General observation of lithium intercalation into graphite in ethylene-carbonate-free superconcentrated electrolytes

Lithium-ion batteries have exclusively employed an ethylene carbonate (EC)-based electrolyte to ensure the reversibility of the graphite negative electrode reaction. Because of the limitation of electrolyte compositions, there has been no remarkable progress in commercial lithium-ion batteries despite active research on positive electrode materials. Herein, we present a salt-superconcentrating strategy as a simple and effective method of universalizing a graphite negative electrode reaction in various organic solvents. A dilute electrolyte (e.g., 1 mol dm(-3)) of sulfoxide, ether, and sulfone results in solvent cointercalation and/or severe electrolyte decomposition at a graphite electrode, whereas their superconcentrated electrolyte (e.g., >3 mol dm(-3)) allows for highly reversible lithium intercalation into graphite. We have found a unique coordination structure in the superconcentrated solution and an anion-based inorganic SEI film on the cycled graphite electrode, which would be the origin of the reversible graphite negative electrode reaction without EC. Our salt-superconcentrating strategy, expanding the graphite negative electrode reaction in various organic solvents other than EC, will contribute to the development of advanced lithium-ion batteries with high-voltage and fast-charging characters based on new EC-free functional electrolytes.

Ligand-Exchange Processes on Solvated Lithium Cations: DMSO and Water/DMSO Mixtures

Solutions of LiClO(4) in solvent mixtures consisting of dimethylsulfoxide (DMSO) and water, or DMSO and gamma-butyrolactone, were studied by (7)Li NMR spectroscopy (for complexation by cryptands in gamma-butyrolactone as a solvent, see: E. Pasgreta, R. Puchta, M. Galle, N. J. R. van Eikema Hommes, A. Zahl, R. van Eldik, J. Incl. Phen., 2007, 58, 81-88). Chemical shifts indicate that the Li(+) ion is coordinated by four DMSO molecules. In the binary solvent mixture of water and DMSO, no selective solvation is detected, thus indicating that on increasing the water content of the solvent mixture, DMSO is gradually displaced by water in the coordination sphere of Li(+). The ligand-exchange mechanism of Li(+) ions solvated by DMSO and water/DMSO mixtures was studied using DFT calculations. Ligand exchange on [Li(DMSO)(4)](+) was found to follow a limiting associative (A) mechanism. The displacement of coordinated H(2)O by DMSO in [Li(H(2)O)(4)](+) follows an associative interchange mechanism. The suggested mechanisms are discussed in reference to available experimental and theoretical data.

Adsorption on hydrophobized surfaces: clusters and self-organization

The arrangement of liquid molecules on surfaces bristling with alkyl chains is deduced from adsorption studies, X-ray powder diffraction data, and microcalorimetric measurements of swelling-type layered materials, especially clay minerals. Small polar molecules such as water, ethanol, formamide, dimethylsulfoxide, and aromatic compounds are clustered between the alkyl chains pointing away from the surface. The energetic contribution related to the movement of the alkyl chains from direct contact with the surface atoms into upright positions is decisive. The importance of the interactions between the liquid molecules on the structure of the adsorption layer is clearly indicated by the changes of the adsorption layer thickness by salt addition. Thermodynamic data are obtained from surface excess adsorption isotherms from binary liquid mixtures combined with microcalorimetric measurements. Long-chain adsorptives such as long-chain alcohols interact with the surface alkyl chains by forming stable bimolecular films. These films undergo a series of higher-order phase transitions into kink- and gauche-block structures as the consequence of rotational isomerization of the alkyl chains. Such transitions are considered elementary processes in self-assembling films (layer-by-layer deposition, fuzzy films, Langmuir-Blodgett technique), and lipid membranes.

Raman spectroscopy of benzenesulfonic and 4-toluenesulfonic acids dissolved in dimethylsulfoxide

Solutions of benzenesulfonic acid (BSA) and 4-toluenesulfonic acid monohydrate (PTSA) in dimethylsulfoxide (DMSO) were studied by FT-Raman spectroscopy in the concentration range 1.0-3.5 mol dm(-3) (BSA) and 1.0-4.8 mol dm(-3) (PTSA). Spectra in the region of the Raman acid complex band (C-S + C-C + SO3) stretches, at 1124 cm(-1) were analysed by band-fitting procedures in order to ascertain the degree of acid dissociation. In BSA solutions, this parameter changes from 0.78 at 1.02 M to 0.47 at 3.5M, despite the strong character of the acid. Interaction of DMSO with undissociated BSA produces a new band in the solvent nu(C-S) Raman spectral region near 671 cm(-1), displaced >15.0 cm(-1), and assigned to DMSO molecules H-bonded to BSA. In PTSA solutions, hydrogen bonds are formed with the oxonium ion (H3O+) dissociated from the acid. In this case, the displacement observed is only >10.0 cm(-1), indicating a weaker interaction. From the concentration of H-bonded DMSO, the solute/solvent coordination number and its inverse, the mean number of H-bonds participating in bonding with each solvent molecule can be calculated. This coordination number changes in BSA solutions in bimodal way, passing through a maximum and reaching a limit of 2 in the most concentrated solution. This number agrees with that found in the solid solvate BSA.2DMSO. In PTSA solutions, the general trend is similar, but low coordination numbers are obtained, in agreement with the low acidity of the oxonium ion. The bimodal behaviour observed in both acids is explained by the self-associated structure of the solvent.