(670d) Appropriate Characterization Techniques for Lithium-Oxygen Batteries, and Implications for Understanding 2e- Vs. 4e- Oxygen Reduction Processes

The lithium-oxygen battery is an intensely studied “beyond lithium-ion” battery technology due to its high theoretical specific energy. Commonly consisting of a lithium metal negative electrode, a gaseous oxygen-saturated nonaqueous electrolyte, and a porous carbon positive electrode, the battery operates via the formation (discharge) and decomposition (charge) of lithium peroxide at the porous carbon cathode. Currently, fundamental electrochemical challenges, including electrolyte instability, porous carbon cathode instability, and cathode passivation due to lithium peroxide’s insulative nature, prevent the realization of the battery’s high theoretical specific energy.¹ Therefore, researchers have focused on developing electrolyte and material engineering approaches to address these fundamental electrochemical challenges.

To assess the impact of electrolyte and material engineering approaches in lithium-ion batteries, researchers have commonly used galvanostatic cycling and cyclic voltammetry. However, differences between the lithium-oxygen battery and the lithium-ion battery, namely the use of gas and a surface reaction forming a solid discharge product, make these typical battery techniques insufficient for studying the lithium-oxygen battery. This talk will focus on critical advances in experimental characterization techniques for metal-air batteries, including differential electrochemical mass spectrometry, titrations of extracted cathodes, impedance spectroscopy, and simply the use of a small ratio of electrolyte to cathode surface area. We will show that these techniques are critical to understanding what is going on inside the battery, with less rigorous characterization resulting in incorrect conclusions.

Highlighted will be our recent work on characterizing the ability of lithium iodide and water to form lithium hydroxide rather than lithium peroxide as the primary discharge product, and how our characterization techniques elucidate the interesting but irreversible nature of this reaction.²

(1) McCloskey, B. D.; Burke, C. M.; Nichols, J. E.; Renfrew, S. E. Chem. Commun. 2015, 51, 12701.

(2) Burke, C. M.; Black, R.; Kochetkov, I. R.; Giordani, V.; Addison, D.; Nazar, L. F.; McCloskey, B. D. ACS Energy Letters 2016, 1, 747.