Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Layered transition metal oxides, especially nickel-rich LiNiO2, offer high energy density for Li-ion batteries.
• Increased nickel content in LiNiO2 cathodes leads to reduced stability and capacity fade.
• Alumina (Al2O3) coatings are explored to improve the surface stability and electrochemical performance of LiNiO2 cathodes.

Purpose of the Study:

• To elucidate the structural characteristics of Al2O3 coatings on LiNiO2 cathodes.
• To understand the interface chemistry between alumina coatings and LiNiO2.
• To correlate coating structure with improved electrochemical performance and capacity retention.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy (27Al, 6,7Li MAS NMR, T1 measurements).
• Powder X-ray diffraction (PXRD).
• Electron microscopy.

Main Results:

• Thick Al2O3 coatings (10 wt%) on LiNiO2 and LiCoO2 exhibit disordered four- and six-coordinate Al-O environments.
• Thin Al2O3 coatings (0.2 wt%) on LiCoO2 reveal interfacial phases of LiCo1-xAlxO2 and LiAlO2.
• Evidence suggests similar interfacial mixing occurs for Al2O3 on LiNiO2, impacting cathode stability.

Conclusions:

• Solid-state NMR provides critical insights into the structure of alumina coatings and their interfaces with LiNiO2.
• Understanding interfacial phase formation is key to optimizing alumina coatings for enhanced Li-ion battery cathode stability.
• Further research can leverage structural knowledge to minimize excess coating and maximize battery performance.