An isotropic high-density graphite was used as a polarizable electrode of all-solid state electric double-layer capacitor using polyethylene oxide (PEO) or gel PEO electrolyte. The all-solid-state capacitor with high-density graphite electrodes possesses higher differential capacity than the other flat electrodes in PEO/LiClO4 ([EO]/[Li+] = 8:1) solid polymer electrolyte at 80°C or PEO/PC/LiClO4 ([EO]/[PC]/[Li+] = 8:8:1) gel electrolyte at ambient temperature. The capacitance of the electric double layer of the high-density graphite electrode was strongly influenced by the cell temperature and concentration of LiClO4, because of the different state of the polymer crystallinity and different interface contact state between the high-density graphite electrode and the solid electrolyte. The all-solid-state capacitor with PEO/LiClO4 ([EO]/[Li+] = 8:1) solid polymer electrolyte and PEO/PC/LiClO4 ([EO]/[PC]/[Li+] = 8:8:1) gel electrolytes showed good charge/discharge behavior with a relatively high capacitance at 80 and 20°C, respectively.
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