Fluorosulfonyl Amide Research Articles

Modeling High Concentration Bisalt-in-Sulfolane Electrolytes and the Observation of Ligand-Bridged Cation-Pair Complexes.

Despite the abundance of sodium over lithium in Earth's crust and the copious amounts of expensive lithium salt required to make Li-ion high-concentration electrolytes (HCEs), studies of HCEs made from sodium salts remain sparse. A comparative molecular-level study of Li- and Na-ion HCEs and mixed cation or bisalt HCEs in an organic solvent is missing. To fill this gap, we studied model HCEs of pure and mixed Li and Na salts of bis(fluorosulfonyl)amide (FSI) in sulfolane using a confluence of classical molecular dynamics (MD), ab initio MD (AIMD) simulations, and quantum chemical cluster calculations. While Li-ion HCEs display transport properties superior to those of Na-ion HCEs, the latter's performance can be considerably improved by replacing even 25% of Na-ions with Li-ions. While the effects of doping are largely systemic, a larger sensitivity of the identity of solvation shells of Li-ions to the Li-content of the HCE is observed; in contrast, those of Na-ions are more oblivious to it. Fascinating ligand-bridged, short-distance cation pairs observed in the classical MD simulations are confirmed using density functional theory-based AIMD simulations. Quantum chemical calculations in the gas phase reveal the thermodynamic stability of such cation pairs complexed with multiple anions and solvent molecules.

Development of low-viscosity phosphonium-based ionic liquid electrolytes for lithium-ion batteries: Charge–discharge performance and ionic transport properties

Phosphonium cation-based ionic liquids (phosphonium ILs) have several advantages for electrochemical device applications compared with ammonium cation-based ionic liquids because of their unique features, such as higher ionic conductivity and a larger electrochemical potential window. In this study, we prepared various phosphonium ILs with different substituents (alkyl, alkyl ether, or allyl) on the cation, and bis(fluorosulfonyl)amide (FSA) or bis(trifluoromethanesulfonyl)amide (TFSA) as the anion. This study describes these phosphonium ILs used as electrolytes for lithium-ion batteries and investigates their performance as typical Li/LiCoO2 cells. We demonstrate that discharge capacity increases with increasing lithium-ion conductivity determined by electrochemical impedance and pulsed-field gradient nuclear magnetic resonance. A discharging rate test conducted in constant current (CC) mode also displays good high conductivity phosphonium IL electrolyte performance. Furthermore, the difference in cycle performance between FSA-based and TFSA-based phosphonium IL electrolytes is explained in terms of solid electrolyte interphase formation, similar to the performance of other cation-based ILs.

Absorption and desorption behaviours of ammonia on bis(fluorosulfonyl)amide salts investigated using the pressure-swing method

Large storage capacity of ammonia (NH3) on bis(fluorosulfonyl)amide (FSA) salts were observed using the pressure-swing method (0.1–0.5 MPa).

Charge–Discharge Behavior of Graphite Negative Electrodes in FSA-Based Ionic Liquid Electrolytes: Comparative Study of Li-, Na-, K-Ion Systems

K-ion batteries utilizing ionic liquid (IL) electrolytes are promising candidates for next-generation batteries because of the abundance of potassium resources, low redox potential of potassium, and high safety of ILs. Our major interest is in the comprehensive understanding of electrochemical alkali metal intercalation/deintercalation into graphite negative electrodes, because graphite can easily form graphite intercalation compounds (GICs) with various ionic species, but not with sodium. In this study, we investigated the potassium storage mechanism of graphite negative electrodes in bis(fluorosulfonyl)amide (FSA)-based ILs, and compared the electrochemical GIC formation of Li-, Na-, and K-ion systems. Charge–discharge tests of graphite in K[FSA]–[C3C1pyrr][FSA] IL (C3C1pyrr = N-methyl-N-propylpyrrolidinium) at 313 K yielded an initial discharge capacity as high as 268 mAh (g-C)−1, leading to the formation of several K-GICs including stage-3 KC36, stage-2 KC24, and stage-1 KC8. The rate capability and long-term cycling tests indicated stable potassiation/depotassiation behavior for 225 cycles. A comparison of the electrochemical behavior of graphite among M[FSA]–[C3C1pyrr][FSA] (M = Li, Na, and K) ILs at 298 K indicated that the formation of binary M-GICs is localized in the potential range below −2.85 V vs. Fc+/Fc (Fc = ferrocene), which possibly hinders Na-GIC formation.

Fluorophosphate-Based Nonflammable Concentrated Electrolytes with a Designed Lithium-Ion-Ordered Structure: Relationship between the Bulk Electrolyte and Electrode Interface Structures.

We propose a molecular design for lithium (Li)-ion-ordered complex structures in nonflammable concentrated electrolytes that facilitates the Li-ion battery (LIB) electrode reaction to produce safer LIBs. The concentrated electrolyte, composed of Li bis(fluorosulfonyl)amide (FSA) salt and a nonflammable tris(2,2,2-trifluoroethyl) phosphate (TFEP) solvent, showed no electrode reaction (i.e., no Li-ion intercalation into the negative graphite electrode); however, introducing a small molecular additive (acetonitrile [AN]) into concentrated TFEP-based electrolytes is shown to improve the battery electrode reaction, leading to reversible charge/discharge behavior. Combined high-energy X-ray total scattering experiments incorporating all-atom molecular dynamics simulations were used to visualize Li-ion complexes at the molecular level and revealed that (1) Li ions form mononuclear complexes in a concentrated LiFSA/TFEP (without additives) owing to solvation steric effects arising from the molecular size of TFEP and (2) adding a small-sized additive, AN, reduces the steric effect and triggers a change in Li-ion structures, i.e., the formation of a specific Li-ion-ordered structure linked via FSA anions. These Li-ion-ordered complexes stabilize the energy of the lowest unoccupied molecular orbital (LUMO) on FSA anions, which is key to producing an anion-derived solid electrolyte interphase (SEI) at the graphite electrode. We performed in situ surface-enhanced infrared absorption spectroscopy and discussed the electrode/electrolyte interface and SEI formation mechanisms in TFEP-based concentrated electrolyte systems.

Characterization of Solid Electrolyte Interphase on Some Electrodes in the Bis(fluorosulfonyl)Amide Anion-Based Ionic Liquids with Different Li Salt Concentrations

Aprotic ionic liquids are investigated as the next generation electrolytes for lithium ion battery (LIB) because non-flammability of ionic liquids is expected to improve the safety of the LIB. Bis(fluorosulfonyl)amide (FSA) anion-based ionic liquids have been attracting attention because of the formation of stable solid-electrolyte interphase (SEI) on the electrode surface during charge-discharge reactions. The SEI is known to form as a result of reductive decomposition of electrolytes and considered as a lithium ion conductor, though its nature like composition has not been clarified yet especially in ionic liquid electrolytes. In the present study, the SEIs on some different electrodes in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)amide (MPPFSA) containing LiFSA at different concentrations were characterized by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The formation and growth of the SEI were confirmed by the EIS spectra of a Cu electrode kept at 0 V vs. Li|Li(I) and Li deposited on a Cu electrode in MPPFSA containing different concentrations of LiFSA with the elapse of time. The SEIs prepared on the Cu electrode and the deposited Li in the electrolytes for 1 week were characterized by XPS washing with monoglyme (G1) without exposure to air. The XPS peaks corresponding to C, N, O, F, S atoms were observed on the Cu electrode, suggesting the ionic liquids are adsorbed on the electrode surfaces even after washing by G1. Such decomposition products of the electrolytes as LiF and LiOH were detected on the Cu electrode and the deposited Li. In case of the deposited Li, the peak assignable to alkyl lithium (R-Li) in the C1s spectra was observed probably due to the reaction of Li with the organic cation of the ionic liquids. The ratio of the peak intensity for LiF to that for SO2-F on the Cu electrode and the deposited Li increased with an increase in the LiFSA concentration in the electrolyte. On the other hand, the relative intensity for R-Li on the deposited Li decreased with an increase in the LiFSA concentration, suggesting an increase in the LiFSA concentration suppressed the decomposition of MPP+ and promoted the decomposition of FSA-.

Electrochemical Behavior of Selenophene in Quaternary Ammonium and Phosphonium Based Ionic Liquids

Room-temperature ionic liquids (RTILs) have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations. For example, we have reported that a bis(fluorosulfonyl)amide (FSA) anion based imidazolium ionic liquid promoted the electropolymerization reaction of pyrrole and the anion doping into the polymerized film, improving the conductivity of the film.2 We also have applied the phosphonium based RTILs to the electropolymerization of pyrrole and thiophene, investigating the influence of the phosphonium RTILs on the polymerized film properties.3 However, electrosynthesis of polyselenophene in phosphonium RTILs has not been examined. In this work, we report the electropolymerization of selenophene in triethylpentylphosphonium FSA (P2225-FSA) (Fig. 1) and the effect of the phosphonium RTIL on the polyselenophene film properties. P2225-FSA was prepared according to the procedure we have previously reported,4 and dried under high vacuum at 80°C for 6 h before use. The electropolymerization of selenophene in P2225-FSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a working electrode of platinum or transparent glass electrode and an IL-based Ag/Ag+ reference electrode. Figure 2 showed the cyclic voltammograms for the electropolymerization of selenophene in P2225-FSA. In the first cycle, the oxidation peak current value of about 0.2 mA was shown around +1.7 V vs Ag/Ag+, and the current decayed with each cycle. This closely resembles the electrochemical behavior observed in CVs using π-conjugated aromatic compounds such as pyrrole and thiophene as substrates. 3 After 10 cycles, a black thin film was grown on the surface of the working electrode, and the oxidation current observed in this CV seems to be due to the electropolymerization reaction of selenophene. Furthermore, we will discuss the comparison between the behaviors in various quaternary onium based ionic liquids from the viewpoint of the morphology of the polymer film grown on the working electrode. References K. Sekiguchi, et al, J. Electroanal. Chem. , 1, 557 (2003).K. Tsunashima, et al, ECS Electrochem. Lett., 3, G1 (2014).K. Nishihata, et al, ECS Trans., 75, 99 (2016).K. Tsunashima, et al, Electro cheml. Commun. , 13, 178 (2011). Figure 1

Effect of Film-Forming Additive in Ionic Liquid Electrolyte on Electrochemical Performance of Si Negative-Electrode for LIBs

1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (EMI-TFSA) is one of the promising ionic liquids as electrolyte solvent to enhance the electrochemical performance of Si electrode for Li-ion batteries (LIBs) because of its low viscosity and high conductivity. However, it has low stability against reduction and its reductive decomposition product inhibits Li+ insertion to electrodes, leading to poor cycling stability. To exert a potential of EMI-TFSA, we employed vinylene carbonate (VC) as film-forming additive. Si electrode exhibited very high cycling stability and rate capability in 20 vol.% VC-added EMI-TFSA-based electrolyte. In addition, by replacing TFSA anion with bis(fluorosulfonyl)amide (FSA) for Li salt and ionic liquid solvent, an excellent cycling performance and outstanding rate capability was achieved. VC cannot only fabricate a good surface film but also lower the interaction between Li+ and FSA−, providing smooth desolvation of FSA− to obtain better high-rate performance. Non-flammability of the VC-added electrolytes was confirmed by fire resistance test in closed-system: no ignition was observed even at 300°C. Consequently, we found that mixture electrolyte consisted of EMI-based ionic liquid and VC, especially 1 M LiFSA/EMI-FSA with 20 vol.% VC, is a prospective candidate for simultaneously enhancing the electrochemical performance of Si electrode as well as safety of LIBs.

Efficient and Stable Solid-State Dye-Sensitized Solar Cells by the Combination of Phosphonium Organic Ionic Plastic Crystals with Silica

Remarkably efficient quasi-solid-state dye-sensitized solar cells (DSSCs) have been fabricated using organic ionic plastic crystal electrolytes based on a small triethyl(methyl)phosphonium [P1222] cation and two types of sulfonamide anions, bis(fluorosulfonyl)amide (FSA) and bis(trifluoromethanesulfonyl)amide (TFSA), in combination with varying amounts of silica (SiO2). Solar cell efficiencies of up to 7.4% were obtained, which is comparable to our benchmark efficiencies of liquid (acetonitrile) electrolyte-based devices. Such a high efficiency for DSSCs using quasi-solid-state electrolytes is attributed to improved ionic conductivity, enhanced redox couple transport, improved interfacial interaction between the electrolyte and the electrode as well as decreased resistance at both electrode interfaces. Notably, the devices with the silica-containing electrolytes displayed excellent stability after 5 months of storage, with the most stable devices, formed with either plastic crystal electrolyte containing 2% silica, showing no decrease in efficiency.

Formation of ionic liquids of divalent metal complexes comprising N‑alkylethylenediamines and the solvation of the nickel(II) complexes

A series of divalent N‑alkylethylenediamine (alkyl‑en) metal(II) (alkyl = hexyl, 2‑ethylhexyl, octyl, dodecyl; metal = Ni, Cu, and Zn) complexes was prepared and their phase behavior was studied using differential scanning calorimetry. This kind of metal complexes is very useful for systematically investigating the relationship between phase behavior and molecular structures. It was found that several of the zinc(II) and nickel(II) complexes form room-temperature ionic liquids (RTILs), despite the divalent cation.Although the solid-to-liquid transition temperatures of metal(II) complex-based ILs are typically higher than those of the more common monovalent ionic liquids (ILs), they are dependent on the nature and combination of the metal(II) ions, alkyl chains, and counter anions. The zinc(II) complexes coupled with weakly coordinating bis(fluorosulfonyl)amide (FSA) or bis(trifluoromethanesulfonyl)amide (Tf2N) anions have significantly lower melting points, which is attributable to the longer distance between the zinc(II) ions and the counter anions upon the formation of tetrahedral bis(alkyl‑en)zinc(II) complexes as compared to the corresponding distances in NO3 and trifluoroacetate (TFA) complexes. The correlation of melting points with the molecular structures of the zinc(II) complexes is similar to that for the silver(I) alkyl‑en complexes. The tris(alkyl‑en)nickel(II) complexes coupled with Tf2N counter ions do not readily solidify and have glass transition temperatures below 0 °C, whereas the corresponding bis complexes have much higher melting points despite the counter-ions residing in the outer-spheres of the nickel(II) ions. The interactions of NO3, TFA, FSA, and Tf2N anions with the nickel(II) ions of the bis(alkyl‑en) complexes and their solvation behaviors were also studied in organic solvents using visible absorption spectroscopy based on the structures of the neat states. The characteristic solvation behaviors of the nickel(II) complexes were rationalized in terms of the counter anions and solvents.

Elucidation of the Reaction Behavior of Silicon Negative Electrodes in a Bis(fluorosulfonyl)amide‐Based Ionic Liquid Electrolyte

AbstractExcellent cycling performance of an electrode composed of silicon alone was achieved in a bis(fluorosulfonyl)amide (FSA)‐based electrolyte, with a high discharge capacity of 950 mA h g−1 observed even at the 500th cycle. To elucidate the reaction behavior of the Si electrode in an FSA‐based ionic liquid electrolyte, we investigated the change in the cross‐sectional morphology of the Si‐active material layer, the distribution of Li in the layer, and the crystallinity of Si on the electrode surface. By cross‐sectional scanning electron microscopy, we confirmed that the electrode thickness increased with the cycle number. The increase in thickness was less noticeable in the FSA‐based electrolyte than in an organic electrolyte. An elemental analysis of the electrode material revealed that a film derived from the electrolyte was formed not only on the surface but also inside of the electrode. Soft X‐ray emission spectroscopy demonstrated that the distribution of Li in the FSA‐based electrolyte was more uniform for the cross‐section of the cycled electrode compared to that in an organic electrolyte. The results of Raman spectroscopy indicated that domains of amorphous Si were homogeneously distributed on the electrode surface in the FSA‐based electrolyte. The uniform distribution of the lithiation−delithiation reaction should help to suppress disintegration of the active material layer.

Formation of silver nanoparticles from ionic liquids comprising N-alkylethylenediamine: Effects of dissolution modes of the silver(I) ions in the ionic liquids

Silver nanoparticles (AgNPs) were prepared from ionic liquids (ILs) of silver(I) N-alkylethylenediamine (N-alkyl=N-2-ethylhexyl, N-octyl, and N-dodecyl) complexes (=AgILs) and from protic ionic liquids (PILs) of N-alkylethylenediamines containing dissolved silver(I) nitrate (=AgNO3-PILs) and the two methods were compared. The difference between the silver(I) ion–ligand interaction modes of the AgIL and AgNO3-PIL systems was distinctly reflected in the formation of the AgNPs. The effects of the molecular structures of the AgILs and PILs, such as the effects of the alkyl chains in the cationic unit and the counter anion, on the shape and size distribution of the AgNPs were also examined using transmission electron microscopy (TEM), visible (VIS) absorption spectra, and extended X-ray absorption fine structure (EXAFS). The effect of the ethyl-branch of the alkyl chains on the physicochemical properties of the AgILs is drastic. The AgILs generally provided a more favorable reaction field for AgNP production than the AgNO3-PIL. The preparation of AgNPs depends on the concentration of AgNO3 in the PILs; at approximately 0.01molkg−1 of AgNO3 in the PILs, the PILs were capable of preventing the aggregation of silver(0) particles to allow the formation of AgNPs, while at higher AgNO3 concentrations (0.05molkg−1), even in the long-chained dodecyl-PIL system, larger continuous-shaped aggregates were detected. The bis(fluorosulfonyl)amide (FSA) anion is effective on decreasing the transition temperature for the formation of the liquid states, but not appropriate for the preparation of the AgNPs when combined with the N-2-ethylhexylethylenediamine-AgIL cationic unit, compared to the NO3 and trifluoroacetate (TFA) salts.

Inorganic-Organic Ionic Liquid Electrolytes Enabling High Energy-Density Metal Electrodes for Energy Storage

It has recently been shown, in the case of the bis(fluorosulfonyl)amide (FSI) based ionic liquids, that as the concentration of the alkali metal salt (LiFSI or NaFSI) is increased, the alkali metal cation transference number increases, despite an increase in viscosity and decrease in conductivity. At the same time significant enhancements in electrochemical stability and rate performance of devices are also observed. Here we overview some of the recent findings already in the literature and in addition demonstrate the feasibility of stable, high rate room temperature lithium battery cycling in an electrolyte comprised of 60 mol% LiFSI in a trimethyl, isobutyl phosphonium FSI ionic liquid using a high voltage NMC cathode. We also demonstrate that the high rate cycling of lithium and sodium metal in these phosphonium FSI electrolytes leads to a nanostructured anode deposit and a lowering of the interfacial impedance, suggesting a stable SEI layer formation. Finally, we propose a hypothesis that may explain some of the observations thus made, by which the high alkali ion concentration in these mixed electrolyte systems leads to the effective elimination of the mass transport limitations that are chiefly responsible for the formation of dendrites in traditional electrolytes. This work suggests that a new type of ionic liquid consisting of a mixture of metal cations with organic cations can provide a solution to the instability of the reactive alkali metal anodes and hence enable higher energy density technologies.

(Invited) Structural Aspect on Ion Solvation in Ionic Liquid-Based Electrolyte Solutions for Electrochemical Devices

In development of ionic liquid (IL)-based electrolytes for electrochemical devices such as Li ion batteries and electric double-layer and Li ion hybrid electrochemical capacitors, one of important issues is to reduce the viscosity. Bis(fluorosulfonyl)amide (FSA)-based IL is well known as one of low viscous ILs. FSA anion has a similar molecular structure to bis(trifluoromethanesulfonyl)amide (TFSA) anion; CF3 groups of TFSA are only substituted by F atoms, however, the FSA-based ILs show a significantly lower viscosity than the TFSA-based ILs.[1] In general, addition of Li salt to solvent IL leads to an increase in viscosity. Interestingly, the viscosity increase of FSA-based ILs with adding LiFSA salt is appreciably small relative to the corresponding TFSA system,[2] resulting in excellent performance of electrochemical devices with FSA-based ILs. Ion-ion interaction, particularly, “ion solvation” in the bulk plays a key role for understanding not just fundamental dynamic properties of electrolytes but electrode/electrolyte interface structure. In this presentation, we report ion-ion interactions (or liquid structures) in neat FSA- and TFSA-based ILs by using Raman spectroscopy, high energy X-ray total scattering (HEXTS), and theoretical calculations. Solvation structure of Li ion in both ILs are also reported and will be discussed their difference and similarity at the molecular level. From radial distribution functions, G(r)s, obtained by HEXTS and molecular dynamics (MD) simulations,[3] we found that static structure (distance and orientation) of the nearest neighbor cation - anion interaction is almost the same in both [C2mIm][FSA] and [C2mIm][TFSA] (C2mIm: 1-ethyl-3-methylimidazolium cation). On the other hand, in the long-range structure, the peak intensity or oscillation in the G(r) is appreciably weaker for [C2mIm][FSA] than for [C2mIm][TFSA]. This implies that the extent of the long-range ordering or structuredness is rather low in FSA system relative to TFSA system. Raman spectra with the aid of DFT calculations revealed that solvation structure of Li ion in [C2mIm][FSA] is largely different from that in [C2mIm][TFSA]. The Li ion is solvated with two TFSA anions acting as a bi-dentate ligand in [C2mIm][TFSA] system to form [Li(TFSA)2]– complex. In [C2mIm][FSA] system, solvation number of FSA anions bound to Li ion was estimated to be »3, indicating the formation of [Li(FSA)3]2 – complex. By quantitative analysis on HEXTS and MD data, it was found that mono- and bi-dentate FSA anions coexist in the [Li(FSA)3]2 – complex, i.e., [Li(mono-FSA)2(bi-FSA)1]2–.[4] [1] H. Matsumoto, H. Sakaebe, K. Tatsumi, M. Kikuta, E. Ishiko, M. Kono, J. Power Sources, 160 (2006) 1308. [2] S. Tsuzuki, K. Hayamizu, S. Seki, J. Phys. Chem. B, 114 (2010) 16329-16336. [3] K. Fujii, S. Seki, K. Ohara, Y. Kameda, H. Doi, S. Saito, Y. Umebayashi, J. Solution Chem., 43 (2014) 1655-1668. [4] K. Fujii, H. Hamano, H. Doi, X. Song, S. Tsuzuki, H. Hayamizu, S. Seki, Y. Kameda, K. Dokko, M. Watanabe, Y. Umebayashi, J. Phys. Chem. C, 117 (2013) 19314-19324.

Influence of Anion Structure of Ionic Liquid on the Electrochemical Performance of Si-Based Negative Electrode for Li-Ion Battery

To use Li-ion battery as a power source in electric vehicles and stationary power supply systems, an additional increase in its energy density is required. While silicon (Si) is a promising active material for use as a negative electrode due to its high theoretical capacity, higher energy density leads to an increase in a risk of ignition of the battery. Electrolyte is one of the most important component determining the battery performance. Ionic liquids have received much attention as an alternative to a conventional organic electrolytes because of their excellent physicochemical properties, such as high thermal stability, negligible vapor pressure, and wide electrochemical window. We have previously reported that the electrochemical performance of Si electrode in ionic liquid electrolyte is superior to that in organic electrolyte,1 and that an initial charge-discharge capacity of Si electrode increases when ether groups is introduced to side chain of cation in ionic liquid; cation structure of ionic liquid influences the electrochemical performance of Si negative electrode.2 Anion of ionic liquid is also key factor because it should affect the solvation structure of Li+. However, the anion structure of ionic liquid has not yet been optimized. In this study, we investigated the effect of anion structure of ionic liquid on the electrochemical performance of Si negative electrode for Li-ion battery. Si electrode was prepared by a gas-deposition method, which is without any binder or conductive agent. We assembled 2032-type coin cell consisted of the fabricated Si electrode as working electrode, Li foil as counter electrode, and glass fiber filter as separator. The ionic liquid used in this study consists of 1-((2-methoxyethoxy)methyl)-1-methylpiperidinium (PP1MEM) cation and three types of anion, including bis(fluorosulfonyl)amide (FSA), bis(trifluoromethanesulfonyl)amide (TFSA), and tetrafluoroborate (BF4). The electrolyte solution used was 1 mol dm-3 LiX-dissolved in PP1MEM-X (X: FSA, TFSA, BF4); anion of Li salt was same as that of ionic liquid. 1 mol dm-3 TFSA in propylene carbonate (PC) was also used for comparison. A galvanostatic charge-discharge test was carried out in the voltage range between 0.005 and 2.000 V at 303 K under a current density of 0.42 A g-1 (0.12 C). The conductivity of ionic liquid electrolytes was investigated by an electrochemical impedance spectroscopic analysis in the frequency of 100 kHz to 500 Hz with amplitude of 10 mV. An initial discharge capacity of Si electrode was less than 800 mA h g-1 in BF4-based electrolyte solution. The cycle performance of Si electrode in BF4-based electrolyte was almost the same as that in PC-based electrolyte; the discharge capacity was about 170 mA h g-1 at 80th cycle in both electrolytes. In FSA- and TFSA-based electrolytes, on the other hand, Si negative electrode exhibited high initial discharge capacity of ca. 3000 mA h g-1. It is well-known that surface film is formed on the Si electrode during an initial charging process through the reductive decomposition of the electrolyte, and that the film works as protective film which prevent continuous decomposition of the electrolyte. Better cycle performance of Si electrode in FSA- and TFSA-based electrolytes should be arising from more protective film compared to the film formed in BF4- and PC-based electrolytes. In addition, the disintegration of Si electrode would be suppressed because of the uniform Li insertion into the Si electrode over the entire surface in these electrolytes.3 Si negative electrode showed an excellent high-rate performance in FSA-based electrolyte; a reversible capacity of 800 mA h g-1 was achieved even at the high current density of 6 C, while Si electrode showed the discharge capacity of 100 mA h g-1 in TFSA-based electrolyte. Conductivity of FSA-based electrolyte (2.06 mS cm-1) is more than tripled compared to that of TFSA-based electrolyte (0.66 mS cm-1). Consequently, it is considered that the conductivity significantly affects the rate performance. References 1) H Usui, T. Masuda, and H. Sakaguchi, Chem. Lett., 41(2012) 521. 2) M. Shimizu, H. Usui, K. Matsumoto, T. Nokami, T. Itoh, and H. Sakaguchi, J. Electrochem. Soc., 161(2014) A1765. 3) M. Shimizu, H. Usui, T. Suzumura, and H. Sakaguchi, J. Phys. Chem. C., 119 (2015) 2975. Acknowledgment This work was partially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI, Grant-in-Aid for Scientific Research B (Grant 24350094).

Electropolymerization of Thiophene in a Bis(fluorosulfonyl)Amide Based Phosphonium Ionic Liquid

Room-temperature ionic liquids (RTILs) have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations. For example, we have reported that a bis(fluorosulfonyl)amide (FSA) anion based imidazolium ionic liquid promoted the electropolymerization reaction of pyrrole and the anion doping into the polymerized film, improving the conductivity of the film.2 We also have applied the phosphonium based RTILs to the electropolymerization of pyrrole, investigating the influence of the phosphonium RTILs on the polymerized film properties.3 However, electrosynthesis of polythiophene in phosphonium RTILs has not been examined. In this work, we report the electropolymerization of thiophene in triethylpentylphosphonium FSA (P2225-FSA) and the effect of the phosphonium RTIL on the polythiophene film properties.P2225-FSA was prepared according to the procedure we have previously reported,4 and dried under high vacuum at 80°C for 6 h before use. The electropolymerization of thiophene in P2225-FSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a working electrode of platinum or transparent glass electrode and an IL-based Ag/Ag+ reference electrode.Fig. 1 showed the cyclic voltammograms for the electropolymerization of thiophene in P2225-FSA. It was found that an irreversible oxidation peak was observed and maintained even when the cycle was repeated, forming the polythiophene film on the electrode surface. It is noted that the peak current at 2.2 V vs Ag/Ag+ was enhanced by cycling, which seems likely to be attributed to the efficient anion doping into the polymerized film grown on the working electrode surface. Fig. 2 depicted a SEM image of the polythiophene film grown in P2225-FSA. A uniform surface of the film grown in P2225-FSA was observed when compared to that in an organic solvent based electrolyte, which is closely similar to the result previously found in the electropolymerization of pyrrole. The electrochemical activity and thermal stability of the polythiophene film obtained will be discussed.

Effects of polyethylene spacer length in polymeric electrolytes on gelation of ionic liquids and ionogel properties

ABSTRACTPolymer electrolytes containing N,N′‐(trans‐cyclohexane‐1,4‐diyl)dibenzamide linkages, polyethylene ((CH2)m, m = 2, 4, 10) spacers, and bis(trifluoromethanesulfonyl)amide (TFSA) or bis(fluorosulfonyl)amide (FSA) counteranions (polymer abbreviation: CDBAm•X; m = 2, 4, 10; X = TFSA, FSA) have been synthesized, adding to our previous report (m = 6). In addition, their ability to effect the gelation of six ionic liquids and the properties of the resulting ionogels have been examined. The polymers, except for CDBA10•TFSA, effect the gelation for all ionic liquids used in this study at fairly low concentrations (0.9–50 g/L). Ionogel ionic conductivity is not dependent on the spacer length, but does decrease slightly as increasing amounts of the gelatinizer are introduced. In contrast to ionic conductivity, the temperatures at which these ionogels transition into isotropic fluids is dependent on the spacer length; the gel composed of [EMI][FSA] and 100 g/L of CDBA6•FSA transforms at 120 °C, while the gel composed of [EMI][FSA] and 5 g/L of CDBA2•FSA does not transform into a sol even when temperatures become 155 °C. In brief, ionogel heat resistance can be improved by changing the spacer length of the polyelectrolyte. Finally, it has been determined using cyclic voltammetry that the potential window of the polyelectrolytes is particularly wide, ranging from −1.6 to 2.5 V. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 249–255

Applicability of ionic liquid electrolytes to LaSi2/Si composite thick-film anodes in Li-ion battery

Anode performances of LaSi2/Si composite thick-films were investigated in ionic liquids as Li-ion battery electrolytes containing cations of N-methyl-N-propylpiperidinium (PP13) or 1-ethyl-3-methylimidazolium and anions of bis(fluorosulfonyl)amide (FSA) or bis(trifluoromethanesulfonyl) amide. The LaSi2/Si electrode exhibited much better performance in PP13-FSA compared with the other electrolytes including a conventional organic solvent one: the reversible capacity at the 250th cycle and its retention were 800 mA h g−1 and 80%. The excellent performance is attributed to a higher stability of PP13 cations against a cathodic decomposition and an easier desolvation of Li ions and FSA anions at the electrode/electrolyte interface. This result offers a promising applicability of ionic liquid electrolyte to various Si-based anodes with high performances by architecture of cation and anion structures.

Li-insertion/extraction Properties of Si Thick-film Anodes in Ionic Liquid Electrolytes Based on Bis(fluorosulfonyl)amide and Bis(trifluoromethanesulfonyl)amide Anions

Abstract Charge–discharge cycling performances of Si thick-film electrodes as Li-ion battery anodes were investigated in several ionic liquids based on bis(fluorosulfonyl)amide (FSA) and bis(trifluoromethanesulfonyl)amide (TFSA) anions. The Si electrodes in FSA-based electrolytes exhibited much better performance than those in TFSA-based electrolytes. An easier desolvation of Li from anions on the electrode surface is probably promoted in FSA-based electrolytes, which enables efficient electrode reactions of Li-insertion/extraction and improvement of cycling performances.