Carbon nanomaterial and preparation method thereof, conductive agent and application thereof

Abstract

The present invention discloses a carbon nanomaterial, a preparation method thereof, a conductive agent, and its application, and relates to the technical field of conductive materials. The method for preparing the carbon nanomaterial of the present invention comprises: (1) pre-treating polymer fibers and then subjecting them to ultraviolet ozone treatment to obtain modified fibers; and (2) carbonizing the modified fibers to obtain carbon nanofibers. By subjecting the polymer fibers to ultraviolet ozone treatment, the present invention successfully introduces oxidizing groups into the polymer, thereby improving the conductivity of the carbon nanomaterial. Furthermore, the method provided by the present invention is simple and can be industrially produced.

Description

Technical field:

[0001] The present invention relates to the technical field of conductive materials, and in particular to a carbon nanomaterial and a preparation method thereof, a conductive agent and applications thereof. Background technology:

[0002] The shortage of oil resources and environmental pollution have always been the focus of attention around the world. It is well known that fuel-powered vehicles are the main fuel consumers and major sources of air pollution. For this reason, new energy vehicles have gradually become the research focus of many scientists to alleviate energy and environmental problems.

[0003] Lithium-ion batteries, with their outstanding advantages such as high energy density, long cycle life, and light weight, have become a current research hotspot. Lithium-ion cathode materials play a crucial role in the entire battery, but most cathode materials suffer from high internal resistance, which hinders the release of active substances and results in low actual discharge capacity. Therefore, it is necessary to add an appropriate amount of conductive agent to the cathode to accelerate electron conduction between the active substances and effectively reduce internal resistance.

[0004] Common conductive agents include granular and fibrous forms. Fibrous conductive agents have a large aspect ratio, which facilitates the formation of a conductive network and allows for superior performance at lower dosages. Carbon nanofibers are a common type of fibrous conductive agent. Their conductivity is typically enhanced through doping, but the doping process is complex and requires chemical reagents such as concentrated acid. This process is highly environmentally friendly and unsuitable for industrial production. Summary of the invention:

[0005] The purpose of the present invention is to overcome the cumbersome technical problems of existing carbon nanomaterial modification methods and to provide a carbon nanomaterial and a preparation method thereof, a conductive agent and applications thereof.

[0006] In order to achieve the above object, one of the objects of the present invention is to provide a method for preparing carbon nanomaterials, the method comprising:

[0007] (1) pre-treating the polymer fiber and then performing ultraviolet ozone treatment to obtain a modified fiber;

[0008] (2) The modified fiber is carbonized to obtain a carbon nanomaterial.

[0009] A second object of the present invention is to provide a carbon nanomaterial prepared according to the aforementioned method.

[0010] A third object of the present invention is to provide a conductive agent comprising the aforementioned carbon nanomaterial.

[0011] A fourth object of the present invention is to provide application of the conductive agent in lithium batteries.

[0012] Beneficial effects of the present invention:

[0013] (1) The present invention can improve the conductivity of carbon nanomaterials by sequentially performing pretreatment, ultraviolet ozone treatment and carbonization treatment on polymer fibers.

[0014] (2) The preparation method provided by the present invention is environmentally friendly, pollution-free, and can be industrially produced. Description of the drawings:

[0015] Figure 1 is a SEM image of carbon nanofiber A1 in Example 1 of the present invention;

[0016] Figure 2 is a SEM image of the modified fiber in Example 1 of the present invention;

[0017] Figure 3 is the XRD pattern of carbon nanofiber A1 in Example 1 of the present invention;

[0018] Figure 4 is a SEM image of product B1 in Comparative Example 1 of the present invention;

[0019] Figure 5 is a SEM image of carbon nanoparticles A8 in Example 8 of the present invention;

[0020] Figure 6 is a SEM image of product B4 in Comparative Example 4 of the present invention;

[0021] Figure 7 It is the SEM picture of the product B5 in comparative example 5 of the present invention. Specific implementation method:

[0022] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific embodiments and illustrations.

[0023] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0024] As mentioned above, the present invention provides a method for preparing carbon nanofibers, the method comprising:

[0025] (1) pre-treating the polymer fiber and then performing ultraviolet ozone treatment to obtain a modified fiber;

[0026] (2) The modified fiber is carbonized to obtain a carbon nanomaterial.

[0027] In the present invention, the carbon nanomaterial includes carbon nanofibers and / or carbon nanoparticles.

[0028] In the present invention, the polymer fiber is an organic polymer fiber containing carbon-hydrogen bonds, and can be a synthetic polymer fiber or a natural polymer fiber. The natural polymer fiber includes but is not limited to alginate fiber, cotton fiber, bamboo fiber, and lignin fiber; the synthetic polymer fiber is formed by polymerizing organic molecules containing unsaturated bonds, and can be either nitrogen-containing or nitrogen-free. The nitrogen-containing polymer fiber includes but is not limited to polyacrylonitrile fiber, polyamide fiber, polyimide fiber, polyester fiber, and polyaniline fiber; the nitrogen-free polymer fiber includes but is not limited to polystyrene fiber, polyethylene fiber, and polypropylene fiber.

[0029] According to the present invention, preferably, the diameter of the polymer fiber is no greater than 500 nm.

[0030] In a preferred embodiment of the present invention, the polymer fibers are prepared by electrospinning, and the electrospinning method comprises: dissolving a high molecular weight polymer in a solvent to obtain a spinning solution; and then electrospinning the spinning solution to obtain polymer fibers.

[0031] In the present invention, the high molecular polymer may be at least one of polyacrylonitrile, polystyrene, lignin, polyamide, polyimide, polyaniline, polyethylene and polypropylene; the solvent may be selected according to the type of the high molecular polymer as long as it can dissolve the high molecular polymer, including but not limited to at least one of water, N,N-dimethylformamide, polytetrafluoroethylene and tetrahydrofuran.

[0032] According to the present invention, the concentration of the high molecular weight polymer in the spinning solution is 8-12wt%; for example, it can be 8wt%, 9wt%, 10wt%, 11wt%, 12wt% or any value in the range composed of any two of the above values, where "wt%" refers to weight percentage.

[0033] In the present invention, the diameter, uniformity, etc. of the polymer fiber can be adjusted by adjusting the electrospinning process; under preferred conditions, the electrospinning conditions include: a voltage of 10-20 kV; a spinning distance of 10-20 cm; further preferably, the electrospinning voltage can be 15 kV and the spinning distance can be 15 cm.

[0034] In the present invention, the conductivity of the product carbon nanomaterial can be improved by subjecting the polymer fiber to ultraviolet ozone treatment. The inventors of the present invention also found that if the ultraviolet ozone treatment time is too short, the polymer fiber cannot be effectively modified, that is, the conductivity of the carbon nanomaterial cannot be effectively improved. If the ultraviolet ozone treatment time is prolonged, the carbon nanofiber structure will be destroyed, and a granular final product will be obtained. Under preferred conditions, the ultraviolet ozone treatment time in step (1) is 24-96h; for example, it can be 24h, 36h, 48h, 60h, 72h, 84h, 96h or any value in the range of any two of the above values; more preferably, it is 48-72h.

[0035] In the present invention, the concentration of ozone depends on the concentration of oxygen. Too low an oxygen concentration will result in a low ozone concentration, which in turn will lead to incomplete modification of the polymer fiber. Under preferred conditions, the ultraviolet ozone treatment is carried out under oxygen-rich conditions. The ultraviolet ozone cleaning machine has at least one oxygen inlet and at least one oxygen outlet. In a preferred embodiment of the present invention, oxygen is introduced into the ultraviolet ozone cleaning machine through the oxygen inlet to put the ultraviolet ozone cleaning machine in an oxygen-rich state. In the present invention, the oxygen introduction rate is 0-100 mL / min, preferably 20-80 mL / min, and more preferably 40-75 mL / min. The oxygen supply can be continuous or intermittent. When the oxygen supply is intermittent, the oxygen outlet can be blocked.

[0036] In the present invention, the pretreatment conditions include: a temperature of 200-300°C for 1-3 hours. Further preferably, the pretreatment conditions include: firstly subjecting the polymer fiber to a first heat treatment at 200-240°C for 0.2-1 hour, followed by a second heat treatment at 250-300°C for 0.5-2 hours.

[0037] In the present invention, the carbonization treatment conditions in step (2) include: keeping the modified fiber at 1000-1600° C. for 0.5-3 h in a non-oxidizing atmosphere.

[0038] The types of the non-oxidizing atmosphere are known to those skilled in the art, including but not limited to nitrogen atmosphere or argon atmosphere.

[0039] A second object of the present invention is to provide a carbon nanomaterial prepared according to the aforementioned method.

[0040] Preferably, the carbon nanomaterial comprises carbon nanofibers or carbon nanoparticles.

[0041] A third object of the present invention is to provide a conductive agent comprising the aforementioned carbon nanomaterial.

[0042] A fourth object of the present invention is to provide application of the conductive agent in lithium batteries.

[0043] In the present invention, the conductive agent can be used as a conductive agent for the negative electrode of a lithium battery, and can also be used as a conductive agent for the positive electrode of a lithium battery; when used as a conductive agent for the positive electrode of a lithium battery, its usage is 5-15wt% of the entire positive electrode material. The types of positive electrode materials are known to technicians in the relevant field and will not be described in detail in the present invention.

[0044] The present invention will be described in detail below through examples.

[0045] The model of the UV-ozone cleaning machine is CIF-UVO9, with a power of 300W. The main wavelengths of the UV lamp are 185nm and 254nm.

[0046] Polyacrylonitrile: average molecular weight (Mn) = 150,000.

[0047] N,N-Dimethylformamide: analytical grade, density 0.948 g / mL.

[0048] Conductivity test method: The product to be tested is mixed with the binder PVDF in a weight ratio of 9:1. N-methylpyrrolidone is used as the solvent. The conductive paste is ground and coated on a PET film (2cm×2cm). After drying, the conductivity is tested using a four-probe conductivity tester. Nine points are tested in each sample, and the average of the nine groups of values ​​is calculated. Then the average Corrected, the conductivity σ of the sample

[0049] In the following examples, three parallel samples were prepared for each example, and the average conductivity of the three parallel samples was taken as the conductivity of the sample in that example.

[0050] Example 1

[0051] 5 parts of polyacrylonitrile were weighed and mixed with 57.5 parts of N,N-dimethylformamide, and magnetically stirred for 12 hours to obtain a spinning solution;

[0052] The spinning solution was loaded into a syringe, equipped with a 21-gauge needle (inner diameter 0.51 mm), and the spinning voltage was set to 15 kV, the spinning distance was 15 cm, the propulsion speed was 1 mL / h, and the electrospinning was performed for 10 h to obtain polymer fibers.

[0053] The polymer fiber was placed in a muffle furnace, heated to 230°C at a rate of 1°C / min and kept warm for 30 minutes, and then heated to 270°C at a rate of 1°C / min and kept warm for 60 minutes to obtain a pretreated fiber;

[0054] Place the pretreated fiber in a UV-ozone cleaning machine (optical density 30 μW / cm2 ), the sample was kept 1 cm away from the UV lamp, and oxygen (60 mL / min) was introduced continuously for 72 h to obtain modified fibers.

[0055] The modified fiber was placed in a tubular furnace, and under a nitrogen atmosphere, the temperature was raised to 1400°C at a rate of 5°C / min and kept at this temperature for 2 h to obtain carbon nanofiber A1, whose electrical conductivity is shown in Table 1.

[0056] Figure 1 is a SEM image of carbon nanofiber A1. Figure 2 This is the SEM picture of the modified fiber. Figure 1 and Figure 2 It can be seen that the modified fiber can maintain the fiber morphology, and the final product can also maintain the fibrous structure.

[0057] Figure 3 This is the XRD pattern of carbon nanofiber A1. Figure 3 It can be seen that characteristic peaks of carbon appear at around 26° and 45°, and their shapes are close to sharp peaks, indicating that the degree of graphitization of the product is high.

[0058] Example 2

[0059] The method of Example 1 was followed, except that the concentration of polyacrylonitrile in the spinning solution was 10 wt %. Specifically, 5 parts of polyacrylonitrile were weighed and mixed with 45 parts of N,N-dimethylformamide, and the mixture was magnetically stirred for 12 hours to obtain the spinning solution.

[0060] The parts not described in this embodiment are the same as those in Example 1.

[0061] Example 3

[0062] The method of Example 1 was followed, except that the concentration of polyacrylonitrile in the spinning solution was 12 wt %. Specifically, 5 parts of polyacrylonitrile were weighed and mixed with 37 parts of N,N-dimethylformamide, and the mixture was magnetically stirred for 12 h to obtain the spinning solution.

[0063] The parts not described in this embodiment are the same as those in Example 1.

[0064] Comparative Example 1

[0065] The method of Example 1 was followed, except that the concentration of polyacrylonitrile in the spinning solution was 6 wt %. Specifically, 5 parts of polyacrylonitrile were weighed and mixed with 78.3 parts of N,N-dimethylformamide, and magnetically stirred for 12 hours to obtain the spinning solution.

[0066] The unexplained parts in this comparative example are the same as those in Example 1.

[0067] Figure 4 This is the SEM image of product B1. Figure 4It can be seen from the figure that when the concentration of polyacrylonitrile in the spinning solution is too low, the spinning product is a "nodular" composite comprising polyacrylonitrile fibers and polyacrylonitrile particles, and polyacrylonitrile fibers with uniform morphology cannot be obtained, which is not suitable for subsequent processing.

[0068] Table 1

[0069] Polyacrylonitrile concentration (wt%) Conductivity (S / m) Example 1 8 444.839 Example 2 10 428.867 Example 3 12 416.234

[0070] It can be seen from Table 1 that as the concentration of polyacrylonitrile in the spinning solution increases, the conductivity of the obtained carbon nanofibers gradually decreases. Therefore, the concentration of polyacrylonitrile in the spinning solution should be controlled at 8-12 wt %.

[0071] Example 4

[0072] The method of Example 1 was followed, except that the spinning distance was 20 cm, to obtain carbon nanofiber A4, whose electrical conductivity was 398.501 S / m.

[0073] The parts not described in this embodiment are the same as those in Example 1.

[0074] Example 5

[0075] The method of Example 1 was followed, except that the spinning distance was 10 cm, to obtain carbon nanofiber A5, which had an electrical conductivity of 440.647 S / m.

[0076] The parts not described in this embodiment are the same as those in Example 1.

[0077] Example 6

[0078] The method of Example 1 was followed, except that the UV-ozone treatment time was 24 h, to obtain carbon nanofiber A6, the electrical conductivity of which is shown in Table 2.

[0079] The parts not described in this embodiment are the same as those in Example 1.

[0080] Example 7

[0081] The method of Example 1 was followed, except that the UV-ozone treatment time was 48 h, to obtain carbon nanofiber A7, the electrical conductivity of which is shown in Table 2.

[0082] The parts not described in this embodiment are the same as those in Example 1.

[0083] Example 8

[0084] The method of Example 1 was followed, except that the UV-ozone treatment time was 96 h, to obtain carbon nanoparticles A8, the electrical conductivity of which is shown in Table 2.

[0085] The parts not described in this embodiment are the same as those in Example 1.

[0086] Comparative Example 2

[0087] The method of Example 1 was followed, except that the UV-ozone treatment time was 12 h, to obtain carbon nanofibers B2, the electrical conductivity of which is shown in Table 2.

[0088] The unexplained parts in this comparative example are the same as those in Example 1.

[0089] Comparative Example 3

[0090] The method of Example 1 was followed, except that the pretreated fiber was not subjected to UV-ozone treatment, that is, the pretreated fiber was directly carbonized to obtain a carbonized product B3, the electrical conductivity of which is shown in Table 2.

[0091] The unexplained parts in this comparative example are the same as those in Example 1.

[0092] Table 2

[0093] UV ozone treatment (h) Conductivity (S / m) Example 1 72 444.839 Example 6 24 387.404 Example 7 48 401.412 Example 8 96 433.513 Comparative Example 2 12 346.358 Comparative Example 3 0 335.501

[0094] It can be seen from Table 2 that when the UVO treatment time is less than 12 hours, there is basically no effect on the conductivity of the carbon nanofibers; when the UVO treatment time is further extended to 24-72 hours, the conductivity of the carbon nanofibers increases with the extension of the treatment time.

[0095] Figure 5 This is the SEM image of carbon nanoparticles A8. Figure 5 It can be seen from the figure that when the UVO treatment time reaches 96 h, the calcined product includes short fibers and non-fibrous particles, and the conductivity of the carbon fibers decreases compared with Example 1.

[0096] Example 9

[0097] The method of Example 1 was followed, except that the pretreatment process was as follows: the polymer fiber was placed in a muffle furnace, heated to 230°C at a rate of 1°C / min, and held at that temperature for 90 minutes to obtain pretreated fiber. The pretreated fiber was then subjected to UV-ozone treatment and carbonization to obtain carbon nanofiber A9, the electrical conductivity of which is shown in Table 3.

[0098] The parts not described in this embodiment are the same as those in Example 1.

[0099] Example 10

[0100] The method of Example 1 was followed, except that the pretreatment process was as follows: the polymer fiber was placed in a muffle furnace, heated to 270°C at a rate of 1°C / min, and held at that temperature for 90 minutes to obtain pretreated fiber. The pretreated fiber was then subjected to UV-ozone treatment and carbonization to obtain carbon nanofiber A10, the electrical conductivity of which is shown in Table 3.

[0101] The parts not described in this embodiment are the same as those in Example 1.

[0102] Comparative Example 4

[0103] The method of Example 1 was followed, except that the polymer fiber was not pretreated. That is, the polymer fiber was directly subjected to UV-ozone treatment and carbonization treatment to obtain product B4, the conductivity of which is shown in Table 3.

[0104] The unexplained parts in this comparative example are the same as those in Example 1.

[0105] Figure 6 This is the SEM image of product B4. Figure 6 It can be seen from the figure that if the polymer fibers are not pretreated, the obtained product B4 will be bonded and will not be fibrous.

[0106] Table 3

[0107]

[0108] Comparative Example 5

[0109] The method of Example 1 was followed, except that the pretreatment was performed in an oven at a rapid, uncontrollable heating rate. Specifically, the polymer fiber was placed in an oven and heated directly from room temperature to 270°C and maintained at that temperature for 90 minutes to obtain pretreated fiber. The pretreated fiber was then subjected to UV-ozone treatment and carbonization to obtain Product B5.

[0110] The unexplained parts in this comparative example are the same as those in Example 1.

[0111] Figure 7 This is the SEM image of product B5. Figure 7 It can be seen that if the pretreatment process is carried out in an oven, the obtained product B5 will be bonded and no fibrous product will be obtained, indicating that the heating rate has a great influence on the morphology of the product.

[0112] Example 12

[0113] The method of Example 1 was followed, except that the carbonization temperature was 1600° C., to obtain carbon nanofiber A12, the electrical conductivity of which is shown in Table 4.

[0114] The parts not described in this embodiment are the same as those in Example 1.

[0115] Example 13

[0116] The method of Example 1 was followed, except that the carbonization temperature was 1200° C., to obtain carbon nanofiber A13, the electrical conductivity of which is shown in Table 4.

[0117] The parts not described in this embodiment are the same as those in Example 1.

[0118] Table 4

[0119] Carbonization temperature (℃) Conductivity (S / m) Example 1 1400 444.839 Example 14 1600 301.121 Example 15 1000 253.019

[0120] It can be seen from Table 4 that the carbonization temperature affects the conductivity of the product. When the carbonization temperature is 1400°C, the conductivity of the product is the highest.

[0121] Comparative Example 6

[0122] The method of Example 1 was followed, except that only ozone was introduced without UV irradiation. Specifically, the pretreated fiber was placed in a tubular furnace, ozone was continuously introduced (60 mL / min), and the temperature was increased at a rate of 2°C / min to 125°C. The fiber was then treated at 125°C for 72 h to obtain a modified fiber. The modified fiber was carbonized to obtain carbon nanofiber B6, which had an electrical conductivity of 340.589 S / m.

[0123] The unexplained parts in this comparative example are the same as those in Example 1.

[0124] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing carbon nanofibers, characterized in that: The method comprises: (1) pre-treating the polymer fiber and then performing ultraviolet ozone treatment to obtain a modified fiber, wherein the pre-treatment conditions include: a temperature of 200-300° C. and a time of 1-3 hours; The UV-ozone treatment time is 24-96h; (2) Carbonizing the modified fibers to obtain carbon nanomaterials.

2. The method according to claim 1, wherein: The polymer fiber is an organic polymer fiber containing carbon-hydrogen bonds.

3. The method according to claim 2, wherein: The polymer fiber is at least one of polyacrylonitrile fiber, polystyrene fiber, lignin fiber, polyamide fiber, polyimide fiber, polyaniline fiber, polyethylene fiber and polypropylene fiber.

4. The method according to claim 1, wherein: The diameter of the polymer fiber is no greater than 500 nm.

5. The method according to claim 1, wherein The carbon nanomaterial includes carbon nanoparticles and / or carbon nanofibers.

6. The method according to claim 1, wherein The pretreatment conditions include: firstly subjecting the polymer fiber to a first heat treatment at 200-240° C. for 0.2-1 h; and then subjecting the polymer fiber to a second heat treatment at 250-300° C. for 0.5-2 h.

7. The method according to any one of claims 1 to 6, wherein: In step (2), the carbonization treatment conditions include: keeping the modified fiber at 1000-1600° C. for 0.5-3 h in a non-oxidizing atmosphere.

8. The method according to any one of claims 1 to 6, wherein: The polymer fiber is prepared by electrostatic spinning, and the electrostatic spinning method comprises: dissolving a high molecular polymer in a solvent to obtain a spinning solution; and then electrostatically spinning the spinning solution to obtain the polymer fiber.

9. The method according to claim 8, wherein The high molecular polymer is selected from at least one of polyacrylonitrile, polystyrene, lignin, polyamide, polyimide, polyaniline, polyethylene and polypropylene.

10. The method according to claim 8, wherein The solvent is selected from at least one of water, N,N-dimethylformamide, polytetrafluoroethylene and tetrahydrofuran.

11. The method according to claim 8, wherein The concentration of the high molecular weight polymer in the spinning solution is 8-12 wt %.

12. The method according to claim 8, wherein The electrospinning conditions include: a voltage of 10-20 kV; and a spinning distance of 10-20 cm.

13. A carbon nanomaterial prepared according to the method according to any one of claims 1 to 12.

14. The carbon nanomaterial according to claim 13, characterized in that The carbon nanomaterial includes carbon nanoparticles or carbon nanofibers. A conductive agent comprising the carbon nanomaterial according to claim 14 .

16. Use of the conductive agent according to claim 15 in lithium batteries.

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