Fabrication of porous Na₃V₂(PO₄)₃/reduced graphene oxide hollow spheres with enhanced sodium storage performance

Sodium-ion batteries (SIBs) have long been recognized as a potential substitute for lithium-ion batteries, while their practical application is greatly hindered owing to the absence of suitable cathode materials with improved rate capability and prolonged cycling life. Na₃V₂(PO₄)₃ (NVP) has drawn extensive attention among the cathode materials for SIBs because of its fast Na⁺-transportable framework which enables high-speed charge transfer, but the poor electric conductivity of NVP significantly restricts the Na⁺ diffusion. To tackle this issue, in this work, porous NVP/reduced graphene oxide hollow spheres (NVP/rGO HSs) are constructed via a spray drying strategy. Due to the unique porous hollow architecture, the synthesized compound manifests a high reversible capacity of 116 mAh g^-1 at 1 C (1 C = 118 mA g^-1), an outstanding high-rate capability of 107.5 mAh g^-1 at 10 C and 98.5 mAh g^-1 at 20 C, as well as a stable cycling performance of 109 mAh g^-1 after 400 cycles at 1 C and 73.1 mAh g^-1 after 1000 cycles at 10 C. Moreover, galvanostatic intermittent titration technique demonstrates that the Na⁺ diffusion coefficient of NVP/rGO HSs is an order of magnitude larger than the pristine NVP. The remarkable electrochemical properties of NVP/rGO HSs in full cells further enable it a potential cathode for SIBs.