Electrochemical performance of rechargeable Li/LiFePO4 cells with ionic liquid electrolyte: Effects of Li salt at 25 °c and 50 °c

Nithinai Wongittharom, Tai Chou Lee*, Ching Hua Hsu, George Ting-Kuo Fey, Kai Pin Huang, Jeng-Kuei Chang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are used as Li salts in butylmethylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (BMP-TFSI) ionic liquid (IL) electrolyte for Li/LiFePO4 cells. This kind of IL electrolyte shows high thermal stability (>400 C) and non-flammability, and is thus ideal for high-safety applications. At 25 C, a maximum capacity of 113 mAh g-1 (at 0.1 C) is found for LiFePO4 in the IL with 0.5 M LiTFSI. An excessive LiTFSI concentration leads to a capacity decrease due to reduced electrolyte ionic conductivity. At 50 C, the measured capacity and rate capability are significantly improved compared to those at 25 C. With 1 M LiTFSI-doped IL electrolyte (the optimum concentration at 50 C), a capacity of 140 mAh g-1 is found at 0.1 C and 45% of the capacity can be retained when the rate increases to 5 C, values which are comparable to those found in a traditional organic electrolyte. In the IL electrolyte, the LiFePO4 electrode shows better cyclic stability at 50 C than it does at 25 C; this trend is opposite to that found in the organic electrolyte. At 50 C, there is negligible capacity loss of LiFePO4 after 100 charge-discharge cycles in 1 M LiTFSI-doped BMP-TFSI IL electrolyte.

Original languageEnglish
Pages (from-to)676-682
Number of pages7
JournalJournal of Power Sources
Volume240
DOIs
StatePublished - 14 Jun 2013

Keywords

  • Electrolyte
  • Ionic liquid
  • Li battery
  • Li salt
  • Temperature

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