Construction of Stable Oxygen Redox by Electrochemical Activation O–TM–Se in Nickel‐Rich Layered Oxides for Lithium‐Ion Batteries

The irreversible oxygen redox and structural degradation of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) at a 4.5 V high voltage cause a severe decline in cycling performance for lithium‐ion batteries. In this study, a novel approach is proposed to enhance the anionic redox chemistry and stability of NCM811 cathode material by introducing gaseous selenium. Se β+ species are selectively adsorbed within oxygen vacancies, leading to the continuous replacement of O α− to form a stable O–TM–Se bond during deep charging. Furthermore, Selenium modification improves cationic redox efficiency and alleviates O α− (α < 2) outward migration, increases oxygen vacancy formation energy. The redox activity of oxygen is diminished, facilitating improved reversibility of oxygen redox and effectively inhibiting irreversible oxygen escape. Additionally, Selenium increases the energy barrier for phase transition, effectively suppressing irreversible phase transition and Ni migration. Selenium reacts with escaping oxygen to form SeO 2 , effectively reducing side reactions during cycling. As a result, the proposed approach significantly inhibits irreversible oxygen release, leading to remarkable cyclic stability with 87.5% capacity retention after 300 cycles at 1C at 4.5 V and maintained 192.9 mAh g −1 after 150 cycles under 60C. The Se modification realizes stability anionic redox strategy to design novel high‐energy‐density cathode materials with superior cycling performance.