Solid Polymer Electrolytes with High Lithium Ion Conductivity and Transport Number for Hybrid Electric Power-train Systems

Current energy storage devices have energy densities that are barely sufficient for low cost electric-vehicles and rely on lithium ion batteries that use flammable, unsafe, liquid electrolytes. However, in order to replace liquid electrolyes in lithium batteries for hybrid electric power train systems, solid polymer electrolytes, which have the advantages of safety and flexibility, must attain conductivities of & gt; 10-3 S/cm. To date, solid polymer electrolytes with good mechanical properties and conductivities of even 10-4 S/cm have not been achieved. Using newly developed multi-ionic POSS-based lithium salts in which the Si-O-Li are replaced with Si-O-BF3Li groups, solid polymer electrolytes with ionic conductivities & gt; 10-3 S/cm will be prepared. The electron withdrawing POSS cage and BF3 groups promote dissociation of the Li+ ions. The salts are Janus-like structures in which one end contains the ionic moieties and the other end contains hydrophobic phenyl groups. When blended with polymers such as polyethylene oxide (PEO), the hydrophobic groups cluster/crystallize and the Li+ ions are solvated by the polar ethylene oxide units. In preliminary studies, the PEO was amorphous although the solid polymer electrolyte was a hard solid until ~ 120 oC, and room temperature conductivities reached 4 x 10-4 S/cm. The solid structure was suggested to be the result of crosslinks arising from Si-O-BFs Li+ (O-CH2CH2) sites, with the PEO chains linking different phenyl clusters. In order to further improve conductivities, POSS-based lithium salts will be synthesized with varying ratios of Li/phenyl groups.