A high power density and long cycle life vanadium redox flow battery

Increasing the power density and prolonging the cycle life are effective to reduce the capital cost of the vanadium redox flow battery (VRFB), and thus is crucial to enable its widespread adoption for large-scale energy storage. In this work, we analyze the source of voltage losses and tailor the design of the battery to simultaneously minimize the ohmic resistance, maximize the transport of electrolytes, and boost the surface area and activity of electrodes. These strategies collectively result in an unprecedented improvement in the performance of VRFBs. At the current densities of 200, 400 and 600 mA cm−2, the battery achieves the energy efficiencies of 91.98%, 86.45% and 80.83%, as well as the electrolyte utilizations of 87.97%, 85.21% and 76.98%, respectively. Even at an ultra-high current density of 1000 mA cm−2, the battery is still able to maintain an energy efficiency of as high as 70.40%. It is also demonstrated that the battery can deliver a high peak power density of 2.78 W cm−2 and a high limiting current density of ~7 A cm−2 at room temperature. Moreover, the battery is stably cycled for more than 20,000 cycles at a high current density of 600 mA cm−2. The data reported in this work represent the best charge-discharge performance, the highest peak power density, and the longest cycle life of flow batteries reported in the literature.