The behavior of Br^–/Br₃^– redox mediator (RM), which has been shown to suppress charging overpotential in lithium–air batteries, has been detected for the first time using operando Br K-edge dispersive X-ray absorption fine structure. Br₃^– ions in the electrolyte increase monotonically after ∼30% charging, which indicates that a part of Br₃^– formed via the oxidation of Br^– during charging does not oxidize Li₂O₂ as RM but gets accumulated in the cell. The accumulated Br₃^– is estimated at ∼20% of the total amount of charging. Consistent with this result, the O₂ evolution efficiency gradually decreases from the initial 100% as the charging progresses, and CO₂ is emitted at the end of the charging. The integrated amount of O₂ evolution during charging accounts for ∼83% of the theoretical two-electron reaction. All these results clearly show that the Br^–/Br₃^– RM functions effectively at the beginning of charging but gradually loses its function as charging proceeds.

中文翻译：

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用于锂空气电池的 Br–/Br3– 氧化还原介质的 Operando Br K-Edge 色散 X 射线吸收精细结构分析

Br ^– /Br ₃ ^–氧化还原介体 (RM) 的行为已被证明可抑制锂空气电池中的充电过电位，首次使用原位Br K 边色散 X 射线吸收精细结构检测到。充电 30% 后电解液中的Br ₃ ^{-离子单调增加，这表明充电过程中}通过Br 氧化形成^{的一部分 Br} ₃不会将 Li ₂ O ₂氧化为 RM 而是在电池中积累。累积的 Br ₃ ^–估计占总充电量的 20%。与该结果一致，随着充电的进行，O ₂的析出效率从最初的100%逐渐降低，并且在充电结束时释放出CO _{2 。}充电过程中O ₂释放的积分量占理论双电子反应的83%。所有这些结果清楚地表明，Br ^- /Br ₃ ^- RM 在充电开始时有效，但随着充电的进行逐渐失去其功能。