Imaging Phase Segregation in Nanoscale LiCoO₂ Single Particles

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lithium cobalt oxide (LiCoO₂) is a key cathode material for batteries, also showing potential in electrocatalysis and electrochemical random access memory (ECRAM).
• Understanding nanoscale phase transformations, strain, and diffusional anisotropy in LiCoO₂ is crucial for optimizing its performance in various applications.

Purpose of the Study:

• To investigate how phase transformations in LiCoO₂ scale down to nanometer dimensions.
• To explore the effects of strain and surface energy on the electrochemical properties of isolated LiCoO₂ islands.

Main Methods:

• Epitaxial growth of LiCoO₂ islands using pulsed laser deposition.
• Electrochemical cycling of individual islands.
• Conductive atomic force microscopy (c-AFM) for phase imaging.
• Photoemission electron microscopy (PEEM) for cross-validation and statistical analysis.

Main Results:

• Above 20 nm thickness, LiCoO₂ islands exhibit a kinetically arrested state with phase boundaries perpendicular to Li-planes.
• Smaller islands (<20 nm) show a higher conductive fraction, suggesting surface energy dominance below a critical dimension and a striping pattern in 14 nm islands.
• Applied strain significantly alters current flow, indicating its critical role in electrochemical performance at the nanoscale.

Conclusions:

• Nanoscale morphology and strain critically influence the electrochemical behavior of LiCoO₂.
• Surface energy effects become dominant in thinner islands, altering their phase behavior.
• The findings are essential for advancing battery technology, electrocatalysis, and ECRAM applications.