Fast cycling of Li/LiCoO2 cell with low-viscosity ionic liquids based on bis(fluorosulfonyl)imide [FSI]

A charge-discharge cycling test of a Li/LiCoO2 cell containing ionic liquids based on bis(fluorosulfonyl)imide ([FSI]-) as the electrolyte media, revealed significantly better rate properties compared to those of cells using conventional ionic liquids. The use of an 1-ethyl-3-methylimidazolium (EMI+) salt permitted the retention of 70% of the discharge capacity at a 4C current rate. In contrast, similar performance of cells containing N-methyl-N-propylpyrrolidinium (Py13+) and N-methyl-N-propylpiperidinium (PP13+) salts of [FSI]- was limited to operation at 2 and 1C current rates, respectively. However, the charge/discharge cycling stability of the cell with Py13[FSI] was much better than that of the cell using EMI[FSI].