Fe2O3@Co-C@hgof nanofiber electrode composite material, and preparation method and application thereof

Abstract

The application discloses a Fe2O3@Co-C@HGOF nanofiber electrode composite material and a preparation method and application thereof, relates to the technical field of electrode material preparation, and comprises the preparation of graphene oxide gel, the preparation of Co-MOF@HGOF, the preparation of Co-C@HGOF and the preparation of Fe2O3@Co-C@HGOF nanofiber electrode composite material steps. The Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the application can provide flow channels for electrolyte, successfully realizes the accommodation of electrolyte in the electrode, greatly improves the ion transmission rate, enhances the conductivity of the electrode interior and surface, increases the electrolyte / electrode surface area, and increases the rich active sites, improves the specific capacity of the main electrode, can effectively improve the conductivity and ion diffusivity of the lithium ion battery electrode, thereby improving the rate performance, relieving the volume change of the electrode in the electrochemical reaction process, ensuring the structural integrity of the main material, and enhancing the cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrode material preparation, and particularly relates to a Fe2O3@Co-C@HGOF nanofiber electrode composite material, a preparation method and application thereof. BACKGROUND

[0002] In the past few decades, lithium ion batteries (LIB) have been widely used in portable electronic devices (such as notebook computers, mobile phones and cameras) and electrical equipment (such as electric vehicles, electric bicycles and smart grids) due to their high operating voltage, no pollution, no "memory effect", high energy density and high power density. It is well known that the low electrode potential, long cycle life and low cost of graphite play an important role in commercialized negative electrode materials. However, on the one hand, the actual capacity of the graphite negative electrode has reached the limit of the theoretical capacity (372mA·h / g); on the other hand, the ion diffusion coefficient (10 -6 cm 2 / s) of graphite is low, which limits its application in the field of large-rate fast charging and discharging batteries. With the increasing demand for the driving range of electric vehicles, the huge market demand for lithium ion batteries with high energy density and high power density has attracted considerable attention, and in order to overcome the shortcomings of graphite negative electrode materials, it is urgent to find a feasible material to replace graphite. The theoretical capacity of transition metal oxide (TMO) is 2-3 times that of graphite, but TMO materials still have problems such as poor conductivity and ion diffusion, resulting in poor rate performance, large volume expansion during charging / discharging, leading to electrode material crushing, which reduces the reversible capacity, and the like; in addition, during the charging / discharging process, the movement of charged particles causes local concentration of like charges and generates an electric field, the charges move directionally in the electric field, generating a magnetic field, and under the action of the electric field and the magnetic field, the oscillation of the charged particles is strengthened to radiate electromagnetic waves outward. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a Fe2O3@Co-C@HGOF nanofiber electrode composite material, a preparation method and application thereof, so as to improve the conductivity and ion diffusion of the lithium ion battery electrode, thereby improving the rate performance, relieving the volume change during the electrochemical reaction process, ensuring the structural integrity of the main material, enhancing the cycle stability, and absorbing the electromagnetic radiation generated during the charging / discharging process.

[0004] To solve the above technical problems, the present application provides a preparation method of a Fe2O3@Co-C@HGOF nanofiber electrode composite material, comprising the following steps:

[0005] S1, preparation of graphene oxide gel: take the graphite powder and KNO3 by mass ratio of 1:1, mix uniformly to obtain mixed powder, add 10-15 times weight of concentrated H2SO4 to the mixed powder, and stir at 40℃ for 5-10min, then slowly add 1.5-1.8 times weight of KMnO4 to the mixed powder, continue to stir at 40℃ for 3-6h, add 35-45 times weight of deionized water to the mixed powder, heat to 60℃, and keep for 30-60min, then add 60-100 times weight of deionized water to the mixed powder, stir for 5-10min, add 2.8-3.5 times weight of 30% H2O2, and stand at room temperature for 5-12h, then remove the upper concentrated H2SO4, add 60-100 times weight of deionized water to the mixed powder, and stand for another 5-12h, centrifugal separation to remove the supernatant, and graphene oxide gel is obtained;

[0006] S2, preparation of Co-MOF@HGOF: dissolve Co(CH3COO)2·4H2O in 80-100 times weight of anhydrous ethanol, add Co(CH3COO)2·4H2O 0.5 times weight of the graphene oxide gel prepared in S1, and then add Co(CH3COO)2·4H2O 40-50 times weight of anhydrous ethanol, stir for 3-12h to obtain A solution, then dissolve Co(CH3COO)2·4H2O 6.1-6.6 times weight in 2-methylimidazole in Co(CH3COO)2·4H2O 120-150 times weight of anhydrous ethanol to obtain B solution, then add B solution to A solution, ultrasonic treat at room temperature for 3-6h, so that 2D graphene self-rolls to form hollow nanofiber structure, and stack into three-dimensional (3D) graphite, part of Co-MOF nanoparticles are rolled into the tube during the rolling process, and the other part is anchored outside the hollow nanofiber, then stand at room temperature for 12-48h, centrifugal separation to obtain solid sample, wash the solid sample with anhydrous ethanol for 2-5 times, vacuum drying, and Co-MOF@HGOF is obtained;

[0007] S3, preparation of Co-C@HGOF: put Co-MOF@HGOF prepared in S2 into a porcelain boat, and transfer to a tube furnace, heat to 600℃ at a heating rate of 3℃ / min under the protection of argon, and keep for 0.5h-2h, so that the organic ligand in the MOF material is carbonized into carbon material with good electrical conductivity, then naturally cool, and Co-C@HGOF is prepared;

[0008] S4, Preparation of Fe2O3@Co-C@HGOF: Take the Co-C@HGOF obtained in S3, add 3-5 times the weight of the Co-C@HGOF of ferric nitrate, mix uniformly to obtain a mixture, then uniformly disperse the mixture in 10-15 times the weight of the Co-C@HGOF of concentrated H2SO4, reflux at 80℃ for 3-5h, so that the ferric nitrate fills in the pore structure of the MOF-derived carbon-based composite material on the Co-C@HGOF, then cool, remove the filtrate by filtration, repeatedly wash the filter residue with deionized water, and then fully dry at 100℃, then under the protection of argon, heat to 500℃ at a heating rate of 3℃ / min, and calcine for 3h, so that the ferric nitrate is converted into iron oxide, that is, the Fe2O3@Co-C@HGOF nanofiber electrode composite material is obtained.

[0009] Lithium ion battery is a kind of rechargeable battery, which works by moving lithium ions between the positive and negative electrodes; during charging and discharging, Li+ embeds and de-embeds between the two electrodes: when charging, Li+ de-embeds from the positive electrode through the electrolyte and embeds in the negative electrode, and when discharging, the opposite is true. The low electrode potential, long cycle life and low cost of graphite make it play an important role in commercialized negative electrode materials. Graphene is a carbon six-membered ring connected by sp2 hybridization, and the carbon six-membered rings are connected to each other to form a two-dimensional (2D) single-layer graphene structure. In the present application, the 2D graphene is self-crimped into a hollow nanofiber structure by an ultrasonic assisted method, and stacked into a three-dimensional (3D) graphite. During the crimping process, part of the Co-MOF nanoparticles are crimped into the tube and anchored inside, and the other part is anchored outside the hollow nanofiber. The prepared Co-MOF@HGOF nanoparticle / hollow graphene fiber as a lithium ion battery negative electrode material successfully realizes the purpose of increasing the ion conductivity inside and enhancing the electron conductivity on the surface, and the 3D structure built by the mutual crossing of the hollow fibers enhances the connection between the electrode material and the current collector, improving the stability of the material in the deep cycle process.

[0010] At the same time, the organic ligand in the MOF material is carbonized into a carbon material with good electrical conductivity, the MOF-derived carbon-based composite material inherits the porous structure of the precursor and obtains a larger specific surface area, which can increase the electrolyte / electrode surface area, increase the active sites, improve the specific capacity of the main electrode, and shorten the ion diffusion path, thereby improving the rate performance, and the larger specific surface area can effectively alleviate the volume change in the electrochemical reaction process, thereby ensuring the structural integrity of the main material, which is conducive to enhancing the cycle stability, and can be used as an ideal lithium ion electrode material.

[0011] In addition, the iron nitrate is filled in the pore structure of the MOF-derived carbon-based composite material on the Co-C@HGOF, and the iron nitrate is converted into iron oxide through high-temperature calcination, and under the joint action of the MOF-derived carbon-based composite material, metal nanoparticles and iron oxide, electromagnetic radiation generated in the charging / discharging process of the lithium ion battery can be simultaneously absorbed and dissipated, the surface energy transmission is hindered, the energy of the electromagnetic radiation is converted into heat energy, so that the energy of the electromagnetic radiation is reduced, and electromagnetic radiation pollution is avoided.

[0012] Further, the method for adding 2.8-3.5 times the weight of the mixed powder 30% mass fraction H2O2 in S1 is: dropwise adding for 3-5 times, and the interval time of each dropwise adding is 3-5 minutes, so as to sufficiently remove the excess KMnO4 and avoid excess H2O2.

[0013] Further, the conditions of vacuum drying in S2 are: drying temperature 60-80 DEG C, vacuum degree 0.09-0.1 MPa, and drying time 8-12 h.

[0014] Further, the process of uniformly dispersing the mixed material in 10-15 times the weight of the Co-C@HGOF 98% mass fraction concentrated sulfuric acid in S4 adopts ultrasonic dispersion, the ultrasonic frequency is 32 KHz, the dispersion speed is 45 r / s, and the dispersion time is 20 min.

[0015] Further, the method further comprises etching of the Co-C@HGOF: before the preparation of the Fe2O3@Co-C@HGOF nanofiber electrode composite material in S4, the Co-C@HGOF prepared in S3 is placed in a tube furnace, hydrogen is introduced, and the hydrogen etching temperature is heated to be kept, so as to obtain the hydrogen etched Co-C@HGOF. By utilizing the catalytic effect of cobalt, the carbon material formed by high-temperature carbonization of the organic ligand in the MOF material is etched at high temperature, so as to obtain a new reinforcing body with the characteristics of carbon and graphene, so that the active sites can be further increased, the specific capacity of the main electrode can be improved, and the rate performance can be improved.

[0016] Further, in the etching process of the Co-C@HGOF: the flow rate of the hydrogen is 35 ml / min, the hydrogen etching treatment temperature is 980 DEG C, the heating rate is 1 DEG C / min, and the holding time is 30 min.

[0017] Further, the mass fraction of the concentrated H2SO4 in S1 and S4 is 98%.

[0018] The application further provides a Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the preparation method.

[0019] The application further provides an application of the Fe2O3@Co-C@HGOF nanofiber electrode composite material in a lithium ion battery electrode.

[0020] The application has the following beneficial effects:

[0021] 1. The Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the application can provide flow channels for electrolyte, successfully realizes accommodation of electrolyte in the electrode, greatly improves ion transmission rate, enhances the electrical conductivity of the electrode interior and surface, increases the electrolyte / electrode surface area, and increases rich active sites, improves the specific capacity of the main electrode, can effectively improve the conductivity and ion diffusivity of the lithium ion battery electrode, thereby improving the rate performance, alleviates the volume change of the electrode in the electrochemical reaction process, ensures the structural integrity of the main material, and enhances the cycle stability.

[0022] 2. The Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the application can simultaneously absorb and dissipate electromagnetic radiation generated in the charging / discharging process of the lithium ion battery, hinders the surface energy transmission, converts the energy of electromagnetic radiation into heat energy, so as to reduce the energy of electromagnetic radiation and avoid electromagnetic radiation pollution. DETAILED DESCRIPTION

[0023] The application will be described in detail below in combination with examples:

[0024] Example 1

[0025] A preparation method of a Fe2O3@Co-C@HGOF nanofiber electrode composite material, comprising the following steps:

[0026] S1, 10g of graphite powder and 10g of KNO3 are respectively weighed, uniformly mixed, 200g of concentrated H2SO4 (mass fraction of 98%) is added, and stirring is carried out at 40℃ for 5min, then 30g of KMnO4 is slowly added, and stirring is continuously carried out at 40℃ for 3h, 700g of deionized water is added, the temperature is increased to 60℃, and after 30min of insulation, 1200g of deionized water is added, stirring is carried out for 5min, 56g of H2O2 with a mass fraction of 30% (dropped in 3 times, and the interval time of each drop is 3min) is added, and after 5h of room temperature standing, the upper concentrated H2SO4 is removed, 1200g of deionized water is added, and after 5h of standing, the supernatant is removed by centrifugal separation, and a graphene oxide gel is obtained;

[0027] S2, 10 g of Co(CH3COO)2·4H2O is dissolved in 800 g of anhydrous ethanol, 5 g of graphene oxide gel is added, and then 400 g of anhydrous ethanol is added, and stirring is carried out for 3 h to obtain solution A; 61 g of 2-methylimidazole is dissolved in 1200 g of anhydrous ethanol to obtain solution B; then the solution B is added to the solution A, and ultrasonic treatment is carried out at room temperature for 3 h to enable the 2D graphene to self-roll to form a hollow nanofiber structure and stack into a three-dimensional (3D) graphite; during the rolling process, part of the Co-MOF nanoparticles are rolled into the tube, and the other part is anchored outside the hollow nanofiber; then the sample is left to stand at room temperature for 12 h, and centrifugal separation is carried out to obtain a solid sample; the solid sample is washed twice with anhydrous ethanol, and then vacuum drying is carried out at 60℃ and 0.09 MPa for 8 h to obtain Co-MOF@HGOF;

[0028] S3, the Co-MOF@HGOF is placed in a porcelain boat and transferred into a tube furnace, and then the temperature is raised to 600℃ at a temperature raising rate of 3℃ / min under the protection of argon, and the temperature is kept for 0.5 h to enable the organic ligand in the MOF material to be carbonized into a carbon material with good electrical conductivity; and then natural cooling is carried out to obtain Co-C@HGOF.

[0029] S4, 5 g of Co-C@HGOF is added into 15 g of iron nitrate, and then mixed uniformly; then 50 g of concentrated H2SO4 (mass fraction of 98%) is added, and ultrasonic treatment is carried out under the condition of a frequency of 32 KHz and a dispersion speed of 45 r / s for 20 min; and then refluxing is carried out at 80℃ for 3 h to enable the iron nitrate to be filled in the pore structure of the MOF-derived carbon-based composite material on the Co-C@HGOF; then cooling is carried out, the filtrate is removed by filtration, the filter residue is repeatedly washed with deionized water, and then sufficient drying is carried out at 100℃; then calcination is carried out at a temperature raising rate of 3℃ / min to 500℃ under the protection of argon for 3 h to enable the iron nitrate to be converted into iron oxide, and thus Fe2O3@Co-C@HGOF nanofiber electrode composite material is obtained.

[0030] Example Two

[0031] A method for preparing Fe2O3@Co-C@HGOF nanofiber electrode composite material, comprising the following steps:

[0032] S1, 10 g of graphite powder and 10 g of KNO3 were weighed separately and mixed uniformly, 260 g of concentrated H2SO4 (mass fraction 98%) was added, and stirred at 40℃ for 7 min, then 32 g of KMnO4 was slowly added, and stirred at 40℃ for 5 h, 800 g of deionized water was added, heated to 60℃, and kept for 45 min, then 1600 g of deionized water was added, stirred for 8 min, 60 g of 30% H2O2 (added dropwise in 4 times, and the interval time of each dropwise addition was 4 min) was added, and then placed at room temperature for 10 h, the upper layer of concentrated H2SO4 was removed, 1600 g of deionized water was added, and then placed for 6 h, the supernatant was removed by centrifugal separation, and then graphene oxide gel was obtained;

[0033] S2, 10 g of Co(CH3COO)2·4H2O was dissolved in 900 g of anhydrous ethanol, 5 g of graphene oxide gel was added, 450 g of anhydrous ethanol was added, and stirred for 6 h to obtain A solution, 63 g of 2-methylimidazole was dissolved in 1300 g of anhydrous ethanol to obtain B solution, then the B solution was added to the A solution, and ultrasonic treatment was carried out at room temperature for 4 h, so that the 2D graphene was self-crimped to form a hollow nanofiber structure, and stacked into a three-dimensional (3D) graphite, part of the Co-MOF nanoparticles was crimped into the tube during the crimping process, and the other part was anchored outside the hollow nanofiber, then the sample was placed at room temperature for 24 h, and the solid sample was obtained by centrifugal separation, the solid sample was washed with anhydrous ethanol for 3 times, and then vacuum dried at 70℃ and 0.095 MPa for 9 h to obtain Co-MOF@HGOF;

[0034] S3, the Co-MOF@HGOF was placed in a porcelain boat and transferred to a tube furnace, and heated to 600℃ at a heating rate of 3℃ / min under the protection of argon, and the organic ligand in the MOF material was carbonized into a carbon material with good electrical conductivity at high temperature, and then naturally cooled to obtain Co-C@HGOF;

[0035] S4, 5 g of Co-C@HGOF was taken, 20 g of iron nitrate was added and uniformly mixed, and then 65 g of concentrated H2SO4 (mass fraction 98%) was added, and ultrasonic treatment was carried out at a frequency of 32 KHz and a dispersion speed of 45 r / s for 20 min, and then refluxed at 80℃ for 4 h, so that the iron nitrate was filled in the pore structure of the MOF-derived carbon-based composite material on the Co-C@HGOF, and then cooled, the filtrate was removed by filtration, the filter residue was repeatedly washed with deionized water, and then fully dried at 100℃, and then calcined at a heating rate of 3℃ / min to 500℃ under the protection of argon for 3 h, so that the iron nitrate was converted into iron oxide, and then Fe2O3@Co-C@HGOF nanofiber electrode composite material was obtained.

[0036] Example Three

[0037] A preparation method of a Fe2O3@Co-C@HGOF nanofiber electrode composite material, comprising the following steps:

[0038] S1, 10g of graphite powder and 10g of KNO3 were weighed respectively, mixed uniformly, 300g of concentrated H2SO4 (mass fraction 98%) was added, and stirred at 40℃ for 10min, then 36g of KMnO4 was slowly added, and stirred at 40℃ for 6h, 900g of deionized water was added, heated to 60℃, and kept for 60min, then 2000g of deionized water was added, stirred for 10min, 70g of 30% H2O2 (added dropwise in 5 times, and the interval time of each dropwise addition was 5min) was added, and after standing at room temperature for 12h, the upper concentrated H2SO4 was removed, 2000g of deionized water was added, and then stood for 12h, centrifugal separation was performed to remove the supernatant, and then a graphene oxide gel was obtained;

[0039] S2, 10g of Co(CH3COO)2·4H2O was dissolved in 1000g of anhydrous ethanol, 5g of the graphene oxide gel was added, 500g of anhydrous ethanol was added, and stirred for 12h to obtain an A solution, 66g of 2-methylimidazole was dissolved in 1500g of anhydrous ethanol to obtain a B solution, then the B solution was added to the A solution, ultrasonic treatment was carried out at room temperature for 6h, 2D graphene was self-crimped to form a hollow nanofiber structure, and stacked into a three-dimensional (3D) graphite, part of the Co-MOF nanoparticles were crimped into the tube during the crimping process, and the other part was anchored outside the hollow nanofiber, then the sample was left to stand at room temperature for 48h, centrifugal separation was performed to obtain a solid sample, the solid sample was washed with anhydrous ethanol for 5 times, and then vacuum dried at 80℃ and 0.1MPa for 12h to obtain a Co-MOF@HGOF;

[0040] S3, the Co-MOF@HGOF was placed in a porcelain boat, transferred into a tube furnace, and heated to 600℃ at a heating rate of 3℃ / min under the protection of argon, and kept for 2h, so that the organic ligand in the MOF material was carbonized into a carbon material with good electrical conductivity, and then naturally cooled, and a Co-C@HGOF was prepared;

[0041] S4, 5 g of Co-C@HGOF was taken, 25 g of iron nitrate was added, and the mixture was uniformly mixed to obtain a mixed material, then the mixed material was added to 75 g of concentrated H2SO4 (mass fraction 98%), and ultrasonic treatment was carried out at a frequency of 32 KHz and a dispersion speed of 45 r / s for 20 min, and refluxed at 80℃ for 5 h, so that the iron nitrate was filled in the pore structure of the MOF-derived carbon-based composite material on the Co-C@HGOF, then cooled, the filtrate was removed by filtration, the filter residue was repeatedly washed with deionized water, and then dried at 100℃, then calcined at 500℃ at a heating rate of 3℃ / min under the protection of argon for 3 h, so that the iron nitrate was converted into iron oxide, and a Fe2O3@Co-C@HGOF nanofiber electrode composite material was obtained.

[0042] Example Four

[0043] The difference between this example and Example Two is that, before preparing the Fe2O3@Co-C@HGOF nanofiber electrode composite material in S4, the Co-C@HGOF prepared in S3 was placed in a tube furnace, hydrogen was introduced at a flow rate of 35 ml / min, and heated to 980℃ at a heating rate of 1℃ / min, and kept for 30 min, to obtain hydrogen-etched Co-C@HGOF. A new reinforcing body with the characteristics of carbon and graphene was obtained, and the active sites were further increased.

[0044] Pore structure test:

[0045] Fe2O3@Co-C@HGOF nanofiber electrode composite materials prepared in Examples One to Four were taken as experimental groups 1, 2, 3 and 4, and Co-C@HGOF and Co-MOF@HGOF prepared in Example Two were taken as control groups 1 and 2, and the specific surface area and pore size analyzer was used to detect the pore structure data, and the test results are shown in Table 1:

[0046] Table 1 Pore structure test data

[0047]

[0048] From the test data in Table 1, it can be seen that the specific surface area, pore size and pore volume of Co-MOF@HGOF in control group 2 are the best, followed by control group 1. Although the pore structure data of the four experimental groups is lower than that of the two control groups, the overall surface area is more than 1000 m 2The pore diameter is greater than or equal to 3.0 nm, and the pore volume is greater than or equal to 0.35. It can be seen that the Fe2O3@Co-C@HGOF nanofiber electrode composite prepared by the method has not only the hollow nanofiber structure formed by the self-rolling of 2D graphene, which increases the specific surface area and pore volume, but also the characteristics of the MOF precursor, such as high porosity and high specific surface area. Therefore, the Fe2O3@Co-C@HGOF nanofiber electrode composite prepared by the method can effectively increase the electrolyte / electrode surface area, increase the active sites, improve the specific capacity of the main electrode, and shorten the ion diffusion path, thereby improving the rate performance. The larger specific surface area can effectively alleviate the volume change in the electrochemical reaction process, thereby ensuring the structural integrity of the main material and being beneficial to the enhancement of the cycle stability. The Fe2O3@Co-C@HGOF nanofiber electrode composite can be used as an ideal lithium ion electrode material.

[0049] Electrochemical performance test:

[0050] The Fe2O3@Co-C@HGOF nanofiber electrode composite prepared in Example 1 was mixed with acetylene black (a conductive agent) and polyvinylidene fluoride (PVDF, a binder) at a mass ratio of 7:2:1, and was fully ground. The ground mixture was dispersed in an appropriate amount of N-methyl pyrrolidone solvent, and was magnetically stirred for 6 h. The uniformly stirred slurry was uniformly coated on a copper foil, and was transferred to a 110℃ vacuum drying box. After 12 h, the Fe2O3@Co-C@HGOF nanofiber electrode composite was taken out, and was cut into a 12 mm diameter electrode piece (each piece had a loading capacity of 2 mg) as a positive electrode. A CR2032 type button cell was assembled, pure lithium was used as a negative electrode, PE was used as a separator, 1.0 mol / L LiPF6+ ethyl carbonate / dimethyl carbonate (EC / DMC, a volume ratio of 1:1) was used as an electrolyte, and the assembly was formed in an argon-filled glove box, and was named as an experimental group 1. Fe2O3@Co-C@HGOF nanofiber electrode composites prepared in Example 2, Example 3 and Example 4 were respectively prepared into electrodes and assembled into the form according to the above method, and were respectively named as an experimental group 2, an experimental group 3 and an experimental group 4. Co-C@HGOF and Co-MOF@HGOF prepared in Example 2 were respectively prepared into electrodes and assembled into the form according to the above method, and were respectively named as a control group 1 and a control group 2.

[0051] Charging and discharging tests were performed using a battery test system (LAND CT2001A), the voltage range of the tests was 0.01-3V (vs. Li / Li+), the current density of the cycle performance test was 100 mA / g, the current density of the rate performance test was 100, 200, 400, 600, 800 and 1000 mA / g, and the electrochemical impedance of the CR2032 type button cell was measured using an electrochemical workstation (a frequency range was 10 5 -10 -2 Hz), and the test results are shown in Tables 2, 3 and 4.

[0052] Table 2 cycle performance test data at a current density of 1000 mA / g

[0053]

[0054]

[0055] As can be seen from the test data in Table 2, the initial capacity of the Fe2O3@Co-C@HGOF nanofiber electrode composite material of the experimental group 1 to the experimental group 4 can reach 970 mA·h / g or more, and the capacity after 200 cycles has almost no attenuation, and the coulombic efficiency is maintained at 99% or more; among them, the experimental group 4 obtains a new reinforcing body with the characteristics of carbon and graphene by etching Co-C@HGOF with hydrogen, further increases the active site, and the performance also reaches the optimum. The initial capacity of Co-C@HGOF of the control group 1 can reach 882 mA·h / g, and the capacity after 200 cycles is still maintained at 863 mA·h / g, but there is a small amount of attenuation, and the coulombic efficiency can reach 95% or more; and the initial capacity of Co-MOF@HGOF of the control group 2 is 765 mA·h / g, and the capacity after 200 cycles is reduced to 683 mA·h / g, which is severely attenuated, and the coulombic efficiency is less than 90%. As can be seen, the Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the present application has very excellent cycle stability, and can be completely used as a negative material of a lithium ion battery.

[0056] Table 3 rate performance test data (10th cycle capacity) at different current densities

[0057]

[0058] As can be seen from the test data in Table 3, the capacity of the Fe2O3@Co-C@HGOF nanofiber electrode composite material of the experimental group 1 to the experimental group 4 does not change much after the 10th cycle at the continuously increasing current density, indicating that the Fe2O3@Co-C@HGOF nanofiber electrode composite material has excellent rate performance; among them, the experimental group 4 obtains a new reinforcing body with the characteristics of carbon and graphene by etching Co-C@HGOF with hydrogen, further increases the active site, and the rate performance also reaches the optimum. And the Co-C@HGOF of the control group 1 also does not change much after the 10th cycle at the continuously increasing current density, indicating that the product Co-C@HGOF prepared in the process of the present application also has excellent rate performance. But the Co-MOF@HGOF of the control group 2 changes greatly after the 10th cycle at the continuously increasing current density, indicating that the rate performance of Co-MOF@HGOF is poor.

[0059] Table 4 Electrochemical impedance spectroscopy (EIS) test data

[0060]

[0061] As can be seen from the test data in Table 4: the Fe2O3@Co-C@HGOF nanofiber electrode composite materials of experimental group 1 to experimental group 4 were used to make electrodes, and the electrochemical impedance spectroscopy (frequency range: 10 5 -10 -2 Hz) of four groups of CR2032 button cells was measured respectively using an electrochemical workstation. The solution resistance of the four groups of CR2032 button cells was 3-4Ω, indicating that the electrolyte and the material were in good contact, and the hollow interior could be used as a transport pipeline for the electrolyte, greatly improving the ion transport rate; and the charge transfer resistance was below 100Ω, indicating that the conductivity of the Fe2O3@Co-C@HGOF nanofiber electrode composite materials of experimental group 1 to experimental group 4 was very excellent. The solution resistance of the control group 1 reached 7Ω, and the charge transfer resistance reached 120Ω, and the solution resistance of the control group 2 reached 12Ω, and the charge transfer resistance reached 150Ω, indicating that the contact between the electrolyte and the material of the control group was relatively poor compared with the experimental group, and the conductivity was not as good as that of the experimental group.

[0062] Wave absorption performance test:

[0063] The Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared in Example One was mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, binder) in a mass ratio of 7:2:1, and was thoroughly ground; the ground mixture was dispersed in an appropriate amount of N-methyl pyrrolidone solvent, and was magnetically stirred for 6h; the uniformly stirred slurry was uniformly coated on a copper foil with a coating thickness of 2mm, and was transferred to a 110℃ vacuum drying oven, and was taken out after 12h, and was cut into a circular piece with a diameter of 3mm, and was covered with PET film on both sides, and was named as experimental group 1. The Fe2O3@Co-C@HGOF nanofiber electrode composite materials prepared in Example Two, Example Three and Example Four were prepared according to the above method respectively, and were named as experimental group 2, experimental group 3 and experimental group 4 respectively. Co-C@HGOF and Co-MOF@HGOF prepared in Example Two were prepared according to the above method respectively, and were named as control group 1 and control group 2 respectively. Then their wave absorption performance was tested by a vector network analyzer, and the test results are shown in Table 5:

[0064] Table 5 Wave absorption performance test data

[0065]

[0066] As can be seen from the test data in Table 5, the Fe2O3@Co-C@HGOF nanofiber electrode composite materials of the experimental group 1 to the experimental group 4 have a lowest reflection loss of about 60 dB and an effective absorption bandwidth of more than 5 Hz at a thickness of 2 mm, and all have very good microwave absorption loss capacity. The lowest reflection loss of the Co-C@HGOF of the control group 1 and the Co-MOF@HGOF of the control group 2 is all less than 15 dB at a thickness of 2 mm, and the effective absorption bandwidth is all less than 1.5 Hz, so the microwave absorption loss capacity of the Co-C@HGOF and the Co-MOF@HGOF of the control group is relatively general. Therefore, the Fe2O3@Co-C@HGOF nanofiber electrode composite material prepared by the present application can simultaneously absorb and lose the electromagnetic radiation generated in the charging / discharging process of the lithium ion battery, hinder the surface energy transmission, and convert the energy of the electromagnetic radiation into heat energy to reduce the energy of the electromagnetic radiation.

[0067] The above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present application, and all should be covered in the scope of the claims of the present application. The technical parts not described in detail in the present application are well-known technologies.

Claims

1. A method for preparing Fe2O3@Co-C@HGOF nanofiber electrode composite material, characterized in that, The preparation method comprises the following steps: S1, preparation of graphene oxide gel: graphite powder and KNO3 are weighed in a mass ratio of 1:1, mixed uniformly to obtain a mixed powder, 10-15 times the weight of the mixed powder of concentrated H2SO4 is added, and stirring is carried out at 40℃ for 5-10 min, then 1.5-1.8 times the weight of the mixed powder of KMnO4 is slowly added, and stirring is continuously carried out at 40℃ for 3-6 h, 35-45 times the weight of the mixed powder of deionized water is added, and the temperature is increased to 60℃, and after being kept for 30-60 min, 60-100 times the weight of the mixed powder of deionized water is added, stirring is carried out for 5-10 min, 2.8-3.5 times the weight of the mixed powder of 30% H2O2 is added, and after being kept at room temperature for 5-12 h, the upper concentrated H2SO4 is removed, 60-100 times the weight of the mixed powder of deionized water is added, and then kept for 5-12 h, and the supernatant is removed by centrifugal separation, and the graphene oxide gel is obtained; S2, preparation of Co-MOF@HGOF: Co(CH3COO)2·4H2O is dissolved in 80-100 times the weight of anhydrous ethanol, Co(CH3COO)2·4H2O 0.5 times the weight of the graphene oxide gel prepared in S1 is added, and then Co(CH3COO)2·4H2O 40-50 times the weight of anhydrous ethanol is added, stirring is carried out for 3-12 h to obtain an A solution, Co(CH3COO)2·4H2O 6.1-6.6 times the weight of 2-methylimidazole is dissolved in Co(CH3COO)2·4H2O 120-150 times the weight of anhydrous ethanol to obtain a B solution, then the B solution is added to the A solution, ultrasonic treatment is carried out at room temperature for 3-6 h, and then kept at room temperature for 12-48 h, and the solid sample is obtained by centrifugal separation, the solid sample is washed with anhydrous ethanol for 2-5 times, and then vacuum dried to obtain the Co-MOF@HGOF; S3, preparation of Co-C@HGOF: the Co-MOF@HGOF prepared in S2 is placed in a porcelain boat, transferred into a tube furnace, and heated to 600℃ at a heating rate of 3℃ / min under the protection of argon, and kept for 0.5 h-2 h, and then naturally cooled to obtain the Co-C@HGOF; S4, preparation of Fe2O3@Co-C@HGOF nanofiber electrode composite material: the Co-C@HGOF obtained in S3 is taken, mixed with 3-5 times the weight of iron nitrate to obtain a mixed material, and then the mixed material is uniformly dispersed in 10-15 times the weight of the Co-C@HGOF of concentrated H2SO4, and then refluxed at 80℃ for 3-5 h, and then cooled, the filtrate is removed by filtration, and then the filter residue is repeatedly washed with deionized water, and then fully dried at 100℃, and then calcined at a heating rate of 3℃ / min to 500℃ under the protection of argon for 3 h to obtain the Fe2O3@Co-C@HGOF nanofiber electrode composite material.

2. The production method according to claim 1, wherein The method of adding 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 2.8-3.5 times the weight of the mixed powder 3. The production method according to claim 2, wherein ​ 4. The production method according to claim 3, wherein ​ 5. The production method according to claim 4, wherein ​ 6. The production method according to claim 5, wherein ​ 7. The production method according to claim 6, wherein ​ ​ ​

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