Highly Stable 4.6 V LiCoO₂ Cathodes for Rechargeable Li Batteries by Rubidium-Based Surface Modifications

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium cobalt oxide (LCO) is a dominant cathode material for portable electronics.
• High charging voltages (up to 4.6 V) increase LCO capacity but cause surface and structural instabilities, leading to rapid cell degradation.
• Surface coatings can stabilize LCO cathodes by forming protective passivation films and preventing electrolyte interactions.

Purpose of the Study:

• To investigate the efficacy of RbAlF4 as a surface coating for LCO cathodes operating at high voltages.
• To evaluate the electrochemical performance and cycling stability of RbAlF4-coated LCO cathodes.
• To elucidate the degradation mechanisms in high-voltage LCO cells.

Main Methods:

• Synthesis of RbAlF4-coated LiCoO2 (LCO) cathode materials.
• Electrochemical testing including capacity measurements and long-term cycling at elevated temperatures (30°C and 45°C).
• Analysis of degradation mechanisms, focusing on both cathode and anode contributions.

Main Results:

• RbAlF4-coated LCO cathodes achieved high capacities exceeding 220 mAh g-1.
• The coated cathodes demonstrated excellent cycling stability, retaining >80% capacity after 500 cycles at 30°C and >77% after 300 cycles at 45°C.
• Degradation analysis indicated that anode instability, not cathode failure, is the primary cause of capacity loss in 4.6 V LCO cells.

Conclusions:

• RbAlF4 surface coating effectively enhances the stability and performance of LCO cathodes at high operating voltages.
• The developed coating strategy offers a promising approach to improve the longevity of high-energy lithium-ion batteries.
• Anode stability is a critical factor limiting the performance of 4.6 V LCO cells and requires further investigation.