Employing the optimized pre-intercalation strategy to design functional Mo pre-intercalated hydrated vanadium oxide for aqueous zinc-ion batteries

Abstract

The traditional metal ions (K+, Na+, Ca2+, etc.) pre-intercalated strategy is widely used to optimize the structure of vanadium oxides as the cathode materials for aqueous zinc-ion batteries (AZIBs). However, these intercalated ions with a single valence state between the layers of vanadium oxides occupy the original active sites and merely act as ‘pillars’ without redox reactions for energy storage. Herein, we employ the optimized pre-intercalation strategy to fabricate a series of Mo pre-intercalated hydrated vanadium oxide materials (x-MoVOH) as the cathode of AZIBs. The intercalated functional Mo ions can not only effectively enlarge the interlayer spacing to expose more active sites for insertion and de-insertion of hydrated Zn2+, but also provide additional electrochemical performance through the redox reactions of Mo4+/Mo5+/Mo6+. The finest material (Mo3V15O35·nH2O, 5-MoVOH) exhibits the electrochemical performance of the specific capacity of 430 mAh·g−1 at 100 mA·g−1 and the capacity retention proportion of 95 % after 1000 cycles at 2 A·g−1. Additionally, the galvanostatic intermittent titration technique (GITT) further confirms that the enlarged layer spacing facilitates the rapid diffusion of hydrated Zn2+. This work provides a novel and feasible way to further enhance the performance of vanadium oxides in AZIBs.