Modifying Li@Mn₆ Superstructure Units by Al Substitution to Enhance the Long‐Cycle Performance of Co‐Free Li‐Rich Cathode

Abstract As one of the most promising cathodes for Li‐ion batteries, Li‐rich layered oxides suffer from low Coulombic efficiency, severe capacity fading, and voltage decay, which are related to the aggregated Li@Mn₆ superstructure units. Herein, a Co‐free Li‐rich oxide Li[Li_1/4Mn_1/2Ni_1/6Al_1/12]O₂ through Al substitution of Co in Li[Li_1/4Mn_1/2Ni_1/6Co_1/12]O₂, is designed. Combining the average structural refinement with the detailed local structural/chemical analysis, it is found that the introduced Al ions occupy the Mn sites in Li@Mn₆ superstructure units, which further induces the partial replacement of the central Li ions in Li@Mn₆ units by Ni²⁺. The modified superstructure units stabilize the anionic framework and suppress structural degradation during long‐term cycling. A superior cyclability (a capacity retention of 91.4% after 500 cycles at 1 C) is achieved. This work not only deepens the understanding into the mechanism of Al substitution, but also provides a novel route to design high‐performance Li‐rich cathodes by modifying the local functional units.