Methylene blue intercalated vanadium oxide with synergistic energy storage mechanism for highly efficient aqueous zinc ion batteries

With the rise of aqueous multivalent rechargeable batteries, inorganic-organic hybrid cathodes have attracted more and more attention due to the complement of each other's advantages. Herein, a strategy of designing hybrid cathode is adopted for high efficient aqueous zinc-ion batteries (AZIBs). Methylene blue (MB) intercalated vanadium oxide (HVO-MB) was synthesized through sol–gel and ion exchange method. Compared with other organic–inorganic intercalation cathode, not only can the MB intercalation enlarge the HVO interlayer spacing to improve ion mobility, but also provide coordination reactions with the Zn2+ to enhance the intrinsic electrochemical reaction kinetics of the hybrid electrode. As a key component for the cathode of AZIBs, HVO-MB contributes a specific capacity of 418 mA h g−1 at 0.1 A g−1, high rate capability (243 mA h g−1 at 5 A g−1) and extraordinary stability (88% of capacity retention after 2 000 cycles at a high current density of 5 A g−1) in 3 M Zn(CF3SO3)2 aqueous electrolyte. The electrochemical kinetics reveals HVO-MB characterized with large pseudocapacitance charge storage behavior due to the fast ion migration provided by the coordination reaction and expanded interlayer distance. Furthermore, a mixed energy storage mechanism involving Zn2+ insertion and coordination reaction is confirmed by various ex-situ characterization. Thus, this work opens up a new path for constructing the high performance cathode of AZIBs through organic-inorganic hybridization.