Noncontact Imaging of Ion Dynamics in Polymer Electrolytes with Time-Resolved Electrostatic Force Microscopy

TL;DR

This study demonstrates that time-resolved electrostatic force microscopy (trEFM) can effectively image and analyze local ion transport dynamics in polymer electrolytes, correlating nanoscale measurements with macroscopic impedance spectroscopy results.

Contribution

The paper introduces the use of trEFM to study ion dynamics in polymer electrolytes and establishes its correlation with traditional impedance spectroscopy, providing nanoscale insights into ionic processes.

Findings

trEFM captures stretched exponential relaxation kinetics similar to EIS.

Ion dynamics trends with temperature, salt concentration, and polymer composition are consistent across methods.

trEFM can image ion transport in novel polymer electrolytes for energy storage.

Abstract

Ionic transport processes govern performance in many classic and emerging devices, ranging from battery storage to modern mixed-conduction electrochemical transistors. Here, we study local ion transport dynamics in polymer films using time-resolved electrostatic force microscopy (trEFM). We establish a correspondence between local and macroscopic measurements using local trEFM and macroscopic electrical impedance spectroscopy (EIS). We use polymer films doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI) as a model system where the polymer backbone has oxanorbornenedicarboximide repeat units with an oligomeric ethylene oxide side chain of length n. Our results show that the local polymer response measured in the time domain with trEFM follows stretched exponential relaxation kinetics, consistent with the Havriliak-Negami relaxation we measure in the frequency-domain EIS data for macroscopic samples of the same polymers. Furthermore, we show that the trEFM results capture the same trends as the EIS results-changes in ion dynamics with increasing temperature, increasing salt concentration, and increasing volume fraction of ethylene oxide side chains in the polymer matrix evolve with the same trends in both measurement techniques. We conclude from this correlation that trEFM data reflect, at the nanoscale, the same ionic processes probed in conventional EIS at the device level. Finally, as an example application for emerging materials syntheses, we use trEFM and infrared photoinduced force microscopy (PiFM) to image a novel diblock copolymer electrolyte for next-generation solid-state energy storage applications.