Synergizing Phase Engineering and Site-selective Substitution Through Rational Design of High-Entropy Layered Oxide Cathode Enables Air-Stable and Long-life Sodium-ion Batteries

Abstract

P2-Na0.67Ni0.33Mn0.67O2 cathodes face commercialization barriers since irreversible P2-O2 phase transitions when charged above 4.0 V and the Mn3+ degradation if discharged to 2.0 V, as well as the moisture sensitivity, resulting in high cost for production and storage. To address these challenges, we realized the synergy of phase engineering and site-selective substitution through rational design of layered oxide of Na0.80Mn0.60Mg0.07Ni0.23Cu0.07Zn0.03O2 (P2/O3-Na8M). Site-selective substitution of Zn at Na-sites acts as a pillar, preventing irreversible phase transitions and resisting H2O insertion via stronger Zn2+-O-Zn2+ attraction compared to Na+-O-Na+, while Cu/Mg in TM sites further enhances structural stability by suppressing oxygen loss through stronger Cu-O covalency than Ni-O, reducing Na+/H+ exchange, thus stabilizing Na-O bonds by lowering its overall cationic potential respectively, in addition to mitigating the Jahn-Teller distortions and enabling ultra-wide potential operation. Theoretical and experimental investigations reveal that the P2/O3 phase heterostructure lowers Na+ diffusion barrier, enabling P2/O3-Na8M to deliver 150 mAh g-1 at 0.1 C with 80.8% retention after 300 cycles at 5 C within 1.8-4.4 V, while preserving structure and performance after 35 days air/water exposure. The full cell can achieve high energy density of 281.2 Wh kg-1 and 82.5% retention after 600 cycles at 1 C.