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

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 resultschanges 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.Ion transport processes in thin film materials affect the performance of a wide variety of technologies ranging from bioelectronics 1,2 and electrochemical energy storage 3 , to the stability of perovskite photovoltaics. 4,5 The ability to characterize ion transport dynamics in solid-state systems at the nanoscale is important to understanding the processing-structure-function relationships of these materials and has therefore attracted considerable interest. 6-8 Many polymer-based systems are, either by design or by consequence of their solution-based deposition kinetics, inherently nanostructured. 9,10 Consequently, to explore the properties of such materials, groups have used a wide range of scanning probe microscopy methods, 11-14 as well as measuring the behavior of a moving ion front via optical methods. 2,8,15 Electrochemical strain microscopy (ESM) in particular has been widely applied to image ion uptake dynamics 16,17 and Prefabricated glass slides coated with a layer of indium tin oxide are sonicated in solutions of acetone and isopropyl alcohol successively. After sonication, the slides are plasma-cleaned for a period of 10 minutes and then immediately transferred to a dry-nitrogen atmosphere glovebox.Within this glovebox, the slides are spin-coated with the pre-prepared solutions containing the requisite solid polymer electrolyte. This process generates films with an average thickness of...

Excitonic Effects in Polymeric Photocatalysts

“…Recent progress in the corresponding fields would be helpful: synthetic methods such as seeded growth, [59] grafting‐from strategy, [83] and blocking‐cyclization technique [84] exhibit remarkable advantage in precisely constructing well‐defined polymers. ; techniques like synchrotron radiation‐based spectroscopies [67] and electrostatic force microscopy [85] present feasibilities in characterizing the fine structures and electronic properties of polymers. In addition, the adsorption of molecular substrates on the surface of photocatalysts is crucial in exciton‐based energy transfer, [62, 86] where coordination geometries and reactive intermediates would determine the efficiency and selectivity.…”

Excitonic Effects in Polymeric Photocatalysts

“…Therefore,ascompared with the well-established chargecarrier one,t he excitonic aspect in polymeric photocatalyst deserves more attention in further, and there are still many challenges need to be overcome: i) It remains difficult to establish accurate relationships between structural factors and excitonic processes in polymeric photocatalysts.P olymeric photocatalysts have long been controversial for their disordered, inhomogeneous structures.I nc ontrast to the rigid structures of inorganic crystals,t he much more flexible structures of polymers make it difficult to selectively introduce certain structural factors.T herefore,a chieving the synthesis and characterization of well-defined polymers can pave the way for gaining insights into relationships between structural factors and excitonic behaviors.R ecent progress in the corresponding fields would be helpful: synthetic methods such as seeded growth, [59] graftingfrom strategy, [83] and blocking-cyclization technique [84] exhibit remarkable advantage in precisely constructing well-defined polymers. ; techniques like synchrotron radiation-based spectroscopies [67] and electrostatic force microscopy [85] present feasibilities in characterizing the fine structures and electronic properties of polymers.I n addition, the adsorption of molecular substrates on the surface of photocatalysts is crucial in exciton-based energy transfer, [62,86] where coordination geometries and reactive intermediates would determine the efficiency and selectivity.Tothese issues,monitoring the adsorption, activation and desorption of molecular substrates on the photocatalysts surfaces is quite necessary.F or instance, reactive sites and coordination geometries can be monitored by in situ FT-IR and XPS, [87,88] while intermediates can be identified by photoionization mass spectrometry. [89] Theoretical study would also be useful to the above problem.…”

Characterizing Batteries by In Situ Electrochemical Atomic Force Microscopy: A Critical Review

“…These broadly fall into two categories; those that rely on electrochemical processes or ionic transport, such as scanning electrochemical microscopy (SECM), [ 302–305 ] scanning ion conductance microscopy (SICM), [ 306 ] scanning electrochemical cell microscopy (SECCM) [ 307 ] and electrochemical strain microscopy (ESM); [ 308–311 ] and those that probe properties intrinsic to the electrode material, like Kelvin probe force microscopy (KPFM) [ 312,313 ] and electrostatic force microscopy (EFM). [ 314 ] These techniques, and their application to study battery materials, have been reviewed elsewhere, [ 23–25,315–317 ] but the degree to which they are less, or more, able than EC‐AFM to study realistic batteries in relevant environments has not and hence will briefly be discussed.…”