We　initiated　a　self-adjusted　oxygen-partial-pressure　approach　to　prepare　high-performance　Li2MnO3-LiMO2　cathode　material.　Four　different　lithium　resources,　lithium　acetate,　lithium　hydrate,　lithium　carbonate,　and　lithium　nitrate　were　used　to　create　the　local　oxygen　partial　pressure　over　the　samples.　Since　the　melting　points　or　decomposition　temperatures　for　these　lithium　resources　decrease　in　a　sequence,　Li　2CO3　≈　LiOH　>　LiNO3　>　CH　3COOLi,　the　oxygen　partial　pressure　of　the　four　crucibles　that　contain　these　lithium　salts　increases　in　a　sequence,　S4　≈　S3　<　S2　<　S1　≈　air　in　muffle　furnace　(S1:　CH3COOLi·2H2O,　S2:　LiNO3,　S3:　LiOH·H2O,　and　S4:　Li2CO　3).　Regardless　of　the　lithium　resources,　the　decomposed　gases　reduced　the　local　oxygen　partial　pressures,　leading　to　an　incomplete　oxidation　of　Mn　ions　in　the　final　product　Li[Li0.14Mn0.47Ni　0.25Co0.14]O2.　That　is,　some　of　the　Mn　3+　ions　existed　in　the　final　product　Li[Li0.14Mn　0.47Ni0.25Co0.14]O2,　and　the　amount　of　Mn3+　ions　was　closely　related　to　the　oxygen　partial　pressure.　The　lower　oxygen　partial　pressure　gave　rise　to　a　larger　amount　of　Mn3+　in　the　final　products,　as　confirmed　by　X-ray　photoelectron　spectroscopy.　Electrochemical　tests　showed　that　the　products　prepared　using　lithium　carbonate　exhibited　the　best　electrochemical　performance:　the　initial　discharge　capacity　was　279.4　mA　h　g-1　at　a　current　density　of　20　mA　g-1,　which　remained　as　high　as　187.2　mA　h　g-1　even　at　a　much　higher　current　density　of　500　mA　g-1.　Such　excellent　electrochemical　performance　could　be　ascribed　to　the　presence　of　Mn3+　that　decreased　the　surface　layer　resistance　and　charge　transfer　resistance,　and　that　further　increased　the　conductivity　and　Li+　ion　diffusion　coefficient.　©　2013　The　Royal　Society　of　Chemistry.