R. T. Carlin

Dual Intercalating Molten Electrolyte Batteries

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[sup +]) or 1,2-dimethyl-3-propylimidazolium (DMPI[sup +]) as the cation and AlCl[sup [minus]][sub 4], BF[sup [minus]][sub 4], PF[sup [minus]][sub 6], CF[sub 3]SO[sup [minus]][sub 3], or C[sub 6]H[sub 5]CO[sup [minus]][sub 2] 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)(AlCl[sub 4]) electrolyte and two graphite rod electrodes achieved an open-circuit voltage of 3.5 V and a cycling efficiency of 85%.

Structure of 1-ethyl-3-methylimidazolium hexafluorophosphate: model for room temperature molten salts

The crystal structure of 1-ethyl-3-methylimidazolium (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.

Alkali Metal Reduction Potentials Measured in Chloroaluminate Ambient‐Temperature Molten Salts

Alkali metal electrochemical reductions at a mercury film electrode (MFE) were studied in AlCl 3 :MEIC (MEIC=1-methyl-3-ethylimidazolium chloride) molten salts buffered to a neutral composition with MCl (M=Li, Na, K, Rb, and Cs). The MFE was formed by mercury deposition on a 127-μm iridium disk electrode. At the Ir-MFE, the reduction potentials for the Li, Na, K, Rb, and Cs amalgams were observed at -1.16, -1.26, -1.62, -1.67, and -1.75 V (vs. Al/Al(III)), respectively

Rechargeable Lithium and Sodium Anodes in Chloroaluminate Molten Salts Containing Thionyl Chloride

Lithium and sodium deposition-stripping studies were performed in room temperature buffered neutral chloroaluminate melts containing low concentrations of thionyl chloride (SOCl{sub 2}). The SOCl{sub 2} solute promotes high cycling efficiencies of the alkali metals in these electrolytes. Staircase cyclic voltammetry and chronopotentiometry show cycling efficiencies of approximately 90% for both lithium and sodium. High cycling efficiencies are maintained following extended exposure of the melt to the dry box atmosphere and after time delays at open circuit. The performance of the SOCl{sub 2}-promoted systems is substantially improved over previous studies in room temperature melts containing hydrogen chloride as the promoting solute.

Electrochemistry of room-temperature chloroaluminate molten salts at graphitic and nongraphitic electrodes

The electrochemistry of unbuffered and buffered neutral AlCl3-EMIC-MC1 (EMIC =1-ethyl-3-methylimidazolium chloride and MC1= LiCl, NaCl or KCl) room-temperature molten salts was studied at graphitic and nongraphitic electrodes. In the case of the unbuffered 1 : 1 AlCl3 : EMIC molten salt, the organic cation reductive intercalation at about −1.6 V and the AlCl4− anion oxidative intercalation at about +1.8 V were evaluated at porous graphite electrodes. It was determined that the instability of the organic cation in the graphite lattice limits the performance of a dual intercalating molten electrolyte (DIME) cell based on this electrolyte. In buffered neutral 1.1 :1.0:0.1 AIC13: EMIC : MCl (MC1= LiCl, NaCl and KCl) molten salts, the organic cation was intercalated into porous and nonporous graphite electrodes with similar cycling efficiencies as the unbuffered 1 : 1 melt; however, additional nonintercalating processes were also found to occur between 1 and −1.6 V in the LiCl and NaCl systems. A black electrodeposit, formed at −1.4 V in the LiCl buffered neutral melt, was analysed with X-ray photoelectron spectroscopy and X-ray diffraction and was found to be composed of LiCl, metallic phases containing lithium and aluminium, and an alumina phase formed from reaction with the atmosphere. A similar film appears to form in the NaCl buffered neutral melt, but at a much slower rate. These films are believed to form by reduction of the AlCl4− anion, a process promoted by decreasing the ionic radius of the alkali metal cation in the molten salt. The partially insulating films may limit the usefulness of the LiCl and NaCl buffered neutral melts as electrolytes for rechargeable graphite intercalation anodes and may interfere with other electrochemical processes occurring negative of −1 V.

Electrodeposition of Palladium and Adsorption of Palladium Chloride onto Solid Electrodes from Room Temperature Molten Salts

The electrodeposition of palladium onto various electrode surfaces was examined in room temperature AlCl[sub 3]-MEIC molten salts with AlCl[sub 3] mole fractions, N, from 0.33 < N < 0.5 (basic melts) to 0.5 < N < 0.67 (acidic melts) and at N = 0.5 (neutral melt). The behavior of palladium electrodeposition was markedly dependent on the mole fraction of AlCl[sub 3] in the molten salts. The palladium reduction potential shifts approximately +2.0 V when the melt is changed from basic to acidic. Nucleation overpotentials were evident in basic melts, and to a lesser extent in acidic and neutral melts. In acidic melts, the reduction of the sparingly soluble palladium complex displays characteristics distinctive of an adsorption phenomenon, while the oxidation process shows considerable broadening. Oxidation of a palladium electrode in an N = 0.55 acidic melt produces an insoluble palladium chloride layer (approximately a monolayer) on the electrode surface which protects the underlying metal from further oxidation. Reduction of this surface anchored palladium chloride layer is rapid and provides a high cathodic current density. This behavior in acidic melts in pointedly different from the reduction process in a basic melt where the reduction of the soluble palladium chloro complex exhibitsmorexa0» a diffusion wave with nucleation effects.«xa0less

Stability and Electrochemistry of Lithium in Room Temperature Chloroaluminate Molten Salts

Room temperature chloroaluminate molten salts derived from AlCl[sub 3], and 1-methyl-3-ethylimidazolum chloride (MEIC) hold great promise as electrolytes for high energy density batteries. Addition of protons to buffered neutral AlCl[sub 3]:MEIC:LiCl melts allows elemental lithium to be deposited and stripped at a 250 [mu]m tungsten electrode. Chronopotentiometric studies performed at current densities from 0.16 to 3.06 mA cm[sup [minus]2] show minimal overpotentials for lithium deposition and stripping. When the lithium is stripped immediately after deposition, the stripping to deposition efficiency approaches 80%; however, when the deposited lithium is allowed to contact the electrolyte circuit for several minutes, the efficiencies drop rapidly due to the reaction of lithium with the melt. In basic (chloride-rich) AlCl[sub 3]:MEIC melts, elemental lithium appears to be stable for long times with and without the addition of protons. In addition, the maximum lithium anodization current density achieved in basic melts is higher than the buffered neutral melts.

Reversible Lithium‐Graphite Anodes in Room‐Temperature Chloroaluminate Melts

Lithium rocking-chair batteries employing a lithium/carbon intercalation node and a transition metal oxide intercalation cathode have captured a significant portion of battery research throughout the world. The intercalation of lithium into a carbon matrix provides a more stable and safer means for lithium utilization than an elemental lithium anode. Reduction of a graphite rod electrode in an AlCl[sub 3]:EMlC;LiCl room-temperature molten salts leads to reversible lithium intercalation into the reduced graphite lattice. The cycling efficiency of the Li-graphite electrode ranges from 80 to 90% for current densities of 0.2 to 1mA cm[sup [minus]2]. In the staircase cyclic voltammogram the oxidation process occurs at a potential approximately 1 V positive of the reduction process.

In Situ Optical Microscopy Investigations of Lithium and Sodium Film Formation in Buffered Room Temperature Molten Salts

Previous work performed in both sodium and lithium buffered chloroaluminate molten salts have shown that the addition of small amounts of SOCl{sub 2} promotes the reversible stripping behavior of lithium and sodium metal with cycling efficiencies between 80 and 90%. The authors have performed a series of optical studies in conjunction with electrochemical experiments at varying SOCl{sub 2} concentrations in both lithium and sodium chloride buffered melts. On investigation, the lithium deposit is dendritic in nature and does not form a uniform film on the tungsten electrode. After discharging at moderate current densities, disconnected lithium metal is observed at the electrode surface. In contrast, the sodium deposits as a uniform, flat film on the tungsten electrode with little or no dendritic growth. The sodium electrodeposits undergo complete stripping from the tungsten electrode without dendritic or disconnected sodium metal left on the electrode surface.

Dialkylimidazolium-sodium chloroaluminate ternary salt system: phase diagram and crystal structure

AbstractThe phase diagram of the buffered neutral aluminum chloride + 1-ethyl-3-methyl-1H-imidazolium chloride + sodium chloride (AlCl3-EMIC-NaCl) ternary melt system can be represented by a binary phase diagram composed of (EMI)AlCl4 and NaAlCl4. In the binary phase diagram, the salts are liquid at, or near, room temperature for a wide range of compositions. At the 1∶1 composition, the congruently melting compound (EMI)(Na)(AlCl4)2 with m.p.=36.7°C is formed. Crystals of this mixed organic-inorganic salt were grown for single crystal x-ray diffraction analysis. The compound crystalizes in the space groupn