Improved properties of polymer electrolyte by ionic liquid PP1.3TFSI for secondary lithium ion battery

A new kind of polymer electrolyte is prepared from N-methyl-N- propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP1.3TFSI), polyethylene oxide (PEO), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). IR and X-ray diffraction results demonstrate that the addition of ionic liquid decreases the crystallization of PEO. Thermal and electrochemical properties have been tested for the solid polymer electrolytes, the addition of the room temperature molten salt PP1.3TFSI to the conventional P(EO) ₂₀LiTFSI polymer electrolyte leads to the improvement of the thermal stability and the ionic conductivity (x=1.27, 2.06×10 ^-4 S cm ^-1 at room temperature), and the reasonable lithium transference number is also obtained. The Li/ LiFePO4 cell using this polymer electrolyte shows promising reversible capacity, 120 mAh g ^-1 at room temperature and 164 mAh g ^-1 at 55 °C.