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Characterization of Composite Electrodes for Solid-State Batteries by Electrochemical AFM Techniques

Figure: Dennis Körmer

Figure 1: Schematic illustration of the different AFM techniques. Adapted from [1] and [2]

Characterization of Composite Electrodes for Solid-State Batteries by Electrochemical AFM Techniques

Summary:

AFM-based electrochemical techniques are well suited for characterizing the electrochemical properties of materials at the nanoscale level. We are using such techniques for characterizing the electrochemical properties of composite electrodes for solid-state batteries. The techniques encompass electrochemical strain microscopy (ESM), Kelvin probe force microscopy (KPFM) and conductive AFM (cAFM). 

Electrochemical Strain Microscopy (ESM)

ESM is a technique for measuring local strains in materials due to compositional changes (Vegard strains). In battery electrodes, such strains are generated by the intercalation and deintercalation of Li+ ions. Experimentally, the AFM tip is brought in contact with the sample surface. Then an AC bias is applied between the AFM tip and the sample. This leads to a change in the local composition beneath the tip and induces a deformation of the surface. This Vegard strain can be measured down to a few picometers due to the resonance enhancements of the AFM cantilever. However, the quantitative interpretation of ESM signal is still challenging due to signal contributions from electrostatic forces.

Kelvin Probe Force Microscopy (KPFM)

In electrochemistry, KPFM is used as a method for measuring the Volta potential of materials with high spatial resolution. KPFM works in a dual-pass technique. That means in the first step, the topography of the sample is mapped in intermitted contact mode. In the second step, the AFM tip is positioned typically 50 nm above the sample surface, a distance at which electrostatic forces between tip and surface are dominant. Consequently, a combined DC and AC potential applied to the tip results in an oscillating motion of the cantilever, with the amplitude being proportional to the DC potential difference between tip and sample. As a result, the Volta potential of the surface is mapped.

Conductive AFM (cAFM)

In cAFM, local electrical currents between a voltage-biased tip and the sample surface are measured in contact mode. This leads to maps of the local electronic conductivity of the sample under study.

[1]V. Lushta, S. Bradler, B. Roling, A. Schirmeisen, ‘Correlation between drive amplitude and resonance frequency in electrochemical strain microscopy: Influence of electrostatic forces‘, Journal of Applied Physics 121 (2017) 224302.
[2]D. H. Agarwal, P. M. Bhatt, A. M. Pathan, ‘Development of portable experimental set-up for AFM to work at cryogenic temperature‘, AIP Conference Proceedings 1447 (1), S. 531-532.

Highlighted Publications:

  • D. Renz, M. Cronau, B. Roling, 'Determination of Lithium Diffusion Coefficients in Single Battery Active Material Particles by Using an AFM-Based Steady-State Diffusion Depolarization Technique', J. Phys. Chem. C 125 (2021), 2230−2239. doi: 10.1021/acs.jpcc.0c07751
  • S. Badur, D. Renz, T. Göddenhenrich, D. Ebeling, B. Roling, A. Schirmeisen, 'Voltage- and Frequency-Based Separation of Nanoscale Electromechanical and Electrostatic Forces in Contact Resonance Force Microscopy: Implications for the Analysis of Battery Materials', ACS Appl. Nano Mater. 3 (2020), 7391-7405. doi: 10.1021/acsanm.0c00989
  • V. Lushta, S. Bradler, B. Roling, A. Schirmeisen, ‘Correlation between drive amplitude and resonance frequency in electrochemical strain microscopy: Influence of electrostatic forces‘, Journal of Applied Physics 121 (2017) 224302. doi: 10.1063/1.4984831