O. Haas

Magnesium insertion electrodes for rechargeable nonaqueous batteries : a competitive alternative to lithium?

Magnesium-based rechargeable batteries might be an interesting future alternative to lithium-based batteries. Here the available results of research, both on rechargeable negative electrodes based either on metallic magnesium or alternative materials, and on materials suitable as positive, magnesium-inserting (counter)electrodes for secondary magnesium batteries, are critically reviewed. The reversible magnesium-metal electrode was scarcely investigated and remains poorly understood. More data are available on host materials capable of reversible magnesium insertion, which are compared with lithium-inserting materials.

Study of radiation-grafted FEP-G-polystyrene membranes as polymer electrolytes in fuel cells

Proton exchange membranes for fuel cell applications were synthesized by pre-irradiation grafting of styrene/divinylbenzene mixtures into poly(fluoroethylene-co-hexafluoropropylene) films and subsequent sulfonation. Grafting of pre-existing films overcomes the problem of shaping the grafted polymer into thin membranes and makes this process a potentially cheap and easy technique for the preparation of solid polymer electrolytes. The grafted membranes were characterized by measuring their ion exchange capacity, swelling, specific resistivity and area resistance. Due to their thickness in the range 67–211 μm, some of the membranes have a considerably lower resistance than the most widely used membrane Nafion® 117 (DuPont). The short-term and long-term performance of these membranes was investigated in H2O2 fuel cells. Thin (< 100 μm), highly crosslinked (12% divinylbenzene) membranes show the best performance in the fuel cells. Tests for periods of up to 1400 h were performed to examine membrane stability and the degradation of grafted membranes.

DIRECT IN SITU EVIDENCE FOR PROTON/ANION EXCHANGE IN POLYANILINE FILMS BY MEANS OF PROBE BEAM DEFLECTION

Probe beam deflection (PBD) was used to monitor the ion exchange between polymer film and bulk electrolyte during the redox reaction in polyaniline in aqueous electrolyte (HCl, HClO 4 , H 2 SO 4 ). The PBD results clearly show that protons as well as anions are exchanged during the first oxidation process

Characterization of Layered Lithium Nickel Manganese Oxides Synthesized by a Novel Oxidative Coprecipitation Method and Their Electrochemical Performance as Lithium Insertion Electrode Materials

Lithium nickel manganese oxides, LiNi 1-y Mn y O 2+δ , (0 ≤ y ≤ 0.5) were prepared via a new solution technique. The corresponding mixed nickel manganese hydroxide precursors were synthesized in an oxidative coprecipitation method. Subsequent calcination in the presence of LiOH leads to crystalline products with a partially disordered layered-type α-NaFeO 2 structure. X-ray photoelectron spectroscopic analysis has indicated a strong enrichment of lithium at the surface. The electrochemical performance of these materials as positive electrodes in lithium-ion batteries was evaluated as a function of the calcination temperature and manganese content. A calcination temperature of 700°C leads to the best cycling stability. At this temperature, a sufficiently high degree of crystallinity was achieved, having a strong influence on the cycling stability of these 4 V materials. The specific charge and cycling stability obtained for the solution-prepared pure lithium nickel oxide, LiNiO 2 , was low, but was significantly enhanced by replacing some nickel with manganese. With increasing manganese content, the specific charge increased to about 170 mAh g -1 for materials with a Ni:Mn ratio of about 1:1. Ex situ magnetic susceptibility measurements proved that during lithium deinsertion, the trivalent manganese is preferentially oxidized, and seems to be the more reactive redox center in these oxides.

Vanadium Oxide Nanotubes. A New Nanostructured Redox‐Active Material for the Electrochemical Insertion of Lithium

Vanadium oxide nanotubes were prepared in a modified sol-gel reaction of vanadium oxide triisopropoxide conducted in the presence of the structurally directing hexadecylamine and followed by hydrothermal treatment. The tubes consist of concentric shells of highly crystalline vanadium oxide separated by alternating organic amine layers. The template molecules were removed without structural breakdown of the nanotubes by a combined ion-exchange reaction and extraction process. The vanadium oxide nanotubes are redox-active and can electrochemically insert lithium reversibly. A specific charge up to 180 mAh g -1 (with respect to the oxide) was measured for Li + insertion into porous electrodes containing template-free nanotubes. The specific charge decreased during cycling, indicating a loss of electroactivity.

Metal Oxide Cathode Materials for Electrochemical Energy Storage: A Review

Due to their rather low molecular weight and their favorable electrochemical and solid‐state properties, first row transition metal oxides seem to be specially attractive as cathode materials in electrochemical energy storage systems. Therefore, we undertook a detailed overview, covering electrochemical, conductivity, ion diffusivity, spectroscopic, and other physico‐chemical data on metal oxides in relation to their behavior in batteries. Metal oxide‐based primary batteries have achieved a high technological level and yield energy densities of up to 300 Wh kg−1 or 880 Wh l−1. Oxide‐based secondary batteries, on the other hand, typically yield less than 100 Wh kg−1. Based on the present review, V, Cr, Mn, and Co oxides seem to be the most promising solid‐state cathode materials for future high performance secondary batteries.

Impedance analysis of electrodes modified with a reversible redox polymer film

The study of the kinetics of an electrode coated with a redox polymer film has been carried out using an impedance technique. A theoretical model is proposed which takes into account the diffusion of the active centres. Experimental results are presented for a glassy carbon electrode coated with a [Ru(bpy)2 poly(4′-vinylpyridine)Cl]Cl film. There is good agreement between these results and the model.

Electrochemical insertion of lithium, sodium, and magnesium in molybdenum(VI) oxide

Abstract The electrochemical insertion of divalent magnesium cations into orthorhombic molybdenum(VI) oxide was studied with regard to their use as electroactive species in ion-transfer battery systems and compared to the insertion of Li + and Na + . Specific charges of up to 300 and 240 Ah kg −1 were obtained in organic, propylene carbonate-based electrolytes for the lithium and sodium insertion, respectively, in the first reduction half-cycle. Reversible Mg 2+ insertion could be demonstrated in a room temperature molten salt electrolyte consisting of 3 wt.% MgCl 2 , 41 wt.% 1-ethyl-3-methylimidazolium chloride, and 56 wt.% AlCl 3 . Specific charges of up to 160 Ah kg −1 were obtained with MoO 3 in the first reduction half-cycle. The Mg 2+ insertion process can be enhanced using an organic electrolyte with traces of H 2 O. In 1 M Mg(ClO 4 ) 2 /acetonitrile with 3 mol% of H 2 O, specific charges of up to 210 Ah kg −1 were measured in the first reduction.

Impedance investigation of the charge transport in film-modified electrodes

Abstract Two kinetic models which can explain the coupling between electrochemical charge transfer and the charge transport in polymer films of film-modified electrodes are analyzed. The first one is based on a diffusion-like process due to the mutual electron exchange between adjacent redox centers. The second one assumes a finite conductivity of the film. The electrochemical impedances characteristic of the models have been derived and also simulated numerically. Some experimental impedance measurements which were obtained from a glassy-carbon electrode modified with a redox-polymer film are reported and discussed in terms of these two models. The influence of film inhomogeneities on the impedance characteristics is also discussed.

Optimized zinc electrode for the rechargeable zinc–air battery

For the development of a long-lived, electrically rechargeable zinc–air battery the structure and wettability of pasted zinc electrodes were optimized. Pasted zinc electrodes containing 1 to 10% cellulose but having almost the same nominal capacities were prepared and tested in zinc/oxygen cells. The effect of discharge rate on cell voltage and delivered capacity, as well as the maximum power, were measured. Furthermore, cell charge–discharge behaviour and cycle life were examined. After different times of operation, the porosity and the pore size distribution of the pasted zinc electrodes were measured by means of mercury porosimetry. The cycle life and peak power drain capability of the Zn/oxygen battery could be substantially improved by the addition of 10wt% cellulose to the pasted zinc electrode.