V-MOFs derived Na₃V₂(PO₄)₃/C core-shell spheres toward ultrastable sodium-ion batteries

Due to the large ionic radius of sodium-ion, the transport of ions is hindered, leading to slow ion diffusion. This, in turn, results in significant structural stresses, causing rapid material deterioration and reduced cycle stability. Furthermore, the low electronic conductivity of Na3V2(PO4)3 further contributes to the unsatisfactory rate performance. To address these challenges, we have employed an adjustable V-MOFs as precursors to synthesize Na3V2(PO4)3/C core-shell spheres with tunable sizes. The incorporation of a carbon shell serves a dual purpose: it not only alleviates the structural stress experienced during charge and discharge processes but also facilitates rapid electron conduction. Moreover, the small-sized core-shell structure effectively shortens the ion and electron transport distances while providing more reactive sites, thus enhancing the kinetics. Consequently, the NVP0.01M sample obtained exhibits exceptional rate performance, with a remarkable reversible capacity of 115.1 mAh g-1 at 0.1C and 92.2 mAh g-1 at 30C. Furthermore, this material demonstrates remarkable long-term stability, as evidenced by a specific discharge capacity of 99.3 mAh g-1 even after 500 cycles at 1C, corresponding to a capacity retention rate of 91.3 %. The NVP-0.01M||HC full cell also display outstanding electrochemical performance. This research introduces a novel approach for synthesizing high-performance cathode materials specifically designed for sodium-ion batteries.