Trilayer Topological Structure with Ni/Mn Concentration Gradient for High‐Performance Cobalt‐Free Lithium‐Rich Oxide Cathode with Enhanced Anionic Redox Reaction

Abstract Lithium‐rich cathode materials have attracted much attention due to the high specific capacity contributed by extra anionic redox. However, the oxygen loss and poor cycling stability caused by the irreversible anionic redox limit the commercial application. Herein, the novel cobalt‐free lithium‐rich manganese‐based oxide cathode with Ni/Mn concentration gradient, “5/5+3/7+1/9” (n/m, nLi 2 MnO 3 ·mLiMn 0.5 Ni 0.5 O 2 , core + transition layer + shell), is successfully synthesized. Since the oxygen release from the “5/5” core is restricted by the stable “1/9” shell and is difficult to be removed from the oxide cathode, the regulated “5/5+3/7+1/9” cathode exhibits a reversible anionic redox reaction and suppressed structural transition compared with the homogeneous “5/5” oxide cathode. Moreover, the transitional 3/7 region relieves the concentration difference and the lattice strain caused by the heterogeneous electrochemistry of the 1/9 shell and 5/5 core. The structural characterization elucidates that the concentration gradient regulation still exists even after long‐term cycling, which interprets the durability and reliability of the regulated strategy. As a result, the “5/5+3/7+1/9” cathode delivers high Coulombic efficiency during cycling, stabilized cycling performance, and enhanced rate capacity. The approach of concentration gradient regulation alleviates the oxygen loss caused by drastic anionic redox and promotes the development of other high‐energy‐density but low‐stability cathode materials.