Simultaneous electron- and ion-conducting polymeric binders for battery electrodes offer a multifunctional alternative to commonly used poly(vinylidene fluoride). Besides mechanically binding and "gluing" the various electrode components together, the multifunctional polymeric binder also offers conductivity and redox activity. One example is P3HT-b-PEO, which conducts electrons and ions in the P3HT and PEO domains, respectively, and the P3HT stores charge by doping and dedoping. Here, the effect of the block copolymer loading and morphology on the redox activity of a V2O5 Li-ion battery cathode will be presented. The synergistic mechanism by which the binder improves the V2O5 performance is analyzed in two aspects: chemical and mechanical. In the first, it is quantitatively shown that the P3HT block contributes to the redox activity. In the second aspect, it is shown that the block copolymer prevents cracking and pulverization of the V2O5 electrode after prolonged cycling. Also, conjugated P3HT has been extensively studied for various solid state applications (e.g., photovoltaic cells, field-effect transistors, and light-emitting diodes), where the performance is strongly affected by regioregularity and molecular weight. However, in electrochemical systems such as in batteries, the effects of regioregularity and molecular weight on the charge storage performance are not understood for P3HT-b-PEO. Here, by comparing different P3HT-b-PEO block copolymers of varying P3HT regioregularity (86-97%) and molecular weight (8-19 kDa), a strong correlation between regioregularity and molecular weight with electrochemical properties (i.e., capacity, and redox potential) is demonstrated. It is shown that the charge storage capacity of P3HT-b-PEO significantly increases with increasing regioregularity. The redox potential increases with decreasing molecular weight. The changes in capacity and redox potential are attributed to P3HT’s backbone conformation, planarity, and chain packing.

Electron- and ion-conducting block copolymers as binders for battery cathodes

256th National Meeting (2018)

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