In-situ nanoscale mapping of surface potential in all-solid-state thin film Li-ion battery using Kelvin probe force microscopy

This paper presents an in-situ study by combining contact dc-writing in biased scanning probe microscopy and non-contact Kelvin probe force microscopy to characterize the effect of bias-induced Li+ insertion/extraction on the changes of surface potential of TiO2 anode in an all-solid-state thin film Li-ion battery at nanoscale. With single layer TiO2 film as the reference, the factors affecting the changes of the surface potential, including the Fermi energy level shift and charge screening related to TiO2 semiconductor behavior, and bias-induced Li+ intercalation/ de-intercalation related to battery behavior are investigated. Surface potential hysteresis loop can be formed for TiO2 anode film, in which the potential value increases under the positive polarization and decreases under the negative polarization. In addition, TiO2 anode film after Li+ insertion/extraction cycles has a lower surface potential, indicating the decrease of charge sustaining capacity and the surface electrical degradation. In addition, surface potential barriers (pits) after the positive (negative) polarization have been also observed, which is mainly attributed to the different electrical properties and charge accumulation at grain boundaries.