Open Access

Electrochemical reactions in metal–oxygen batteries come along with the consumption or release of gaseous oxygen. We present a novel methodology for investigating electrode reactions and transport phenomena in metal–oxygen batteries by measuring the pressure dynamics in an enclosed gas reservoir above the oxygen electrode. The methodology is exemplified by a room-temperature sodium–oxygen battery forming sodium superoxide (NaO2) in an electrolyte of diethylene glycol dimethyl ether (diglyme) and sodium trifluoromethanesulfonate (NaOSO2CF3, NaOTf). The experiments are supported by microkinetic simulations with a one-dimensional multiphysics continuum model. During galvanostatic cycling over 30 cycles, a constant oxygen consumption/release rate is observed upon discharge/charge. The number of transferred electrons per oxygen molecule is calculated to 1.01 ± 0.02 and 1.03 ± 0.02 for discharge and charge, respectively, confirming the nature of the oxygen reaction product as superoxide O2–. The same ratio is observed in cyclic voltammetry experiments with low scan rate (<1 mV/s). However, at higher scan rates, the ratio increases as a result of oxygen transport limitations in the electrolyte. We introduce electrochemical pressure impedance spectroscopy (EPIS) for simultaneously analyzing current, voltage, and pressure of electrochemical cells. Pressure recording significantly increases the sensitivity of impedance toward oxygen transport properties of the porous electrode systems. In addition, we report experimental data on the diffusion coefficient and solubility of oxygen in electrolyte solutions as important parameters for the microkinetic models.

Der vorliegende Bericht dokumentiert die Arbeiten und Ergebnisse des Forschungsprojekts GaIN – Gewinnbringende Partizipation der mittelständischen Industrie am Energiemarkt der Zukunft (Laufzeit 01.12.2019 bis 30.11.2022), das vom Bundesministerium für Wirtschaft und Klimaschutz „BMWK“ unter den Kennzeichen 03EI6019E gefördert wurde. Das Ziel des Projektes bestand darin, durch die Digitalisierung der (mittelständischen) Industrie die Unternehmen zu befähigen aktiv gewinnbringend am volatilen Energiemarkt der Zukunft zu partizipieren.