Li Intercalation into Graphite: Direct Optical Imaging and Cahn-Hilliard Reaction Dynamics

• Main Authors: Guo, Yinsheng (Author), Yu, Zhonghua (Author), Efetov, Dmitri K. (Author), Wang, Junpu (Author), Kim, Philip (Author), Brus, Louis E. (Author), Smith, Raymond Barrett (Contributor), Bazant, Martin Z (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Chemical Engineering (Contributor), Massachusetts Institute of Technology. Department of Mathematics (Contributor), Bazant, Martin Z. (Contributor)
• Format: Article
• Language: English
• Published: American Chemical Society (ACS), 2017-08-03T14:19:07Z.
• Subjects: Article
• Online Access: Get fulltext

 Lithium intercalation into graphite is a critical process in energy storage technology. Studies of Li intercalation kinetics have proved challenging due to structural and phase complexity, and sample heterogeneity. Here we report direct time- and space-resolved, all-optical measurement of Li intercalation. We use a single crystal graphite electrode with lithographically defined disc geometry. All-optical, Raman and reflectance measurements distinguish the intrinsic intercalation process from side reactions, and provide new insight into the microscopic intercalation process. The recently proposed Cahn-Hilliard reaction (CHR) theory quantitatively captures the observed phase front spatial patterns and dynamics, using a two-layer free-energy model with novel, generalized Butler-Volmer kinetics. This approach unites Cahn-Hilliard and electrochemical kinetics, using a thermodynamically consistent description of the Li injection reaction at the crystal edge that involves a cooperative opening of graphene planes. The excellent agreement between experiment and theory presented here, with single-crystal resolution, provides strong support for the CHR theory of solid-state reactions.