Constructing　robust　surface　and　bulk　structure　is　the　prerequisite　for　realizing　high　performance　high　voltage　LiCoO2　(LCO).　Herein,　we　manage　to　synthesize　a　surface　Mg-doping　and　bulk　Al-doping　core-shell　structured　LCO,　which　demonstrates　excellent　cycling　performance.　Half-cell　shows　94.2%　capacity　retention　after　100　cycles　at　3.0–4.6　V　(vs.　Li/Li+)　cycling,　and　no　capacity　decay　after　300　cycles　for　full-cell　test　(3.0–4.55　V).　Based　on　comprehensive　microanalysis　and　theoretical　calculations,　the　degradation　mechanisms　and　doping　effects　are　systematically　revealed.　For　the　undoped　LCO,　high　voltage　cycling　induces　severe　interfacial　and　bulk　degradations,　where　cracks,　stripe　defects,　fatigue　H2　phase,　and　spinel　phase　are　identified　in　grain　bulk.　For　the　doped　LCO,　Mg-doped　surface　shell　can　suppress　the　interfacial　degradations,　which　not　only　stabilizes　the　surface　structure　by　forming　a　thin　rock-salt　layer　but　also　significantly　improves　the　electronic　conductivity,　thus　enabling　superior　rate　performance.　Bulk　Al-doping　can　suppress　the　lattice　“breathing”　effect　and　the　detrimental　H3　to　H1-3　phase　transition,　which　minimizes　the　internal　strain　and　defects　growth,　maintaining　the　layered　structure　after　prolonged　cycling.　Combining　theoretical　calculations,　this　work　deepens　our　understanding　of　the　doping　effects　of　Mg　and　Al,　which　is　valuable　in　guiding　the　future　material　design　of　high　voltage　LCO.　©　2024　Science　Press