Constructing　a　stable　cathode-electrolyte-interphase　(CEI)　on　cathode　surface　constitutes　the　foundation　of　realizing　high-voltage　Li-ion　batteries,　yet　its　formation,　a　highly　heterogeneous　process　involving　irreversible　reactions　between　electrolyte　components　and　cathode　materials,　remains　poorly　understood.　Herein,　combining　multiple　in　situ/operando　interfacial　characterization　techniques,　we　establish　the　correlation　between　interfacial　structure　and　interphasial　chemistry,　and　reveal　the　key　role　played　by　adsorptive　behavior　of　various　electrolyte　components　in　the　inner-Helmholtz　plane　during　CEI　formation.　Quartz　crystal　microbalance　equipped　with　dissipation　modification　detects　that　difluorooxalatoborate　(DFOB-)　anion　preferentially　adsorbed　on　LiCoO2　tends　to　expel　carbonate　solvents　from　the　adsorption　layer,　thus　suppressing　their　electrochemical　decomposition　at　high　voltages　and　leading　to　a　more　compact　CEI　derived　from　anions　with　limited　contribution　from　organic　ingredients.　Consequently,　the　CoO2　lattice　structure　protected　by　the　dense　CEI　remains　intact　despite　near-complete　delithiation,　thereby　ensuring　excellent　cycling　stability　for　4.7　V　operation　of　LiCoO2　cathode.　The　atomistic-level　insight　into　the　key　factors　that　govern　CEI　formation　provides　directive　knowledge　that　accelerates　electrolyte　design　for　high-voltage　batteries.