Self-terminating, heterogeneous solid-electrolyte interphase enables reversible Li-ether cointercalation in graphite...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Ether solvents are suitable for Na-ion and K-ion batteries but historically cause graphite exfoliation in Li-ion batteries.
• Developing stable Li-ion battery electrolytes is crucial for high-performance energy storage.

Purpose of the Study:

• To achieve reversible Li-solvent cointercalation in graphite using ether-based electrolytes for Li-ion batteries.
• To overcome the historical challenges of graphite exfoliation and cell failure associated with ether electrolytes.

Main Methods:

• Design and formulation of a novel electrolyte: 1M LiBF4 in 1,2-dimethoxyethane (G1).
• Electrochemical testing of natural graphite anodes with the developed electrolyte.
• Characterization of the solid-electrolyte interphase (SEI) using various techniques, including synchrotron analyses.
• Computational modeling using ab initio molecular dynamics (AIMD) simulations.

Main Results:

• The designed electrolyte (1M LiBF4 in G1) enabled natural graphite to achieve ~91% initial Coulombic efficiency and >88% capacity retention after 400 cycles.
• A self-terminated, grainy, fluorinated pseudo-SEI was formed on graphite edge planes, mitigating exfoliation.
• AIMD simulations elucidated the molecular origin of the pseudo-SEI, and operando synchrotron analyses confirmed reversible graphite phase transformations.

Conclusions:

• Demonstrated the feasibility of Li cointercalation chemistry in graphite for extreme-condition batteries.
• Established strategies for reversible Li-solvent cointercalation in graphite using ether electrolytes.
• Provided a foundation for understanding and controlling interphase formation in various battery systems.