Improving Cycling Performance of LiMn2O4 Battery by Adding an Ester-Functionalized Ionic Liquid to Electrolyte

Addressing capacity fading during electrochemical cycling is one of the most challenging issues of lithium-ion batteries based on LiMn2O4. Accordingly, in this work, an ester-functionalized ionic liquid, N-methylpyrrolidinium-N-acetate bis (trifluoromethylsulfonyl) imide ([MMEPyr][TFSI]), was designed as an additive to the electrolyte employed for Li/LiMn2O4 batteries to improve their electrochemical performance. A systematic comparative study was carried out using the LiTFSI-based electrolyte with and without [MMEPyr][TFSI] additive. After 100 cycles, the Li/LiMn2O4 half-cells retained 94% of their initial discharge capacity in the electrolyte containing 10 wt-% [MMEPyr][TFSI]. However, the cycling capacity of the half-cells in the electrolyte without [MMEPyr][TFSI] decreased considerably to, similar to 21 mAhg(-1) within the first 10 cycles. One of the main reasons for the decrease is the stabilization of the Al current collector by the [MMEPyr][TFSI] additive, as demonstrated by scanning electron microscopy, cyclic voltammetry, and Fourier transform infrared spectroscopy. Moreover, the Li/LiMn2O4 cells in the electrolyte containing [MMEPyr][TFSI] displayed high-rate performance, whereby similar to 90% of the cell initial discharge capacity was retained at 2.5C.