Li-rich　Mn-based　cathode　materials　(LRMs)　are　potential　cathode　materials　for　high　energy　density　lithium-ion　batteries.　However,　low　initial　Coulombic　efficiency　(ICE)　severely　hinders　the　commercialization　of　LRM.　Herein,　a　facile　oleic　acid-assisted　interface　engineering　is　put　forward　to　precisely　control　the　ICE,　enhance　reversible　capacity　and　rate　performance　of　LRM　effectively.　As　a　result,　the　ICE　of　LRM　can　be　precisely　adjusted　from　84.1%　to　100.7%,　and　a　very　high　specific　capacity　of　330　mAh　g−1　at　0.1　C,　as　well　as　outstanding　rate　capability　with　a　fascinating　specific　capacity　of　250　mAh　g−1　at　5　C,　are　harvested.　Theoretical　calculations　reveal　that　the　introduced　cation/anion　double　defects　can　reduce　the　diffusion　barrier　of　Li+　ions,　and　in　situ　surface　reconstruction　layer　can　induce　a　self-built-in　electric　field　to　stabilize　the　surface　lattice　oxygen.　Moreover,　this　facile　interface　engineering　is　universal　and　can　enhance　the　ICEs　of　other　kinds　of　LRM　effectively.　This　work　provides　a　valuable　new　idea　for　improving　the　comprehensive　electrochemical　performance　of　LRM　through　multistrategy　collaborative　interface　engineering　technology.　©　2021　Wiley-VCH　GmbH