Preparation method and application of soft-hard heterogeneous carbon fiber composite material

Abstract

The present application relates to the preparation of carbon fiber composite materials and the field of sodium ion battery energy storage. The present application discloses a preparation method and application of a soft and hard heterogeneous carbon fiber composite material. The pre-processed anthracite is high-temperature carbonized, and polyacrylonitrile is dissolved in a dispersing agent. After water bath heating, a reinforcing agent is added to obtain a thick liquid. The thick liquid is then injected into a spinning needle tube, and through an electrostatic spinning process and a high-temperature pyrolysis process, a soft and hard heterogeneous carbon fiber composite material is obtained. The soft and hard heterogeneous carbon fiber composite material prepared by the present application has excellent electronic conductivity and rate performance of soft carbon, high reversible sodium storage capacity advantage of hard carbon, and synergistic sodium storage effect of the soft and hard carbon heterogeneous interface, and exhibits excellent reversible capacity and rate performance when applied to sodium ion battery negative materials. The method of the present application is simple, the raw materials are widely available, and the soft and hard carbon heterogeneous interface can be controlled and constructed, which is easy to realize large-scale production for the development of sodium ion battery negative materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of preparation of advanced carbon materials and sodium-ion battery energy storage technology, and in particular to a controllable preparation method of a soft-hard heterogeneous carbon fiber composite material for a sodium-ion battery negative electrode. BACKGROUND

[0002] The scarcity of lithium resources makes the cost of future lithium-ion batteries continue to rise, and seeking an alternative low-cost electrochemical energy storage device has become a problem to be solved. Sodium is abundant in the earth's crust (23000 ppm) and widely distributed, has similar physical and chemical properties to lithium, and the working principle and battery components of sodium-ion batteries are similar to those of lithium-ion batteries, which has become one of the energy storage technologies developed by countries around the world.

[0003] However, due to the Na + The large radius ratio of Li + The sodium-ion battery still faces the following key scientific and technical problems: 1) slow sodium-ion deintercalation kinetics process of the negative electrode, which inhibits the rate performance of the sodium-ion battery; 2) severe volume change and structure collapse of the negative electrode, which shortens the cycle service life of the sodium-ion battery; 3) complex physical and chemical processes of the negative electrode, and the real-time working condition sodium storage mechanism is not clear. Therefore, in order to realize the excellent sodium storage kinetics behavior and cycle stability of the sodium-ion battery negative electrode material, efforts are made to develop new sodium storage negative electrode materials with high efficient electron transport / ion transfer rate and excellent cycle performance, and to explore their sodium storage characteristics and mechanism, which has become a hot spot in the current field of sodium-ion batteries.

[0004] Among the negative electrode materials of sodium-ion batteries, carbon materials have low sodium storage potential, moderate sodium storage capacity, small volume change after sodium intercalation, good cycle stability, and other advantages such as abundant reserves, low price and environmental friendliness. Carbon materials can be divided into hard carbon and soft carbon according to the degree of graphitization, and single amorphous carbon material has advantages and disadvantages when used as a sodium storage negative electrode. Hard carbon (highly disordered) has an amorphous structure, rich sodium storage active sites and high sodium storage reversible capacity, but the low conductivity and many intrinsic defects result in low first-cycle coulombic efficiency and poor rate performance. Compared with hard carbon, soft carbon (highly ordered) has high crystallinity, rich sp 2 Carbon can bring high electronic conductivity and rate performance, but the regular arrangement of carbon layers and the narrow interlayer space result in low sodium storage capacity (usually less than 100mA h / g). Anthracite is the lowest cost and highest carbon-containing carbon source in nature, and high-temperature pyrolysis of anthracite is a soft carbon material. Compared with other pitch-based carbon sources, it still has a high degree of disorder below 1600℃, with a carbon yield of up to 90% and a sodium storage theoretical capacity of up to 220mA h / g.

[0005] Therefore, based on the respective sodium storage advantages of hard carbon and soft carbon, how to design advanced soft and hard heterogeneous carbon composites to organically combine the two provides an opportunity for developing low-cost / high-performance carbon-based sodium storage negative electrode materials, and is of great significance for the commercialization of sodium ion batteries.

[0006] In the prior art, CN114516627A discloses a preparation method of a soft and hard carbon composite nanomaterial. The method uses a pore regulator to combine soft and hard carbon sources, and two-step high-temperature reactions are performed to prepare a soft and hard carbon composite material. The method prepares a soft and hard carbon composite material with a rich porous structure and stable physical structure. However, the above method needs to undergo two-step high-temperature reactions, and the process is relatively complex, and the heating energy consumption cost is relatively high.

[0007] In the prior art, CN107240680A discloses a hard carbon-metal oxide-soft carbon composite material, a preparation method and application thereof. The invention uses a hydrocarbon compound to prepare a hard carbon precursor in a reaction kettle by a hydrothermal method, then the hard carbon precursor and a titanium salt are pre-coated, pitch is placed in a muffle furnace to perform a low-temperature pyrolysis reaction to obtain a soft carbon precursor; finally, the pre-coated hard carbon precursor and the soft carbon precursor are fully mixed, and a high-temperature pyrolysis reaction is performed under the protection of an inert gas to obtain a product, i.e., a hard carbon-metal oxide-soft carbon composite material. The composite material prepared by the invention has the advantages of large reversible capacity, high first charge and discharge coulomb efficiency, good cycle performance and the like. However, the process for treating the precursors of the soft carbon and the hard carbon is complex, and the cost of obtaining the composite material is high.

[0008] In the prior art, CN115520851A discloses a preparation method of a hard carbon-soft carbon-fast ion conductor composite material. The invention coats a fast ion conductor and a soft carbon material on the outer layer of hard carbon doped with a rare earth compound by a hydrothermal method to prepare a hard carbon-soft carbon-fast ion conductor composite material with high specific capacity, high first efficiency and good power performance. However, the hard carbon precursor of the invention needs complex materials, including a rare earth coupling agent and a crosslinking agent, and the material collection is difficult, and the preparation cost is high.

[0009] Based on the above problems, the present application provides a electrospinning method for preparing a soft and hard heterogeneous carbon fiber composite material from polyacrylonitrile and anthracite, and then performing sodium storage performance testing. The carbon composite material prepared by the process not only has excellent sodium storage electrochemical performance, but also has the advantages of simple process, low cost and controllable composition. SUMMARY

[0010] To solve the problems of the prior art, the present application provides a preparation method of a soft and hard heterogeneous carbon fiber composite material. The method can controllably construct a soft and hard heterogeneous carbon fiber structure composite material at the same interface through a simple process, and the composite material exhibits high specific capacity and excellent cycle stability when used as a negative electrode material of a sodium ion battery.

[0011] A preparation method of a controllable construction of a soft and hard heterogeneous carbon fiber composite material, comprising the following steps:

[0012] S1: 2-4g anthracite is uniformly ground by a ball mill and passed through a 150 mesh screen.

[0013] S2: the product of S1 is respectively treated by hydrochloric acid and hydrofluoric acid to remove metal impurity ions, then washed with water until the filtrate is a neutral solution, and finally dried to obtain anthracite powder.

[0014] S3: the powder of S2 is placed in a tube furnace, heated to 800-1200 DEG C at a heating rate of 5 DEG C / min in an argon atmosphere, and kept at 800-1200 DEG C for 2h.

[0015] S4: the anthracite and polyacrylonitrile obtained in S3 are dissolved in 24mL N,N-dimethylformamide at a certain ratio, water bathed to 60 DEG C, and 0.2g polymethyl methacrylate is added to obtain a black liquid with certain consistency.

[0016] S5: the above liquid is added to a needle tube, and a carbon film with a certain thickness is obtained by electrospinning.

[0017] Preferably, in S1, the rotation speed of the ball mill is 150-250r / min, and the ball milling time is 2-5h.

[0018] Preferably, the particle size of the anthracite ranges from 10 to 50 microns.

[0019] Preferably, in S2, the concentration of hydrochloric acid is 10%, the concentration of hydrofluoric acid is 5-10wt.%, the pickling time is about 24h, and the washing solution is neutral.

[0020] Preferably, in S3, the carbonization temperature is 1000 DEG C.

[0021] Preferably, in S4, the ratio of anthracite to polyacrylonitrile is 2:5.

[0022] Preferably, in S5, 6-8mL is added to a 10mL disposable medical needle tube, the electrospinning voltage parameter is 18kV, the winding rate is 0.5mL / h, and the collection distance is 10-15cm.

[0023] The carbon fiber composite material prepared by the method has the structural characteristics of soft carbon and hard carbon, so that when used as a negative electrode material of a sodium ion battery, it has good electronic conductivity and excellent stability, and the controllable construction of the carbon fiber interface can synergistically improve the sodium storage performance.

[0024] The present application has the following advantages:

[0025] 1. The present application uses anthracite and polyacrylonitrile as carbon source precursors, and through electrospinning and high-temperature carbonization process, a sodium ion battery carbon negative electrode material with large interlayer spacing, multiple active sites and fast ion migration channels is prepared. Compared with the traditional chemical method, as a continuous synthesis technology, the present application can achieve lower consumption of raw materials and solvents, lower operating cost, only one experimental personnel is needed for 16h continuous work, and the equipment is simple and safe.

[0026] 2. The present application overcomes the limitations of traditional synthesis methods in preparing carbon negative electrode materials, and proposes an electrospinning strategy to prepare controllable carbon negative electrode materials, which breaks through the problem of low capacity of traditional anthracite in sodium ion batteries. The present application can exhibit a discharge specific capacity of 236mA h / g at 0.1A / g.

[0027] 3. The present application develops a carbon fiber preparation technology which can be synthesized on a large scale and has excellent sodium storage performance, promotes the development of current sodium ion batteries, and deeply researches the key technical problems in the preparation technology of soft and hard heterogeneous carbon fiber composite materials. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings used herein to illustrate the specific embodiments of the present application constitute a part of the application and do not constitute a limitation on the embodiments of the present application.

[0029] Figure 1 The X-ray diffraction analysis diagram of the soft and hard heterogeneous carbon fiber composite material prepared in the present application examples 1-3; wherein the example 1 is hard carbon fiber, the example 2 is soft and hard heterogeneous carbon fiber, and the example 3 is soft carbon anthracite.

[0030] Figure 2 The scanning electron microscope diagram of the soft and hard heterogeneous carbon fiber composite material prepared in the present application example 2.

[0031] Figure 3 The performance diagram of the soft and hard heterogeneous carbon fiber composite material prepared in the present application example 2 under the current density of 0.1A / g for 100 cycles.

[0032] SPECIFIC IMPLEMENTATION CASE

[0033] The content of the present application will be further described in combination with specific examples and drawings, but the present application is not limited to the following examples.

[0034] Example 1

[0035] In this embodiment, a method for controllable construction of polyacrylonitrile hard carbon carbon fiber composite material is disclosed.

[0036] S1: 2 g of polyacrylonitrile was added to 24 mL of N,N-dimethylformamide, the water bath was warmed to 60℃, 0.2 g of polymethyl methacrylate was added, and stirring was performed for 2 h;

[0037] S2: 8 mL of the S1 sample was taken into a disposable sampler, and electrospinning was performed by using an electrospinning instrument with a voltage of 18 kV, a winding speed of 0.5 mL / h, and a collection distance of 10 cm for 16 h;

[0038] S3: The product of S2 was placed into a tube furnace in an argon atmosphere, and carbonization was performed by heating, the heating mode being: the temperature was raised to 250℃ at a rate of 2℃ / min, and then the temperature was raised to 800℃ at a rate of 5℃ / min, and the temperature was maintained for 2 h, and then the temperature was cooled to room temperature, to obtain a sodium ion battery carbon negative electrode material.

[0039] Example 2

[0040] In this example, a method for controllable construction of a soft and hard heterogeneous carbon fiber composite material is disclosed.

[0041] S1: The anthracite was crushed into powder by a ball mill, and the powder particle size was 10-60 μm. The anthracite powder was treated with hydrochloric acid and hydrofluoric acid to remove impurity metal ions, and finally dried in a vacuum oven at 60℃ for 12 h;

[0042] S2: The product in S1 was heated to 1000℃ at a rate of 5℃ / min in an argon atmosphere, and the temperature was maintained for 2 h;

[0043] S3: 0.8 g of the product in S2 was added to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, the water bath was warmed to 60℃, 0.2 g of polymethyl methacrylate was added, and stirring was performed for 2 h;

[0044] S4: 8 mL of the S3 sample was taken into a disposable sampler, and electrospinning was performed by using an electrospinning instrument with a voltage of 18 kV, a winding speed of 0.5 mL / h, and a collection distance of 10 cm for 16 h;

[0045] S5: The product of S4 was placed into a tube furnace in an argon atmosphere, and carbonization was performed by heating, the heating mode being: the temperature was raised to 250℃ at a rate of 2℃ / min, and then the temperature was raised to 800℃ at a rate of 5℃ / min, and the temperature was maintained for 2 h, and then the temperature was cooled to room temperature, to obtain a sodium ion battery carbon negative electrode material.

[0046] Example 3:

[0047] In this example, a method for controllable construction of a soft carbon anthracite is disclosed.

[0048] S1: The anthracite is crushed into powder by a ball mill, and the particle size of the powder is 10-60 pm. The anthracite powder is treated with hydrochloric acid and hydrofluoric acid to remove impurity metal ions, and finally dried in a vacuum oven at 60°C for 12 hours

[0049] S2: The product in S1 is heated to 1000°C at a heating rate of 5°C / min in an argon atmosphere, and then kept for 2 hours. After cooling to room temperature, a sodium-ion battery carbon negative electrode material is obtained.

[0050] The carbon fiber composite materials prepared in Examples 1-3 are respectively hard carbon fibers prepared in Example 1, soft and hard heterogeneous carbon fibers prepared in Example 2, and soft carbon anthracite prepared in Example 3.

[0051] For the three prepared materials, Figure 1 It can be seen from the X-ray diffraction pattern that the soft and hard heterogeneous carbon fibers prepared in Example 2 have two wide and weak diffraction peaks at 2θ = 22-26°C and 2θ = 43°C, corresponding to the (002) and (001) crystal planes of graphite, indicating that carbon fibers with a certain degree of graphitization are prepared. Compared with Examples 1 and 3, the carbon layer has high regularity, large specific surface area, and relatively good rate performance.

[0052] It can be seen from the scanning electron microscope image of the prepared soft and hard heterogeneous carbon fibers that the sample is mainly connected into a carbon network by carbon fibers of different diameters. Figure 2

[0053] Example 4:

[0054] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is as follows:

[0055] S1: The anthracite is crushed into powder by a ball mill, and the particle size of the powder is 10-60 pm. The anthracite powder is treated with hydrochloric acid and hydrofluoric acid to remove impurity metal ions, and finally dried in a vacuum oven at 60°C for 12 hours

[0056] S2: The product in S1 is heated to 1000°C at a heating rate of 5°C / min in an argon atmosphere, and then kept for 2 hours.

[0057] S3: 0.8g of the product in S2 is added to 24mL of N,N-dimethylformamide and 2g of polyacrylonitrile, and the water bath is heated to 60°C. 0.2g of polymethyl methacrylate is added, and stirred for 2 hours.

[0058] S4: 8mL of the sample in S3 is taken into a disposable sampler, and spun for 16 hours by an electrospinning instrument with a voltage of 18kV, a winding speed of 0.5mL / h, and a collection distance of 10cm.

[0059] ​S5: Put the product of S4 into a tube furnace in a high-purity argon atmosphere for carbonization heating, heating method: 2 ℃ / min heating rate to 250 ℃ for 1 h, and then 5 ℃ / min heating rate to 600 ℃ for 2 h, and then cool to room temperature to obtain a sodium-ion battery carbon negative electrode material.

[0060] Example 5:

[0061] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is as follows:

[0062] S1: Crush the anthracite into powder by a ball mill, and the powder particle size is 10-60 μm. Treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid, respectively, and finally dry in a vacuum oven at 60 ℃ for 12 h;

[0063] S2: Heat the product in S1 to 1000 ℃ at a heating rate of 5 ℃ / min in an argon atmosphere for 2 h;

[0064] S3: Take 0.8 g of the product in S2 and add it to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, heat the water bath to 60 ℃, add 0.2 g of polymethyl methacrylate, and stir for 2 h;

[0065] S4: Take 8 mL of the S3 sample and add it to a disposable sampler, and spin for 16 h by using an electrospinning instrument with a voltage of 18 kV, a winding speed of 0.5 mL / h, and a collection distance of 10 cm;

[0066] S5: Put the product of S4 into a tube furnace in a high-purity argon atmosphere for carbonization heating, heating method: 2 ℃ / min heating rate to 250 ℃ for 1 h, and then 5 ℃ / min heating rate to 1000 ℃ for 2 h, and then cool to room temperature to obtain a sodium-ion battery carbon negative electrode material.

[0067] Example 6:

[0068] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is as follows:

[0069] S1: Crush the anthracite into powder by a ball mill, and the powder particle size is 10-60 μm. Treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid, respectively, and finally dry in a vacuum oven at 60 ℃ for 12 h;

[0070] S2: Heat the product in S1 to 1000 ℃ at a heating rate of 5 ℃ / min in an argon atmosphere for 2 h;

[0071] S3: Take 0.8 g of the product in S2 and add it to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, heat the water bath to 60°C, add 0.2 g of polymethyl methacrylate, stir for 2 h;

[0072] S4: Take 8 mL of the sample in S3 and add it to a disposable sampler, spin for 16 h by using an electrospinning instrument with a voltage of 20 kV, a winding speed of 0.5 mL / h, and a collection distance of 10 cm;

[0073] S5: The amount of spun fibers is extremely small and insufficient for carbonization as a negative electrode material for sodium ion batteries.

[0074] Example 7:

[0075] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is:

[0076] S1: Crush anthracite into powder by a ball mill, with a particle size of 10-60 μm, treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid respectively, and finally dry in a vacuum oven at 60°C for 12 h;

[0077] S2: Heat the product in S1 to 1000°C at a heating rate of 5°C / min in an argon atmosphere and keep it for 2 h;

[0078] S3: Take 0.8 g of the product in S2 and add it to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, heat the water bath to 60°C, add 0.2 g of polymethyl methacrylate, stir for 2 h;

[0079] S4: Take 8 mL of the sample in S3 and add it to a disposable sampler, spin for 16 h by using an electrospinning instrument with a voltage of 20 kV, a winding speed of 0.5 mL / h, and a collection distance of 10 cm;

[0080] S5: The amount of spun fibers is extremely small and insufficient for carbonization as a negative electrode material for sodium ion batteries.

[0081] Example 8:

[0082] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is:

[0083] S1: Crush anthracite into powder by a ball mill, with a particle size of 10-60 μm, treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid respectively, and finally dry in a vacuum oven at 60°C for 12 h;

[0084] S2: Heat the product in S1 to 1000°C at a heating rate of 5°C / min in an argon atmosphere and keep it for 2 h;

[0085] S3: Take 0.8 g of the product in S2 and add it to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, and heat the water bath to 60°C. Add 0.2 g of polymethyl methacrylate and stir for 2 h;

[0086] S4: Take 8 mL of the sample in S3 and add it to a disposable sampler. Use an electrospinning instrument with a voltage of 18 kV, a winding speed of 1.0 mL / h, and a collection distance of 10 cm to spin for 16 h;

[0087] S5: Place the product in S4 in a tube furnace in an argon atmosphere and heat it to carbonize. The heating method is to heat it to 250°C at a rate of 2°C / min and hold for 1 h, then heat it to 800°C at a rate of 5°C / min and hold for 2 h, then cool it to room temperature to obtain a sodium-ion battery carbon negative electrode material.

[0088] Example 9:

[0089] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is:

[0090] S1: Crush the anthracite into powder by a ball mill, with a particle size of 10-60 μm. Treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid, respectively, and finally dry it in a vacuum oven at 60°C for 12 h;

[0091] S2: Heat the product in S1 to 1000°C at a rate of 5°C / min in an argon atmosphere and hold for 2 h;

[0092] S3: Take 0.8 g of the product in S2 and add it to 24 mL of N,N-dimethylformamide and 2 g of polyacrylonitrile, and heat the water bath to 60°C. Add 0.2 g of polymethyl methacrylate and stir for 2 h;

[0093] S4: Take 8 mL of the sample in S3 and add it to a disposable sampler. Use an electrospinning instrument with a voltage of 18 kV, a winding speed of 2.0 mL / h, and a collection distance of 10 cm to spin for 16 h;

[0094] S5: Obtain less spinning fibers with a lower yield.

[0095] Example 10:

[0096] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is:

[0097] S1: Crush the anthracite into powder by a ball mill, with a particle size of 10-60 μm. Treat the impurity metal ions in the anthracite powder with hydrochloric acid and hydrofluoric acid, respectively, and finally dry it in a vacuum oven at 60°C for 12 h;

[0098] S2: The product in S1 was heated to 1000℃ at a heating rate of 5℃ / min in an argon atmosphere for 2h;

[0099] S3: 0.8g of the product in S2 was added to 24mL of N,N-dimethylformamide and 2g of polyacrylonitrile, the water bath was heated to 60℃, 0.2g of polymethyl methacrylate was added, and stirred for 2h;

[0100] S4: 8mL of the sample in S3 was added to a disposable sampler, and spun for 16h by an electrospinning instrument with a voltage of 18kV, a winding speed of 0.3mL / h, and a collection distance of 10cm;

[0101] S5: The obtained spinning fibers were less, the collection rate was too slow, and the instrument was damaged and required more time.

[0102] Example 11:

[0103] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is as follows:

[0104] S1: The anthracite was crushed into powder by a ball mill, and the powder particle size was 10-60μm. The anthracite powder was treated with hydrochloric acid and hydrofluoric acid to remove impurity metal ions, and finally dried in a vacuum oven at 60℃ for 12h;

[0105] S2: The product in S1 was heated to 1000℃ at a heating rate of 5℃ / min in an argon atmosphere for 2h;

[0106] S3: 0.6g of the product in S2 was added to 24mL of N,N-dimethylformamide and 2g of polyacrylonitrile, the water bath was heated to 60℃, 0.2g of polymethyl methacrylate was added, and stirred for 2h;

[0107] S4: 8mL of the sample in S3 was added to a disposable sampler, and spun for 16h by an electrospinning instrument with a voltage of 18kV, a winding speed of 0.5mL / h, and a collection distance of 10cm;

[0108] S5: The product in S4 was placed in a tube furnace in a high-purity argon atmosphere for carbonization, and the heating method was as follows: heated to 250℃ at a heating rate of 2℃ / min for 1h, then heated to 800℃ at a heating rate of 5℃ / min for 2h, and then cooled to room temperature to obtain a sodium ion battery carbon negative electrode material.

[0109] Example 12:

[0110] In this embodiment, the method for controllable construction of the soft and hard heterogeneous carbon fiber composite material is as follows:

[0111] S1: The anthracite is crushed into powder by a ball mill, and the particle size of the powder is 10-60 μm. The anthracite powder is treated with hydrochloric acid and hydrofluoric acid to remove impurity metal ions, and finally dried in a vacuum oven at 60°C for 12h;

[0112] S2: The product in S1 is heated to 1000°C at a heating rate of 5°C / min in an argon atmosphere for 2h;

[0113] S3: 1.0g of the product in S2 is added to 24mL of N,N-dimethylformamide and 2g of polyacrylonitrile, and the water bath is heated to 60°C. 0.2g of polymethyl methacrylate is added, and stirred for 2h;

[0114] S4: 8mL of the sample in S3 is added to a disposable sampler, and spun for 16h by an electrospinning instrument with a voltage of 18kV, a winding speed of 0.5mL / h, and a collection distance of 10cm;

[0115] S5: The product in S4 is placed in a tube furnace in a high-purity argon atmosphere for carbonization. The heating method is: heating to 250°C at a heating rate of 2°C / min for 1h, then heating to 800°C at a heating rate of 5°C / min for 2h, and then cooling to room temperature to obtain a sodium-ion battery carbon negative electrode material.

[0116] The parameters of the above different embodiments are compared and summarized as follows (Table 1):

[0117] Table 1. Comparison of parameters of different embodiments

[0118]

[0119] Example 1 is a comparative sample, and experimental example 3 is soft carbon anthracite. Examples 2, 4, and 5 explore the effect of different carbonization temperatures on carbon fibers. Lower temperatures are not conducive to the removal of non-carbon atoms and the formation of carbon fibers, and higher temperatures can damage the structure of carbon fibers.

[0120] Examples 2, 6, and 7 explore the effect of spinning voltage on the spinning fiber. Lower voltage can cause liquid leakage, and part of the solution does not form carbon cloth. Higher voltage can cause the fiber to spin everywhere and cannot be effectively collected.

[0121] Examples 2, 8, 9, and 10 explore the effect of different spinning rates on the collection efficiency. A slower spinning rate results in less collection yield, which is not conducive to the experiment. A faster rate can result in low collection efficiency.

[0122] Examples 2, 11, and 12 explore the effect of different proportions of anthracite and polyacrylonitrile on carbon fibers. Too little anthracite can reduce the sodium storage capacity, and too much anthracite can cause carbon fiber clumping, resulting in a decrease in sodium storage capacity.

[0123] The performance comparison of the different embodiments described above is summarized below (Table 2):

[0124] Table 2. Performance comparison of different embodiments

[0125]

[0126]

[0127] While the present application has been described and illustrated with reference to the preferred embodiments, it will be apparent to those of ordinary skill in the art that numerous modifications, arrangements, substitutions, and alterations can be made to the embodiments without departing from the spirit and scope of the application. Accordingly, the scope of the application is not intended to be limited to the described embodiments but is to be accorded the widest scope consistent with the claims and their equivalents.

Claims

1. A method for preparing a soft-hard heterogeneous carbon fiber composite material, characterized in that, Includes the following steps: S1: Pretreatment of anthracite: Select 2-4 g of anthracite and grind it in a ball mill at a speed of 100-300 r / min for 4-7 h. Then pass it through a 150 mesh sieve. The particle size range of the obtained anthracite is 10-60 μm. Then, the anthracite is washed with 10% hydrochloric acid and 5-10 wt.% hydrofluoric acid for 24 h to remove metal impurity ions. Then, it is filtered and washed with water until the filtrate is a neutral solution. Finally, it is vacuum dried to obtain anthracite powder. S2: The pretreated anthracite is carbonized at high temperature under an argon atmosphere. The reaction is cooled to room temperature, and the product is ground to obtain anthracite-derived soft carbon material. The high-temperature carbonization conditions for the S2 anthracite are as follows: in an argon atmosphere, the temperature is increased to 800-1200 ℃ at a heating rate of 5 ℃ / min, and maintained at the temperature range of 800-1200 ℃ for 2 hours. S3: Anthracite-derived soft carbon material and polyacrylonitrile are dissolved in a dispersant, and a reinforcing agent is added to obtain a black, thick liquid; The ratio of S3 anthracite to polyacrylonitrile is 2:5, 3:10 or 1:2, the dispersant is N,N-dimethylformamide, the amount is 24 mL, the water bath heating is carried out at 60 °C, and 0.2 g of polymethyl methacrylate is added as a reinforcing agent. S4: Add 6-8 mL of viscous liquid to a 10 mL disposable medical syringe and obtain carbon fiber precursor by electrospinning. The electrospinning voltage parameters are 18 kV, the swirling speed is 0.5 ml / h, and the collection distance is 10-15 cm. S5: High-temperature pyrolysis of carbon fiber precursor to obtain the target product, soft and hard heterogeneous carbon fiber composite material. The high-temperature pyrolysis heating conditions for the S5 carbon fiber precursor are as follows: in an air atmosphere, the temperature is increased to 250 ℃ at a heating rate of 2 ℃ / min and held for 2 h, and then in an argon atmosphere, the temperature is increased to 800 ℃ at a heating rate of 5 ℃ / min and held for 2 h.

2. A soft-hard heterogeneous carbon fiber composite material, characterized in that: The soft and hard heterogeneous carbon fiber composite material is prepared by the preparation method of the soft and hard heterogeneous carbon fiber composite material according to claim 1.

3. The preparation method of the soft and hard heterogeneous carbon fiber composite material according to claim 1 and the application of the soft and hard heterogeneous carbon fiber composite material according to claim 2 in the field of sodium-ion battery energy storage.

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