All-Iron Redox Flow Battery Tailored for Off-Grid Portable Applications

An all-iron redox flow battery is proposed and developed for end users without access to an electricity grid. The concept is a low-cost battery which the user assembles, discharges, and then disposes of the active materials. The design goals are: (1)minimize upfront cost, (2)maximize discharge energy, and (3)utilize non-toxic and environmentally benign materials. These are different goals than typically considered for electrochemical battery technology, which provides the opportunity for a novel solution. The selected materials are: low-carbon-steel negative electrode, paper separator, porous-carbon-paper positive electrode, and electrolyte solution containing 0.5m Fe-2(SO4)(3) active material and 1.2m NaCl supporting electrolyte. With these materials, an average power density around 20mWcm(-2) and a maximum energy density of 11.5WhL(-1) are achieved. A simple cost model indicates the consumable materials cost US$6.45 per kWh(-1), or only US$0.034 per mobile phone charge.