Vertical Diffusion of Ions within Single Particles during Electrochemical Charging

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Understanding ion transport in electroactive nanomaterials is key for improving ion battery performance and longevity.
• Current methods struggle to determine the vertical trajectory of ion diffusion within nanomaterials.
• Horizontal ion transport has been studied, but vertical pathways remain a challenge.

Purpose of the Study:

• To develop a novel microscopy technique for precisely measuring vertical ionic transport in single nanomaterials.
• To investigate the ionic transport pathway within Prussian blue particles during electrochemical cycling.

Main Methods:

• Development of dual-angle total internal reflection microscopy (DATIRM).
• DATIRM uses angle-dependent illumination depths to trace vertical centroid shifts of nano-objects.
• Application to observe ion insertion/extraction in single Prussian blue particles.

Main Results:

• Successfully demonstrated DATIRM by tracking Brownian motion of a nanosphere in the vertical dimension.
• Observed that the vertical centroids of single Prussian blue particles did not change during ion insertion/extraction.
• This indicates an outside-in ion diffusion pathway within the particles.

Conclusions:

• The developed DATIRM technique effectively resolves vertical ion trajectories in nanomaterials.
• Ionic transport in Prussian blue particles occurs via an outside-in mechanism.
• Findings challenge intuitive bottom-up models and inform the design of advanced electrode materials for ion batteries.