Ruocun Wang¹ James Mitchell¹ Qiang Gao² Wan-Yu Tsai² Shelby Boyd¹ Matt Pharr³ Nina Balke² Veronica Augustyn¹

1, North Carolina State University, Raleigh, North Carolina, United States
2, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
3, Texas A&M University, College Station, Texas, United States

The presence of structural water in tungsten oxides leads to a transition in the energy storage mechanism from battery-type intercalation (limited by solid state diffusion) to intercalation pseudocapacitance (limited by surface kinetics). Here, we explore how these mechanisms affect mechanical electrode properties and present a pathway to utilize the mechanical coupling for local studies of electrochemistry. In operando atomic force microscopy (AFM) dilatometry at fast voltammetry sweep rates (up to 4 second charge/discharge timescales) is utilized to measure the electrode height changes via the AFM cantilever displacement during proton intercalation in anhydrous and hydrated tungsten oxides. It is found that the local mechanical deformation of the hydrated tungsten oxide is smaller and more gradual than for the anhydrous oxide, and occurs without hysteresis for the intercalation and de-intercalation processes, highlighting the different mechanical response of battery vs. intercalation pseudocapacitance mechanisms.