Self-supported VO₂ on polydopamine-derived pyroprotein-based fibers for ultrastable and flexible aqueous zinc-ion batteries

A conventional electrode composite for rechargeable zinc-ion batteries (ZIBs) includes a binder for strong adhesion between the electrode material and the current collector. However, the introduction of a binder leads to electrochemical inactivity and low electrical conductivity, resulting in the decay of the capacity and a low rate capability. We present a binder- and conducting agent-free VO2 composite electrode using in situ polymerization of dopamine on a flexible current collector of pyroprotein-based fibers. The as-fabricated composite electrode was used as a substrate for the direct growth of VO2 as a self-supported form on polydopamine-derived pyroprotein-based fibers (pp-fibers@VO2(B)). It has a high conductivity and flexible nature as a current collector and moderate binding without conventional binders and conducting agents for the VO2(B) cathode. In addition, their electrochemical mechanism was elucidated. Their energy storage is induced by Zn2+/H+ coinsertion during discharging, which can be confirmed by the lattice expansion, the formation of by-products including Znx(OTf)y(OH)(2x-y)center dot nH(2)O, and the reduction of V4+ to V3+. Furthermore, the assembled Zn//pp-fibers@VO2(B) pouch cells have excellent flexibility and stable electrochemical performance under various bending states, showing application possibilities for portable and wearable power sources.