Fabrication and basic investigation of flat lignocellulosic carbon material for self-supporting electrodes in electric double-layer capacitors

A novel flat, wood-based carbon material with heterogeneous pores, referred to as flat lignocellulosic carbon material (FLCM), was successfully fabricated by carbonizing samples of the softwood Picea jezoensis (Ezomatsu or Jezo spruce, a Japanese conifer). Simultaneous improvements of the specific surface area of the FLCM and the affinity of electric double-layer capacitor (EDLC) for electrolyte solvents were achieved by vacuum ultraviolet/ozone (VUV/O₃) treatment. The specific surface area of the VUV/O₃-treated FLCM showed a 50% increase over that of the original FLCM. The spectra measured by X-ray photoelectron spectroscopy (XPS) indicated that the number of O-C=O (carboxyl or ester) bonds increased, whereas the number of C-C bonds decreased. Additionally, the feasibility of using the FLCM as a self-supporting electrode in EDLCs was examined by measuring the electrochemical properties in a three-electrode system. The FLCM was confirmed as an appropriate self-supporting EDLC electrode material without warps and cracks. In addition, the FLCM can be used without any binder. Realization of FLCM-based EDLC electrodes with bendability, an area of several tens of square centimeters, and no risk of warp or crack formation, were indicated. Thus, FLCMs present a fascinating class of self-supporting carbon electrode materials for EDLCs.