  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.
