Gradient Entropy Surface Architecture Stabilizes LiCoO₂ to 4.7 V

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium cobalt oxide (LiCoO2) is a primary cathode material for 3C-type lithium-ion batteries.
• High operating voltages above 4.55 V lead to significant structural and interfacial degradation in LiCoO2.

Purpose of the Study:

• To develop a gradient entropy (GE) surface architecture to enhance the stability of LiCoO2 at ultrahigh cutoff voltages (4.7 V).
• To investigate the mechanisms by which the GE architecture improves electrochemical performance and stability.

Main Methods:

• A homogeneous self-encapsulation layer was created using phytic acid and metal ions (Mg/Al/Ni) on the LiCoO2 surface.
• Calcination was employed to form the gradient entropy surface architecture.
• Electrochemical performance was evaluated, including capacity retention and cycling stability at 4.7 V.

Main Results:

• The GE-LCO material exhibited a gradient surface architecture with decreasing entropy from exterior to interior.
• The high-entropy surface enhanced thermodynamic stability, while expanded Li+ channels improved kinetic mobility.
• The GE layer effectively suppressed interfacial cobalt migration and improved electrochemical-mechanical stability.

Conclusions:

• The gradient entropy surface architecture successfully stabilizes LiCoO2 at 4.7 V, overcoming limitations of conventional materials.
• This approach preserves bulk electrochemical activity while enhancing surface stability through entropy-driven mechanisms.
• GE-LCO demonstrated a high capacity of 230.9 mAh/g and 80.6% capacity retention after 100 cycles at 4.7 V.