A novel ionic liquid for Li ion batteries-uniting the advantages of guanidinium and piperidinium cations

We report on the synthesis and the properties of N,N,N′,N′- tetramethyl-N′′,N′′-pentamethyleneguanidinium bis(trifluoromethylsulfonyl)imide (PipGuan-TFSI). The cation of this novel ionic liquid combines guanidinium and piperidinium structural elements. We tested it for its viscosity, ion conductivity, and also for its thermal and electrochemical stability. Furthermore, a 0.5 M solution of lithium TFSI in PipGuan-TFSI was tested as an electrolyte for Li-ion batteries. These experiments included cycles of Li deposition/dissolution on stainless steel and (de)intercalation into/from LiFePO₄ electrodes. The tests involving LiFePO₄ cathodes were performed at various C-rates and temperatures for a better quantitative comparison to other electrolyte systems. We discuss in how far PipGuan-TFSI successfully combines the advantages of guanidinium and piperidinium ionic liquids for battery electrolyte applications. © 2014 The Royal Society of Chemistry.