Oxygen Reduction Reaction in Non-Aqueous Lithium Containing Electrolyte

MOZHZHUKHINA, NATALIIA; TORRES, WALTER R.; TESIO, ALVARO Y.; DEL POZO, MARIA; HERRERA, SANTIAGO E.; CALVO, ERNESTO J.

Buenos Aires

Congreso; 20th Topical Meeting of the International Society of Electrochemistry; 2017

International Society of Electrochemistry

Nowadays electrical devices? requires for a newest clean and sustainable energy sources. Rechargeable lithium-air battery could be the solution for these applications due to its high theoretical energy density.Lithium-air battery was accidentally introduced by Abraham in 1996. It consists in a metallic lithium anode immersed in a non-aqueous electrolyte, and a porous carbon cathode where oxygen reduction reaction (ORR) takes place.In recent years a high donor number solvent was proposed due to its capacity to solvate peroxide anion, a product formed during ORR. Dimethyl sulfoxide (DMSO) has this property. Its advantages against other non-aqueous solvents lie in the ORR or OER mechanism elucidation, intermediates and products stabilization and reverse reaction facility.It is known, ORR products and by-products are mainly LiO2 that could dismutate to Li2O2 or could be formed this one by a second electron transfer. That means lithium peroxide could form by two mechanisms, solution phase or surface phase mechanisms.It is necessary to improve batteries? capacity by adding small quantities of water or redox mediators. This last one can facilitate too OER by oxidation of products and side products formed during the ORR.Extensive studies for LiPF6 0.1 M in DMSO was carried out in agreement with those mechanisms.Rotating ring disc electrode transient experiments show two processes, the first one can be attributed to lithium superoxide formation and the second one could be the dismutation?s solution mechanism. This chemical mechanism was followed by a simple experiment. Superoxide anion was produced by applying 2.2 V in a lithium-free solution. Lithium peroxide was formed by incorporating LiPF6 at 0.1 M final concentration and followed by electrochemical quartz crystal microbalance (EQCM) and atomic force microscopy (AFM).The ORR products? pathway depends on the solvent properties, lithium salt and cathode material as well as current density or potential applied. Lithium superoxide and lithium peroxide formation depend on the lithium concentration also in the water content. By using EQCM and Differential Electrochemical Mass Spectroscopy (DEMS) was shown that 5 mM LiPF6 final concentration lithium containing electrolyte is necessary to produce Li2O2 by a second electron transfer pathway or LiO2 disproportionation. Also by EQCM was demonstrated solvent co-deposition during the ORR.To recover surface electrode it is imperative to apply high potential close to 4.5 V. However, at 4.2 V DMSO electrochemically decompose to form dimethyl sulfone producing CO2 and consuming H2O in according to Aurbach mechanism. This was seen by Subtractively Normalized Interfacial Fourier Transform IR Spectroscopy (SNIFTIRS). To avoid this problem, the use of redox mediator it is needed. Tetrathiafulvalene can be used to facilitate the OER by removing all the products and by-products formed during the ORR. Indeed, iron (II) phthalocyanine can be employed to enhance battery?s capacity by increasing lithium peroxide deposits on the electrode surface or removing those ORR?s products.