title: Li Intercalation into Graphite: Direct Optical Imaging and Cahn-Hilliard Reaction Dynamics.
abstract: 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.
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Yinsheng
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Raymond B
authors.initials: RB
authors.lastname: Smith
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Zhonghua
authors.initials: Z
authors.lastname: Yu
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Dmitri K
authors.initials: DK
authors.lastname: Efetov
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Junpu
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Philip
authors.initials: P
authors.lastname: Kim
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Martin Z
authors.initials: MZ
authors.lastname: Bazant
authors.affiliation: Department of Chemistry and §Department of Physics, Columbia University , New York, 10027, United States.|Department of Chemical Engineering and ∥Department of Mathematics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Louis E
authors.initials: LE
authors.lastname: Brus