▎ 摘　　要

The effect of solvent on specific capacitance, bulk resistance, and charge/discharge capacity of graphene/polyimide composite films is studied by electrochemical methods. Composite films are synthesized by in situ condensation polymerization of poly (amic acid) in the presence of 50 wt % partly exfoliated graphene sheets followed by thermal curing at 250 degrees C. Raman spectrum of the exfoliated graphene sheets show an increase in the ratio of I-D to I-G peak intensities from 0.167 to 0.222, suggesting increased defects in graphene basal planes. Electrochemical measurements carried out by using 0.4M potassium hexafluorophosphate (KPF6) dissolved in propylene carbonate and N-methylpyrrolidone at 25 degrees C show that the composite system exhibits both pseudocapacitance and supercapacitance behaviors, with an average capacitance of 40 and 36.5 F g(-1), respectively. Bulk resistance of the composite obtained by using KPF6-propylene carbonate electrolyte solution is 300% lower than that obtained in KPF6-N-methylpyrrolidone solution, with a fairly stable specific capacity of 85 mu Ahr g(-1), with 80% retention observed after 30 charge-discharge cycles. Fourier transform infrared spectroscopy measurements show shifts in the cyclic imide carbonyl peak from 1778 to 1774 cm 21, which suggests that some form of interaction exists between the graphene and polyimide. (C) 2015 Wiley Periodicals, Inc.