The development of SIB has attracted attention as a substitute for LIB. Low-temperature-fired soft carbon (LFSC) has been the target of study as SIB’s useful negative electrode material. We estimated Na chemical diffusion coefficient Dchem using the same approach and samples of previous report on LIB. The approach was potential step chronoamperometry (PSCA) method, and the samples were mesophase-pitch-based carbon fiber fired at four different low temperatures (600, 700, 800 and 950°C). The PSCA measurements by using a single LFSC fiber electrode were performed in an electrolyte of propylene carbonate (PC) containing 1 M NaClO4 at room temperature in a glove box filled with dried Ar. The largest Dchem value we obtained with four pristine LFSC was about 10−9 cm2/sec. The Dchem values depended not only on firing temperature of LFSC but also on the nature of LFSC’s surface. The effective surface treatment promoted Na insertion/extraction reaction rate on the carbon surface. The largest Na Dchem value we obtained after surface treatment was 10−8 cm2/sec. This Na Dchem value was close to the Li Dchem value (10−7.5 cm2/sec) by previous report, which suggests possibility of SIB’s practical use.
A sequential injection analysis (SIA) system with on-line preconcentration technique using a microfluidic chip with an embedded anionic surfactant ion-selective electrode (AS-ISE) as a detector, was developed for the determination of anionic surfactants. Under the SIA system with no on-line preconcentration technique, the AS-ISE in the SIA system showed a linear relationship between peak heights and logarithmic concentrations of AS ion such as dodecylbenzene sulfonate (DBS) ion with a Nernstian slope of 60.4 mV decade−1 in a concentration range from 3.0 × 10−6 to 1.0 × 10−3 mol dm−3. For the determination of trace levels of ASs, on-line preconcentration technique with solid-phase extraction process was incorporated into the SIA system. By using the on-line preconcentration technique in the SIA system, DBS ion in a concentration range from 1.0 × 10−7 to 3.0 × 10−6 mol dm−3 was successfully determined. The recovery for DBS ion added to river water samples was ca. 91–97% using on-line preconcentration technique in the SIA system. The result shows that the present SIA system with the on-line preconcentration technique can be applicable to the determination of the level of AS ion in river and tap water samples.
Phase behavior of the [N2222][BF4]-[N3333][BF4] (N2222+ = tetraethylammonium, and N3333+ = tetrapropylammonium,) binary system has been investigated by differential scanning calorimetry and powder X-ray diffraction. Two solid-solid phase transitions are observed in differential scanning calorimetric curve in the range of x([N3333][BF4]) = 0.1–0.9 (x([N3333][BF4]) = the molar fraction of [N3333][BF4]) reflecting the solid-solid phase transition of each single salt, and only slight shift was observed for the transition temperatures. Powder X-ray diffraction patterns confirmed phase transitions. Although the amount of the minor constituent is low in the solid solution phase based on each single salt at 313, 373, and 423 K, Phase I of [N2222][BF4] at 483 K with the NaCl-type structure, which is regarded as an ionic plastic crystal (IPC) phase, can accommodate [N3333][BF4] up to the level where significant change in lattice parameter is observed (5.7% volume expansion). Drop of the liquidus line was observed for the salts with the mixing ratio x([N3333][BF4]) = 0.8 to 0.9 approaching to the eutectic temperature of 475 K. Ionic conductivity of Phase I increases by two orders of magnitude from x([N3333][BF4]) = 0 to 0.1 owing to the lattice expansion by inclusion of N3333+.
An electrochemical cell was developed for operando soft X-ray absorption spectroscopic (XAS) study of an all-solid-state lithium-ion battery. Operando XAS experiments were performed for a battery using LiMn2O4 as a cathode material and a NASICON-type lithium conductive glass ceramic sheet (LICGC) as a solid electrolyte. O K-edge, Mn L-edge and Ti L-edge XAS spectra were taken during the charging process up to 2.2 V. Detailed analysis of the XAS spectra revealed that the valence change from Mn3+ to Mn4+ occurred during charge with simultaneous change in the spectrum of O K-pre-edge region. Ti L-edge spectra revealed a partial change from Ti4+ to Ti3+ in the LICGC at the anode side, indicating a rather dispersed anode formation.
An equimolar mixture of oligoether solvents, glymes, and Li salt yields a new subclass of ionic liquids (ILs), referred to as solvate ILs, when using an appropriate combination of glyme and Li salt. In this paper a triglyme-Li tetrabromoferrate complex [Li(G3)][FeBr4] is prepared by combining a crystalline glyme-Li salt complex, [Li(G3)]Br, and an iron(III) bromide Lewis acid, FeBr3, to demonstrate a solvate IL comprised entirely of complex ions. [Li(G3)][FeBr4] is characterized in terms of thermal properties, coordination structure, and transport properties. This study reveals that the melting point of [Li(G3)][FeBr4] is lower than 100°C and that highly dissociated complex ions, [Li(G3)]+ and [FeBr4]−, are present both in the molten state and in polar acetonitrile solutions. [Li(G3)][FeBr4] is thus deemed a good solvate IL. The reversible redox property of the [FeBr4]−/[FeBr4]2− couple is exploited for the catholytes of rechargeable lithium batteries. The catholyte based on this redox active solvate IL exhibits a highly reversible charge-discharge behavior.
Electrochemical formation of selenium (Se) nanoparticles in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing selenium tetrachloride (SeCl4) was investigated in the presence of excess chloride anion on a glassy carbon electrode. Electrochemical reduction of [SeCl6]2− resulted in deposition of Se on the electrode surface. The deposited Se was further reduced electrochemically at the more negative potential region to form [Se2]2−, which was suggested to exist by ultraviolet-visible spectroscopy. Se nanoparticles dispersed in the ionic liquid were formed by the proportionation reaction between [SeCl6]2− and [Se2]2− in the ionic liquid. The Se nanoparticles were characterized by energy dispersive X-ray spectroscopy and transmission electron microscopy.
Aluminum species forming in Lewis acidic chloroaluminate and bis(trifluoromethylsulfonyl)amide (TFSA−) mixed ionic liquids having 1-butyl-3-methylimidazolium (BMI+) was investigated by potentiometry and Raman spectroscopy. A decrease in the concentration of [Al2Cl7]− and an increase in that of [AlCl4]− with addition of BMITFSA into acidic BMICl-AlCl3 were observed by Raman spectroscopy. The redox potential of Al(III)/Al in BMICl-AlCl3 (1:2 in molar ratio) was found to be −0.68 V vs. an Ag|Ag(I) reference electrode, which was corresponding to −0.25 V vs. the ferrocene/ferrocenium couple at 25°C. The potentiometry of an Al electrode in the mixed ionic liquids with different compositions using the Ag|Ag(I) reference electrode suggested formation of a mixed ligand aluminum complex, Al(TFSA)Cl2, indicating the instability of [Al2Cl7]− against TFSA−.
The solubility of sodium tungstate (Na2WO4) in a molten sodium hydroxide (NaOH) bath and its dependence on the partial pressure of water vapor were measured. This was done as part of an ongoing study of a new tungsten (W)-recycling process using molten NaOH. First, the nature of the chemical compound in the equilibrium solid phase in a molten NaOH bath was confirmed by adding excess amount of tungsten oxide as a tungstate ion source into the bath. X-ray diffraction analysis indicated that anhydrous Na2WO4 is the solid phase in equilibrium with the liquid phase of molten NaOH saturated with Na2WO4. Then, the solubility of the anhydrous Na2WO4 was measured under various partial pressures of water vapor. The results revealed that the solubility of anhydrous Na2WO4 drastically increased with the partial pressure of water vapor and the bath temperature from a molar fraction of 0.06–0.17. This value was much higher than those previously reported for molten nitrate and nitrites.
The redox reaction of tris(acetylacetonato)iron(III) (Fe(acac)3) on a glassy carbon electrode was investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA). A one-electron transfer redox reaction of [Fe(acac)3]0/− showed the relatively negative potential of −1.4 V vs. Ag|Ag(I). The diffusion coefficient of Fe(acac)3 estimated by chronoamperometry was (1.4 ± 0.1) × 10−7 cm2 s−1. The redox properties examined in this study suggested that the redox reaction of [Fe(acac)3]0/− can be utilized in the negative half-cell reaction of redox flow batteries.
Static differential capacitance (Cdc) at the liquid-liquid interface between ionic liquids (ILs) and eutectic Ga-In alloy (EGaIn) has been measured using the pendant drop method for two ILs: 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim+]BF4-) and 1-octyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide ([C8mim+][C4C4N−]). The potentials of zero charge for the IL|EGaIn interfaces are shifted compared with the IL|Hg interfaces with an amount that can be considered by the difference in the work functions of EGaIn and Hg. The measured Cdc at the [C2mim+]BF4-|EGaIn interface has well reproduced the camel-shape potential dependence of Cdc at the Hg interface of the same IL at the negatively charged potential region. This suggests that there are little specific interaction between the IL ions with EGaIn and Hg. The [C8mim+][C4C4N−]|EGaIn has been compared with the [C8mim+]BF4-|Hg interface where IL-cation is the same but IL-anion is different. Also in that case, Cdc is similar to each other at the negatively charged potential region, which means that accumulated C8mim+ ions at the interface mainly govern the Cdc behavior.
To clarify the relationship between adhesive strength of Al electroplating film and Mg alloy substrate, the amounts of γ-phase (Mg17Al12) and α-phase (Mg solid solution phase) in Mg alloy surface was investigated. Al electroplating film on Mg alloy was formed by current pulse electrolysis in AlCl3-1-ethyle-3-methyl-imidazolium chloride mixture ionic liquid at 283 K. It was found that the adhesive strength was affected by the ratio of γ-phase in the Mg alloys and it increased with increasing ratios of γ-phase on the Mg alloy surface. The results suggest that the adhesive strength of the electrodeposits on the γ-phase is stronger than that of the α-phase due to little oxide formation on the γ-phase.
We investigated effects of high lithium bis(fluorosulfonyl)imide (LiFSI) salt concentration or heat treatment before initial charge on charge-discharge performance of a graphite electrode in a 1-ethyl-3-methylimidazolium (EMImFSI)-based ionic liquid (IL) electrolyte. LiF was observed at the surface of graphite electrodes taken out from 2.00 mol kg−1 LiFSI/EMImFSI system and from 0.32 mol kg−1 LiFSI/EMImFSI system with pre-heat treatment before the initial charge. The surface LiF effectively suppresses the reductive decomposition of EMIm+. As a result, the irreversible capacity of initial cycle was significantly suppressed and the coulombic efficiency of subsequent cycles was greatly improved.