UC Berkeley

Conducting polymers such as poly(3-hexylthiophene) (P3HT) can be used to convey electronic charge in battery electrodes. The electronic conductivity of P3HT (and other electronically conducting polymers) is potential-dependent. The main advance in this work is to quantify the effect of this potential dependency on battery performance. The discharge characteristics of a battery consisting of a cathode with LiFePO4 particles in a poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) copolymer matrix that conveys electrons and ions to the active particles, a polystyrene-b-poly(ethylene oxide) (PS-PEO) copolymer electrolyte layer, and a lithium metal anode were examined by experiments and macro-homogeneous modeling; lithium bis (trifluoromethanesulfonyl) imide was the salt in the cathode and the electrolyte. By comparing the model predictions with experiments, we conclude that the electronic conductivity of the polymer in the cathode is significantly lower than that obtained from measurements in the absence of active particles. The potential-dependent conductivity is manifested in the shape of the discharge curve wherein the slope increases continuously with capacity. The model provides insight into the underpinnings of the observed rate-dependency of electrode capacity, thereby guiding the design of the next generation of electrodes.