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.
A diffraction profile is here derived from classical Molecular Dynamics (MD) simulation for the hydrated perfluorosulphonic acid fuel-cell membrane material Nafion at 363 K using a 76 angstrom x 76 angstrom x 76 angstrom box. The MD simulation reproduces the phase-separated nanoscale structure of Nafion and water channels. No specific structural features, such as a characteristic channel diameter, could be distinguished. Nevertheless, the envelope of the simulated diffraction profile based on 6000 MD "snapshots" reproduced well the key features of the experimental SAXS profile. This draws into questions previous interpretations of diffraction data for the Nafion (R) system which involve simplistic notions of channel- and cluster-diameter.
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 first discharge of the Li+ ion anode material LiSn2(PO4)3 was investigated with Mössbauer spectroscopy and electrochemical techniques. Mössbauer spectroscopy provided insight into the structure of the tin atoms of the fully discharged anode materials. Spectra consist of overlapping peaks, which are assigned to noncrystalline β-Sn and Li–Sn alloy domains. An analysis of the relative intensities of the Mössbauer spectra shows the relative abundance of β-Sn increases at the expense of the Li–Sn alloy as the discharge rate increases. Cell polarization occurs at higher discharge rates, leading to inefficient electrode utilization and poor cycling performance. Sluggish Li+ ion diffusion through the amorphous Li3PO4 network that is formed early in the discharge process might be responsible for the poor electrochemical performance and the accumulation of unalloyed tin.
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
X-Ray photoelectron spectroscopy (XPS) has been used to characterise the surfaces of carbon-coated Li2FeSiO4 cathodes extracted from Li-ion batteries in both a charged and discharged state. 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6) based electrolytes were used with ethylene carbonate (EC) and diethyl carbonate (DEC) as organic solvents. The LiTFSI-based electrolyte exhibited high salt stability and no significant formation of LiF. However, solvent reaction products from EC were found together with lithium carbonate. A LiPF6-based electrolyte, on the other hand, showed inferior salt stability with LixPFy, LixPOyFz and LiF species formed on the surface. Solvent reaction products together with lithium carbonate were also found. There are also indications that Li2FeSiO4 is degraded by the HF formed in the electrolyte by the hydrolysis of LiPF6. A better understanding of the surface chemistry of carbon-coated Li2FeSiO4 after the first cycles in a Li-ion battery has thus been achieved, thereby facilitating the optimisation of Li-ion batteries based on this potentially cheap and electrochemically most promising cathode material giving excellent capacity retention: <3% drop over 120 cycles.
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.