Thermal stability of alkyl carbonate mixed-solvent electrolytes for lithium ion cells

• Published in: Journal of power sources Vol. 104; no. 2; pp. 260 - 264
• Main Authors: Kawamura, Tetsuya, Kimura, Arihisa, Egashira, Minato, Okada, Shigeto, Yamaki, Jun-Ichi
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-02-2002; Elsevier Sequoia
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrolyte; Exact sciences and technology; Lithium ion cell; Lithium metal; Safety; Thermal stability; Water; Water; Lithium metal; Lithium ion cell; Safety; Electrolyte; Thermal stability; Differential scanning calorimetry; Mixed solvent; Organic carbonate; Thermal behavior; Secondary cell; Lithium ion
• DOI: 10.1016/S0378-7753(01)00960-0
• EISSN: 1873-2755
• ISSN: 0378-7753

The thermal stability of some mixed-solvent electrolytes used in lithium cells was measured by differential scanning calorimetry (DSC) using airtight containers. The electrolytes used were ethylene carbonate (
EC)+
diethyl
carbonate
(
DEC)
,
EC+
dimethyl
carbonate
(
DMC)
, propylene carbonate (PC)+DEC, and PC+DMC in which was dissolved 1
M LiPF
6 or 1
M LiClO
4. The influence of water addition and lithium metal addition on the thermal behavior of these electrolytes was also investigated. The exothermic peak of LiPF
6 electrolytes containing DEC was found at 255
°C, and the peak temperature of the electrolytes containing DEC was 15–20
°C lower than that of LiPF
6 electrolytes containing DMC. This effect was also observed in the electrolytes including LiClO
4. DMC was found to be more reactive than DEC. The thermal behavior of various kinds of LiPF
6 electrolytes with lithium metal was measured by DSC. The exothermic reaction of 1
M LiPF
6/EC+DEC, 1
M LiPF
6/EC+DMC, and 1
M LiPF
6/PC+DMC with lithium metal began at the melting point of lithium metal because of the break down of the solid electrolyte interface (SEI). The temperature was approximately 180
°C, whereas the self-heating of 1
M LiPF
6/PC+DEC occurred before the melting point of lithium metal. The temperature at which the self-exothermal reaction began was 140
°C. Therefore, the lithium metal in this electrolyte was found to be thermally unstable. When water was added to the above electrolytes with lithium metal, the exothermic reaction began at less than 130
°C, probably due to a collapse of SEI in response to the HF that was a product of the reaction between LiPF
6 and the added water.