奈良　洋希

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ISSN：2045-2322

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概要：:Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO2, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li21Si5. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

ISSN：00134651

概要：© The Author(s) 2015.Electrochemical impedance spectroscopy (EIS) using an equivalent circuit is a powerful tool in the diagnosis of lithium-ion batteries (LIBs). However, LIBs have been increasingly used in applications requiring power higher than that used for conventional LIBs for portable electric devices. Considering this demand for LIBs, the ionic resistances in the electrodes, which raise a reaction distribution under high-power operation, are important. This consequently means EIS analysis should include ionic resistances in the electrodes in equivalent circuits. Additionally, the impedance response of LIBs are too complicated to be analyzed in detail because the impedance response consists of overlapping elemental processes such as chemical reactions and ion migration. This paper therefore presents an analysis of impedance responses, which are independently obtained by a micro reference electrode, by using a transmission line model (TLM) that possesses the ability to count the ionic resistances in the electrodes. Similar to the conventional Randles equivalent circuit, the equivalent circuit with TLM could fit the impedance responses simulated by the equivalent circuit with measured responses. This paper discusses the potential of EIS using an equivalent circuit coupled with a TLM for diagnosis of LIBs in power applications.

ISSN：00134686

概要：© 2015 Elsevier Ltd. All rights reserved.Novel three-dimensional hierarchical heterostructures composed of two-dimensional SnS2 nanoflakes and zero-dimensional SnO2 nanoparticles were fabricated via a one-step hydrothermal method. Size of the heterostructures was ca. 2 μm in diameter, and individual SnS2 nanoflakes with thickness of ca. 150 nm were connected to central core of the heterostructures. The SnO2 nanoparticles in a diameter of ca. 5 nm uniformly covered entire surface of the SnS2 nanoflakes. Moreover, both of these structures were highly crystalline. Meanwhile, amorphous carbon was formed within the heterostructures. The SnS2/SnO2/C hierarchical heterostructures had a high initial specific reversible capacity of 1065.7 mAh g-1, stable cycling stability of 638 mAh g-1 after 30 cycles, and superior rate capability of 550.8 mAh g-1 at 1C rate. These SnS2/SnO2/C hierarchical heterostructures showed better performance than individual SnS2 and SnO2 nanomaterials, and the performance was even higher than the graphene-SnS2 and graphene-SnO2 nanohybrid materials. This is attributed to a synergistic effect of high surface area, which is provided by the unique SnS2 internal nanoflake layered structures decorated with ultra-fine SnO2 nanoparticles, and an effective beneficial buffer matrix to accommodate the large volume change upon cycling, which is caused by the side-products such as Li2S or Li2O. The SnS2 nanoflake was deduced to play a similar role as graphene material, since both possess 2D conducting layer structures. The uniform carbon dispersion within the structures also stabilizes the structures and improves electrical conductivity of the hierarchical heterostructures.

ISSN：00134686

概要：© 2015 Elsevier Ltd. All rights reserved.A facile and scalable method is proposed to prepare microscale Li2S-C composite from Li2SO4 through carbon-thermal reduction, followed by a carbon coating process. Multi-solvent recrystallization was utilized to reduce the particle size of Li2SO4 to 2 μm. This fine-grain Li2SO4 helps to shorten the particle size of reduction product from 10 μm to 3 μm. Using fine Li2SO4 also brings the benefit of greatly reducing the over potential during the initial charge process and increasing the kinetics for Li2S materials. Finally, the microscale Li2S-C composite prepared from fine Li2SO4 enables a stable capacity of 350 mAh g-1 at 0.2 C, higher than that obtained using a cathode prepared from commercial Li2SO4.

ISSN：2211-2855

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概要：© 2016 Elsevier B.V.Lithium metal free sulfur battery paired by lithium sulfide (Li2S) is a hot point in recent years because of its potential for relatively high capacity and its safety advantage. Due to the insulating nature and high sensitivity to moisture of Li2S, it calls for new way to introduce Li ion into S cathode besides the method of directly using the Li2S powder for the battery pre-lithiation. Herein, we proposed a pre-lithiation method to lithiate the polypyrrole (PPy)/S/Ketjenblack (KB) electrode into PPy/Li2S/KB cathode at room temperature. By this process, the fully lithiated PPy/Li2S/KB cathode showed facilitated charge transfer than the original PPy/S/KB cathode, leading to better cycling performance at high C-rates and disappearance of over potential phenomenon. In this work, the ion-selective PPy layer has been introduced on the cathode surface by an electrodeposition method, which can suppress the polysulfide dissolution from the cathode source. The lithium metal free full battery coupled by the prepared Li2S/KB cathode and graphite anode exhibited excellent cycling performance. Hence, we believe this comprehensive fabrication approach of Li2S cathode will pave a way for the application of new type lithium metal free secondary battery.

ISSN：00134651

概要：© The Author(s) 2016. Published by ECS.Ahigh areal capacity lithium-sulfur batterymaking use of mass produced aluminum metal foam as a current collectorwas investigated. A sulfur/Ketjenblack (KB) composite was filled and deposited into the aluminum foam current collector via a predetermined filling procedure, resulting in high sulfur loading. The value for this loading was found to be 17.7 mg sulfur/cm2 by using carboxymethyl cellulose and styrene butadiene rubber (CMC + SBR) as a binder. An operating single-layer pouch-Type cell with an S/KBCMC+ SBR on Al foam cathode was created as a result of this synthesis and found to possess an unprecedentedly high areal capacity of 21.9 mAh/cm2. On the basis of the achieved areal capacity, the energy density of a theoretical lithium-sulfur battery was estimated with the assumption of an electrolyte/sulfur ratio of 2.7 μL/mg. This was calculated upon 100% of the pore volume in the S/KB-CMC + SBR on Al foam cathodes and polyolefin separator, along with the inclusion of the weights of the tabs for the current lead and pouch film packaging in the case of a seven-layer pouch-Type battery. With this calculation, it was determined that the creation of a lithium-sulfur battery with an energy density of greater than 200 Wh/kg is plausible.

ISSN：00134686

概要：© 2017 Elsevier Ltd Mid to low frequency impedance for a cathode in a lithium ion battery (LIB), which is affected by lithium-ion diffusion into active materials, was investigated. We had earlier suggested that charge-transfer and diffusion impedances are attributed to a particle size distribution for a commercially available LIB, and we designed an equivalent circuit in which two series circuits of charge-transfer resistance and Warburg impedance were connected in parallel. Here, to validate the design of the equivalent circuit, the secondary-particle size distribution of the LiNi 1/3 Mn 1/3 Co 1/3 O 2 cathode in a lab-made LIB, in which the secondary-particles were controlled into wide and narrow distribution by sieving, was investigated by electrochemical impedance spectroscopy. The equivalent circuit was designed in which series circuits of charge-transfer resistance and Warburg impedance were connected in parallel. Dependency of impedance response on the number of parallels of the series circuits was evaluated for the cathodes using different secondary-particle size distributions of the active material. Additionally, the tendency of change in the charge-transfer resistance and the limiting capacitance was discussed from the standpoint of secondary-particle size distribution. The results confirm the effectiveness of the designed equivalent circuit which reflects the secondary-particle size distribution of cathode active materials.

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概要：© 2017 Elsevier Ltd The cycle durability of electrodeposited Si-O-C composite anodes in glyme-based ionic liquid electrolytes, known as Li(G3)TFSI or Li(G4)TFSI (triglyme: G3 and tetraglyme: G4), which is one of the most promising electrolytes for sulfur cathode, was improved for use in lithium secondary batteries by using additives, fluoroethylene carbonate (FEC) or vinylene carbonate (VC). We revealed an importance of the activation process and the effects of additives in the Si-O-C composite anode. The capacity of the Si-O-C composite anode decreased with charge-discharge cycles in electrolytes without additives. Meanwhile, although the capacity retention in electrolytes with additives was improved by 10–20%, their initial capacity was smaller than those without additives. To solve the contradiction, an activation process, in which the Si-O-C composite anode was charged and discharged in electrolytes without additives, was introduced before charge-discharge cycles in electrolytes with additives. Owing to the optimized activation process, the initial capacity in electrolytes with additives showed as high as 1100–1300 mAh g −1 as those without additives with better capacity retention. Therefore, the necessity to adequately generate an activation reaction and to form SEI derived from additives for the Si-O-C composite anode to have better charge-discharge performance was demonstrated.

ISSN：14328488

概要：© 2017, Springer-Verlag Berlin Heidelberg. The development of lithium-sulfur batteries is associated with many problems. These problems include polysulfide dissolution, the shuttle phenomenon, the low electric and ionic conductivity of S, and the volume change that occurs during charge and discharge. In this review, various elemental techniques for overcoming these problems are summarized from the standpoints of the supporting materials. These techniques include preventing polysulfide dissolution from the cathodes through physical and chemical adsorption on the supporting materials, the use of electrolytes that do not dissolve polysulfides via the coordination of Li + and solvents, and the use of ion-exchange polymers to permeate Li + selectively. The following approaches to enable practical applications of S cathodes in future Li-ion batteries are introduced: the utilization of Li-free anode materials, such as C and Si; the use of Li 2 S cathodes, which are prepared via a pre-lithiation process; and increasing the areal capacity of the S cathode by using a suitable current collector such as Al foam, thus providing a large amount of space for Li + to migrate and the electron-conductive path. The utilization of an Al foam current collector is one of the promising approaches to creating a cost-effective Li-ion battery owing to the established mass production of Al foam for use in NiMH batteries; such Li-ion battery can achieve an unprecedentedly high areal capacity of 21.9 mAh cm −2 . Owing to the resulting areal capacity, the possibility of developing a lithium-sulfur battery with an energy density greater than 200 Wh kg −1 has been demonstrated. Consequently, the combination of these approaches, as introduced in this review, would help create a bright, sustainable society.

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概要：© 2017 Elsevier Ltd Electrochemical impedance measurements of lithium ion batteries (LIBs) in energy storage systems (ESS) were performed. Square-current electrochemical impedance spectroscopy (SC-EIS), which is a simple and cost-effective approach to measure impedance, was chosen to investigate a large-scale LIB system. Harmonics calculated by Fourier transform from a square waveform were used to determine the impedance. On the basis of a simple electrochemical reaction involving the ferri/ferro-cyanide redox couple and the LIB, the accuracy of the impedance measurement was found to depend on both the signal-to-noise ratio of the power spectra of the harmonics as well as the attenuation rate of the “measured value of impedance” and the “theoretical spectra value” from Fourier series. The accuracy was improved by adjusting the input waveform to be close to an ideal square waveform from Fourier series. The accuracy was further improved by the combined use of a simple moving average and an overall average. The impedance from a degraded square waveform generated by a cost-effective power controller was able to be deter mined by increasing the measurement time, which aided averaging. By designing the input signal to be close to an ideal square waveform from Fourier series, kilowatt-class LIB modules/cubicles in an ESS was able to be measured. Moreover, a degraded LIB module in an ESS was able to be detected using EIS, which highlights the utility of this technique for in situ impedance measurements of large-scale LIB systems.

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概要：© 2017 The Authors This work reports a new chemical pre-lithiation method to fabricate lithium sulfide (Li 2 S) cathode. This pre-lithiation process is taken place simply by dropping the organolithium reagent lithium naphthalenide (Li + Naph − ) on the prepared sulfur cathode. It is the first time realizing the room temperature chemical pre-lithaition reaction attributed by the 3D nanostructured carbon nanotube (CNT) current collector. It is confirmed that the Li 2 S cathode fabricated at room temperature showing higher capacity and lower hysteresis than the Li 2 S cathode fabricated at high temperature pre-lithiation. The pre-lithiated Li 2 S cathode at room temperature shows stable cycling performance with a 600 mAh g −1 capacity after 100 cycles at 0.1 C-rate and high capacity of 500 mAh g −1 at 2 C-rate. This simple on-site pre-lithiation method at room temperature is demonstrated to be applicable for the in-situ pre-lithiation in a Li metal free battery.

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概要：A simple numerical simulation of current flowing through electronic devices was examined for a hybrid power supply system composed of a DMFC and a capacitor connected in parallel. The simulation was investigated by representing a combination of ohmic resistance, charge transfer reaction resistance, mass transfer resistance and double layer capacitance of a DMFC as a simple ideal resistor, based on measured data when DMFC was generating electricity. The simulation result was found to agree with experimental measured current flowing through the DMFC and the capacitor, although a slight disagreement was observed because of the presence of ohmic resistance between circuit components. The simulation of DMFC-capacitor hybrid power supply system indicated the importance of the inner resistance of the capacitor. The hybrid simulation was also applied to a system assumed to consist of μDMFC and micro electrochemical capacitor (MECC) system. The effect of applying a DC-DC converter to the system was indicated. The simulation allows to predict the degree of improvement required without performing actual fabrication of μDMFC and MECC.

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概要：The feasibility of a di-block copolymer, composed of a polyethylene oxide (PEO) chain and a polystyrene (PS) chain covalently bonded, as the gel electrolyte for lithium secondary batteries was investigated. The PEO-PS di-block copolymer gel electrolyte showed a high ionic conductivity of ∼1 mS/cm at room temperature. Moreover, it retained good mechanical strength within a co-continuous phase separated structure, and it suppressed the dendritic deposition of Li. Indications were that the interface between the electrolyte and the Li metal was chemically stable, as a result of the PEO phase fixed to PS by covalent bonding. In addition, it was indicated that the Li/PEOPS di-block copolymer gel electrolyte/LiFePO₄ cell had a high charge-discharge efficiency of ∼99% during 30 cycles, while maintaining a discharge capacity of 124 mAh/g.

ISSN：0366-7022

概要：A mesoporous Sn anode was electrodeposited in the presence of lyotropic liquid crystals made of nonionic surfactants. The introduction of mesoporous structure was effective for the accommodation of volume change of Sn during charge and discharge cycling of Li ions. The discharge capacity of the mesoporous Sn anode at 1 C rate was as high as 425 mA h g⁻¹ at the 100th cycle, and that was as high as 320 mA h g⁻¹ at the 100th cycle even though at 5 C rate.

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概要：The degradation of the commercial Li ion battery was analyzed by electrochemical impedance spectroscopy, where our previous proposed equivalent circuit was applied. The degradation with the cycling was clearly explained by the main parameters of capacitive and resistive components, i.e., it responded until 300 cycles to the decrease in capacitive component, while after 300 to 550 cycles to the increase in resistive component.

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概要：A carbon-coated Li₂S was prepared through an adsorption and successive annealing process by using poly(vinylpyrrolidone) (PVP) and acetylene black (AB) as carbon source with Li₂S powder. The coating layer was composed of amorphous carbon and embedded AB particles. The carbon coating was found to effectively alleviate the dissolution of polysulfide and the discharge capacity at the first 15 cycles was 800 mA h g⁻¹ with gradual fading afterward.

ISSN：00134686

概要：© 2015 Published by Elsevier Ltd.To realize electrochemical impedance spectroscopy (EIS) using a simple measurement system, application of a square potential/current waveform to the input signals of EIS was investigated. The impedance of a simple redox reaction of [Fe(CN)6]^4-/[Fe(CN)6]^3- solution was measured by the potentio-EIS using a square waveform as the input signal, which was generated by a potentiostat system without a frequency response analyzer (FRA). A steady impedance response in the frequency range of 40 Hz-3.5 kHz was obtained, and the impedance was obtained by the potentiostat system with an FRA. The errors - the differences between the impedance measured by EIS with a square potential waveform and that of conventional EIS - were sufficiently low to allow impedance analysis. The impedance of a lithium-ion battery (LIB) was measured by galvano-EIS using a square waveform input signal generated by a power controller. A steady impedance response in the frequency range of 5 Hz-2.5 kHz was obtained, and the errors were sufficiently low to allow impedance analysis. It was demonstrated that both square potential-EIS (SP-EIS) and square current-EIS (SC-EIS) have great potential as simple systems for measuring impedance. Moreover, it was demonstrated that SC-EIS has potential as a simple measurement system for analyzing the state of an LIB. Thus, the potential of the SP/SC-EIS methodology was confirmed for electrochemical systems.

ISSN：22112855

概要：© 2016 Elsevier LtdThe poor electrical conductivity of Si-based anode materials is a critical challenge for the development of high-performance Li secondary batteries. We propose a new approach for enhancing the electrical conductivity of an electrodeposited Si–O–C composite anode via self-incorporation of nano Cu metal (n-Cu) using a facile and inexpensive electrochemical synthetic method. The Si–O–C composite with n-Cu (Cu/Si–O–C composite) shows stable cycle performance with a fairly high specific capacity. Since Cu precursor ions for the electrodeposition of n-Cu are directly dissolved from a Cu substrate used as the current collector for the anode, electrical conducting additives that causes increase in the weight and volume of the electrode are not unnecessarily supplemented. In the synthesis process, the n-Cu metal and Si–O–C composite are electrodeposited simultaneously. The n-Cu/Si–O–C composite anode results in improved electrochemical performance, including enhancement of areal and specific capacity; coulombic efficiency; and rate capability. Electrochemical impedance spectroscopy suggests that such improvements in performance are due to the enhanced electrical conductivity resulting from the conductive network of the incorporated n-Cu. Moreover, the electrical conductive properties of the incorporated n-Cu suppress electrochemical degradation of the n-Cu/Si–O–C composite anode.

ISSN：03787753

概要：© 2016 Elsevier B.V.In this study, we report the preparation of carbon nanotubes (CNTs) anchor layer on a Cu substrate (CNTs/Cu) by using electrophoretic deposition technique. The CNTs anchor layer increases adhesion strength between Si-O-C composites and Cu substrate, as a result, it is possible to improve deposited Si amounts and areal capacity. The electrodeposited Si-O-C composites on CNTs/Cu (Si-O-C/CNTs/Cu) show homogenously coated surface morphology without cracks even large passing charge for electrodeposition of 15 C cm−2, resulting in 0.21 mg cm−2 of deposited Si amounts. On the other hand, Si-O-C composites deposited on as-received Cu substrate (Si-O-C/Cu) begin to peel off from substrate at 8 C cm−2 of passing charge, resulting in 0.13 mg cm−2 of deposited Si amounts, and decrease down to 0.10 mg cm−2 at 15 C cm−2 of passing charge. As a results, the improved Si amounts deposited on CNTs/Cu substrate achieve higher areal capacity, delivering 0.24 mA h cm−2, which attains increase in 84.6% in comparison to Si-O-C/Cu, which has areal capacity of 0.13 mA g cm−2 at 8 C cm−2 of passing charge. Moreover, the Si-O-C/CNTs/Cu shows improved anode performances including discharge capacity and C-rate performance of the Si-O-C composites than Si-O-C/Cu without CNTs anchor layer.

ISBN：978-0444535320

ISBN：978-4-86043-263-8

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概要：現代社会のエネルギー消費について、特に電気エネルギー利用の観点から、社会的ニーズに対応するための発電、蓄電デバイスについて概説する。電気化学の概念を習得するとともに、化学エネルギーや物理エネルギーから電気エネルギーへと変換する反応を理解する。また電気エネルギー利用のための電気化学発電・蓄電デバイスの将来を議論する。