Research On Electrochemical Performance Of Iron Nickel Oxide Nanomaterials In Supercapacitor

Supercapacitors are one of the devices that complement with cell each other in the field of energy storage.It has been widely applied in urban transportation,aerospace,smart grid and energy and power system because of its high power density,fast charging and discharging,good cycling stability and safety and environmental protection and so on.Compared with the battery,the lower energy density restricted his development.The main reason is that the research on the negative material is so behind and its low performance can't meet the demand of high performance supercapacitor.In order to solve the problem of low performance and low energy density of supercapacitor,in this paper we successfully prepared iron nickel oxide nanomaterials as negative electrode material by adding nickel element to the Iron oxide,and cobalt nickel sulfide as positive electrode based on literature research.Finally we assembled Pseudocapacitance supercapacitor based on cobalt nickel sulfide and iron nickel oxide.The main research content is as follows:(1)Preparation of iron nickel oxide nanomaterial and analyzing on its electrochemical performance.We successfully prepared iron nickel oxide nanosheet on carbon cloth via hydrothermal method,and we changed the proportion of iron and nickel elements by 2 to 1,1 to 1and 1 to 2,respectively.From the SEM and TEM images of nanosheet,we found the nanosheet of Fe-Ni-2-1 is the best,the nanosheet is very thin and there is no signs of shedding on carbon fiber substrate.But the nanosheet of Fe-Ni-1-1 and Fe-Ni-1-2 is thick and compact,and some has been dropped.From the XRD,Raman,and XPS of iron nickel oxide nanosheet,we found that nanosheet is growing along the direction of(440).The oxide nanosheet contains iron,nickel and oxygen element,the iron and nickel element both has+2 and+3 valence.Then the electrochemical test of three kinds iron nickel oxide nanomaterials has been conducted.Fe-Ni-2-1 oxide nanosheet exhibits a high specific capacitance 667 F/g at the current density of 2 A/g,with a large current density of50 A/g its specific capacitance still can reach about 380 F/g,the electrochemical performance is remarkable.The electrochemical performance of Fe-Ni-1-1 oxide nanosheets and Fe-Ni-1-2 oxide nanosheets is poor,their specific capacitance are 457 F/g and 378 F/g,respectively.The above data show that the specific capacitance of the Fe-Ni-2-1 oxide nanosheets is the best and with the increase of the nickel content,the electrochemical performance has a significant decrease.(2)Prepartion of cobalt nickel sulfide as positive material.To assemble high performance capacitance,we prepared cobalt nickel sulfide nanosheets on carbon cloth via electrochemical deposition.The SEM and XPS of cobalt nickel sulfide show that the nanosheets grown well,its thickness is very thin and the structure is polycrystalline.The nanosheets contain cobalt,nickel and sulfide element,most of cobalt and nickel element has+2 valence which has rich redox from the XPS result.Electrochemical performance tests showed that the nanosheets had a specific capacitance of 1643 F/g at the current density of 2 A/g.When the current density increased to 50A/g,the specific capacitance remained at 1267 F/g,and the retention rate was 77%.The above data show that the electrochemical performance of cobalt nickel nanosheets is so excellent that can meet the demand of high performance supercapacitor.(3)Fabrication of Ni-Co-S//Fe-Ni-2-1 Pseudocapacitance supercapacitor.We fabricate a Pseudocapacitance supercapacitor with the Ni-Co-S as positive electrode and Fe-Ni-2-1 as the negative electrode and then conducted electrochemical performance tests.Pseudocapacitance supercapacitor had an areal capacitance of 134 mF/cm~2 at the current density of 0.5 mA/cm~2,with an increasing of current density to 20 mA/cm~2,the areal capacitance dropped to 80 mF/cm~2.When Pseudocapacitance supercapacitor was in a charge-discharge process at a current density of 10mA/cm~2,there is no obvious decline after 10000 cycles,it shown the excellent cycling ability of both positive electrode and negative electrode.The substrate of the negative electrode provides a certain capacitance,so we calculated that the capacity of the active material iron nickel oxide Fe-Ni-2-1 and the proportion of the capacitance of the whole negative electrode,and then the capacitance provided by the active material Ni-Co-S//Fe-Ni-2-1 in the whole capacitor is calculated according to this proportion.The results show that the specific capacitance provided by the active material Ni-Co-S//Fe-Ni-2-1 in the capacitor is 226 F/g at a 0.5 mA/cm~2 current density,and the energy density can reach 70.6 Wh/Kg when the power density is 970 W/Kg,showing a higher specific capacitance and energy density.As a comparison,we assembled Ni-Co-S//AC(active carbon)asymmetric supercapacitor,the energy density can be only 23 Wh/Kg and its electrochemical performance is much lower than the Ni-Co-S//Fe-Ni-2-1 Pseudocapacitance supercapacitor.Above data shown that the electrochemical performance of Fe-Ni-2-1 nanosheets is so excellent that can meet the demand of high performance supercapacitor,which is much better than asymmetry supercapacitor.