INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Studies of Oxygen Cathodes in LiPF6 DMSO electrolyte for Lithium Air Batteries
N. MOZHZHUKHINA; S. H. HERRERA; W. R. TORRES; A. Y. TESIO; E. J. CALVO
Congreso; 1st International Workshop in Lithium; 2014
Center for Advanced Research in Lithium and Industrial Minerals (CELIMIN)
The rechargeable Li-air battery exhibits a very large theoretical energy density that can compete with fossil fuels for electric vehicle applications with extended mileage range. The non aqueous Li-air battery introduced in 1996 by Abraham, consists of a lithium metal anode that dissolves in non aqueous electrolyte and the resulting Li+ ions react with oxygen reduction products to form insoluble lithium peroxide, Li2O2, at a porous carbon cathode during discharge. The electro-chemical reaction of Li+ with O2 to yield insoluble Li2O2 in non aqueous electrolyte is reversible sustaining more than ten charge/ discharge cycles. The electrode kinetics of the oxygen reduction reaction (ORR) in lithium air battery cathodes strongly depends on the solvent, electrolyte cation and electrode material since the reaction product is solid. On carbon and gold electrodes the first electro-reduction product, superoxide is stable in non aqueous solutions containing tetra-alkyl ammonium cations. Among non aqueous solvents, DMSO with a very large dipole moment and the appropriate geometry to coordinate Li+ ions has been recently proposed for rechargeable Li-O2 batteries. Peng et. al. have shown that the Li-air battery can be recharged with 95% capacity retention in 100 cycles using dimethyl sulfoxide (DMSO) electrolyte and porous gold electrode. On recharging, the Li-air battery exhibits a large overpotential, ie. > 4 V, and thus is needed to oxidise Li2O2 into O2 and Li+. At such high potentials DMSO is electrochemically oxidized to dimethyl sulfone on Au above 4.2 V so that it is imperative to reduce the charging overpotential by using a catalyst. We will present electrochemical studies using the rotating ring disc electrode to detect soluble superoxide at a ring electode polarized at a suitable potential to oxidize superoxide under convective diffusion conditions. We have complemented these studies with atomic force micros-copy (AFM) to detect the insoluble products of the oxygen reduction reaction (ORR) on carbon surfaces. The reaction has been studied on gold, glassy carbon and highly oriented pyrolytic carbon (HOPG). In-situ infrared spectroscopy under potential control has been shown that at high re-charging potentials DMSO oxidizes on Au and Pt to yield dimethyl sulfone. Additionally, the study of mixtures of acetonitrile and DMSO has shown a preferential solvation of Li+ ions by DMSO, this was observed by the stabilization of soluble superoxide detected in the solution by RRDE, molecular dynamic simulations and conductivity measurements of lithium electrolytes. A mechanistic discussion on the role of adsorbed lithium superoxide disproportionation to yield the insoluble Li2O2 on discharging is relevant to the development of lithium air batteries that can sustain a large number of charge-discharge cycles.