Thermal Enhancement of Product Conductivity Permits Deep Discharge in Solid State Li-O2 Batteries

Li-O2 batteries are mainly limited by the poor conductivity of their discharge products as well as parasitic reactions with carbon-containing electrodes and electrolytes. Here, Li-O2 cells utilizing inorganic solid state electrolytes are investigated as a means to operate at elevated temperature, thereby increasing the conductivity of discharge products. Growth of dense, conductive LixOy products further removes the need for high surface area support structures commonly made of carbon. Patterned Au electrodes, evaporated onto Li7La3Zr2O12 (LLZO) solid electrolyte, are used to create a triple phase boundary for the nucleation of discharge product, with growth outward into the cell headspace with gaseous O2. Through capacity measurements and imaging, discharge product growths are estimated to reach a critical dimension of approximately 10 microns, far exceeding what would be possible for a conformal film based on its room temperature electronic conductivity. Raman spectroscopy and electrochemical mass spectrometry (EC-MS) are used to characterize the discharge chemistry and reveal a mixed lithium oxide character, with evidence of trace lithium hydroxides and initial carbonate contamination. These results showcase that thermal enhancement of Li-O2 batteries could be a viable strategy to increase capacity when paired with solid electrolytes.