First-Principles Computational and Experimental Investigation of Molten- Salt Electrolytes: Implications for Li-O-2 Battery

B Radhakrishnan and JB Haskins and KB Knudsen and BD McCloskey and JW Lawson, JOURNAL OF PHYSICAL CHEMISTRY C, 125, 3698-3705 (2021).

DOI: 10.1021/acs.jpcc.0c09755

Nitrate-based molten salts have been the most stable electrolytes in Li-O-2 electrochemical systems. While the high temperature of operation is a disadvantage, the molten-salt electrolytes offer a compelling inorganic alternative to both organic electrolytes and inorganic solid electrolytes. In this article, we explore the electrochemical and transport properties of the eutectic binary mixture, Li-K/NO3, using ab initio simulations and compare against experimental studies. Our analysis of the eutectic mixture shows that the Li+ ions are the most mobile species while K+ and NO3- ions have lower, comparable mobilities. The high mobility of the Li+ ion is found to result from its small atomic radius, which allows more transport through "hopping" between solvation shells than larger ions such as K+. Furthermore, ab initio computations of band gaps show much larger stability windows than observed in experiments. Electrochemical stability analysis, performed for the first time using grand-potential analysis on liquid electrolytes, shows that the electrochemical window of the nitrate mixture is restricted by the interface reactions with the electrodes.

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