Improved Shelf Life and Energy Density in Nonaqueous Electrolyte-Based Supercapacitors

Supercapacitor devices have been fabricated by using poly-PHEN-C-900 (a carbonized product of the hypercrosslinked polymer of phenanthrene) using lithium perchlorate in adiponitrile as a nonaqueous electrolyte. A device designated as D-6 was fabricated when 5 mg of poly-PHEN-C-900 was coated in 2 × 2 cm2 on a graphite sheet current collector. 0.5 M lithium perchlorate in adiponitrile (0.5 M LiClO4/ADN) was used as the nonaqueous electrolyte. This device exhibited areal capacitance (Car) and specific capacitance (Csp) values of 463 mF cm–2 and 186 F g–1, respectively. The estimated areal (Ear) and specific (Esp) energy densities could reach as high as 505 μWh cm–2 and 201.9 Wh kg–1 with maximum areal (Par) and specific (Psp) power densities of 8.7 mW cm–2 and 7 kW kg–1, respectively. An unprecedented retention in the self-discharge voltage of 0.3 V even after 24 h has been observed in D-6 with high Coulombic efficiency (∼98–100%) and capacitance retention (85.7%) after 11,000 cycles, making it one of the most promising next-generation supercapacitor devices. The superior performance of the device could be attributed to the controlled textural properties of poly-PHEN-C-900 with adequate active sites that are compatible with the explored nonaqueous electrolyte.