A novel single flow zinc–bromine battery is designed and fabricated to improve the energy density of currently used zinc–bromine flow battery. In the assembled battery, liquid storage tank and pump of positive side are avoided and semi solid positive electrode is used for improving energy efficiency and inhibiting bromine diffusion into environment. The single flow battery with this design shows columbic efficiency (CE) of 92% and energy efficiency (EE) of 82% over 70 cycles at the current density of 20 mA cm−2, which is comparable with the performance of the traditional zinc–bromine flow battery; furthermore, it has much lower weight and bromine emission.