Phenol‐Catalyzed Discharge in the Aprotic Lithium‐Oxygen Battery

Abstract

Discharge in the lithium-O 2 battery is knownt o occur either by as olution mechanism, whiche nables high capacity and rates,o rasurface mechanism, which passivates the electrode surface and limits performance.The development of strategies to promote solution-phase dischargei ns table electrolyte solutions is ac entral challenge for development of the lithium-O 2 battery.H ere we show that the introduction of the protic additive phenol to ethers can promote as olutionphase discharge mechanism. Phenol acts as ap hase-transfer catalyst, dissolving the product Li 2 O 2 ,a voiding electrode passivation and forming large particles of Li 2 O 2 productvital requirements for high performance.A saresult, we demonstrate capacities of over 9mAh cm À2 areal ,w hichi sa35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li 2 O 2 .

Dual‐Functioning Molecular Carrier of Superoxide Radicals for Stable and Efficient Lithium–Oxygen Batteries

“…Consistent with previous reports, the ORR and corresponding oxygen evolution reaction (OER) were observed with peak currents appearing at 1.88 and 2.25 V, respectively, only in the presence of O 2 . [ 59,60 ] Similarly, for the CV curves with DMPO in Figure 4d, there was no electrochemical reaction under the Ar atmosphere in the voltage range of 1.8–4.0 V (see Figure S3 in the Supporting Information for the CV scan in the extended voltage range). Under the O 2 atmosphere, the ORR was observed with a peak current at 1.88 V, similar to the observation for the reference cell; however, the corresponding OER peak expected at 2.25 V was significantly weakened.…”

Unraveling the Mechanism of the Solution‐Mediated Oxygen Reduction in Metal‐O2 Batteries: The Importance of Ion Association

“…In batteries, this phenomenon is leading to a big discrepancy between the experimental and the theoretical capacity of the operating system. Therefore, a lot of publications in the metal‐O 2 field are dealing with the research on improving the crystal growth of the insulating discharge products (toroidal growth of Li 2 O 2 ) . One promising idea is the use of soluble redox mediators for the ORR.…”

“…Therefore, a lot of publications in the metal-O 2 field are dealing with the research on improving the crystal growth of the insulating discharge products (toroidal growth of Li 2 O 2 ). [11,[17][18][19] One promising idea is the use of soluble redox mediators for the ORR. In the LiÀ O 2 field ethyl viologen, [20,21] phthalocyanine [22] and benzoquinones [23][24][25] were suggested.…”

An Unsuitable Li–O2 Battery Electrolyte Made Suitable with the Use of Redox Mediators

“…[27][28][29] The use of high donor number solvents and the addition of redox mediators to the electrolyte have been found to circumvent the electrode passivation problem thus improving the storage capacity. [30][31][32][33][34][35][36][37][38][39] High donor number solvents tend to be less stable against oxygen reduction products; hence, the use of redox mediators seems more promising. Generally, redox mediators are used in Li-O 2 batteries to mediate the oxygen electrode reactions by transporting electrons from the electrode to oxygen (during cell discharge) or from the discharge products to the electrode (during charging) thus improving electron transfer kinetics whilst encouraging the formation of discharge products away from the electrode surface.…”