Facile Polymer/Carbon Electrodes Fabrication for Low-Cost, High-Energy Supercapacitors

Due to their potential for combined high power and high energy, supercapacitors provide exciting opportunities for future energy storage systems. Limitations in material performance and processing must be overcome to achieve large-scale manufacturing and utilization. Activated carbon has found application in supercapacitors due to its large surface area and chemical stability, however their energy density is limited by their electrochemical double layer capacitance, which depends on surface area. Conducting polymers (CPs), on the other hand, can store charge through Faradaic processes, which allows more efficient material utilization. Commercial application requires advances in continuous manufacturing methods and material performance, including cycle stability, charge capacity and operating potential.

In the past decade, research on CPs has focused on achieving nanostructured electrodes by modifying the synthesis processes to increase mechanical, electrical and electrochemical properties. An alternative is to incorporate a complementary material to reinforce the polymer structure, and carbon nanotubes (CNTs) provide a suitable option due to their superior mechanical properties, electronic conductivity and chemical stability. Composite materials can be engineered with CPs and CNTs to achieve significant property enhancement. The combination of conducting polymers with carbon materials has been studied in the past to enable the use of CPs in commercial supercapacitors, by making electrode material more stable, lighter, stronger and tougher. CNTs improve the cycle life and mechanical properties of CP since they can adapt easily to changes in volume, and also introduce new electronic properties based on interactions between the two compounds. On the other hand, CPs enhance the charge storage capacity and capacitance of CNT materials and can help overcome their bundling and aggregation.

In this work, we prepared free-standing CNTs/CP composite electrodes in a fast and scalable process by dispersing CNTs and CPs in suspension, filtering the mixture through a membrane and peeling off the dried filtrate. This process eliminates the need for a binder, substrate or additional processing and pressing, which can affect the properties of the material. These composite electrodes showed specific capacitances as high as 366 F/g. CNTs work well as both anode and cathode materials for supercapacitor devices due to their wide potential stability, and when combined with the appropriate redox polymer, high performances can be obtained. Asymmetric CNTs/CP supercapacitor cells fabricated with polymer-CNT cathodes and anodes exhibited high power and high energy densities, especially when compared to pure CNT and good cycling stability. Given the process simplicity, relatively low cost and high throughput, the present composites have great potential for large-scale CP/CNTs supercapacitor production.