Abstract:

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.

Key words: V₂O₅∙nH₂O/rGO/PVA film, Li⁺ storage, Zn²⁺ storage, High specific capacitance, Outstanding cycle performance