Probing Electrochemical Properties of Materials at the Nano-Scale by Using Scanning Thermo-ionic Microscopy

Batteries and fuel cells produce electricity through chemical reactions. The rates of these reactions determine that the power of the battery, its charge rate and degradation. Near the surface and at the interfaces between materials, huge changes in properties can occur that can affect the reaction rates, which are complex and difficult-to-understand. Research in the last years has revealed that local variations in material properties can affect the performance of batteries and other electrochemical systems. The concentration of ionic and electronic species often depend on the important electrochemical properties of materials, such as surface reactions, interfacial charge transfer, and bulk and surface diffusion. Measuring these properties locally on the nanoscale build a good understanding of how electrochemical systems really work, and thus new materials with much higher performance can be created and increased the battery life. Scanning thermo-ionic microscopy is developed to probe local electrochemical activities at the nanoscale. The mechanism of this microscopy is based on imaging the Vegard strain induced by thermally driven stress and temperature oscillation. The Vegard strain linearly correlates with material lattice constant and can be used as a measure of ionic species concentration. Theoretical analysis and experimental validation are indicated that second and fourth harmonic components of the AFM deflection signal contain valuable information about species concentration. Second harmonic response of thermally induced cantilever vibration, is present in all solids predominantly correlates with the local thermal expansion information, while the fourth harmonic one is characteristic of local transport of mobile species that is presented only in ionic systems.