Potential-Dependent Generation of O₂^– and LiO₂ and Their Critical Roles in O₂ Reduction to Li₂O₂ in Aprotic Li–O₂ Batteries

Abstract

Discharging of the aprotic Li−O 2 battery relies on the oxygen reduction reaction (ORR) producing Li 2 O 2 in the positive electrode, which remains incompletely understood. Here, we report a mechanistic study of the Li-ORR on a model system, i.e., an Au electrode in a Li + dimethyl sulfoxide (DMSO) electrolyte. By spectroscopic identification of the reaction intermediates coupled with density functional theory calculations, we conclude that the formation of O 2 − and LiO 2 in the Li-ORR critically depends on electrode potentials and determines the Li 2 O 2 formation mechanism. At low overpotentials (> 2.0 V vs Li/ Li + ) O 2− is identified to be the first surface intermediate, which diffuses into the bulk electrolyte and forms Li 2 O 2 therein via a solution-mediated disproportionation mechanism. At high overpotentials (ca. 2.0−1.6 V vs Li/Li + ) LiO 2 has been observed, which can rapidly transform to Li 2 O 2 by further electro-reduction, suggesting a surface-mediated mechanism. The solution-mediated Li 2 O 2 formation that can account for the widely observed toroid-shaped discharged Li 2 O 2 particles has also been thoroughly examined. Thus, O 2 − formation controls the overall reaction onset potential, and LiO 2 formation demarcates the change from a solution-to surface-mediated reaction mechanism. The new findings and improved understandings of the Li-ORR in DMSO will contribute to the further development of aprotic Li−O 2 batteries.

High‐Capacity and Long‐Cycle Lifetime Li−CO2/O2 Battery Based on Dandelion‐like NiCo2O4 Hollow Microspheres

“…As shown in Figure , no current response is observed with pure CO 2 ‐saturated DMSO, indicating that pure CO 2 cannot be electrochemically reduced in this voltage range. For electrolytes saturated with pure O 2 , the reduction of O 2 to O 2 .− occurs at approximately 2.5 V through a one‐electron pathway, followed by reoxidation at 3.2 V, which has already been confirmed in previous studies …”

Electrolytes for Rechargeable Lithium–Air Batteries

“…Thus, controlling the formation route and morphology of Li 2 O 2 is important to improve the performance of Li–air batteries . Recent studies have shown that even small changes in electrolytes, including differences in solvents, lithium salts, and additives, can dramatically alter the pathway of the discharge reactions …”

First-principles study of the initial oxygen reduction reaction on stoichiometric and reduced CeO2(111) surfaces as a cathode catalyst for lithium–oxygen batteries

“…To understand the mechanism and improve batteries' performance, many theoretical calculation works have also been conducted, such as the ORR and OER mechanism at different catalysts and aprotic solvent [24][25][26][27][28] , prediction of possible product 29 , and influence of electrolytes 30 . Although many studies have been carried out, there is no report as far as we know to investigate the mechanisms about lithium oxide reaction on the CeO2 surface, including those related to lithium adsorption, formation and decomposition of lithium peroxide or other oxides.…”