Dynamic Evolution of Antisite Defect and Coupling Anionic Redox in High‐Voltage Ultrahigh‐Ni Cathode

Abstract High‐voltage ultrahigh‐Ni cathodes (LiNi x Co y Mn 1−x−y O 2 , x≥0.9) can significantly enhance the energy density and cost‐effectiveness of Li‐ion batteries beyond current levels. However, severe Li−Ni antisite defects and their undetermined dynamic evolutions during high‐voltage cycling limit the further development of these ultrahigh‐Ni cathodes. In this study, we quantify the dynamic evolutions of the Li−Ni antisite defect using operando neutron diffraction and reveal its coupling relationship with anionic redox, another critical challenge restricting ultrahigh‐Ni cathodes. We detect a clear Ni migration coupled with an unstable oxygen lattice, which accompanies the oxidation of oxygen anions at high voltages. Based on these findings, we propose that minimized Li−Ni antisite defects and controlled Ni migrations are essential for achieving stable high‐voltage cycling structures in ultrahigh‐Ni cathodes. This is further demonstrated by the optimized ultrahigh‐Ni cathode, where reduced dynamic evolutions of the Li−Ni antisite defect effectively inhibit the anionic redox, enhancing the 4.5 V cycling stability.