Insight into Preparation of Fe-Doped Na3V2(PO4)3@C from Aspects of Particle Morphology Design, Crystal Structure Modulation, and Carbon Graphitization Regulation

The peak-loading shift function of sodium-ion batteries in large-grid energy store station poses a giant challenge on the account of poor rate performance of cathodes. NASICON type Na3V2(PO4)3 with a stable three-dimensional framework and fast ion diffusion channels has been regarded as one of the potential candidates and extensively studied. Nevertheless, a multilevel integrated tactic to boost the performance of Na3V2(PO4)3 in terms of crystal structure modulation, coated carbon graphitization regulation, and particle morphology design is rarely reported and deserves much attention. In this study, organic ferric was used to prepare Fe-doped Na3V2(PO4)3@C cathode on the account of low cost, environmental friendliness, and catalytic function of Fe on carbon graphitization. The density functional theory calculation depicts that the most stable site for Fe atom is the V site and moderate replacement of Fe at V position would reduce the band gap energy from 2.19 by 0.43 eV and improve the electron transfer, which is crucial for the intrinsic poor conductivity of Na3V2(PO4)3. The experimental results show that Fe element can be introduced into the bulk structure successfully, modulating relevant structural parameters. In addition, the coated carbon layer graphitization degree is also regulated due to the catalysis function of Fe. And, the decomposition of organic ferric would infuse the formation of porous structure, which can promote electrolyte permeation and shorten the electron/ion diffusion. Finally, the optimized Na3V1.85Fe0.15(PO4)3@C could possess a high capacity of 103.69 mA h g–1 and retain 91.45% after 1200 cycles at 1.0C as well as 94.45 mA h g–1 at 20C. In addition, the excellent performance is comprehensively elucidated via ex situ X-ray diffraction and pseudocapacitance characterization. The multifunction contribution of Fe-doping may provide new clue for designing porous electrode materials and a new sight into Fe-doped carbon-coated material.