Yuichi Itou

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries I. Analysis by Electrochemical and Spectroscopic Examination

I. Analysis by Electrochemical and Spectroscopic Examination Tsuyoshi Sasaki,* Takamasa Nonaka, Hideaki Oka, Chikaaki Okuda, Yuichi Itou, Yasuhito Kondo, Yoji Takeuchi, Yoshio Ukyo,* Kazuyoshi Tatsumi, and Shunsuke Muto* Toyota Central Research and Development Laboratories, Incorporated, Nagoakute 480-1192, Japan Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan

Fatigue strength at a number of cycles of thin hard coated steels with quench-hardened substrates

Abstract Bending fatigue tests were carried out to clarify the effects of thin hard coatings on the fatigue strength at a number of cycles for steels. Coatings of carbides and nitrides produced by thermoreactive deposition and diffusion, chemical vapour deposition and physical vapour deposition, processes and of electroplated chromium on various steels were tested as well as hardened steels. The results thus obtained revealed that the fatigue strength at a number of cycles highly depended on hardness and residual stress at the substrate surface as in the case of the endurance limit and that the existence of the coatings suppressed the cracking in the substrates to increase the fatigue strength after loading cycles. Effects of coating thickness, surface roughness, notch shape, and post-heat treatment were also examined.

Factors affecting cycling life of LiNi0.8Co0.15Al0.05O2 for lithium-ion batteries

Factors affecting the cycling life of cylindrical lithium-ion batteries of LiNi0.8Co0.15Al0.05O2 (NCA) with graphite were examined in terms of the rechargeable capacity and polarization of NCA derivatives of LizNi0.8Co0.15Al0.05O2−δ (0.8 ≤ z ≤ 1.05). NCA derivatives with rock-salt domains in the structure were prepared by a co-precipitation method and the structures of [Li1−yNiy]3(b)[Ni,Co,Al]3(a)O26(c) based on a space group of Rm were refined by a Rietveld method of the XRD patterns. The electrochemical reactivity of the NCA derivatives with rock-salt domains was examined in non-aqueous lithium cells, and it was found that the rechargeable capacities (Q) of the samples decrease linearly as the amount of rock-salt domain (y) increases. An empirical relation is obtained to be Q = 181.4 − 725.5y in which Q reaches zero at y = 0.25, which is derived from not only the capacity loss owing to inactive rock-salt domains but also the polarization increase. The galvanostatic intermittent titration technique (GITT) measurement told us that polarization of NCA derivatives increases when the amount of rock-salt domains is above 2%, i.e., y > 0.02, and such a relation is remarkable in the lithium insertion direction into the structure, which is ascribed to slow lithium ion mobility due to nickel ions in the lithium layers. The NCA derivatives with increased rock-salt domains of above 2% deteriorate rapidly in non-aqueous lithium cells upon charge and discharge cycles, which is ascribed to the cumulative increase in polarization during charge and discharge. An extended cycling test for cylindrical lithium-ion batteries of the NCA derivatives with a graphite negative electrode at elevated temperature was performed and the quantitative relation is discussed thereof.