Effect of doping ratio on lithium-ion conductivity in nanostructured self-doped block polymer electrolytes*

Self-doped polymers, in which the salt anions are attached covalently to the polymer, are promising alternatives to salt-doped polymer electrolytes because concentration polarization is reduced and stability is enhanced in the electrolyte. A self-doped diblock terpolymer electrolyte was synthesized such that one block was composed of a high modulus material and the other block consisted of both ion-conducting and self-doping monomer segments. The self-doped block polymers were made with a series of self-doped lithium concentrations (by altering the relative amounts of ion-conducting and self-doping monomer segments). Small-angle X-ray scattering results suggested that all self-doped block polymers exhibited ordered nanostructures. AC impedance spectroscopy and DC polarization were used to evaluate the conducting properties of the electrolyte (ionic conductivity and transference number), and the conductivities increased with self-doping ratio. Thus, with the framework for nanostructured self-doped block polymer electrolytes realized, the ion content can be manipulated to design improved electrolyte systems.