Transport of Li+ and O2 in glymes in relation to lithium-air batteries

H. R. CORTI; H.A. CORTES PAEZ; G. HORWITZ; M. P. LONGINOTTI; M. FACTOROVICH

Porto

Congreso; 6th Symposium on Hydrogen, Fuel Cells and Advanced Batteries; 2017

Lithium air batteries (LAB) promiseshigher energy density than available commercial advanced batteries [1], buttheir development is hindered by the lack of a suitable electrolyte. Abraham and coworkers [2] emphasized the role of asolvent with high donor number (DN) on the stability of Li+-O2-ion-pairs. Thus, solvents like DMSO can support higher discharge/dischargecapacities, but it seems to be chemically unstable in the presence of Li2O2[3]. Recent interest in glymes (glycol ethers) aselectrolytes for LAB is based in their relatively low volatility and the factthat the main discharge product is Li2O2 [3]. Schwenke et al. [4] studied glymes of variouschain lengths, and concluded that pure mono-, di-, tri-, and tetra-glyme aresufficiently stable against superoxide attack. The dissociation level of the lithium salt used in aLAB plays a significant role in the oxygen reduction reaction (ORR) [5]. Theion clustering of lithium salts in solvents of low dielectric constant, likeglymes, could be very large and have a huge influence on the ohmic overpotentials during charge/discharge of LABs [6]. Moreover, the solubility and diffusivity of oxygen in the electrolyte determine the efficiency of thecathodic process in LABs [7]. In this work we study theconductivity and speciation of lithiumtrifuorosulfonate (Li Triflate) and lithium bis(tri- fluoromethylsulfone)imide(LiTFSI) in two glymes: 1,2-di-methoxyethane (DME or monoglyme), and bis(2-methoxy-ethyl)ether (diglyme). We also analyze the diffusion of oxygen in glymes by resortingto semiempirical models.