Gradient Structural Design Inducing Rocksalt Interface and P2/P3 Biphasic Bulk for Layered Oxide Cathode with Prolonged Sodium Ion Storage

Abstract Layered transition metal oxides are the most promising cathode materials for sodium‐ion batteries (SIBs), which unfortunately suffer from rapid capacity decay and sluggish Na‐ion kinetics due to irreversible phase transition and aggravated interface side reactions during de/sodiation. Herein, a material with coherent gradient architecture ranging from rocksalt interface to P2/P3 layered bulk heterostructure is prepared via a precursor‐oriented driven reaction method. Such core‐shell structure design reduces the detrimental phase transition through the interlocking effect, which improves the structural integrity of resulting cathode. Specifically, the rocksalt surface is structurally robust, mitigating interfacial parasitic reactions and stabilizing surface oxygen. With this unique design, the resulting cathode delivers a discharge capacity of 94 mAh g ⁻¹ at 5C in the voltage range of 2.0–4.3 V and demonstrates excellent cycling stability with 76% capacity retention after 1000 cycles. Moreover, the precursor‐induced gradient structural design significantly enhances the thermal stability of the cathode, which is of additional advantage with respect to the safety of SIBs. This work offers future guidance toward designing high‐performance cathode materials for advanced SIBs.