Operando detection and suppression of spurious singlet oxygen in Li–O2 batteries

DANIEL CÓRDOBA; ABIGAIL ROZENBLIT; LEANDRO BENAVIDES; DANIEL MURGIDA; HERNÁN B. RODRÍGUEZ; ERNESTO J. CALVO

York

Otro; Rechargeable non-aqueous metal-oxygen batteries Faraday Discussion; 2023

Royal Society of Chemistry (RSC)

The rechargeable lithium air battery (Li‐O2) with very high energy density comparable to fosil fuels was introduced by Abraham [1]. However, the parasitic reactions of the O2 reduction products with solvent and electrolyte lead to capacity fading and high charging overpotentials. During the oxygen reduction reaction (ORR) in aprotic solvents superoxide radical anion (O2‐.) is the main one-electron reaction product, which in the presence of Li+ ions undergoes disproportionation to yield Li2O2 and O2, a fraction of which results in singlet oxygen (1O2). Very reactive 1O2 is responsible for the spurious reactions that lead to high charging overpotential and low cycle life due to solvent and electrolyte degradation [2]. Herein, we extend our previous ex‐situ studies [3] and report on severalexperimental findings in operando for the detection and suppression of 1O2 inside a Li‐O2 battery under operation and test the efficiency and electrochemical stability of different physical quenchers of 1O2. In operando detection of 1O2 inside the battery was accomplished with dimethyl anthracene fluorescence quenching with a bifurcated optical fiber in front face mode through a quartz window in the battery [4]. Sodium Azide, DABCO and triphenylamine (TPA) 1O2 physical quenchers proved effective to offset the spurious chemistries in different solvents such as DMSO, diglyme and tetraglyme. Plots of differential pressure vs. charge during battery operation showed that the number of electrons per oxygen molecule was n > 2 in the absence of 1O2 quenchers due to spurious reactions and n = 2 in the presence of 1O2 quenchers proving the suppression of spurious reactions. Battery cycling at limited specific capacity of 500 mAh/g of MWCNTs cathode and 125‐250 mA/g current density in the absence and presence of physical quenchers and physical quencher plus the redox mediator I3‐/I- (with lithiated Nafion membrane) showed increasing cyclability from coulombic efficiency and cell voltage data over 100 cycles. The electrochemical stability of several 1O2 quenchers has been studied in detail. In operando Raman studies with the same quartz window at the bottom of the battery allowed detection of Li2O2 and excess I3‐ redox mediator during discharge and charge respectively. In the absence of 1O2 quenchers spurious reaction products such as carbonate were detected at the MWCNT cathode. Numerical simulations of the Li‐02 battery operating under thin layer cell electrochemical conditions under COMSOL environment showed the concentration profiles.[1]. K. M. Abraham, Z. Jiang, J. Electrochem. Soc 1996, 143, 1–5.[2]. A.Y. Tesio, W. Torres, M. Villalba, F. Davia, M. del Pozo, D. Córdoba,F.J. Williams, E.J. Calvo, ChemElectroChem. 2022 in press.[3]. D. Córdoba, H.B. Rodríguez, E. J. Calvo, ChemistrySelect 2019, 4, 12304– 12307.[4]. D. Córdoba, H.B. Rodríguez, E. J. Calvo, J. Phys. Chem. C, (2022), under review.