Details of a Researcher - Serizawa, Nobuyuki

Papers - Serizawa, Nobuyuki

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The Local Changes in the Physicochemical Properties during Electrode Reactions in a Chlorocuprate Ionic Liquid

Serizawa N., Kuwahara S., Li X., Katayama Y.

Journal of the Electrochemical Society 172 ( 4 ) 2025.04

ISSN 00134651

The physicochemical and electrochemical properties of an ionic liquid consisting of the dichlorocuprate anion, [CuCl2]-, were investigated. The equimolar mixture of CuCl and 1-butyl-1-methylpyrrolidinium chloride (BMPCl) was found to yield an ionic liquid at 298 K composed predominantly of BMP+ and [CuCl2]-. Fine deposits of metallic Cu were obtained on a glassy carbon electrode by potentiostatic and galvanostatic reduction of [CuCl2]- in CuCl-BMPCl (50.0-50.0 mol%). The overpotential for Cu nucleation was larger on a glassy carbon electrode than on a Pt electrode. The electrochemical deposition and dissolution of Cu were analyzed using an electrochemical quartz crystal microbalance. The local viscosity and density of the electrolyte near the electrode/electrolyte interface increased during both deposition and dissolution of Cu, probably reflecting the shift in the electrolyte composition to the local basic and acidic conditions, respectively.

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Evaluation of the Solid-Electrolyte Interphase Formed in the Carbonate-Based Electrolytes with Different Lithium Salts Using the Redox Probe Method

Katayama Y., Okazaki S., Serizawa N.

Electrochemistry 93 ( 6 ) 2025

ISSN 13443542

The formation of solid-electrolyte interphase (SEI) on a Pt electrode was investigated in ethylene carbonate (EC) and diethyl carbonate (DEC) containing LiPF<inf>6</inf> and lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) using the redox probe method. The formation and properties of the SEI were examined in the electrolytes containing ferrocene as a redox probe. Inhomogeneous and rigid SEI was found to form in 1 M (= mol dm−3) LiPF<inf>6</inf>/EC+DEC, probably due to the conversion of decomposition products to LiF by the reaction with HF derived from LiPF<inf>6</inf>. On the other hand, the formation of homogeneous and soluble (or dispersible) SEI was suggested in 1 M LiTFSA/EC+DEC.

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Electrode Reactions of Copper Species in a Bis(fluorosulfonyl)amide Ionic Liquid

Nobuyuki Serizawa, Takumi Hisada, Yasushi Katayama

Electrochemistry ((公社)電気化学会) 92 ( 4 ) 043009 2024.04

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 13443542

The electrode reactions of copper species were investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl) amide (BMPFSA). The anodic current assignable to the dissolution of Cu to form monovalent Cu(I) complex was observed at −0.42 V vs. Ag|Ag(I). A pair of anodic and cathodic current peaks attributable to Cu(II)/Cu(I) was observed at 0.5 V, suggesting that a 4 V class redox flow battery combined with a Li metal anode is expected using the redox reaction of Cu(II)/Cu(I) in BMPFSA as the cathode reaction. The electrodeposition of Cu and the quasi-reversible redox reaction of Cu(II)/Cu(I) were affected by the electrode materials.

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Formation and Breakdown of the Solid-electrolyte Interphase in a Bis(fluorosulfonyl)amide-based Ionic Liquid in the Presence of Lithium Ion

Sho Okazaki, Nobuyuki Serizawa, Yasushi Katayama

Electrochemistry ((公社)電気化学会) 92 ( 4 ) 043006 2024.04

Research paper (scientific journal), Joint Work, Accepted, ISSN 13443542

The formation and breakdown of the solid electrolyte interphase (SEI) on a Pt electrode were investigated in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) containing a high concentration of LiFSA using a ferrocene/ferrocenium couple as a redox probe. The formation of the SEI was confirmed at the potential more negative than −1.1 V vs. Ag|Ag(I). However, the SEI was found to disappear at the open circuit potential. The SEI was suggested to form by the dissolution and/or dispersion of the decomposition products in the electrolyte.

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Formation and Aging of the Solid Electrolyte Interphase on Lithium in Bis(fluorosulfonyl)amide-Type Ionic Liquids

Serizawa N., Yamashita R., Katayama Y.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 127 ( 22 ) 10434 - 10444 2023.04

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 19327447

The formation and aging of the solid electrolyte interphase (SEI) formed on a Li and Cu electrode in two bis(fluorosulfonyl)amide (FSA-)-type ionic liquids (ILs), 1-methyl-1-butylpyrrolidinium bis(fluorosulfonyl)amide and 1-methyl-1-methoxyethylpyrrolidinium bis(fluorosulfonyl)amide, containing a high concentration of LiFSA were investigated using electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy. The intensity of peaks corresponding to the decomposition of the electrolyte in XPS spectra changed with time. The thicknesses of the SEI formed on a Cu electrode in both ILs were estimated to be 20-100 nm by TEM observation. The resistance of SEI increased with the lapse of time although the change in the thickness of the SEI was small, suggesting the aging of the SEI in the ILs was considered to depend on the composition of the SEI rather than the thickness of the SEI. The Li deposits shrank during dissolution. The Li anode became sparse and porous after deposition and dissolution cycles, probably due to the inhomogeneous reaction through the aged SEI. The SEI formation on the surface of the porous deposits was considered to lead to an increase in the polarization and the isolation of the deposits, i.e., the formation of “dead lithium”.

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Redox Reactions of Ag(I)/Ag and Ferrocenium/Ferrocene in 1-Butyl-1-methylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 170 ( 4 ) 2023.04

ISSN 00134651

The electrode reactions of Ag(I)/Ag and ferrocenium/ferrocene (Fc+/Fc) were investigated in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA). The potential of Ag(I)/Ag depended on the logarithm of the concentration of Ag(I), as predicted by the Nernst equation, indicating the Ag(I)/Ag can be used as a reference electrode reaction in BMPFSA. The reversible electrode reaction of Fc+/Fc was observed in BMPFSA by cyclic voltammetry. The donor number of BMPFSA was estimated to be 13 from the difference in the formal potentials of Ag(I)/Ag and Fc+/Fc, indicating the coordination ability of FSA- was slightly stronger than that of bis(trifluoromethylsulfonyl)amide (TFSA-). The diffusion coefficients (D) of Fc and Fc+ were (5.7 ± 0.7) and (3.3 ± 0.2) × 10-7 cm2 s-1, respectively. The ratio of D of Fc+ against that of Fc was smaller than those in TFSA--type ionic liquids, reflecting the higher charge density of FSA-. The standard rate constant (k 0) of Fc+/Fc was estimated to be (5.4 ± 1.1) × 10-3 cm s-1. The apparent activation energy for k 0 was close to the activation energy for D, suggesting the electrode reaction of Fc+/Fc can be regarded as the outer sphere electron transfer reaction with a very small reorganization energy.

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Solid-Electrolyte Interphase Formation in Amide-Type Ionic Liquids in the Presence of Different Metal Cations

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 170 ( 5 ) 2023

ISSN 00134651

The formation of solid-electrolyte interphase (SEI) on a glassy carbon (GC) electrode in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Li+, Na+, K+, and Ni2+ was investigated using the redox reaction of ferrocene (Fc). The anodic peak potential (E pa) for the oxidation of Fc changed after holding the electrode at -1.4 to -1.5 V vs Ag|Ag(I) in BMPFSA in the presence of the alkali metal ions. The decomposition of FSA- was confirmed by X-ray photoelectron spectroscopy (XPS) on a GC electrode held at -1.5 V vs Ag|Ag(I) for 6 h in BMPFSA containing the alkali metal ions. The change in E pa may also suggest the formation of homogeneous SEI in the FSA--type ionic liquid. Moreover, E pa changed after holding the electrode at the potential more negative than -0.9 V vs Ag|Ag(I) in 50 mM Ni(TFSA)2/BMPTFSA while the decomposition of TFSA- was not confirmed by XPS on the electrode held at -1.1 V vs Ag|Ag(I) for 6 h, suggesting the bonds except C-F (e.g., S-C) were dissociated to form the SEI. Since the deposition potential of Ni in BMPTFSA was more negative than the SEI formation potential, the deposition of Ni may be inhibited by the SEI.

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Electrochemical Behavior of Silver Halogenocomplexes in an Amide-Type Ionic Liquid

Nobuyuki Serizawa, Suguru Kuwahara, Yasushi Katayama

Journal of The Electrochemical Society 169 092502 2022.09

Research paper (scientific journal), Joint Work, Lead author, Accepted

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Communication - Determination of the Formation Potential of Solid-Electrolyte Interphase in Amide-Type Ionic Liquids Containing Lithium Salts

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 169 ( 7 ) 2022.07

ISSN 00134651

The formation potentials of solid-electrolyte interphase (SEI) were investigated in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing LiFSA and LiTFSA, respectively, by monitoring the redox reaction of ferrocene with high sensitivity. The SEI was found to affect the electrode kinetics of the outersphere electron transfer reaction. The SEIs with the thickness of less than a few nm formed in LiFSA/BMPFSA and LiTFSA/BMPTFSA at 2.4 and 2.5 V vs Li|Li(I), respectively. The cathodic decomposition of FSA- and TFSA- was considered to be promoted by the interaction with Li+ based on the ab-initio calculation.

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Potential Dependence of the Impedance of Solid Electrolyte Interphase in Some Electrolytes

Furuya R., Serizawa N., Katayama Y.

Electrochemistry (Electrochemistry) 90 ( 5 ) 2022

ISSN 13443542

The dependence of the impedances of lithium phosphorous oxynitride (LiPON) thin film and solid electrolyte interphase (SEI) formed by decomposition of some electrolytes on the electrode potential was investigated by electrochemical impedance spectroscopy. A LiPON thin film was prepared on a Ni electrode by radio frequency magnetron sputtering of Li3PO4 under nitrogen atmosphere. The resistance of the LiPON thin film decreased with lowering the electrode potential in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (BMPTFSA) containing 1M LiTFSA. The similar potential dependence of the impedance of the SEI formed in 1M LiTFSA/BMPTFSA was observed, suggesting that the Li+ carrier density in the LiPON thin film and SEI increased with lowering the electrode potential probably due to the doping of Li+ from the electrolyte into the thin Li+ conductors in order to compensate the negative charge on the electrode. On the other hand, the potential dependence of the SEI formed in LiTFSA-tetraglyme (G4) solvate ionic liquid was insignificant because of the high concentration of Li+ in the SEI and electrolyte. The resistance of the SEI formed in 1M LiClO4/EC (ethylene carbonate) + DMC (dimethyl carbonate) (1 : 1 vol%) did not depend on the electrode potential, suggesting the thin and highly Li+ conductive SEI is formed in the organic electrolyte.

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Electrodeposition of Nickel From an Amide-Type Ionic Liquid Under a Magnetic Field

Katayama Y., Manabe Y., Serizawa N.

ECS Transactions (ECS Transactions) 109 ( 14 ) 235 - 238 2022

ISSN 19386737

Electrodeposition of nickel was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (BMPTFSA) containing Ni(TFSA)2 under a external magnetic field. The onset potential of cathodic reduction of Ni(II) with a magnetic field was more positive than that without the magnet field. Ni nanowires were deposited by potentiostatic cathodic reduction with the magnetic field, indicating the magnetic field influence not only the electrode kinetics of the magnetic species but also the morphology of the ferromagnetic metal.

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Determination of the Formation Potential of Solid-Electrolyte Interphase in Some Amide-Type Ionic Liquids Containing Metal Salts

Kato S., Serizawa N., Katayama Y.

ECS Transactions (ECS Transactions) 109 ( 14 ) 215 - 223 2022

ISSN 19386737

The formation potentials of the solid-electrolyte interphase (SEI) on a platinum and glassy carbon electrode in two amide-type ionic liquids, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing some metal salts were investigated by cyclic voltammetry in the presence of ferrocene (Fc). It is considered that the SEI with the thickness of less than a few nm can be observed by monitoring the shift in the peak potential of Fc+/Fc. The SEIs began to form at ∼2.4 V vs. Li|Li(I) in the presence of lithium salts because of a lowering of the lowest unoccupied molecular orbital level of the anion by the interaction with lithium ion. In the case of BMPTFSA containing Ni(TFSA)2, the SEI began to form at -0.7 V vs. Ag|Ag(I), suggesting that the deposition of Ni may be hindered by the SEI formation.

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Deposition and Dissolution of Lithium in 1-Methyl-1-methoxyethylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid Electrolyte with Different Compositions

Furuya R., Hara T., Fukunaga T., Kawakami K., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 168 ( 10 ) 2021.10

ISSN 00134651

The solid electrolyte interphase (SEI) between Li and ionic liquid electrolytes was investigated in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)amide (MPPFSA) and 1-methyl-1-methoxyethylpyrrolidinium bis(fluorosulfonyl)amide (MOEMPFSA) with different LiFSA concentrations. The physicochemical properties and the coordination states of Li+ with FSA- with increasing the LiFSA concentration were similar between xLiFSA-MPPFSA and MOEMPFSA. On the other hand, the SEI resistance obtained by electrochemical impedance spectroscopy using a Li|Li symmetrical cell increased with the lapse of time in xLiFSA-MPPFSA more significantly than in xLiFSA-MOEMPFSA, suggesting that the SEI formed in xLiFSA-MOEMPFSA was more conductive than that in xLiFSA-MPPFSA. The SEI formed on Li was considered to be composed mainly of the ions in the electrolytes and their decomposed products by X-ray photoelectron spectroscopy. The cyclability of deposition and dissolution of Li was improved with increasing the LiFSA concentration in both xLiFSA-MPPFSA and MOEMPFSA. An increase in the conductivity of the SEI with increasing the LiFSA concentration may lead to the promotion of homogeneous growth of Li rather than dendritic growth of Li.

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Electrochemical Recovery of Cobalt from Cobalt Oxide in an Amide-Type Ionic Liquid with Low-Temperature Carbochlorination

Yeh H.W., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 168 ( 8 ) 2021.08

ISSN 00134651

Electrochemical recovery of metallic Co was attempted from CoO in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing 0.5 M BMPCl. CoO was dissolved in 0.5 M BMPCl/BMPTFSA with a carbochlorination reagent, C2Cl6, to form [CoCl4]2- at 150 °C. After the removal of electroactive C2Cl6 and byproducts, the electrochemical reduction of [CoCl4]2- was found to be possible on a glassy carbon electrode in the ionic liquid. Co nanowires were deposited by electrochemical reduction of [CoCl4]2- in 0.5 M BMPCl/BMPTFSA under an external magnetic field, which promoted the cathodic reduction and affected the morphology of the deposits. The deposited Co nanowires were found to be composed of crystalline Co nanoparticles by transmission electron microscopy.

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Electrodeposition of Co in an Amide-Type Ionic Liquid under an External Magnetic Field

Manjum M., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 168 ( 4 ) 2021.04

ISSN 00134651

Electrodeposition of Co was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), under an external magnetic field. Neodymium magnets were used as a source of the magnetic field, which was parallel to the ionic current during the electrodeposition of Co on a glassy carbon electrode. Potentiostatic cathodic reduction applying -1.6 and -2.0 V vs Ag|Ag(I) under the magnetic field in BMPTFSA containing Co(TFSA)2 at 25 C gave nanowire-shaped deposits on the electrode surface. The deposits were found to be composed of Co, which was confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. However, no diffraction peak was observed in the deposits by X-ray diffraction. The nanowires were further examined by transmission electron microscopy. The lattice fringe corresponding to (111) plane of Co was found in the deposits, indicating the nanowires were composed of metallic Co nanoparticles. Therefore, crystalline Co nanoparticles were considered to be formed in the presence of the magnetic field.

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Electropolishing of Tin in an Amide-Type Ionic Liquid

Yuza N., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 168 ( 3 ) 2021.03

ISSN 00134651

Anodic dissolution and electropolishing of Sn were investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. The rate of anodic dissolution was considered to be determined by the diffusion of anodically dissolved Sn(II) species. A large increase in the local viscosity during dissolution was observed in-situ by the impedance-type electrochemical quartz crystal microbalance, reflecting an increase in the local concentration of Sn(II) near the electrode. A shiny and smooth surface was obtained after anodic dissolution at 0.1 V vs Ag|Ag(I) with agitation. A decrease in the surface roughness estimated by confocal laser scanning microscopy suggested electropolishing of Sn was possible in the ionic liquid within the electrochemical potential window probably due to the formation of the viscous layer near the electrode.

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Redox Reaction of 2,2,6,6,-Tetramethylpiperidine-1-oxyl in Lithium Bis(trifluoromethylsulfonyl)amide-tetraglyme Solvate Ionic Liquid

Serizawa N., Wada K., Tachikawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 167 ( 4 ) 2020.03

ISSN 00134651

© 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited. The electrode reaction of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was investigated in a solvate ionic liquid composed of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) and tetraglyme (G4), [Li(G4)]TFSA. A quasi-reversible redox reaction of the oxoammonium (TEMPO+) and TEMPO was observed with a formal potential of 0.19 V vs ferrocene|ferrocenium. The diffusion coefficient of TEMPO+ (2.1 × 10-8 cm2 s-1) was smaller than that of neutral TEMPO (1.3 × 10-7 cm2 s-1), reflecting the coulombic interaction between monovalent TEMPO+ and TFSA- in the solvate ionic liquid. The standard rate constant for TEMPO+/TEMPO redox reaction was estimated to be 1.9 × 10-4 cm s-1 at 25 C by electrochemical impedance spectroscopy. The solubility of TEMPO in [Li(G4)]TFSA was found to be 4.4 M at 25 C.

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Electrochemical Preparation of Cobalt-Samarium Nanoparticles in an Aprotic Ionic Liquid

Manjum M., Serizawa N., Ispas A., Bund A., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 167 ( 4 ) 2020.03

ISSN 00134651

© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. Electrochemical preparation of Co-Sm nanoparticles was conducted in an aprotic room temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Co(TFSA)2 and Sm(TFSA)3. The cyclic voltammetry on a glassy carbon (GC) electrode indicated the electrochemically generated Sm(II) reacted with Co(II) at 25 C. Potentiostatic cathodic reduction on a GC electrode in BMPTFSA containing 30 mM Co(TFSA)2 and 5 mM Sm(TFSA)3 at 25 C gave the deposits, which were found to be composed of Co and Sm by energy dispersive X-ray spectroscopy (EDX). The deposits were found to be the aggregates of SmCo7 nanoparticles by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formation of SmCo7 nanoparticles dispersed in the ionic liquid was also confirmed by TEM. SmCo7 nanoparticles were considered to form by the disproportionation reaction of Sm(II) in the presence of elementary Co, which was formed by the reduction of Co(II) by Sm(II).

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Characterization of the Solid-Electrolyte Interphase between a Cu Electrode and LiN(CF<inf>3</inf>SO<inf>2</inf>)<inf>2</inf>-triglyme Solvate Ionic Liquid

Serizawa N., Kitta K., Tachikawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 167 ( 11 ) 2020.01

ISSN 00134651

© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. The formation of the solid electrolyte interphase (SEI) on a Cu electrode was investigated in 50.0-50.0 mol% lithium bis(trifluoromethylsulfonyl)amide (LiTFSA)-triglyme (G3, CH3(OCH2CH2)3OCH3) solvate ionic liquid, [Li(G3)]TFSA, using electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The Li+ conductive SEI was formed on a Cu electrode by keeping the potential at 0 V vs Li|Li(I). The resistance and capacitance attributable to the SEI changed over a period of 24 h in EIS spectra, suggesting the sluggish SEI formation on the Cu electrode in [Li(G3)]TFSA. XPS and FT-IR spectra indicated the existence of G3, TFSA-, [Li(G3)]+, and/or their decomposition products in the SEI. In contrast, LiF was not found in the SEI, suggesting LiF was not formed by the cathodic decomposition of [Li(G3)]TFSA on the Cu electrode at 0 V. The whisker-like growth of Li on a Cu electrode was suppressed after the SEI formation at 0 V probably due to the formation of homogeneous and low-conductive SEI layer. The coulombic efficiency for deposition and dissolution of Li was improved with the SEI formation at 0 V prior to the measurements, suggesting the SEI on a Cu electrode affected the reversibility of the Li anode.

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Electrochemical Behavior of a Ni Chlorocomplex in a Lewis Basic Ionic Liquid Containing Chloride Ion

Ando K., Tachikawa N., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 167 ( 6 ) 2020.01

ISSN 00134651

© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. The electrochemical behavior of a chlorocomplex of nickel (Ni) was investigated in a Lewis basic and hydrophobic ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Cl-. NiCl2 dissolved in BMPTFSA with addition of 0.5 M BMPCl. The dissolved species of Ni(II) in BMPTFSA was identified as [NiCl4]2- by UV-visible spectrometry and magnetic susceptibility balance. The cathodic and anodic currents assignable to deposition and dissolution of Ni, respectively, were observed in cyclic voltammetry. The granular deposits of Ni were obtained on a glassy carbon electrode at 25 and 100 °C. Ni nanoparticles were dispersed in the electrolyte by galvanostatic cathodic reduction. The initial stage of Ni deposition was found to be regarded as instantaneous. The diffusion coefficient of [NiCl4]2- was calculated to be 6.6 × 10-8 cm2 s-1

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Electrochemical behavior of silver halogenocomplexes in an amide-type ionic liquid

Serizawa N., Kuwahara S., Katayama Y.

ECS Transactions (ECS Transactions) 98 ( 10 ) 209 - 214 2020

© The Electrochemical Society The electrochemical behavior of halogenocomplexes of Ag was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) in the presence of the corresponding halogen anion. Silver halides, AgX (X- = Cl-, Br-, and I-) were found to be soluble in BMPTFSA containing 0.5 M BMPX by forming [AgX3]2-. The cathodic reduction of [AgX3]2- to metallic Ag was possible within the electrochemical window of BMPTFSA. The reduction potentials were in the order of [AgCl3]2- > [AgBr3]2- > [AgI3]2-. The morphology of Ag deposits depended on the reduction potential. The diffusion coefficients of [AgCl3]2-, [AgBr3]2-, and [AgI3]2- were 2.5, 2.0, and 1.6 × 10-7 cm2 s-1, respectively. Formation of Ag nanoparticles dispersed in the ionic liquids was confirmed after potentiostatic cathodic reduction at -2.5 V using transmission electron microscopy.

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イオン液体中での金属析出・溶解反応への水晶振動子マイクロバランス

芹澤　信幸，片山靖

溶融塩および高温化学 62 ( 3 ) 162 - 169 2019.09

Research paper (conference, symposium, etc.), Joint Work

溶融塩系での常圧アンモニア電解合成技術の開発

錦織　徳二郎，芹澤　信幸，竹井　勝仁，伊藤　靖彦

溶融塩および高温化学 62 ( 2 ) 81 - 90 2019.04

Research paper (conference, symposium, etc.), Joint Work

Densities, Viscosities, and Refractive Indices of Binary Room-Temperature Ionic Liquids with Common Cations/Anions

Seki S., Serizawa N., Ono S., Takei K., Hayamizu K., Tsuzuki S., Umebayashi Y.

Journal of Chemical and Engineering Data (Journal of Chemical and Engineering Data) 64 ( 2 ) 433 - 441 2019.02

ISSN 00219568

Copyright © 2019 American Chemical Society. To elucidate the properties of binary system of room temperature ionic liquids (RTILs), we measured and compared the temperature dependence of densities, viscosities, and refractive indices of seven binary RTILs as well as neat RTILs. The observed densities, viscosities, and refractive indices of the binary systems showed intermediate properties between those of two starting RTILs. The values observed for the binary RTILs were only deviated from the values estimated based on the data of neat RTILs (±0.5%), and this deviation depended on both the combination of RTILs and the structures of the cation/anion. These results indicate that the properties of RTILs can be easily tuned by mixing RTILs depending on their applications.

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Electrochemical behavior of samarium species in an amide-type ionic liquid at different temperatures

Manjum M., Tachikawa N., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society) 166 ( 12 ) D483 - D486 2019

ISSN 00134651

© The Author(s) 2019. Electrochemical reaction of samarium (Sm) species was explored in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), at 25 and 100°C. The cathodic and anodic current peaks corresponding to the reduction of Sm(III) and the oxidation of Sm(II), respectively, were observed in BMPTFSA containing Sm(TFSA)3 by cyclic voltammetry at 25°C. However, the anodic current peak corresponding to the oxidation of Sm(II) diminished significantly at lower scan rates when the temperature was elevated to 100°C, suggesting the disproportionation of Sm(II) at higher temperatures. Deposits were obtained on a glassy carbon electrode by potentiostatic cathodic reduction at -1.6 and -2.5 V in BMPTFSA containing Sm(TFSA)3 at 100°C. The deposits were found to contain Sm by energy dispersive X-ray spectroscopy (EDX), although no diffraction peak was observed by X-ray diffraction. The formation and dispersion of nanoparticles in the ionic liquid were also confirmed by transmission electron microscopy with and without exposure of the samples to air. The nanoparticles were considered to be metallic Sm, which was identified by electron diffraction and EDX. Sm nanoparticles were anticipated to be formed by the disproportionation reaction of Sm(II) to Sm(III) and Sm in the ionic liquid.

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Electrodeposition of Tin in an Amide Type Ionic Liquid Containing Chloride Ion

Maoko Sano, Naoki Tachikawa, Kazuki Yoshii, Nobuyuki Serizawa, Yasushi Katayama

Electrochemistry (Electrochemistry) 86 ( 5 ) 260 - 264 2018.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 13443542

© 2018 The Electrochemical Society of Japan, All rights reserved. Electrochemical behavior of Sn was investigated on a GC electrode in an aprotic ionic liquid, 1-butyl-1- methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing BMPCl and SnCl2 at 298K. SnCl2 was found to dissolve as [SnCl4]2- by potentiometry. The formal potential of [SnCl4]2-/Sn was -1.67V vs. Ag|Ag(I) (-1.24V vs. ferrocene|ferrocenium), which was more negative than that in BMPTFSA without chloride ions. Electrodeposition of Sn was possible by reduction of [SnCl4]2- in the ionic liquid. The dissociation of [SnCl4]2- was suggested from the diffusion coefficient of [SnCl4]2-. Tubular deposits with an inner diameter of 1-1.5μm were obtained in addition to granular deposits by potentiostatic cathodic reduction at -2.0V.

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Electrodeposition of Cadmium from Lewis Basic Hydrophobic Room-temperature Ionic Liquid

Shimul Saha, Naoki Tachikawa, Kazuki Yoshii, Nobuyuki Serizawa, Yasushi Katayama

Electrochemistry (Electrochemistry) 86 ( 5 ) 229 - 234 2018.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 13443542

© 2018 The Electrochemical Society of Japan, All rights reserved. Electrodeposition of cadmium (Cd) was investigated in a hydrophobic room-temperature ionic liquid, 1-butyl-1- methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) using CdCl2 as the source of Cd species in the presence of excess chloride ion. Raman spectroscopy and potentiometric measurement suggested formation of a cadmium tetrachlocomplex, [CdCl4]2-, in BMPCl/BMPTFSA. Cyclic voltammetry showed the possibility of electrochemical reduction from [CdCl4]2- to Cd(0) with interesting unusual electrochemical behavior, probably derived from the potential-dependent electric double layer structure typical to the ionic liquid. Electrodeposition of Cd was performed by potentiostatic electrolysis and the deposits were characterized by X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy.

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Deposition and Dissolution of Copper on a Quartz Crystal Resonator in Contact with a Separator

Nobuyuki Serizawa, Yo Kobayashi, Hajime Miyashiro, Yasushi Katayama

Electrochemistry (Electrochemistry) 86 ( 5 ) 250 - 253 2018.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 13443542

© 2018 The Electrochemical Society of Japan, All rights reserved. Deposition and dissolution of copper were investigated by electrochemical quartz crystal microbalance (EQCM) technique using a Pt-coated quartz crystal resonator in contact with a separator in order to simulate the configuration of practical batteries. The admittance analysis indicated the quartz crystal resonated even in contact with a glass separator impregnated with the electrolyte under pressure. The mass change estimated from the change in the resonance frequency during deposition and dissolution of Cu on a Pt-coated resonator in contact with the separator was linearly related to the passed electric charge and closed to that without the separator, suggesting the mass monitoring according to Saurbrey equation is possible in the presence of the separator on the electrode. The highly sensitive mass monitoring with an overtone resonance was also found to be possible in the presence of the separator using the third harmonic vibration mode.

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Redox reaction of Tris(acetylacetonato)iron(III) complex in an amide-type ionic liquid

Tachikawa Naoki, Haruyama Ryo, Yoshii Kazuki, Serizawa Nobuyuki, Katayama Yasushi

Electrochemistry (Electrochemistry) 86 ( 2 ) 32 - 34 2018.01

ISSN 1344-3542

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 -1.4V vs. Ag|Ag(I). The diffusion coefficient of Fe(acac)₃ estimated by chronoamperometry was (1.4 + 0.1) × 10^-7cm² 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.

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Determination of nitride ion electrochemically produced in a molten chloride system by ion chromatography

Takei Katsuhito, Serizawa Nobuyuki, Nishikiori Tokujiro, Ito Yasuhiko

Electrochemistry (Electrochemistry) 86 ( 2 ) 35 - 37 2018.01

ISSN 1344-3542

The cathodic reduction of nitrogen (N₂) gas in molten chloride was investigated using a porous nickel (Ni) electrode. A LiCl-KCl-CsCl melt containing cathodically formed nitride ion (N^3-) was sampled from an electrolytic bath and analyzed quantitatively by ion chromatography. The current efficiency of the cathodic reaction calculated from the ratio of quantity of the produced N^3- was approximately 78% on average. The main reason why the measured efficiency did not reach 100% is considered as the amount of N^3- increased more in the pores of the gas electrode than in the bulk of the electrolytic bath.

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Electrochemical formation of selenium nanoparticle in an amide-type ionic liquid

Sato Hiroki, Saha Shimul, Tachikawa Naoki, Yoshii Kazuki, Serizawa Nobuyuki, Katayama Yasushi

Electrochemistry (Electrochemistry) 86 ( 2 ) 57 - 60 2018.01

ISSN 1344-3542

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.

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Electrochemical study on aluminum speciation in Lewis acidic chloroaluminate-bis(trifluoromethylsulfonyl)amide mixed ionic liquids

Katayama Yasushi, Wakayama Takumi, Tachikawa Naoki, Yoshii Kazuki, Serizawa Nobuyuki

Electrochemistry (Electrochemistry) 86 ( 2 ) 42 - 45 2018.01

ISSN 1344-3542

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 -0.68V vs. an Ag|Ag(I) reference electrode, which was corresponding to -0.25V 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^-.

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Infrared spectra of N-H compounds in LiCl-KCl-CsCl molten salts using the diffuse reflectance optical system

Serizawa Nobuyuki, Takei Katsuhito, Nishikiori Tokujiro, Katayama Yasushi, Ito Yasuhiko

Electrochemistry (Electrochemistry) 86 ( 2 ) 88 - 91 2018.01

ISSN 1344-3542

The in-situ Fourier transform infrared spectroscopy of molten eutectic LiCl-KCl-CsCl was conducted in order to identify the dissolved ions in the molten salt electrolytes. The transflectance spectrum of the melts could be easily obtained at temperatures higher than 350°C using the commercially available diffuse reflectance optical system and an air-tight chamber with a built-in heater. The sharp absorption peak attributable to the stretching vibration of OH^- was observed in the melt containing LiOH, indicating the availability of identification of dissolved species in the melts. The intensities of transflection possibly assignable to N-H bonds in imide (NH^2-) and amide (NH₂ ^-) anions in the melt containing Li₃N changed during supplying H₂ gas because of the progress of the protonation reactions of these anions to form NH₃. The in-situ analysis of the dissolved ions in the melts under the reaction conditions by infrared spectroscopy with the diffuse reflectance optical system can be a simple and powerful tool for understanding the reaction mechanism.

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Redox reaction of 2, 2, 6, 6-tetramethylpiperidine-l-oxyI (TEMPO) in lithium bis(trifluoromethylsulfonyl)amide-tetraglyme solvate ionic liquid

Katayama Y., Wada K., Tachikawa N., Serizawa N.

ECS Transactions (ECS Transactions) 86 ( 14 ) 113 - 116 2018

© 2018 Electrochemical Society Inc.All rights reserved. The redox reaction of 2, 2, 6, 6-tetramethylpiperidine-l-oxyl (TEMPO) has been investigated in a solvate ionic liquid composed of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) and tetraglyme (G4). The one-electron transfer and quasi-reversible redox reaction of TEMPO+/TEMPO was observed in the stable electrochemical potential window of the solvate ionic liquid. The formal potential of TEMPO'S/TEMPO was 0.19 V vs. Ferrocene/ferrocenium. The diffusion coefficients of TEMPO and TEMPO + at 298 K were 1.8 × 10 -7 and 7.6 × 10 -8 cm 2 s -1 , respectively, reflecting the coulombic interaction between the charged species with the anion of the solvate ionic liquid. The standard rate constant for the redox reaction of TEMPO + /TEMPO at 298 K was 1.9 × 10 -4 cm s -1 . Charge-discharge of a lithium secondary cell using a lithium-ion conductive glass-ceramics (LICGC) as a diaphragm and [Li(G4)]TFSA containing TEMPO as a catholyte was found to be possible with the average discharge voltage of 3.4 V.

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Design and New Energy Application of Ionic Liquids

Seki S., Ono S., Serizawa N., Umebayashi Y., Tsuzuki S., Ueno K., Watanabe M.

RSC Smart Materials (RSC Smart Materials) 2018-January ( 28 ) 365 - 389 2018

ISSN 20460066

© The Royal Society of Chemistry 2018. New electrochemical application using room-temperature ionic liquids (ILs) are introduced, such as lithium secondary batteries, electrochemical double layer capacitors, and novel types of electrical devices for sustainable and renewal energy society. ILs have so many combinations, owing to many cation/anion species. In this chapter, we introduce properties from fundamental (general and special physicochemical properties) to electrochemical applications of ILs. We also discuss importance of molecular design and application target of ILs.

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Long-cycle-life lithium-sulfur batteries with lithium solvate ionic liquids

Seki Shiro, Serizawa Nobuyuki, Takei Katsuhito, Umebayashi Yasuhiro, Tsuzuki Seiji, Watanabe Masayoshi

Electrochemistry 85 ( 10 ) 680 - 682 2017

ISSN 1344-3542

The electrochemical properties of a sulfur positive electrode in equimolar glyme-Li salt mixtures were investigated. Cyclic voltammograms indicated that the insertion of Li into the sulfur/carbon composite electrode took place over at least three steps during the reduction process. In contrast, the broad anodic current suggested that the electrode kinetics for the extraction of Li were relatively slow. Stable charge-discharge operation of the Li-S cell consisting of a Li negative electrode with [Li(triglyme)][bis(trifluoromethanesulfonyl)amide] as the electrolyte was achieved at 800 cycles. This indicates that dissolution of Li₂S_x into the electrolyte was effectively suppressed in this system.

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Effects of non-equimolar lithium salt glyme solvate ionic liquid on the control of interfacial degradation in lithium secondary batteries

Seki Shiro, Serizawa Nobuyuki, Takei Katsuhito, Tsuzuki Seiji, Umebayashi Yasuhiro, Katayama Yasushi, Miura Takashi, Dokko Kaoru, Watanabe Masayoshi

RSC Advances 6 ( 39 ) 33043 - 33047 2016

Control of interfacial properties between the electrode and electrolyte is important for obtaining long life-cycle lithium-ion secondary batteries. To control interfacial degradation, we investigated the effect of changing the composition ratio of lithium salt (LiN(SO₂CF₃)₂) and low-molecular-weight ether (CH₃-O-(C₂H₄O)₃-CH₃) in the system. A highly electrochemically stable lithium salt glyme solvated ionic liquid electrolyte was realized, with long-lived, robust lithium solvation complexes by increasing the lithium salt composition ratio. Lithium secondary batteries using the electrolyte show notable suppression of the degradation of interfacial resistance at the interface of the electrolyte and the positive electrode (high oxidation state), which leads to a longer life-cycle of the batteries.

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Electrochemical quartz crystal microbalance measurement of a Li4Ti5O12 composite electrode in a carbonate electrolyte

Serizawa Nobuyuki, Shono Kumi, Kobayashi Yo, Miyashiro Hajime, Katayama Yasushi, Miura Takashi

Journal of Power Sources 295 162 - 166 2015.07

Research paper (scientific journal), Joint Work, ISSN 0378-7753

Abstract Electrochemical quartz crystal microbalance (EQCM) measurement is conducted with a Li4Ti5O12 (lithium titanium oxide, LTO)-coated quartz crystal electrode in a carbonate electrolyte (ethylene carbonate + dimethyl carbonate; 50: 50 vol%) containing 1 M LiPF6. In-situ monitoring of the mass change during the charge and discharge of the LTO electrode can be achieved quantitatively because of the "zero-strain" property of LTO with Li+ insertion and the probably low reactivity between LTO and the electrolyte. The local changes of viscosity and density of the electrolyte contacting the LTO electrode are detected via the resonance resistance of the quartz crystal electrode, suggesting the local concentrations of Li+ and counter anion changed significantly during insertion and extraction of Li+ in the organic electrolyte.

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Static and transport properties of alkyltrimethylammonium cation-based room-temperature ionic liquids

Seki Shiro, Tsuzuki Seiji, Hayamizu Kikuko, Serizawa Nobuyuki, Ono Shimpei, Takei Katsuhito, Doi Hiroyuki, Umebayashi Yasuhiro

Journal of Physical Chemistry B 118 ( 17 ) 4590 - 4599 2014.05

ISSN 1520-6106

We have measured physicochemical properties of five alkyltrimethylammonium cation-based room-temperature ionic liquids and compared them with those obtained from computational methods. We have found that static properties (density and refractive index) and transport properties (ionic conductivity, self-diffusion coefficient, and viscosity) of these ionic liquids show close relations with the length of the alkyl chain. In particular, static properties obtained by experimental methods exhibit a trend complementary to that by computational methods (refractive index ∞ [polarizability/molar volume]). Moreover, the self-diffusion coefficient obtained by molecular dynamics (MD) simulation was consistent with the data obtained by the pulsed-gradient spin-echo nuclear magnetic resonance technique, which suggests that computational methods can be supplemental tools to predict physicochemical properties of room-temperature ionic liquids.

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常圧アンモニア電解合成法の高収率化に向けた要素技術開発－H–共存下でのNH3溶解機構－

芹澤信幸，竹井勝仁，錦織徳二郎，伊藤靖彦

電力中央研究所報告書 Q13004 2014.05

Research paper (other academic)

Solvate Ionic Liquid Electrolyte for Li-S Batteries

Dokko Kaoru, Tachikawa Naoki, Yamauchi Kento, Tsuchiya Mizuho, Yamazaki Azusa, Takashima Eriko, Park Jun Woo, Ueno Kazuhide, Watanabe Masayoshi, Seki Shiro, Serizawa Nobuyuki

Journal of the Electrochemical Society 160 ( 8 ) A1304 - A1310 2013

ISSN 0013-4651

Innovation in the design of electrolyte materials is crucial for realizing next-generation electrochemical energy storage devices such as Li-S batteries. The theoretical capacity of the S cathode is 10 times higher than that of conventional cathode materials used in current Li-ion batteries. However, Li-S batteries suffer from the dissolution of lithium polysulfides, which are formed by the redox reaction at the S cathode. Herein, we present simple solvate ionic liquids, glyme-Li salt molten complexes, as excellent electrolyte candidates because they greatly suppress the dissolution of lithium polysulfides. The molten complexes do not readily dissolve other ionic solutes, which leads to the stable operation of the Li-S battery over more than 400 cycles with discharge capacities higher than 700 mAh g-sulfür-1 and with coulombic efficiencies higher than 98% throughout the cycles. Such high performance has not been realized to the best of our knowledge. fürthermore, the addition of a nonflammable fluorinated solvent, which does not break the solvate structure of the glyme-Li salt molten complexes, greatly enhances the power density of the Li-S battery. The strategic design of electrolyte properties provides opportunities for the development of new electrochemical devices with many different electrode materials.

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Charge/discharge performances of glyme-lithium salt equimolar complex electrolyte for lithium secondary batteries

Seki Shiro, Serizawa Nobuyuki, Takei Katsuhito, Dokko Kaoru, Watanabe Masayoshi

Journal of Power Sources 243 323 - 327 2013

ISSN 0378-7753

The electrochemical and battery performances of a CH₃-O-(C ₂H₄O)₃-CH₃/LiN(SO₂CF ₃)₂ 1:1 equimolar complex electrolyte were evaluated using [Li metal|Li metal], [LiFePO₄|Li metal], and [LiNi _1/3Mn_1/3Co_1/3O₂|Li metal] cells. A relatively favorable surface was formed at the Li metal/electrolyte interface revealed by observation of the storage time dependence of the electrochemical impedance spectroscopy. A 3V-class [LiFePO₄|Li metal] cell exhibited favorable capacity retention with little degradation after 600 cycles (2.5-4.0 V). A 4V-class [LiNi_1/3Mn_1/3Co_1/3O ₂|Li metal] cell also exhibited good capacity retention of approximately 60% of the initial discharge capacity after 400 cycles (2.7-4.2 V), while the capacity retention decreased markedly upon increasing the upper charge cutoff voltage above 4.4 V.

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Electrochemical quartz crystal microbalance measurements of lithium-aluminum alloy in a glyme-lithium salt molten complex

Serizawa N., Kobayashi T., Seki S., Takei K., Miyashiro H., Katayama Y., Watanabe M., Miura T.

ECS Transactions 58 37 - 45 2013

Research paper (international conference proceedings), Joint Work

Lithium-aluminum alloying reaction was investigated in lithium bis(trifluoromethylsulfonyl)amide triglyme solvate ionic liquid as a model system for the negative electrode of lithium secondary batteries. The formation of β-phase LiAl was confirmed by X-ray diffraction. The potential of α+β coexisting region was approximately 0.35 V vs. Li/Li(I). The slow relaxation of open circuit voltage and scanning electron microscope images suggested the inhomogeneous alloying reaction along with the active sites. The mass changes with doping and undoping of Li were measured qualitatively by electrochemical quartz crystal microbalance technique.

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EQCM measurement of deposition and dissolution of lithium in glyme-Li salt molten complex

Serizawa Nobuyuki, Seki Shiro, Takei Katsuhito, Miyashiro Hajime, Yoshida Kazuki, Ueno Kazuhide, Tachikawa Naoki, Dokko Kaoru, Katayama Yasushi, Watanabe Masayoshi, Miura Takashi

Journal of the Electrochemical Society 160 ( 9 ) 2013

ISSN 0013-4651

The electrodeposition and dissolution of lithium were investigated in an equimolar mixture of glyme and lithium bis(trifluoromethylsulfonyl)amide. An impedance technique electrochemical quartz crystal microbalance (EQCM-A) was used to monitor the product of the viscosity (ηL) and density (ρL) of the electrolyte, ηLρL, near the electrode in addition to the mass change. The value of ηLρL decreased during Li deposition and sharply increased during Li dissolution because of the changes in the concentration and the dissolved state of Li ion around the electrode. The sharp increase in viscosity during Li dissolution may affect the diffusion of Li(I) near the electrode/electrolyte interface, which is a key issue for the Li secondary battery.

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Comprehensive refractive index property for room-temperature ionic liquids

Seki Shiro, Tsuzuki Seiji, Hayamizu Kikuko, Umebayashi Yasuhiro, Serizawa Nobuyuki, Takei Katsuhito, Miyashiro Hajime

Journal of Chemical and Engineering Data 57 ( 8 ) 2211 - 2216 2012.08

ISSN 0021-9568

Refractive index, an optical property, and liquid density were measured for 17 types of room-temperature ionic liquids at various temperatures. Ab initio calculations were performed to yield theoretical polarizability of the respective ionic liquid composing ions. A highly linear correlation was found between the experimental refractive index and the predicted polarizability normalized in terms of the molar volume. This suggests that the electronic polarization of the ionic liquid composing ions predominantly contributes to the refractive index of the room-temperature ionic liquids.

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Effects of lithium salts on shear relaxation spectra of pyrrolidinium-based ionic liquids

Yamaguchi Tsuyoshi, Mikawa Ken Ichi, Koda Shinobu, Serizawa Nobuyuki, Seki Shiro, Fujii Kenta, Umebayashi Yasuhiro

Journal of Physical Chemistry B 116 ( 24 ) 7322 - 7327 2012.06

ISSN 1520-6106

The shear relaxation spectra of the solutions of lithium salts in ionic liquids composed of N-methyl-N-propylpyrrolidinium cation paired with bis(trifluoromethanesulfonyl)amide (TFSA^-) or bis(fluorosulfonyl) amide (FSA^-) anions are determined from 5 to 205 MHz at various concentrations of lithium salts. The addition of lithium salt retards the shear relaxation, together with the increase in the shear viscosity. The normalized spectra reduce to a single curve when plotted against the product of the frequency and zero-frequency shear viscosity, which indicates that the increase in the shear viscosity by lithium salts is ascribed to the increase in the relaxation time. The difference in the shear viscosity of TFSA- and FSA-based ionic liquids is also elucidated in terms of the shear relaxation time. The relationship with previous studies on ionic mobility and liquid structure is also discussed.

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エーテル/リチウム塩混合錯体電解液のリチウムイオン二次電池への適用（II）－各種電極材料を用いた場合の特性把握－

関志朗，芹澤信幸，竹井勝仁，宮代一

電力中央研究所報告書 Q11018 2012.05

Research paper (other academic), Joint Work

Physicochemical and Electrochemical Properties of 1-Ethyl-3- Methylimidazolium Tris(pentafluoroethyl)trifluorophosphate and 1-Ethyl-3-Methylimidazolium Tetracyanoborate

Seki Shiro, Serizawa Nobuyuki, Hayamizu Kikuko, Tsuzuki Seiji, Umebayashi Yasuhiro, Takei Katsuhito, Miyashiro Hajime

Journal of the Electrochemical Society 159 ( 7 ) 2012

ISSN 0013-4651

The physicochemical (e.g., density, viscosity, ionic conductivity, and self-diffusion coefficient) and electrochemical (e.g., electrochemical window and electric double-layer capacitor performance) properties of two new types of room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMIm-FAP) and 1-ethyl-3- methylimidazolium tetracyanoborate (EMIm-TCB), were investigated and compared. EMIm-FAP showed a wider electrochemical window with a carbon working electrode compared with EMIm-TCB, in spite of lower viscosity, larger self-diffusion coefficients and higher ionic conductivity. Also, the electric double-layer capacitor using EMIm-FAP shows better cycle reversibility and higher charge/discharge voltage operation (over 3 V) than that using EMIm-TCB.

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Dissolution behavior of ammonia electrosynthesized in molten LiCl-KCl-CsCl system

Serizawa Nobuyuki, Miyashiro Hajime, Takei Katsuhito, Ikezumi Taro, Nishikiori Tokujiro, Ito Yasuhiko

Journal of the Electrochemical Society 159 ( 4 ) 2012

ISSN 0013-4651

The dissolution behavior of ammonia (NH ₃) in a molten LiCl-KCl-CsCl system was studied in order to determine the feasibility of low-energy NH ₃ production via electrochemical synthesis in a high temperature molten salt system. In the presence of nitride ion (N ^3-), a portion of NH ₃ chemically dissolved in the melt as imide (NH ^2-) and amide (NH ₂ ^-) anions formed by the reaction between N ^3- and NH ₃. Although the dissolved NH ₂ ^- anion thermally decomposed to form NH ₃ and NH ^2- anion, this phenomena may lower the yield of electrochemical NH ₃ production. The dissolved NH ₃ can be recovered by supplying hydrogen or water vapor to the melt. The anodic reaction between N ^3- and H ₂ to form NH ₃ at a hydrogen gas-diffusion electrode was also examined and the NH ₃ yield was estimated. Although the competing N ₂ evolution reaction occurred at potentials more positive than 1.2 V vs. Li(I)Li, the conversion of Li ₃N approached 70%, following the recovery processes.

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Imidazolium-based room-temperature ionic liquid for lithium secondary batteries

Seki Shiro, Ohno Yasutaka, Mita Yuichi, Serizawa Nobuyuki, Takei Katsuhito, Miyashiro Hajime

ECS Electrochemistry Letters 1 ( 6 ) 2012

ISSN 2162-8726

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イオン液体に共通する物理化学的性質の探索と機能化

関志朗，芹澤信幸，竹井勝仁，宮代一，都築誠二，早水紀久子，梅林泰宏

電力中央研究所報告書 Q10032 2011.06

Research paper (other academic), Joint Work

常圧アンモニア電解合成法の開発－アンモニア溶解機構の検討－

芹澤信幸，竹井勝仁

電力中央研究所報告書 Q10015 2011.06

Research paper (other academic), Joint Work

Physicochemical properties and application of ionic liquids with N-P bonds as lithium secondary battery electrolytes

Serizawa Nobuyuki, Seki Shiro, Tsuzuki Seiji, Hayamizu Kikuko, Umebayashi Yasuhiro, Takei Katsuhito, Miyashiro Hajime

Journal of the Electrochemical Society 158 ( 9 ) 2011

ISSN 0013-4651

Physicochemical properties such as density, viscosity, ionic conductivity, and self-diffusion coefficient of two types of room-temperatureionic liquids composed of cations with N-P bonds were investigated. One is an ionic liquid composed of cations with N-P-O bond, namely, tri(N,N-dimethylamino)-n- butoxyphosphonium bis(trifluoromethanesulfonyl)amide (TABP-TFSA) and has a relatively low viscosity (38 mPa s at 30C) due to the high internal mobility of the cation, despite its large ion size. TABP-TFSA showed a characteristic electrochemical oxidation behavior, such as a wide electrochemical potential window of stability without gas evolution. Formation of passivation film on a Pt electrode was suggested from the results of potential sweep experiments. The lithium secondary battery ([LiCoO₂Li] cell) using TABP-TFSA as the electrolyte achieved stable charge-discharge operations in over 500 cycles. For another ionic liquid with N-P bond, namely, TAEP-TFSA (TAEP⁺ tri(N-methyl-N-(n-butylamino))ethylphosphonium), less battery cycle stability and low rate performances were observed, despite the higher ionic dissociation than TABP-TFSA, probably because of the high viscosity and low electrochemical oxidative stability. It is shown that the introduction of oxygen in the cation like N-P-O produces better performances compared with the cation having N-P structure.

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Evaluation of SrTi 1-xCo xO 3 perovskites (0 ≤ × ≤ 0.2) as interconnect materials for solid oxide fuel cells

Mori Masashi, Wang Zhenwei, Serizawa Nobuyuki, Itoh Takanori

Journal of Fuel Cell Science and Technology 8 ( 5 ) 2011

ISSN 1550-624X

The compatibility of SrTi _1-xCo _xO ₃ perovskites (0 ≤ × ≤ 0.2) was evaluated for use as interconnect materials in solid oxide fuel cells (SOFCs). Although SrTi _1-xCo _xO ₃ perovskites have a single perovskite phase in the range of 0 ≤ × ≤ 0.2, it was observed for SrTi _0.8Co _0.2O ₃ that Co element agglomerated at the grain boundary during sintering. The dense SrTi _0.8Co _0.2O ₃ sample was destroyed and included Sr ₂TiO ₄ as a secondary phase after reducing treatment at 1000°C. As a result of Co doping, the linear thermal expansion coefficient (TEC) increased remarkably with increasing Co content, but the TEC of SrTi _0.9Co _0.1O ₃ was comparable with those of SOFC cathodes and anodes. Co doping of SrTiO ₃ effectively increased electrical conductivity in air, whereas the conductivity of Co-doped SrTiO ₃ in a reducing atmosphere was much lower than that in air. This suggests that the Co ions ^3+/4+ in the perovskites were earlier reduced into Co ²⁺ ions, compared to Ti ⁴⁺ ions.

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Electrolyte properties of 1-alkyl-2,3,5-trimethylpyrazolium cation-based room-temperature ionic liquids for lithium secondary batteries

Seki Shiro, Kobayashi Takeshi, Serizawa Nobuyuki, Kobayashi Yo, Takei Katsuhito, Miyashiro Hajime, Hayamizu Kikuko, Tsuzuki Seiji, Mitsugi Takushi, Umebayashi Yasuhiro, Watanabe Masayoshi

Journal of Power Sources 195 ( 18 ) 6207 - 6211 2010.09

ISSN 0378-7753

The physicochemical and electrochemical properties of three 1-alkyl-2,3,5-trimethylpyrazolium cation-based room-temperature ionic liquids with various alkyl chain lengths were investigated. The temperature dependences of density, viscosity, and ionic conductivity were obtained by precise measurements. Electrolyte properties of these room-temperature ionic liquids were also examined from the viewpoint of their uses in lithium secondary batteries ([LiCoO₂ positive electrode|electrolyte|lithium metal negative electrode]). It was found that the alkyl chain length affects the charge-discharge performances of cells.

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イオン液体を用いたリチウム二次電池の長寿命化

関志朗，芹澤信幸，都築誠二，早水紀久子，小林剛，小林陽，竹井勝仁，宮代一，寺田信之

電力中央研究所報告書 Q09024 2010.08

Research paper (other academic), Joint Work

Ag(I)/Ag electrode reaction in amide-type room-temperature ionic liquids

Serizawa Nobuyuki, Katayama Yasushi, Miura Takashi

Electrochimica Acta 56 ( 1 ) 346 - 351 2010

ISSN 0013-4686

Ag(I)/Ag electrode reaction was investigated in some amide-type room-temperature ionic liquids composed of different cations. The morphology of silver deposits and the electrochemical behavior were not sensitive to the difference in the cations of ionic liquids. On the other hand, it was suggested that the adsorption of bis(trifluoromethylsulfonyl)amide (TFSA^-) is more important for electrodeposition of silver in both ionic liquids and aqueous solutions. The diffusion coefficients of silver cation in the ionic liquids indicated the silver cation is surrounded by TFSA^- to form a bulky species. The rate of crystal growth of silver particles in the ionic liquids by electrochemical Ostwald ripening was much slower than that in a nitrate aqueous solution, suggesting the charge transfer in the ionic liquids is slower than that in the aqueous solution.

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EQCM measurement of Sn(II)/Sn reaction in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room-temperature Ionic liquid

Serizawa Nobuyuki, Tachikawa Naoki, Katayama Yasushi, Miura Takashi

Electrochemistry 77 ( 8 ) 630 - 632 2009.08

ISSN 1344-3542

EQCM (Electrochemical Quartz Crystal Microbalance) measurement during Sn(II)/Sn electrode reaction in a roomtemperature ionic liquid was conducted using an impedance method EQCM, which can measure the resonance resistance and frequency simultaneously. The mass increased during Sn deposition and decreased during Sn dissolution. The viscosity and density of the electrolyte near the electrode, η_Lρ_L, can be estimated by monitoring the resonance resistance. The change of the η_Lρ_L value during Sn(II)/Sn electrode reaction could be accounted for by the concentration profile of Sn(II) near the electrode.

EQCM measurement of Ag (I) /Ag reaction in an amide-type room-temperature ionic liquid

Serizawa Nobuyuki, Katayama Yasushi, Miura Takashi

Journal of the Electrochemical Society 156 ( 11 ) 2009

ISSN 0013-4651

Electrodeposition of silver was investigated using an impedance technique (separately excited, passive technique) electrochemical quartz crystal microbalance (EQCM) in a room-temperature ionic liquid. The mass changes during silver deposition and dissolution were observed with the current efficiencies of nearly 100% during potential sweep, constant potential step, and constant current step experiments. The product of the viscosity and density of the electrolyte near the electrode, ν_Lρ_L, can be estimated by the resonance resistance, which can be monitored simultaneously with the resonance frequency. The change in the ν_Lρ _L value during silver deposition was consistent with the change in the calculated concentration of Ag(I) near the electrode. During the outer-sphere electron-transfer reaction between ferrocenium and ferrocene, no significant changes in the mass and the L_{ρ L} value were observed.

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Electrochemistry of Sn(II)/Sn in a hydrophobic room-temperature ionic liquid

Tachikawa Naoki, Serizawa Nobuyuki, Katayama Yasushi, Miura Takashi

Electrochimica Acta 53 ( 22 ) 6530 - 6534 2008.09

ISSN 0013-4686

The electrochemical reaction of Sn(II)/Sn was investigated in a room-temperature ionic liquid, 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) at 25 °C. The anodic dissolution of Sn metal proceeded by a two-electron transfer reaction with a current efficiency of nearly 100%. Electrodeposition of Sn on a Cu substrate is possible in BMPTFSI containing Sn(II). The formal potential of the Sn(II)/Sn is -0.57 V vs. Ag/Ag(I). The diffusion coefficient of Sn(II) was estimated to be ∼ × 10^-7 cm² s^-1 from chronoamperometric and chronopotentiometric techniques. The initial stage of nucleation of Sn on a polycrystalline Pt substrate was found to be classified into a three-dimensional progressive nucleation under diffusion control by chronoamperometry, suggesting the rate of nucleation is faster than that of crystal growth.

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