Simultaneous Electronic and Ionic Conduction In Block Copolymers

Redox reactions occurring within battery electrodes require transport of both ions and electrons to the active centers. We report on the synthesis of a block copolymer, poly(3-hexyl thiophene)-b-poly (ethylene oxide) (P3HT-PEO), that exhibits simultaneous electronic and ionic conduction. Separate values of the electronic [(6.73±2.05) x 10^-6 S/cm] and ionic [(1.09±0.469) x 10^-4 S/cm] conductivity of a mixture of P3HT-PEO and a lithium salt were determined by a combination of AC impedance and DC techniques.  The P3HT-PEO/salt mixture was used to make lithium battery cathodes, with the active material LiFePO₄ as the only other component.  All-solid lithium batteries were assembled to demonstrate that the P3HT-PEO/salt mixture serves all of the transport and binding functions required in the cathode.  The semiconducting nature of P3HT enables using cell potential to control charge transport within the electrode.