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Minami-rinkan, Japan

We report a numerical study to define moisture barrier performance of a multilayer barrier stack. Thin film electronic devices require a moisture barrier coating to prevent degradation of the devices. However a required barrier performance is an ultimate level which is indefinable value owing to uncertainness in the metrological control. Using diffusion simulation, we discuss validity of barrier performance in the conventional definition of water vapor permeation rate and the actuality of water permeation into an encapsulated volume. The diffusion simulation predicted that the multilayer barrier-stack shows a window of permeation rate related to environmental moisture, a determinant for measureable limit, detail of moisture diffusion in an encapsulated system. An integrative evaluation method suggested that the barrier performance can be consistently defined from total amount of water permeation. The simulation results were obtained from the calculation of multilayer numerical components which were determined by data fitting with measured data, showed 1gm-2 of total permeation in 3years with 3 dyad barrier-stacks. copy; 2014 Elsevier B.V.

Okubo T.,Doshisha University | Yamada T.,Doshisha University | Saito M.,Doshisha University | Yodoya C.,Doshisha University | And 5 more authors.
Electrochemistry | Year: 2012

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, 14wt% for each). The irreversible capacity Qirr was successfully reduced to about a half (ca. 1100 mAhg-1) of that of the pristine Si-LP (2336 mAhg -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 mAhg-1 even after 50 cycles with a reduced Qirr of ca. 1300 mAhg-1 compared with the pristine Si-LP (ca. 2450 mAhg-1). © The Electrochemical Society of Japan.

Okubo T.,Doshisha University | Saito M.,Doshisha University | Yodoya C.,Oike and Co. | Kamei A.,Oike and Co. | And 5 more authors.
Solid State Ionics | Year: 2014

To compensate the large irreversible capacity (Qirr), lithium was pre-doped to Si thin flakes (Si Leaf Powder® (Si-LP), thickness: 100 nm) for different times, and its effects on the charge/discharge characteristics such as reversible capacity, cycleability, and rate-capability were investigated in detail. The charge/discharge test results showed that a large initial Q irr of ca. 2300 mAh g- 1 for the Si-LP can be completely compensated by Li pre-doping, and a high capacity (> 2500 mAh g - 1) was obtained for pre-doped Si-LPs. The pre-doping did not cause any harmful effects on cycleability as long as lithium was uniformly pre-doped. The addition of vinylene carbonate to the electrolyte solution in the pre-doping and in the test cell greatly improved the cycleability, and a high discharge capacity of ca. 2300 mAh g- 1 was kept after 40 cycles. © 2013 Elsevier B.V.

Nakai K.,Doshisha University | Tsuchioka I.,Doshisha University | Saito M.,Doshisha University | Tasaka A.,Doshisha University | And 4 more authors.
Electrochemistry | Year: 2010

Pure Si platelets (Si-LP, thickness: 100 nm) and Ni layer-laminated Si platelets with different thicknesses (Si/Ni/SiLP50 (50/50/50 nm) and Si/Ni/Si-LP30 (30/30/30 nm)) were prepared by a vapor deposition method, and their charge/discharge properties were investigated as alternative negative electrode materials to graphite for lithiumion batteries. The shape of thin platelet effectively relieved the stress during the alloying and de-alloying processes, and improved the charge/discharge cycleability as compared with a commercially available Si powder. In particular, the laminated platelet samples showed very good cycleability, probably because of a shorter diffusion length of Li+ ions in the Si layers and an improved mechanical strength by the presence of the Ni layer.

Saito M.,Doshisha University | Nakai K.,Doshisha University | Yamada T.,Doshisha University | Takenaka T.,Oike and Co. | And 4 more authors.
Journal of Power Sources | Year: 2011

Pure Si platelets and Ni or Cu layer-laminated Si platelets with difference thickness were prepared, and their charge/discharge properties were examined in 1 M LiClO4/EC + DEC (1:1 by volume) as alternative negative electrode materials to graphite for Li-ion batteries. The shape of thin platelets and lamination with Ni layer are significantly effective to improve the cycleability in Li-Si alloy system by relieving the stress during the alloying/de-alloying processes, reinforcing the mechanical strength and reducing the Li+ ion diffusion length. Moreover, the first irreversible capacity is minimized by reduction of the amount of Ketjen Black (KB) in the composite electrode because of electrolyte decomposition on the surface of KB. Consequently, the Si/Ni/Si-LP30 (30/30/30 nm) composite electrode with 5 wt% KB also exhibits over 700 mAh g-1 even after 50 cycles in 1 M LiPF 6/EC + DEC (1:1). © 2011 Elsevier B.V. All rights reserved.

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