Application of bis(trifluoromethanesulfonyl)imide lithium-N-methyl-N-butylpiperidinium-bis(trifluoromethanesulfonyl)imide-poly(vinylidene difluoride-co-hexafluoropropylene) ionic liquid gel polymer electrolytes in Li/LiFePO4 batteries at different temperatures

Ionic liquid gel polymer electrolyte (ILGPE) based on N-methyl-N-butylpiperidinium-bis(trifluoromethanesulfonyl)imide (PP14TFSI), bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI) and poly(vinylidene difluoride-co-hexafluoropropylene) (P(VdF-HFP)) is prepared for lithium ion batteries by solution casting. The ILGPE is characterized by scanning electron microscopy (SEM), thermogravimetry (TG) and electrochemical tests. The results indicate that the addition of PP14TFSI to the P(VdF-HFP)-LiTESI polymer electrolyte leads to 3-dimensional network structures, and the ILGPE is stable below 150 degrees C and will not decompose until 310 degrees C without considering the volatilizing of the residual solvent. The ionic conductivity increases with the temperature rising, and the ionic conductivity is 0.23 x 10(-3) S cm(-1) and 2.1 x 10(-3) S cm(-1) at 20 degrees C and 80 degrees C, respectively. The electrochemical window is -0.15 to 4.85 V vs. Li+/Li, which is wide enough to be used with common electrode materials. Battery tests show that the ILGPE is stable even at 80 degrees C when operated in Li/LiFePO4 batteries, and Li/LiFePO4 batteries with the gel polymer electrolyte exhibit good cycling performance at 60 degrees C at 1C current rate. The discharge capacity was 131.01 mAh g(-1) after 100 cycles with 90% capacity retention. (C) 2012 Elsevier Ltd. All rights reserved.