Ni‐MOFs Mediated Ni 2+/4+ Balancing and Enhanced Metal–Oxygen Covalency Unlocks Fast and Stable Sodium Storage in High‐Entropy Layered Cathode

ABSTRACT O3‐type cathodes suffer from heterogeneous metal distribution and insufficient active nickel content, limiting specific capacity, cyclic stability, and electrochemical kinetics. Herein, Ni‐based metal‐organic frameworks (Ni‐MOFs) are applied as precursors to enable atomic‐level control over regulated active nickel content and metal‐oxygen bonds in high‐entropy NaTMO 2 cathodes. It is found that the introduction of Ni‐MOFs can accelerate the crystallization and purity of O3‐type structures. Ni‐MOFs‐derived high‐entropy cathode (M‐HEO) exhibits an optimized electrochemically active Ni 2+ , which can balance the capacity depth and structural stability, contrasting with excessive Ni 2+ in normal high‐entropy oxide or insufficient Ni 2+ in commercial oxide. Concurrently, enhanced transition metal‐oxygen covalency, especially Ni‐O covalency, could form a robust metal‐oxygen network with an ultrafast Na + transport path and suppress lattice degradation. The reinforced covalent Ni‐O‐TM network enables a highly reversible phase transition with a small volume change, as well as the modified, thinner double‐layer cathode‐electrolyte interface, together with fast Na + ion transport kinetics. As a result, M‐HEO delivers a higher discharge capacity of ∼130 mAh g −1 with an initial Coulombic efficiency of 92.6% under 0.1C and stable cyclic property under 1C and 2C.