Layered　Mn-based　oxides　are　promising　candidates　for　next-generation　high-energy-density　cathodes　of　rechargeable　batteries　owing　to　their　prominent　energy　density　and　cost-effectiveness.　However,　the　obvious　structural　degradation　such　as　the　layered-to-spinel　transformation,　associating　with　deteriorated　electrochemical　cycle　stability,　hinder　their　extensive　applications　in　batteries.　Herein,　a　composite　structure　is　designed　based　on　a　Mn-based　oxide　of　LiMn0.8Ni0.2O2　with　a　high-voltage　spinel　crystal　domain　pre-introduced　into　the　parent　layered　structure,　showing　good　structural　stability　during　electrochemical　process.　Results　show　that　Li2MnO3　crystal　domain　suffers　from　sluggish　Li+　ions　kinetics　and　structural　transformation　from　layered　to　metastable　spinel,　while　the　pre-introduced　high-voltage　spinel　crystal　domain　exhibits　almost　maintained　structure,　and　the　optimal　performance　near　to　theoretical　capacity　of　LiMn0.8Ni0.2O2　cathode　can　be　harvested　after　electrochemical　activation.　This　design　is　useful　for　stabilizing　the　entire　structure　prior　to　the　degradation　of　the　parent　structures,　and　the　electrochemical　contributions　of　layered　Li2MnO3　and　pre-introduced　high-voltage　spinel　crystal　domains　are　also　discerned.　This　study　provides　new　guidelines　for　designing　high-performance　composite-structure　Mn-based　cathode　materials　by　pre-introduction　of　stable　crystal　domains.