Nanocellulose enabled all-nanofiber, high performance supercapacitor.

Nanocellulose has emerged as a promising sustainable nanomaterial for constructing advanced electrochemical energy storage systems with renewability, lightweight, flexibility, high performance, and good safety. Here, we demonstrate a high-performance all-nanofiber asymmetric supercapacitor (ASC) using a forest-based, nanocellulose-derived hierarchical porous carbon (nanocellulose-carbon, HPC) anode, a mesoporous nanocellulose membrane separator (nanocellulose-separator) and a NiCo2O4 cathode with nanocellulose carbon as support matrix (nanocellulose-cathode, HPC/NiCo2O4). Nanocellulose-carbon possesses a three-dimensional (3D) porous structure comprised of interconnected nanofibers with an ultrahigh surface area of 2046 m2 g-1. When combined with the mesoporous structure of the nanocellulose membrane separator, these properties facilitate both the fast transport of ions and electrons even with thick (up to several hundreds of micrometres) and highly-loaded (up to 5.8 mg cm-2) ASC design. Consequently, the all-nanofiber ASC demonstrates a high electrochemical performance (64.83 F g-1 or 10.84 F cm-3 at 0.25 A g-1 and 32.78 F g-1 or 5.48 F cm-3 at 4 A g-1) that surpasses most cellulose-based ASCs ever reported. Moreover, the nanocellulose components promise renewability, low cost, and biodegradability, thereby representing a promising direction toward high-power, environmentally friendly, and renewable energy storage devices that are not limited to supercapacitors.