Towards the development of safe and commercially viable nickel-iron batteries: improvements to Coulombic efficiency at high iron sulphide electrode formulations

NiFe batteries are emerging as an important energy storage technology but suffer from a hydrogen-producing side reaction which has safety implications and reduces coulombic efficiency. This manuscript describes a systematic improvement approach for the production of Fe/FeS-based anodes at high concentrations of iron sulphide. Electrodes were made by mixing varying amounts of iron sulphide in such a way that its concentration ranges from between 50 and 100 % (compositions expressed on a PTFE-free basis). Electrode performance was evaluated by cycling our in-house-produced anodes against commercially available nickel electrodes. The results show that anodes produced with larger concentrations outperform their lower concentration counterparts in terms of coulombic efficiency although a slight decrease in the overall cell performance was found when using pure FeS anodes. At high FeS concentrations a hydrogen-producing side reaction has been virtually eliminated resulting in coulombic efficiencies of over 95 %. This has important implications for the safety and commercial development of NiFe batteries.