Shigeo Tanase

Micrometer-Scale Amorphous Si Thin-Film Electrodes Fabricated by Electron-Beam Deposition for Li-Ion Batteries

A series of micrometer-scale Si thin films were fabricated by electron-beam deposition on the Cu substrate with specially treated concave-convex surface. The combined analyses involving scanning and transmission electron microscopy, selected area electron diffraction, and X-ray diffraction revealed that the deposited Si layer possessed good adhesion to the substrate and a discontinuous amorphous microstructure in which there existed large amounts of interface regions. The surface changes of the Si thin-film electrodes during Li insertion and extraction were investigated by glow discharge optical emission spectroscopy. The half-cell tests showed that these thicker films had higher capacity and more impressive cycleability relative to those reported in the literature; their cycleability could be substantially improved by limiting Li insertion depth. The full-cell tests indicated that Si films thicker than 4 μm could provide sufficient capacity to match the standard LiCoO 2 cathode with a ∼70-μm-thick coating layer. Such cells demonstrated small self-discharge rate as well as good cycling stability and efficiency in the long run, suggesting feasibility for potential practical applications.

Electrochemical performances of polyacrylonitrile nanofiber-based nonwoven separator for lithium-ion battery

The polyacrylonitrile (PAN) nanofiber-based nonwoven separators for lithium-ion batteries have been developed by electrospinning technique. Scanning electron microscopic observation showed that the electrospun PAN nanofibers had homogeneous thickness and their diameters were around 350 nm. Cyclic voltammetry revealed that the separator was electrochemically stable between 3 and 4.5 V vs Li. The cells with the PAN separators showed better cycle performance than conventional ones at a moderate rate of C/2. In the rate-capability and pulse discharging tests, the cells with the PAN-based separators exhibited superior rate-capabilities and smaller diffusion resistance at high rate test than conventional one.

New Ag-Sn Alloy Anode Materials for Lithium-Ion Batteries

The Ag-Sn alloys prepared by mechanical alloying technique have been studied as negative electrode materials for lithium-ion batteries. With optimized compositions and structure morphologies, both Ag 52 Sn 48 and Ag 46 Sn 54 composite electrodes exhibit an initial capacity of ∼800 mAh/g and maintain a reversible capacity of above 350 mAh/g for more than 50 cycles. Even after 300 cycles, the former still keeps a reversible capacity of approximately 200 mAh/g. Typically, the structural changes of Ag 52 Sn 48 electrode accompanied by Li insertion/extraction processes were examined by means of X-ray diffraction analyses. The results reveal that the composite alloy consisting of β-Sn and Ag 3 Sn phases transforms mostly into that of ternary lithiated phase during Li insertion and recovers to one involving β-Sn, Ag 3 Sn, and residual Ag 2 LiSn phases after Li extraction. It is considered that the composite structure containing the ternary lithiated phase, which is formed during the first cycle, is beneficial for the improvement of the cycle life of the Ag-Sn alloy electrode, although the residual lithiated product possibly leads to an increase of the irreversible loss.

Nanostructured Ag–Fe–Sn/Carbon Nanotubes Composites as Anode Materials for Advanced Lithium‐Ion Batteries

Nanostructured Ag-Fe-Sn/C composites were synthesized by mechanical milling Ag-Fe-Sn alloys with carbon nanotubes (CNTs). The milled composites were characterized by X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectrometry, and selected area electron diffraction techniques. These analyses revealed that, except for residual CNTs segments protruding from the edges of the composite particles, most CNTs were converted to an amorphous structure that formed a shell around alloy particles during mechanical processing. The electrode behaviors of the synthesized materials were examined and compared with those of their unmilled counterparts as well as the original alloys. It was demonstrated that the formed amorphous carbon shell around the alloy particles significantly improved the cycling performance of the composite electrodes, though the initial irreversible capacity loss was increased. For instance, the milled Ag 3 6 . 4 Fe 1 5 . 6 Sn 4 8 /CNTs electrode provided a discharge capacity of ∼530 mAh/g in the second cycle, maintaining a rechargeable capacity of ∼420 mAh/g after 300 cycles.

Proton conduction in (La0.9Sr0.1)MIIIO3−δ (MIII=Sc, In, and Lu) perovskites

Abstract The electrical conductivity of A 3+ B 3+ O 3 -type perovskites, (La 0.9 Sr 0.1 )M III O 3− δ (M III =Sc, In, and Lu) (LSM), was investigated under controlled atmospheres between 573 and 1273 K. At P (O 2 )>10 −5 atm, all the compounds showed the predominant proton conduction below 873 K under wet conditions; at P (O 2 ) −10 atm, the Sc and In compounds below 873 K and the Lu-one at all temperatures under hydrogen-containing conditions. The Sc compound showed the highest proton conductivity of ca. 4×10 −3 S· cm −1 at 873 K in the presence of water vapor or hydrogen. The proton conductivity of LSM decreased with increasing the size of B-site (M III ) cation.

Electroplated Sn-Zn Alloy Electrode for Li Secondary Batteries

Sn-based compounds have attracted great attentions because of their larger specific capacity for Li secondary batteries. An electroplating method has been developed to prepare a Sn-Zn based alloy. The structure and electrochemical performance of as-plated and heat-treated electrodes have been investigated in detail. Experimental results show that Cu 6 Sn 5 phase and many voids were formed in plated film after heat-treatment. At the same time, the component of Zn was segregated, forming two Zn layers. This multilayer structure in electrode was beneficial to strengthen the contact between the plated film and Cu foil, and to relax the volume expansion during cycling, which improved the cyclability of electrode. The discharge capacity of the heat-treated electrode remained over 450 mAh g -1 after 50 cycles, while that of as-plated anode decreased seriously to 25 mAh g -1 . The charge-discharge reaction mechanism of a heat-treated anode also changed due to the formation of Cu 6 Sn 5 phase in the plated film. These results show that electroplated Sn-Zn alloy film on Cu foil is a promising anode material with larger specific capacity and long cycle life for Li secondary batteries.

Silica-Composite Nonwoven Separators for Lithium-Ion Battery: Development and Characterization

We have developed silica-composite nonwovens using polyolefin fiber and nanosize silica powder. The silica-composite nonwoven showed better wettability than the polyolefin-based microporous membrane and nonwoven. It was found that the Gurley value of the silica-composite nonwoven has to be higher than 200 s 100 cm -3 in order to suppress a microshort of battery. It was confirmed that the silica-composite nonwovens showed higher maximum power than that of the Celgard membrane by instantaneous discharging test. The cells with the silica-composite nonwovens showed better cycling performances than that of the Celgard membrane at a moderate C-rate of 0.5. A hot-oven test using charged cells up to 4.2 V exhibited that the cells with the silica-composite nonwovens are thermally stable at 150°C, whereas the cell with the Celgard membrane showed a short circuit probably due to thermal shrinkage of the separator.

Electrode Properties and Lithiation/Delithiation Reactions of Ag-Sb-Sn Nanocomposite Anodes in Li-Ion Batteries

Based on the mechanical alloying technique and expedient microstructural design, the Ag 52-x Sb x Sn 48 system has been established as a promising candidate of anode materials in Li-ion batteries. The half-cell tests revealed that the Ag 36.4 Sb 15.6 Sn 48 electrode with a heterophase structure involving SnSb, Ag 3 Sn, and Sn was capable of maintaining a rechargeable capacity as high as 380 mAh/g over 300 cycles when cycled in a proper organic electrolyte between 0.0 and 1.0 V (vs. Li) under a constant current density of 0.2 mA/cm 2 . The analysis for the structural changes of the electrode during cycling indicated that the superior cycling performance of the Ag 36.4 Sb 15.6 Sn 48 electrode was attributable to the presence of the structurally stable intermetallic compounds of SnSb and Ag 3 Sn in the host structure, the stepwise lithiation/delithiation mechanisms, and the AgLi 2 Sn-oriented phase transformations. In addition to the phase structure of the alloy, which essentially affected the cycling stability of the alloy electrode, the effects of different organic electrolytes on the cycling performance were also examined.

Surface Characterization on Lithium Insertion∕Deinsertion Process for Sputter-Deposited AgSn Thin-Film Electrodes by XPS

In this paper, the structural and surface changes of the sputter-deposited Ag 5 2 Sn 4 8 thin-film electrodes during Li insertion/ deinsertion have been investigated by exsitu X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The study revealed a possible type of capacity decay mechanism for the Sn-based alloy electrodes. It was considered that the surface reactions of active material with electrolyte led to the formation of solid electrolyte interphase (SEI) layer in the first Li insertion process, which was damaged during the Li deinsertion process due to the strong shrinkage of the inner active material. Thus, in the Li deinsertion process, the electrolyte could readily permeate through the damaged SEI layer and reacted with the inner active material to form tin oxides. These tin oxides were conductively isolated, leading to the consuming of active material and capacity decay. It was found that the degree of the formation of tin oxides was strongly related to the identity of electrolyte. Much more SEI layer and tin oxides were formed in the propylene carbonate (PC)-based electrolyte than in the ethylene carbonate (EC)-based electrolyte, due probably to their different reactivity with the active material. This could be the reason why both the sputter-deposited thin film and the powder-pasted alloy electrodes showed rather poor cycling stability in the PC-based electrolyte.

Nanocrystalline Ag-Fe-Sn Anode Materials for Li-Ion Batteries

The Ag-Fe-Sn alloy powders prepared by mechanical alloying technique have been studied as anode material for lithium-ion batteries. The half-cell tests with lithium counter electrode revealed that a suitable substitution of Fe for Ag led to a significant improvement of the cycling performance of the electrodes. Among these electrodes, the Ag 36.4 Fe 15.6 Sn 48 electrode was found to be capable of keeping a rechargeable capacity of about 280 mAh/g over 300 cycles, which was better than that of the Fe-free Ag 52 Sn 48 electrode. Typically, the structural changes of the Ag 26 Fe 26 Sn 48 electrode during Li insertion and/or extraction were characterized using the combined techniques involving X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray spectrometry. It is considered that the electrochemical properties of these electrodes are associated with their microstructure and morphology, such as the distribution of intermetallic compound Ag 3 Sn in Sn matrix, the Ag 3 Sn/Sn ratio as well as the presence of inactive Fe.