The O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) has emerged as a highly promising cathode material for sodium-ion batteries due to its facile synthesis and high theoretical capacity. However, it suffers from severe capacity and rate capability degradation caused by multiple coupled failure mechanisms, including irreversible phase transitions, structural deterioration at high voltages, and electrolyte-induced surface corrosion. This work addresses the challenge of high-voltage stability in NFM cathodes via a synergistic bulk-phase and interface engineering strategy. Firstly, Li, Ti, and Co are co-doped into the bulk lattice structure to suppress the Mn³⁺-induced Jahn-Teller distortion and improve Na⁺ diffusion kinetics. And then, an AlPO₄ protective coating layer is fabricated to mitigate electrolyte corrosion and interfacial side reactions. Consequently, the as-designed composite cathode (AP@NFMLTC) can effectively suppress the P3 to O3’ phase transition within the voltage range of 2.0 to 4.2 V, resulting in a highly reversible sodium storage mechanism. After 100 cycles at a rate of 1 C, the capacity retention rate significantly improves from 45.6% to 83.6%, with a minimal voltage decay of just 0.08 V. The dual bulk-interface synergistic strategy in this work provides valuable insights into achieving high stable operation for sodium-ion batteries (SIBs) cathodes under enhanced voltage.

The development and synthesis of cathode electrocatalysts with high activity and durable stability for metal-air batteries is an important challenge in the area of electrocatalysis. Herein, we introduce a novel in-situ nitriding and phosphating strategy for producing W₃N₄ and WP from phosphotungstic acid (HPW)-polyaniline-phytic acid-Fe³⁺ organic–inorganic hybrid material. The final material has a three-dimensional porous framework with W₃N₄-WP heterostructures embedded in the carbon matrix (W₃N₄-WP@NPC). As-made materials exhibit exceptional electrocatalytic performance for the oxygen reduction reaction (ORR), with a diffusion-limiting current density of 6.9 mA·cm⁻² and a half-wave potential of 0.82 V. As a Zn-air primary cathode, the W₃N₄-WP@NPC assembled battery can provide a relatively high peak power density (194.2 mW·cm⁻²). As a Zn-air secondary air-cathode, it has great cycling stability over 500 h. This work provides a simple and efficient method for rationally designing high-performance air cathodes from copolymer-anchored polyoxometalates.