Electrochemical performance of Na/NaFePO4 sodium-ion batteries with ionic liquid electrolytes

Nithinai Wongittharom, Tai Chou Lee, Chueh Han Wang, Yi Chen Wang, Jeng Kuei Chang

Research output: Contribution to journalArticlepeer-review

144 Scopus citations


Rechargeable Na/NaFePO4 cells with a sodium bis(trifluoromethanesulfonyl)imide (NaTFSI)-incorporated butylmethylpyrrolidinium (BMP)-TFSI ionic liquid (IL) electrolyte are demonstrated with an operation voltage of ∼3 V. High-performance NaFePO 4 cathode powder with an olivine crystal structure is prepared by chemical delithiation of LiFePO4 powder followed by electrochemical sodiation of FePO4. This IL electrolyte shows high thermal stability (>400 °C) and non-flammability, and is thus ideal for high-safety applications. The effects of NaTFSI concentration (0.1-1.0 M) on cell performance at 25 °C and 50 °C are studied. At 50 °C, an optimal capacity of 125 mA h g-1 (at 0.05 C) is found for NaFePO4 in a 0.5 M NaTFSI-incorporated IL electrolyte; moreover, 65% of this capacity can be retained when the charge-discharge rate increases to 1 C. This ratio (reflecting the rate capability) is higher than that found in a traditional organic electrolyte. With a 1 M NaTFSI-incorporated IL electrolyte, a 13% cell capacity loss after 100 charge-discharge cycles is measured at 50 °C, compared to the 38% observed in an organic electrolyte under the same conditions.

Original languageEnglish
Pages (from-to)5655-5661
Number of pages7
JournalJournal of Materials Chemistry A
Issue number16
StatePublished - 28 Apr 2014


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