Role of Superoxide and Singlet Oxygen on the Oxygen Reduction Pathways in Li−O2 Cathodes at Different Li+ Ion Concentration

A.Y. TESIO; WALTER TORRES; VILLALBA MATIAS; FEDERICO DAVIA; MARIA DEL POZO VAZQUEZ; DANIEL CORDOBA; FEDERICO JOSE WILLIAMS; ERNESTO JUILIO CALVO

ChemElectroChem

Wiley-VCH GmbH

Lugar: Weinheim; Año: 2022 vol. 9

The oxygen reduction reaction (ORR) on Au electrodes has beenstudied in DMSO at different Li+ concentrations. In-operandofluorescence decay of 9,10-dimethyl anthracene (DMA) hasshown that disproportionation of lithium superoxide Li+O2􀀀into Li2O2 and O2 leads to an increasing fraction of very reactivesinglet oxygen (1O2) at high lithium concentration. Singletoxygen has been identified as the major cause of parasiticreactions leading to capacity fading and high charge overpotentialof Li􀀀 O2 batteries. Rotating ring-disk electrode showsquantitative formation of soluble superoxide at low Li+concentration, a decrease in superoxide yield at high Li+concentrations is consistent with electrochemical quartz crystalmicrobalance (EQCM) evidence of Li2O2 deposits. Differentialelectro chemical mass spectrometry (DEMS) confirms oxygendepletion at the electrode surface during ORR, and O2 evolutionduring oxidation at 3.1 V (vs. Li/Li+ in DMSO). The spurioussolvent decomposition due to the very reactive 1O2 fromsuperoxide disproportionation is revealed by gravimetric EQCMof insoluble by-products. Furthermore, DEMS provides evidenceof CO2 gas evolution from decomposition of Li2CO3 by-productat 3.7 V (vs. Li/Li+ in DMSO). Preliminary in-operando fulldischarge-charge tests of a Li􀀀 O2 battery with 1O2 quencherazide resulted in stable cycling, enhanced capacity and fullcharge recovery in a round trip.