Boosted electrochemical performance of flower-like carbon microspheres derived from polyimides containing hydroxyl groups for supercapacitor electrodes

Herein, the flower-like microspheres derived from polyimides containing hydroxyl groups are firstly synthesized through a solvothermal technique. Then, the corresponding flower-like carbon microspheres are obtained after high -temperature carbonization. The influences of the poly(amic acid) concentration, solvothermal temperature, and treatment time on the electrochemical behaviors of carbon microspheres are investigated. The optimized carbon sample PC -2-180-10 demonstrates a distinct micro/mesopore characteristic, leading to a specific capacitance of 254.4 F g -1 at 0.5 A g -1 . Subsequently, the sample is chemically activated with HNO 3 for improving its electrochemical performance. When the HNO 3 concentration is optimized as 6 M, the treatment temperature and time are 75 degrees C and 30 h respectively, the activated carbon microspheres APC-6-75-30 exhibit a maximum specific capacitance of 387.6 F g -1 . Moreover, the APC-6-75-30 is symmetrically fabricated into a button -type supercapacitor (SC) device, and the SC shows a specific capacitance of 88.5 F g -1 , with an energy density of 11.81 Wh kg - 1 at a power density of 240.1 W kg - 1 . Six months later, the SC still demonstrates a better capacitive performance. Optimizing the solvothermal parameters and HNO 3 treatment conditions, this work presents an effective strategy for boosting the electrochemical performance of flower-like carbon microspheres as a promising electrode for energy storage applications.