Band 226, Heft 5-6 -

Ion transport through a Ca30 glass, a sodium ion (Na + ) conductor, has been induced by bombardment with a potassium ion (K + ) beam. The measurement of back side ion currents as a function of the ion beam kinetic energy by means of the recently developed BIIT (bombardment induced ion transport) approach allows determining the conductivity of the material. Measurement of this conductivity as a function of the temperature allows deriving the activation energy for ion transport as 0.99 eV ± 0.01 eV in perfect agreement with impedance spectroscopy. While the conductivity as well as the activation energy clearly correspond to the bulk property, i.e. the transport of Na + , depth profiling of the glass sample after the BIIT experiment exhibits K + profiles reaching up to 100 nm into the glass. Ultimately, modeling of the experimental data by means of the Nernst–Planck–Poisson theory provides access to a quantitative understanding of the conductivities and the diffusion profiles under the condition of competing Na + /K + ion transport.

Metastable nanoclusters grown on surfaces by vapour deposition or molecular beam epitaxy techniques have become an active topic in surface science because of their potential to display new physical properties useful for applications. Atomistic modelling and Kinetic Monte Carlo (KMC) simulations of these processes are reviewed with emphasis on two-component adatom systems. The situation we consider is that two types of atoms are co-deposited to the substrate. In this field of binary growth, systematic theoretical investigation is only at its beginning. Surface diffusion and nucleation leads to the formation of two-dimensional islands, before two-dimensional cluster growth sets in. In distinction to well-known growth scenarios for one species of adatoms, a wealth of new aspects arises in binary systems. Already in the regime of submonolayer growth, differences in adatom diffusion coefficients and binding energies make it necessary to generalise traditional scaling relations for island densities. Surface segregation and compositional fluctuations in growing 3-D clusters are issues requiring renewed examination under the point of view that the atomic short-range order, which is frozen in the bulk, was generated through the surface kinetics during previous stages of growth. We discuss the current theoretical understanding and experimental implications of these problems, including a description of perpendicular magnetic anisotropy (PMA) in metastable CoPt 3 nanoalloys, as detected recently.

Three novel lithium salts, lithium bis(pentafluorophenyl)amide LiN(Pfp) 2 , lithium pentafluorphenyl(trifluormethylsulfonyl)imide LiN(Pfp)(Tf) and lithium pentafluorphenyl(nonafluorbutylsulfonyl)imide LiN(Pfp)(Nf) were synthesized and characterized with respect to their thermal and electrochemical properties. LiN(Pfp) 2 decomposes at 108 ºC, whereas Li-N(Pfp)(Tf) and Li-N(Pfp)(Nf) show a much higher thermal stability of 307 ºC and 316 ºC, respectively. The ionic conductivity at 100 ºC measured by means of impedance spectroscopy decreases in the order LiN(Pfp)(Tf) > LiN(Tf) 2 > LiN(Pfp)(Nf). Both, the activation energy and entropy for ion conduction in the new salts are lower than in LiN(Tf) 2 (LiTFSI), most likely due to the lower symmetry of the new anions. The electrochemical stability and ionic conductivity of LiN(Pfp)(Tf) and LiN(Pfp)(Nf) solutions (0.1 mol/l) in ethylene carbonate/dimethyl carbonate ( 1:3 w/w) are slightly lower than those of the LiTFSI solution, but still sufficient for application in lithium ion batteries. The high thermal stability of the novel salts and their stability towards hydrolysis makes them attractive candidates for overcoming the drawbacks of LiPF 6 -based electrolytes at elevated temperatures.

Electrochemical energy storage systems using graphite as both the negative and the positive electrode have been proposed as “dual-graphite cells”. In this kind of electrochemical system, the electrolyte cations intercalate into the negative electrode and the electrolyte anions intercalate into the positive electrode, both based on graphite, during the charging process. On discharge, cations and anions are released back into the electrolyte. So far, the systems proposed in literature are primarily based on Li + and PF 6 - intercalation/de-intercalation into/from graphite from non-aqueous organic solvent based electrolytes. As the positive electrode potential during charging always exceeds 4.2 V vs. Li/Li + , the organic electrolyte starts to decompose at these highly oxidizing conditions resulting in insufficient discharge/charge efficiencies. The replacement of organic solvent by ionic liquids (ILs) leads an increased stability of the electrolyte towards oxidation and thus to remarkably higher efficiencies as well as an increased cycling stability. In fact, ionic liquids provide extended anodic electrochemical stability and in addition, no solvent co-intercalation occurs in parallel to anion intercalation at high potentials. Here, we present highly promising results for “dual-ion cells” based on a graphite cathode and an ionic liquid based electrolyte, namely N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr 14 TFSI). As the compatibility of this IL with graphite anodes is poor, alternative anodes such as metallic lithium or lithium titanate (Li 4 Ti 5 O 12 , LTO) are used. Consequently, the “dual-graphite” cell is renamed to “dual-ion” cell. In addition, the calculation of the specific energy of these systems will be in the focus of the discussion.

There is considerable interest in plastic crystalline electrolytes which have good room temperature ionic conductivities and potential technological applications as membranes for devices such as batteries. Conductivity and X-ray absorption spectroscopy measurements have been used to study succinonitrile (1, 2-dicyanoethane) doped with copper(I) and (II) triflate (trifluoromethanesulfonate) and TFSI (bis(trifluoromethane)sulfonimide). The conductivities at room temperature are reasonably good, particularly for Cu(I)TFSI doped at 1 mol %, where the conductivity is ∼1 × 10 3 S cm -1 , which is consistent with previous work on this system. The Cu K-edge EXAFS in 1 mol % doped copper salts show that in all cases, whether Cu(I) or Cu(II), the ion is predominantly in a well-defined and ordered local environment. A tentative model of the conduction process is described that will account for this local structural information; however, the process is clearly complex even in these apparently simple systems.

Z- and X-cut lithium niobate samples with varying lithium content from 48.3 to 50.0 mol % are investigated at high temperatures. Electrical and electromechanical properties are obtained by impedance spectroscopy. Mixed ionic and electronic conductivity in the temperature range from 500–900 ºC is found to be thermally activated. For 700 ºC and 1000 ºC the diffusion coefficient of lithium ions is calculated. The resonance frequency and the inverse Qf product are determined as a function of temperature up to 900 ºC for shear and thickness mode vibrations. In addition, the tracer diffusion of 18 O is investigated by SIMS/SNMS. The 18 O depth profile is analyzed and the lithium concentration dependent oxygen diffusion coefficient at 950 ºC for 49.9 mol % Li 2 O is determined to be D O ≈ 3 × 10 -17 m 2 /s .

We report on conductivity measurements of LiNbO 3 single crystals with congruent composition in ambient atmosphere between 449 and 727 K which include the lowest temperatures covered so far. The ionic DC conductivity observed along the c -axis at, e. g. , 650 K is 6.7 × 10 -9 S/cm and shows an activation energy of 1.33 eV. The corresponding Li + diffusion coefficients range between 2.5 × 10 -22 and 1.4 × 10 -16 m 2 /s. These results are perfectly consistent with our conductivity results in the high-temperature regime as well as SIMS measurements published recently (Rahn et al. , Phys. Chem. Chem. Phys. 14 (2012) 2427). From the Li + diffusion coefficients obtained here a Haven ratio of 0.7(2) can be deduced.

We investigated lithium self-diffusion in amorphous lithium niobate layers between 298 and 423 K. For the experiments, amorphous 6 LiNbO 3 / 7 LiNbO 3 isotope hetero-structures were deposited by ion beam sputtering and analysed after diffusion annealing by secondary ion mass spectrometry (SIMS). This arrangement allows one to study pure isotope interdiffusion. The results show that the diffusivities obey the Arrhenius law with an activation enthalpy of 0.7 eV, which is considerably lower than the activation enthalpy found for LiNbO 3 single crystals in literature. Consequently, the Li diffusivities are higher by at least eight orders of magnitude in the amorphous samples in the temperature range studied.