Ultra-thin and Mechanically Stable LiCoO₂-Electrolyte Interphase Enabled by Mg²⁺ Involved Electrolyte.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium cobalt oxide (LCO) is a key cathode material for lithium-ion batteries (LIBs), offering high energy density.
• Performance degradation and structural instability occur at high voltages due to electrolyte reactions with delithiated LCO.
• Developing strategies to protect the cathode-electrolyte interface is crucial for high-voltage LIBs.

Purpose of the Study:

• To create a physically and chemically robust Mg-integrated cathode-electrolyte interface (MCEI).
• To enhance the cycling stability and high-voltage performance of LiCoO2 (LCO) cathode materials.
• To investigate the role of Magnesium bis(trifluoromethanesulfonyl)imide (Mg[TFSI]2) as an electrolyte additive.

Main Methods:

• Incorporation of Magnesium bis(trifluoromethanesulfonyl)imide (Mg[TFSI]2) as an electrolyte additive.
• Formation and characterization of the Mg-integrated cathode-electrolyte interface (MCEI) during cycling.
• Electrochemical testing of Li||LCO coin cells and Graphite||LCO pouch cells.

Main Results:

• A stable, 2 nm thick MCEI was formed and maintained throughout long-term cycling.
• Magnesium (Mg) was detected within the MCEI and on the LCO lattice surface.
• Parasitic reactions, surface reconstruction, particle cracking, and cobalt dissolution were significantly suppressed.
• LCO cathodes demonstrated long-term cycling stability up to 4.5 V.
• Li||LCO coin cells retained 88.13% capacity after 200 cycles, and Graphite||LCO pouch cells retained 90.4% after 300 cycles.

Conclusions:

• The Mg-integrated cathode-electrolyte interface effectively protects LCO cathodes at high voltages.
• Mg[TFSI]2 serves as a novel electrolyte additive for improving LIB performance and stability.
• This approach offers a promising strategy for designing advanced electrolyte additives for next-generation LIBs.