Preparation Of Supercapacitive Materials For Asymmetric Supercapacitor

Supercapacitors as a new type of energy storage device, which is catching more and more attention in recent years for their low cost, environmental friendly, good stability, long cycle life and other excellent properties. Supercapacitors appropriately fill the gap between conventional solid state and electrolytic capacitors and batteries, which play an important role in electrical vehicles, portable electronics, power back-up, and so on. In this paper, the electrode materials including camellia fruit shell activated carbon(C-AC), Ni/Al layered double hydroxides(Ni/Al LDHs), N-rGO@CNF, and Co3O4 were prepared. The structure, morphologies, characteristics and electrochemical performances of these materials were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD) patterns, transmission electron microscopy(TEM) and high-resolution transmission electron microscope(HRTEM), N2 absorption-desorption, X-ray photoelectronic spectroscopy(XPS) and electrochemical measurements.(1) Camellia fruit shell activated carbon(C-AC) was successfully prepared via carbonization and activation by using microwave radiation. Ni/Al layered double hydroxides(Ni/Al LDHs) were synthesized by using a facile and free-template hydrothermal method. For their microporous structure, both materials exhibit excellent electrochemical performances, which the maximum specific capacitance of C-AC is 243 F/g and Ni/Al LDHs is 2163 F/g in 6M KOH aqueous electrolyte. An asymmetric capacitor incorporating the C-AC as the negative electrode and the Ni/Al LDHs as the positive electrode was fabricated. The experimental results illustrate that the optimized asymmetric supercapacitor shows intriguing performances with the maximum specific capacitance of 97 F/g and high energy density of 28.6 Wh/kg at a cell voltage of 1.7 V. A good electrochemical stability with 87% specific capacitance retained was demonstrated after consecutive 2000 cycle numbers. Due to thiese excellent electrochemical performances, the device after 2000 cycles still drives a red light-emitting-diode(LED).(2) N-rGO@CNFs were prepared by inserting the bacterial cellulose into the layer of graphene, and then nitrogen-doped. Also, Co3O4 was fabricated through a simple, eco-friendly, and effective way. Both of them exhibit high specific capacitance, which the maximum specific capacitance of N-rGO@CNFs is 340 F/g and Co3O4 is 857 F/g in 6 M KOH aqueous solution, and good cycle stability. The asymmetric supercapacitor was designed to contain the N-rGO@CNFs as negative electrode and Co3O4 as positive electrode in 6 M KOH electrolyte. Due to the synergistic effects of the two electrodes, asymmetric cell showed superior electrochemical performances. The optimized asymmetric supercapacitor gave a operating potential of 1.7 V, exhibiting a high specific capacitance of 80 F/g at 1 A/g and considerably high energy density of 24.1 Wh/kg at a power density of 365.1 W/kg and excellent cycling stability with 93.7% specific capacitance retained after 1000 cycles.