The widespread application of vanadium redox flow batteries (VRFBs) presents an imperative need to mass produce electrodes with simple and cost-effective method. In this work, a novel room-temperature activation method is developed and adopted to fabricate electrodes for VRFBs. The VRFB with the prepared electrodes exhibits an energy efficiency of 84.0% at the current density of 200 mA cm−2, and can be stably cycled for more than 500 cycles with a high capacity retention rate of 99.94% per cycle. In addition, the battery can be operated at the high current densities of 250 and 300 mA cm−2 with energy efficiencies of 80.9% and 77.8%, which is the highest performance for the electrodes activated at room temperature. More remarkably, the room-temperature activated graphite felt electrode outperforms the thermally treated graphite felt electrode. Therefore, compared with the conventional method for thermally treating graphite felts, which requires expensive equipment to withstand high temperatures and consume a large amount of energy, the present room-temperature activation method offers a more promising choice to mass produce high-performance electrodes for VRFBs.