Superior sodium intercalation of honeycomb-structured hierarchical porous Na3V2(PO4)(3)/C microballs prepared by a facile one-pot synthesis

Tailoring materials into a hierarchical porous micro/nanostructure offers unprecedented opportunities in the utilization of their functional properties. Particularly, it is crucial for the electrode materials to realize high-performance because of the advantages such as large surface area, superior structure stability and short ion transport pathway. Here we report the design of a new architecture, named honeycomb-type hierarchical porous microball, for Na3V2(PO4)(3) by a facile one-pot synthesis. The network between nanovoids is formed by in situ carbonization of surfactants (CTAB)along with the crystallization of Na3V2(PO4)(3), which results in the hierarchical porous Na3V2(PO4)(3) skeleton with a surface conductive layer. The prepared Na3V2(PO4)(3)/C composite consists of spherical particles filled with hierarchical pores and interconnective nanochannels, resulting in the honeycomb-type architecture. It not only enables easier electrolyte penetration, but also provides a high-efficiency electron/ion transport pathway for fast sodium intercalation. Both the GITT and EIS results demonstrate the improved sodium diffusion capability and decreased electrochemical resistance for the honeycomb-structured microball in comparison to the microsized nonporous reference samples. Moreover, it also delivers superior high rate capability and cycling stability, which retains 93.6% of the initial capacity after 200 cycles at the 1 C rate. Even at 20 C, it still delivers a high capacity of 80.2 mA h g(-1) corresponding to 71% of the capacity. Given the superior ion intercalation kinetics and excellent structure stability, the honeycomb-type structure puts forward a new strategy to develop high-performance polyanion-based materials for low-cost and high-power rocking-chair batteries.