Quantifying oxygen distortions in lithium-rich transition-metal-oxide cathodes using ABF STEM

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lithium-rich cathodes enable high energy densities through anionic redox reactions involving oxygen.
• Understanding the structural origins of these oxygen redox processes is critical for optimizing battery performance.
• Existing methods face challenges in accurately quantifying oxygen-related structural changes.

Purpose of the Study:

• To investigate oxygen distortions in charged lithium-rich cathode materials using advanced electron microscopy.
• To assess the capability of annular bright-field scanning transmission electron microscopy (ABF-STEM) for precise atomic-level measurements.
• To determine the experimental limitations and reliability of ABF-STEM for quantifying oxygen displacements.

Main Methods:

• Utilized annular bright-field (ABF) imaging within scanning transmission electron microscopy (STEM).
• Applied ABF-STEM to analyze the structure of charged Li_1.2Ni_0.2Mn_0.6O₂ cathode material.
• Focused on measuring atomic positions and quantifying oxygen distortions with high precision.

Main Results:

• Demonstrated that ABF-STEM can achieve positional accuracies below 20 picometers for oxygen atoms.
• Identified critical experimental constraints: measurements are reliable only for specimens without mistilt and above 3.5 nm thickness.
• Observed that measurement reliability is compromised even with optimized experimental and post-processing techniques.

Conclusions:

• ABF-STEM is a powerful tool for probing oxygen distortions in lithium-rich cathodes.
• Strict control over specimen preparation (minimizing mistilt) and sample thickness is essential for accurate quantification.
• Extreme caution and careful consideration of experimental parameters are necessary when interpreting ABF-STEM data for these materials.