Intercalation and Deintercalation of Lithium at the Ionic Liquid-Graphite(0001) Interface.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Lithium-ion batteries rely on efficient lithium intercalation/deintercalation in graphite anodes.
• Understanding interfacial processes is key to improving battery performance and safety.
• Ionic liquids are promising electrolytes but their interfacial behavior needs detailed study.

Purpose of the Study:

• To investigate the interfacial behavior of a specific ionic liquid on lithiated graphite during heating.
• To elucidate the role of temperature in lithium accumulation and interfacial reactions.
• To identify early stages of solid-electrolyte interphase formation.

Main Methods:

• Ultrahigh vacuum conditions were employed for controlled experiments.
• X-ray and ultraviolet photoelectron spectroscopy were used to analyze surface electronic properties.
• Variable temperature studies from 80 K to >230 K were conducted.

Main Results:

• Heating the ionic liquid ([BMP]+[TFSI]-) on lithiated graphite led to core-level binding energy up-shifts.
• A lowering of the work function (ΔΦ) indicated changes at the interface.
• Partially charged lithium (Liδ+) accumulation was observed at the ionic liquid-graphite interface.
• Partial decomposition of the ionic liquid was detected.

Conclusions:

• Temperature plays a critical role in facilitating lithium accumulation at the IL-graphite interface.
• The observed ionic liquid decomposition is linked to the initial chemical formation of the solid-electrolyte interphase.
• These findings provide insights into the fundamental processes governing Li-ion battery operation at the electrode-electrolyte interface.