Organic Cathode Electrolyte Interphase Achieving 4.8 V LiCoO₂.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Stabilizing high-voltage lithium-ion batteries, particularly those using lithium cobalt oxide (LCO), is a significant challenge.
• Effective cathode electrolyte interphase (CEI) formation is critical for mitigating detrimental reactions at elevated voltages.
• Existing inorganic CEIs, often based on LiF, exhibit insufficient performance for high-voltage LCO applications.

Purpose of the Study:

• To develop a novel electrolyte system for enhancing the stability and cycling performance of high-voltage lithium-ion batteries.
• To investigate the formation and properties of a cathode electrolyte interphase (CEI) using an ionic liquid electrolyte (ILE) with a high donor number additive.
• To demonstrate the efficacy of the proposed CEI in suppressing degradation mechanisms in LCO and other high-voltage cathode materials.

Main Methods:

• Utilized an ionic liquid electrolyte (ILE) incorporating a high donor number additive.
• Investigated Li//LCO cells cycled at high cut-off voltages (4.7 V/4.8 V).
• Analyzed the composition and properties of the formed CEI, focusing on C-F bond characteristics.

Main Results:

• Achieved high capacity retention (86.9%/74.2% after 100 cycles at 0.5 C) for Li//LCO cells at 4.7 V/4.8 V.
• Discovered the formation of a stable organic CEI rich in C-F bonds, attributed to the high donor number additive.
• Demonstrated superior cycling stability in other high-voltage systems (Li//LiNi0.6Co0.2Mn0.2O2 at 4.8 V and Li//LiNi0.5Mn1.5O4 at 4.95 V), even at 60°C.

Conclusions:

• The developed organic CEI, rich in C-F bonds, effectively passivates the cathode surface, suppressing phase transitions, cobalt dissolution, and gas evolution.
• This organic CEI strategy offers a promising pathway for significantly improving the electrochemical stability of high-voltage cathodes in lithium-ion batteries.
• The findings pave the way for the development of more efficient and durable high-voltage lithium-ion battery technologies.