Ion/electron mixed conductors based on polymer electrolytes

Abstract

This paper demonstrates that ion/electron mixed conductors (redox conductors) based on polymer electrolytes can be obtained by incorporating redox molecules into ion-conducting polymer phases. The incorporation has been attained by simple dissolution of redox molecules into polymer electrolytes and by copolymerization of a redox monomer with an ion-conducting monomer. The former examples are the poly(ethylene oxide) (PEO) networks in which LiTCNQ and LiClO 4 are dissolved, and the latter examples are the copolymers of vinylferrocene and methoxy-nona(ethylene oxide)methacrylate in which LiClO 4 is dissolved. Oxidation of TCNQ − in the PEO networks occurs via both of physical diffusion of TCNQ − toward the electrode and the electron self exchange between TCNQ − and TCNQ 0 in the diffusion layer. The electron diffusivity at 42°C is 10 −9–10 −8cm 2 s −1, linearly increases with increasing LiTCNQ concentration, and surpasses the physical diffusivity at [LiTCNQ] = 0.05 M. Reversible redox reaction of ferrocene sites occurs in the copolymers where the ferrocene sites are covalently fixed to the polymer backbone and can not largely diffuse. The redox reaction is caused by the electron hopping (redox conduction). The electron diffusivity at 40°C is estimated at ca 10 −10 cm 2 s −1.