Fe-Mn　based　Li-rich　cathode　materials　are　regarded　as　one　of　the　most　promising　cathode　materials　for　their　low　cost　and　high　energy　density　but　possess　drawbacks　such　as　high　oxygen　release,　low　conduc-tivity,　and　slow　kinetics　for　lithium-ion　transport.　To　address　these　issues,　herein,　we　proposed　a　high-valance　cations　Nb5+　doping　strategy　and　synthesized　a　series　of　Li-1.26[Fe0.22Mn0.52](1-x)Nb0.74xO2　(x　=　0,　0.02,　0.03,　0.04)　cathode　materials.　Using　a　combination　of　experimental　approaches　and　density　func-tional　theory　(DFT)　calculations,　we　found　that　the　doped　samples　presented　expanded　interlayer　spacing　for　Li-ion　migration　and　better　structural　stability　due　to　the　large　ionic　radius　of　Nb5+　and　the　strength-ened　Nb-O　bond.　Moreover,　Nb　doping　could　not　only　decrease　the　band　gap　and　the　density　of　states　of　the　O　2p　band　but　also　contribute　extra　electrons　to　surrounding　O　atoms,　thereby　enhancing　electronic　conductivity　and　stabilizing　lattice　oxygen.　Benefit　from　the　underlying　mechanisms　mentioned　above,　the　Nb-0.022　sample　possessed　a　higher　Coulombic　efficiency　(71.1　vs　65.0%)　at　0.2　C,　showing　more　stable　cycling　performance　(90.4　vs　67.7　mAh　g(-1))　at　0.5　C　and　rate　capability.　These　favorable　results　can　assist　in　the　development　of　Fe-Mn　based　Li-rich　cathode　materials　with　excellent　electrochemical　properties.　(C)　2021　Elsevier　Ltd.　All　rights　reserved.