Mutual Conservation of Redox Mediator and Singlet Oxygen Quencher in Lithium–Oxygen Batteries

Abstract

Li–O2 batteries are plagued by side reactions that cause poor rechargeability and efficiency. These reactions were recently revealed to be predominantly caused by singlet oxygen, which can be neutralized by chemical traps or physical quenchers. However, traps are irreversibly consumed and thus only active for a limited time, and so far identified quenchers lack oxidative stability to be suitable for typically required recharge potentials. Thus, reducing the charge potential within the stability limit of the quencher and/or finding more stable quenchers is required. Here, we show that dimethylphenazine as a redox mediator decreases the charge potential well within the stability limit of the quencher 1,4-diazabicyclo[2.2.2]­octane. The quencher can thus mitigate the parasitic reactions without being oxidatively decomposed. At the same time the quencher protects the redox mediator from singlet oxygen attack. The mutual conservation of the redox mediator and the quencher is rational for stable and effective Li–O2 batteries.

Singlet Oxygen in Lithium−Oxygen Batteries

“…For example, the absorption/emission spectra of DMA appear 300–700 nm region, and their signals are reduced after capturing 1 O 2 via [4+2] cycloaddition (Figure 4c) [5b] . Various examples of adapting trapping agents to Li−O 2 and Na–O 2 cells are summarized in Table S1 [5,13a,14,21,22,24,26,31] in the Supporting Information. Delithiated lithium iron phosphate (Li 1− x FePO 4 ) was used as the anode to avoid unintended decomposition of the trapping agents.…”

“…Accordingly, the charging potential of Li–O 2 cells is determined by the oxidation potential of the RMs. Kwak et al [31] . used 5,10‐dihydro‐5,10‐dimethylphenazine (DMPZ) as RM to maintain the potential at ∼3.2 V, and evaluated the effect of DABCO (Figure 7).…”

Tunable Cationic Vacancies of Cobalt Oxides for Efficient Electrocatalysis in Li–O2 Batteries

“…[14] Redox mediators are employed as the soluble cocatalysts to increase roundtrip energy efficiency and electron-transfer kinetics for better rechargeability. [15,16] Alternatively, it is still highly desirable to develop efficient bifunctional electrocatalysts to lower energy barriers of both ORR and, in order to improve the battery reversibility on the basis of the rational modulation of active sites and thorough understanding on the catalytic mechanism.…”

Confining Li2O2 in tortuous pores of mesoporous cathodes to facilitate low charge overpotentials for Li-O2 batteries

“…With increasing demand for electronic vehicles (EVs) to mitigate the serious environmental issues, the rechargeable lithium batteries have received substantial attention in recent years [1][2][3][4][5]. However, the low theoretical energy density of the current lithium ion batteries (LIBs) cannot satisfy the requirement for long-distance EVs.…”