Poly(ethylene oxide) based electrolytes are systems in which ionic salts are dissolved into an amorphous EO matrix. Potentials developed earlier to model crystalline and amorphous bulk PEO systems are here used for the MD simulation at 400 K of the behavi
Potentials developed earlier for crystalline and amorphous bulk PEO systems have been used for the MD simulation of a PEO surface model. The surface comprises the outer region of a 122 Angstrom-thick sheet of PEO in which the PEO, -(CH2-CH2-O)(n)- chains
Thermal stability of the SEI layer on graphite in < Li(liquid electrolyte)graphite > half-cells has been investigated. DSC measurements reveal a two-stage exothermal reaction. The first, corresponding to a breakdown of the SEI layer, begins at 58 degrees
There is a considerable lack of detailed information on the structure of lithiated phases of popular-consensus positive electrode materials for lithium/polymer and lithium-ion/polymer batteries. Having illustrated this phenomenon for the specific cases o
It is demonstrated here that the electron redistribution occurring as lithium becomes incorporated into or extracted from a crystalline transition-metal oxide (TMO) host can be studied experimentally by single-crystal X-ray diffraction (XRD) for the case
An attachment is described for in situ X-ray diffraction studies in transmission mode of ion insertion processes in potential electrode materials. The method exploits the flat-cell geometry of the lithium polymer battery concept, in which the cell compone
Single crystals of V6O13 Were grown by chemical vapour transport (CVT) and subsequently electrochemically lithiated. The title compound, trilithium hexavanadium tridecaoxide, was the phase formed during electrochemical lithiation at 2.45 V versus Li/Li+.
Deformation electron density refinement of single-crystal X-ray data has been performed for V6O13 and for one of its electrochemically lithiated phases Li2V6O13. The electron rearrangement associated with lithium insertion is extracted by subtracting the
Single crystals of V6O13 were grown by chemical vapour transport and then electrochemically lithiated, The title compound, dilithium hexavanadium tridecaoxide, was the first phase formed during electrochemical lithiation at 2.65 V Versus Li/Li+. The Li2V
The Nafion, Dow and Aciplex systems – where the prime differences lies in the side-chain length – have been studied by molecular dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15 water molecules per (H)SO3 end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains. It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the H3O+/H2O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.
Molecular dynamics (MD) simulations have been made under imposed electric fields for crystalline LiPF6·PEO6, (LiPF6)1-x(Li2SiF6)x·PEO6, and (LiPF6)1-x(SF6)x·PEO6 for x = 0.01 under standard pressure and temperature conditions with the aim of identifying the conduction mechanisms in the systems. Contrary to the results of earlier experimental investigations where only cation mobility was observed, ionic transport is here found to occur in regions between the polymer hemi-helices, with a high transference number (0.9-1.0) for the PF6- anions.
The crystal structure and ionic distribution in the conduction plane of the partially exchanged Na+ beta-alumina system Li0.75Na0.47Al11O17.11 has been determined from single-crystal X-ray diffraction at 30 and 298 K, in combination with a single-crystal
The same experimental techniques as used earlier to characterize the composition and properties of the so-called solid electrlyte interphase (SEI) layer formed at the graphite-anode-electrolyte interface of a Li-ion battery are used here to acquire some degree of understanding of face phenomena occurring on the cathode side of the cell, even though the validity of the SEI-layer concept is still somewhat tenuous "cathode" context. We here probe cathode-related SEI phenomena for the three cases: LiMujO^ LiCoOz/LiNio gCoo 202, and carboncoated LLFePCU. The various layer types formed have been analyzed systematically for different salts, solvents, cycling modes, storage temperatures, etc., using photoelectron spectroscopy (PES). Depth-profiling of the layers formed was achieved using Al Ka radiation th Ar-ion sputtering; non-destructive depth-profiling was made possible using synchrotron radiation, and applied to the important case of carbon-coated LiFePO4. A number of trends have emerged from our studies, and some general models are proposed to reflect features characteristic of the various systems studied. Our results are related to the more familiar SEI-layer formed on graphite.
The structure of a mixed-ion Ba2+-K+ beta-ferrite, Ba0.39K0.39Fe11O17.03, has been determined by X-ray diffraction, and refined in the hexagonal space-group P6(3)/mmc, R(F)=3.4%, R(W)(F-2)=5.9%. At least two possible charge compensation mechanisms could
Silver and sodium have qualitatively different diffraction-determined ionic distributions in the conduction planes of a beta-alumina host. That this can imply different conduction mechanisms in the two cases is probed by partially exchanging Cd2+ ions in
A furnace is described for in situ X-ray diffraction studies, in transmission mode, of structural changes in electrode materials for Li-ion (polymer) batteries in the ambient to 300 degreesC temperature range. The method exploits the thin flat-cell geomet
Copper antimonide, Cu(2)sb, has been investigated as a negative electrode (anode) for rechargeable lithium batteries by in situ X-ray diffraction of Li/Cu2Sb cells. The data show that lithium is inserted into Cu2Sb with a concomitant extrusion of copper,
The structures of Li3 V6O13 and Li3+V6O13, 0.3, have been determined by single-crystal X-ray diffraction. Both compounds have the space group C2/m, with very similar cell parameters. In Li3V6O13, the Li atoms are found in the Wyckoff positions 4(i) and 2(b) with multiplicities of four and two, respectively. Since Li3V6O13 exhibits no superstructure reflections, it is concluded that Li3V6O13 contains one disordered lithium ion in an otherwise ordered centrosymmetric structure. On inserting more lithium into the structure, the Li3+V6O13 phase is formed with the homogeneity range 0 < < 1. It is concluded that the site for the extra inserted lithium ion is closely coupled to the position of the disordered lithium ion in Li3V6O13. A mechanism for this behaviour and for the further formation of the Li6V6O13 end-phase in the LixV6O13 system is proposed.
We have performed an ab initio study of the surface energies, surface electronic structures and work functions for the (1 0 0) surface of the, existent and hypothetical, cubic 3d (Sc–Cu), 4d (Zr–Ag) and 5d (La–Au) transition metal carbides. The calculated surface energies have been compared to predictions using a so-called bond-cutting model and a model based on the so-called bonding energies. The absolute values and rough trends of the surface energies are fairly well predicted within the simple bond-cutting model, as compared to fully self-consistent calculations, while both trends and absolute values are well reproduced within the bonding energy model. The electronic structure (densities of states) of the transition metal carbides at the surface and in the bulk have been calculated. The trends are discussed in relation to the behavior of the surface energy and the work function across the series.
The effect on polymer dynamics of adding methoxy-terminated poly(ethylene oxide) (PEO) side-chains with different lengths and separations to an amorphous long-chain PEO backbone has been studied by Molecular Dynamics (MD) simulation at 293 K and 330 K. The study is seen as having a direct general relevance to the optimal design of ion-conducting polymer hosts for both Li-ion battery and polymer fuel-cell applications. The MD box used contains a long-chain PEO backbone to which side-chains comprising 3, 6, 7, 8, 9 and 15 EO units are added. The chosen separations between the side-chains are 5, 10, 15, 20 and 50 EO units. All potentials used to describe these systems are taken from earlier work (J. Mater. Chem., 13 (2003) 214). The overall mobility of the polymer host system is found to have both minima and maxima at both temperatures for side-chain lengths in the range 6–9 EO units. This is almost totally independent of side-chain separation at 293 K, while the situation is more complex at 330 K.
Classical molecular dynamics modeling studies at 363 K are reported of the local atomic-level and macroscopic nanostructures of two well-known perfluorosulfonic acid proton exchange polymer membrane materials: Nation and Hyflon. The influence of the different side-chain lengths in the two polymers on local structure is relatively small: Hyflon exhibits slightly greater sulfonate-group clustering, while Nation has more isolated side chains with a higher degree of hydration around the SO3- side-chain ends. This results in shorter mean residence times for water molecules around the end groups in Nation. Hyflon also displays a lower degree of phase separation than Nafion. The velocities of the water molecules and hydronium ions are seen to increase steadily from the polymer backbone/water interface toward the center of the water channels. Because of its shorter side chains, the number of hydronium ions is similar to 50% higher at the center of the water channels in Hyflon, and their velocities are similar to 10% higher. The water and H3O+ diffusion coefficients are therefore higher in the shorter side-chain Hyflon system: 6.5 x 10(-6) cm(2)/s and 25.2 x 10(-6) cm(2)/s, respectively; the corresponding values for Nation are 6.1 x 10(-6) cm(2)/s and 21.3 x 10(-6) cm(2)/s, respectively. These calculated values compare well with experiment: 4 x 10(-6) cm(2)/s for vehicular H3O+ diffusion.