Tuning the Azo Location in Conjugated Polymers Toward High-Performance Lithium-Ion Batteries

Redox-active pi-conjugated polymers exhibit great potential in energy storage applications. However, how the location of redox-active sites affects the electrochemistry and battery performance remains elusive. In this study, three isomeric conjugated polymers with redox-active azo units linked with thiophene were designed and synthesized. The impact of the location of azo units (para vs meta linkage, main chain vs side chain) in the conjugated polymers on the properties of electro-chemistry and battery performance were systematically studied. Experimental and theoretical studies clearly demonstrate that "redox-pendant" and "meta junction" are two effective features to design redox-conjugated polymers for high-performance energy storage. By merging the two features, the polymer exhibits a high azo utilization of close to 100% and displays the highest specific capacity of 215 mAh g-1 at 0.1 A g-1, along with a long and flat charge/ discharge plateau appearing at 1.7 V. Moreover, the as-fabricated full battery using polymers with such a design as the anode coupled with LiFePO4 or LiCoO2 as the cathode delivers satisfactory discharge specific capacities of 110 and 95 mA h g-1 at 0.1 A g-1, along with output voltages of 1.9 and 2.3 V, respectively. The practical application of the full battery to power an LED bulb was also demonstrated. The present study provides useful insights into the tuning of the structures for high-performance batteries.