Molten-salt directed mesopore engineering of carbon nanotubes for energetic quasi-solid-state supercapacitors

Polymer gel electrolytes have been actively employed in exploiting solid-state supercapacitors. However, the access to tiny pores of electrode materials is hindered by the sticky nature and sluggish ion transport of polymers. Consequently, supercapacitors usually present much lower capacitance in gel electrolytes than in liquid electrolytes. Here, we develop a molten-salt-directed mesopore engineering to design carbon nanotubes that are highly accessible to gel electrolytes. The rich mesopores, 12–15 nm in diameter and cross-linked, drastically facilitate the infilling of gel electrolytes into carbon nanotubes, leading to robust capacitive performance. Such mesoporous carbon nanotubes exhibit a high capacitance of 195.2 F g −1 in polyvinyl alcohol electrolyte and an ion diffusion coefficient of 2.8 × 10 −7 cm 2 s −1 , close to that in liquid electrolyte. Additionally, solid-state supercapacitors based on mesoporous carbon nanotubes exhibit a short relaxation time of 39 ms and a capacity retention of 93% over 10000 cycles, thus demonstrating their great potential in practical applications. • An efficient mesopore engineering strategy is developed in molten-salt medium. • Three synthetic routes have been designed to create different porous structure. • The mesoporous carbon nanotubes greatly promote the infilling of gel electrolyte. • The mesoporous carbon nanotubes exhibit a high capacitance in gel electrolyte. • The assembled solid-state supercapacitor shows a short relaxation time of 39 ms.