Preparation method and application of high-strength soft carbon fiber

Abstract

The application relates to a preparation method and application of high-strength soft carbon fibers, and the specific steps of the preparation method include the following: polyamide acid is obtained through electrostatic spinning to obtain polyamide acid nanofibers; high-strength polyimide nanofibers are further obtained through solidification and thermal imidization; the obtained nanofibers are subjected to carbonization reaction at 900-1300 DEG C under different pressures of 0-500 Pa under the protection of argon gas to obtain high-strength soft carbon fibers; the preparation process is simple, the reaction condition is simple, and the cost of preparing the negative electrode material is low; the high-strength soft carbon fibers prepared by the application can realize excellent sodium storage characteristics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and particularly relates to a preparation method and application of a high-strength soft carbon fiber based on polyimide. BACKGROUND

[0002] Energy problems have become an important research topic in the world, and efficient, safe and environmentally friendly energy conversion, storage and release are important basic research directions. In recent years, sodium-ion batteries as a new type of electrochemical energy storage device have been widely concerned in the academic field. However, the commercial mature graphite negative electrode of lithium-ion batteries shows almost negligible low sodium storage capacity when used as a negative electrode of sodium-ion batteries. Researchers have begun to study metal alloys / oxides / calcium compounds, phosphorus and carbon materials as negative electrode materials for sodium-ion batteries. However, the sodium storage performance of these negative electrode materials is still far from the requirements of large-scale industrial production. In summary, designing and preparing negative electrode materials with excellent sodium-ion storage performance and constructing sodium-ion battery systems with low cost and commercial application value are related to the national economic development and the realization of the "double carbon" goal in the future. The diameter of traditional polyimide nanofibers ranges from several microns to several hundred microns, which are often used to make high-temperature protective clothing, high-temperature waste filtration membranes, and reinforcing materials. However, the fiber diameter required in the energy storage application field is smaller. Electrospinning nanofibers have continuous fibers, smaller diameters, higher specific surface areas, controllable fiber structures, low densities and high porosities. SUMMARY

[0003] To overcome the above-mentioned deficiencies of the prior art, the purpose of the present application is to provide a preparation method and application of a high-strength soft carbon fiber. Polyimide is used as the raw material for electrospinning soft carbon fiber. Under the action of different calcination temperatures and different pressures, orthogonal experiments are designed, and the microstructure of the carbon layer of the soft carbon fiber is synergistically regulated by pressure and thermal field, thereby optimizing the sodium storage performance of the carbon fiber and providing a theoretical basis for preparing high-performance soft carbon fiber.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0005] A preparation method of a high-strength soft carbon fiber, which utilizes electrospinning combined with a thermal field to prepare a high-strength soft carbon fiber, and comprises the following steps:

[0006] Step 1, nanofillers were prepared with 2.5~3.5g pyromellitic dianhydride (PMDA) and 2~3g 4,4'-oxydianiline (ODA) as monomers, and the prepared nanofillers were added into 30~50 mL N,N-dimethylformamide (DMF) to prepare polyamic acid (PAA); the prepared polyamic acid was obtained by electrospinning to obtain polyamic acid nanofibers; the polyamic acid nanofibers were dried in a vacuum oven, and then heat imidization treatment was carried out by using a high-temperature drying box, the heating rate was 1~2℃ / min, and the temperature was 100℃, 200℃ and 300℃ respectively; after the high-temperature drying box was naturally cooled, high-strength polyimide (PI) nanofibers were obtained;

[0007] Step 2, the polyimide (PI) nanofibers were placed on a graphite plate, pressure was applied, argon was introduced into a tube furnace for 1~2h, and then the temperature was raised to different carbonization temperatures at a rate of 2~3℃ / min under argon protection gas, carbonization reaction was carried out for 2h, the temperature was lowered to 200℃ at a rate of 2~3℃ / min, and then naturally cooled to room temperature, and the product was collected to obtain polyimide-based high-strength soft carbon fibers.

[0008] In step 1, the polyamic acid nanofibers were placed in a vacuum oven at 80℃ and vacuum dried for 12h.

[0009] The heat imidization treatment has the following specific heating steps: 100℃ for 0.5~1h; 200℃ for 0.5~1h; 300℃ for 0.5~1h, the power was turned off, and the sample was collected after the high-temperature drying box was naturally cooled.

[0010] In step 2, the pressure was 0Pa, 100Pa, 200Pa, 300Pa or 500Pa respectively.

[0011] In step 2, the different carbonization temperatures were 900℃, 1100℃ or 1300℃ respectively.

[0012] The polyimide-based high-strength soft carbon fibers have uniform fiber structure distribution.

[0013] The polyimide-based high-strength soft carbon fibers are applied in sodium ion batteries.

[0014] A preparation method of high-strength soft carbon fibers, comprising the following steps:

[0015] Step one, 3g 4,4'-diaminodiphenyl ether (ODA) is dissolved in N,N-dimethylformamide (DMF), and is magnetically stirred for 15-20min to make it fully dissolved, and 3.28g of pyromellitic dianhydride (PMDA) is slowly added in batches to ensure that the reaction proceeds stably, until the molar ratio of pyromellitic dianhydride PMDA to 4,4'-diaminodiphenyl ether ODA reaches 1.03:1, and is magnetically stirred for 3-5h to make it fully react, and then is vacuumized and defoamed in a vacuum oven to prepare a polyamic acid (PAA) spinning solution, which is stored at 0-5℃ for standby;

[0016] Step two, the prepared polyamic acid (PAA) spinning solution is placed in a 5-10mL syringe, the injection rate is set to 0.08-1.5mm / min, the spinning voltage is controlled to be 12-15kV, and the high-speed orientation collection device is used for directional spinning, the distance from the needle to the collection device is 8-10cm, and the roller speed of the collection device is 2000-2800r / min; in order to conveniently tear off the fiber membrane completely, an aluminum foil is pre-coated on the collection device, and a polyamic acid PAA nanofiber is obtained;

[0017] Step three, the prepared polyamic acid PAA nanofiber is placed in a vacuum oven at 80℃ and vacuum dried for 12h to remove residual solvents, and heat imidization treatment is carried out by using a high-temperature drying box, the heating speed is 1-2℃ / min, and the specific heating steps are as follows: (1) 100℃ for 0.5-1h to remove water vapor and keep dry; (2) 200℃ for 0.5-1h to stabilize the thermodynamic state of the PAA nanofiber and prepare for heat imidization; (3) 300℃ for 0.5-1h to complete the heat imidization conversion; the power is turned off, and after the high-temperature drying box is naturally cooled, a deep yellow high-strength polyimide (PI) nanofiber is obtained;

[0018] Step four, the polyimide (PI) nanofiber is placed on a graphite plate and given a pressure of 0-500Pa, argon gas is introduced into a tube furnace for 1-2h, and then the argon gas is used as a protective gas, the temperature is increased from room temperature to 900-1300℃ at a rate of 2-3℃ / min, the carbonization reaction is carried out for 2h, the temperature is decreased to 200℃ at a rate of 2-3℃ / min, and then the temperature is naturally decreased to room temperature, and the product is collected to obtain a polyimide-based high-strength soft carbon fiber.

[0019] The injection is carried out by using a syringe, and the spinning needle type of the syringe is 22G, the outer diameter is 0.7mm, and the inner diameter is 0.4mm.

[0020] Compared with the prior art, the beneficial effects of the present application are:

[0021] The prepared polyamide acid (PAA) spinning solution is injected into a syringe, a high-voltage power supply is connected, and the spinning solution can be sprayed onto a high-speed orientation collecting device under the action of high-voltage static electricity to obtain polyamide acid nanofibers. Then, polyimide (PI) nanofibers are obtained through solidification and thermal imidization. The tensile strength of the polyimide nanofibers is 10.45-11.31 MPa, which can ensure that the carbonized fibers have good flexibility. The obtained nanofibers are subjected to a carbonization reaction at 900-1300 DEG C under the protection of argon gas at a pressure of 0-500 Pa to obtain high-strength soft carbon fibers.

[0022] As can be seen from the technical solutions provided by the application, the process parameters provided by the embodiments of the application can obtain high-strength soft carbon fibers, the process is simple and mature and stable. The prepared soft carbon fibers can be applied to the negative electrode of a sodium ion battery.

[0023] The polyimide nanofibers are used as carbon matrix materials, the polyimide nanofibers with excellent performance ensure that the carbon fibers have good flexibility and certain self-supporting strength. The microstructure of the soft carbon fibers is synergistically regulated by pressure and temperature to obtain a negative electrode material with high sodium storage performance.

[0024] 1) The microstructure of the soft carbon fibers is synergistically regulated by different pressures and different calcination temperatures to obtain a negative electrode material with high sodium storage performance.

[0025] 2) The preparation process of the application is simple, the reaction conditions are simple, the cost of preparing the soft carbon fiber negative electrode material is low, and the application is conducive to large-scale production and application. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The scanning electron microscope (SEM) photos of the high-strength soft carbon fibers prepared in Example 6 and Example 10 of the application.

[0027] Figure 2 The X-ray diffraction (XRD) patterns of the high-strength soft carbon fibers prepared in Example 6 and Example 10 of the application.

[0028] Figure 3 The constant current charge-discharge curve diagrams of the high-strength soft carbon fiber negative electrode materials prepared in Example 6 and Example 10 of the application in a sodium ion battery (ether-based electrolyte).

[0029] Figure 4 The constant current charge-discharge curve diagrams of the high-strength soft carbon fiber negative electrode materials prepared in Example 6, Example 8, Example 12 and Example 14 of the application in a sodium ion battery (ether-based electrolyte). DETAILED DESCRIPTION

[0030] The application will be described in further detail below with reference to the drawings and specific embodiments.

[0031] Example 1

[0032] Step one, 3g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 30mL of N,N-dimethylformamide (DMF), and stirred magnetically for 15min to ensure complete dissolution. Then 3.28g of pyromellitic dianhydride (PMDA) was added slowly in batches to ensure stable reaction, until the molar ratio of PMDA to ODA reached 1.03:1. The mixture was stirred magnetically for 3h to ensure complete reaction. Then the polyamic acid (PAA) spinning solution was prepared by vacuumizing and defoaming in a vacuum oven, and stored at 0~5℃ for later use.

[0033] Step two, the prepared polyamic acid (PAA) spinning solution was placed in a 5mL syringe. A 22G needle (outer diameter 0.7mm, inner diameter 0.4mm) was used for spinning. The injection rate was set at 0.08mm / min, and the spinning voltage was controlled at 12kV. The needle was placed 10cm away from the collection device, and the roller speed of the collection device was set at 2800r / min. An aluminum foil was pre-coated on the collection device to facilitate the tearing of the fiber membrane. Finally, the polyamic acid PAA nanofiber was obtained.

[0034] Step three, the prepared polyamic acid PAA nanofiber was placed in a vacuum oven at 80℃ and vacuum dried for 12h to remove residual solvents. Then, the PAA nanofiber was subjected to thermal imidization treatment in a high-temperature drying oven at a heating rate of 2℃ / min. The specific heating steps were as follows: 1) 100℃ for 0.5h to remove water vapor and maintain dryness; 2) 200℃ for 0.5h to stabilize the thermodynamic state of the PAA nanofiber and prepare for thermal imidization; 3) 300℃ for 0.5h to complete the thermal imidization transformation. After the power was turned off and the high-temperature drying oven was naturally cooled, the deep yellow polyimide (PI) nanofiber was obtained. The tensile strength of the PI nanofiber was 11.24MPa, which ensured that the carbonized fiber had good flexibility.

[0035] Step four, the polyimide (PI) nanofiber was placed on a graphite plate and given a pressure of 0Pa. After 1h of argon gas flow in the tube furnace, the PI nanofiber was carbonized at a heating rate of 2℃ / min from room temperature to 900℃ under argon protection for 2h. Then, the temperature was decreased to 200℃ at a rate of 2℃ / min, and the sample was naturally cooled to room temperature. Finally, the product was collected to obtain the polyimide-based high-strength soft carbon fiber.

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that in step four, the polyimide (PI) nanofiber is placed on a graphite plate, a pressure of 100 Pa is given, and after 1 h of argon gas flow in a tube furnace, the product is collected to obtain polyimide-based high-strength soft carbon fiber by carbonization reaction at a temperature rising rate of 2 ℃ / min from room temperature to 900 ℃ under argon protective gas for 2 h, a temperature falling rate of 2 ℃ / min to 200 ℃, and then natural cooling to room temperature. The other steps are the same as those in embodiment 1.

[0038] Embodiment 3

[0039] The difference between embodiment 3 and embodiment 1 or embodiment 2 is that in step four, the polyimide (PI) nanofiber is placed on a graphite plate, a pressure of 200 Pa is given, and after 1 h of argon gas flow in a tube furnace, the product is collected to obtain polyimide-based high-strength soft carbon fiber by carbonization reaction at a temperature rising rate of 2 ℃ / min from room temperature to 900 ℃ under argon protective gas for 2 h, a temperature falling rate of 2 ℃ / min to 200 ℃, and then natural cooling to room temperature. The other steps are the same as those in embodiment 1 or embodiment 2.

[0040] Embodiment 4

[0041] The difference between embodiment 4 and embodiments 1-3 is that in step four, the polyimide (PI) nanofiber is placed on a graphite plate, a pressure of 300 Pa is given, and after 1 h of argon gas flow in a tube furnace, the product is collected to obtain polyimide-based high-strength soft carbon fiber by carbonization reaction at a temperature rising rate of 2 ℃ / min from room temperature to 900 ℃ under argon protective gas for 2 h, a temperature falling rate of 2 ℃ / min to 200 ℃, and then natural cooling to room temperature. The other steps are the same as those in embodiments 1-3.

[0042] Embodiment 5

[0043] The difference between embodiment 5 and embodiments 1-4 is that in step four, the polyimide (PI) nanofiber is placed on a graphite plate, a pressure of 500 Pa is given, and after 1 h of argon gas flow in a tube furnace, the product is collected to obtain polyimide-based high-strength soft carbon fiber by carbonization reaction at a temperature rising rate of 2 ℃ / min from room temperature to 900 ℃ under argon protective gas for 2 h, a temperature falling rate of 2 ℃ / min to 200 ℃, and then natural cooling to room temperature. The other steps are the same as those in embodiments 1-4.

[0044] Embodiment 6

[0045] The difference between embodiment 6 and embodiment 1 is that in step four, the carbonization temperature is 1100 ℃. The other steps are the same as those in embodiment 1.

[0046] Embodiment 7

[0047] Example 7 differs from Example 1 by step four, the carbonization temperature is 1300 °C. The other steps are the same as Example 1.

[0048] Example 8

[0049] Example 8 differs from Example 2 by step four, the carbonization temperature is 1100 °C. The other steps are the same as Example 2.

[0050] Example 9

[0051] Example 9 differs from Example 2 by step four, the carbonization temperature is 1300 °C. The other steps are the same as Example 2.

[0052] Example 10

[0053] Example 10 differs from Example 3 by step four, the carbonization temperature is 1100 °C. The other steps are the same as Example 3.

[0054] Example 11

[0055] Example 11 differs from Example 3 by step four, the carbonization temperature is 1300 °C. The other steps are the same as Example 3.

[0056] Example 12

[0057] Example 12 differs from Example 4 by step four, the carbonization temperature is 1100 °C. The other steps are the same as Example 4.

[0058] Example 13

[0059] Example 13 differs from Example 4 by step four, the carbonization temperature is 1300 °C. The other steps are the same as Example 4.

[0060] Example 14

[0061] Example 14 differs from Example 5 by step four, the carbonization temperature is 1100 °C. The other steps are the same as Example 5.

[0062] Example 15

[0063] Example 15 differs from Example 5 by step four, the carbonization temperature is 1300 °C. The other steps are the same as Example 5.

[0064] Use of the high-strength soft carbon fiber material described in claims 1-15 in sodium-ion batteries.

[0065] Example 16

[0066] A method of making a high-strength soft carbon fiber, comprising the steps of:

[0067] Step 1, prepare nanofiller with 2.5g of pyromellitic dianhydride and 2g of 4,4'-oxydianiline as monomers, and add the prepared nanofiller into 40mL of N,N-dimethylformamide to prepare polyamic acid;

[0068] Step 2, obtain polyamic acid nanofiber by electrospinning the prepared polyamic acid, and dry the polyamic acid nanofiber in a vacuum oven;

[0069] Step 3, perform thermal imidization treatment on the dried polyamic acid nanofiber by using a high-temperature drying box, the temperature increasing rate is 1℃ / min, the temperature is 100℃, and after the high-temperature drying box is naturally cooled, high-strength polyimide nanofiber is obtained;

[0070] Step 4, place the polyimide nanofiber on a graphite plate, apply pressure, introduce argon into a tube furnace for 2h, carbonize the polyimide nanofiber at different carbonization temperatures at a temperature increasing rate of 3℃ / min under argon protection gas for 2h, cool the polyimide nanofiber to 200℃ at a temperature decreasing rate of 3℃ / min, and then naturally cool the polyimide nanofiber to room temperature, and collect the product to obtain polyimide-based high-strength soft carbon fiber.

[0071] Example 17

[0072] A method for preparing high-strength soft carbon fiber, comprising the following steps:

[0073] Step 1, prepare nanofiller with 3.5g of pyromellitic dianhydride and 3g of 4,4'-oxydianiline as monomers, and add the prepared nanofiller into 50mL of N,N-dimethylformamide to prepare polyamic acid;

[0074] Step 2, obtain polyamic acid nanofiber by electrospinning the prepared polyamic acid, and dry the polyamic acid nanofiber in a vacuum oven;

[0075] Step 3, perform thermal imidization treatment on the dried polyamic acid nanofiber by using a high-temperature drying box, the temperature increasing rate is 1~2℃ / min, the temperature is 300℃, and after the high-temperature drying box is naturally cooled, high-strength polyimide nanofiber is obtained;

[0076] Step 4, place the polyimide nanofiber on a graphite plate, apply pressure, introduce argon into a tube furnace for 1h, carbonize the polyimide nanofiber at different carbonization temperatures at a temperature increasing rate of 2℃ / min under argon protection gas for 2h, cool the polyimide nanofiber to 200℃ at a temperature decreasing rate of 2℃ / min, and then naturally cool the polyimide nanofiber to room temperature, and collect the product to obtain polyimide-based high-strength soft carbon fiber.

[0077] Example 18

[0078] A method for preparing high-strength soft carbon fiber, comprising the following steps:

[0079] Step one, 3g 4,4'-diaminodiphenyl ether (ODA) was dissolved in N,N-dimethylformamide (DMF) and stirred magnetically for 15 min to ensure complete dissolution. Then 3.28g of pyromellitic dianhydride (PMDA) was added slowly in batches to ensure stable reaction, until the molar ratio of pyromellitic dianhydride PMDA to 4,4'-diaminodiphenyl ether ODA reached 1.03:1. The mixture was stirred magnetically for 3h to ensure complete reaction. Then the polyamic acid (PAA) spinning solution was prepared in a vacuum oven with vacuum degassing. The solution was stored at 0℃ for later use.

[0080] Step two, the prepared polyamic acid (PAA) spinning solution was placed in a 5mL syringe. The injection rate was set to 0.08mm / min, the spinning voltage was controlled at 12kV, and the high-speed orientation collection device was used for directional spinning. The distance between the needle and the collection device was 8cm, and the roller speed of the collection device was 2000r / min. To facilitate the complete tearing of the fiber membrane, an aluminum foil was pre-coated on the collection device. The polyamic acid PAA nanofiber was obtained.

[0081] Step three, the prepared polyamic acid PAA nanofiber was placed in a vacuum oven at 80℃ and vacuum dried for 12h to remove residual solvents. The high-temperature drying box was used for thermal imidization treatment, with a heating rate of 1℃ / min. The specific heating steps were as follows: 1) 100℃ for 0.5h to remove water vapor and maintain dryness; 2) 200℃ for 0.5h to stabilize the thermodynamic state of PAA nanofiber and prepare for thermal imidization; 3) 300℃ for 0.5h to complete the thermal imidization conversion. After the power was turned off and the high-temperature drying box was naturally cooled, the deep yellow high-strength polyimide (PI) nanofiber was obtained.

[0082] Step four, the polyimide (PI) nanofiber was placed on a graphite plate and given a pressure of 0Pa. After argon was introduced into the tube furnace for 1h, the product was collected by carbonization reaction at 900℃ under argon protection gas with a heating rate of 3℃ / min for 2h, and then cooled to 200℃ at a cooling rate of 2℃ / min, and finally naturally cooled to room temperature. The polyimide-based high-strength soft carbon fiber was obtained.

[0083] The injection was performed using a syringe with a 22G needle, an outer diameter of 0.7mm, and an inner diameter of 0.4mm.

[0084] Example 19

[0085] A method for preparing a high-strength soft carbon fiber, comprising the following steps:

[0086] Step one, 3g 4,4'-diaminodiphenyl ether (ODA) was dissolved in N,N-dimethylformamide (DMF) and stirred magnetically for 18 min to ensure complete dissolution. Then 3.28g of pyromellitic dianhydride (PMDA) was added slowly in batches to ensure stable reaction, until the molar ratio of PMDA to ODA reached 1.03:1. The mixture was stirred magnetically for 4h to ensure complete reaction. Then the polyamic acid (PAA) spinning solution was prepared by vacuum drying and defoaming in a vacuum oven at 3℃ for storage.

[0087] Step two, the prepared polyamic acid (PAA) spinning solution was placed in an 8mL syringe, the injection rate was set to 1.0mm / min, the spinning voltage was controlled at 14kV, and the high-speed orientation collection device was used for directional spinning. The distance between the needle and the collection device was 9cm, and the roller speed of the collection device was 2400r / min. To facilitate the complete tearing of the fiber membrane, an aluminum foil was pre-coated on the collection device. The polyamic acid PAA nanofiber was obtained.

[0088] Step three, the prepared polyamic acid PAA nanofiber was placed in a vacuum oven at 80℃ and vacuum dried for 12h to remove residual solvents. Then, the high-temperature drying box was used for thermal imidization treatment, with a heating rate of 1.5℃ / min. The specific heating steps were as follows: 1) 100℃ for 0.8h to remove water vapor and maintain dryness; 2) 200℃ for 0.8h to stabilize the thermodynamic state of PAA nanofiber and prepare for thermal imidization; 3) 300℃ for 0.8h to complete the thermal imidization conversion. After turning off the power and naturally cooling the high-temperature drying box, the deep yellow high-strength polyimide (PI) nanofiber was obtained.

[0089] Step four, the polyimide (PI) nanofiber was placed on a graphite plate and given a pressure of 300Pa. After passing argon gas into the tube furnace for 2h, the argon gas was used as a protective gas to heat the sample from room temperature to 1100℃ at a rate of 2.5℃ / min for 2h of carbonization reaction. Then, the temperature was decreased to 200℃ at a rate of 3℃ / min, and the sample was naturally cooled to room temperature. The product was collected to obtain the polyimide-based high-strength soft carbon fiber.

[0090] The injection was performed using a syringe with a 22G needle, an outer diameter of 0.7mm, and an inner diameter of 0.4mm.

[0091] Example 20

[0092] A method for preparing a high-strength soft carbon fiber, comprising the following steps:

[0093] Step one, 3g 4,4'-diaminodiphenyl ether (ODA) is dissolved in N,N-dimethylformamide (DMF), magnetically stirred for 20min, so that it is fully dissolved, and 3.28g of pyromellitic dianhydride (PMDA) is slowly added in batches, to ensure that the reaction is stable, until the molar ratio of pyromellitic dianhydride PMDA to 4,4'-diaminodiphenyl ether ODA reaches 1.03:1, magnetically stirred for 5h to make it fully react, and then vacuumized and defoamed in a vacuum oven to prepare a polyamic acid (PAA) spinning solution, which is stored at 5℃ for standby;

[0094] Step two, the prepared polyamic acid (PAA) spinning solution is placed in a 10mL syringe, the injection rate is set to 1.5mm / min, the spinning voltage is controlled at 15kV, and the high-speed orientation collection device is used for directional spinning, the distance from the needle to the collection device is 10cm, and the roller speed of the collection device is 2000~2800r / min; in order to facilitate the complete tearing of the fiber membrane, an aluminum foil is pre-coated on the collection device, and a polyamic acid PAA nanofiber is obtained;

[0095] Step three, the prepared polyamic acid PAA nanofiber is placed in a vacuum oven at 80℃ and vacuum dried for 12h to remove residual solvents, and heat imidization treatment is carried out by using a high-temperature drying box, the heating speed is 1.5℃ / min, and the specific heating steps are as follows: 1) 100℃ for 0.8h to remove water vapor and keep dry; 2) 200℃ for 0.8h to stabilize the thermodynamic state of the PAA nanofiber and prepare for heat imidization; 3) 300℃ for 1h to complete the heat imidization conversion; after the power is turned off, the high-temperature drying box is naturally cooled to obtain deep yellow high-strength polyimide (PI) nanofiber;

[0096] Step four, the polyimide (PI) nanofiber is placed on a graphite plate and given a pressure of 500Pa, argon gas is introduced into a tube furnace for 2h, and then the temperature is raised to 1300℃ at a rate of 3℃ / min under argon protection gas for carbonization reaction for 2h, the temperature is lowered to 200℃ at a rate of 3℃ / min, and then naturally cooled to room temperature, and the product is collected to obtain a polyimide-based high-strength soft carbon fiber.

[0097] The injection is performed by using a syringe, and the spinning needle type of the syringe is 22G, with an outer diameter of 0.7mm and an inner diameter of 0.4mm.

[0098] Figure 1 For example 6 of the present application Figure 1 a,b) and example 10 Figure 1c,d) Scanning electron microscope (SEM) images of the prepared high-strength soft carbon fibers. As can be seen from the images, the fiber surface is smooth, although there are broken fibers, the fiber distribution is relatively uniform, the fiber diameter is 300-400 nm, and the degree of pressure has no obvious effect on the fiber diameter.

[0099] Figure 2 X-ray diffraction (XRD) patterns of the high-strength soft carbon fibers prepared for the present application Example 6 and Example 10. As can be seen from the images, the soft carbon fibers prepared at pressures of 0 Pa and 200 Pa respectively have relatively strong (002) crystal face diffraction peaks and weak (100) crystal face diffraction peaks at about 24° and 43°, which are typical of amorphous graphite structure. With the increase of pressure, the diffraction peak angle does not shift, indicating that pressure does not affect the carbon layer spacing. However, the slight change in half-height width indicates that pressure affects the grain size and defects.

[0100] Figure 3 Constant current charge-discharge curves of the high-strength soft carbon fiber negative electrode material prepared for the present application Example 3 Figure 3 a), Example 10 Figure 3 b) and Example 11 Figure 3 c) in a sodium ion battery (ether-based electrolyte). As can be seen from the images, the soft carbon fiber negative electrode materials prepared at the same pressure and different temperatures exhibit different charge-discharge curves in the sodium ion battery. The charge-discharge curve of the soft carbon fiber negative electrode material prepared at 900°C does not show a low plateau region, while the soft carbon fiber negative electrode materials prepared at 1100°C and 1300°C have an observable specific capacity, and the charge-discharge curve has a low plateau region, and the plateau region capacity is about 200 mAh g -1 .

[0101] Figure 4 Constant current charge-discharge curves of the high-strength soft carbon fiber negative electrode material prepared for the present application Example 6 Figure 4 a), Example 8 Figure 4 b), Example 12 Figure 4 c) and Example 14 Figure 4 d) in a sodium ion battery (ether-based electrolyte). As can be seen from the images, the soft carbon fiber negative electrode materials prepared at the same temperature and different pressures also exhibit different charge-discharge curves in the sodium ion battery. When carbonized with pressure, the soft carbon fiber negative electrode material exhibits a low plateau region in the ether-based electrolyte, while the charge-discharge curve of the soft carbon fiber negative electrode material prepared at a pressure of 0 Pa does not have a low plateau region.

Claims

1. A method for producing high-strength soft carbon fibers, characterized by, The method comprises the following steps: Step 1, nanofillers are prepared by using 2.5-3.5 g of pyromellitic dianhydride and 2-3 g of 4,4'-oxydianiline as monomers, and the prepared nanofillers are added into 30-50 mL of N,N-dimethylformamide to prepare polyamic acid; Step 2, polyamic acid nanofibers are obtained by electrospinning the prepared polyamic acid, and the polyamic acid nanofibers are dried in a vacuum oven; Step 3, the dried polyamic acid nanofibers are subjected to thermal imidization treatment by using a high-temperature drying oven, and the heating rate is 1-2 ℃ / min, so that high-strength polyimide nanofibers are obtained; The thermal imidization treatment comprises the following heating steps: 100 ℃ for 0.5-1 h; 200 ℃ for 0.5-1 h; 300 ℃ for 0.5-1 h, the power is turned off, and the sample is collected after the high-temperature drying oven is naturally cooled; Step 4, the polyimide nanofibers are placed on a graphite plate, pressure is applied, argon is introduced into a tube furnace for 1-2 h, and then the polyimide nanofibers are carbonized at different carbonization temperatures at a heating rate of 2-3 ℃ / min from room temperature to the different carbonization temperatures under the protection of argon, carbonization is performed for 2 h, the temperature is decreased to 200 ℃ at a cooling rate of 2-3 ℃ / min, and then the temperature is naturally decreased to room temperature, and the product is collected to obtain polyimide-based high-strength soft carbon fibers; The pressure is 100 Pa, 200 Pa, 300 Pa or 500 Pa respectively; The different carbonization temperatures are 1100 ℃ or 1300 ℃ respectively.

2. The method for preparing high-strength soft carbon fiber according to claim 1, characterized in that, In step 2, the polyamic acid nanofibers are dried in a vacuum oven at 80 ℃ for 12 h.

3. The method for preparing high-strength soft carbon fiber according to claim 1, characterized in that, The polyimide-based high-strength soft carbon fiber has uniform fiber structure distribution, and the capacity of the low platform region of the sodium ion battery charge-discharge curve is 200 mAhg -1 .

4. Application of the polyimide-based high-strength soft carbon fibers prepared by the method of any one of claims 1-3 in a sodium ion battery.

5. A method of producing high-strength soft carbon fibers, characterized by, The method comprises the following steps: Step 1, 3 g of 4,4'-oxydianiline is dissolved in N,N-dimethylformamide, and magnetic stirring is performed for 15-20 min to ensure that the 4,4'-oxydianiline is fully dissolved, and then 3.28 g of pyromellitic dianhydride is slowly added in batches to ensure that the reaction is stable, until the molar ratio of pyromellitic dianhydride PMDA to 4,4'-oxydianiline reaches 1.03:1, and then magnetic stirring is performed for 3-5 h to ensure that the polyamic acid spinning solution is fully reacted, and then the polyamic acid spinning solution is vacuumized and defoamed in a vacuum oven, and the polyamic acid spinning solution is stored at 0-5 ℃ for later use; Step 2, the prepared polyamic acid spinning solution is placed in 5-10 mL, the injection rate is set to 0.08-1.5 mm / min, the spinning voltage is controlled to be 12-15 kV, high-speed orientation collection equipment is used for directional spinning, the distance from the needle to the collection equipment is 8-10 cm, and the rotating speed of the roller of the collection equipment is 2000-2800 r / min; in order to facilitate tearing off the fiber membrane completely, an aluminum foil is pre-coated on the collection equipment, and polyamic acid PAA nanofibers are obtained; Step three, the prepared polyamide acid PAA nanofiber is placed in a vacuum oven at 80 DEG C, vacuum dried for 12h, remove residual solvent, using high temperature drying box heat imidization treatment, the heating rate is 1~2 DEG C / min, the specific heating steps as follows: 1) 100 DEG C for 0.5~1h, to remove water vapor, keep dry; 2) 200 DEG C for 0.5~1h, to stabilize the thermodynamic state of polyamide acid PAA nanofiber, for heat imidization preparation; 3) 300 DEG C for 0.5~1h, complete heat imidization conversion; turn off the power, after the high temperature drying box natural cooling, get deep yellow high strength polyimide (PI) nanofiber; Step four, the polyimide (PI) nanofiber is placed on the graphite plate, give 100-500Pa pressure, after 1~2h argon is passed into the tube furnace, under the protection of argon gas, with the rate of 2~3 DEG C / min from room temperature to 1100 DEG C carbonization reaction 2h, with the rate of 2~3 DEG C / min from 200 DEG C, then natural cooling to room temperature, collect the product to get polyimide based high strength soft carbon fiber.

6. The method for preparing high-strength soft carbon fiber according to claim 5, characterized in that, The injection is performed by using a syringe, and the syringe is provided with a spinning needle with a model of 22G, an outer diameter of 0.7mm and an inner diameter of 0.4mm.

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