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8. Morphological Stability Limits of Ag–Cu–Al Nanocrystalline Thin Films Prepared via Reactive Sputtering in Ar–O2 Mixed Gas.

Author

Ueshima, Yoshiyuki, Hasegawa, Masakatsu, Kubota, Naoyoshi, Matamura, Yuya, Matsubara, Eiichiro, Seki, Kazuaki, and Hirato, Tetsuji

Subjects
THIN films, KIRKENDALL effect, REACTIVE sputtering, SPUTTER deposition, CRYSTAL grain boundaries
Abstract

As a first step toward developing a downsized and high-performance O2 separator suitable for large-scale industrial applications, such as steelmaking, we have studied nanocrystalline Ag alloy thin films with high O2 permeability via rapid diffusion at Ag grain boundaries, operating at plant-waste heat temperatures (200 °C to 500 °C). In the present study, fabrication of nanocrystalline Ag–2at. pctCu–10at. pctAl alloy thin films with Ag grain size below 10 nm was attempted via reactive sputtering in Ar–O2 using grain boundary pinning force of a large number of alumina particles. Cross-sectional observation of the fabricated thin film showed that the Ag grain size ranged from 4 to 15 nm when the film thickness was less than 200 nm, but when the film thickness exceeded 200 nm, the Ag grains abruptly coarsened, reaching a maximum grain size of 214 nm. Furthermore, large surface irregularities with sizes of up to 500 to 600 nm (equivalent to 2/3 of the film thickness) were also observed. Heat transfer analysis revealed that the Ag film partially melted because of the large amount of heat released by the oxidation of Al during sputtering deposition. The conditions necessary for the fabrication of high-Al nanocrystalline Ag alloy thin films via reactive sputtering in Ar–O2 gas without film melting were clarified. [ABSTRACT FROM AUTHOR]

Published
2024
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17. Appendix A

Author

Waseda, Yoshio, Matsubara, Eiichiro, Shinoda, Kozo, Waseda, Yoshio, Matsubara, Eiichiro, and Shinoda, Kozo

Published
2011
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41. Structural characterization of an amorphous VS₄ and its lithiation/delithiation behavior studied by solid-state NMR spectroscopy

Author

Shimoda, Keiji, Koganei, Kazuto, Takeuchi, Tomonari, Matsunaga, Toshiyuki, Murakami, Miwa, Sakaebe, Hikari, Kobayashi, Hironori, and Matsubara, Eiichiro

Abstract

Vanadium sulfide (VS₄) is one of the promising positive electrode materials for next-generation rechargeable lithium-ion batteries because of its high theoretical capacity (1196 mA h g⁻¹). Crystalline VS₄ has a unique structure, in which the Peierls-distorted one-dimensional chains of V-V bonds along the c axis are loosely connected to each other through van der Waals interactions. In this study, an amorphous VS₄ is prepared by mechanical milling of the crystalline material, and its lithiation/delithiation behavior is investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy. The amorphous VS₄ shows a chain structure similar to that of crystalline VS₄. The amorphous host structure is found to change drastically during the lithiation process to form Li₃VS₄: the V ions become tetrahedrally coordinated by S ions, in which the valence states of V and S ions simultaneously change from V⁴⁺ to V⁵⁺ and S⁻ to S²⁻, respectively. When the Li insertion proceeds further, the valence state of V ions is reduced. After the 1[st] cycle, the amorphous VS₄ recovers to the chain-like structure although it is highly disordered. No conversion to elemental V is observed, and a high capacity of 700 mA h g⁻¹ is reversibly delivered between 1.5 and 2.6 V.

Published
2019

43. Improvement of Cycle Capability of Fe-Substituted Li2S-Based Positive Electrode Materials by Doping with Lithium Iodide

Author

Takeuchi, Tomonari, Kageyama, Hiroyuki, Nakanishi, Koji, Kiuchi, Hisao, Katayama, Misaki, Inada, Yasuhiro, Ohta, Toshiaki, Fukunaga, Toshiharu, Sakaebe, Hikari, Kobayashi, Hironori, and Matsubara, Eiichiro

Subjects
Batteries - Lithium, Lithium sulfur battery, cycle performance, high capacity
Abstract

For an attempt to improve the cycle capability of the Li8FeS5 cells, we have prepared LiI-doped Li8FeS5 composite positive electrode materials. The obtained Li8FeS5·xLiI sample cells showed the improved cycle capability, though the initial capacity value decreased with proportional to the mass of LiI. The improved cycle performance was attributable to the suppressed resistance rise of the cells, due probably to the suppression of high-resistive surface precipitates formed by the reaction between the active material and the electrolyte. The dopant LiI would stabilize the local structure against Li extraction/insertion reactions, as well as suppress the reaction with the electrolyte, leading to the improved cycle performance.

Published
2018

44. Structural and dynamic behavior of lithium iron polysulfide Li₈FeS₅ during charge–discharge cycling

Author

Shimoda, Keiji, Murakami, Miwa, Takeuchi, Tomonari, Matsunaga, Toshiyuki, Ukyo, Yoshio, Sakaebe, Hikari, Kobayashi, Hironori, and Matsubara, Eiichiro

Subjects
Li diffusive motion, Lithium-sulfur batteries, S-S polysulfide bond, Delithiation-induced amorphization, Lithium metal polysulfide
Abstract

Lithium sulfide (Li₂S) is one of the promising positive electrode materials for next-generation rechargeable lithium batteries. To improve the electrochemical performance of electronically resistive Li₂S, a Fe-doped Li₂S-based positive electrode material (Li₈FeS₅) has been recently designed and found to exhibit excellent discharge capacity close to 800 mAh g⁻¹. In the present study, we investigate the structural and dynamic behavior of Li₈FeS₅ during charge–discharge cycling. In Li₈FeS₅, Fe ions are incorporated into the Li₂S framework structure. The Li₂S-based structure is found to transform to an amorphous phase during the charge process. The delithiation-induced amorphization is associated with the formation of S-S polysulfide bonds, indicating charge compensation by S ions. The crystalline to non-crystalline structural transformation is reversible, but Li ions are extracted from the material via a two-phase reaction, although they are inserted via a single-phase process. These results indicate that the delithiation/lithiation mechanism is neither a topotactic extraction/insertion nor a conversion-type reaction. Moreover, the activation energies for Li ion diffusion in the pristine, delithiated, and lithiated materials are estimated to be in the 0.30–0.37 eV range, which corresponds to the energy barriers for local hopping of Li ions along the Li sublattice in the Li₂S framework.

Published
2018

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