Details of a Researcher - Serizawa, Nobuyuki

Papers - Serizawa, Nobuyuki

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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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