Preparation And Supercapacitor Performance Of Polymetallic Phosphide And Biomass Carbon Material

Among the existing energy storage systems,supercapacitors have attracted much attention owe to their high power density,fast charge-discharge time,long cycle life,and environmental friendly electrode materials.Currently,supercapacitors are widely used in electric vehicles,aerospace,defense technology and Wearable smart devices.However,to some extent,the practical problem of low energy density of supercapacitors limited their commercial application.Therefore,on the premise of ensuring its original advantages,how to effectively improve the energy density has always been a research hotspot in the field of supercapacitors.According to the formula of energy density,the specific capacity of the electrode material and the width of the voltage window play a decisive role in the energy density of the supercapacitor.So,in this paper,We prepared electrode materials that have high specific capacitance and assembled its into symmetric and asymmetric supercapacitors to widen the voltage window,so as to improve the energy density of supercapacitors.Some of research contents are as follows:（1）Transition metal phosphates were prepared by solvothermal and low temperature phosphating method.Through adjusting the ratio of nickel and cobalt salts,we got the micro-sphere metal phosphates with different nickel-cobalt ratios.The best electrochemical performance material obtained with the mass ratio of nickel salts to cobalt salts was 1:1（Ni Co P）which specific capacitance reached1050F·g^-1 at 1A·g^-1.Then,on that basis,a series of micro-nano spherical zinc doped nickel-cobalt phosphates were prepared by introducing zinc salts to replace part of cobalt salts.The addition of zinc salts not only improved the electrochemical performance,but also reduced the cost.It means zinc doped nickel-cobalt phosphates had practicability and economy at the same time.When the doping amount of zinc salt is 20%(Ni Co_0.8Zn_0.2P),the best effect is achieved.Specific capacitance of Ni Co_0.8Zn_0.2P reached 1362 F·g^-1 at 1A·g^-1.（2）HFC-X was prepared successfully by withered Hibiscus Flowers through a convenient and efficient method of pre-carbonization and activation.HFC-3synthesized with the mass ratio of KOH to HF derived carbon（HFC）to be 3:1during activation step,which had the best electrochemical performance.In the test of the three-electrode system,the specific capacitance of HFC-3 was 216 F·g^-1 at 1A·g^-1.After activation,the specific surface area of HFC-3 was up to 1699.96 m² g^-1,the total pore volume was 0.95 m² g^-1,and the average pore size was 11.2 nm.（3）The Symmetrical supercapacitor（HFC-3//HFC-3）composed of Hibiscus Flowers biomass carbon material which specific capacitance、energy density and power density was 44F·g^-1、15.64Wh·kg^-1 and 799.77W·kg^-1 at 1A·g^-1 respectively owns an extended voltage window of 0-1.6V,After 5000 cycles,90.4%capacitance retention was retained.Asymmetric supercapacitor(Ni Co_0.8Zn_0.2P//HFC-3)was made up of Ni Co_0.8Zn_0.2P as positive electrode and HFC-3 as negative electrode,which specific capacitance、energy density and power density reached 113 F·g^-1、35.31 Wh·kg^-1 and 747.74 W·kg^-1 at 1 A·g^-1 respectively under the potential window of 0-1.5V.Moreover,after 5000 cycles,80.6%of the initial specific capacity was still retained.