Core/Double-Shell Structured Na₃V₂(PO₄)₂F₃@C Nanocomposite as the High Power and Long Lifespan Cathode for Sodium-Ion Batteries

NASICON-structured Na₃V₂(PO₄)₂F₃ is considered as a potentially high-capacity cathode material for Na-ion batteries; however, its poor rate capability and insufficient cyclability remain a challenge for battery applications. To address this issue, we designed and successfully synthesized a core/double-shell structured Na₃V₂(PO₄)₂F₃@C nanocomposite (Na₃V₂(PO₄)₂F₃@CD) by in situ carbon coating and embedding the Na₃V₂(PO₄)₂F₃ nanoparticles in ordered mesoporous carbon framework. Benefiting from the sufficient electrochemically available interfaces and abundant electronic/ionic pathways, this Na₃V₂(PO₄)₂F₃@CD material demonstrated superior Na⁺-storage performance with a high reversible capacity of 120 mA h g⁻¹ at a moderate current of 1 C, a strong high-rate capability with 63 mA h g⁻¹ at an extremely high rate of 100 C, and a long-cycle lifespan with 65% capacity retention over 5000 cycles. These superior electrochemical performances remained stable when the Na₃V₂(PO₄)₂F₃@CD cathode was used in a full cell, suggesting a promising application of the material for high rate and long lifespan sodium-ion batteries. Moreover, the architectural design and synthetic method developed in this work may provide a new avenue to create high performance Na⁺-host materials for a wide range of electric energy storage applications.