Layered　iron/manganese-based　oxides　are　a　class　of　promising　cathode　materials　for　sustainable　batteries　due　to　their　high　energy　densities　and　earth　abundance.　However,　the　stabilization　of　cationic　and　anionic　redox　reactions　in　these　cathodes　during　cycling　at　high　voltage　remain　elusive.　Here,　an　electrochemically/thermally　stable　P2-Na0.67Fe0.3Mn0.5Mg0.1Ti0.1O2　cathode　material　with　zero　critical　elements　is　designed　for　sodium-ion　batteries　(NIBs)　to　realize　a　highly　reversible　capacity　of　≈210 mAh g−1　at　20 mA g−1　and　good　cycling　stability　with　a　capacity　retention　of　74%　after　300　cycles　at　200 mA g−1,　even　when　operated　with　a　high　charge　cut-off　voltage　of　4.5 V　versus　sodium　metal.　Combining　a　suite　of　cutting-edge　characterizations　and　computational　modeling,　it　is　shown　that　Mg/Ti　co-doping　leads　to　stabilized　surface/bulk　structure　at　high　voltage　and　high　temperature,　and　more　importantly,　enhances　cationic/anionic　redox　reaction　reversibility　over　extended　cycles　with　the　suppression　of　other　undesired　oxygen　activities.　This　work　fundamentally　deepens　the　failure　mechanism　of　Fe/Mn-based　layered　cathodes　and　highlights　the　importance　of　dopant　engineering　to　achieve　high-energy　and　earth-abundant　cathode　material　for　sustainable　and　long-lasting　NIBs.　©　2024　UChicago　Argonne,　LLC,　Operator　of　Argonne　National　Laboratory　and　University　of　California,　Operator　of　Lawrence　Berkeley　National　Laboratory　and　The　Author(s).　Advanced　Materials　published　by　Wiley-VCH　GmbH.