XRD, SEM micrographs, BET analyses and typical electrochemical experiments (cyclic voltammetry, step voltammetry and Li insertion/deinsertion at constant current) have been carried out to characterize a new type of soft carbons obtained by pyrolysis of hexaphenylbenzene (HPB). By means of XRD and cyclic voltammetry at least three different type of sites for lithium storage were found. The first is graphite like type with d002 graphene layer distance greater than pure graphite; the second is associated to disordered volumes among crystallities and the third is represented by Li sites at the hydrogen-terminated edges of hexagonal carbon fragments, characterized by higher energy in comparison with simple insertion sites. These last two types of sites are able to store some extra lithium, compared to pure graphite. BET analyses and cyclic voltammetries demonstrate the key role of the milling time on the characteristics and properties of this HPB pyrolysed carbon. Specific capacities shown by this pyrolysed material in Li coin-type cell have been also reported.

Hexa(phenyl)benzene (HPB) and hexakis(p-bromophenyl)benzene (HPB-Br) were submitted to controlled pyrolysis under mild conditions to prepare carbonaceous materials for Li-ion storage. Experiments were performed in evacuated sealed ampoules and different temperatures (in the range 500–600°C) and heating times (1 upto 5 days) were applied. Pyrolytic products were obtained as black flakes and characterised by elemental analysis, thermogravimetric analysis, UV–vis–NIR and Raman spectroscopies. Scanning electron microscopy exhibited several structures (nanorods, bundles, microspheres) on the surface of the flakes, depending on the precursor and on the pyrolysis procedure. Preliminary electrochemical measurements revealed lithium storage capacities upto 500mAhg−1.

The electrochemical behavior of a disordered carbon used as the anode in a lithium battery has been tested. The characteristics of this carbon, especially its specific capacity and cycle life, are such that it is a potentially unique, high-performance anode material for new types of lithium-ion batteries. The Figure shows the specific capacity versus cycle number of the disordered carbon electrode in a lithium-ion cell.

A low-temperature pyrolytic stepwise method is proposed to produce substantial amount of a carbonaceous material, characterized by a graphenic structure. The pyrolyzed material has been submitted to ballmilling steps of different times, and the samples obtained were studied from their structural and electrochemical points of view. The crystallographic data have evidenced crystallites with a crystal domain size less than one nanometer and the grinding influence is discussed. Electrochemical experiments have been carried out in order to study the mechanism of the Li insertion/deinsertion process in the host material. Interesting values of Li specific capacity have been calculated from cycle experiments in Li coin cells at constant current and a test in a Li-ion laboratory-type cell is proposed. (c) 2005 The Electrochemical Society.

Some oxides have been investigated as alternative materials for Li-ion batteries. In particular, the In2O3 anodic compound, synthesized in our laboratory, and some commercial powders (PbO, PbO2 and Fe2O3) were studied. The morphology of the oxides was analyzed by SEM investigation. The electrochemical characteristics obtained on composite thin-film electrodes based on these materials are here reported, in term of specific capacity and cyclability.

The kinetics of electrochemical lithium insertion inside RF sputtered Ni/V mixed oxides thin films have been investigated employing different electrochemical techniques. The AC electrochemical impedance spectra, recorded after 10 cycles, showed three steps clearly involved in the intercalation mechanism of lithium in the oxide films: (i) a charge transfer process to the electrolyte/electrode interface; (ii) a solid-state diffusion of Li; and (iii) a space limited diffusion due to the finite volume of the film. This latter portion of the impedance spectra was used to calculate the Li chemical diffusion coefficients (DLi). DLi values show an initial increase up to an injected charge of 30 mC cm−2 and then, upon further intercalation, a decay probably due to the limited Li motion through a decreased number of available sites. These results are in good agreement with the ones obtained by potentiostatic intermittent titration technique applied to the same electrodes. Both techniques agree in giving the same trend for DLi upon Li intercalation. The same sets of measurements were carried out after 100 and 1000 Li insertion/deinsertion cycles in order to analyze the effect of prolonged cycling on the mechanism of lithium diffusion.

Iron containing CeVO4 films were prepared using the sol-gel method. The crystalline structure of powders and films with Fe/Ce/V ratios of 0.1:1:1, 0.3:1:1 and 0.5:1:1 were investigated by X-ray diffraction (XRD) and infrared (IR) spectroscopy. XRD revealed the predominance of a CeVO4-W (wakefieldite) crystalline phase with a small amount of monoclinic CeVO4, CeO2 and Fe2O3. Ex situ IR absorbance spectra of charged and discharged films show the changes in intensity of the V-O stretching mode at 770 cm(-1).Cyclic voltammetry showed that Li+ intercalation occurs in three steps with total capacities of 22 mC cm(-2) (Fe/Ce = 0.1), 32 mC cm(-2) (Fe/Ce = 0.3) and 37 mC cm (-2) (Fe/Ce = 0.5). The increase in the overall charge capacity with increasing Fe content is accompanied by a loss of capacity with cycling. The lithium diffusion coefficient: calculated by the galvanostatic intermittent titration method (GITT), the potentiostatic intermittent titration method (PITT) and electrochemical impedance spectroscopy (EIS), ranges from 10(-12) to 10(-14) cm(2) s(-1). UV-vis in situ transmittance spectra showed that these films are highly transparent with a photopic transmittance T-Vis similar to 0.85 for intercalated and deintercalated states. This suggests that Fe/Ce/V oxide films are good candidates for optically passive counter-electrodes in electrochromic (EC) devices. (C) 2001 Elsevier Science Ltd. All rights reserved.

We describe the preparation and the electrochemical properties of Li2MxMn4−xO8, spinel-structured compounds. The results demonstrate that these materials may operate as high-voltage cathodes in new concept lithium-ion batteries. An example of these batteries has been fabricated and successfully tested.

A family of mixed LiCoyNi(1−y)VO4 (y=0.2, 0.5 and 0.8) compounds of potential use as high voltage cathode materials in lithium batteries, has been synthesized and characterized. The X-ray diffraction analysis showed that these compounds adopt an inverse spinel structure where in average 85% of the Ni2+ and Co2+ ions occupy octahedral sites and the other 15% occupy tetrahedral sites with the V5+ ions, although this occupation share is somewhat influenced by the preparation temperature. The annealing temperature plays also a key role in determining the particle size, as demonstrated by scanning electron microscope analysis. Cycling voltammetry tests showed that the lithium insertion–deinsertion process in the LiCoyNi(1−y)VO4 electrode materials occurs reversibly around 4.3–4.4 V vs. Li, as also confirmed by cycling tests. The cycling capacity is somewhat modest; however, the trend of the cycling curves leads to foresee that a consistent increase in capacity may be obtained by extending the charging process beyond 4.6 V vs. Li, once a stable electrolyte will be available.

Low-temperature thin films of Li1 + xV3O8 have been fabricated and tested in LiClO4/propylene carbonate-1,2-dimethoxyethane/Li cells. These cells show very good intercalation kinetics, and at 0.4 C discharge rate produce a specific energy of ≈ 110 Wh/kg. The films could be used in microbatteries for electronic devices, and applications requiring more power could also be envisaged.

Preliminary applications of low molecular weight polymer electrolyte (PEG) and lithium salt in lithium rechargeable batteries have been reported. The electrochemical characteristics of these electrolytes have been tested by cyclic voltammetry, charge-discharge cycles and ac impedance methods. Surface layers appear to be present on botg electrodes, but they develop upon time with different extension.

Multivalent salt polymer complexes offer important prospects of the investigation and understanding of the fundamental properties of Polymer electrolytes. In this work we present some recent results obtained by complex impedance, cyclic voltammetry and electron spin resonance on a series of polymer electrolyte systems based on the combination of poly(ethyleneoxide) PEO and copper salts of the Cu(CF3SO3)2 type. The data appear to confirm that copper ions contribute to the overall transport in these complexes. However, the mechanism of conductivity may also include a mixed ionic-electronic effect.

Consistent interest has lately been devoted to complexes formed between poly(ethylene oxide), PEO, and multivalent metal salts, since these polymer electrolytes offer challenging prospects for investigation, both in terms of definition of bulk transport properties of complicated, multiphase systems and in terms of the evaluation of practical application in advanced electrochemical devices, such as flat, thin-layer batteries and laminated electrochromic windows. In this work we present results obtained by complex impedance spectroscopy, cyclic voltammetry and differential scanning calorimetry on a series of PEOCU(CF3SO3)2 complexes prepared using different techniques. The data suggest that these complexes are copper ion conductors, although the overall transport mechanism is still unclear.

AbstractThe electrochemical characteristics are determined for polymer electrolytes formed by complexes of poly(ethylene oxide), PEO, and Cu(CF3SO3)2 with varying molar ratio.

The characteristics of polymer electrolyte, formed by complexes of poly(ethylene oxide) PEO and copper trifluorosulfonate in various molar ratio of salt to polymer repeat unit, have been investigated. The results, based on ac impedance analysis and dc polarizations, indicate that the polymer complexes have a high conductivity, which around 100°C is mostly ionic in character. Preliminary evaluations of copper transport number suggest that the complexes are mainly anion conductors. However, under optimized conditions, copper cyclability can still be obtained in solid‐state cells based on the new family of the polymer electrolytes.

The system CuI-Ag3AsO4, which shows a structure associated with fast ionic transport, has been examined with the hope to investigate the reciprocal role of silver and copper in disordered materials. Ionic and electronic conductivity and transport number were determined. X-ray, differential scanning calorimetry and electrochemical analyses were carried out using standard procedures and equipment. Results reported show that CuI-Ag3AsO4 acts as a silver ionic conductor, even starting with a mixture with a high CuI (50 m/o) content. The observed behaviour is discussed in connection with the structural and chemical features of the material.

The characteristics of the lithium electrode were examined in an organic and a polymeric electrolyte of interest for the development of rechargeable batteries. Results obtained by frequency response analysis and by polarization curves, were used to identify charge-transfer resistance, double layer capacity and properties of passivation films.

The characteristics of electrochemically synthesized polypyrrole electrodes have been examined in the lithium perchlorate-propylene carbonate electrolyte, by cyclic voltammetry, charge-discharge cycling, frequency response analysis and by vis-near ir absorbtion spectra. The results show that these polymer electrodes behave satisfactorily in terms of kinetics of the electrochemical doping process, cyclability and charge-discharge efficiency. However, their performance under high rates may be limited by the diffusion of the perchlorate counterion. The preliminary evaluation seems to indicate that polypyrrole may be more stable than other conducting polymers in organic electrolytes of interest for the development of rechargeable lithium batteries.

The behaviour of lithium metal, and of a selected intercalation compound in electrochemical cells with polymeric electrolytes, is discussed on the basis of cyclic voltammetry, polarisation curves, and frequency response analysis. Some preliminary results on a polymeric electrolyte, rechargeable, lithium battery are also presented.

The electrical conductivity measurement carried out on HTaWO6·H2O and HTaWO6 are reported. The activation energy for the conduction process as well as the diffusion coefficient of hydrogen ion are compared with the results obtained by NMR technique.