Flexible free-standing paper electrodes based on reduced graphene oxide/δ-NaxV2O5·nH2O nanocomposite for high-performance aqueous zinc-ion batteries

Most recently, aqueous zinc-ion batteries (AZIBs) are the research focus because of their low cost, high safety, and eco-friendliness. In this respect, flexible binder-free electrodes have been investigated by several studies to keep pace with the development of wearable electronics. However, the mass loading of active materials in these electrodes is usually below 2 mg cm −2 , considerably limiting the areal capacity. Herein, we report a paper electrode prepared via a facile vacuum filtration technique with a high mass loading of 5 mg cm −2 for the active material, namely, reduced graphene oxide (rGO)/δ-Na x V 2 O 5 ·nH 2 O nanocomposite . Thanks to the homogeneous distribution and synergistic effect of the active material, carbon nanotubes , and cellulose fibers, the electrode not only exhibits good mechanical property and high electrical conductivity but also displays impressive performances for AZIBs. It achieves an admirable areal specific capacity of 1.87 mAh cm −2 (corresponding to 374.9 mAh g −1 for the active material), substantially higher than that of other flexible binder-free electrodes for (hybrid) AZIBs. Meanwhile, this electrode also shows good rate capability and excellent long-term cyclability (with a capacity retention of 92% over 4000 cycles). This work opens new opportunities towards flexible free-standing electrodes.