Lithium-excess　cation-disordered　rock-salt　oxides　(DRXs)　are　investigated　intensively　as　cathode　materials　for　future　lithium-ion　batteries　combining　cationic　and　anionic　redox　reactions.　However,　the　lattice　oxygen　redox　can　cause　severe　oxygen　release　resulting　in　rapid　capacity　fading.　Here,　we　investigate　a　series　of　xLi(2)TiO(3)-(1　-　x)LiMnO2　(0　＜=　x　＜=　1)　materials　and　find　that　only　Li1.2Mn0.4Ti0.4O2　(x　=　0.4)　and　Li1.1Mn0.7Ti0.2O2　(x　=　0.2)　can　form　phase-pure　DRXs,　which　both　deliver　high　capacity　(250　mAh　g(-1)).　The　newly　discovered　Li1.1Mn0.7Ti0.2O2　DRX　exhibits　remarkably　high　capacity　retention　of　84.4%　after　20　cycles　compared　to　only　60.8%　for　Li1.2Mn0.4Ti0.4O2.　Our　result　indicates　that　the　irreversible　oxygen　loss　is　reduced　by　raising　the　Mn　content.　Theoretical　calculations　further　reveal　that　increasing　the　redox-active　Mn　content　from　Li1.2Mn0.4Ti0.4O2　to　Li1.1Mn0.7Ti0.2O2　causes　the　orbitals　near　the　Fermi　level　to　change　from　O(2)p　non-bonding　(Li-O-Li　unhybridized　orbitals)　to　(Mn-O)*　antibonding　bands,　exhibiting　a　high　O-O　aggregation　barrier,　preventing　O-2　release　and　resulting　in　sustained　capacity　retention.　Hence,　these　new　findings　demonstrate　that　regulating　oxygen　redox　by　tailoring　the　redox-active　transition　metal　content　is　an　effective　strategy　to　enhance　the　cycling　stability　of　DRXs.