Near-Field IR Nanoscale Imaging of the Solid Electrolyte Interphase on a HOPG Electrode

The SEI layer on graphitic carbon electrodes is well known to protect effectively the electrode from further electrolyte reduction during long-term charge-discharge cycling process. Many different techniques have been applied to characterize the chemical and structural composition of this complex surface film. The standard vibrational optical spectroscopies, which offer molecular-level information are subject to the diffraction limit, which restricts their ability to probe at the nanoscale level of the SEI building blocks. This work exploits infrared apertureless near-field microscopy that operates below the diffraction limit to characterize the SEI layer on a model HOPG electrode. Variations in surface topography and chemical contrast are discussed in the context of SEI composition and function. The promise of near-field techniques for characterization of electrochemical interfaces is briefly evaluated.