TTF Redox Titration of Li 2O2for Li-O 2 Battery Cathode in LiPF6 DMSO Electrolyte

W. R. TORRES; N. MOZHZHUKHINA; S. H. HERRERA; M. VILLALBA; A. Y. TESIO; E. J. CALVO

Lausanne

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

International Society of Electrochemistry

The rechargeable lithium-air battery exhibits a very large theoretical energy density that can compete with fossil fuels for electric vehicle applications with extended millage range. That is the motivation for this work. At first, we performed the ORR reactions by RRDE technique in solutions containing lithium ions in DMSO electrolyte to know the potential for recharge it. This solvent presents advantages over other by their ability to solvate the superoxide ion in solution. Cyclic voltammetry and chronoamperometry experiments indicate that the mechanism of superoxide ion generation and solvation is not trivial. Oxygen molecule could approach to the surface and be reduced to superoxide ions, which are stabilized by solvent molecules in presence of lithium ions. Its rate of formation depends on the potential. This can be seeing easily by transients, because time and potential convolved in VC data. These two ions can diffuse to the solution or be adsorbed onto the surface of the cathode and then disproportionate to insoluble lithium peroxide. Dissolve this solid deposited in cathode is important in recharging the battery. By the EQCM technique we could say that the formation of the solid Li2O2 on the electrode surface is not simple. Before LiO 2 disproportionate, lithium ions are solvated on surface for at least one molecule of DMSO. Furthermore, the deposition of this solid by a potential sweep 20mV.s -1 shows that the layer is greater than 100nm. Resistance values of the quartz crystal compared with the values of the impedance change of the quartz crystal indicate that the solid did not have a viscoelastic behaviour, which disagrees with Sauerbrey law indicating that the frequency variation and the deposited mass are proportional. Previous work from our group, by the SNIFTIR technique, shows that the solvent electrochemically decompose at the potential of recharge. That is the reason why the use of TTF as a redox mediator could be an alternative to recharge the battery. This shortens the potential window to a value smaller than that corresponding to the electrochemical decomposition of the DMSO. The electrochemistry of TTF (tetrathiafulvalene) in DMSO exhibits two one-electron reversible waves with half-wave potentials at 3.65V and 3.87V respectively. When the battery is discharged, the TTF + could oxidize lithium peroxide deposited on the surface. By successive sweeps in the potential window of the TTF, the surface might recovered completely and the recharge of the battery at low potentials it is feasible