of complex dielectric permittivity. Calibration techniques serve to relate the distributed dielectric properties of materials to other physical variables, such as density, porosity, cracking, lamination, and diffusion of contaminants into the material. The specific problem treated in this paper is in the measurement of moisture concentration distribution in transformer pressboard during the diffusion of water molecules from ambient transformer oil. The output of interdigital sensors is strongly influenced by the microgranularity of the material's surface. Although this dependence complicates interpretation of the measurements in some applications, the variation of the output may also be used to characterize the shape of the surface on the microscale.
Extended D.C. Electrical Transport Measurements on the Mixed Conductor Cu3Cs2
Authors: Lemaire P. K. , Benoit J. , Speel R. 
Published: April 2011

ABSTRACTD.C. electrical transport measurements have been done over the temperature range 200 K. to 450 K on the mixed conductor Cu3.0CS2 This work extends the original work done on CuxCS2 over the temperature range 260 K to 350 K. Above 220 K, the voltage versus time curves follow the Yokota model for mixed conductors. Below 220K, the voltage versus time curves were practically constant, suggesting very little ionic transport below this temperature, and an electronic conductivity of the order of 10−5 (Ω cm)−1 at 200 K. At ambient temperatures, the ionic conductivity and electronic conductivity were both of the order of 10−3 (Ω cm)−1, and the chemical diffusion coefficient found to be of the order of 10−6 cm2s−1, in agreement with earlier work on Cu3CS2. Above 220 K, the ionic conductivity versus temperature plots were of the Arrhenius form with an activation energy of about 0.36 eV. The jump time and residence time were estimated to be of the order of 10−12s and 10−6s respectively, confirming hopping as the mode of ionic transport. The electronic conductivity versus temperature plot confirmed thermal activation as the mode of electronic transport. The results suggest CuxCS2 to be very stable and the Yokota model, with very little modification, to be very reliable for the analysis of these mixed conductors.
Dielectric Spectroscopy of Insulator/Conductor Composites
Authors: Kolcan Julie Runyan , Gerhardt Rosario , Ruh Robert , McLachlan David S. 
Published: April 2011

ABSTRACTThe dielectric properties of composites are affected in different ways by a number of parameters. These include the electrical properties of both the filler and matrix, the wetting properties of the matrix on the filler, the size and shape of the filler, and the amount of the filler. Most composite systems have been studied via dc resistivity measurements which clearly show the effect of the addition of a second phase to an insulating matrix. However, frequency dependent measurements can provide additional insight into the mechanisms controlling the electrical response. The frequency dependence of the dielectric properties of composites will be shown. The permittivity and admittance plots of BN/B4C composites will be given and the relevance of the trends seen in them will be discussed.
Understanding Coating and Substrate Heterogeneities using Electrochemical Impedance Methods
Authors: Mierisch A. M. , Taylor S. R. 
Published: April 2011

ABSTRACTThis study examines natural breakdown events on organic coated AA 2024-T3 coated using Local Electrochemical Impedance (LEI) mapping (M) and spectroscopy (S). LEIM was able to identify not only different types of defects on this system, but also provided information about the kinetics and stages of development of these defects. Supportive evidence regarding the impedance characteristics of these defects was provided by Capillary Electrophoresis (CE). Data from early stages of defect development indicate that an increased impedance develops at the site. This is related to either the development of aggregated water or electrolyte, as well as corrosion product development. Direct evidence of defect healing is also provided.
Scaling Behavior of the Complex Conductivity of Graphite-Boron Nitride Percolation Systems
Authors: Wu Jungie , McLachlan D S 
Published: April 2011

ABSTRACTMeasurements of both components of the complex AC conductivity σ*m of continuum percolation systems, based on Graphite and hexagonal Boron Nitride, over a large frequency range, for samples near the conductor insulator composition, are reported. The results of the real part of σ*m (σmr) above the critical volume fraction (φc) and the imaginary component (σmi = iωεoεmr) below φo are shown to have the correct power law dispersion behavior, but only if the non-universal exponents measured in previously described DC experiments are used. It is also shown that all the results can be scaled, as is predicted by percolation theory, so as to lie on two continuous curves, one below and one above φc. Unfortunately the actual ωc values used to scale the experimental results are found not to be in good agreement with theoretical predictions.