Enhanced Lithium-Ion Conductivity in Single-ion Conducting Polyelectrolytes with Low-T_g Zwitterion Addition

To achieve high conductivity in single-ion conducting polymer electrolytes (SIPEs), we strategized to add zwitterionic compounds owing to their very high dipole moment. When the zwitterions have lower T_g than the SIPE, the zwitterions can also act as plasticizers. Therefore, in this research, two novel low-T_g imidazole-based zwitterions with different anions (sulfonate and trifluoromethane sulfonimide (TFSI)) were synthesized. The addition of either zwitterion significantly increases the ionic conductivity of the SIPE, and a 100X increase in conductivity has been achieved by the addition of the TFSI-containing zwitterion. The origin of the conductivity enhancement of the two zwitterion-containing SIPEs was systematically investigated using broadband dielectric spectroscopy, rheology, X-ray scattering and density functional theory calculations.