High-performance porous soft and hard carbon fiber negative electrode material for lithium ion battery and preparation method of high-performance porous soft and hard carbon fiber negative electrode material

Abstract

The invention discloses a high-performance porous soft and hard carbon fiber lithium ion battery negative electrode material and a preparation method thereof. The thickness of the material is 20-100 [mu] m, the material is composed of porous carbon nanofibers with the diameter of 300-800 nm, and the material has the excellent conductivity of soft carbon and the high capacity of hard carbon. The preparation method is simple and convenient, the coal pitch is subjected to liquid-phase oxidation and then mixed with two high-molecular polymers for electrostatic spinning, then oxidation and carbonization treatment is performed, and finally the porous soft and hard carbon fiber membrane is obtained. Wherein the coal pitch is used as a soft carbon precursor, the high-molecular polymer 1 is used as a hard carbon precursor, and the high-molecular polymer 2 is used as a pore-forming agent to form a porous structure in a high-temperature decomposition process. The material is excellent in performance, and the capacity is gt after 2000 cycles under the current density of 1A / g; the capacity retention ratio is gt, and is 400mAh / g; therefore, the rate capability and the cycling stability of the battery can be remarkably improved. The method does not need a complicated post-treatment process, is low in cost and environment-friendly, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber material preparation and battery negative electrode material, and specifically relates to a high-performance porous soft and hard carbon fiber negative electrode material for lithium-ion batteries and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of portable electronic devices, electric vehicles and energy storage systems, the demand for lithium-ion batteries has been growing. However, the theoretical capacity of traditional graphite anode materials is limited and the rate performance is poor, which makes it difficult to meet the growing demand for high energy density and high power output. Therefore, it is urgent to develop new high-performance anode materials. Soft and hard carbon composites have attracted much attention because of their potential to combine high capacity with excellent rate performance. At the same time, regulating the pore structure of the material is also an important means to improve the electrochemical performance. Appropriate pore size distribution and porosity can promote electrolyte infiltration and lithium ion transmission. Carbon fiber, as a high-performance carbon material, has the advantages of high strength, high modulus, corrosion resistance, etc., which can improve the conductivity and structural stability of the material. Therefore, the research on its application in lithium-ion battery anode is increasing. However, the traditional carbon fiber preparation method is often costly, and it is difficult to achieve effective composite with soft and hard carbon and controllable regulation of pore structure, which limits its application in the field of high-performance lithium-ion batteries.

[0003] The patent document with publication number CN107881600A discloses a method for preparing carbon nanofibers for negative electrodes of lithium-ion batteries and its application, characterized in that: the method uses aluminum chloride and quinoline as raw materials, and obtains nitrogen-rich quinoline oligomers after high-temperature reaction, washing and drying, crushing it, and then adding polyacrylonitrile and stirring to obtain spinning solution. Then, the nanofibers are prepared by electrostatic spinning technology, and finally the target carbon nanofiber materials are obtained by pre-oxidation and high-temperature carbonization. This preparation method uses quinoline as raw material, undergoes high-temperature reaction, multiple washings and other links, and needs to crush the material to about 5-10μm, so the preparation cycle is relatively long. Summary of the invention

[0004] In order to solve the shortcomings of current lithium-ion battery negative electrode materials in terms of capacity, rate performance and cycle life, the present invention provides a high-performance porous soft and hard carbon fiber negative electrode material for lithium-ion batteries and a preparation method thereof. Coal tar and two polymers are cleverly mixed, and a fiber precursor with a uniformly dispersed structure is prepared in combination with electrostatic spinning technology. In the subsequent carbonization process, polymer 2 mainly undergoes a depolymerization reaction and decomposes into volatile gases, thereby forming a controllable porous structure inside the material; at the same time, the soft carbon derived from coal tar and the hard carbon derived from polymer 1 undergo a cross-linking reaction at high temperature and are interconnected to form a stable composite structure. This unique structural evolution mechanism enables the final carbon material to have good conductivity, excellent structural stability and efficient ion transfer rate, thereby significantly improving the electrochemical performance of lithium-ion batteries. The present invention proposes a method for preparing multi-channel soft and hard carbon fiber negative electrode materials using electrostatic spinning and high-temperature heat treatment technology, aiming to develop high-performance, low-cost new lithium-ion battery negative electrode materials to promote the development of electric vehicles, portable electronic devices and other fields.

[0005] To achieve the above purpose, the preparation process of the present invention is as follows:

[0006] (1) mixing coal tar and a liquid oxidant, stirring at 30 to 60° C. for 2 to 10 hours to obtain a mixture of coal tar and the liquid oxidant, and removing the liquid oxidant by filtering and washing to obtain oxidized coal tar;

[0007] (2) dissolving polymer 1 and polymer 2 in a solvent, and stirring at 30 to 60° C. for 1 to 5 hours to obtain a mixed solution;

[0008] (3) stirring the oxidized coal tar pitch prepared in step (1) and the mixed solution prepared in step (2) at 30 to 60° C. for 2 to 10 hours to obtain a spinning solution;

[0009] (4) electrospinning the spinning solution obtained in step (3) to obtain a precursor fiber membrane;

[0010] (5) placing the precursor fiber obtained in step (4) in a muffle furnace for pre-oxidation to obtain an oxidized fiber membrane;

[0011] (6) The pre-oxidized fiber membrane obtained in step (5) is placed in a tubular furnace for carbonization to obtain a porous soft and hard carbon fiber membrane for lithium-ion batteries.

[0012] In the step (1), the liquid phase oxidant is one or more of concentrated sulfuric acid and concentrated nitric acid; the ratio of coal tar pitch to liquid phase oxidant is 1:5 to 1:20.

[0013] In the step (2), polymer 1 is one or more of polyacrylonitrile, polyvinylidene fluoride, polystyrene, polyvinyl alcohol, and polyurethane; polymer 2 is one or more of polyvinyl pyrrolidone, polymethyl methacrylate, and polylactic acid; the solvent is one or more of N,N-dimethylformamide, tetrahydrofuran, and toluene; the ratio of polymer 1 to polymer 2 is 1:1 to 1:5; and the ratio of polymer to solvent is 1:8 to 1:15.

[0014] In the step (3), the ratio of oxidized coal tar pitch to the mixed solution is 1:5 to 1:15.

[0015] In the step (4), the voltage of the electrospinning is 8-20 kV; the propulsion speed is 0.05-0.2 mm / min; the distance between the electrospinning needle and the receiving plate is 10-30 cm; the temperature is 30-50° C.; and the humidity is 30-60%.

[0016] In the step (5), the heating rate of the muffle furnace is 1 to 3°C / min; the insulation temperature is 250 to 300°C; and the insulation time is 1 to 3 hours.

[0017] In the step (6), the heating rate of the tubular furnace is 5 to 10°C / min; the protective atmosphere is one or more of argon, nitrogen, and helium; the insulation temperature is 500 to 1000°C; and the insulation time is 1 to 5 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention adopts a simple high-temperature carbonization method, ingeniously using polymer 1 as a connecting bridge between soft and hard carbons, and polymer 2 as a pore former. The pore former decomposes in situ during the high-temperature treatment process, without the need for additional etching or other complex post-processing steps, which greatly simplifies the process flow and reduces production costs. More importantly, this method avoids the use of corrosive or toxic reagents, while achieving oxygen doping, which improves electrochemical activity while being more in line with the concept of green environmental protection and has good economic and social benefits.

[0020] (2) The present invention effectively realizes the complementary advantages of soft and hard carbon, ensures their uniform dispersion and tight integration in the material, and gives full play to the excellent conductivity of soft carbon and the high capacity characteristics of hard carbon. At the same time, by precisely controlling the pyrolysis process of the polymer, a controllable porous structure is successfully constructed, which can not only promote the full infiltration of the electrolyte and the rapid transmission of ions, but also effectively alleviate the volume change during the charge and discharge process. These synergistic optimizations in structure and performance have jointly contributed to the significant improvement of the rate performance and cycle stability of porous soft and hard carbon fiber negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the test image of element content of coal tar pitch before and after oxidation;

[0022] Figure 2 This is a scanning electron microscope photograph of the cross section of the porous soft and hard carbon fibers prepared in Example 1 of the present invention;

[0023] Figure 3 This is a transmission electron microscope photo of the porous soft and hard carbon fibers prepared in Example 1 of the present invention;

[0024] Figure 4 This is an X-ray diffraction test image of the porous soft and hard carbon fibers prepared in Example 1 of the present invention;

[0025] Figure 5 This is a nitrogen desorption test image of the porous soft and hard carbon fibers prepared in Example 1 of the present invention;

[0026] Figure 6 The cycle performance curve of the CR2032 battery assembled with porous soft and hard carbon fibers prepared in Example 1 of the present invention at a current density of 0.1 A / g;

[0027] Figure 7 The cycle performance curve of the CR2032 battery assembled with porous soft and hard carbon fibers prepared in Example 1 of the present invention at a current density of 10 A / g;

[0028] Figure 8 The rate test curve of the porous soft and hard carbon fiber assembled CR2032 battery prepared in Example 1 of the present invention at different current densities; DETAILED DESCRIPTION

[0029] The present invention will be described in detail below in conjunction with the examples. The present invention will be described in detail below in conjunction with the specific examples, but the scope of the present invention is not limited. It should be understood that for those of ordinary skill in the art, improvements or changes can be made according to the above description, and all these improvements and changes should belong to the protection scope of the claims attached to the present invention. If the specific conditions are not specified in the examples, they are prepared according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0030] Example 1

[0031] (1) 5 g of coal tar was added to 90 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1 and stirred for 5 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0032] (2) adding 1 g of polyacrylonitrile and 1 g of polyvinyl pyrrolidone into 18 ml of N,N-dimethylformamide solution, and heating at 40° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0033] (3) 0.5 g of the oxidized coal tar pitch prepared in step (1) was added to 10 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0034] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 8 KV, a propulsion speed of 0.05 mm / min, a spinning temperature of 35°C, a distance between the syringe needle tip and the receiving plate of 10 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0035] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 260°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0036] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 700°C at a heating rate of 6°C / min, and then cooled to room temperature after being kept for 3 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0037] Example 2

[0038] (1) Add 3 g of coal tar pitch into 30 mL of concentrated nitric acid solution and stir for 5 h, then neutralize with deionized water, filter and wash, and dry in a forced air oven at 80 °C for 12 h.

[0039] (2) adding 1 g of polyacrylonitrile and 2 g of polyvinyl pyrrolidone into 25 ml of tetrahydrofuran solution, and heating at 50° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0040] (3) Add 1 g of the oxidized coal tar pitch prepared in step (1) to 10 ml of the mixed solution prepared in step (2), and stir at 50° C. for 7 h to obtain a spinning solution.

[0041] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 9 KV, a propulsion speed of 0.07 mm / min, a spinning temperature of 45°C, a distance between the syringe needle tip and the receiving plate of 10 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0042] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 280°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0043] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 800°C at a heating rate of 6°C / min, and then cooled to room temperature after being kept for 3 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0044] Example 3

[0045] (1) 5 g of coal tar was added to 50 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1 and stirred for 10 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0046] (2) adding 1 g of polyacrylonitrile and 4 g of polyvinyl pyrrolidone into 50 ml of toluene solution, heating at 50° C. for 5 h at a speed of 400 r / min to obtain a mixed solution;

[0047] (3) Add 1 g of the oxidized coal tar pitch prepared in step (1) to 10 ml of the mixed solution prepared in step (2), and stir at 50° C. for 6 h to obtain a spinning solution.

[0048] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 15 KV, a propulsion speed of 0.1 mm / min, a spinning temperature of 40°C, a distance between the syringe needle tip and the receiving plate of 15 cm, and a relative humidity of 60% to obtain a precursor fiber membrane.

[0049] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 300°C at a heating rate of 2°C / min, kept at this temperature for 1 hour, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0050] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 1000°C at a heating rate of 10°C / min, and then cooled to room temperature after keeping the temperature for 1 hour to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0051] Example 4

[0052] (1) Add 5 g of coal tar into 60 mL of concentrated sulfuric acid solution and stir for 5 h, then neutralize with deionized water, filter and wash, and dry in a forced air oven at 80 °C for 12 h.

[0053] (2) adding 1 g of polyvinylidene fluoride and 1 g of polyvinyl pyrrolidone into 20 ml of tetrahydrofuran solution, heating at 40° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0054] (3) 1.5 g of the oxidized coal tar pitch prepared in step (1) was added to 15 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0055] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 8 KV, a propulsion speed of 0.05 mm / min, a spinning temperature of 40°C, a distance between the syringe needle tip and the receiving plate of 10 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0056] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 260°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0057] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 700°C at a heating rate of 6°C / min, and then cooled to room temperature after being kept for 3 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0058] Example 5

[0059] (1) 5 g of coal tar was added to 90 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 5:1 and stirred for 5 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0060] (2) adding 1 g of polystyrene and 1 g of polymethyl methacrylate into 18 ml of toluene solution, heating at 60° C. for 5 h at a speed of 400 r / min to obtain a mixed solution;

[0061] (3) 0.5 g of the oxidized coal tar pitch prepared in step (1) was added to 12 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0062] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 17 KV, a propulsion speed of 0.08 mm / min, a spinning temperature of 45°C, a distance between the syringe needle tip and the receiving plate of 10 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0063] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 270°C at a heating rate of 2°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0064] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 800°C at a heating rate of 5°C / min, and then cooled to room temperature after being kept for 2 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0065] Example 6

[0066] (1) 5 g of coal tar was added to 90 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 and stirred for 5 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0067] (2) adding 0.6 g of polyvinyl alcohol and 1 g of polylactic acid into 13 ml of N,N-dimethylformamide solution, and heating at 60° C. for 2 h at a speed of 400 r / min to obtain a mixed solution;

[0068] (3) 0.8 g of the oxidized coal tar pitch prepared in step (1) was added to 11 ml of the mixed solution prepared in step (2), and the mixture was stirred at 60° C. for 4 h to obtain a spinning solution.

[0069] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 18 KV, a propulsion speed of 0.05 mm / min, a spinning temperature of 40°C, a distance between the syringe needle tip and the receiving plate of 15 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0070] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 250°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0071] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 900°C at a heating rate of 6°C / min, and then cooled to room temperature after keeping the temperature for 1 hour to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0072] Example 7

[0073] (1) 4.5 g of coal tar was added to 80 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1 and stirred for 5 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0074] (2) adding 0.8 g of polyacrylonitrile and 1 g of polymethyl methacrylate into 15 ml of tetrahydrofuran solution, and heating at 40° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0075] (3) 0.5 g of the oxidized coal tar pitch prepared in step (1) was added to 10 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0076] (4) 10 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 16 KV, a propulsion speed of 0.07 mm / min, a spinning temperature of 45°C, a distance between the syringe needle tip and the receiving plate of 20 cm, and a relative humidity of 50% to obtain a precursor fiber membrane.

[0077] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 290°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0078] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 500°C at a heating rate of 8°C / min, and then cooled to room temperature after keeping the temperature for 4 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0079] Example 8

[0080] (1) 5 g of coal tar was added to 45 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 4:1 and stirred for 8 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0081] (2) adding 0.6 g of polyacrylonitrile and 1.2 g of polyvinyl pyrrolidone into 16 ml of toluene solution, heating at 50° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0082] (3) 0.7 g of the oxidized coal tar pitch prepared in step (1) was added to 9.5 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0083] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 11 KV, a propulsion speed of 0.05 mm / min, a spinning temperature of 35°C, a distance between the syringe needle tip and the receiving plate of 25 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0084] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 260°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0085] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 700°C at a heating rate of 6°C / min, and then cooled to room temperature after being kept for 3 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0086] Example 9

[0087] (1) 3 g of coal tar was added to 50 mL of concentrated sulfuric acid solution and stirred for 8 h. The solution was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0088] (2) adding 1.5 g of polystyrene and 1.5 g of polylactic acid into 30 ml of N,N-dimethylformamide solution, and heating at 40° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0089] (3) 1.2 g of the oxidized coal tar pitch prepared in step (1) was added to 15 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0090] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 16 KV, a propulsion speed of 0.09 mm / min, a spinning temperature of 35°C, a distance between the syringe needle tip and the receiving plate of 27 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0091] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 270°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0092] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 500°C at a heating rate of 7°C / min, and then cooled to room temperature after being kept for 3 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0093] Example 10

[0094] (1) 5 g of coal tar was added to 55 mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 4:1 and stirred for 5 h. The mixture was then neutralized with deionized water, filtered and washed, and dried in a forced air oven at 80 °C for 12 h.

[0095] (2) adding 0.7 g of polyacrylonitrile and 2.1 g of polyvinyl pyrrolidone into 27 ml of N,N-dimethylformamide solution, and heating at 40° C. for 4 h at a speed of 400 r / min to obtain a mixed solution;

[0096] (3) 0.5 g of the oxidized coal tar pitch prepared in step (1) was added to 10 ml of the mixed solution prepared in step (2), and the mixture was stirred at 50° C. for 6 h to obtain a spinning solution.

[0097] (4) 5 mL of the spinning solution prepared in step (3) is placed in a syringe, and spinning is performed at a voltage of 14 KV, a propulsion speed of 0.15 mm / min, a spinning temperature of 35°C, a distance between the syringe needle tip and the receiving plate of 18 cm, and a relative humidity of 40% to obtain a precursor fiber membrane.

[0098] (5) The precursor fiber membrane obtained in step (4) is placed in a muffle furnace, heated to 300°C at a heating rate of 3°C / min, kept at this temperature for 2 hours, and then cooled to room temperature to obtain an oxidized fiber membrane.

[0099] (6) The oxidized fiber membrane obtained in step (5) is placed in a tubular furnace, and in an argon atmosphere, the temperature is increased to 800°C at a heating rate of 6°C / min, and then cooled to room temperature after keeping the temperature for 2 hours to obtain a porous soft and hard carbon fiber material for the negative electrode of a lithium-ion battery.

[0100] The porous soft and hard carbon fiber materials for lithium ion batteries obtained in Examples 1-10 were cycled for 2000 cycles at a current of 1 A / g for relevant characterization and battery performance testing. The test results are shown in Table 1.

[0101] Table 1 Performance test table

[0102] Example Capacity (mAh / g) Capacity retention rate (%) Example 1 411.8 81.8 Example 2 423.3 84.1 Example 3 402.8 85.3 Example 4 415.4 84.6 Example 5 408.4 83.5 Example 6 426.9 83.2 Example 7 415.7 82.9 Example 8 419.5 82.1 Example 9 428.1 80.4 Example 10 422.2 80.2 average value 417.4 82.8

[0103] The porous soft and hard carbon fiber materials prepared in Examples 1-10 have been experimentally verified to have an average capacity of 417.4 mAh / g and an average capacity retention rate of 82.8%. The porous soft and hard carbon fiber materials for lithium-ion batteries prepared by the formula of Example 9 have been experimentally verified to have the largest capacity, reaching 428.1 mAh / g, but its capacity retention rate is relatively low; the porous soft and hard carbon fiber materials for lithium-ion batteries prepared by the formula of Example 3 have been experimentally verified to have the smallest capacity, but its capacity retention rate is the highest, reaching 85.3%. Evaluated by the average values ​​of various indicators, the comprehensive performance of the porous soft and hard carbon fiber materials for lithium-ion batteries prepared by the formulas of Examples 2 and 6 is the best.

Claims

1. A high-performance porous soft and hard carbon fiber negative electrode material for lithium-ion batteries and a preparation method thereof, characterized in that: The following steps are involved: (1) mixing coal tar pitch with a liquid oxidant, stirring at 30 to 60° C. for 2 to 10 hours, and then filtering and washing to obtain oxidized coal tar pitch; (2) dissolving polymer 1 and polymer 2 in a solvent, and stirring at 30 to 60° C. for 1 to 5 hours to obtain a mixed solution; (3) stirring the oxidized coal tar pitch prepared in step (1) and the mixed solution prepared in step (2) at 30 to 60° C. for 2 to 10 hours to obtain a spinning solution; (4) electrospinning the spinning solution obtained in step (3) to obtain a precursor fiber membrane; (5) placing the precursor fiber obtained in step (4) in a muffle furnace for pre-oxidation to obtain an oxidized fiber membrane; (6) The pre-oxidized fiber membrane obtained in step (5) is placed in a tubular furnace for carbonization to obtain a porous soft and hard carbon fiber membrane for lithium-ion batteries.

2. The preparation method according to claim 1, characterized in that: In the step (1), the liquid phase oxidant is one or more of concentrated sulfuric acid and concentrated nitric acid; the ratio of coal tar pitch to liquid phase oxidant is 1:5 to 1:

20.

3. The preparation method according to claim 1, characterized in that: In the step (2), polymer 1 is one or more of polyacrylonitrile, polyvinylidene fluoride, polystyrene, and polyvinyl alcohol; polymer 2 is one or more of polyvinyl pyrrolidone, polymethyl methacrylate, and polylactic acid; the solvent is one or more of N,N-dimethylformamide, tetrahydrofuran, and toluene; the ratio of polymer 1 to polymer 2 is 1:1 to 1:5; and the ratio of polymer to solvent is 1:5 to 1:

10.

4. The preparation method according to claim 1, characterized in that: In the step (3), the ratio of oxidized coal tar pitch to the mixed solution is 1:5 to 1:

15.

5. The preparation method according to claim 1, characterized in that: In the step (4), the voltage of the electrospinning is 8-20 kV; the propulsion speed is 0.05-0.2 mm / min; the distance between the electrospinning needle and the receiving plate is 10-30 cm; the temperature is 30-50° C.; and the humidity is 30-60%.

6. The preparation method according to claim 1, characterized in that: In the step (5), the heating rate of the muffle furnace is 1 to 3°C / min; the insulation temperature is 250 to 300°C; and the insulation time is 1 to 3 hours.

7. The preparation method according to claim 1, characterized in that: In the step (6), the heating rate of the tubular furnace is 5 to 10°C / min; the protective atmosphere is one or more of argon, nitrogen, and helium; the insulation temperature is 500 to 1000°C; and the insulation time is 1 to 5 hours.

8. The preparation method according to claim 1, characterized in that: The carbon source includes hard carbon and soft carbon; the hard carbon source is high molecular polymer 1 and high molecular polymer 2; and the soft carbon source is coal tar pitch.

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