Visualization of Local Ionic Concentration and Diffusion Constants Using a Tailored Electrochemical Strain Microscopy Method

Abstract

A tailored electrochemical strain microscopy technique is presented and used to analyze the ionic mobility and diffusion coefficients in composite Si/C anodes. The resulting surface displacement after a voltage pulse is proportional to the ionic concentration change and is measured by the deflection of an atomic force microscopy tip. The results show a higher ionic mobility at the steps of silicon composite anode microcrystals compared to the crystal centers. Diffusion coefficients are extracted from the time dependence of the surface displacement. Mappings with nanoscale resolution of local diffusion coefficients are displayed. The results demonstrate higher diffusion coefficients at the steps.

Comparison of fresh and aged lithium iron phosphate cathodes using a tailored electrochemical strain microscopy technique

“…The ESM signal is based on the real, in-phase amplitude X from the lock-in, because, following the theory of Morozovska et al [26,50], it is the main signal part carrying the ESM signal. This was already shown in previous measurements, for which the signal intensity of the real, in-phase amplitude (X) has the same magnitude as the absolute signal amplitude (R) [34]. For data acquisition, we use a National Instruments card (PCI-6111) on a separate computer controlled by a LabVIEW (R2016) routine.…”

“…Additionally, since in a dry argon atmosphere no water meniscus is available to serve as electrolyte, side reactions are avoided. Further information of the non-Vegard expansion related influences is given in the supporting information in [34]. It is possible that the ESM signal is not solely generated by one mechanism, but the sum of several contributions (as it is as well assumed by Kalinin and Morozovska [32], with the Vegard contribution being the predominant).…”

“…Nevertheless, the theoretical background is still based on the comprehensive publications by Morozovska et al [26,27,50,51]. Further information about the set-up with control experiments regarding the origin of the signal can be found in [34]. The ESM measurements were performed on micrometre-sized single particles of a cross-section of the electrodes cut as specified above.…”

“…These mechanisms are piezoelectricity, flexoelectricity and electrostriction. Further contributions are possible by deformation potential generation, electron-hole formation, coupling of electrons and phonons, electrochemical side reactions in the tip-sample junction, electrostatic interaction, and volume expansion related to temperature changes and charge injection from the tip [27,[29][30][31][32][33][34]. However, the current state of research assumes the Vegard expansion to be the main signal generation mechanism.…”

Signal Origin of Electrochemical Strain Microscopy and Link to Local Chemical Distribution in Solid State Electrolytes

“…[ 28–36 ] Recently, time‐dependent ESM has been proposed to estimate local diffusion constants on electrode materials. [ 37–40 ] Reports about employing ESM on SSEs are scarce. Sasano et al.…”