In Situ and Operando Force-Based Atomic Force Microscopy for Probing Local Functionality in Energy Storage Materials

Electrochemical energy storage is the key enabling component of electric vehicles and solar/wind-based energy technologies. The enhancement of energy stored requires the detailed understanding of ionic transport and electrochemical and electromechanical phenomena on <i>local</i> scales which are not always accessible with classical electrochemical techniques, such as voltammetry. Therefore, local probing of electrochemical and electromechanical behaviors on individual structural elements and heterogeneities, from grains to defects and further to individual atomic and molecular species, are invaluable. In this talk, I want to introduce force-based atomic force microscopies (AFM) to provided novel insights into local electrochemical processes on tens of nanometer and even molecular length under electrochemical control. I will highlight the development and application of in situ/operando force-based AFM methods to elucidate the local charge storage mechanism in a variety of energy related materials.<br/><br/>In the first part of the talk, I will showcase how AFM can be used to investigate the structure and dynamics of the electric double layer (EDL) for electrochemical capacitors. I want to highlight work on room temperature ionic liquids on model graphene electrodes since ionic liquids hold the promise of increasing the electrochemical stability windows for electrochemical capacitors. AFM was used to observe topological defects and show the existence of structural domains parallel to the solid-liquid interface towards a full picture of the double layer structure and their change with applied bias. In the second part of the talk, I want to highlight how AFM-based methods can be used to study ionic transport and local electrochemical reactions in supercapacitors and battery materials. Here, electro-chemo-mechanical coupling is the key to study ion insertion pathways and heterogeneities in local redox reactions. The first is demonstrated for the cation insertion into layered Ti₃C₂ electrodes based on their change in mechanical stiffness whereas the second is highlighted for proton insertion into WO₃ where the relationship between electrochemical current and electrode strain are discussed.