All‐in‐one Biomass‐Based Flexible Supercapacitors with High Rate Performance and High Energy Density

Abstract Taking advantage of the unique structure and properties of gramineous straw that are available across the world in a yearly scale of several hundred million tons, a strategy to design and fabricate flexible high‐performance supercapacitors (SCs) is developed, of which the key components including electrode, separator, and electrolyte are all made from the eulaliopsis binata (EB), a ubiquitous gramineous straw. This kind of all‐in‐one biomass‐based flexible supercapacitors (BFSs) is first proposed, with the cuticle‐derived fibers (EBMs) as a separator, the pith‐derived carbon sponges (EBCs) as an electrode, and the sodium salts of the extracted carboxymethyl cellulose as gel electrolyte. The EBM with uniform diameter size, developed porosity, and abundant ‐OH/‐COOH groups have good flexibility, wettability, and ionic conductivity, far exceeding those of commercial glass‐fiber separators. The EBC has a high level of N/O/S co‐doping and hierarchical porous structure, resulting in enhanced ion accessibility and supercapacitance. With these advantages, the as‐fabricated BFS has shown ultra‐high‐rate performance, high energy density, and excellent flexibility, surpassing the biomass‐derived flexible supercapacitors reported thus far. This novel approach will shed light on the value‐added utilization of biomass from the viewpoint of molecular chemical engineering and product engineering and pave the way for fabricating flexible high‐performance SCs and beyond.