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

Abstract

Electrochemical strain microscopy (ESM) is a distinguished method to characterize Li‐ion mobility in energy materials with extremely high spatial resolution. The exact origin of the cantilever deflection when the technique is applied on solid state electrolytes (SSEs) is currently discussed in the literature. Understanding local properties and influences on ion mobility in SSEs is of utmost importance to improve such materials for next generation batteries. Here, the exact signal formation process of ESM when applied on sodium super ionic conductor (NASICON)‐type SSE containing Na‐ and Li‐ions is investigated. Changes in the dielectric properties, which are linked to the local chemical composition, are found to be responsible for the observed contrast in the deflection of the cantilever instead of a physical volume change as a result of Vegard´s Law. The cantilever response is strongly reduced in areas of high sodium content which is attributed to a reduction of the tip‐sample capacitance in comparison to areas with high lithium content. This is the first time a direct link between electrostatic forces in contact mode and local chemical information is demonstrated on SSEs. The results open up new possibilities in information gain since dielectric properties are sensitive to subtle changes in local chemical composition.

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

“…Complex and challenging results also arise when using ESM to study multi‐component systems or low strain materials as it relies on the strain response, [ 321,322 ] although as it has been primarily to study processes in solid‐state batteries the electrochemical environments used can be somewhat representative. [ 323–325 ] KPFM [ 326 ] and EFM [ 327 ] have similarly found application for the study of solid‐state battery materials, but here too issues arise relating to representation of realistic battery environments due to a lack of consideration for factors such as cell compression, standard in high energy density solid‐state batteries. [ 328,329 ]…”

Lithium Deposition in Single-Ion Conducting Polymer Electrolytes

“…While various mechanisms may contribute to the observed strain, ESM probes ionic flows with outstanding resolution on a nanometer scale. 62,[64][65][66][67] However, while being applied to various solid battery compounds, in particular, electrode materials 62,63 and ceramic electrolytes (e.g., Li 1+x Al x Ti 2-x (PO 4 ) 3 , Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 and Li 0.33 La 0.56 TiO 3 ), [66][67][68] polymer electrolytes have been rarely analyzed by ESM, 64 but they revealed electroosmotic flow as the dominant contribution to the observed ESM signal in PVdF-based polymers. 64 Figures 6A-6C show the AFM topography and the ESM and QNM images, respectively.…”

Investigating the Interface between Ceramic Particles and Polymer Matrix in Hybrid Electrolytes by Electrochemical Strain Microscopy

“…Schön et al showed on Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) that the dominant contribution to the resulting ESM signal is caused by electrostatic forces [36]. A link between the chemical composition and local tip-sample interaction was found.…”