In this paper, we found that (NH4)2V4O9 undergoes an electrochemical activation process in the first charging process at ∼1.4 V (vs. Zn2+/Zn), leading to a significant improvement of capacity and cycling stability. The activated vanadium oxides delivered a high specific capacity of 477 mA h g-1 at 50 mA g-1 and outstanding cycling stability with 97.7% capacity retention after 5000 cycles at 15 A g-1.