Chemical States of Overcharged LiCoO2 Particle Surfaces and Interiors Observed Using Electron Energy-Loss Spectroscopy

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• 作者：Jun Kikkawa ; Shohei Terada ; Akira Gunji ; Takuro Nagai ; Keiji Kurashima ; Koji Kimoto
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 16, 2015
• 年：2015
• 卷：119
• 期：28
• 页码：15823-15830
• 全文大小：572K
• ISSN：1932-7455

文摘

Deterioration mechanisms of LiCoO₂ electrode materials for lithium ion batteries remain unclear. Using electron energy-loss spectroscopy and transmission electron microscopy, this study investigated chemical states of LiCoO₂ particles on first overcharging. We present a scheme for quantification of the Li/Co atomic ratio. Using quantitative Li mapping and comprehensive probing of Li鈥揔, Co鈥揗_2,3, Co鈥揕₃, and O鈥揔 edges, we observed that overcharging causes the progression of Co³⁺/Co²⁺ reduction with oxygen extraction from the particle surface to the interior. A gradual change in the chemical composition at and around the particle surfaces after charging of 60% revealed the presence of Co₃O₄-like and CoO-like phases at surface regions. We also observed nanocracks with deficient Li ions. These results are key factors affecting degradation on overcharging.