Predicting the Electrochemical Behavior of Lithium Nitrite in Acetonitrile with Quantum Chemical Methods Vyacheslav S. Bryantsev,* Jasim Uddin, Vincent Giordani, Wesley Walker, Gregory V. Chase, and Dan Addison Liox Power, Inc., 129 N. Hill Ave., Suite 103, Pasadena, California 91106, United States * S Supporting Information ABSTRACT: Electrolyte stability is an essential prerequisite for the successful development of a rechargeable organic electrolyte Li-O 2 battery. Lithium nitrate (LiNO 3 ) 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 (LiNO 2 ), the fate of which in a Li-O 2 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 LiNO 2 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 (NO 2 ), in AN solution proceeds via the initial formation of a trans-ONO-NO 2 dimer that is subject to autoionization and the subsequent reaction of produced nitrosyl ion (NO + ) with NO 2 - . Good agreement between experimental and simulated cyclic voltammograms for electrochemical oxidation of LiNO 2 in AN provides support to the proposed mechanism of coupled electrochemical and chemical reactions. The results suggest a possible mechanism of regeneration of LiNO 3 in electrolyte in the presence of oxygen, which is uniquely possible under charging conditions in a Li-O 2 battery. 1. INTRODUCTION As hybrid and full electric vehicles continue to increase in sales and popularity around the world, the race is on to develop batteries that can deliver higher capacities at lower costs. Li-O 2 batteries have been heavily investigated as a potential battery system to replace Li-ion because of a high theoretical specific energy, however research into Li-O 2 cells has been hampered by degradation issues with every major component of the system upon cycling, and progress has been slow. 1-5 Liquid electrolyte plays a critical role in determining the nature of discharge products and cycling characteristics of a rechargeable Li-O 2 battery. One of the biggest challenges is to develop an electrolyte composition that is sufficiently stable to both the Li anode and O 2 cathode environments upon long- term cycling. 1-5 We have recently reported 6 on the Li-O 2 cell that enables longer duration cycling (>2000 h) with significantly reduced decomposition of electrolyte materials compared to Li-O 2 cells previously reported in the field. This performance is achieved by combining straight-chain alkyl amides, which are significantly more stable to the reactions of the O 2 electrode than conventional electrolyte solvents, 6,7 with the lithium nitrate (LiNO 3 ) salt, which is capable of stabilizing a solid-electrolyte interphase (SEI) on the Li anode. 8-11 It was suggested 8 that a stabilizing effect of LiNO 3 on Li metal cycling is due to the formation of a passivating layer of Li 2 O on the Li electrode surface through the following reaction: + → + 2Li LiNO Li O LiNO 3 2 2 (1) Another product of this reaction, lithium nitrite (LiNO 2 ), is expected to be soluble and electroactive in the charging potential range of a Li-O 2 cell. Indeed, small oxidative processes at 3.6-3.7 V observed in a Li-O 2 cell with a LiNO 3 / dimethylacetamide (DMA) electrolyte 6 are consistent with the presence of LiNO 2 in an electrolyte solution. LiNO 3 is used as an electrolyte additive in rechargeable lithium-sulfur (Li-S) batteries to promote the formation of a stable passivation film on Li anode, which is known to significantly suppress the reduction of polysulfide species in solution. 9,10 However, the progressive consumption of LiNO 3 on the Li anode in Li-S batteries limits the number of cycles over which LiNO 3 is able to prevent the redox shuttle of lithium polysulfides. We have recently shown 12 that LiNO 3 can be regenerated from LiNO 2 in the presence of dissolved O 2 during the charging of a Li-O 2 battery, which could be a contributing factor to the observed interfacial stability and cycling of Li metal when both LiNO 3 and O 2 are present. 11 Detailed knowledge of the chemical and electrochemical behavior of LiNO 2 in aprotic solvents is thus essential to gain further insights into the mechanism of regeneration of NO 3 - in rechargeable Li-O 2 cells. Received: October 21, 2013 Article pubs.acs.org/JACS © XXXX American Chemical Society A dx.doi.org/10.1021/ja410766n | J. Am. Chem. Soc. XXXX, XXX, XXX-XXX