The oxygen electroreduction reaction in LiPF6 in DMSO

E. J. CALVO; W. R. TORRES; S. H. HERRERA; N. MOZHZHUKHINA; F. MARCHINI; A. Y. TESIO; F. WILLIAMS

Lausanne

Congreso; 65th Annual Meeting of International Society of Electrochemistry; 2014

International Society of Electrochemistry

The rechargeable Li?air battery exhibits a very large theoretical energy density that can compete with fossil fuels for electric vehicle applications. The non-aqueous Li?air battery consists of a Li metal anode that dissolves in a non aqueous electrolyte and the resulting Li+ ions react with O2 products to form insoluble lithium peroxide Li2O2 at a porous carbon cathode during discharge. The electrode kinetics of the oxygen reduction reaction (ORR) in lithium air battery cathodes depends on the solvent, the electrolyte cation and electrode material because the ORR product is a solid. We report experimental results using a variety of techniques: cyclic voltammetry (CV), rotating ring disc electrode (RRDE), quartz crystal microbalance under electrochemical control (EC-EQCM), atomic force microscpy, (AFM), X-Ray spectroscopy on dif- ferent surfaces, namely gold, glassy carbon, and HOPG for the study of the ORR. DMSO with a very large dipole moment and the appropriate geometry to coordinate Li+ strongly solvates Li+ and thus stabilizes soluble O2- which can be detected with an Au ring of a RRDE, cyclic voltammetry of 0.1 M LiPF6 in O2 saturated DMSO shows distinctive features in HOPG, GC and Au respectively. Ex-situ AFM examination of the surfaces with electrochemical pre-treatment at selected potentials shows that HOPG is much less reactive than GC or Au for the ORR and formation of Li2O2 deposit. In the early stages of ORR the insoluble products in O2 saturated solutions nucleates at step edges. The formation and removal of ORR reaction products were monitored with AFM, EQCM and XPS: changes in the morphology at different potentials and CV reproducibility in subsequent cathodic cycles has shown consistent results with the EQCM while XPS detected LiO2, Li2O2 and side products such as lithium carbonate, fluoride, etc. The EQCM can measure de mass to charge ratio at different potentials in a CV or at different times during a chrono-amperommetry and thus evaluate ions being discharged as well as neutrals as solvent molecules. Preliminary results have shown that in the beginning of oxygen reduction DMSO is also incorporated in the deposit. References:1. "A rotating ring disk electrode study of the oxygen reduction reaction in lithium containing non aqueous electrolyte", Calvo, E.J., Mozhzhukhina, N., Electrochemistry Communications, 2013,31,56?58 2."Infrared spectroscopy studies on stability of dimethyl sulfoxide for application in a Li-air battery", J. Physical Chemistry C, 2013, 117 (36), pp 18375?18380. 3. "AFM study of oxygen reduction products on HOPG in the LiPF6?DMSO electrolyte", Phys. Chem. Chem. Phys., 2014, Advance Article. DOI 10.1039/C3CP54621G.