A recently reported new phase of LiCoO2, called LT-LiCoO2 (LT stands for Low Temperature) by the discoverers, was synthesized at 400°C and studied using X-ray diffraction and electrochemical de-intercalation of lithium. The first reports of LT-LiCoO2 give convincing evidence that the compound is layered with the same structure type as LiCoO2 prepared at 850°C (HT-LiCoO2). However, the electrochemical properties of LT and HT LiCoO2 are markedly different, which is hard to understand if the crystal structures are almost the same. A better understanding of the diffraction and electrochemical data is attained if the LT structure is assumed to be spinel related analogous to Li2Ti2O4. We show that the layered structure (with suitable lattice constants and layer spacings) and spinel structure give identical powder diffraction patterns. We also show that the formation energies of the layered and spinel structures are also identical using a lattice gas model with pair-wise atom-atom interactions.

NiO2 slabs made of edge-sharing NiO6 octahedra are the main structural parts of the positive electrode materials involved in Ni-Cd, Ni-M- and Li-LiNiO2 secondary batteries. These electrochemical systems are among the best ones for applications. The behavior of all these electrode materials can be optimized by substituting several cations for nickel.

The effect of iron and cobalt substitution has been investigated in detail. The oxidation state modifications resulting from the electrochemical cycling have been characterized from magnetic, conductivity, thermoelectric-power and Mössbauer studies. The overall results show that nickel ions are oxidized to the tetravalent state before cobalt ions. More surprisingly, the oxidation of iron-nickel mixed phases shows the simultaneous presence of tetravalent iron and nickel ions in the low spin configuration. For the first time, in situ M6ssbauer measurements have been performed during the cycling of a nickel-cadmium cell.

This cationic distribution results from the competition between the intrinsic redox properties of the 3d cations and the accommodation of the oxidation levels to the ligand field imposed by the prevailing cation.

Numerous layered compounds are interesting materials in which lithium intercalation occurs primarily without destruction of the host lattice. In many cases a rigid-band model is a useful first approximation for describing the changes in electronic properties of the host material with intercalation. This paper presents some recent experimental results obtained on transition-metal chalcogenide compounds and on transition-metal oxides as well. We shall observe, nevertheless, that the rigid-band model is not applicable to all of the intercalated materials. The applicability of the rigid-band model may be used as a test for the most desirable properties of a good intercalation material. This needs to be more extensively documented for their possible applications as insertion electrodes in solid state batteries.

Experimental results for a number of oxide host materials as electrodes in lithium batteries are compared in order to obtain a better understanding of the factors influencing the emf-composition relationships. These factors are divided into two main groups: Those that are consequences of the structure of the host lattice, and those who follow from the chemistry of the host material. Series of materials with the same structure, but different chemical composition (spinels and MO2(B)) are compared, as well as series of materials with the same chemical composition, LixV2O5, but different structure. These data show that the potential level is mainly determined by the host chemistry, although destabilisation of the host can also give a significant contribution. The host structure will determine the width of the composition interval as well as the inflexions on the emf-curve. The possibility for tailoring the emf by using mixtures of transition metals in the host lattice is discussed.

A fast in situ X-ray powder diffraction set-up working in transmission mode is used to explore the structural changes occurring on Li+ insertion into the active V6O13 component of the cathode in a thin-film < Li I polymer electrolyte | V6O13 > battery. It is confirmed that the V6O13 is indeed converted reversibly into three discrete phases, LixV6O13 for x = 1, 4 and 8, as the fully charged cell (ca. 3.OV) is discharged to 1.8V. The effect on the insertion process of repeated cycling with different currents has been studied. Cell collapse was induced after ca. 35 cycles for 0.2 mA/cm2. This was not reflected, however, in any significant change in the diffraction pattern from the battery. Moreover, the battery returned to normal functioning after lying on open circuit for 7 days. A gradual loss of reflection intensity is observed, but no particle line-broadening. The implications of these results are discussed as they relate to the nature of the solid-state insertion process of Li+ into V6O13.

The microscopic mechanism of the operation of the well - known “nickel” electrode involves the transport of protons through an outer layer of the Ni(OH)2 phase to the two-phase Ni(OH)2/NiOOH boundary, where the electrochemical reaction takes place. This boundary is displaced as the reaction proceeds. When it reaches the outer surface so that the NiOOH phase is in contact with the electrolyte, an additional process takes place, resulting in the rapid evolution of gaseous oxygen. Interpretation of the available thermodynamic data in terms of ternary phase equilibria shows that the equilibrium electrode potential should be more positive than that for the decomposition of water, as is experimentally observed.

Layered oxides AxMnO≈2,yH20 (A = Na, K, NH4, Cs or Mn2+) have been dehydrated and intercalated by lithium. Dehydration is accompanied by a shrinking of the interlayer space height depending on the size of A. The valence of Mn is reduced to +2 by reaction with n-butyllithium. Electrochemical studies of cells AxMnO≈2-graphite | LiClO4-PC|I Li showed two main reaction peaks at ca. 3V and below 2 V. The first reaction is a reversible reduction to a disordered Mn3+ phased. Capacities at the third cycle are ca. 300 Wh/kg. No marked difference was found as a function of A or of the degree of order of the starting compound.

Titanium disulfide is a particularly promising cathode material for very high cycle life applications in secondary lithium batteries due to the reversible nature of the intercalation of lithium into the host TiS2 lattice. It has long been known that the mechanical stress of the intercalation process is minimized if TiS2 crystal size is kept below 10μm. It has also been suspected that minimizing crystal thickness would improve the kinetics of at the onset of lithiation by minimizing the forces which would have to be overcome in expanding the host lattice. We have synthesized three different types of microcrystalline TiS2, two thin film and one powder, and have compared their performances to that of a large crystalline powder. Lithium ion diffusivity and pulse power performance of the four materials were compared. It was found that the two thin film materials exhibited extraordinary pulse power rate capabilities while the two powder materials were limited in their performance by the constraints of the composite cathode matrix.

We show that the conductivity maximum, well known for salt-in-polymer electrolytes is not the maximum conductivity in the system when the salts used are chosen for their resistance to crystallization at high concentration. The polymer + salt system, with increasing salt content, goes through a transition zone characterized by a maximum in glass transition temperature. Beyond this point additional salt serves to plasticize the salt-crosslinked polymer system, establishing thereby a region of increasing conductivity in which the conductivity can reach very large values. We show that “polymer in-salt” solutions constitute a new type of rubbery solid electrolyte in which the conductivity is dominated by cation motion. Such systems are true hybrids of the previously distinct “superionic glass” and “polymer electrolyte” types of amorphous solid conductors.

We report 7Li spin lattice relaxation times at 12.82 MHz over a range of temperatures for liquid electrolytes of various salt:polymer ratios, and compare the NMR correlation time obtained at the temperature of the T1 minimum with the conductivity relaxation time at the same temperature. We find that at low salt contents the two relaxation times have the same value, but beyond the “salt-inpolymer to polymer-in-salt transition” zone at the Tg maximum, the two times increasingly separate. This is taken as evidence for the onset of cation-matrix mobility decoupling, which maximizes at the pure salt extreme.

A solid state electrochemical cell, K1-xFe11O17/potassium beta-alumina/metal gauze, is presented which is capable of producing a beam of potassium vapour. The generation of potassium vapour has been demonstrated and the cell has been used to dope ZnSe during growth of the chalcogenide by molecular beam epitaxy, thus forming p-type ZnSe. The electrochemical source has the advantage that the potassium flux is controlled by the current passing through the cell and eliminates the need to handle potassium metal. Cyclic voltammetric measurements at 350'C suggest that potassium metal is first generated electrochemically by a mechanism of nucleation and growth, then evaporates from the cell.

Deuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at σ75% and σ100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.

The use of transient and steady-state 4-probe techniques for the evaluation of the limitations to performance in solid-state electrochemical devices is described. The application of sequential, bipolar square-wave current pulses to a solid polymer cell with two internal reference electrodes allows separation of the polarization behavior of the various components of the cell, and indicates the rate limiting processes in the cell. Careful design of the experimental cell and appropriate selection of current pulse width allows evaluation of fundamental kinetic and transport properties, as well as activation parameters. Steady state constant-current measurements using 4-probe cells allows in situ observation of interface stability and/or polarization as a function of time as the cell is cycling.

The excitation and fluorescence spectra of PEOx EuBr3 (x=8, 16, 20, 24, 32) and PPO32 EuBr3 were recorded and analyzed in terms of the barycenters of each level of the ground septet of Eu3+. The site symmetry of the Europium ion is tentatively assigned to the C1,2, C5 or C2v cases. The maximum fluorescence intensity for each composition, together with the measured values for the lifetimes, suggest the possibility of these two polymeric electrolytes being used as fluorescent materials.

Ionically conducting materials containing PEO were prepared from telechelic di(methyl-diethoxy-silane) PEO, synthesized by the hydrosilylation of telechelic diallyl-PEO with methyldiethoxysilane. The network is obtained by the usual sol-gel chemistry. Then, it is filled with LiClO4 by diffusion of the salt and further drying. A comparison is made with the same kind of materials crosslinked using urethane chemistry. Diffusion studies show that the diffusion coefficient of solvent is similar for both types of materials, whilst the ionic conductivity is higher for the networks crosslinked with siloxane bonds. An experiment of diffusion of LiClO4 without solvent showed that this salt has a diffusion coefficient of the order of 2.10-8 cm2.sec-1 at 34°C. The conductivity calculated from this determination is compatible with the mechanism of lithium cation transport by the diffusion of salt molecules. Elasticity modulus measurements show that the salt aggregates are essentially located within the crosslinks at low concentration, but also in the PEO chains for salt concentrations higher than 1 mol/l.

New ion conductive polymer complexes were formed by dissolving poly(1-butyl-4- vinylpyridinium) salts into room temperature molten salts consisting of 1-butylpyridinium salts and aluminium chloride. The viscoelastic films were fabricated from the molten salts added at least 10 mol % of the polypyridinium salts. The ionic conductivities of the polymer complexes were in the range of 10−3−10−4 Scm−1 at room temperature and were affected by their composition.

Polypyrrole has been synthesized electrochemically at current densities from 6.4 μA/cm2 to 3.84 mA/cm2. Low current density is crucial to the formation of a highly conjugated modification as shown by the low value of the π-π* transition energy (2.83 eV). The low current form displays a cyclic voltammogram with a detailed structure with narrow peaks. Following the presence and evolution of the peaks is a powerful diagnostic method of monitoring the state of the polymer. The solvent (water-free propylene carbonate or acetonitrile) can be reversibly exchanged during oxidation/reduction cycling and has little effect on the nature of the polymer formed, but influences the properties during the doping process greatly. In contrast, the ion present during polymerization (ClO4 or CF3SO3) seems to irreversibly influence the morphology of the film. The highly conjugated, low current form is to be preferred as a well-defined point of reference close to the intrinsic properties of pure polypyrrole.

We describe in this paper an experiment involving an electronically conductive polymer (ECP) which, to our knowledge, has not been described previously. A free-standing ECP (polypyrrole)-based membrane separates a solution of an electron donor from a solution of an electron acceptor. Because the ECP is both electronically and anionically conductive, the membrane can transport electrons from the donor solution to the acceptor solution, and anions in the opposite direction, such that a sustainable electron-transfer reaction is driven across the ECP membrane. We demonstrate such transmembrane electron/ion-transfer processes using both an inorganic and a biochemical electron donor/acceptor system. The biochemical case is of particular interest because we show that the reduced form of the enzyme glucose oxidase can give its electrons directly to the synthetic metal. Direct electron transfer is usually not possible at inorganic metals.

Thin films of the electrically conducting polymer, poly(3-hexylthiophene) (P3HT), were developed as sensors for hydrazine vapor at the part-per-billion level. The P3HT films were fabricated by a spin coating technique onto quartz substrates incorporating gold interdigitated electrodes, and were rendered conductive by doping with an NOPF6 solution. The sensors respond strongly and instantaneously to hydrazine concentrations as low as 1 part-per-billion with a measurement accuracy of ±20%. In addition, the sensors exhibited excellent environmental stability, long shelf life, and good interference rejection.

The microwave properties of polypyrrole, polyaniline and poly(3-hydroquinonylpyrrole) films were examined as a function of doping level, conductivity, counter anion and thickness. The microwave transmittance of the polymer films was varied from less than 10% to greater than 90%; by oxidizing and reducing the polymers. The potential use of conductive polymers in the design of an electromagnetic modulator for the tunable attenuation of microwave radiation is described.