On the use of LiPF3(CF2CF3)3 (LiFAP) solutions for Li-ion batteries. Electrochemical and thermal studies

J. S. Gnanaraj, E. Zinigrad, L. Asraf, M. Sprecher, H. E. Gottlieb, W. Geissler, M. Schmidt, D. Aurbach*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations

Abstract

Electrolyte solutions comprising a mixture of LiPF6 and LiPF3(CF2CF3)3 (LiFAP) in alkyl carbonates (ethylene, dimethyl and diethyl carbonate) were found to be superior to single salt LiFAP or LiPF6 solutions for lithium-graphite anodes at elevated temperatures. Graphite electrodes could be cycled (Li insertion-deinsertion) more than hundred times at 80 °C with high and stable capacity in the two-salt solutions, while in the single-salt solutions this was impossible. Preliminary studies by voltammetry and impedance spectroscopy indicate that the combination of the two salts in solution has a unique influence on the electrodes surface (not yet defined). Thermal studies by accelerating rate and differential scanning calorimetry show that thermal decomposition of LiFAP solutions has a higher onset, but very high heat and pressure developing rates, compared to LiPF6 solutions. The presence of LiPF6 in LiFAP solutions decreased their self-heating and pressure-developing rates pronouncedly. From product analysis of the thermal reactions by NMR, FTIR and MS, we can suggest possible unique bulk reactions that occur in LiPF6-LiFAP solutions. One of these is a nucleophilic reaction between F- and PF3(CF2CF 3)3-, which may neutralize the effect of trace HF in solutions (thus forming new P-F bonds and HCF2CF3). Such a reaction should have a positive effect on both the performance of the Li-graphite electrodes and the thermal behavior of the solutions.

Original languageAmerican English
Pages (from-to)946-951
Number of pages6
JournalElectrochemistry Communications
Volume5
Issue number11
DOIs
StatePublished - Nov 2003
Externally publishedYes

Bibliographical note

Funding Information:
This work was partially supported by the BMBF, the German Ministry of Science, in the framework of the DIP program for Collaboration between Israeli and German Scientists.

Keywords

  • Accelerating rate calorimetry
  • Alkyl carbonate solutions
  • DEC
  • DMC
  • Differential scanning calorimetry
  • EC
  • FTIR
  • LiPF
  • LiPF(CFCF) (LiFAP)
  • Thermal stability

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