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 (C_ar) and specific capacitance (C_sp) values of 463 mF cm^–2 and 186 F g^–1, respectively. The estimated areal (E_ar) and specific (E_sp) energy densities could reach as high as 505 μWh cm^–2 and 201.9 Wh kg^–1 with maximum areal (P_ar) and specific (P_sp) 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.