The nonaqueous lithium-oxygen (Li-O2) battery has received increasing attention over the past decade, owing largely to its high theoretical specific energy density. Prior study has demonstrated that the primary discharge product is produced via a two-electron oxygen reduction reaction at the cathode, though the efficiency of O2 conversion on discharge and the evolution of O2 on charge are less than ideal. A similar system, the nonaqueous sodium-oxygen (Na-O2) battery, has been reported as a possible alternative. Despite its lower theoretical specific energy, Na-O2 batteries have been reported to provide improved cyclability and energy efficiency compared to their Li counterparts. Nevertheless, many questions remain about the processes occurring in a Na-O2 cell. In this work, we present research concerning the operation of nonaqueous Na-O2 cells while varying key parameters, including the sodium ion concentration in the electrolyte, the oxygen pressure in the headspace, and the current density employed on discharge and charge. We characterize the dependence of cell performance on these conditions, including cell capacity, discharge and charge overpotentials, and the “sudden death” phenomena, a precipitous increase in overpotential that limits cell capacity and efficiency on both discharge and charge. The one-electron oxygen reduction and evolution reactions at the cathode are verified quantitatively by pressure decay/rise measurements and differential electrochemical mass spectrometry (DEMS), regardless of operating conditions. Further qualitative study is performed using scanning electron microscopy to examine the morphology and deposition of the discharge product. Through this study, we elucidate the limitations of Na-O2 cell capacity and the origins of the “sudden death” phenomenon.

Insights into the sodium-oxygen battery cathode electrochemistry

253rd National Meeting (2017)

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