Nanoflake-Assembled Hierarchical Na3V2(PO4)3/C Microflowers: Superior Li Storage Performance and Insertion/Extraction Mechanism

Na3V2(PO4)(3) (NVP) has excellent electrochemical stability and fast ion diffusion coefficient due to the 3D Na+ ion superionic conductor framework, which make it an attractive cathode material for lithium ion batteries (LIBs). However, the electrochemical performance of NVP needs to be further improved for applications in electric vehicles and hybrid electric vehicles. Here, nanoflake-assembled hierarchical NVP/C microflowers are synthesized using a facile method. The structure of as-synthesized materials enhances the electrochemical performance by improving the electron conductivity, increasing electrode-electrolyte contact area, and shortening the diffusion distance. The as-synthesized material exhibits a high capacity (230 mAh g(-1)), excellent cycling stability (83.6% of the initial capacity is retained after 5000 cycles), and remarkable rate performance (91 C) in hybrid LIBs. Meanwhile, the hybrid LIBs with the structure of NVP || 1 m LiPF6/EC (ethylene carbonate) + DMC (dimethyl carbonate) || NVP and Li4Ti5O12 || 1 m LiPF6/EC + DMC || NVP are assembled and display capacities of 79 and 73 mAh g(-1), respectively. The insertion/extraction mechanism of NVP is systematically investigated, based on in situ X-ray diffraction. The superior electrochemical performance, the design of hybrid LIBs, and the insertion/extraction mechanism investigation will have profound implications for developing safe and stable, high-energy, and high-power LIBs.