► We report on dramatic performance gains achieved for a vanadium redox flow battery. ► The maximum power density was greatly increased to levels exceeding 500 mW/cm2. ► The increase in power density represents a significant reduction in ultimate system cost using this design. ► The results show a trade-off between ohmic and kinetic losses. We demonstrate a vanadium redox flow battery with a peak power density of 557mWcm−2 at a state of charge of 60%. This power density, the highest reported to date, was obtained with a zero-gap flow field cell architecture and non-wetproofed carbon paper electrodes. The electrodes were comprised of stacked sheets of carbon paper and optimized through systematic variation of the total electrode thickness. We anticipate significant reductions in the ultimate system cost of redox flow battery systems based on this design.