Eu³⁺ Doping in Sodium Vanadium Phosphate: Synergistically Unlocking Fast Sodium Storage Kinetics and Stable Cycles

Sodium vanadium phosphate [Na₃V₂(PO₄)₃] stands out as an appealing cathode material for next-generation sodium-ion batteries owing to beneficial properties, such as high operating voltage, fast ion diffusion, and robust structural integrity. Nonetheless, its commercialization is challenged by an inherently poor electronic conductivity. Herein, a europium³⁺ (Eu³⁺) doping strategy was employed to synthesize a Na₃V_1.95Eu_0.05(PO₄)₃@C composite (Eu0.05-NVP@C), aiming to enhance its high-rate capability and cycling durability. Based on electrochemical kinetic studies and theoretical computations, the introduction of Eu³⁺ into Eu0.05-NVP@C effectively reduces the band gap and activation energy for Na⁺ migration, which synergistically promotes faster charge transfers. Moreover, the smaller integrated crystal orbital Hamilton population values for the V-O and Eu-O bonds indicate enhanced lattice cohesion. Consequently, the fabricated Eu0.05-NVP@C cathode exhibits a high reversible capacity of 97.63 mAh g^-1 at 10C and achieves 93.60% capacity retention after 2000 cycles at 5C. In situ X-ray diffraction analysis further reveals the highly reversible biphasic transition reaction during cycling. This work not only validates Eu³⁺ doping as an effective approach for optimizing NASICON-type cathodes but also offers strategic guidance for the development of next-generation Na₃V₂(PO₄)₃-based electrodes with a superior rate performance and extended cycle life.