Direct Correlation between Local Surface Potential Measured by Kelvin Probe Force Microscope and Electrochemical Potential of LiNi_0.80Co_0.15Al_0.05O₂ Cathode at Different State of Charge

Abstract

Kelvin probe force microscope (KPFM) is an AFM-based technique, which can be used for studying lithium ion batteries (LIBs). The capabilities of this technique for practical applications have been explored further in this work. A direct correlation between the local surface potential measured by KPFM and the electrochemical potential of LiNi0.80Co0.15Al0.05O2 cathode material is revealed. On the basis of this correlation, a quantitative approach to investigate the local behavior of the cathode material has been developed. We then demonstrate the potentials of this correlation by applying this methodology in three different situations. The surface inhomogeneity of the electrode is visualized and estimated from the microscale down to the nanoscale. In addition, the surface overdelithiation state induced by insufficient Li+ solid-state diffusivity is also observed on the electrodes charged at elevated C-rates. Accordingly, it indicates the presence of an uneven delithiation from the surface toward the bulk of the active particle. This work demonstrates that KPFM is a robust technique to investigate LIB systems due to its prominent experimental compatibility, surface sensitivity, and high spatial resolution (<100 nm).