Low-Electronegativity Cationic High-Entropy Doping to Trigger Stable Anion Redox Activity for High-Ni Co-Free Layered...

LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM-811) exhibits the highest capacity in commercial lithium-ion batteries (LIBs), and the high Ni content (80 %) provides the only route for high energy density. However, the cationic structure instability arisen from the increase of Ni content (>80 %) limits the further increase of the capacity, and inevitable O₂ release related to anionic structure instability hinders the utilization of anion redox activity. Here, by comparing various combinations of high-entropy dopants substituted Co element, we propose a low-electronegativity cationic high-entropy doping strategy to fabricate the high-Ni Co-free layered cathode (LiNi_0.8 Mn_0.12 Al_0.02 Ti_0.02 Cr_0.02 Fe_0.02 O₂ ) that exhibits much higher capacity and cycling stability. Configurational disorder originated from cationic high-entropy doping in transition metal (TM) layer, anchors the oxidized lattice oxygen ((O₂ )^n- ) to preserve high (O₂ )^n- content, triggering the anion redox activity. Electron transfer induced by applying TM dopants with lower electronegativity than that of Co element, increases the electron density of O in TM-O octahedron (TM-O₆ ) configuration to reach higher (O₂ )^n- content, resulting in the higher anion redox activity. With exploring the stabilization effect on both cations and anions of high-entropy doping and low-electronegativity cationic modified anion redox activity, we propose an innovative and variable pathway for rationally tuning the properties of commercial cathodes.