Improvement of thermal stability of lithium ion batteries by using methyl difluoroacetate as an electrolyte solvent

The thermal stability of 1M LiPF/sub 6// CHF/sub 2/COOCH/sub 3/ (methyl difluoroacetate, MFA) with lithiated carbon anodes and the electrochemical characteristics of carbon anodes in this electrolyte have been investigated in terms of the use of this electrolyte in lithium-ion batteries. Differential scanning calorimeter (DSC) measurement of LiPF/sub 6// MFA with lithiated carbon anodes indicated that the main exothermic peak is around 400 /spl deg/C. The peak temperature was 110 /spl deg/C higher than the peak of LiPF/sub 6// EC-DMC [1:1 in vol.] with lithiated carbon anodes. Compared with the case in 1M LiPF6/ EC-DMC [1:1 in vol.], the discharge capacity of carbon anodes was slightly smaller in 1M LiPF/sub 6// MFA, while the cycling performance was quite similar in both electrolytes. From the result of the impedance measurement, the reason for the small capacity is the large resistance of SEI. Moreover, good cycle performance was obtained for the lithium ion cell used in 1M LiPF/sub 6// MFA, while the cell's discharge capacity was slightly lower than that of the lithium-ion cell in 1M LiPF/sub 6// EC-DMC [1:1 in vol.]. It is noted that 1M LiPF/sub 6// MFA electrolyte is a good candidate to improve the thermal stability of the lithium-ion and lithium metal anode battery.