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

Highlights: ► LiTFSI–PP14TFSI–P(VdF-HFP) ionic liquid gel polymer electrolyte with a 3-dimensional network structure. ► The electrolyte can be stable at 80 °C in Li/LiFePO4 batteries. ► After 100 cycles, the discharge capacity is 131.01 mAh g−1 at 60 °C, 1C current rate, with 90% capacity retention. - Abstract: 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)–LiTFSI polymer electrolyte leads to 3-dimensional network structures, and the ILGPE is stable below 150 °C and will not decompose until 310 °C without considering the volatilizing of the residual solvent. The ionic conductivity increases with the temperature rising, and the ionic conductivity is 0.23 × 10−3 S cm−1 and 2.1 × 10−3 S cm−1 at 20 °C and 80 °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 °C when operated in Li/LiFePO4 batteries, and Li/LiFePO4 batteries with the gel polymer electrolyte exhibit good cycling performance at 60 °C at 1C current rate. The discharge capacity was 131.01 mAh g−1 after 100 cycles with 90% capacity retention.