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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium intercalation into graphite is crucial for battery technology.
• Studying intercalation kinetics is difficult due to complexity and heterogeneity.
• Existing methods lack time- and space-resolved insights into the microscopic process.

Purpose of the Study:

• To develop and apply a direct, all-optical measurement technique for lithium intercalation.
• To investigate the microscopic intercalation process in single-crystal graphite.
• To validate the Cahn-Hilliard reaction (CHR) theory for solid-state reactions.

Main Methods:

• Utilized a single-crystal graphite electrode with lithographically defined disc geometry.
• Employed time- and space-resolved, all-optical measurements, including Raman and reflectance spectroscopy.
• Distinguished intrinsic intercalation from side reactions using optical techniques.

Main Results:

• Successfully measured lithium intercalation directly with high temporal and spatial resolution.
• Observed distinct phase front spatial patterns and dynamics during intercalation.
• The Cahn-Hilliard reaction (CHR) theory, with a generalized Butler-Volmer kinetics model, quantitatively matched experimental observations.

Conclusions:

• The study provides unprecedented insight into the microscopic intercalation process.
• The Cahn-Hilliard reaction theory accurately describes lithium intercalation dynamics in graphite.
• The combined electrochemical and Cahn-Hilliard approach offers a thermodynamically consistent model for solid-state reactions.