Organic Solvents Containing Zwitterion as Electrolyte for Li Ion Cells

Abstract

Imidazolium based zwitterions, 1,2-dimethylimidazolium-3-n-propanesulfonate (DMIm-3S) and 1-Butylimidazolium-3-n-butanesulphonate (BIm-4S), were synthesized, and utilized them as additive for Li ion cell comprising of graphite anode and LiCoO2 cathode. The use of 10 wt% of DMIm-3S in 1 M LiPF6, Ec-EMC-DMC (1:1:1 (v/v)) resulted in the increased high rate charge-discharge performance. The low temperature performance of the Li ion cells at about -20 degrees C was also enhanced by these zwitterion additives. The DMIm-3S additive resulted in the better capacity retention by the Li-ion cells even after 120 cycles with 100% depth of discharge (DOD) at 1 C rate in room temperature. Surface morphology of both graphite and LiCoO2 electrode before and after 300 cycles was studied by scanning electron microscopy. An analogous study was performed using liquid electrolyte without any additive.