Pyrrolinium-based ionic liquids as electrolytes at high temperature for LiFePO4 cells of lithium ion batteries

Abstract

Due to their unusual sets of properties, ionic liquids (ILs) have many important applications in many field. Above all the advantages of ILs, the superior high temperature characteristics provide a appropriate solution to high temperature electrolyte problems related with device internal pressure build-up, corrosion, and thermal stability. Our group have been reported characteristics of different kinds of ionic liquids (ILs)bis(trifluoromethanesulfonyl)imide (TFSI) include in imidazolium, ammonium, pyrrolidinium and piperidinium based compounds. Several research trials have contributed to develop the novel pyrrolinium based ionic liquid which is containing heteroatom substituent such as ether moiety have affirmative effect on cathodic stability, viscosity and ionic conductivity. In addition to this, the plane structure caused higher conductivity different with pyrrolidinium and piperidinium based ILs. With this target ILs, we measured the function of the lithium salt concentration to influence on the conductivity that has been studied with carbonate. The E(OMe)Pyrl-FSI(6) and P(OMe)Pyrl-FSI(7) A(OMe)Pyrl-FSI(8) had the highest conductivity of 6.56 mS/cm , 4.69 mS/cm and 5.91 mS/cm at 0.5 M / 0.8 M LiTFSI which were described higher than values of ILs including 1 M salt concentration. Gratifyingly we expected, they not only presented better discharge capacity than other ILs had 1.0 M lithium salt concentration but these results were performed at 1 C rate. We envisaged that these ILs transcend the barrier of the carbonate electrochemical property is known as the superior electrolyte until now. The thermal stability is the remarkable property of the ILs as mentioned and we embarked on the comparison of cycling performance with carbonate at high temperature. The results was same as we expected that ILs could have prominent cycle life and discharge capacity, specially the result of P(OMe)Pyrl-FSI 0.5 M LiTFSI and A(OMe)Pyrl-FSI 0.8 M LiTFSI stands out clearly. As the result of analysis of electrolyte after reaction, decomposition rate led to the value of the discharge capacity which is why the previous ILs with lower decomposition rate had higher discharge capacity.