Study On Electrochemical Capacitance Performance Of Sterculia Lychnophora-derived Carbon And Their Composite Materials

Supercapacitors have received extensive attention due to their advantages such as long cycle life and high power density,but the lower energy density limits their application range.Therefore,how to improve the energy density of supercapacitors is the focus of current research.Electrode material is one of the important components of supercapacitors,and its performance directly affects the energy density of supercapacitors.In recent years,biomass carbon-based materials with features of low cost,renewable,and environmentally friendly have come to the view of many researchers.In this paper,a porous carbon material is prepared by using sterculia lychnophora as carbon source.The effect of activation conditions on the morphology and electrochemical performance of the as-prepared carbon material is investigated.Meanwhile,the composite of metal sulfide-carbon is used as an electrode of a supercapacitor to improve its specific capacitance performance.The main research content is as follows:The porous carbon material was prepared by a high-temperature calcination using sterculia lychnophora as the biomass raw material and KOH as the activator.A series of electrochemical tests were conducted to investigate the optimal KOH concentration.Results reveals that when the KOH concentration is 0.1 mol L^-1,the porous carbon material shows the excellent electrochemical performance.The specific capacitance of the as-prepared carbon is321.4 F g^-1 at a current density of 1 A g^-1.With the current density increased to 20 A g^-1,the specific capacitance still remains 256.0 F g^-1.In addition,a symmetrical supercapacitor was assembled using this porous carbon material as the positive and negative electrode.The assembled supercapacitor exhibited an energy density of 18.1 Wh kg^-1 at a power density of799.9 W kg^-1.The specific capacitance retention rate can still reach 91.2%after 10,000 cycles at 5 A g^-1.Taking advantage of the strong ability of water absorption of sterculia lychnophora,immersion and freeze-dryin were firstly applied to prepare a pretreated sterculia lychnophora by soaking-recrystallization method.The pretreated sterculia lychnophora was then mixed with sulfur powder and calcined at a high temperature.The composite of Ni S and sterculia lychnophora-derived carbon material was prepared through a one-step carbonization and sulfuration.The effects of the nickel nitrate concentration on the performance of the prepared composite material was firstly investigated.Results showed that when the concentration of nickel nitrate was 0.2 mol L^-1,the composite exhibited a better electrochemical performance,the specific capacitance was 1080.0 F g^-1 at a current density of 2 A g^-1.Furthermore,an asymmetric supercapacitor was assembled using the composite and the sterculia lychnophora-derived carbon material as positive electrode and lychnophora-derived porous carbon as negative electrode.When the power density is 700.0 W kg^-1,an energy density of29.2 Wh kg^-1was obtained.The capacity retention rate of the assembled supercapacitor can still reach 88.2%after 10,000 cycles at a current density of 5 A g^-1,which revealing an outstanding cycling stability.A composite of bimetallic sulfide and the porous carbon was also prepared and used as an electrode for supercapacitors.Firstly,the effect of the ratio of Ni²⁺to Co²⁺in the precursor solution on the electrochemical performance was investigated.It can be concluded from the electrochemical tests that the composite of Ni S/Ni Co₂S₄/carbon showed the best performance when the ratio of Ni²⁺to Co²⁺was 1:1,the specific capacitance was 1634.0 F g^-1 at a current density of 1 A g^-1.An asymmetric supercapacitor was also assembled by using the sterculia lychnophora-derived carbon material as negative and the Ni S/Ni Co₂S₄/carbon composite as positive electrodes.The maximum energy density could achieve at 42.9 Wh kg^-1 when the power density is 700.4 W kg^-1.Meanwhile,a good cycling stability was also achieved by the assembled supercapacitor.,the specific capacitance retention rate can still reach 85.7%after10,000 cycles at a current density of 5 A g^-1.