Development of electrochemical high-speed atomic force microscopy for visualizing dynamic processes of battery electrode materials

Development of lithium ion batteries with ultrafast charging rate as well as high energy/power densities and long cycle-life is one of the imperative works in the field of batteries. To achieve this goal, it requires not only to develop new electrode materials but also to develop nano-characterization techniques that are capable of investigating the dynamic evolution of the surface/interface morphology and property of fast charging electrode materials during battery operation. Although electrochemical atomic force microscopy (EC-AFM) holds high spatial resolution, its imaging speed is too slow to visualize dynamics occurring on the timescale of minutes. In this article, we present an electrochemical high-speed AFM (EC-HS-AFM), developed by addressing key technologies involving optical detection of small cantilever deflection, dual scanner capable of high-speed and wide-range imaging, and electrochemical cell with three electrodes. EC-HS-AFM imaging from 1 fpm to ∼1 fps with a maximum scan range of 40 × 40 µm² has been stably and reliably realized. Dynamic morphological changes in the LiMn₂O₄ nanoparticles during cyclic voltammetry measurements in the 0.5 mol/l Li₂SO₄ solution were successfully visualized. This technique will provide the possibility of tracking dynamic processes of fast charging battery materials and other surface/interface processes such as the formation of the solid electrolyte interphase layer.