Flexible and internal series-connected supercapacitors with high working voltage using ultralight porous carbon nanofilms

Highly flexible carbon nanofibers with hierarchical nanostructure, which provide an excellent distribution of differently functionalized-carbon nanotubes and terephthalic acid, were prepared cost-effectively and demonstrated as binder-free electrodes. Symmetric solid-state supercapacitors were then fabricated and could be operated reversibly in the voltage range of 0–1.8 V with excellent electrochemical performance due to the hierarchical porosity and hybrid architecture. Furthermore, internal series-connected supercapacitors based on the prepared porous carbon nanofibers were designed and fabricated. Such supercapacitors were found to be flexible enough to be rolled up or twisted with constant capacitive performance at a high working voltage of up to 3.6 V and exhibited a 38.9% increase in energy density than that of the single-cell supercapacitor. This one-step approach leads to simplicity of operation and economical efficiency for fabricating lightweight supercapacitors with high working voltage and energy density, which may be beneficial for the development of flexible and wearable energy storage devices.