Multifunctional dual Na₃V₂(PO₄)₂F₃cathode for both lithium-ion and sodium-ion batteries

Abstract

Na3V2(PO4)2F3 with a NASICON-type structure is shown to be synthesised with the particle surface found to \nbe coated with amorphous carbon with its thickness in the range of 25–32 nm. The crystallographic planes \n(hkl) are labelled according to Density Functional Theory (DFT) calculations towards the as-prepared \nNa3V2(PO4)2F3. The performances of Na3V2(PO4)2F3 have been investigated in lithium- and sodium-ion \nbatteries, exhibiting a specific capacity of 147 mA h g 1 with an average discharge plateau around 4 V vs. \nLi+/Li, and 111.5 mA h g 1 with three discharge plateaus in sodium-ion batteries. A predominant Li ion \ninsertion mechanism is verified by comparing the redox potentials from CV and charge/discharge curves. \nIt is found that the main migration from/into the crystallographic sites of Na3V2(PO4)2F3 of Li ions is \nfavoured to obtain satisfactory properties by a two-step process, while the Na ions are found to require \nthree steps. The stable and three-dimensional open framework of Na3V2(PO4)2F3 is considered to be vital \nfor the excellent C-rate and cycling performances, as well as the fast ion diffusion with a magnitude of \n10 11 cm2 s 1, which could demonstrate that Na3V2(PO4)2F3 is a multifunctional dual cathode for both \nlithium and sodium ion batteries and capable to be a promising candidate in the construction of highenergy \nbatteries.