In-depth　understanding　interfacial　failures　and　differentiating　their　contributions　to　the　overall　performance　decay　are　in　urgent　need　for　cell　design　and　optimization.　Herein,　with　the　focus　on　the　frequently　observed　surface　phase　transition　layer　(SPTL)　of　LiCoO2　layered　cathode　and　by　virtue　of　electrochemical　tests　and　microstructure　analysis,　we　systematically　investigate　the　structural　and　chemical　properties　of　LiCoO2　SPTL　under　different　cycling　conditions　and　reveal　that　the　LiCoO2　SPTL　does　not　contribute　performance　decay　significantly.　In　comparison　with　Ni-contained　LiN1-x-yMnxCoyO2　layered　cathodes,　LiCoO2　SPTL　shows　two　distinctive　features.　One　is　the　porous　morphology　due　to　severe　surface　corrosion/dissolution　and　the　other　is　the　spinel-like　lattice　structure.　The　porous　surface　layer　enables　a　percolating　surface　diffusion　and　the　spinel　structure　offers　a　bulk　diffusion　for　Li　ions,　which　jointly　leads　to　a　minor　blocking　effect　of　Li　ion　during　its　intercalation/deintercalation.　We　experimentally　verified　that　the　LiCoO2　SPTL　is　formed　in　the　discharging　process,　particularly　at　lower　discharge　voltages.　Our　work　deepens　the　understanding　on　the　LiCoO2　SPTL　and　its　effect　on　the　overall　performance　decay,　which　sheds　new　lights　on　the　interfacial　failures　of　layered　cathodes.