Confined Growth of Nano-Na₃V₂(PO₄)₃ in Porous Carbon Framework for High-Rate Na-Ion Storage

Nanoscale Na₃V₂(PO₄)₃ particles are grown in the interconnected conductive framework via a simple sol-gel method with the assistance of a hierarchical porous carbon. The porous carbon with strong adsorption ability absorbs the Na₃V₂(PO₄)₃ reactants from the aqueous solution during the sol-gel process. After crystallization, the Na₃V₂(PO₄)₃ particles are grown in the carbon pores with a spatially confined effect. Due to the pore size confinement, the Na₃V₂(PO₄)₃ particles are limited to nanoscale size and prevented from aggregation. Furthermore, the carbon matrix provides the electric conductive framework and the unfilled pores offer interconnected ion transport channels as well as capacitive contribution, which are beneficial for tolerating high current attack. As a result, the pore-confined nano-Na₃V₂(PO₄)₃ in the carbon framework exhibits high Na-ion storage capacity (116.2 mAh g^-1 at 0.2 C), excellent long-term cycling stability (capacity retention of 82.1% after 10 000 cycles), and especially, outstanding high-rate performance (80.1, 60.6, and 45.7 mAh g^-1 at 50, 75, and 100 C). The pore-confined nano-Na₃V₂(PO₄)₃ with superior rate performance is believed to be a promising candidate for Na-ion batteries, and the preparation method based on confined growth in porous carbon framework provides a simple and effective strategy for high-rate electrode material design.