Transport of Li+ in electrolytes of lithium- air batteries

GABRIELA HORWITZ; MATIAS FACTOROVICH; HORACIO CORTI

Congreso; XVI Brazil MRS Meeting; 2017

Brasilian Materials Research Society

It has been recognized that the level of dissociation of the lithium salt used in a lithium-air battery (LAB) plays a significant role in the oxygen reduction reaction [1]. Moreover, the conductivity of the lithium electrolyte contributes to the overpotentials during charge/discharge of LABs. Thus, it is relevant to have tools for predicting the values of these transport parameters, along with the speciation of lithium salts, in solvents used in LABs, such as glymes (glycol ethers). These solvents seem to be good candidates for non-aqueous LAB, in view of their good stability under the electrochemical conditions of the cathodic processes. We performed a detailed analysis of the electrical conductivity of lithium trifluoromethanesulfonate (LiTf: lithium triflate) and lithium bistrifluoromethanesulfonimidate (LiTFSI) in DME and diglyme, over a wide range of concentrations, including the concentrated region where the formation of triplets and quadruplets ions predominates.   The maximum specific conductivities of these electrolytes are of the order of several mS.cm-1, which is appropriate for non-aqueous LABs. Precise measurements of the ionic conductivity of lithium salts in the dilute and moderate concentration regime allowed us to obtain reliable values of ion pairs and triplet ions formation constants, improving the speciation analysis of lithium salts in glymes, previously reported. It is interesting to note that the infinite dilution conductivity of Li+ ions in aprotic solvents of different molecular sizes obeys WR.Finally, we studied the effect of small amounts of water in the conductivity of the electrolytes. We found that there is not a significant effect with concentrations lower than 1500 ppm.