Charging layered cathode materials such as LiCoO₂ to a higher voltage may simultaneously enhance the specific capacity and average operating voltage, and thus improve the energy density of lithium ion battery (LIB). However, the battery cycle life is influenced by the lattice instability and undesired oxidation reactions of the electrolyte, which will degrade the structure of cathode materials, consume the limited electrolyte and hamper the charge transfer at cathode/electrode interface. In all these factors, cathode electrolyte interphase (CEI), a layer in-situ formed at the cathode-electrolyte interface in high voltage, is critically important for the performances of LIB cycling at high voltage. Investigating the formation mechanism and evolution processes of CEI layer are important for the understanding the high voltage cathode degradation process and crucial in improving high voltage cycle stability of LIBs. Here we present an in-situ atomic force microscopy (AFM) investigation of CEI on LiCoO₂ at high voltage. The formation of CEI is only observed at the LiCoO2 edge plane, not at the basal plane. Thin layer of Al₂O₃ coating completely suppresses the formation of CEI at the edge planes, and is shown to significantly improve coin cell high voltage cycle stability. And we also used this technique to study the CEI evolution on LiNi_0.5Mn_1.5O₄ cathode with ~5.0 V working voltage.