Low-Cost, Non-Hazardous All-Iron Battery for the Developing World
Authors: Tucker Michael C , Lambelet David , Phillips Adam , Oueslati Mohamed , Williams Benjamin , Wang Wu-Chieh , Weber Adam Z 
Published: February 2020

Access to energy is critically lacking throughout the developing world.[1] Purchasing electricity for basic household needs such as LED lighting, mobile phone charging, and radio is expensive and difficult. Solar home systems are beyond the means of most of these households, and charging mobile phones at pay-per-charge kiosk businesses is time consuming and expensive, costing about $0.25 per charge. Kerosene lighting is also expensive, with fuel costs around $4 per month for a household.[2]

The concept proposed to address this need is a low-cost battery which the user assembles, discharges, and then disposes of the active materials. The battery is “recharged” by adding fresh active material (iron salt solution and iron sheet metal). The battery is sized for LED lighting and mobile-phone charging. The design goals are: (1) minimize upfront cost, (2) maximize discharge energy, and (3) utilize non-toxic and environmentally benign materials that may be dumped on the ground after use. These are different goals than typically considered for electrochemical battery technology, which provides the opportunity for a novel solution.

To meet the above targets, an all-iron system that uses iron metal and ferric ions is attractive. Iron, among the common metals, is notable for its low cost, low health risk, and ubiquitous availability. The critical electrochemical cell components are shown schematically in Figure 1, with the reactions:

Cathode 2 Fe3+ + 2e- --> 2 Fe2+ E0 = 0.77V vs SHE (1)

Anode Fe0 --> Fe2+ + 2e- E0 = -0.44V vs. SHE (2)

Total 2Fe3+ + Fe0 --> 3Fe2+ E0 = 1.21V (3)

The anode is iron metal, the cathode is a carbon porous electrode (CPE), and they are separated by paper separator. The cathode active material is Fe3+, present as an aqueous salt that flows through the CPE and reacts on its surface. If crossover of Fe3+ occurs, this introduces a self-discharge inefficiency. Many candidate materials for the electrodes, separator, and Fe3+ solution were screened for cost and performance. The selected materials are: low carbon steel negative electrode, paper separator, porous carbon felt positive electrode, and electrolyte solution containing 0.5 M Fe2(SO4)3 active material and 1.2 M NaCl supporting electrolyte. With these materials, a peak power density around 80 mW cm-2, average power density around 20 mW cm-2, and a maximum energy density of 11.5 Wh L-1 are achieved. Figure 2 shows how performance evolves with state of charge (SOC). The ASR slope of the discharge curves increases as Fe3+ is consumed, presumably due to both decreased reactant concentration and increased solution viscosity. A simple cost model indicates the consumable materials cost $6.45 kWh-1, or only $0.034 per mobile phone charge.[3]

This paper will also present development of a simple user-friendly prototype consumer product incorporating multiple iron battery cells, liquid delivery, power conditioning circuitry, and LED/mobile phone charging capability all integrated in an inexpensive plastic housing.

[1] S. Buluswar, Z. Friedman, P. Mehta, S. Mitra, R. Sathre, 50 Breakthroughs: Critical Scientific and Technological Advances Needed for Sustainable Global Development. LBNL Institute for Globally Transformative Technologies, Berkeley, CA, USA 2014

[2] D. Soto, IEEE Global Humanitarian Technology Conference 2014, 188-191

[3] M.C. Tucker, A Phillips, A.Z. Weber, ChemSusChem, 8, 3996-4004 (2015)

Figure 1