Mixed solvent electrolytes containing fluorinated carboxylic acid esters to improve the thermal stability of lithium metal anode cells

A safety aspect is one of the most important problems to utilize lithium metal anode battery which can show significant higher capacity than conventional lithium ion battery. The thermal stabilities of electrolytes containing fluorinated carboxylic acid esters were assessed at the coexistence of lithium metal using differential scanning calorimeter. Among the fluorinated carboxylic esters used here, CHF2COOCH3 (Methyl difluoro acetate; MFA) exhibited the highest onset temperature and smallest amount of exothermic heat at the coexistence of lithium. A similar trend was observed for apparent I-M solution of LiPF6 with fluorinated carboxylic acid esters and ethylene carbonate (EC) + dimethyl carbonate (DMC) (1: 1 in vol.). Precise thermal study was undertaken for 1 M LiPF6/MFA and 1 M LiPF6/EC + DMC or propylene carbonate (PC), changing the mixing ratio at the coexistence of lithium metal. Surviving lithium metal content was estimated by endothermic vs. exothermic heat ratio at lithium melting and freezing from 300 degreesC. With the increase of volume ratio of MFA from 0% to 100%, the amount of surviving lithium metal increased from 0% to 95%. (C) 2002 Elsevier Science B.V. All rights reserved.