Electro-insertion of Mn2+ ions into V2O5·nH2O on MWCNTs coated carbon felt for binder-free Na+ ion battery electrodes

Abstract

In the present article, we report the electrochemical deposition of hydrated and amorphous V₂O₅·nH₂O nanostructures and related Mn²⁺ cations insertion during anodic polarization. The hydrated phase was synthesized on hydrophilic carbon felt substrates coated by defective multiwall carbon nanotubes (MWCNTs). From the combined data of micro-Raman scattering and X-ray photoelectron spectroscopy (XPS), it was possible to see that the Mn²⁺ cations were intercalated into V₂O₅ under anodic polarization. When MnOOH is inserted between atomic bilayers of V₂O₅·nH₂O (V⁵⁺), a 3D complex monoclinic-Mn_xV₂O₅ system arises. This novel method of Mn doping into V₂O₅·nH₂O/MWCNT produces an amorphous Mn_xV₂O₅/MWCNT but without hydration. The resulting binder-free Mn_xV₂O₅/MWCNT/felt composite electrode provides remarkable Na⁺ reversible specific capacities of 400 mA h g⁻¹ and 224 mA h g⁻¹ in the 3.5–1.0 V and 3.5–1.5 V ranges, respectively, while the V₂O₅·nH₂O/MWCNT/felt provides only 120 mA h g⁻¹ between the smaller cut-off potential limits. The Mn_xV₂O₅/MWCNT nanostructures synthesis onto fibers of graphitic felt does not present a fading capacity during the polarization of 100 discharge/charge cycles.