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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.

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 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.

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.

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.

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.

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.

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.

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.

The improvement of cycling behaviour and self discharge of lithium—carbon intercalation electrodes as well as metallic lithium electrodes in polysulfide-containing propylene carbonate-based electrolyte is demonstrated. Cyclic voltammetry of LiC n electrodes indicates a more complex reductive behaviour only during the first charge/discharge cycle than in an additive-free electrolyte. The products of the polysulfide reduction seem to improve the properties and the quality of the film that is also produced in the absence of S x 2− and promotes its formation on Li or LiC n , respectively. The improvement may be related to thinner polymer—electrolyte interface layers (PEI layers) and/or a larger amount of insulated inorganic compounds in the PEI layers.

The high packing density of lithium is a significant advantage of lithium insertion into metallic matrices that can be achieved in lithium alloys compared with lithium intercalation into carbonaceous materials. Moreover, the operating voltage of lithium-alloy anodes may be chosen well-above the potential of metallic lithium and the solvent co-intercalation has not been observed at lithium-alloy electrodes. On the other hand, the volume changes related with insertion/removal of lithium into/ from the metallic matrices cause pulverization and rapid failure of lithium-alloy anodes. This paper demonstrates the dramatic effect of the morphology of the metallic host matrix on the performance of the lithium-alloy anodes. Two component host matrices with ultrasmall (submicro- or nanoscale) particle size show an impressive cycling performance. This is related with the small absolute changes of the dimensions of the individual particles and also with the fact that in the first charging step the more reactive particles are allowed to expand in a ductile surrounding of still unreacted material.

On lithium-carbon intercalation electrodes a thin protective layer on the electrode surface is formed during the first charge/discharge cycle. This film formation is investigated by means of impedance spectroscopy and cyclic voltammetry. Uncoated LiC n electrodes show a continuous increasement of the low frequency semicircles during the first charge/discharge cycle. The protective films can be simulated by a polymer precoating. But any coating of the electrode should influence the behaviour due to modification of the film and/or modification of the surface in general. The influence of different coatings like poly-2-vinylpyridine, poly(ethylene oxide) and TiO 2 on the electrochemical behaviour of lithium-carbon electrodes is demonstrated in propylene carbonate electrolyte. Inpedance studies during charge and discharge show that the low frequency semicircles decrease due to a modification of the resistances and the capacities. Cyclic voltammograms are also clearly influenced by the coatings and demonstrate differences in the electrode kinetics and the film formation from decomposition products of the electrolyte.

To study the filming mechanism of graphite-based LiCn electrodes, electrochemical reduction of graphite materials was carried out in 1 M LiClO4/ethylene carbonate (EC)-1,2-dimethoxyethane (DME) (1:1 by volume). Due to film forming a peak at potentials around 0.8 V versus Li Li + was observed during the first reduction. The reversibility of this peak was examined by cyclic voltammetry; in addition, the crystal expansion/contraction was checked by means of dilatometry. The results indicate that ternary solvated graphite-intercalation compounds (GICs) were formed at those potentials leading to drastic expansion of the graphite matrix (>150%). These Li(EC)y1(DME)y2Cn-GICs decompose and build up a protective layer on the graphite that prevents further solvent co-intercalation. The beneficial effect of EC-containing electrolytes on the stability of lithium-carbon anodes seems to be related to inorganic films formed via secondary chemical decomposition of electrochemically formed EC-GICs. The key-role of inorganic films is also demonstrated by the fact that inorganic additives, such as carbon dioxide, suppress the formation of solvated GICs. Furthermore, it can be seen that lithium-carbon negatives can even be operated in inorganic electrolytes such as SO2 and SOCl2.

The beneficial effect of some inorganic electrolyte additives like CO2, N2O, CO, CO-complexes and polysulfides Sx2− on self-discharge and cycling behaviour of metallic lithium electrodes as well as of carbon—lithium intercalation electrodes is demonstrated in propylene carbonate (PC) electrolytes. Obviously, the above listed additives promote the formation of thin inorganic films on Li or LICn, respectively. Films of this kind, being permeable to unsolvated Li+ cations and almost impermeable to organic solvent molecules, are also formed in the absence of any additives, however, the additives seem to improve their quality and/or rate of formation. Impedance spectra indicate that the additives decrease in particular low frequency resistances. These low frequency resistances are apparently dominated by diffusion in pores, giving rise to curved Warburg branches. In view of the polymer electrolyte interphase (PEI) model the strong effect of the additives on the low frequency resistances may be related with smaller amounts of polymeric electrolyte decomposition products, i.e., thinner PEI layers. Although the chemical nature of the films formed in the presence of inorganic additives is still unknown, it may be concluded that a variety of material-different inorganic films is characterized by basically similar selective transport properties for Li+ ions and organic solvent molecules.

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, during battery charging. In this paper we compare graphite powders and carbon fibres as model materials for studies of the effects of CO 2 pre-treatments on solid electrolyte interphase (SEI) formation using X-ray photoemission spectroscopy (XPS). We observe significant modification in the surface elemental composition as a function of CO 2 treatment temperature for carbon fibres, but no strong changes for graphite powders. We conclude that the predominance of the relatively unreactive basal plane in the surface area of the powders makes them far less suitable for detailed XPS studies than the fibres, where the more reactive prismatic planes predominate.

The low viscosities of the linear sulfites dimethyl sulfite and diethyl sulfite are suggesting an investigation of their suitability as low viscosity co-solvents for ethylene carbonate based electrolytes. In this study, electrochemical performances at graphitic anodes and conductivities in the temperature range −60 to +60°C are presented. Comparisons with the linear carbonates dimethyl carbonate and diethyl carbonate, which have been currently used as low viscosity solvents in lithium ion batteries, are made.

Graphite surface modification by silylation in nonaqueous solution has been examined. Silane coupling with hydroxyl-containing carbon surface species, such as hydroxyl-groups and adsorbed water is assumed to be the main surface reaction introduced by this modification treatment. In terms of reduced irreversible charge losses, best results were obtained when graphites pre-oxidized in oxygen atmosphere at elevated temperatures have been silylated.

A novel partly fluorinated solvent for lithium ion batteries, N,N-dimethyl trifluoracetamide (DTA), is presented. The physical properties and the electrochemical behaviour of this compound are investigated. With its low viscosity and high boiling point and flash point it could replace low viscosity solvents (thinners) such as dimethyl carbonate or diethyl carbonate currently used in lithium ion battery electrolytes to achieve the demand for safer lithium ion batteries. The outstanding filming properties allow to use the DTA even in mixtures with PC in amounts of 10%. With both solvents having a freezing point below −40°C, the mixture is promising as low temperature electrolyte.

Hydrocarbons show considerable surface activity in organic electrolytes; they, at least partially, displace the polar organic solvent molecules from any solid/electrolyte interface. Saturated hydrocarbons are chemically stable even versus lithium or lithium-rich alloys, and thus they are able to delay the irreversible reduction of organic electrolytes by these highly active negatives, i.e., they delay corrosion and surface filming of the negatives. As surface filming of lithium strongly controls the growth of lithium dendrites during electroplating, a delay in the filming process significantly decreases dendrite growth. Prevention of dendrite growth, however, requires speedy protection of freshly created “dynamic’ surfaces and, hence, a high concentration (and solubility) of the hydrocarbon surfactant. On the other hand, for the protection of “static‘ electrodes under open cell conditions, even relatively insoluble surfactants may suffice.

Normal pressure thermal decomposition of CrO 3 containing ca. 2.5 wt.% SO 3 yields a new chromium oxide phase CrO x (SO) 3 , x being close to 2.5. This material is different from Cr 2 O 5 and is practically free from sulfur. Sulphur trioxide obviously acts as a catalyst for oxygen removal. Compared with Cr 3 O 8 , CrO x (SO 3 ) is characterized by better high rate discharge behaviour. Moreover, CrO 3 contamination in CrO x (SO 3 ) is much lower than in Cr 3 O 8 prepared at normal pressure; this is of importance for the long-term storage behaviour of Li/CrO x batteries. The low-rate energy density of CrO x (SO 3 ) is inferior to that of Cr 3 O 8 .