Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 80 , Issue 10
Showing 1-41 articles out of 41 articles from the selected issue
Increasing Demands for Next Generation New Rechargeable Batteries
Visions
Headlines
  • Zempachi OGUMI, Hajime ARAI
    2012 Volume 80 Issue 10 Pages 695-699
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Innovation in rechargeable batteries is urgently required to meet demands for application such as electric vehicles, renewable energy storage, and emergency backups. Next-generation rechargeable batteries include novel rocking-chair batteries, metallic lithium/sodium batteries, metal-air batteries, and flow cell systems. In order to improve battery performances and to bring innovation in rechargeable batteries, detailed knowledge on the battery reaction is indispensable. For clarifying the reaction mechanisms in details and proposing a guideline for the improvement, it is required to understand the heterogeneity (inhomogeneity), non-equilibrium and dynamic phenomena inside batteries under operating conditions. As an example, phenomena at electrode/electrolyte interface are elucidated by using surface-sensitive X-ray absorption fine structure analysis, X-ray photoelectron spectroscopy and nuclear magnetic resonance analysis. These analytical methods are applicable not only for the advanced LIB systems but also for totally innovative systems. Elucidating and understanding the reasons for the inactivity, slow kinetics and deterioration of LIB will be the key to open post LIB technology.
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  • Esther S. TAKEUCHI, Amy C. MARSCHILOK, Kenneth J. TAKEUCHI
    2012 Volume 80 Issue 10 Pages 700-705
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Considerations of energy density, power, and calendar life are critical to effectively develop advanced secondary systems. For next generation battery applications requiring multiple features including long life, large cycle count, high energy density and high power, new strategies are needed for the rational design of electroactive materials and electrodes. This article discusses several conceptual approaches under exploration with examples from our research group. The first approach is the systematic synthesis of materials with structures facilitating ion insertion and deinsertion at high voltage and energy density, where we control materials properties such as surface area, particle size and in particular crystallite size. A second approach is the investigation of novel electrode structures and substrates to increase energy density and capacity retention under cycling, where we have developed strategies for minimizing passive components. A third approach is investigation of catalysts for metal air batteries where the cathode active material is drawn from the air rather than carried in the battery.
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Comprehensive Papers
  • Nobuyuki IMANISHI, Yasuo TAKEDA, Osamu YAMAMOTO
    2012 Volume 80 Issue 10 Pages 706-715
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    This article summarizes our research on aqueous lithium-air rechargeable batteries. Lithium-air batteries have a far higher energy density and lower material cost than lithium-ion batteries, so that they are now attracting growing attention as possible power sources for electric vehicles. Presently, two types of rechargeable lithium-air batteries have been developed; non-aqueous and aqueous types. The aqueous type has a lower specific energy density than the non-aqueous system, but overcomes some severe problems that must still be addressed for the non-aqueous type, such as lithium metal corrosion by water from air and the high polarization of electrode reactions. The key component of the aqueous lithium-air battery is a water-stable lithium metal electrode (WSLE). The WSLE developed in our laboratory consists of lithium metal covered with a lithium conducting polymer electrolyte and a lithium conducting water-stable solid electrolyte, which was successfully operated in a saturated LiOH and LiCl aqueous solution.
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  • Naoaki YABUUCHI, Hiroaki YOSHIDA, Shinichi KOMABA
    2012 Volume 80 Issue 10 Pages 716-719
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Single phase, well-crystallized O3-type NaFeO2 (alpha NaFeO2) is prepared by a solid-state method. Electrode performance of O3-type NaFeO2 is examined as positive electrode materials for rechargeable sodium batteries. O3-type NaFeO2 can deliver 80–100 mAh g−1 of reversible capacity with a nearly flat voltage profile at approximately 3.3 V vs. Na metal. The electrode performance is significantly deteriorated by oxidation beyond x > 0.5 in Na1−xFeO2. X-ray diffraction study reveals that loss of electrode reversibility originates from irreversible structural change, possibly accompanied by iron ion migration in layered host structures. The sodium ion insertion into the host structures would be disturbed by the irreversible structural change when charged beyond x > 0.5 in Na1−xFeO2. Acceptable cyclability is, therefore, achieved for O3-type NaFeO2 as the positive electrode materials in the limited composition of x = 0–0.45 in Na1−xFeO2.
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  • Takashi OKUBO, Tomoyuki YAMADA, Morihiro SAITO, Chihiro YODOYA, Akika ...
    2012 Volume 80 Issue 10 Pages 720-724
    Published: October 05, 2012
    Released: October 05, 2012
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    To reduce the high irreversible capacity (Qirr) of Si thin flake (Si-LP) negative electrode, carbon-coated Si-LPs were prepared using citric acid as a precursor and their charge/discharge properties were investigated as negative electrodes in lithium-ion batteries. The carbon-coated powder was homogeneously coated with a thin carbon layer (8–10 and 6–8 nm in thickness for Si-LPs heat-treated at 600 and 700°C, respectively, 14 wt% for each). The irreversible capacity Qirr was successfully reduced to about a half (ca. 1100 mAh g−1) of that of the pristine Si-LP (2336 mAh g−1), though the cycleability was slightly deteriorated. The cycleability of Si-LP@Cs was significantly improved by the addition of 10 wt% VC in the electrolyte solution. Si-LP@C(700°C) kept high discharge capacities over 2000 mAh g−1 even after 50 cycles with a reduced Qirr of ca. 1300 mAh g−1 compared with the pristine Si-LP (ca. 2450 mAh g−1).
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Communications
  • Kohei MIYAZAKI, You Shin LEE, Tomokazu FUKUTSUKA, Takeshi ABE
    2012 Volume 80 Issue 10 Pages 725-727
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Zinc oxide electrodes modified with an anion-exchange ionomer (AEI) are fabricated to suppress the dendrite formation of metallic zinc deposition. Charge-discharge measurements show that the discharge capacities and efficiencies of AEI-modified ZnO electrodes are superior to those of bare ZnO electrodes. These improvements are explained by the selective ion permeation through the AEI films. In addition, we demonstrate that the AEI-modified ZnO electrodes work well as a rechargeable negative electrode in an alkaline solution which contains no ZnO additive.
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  • Kohei MIYAZAKI, Koji NISHIO, Takeshi ABE, Koji SUTO, Yukinari KOTANI, ...
    2012 Volume 80 Issue 10 Pages 728-730
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    In order to improve oxygen reduction performances of an air electrode using perovskite type La0.7Ca0.3CoO3 as an electrocatalyst, a layered double hydroxide (LDH) containing magnesium and aluminum was examined as an ion-conducting additive. Although the addition of LDH impeded gas permeation of the catalyst layer of the electrode, it was effective in reducing charge transfer resistance of the electrode, and as a result, the oxygen reduction reaction of the air electrode was remarkably enhanced.
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  • Tatsumi ISHIHARA, Arjun Kumar THAPA, Yuiko HIDAKA, Shintaro IDA
    2012 Volume 80 Issue 10 Pages 731-733
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Mesoporous cobalt oxide (Co3O4) was studied for air electrode of Li-air rechargeable battery. In this study, mesoporous Co3O4 with an average pore radius of 3.09 nm and BET surface area of 99 m2/g was successfully prepared by using mesoporous SiO2 for template. Prepared mesoporous Co3O4 was applied for air electrode of Li-air battery after mixing with Pd and it was found that the cell showed a reasonably large discharge capacity of 481 mAh/g-cat. at 0.1 mA/cm2 at the initial cycle. Energy efficiency for charge and discharge was estimated to be ca. 75%. Raman spectroscopy suggests that the main product during discharge was Li2O2 and formation of Li2CO3 was hardly observed.
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  • Motohiro NAGAO, Akitoshi HAYASHI, Masahiro TATSUMISAGO
    2012 Volume 80 Issue 10 Pages 734-736
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    To enhance a cyclability and a rate capability in bulk-type solid-state cells using a lithium metal electrode, an indium thin layer prepared by vacuum-evaporation was inserted at the interface between a lithium electrode and an Li2S-P2S5 solid electrolyte layer. The Li/Li4Ti5O12 cells using indium thin film were charged and discharged for 120 cycles reversibly and worked at the high current density of 1.3 mA cm−2. Inserting lithium-alloy thin layer at the interface between the lithium electrode and the solid electrolyte layer brought about a good cyclability and a high rate capability for the all-solid-state lithium metal cells because of the formation and retention of intimate contacts at the interface. The obtained results are useful for achieving bulk-type solid-state lithium batteries with high power and energy densities.
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  • Hiroyuki USUI, Naoki UCHIDA, Hiroki SAKAGUCHI
    2012 Volume 80 Issue 10 Pages 737-739
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    To improve the deviation of cycling performances as Li-ion battery anode, we controlled the morphology of Ni-P layers deposited on Si particles in thick-film electrodes prepared by a gas-deposition method. The spotty Ni-P layers were uniformly coated on Si particles by an electroless deposition in a neutral bath. The resulting electrodes using Ni-P-coated Si exhibited excellent cycling performances and their good reproducibility. The reason for the improvement of performances is probably that the Ni-P layers can effectively release a stress generated by alloying/dealloying reactions of Li with Si.
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  • Masanobu CHIKU, Wataru TSUJIWAKI, Eiji HIGUCHI, Hiroshi INOUE
    2012 Volume 80 Issue 10 Pages 740-742
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Charge transfer kinetics at the Li metal electrode/electrolyte interface for three inorganic solid electrolytes and an organic liquid electrolyte were elucidated with two parameters, exchange current density (i0) for Li/Li+ couple reactions and ionic conductivity in electrolyte. The former was evaluated by potential step method with a microelectrode, while the latter was done by electrochemical impedance spectroscopy. Both i0 and ionic conductivity showed Arrhenius type dependence, and activation energies (Ea) for the charge transfer reactions and ionic conduction were evaluated. In the case of the organic liquid electrolyte, Ea for the Li/Li+ couple reactions was higher than that for ionic conduction because of the solvation/desolvation of Li+ ion. However, for the Li2S-P2S5 solid solid electrolytes, the Ea for the Li/Li+ couple reactions was quite close to that for ionic conduction due to the lack of the solvation/desolvation.
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  • Naoyoshi NUNOTANI, Shinji TAMURA, Nobuhito IMANAKA
    2012 Volume 80 Issue 10 Pages 743-745
    Published: October 05, 2012
    Released: October 05, 2012
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    Tetravalent Hf4+ ion conducting solid electrolytes, Hf1−x/4(Nb1−yWy)5/(5+y)P3−xWxO12, were developed by partially replacing both the Nb5+ and P5+ sites in the NASICON-type HfNb(PO4)3 solid simultaneously with higher valence W6+ ions. Among the samples prepared, the highest conductivity was obtained for the Hf3.85/4(Nb0.8W0.2)5/5.2P2.85W0.15O12 (y = 0.2; x = 0.15) solid, which contains a high amount of W6+ ions and holds the optimum lattice volume for Hf4+ ion conduction, enabling a significant reduction of the electrostatic interaction between the Hf4+ cation and the O2− anions in the solid. The conducting species in the Hf3.85/4(Nb0.8W0.2)5/5.2P2.85W0.15O12 solid was directly demonstrated to be the Hf4+ ion via DC electrolysis.
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  • Noritoshi NAMBU, Kiyoshi OHTSUKI, Hitomi MUTSUGA, Yuta SUZUKI, Masahir ...
    2012 Volume 80 Issue 10 Pages 746-748
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    We have used 2-fluoroethyl propionate (2FEP), ethyl 2-fluoropropionate (E2FP), and ethyl 3-fluoropropionate (E3FP) as organic solvents for lithium secondary batteries. We describe the effect of position isomerism on the physical and electrochemical properties of monofluorinated ethyl propionates (EPs). The relative permittivities of E2FP and E3FP were higher than that of 2FEP, whereas the viscosity of E2FP was lower than those of 2FEP and E3FP. The ionic conductivities of 1 mol dm−3 LiPF6 solutions in E2FP and E3FP were higher than those in 2FEP and EP above room temperature. The use of 2FEP or E2FP as a co-solvent greatly improved discharge capacities of Li | LiCoO2 coin cells.
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  • Yuki KATO, Koji KAWAMOTO, Ryoji KANNO, Masaaki HIRAYAMA
    2012 Volume 80 Issue 10 Pages 749-751
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    A solid electrolyte, Li10GeP2S12, exhibits a high lithium ionic conductivity of 12 mS/cm at room temperature. Because of its high ionic conductivity, high charge-discharge performance would be expected for the all-solid-state batteries using the Li10GeP2S12 electrolytes. In this study, all-solid-state batteries using Li10GeP2S12, were constructed and their battery performances were examined. The batteries using the Li10GeP2S12 electrolyte showed higher discharge capacities than those with glass electrolyte, 75Li2S·25P2S5, particularly under the high-rate current discharge.
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  • Masahiro TOKITA, Minato EGASHIRA, Nobuko YOSHIMOTO, Masayuki MORITA
    2012 Volume 80 Issue 10 Pages 752-754
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The double-layer capacitors and their degradation after aging process for nano-fibrous carbon electrodes with various graphitic structures have been compared. The nano-fibrous carbon with amorphous structure has successfully been prepared from biomass precursor. The nano-fibrous carbons with graphitic and amorphous structures exhibit similar specific surface area and double-layer capacitance. However, the change of the capacitances of the cells consisting of both carbons by the aging process under high temperature and high voltage condition are different. The amorphous nano-fibrous carbon electrode provides capacitance decrease by the deposit on electrode, while the graphitic nano-fiber provides capacitance increased likely due to the gas evolution.
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  • Minato EGASHIRA, Tomoyo TANAKA, Nobuko YOSHIMOTO, Masayuki MORITA
    2012 Volume 80 Issue 10 Pages 755-758
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The electrochemical insertion and de-insertion of sodium ion in hard carbon has been monitored in electrolytes consisting of sodium perchlorate (NaClO4), propylene carbonate (PC), and an ionic liquid N,N-diethyl-N-methoxyethyl ammonium bis(trifluoromethane sulfonyl)imide (DEMETFSI). Voltammetric observation revealed that the reversible sodium insertion is inhibited by the content of DEMETFSI in the electrolyte. The reversible signs of sodium insertion become obvious when the volumetric content of DEMETFSI was 70%. The inhibition effect for sodium insertion by DEMETFSI is somewhat in relation to the change in coordination with sodium ion in electrolyte.
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  • Yoshihiro KADOMA, Yusuke CHIBA, Daisuke YOSHIKAWA, Yuko MITOBE, Naoaki ...
    2012 Volume 80 Issue 10 Pages 759-761
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    We have investigated the preparation and electrochemical characteristics of a lithium excess Li4.3Ti5O12 carbon composite (Li4.3Ti5O12/C) with different carbon sources (polyacryl acid, polyvinyl alcohol, and carboxy methyl cellulose sodium). We have prepared the lithium excess Li4.3Ti5O12/C by a spray-drying method followed by calcining at 800°C in a nitrogen atmosphere. The TEM observations indicated that the surface of the Li4.3Ti5O12/C particle was clearly covered with an amorphous carbon layer. The Li4.3Ti5O12/C materials employing polyvinyl alcohol as the carbon source showed the best rate performance with the highest discharge capacity of 117 mAh (g-Li4.3Ti5O12/C)−1 at the 10C rate.
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  • Hiroaki ISHIKAWA, Yuuki NISHIKAWA, Omar MENDOZA, Yuki MARUYAMA, Yoshit ...
    2012 Volume 80 Issue 10 Pages 762-764
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    We were able to derive the dQ/dE vs. E curve by carrying out chronopotentiometric measurements using a lithium ion secondary cell incorporating a reference electrode. These in-situ measurements were found to be comparable to the ex-situ measurements, which were obtained using a graphite single particle method. The dQ/dE vs. E curves for the anode of the same type of cells, which contain storage deterioration and cyclic test deterioration data, were then obtained. As a result, an over potential increase in the charge and discharge peaks, as well as a decrease in the charge coulombs was observed. As a result of the dQ/dE vs. E curves of the anode of degraded lithium ion secondary cells incorporating a reference electrode, we were able to evaluate the graphite degradation under conditions close to real environmental conditions.
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  • Hideyuki OGAWA, Atsushi UNEMOTO, Itaru HONMA
    2012 Volume 80 Issue 10 Pages 765-767
    Published: October 05, 2012
    Released: October 05, 2012
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    A quasi-solid-state composite electrolyte, consisting of N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)amide (DEME-TFSA)-lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA)-fumed silica nanoparticles, has been prepared for use in the electrolyte of a lithium-sulfur battery. Regardless of the solid-state like appearance, the quasi-solid-state electrolyte exhibited a high liquid-like apparent conductivity of 1.2 × 10−4 S cm−1 at 308 K when the volume ratio of DEME-TFSA-Li-TFSA is 75% in the quasi-solid-state composite. By using the quasi-solid-state electrolyte, a quasi-solid-state lithium-sulfur battery was developed and the cell performance was evaluated. The cell has successfully exhibited initial discharge capacities of 1370 mAh g−1 at 308 K with a 0.05 C via the conversion reaction of sulfur and lithium. During 10 charge-discharge cycles, the discharge capacity decreased to 600 mAh g−1 due to the lower utilization ratio of sulfur by agglomeration of Li2S at the electrode/electrolyte interface.
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  • Tomohiro SATOH, Keita KURIHARA, Noritoshi NAMBU, Masahiro TAKEHARA, Ma ...
    2012 Volume 80 Issue 10 Pages 768-770
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    A trifluoromethyl group (CF3-) is a strong electron-withdrawing substituent. We have synthesized 1-(2,2,2-trifluoroethoxy)-2-(2-methoxyethoxy)ethane (TFEMEE). The relative permittivity, viscosity, and anodic stability of TFEMEE were higher than those of 1-ethoxy-2-(2-methoxyethoxy)ethane (EMEE). The presence of the trifluomethyl group can weaken the attractive forces between molecules. The kinematic viscosity of TFEMEE was as low as that of EMEE especially at high temperatures. The use of TFEMEE as a co-solvent greatly improved cycling efficiency of a lithium anode.
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  • Noritoshi NAMBU, Tokuma NACHI, Masahiro TAKEHARA, Makoto UE, Yukio SAS ...
    2012 Volume 80 Issue 10 Pages 771-773
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Methyl propyl carbonate (MPC) shows a liquid temperature range that is wider than that of diethyl carbonate (DEC). Monofluorinated organic solvents exert the strong polar effect on the physical and the electrochemical properties. 2-Fluoropropyl methyl carbonate (2FPMC) and ethyl 2-fluoroethyl carbonate (E2FEC) are isomeric with each other. The relative permittivity and viscosity of 2FPMC were higher than those of E2FEC, MPC, and DEC. The ionic conductivity of 1 mol dm−3 LiPF6 solution in 2FPMC was lower than those in E2FEC, MPC, and DEC. The use of 2FPMC as a co-solvent greatly improved cycling efficiency of a lithium anode.
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  • Nobuko YOSHIMOTO, Keisuke HOTTA, Minato EGASHIRA, Masayuki MORITA
    2012 Volume 80 Issue 10 Pages 774-776
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Electrochemical deposition and dissolution of magnesium have been investigated in organic solutions consisting of alkylmagnesiumbromides/tetrahydrofuran (RMgBr/THF) having different alkyl-chains mixed with an ionic liquid. Coulombic efficiency for cathodic deposition and anodic dissolution of magnesium, obtained from voltammetric responses, decreased with the increase in the alkyl-chain length of the magnesium complex. The highest current response was observed in the electrolyte system consisting of CH3MgBr/THF with a quaternary ammonium salt-based ionic liquid.
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  • Hikaru SANO, Hikari SAKAEBE, Hajime MATSUMOTO
    2012 Volume 80 Issue 10 Pages 777-779
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The behavior of lithium (Li) electrodeposition in room temperature ionic liquids (RTILs) containing aliphatic quaternary ammonium cation was investigated by in-situ optical microscope observation. As a result, round shape Li deposits were obtained after deposition in all cases with vinylene carbonate (VC) as an additive, while most deposits were dendritic without VC. AC impedance spectroscopic measurements indicated that the dendrite growth was suppressed when a surface film with large resistance was generated. The dendrite suppression effect by VC addition was confirmed in the Py14[TFSA]-based and TMHA[TFSA]-based electrolytes as well as in the PP13[TFSA]-based electrolyte.
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  • Noritoshi NAMBU, Jyunya YAMAMOTO, Kohei YAMAGUCHI, Yukio SASAKI
    2012 Volume 80 Issue 10 Pages 780-782
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Sydnone is one of the mesoionic heterocyclic aromatic compounds and is represented by the resonance hybrid of different polarized ionic structures. We have newly synthesized 3-propyl-4-propylsydnone (PPSD) and investigated its physical, chemical, and electrochemical properties. The electron-pair donability for PPSD was higher than that for propylene carbonate (PC), but the electron-pair acceptability for PPSD was lower. The addition of PPSD to an ethylene carbonate (EC)-diethyl carbonate (DEC) equimolar binary mixture at the molar ratio of 1:1:0.05 was effective for an increase in cycling efficiency of a lithium anode.
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Articles
  • Shinji NAKANISHI, Fuminori MIZUNO, Takeshi ABE, Hideki IBA
    2012 Volume 80 Issue 10 Pages 783-786
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Influence of carbon surface on the discharge voltage of non-aqueous Li-O2 battery was investigated. The discharge voltage definitely decreased with the graphitization of as-prepared carbon in spite of almost the same chemical information of carbon surface. Graphitization of carbon led to the dramatic morphological change from granular-type to angulated-type, and as a consequence, the number of defect part toward basal part was decreased. The defect parts of the carbon surface were suggested to promote the Li+ containing oxygen reduction reaction (Li+-ORR) related with the discharge voltage. Cyclic voltammetry indicated that the ORR potential in the Li+ containing media was positively shifted on the edge oriented carbon model plane, compared with those of the graphitized ones. It was, thus, concluded that the carbon surface including defects activated the Li+-ORR process on a cathode, resulting in the increase of discharge voltage.
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  • Hideyuki NOGUCHI, Satoshi MIYAZAKI, Yoshihiro TANAKA, Wenwen ZHAO
    2012 Volume 80 Issue 10 Pages 787-790
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    A new synthetic route for TiO2(B) via lepidocrocite type KxLiyTi2−(x+y)/4O4 (KLTO) was established. Pure layered titanic acids were obtained by proton exchange of KLTO in 3 mol dm−3 HNO3 and HCl solution. The obtained titanic acid transformed into TiO2(B) phase at 350°C and it was stable up to 450°C. Plate-like morphology particles was formed during proton exchange and transformation process to TiO2(B). TiO2(B) samples with high tapping density (0.9–1.1 g cm−3) was prepared and they delivered discharge capacities of more than 100 mAh g−1 even at 2 C.
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  • Yasushi IDEMOTO, Tetsuya KASHIMA, Naoto KITAMURA
    2012 Volume 80 Issue 10 Pages 791-799
    Published: October 05, 2012
    Released: October 05, 2012
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    We prepared two 0.5Li2MnO3-0.5LiMnxNixCo(1−2x)O2 (x = 1/3, 5/12) samples using the solution method, followed by heat treatment under vacuum reducing conditions. ICP and average-valence analyses clarified that the amounts of lithium and oxygen were decreased by reductive heat treatments. Results of a cycle performance test showed that the heat-treated samples exhibited a high discharge capacity, although the voltage regions contributing to the improvements depended on the metal composition, i.e., 3.3 and 3.8 V for x = 1/3 and x = 5/12, respectively. In order to discuss the crystal structure, a Rietveld analysis by neutron diffraction was carried out. A localized model in which Mn occupied the 4g site and Li occupied the 2b site in the Li2MnO3-type structure (S.G.; C2/m) resulted in good fitting.
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  • Kyungsu KIM, Takeshi TOUJIGAMORI, Kota SUZUKI, Sou TAMINATO, Kazuhisa ...
    2012 Volume 80 Issue 10 Pages 800-803
    Published: October 05, 2012
    Released: October 05, 2012
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    Electrochemical properties and structure changes of nano-sized Li4Ti5O12 during lithium (de)intercalation were investigated using a two-dimensional thin film electrode. Li4Ti5O12 thin films were deposited on a Nb:SrTiO3(110) substrate by a pulsed laser deposition technique. X-ray diffraction and reflectometry measurements confirmed the epitaxial growth of 27.6-nm-thick Li4Ti5O12(110) films. Galvanostatic charge-discharge curves showed a large discharge capacity of 217 mAh g−1 at the initial discharge cycle, although the reversible capacity decreased in subsequent cycles. In situ X-ray diffraction measurements clarified the drastic structural changes of the Li4Ti5O12 film upon soaking in the electrolyte and during the first intercalation and deintercalation processes. The surface region of Li4Ti5O12 had a different structure from the bulk during electrochemical cycling and could cause the nano-sized Li4Ti5O12 electrodes to have high capacities and poor stabilities.
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  • Seungwon PARK, Shota ITO, Kaoru TAKASU, Takeshi YAO
    2012 Volume 80 Issue 10 Pages 804-807
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    We inserted Li into or extracted Li from Li-inserted γ-Fe2O3, and analyzed the structure at relaxation time. For multi-stage Li insertion sample, it was indicated that Fe moved from 8a site to 16c site during Li insertion process and Fe moved from 16c site to 8a site at relaxation process after the Li insertion, and it was suggested that Li is inserted at 8a site with Li insertion process and Li moves from 8a site to 16c site after the Li insertion. For extraction sample, it was indicated that Fe moved from 16c site to 8a site during Li extraction process and it was suggested that Li is extracted from 8a site and Fe at 16c site moves into 8a site. It was considered that Li prefer 8a site to occupy kinetically and prefer 16c site thermodynamically, and that 8a site take a role as a diffusion path for both Li insertion and Li extraction. From the first principle calculation, 16c site preference to 8a site of Li was indicated.
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  • Yukiko MATSUI, Shunsuke KAWAGUCHI, Toshinori SUGIMOTO, Manabu KIKUTA, ...
    2012 Volume 80 Issue 10 Pages 808-811
    Published: October 05, 2012
    Released: October 05, 2012
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    We evaluated the charge-discharge behavior of a LiNi1/3Mn1/3Co1/3O2 (NMC) electrode in a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid. At 163 mAh g−1 after 50 cycles, the discharge capacity of the NMC cathode in LiTFSI/EMImFSI (TFSI = bis(trifluoromethylsulfonyl)imide) at 1.0 C in the voltage range 3.0–4.5 V (vs. Li/Li+) is comparable to that in the conventional electrolyte, LiPF6/EC+DMC. Moreover, the rate capability of the cell with LiTFSI/EMImFSI exceeded that with LiPF6/EC+DMC, especially at high rates, probably owing to the low resistance at the electrode/electrolyte interface. These results suggest that EMImFSI is a suitable electrolyte for lithium-ion batteries utilizing an NMC cathode.
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  • Hideyuki MORIMOTO, Tatsuya SUDO, Hiroki WATANABE, Shin-ichi TOBISHIMA
    2012 Volume 80 Issue 10 Pages 812-816
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The anode properties of SiO-C electrode materials [SiO-C:α-Fe2O3 = x:100 − x (wt%)] containing α-Fe2O3 fine powder (spherical particles, ca. 0.16 µm) as the additive were investigated in a lithium cell using lithium metal as the counter electrode. It was observed by scanning electron microscopy (SEM) that spherical α-Fe2O3 particles are present between the SiO-C particles. The SiO-C alloying-reaction electrode exhibited a high capacity of ca. 1330 mAh g−1. However, the electrode caused a gradual decrease in cycle capacity at around 30 cycles. On the other hand, the α-Fe2O3 conversion-reaction electrode showed a high discharge capacity of ca. 800 mAh g−1, and a good cycle performance over 50 cycles. In addition, charge and discharge were possible even for an α-Fe2O3 electrode without the addition of an electronic conductive material such as carbon. SiO-C electrodes containing a small amount of α-Fe2O3 fine powder exhibited higher capacities and improved cycle performances compared with the SiO-C electrode. The electrode with x = 50 exhibited a discharge capacity of ca. 1000 mAh g−1 and a good cycle performance over 70 cycles. The α-Fe2O3 fine powder works as a conductive path between the SiO-C particles, and prevents the disintegration of the electrode.
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  • Yoshitsugu SONE, Kohichi HATAKEYAMA, Shigeaki YAMADA, Minoru UMEDA
    2012 Volume 80 Issue 10 Pages 817-820
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Two 7.5 Ah lithium-ion secondary cells were fabricated with the same design of electrodes and separator. One cell had the mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as an electrolyte solution containing vinylene carbonate as an additive to control the solid electrolyte interphace, while the other cell used a conventional electrolyte solution. These cells were used in cycle-life and storage tests and the increases in their impedances were monitored. The activation energy calculated from the temperature dependence of the impedance remained constant after 1,000 h. It was found that the additive like vinylene carbonate do not influence to the activation energy as a function of time for the electrochemical reaction inside the cell.
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  • Shinji KOIKE, Hironori KOBAYASHI
    2012 Volume 80 Issue 10 Pages 821-824
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    SnO2 and CuSnO2 were successfully sprayed onto a Ni substrate using electrostatic spray deposition to produce negative electrode films with highly porous morphologies for use in lithium batteries. The spray-deposited SnCl2 decomposed to Sn during heat treatment at 230°C under inert atmosphere and then was oxidized to SnO2 being exposed to the air. The resultant SnO2 film, which did not contain any additives such as binders or conductive additives, was used as a negative electrode. At the beginning of some charge-discharge cycles, the SnO2 film achieved a capacity of 780 mAh g−1, which was close to its theoretical capacity. However, its capacity subsequently decreased because of crystal growth during the Li alloying-dealloying process. The capacity retention of the film was improved by adding Cu to the precursor solution. Although the initial capacity of the CuSnO2 film was lower than that of the SnO2 film, the CuSnO2 film displayed better cycle performance; i.e., it possessed more than double the capacity of the SnO2 film after 100 cycles.
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  • Satoshi UCHIDA, Masaki YAMAGATA, Masashi ISHIKAWA
    2012 Volume 80 Issue 10 Pages 825-828
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The present LiFePO4/C cathode material is synthesized via carbothermal reduction by a high-frequency induction heating method in extremely short heating time (within a few minutes). The electric conductivity of LiFePO4/C is improved to 1.9 × 10−2 S cm−1 by a short-time annealing process following a sintering process at 900°C. An increase in the particle size and formation of Fe2P as impurity are suppressed by annealing at a relatively low temperature: 700°C. The cathode containing annealed LiFePO4/C shows discharge capacities of 156.0, 136.3, and 100.1 mAh g−1 at 1/10, 1, and 10 C-rates (1 C = 170 mA g−1), respectively, and its polarization between charge and discharge is smaller than that of non-annealed LiFePO4/C. Furthermore, the annealed LiFePO4/C cathode shows better charge and discharge rate performance than the non-annealed LiFePO4/C cathode.
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  • Yoshinori ARACHI, Momoko NAKAMURA, Hiroyuki MAEDA, Hironori KOBAYASHI
    2012 Volume 80 Issue 10 Pages 829-833
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    An order-disorder behavior of Li and Ni in LiNi0.5Mn0.5O2 was investigated by means of the ion-exchange preparation and the high-temperature X-ray diffraction measurement using synchrotron radiation. Rietveld refinements at room temperature showed that the occupancy of Ni at the Li site prepared by ion-exchange is less than those by co-precipitation and it increases with an increase in temperature and time for the ion-exchange reaction. In addition, it was found that by high-temperature XRD measurements an order-disorder transition occurs at around 700 K for the sample prepared by the ion-exchange. Further, we have confirmed that an optimum ion distribution in LiNi0.5Mn0.5O2 exists to show superior electrochemical performance as a positive electrode for Li-ion batteries. These results demonstrate a close relation between crystal structure and electrochemical properties for LiNi0.5Mn0.5O2 which is a member of Li2MnO3-based materials. It is the first report that presents an order-disorder transition of LiNi0.5Mn0.5O2 at elevated temperatures, on the basis of the experimental results.
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  • Mamoru KOMO, Asuna HAGIWARA, Sou TAMINATO, Masaaki HIRAYAMA, Ryoji KAN ...
    2012 Volume 80 Issue 10 Pages 834-838
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    The oxygen evolution and reduction properties of La0.8Sr0.2CoO3 are characterized using two-dimensional model electrodes with different reaction planes, synthesized on SrTiO3 single crystal substrates by pulsed laser deposition. Thin-film X-ray diffraction and reflectivity measurements confirm the epitaxial growth of 29-nm-thick La0.8Sr0.2CoO3 (001), (110), and (111) films on SrTiO3 (001), (110), and (111) substrates, respectively. Cyclic voltammetry curves in 1-M KOH aqueous solution indicate that the (110) film has the highest activity for oxygen evolution and reduction reactions. An expansion of the La0.8Sr0.2CoO3 lattice is observed after the oxygen reduction process, indicating the formation of oxygen defects, with the highest number of defects being produced in the (110) film. X-ray reflectivity analysis demonstrates the formation of a surface layer on the La0.8Sr0.2CoO3 films during electrochemical cycling due to the decomposition of La0.8Sr0.2CoO3. The surface structure constructed at the electrode/electrolyte interface is a crucial factor influencing oxygen evolution and reduction activity of La0.8Sr0.2CoO3.
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Technological Report
  • Atsushi SAKUDA, Akitoshi HAYASHI, Takamasa OHTOMO, Shigenori HAMA, Mas ...
    2012 Volume 80 Issue 10 Pages 839-841
    Published: October 05, 2012
    Released: October 05, 2012
    JOURNALS OPEN ACCESS
    Bulk-type all-solid-state batteries currently use a compressed powder pellet with the thickness of several hundred micrometers as a solid electrolyte separator. In this study, all-solid-state lithium secondary batteries (In/LiCoO2) with a thin Li2S-P2S5 solid electrolyte separator were constructed; their charge-discharge performance was investigated. The all-solid-state batteries using the Li2S-P2S5 separator with a thickness of 3 µm were charged and discharged with the capacity of 93 mAh g−1. This result suggests that bulk-type all-solid-state batteries were successfully prepared with the solid electrolyte separator with several micrometer thicknesses.
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