PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li+ and Zn2+ storage properties

Low-cost, high safety and environment-friendly aqueous energy storage systems (ESSs) are huge potential for grid-level energy storage, but the (de)intercalation of metal ions in the electrode materials (e.g. vanadium oxides) to obtain superior long-term cycling stability is a significant challenge. Herein, we demonstrate that polyvinyl alcohol (PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide (V2O5∙nH2O/rGO/PVA, denoted as the VGP) films enable long cycle stability and high capacity for the Li+ and Zn2+ storages in both the VGP//LiCl (aq)//VGP and the VGP//ZnSO4 (aq)//Zn cells. The binder-free VGP films are synthesized by a one-step hydrothermal method combination with the filtration. The extensive hydrogen bonds are formed among PVA, GO and H2O, and they act as structural pillars and connect the adjacent layers as glue, which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li+ and Zn2+ storage properties. As for Li+ storage, the binder-free VGP4 film (4 mg PVA) electrode achieves the highest specific capacitance up to 1381 F g−1 at 1.0 A g−1 in the three-electrode system and 962 F g−1 at 1.0 A g−1 in the symmetric two-electrode system. It also behaves the outstanding cyclic performance with the capacitance retention of 96.5 % after 15000 cycles in the three-electrode system and 99.7 % after 25000 cycles in the symmetric two-electrode system. As for Zn2+ storage, the binder-free VGP4 film electrode exhibits the high specific capacity of 184 mA h g−1 at 0.5 A g−1 in the VGP4//ZnSO4 (aq)//Zn cell and the superb cycle performance of 98.5 % after 25000 cycles. This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties, but also extends to construct other potential electrode materials for metal ion storage cells.