阅读说明：本技术 一种纺丝液及其制备方法 (Spinning solution and preparation method thereof ) 是由 袁淑霞 吕春祥 李东升 于 2020-03-18 设计创作，主要内容包括：本发明是关于一种纺丝液及其制备方法,涉及Si/C复合材料制备技术领域。主要采用的技术方案为：一种纺丝液,用于制备Si/C复合纤维材料,其中,所述纺丝液中含有：溶剂、分散在所述溶剂中的硅颗粒、溶解在所述溶剂中的第一聚合物；其中,所述第一聚合物为能进行溶液纺丝的聚合物；其中,在所述纺丝液中,所述第一聚合物的质量分数为5-35％；在所述纺丝液中,所述硅颗粒的质量大于0,且不超过所述第一聚合物质量的50％。本发明主要用于提供一种能基于相分离工艺的溶液纺丝技术制备出Si/C复合纤维材料的纺丝液。该技术利于工业放大,便于Si/C复合纤维材料的批量化生产,同时生产成本也会大幅降低。(The invention relates to a spinning solution and a preparation method thereof, and relates to the technical field of preparation of Si/C composite materials. The main technical scheme adopted is as follows: a spinning solution for preparing a Si/C composite fiber material, wherein the spinning solution comprises: a solvent, silicon particles dispersed in the solvent, a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning; wherein, in the spinning solution, the mass fraction of the first polymer is 5-35%; the mass of the silicon particles in the spinning dope is greater than 0 and not more than 50% of the mass of the first polymer. The invention is mainly used for providing spinning solution which can prepare Si/C composite fiber material based on the solution spinning technology of the phase separation process. The technology is beneficial to industrial amplification, is convenient for batch production of the Si/C composite fiber material, and can greatly reduce the production cost.)

1. A spinning solution for preparing Si/C composite fiber materials, which is characterized by comprising: a solvent, silicon particles dispersed in the solvent, a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning; wherein the content of the first and second substances,

in the spinning solution, the mass fraction of the first polymer is 5-35%;

the mass of the silicon particles in the spinning dope is greater than 0 and not more than 50% of the mass of the first polymer; preferably, the mass of the silicon particles is 1 to 50% of the mass of the first polymer.

2. The dope of claim 1, further comprising other auxiliary agents; wherein the mass of the other auxiliary agents is 0-10% of the mass of the first polymer.

3. The spinning solution according to claim 2, wherein the other auxiliary agent is one or more selected from the group consisting of γ - (2, 3-glycidoxy) propyltrimethoxysilane, amino-functional silane, cetyltrimethylammonium bromide, ethylene glycol, glycerol, F127, P123, and ethanol.

4. The dope according to claim 1, further comprising lignin; wherein the mass of the lignin is 0-50% of the mass of the first polymer.

5. The spinning dope of claim 4, wherein the lignin comprises one or more of organosolv lignin, hydrolyzed lignin, lignin extracted from black liquor;

preferably, the lignin extracted from the papermaking black liquor comprises alkali lignin and lignosulfonic acid;

preferably, the organosolv lignin comprises high boiling alcohol lignin, acetic acid lignin.

6. The spinning solution of claim 1, wherein the solvent is one or more selected from the group consisting of dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, and dimethylacetamide.

7. The spinning dope of claim 1,

the first polymer is one or more of polyacrylonitrile PAN, cellulose acetate CA, polyvinyl alcohol PLA and polyimide PI; and/or

The silicon particles are nano silicon particles; preferably, the particle size of the nano silicon particles is 20-200 nm.

8. The method of preparing the spinning dope of any one of claims 1 to 7, comprising the steps of:

preparing a silicon dispersion liquid: dispersing silicon powder in a solvent, and stirring and mixing uniformly at the temperature of 25-80 ℃ to obtain a silicon dispersion liquid;

blending: and mixing the silicon dispersion liquid, the first polymer or the first polymer solution and the solvent, and mechanically stirring uniformly at 25-80 ℃ to obtain the spinning solution.

9. The method for producing a spinning dope according to claim 8,

in the step of preparing the silicon dispersion, other auxiliaries are further added to the silicon dispersion; and/or

In the blending step, lignin is further added to the spinning solution.

10. The method of producing a spinning dope according to claim 8, further comprising a step of subjecting the spinning dope to a defoaming treatment after the step of blending;

preferably, the spinning solution is deaerated in a vacuum state at 25 to 80 ℃.

Technical Field

The invention relates to the technical field of preparation of Si/C composite materials, in particular to a spinning solution and a preparation method thereof.

Background

Along with the exploitation and consumption of fossil fuels, resource exhaustion and environmental problems are increasingly prominent, and the adjustment of energy structures is imperative. The lithium ion battery has the advantages of high energy density, good high-rate charge and discharge performance, high charge and discharge rate, small self-discharge and the like, and is considered as a 'chemical power supply with the greatest application prospect'. Currently, commercial lithium ion batteries generally employ graphite as a negative electrode material. However, the specific capacitance of the graphite negative electrode is low and is only 372mAhg^-1The requirements for energy density and power density cannot be satisfied for small-sized devices (e.g., mobile phones, notebook computers, video cameras, etc.) and large-sized vehicles (e.g., electric devices powered mainly by batteries, such as electric automobiles).

The theoretical specific capacitance of Si is high (Li)_4.4Si≈4200mAhg^-1) While the discharge voltage is close to 0V (0.2V vs. Li/Li)⁺) Becoming one of the most potential battery negative electrode materials to replace graphite. However, Si has poor conductivity and is accompanied by Li during the cycle⁺Intercalation/deintercalation of Si undergoes volume expansion/contraction: (>300%), causing its structure to crack or pulverize, resulting in Si coming off the current collector and cell failure; meanwhile, due to cracking and pulverization of Si, an SEI film formed on the surface of Si is continuously cracked/formed, so that the consumption of electrolyte and the loss of a large amount of irreversible capacity are caused, the cycle life is reduced, and the safety performance is challenged.

In order to solve the above problems, researchers at home and abroad have made a lot of work, and among them, the nano-sizing and porous formation of Si and the research on the preparation of Si-containing composite materials are the most extensive and intensive. The nano-and porous design of Si endows the material with excellent electrochemical performance, but the specific energy density and the volume energy density of the material are lower due to the higher specific surface area of the material. And Si is a semiconductor, so that the conductivity is poor, and the rate capability of the electrode material is poor. The carbon material has the advantages of good conductivity, stable structure, low reaction voltage and the like when being used as the traditional cathode material of the lithium ion battery; after the composite material is compounded with Si, the volume expansion of the Si can be inhibited to a certain degree, and meanwhile, a buffer space is provided for the volume expansion of the Si, so that the cracking and pulverization of the material structure are avoided, and the structural stability of the SEI film is ensured. On the other hand, the three-dimensional network structure of the carbon material can shorten the migration path of ions, increase the transmission capability of electrons, improve the rate capability of the electrode and the like. Common silicon-carbon composite materials mainly comprise Si-CF, Si-CNTs, Si-rGO, Si/graphite, Si/C and the like, the structure mainly relates to a coated core-shell structure, a porous structure, a sandwich structure and the like, and the preparation method mainly comprises a mechanical blending method, a pyrolysis precursor method, a magnetic sputtering method, an electrostatic spinning method and the like.

At present, Si/C composite materials mostly adopt a coated core-shell structure. Research shows that the one-dimensional material has directional electron and ion transmission paths and excellent electrochemical reaction kinetic characteristics. Therefore, it is considered to prepare the Si/C composite material in a fiber shape. However, most of the currently developed research methods for fibrous Si/C negative electrode materials adopt an electrostatic spinning technology, the yield is not high, and the difficulty of large-scale mass production is high.

Disclosure of Invention

In view of the above, the present invention provides a spinning solution and a preparation method thereof, and mainly aims to provide a spinning solution capable of preparing a Si/C composite fiber material based on a solution spinning technology of a phase separation process.

In order to achieve the purpose, the invention mainly provides the following technical scheme:

in one aspect, embodiments of the present invention provide a spinning solution for preparing a Si/C composite fiber material, wherein the spinning solution comprises: a solvent, silicon particles dispersed in the solvent, a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning; wherein the content of the first and second substances,

in the spinning solution, the mass fraction of the first polymer is 5-35%;

the mass of the silicon particles in the spinning dope is greater than 0 and not more than 50% of the mass of the first polymer; preferably, the mass of the silicon particles is 1 to 50% of the mass of the first polymer.

Preferably, the spinning solution also contains other auxiliary agents; wherein the mass of the other auxiliary agents is 0-10% of the mass of the first polymer.

Preferably, the other auxiliary agents are one or more of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane kh-560, amino functional group silane kh-550, cetyl trimethyl ammonium bromide CTAB, ethylene glycol, glycerol, F127, P123 and ethanol.

Preferably, the spinning solution further contains lignin; wherein the mass of the lignin is 0-50% of the mass of the first polymer.

Preferably, the lignin comprises one or more of organic solvent lignin, hydrolyzed lignin and lignin extracted from papermaking black liquor;

preferably, the lignin extracted from the papermaking black liquor comprises alkali lignin and lignosulfonic acid;

preferably, the organosolv lignin comprises high boiling alcohol lignin, acetic acid lignin.

Preferably, the solvent is a polar solvent which can uniformly disperse the silicon and can dissolve the first polymer; preferably, the solvent is one or more of dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone and dimethylacetamide.

Preferably, the first polymer is one or more of polyacrylonitrile PAN (preferably PAN of 50000-300000g/mol, further preferably PAN of 100000-250000 g/mol), cellulose acetate CA (preferably CA with molecular weight of 4000-100000 g/mol), polyvinyl alcohol PLA (preferably PLA with molecular weight of 10000-1000000 g/mol), polyimide PI (preferably PLA with molecular weight of 3000-60000 g/mol); and/or the silicon particles are nano silicon particles; preferably, the particle size of the nano silicon particles is 20-200 nm.

In another aspect, an embodiment of the present invention provides a method for preparing a spinning solution, including the steps of:

preparing a silicon dispersion liquid: dispersing silicon powder in a solvent, and uniformly stirring (preferably stirring for 4-12h) at the temperature of 25-80 ℃ to obtain a silicon dispersion liquid;

blending: and mixing the silicon dispersion liquid, the first polymer or the first polymer solution and the solvent, and mechanically stirring uniformly at 25-80 ℃ to obtain the spinning solution.

Preferably, in the step of preparing a silicon dispersion, other auxiliary agents are further added to the silicon dispersion.

Preferably, in the blending step, lignin is further added to the spinning solution.

Preferably, after the blending step, a step of defoaming the spinning solution is further included; preferably, the spinning solution is placed in a vacuum state at 25-80 ℃ for deaeration treatment (preferably deaeration treatment for 12-48 h).

Compared with the prior art, the spinning solution and the preparation method thereof have the following beneficial effects:

the embodiment of the invention provides a spinning solution, which can be used for preparing Si/C composite fiber material protofilaments by a wet spinning method or a dry-jet wet spinning method based on a phase separation process, and the protofilaments can be pre-oxidized and carbonized to obtain a long-fiber Si/C composite fiber material. The solution spinning technology based on the phase separation process is a mature technology which is already used in the industrial field in a large scale, and the Si/C composite fiber material is prepared by utilizing the technology, so that the mass production of the Si/C composite fiber material is facilitated, and the production cost is reduced.

Furthermore, other additives are added into the spinning solution provided by the embodiment of the invention, so that the dispersibility and stability of the nano Si in the spinning solution can be improved; the spinning solution can be used for preparing Si/C composite fiber materials with uniformly dispersed Si.

Furthermore, the spinning solution provided by the embodiment of the invention is added with lignin, and after the lignin is added into the spinning solution, a fiber skin layer is weakened in a fiber forming process, so that uniform oxidation and carbonization of fibers are promoted. Meanwhile, the green, environment-friendly and low-cost lignin is used as a pore forming agent and a pore structure regulator for preparing the Si/C composite fiber material (the Si/C composite fiber material has a large amount of pore structures, and Si particles are coated in pores, so that when the Si/C composite fiber material is used as a lithium battery cathode material, the Si composite fiber material can inhibit the volume expansion of Si, simultaneously provides a buffer space for the volume expansion of Si, avoids the cracking and pulverization of the material structure, ensures the structural stability of an SEI film), and avoids the use of acid and alkali.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

FIG. 1 is a scanning electron micrograph of a sample of the Si/C composite fiber material prepared in example 1;

FIG. 2 is a scanning electron micrograph of a sample of the Si/C composite fiber material prepared in example 2; wherein, in FIG. 2, a is a scanning electron microscope image of the surface of the composite fiber material, b is a microscopic morphology of the surface of the Si/C composite fiber material, C is a scanning electron microscope image of the cross section of the Si/C composite fiber material, and d is a microscopic morphology of the cross section of the Si/C composite fiber material;

FIG. 3a is a sorption-desorption isotherm diagram of the Si/C composite fiber material prepared in example 2 under nitrogen;

FIG. 3b is a pore size distribution diagram of the Si/C composite fiber material prepared in example 2;

FIG. 4 is an external view of the Si/C composite fiber material prepared in example 1.

Detailed Description

To further explain the technical means and effects of the present invention adopted to achieve the predetermined object, the following detailed description of the embodiments, structures, features and effects according to the present invention will be made with reference to the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "an embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

In the prior art, electrostatic spinning technology is mostly adopted for research methods aiming at fibrous Si/C composite materials, the yield is not high, and the difficulty of large-scale batch production is high. In view of the above-described drawbacks, the present invention proposes a spinning solution by which a Si/C composite fiber material can be produced by a solution spinning technique based on a phase separation process, and the produced Si/C composite fiber material is in a long fiber form (it is known to those skilled in the art that "long fiber form" refers to a continuous yarn, that is, a continuous yarn ejected at the time of yarn production). Here, the solution spinning technology based on the phase separation process is a mature technology that has been used in industrial fields on a large scale, and is low in cost.

In one aspect, embodiments of the present invention provide a spinning solution for preparing a Si/C composite fiber material, wherein the spinning solution comprises: a solvent, silicon particles dispersed in the solvent, a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning; wherein, in the spinning solution, the mass fraction of the first polymer is 5-35%; the mass of the silicon particles in the spinning dope is greater than 0 and not more than 50% of the mass of the first polymer; preferably, the mass of the silicon particles is 1 to 50% of the mass of the first polymer.

The silicon particles are nano silicon particles with the particle size of 20-200 nm.

Preferably, the first polymer is one or more of Polyacrylonitrile (PAN), Cellulose Acetate (CA), polyvinyl alcohol (PLA) and Polyimide (PI). Further preferably, the molecular weight of polyacrylonitrile PAN is 50000-300000g/mol, preferably 100000-250000 g/mol. Preferably, the molecular weight of cellulose acetate CA is 4000-100000 g/mol. Preferably, the molecular weight of the polyvinyl alcohol PLA is 10000-1000000 g/mol. Preferably, the molecular weight of the polyvinyl alcohol PLA is 3000-60000 g/mol.

Preferably, the spinning solution also contains other auxiliary agents; wherein the mass of the other auxiliary agents is 0-10% of the mass of the first polymer. Preferably, the other auxiliary agents are one or more of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane kh-560, amino functional group silane kh-550, cetyl trimethyl ammonium bromide CTAB, ethylene glycol, glycerol, F127, P123 and ethanol. Here, Si is a main contributor to the capacitance of the lithium ion battery, and the content and dispersibility of Si in the spinning solution directly determine the specific capacitance of the electrode material and the utilization rate of Si. Here, the dispersibility and stability of the nano Si in the spinning solution can be improved by adding other additives.

Preferably, the spinning solution also contains lignin; wherein the mass of the lignin is 0-50% of the mass of the first polymer. The lignin comprises one or more of organic solvent lignin (such as high-boiling alcohol lignin and acetic acid lignin), hydrolyzed lignin, and lignin extracted from papermaking black liquor (such as alkali lignin and lignosulfonic acid). Here, too, the appropriate porosity and pore size distribution in the material are critical for the production of the material. After the lignin is added into the spinning solution, the fiber skin layer is weakened in the fiber forming process, and uniform oxidation and carbonization of the fiber are promoted. Meanwhile, the green, environment-friendly and cheap lignin is used as a pore-forming agent and a pore structure regulator for preparing the fibrous Si/C electrode material, so that the use of acid and alkali is avoided.

Preferably, the solvent is a polar solvent which can uniformly disperse the silicon and can dissolve the first polymer; preferably, the solvent is one or more of dimethyl sulfoxide DMSO, dimethylformamide DMF, N-methylpyrrolidone NMP and dimethylacetamide DMAc.

In another aspect, an embodiment of the present invention provides a method for preparing a spinning solution, including the steps of:

1) preparing a silicon dispersion liquid: dispersing silicon powder (preferably nano silicon particle powder) in a solvent, and mechanically stirring uniformly (preferably, stirring for 4-12hh) at 25-80 ℃ to obtain a uniformly dispersed silicon dispersion liquid.

Preferably, other auxiliaries may be added to the silicon dispersion in this step.

2) Preparing a blending spinning solution: and (2) mixing the silicon dispersion liquid, the polymer solution and the solvent obtained in the step (1) according to a certain proportion, and then mechanically stirring and uniformly mixing at 25-80 ℃ to obtain the spinning solution with the mass fraction of the first polymer of 5-35%.

Preferably, lignin may be added to the spinning dope in this step.

3) Vacuum defoaming: the spinning solution obtained in the above (2) is subjected to a defoaming treatment (preferably a vacuum defoaming treatment for 12 to 48 hours) at a temperature of 25 to 80 ℃ in a vacuum state.

In addition, the spinning solution provided by the embodiment of the invention is prepared into a fibrous Si/C composite material by the following method:

1. preparing nascent fiber: and spraying the spinning solution into a coagulating bath through a common circular spinneret plate to obtain the nascent composite fiber.

In this step, either wet spinning or dry-jet wet spinning may be used. Unlike wet spinning, dry-jet wet spinning refers to: the fiber after being spun passes through an air section with a certain distance and then enters a coagulating bath, and the distance can be set to be 1-20 cm.

Preferably, the coagulating bath is a mixture of solvent and water, and the volume ratio of the solvent to the water is 0:10-7: 3. Preferably, the solvent of the coagulation bath is the same as the solvent used for the spinning dope. Preferably, the draw down ratio of the fiber in the coagulation bath is 0.5 to 2 times.

Preferably, the temperature of the spinning solution is 30-65 ℃ and the temperature of the coagulation bath is 25-75 ℃.

Preferably, the diameter of the spinneret plate is 0.1-0.6mm, and the spinneret plate with the proper diameter can be selected according to the diameter requirement of the fiber.

2. Water washing and hot drawing: and (3) sequentially carrying out water washing and hot drawing treatment on the nascent composite fiber in a multistage water bath with the temperature gradient of 40 ℃, 50 ℃ and 60 ℃.

Preferably, the time for each stage of water washing is 1-30min, and the fiber is washed with deionized water or distilled water.

Preferably, the hot water drawing temperature is 60-95 ℃. The hot water drawing ratio is 1:1-5: 1.

3. And (3) drying: and (3) carrying out freeze drying treatment on the nascent composite fiber after the hot drawing treatment to obtain the Si/C composite precursor.

Here, the fiber may be dried by using a method such as vacuum drying, atmospheric drying, etc., without changing the structural properties of the fiber.

4. Pre-oxidation: heating the Si/C composite protofilament to 180-300 ℃ at the heating rate of 2-10 ℃/min in the air atmosphere, and then keeping the temperature for 10-80min to obtain Si/C pre-oxidized composite fiber;

5. carbonizing: heating the Si/C pre-oxidized composite fiber to 600-1400 ℃ at the heating rate of 2-10 ℃/min in the inert atmosphere, and then keeping the temperature for 10-120s to obtain the fibrous Si/C composite material. Preferably, the inert atmosphere is nitrogen or argon.

The structure of the Si/C composite fiber material prepared by the above method can be seen in fig. 1, 2 and 4. The Si/C composite fiber material is formed by compounding a carbon matrix and Si particles dispersed in the carbon matrix; wherein the Si/C composite fiber material has a long fiber-like appearance; the microstructure of the Si/C composite fiber material is porous carbon coated with silicon particles; the porous carbon is honeycomb or sponge-shaped. The average pore diameter of the Si/C composite fiber material is 5-25 nm. In the Si/C composite fiber material, the mass fraction of the silicon particles is more than 0 and less than 45 percent, and preferably 5 to 30 percent. The silicon particles have a particle size of 20-200 nm. The diameter of the Si/C composite fiber material is 30-250 μm.

The present invention is further illustrated by the following specific examples:

example 1

Dispersing silicon particles with the particle size of 100nm into DMSO at 26 ℃, and stirring for 4 hours to obtain a silicon dispersion liquid; mixing the silicon dispersion liquid, polyacrylonitrile and DMSO to obtain a spinning solution with the mass fraction of the polyacrylonitrile being 16 wt% (wherein, the addition amount of the silicon particles is 20% of the mass of the polyacrylonitrile), mechanically stirring until the silicon particles are uniformly mixed, defoaming at 25 ℃ for 12h in a vacuum state, and standing for later use.

The spinning solution at 30 ℃ was passed through a spinneret having a hole diameter of 0.51mm, and then coagulated in a coagulation bath at 50 ℃ (volume ratio of DMSO/water in the coagulation bath: 20/80) to obtain a Si/C composite nascent fiber. And sequentially putting the Si/C composite nascent fiber into a multi-stage water bath at 40 ℃, 50 ℃ and 60 ℃ for water washing, wherein each stage of water washing is 6 min. Then, the resultant was drawn in pure water at 80 ℃ by a factor of 1, and then freeze-dried to obtain Si/C composite filaments.

Heating the Si/C composite fiber precursor to 220 ℃ in the air at a heating rate of 5 ℃/min, and keeping the temperature at 220 ℃ for 20min to obtain the Si/C composite pre-oxidized fiber. And finally, heating the Si/C composite pre-oxidized fiber to 1200 ℃ in nitrogen at a heating rate of 5 ℃/min, and then keeping the temperature at 1200 ℃ for 10s to obtain the Si/C composite fiber material.

The diameter of the Si/C composite fiber material prepared in example 1 was 246.8. mu.m, the average pore diameter was 24.9nm, and the Si content in the Si/C composite fiber material was 19.8%.

FIG. 1 is a scanning electron microscope image of the Si/C composite fiber material prepared in example 1. As can be seen from FIG. 1, the cross section of the fibrous Si/C composite material has a large number of pores.

FIG. 4 is an appearance view of a sample of Si/C composite fiber prepared in example 1 (the sample was wound on a smooth beaker for effective suppression of fuzz).

Example 2

Dispersing silicon particles with the particle size of 30nm and Cetyl Trimethyl Ammonium Bromide (CTAB) into DMSO at the temperature of 50 ℃, and stirring for 6 hours to obtain a silicon dispersion liquid; mixing the silicon dispersion liquid, polyacrylonitrile, alkali lignin and DMSO to obtain a spinning solution with the mass fraction of the polyacrylonitrile being 10 wt% (wherein, the adding amount of CTAB is 5% of the mass of the polyacrylonitrile, the adding amount of silicon particles is 15% of the mass of the polyacrylonitrile, and the adding amount of alkali lignin is 5% of the mass of the polyacrylonitrile), mechanically stirring until the materials are uniformly mixed, defoaming at 60 ℃ in a vacuum state for 12 hours, and standing for later use.

The spinning solution at 60 ℃ was passed through a 0.21mm spinneret, and then coagulated in a coagulation bath at 25 ℃ (volume ratio of DMSO/water in the coagulation bath: 20/80), and the nascent fiber was washed in a multistage water bath at 40 ℃, 50 ℃, and 60 ℃ for 6min each stage. Then drawing in pure water at 80 ℃ by 1 time to obtain the Si/C composite nascent fiber. And then, carrying out freeze drying to obtain the Si/C composite protofilament.

Heating the Si/C composite protofilament to 250 ℃ in the air at the heating rate of 5 ℃/min, and keeping the temperature at 250 ℃ for 30min to obtain the Si/C composite pre-oxidized fiber. And finally, heating the pre-oxidized fiber to 800 ℃ in nitrogen at a heating rate of 5 ℃/min, and then keeping the temperature at 800 ℃ for 120s to obtain the Si/C composite fiber material.

The Si/C composite prepared in example 2 had a diameter of 110.7 μm and an average pore diameter of 2.4 nm. The Si content in the Si/C composite fiber material in example 2 was 12.8%. FIG. 2 is a scanning electron microscope image of a sample of the Si/C composite fiber material prepared in example 2 (a is a scanning electron microscope image of the surface of the composite fiber material, b is a microscopic morphology of the surface of the Si/C composite fiber material, C is a scanning electron microscope image of the cross section of the Si/C composite fiber material, and d is a microscopic morphology of the cross section of the Si/C composite fiber material). As can be seen from fig. 2, a large number of pore structures are present in the cross-section.

FIG. 3a is a spectrum obtained by pore structure analysis of the Si/C composite fiber material prepared in example 2. It can be seen from the sorption-desorption isotherms of fig. 3a that hysteresis loops appear after a relative pressure of greater than 0.2, indicating the presence of a mesoporous structure in the material. FIG. 3b is a graph showing the pore size distribution of a sample of the Si/C composite fiber material prepared in example 2, and it can be seen from FIG. 3b that the material has not only micropores but also a certain proportion of mesopores, and the pore size distribution is: 0.8-2nm micropores, 2-50nm mesopores and 50-120nm macropores.

The compositions of the spinning solutions of examples 3 to 8 are shown in table 1, the preparation process conditions are shown in tables 2a and 2b, and the rest of the experimental operation steps are shown in examples 1 and 2.

The compositions of the spinning solutions of examples 1 to 8 are shown in table 1.

Table 1 spin fluid compositions of examples 1-8

Note: in table 1, the amounts of silicon and lignin added were measured based on the mass of the first polymer used.

The preparation process conditions in examples 1 to 8 are shown in tables 2a and 2 b.

TABLE 2a preparation Process conditions for examples 1-8

TABLE 2b preparation of examples 1-8 Process conditions

The diameter, pore size and Si particle content data of the Si/C composite fiber materials prepared in examples 1-8 are shown in Table 3.

TABLE 3 test data for Si/C composite fiber materials prepared in examples 1-8

It can be seen from examples 1 to 8, fig. 1 to 4, and tables 1 to 3 that the long fibrous Si/C composite fiber material can be prepared by using the spinning solution provided by the present invention and using a wet spinning method or a dry-jet wet spinning method, and the Si/C composite fiber material has a rich pore structure, so that when the Si/C composite fiber material is used as a negative electrode material of a lithium battery, the Si/C composite fiber material can inhibit the volume expansion of Si, and simultaneously provide a buffer space for the volume expansion of Si, thereby avoiding the cracking and pulverization of the material structure, and ensuring the structural stability of an SEI film.

In conclusion, the spinning solution provided by the invention can be used for preparing the Si/C composite fiber material by a solution spinning technology based on a phase separation process. The solution spinning technology is mature and is already used in the industrial field in a large scale, has low cost and is beneficial to industrial amplification. In addition, a pore structure is formed in the fiber during phase separation in the spinning process, and the introduction of lignin can become a pore-forming agent and a pore structure regulator, so that the further enrichment and optimization of the pore structure in the fiber are promoted.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.