Abstract:

The increased demand for high-performance supercapacitors has fueled the development of electrode materials. As an important part of supercapacitors, the electrochemical performance of the supercapacitor is directly affected by the specific surface area, conductivity, electrochemical activity, and stability of electrode materials. In the traditional manufacturing method, a binder must be added to powdered electrode materials to enhance their combination with the current collector, which could lead to morphology damage, pore blockage, and reduced conductivity of active materials that will adversely affect their electrochemical behavior. Thus, research on binder-free electrode materials has attracted significant interest. Recently, electrospun nanofibers have been widely used as supercapacitor electrode materials because of their advantages such as large specific surface area, high porosity, and easy preparation. The attainable continuity and flexibility endow electrospun nanofiber membranes outstanding performance among large numbers of binder-free materials. This review considers recent studies on electrospun nanofiber-based binder-free electrode materials for supercapacitors, including carbon nanofibers, carbon-based composite nanofibers, conductive polymer-based composite nanofibers, and metal oxide nanofibers. These studies demonstrate that pore structure construction, activation treatment, and nitrogen doping can improve the specific surface area, electrochemical activity, wettability, and graphitization degree of carbon nanofibers to enhance their electrochemical properties. Moreover, combining carbon nanofibers with metal oxides, metal sulfides, metal carbides, and conductive polymers by methods such as blending, chemical deposition, electrochemical deposition, etc., can improve their capacitance, rate performance, and cycling stabilities, which complement the advantages of different materials and proves that the performance of multicomponent materials is better than that of single-component materials. In particular, conductive polymers based on composite nanofibers and metal oxide nanofibers can be used as binder-free materials by electrospinning technology, but their dependence on other substances as well as fragile fiber membrane limit their widespread application. Therefore, in order to ensure the continuity or flexibility of fiber membranes, carbon-based composite nanofibers with multicomponent and hierarchical structure could potentially be used/constructed as binder-free electrode materials. Combinations with new types of electrode materials such as metal-organic frameworks (MOF), covalent organic frameworks (COF), MXenes, metal nitride, metal phosphide, etc., and the preparation of materials with novel structures have also been attempted. In order to realize the practical application of eletrospun nanofiber-based binder-free electrode materials, more attention should be given to improving their mechanical properties, production efficiency, and research on the application of flexible devices. We hope that this review can broaden ideas for improving the development and application of electrospun nanofiber-based binder-free electrode materials for high-performance supercapacitors.

Key words: Supercapacitor, Binder-free, Electrospinning, Nanofiber, Electrode material