Predicting the electrochemical behavior of lithium nitrite in acetonitrile with quantum chemical methods

Electrolyte stability is an essential prerequisite for the successful development of a rechargeable organic electrolyte Li-O₂ battery. Lithium nitrate (LiNO₃) salt was employed in our previous work because it was capable of stabilizing a solid-electrolyte interphase on the Li anode. The byproduct of this process is lithium nitrite (LiNO₂), the fate of which in a Li-O₂ battery is unknown. In this work, we employ density functional theory and coupled-cluster calculations combined with an implicit solvation model for neutral molecules and a mixed cluster/continuum model for single ions to understand the chemical and electrochemical behavior of LiNO₂ in acetonitrile (AN). The redox potentials of oxygenated nitrogen compounds predicted in this study are in excellent agreement with the experimental results (the average accuracy is 0.10 V). Theoretical calculations suggest that the reaction between the nitrite ion and its first oxidation product, nitrogen dioxide (NO₂), in AN solution proceeds via the initial formation of a trans-ONO-NO₂ dimer that is subject to autoionization and the subsequent reaction of produced nitrosyl ion (NO ⁺) with NO₂^-. Good agreement between experimental and simulated cyclic voltammograms for electrochemical oxidation of LiNO₂ in AN provides support to the proposed mechanism of coupled electrochemical and chemical reactions. The results suggest a possible mechanism of regeneration of LiNO₃ in electrolyte in the presence of oxygen, which is uniquely possible under charging conditions in a Li-O₂ battery.