Organic solvents containing zwitterion as electrolyte for Li ion cells

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-EMCDMC (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 °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.