Porous yolk-shell structured Na3(VO)2(PO4)2F microspheres with enhanced Na-ion storage properties

Na3(VO)2(PO4)2F (NVPOF) has been considered as one potential candidate for sodium-ion batteries because of its high operating voltage and theoretical capacity. However, the poor intrinsic electronic conductivity significantly restricts its widespread application. In response to this drawback, we adopt the optimization strategy of tuning the morphology and structure to boost the electrical conductivity and mitigate the capacity fading. In this paper, NVPOF microspheres with unique porous yolk-shell structure were fabricated via a facile one-step solvothermal method for the first time. By monitoring the morphological evolution with time-dependent experiments, the self-sacrifice and Ostwald ripening mechanism from rough spheres to yolk-shell structure was revealed. Benefited from the favorable interwoven nanosheets shell, inner cavity and porous core structure, the resulting NVPOF electrode exhibits superior rate capability of 63 mA h g−1 at 20 C as well as outstanding long-cycling performance with the capacity retention up to 92.1% over 1000 cycles at 5 C.