Self-standing electrochemical double layer capacitors for operation in severe temperature conditions

Safe and ecological electrochemical double layer capacitors (EDLCs) are nowadays needed as energy sources for wearable electronics working in hard temperature conditions. Here, we report a method based on the use of an organic solvent without any surfactant to synthesize a self-supported paper-like electrode composed solely by multiwall carbon nanotubes, named buckypapers. Using an eutectic mixture of ionic liquids (1:1 in molar ratio), N -methyl- N -propylpiperidinium bis(fluorosulfonyl)imide and N -butyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide, as electrolyte, EDLCs based on buckypapers were assembled and tested up to 3 V. Ionic liquids are well known as green solvents for the environment and are safe for humans in their use thanks to their low vapor pressure. In addition to these problems of security solved, this electrolyte allows working in a wide temperature range, i.e. from −50 to +100 °C, delivering capacitances similar to those obtained in usual organic solvents.