Recent progresses in the synthesis and strategic designs of sustainable carbon-based fibrous electrodes for flexible batteries

Electrochemical energy storage devices, such as rechargeable batteries and supercapacitors, have replaced conventional batteries and dielectric capacitors owing to their excellent charge storage abilities and other electrochemical performances. However, a major challenge exists in terms of their flexibility in application because most of the rechargeable batteries and supercapacitors available commercially are rigid and hence cannot be used in wearable electronic applications. The flexibility of the devices is mainly imparted by electrodes; hence, the preparation of electrodes is of utmost importance in determining their flexibility. During the fabrication of electrodes, electrode-active materials are coated over an electrically conducting substratum and it is further used as a current collector for the electrodes. The electrodes are flexible if the substratum used is flexible. In this respect, carbon fibers (CFs) have evolved as a suitable and sustainable substratum for the preparation of electrodes for rechargeable batteries to power flexible electronic devices. Micron-sized or nano-sized CFs are invariably used as substrata; hence, flexibility can easily be imparted to the devices assembled. This review outlines the development of rechargeable batteries manufactured from different electrode-active materials coated over this CF substratum. This article provides an in-depth insight into the preparation of flexible electrodes for rechargeable batteries, particularly for application in wearable electronics.