Cobalt ion doping and morphology tailoring enable superior zinc-ion storage in sodium vanadate nanoflowers

Layered sodium vanadium materials have aroused increasing interest owing to their open layered structures and high theoretical capacity. Nevertheless, the strong electrostatic interactions between vanadium oxide layers and intercalated Zn2+ and the weak electronic conductivity severely limit their further development. Here, we design a series of cobalt ion-doped sodium vanadium electrode materials with nanoflower-like morphologies. Due to the open interlayer space and improved electron transfer enabled by cobalt ion preintercalation and sufficient contact area between the electrode and electrolyte provided by the three-dimensional (3D) flower-like morphology, the cobalt ion-doped sodium vanadate (CNVO-2) cathode exhibits excellent electrochemical performance, including an exceptional specific capacity (411 mA h g−1 at 0.5 A g−1) and ultrahigh structural stability (90.4 % capacity retention after 3000 cycles at 10 A g−1), outperforming many advanced ZIBs cathode materials. In addition, through various ex situ characterization techniques, an ionic exchange and multiple ion cointercalation mechanism is first revealed in sodium vanadate cathode material.