Surface Vacancy Engineering Re-Routes First-Cycle Redox for Stabilized Li-Rich Layered Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Lithium-rich layered oxides (LRLO) are promising for high-energy-density batteries.
• First-cycle performance degradation, including oxygen release and lattice collapse, limits LRLO application.
• Controlling surface chemistry is crucial for mitigating these degradation pathways.

Purpose of the Study:

• To investigate how atomic-scale surface disorder influences the redox sequence in LRLO.
• To develop a strategy for enhancing the electrochemical performance and stability of Li_1.14Ni_0.32Mn_0.54O₂ (LNMO) cathodes.
• To establish a general design principle for durable LRLO cathodes.

Main Methods:

• Chemical treatment to introduce surface oxygen and transition metal vacancies in LNMO.
• Multi-modal synchrotron analyses (e.g., X-ray diffraction, X-ray absorption spectroscopy) to characterize surface structure and oxidation states.
• Electrochemical testing to evaluate first-cycle Coulombic efficiency, voltage fade, and capacity retention.

Main Results:

• Surface vacancies were successfully introduced in LNMO, confined to the particle surface.
• The treated LNMO exhibited an early oxygen oxidation below 4.4 V and delayed nickel oxidation.
• Suppression of detrimental Ni⁴⁺─O covalent states, irreversible oxygen release, and manganese dissolution was observed.
• The modified redox pathway maintained metal-oxygen coordination at high voltages.

Conclusions:

• Atomic-scale surface disorder effectively controls the first-cycle redox sequence in LRLO.
• Engineered surface vacancies prevent oxygen release and lattice collapse, enhancing electrochemical performance.
• This work provides a general design strategy for developing stable, high-energy-density LRLO cathodes.