Indirect Synthesis Route toward Cross-Coupled Polymers for High Voltage Organic Positive Electrodes

Cross-coupling polymerization using Ni(COD)2 is a simple method to obtain redox active polymers. It requires readily available dihalogenated quinones as starting compounds. In this article, we propose a new synthesis route to obtain a high voltage redox active polymer, poly(9,10-phenanthrenequinone) (PFQ), as a positive electrode material, because direct polymerization with Ni(COD)2 cannot be used for synthesis of high voltage quinone polymers. Thus, we protected the quinone groups with acetyl groups before polymerization reaction, developing an indirect synthesis route. As a positive electrode material in a lithium battery, PFQ shows 400 mV higher voltage (2.54 V vs Li/Li+) compared to the more known para counterparts, due to the ortho quinone structure. PFQ was tested in several electrolytes, and the best performance was obtained in 1 M trifluoromethanesulfonimide lithium salt dissolved in a mixture of 1,3-dioxolane and dimethoxyethane (1 M LiTFSI/DOL+DME). Furthermore, PFQ redox utilization was improved by the addition of reduced graphene oxide (rGO) during polymerization (PFQ/rGO) to obtain 153 mAh/g of specific capacity. The PFQ/rGO composite showed very good capacity retention; 91% of starting capacity was retained after 500 cycles at C/5 coupled with good rate capability.