Solid, mixed ion-electron conducting (MIEC) oxides are frequently used in energy applications, such as high temperature solid oxide fuel cells (SOFC), electrolysis cells (SOEC) and oxygen permeation membranes. Their ability to conduct both ionic oxygen vacancies and electronic charge carriers and the resulting variability of the oxygen non-stoichiometry also makes it possible to use them as anode and cathode materials in newly developed, solid-state oxygen ion batteries. [1] Oxygen ion batteries (OIB) are based on the transport of O^2--ions between anode and cathode through an electrolyte via oxygen vacancies. Therefore suitable electrode materials not only need good ion and electron conductivity, but also a highly variable oxygen non-stoichiometry (δ) to chemically store large amounts of charge. Another desirable characteristic is a good material stability down to very reducing oxygen chemical potentials. A crucial step towards the development of functional OIB cells, is the understanding of the defect chemical reactions across a wide potential range. Previous works focused on first investigations of a number of materials and looked at their usability in oxygen ion batteries. It was found that LSCrMn (La_0.5Sr_0.5Cr_0.2Mn_0.8O_3-δ) is an attractive material for OIB anodes due to its potentially very high  electrode capacity of up to 1200 mAh/cm³ at voltages as low as -1.9 V, predicted from chemical capacitance measurements. [2]

This work focuses on the further exploration of LSCrMn, its properties and applicability in oxygen ion batteries. Electrochemical impedance measurements on micro electrodes (d = 300 µm, h = 300 nm) with varying applied biases were used to look at the chemical capacitance of the material over a wide range of electrode potentials (0 to -2.2 V vs. 1 bar O₂) at intermediate temperatures (T = 350 – 500 °C). Repeated measurements confirmed that the high capacity values are stable across multiple bias cycles. An improved sample design (placement of the current collector) was used to further reduce the complexity of recorded impedance spectra. This allowed resolving the C_chem vs. µ_O curve in very high detail, revealing several, clearly separated peaks. These indicate that multiple redox processes are responsible for the high capacity of LSCrMn. Understanding and successfully allocating these peaks to certain processes, makes it further possible to develop a defect chemical model (Brouwer diagram) for LSCrMn in the future. In addition, DC measurements of planar half-cells, sealed with glass to inhibit the oxygen exchange with the atmosphere, will be used to validate the battery curves predicted from the chemical capacitance.