Synthesis Of Iron-based Nanocomposites As Negative Electrode Materials For Supercapacitors And Study Of Their Electrochemical Performance

Nowadays,with the rapid development of the world,new energy is attracting more and more attention.As an energy storage device,supercapacitors are considered a supplement or alternative to conventional batteries which have high application value and development prospect in many fields.As an important part of supercapacitors,electrode materials have a decisive influence on the performance of supercapacitors.Therefore,how to design and synthesize high-performance electrode materials is an important direction for the development of ultracapacitors.Iron-based materials have been extensively studied for their ideal theoretical specific capacitance,good redox activity,abundant resources,eco-friendliness,and wide working window.However,the poor stability and low conductivity of iron-based materials limit their application.It is an important research direction to combine with other electrode materials or to design and prepare iron-based materials with precise control composition and structure.In this paper,different iron-based nanocomposites were prepared as a negative electrode material for supercapacitors by a reliable and easy hydrothermal method.The structure,morphology and composition were characterized and analyzed by TEM,XRD,SEM and XPS.At the same time,electrochemical performance tests were carried out under three-electrode and two-electrode systems.The research contents and conclusions of this experiment are as follows:First,the MnO₂@FeOOH nanosheet composite was synthesized in situ on the titanium grid by hydrothermal deposition.The effects of different composite ratios on the structure,morphology and capacitance performance were further investigated.FeOOH is compounded with MnO₂ nanosheets with porous structure and high specific surface area,which increases the reactivity site of the material and improves electrochemical performance.The MnO₂@FeOOH electrode material on the titanium mesh has a high specific capacitance(the specific capacitance is 163.4 F g^-1 at a current density of 0.5 A g^-1)and excellent cycle stability?92.6%of the remaining capacitance after 1000 cycles?.In addition,a flexible capacitor is composed of the positive electrode of Ti@MnO₂ and the negative electrode of Ti@MnO₂@FeOOH,which achieves an energy density of 23.945 W h kg^-1 at a power density of 400 W Kg^-1.Secondly,the electrode material of FeOOH nanoflower structure was first prepared by sacrificial template method based on titanium mesh.The FeOOH grown on the titanium mesh?Ti@FeOOH?was then heat-treated under different conditions to further prepare electrode materials of?-Fe₂O₃ and?-Fe₂O₃ nanoflower structures for different crystal structures.The electrochemical test results of the three materials show that the nanoflower structure FeOOH has the highest capacitance performance,and its specific capacitance can reach 216 F g_-1 at a current density of 0.5 A g_-1,and it has excellent rate performance and cycle stability?90.8%of the remaining capacitance after 1000 cycles?.In addition,a flexible capacitor composed of a Ti@MnO₂ electrode as a positive electrode and a Ti@FeOOH electrode as a negative electrode achieves an energy density of 22.1 W h kg^-1 at a power density of 400 W kg^-1.Its excellent performance is attributed to the unique nanoflower structure,which can better infiltrate in the electrolyte,the multi-hole open structure can also reduce the internal resistance,shorten the transmission path of electrolyte ions.Finally,FeOOH was combined with NiFe-LDH on a nickel foam by two-step hydrothermal method.The porous nanostructure of FeOOH nanosheets can provide a large number of electroactive sites,and the two-dimensional layered nanosheets of NiFe-LDH have high specific surface area and open space,which can enhance the diffusion of ions in the active material.The NiFe-LDH@FeOOH composite exhibits high electrochemical properties.The specific capacitance of the NiFe-LDH@FeOOH nanocomposite is 1195 F g^-11 at the current density of 1 A g^-1.It also has good cycle stability,and a residual capacitance of 90.36%after 1000 cycles.In addition,a supercapacitor composed of a NiFe-LDH@MnO₂ electrode as positive electrode and a NiFe-LDH@FeOOH electrode as a negative electrode achieves an energy density of22.68 W h kg^-1 at a power density of 750 W kg^-1.In this paper,different iron-based nanocomposites were designed and prepared because of its problems of poor cycle performance and low rate performance.It opens up new ideas for the design of the structure of iron-based materials and the composite research of metal oxides or hydroxides and promotes its application in supercapacitors.