Operando Synchrotron XRD of Bromide Mediated Li–O₂ Battery

Abstract

Li–O2 battery technology offers large theoretical energy density, considered a promising alternative energy storage technology for a variety of applications. One of the main advances made in recent years is the use of soluble catalysts, known as redox mediators (RM), decreasing the charge overpotential and improving cyclability. Despite its potential, much is still unknown regarding its dynamic, especially over higher loading electrodes, where mass transport may be an issue and the interplay with common impurities in the electrolyte, like residual water. Here we perform for the first time an operando XRD characterization of a DMSO-based LiBr mediated Li–O2 battery with a high loading electrode based on CNTs aiming to reveal these dynamics and track chemical changes in the electrode. Our results show that, depending on the electrode architecture, the system’s issue can move from catalytic to a mass transfer. We also assess the effect of residual water in the system to better understand the reaction routes. As a result, we observed that with DMSO, the system is even more sensitive to water contamination compared to glyme-based studies reported in the literature. Despite the activity of LiBr on the Li-peroxide oxidation and its contribution to cyclability, with the system and electrode configuration used in this study, we verified that a mass transfer limitation caused a cell “sudden death” caused by clogging after cycling.

Tuning aprotic solvent properties with long alkyl chain ionic liquid for lithium-based electrolytes

“…The chemical reaction with the mediator during the charge process of Li-O 2 cells favors the charge reaction, thus decreasing the overpotential and therefore improving the stability of the electrolyte and the cyclability of the battery. 16 A second oxidation peak above 4.50 V is clearly observed in the diluted solution (0.050 M), which is assigned to the Br 3 À oxidation to Br 2 (eqn (3)),…”

“…À formed electrochemically is reported as an efficient redox mediator, 49 which reacts chemically with the main discharge product, Li 2 O 2 , and releases Li + , O 2 , and Br À during the battery charge, 16 as indicated by the equation below,…”

“…To characterize the aggregate structure, we calculated the combined distribution function (CDF) joining the CR([C 16 mim] + )-CR([C 16 mim] + ) g(r) and the angular distribution function for the angle between the normal vectors in the imidazolium ring plane, centered on the CR atoms, Fig. 7.…”

“…5,16 The latter indicates that the Li + ion solvation is facilitated by DMSO molecules, which also stabilizes the main and the intermediate (Li 2 O 2 and LiO 2 , respectively) discharge products formed during the Li-O 2 batteries operation. 5,16 Moreover, the high DN enables the formation of hydrogen bonds between DMSO molecules and some other solvents and salts in binary 17 and ternary mixtures, 18 which affect the physical properties of the electrolyte. 17 Despite these great features, DMSO has an electrochemical window limited to 4.20 V, 19 which means it can degrade during the electrochemical reactions in the Li-O 2 battery operation, forming undesirable and irreversible products, such as DMSO 2 .…”

“…25 Beyond that, MD simulations have also been used as a tool to complement and improve the understanding of experimental measurements for electrolytes. 26,27 In summary, we performed an experimental-theoretical investigation of the effects of the addition of the ionic liquid crystal 1-hexadecyl-3-methylimidazolium bromide, [C 16…”