Hydroperoxide‐Mediated Degradation of Acetonitrile in the Lithium–Air Battery

Abstract

Understanding and eliminating degradation of the electrolyte solution is arguably the major challenge in the development of high energy density lithium-air batteries. The use of acetonitrile provides cycle stability comparable to current state-of-the-art glyme ethers and, while solvent degradation has been extensively studied, no mechanism for acetonitrile degradation has been proposed. Through the application of in situ pressure measurements and ex situ characterization to monitor the degradation of acetonitrile in the lithium-air battery, a correlation between H 2 O concentration within the cell and deviation from the idealized electron/oxygen ratio is revealed. Characterization of the cycled electrolyte solution identifies acetamide as the major degradation product under both cell and model conditions. A new degradation pathway is proposed that rationalizes the formation of acetamide, identifies the role of H 2 O in the degradation process, and confirms lithium hydroperoxide as a critical antagonistic species in lithium-air cells for the first time. These studies highlight the importance of considering the impact of atmospheric gases when exploring lithium-air cell chemistry and suggest that further exploration of the impact of hydroperoxide species on the degradation in lithium-air cells may lead to identification of more effective electrolyte solvents.

An overview of the unstable and irreversible lithium metal anode-related issues in nonaqueous Li–O2/air batteries

“…Until now, there has been absolutely no stable aprotic solvent/salt used for the healthy operation of LOBs/LABs. 93–97 Here, we take the commonly-used TEGDME solvent of LOBs as an example to introduce its instability in LOBs. 98,99 As shown in Fig.…”

A lithium–air battery and gas handling system demonstrator

“…5 During charging, the reactions are reversed, reforming O 2 and Li. However, the battery faces significant challenges, 3,6,7 such as degradation of the electrolyte during operation, 8–12 slow electrochemistry due to the insulating nature of Li 2 O 2 , 13–15 resulting in the need for homogeneous redox mediators to oxidise Li 2 O 2, 16–22 instability of Li metal 23 and the need for anode-protection layers. 24 Significant progress has been made in these areas, however, most studies of the Li–air battery involve the use of pure O 2 gas as the feedstock for the positive electrode and often only low-capacity systems (<1 mA h cm −2 ) are explored.…”