Anomalous Sodium Insertion in Highly Oriented Graphite: Thermodynamics, Kinetics and Evidence for Two-Sided...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Intercalation of sodium (Na) into graphite is crucial for Na-based batteries but remains challenging.
• Understanding the thermodynamics, kinetics, and atomistic storage mechanisms is key to improving battery performance.

Purpose of the Study:

• To comprehensively investigate the intercalation of sodium into highly oriented pyrolytic graphite (HOPG).
• To elucidate the thermodynamic and kinetic limitations of sodium storage.
• To understand the anomalous behavior of sodium compared to other alkali metals in graphite.

Main Methods:

• Systematic, long-term (up to 2 years) investigations of sodium intercalation into HOPG.
• Chemical and electrochemical storage methods across a wide temperature range.
• Advanced electron microscopy, electrochemical tools, and chemical analysis for sample characterization.

Main Results:

• Sodium intercalation into HOPG is thermodynamically possible at higher concentrations at room temperature but kinetically hindered.
• Sodium storage follows a unique pattern, forming bilayers in HOPG before larger aggregates and staging compounds.
• This behavior differs significantly from other alkali metals, impacting storage capacity and kinetics.

Conclusions:

• The findings provide insights into the challenges and potential of sodium-graphite intercalation for battery applications.
• Including entropic effects and space charges is necessary for a complete understanding of sodium storage mechanisms.
• The unique bilayer formation of sodium in HOPG necessitates tailored strategies for efficient sodium-ion battery design.