Copolymer from electropolymerization of thiophene and 3,4-ethylenedioxythiophene and its use as cathode for lithium ion battery

Electropolymerizations (EPs) of thiophene (Th), 3,4-ethylenedioxythiophene (EDOT) and the mixed monomers of Th and EDOT in 0.05 M Et₄NClO₄/propylene carbonate (PC) solution were performed to prepare polymer films as potential cathode materials in lithium ion battery. The incorporation of EDOT units into pure polythiophene (PTh) chain leads to large alternations on the experimental conditions of EPs and the properties of the resulting polymer films. Onset potential of the EPs was reduced with the participation of EDOT component. The resulting polymers, PTh, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(thiophene-co-3,4-ethylenedioxythiophene) (PTh-EDOT) were then served as cathode materials to test their capabilities to transport lithium ion in 1.0 M LiPF₆/ethylene carbonate/dimethyl carbonate solution. With the inherent EDOT unit, PEDOT and PTh-EDOT have better charge capacity, stability and response rate than pure PTh. Among the copolymers, PTh-EDOT (1/1) even shows better stability than pure PEDOT homopolymer, advantage of using EDOT as copolymer component is thus evaluated.