Microscopy Study of Structural Evolution in Epitaxial LiCoO2 Positive Electrode Films during Electrochemical Cycling

详细信息    查看全文

• 作者：Haiyan Tan ; Saya Takeuchi ; K. Kamala Bharathi ; Ichiro Takeuchi ; Leonid A. Bendersky
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：March 16, 2016
• 年：2016
• 卷：8
• 期：10
• 页码：6727-6735
• 全文大小：546K
• ISSN：1944-8252

文摘

The evolution of interface between the epitaxial thin film LiCoO₂ (LCO) electrode and liquid electrolyte and inside the LCO film during electrochemical cycling has been analyzed by high resolution scanning transmission electron microscopy. Relaxation of sharp translational domain boundaries with mismatched layers of CoO₂ octahedra occurs during cycling and results in formation of continuous CoO₂ layers across the boundaries. The original trigonal layered structure of LiCoO₂ tends to change into a spinel structure at the electrode/electrolyte interface after significant extraction of Li from LCO. This change is more pronounced at 4.2 V peak of CV, indicating lower stability of the layered LCO structure near its surface after Li is extracted above 60%. The transformed structure is identified to be close to Co₃O₄, with Co both on tetrahedral and octahedral sites, rather than to LiCo₂O₄ as it was suggested in earlier publications. Electron energy-loss spectroscopy measurements also show that Co ions oxidation state is reduced to mixed valence state Co²⁺/Co³⁺ during the structure changes to spinel rather than oxidized.