Lithium-Ion Transport in Polymer Electrolytes with Ion Clusters

Li-ion batteries based on organic liquid electrolytes have been commercialized for decades. However, the flammability of the liquid electrolyte and propensity for reaction with metallic lithium anodes warrants the study of alternative electrolyte materials to satisfy modern demands such as higher safety and energy density. Polymer electrolytes are non-flammable, processable, and more inert towards lithium metal and electrochemical side reactions. But ionic conductivity in common polymer electrolytes, such as poly(ethylene oxide)-based polymer electrolytes, is limited by the segmental relaxation of the polymer matrix that is solvating the lithium cation. Recently, metal-ion containing polymers with regulated, repeating chain architecture have drawn attention as ion conductors due to their ionic domain segregation. In this dissertation, a new type of single-ion polymer electrolytes without solvating functions have been developed. They can form various ionic phase morphology like hexagonal and layered. Their ionic conductivity of the material bulk transport is coupled with α relaxation while in-cluster transport is decoupled with α relaxation or ionic cluster rearrangements. The in-cluster transport rate is much faster than the bulk transport rate because of the difference in transfer mechanisms. The in-cluster transport is supported by lowered potential barrier as a result of Coulombic interactions and disordered defects. A new design rule of polymer electrolyte has been elucidated for achieving highly conductive and mechanical stiff properties.