Partial redox cycling of composite storage materials for rechargeable oxide batteries

The redox behavior of Fe2NiO4/YSZ composites for application as oxygen storage material in rechargeable oxide batteries (ROBs) is investigated by means of thermogravimetric experiments in varying oxygen partial pressures, chosen to simulate the expected redox conditions that would occur during the operation of a ROB. The thermodynamic window of operation limits the oxidation to the formation of magnetite, as a continuation towards the nickel iron spinel or hematite risk compromising the anode of the ROBs solid oxide cell unit by exceeding the Ni/NiO redox equilibrium. The resulting mass change curves of the partial cycling showed no significant signs of capacity fading for the 104 cycles investigated, in addition to showing signs of increasing initial oxidation kinetics. Furthermore, evaluation of the oxidation process by means of Johnson-Mehl-Avrami-Kolmogorow (JMAK) equations was conducted. The resulting kinetic and geometric parameters are related to the microstructural development of the samples obtains by scanning electron microscopy (SEM) images, providing insights into the oxidation processes that result in the stable redox cycling of the material. The work expands on a previous study where the general redox behavior of the material was investigated with oxidations in air.