Impact of Water on the Stability of Electrolytes in Sodium-Air Batteries

Metal-air (O 2 ) batteries have recently gained significant attention as high-energy alternatives to state-of-the-art Li-ion batteries. While Li-O 2 batteries offer higher theoretical specific energies, Na-O 2 cells have been reported to exhibit superior reversible electrochemistry, achieving higher capacities on discharge and much lower overpotentials on charge compared to their Li-O 2 counterparts [1,2]. To support the transition from Na-O 2 to practical Na-air systems, it is essential to understand how humidity affects key aspects of aprotic electrolyte performance, particularly the stability window. In this talk, we investigate the role of water across both low potentials—relevant for deposition and stripping processes—and high potentials, where electrolyte anodically decomposes. To accomplish this, we employ the rotating (ring) disk electrode (R(R)DE) technique for in situ detection of proton generation as a direct indicator of anodic electrolyte breakdown [3]. This approach not only enables rapid screening of the stability window but also provides a robust method for generating a high-quality data library, leveraging well-defined, inert, and atomically flat surfaces. Accurate and reliable electrochemical data of this kind are essential for machine learning (ML) and artificial intelligence (AI) to achieve their full predictive potential in materials and electrolyte discovery. These insights offer a pathway toward the rational design of more stable organic electrolytes, a key requirement for enabling high-capacity sodium–air batteries. References: [1] McCloskey, B.D., Garcia, J.M. and Luntz, A.C., 2014. Chemical and electrochemical differences in nonaqueous Li–O2 and Na–O2 batteries. The Journal of Physical Chemistry Letters , 5 (7), pp.1230-1235. [2] Xia, C., Black, R., Fernandes, R., Adams, B. and Nazar, L.F., 2015. The critical role of phase-transfer catalysis in aprotic sodium oxygen batteries. Nature chemistry , 7 (6), pp.496-501. [3] Hatsukade, T., Zorko, M., Haering, D., Markovic, N.M., Stamenkovic, V.R. and Strmcnik, D., 2020. Detection of protons using the rotating ring disk electrode method during electrochemical oxidation of battery electrolytes. Electrochemistry Communications , 120 , p.106785. ___________________ The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan