Reversible solid state Fe-air rechargeable battery using LaGaO₃ based oxide ion conducting electrolyte

The combination of solid oxide fuel cell technology with Fe-air battery concept was proposed by using H₂/H₂O as a redox mediator and LaGaO₃ based oxide for electrolyte. Since large internal resistance and large degradation during charge and discharge cycles are observed on anode, improvement in discharge potential and cycle stability are strongly required by improving stability of anode. In this study, cermet anode consisting of Ni-Fe alloy combined with oxide ion conductor was investigated. It was found that by using cermet anode of Ni-Fe combined with Ce_0.6Mn_0.3Fe_0.1O₂ (CMF), the observed energy density of the cell is improved to be 1109 Wh/Kg-Fe at 10 mA/cm², 873 K, which is about 92% of the theoretical energy density assuming the formation of Fe₃O₄ (1290 Wh/Kg-Fe). Cycle stability was also much improved on the cell using Ni-Fe-CMF anode comparing with that of Ni-Fe metal because of suppressed aggregation of Ni by mixing with CMF. Electrochemical charge-discharge measurement at 773 K showed excellent cycle stability over 30 cycles with high energy density (Round trip efficiency is higher than 80%). The excellent performance and stability with operating at lower temperature promise this Fe-air solid oxide battery as the next generation energy storage device for averaging electricity and electric vehicle.