LiCoO$_{2}$ Epitaxial Film Enabling Precise Analysis of Interfacial Degradations
Changdong Qin1, Le Wang2, Pengfei Yan1*, Yingge Du2*, and Manling Sui1*
1Beijing Key Laboratory of Microstructure and Property of Solids, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China 2Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory Richland, WA 99354, USA
Abstract：Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO$_{2}$ (LCO), the most widely studied and used cathode material in lithium ion batteries. To understand such processes requires precise and quantitative measurements. Herein, we use well-defined epitaxial LCO thin films to reveal the interfacial degradation mechanisms. Through our systematical investigations, we find that surface corrosion is significant after forming the surface phase transition layer, and the cathode electrolyte interphase (CEI) has a double layer structure, an inorganic inner layer containing CoO, LiF, LiOH/Li$_{2}$O and Li$_{x}$PF$_{y}$O$_{z}$, and an outmost layer containing Li$_{2}$CO$_{3}$ and organic carbonaceous components. Furthermore, surface cracks are found to be pronounced due to mechanical failures and chemical etching. This work demonstrates a model material to realize the precise measurements of LCO interfacial degradations, which deepens our understanding on the interfacial degradation mechanisms.
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2021, Vol. 38 
