Use of in situ electrochemical atomic force microscopy (EC-AFM) to monitor cathode surface reaction in organic electrolyte

Surface reactions are responsible for the cycling performance of Li-ion rechargeable batteries based on LiMn2O4, We report structural and electrochemical studies of the LiMn2O4 cathode at room temperature in LiPF6 electrolyte using in situ electrochemical atomic force microscopy (EC-AFM) and lateral force microscopy (LFM). Surface dynamics were monitored in situ in organic electrolyte under potentiostatic conditions, After the first charge/discharge cycle, surface features were clearly visible. During the second charging process at 4.3 V vs Li/Li+, dissolution of surface particles was observed. The surface topography was quantitatively analyzed by height distribution functions. The dissolution rate (calculated from the change of particle volume with time) was found to follow the square root of time. During the second discharge process at 3.8 V vs Li/Li+, new particles were formed on the surface. However, there were no further changes in the surface topography with time during polarization at 3.8 V vs Li/Li+. The surface dynamics monitored for various charge/discharge conditions showed that a complex dissolution/precipitation reaction of manganese and lithium compounds is involved in the charge/discharge process of spinel LiMn2O4-based cathode material.