High voltage cathode materials for Na-ion batteries of general formula Na3V2O2x(PO4)2F3−2x

Abstract

Different samples of the sodium-vanadium fluorophosphate cathodic materials have been synthesized via the hydrothermal method, varying the type and content of carbon used in the synthesis. Structural characterization of the composites was performed by powder X-ray diffraction. Magnetic susceptibility measurements and EPR (Electron Paramagnetic Resonance) polycrystalline spectra indicate that some of the samples exhibit V 3+ /V 4+ mixed valence, with the general formula Na 3 V 2 O 2x (PO 4 ) 2 F 3À2x where 0 # x < 1. The morphology of the materials was analyzed by Transmission Electron Microscopy (TEM). A correlation between the type and content of carbon with the electrochemical behavior of the different samples was established. Electrochemical measurements conducted using Swagelok-type cells showed two voltage plateaux at 3.6 and 4.1 V vs. Na/Na + . The best performing sample, which comprised a moderate percentage of electrochemical grade carbon as additive, exhibited specific capacity values of about 100 mA h g À1 at 1C (z80% of theoretical specific capacity). Cyclability tests at 1C proved good reversibility of the material that maintained 98% of initial specific capacity for 30 cycles.

Review—Practical Issues and Future Perspective for Na-Ion Batteries

“…Therefore, increase in the operating potential has been targeted by changing structure and composition in not only layered oxides but also polyanionic compounds to demonstrate comparable energy density to LIB. 15,28,29,111,114 Na system has clear difference from Li one in the crystal polymorphism of layered oxides. The most common layered structures such as α-NaFeO 2 are built up by stacking sheets of edge-sharing MeO 6 octahedra.…”

Electrochemical and Chemical Na+/Li+Ion Exchange in Na-Based Cathode Materials: Na1.56Fe1.22P2O7and Na3V2(PO4)2F3

“…A new design concept of the simultaneously energy storage of multi-metal ions may overcome respective disadvantages of singlemetal ions and bring to a synergy effect. 6,7 Since the operation of hybrid-ion batteries depends on the reactivity of the selected electrodes in respect of Li + and Na + ions, two Na-based cathode materials, differing by crystal structure, triclinic Na 1.56 Fe 1.22 P 2 O 7 and tetragonal Na 3 V 2 (PO 4 ) 2 F 3 , were selected in this work to study electrochemical and chemical Na + /Li + ion exchange and their performance in hybridion cells.Sodium iron pyrophosphates 8,9 with a triclinic symmetry (S.G. P-1) and sodium vanadium fluorophosphates with tetragonal symmetry (S.G. P4 2 /mnm) [10][11][12] were recently examined and showed good electrochemical properties in Na-cells. To increase a rechargeable capacity of Na 2 FeP 2 O 7 , a series of isostructural compositions Na 2−y Fe 1+y/2 P 2 O 7 (where 0 < y < 0.44) similar to the previously reported Na 2−x M 1+x/2 P 2 O 7 (M = Mg, Ni) 13 were recently synthesized z E-mail: kosova@solid.nsc.ru and evaluated as positive electrodes for sodium batteries.…”

“…Sodium iron pyrophosphates 8,9 with a triclinic symmetry (S.G. P-1) and sodium vanadium fluorophosphates with tetragonal symmetry (S.G. P4 2 /mnm) [10][11][12] were recently examined and showed good electrochemical properties in Na-cells. To increase a rechargeable capacity of Na 2 FeP 2 O 7 , a series of isostructural compositions Na 2−y Fe 1+y/2 P 2 O 7 (where 0 < y < 0.44) similar to the previously reported Na 2−x M 1+x/2 P 2 O 7 (M = Mg, Ni) 13 were recently synthesized z E-mail: kosova@solid.nsc.ru and evaluated as positive electrodes for sodium batteries.…”

Recent Advances in Sodium-Ion Battery Materials

“…As the formation of a NASICON-type phase Na 3 V 2 (PO 4 ) 3 instead of NaVPO 4 F could be possible, the samples were prepared by the high-temperature solid-state method and sublimation of VF 3 could occur. The existence of the NaVPO 4 F phase was questioned by some researchers [118,119].…”