Design Of Iron-based Composites And Study On Their Energy Storage Properties

With the continuous development and utilization of renewable energy such as solar energy,wind energy and tidal energy,current energy storage equipment has been unable to meet daily production needs.Finding high-performance energy storage devices has become one of the main ways to solve energy storage problems,among which sodium-ion batteries and supercapacitors stand out with their unique advantages.In general,electrode materials are considered to be a key factor in determining the performance of energy storage devices.Iron-based materials have been favored by researchers because of their low price,broad variety of sources,high theoretical capacity,and high electrochemical activity.They are widely used as electrode materials for various energy storage devices.However,the iron-based materials own serious problems such as serious volume effect and poor conductivity.This paper mainly solves this problem by combining it with biomass carbon materials and constructing porous structure to increase its specific surface area.In this paper,three kinds of iron-based materials such as iron phosphide/biomass carbon composite,iron-cobalt-phosphide/biomass carbon composite and porous Fe₃O₄/C nanoaggregates material were prepared.Their synthetic routes and electrochemical performances as electrode materials applied in sodium ion batteries and supercapacitors were explored.The details are as follows:（1）The iron phosphide/biomass carbon composite was prepared by electrochemical deposition on the carbonized magnolia leaves.The unique hierarchical structures allowed the electrode materials to exhibit reversible specific capacity of 500.9 mAh g^-1 at low current density of 50 mA g^-1.In addition,the electrode material retained reversible specific capacity of 197 mAh g^-1 after prolonged cycling at a high current density of 500 mA g^-1.（2）The Fe-Co-P/BC alloy composite was prepared by electrochemical deposition at a constant voltage of-1.4 V,and the material was applied to the negative electrode material of sodium ion battery.Test its electrochemical performance.The strong interaction between the metal elements and between the metal elements and the carbon material facilitates the electron transport of the electrode material at high current densities.The Fe-Co-P/BC alloy composite retained a reversible capacity of466.6 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1.In addition,the Fe-Co-P/BC composite electrode exhibited excellent long-term cycling characteristics at a current density of 500 mA g^-1,and maintained a reversible capacity of 292.8 mAh g^-11 after 500 cycles.（3）The porous Fe₃O₄/C nanoaggregates prepared with carbonized ZIF-67 as template.It was used as electrode material for supercapacitors and its electrochemical performances were tested.The composite electrode materials with polyhedral structures had high specific surface area and multiple active sites.The porous Fe3O4/C nanoaggregates nanomaterials owned unique 3D porous structures,which could shorten the ion transport path during charge and discharge greatly to improve their electrochemical performances.In the 3 mol L^-1 KOH electrolyte,the electrode materials showed a high discharge specific capacity of 643.6 F g^-1 at the current density of 2 A g^-1 in the first cycling.Subsequently,the discharge specific capacity was rising as a whole.After 3000 cycling,it exhibited a high specific capacity of571.7 F g^-1,showing good cycle stability.In addition,the cycle performance of assembled asymmetric supercapacitor was carried out at the current density of 1 A g^-1for 5000 cycles and the results showed that it had excellent electrochemical performance.In the first cycle,the electrode materials exhibited high discharge capacity of 70.4 F g^-1.After 5000 cycles,the specific capacities of electrode materials could stabilize at 52.8 F g^-1.