Tailoring the Redox Reactions for High-Capacity Cycling of Cation-Disordered Rocksalt Cathodes

Cation-disordered rocksalts (DRXs) have emerged as a new class of high-capacity Li-ion cathode materials. One unique advantage of the DRX chemistry is the structural flexibility that substantially lessens the elemental constraints in the crystal lattice, such as Li content, choice of transition metal redox center paired with appropriate d⁰ metal, and incorporation of F anion, which allows optimization of the key redox reactions. Herein, a series of the DRX oxyfluorides based on the Mn redox have been designed and synthesized. By tailoring the stoichiometry of the DRX compositions, high-capacity cycling by promoting the cationic Mn²⁺/Mn⁴⁺ redox reactions while suppressing those from anionic O is successfully demonstrated. A highly fluorinated DRX compound, Li_1.2Mn_0.625Nb_0.175O_1.325F_0.675 (M_0.625F_0.675), delivers a capacity of ≈170 mAh g⁻¹ at C/3 for 100 cycles. This work showcases the concept of balancing the cationic and anionic redox reactions in the DRX cathodes for improved electrochemical performance through the rational composition design.