THERMAL-STABILITY STUDY OF LIASF6 ELECTROLYTES USING ACCELERATING RATE CALORIMETRY

Binary and ternary electrolytes containing solvent mixtures of cyclic esters and cyclic ethers and lithium hexafluoroarsenate (LiAsF6) as the electrolyte salt have been popular for some time for use in secondary lithium batteries because of their good conductivity and lithium cycling efficiency. The main concern regarding safety of lithium batteries is the initiation of self-heating when the cell is under abusive conditions which in the extreme cass can lead to a thermal runaway. There are a number of processes contributing to the self-heating; such as reactions between the electrolyte and electrode materials and thermal decomposition of the electrolyte. Heating resulting from chemical reactions and thermal decompositions can also involve reaction products. Accelerating rate calorimetry is a simple technique which allows the study of self-heating, in particular the thermal decomposition of the electrolyte. In the work reported here, the effect of the addition of a cyclic ether to an electrolyte consisting of LiAsF6 salt dissolved in a mixture of cyclic esters and the replacement of LiAsF6 by lithium triflate salt (LiCF3SO3) on the thermal stability of the electrolyte, were determined. To establish the effect of at least one abusive condition such as battery overcharge, the thermal stabilities of the oxidized forms of two electrolytes containing LiAsF6 electrolyte salt and cyclic ester/ether solvent mixtures were also measured.