High mass loading CaV4O9 microflowers with amorphous phase transformation as cathode for aqueous zinc-ion battery

Rechargeable zinc-ion batteries (ZIBs) have shown significant promise as alternative battery technology due to their environmental benignity and cost-effectiveness. However, the current development of ZIB cathode is still hindered by various challenges such as less-than-ideal capacity, poor cyclic performance, and the typical use of low mass loading during battery evaluation. Here we prepared a nanosheet-assembled compact CaV4O9 microflowers/carbon nanotubes (CaVO/CNTs) composite film via a facile spray printing technique. The resultant CaVO/CNTs composite film possessed extremely short ion diffusion pathways, excellent electrical conductivity, and superior structural stability. At a high mass loading of 50 mg cm−2, the as-fabricated electrode could attain an areal capacity of 10.5 mAh cm−2. Furthermore, CaVO/CNTs underwent phase transformation during the initial charging process to form amorphous V2O5·nH2O, which could provide more active sites for Zn2+ storage. As a result, CaVO/CNTs electrode was able to deliver 410 mAh g−1 at 0.1 A g−1, high-rate performance (270 mAh g−1 at 10 A g−1), and ultra-long cyclic life of 91% retention after 3000 cycles. Since CaVO/CNTs film possessed good flexibility and excellent electrical conductivity, a flexible soft-packaged ZIB was assembled based on this film, and it was able to exhibit consistent electrochemical properties under various bending states.