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Several isocyanate compounds have been investigated with regard to their performance as film forming electrolyte additives in propylene carbonate (PC) and EC/EMC-based electrolytes. In situ and ex situ analytical methods were applied to understand the differences in performance. Particular attention was paid to the differences of aromatic and linear isocyanate compounds.

Two tin–graphite composites (“core-shell” structures) with different metal content (80 wt% and 20 wt%) as well as their structural and electrochemical characteristics are presented. Mitsubishi's synthetic carbon was used as starting material for the modification experiments. Chemical reduction was applied for the coating process, which was carried out under inert argon atmosphere. Although a homogeneous film of the nanoscale tin particles (∼60 nm) have been achieved, the electrochemical performance improvement strongly depends on the thickness of the “shell’ layer and the progressively increased active surface area together with the tin metal contents. The electrode with low metal concentration displayed both improved cycling performance and stable discharge capacity of 435 Ah kg −1 compared with untreated graphite electrode. The tin-rich composite shows a higher medial discharge capacity (540 mAh g −1 ) but increased capacity fading, while higher metal contents lead to bulk-coated film with disassociated and agglomerated tin nanoparticles as well as higher surface area and likely presence of oxide impurities. The obtained electrochemical results lead to the assumption, that there is a critical metal ratio up to which good cycling behavior can be achieved. Moreover, the properties of the coating film are closely related with the synthesis conditions and the type of the graphite. In this case, the optimal amount for tin–graphite composite with improved electrochemical performance is about 20 wt%.

To avoid solvent co-intercalation into graphite, the presence of a solid electrolyte interphase (SEI) is required. This film is formed via the reductive decomposition of electrolyte species, i.e. a film forming electrolyte additives. In this contribution we focus on an isocyanate compound, ethyl isocyanate (EtNCO) which performs well in a propylene carbonate electrolyte at both graphite anode and LiCoO2 cathode. EtNCO is investigated by in situ Fourier transform infrared (FTIR) spectroscopy. We conclude that the formation of a radical anion via electrochemical reduction of the electrolyte additive is the initiating step of the SEI formation process. The electro-polymerization of isocyanate monomers in small additive amounts in the PC electrolyte is critically discussed.

Electrochemical properties and working mechanisms of benzyl isocyanate compounds as polymerizable electrolyte additives for overcharge protection of lithium ion batteries have been studied by cyclic voltammetry, charge–discharge cycling, overcharge tests, accelerating rate calorimetry (ARC) and in situ Fourier transform infrared spectroscopy (FTIRS). The overcharge and FTIRS data clearly reveal that 4-bromobenzyl isocyanate (Br-BIC) can electrochemically polymerize at 5.5 V (versus Li/Li + ) to form an overcharge-inhibiting (probably insulating) film on the cathode surface. In addition, is found the Br-BIC does slightly improve the charge/discharge performance of a lithium ion battery. Furthermore, Br-BIC and benzyl isocyanate show beneficial solid electrolyte interphase (SEI) formation behaviour on graphite in propylene carbonate based electrolyte solutions.

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

The reformer sponge iron cycle produces hydrogen from hydrocarbons with high efficiencies and a high degree of purity. In this process, the gas purification step is performed by a cyclic redox reaction of the contact mass (iron oxide) with synthesis gas and steam at high temperatures. In order to get information about the lifetime of the contact mass, investigations of the cycle behaviour of the contact mass have been carried out. First experiments showed that iron oxide pellets without additives were deactivated quickly for the redox reaction due to sintering effects. SiO 2 , CaO and Al 2 O 3 were added to the iron oxides, and the effects of different compositions were investigated. The contact mass was characterized before cycling, after 10, and 20 cycles by XRD, SEM, mercury porosimetry and Raman spectroscopy. It was shown that a higher content of SiO 2 prevents sintering of iron species during reduction and the subsequent oxidation with water vapour over 20 cycles at 800 ∘ C . A quartz content below 6.5 wt% prevented the contact mass from reacting already after 5 cycles.

In this contribution, we focus on propylene carbonate (PC)-based electrolytes for lithium-ion batteries. In order to avoid solvent co-intercalation into graphite the presence of a solid electrolyte interphase (SEI) is required. This film is formed due to a film-forming species, i.e. a film-forming electrolyte additive. In this contribution, we focus on a vinylene compound, 2-cyanofuran (2CF) which proves to perform well in propylene carbonate electrolytes. 2CF is investigated by in situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. We conclude that the cathodic reduction of the vinylene groups (=via reduction of the double bond) in the electrolyte additive is the initiating, and thus an important step of the SEI formation process. The possibility of an electropolymerization reaction of the vinylene monomers in the used electrolytes is critically discussed on the basis of the obtained IR data.

Methanol diffusion and electroosmotic drag coefficients for different polymer–electrolyte-membranes have been investigated. It is essential to understand the transport phenomena of water and methanol transport in perfluoro sulfonic acid (PSA) membranes under different methanol concentrations and current densities in order to optimize cell performance and operation. The dependence of the methanol diffusion coefficient as well as the electroosmotic drag coefficient on methanol concentration and current density were observed. The results are discussed in comparison to measured values obtained by other scientific groups.

Bipolar designs for a direct methanol fuel cell (DMFC) with liquid electrolyte have been investigated, aiming at a reduction of methanol crossover. A “spacer” (separator) material has to be applied which is inert in a sulphuric acid/methanol surrounding. This material has to be porous so that the liquid electrolyte can be pumped through. Swelling characteristics as well as variation of material properties with temperature and pressure have been investigated with several materials. It is essential to minimize the internal cell resistance in order to achieve a good performance of the DMFC. Due to the importance of electrolyte canal thickness with respect to ohmic resistance of the cell assembly, the variation of cell power output with electrolyte canal thickness was investigated.

The long-term formation kinetics of the solid electrolyte interphase (SEI) was studied on graphite electrodes in 1 M LiClO 4 /PC with 5% acrylonitrile (AN) as electrolyte additive by electrochemical impedance spectroscopy at 1.0 and 0.5 V versus Li/Li + , i.e. mainly outside the graphite intercalation region. To support the interpretation of the results, comparative experiments with Ni and Pt electrodes were performed at the same potentials. The resistance of the SEI on graphite and nickel shows similar time dependence. Whereas, R SEI of both electrodes exhibits a linear increase after 5–10 h at 1.0 V, a parabolic behavior could be observed at 0.5 V (and even more expressed for Ni at 0.05 V) typical of diffusion controlled growth kinetics. Temperature dependent measurements yielded activation energies for the ionic conduction of the SEI between 0.61 and 0.66 eV. The results were the same for graphite at 0.5 V and nickel at 1.0, 0.5 and 0.05 V.

Electrochemical characterization has been carried out for electrodes prepared of several activated carbon fiber samples derived from poly (m-phenylene isophthalamide) (Nomex) in an aqueous solution. Depending on the burn-off due to activation the BET surface area of the carbons was in the order of 1300–2800 m2 g−1, providing an extensive network of micropores. Their capability as active material for supercapacitors was evaluated by using cyclic voltammetry and impedance spectroscopy. Values for the capacitance of 175 F g−1 in sulfuric acid were obtained. Further on, it was observed that the specific capacitance and the performance of the electrode increase significantly with increasing burn-off degree. We believe that this fact can be attributed to the increase of surface area and porosity with increasing burn-off.

The reduction of graphite in propylene carbonate (PC) based electrolytes is a complex process involving solvated lithium–graphite intercalation compounds (GICs), Li+(PC)yCn-. XRD performed in situ to cyclic voltammetry allows to monitor the intercalation/de-intercalation of PC-solvated lithium into/from a crystalline graphite electrode, which is associated with up to 374% expansion of the basal plane spacing in c-direction of the graphite structure. The XRD data further allows to estimate the structure and stoichiometry of the ternary GIC: Li+(PC)yCn-, with y ⩾ 4, indicating a 3-dimensional, tetrahedral solvate shell. The stability of ternary GICs vs. reduction is addressed in view of graphite exfoliation and electrode failure. Keywords: In situ XRD, Graphite, Solvent co-intercalation, Solid electrolyte interphase (SEI), Lithium ion battery

The rechargeable lithium-ion battery has been extensively used in mobile communication and portable instruments due to its many advantages, such as high volumetric and gravimetric energy density and low self-discharge rate. In addition, it is the most promising candidate as the power source for (hybrid) electric vehicles and stationary energy storage. For these applications in durable equipment, the long-term cycling and storage behaviour becomes of increasing interest. In this paper, the mechanisms of lithium-ion battery ageing are reviewed and evaluated.

The protonic conductivity of the polymer electrolyte membrane (PEM) in the PEM fuel cell is critical to the overall power density of the fuel cell system. The conductivity can be influenced by the presence of impurity cations in the membrane. By the use of electrochemical impedance spectroscopy with microelectrodes, the local conductivity of Nafion membranes, which had been exposed to part per million (ppm) concentrations of impurity cations, was evaluated. Inorganic impurity cations studied included Cu2+, Fe3+, Na+ and Ni2+. Membranes were immersed in sulphate salt solutions of these cations, prepared in distilled water. Conductivity values at 0.1, 1 and 10 ppm cation impurity level were found to vary little from values for the blank solution. However at 100 ppm, a significant decrease in conductivity was observed. At this higher concentration of impurity, the Ni2+ and Cu2+ contaminated membranes displayed lower conductivity than that contaminated by Na+. Meanwhile Fe3+ contaminated membrane had the lowest conductivity. That this decrease in conductivity was greater for cations of higher valence corresponds with the high affinity of the sulphonic acid sites in Nafion to multivalent foreign cations. The results illustrate the detrimental effect of small amounts of contaminants on conductivity in Nafion membrane.

Using a simple method for manufacturing of micro-tips, numerous microelectrodes with reasonably small electroactive area were produced by insulating the micro-tips into glass capillaries. Microelectrode characterisation was carried out with steady state diffusion limited current measurements in acidic FeCl 3 solution. The microelectrodes were used for different purposes, the simplest of which was measuring the impedance in the region of a small conductive area placed in an insulating surrounding. Other measurements were carried out by generating impedance profiles in different electrolytes, as a microelectrode approached a conversion-coated metal surface, in order to gain information about the properties of the coating.

Direct methanol fuel cells (DMFCs) are capable of utilising a liquid fuel directly in the fuel cell and they are therefore an interesting option for a variety of mobile and portable applications. Still there are several barriers which have to be overcome before DMFCs are able to compete with conventional technologies. A major restriction in reaching high efficiencies with DMFCs is methanol crossover from anode to cathode. This work discusses several methods to characterise the methanol crossover and introduces a newly developed measurement method which allows an exact determination of methanol crossover in DMFCs with liquid and solid electrolytes.

The reformer sponge iron cycle (RESC) process was introduced for the stationary, decentralised production of hydrogen from hydrocarbon-containing fuels. The RESC process consists of two steps: the reformation of higher hydrocarbon to synthesis gas and the fine purification of this gas to pure hydrogen with the sponge iron reaction (SIR) process. The SIR process uses iron ore as contact mass. The contact mass (iron oxide) is reduced to iron in the first cycle by a synthesis gas, and is re-oxidised into iron oxide in the second cycle, utilizing steam. Pure hydrogen is produced in the second cycle as reaction product of the process. Iron ore is a very inexpensive base material for the contact mass, but the contact mass still has to be stable over several thousand redox cycles. Test series with varying contact mass compositions have been performed in order to investigate the influence of the composition on the durability of the contact mass. Carbon monoxide and hydrogen were used for the reduction process. Thermogravimetry (TG), X-ray diffractometry (XRD), scanning electron microscope (SEM) and mercury porosimetry were applied for the evaluation of structural changes after cycling the contact mass. The results confirm the importance of the skeletal structure of the pellets.

During its lifetime, the polymer electrolyte membrane of a fuel cell may be exposed to numerous impurities originating from sources such as materials used in various components of the fuel cell stack and contaminants in the coolant and reactant gas. The contamination of the membrane by cationic impurities has detrimental effects on membrane properties with regard to conductivity, water management and durability. Thus the measurement of absorption of contaminants into the membrane and the investigation of its relation to these detrimental effects is of interest. Samples of Nafion 117 polymer electrolyte membrane were soaked in deionised water solutions containing part per million (ppm) concentrations of cation impurities, ranging from 0.1 to 100 ppm. Upon removal of the membranes from the soaking solutions, conductivity of the membranes and the effect of different cationic impurity concentrations on the conductivity was measured by impedance spectroscopy methods. Using atomic absorption spectrophotometry, the concentration of the cationic impurity species remaining in the soaking solutions was determined and the extent of ion absorption by the membranes calculated. Energy dispersive X-ray analysis was also employed and confirmed the presence of the contaminant ions in the membrane. Impedance studies exhibited a loss of conductivity, while an increase in ion absorption into the membrane was observed, when membranes were soaked in solutions of higher contaminant concentration. In this study, the capacity for ion absorption into the membranes was determined and the extent of membrane contamination was compared and correlated with the loss in conductivity of the membrane for different levels of contamination.

Cathodes with silver and platinum as catalysts supported on carbon nanofibers for the oxygen reduction reaction were investigated with an alkaline electrolyte. Nowadays, alkaline fuel cells serve again as an interesting alternative to polymer electrolyte fuel cells, due to the fact that silver can be used as catalyst for the oxygen reduction reaction. The investigated electrodes are prepared by a rolling process and consist of an active layer, prepared of carbon nanofibers as catalyst support and polytetrafluorethylene (PTFE) connected onto a gas diffusion electrode (GDE). The electrodes were electrochemically investigated by measuring polarization curves. It is shown that, together with a certain PTFE content, the fibers are capable of providing the required porosity and pore structure, as well as an excellent electrical conductivity in order to be used as material for GDE production. The measurements are carried out in half cell tests at 80 °C with 9 M KOH as electrolyte. In addition, carbon nanofibers and electrodes were physically characterized by scanning electron microscopy. Keywords: Alkaline fuel cell, Carbon nanofibers, Oxygen reduction reaction, Silver cathode, Platinum cathode, Gas-diffusion electrode, Scanning electron microscopy

Substrate-induced coagulation (SIC) is a coating process based on self-assembly for coating different surfaces with fine particulate materials. The particles are dispersed in a suitable solvent and the stability of the dispersion is adjusted by additives. When a surface, pre-treated with a flocculant e.g. a polyelectrolyte, is dipped into the dispersion, it induces coagulation resulting in the deposition of the particles on the surface. A non-aqueous SIC process for carbon coating is presented, which can be performed in polar, aprotic solvents such as N-Methyl-2-pyrrolidinone (NMP). Polyvinylalcohol (PVA) is used to condition the surface of substrates such as mica, copper-foil, silicon-wafers and lithiumcobalt oxide powder, a cathode material used for Li-ion batteries. The subsequent SIC carbon coating produces uniform layers on the substrates and causes the conductivity of lithiumcobalt oxide to increase drastically, while retaining a high percentage of active battery material.

Dispersions of carbon black in water and N -methyl-2-pyrrolidinone were investigated with respect to their stability in order to find conditions for the substrate induced coagulation (SIC) process. The SIC process is a dip coating process based on enhanced adsorption of particles or coagulation of dispersions on surfaces which are conditioned with flocculants. Efficient SIC coating requires careful adjustment of the stability of the dispersion; “over-stabilised” dispersions will not show sufficient interaction with the conditioned surfaces. Zeta potentials of carbon black particles in aqueous and non-aqueous solutions were calculated from electrophoretic mobilities determined by phase analysis light scattering (PALS) and the electroacoustic method. The electrophoretic mobilities of carbon black in NMP decreased in magnitude on addition of bis-2-ethylhexyl sodium sulfosuccinate (AOT), which is the opposite effect to that observed in water. This is attributed to the AOT behaving as a normal electrolyte in NMP, with no evidence of the surfactant behaviour that it displays in water.

Nafion 117 was coated with thin layers of metallic Pd by electroless deposition from commercial plating baths. The deposits were well adhering and crack-free. In a purpose-built direct methanol fuel cell for liquid electrolyte, the methanol-blocking ability of the Nafion/Pd composites was studied. The cell construction allowed determining the methanol concentration directly in the catholyte while recording electrochemical parameters. Compared to bare Nafion, the Nafion/Pd composites considerably reduced methanol crossover. This resulted in enhanced cell performance, which was found to be somewhat dependent also on the potential of the Pd layer.

Carbon electrodes have been modified with 2-nitro-1-naphthol with the aim of producing composite supercapacitor electrodes, which make use of both the electric double layer (EDL) capacitance of high surface area carbon and the redox capacity (pseudocapacitance) of the organic compound. In situ FTIR and cyclic voltammetric data confirm literature reports of the reduction of 2-nitro-1-naphthol to 2-amino-1-naphthol and the subsequent oxidation of the o -aminonaphthol to the corresponding o -naphthaquinoneimine in aqueous acidic media. The measurements also show that the quinoneimine is not stable and hydrolized in sulphuric acid electrolyte to 1,2-naphthaquinone. The chemically highly reversible o -naphthaquinone/ o -naphthahydroquinone couple remains immobilized on the carbon electrodes during redox cycling. The organic redox couple contributes a capacity of 35 mA h g −1 of the bare carbon to the overall charge storage capability of the composite electrode. Surprisingly, it does not affect the capacitance of the electric double layer of the carbon. During 1000 charge/discharge cycles, the pseudocapacitance decreases by less than 20% in a normal large-volume electrochemical cell. Electrochemical impedance measurements show that the full capacity of the electrode is accessible at frequencies below 0.1 Hz.

Alkoxy substituted derivatives of poly- and oligo-[(m-phenylenevinylene)-alt-(p-phenylenevinylene)] were synthesized via the Wittig (P1, OPV1, OPV2) and the Wittig-Horner (P2, OPV3, OPV4) condensation routes. The polymers were characterized by 13 C NMR, 1 H NMR, FT-IR spectroscopy and GPC. 1 H NMR was a convenient tool to distinguish between the cis and trans double bonds in the compounds. Poly [(4-decycloxy-1,3-phenylenevinylene)-alt-(1,4-phenylene)] (P1) contained cis and trans double bonds in significant amounts, the vinylene configuration of poly [(4-decycloxy-1,3-phenylenevinylene)-alt-(2,5-dipentyloxy-1,4-phenylenevinylene)] (P2) was nearly exclusively trans. Model compounds (OPV1-4) were also synthesized to support the structural and optical characterization. UV-vis absorption, photoluminescence (PL) and cyclic voltammetry measurements have been performed to investigate the influence of the positions and the number of substituents on electronic levels. The polymers exhibited an intensive solid-state emission in the blue-green (P1) and the green (P2) region of the spectrum. Light emitting diodes have been fabricated consisting of ITO, PEDOT:PSS, P2 and Ca/A1. They exhibited high luminance of 100 cd.m -2 at 5.9 V and low onset voltages (4.3 V) for the electroluminescence (EL).

Molecular dynamics simulations at 298 K are used to study the interaction of adsorbed silane molecules (octyltrihydroxysilane, butyltrihydroxysilane, aminopropyltrihydroxysilane and thiolpropyltrihydroxysilane) with the polar (0 0 0 1 ) zinc oxide surface. Special emphasis is placed on the influence of the metal oxide surface on the orientation and adsorption energy of the silanes. We compare a model of a reconstructed surface with a previous model using an ideal surface. Surface morphology is shown to have little effect on the orientation of silane adsorbates (except thiolpropyltrihydroxysilane) with the adsorption energy being correlated with the surface polarity.

Lithium storage metals and alloys can be suitable high-capacity anode materials for lithium-ion batteries, when the morphology is specifically designed. Here, we compare three different Sn/SnSb multiphase anode materials in powder form, which have been prepared in aqueous and organic solution by chemical precipitation using NaBH4 or Zn as reductive agents. The obtained morphologies, chemical compositions, and the electrochemical performance will be comparatively discussed. The variety of synthesis parameters which have an effect on the morphology of the obtained anode materials will be particularly highlighted.

The physical behavior of different adsorbed silane molecules (octyltrihydroxysilane, aminopropyltrihydroxysilane, and thiolpropyltrihydroxysilane) at a ZnO surface (0001) dissolved in isopropanol are studied via constant temperature (298 K) molecular dynamics simulations. The adsorbed silane molecules exhibit a different behavior depending on the chemical nature of their tail. Octyltrihydroxysilane molecules with their rather unpolar tail show two distinct, energetic different orientations at the polar metal oxide surface. Mostly the three polar hydroxy groups of the head are in contact with ZnO the unpolar tail remaining in the isopropanol phase. Occasionally only two hydroxy groups interact with the surface the whole tail simultaneously being attached. On the contrary, due to their highly polar tail aminopropyltrihydroxysilane molecules have only one favorite orientation at the surface: Apart from some minor fluctuations two hydroxy groups as well as the amino group of the tail are in contact with the ...

In a combinatorial electrochemistry experiment quinine was used as a pH sensitive fluorescing indicator to detect the catalytic activity of methanol oxidation catalysts. During electrochemical experiments the surface of the electrode array was monitored with a CCD camera. The dependence of the intensity of the fluorescence on the applied potential was used as an analytical tool; to investigate the electrochemical performance of Pt based electrocatalysts, for the electrooxidation of methanol, in both short and long term tests.

Acrylic acid nitrile (AAN) is introduced as a novel example out of the large class of vinylene groups containing film-forming additives for lithium-ion batteries. The electrochemical behaviour, especially the electrolyte additive reduction and the associated film formation in the presence of this compound is investigated with the in situ methods of Fourier transform infrared (FT-IR) spectroscopy and electrochemical quartz crystal micro balance (EQCMB). The results clearly point at a solid electrolyte interphase (SEI) formation mechanism, which proceeds via the cathodically induced polymerization of AAN. We suggest that the electro-polymerisation of vinylene groups is a main electrolyte reduction mechanism for a vinylene group containing electrolyte additives. The outstanding filming properties of vinylene compounds such as AAN allow the use of graphitic carbon anodes in PC-based electrolytes even when only 1% of the additive is present in the electrolyte.

We present results on the electrolyte additive acrylic acid nitrile (AAN), which allows the use of propylene carbonate (PC)-based electrolytes together with graphitic anodes. This report will focus on the basic electrochemical properties and on XPS results of the films formed in the presence of AAN. Further data on in situ investigations of AAN is presented in another paper of this proceedings. The combination of both reports gives strong evidence, that the initiative step for solid electrolyte interphase (SEI) formation is a cathodic, i.e. by reduction induced electro-polymerisation of the vinyl-group. It is concluded that this electro-polymerisation may also be a main reduction mechanism of other vinyl compounds such as vinylene carbonate (VC), vinylene acetate and others.

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH4 and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH4 yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g−1, ∼ 350 – 400 mAh g−1, and ∼ 500 mAh g−1 were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation.

We report on the synthesis and structural, thermal and electrochemical characterisation of reduced molybdenum oxides with layered α-MoO3 type structure. The samples have been prepared by reactions of various amounts of water-free tin dichloride with fine-particulated orthorhombic molybdenum trioxide in n-hexane (non-aqueous media) or in aqueous media, which yielded materials with different Sn:Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO3 has been maintained after the reduction process. No crystalline impurity phases (e.g. tin oxides) could be detected by XRD. The tin-reduced samples exhibited a drastically improved cycling stability and capacity retention on cycling in 1 M LiClO4/propylene carbonate, i.e. the discharge capacities were well above 100 mAh g−1 after 20 cycles whereas the non-treated MoO3 (reference sample) has retained only about 45 mAh g−1. At higher cycle numbers (approx. cycle 100) the discharge capacity of the reduced molybdenum oxides stabilises at a level of approx. 100 mAh g−1. This significant improvement of the rechargeability may be related to improved electronic conductivity and/or higher structural stabilisation of the layered MoO3 structure either due to (i) a coating of the MoO3 particles with a protective thin layer of a tin containing compounds, and/or (ii) an amorphisation of the structure after reductive treatment. Further efforts of this study were devoted to a variation of the conductive carbon content in the electrode composition and to changes of cut-off voltages and current densities.

Six sub-micro-crystalline alloy powders (Sn–Sb, Sn–Ag, Sb–Ag, and Sn–Sb–Ag alloys), where all constituents are able to alloy reversibly with Li and which are therefore characterized by large theoretical Li storage capacities, have been synthesized by chemical precipitation with NaBH 4 , and their composite electrodes have been electrochemically tested by constant current cycling and cyclic voltammetry. Sn/SnSb and SnSb showed the best performance, with stable capacities of 600 and 500 mAh g −1 , respectively, for more than 30 cycles. All of the materials exhibit large irreversible capacities in the first cycle, which are also often found for other metallic–intermetallic systems. Since, however, first cycle efficiencies of 89–95% can be achieved with electroplated thin Sn films, this is not an intrinsic problem of Sn or Sn-containing compounds, and it is not the trapping of Li in any of the many lithiated Sn phases that should be the main reason for the large irreversible capacities of the composite electrodes, but rather other factors, such as oxide impurities and especially contact problems in the composite electrode.

The synthesis of 2,6-disubstituted N,N,N′,N′-tetramethyl-p-phenylenediamines (R = Cl, Br, I, CN, or CCSi(CH3)3), potential precursors/building blocks for molecular magnets, is presented. In addition to standard methods (1H NMR, 13C NMR, MS, IR, UV), the products were also characterised by means of cyclic voltammetry. Completely reversible electrochemical behaviour was observed for both the CN and the CCSi(CH3)3 derivatives. Moreover, the corresponding radical cations and the dications were observed by cyclic voltammetry for these compounds. The first oxidation step of the Cl and the Br derivatives was also found to be reversible, although a chemical side reaction was detected after oxidation to the corresponding dication. The radical cation could not be detected for the I derivative. In this case direct oxidation to the dication followed by a chemical reaction was observed.

It is demonstrated that the design of the composite electrode, or more precisely the morphology and distribution of the binder poly(vinylidine fluoride) (PVdF) within the composite electrode, has a significant impact on the cycling performance of Li storage alloy (Sn/SnSb) electrodes. Different binder morphologies and distributions have been obtained by using different solvents for the slurry preparation, such as 1-methyl-2-pyrrolidinone (NMP), in which PVdF is dissolved, yielding electrodes with a homogeneously and finely distributed binder, or decane, in which PVdF is only dispersed, yielding electrodes in which the original particle morphology of the binder powder is preserved. In constant current cycling tests carried out in an excess of electrolyte, the electrodes with the ‘dispersed’ binder show far better cycling capacities and stabilities than those with the ‘dissolved’ binder. This is explained by the different binding strengths, swelling behaviour in the electrolyte, electrode porosities, and possible ‘buffer’ effects of the compact and the finely distributed binders.

Lithium storage alloys such as Sn/SnSb are promising new anode materials for Li-ion batteries. Due to a proper design of the active Sn/SnSb material as well as the composite electrode, capacities exceeding 500 mAh g−1 have been achieved with this system for more than 30 cycles. The observation of micro- and nano-structural changes in the composite electrode during charge/discharge cycling is of immense importance for a further improvement of the cycling performance. Electron microscopy (SEM and TEM) in combination with analytical techniques (EFTEM, EDXS and EELS) has been used for the characterization of Sn/SnSb raw powder as well as the Sn/SnSb composite electrodes. The pristine morphology and the changes of morphology during cycling of the electrode material have been studied. Furthermore, the chemical composition and particularly compositional fluctuations within the composite material have been investigated using EFTEM and EDXS. The electron microscopy results indicate that parts of the active material get finer during the initial cycles. Moreover, amorphous regions are detected in the cycled material. The experimental results are discussed with regard to the reaction mechanism of SnSb with Li.

A novel, quite flexible strategy for the surface pre-treatment of graphite anodes for lithium ion cells has been developed. The treatment involves a high temperature cleaning step in inert Ar atmosphere before treatment with gaseous reactants such as CO2 or O2. The effects of surface modification on the formation of the solid electrolyte interphase (SEI) and the corresponding irreversible charge losses are discussed by way of several examples. Morphology changes due to burn-off of carbon are particularly highlighted.

The galvanostatic cycling behaviour of Sn/SnSb composite electrodes has been studied in 1 mol l−1 LiClO4/propylene carbonate (PC), 1 mol l−1 LiPF6/ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1), and 1 mol l−1 LiClO4/PC saturated with trans-decalin (t-Dec). Capacities between 500 and 600 mA h g−1 (with respect to the mass of active material) were obtained. Reasons for the irreversible capacities are given and film formation on lithium storage metals and alloys is discussed. The observed coulombic efficiencies were slightly higher for the EC-containing electrolyte than for the PC-based one. Alternatively, improved efficiencies and stand-time behaviour were obtained when the PC electrolyte was saturated with t-Dec, which acts as a surfactant.

Surface pre-treatment of graphitic electrode materials for lithium ion cells has recently been shown to significantly reduce the irreversible consumption of material and charge due to the formation of the so-called solid electrolyte interphase (SEI) during battery charging. In this paper, we compare graphite powders and carbon fibres as model materials for X-ray photoemission spectroscopy (XPS) studies of the effects of surface pre-treatments. For carbon fibres, the surface carbon percentage was found to vary from 70–95% depending on the surface treatment, with corresponding changes in the relative proportion of graphitic compared to CO bonds, as determined from C 1s curve fits. In contrast, results from the graphite powders show very little change in surface chemical composition and an essentially constant C 1s lineshape dominated by graphitic carbon. SEM data show the carbon fibre cross-section to be composed of a radial array of layered graphite, leaving a surface consisting largely of prismatic planes, while the graphite powder consists of graphite platelets with the surface area predominantly of basal planes. We conclude that the chemical modification occurs at the prismatic planes, and that the powders are unsuitable as models for XPS studies of electrode surface modification, while the fibres are very well suited.

An atomic force microscope (AFM) was used to measure the distance dependence of the forces between microscopic-size glass spheres coated with gelatin and a solid surface in the presence of aqueous ...

In the process of substrate-induced deposition of carbon black, a printed wiring board (PWB) surface is first covered with a gelatin film. The subsequent immersion of such substrates into a deposit-able dispersion leads to deposition of dispersed particles on the surface of the substrate. Current studies show that an essential point in the successful preparation of deposit-able dispersions is control of surfactant and salt concentrations, both of which have a decisive influence on particle deposition. On one hand, the dispersion must be stable. For this purpose surfactants are used. On the other hand, the dispersion must be near the point where deposition can occur. This point is controlled by the appropriate addition of a salt, which screens the electric field of the surfaces and allows particles to approach to shorter distances during their Brownian motion. Atomic force microscope (AFM) has been used to measure distance dependence of the forces between microscopic-size glass spheres coated with gelatin and a solid surface covered with carbon black in the presence of aqueous solution.

Rechargeable lithium ion cells operate at voltages of ∼4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and corrosion of the negative electrode has to be anticipated, which leads to irreversible loss of electroactive material and electrolyte, and thus strongly deteriorates cell performance. To minimize these reactions, negative electrode and electrolyte components have to be combined bringing about the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface. This film hinders further electrolyte decomposition reactions and acts as membrane for the lithium cations, i.e., behaves as asolidelectrolytei2nt erphase (SEI). The present paper gives a review of our recent work in the field of negative electrodes in lithium ion batteries. The effects of the graphite anode surface and graphite anode surface modification on the formation of the SEI are discussed in detail by using the example: modification with carbon dioxide.

This article gives an overview on lithium alloys and lithium alloying metals for use as anodes in ambient temperature rechargeable lithium batteries. After a brief introduction about advantages and drawbacks of lithium alloy anodes and a chronological review of their development, principle concepts to overcome the problems with the dimensional stability of the metallic host materials will be presented. Recent work on promising multiphase (composite and/or intermetallic) tin-based lithium alloying materials will be highlighted.

The adsorption of gelatine in an aqueous solution on to the surface of FR4-type printed wiring boards (PWB) consisting of brominated epoxy resin and glass fibre was studied as a function of pH and of the presence of an anionic surfactant using the streaming potential and the charge titration technique. The highest adsorption occurred at a pH of between pHIEP,1

Abrasive stripping voltammetry is applied in order to characterize barium and strontium manganates-(V) and -(VI) in solid state phases. Voltammetric reduction peak potential values of KBaMnO4, Ba3(MnO4)2, Ba3(MnO4)2− x (BO3) x (x=0.031(1)), Ba5(MnO4)3OH, Ba5(MnO4)3Cl, Sr5(MnO4)3OH and BaMnO4 are shown to be proportional to the corresponding average Mn-O distances, which were determined from X-ray powder diffractometric data through Rietveld refinement analyses.

The performance and safety of rechargeable batteries depend strongly on the materials used. Lithium insertion materials suitable for negative and positive insertion electrodes are reviewed. Future trends, such as alternative materials for achieving higher specific charges are discussed. (orig.) 1041 refs.

The adsorption of cationic surfactant cetyltrimethylammonium bromide (CTAB) from aqueous solution onto carbon black was studied using charge-compensating polyelectrolyte titration for quantitative determination of the surfactant content in solution and X-ray powder diffraction analysis of air-dried dispersions. Sharp saturation was observed. The saturated surface concentration of the adsorbed CTAB was found to be the same in the dispersed and air-dried product. Fourier transformed infrared spectroscopy and extended X-ray absorption fine structure (EXAFS) analyses suggest -CTA+ and Br- ion sites in the dried product.

Battery electrode materials such as Li 2 Mn 2 O 4 and γ-MnO 2 are characterized in the solid state by cyclic voltammetry when mechanically attached to an electrode surface. At voltammetric scan rates in the mV/s range, identical peak potentials and essentially the same peak shapes are observed when compared with voltammograms recorded at conventional composite electrodes at scan rates in the μV/s range. The method provides a convenient tool for the rapid screening of battery electrode materials.