Synthesis of ultrasmall vanadium ferricyanide nanocrystallines with the aidance of graphene self-assembled fibers towards reinforced zinc storage performance

Vanadium-based Prussian Blue Analogues (PBAs) are a novel idea to couple the high voltage platform of PBAs with the large energy density of vanadium-based compounds. However, in aqueous zinc ion batteries (AZIBs), PBA cathodes are still limited by their inherent defects and poor conductivity, thus limiting their use. Herein, a graphene self-assembled fiber (GSAF) forming a stereoscopic conductive carbon framework is obtained by a one-step carbothermal reduction method, after which vanadyl Prussian blue hexacyanoferrate (KVO-HCF) nano-units are grown in-situ on the GSAF surface by a one-step co-precipitation method to obtain the composite GSAF@KVO-HCF. Benefiting from the tight binding of PBA particles to the three-dimensional carbon architecture, the transport distance of Zn2+ becomes shorter, the system conductivity is enhanced and the solubilization of V is suppressed. In terms of specific capacity, the composite cathode demonstrates a performance of 119 mAh g−1 with stable reversibility. In the aspect of cycling performance, its specific capacity still holds 103 mAh g−1 after 1000 cycles. By combining experimental studies (in/ex-situ characterizations) and theoretical calculations, Zn2+ and proton co-insertion/extraction mechanisms for this composite as a cathode for AZIBs are described. The testing of the soft-packed pack battery highlights the practical application prospect of the composite.