Anion Adsorption at the Inner-Helmholtz Plane Directs Cathode Electrolyte Interphase Formation

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• High-voltage Li-ion batteries require a stable cathode-electrolyte interphase (CEI).
• CEI formation is a complex process involving irreversible reactions, poorly understood at the atomic level.
• Understanding CEI formation is key to improving battery performance and longevity.

Purpose of the Study:

• To elucidate the formation mechanism of the cathode-electrolyte interphase (CEI) on LiCoO2 cathodes.
• To correlate interfacial structure with interphasial chemistry during CEI formation.
• To identify key factors governing CEI formation for advanced electrolyte design.

Main Methods:

• In situ/operando interfacial characterization techniques were employed.
• Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study adsorption.
• Electrochemical analysis confirmed the impact of CEI on battery performance.

Main Results:

• Difluorooxalatoborate (DFOB-) anions preferentially adsorb on LiCoO2, displacing carbonate solvents.
• This anion-driven adsorption leads to a compact CEI with suppressed solvent decomposition at high voltages.
• The LiCoO2 cathode with the dense CEI maintained structural integrity and showed excellent cycling stability at 4.7V.

Conclusions:

• Anion adsorption behavior is critical for forming a stable and compact CEI.
• The findings provide atomistic insights into CEI formation, guiding electrolyte design for high-voltage batteries.
• This research accelerates the development of next-generation Li-ion batteries with enhanced stability and performance.