Thermal stability of electrolytes with mixtures of LiPF6 and LiBF4 used in lithium-ion cells

Eui Sun Hong, Shigeto Okada, Takaki Sonoda, S. Gopukumar, Jun Ichi Yamaki

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Thermal stability studies of electrolytes with mixtures of LiPF6 and LiBF4 were carried out using differential scanning calorimetry. The solvent was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in the volume ratio of 3:3:1, respectively. We expected the occurrence of two independent exothermic peaks associated with LiPF6 at the lower temperature and lithium LiBF4 at the higher temperature, due to decomposition reactions resulting in the Lewis acids PF5 and BF3. Instead, the mixed salt electrolyte exhibited a single exothermic peak. We deduced that the HF produced by the reaction of LiPF 6 with solvent was the reason for the existence of one exothermic reaction peak. The HF may react with LiBF4 to give HBF4, which is very unstable and decomposes easily to HF and BF3 at a lower temperature than the decomposition temperature of LiBF4 itself. By comparison, a thermal study of a mixed salt electrolyte including LiPF 6 and LiN(SO2CF3)2 showed that the exothermic reaction of LiN(SO2CF3)2 with solvents is also influenced by HF produced in the reaction of LiPF6 with solvents but that the strength of the influence is small compared with its effect on an electrolyte mixture including LiBF4.

Original languageEnglish
Pages (from-to)A1836-A1840
JournalJournal of the Electrochemical Society
Volume151
Issue number11
DOIs
Publication statusPublished - Dec 1 2004

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Lithium
Electrolytes
Thermodynamic stability
thermal stability
lithium
electrolytes
Ions
Carbonates
carbonates
Exothermic reactions
exothermic reactions
cells
ions
Salts
salts
Decomposition
decomposition
Lewis Acids
Temperature
Differential scanning calorimetry

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

Cite this

Thermal stability of electrolytes with mixtures of LiPF6 and LiBF4 used in lithium-ion cells. / Hong, Eui Sun; Okada, Shigeto; Sonoda, Takaki; Gopukumar, S.; Yamaki, Jun Ichi.

In: Journal of the Electrochemical Society, Vol. 151, No. 11, 01.12.2004, p. A1836-A1840.

Research output: Contribution to journalArticle

Hong, Eui Sun ; Okada, Shigeto ; Sonoda, Takaki ; Gopukumar, S. ; Yamaki, Jun Ichi. / Thermal stability of electrolytes with mixtures of LiPF6 and LiBF4 used in lithium-ion cells. In: Journal of the Electrochemical Society. 2004 ; Vol. 151, No. 11. pp. A1836-A1840.
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abstract = "Thermal stability studies of electrolytes with mixtures of LiPF6 and LiBF4 were carried out using differential scanning calorimetry. The solvent was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in the volume ratio of 3:3:1, respectively. We expected the occurrence of two independent exothermic peaks associated with LiPF6 at the lower temperature and lithium LiBF4 at the higher temperature, due to decomposition reactions resulting in the Lewis acids PF5 and BF3. Instead, the mixed salt electrolyte exhibited a single exothermic peak. We deduced that the HF produced by the reaction of LiPF 6 with solvent was the reason for the existence of one exothermic reaction peak. The HF may react with LiBF4 to give HBF4, which is very unstable and decomposes easily to HF and BF3 at a lower temperature than the decomposition temperature of LiBF4 itself. By comparison, a thermal study of a mixed salt electrolyte including LiPF 6 and LiN(SO2CF3)2 showed that the exothermic reaction of LiN(SO2CF3)2 with solvents is also influenced by HF produced in the reaction of LiPF6 with solvents but that the strength of the influence is small compared with its effect on an electrolyte mixture including LiBF4.",
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