Iron-carbon composite negative electrode, and preparation method and application thereof

Abstract

The application provides an iron-carbon composite negative electrode and a preparation method and application thereof, the iron-carbon composite negative electrode comprises a substrate and a coating layer on the surface of the substrate, the coating layer comprises a carbon coating layer, and the substrate comprises carbon fibers and Fe2O3 particles dispersed in the carbon fibers and on the surface of the carbon fibers; the Fe2O3 in the iron-carbon composite negative electrode is stably dispersed in the carbon fibers coated by the carbon coating layer, the expansion of the Fe2O3 is inhibited through the synergistic effect of the carbon fibers and the carbon coating layer, meanwhile, space is provided for the expansion of the Fe2O3, and the long cycle performance of the battery is greatly improved; meanwhile, the negative electrode can be directly used as a negative electrode, does not need to be used in combination with a binder and a conductive agent, and does not need to use a current collector, so that the preparation process of the lithium ion battery is greatly simplified.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to an iron-carbon composite negative electrode and a preparation method and application thereof. BACKGROUND

[0002] Since the ferroferric oxide has a high theoretical specific capacity and is environmentally friendly when used as a negative electrode material of a lithium ion battery, the ferroferric oxide needs to be modified to inhibit volume expansion and improve conductivity due to the large volume change of the ferroferric oxide negative electrode material during charging and discharging, the easy pulverization of the ferroferric oxide negative electrode material, and the poor conductivity of the ferroferric oxide.

[0003] CN 105355908A discloses a lithium ion battery composite negative electrode material, a preparation method thereof, a negative electrode using the material, and a lithium ion battery. The preparation method of the lithium ion battery composite negative electrode material comprises the following steps: ball milling raw material Fe2O3 and raw material carbon material to obtain Fe2O3 / carbon composite powder material, and calcining the obtained Fe2O3 / carbon composite powder material to obtain the lithium ion battery composite negative electrode material. Although the Fe2O3 is combined with the carbon material, the obtained composite material still has the problem of rapid capacity attenuation after being assembled into a battery and subjected to electrochemical testing, and has a low reversible capacity.

[0004] In addition, the ferroferric oxide material in the prior art needs to be mixed with a binder, a conductive agent, and a solvent to form a slurry, and the slurry is coated on a current collector for use, which limits the capacity of the ferroferric oxide and reduces the energy density of the battery, and is not conducive to the application of the ferroferric oxide negative electrode material.

[0005] Based on the above research, it is necessary to provide an iron-carbon composite negative electrode, in which the stability of the ferroferric oxide is high, and there is sufficient expansion space, so that the iron-carbon composite negative electrode not only has excellent conductivity and cycle performance, but also can be directly used as a lithium battery negative electrode, thereby improving the volume energy density of the battery. SUMMARY

[0006] The application aims to provide an iron-carbon composite negative electrode and a preparation method and application thereof. The ferroferric oxide in the iron-carbon composite negative electrode is stably dispersed in carbon fibers coated with a carbon coating layer. Through the synergistic effect of the carbon fibers and the carbon coating layer, the expansion of the ferroferric oxide is inhibited, and space is provided for the expansion of the ferroferric oxide, thereby greatly improving the long cycle performance of the battery. At the same time, the negative electrode can be directly used as a negative electrode without the need for compounding with a binder and a conductive agent, and without the need for using a current collector, thereby greatly simplifying the preparation process of the lithium ion battery.

[0007] To achieve the object of the present application, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides an iron-carbon composite negative electrode, which comprises a substrate and a coating layer on the surface of the substrate, wherein the coating layer comprises a carbon coating layer, and the substrate comprises carbon fibers and Fe2O3 particles dispersed in the carbon fibers.

[0009] The Fe2O3 particles are dispersed in the carbon fibers, on the one hand, due to the structure of the carbon fibers, the stability of the Fe2O3 in the carbon fibers is high, and the carbon fibers can provide space for the expansion of the Fe2O3; on the other hand, the surface of the composite negative electrode of the present application is also coated with a carbon coating layer, which can not only improve the conductivity of the negative electrode, but also inhibit the expansion of the Fe2O3 dispersed on the surface of the carbon fibers, thereby further improving the cycle performance of the negative electrode; in addition, the negative electrode of the present application uses carbon fibers as the substrate, so that the composite negative electrode of the present application can be directly used as a negative electrode without the need for additional binders, conductive agents and current collectors.

[0010] Preferably, the carbon coating layer is a nitrogen-containing carbon coating layer.

[0011] The present application uses a nitrogen-containing carbon coating layer for coating, which can further improve the conductivity of the negative electrode.

[0012] Preferably, the carbon in the carbon coating layer is a polymer-based carbon and a metal-organic framework-based carbon.

[0013] The present application contains carbon fibers, a polymer-based carbon layer and a metal-organic framework-based carbon layer, that is, the negative electrode of the present application contains three kinds of carbon, and the synergistic effect of the three kinds of carbon maximally inhibits the expansion of the Fe2O3, thereby improving the conductivity of the negative electrode; and the metal-organic framework-based carbon of the present application is a porous carbon, which can further provide space for the expansion of the surface Fe2O3 particles.

[0014] In a second aspect, the present application provides a preparation method of the iron-carbon composite negative electrode according to the first aspect, which comprises the following steps:

[0015] (1) mixing Fe2O3, a high molecular material and a solvent to obtain a spinning solution, and performing electrostatic spinning and heat treatment on the spinning solution to obtain carbon fibers;

[0016] (2) mixing a coating liquid with the carbon fibers of step (1) and carbonizing to obtain the iron-carbon composite negative electrode.

[0017] The application prepares a spinning solution by preparing the ferric sesquioxide together with the polymer material and the solvent, and the ferric sesquioxide particles are uniformly dispersed in the interior and surface of the nanometer carbon fiber, but the ferric sesquioxide will cause severe volume expansion in the charging and discharging process when used as the negative electrode of the lithium battery, so the structure of the ferric oxide nanometer fiber is still unstable in the battery cycle process, therefore, the application forms a core-shell structure by coating, and provides a buffer space for the expansion of the ferric oxide.

[0018] Preferably, the carbon fiber in step (1) is subjected to surface acid treatment before step (2) is performed.

[0019] The application can convert the unstable ferric oxide particles on the fiber surface into ferric ions by surface acid treatment, so as to prepare the metal organic framework material-based carbon subsequently.

[0020] Preferably, the surface acid treatment comprises: dropping and / or spraying acid on the surface of the spinning fiber in step (1), and then drying to complete the surface acid treatment.

[0021] The application directly dries after acid treatment, removes water and volatilizes acid gas, and makes the iron salt generated in the reaction adhere to the surface of the fiber.

[0022] Preferably, the concentration of the acid used in the surface acid treatment is 0.05-0.3 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L or 0.3 mol / L, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0023] The concentration of the acid in the application will affect the effect of the surface treatment and the stability of the ferric sesquioxide in the carbon fiber, if the concentration of the acid is too high, the internal ferric sesquioxide will be decomposed by excessive acidification, and if the concentration of the acid is too low, the effect of the surface treatment will decrease.

[0024] Preferably, the acid used in the surface acid treatment comprises hydrochloric acid.

[0025] Preferably, the reaction is performed for 2-10 min after the acid is dropped and / or sprayed on the surface, for example, it can be 2 min, 5 min or 10 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0026] Preferably, the drying temperature is 30-50℃, for example, it can be 30℃, 40℃ or 50℃, and the time is 1-3 h, for example, it can be 1 h, 2 h or 3 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0027] Preferably, the coating liquid in step (2) comprises a carbon source and an organic ligand.

[0028] The carbon source in the coating solution can coat the carbon fiber, the organic ligand can react with the trivalent iron ion after surface acid treatment to generate a metal organic framework material, and after carbonization, the metal organic framework material can generate porous carbon, thereby further improving the stability of the ferric oxide on the surface of the carbon fiber, and providing a buffer space for the expansion of the ferric oxide on the surface of the carbon fiber.

[0029] Preferably, the carbon source comprises dopamine.

[0030] The present application uses dopamine as the carbon source of the carbon coating layer, and the dopamine in the coating solution can first polymerize in situ on the surface of the carbon fiber to generate polydopamine. Compared with other conventional coating methods, the in-situ coated coating layer is more uniform and dense.

[0031] Preferably, the organic ligand comprises 2-methylimidazole.

[0032] Preferably, the coating solution further comprises tris-hydroxymethyl aminomethane and deionized water.

[0033] Preferably, the coating solution further comprises urea.

[0034] The present application further adds urea during the hydrothermal reaction. The addition of urea increases the N element content of the carbon fiber. Nitrogen doping can improve the chemical reaction activity, electrical conductivity and adsorption speed of lithium ions of the carbon material. The nitrogen-containing functional group promotes electron conduction and provides a large number of chemical reaction active sites during high-current charge and discharge, and can quickly embed lithium, avoid the precipitation of lithium ions on the surface of the negative electrode, and provide battery cycle performance.

[0035] Preferably, the pH of the coating solution is 8.5-9, for example, it can be 8.5, 8.7 or 9.0, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0036] Preferably, in the coating solution, the mass ratio of the carbon source to deionized water is (0.5-2):50, for example, it can be 0.5:50, 1:50 or 2:50, the mass ratio of the organic ligand to deionized water is (1-3):50, for example, it can be 1:50, 2:50 or 3:50, and the mass ratio of urea to deionized water is (1-3):50, for example, it can be 1:50, 2:50 or 3:50, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0037] Preferably, the mixing of step (2) comprises hydrothermal reaction of the carbon fiber in the coating solution.

[0038] The step (2) of the present application is carried out in a reaction kettle to promote in-situ polymerization of polydopamine on the surface of the carbon fiber and coordination of ferric ions on the surface of the carbon fiber with organic ligands, thereby promoting generation of the metal organic framework material.

[0039] Preferably, the temperature of the hydrothermal reaction is 100-150 DEG C, for example, 100 DEG C, 125 DEG C or 150 DEG C, and the time is 10-20 h, for example, 10 h, 15 h or 20 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0040] Preferably, the temperature of the carbonization in step (2) is 800-1000 DEG C, for example, 800 DEG C, 900 DEG C or 1000 DEG C, and the time is 1-3 h, for example, 1 h, 2 h or 3 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0041] Preferably, the heating rate of the carbonization in step (2) is 1-5 DEG C / min, for example, 1 DEG C / min, 3 DEG C / min or 5 DEG C / min, and the atmosphere is a nitrogen atmosphere.

[0042] Preferably, the mass ratio of the ferric oxide and the polymer material in step (1) is (0.5-1):1, for example, 0.5:1, 0.75:1 or 1:1, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0043] Preferably, the mass ratio of the polymer material and the solvent in step (1) is (0.1-0.5):1, for example, 0.5:1, 1:1 or 2:1, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0044] Preferably, the polymer material in step (1) comprises PAN (polyacrylonitrile).

[0045] Preferably, the mixing in step (1) comprises ultrasonic dispersion of the ferric oxide and the solvent, followed by heating and stirring with the polymer material.

[0046] Preferably, the ultrasonic dispersion is carried out for 10-30 min, for example, 10 min, 20 min or 30 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0047] Preferably, the heating and stirring is carried out at a temperature of 60-80 DEG C, for example, 60 DEG C, 70 DEG C or 80 DEG C, and for a time of 10-14 h, for example, 10 h, 12 h or 14 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0048] Preferably, the heat treatment of step (1) comprises solidification and calcination in sequence.

[0049] Preferably, the solidification is performed at a temperature of 200-300℃, for example 200℃, 250℃ or 300℃, for a time of 1-3h, for example 1h, 2h or 3h, at a heating rate of 0.5-1.5℃ / min, for example 0.5℃ / min, 1℃ / min or 1.5℃ / min, in an air atmosphere.

[0050] Preferably, the calcination is performed at a heating rate of 0.5-1.5℃ / min, for example 0.5℃ / min, 1℃ / min or 1.5℃ / min, at a temperature of 600-800℃, for example 600℃, 700℃ or 800℃, for a time of 1-3h, for example 1h, 2h or 3h, in an inert gas atmosphere.

[0051] Preferably, the electrospinning of step (1) is performed at a voltage of 10-20KV, for example 10KV, 15KV or 20KV, at a temperature of 25-35℃, for example 25℃, 30℃ or 35℃, at a humidity of 10-30%, for example 10%, 20% or 30%, but not limited to the listed values, other values within the range of values are also applicable.

[0052] Preferably, the electrospinning of step (1) is performed at an injection speed of 0.2-1mL / h, for example 0.2mL / h, 0.5mL / h or 1mL / h, for a time of 8-12h, for example 8h, 10h or 12h, but not limited to the listed values, other values within the range of values are also applicable.

[0053] Preferably, the electrospinning of step (1) is performed at a distance of 15-20cm, for example 15cm, 17.5cm or 20cm, between the needle tip and the receiving plate, but not limited to the listed values, other values within the range of values are also applicable.

[0054] As a preferred technical case of the preparation method of the present application, the preparation method comprises the following steps:

[0055] (1) ultrasonic dispersion of the ferric sesquioxide and a solvent for 10-30 min, then adding a polymer material, heating and stirring at a temperature of 60-80 DEG C for 10-14 h to obtain a spinning solution, electrospinning of the spinning solution at a voltage of 10-20 KV, a temperature of 25-35 DEG C, a humidity of 10-30 %, an injection speed of 0.2-1 mL / h, a needle tip to receiving plate distance of 15-20 cm, after the electrospinning, curing in an air atmosphere at a temperature of 200-300 DEG C at a temperature increasing rate of 0.5-1.5 DEG C / min for 1-3 h, and then calcining in an inert gas atmosphere at a temperature of 600-800 DEG C at a temperature increasing rate of 0.5-1.5 DEG C / min for 1-3 h to obtain carbon fibers;

[0056] wherein the mass ratio of the ferric sesquioxide to the polymer material is (0.5-1):1, and the mass ratio of the polymer material to the solvent is (0.1-0.5):1;

[0057] (2) adding and / or spraying an acid with a concentration of 0.05-0.3 mol / L on the surface of the carbon fibers obtained in step (1) and reacting for 2-10 min, and then drying at 30-50 DEG C for 1-3 h to obtain carbon fibers with a surface acid treatment;

[0058] (3) hydrothermal reaction of the carbon fibers with a surface acid treatment obtained in step (2) in a coating liquid at a temperature of 100-150 DEG C for 10-20 h, and then carbonizing at a temperature of 800-1000 DEG C at a temperature increasing rate of 1-5 DEG C / min for 1-3 h to obtain the iron-carbon composite negative electrode.

[0059] The coating liquid comprises a carbon source, an organic ligand, urea, tris-hydroxymethyl aminomethane and deionized water, wherein the carbon source comprises dopamine; and the pH of the coating liquid is 8.5-9.

[0060] In a third aspect, the application provides a battery comprising the iron-carbon composite negative electrode according to the first aspect.

[0061] Compared with the prior art, the application has the following beneficial effects:

[0062] On the one hand, the carbon fibers are used as the matrix, and the ferric sesquioxide particles are dispersed in the carbon fibers, which improves the stability of the ferric sesquioxide, provides space for the expansion of the ferric sesquioxide, and enables the composite negative electrode to be directly used as a negative electrode without the need for a binder, a conductive agent and a current collector; on the other hand, the carbon coating layer on the surface of the matrix improves the conductivity of the negative electrode and inhibits the expansion of the ferric sesquioxide on the surface of the carbon fibers, further improving the cycle performance of the negative electrode. DETAILED DESCRIPTION

[0063] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0064] Embodiment 1

[0065] The present embodiment provides an iron-carbon composite negative electrode, which comprises a substrate and a coating layer on the surface of the substrate, the coating layer comprises a carbon coating layer, the substrate comprises carbon fibers and Fe2O3 particles dispersed in the interior and surface of the carbon fibers, the carbon coating layer is a nitrogen-containing carbon coating layer, and the carbon in the carbon coating layer is polymer-based carbon and metal organic framework material-based carbon.

[0066] The preparation method of the iron-carbon composite negative electrode comprises the following steps:

[0067] (1) ultrasonic dispersion of Fe2O3 and DMF for 20 min, then PAN is added and heated and stirred at a temperature of 70℃ for 12 h to obtain a spinning solution, electrospinning of the spinning solution is carried out at a voltage of 15KV, a temperature of 30℃, a humidity of 20%, an injection speed of 0.8mL / h, and a needle tip to receiving plate distance of 18cm, after spinning, curing in an air atmosphere at a temperature of 250℃ and a temperature rising rate of 1℃ / min for 2h, and then calcination in an argon atmosphere at a temperature of 700℃ and a temperature rising rate of 1℃ / min for 2h to obtain carbon fibers;

[0068] wherein the mass ratio of Fe2O3 to PAN is 0.75:1, and the mass ratio of PAN to DMF is 0.1:1;

[0069] (2) the surface of the carbon fibers in step (1) is sprayed with 0.1mol / L hydrochloric acid and reacted for 5min, and then dried at 40℃ for 2h to obtain carbon fibers after surface acid treatment;

[0070] (3) mixing dopamine, deionized water, urea and tris, then adding an organic ligand, stirring to obtain a coating solution with a pH of 9, and placing the carbon fibers after surface acid treatment in step (2) in the coating solution for hydrothermal reaction, the temperature of the hydrothermal reaction is 125℃, and the time is 15h, then taking out and carbonizing in a nitrogen atmosphere at a temperature of 900℃ and a temperature rising rate of 3℃ / min for 2h to obtain the iron-carbon composite negative electrode;

[0071] In the coating solution, the mass ratio of dopamine to deionized water is 1:50, the mass ratio of organic ligand to deionized water is 2:50, and the mass ratio of urea to deionized water is 2:50; the organic ligand is 2-methylimidazole.

[0072] Embodiment 2

[0073] The embodiment provides an iron-carbon composite negative electrode, which comprises a substrate and a coating layer on the surface of the substrate, the coating layer comprises a carbon coating layer, the substrate comprises carbon fibers and Fe2O3 particles dispersed in the interior and surface of the carbon fibers, the carbon coating layer is a nitrogen-containing carbon coating layer, and the carbon in the carbon coating layer is polymer-based carbon and metal organic framework material-based carbon.

[0074] The preparation method of the iron-carbon composite negative electrode comprises the following steps:

[0075] (1) ultrasonic dispersion of Fe2O3 and DMF for 30 min, then PAN is added, heating and stirring at a temperature of 60 DEG C for 14 h to obtain a spinning solution, electrospinning of the spinning solution at a voltage of 20 KV, a temperature of 25 DEG C, a humidity of 10%, an injection speed of 1 mL / h, a needle tip to receiving plate distance of 15 cm, after spinning, curing at a temperature of 300 DEG C at a temperature rising rate of 0.5 DEG C / min for 1 h, and then calcining at a temperature of 600 DEG C at a temperature rising rate of 1.5 DEG C / min for 3 h in an argon gas atmosphere to obtain carbon fibers;

[0076] wherein the mass ratio of Fe2O3 to PAN is 1:1, and the mass ratio of PAN to DMF is 0.25:1;

[0077] (2) the surface of the carbon fibers in step (1) is sprayed with hydrochloric acid with a concentration of 0.05 mol / L, and reacted for 10 min, and then dried at 30 DEG C for 1 h to obtain carbon fibers after surface acid treatment;

[0078] (3) mixing dopamine, deionized water, urea and tris, then adding an organic ligand, stirring to obtain a coating solution with a pH of 8.5, and placing the carbon fibers after surface acid treatment in step (2) in the coating solution for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 100 DEG C, and the time is 20 h, then taking out, carbonizing at a temperature of 1000 DEG C at a temperature rising rate of 1 DEG C / min for 1 h in a nitrogen atmosphere to obtain the iron-carbon composite negative electrode;

[0079] In the coating solution, the mass ratio of dopamine to deionized water is 2:50, the mass ratio of the organic ligand to deionized water is 3:50, and the mass ratio of urea to deionized water is 1:50; and the organic ligand is 2-methylimidazole.

[0080] Example 3

[0081] The embodiment provides an iron-carbon composite negative electrode, which comprises a substrate and a coating layer on the surface of the substrate, the coating layer comprises a carbon coating layer, the substrate comprises carbon fibers and ferroferric oxide particles dispersed in the carbon fibers and on the surface of the carbon fibers, the carbon coating layer is a nitrogen-containing carbon coating layer, and the carbon in the carbon coating layer is polymer-based carbon and metal organic framework material-based carbon.

[0082] The preparation method of the iron-carbon composite negative electrode comprises the following steps:

[0083] (1) ultrasonic dispersion of ferroferric oxide and DMF for 10 min, then PAN is added, heating and stirring at a temperature of 80 DEG C for 10 h to obtain a spinning solution, electrospinning of the spinning solution at a voltage of 10 KV, a temperature of 35 DEG C, a humidity of 30%, an injection speed of 0.2 mL / h, and a needle tip to receiving plate distance of 20 cm, after spinning, curing at a temperature of 200 DEG C for 3 h in an air atmosphere at a temperature rising rate of 1.5 DEG C / min, and then calcining at a temperature of 800 DEG C for 1 h in an argon atmosphere at a temperature rising rate of 0.5 DEG C / min to obtain carbon fibers;

[0084] The mass ratio of the ferroferric oxide to the PAN is 0.5:1, and the mass ratio of the PAN to the DMF is 0.5:1.

[0085] (2) the surface of the carbon fibers in step (1) is sprayed with hydrochloric acid with a concentration of 0.3 mol / L, and reacts for 2 min, and then is dried at 50 DEG C for 3 h to obtain carbon fibers with a surface acid treatment;

[0086] (3) mixing dopamine, deionized water, urea and tris, then adding an organic ligand, stirring to obtain a coating solution with a pH of 9, and then placing the carbon fibers with a surface acid treatment in step (2) in the coating solution to perform a hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 150 DEG C, and the time is 10 h, and then taking out, carbonizing at a temperature of 800 DEG C for 3 h in a nitrogen atmosphere at a temperature rising rate of 5 DEG C / min to obtain the iron-carbon composite negative electrode.

[0087] In the coating solution, the mass ratio of dopamine to deionized water is 0.5:50, the mass ratio of the organic ligand to deionized water is 1:50, and the mass ratio of urea to deionized water is 3:50; and the organic ligand is 2-methylimidazole.

[0088] Embodiment 4

[0089] The embodiment provides an iron-carbon composite negative electrode, which comprises a substrate and a coating layer on the surface of the substrate, the coating layer comprises a carbon coating layer, the substrate comprises carbon fibers and ferroferric oxide particles dispersed in the carbon fibers and on the surface of the carbon fibers, the carbon coating layer is a nitrogen-containing carbon coating layer, and the carbon in the carbon coating layer is polymer-based carbon and metal organic framework material-based carbon.

[0090] Example 5

[0091] This example provides a kind of iron-carbon composite negative electrode, the concentration of hydrochloric acid in the preparation method, step (2) is 0.01 mol / L, except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0092] Example 6

[0093] This example provides a kind of iron-carbon composite negative electrode, the preparation method does not carry out surface acid treatment in step (2), except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0094] Example 7

[0095] This example provides a kind of iron-carbon composite negative electrode, the preparation method does not add organic ligand in step (3), except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0096] Example 8

[0097] This example provides a kind of iron-carbon composite negative electrode, the preparation method does not add urea in step (3), except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0098] Example 9

[0099] This example provides a kind of iron-carbon composite negative electrode, the preparation method in step (3) is replaced by polydopamine with dopamine of equal quality, except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0100] Example 10

[0101] This example provides a kind of iron-carbon composite negative electrode, the preparation method does not carry out hydrothermal reaction in step (3), but directly stirs and mixes 15h at normal temperature, except that the adaptability of the obtained iron-carbon composite negative electrode changes, otherwise it is identical with example 1.

[0102] Comparative Example 1

[0103] This comparative example provides a kind of iron-carbon composite negative electrode, which includes carbon fiber and iron oxide particles dispersed inside and on the surface of the carbon fiber.

[0104] The preparation method of the iron-carbon composite negative electrode is identical with example 1, except that steps (2) and (3) are not carried out.

[0105] The iron-carbon composite negative electrode obtained in the above examples and comparative examples was prepared into a lithium ion battery together with a lithium cobalt oxide positive electrode, an electrolyte (including 85% ethylene carbonate, 12% lithium hexafluorophosphate, and 3% vinylene carbonate) and a polyethylene separator. The lithium ion battery was tested under the conditions of constant current and constant voltage charging at 0.5 C to 4.2 V, a cutoff current of 0.02 C, constant current discharging at 1 C, and a cutoff voltage of 3.0 V. The initial efficiency, capacity retention rate after 100 cycles and 500 cycles were tested.

[0106] The test results are shown in the following table:

[0107] Table 1

[0108]

[0109]

[0110] From the above table, it can be seen that:

[0111] (1) The iron-carbon composite negative electrode obtained by the present application can be directly used as a negative electrode and has excellent cycle performance; as can be seen from Example 1 and Comparative Example 1, surface treatment and in-situ carbon coating on the substrate surface can further improve the stability of the ferric oxide and inhibit the expansion of the ferric oxide; as can be seen from Example 1 and Examples 4-5, the acid concentration of the surface acid treatment affects the effect of the surface treatment and the stability of the particles inside the fiber, and the optimal surface treatment effect can be obtained when the acid concentration is within a reasonable range; as can be seen from Example 1 and Example 6, when no surface acid treatment is performed, the carbon coating layer on the surface of the substrate does not include metal organic framework-based carbon, and compared to Example 1, no ZIF material is generated on the surface of Example 6, and the stability of the ferric oxide particles on the surface of the carbon fiber decreases.

[0112] (2) As can be seen from Example 1 and Example 7, surface acid treatment was performed, but no metal organic framework material was generated when the organic ligand was added to coordinate with the trivalent iron ion during the hydrothermal reaction, which resulted in a decrease in the performance of the negative electrode; as can be seen from Example 1 and Example 8, the addition of urea can further improve the conductivity and other properties of the negative electrode, thereby further improving the performance of the negative electrode; as can be seen from Example 1 and Example 9, in-situ coating of polydopamine and then carbonization can improve the uniformity and coating strength of the carbon coating layer compared to direct coating of dopamine and then carbonization; as can be seen from Example 1 and Example 10, the hydrothermal reaction of the carbon fiber with the coating liquid in the present application can promote the generation of polydopamine on the surface of the carbon fiber and also promote the generation of metal organic framework material, thereby further improving the performance of the negative electrode.

[0113] In summary, the application provides an iron-carbon composite negative electrode and a preparation method and application thereof, in which the ferric oxide particles are stably dispersed in the interior and surface of the carbon fiber coated by the carbon coating layer, the expansion of the ferric oxide is inhibited by the synergistic effect of the carbon fiber and the carbon coating layer, meanwhile, the space for the expansion of the ferric oxide is provided, and the long cycle performance of the battery is greatly improved; meanwhile, the negative electrode can be directly used as the negative electrode without the use of the binder and the conductive agent, and the current collector is not needed, so that the preparation process of the lithium ion battery is greatly simplified.

[0114] The above merely provides a specific implementation of the application, but the protection scope of the application is not limited thereto, and those skilled in the art should understand that any change or replacement within the technical scope disclosed by the application can be easily thought of by those skilled in the art, and falls within the protection scope and disclosure scope of the application.

Claims

1. An iron-carbon composite negative electrode, characterized by, The iron-carbon composite negative electrode comprises a substrate and a coating layer on the surface of the substrate, wherein the coating layer comprises a carbon coating layer, and the substrate comprises carbon fibers and Fe2O3 particles dispersed inside and on the surface of the carbon fibers. The preparation method of the iron-carbon composite negative electrode comprises the following steps: (1) mixing Fe2O3, a polymer material and a solvent to obtain a spinning solution, and performing electrostatic spinning and heat treatment on the spinning solution to obtain carbon fibers; (2) performing hydrothermal reaction and carbonization on the carbon fibers obtained in step (1) with a coating solution to obtain the iron-carbon composite negative electrode; Before step (2) is performed, the carbon fibers obtained in step (1) are subjected to surface acid treatment; The coating solution in step (2) comprises a carbon source and an organic ligand.

2. The Fe-C composite negative electrode according to claim 1, characterized by The carbon coating layer is a nitrogen-containing carbon coating layer.

3. The Fe-C composite negative electrode according to claim 1, characterized by The carbon in the carbon coating layer is polymer-based carbon and metal organic framework material-based carbon.

4. A method for producing the iron-carbon composite negative electrode according to any one of claims 1 to 3, characterized by, The preparation method comprises the following steps: (1) mixing Fe2O3, a polymer material and a solvent to obtain a spinning solution, and performing electrostatic spinning and heat treatment on the spinning solution to obtain carbon fibers; (2) performing hydrothermal reaction and carbonization on the carbon fibers obtained in step (1) with a coating solution to obtain the iron-carbon composite negative electrode; Before step (2) is performed, the carbon fibers obtained in step (1) are subjected to surface acid treatment; The coating solution in step (2) comprises a carbon source and an organic ligand.

5. The preparation method according to claim 4, characterized in that, The surface acid treatment comprises: dropping and / or spraying acid on the surface of the carbon fibers obtained in step (1), and then drying to complete the surface acid treatment.

6. The preparation method according to claim 4, characterized in that, The concentration of the acid used in the surface acid treatment is 0.05-0.3 mol / L.

7. The preparation method according to claim 4, characterized in that, The acid used in the surface acid treatment comprises hydrochloric acid.

8. The preparation method according to claim 5, characterized in that, After the surface dropping and / or spraying of the acid, the reaction is performed for 2-10 min, and then drying is performed.

9. The preparation method according to claim 5, characterized in that, The temperature of the drying is 30-50℃, and the time is 1-3 h.

10. The method of claim 4, wherein, The carbon source comprises dopamine.

11. The preparation method according to claim 4, characterized in that, The organic ligand comprises 2-methylimidazole.

12. The method of claim 4, wherein, The coating solution in step (2) further comprises urea.

13. The preparation method according to claim 4, characterized in that, The coating solution in step (2) further comprises tris-hydroxymethyl aminomethane and deionized water.

14. The method of claim 4, wherein, The pH of the coating solution in step (2) is 8.5-9.

15. The preparation method according to claim 4, characterized in that, The temperature of the hydrothermal reaction in step (2) is 100-150℃, and the time is 10-20 h.

16. The method of claim 4, wherein, The temperature of the carbonization in step (2) is 800-1000℃, and the time is 1-3 h.

17. The preparation method according to claim 4, characterized in that, The heating rate of the carbonization in step (2) is 1-5℃ / min, and the atmosphere is a nitrogen atmosphere.

18. The method of claim 4, wherein, The mass ratio of Fe2O3 to the polymer material in step (1) is (0.5-1):

1.

19. The method of claim 4, wherein, The mass ratio of the polymer material to the solvent in step (1) is (0.1-0.5):

1.

20. The method of claim 4, wherein, The polymer material in step (1) comprises PAN.

21. The method of claim 4, wherein, The mixing in step (1) comprises: first ultrasonic dispersion of Fe2O3 and the solvent, and then heating and stirring with the polymer material.

22. The method of claim 21, wherein, The ultrasonic dispersion time is 10-30 min.

23. The preparation method according to claim 21, characterized in that, The heating and stirring temperature is 60-80℃, and the time is 10-14 h.

24. The method of claim 4, wherein, The heat treatment in step (1) comprises solidification and calcination performed in sequence.

25. The method of claim 24, wherein, The solidification temperature is 200-300℃, the time is 1-3 h, the heating rate is 0.5-1.5℃ / min, and the atmosphere is an air atmosphere.

26. The method of claim 24, wherein, The roasting has a temperature raising rate of 0.5-1.5℃ / min, a temperature of 600-800℃, a time of 1-3h, and an inert gas atmosphere.

27. The method of claim 4, wherein, The electrospinning in step (1) has a voltage of 10-20KV, a temperature of 25-35℃, and a humidity of 10-30%.

28. The method of claim 4, wherein, The electrospinning in step (1) has an injection speed of 0.2-1mL / h and a time of 8-12h.

29. The method of claim 4, wherein, The electrospinning in step (1) has a distance between the needle tip and the receiving plate of 15-20cm.

30. The method of claim 4, wherein, The preparation method comprises the following steps: (1) ultrasonic dispersion of ferroferric oxide and solvent for 10-30min, then adding a polymer material, heating and stirring at a temperature of 60-80℃ for 10-14h to obtain a spinning solution, electrospinning of the spinning solution at a voltage of 10-20KV, a temperature of 25-35℃, a humidity of 10-30%, an injection speed of 0.2-1mL / h, and a distance between the needle tip and the receiving plate of 15-20cm, after the electrospinning, curing in an air atmosphere at a temperature of 200-300℃ for 1-3h with a temperature raising rate of 0.5-1.5℃ / min, and roasting in an inert gas atmosphere at a temperature of 600-800℃ for 1-3h with a temperature raising rate of 0.5-1.5℃ / min to obtain carbon fibers; wherein the mass ratio of the ferroferric oxide and the polymer material is (0.5-1):1, and the mass ratio of the polymer material and the solvent is (0.1-0.5):1; (2) adding and / or spraying an acid with a concentration of 0.05-0.3mol / L on the surface of the carbon fibers in step (1) for reaction for 2-10min, and then drying at 30-50℃ for 1-3h to obtain carbon fibers with surface acid treatment; (3) hydrothermal reaction of the carbon fibers with surface acid treatment in step (2) in a coating liquid, the hydrothermal reaction having a temperature of 100-150℃ and a time of 10-20h, and then taking out and carbonizing at a temperature of 800-1000℃ for 1-3h with a temperature raising rate of 1-5℃ / min to obtain the iron-carbon composite negative electrode; the coating liquid comprising a carbon source, an organic ligand, urea, tris-hydroxymethyl aminomethane, and deionized water, wherein the carbon source comprises dopamine; and the coating liquid has a pH of 8.5-9.

31. A battery, characterized by The battery comprises the iron-carbon composite negative electrode according to any one of claims 1-3.

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