The room temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF,) was demonstrated as a versatile electrolyte by examining three representative electrochemical couples: ferrocene and tetrathiafulvalene oxidations and lithium ion reduction. Square-wave voltammetric data for ferrocene oxidation were fit to a reversible one-electron process using the COOL"' algorithm to give a half-wave potential of 0.490 V vs. Al/Al(III) and a diffusion coefficient of 5.1 x 10-7 cm 2 s-'. The two-electron oxidation-of tetrathiafulvalene was reversible and proceeded through two consecutive one-electron steps; although data collected at lower square-wave frequencies indicated a slow precipitation of the TTF' species. Lithium ion was reduced to lithium metal at a Pt electrode following the addition of water to the EMIBF 4 electrolyte, whereas lithium ion reduction at an Al wire produced the -LiAl alloy. Conductivities and kinematic viscosities of EMIBF 4 were measured from 20 to 100'C and had values of 14 mS cm-' and 0.275 cm' sl, respectively, at 25°C.

The crystal structure of 1 -ethyl-3-methylimidatolium (EMI+) hexafluorophosphate consists of interionic interactions dominated by cation-anion coulombic forces with minimal hydrogen bonding and serves as a model for EMI+ room temperature molten salts containing weakly complexing anions.

The reductive and oxidative intercalation of ions into graphite from room-temperature and low temperature molten salts is demonstrated. For this investigation, the molten salts use 1 -ethyl-3-methylimidazolium (EMI +) or 1,2-dimethyl-3-propylimidazolium (DMPI +) as the cation and AICI4, BF~, PF6, CF3SO~, or C6H5CO~ as the anion. In a two-electrode battery configuration, the molten salt electrolyte provides both the cation and anion which are intercalated into the graphite anode and cathode, respectively. A cell employing a (DMPI)(AICI4) electrolyte and two graphite rod electrodes achieved an open-circuit voltage of 3.5 V and a cycling efficiency of 85%.

New rubbery gel electrolytes have been prepared from room temperature ionic liquids and poly(vinylidene fluoride)-hexafluoropropylene copolymer [PVdF(HFP)]. The ionic liquids employed in these preparations were 1-ethyl-3-methylimidazolium salts of triflate (CF 3 SO3) and BF4. When properly processed, the ionic liquid-PVdF(HFP) gels are freestanding, flexible films with room temperature conductivities ranging from 1.1 to 5.8 mS cm-'. Because both the ionic liquids and the PVdF(HFP) are nonvolatile and are thermally stable, the gels can be operated at elevated temperatures without performance degradation. An ionic conductivity of 41 mS cm ' was measured for a triflate ionic liquid-PVdF(HFP) gel at 205°C.

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Aluminumdeposition from AICI3:MEIC (l-methyl-3-ethylimidazolium chloride) has been studied employing an inverted optical microscope to perform in situ optical observations during the deposition process at a 250 ~Im diam tungsten electrode. Thin, continuous aluminum coatings with nuclei (or cluster) sizes below optical microscopic resolution are produced from a i. i:I.0 AICI3:MEIC molten salt using constant potential deposition at potentials < -0.2 V vs. an AI(III)/AI reference electrode. At less negative potentials, the microscopic structure consists of larger (>0.5 ~Im), optically resolved nuclei. Analysis of chronoamperograms indicate that the deposition process involves progressive nucleation with diffusion-controlled growth of the three-dimensional nuclei. Calculated nuclear site densities and average nuclei sizes are in agreement with optical and electron microscope images.