Noritoshi Nanbu

In situ FT-IR spectroscopic observation of a room-temperature molten salt | gold electrode interphase

We have investigated the molecular structure of an 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) | gold electrode interphase by means of in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). The feature in the FT-IRA spectra obtained suggests that EMI+ present in the interphase orients vertically with the molecular axis in the imidazole ring nearly parallel to the electrode surface in a potential range of −1.3 to +0.6 V vs. Ag|Ag+. The applied electrode potential causes the unbalance of the charge in the interphase, as usually seen in electrolyte solution | electrode interphases.

Direct fluorination of γ-butyrolactone

Abstract γ-Butyrolactone was fluorinated by molecular fluorine to obtain its mono-fluorinated derivatives for possible lithium battery electrolyte application. The reaction was carried out at 30°C by introducing 20% F 2 /N 2 gas into γ-butyrolactone without solvent. Major products were β-fluoro-γ-butyrolactone and γ-fluoro-γ-butyrolactone, which cannot be obtained by conventional organic synthesis. Selectivity to γ-isomer was enhanced by the addition of NaF as a HF scavenger.

Synthesis of Fluorinated Dimethyl Carbonates by Direct Fluorination

Abstract Growing interest has been focused on the development of fluorinated solvents for lithium batteries, because they have a number of benefits such as excellent oxidation durability, wide liquidus ranges, and nonflammability. Fluorination of dimethyl carbonate (DMC) is carried out using molecular fluorine (15 vol.% F2/N2) at 5°C, and the fluorinated derivatives of the DMC are identified and characterized. The selectivity of monofluorinated dimethyl carbonate (MFDMC) is ca. 90% at early stage of the fluorination. The successive electrophilic substitution of a hydrogen with a fluorine is found to proceed for the direct fluorination of the DMC.

Physical and Electrolytic Properties of Partially Fluorinated Organic Solvents and Its Application to Secondary Lithium Batteries: Partially Fluorinated Dialkoxyethanes

Secondary lithium batteries (lithium ion batteries) are becoming in dispensable power sources for various portable electronic devices and they are also being applied for powering electric vehicles. The safety and reliability of the battery are very important for electric vehicles to be widely applicable. To improve the performance of secondary lithium batteries, much efforts have been focused on the development of the effective solvents (electrolytes) with high energy density, oxidation durability and non-flammability. Fluorinated organic solvents show very different physical properties compared with those of common organic solvents because of very high electronegativity, high ionic potential and low polarizability of the fluorine atom. In particular, partially fluorinated organic solvents show fairly high polarity in comparison with that of perfluoro organic solvents. One of the appropriate methods to find a solvent with good cell performance is the introduction of fluorine atoms into the solvent molecules. The present paper reviews partially fluorinated several important solvents for lithium batteries in view of their physical and electrolytic properties, and charge-discharge characterisics for rechargeability . Table1 shows dielectric constants (e) and viscosities (η) of three kinds of partially fluorinated ethoxymethoxyethane (EME) derivatives, which are fluoroethoxymethoxyethane (FEME), difluoroethoxymethoxyethane (DFEME) and trifluoroethoxymethoxyethane (TFEME). The dielectric constants of these EME derivatives are very higher than that of EME because of high electron withdrawing of fluorine. However, the dielectric constants are not appreciably dependent on the number of fluorine atom. Though these EME derivatives show very high viscosities compared with that of EME, viscosity of TFEME with higher molecular weight becomes small rather than those of FEME and DFEME. It seems that the introduction of three fluorine atoms to EME decreases the molecular interaction in TFEME molecule by steric hindrance and electron repulsion among the fluorine atoms. Figure 1 shows specific conductivities in EME, FEME, DFEME and TFEME solutions in the range of 5°C to 60°C. The solution with low viscosity tends to increase the specific conductivity. However, the specific conductivity of TFEME solution with lower viscosity than those of FEME and DFEME solutions becomes small. This means that the solvation in TFEME is different from those in FEME and DFEME. Figure 2 shows variation of Li electrode cycling efficiencies (charge-discharge coulombic efficiencies for Li electrode) in ethylene carbonate (EC)-based equimolar binary solutions. EC-TFEME electrolyte shows higher efficiency in a high cycle number range than those of other electrolytes. This is a good electrolyte for rechargeable lithium batteries. References 1) J.O.Besenhard and M. Winter, Chem. Phys. Chem., 3, 155 (2002) 2)K.Uneyama, “Organo Fluorine Chemistry” Blackwell Publishing Ltd (2006). 3) Y.Sasaki, Electrochemistry, 76, 2 (2008). Solvent M.W. e η

Thermal and Electrolytic Properties of Quaternary Ammonium Salts Based on Fluorine-Free Chelatoborate Anions and Their Application to EDLCs

The use of bis(oxalato)borate ion makes it possible to increase the solubility of the tetramethylammonium salt in propylene carbonate (PC). We have investigated the thermal and electrolytic properties of tetramethylammonium bis(oxalato)borate (TMABOB), tetraethylammonium bis(oxalato)borate (TEABOB), and tetraethylammonium bis[salicylato(2-)]borate and their application to electric double-layer capacitors (EDLCs). The anion sizes of the fluorine-free chelatoborates are larger than that of tetrafluoroborate, and the ionic conductivities and wettability of the PC solutions become lower. Nevertheless, the gravimetric capacitances of model cells using the TMABOB and the TEABOB are comparable to that obtained for tetraethylammonium tetrafluoroborate (TEABF 4 ).