阅读说明：本技术 一种Si/C复合纤维材料及其制备方法和应用 (Si/C composite fiber material and preparation method and application 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Si/C复合纤维材料及其制备方法和应用,涉及Si/C复合材料制备技术领域。主要采用的技术方案为：所述Si/C复合纤维材料由炭基体和分散于其中的Si颗粒复合而成；其中,所述Si/C复合纤维材料的外观呈长纤维状；所述Si/C复合纤维材料的微观结构为包覆硅颗粒的多孔炭。本发明主要提供一种基于相分离法的溶液纺丝技术制备的长纤维状的Si/C复合纤维材料及其制备方法,在此,所采用的基于相分离法的溶液纺丝技术工艺流程相对简单,利于工业放大,便于Si/C复合材料的批量化生产,同时生产成本也会大幅降低。(The invention relates to a Si/C composite fiber material and a preparation method and application thereof, relating to the technical field of Si/C composite material preparation. The main technical scheme adopted is as follows: 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 invention mainly provides a long fibrous Si/C composite fiber material prepared by a solution spinning technology based on a phase separation method and a preparation method thereof.)

1. The Si/C composite fiber material is characterized by being 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; preferably, the microstructure of the Si/C composite fiber material is porous carbon coated with silicon particles; further preferably, the porous carbon is honeycomb or sponge-like.

2. The Si/C composite fiber material according to claim 1,

the Si/C composite fiber material is distributed in a multi-stage pore, the average pore diameter is 5-25nm, and the pore volume is 0.3-5.6cm³/g。

3. The Si/C composite fiber material according to claim 1 or 2,

in the Si/C composite fiber material: the mass fraction of the silicon particles is more than 0 and less than or equal to 45 percent; and/or

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

The diameter of the Si/C composite fiber material is 30-250 mu m.

4. A method for preparing a Si/C composite fiber material according to any one of claims 1 to 3, characterized by comprising the steps of:

preparing a spinning solution: preparing a spinning dope containing a solvent, silicon particles dispersed in the solvent, and a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning;

preparing Si/C composite fiber precursor: solidifying the spinning solution by adopting a wet spinning method or a dry-jet wet spinning method to form nascent fibers, and then carrying out water washing, hot drawing and drying treatment on the nascent fibers to obtain Si/C composite fiber protofilaments;

pre-oxidation and carbonization treatment: and carrying out pre-oxidation and carbonization treatment on the Si/C composite fiber protofilament to obtain the Si/C composite fiber material.

5. The method for producing a Si/C composite fiber material according to claim 4,

in the spinning solution, the mass fraction of the first polymer is 5-35%; the mass of the silicon particles is greater than 0, and the mass of the silicon particles is not more than 50% of the mass of the first polymer; and/or

The spinning solution also contains other auxiliary agents; wherein the mass of the other auxiliary agents is 0-10% of that of the first polymer; further preferably, the other auxiliary agents are one or more of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, amino functional group silane, hexadecyl trimethyl ammonium bromide, ethylene glycol, glycerol, F127, P123 and ethanol; and/or

The spinning solution also contains lignin; wherein the mass of the lignin is 0-50% of the mass of the first polymer; further preferably, the lignin comprises one or more of organic solvent lignin, hydrolyzed lignin and lignin extracted from papermaking black liquor; and/or

The solvent is one or more of dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone and dimethylacetamide; and/or

The first polymer is one or more of polyacrylonitrile PAN, cellulose acetate CA, polyvinyl alcohol PLA and polyimide PI.

6. The method for preparing a Si/C composite fiber material according to claim 4 or 5, wherein the step of preparing the spinning solution comprises:

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

blending: 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 a spinning solution;

preferably, in the step of preparing the silicon dispersion, other auxiliaries 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; more preferably, the spinning solution is deaerated by placing the spinning solution in a vacuum state at 25 to 80 ℃.

7. The method for producing the Si/C composite fiber material according to claim 4, wherein the step of producing the Si/C composite fiber strand comprises:

step 1): the spinning solution enters a coagulating bath through a spinning trickle formed by a spinning pack to be coagulated and formed to obtain nascent composite fibers;

step 2): carrying out multi-stage water washing and hot drawing treatment on the nascent composite fiber;

step 3): drying the nascent composite fiber after the hot drawing treatment to obtain Si/C composite fiber protofilament;

preferably, in the step 1), the coagulation bath includes a solvent and water; wherein the volume ratio of the solvent to the water is 0:10-7: 3; further preferably, the solvent in the coagulation bath is the same type as the solvent in the spinning dope;

preferably, in the step 1), the temperature of the spinning solution is 30-65 ℃, and the temperature of the coagulation bath is 25-75 ℃;

preferably, in the step 1), the aperture of the spinneret plate in the spinneret assembly is 0.1-0.6 mm.

8. The method for producing a Si/C composite fiber material according to claim 7,

the step 2) comprises the following steps: sequentially carrying out primary washing treatment, secondary washing treatment and tertiary washing treatment on the nascent composite fiber; wherein the temperature of the first-stage water washing treatment is 38-42 ℃, the temperature of the second-stage water washing treatment is 48-52 ℃, and the temperature of the third-stage water washing treatment is 58-65 ℃; preferably, the time of each stage of water washing treatment is 1-30 min; and/or

In the step 2), the hot drawing treatment is carried out in water, the temperature of the hot drawing treatment is 60-95 ℃, and the drawing ratio of the hot drawing treatment is 1:1-5: 1;

in the step 3), the drying treatment is any one of freeze drying treatment, vacuum drying treatment and normal pressure drying treatment.

9. The method for preparing the Si/C composite fiber material according to claim 4, wherein the pre-oxidation and carbonization treatment comprises:

pre-oxidation: heating the Si/C composite fiber precursor 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;

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 Si/C composite fiber material.

10. Use of the Si/C composite fiber material of any one of claims 1 to 3 in a lithium ion battery negative electrode material.

Technical Field

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

Background

Along with the exploitation and consumption of fossil fuels, resource exhaustion and environmental problems are increasingly prominent, and energy structure adjustment 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 (0.2Vvs. 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⁺The volume expansion/contraction of Si (more than 300 percent) causes the structure to crack or pulverize, so that the Si falls off from a current collector and the battery fails; meanwhile, the SEI film formed on the surface of Si is continuously broken/formed due to the breakage and pulverization of Si, so that the consumption of electrolyte and the loss of a large amount of irreversible capacity are caused, and the cycle life is prolongedThe lifetime decreases and security performance encounters challenges.

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. Although Si is designed to be nano-sized and porous, the material has excellent electrochemical performance, but because the specific surface area of the material is high, the specific energy density and the volume energy density of the material are low, and Si is a semiconductor and has poor conductivity, 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.

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 Si/C composite fiber material and a method for preparing the same, and mainly aims to provide a long fibrous Si/C composite fiber material prepared by a solution spinning technology based on a phase separation method and a method for preparing the same.

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

in one aspect, embodiments of the present invention provide a Si/C composite fiber material, wherein the Si/C composite fiber material is compounded by a carbon matrix and Si particles dispersed therein; wherein the Si/C composite fiber material has a long fiber-like appearance; preferably, the microstructure of the Si/C composite fiber material is porous carbon coated with silicon particles; further preferably, the porous carbon is honeycomb or sponge-like.

Preferably, the Si/C composite fiber material is distributed in a multi-stage pore, the average pore diameter is 5-25nm, and the pore volume is 0.3-5.6cm³/g。

Preferably, in the Si/C composite fiber material, the mass fraction of the silicon particles is greater than 0 and equal to or less than 45%, and preferably, the mass fraction of the silicon particles is 5 to 30%; and/or the silicon particles are nano-silicon particles; preferably, the particle size of the nano silicon particles is 20-200 nm; and/or the diameter of the Si/C composite fiber material is 30-250 mu m.

In another aspect, an embodiment of the present invention provides a method for preparing a Si/C composite fiber material, including the steps of:

preparing a spinning solution: preparing a spinning dope containing a solvent, silicon particles dispersed in the solvent, and a first polymer dissolved in the solvent; wherein the first polymer is a polymer capable of solution spinning;

preparing Si/C composite fiber precursor: solidifying the spinning solution by adopting a wet spinning method or a dry-jet wet spinning method to form nascent fibers, and then carrying out water washing, hot drawing and drying treatment on the nascent fibers to obtain Si/C composite fiber protofilaments;

pre-oxidation and carbonization treatment: and carrying out pre-oxidation and carbonization treatment on the Si/C composite fiber protofilament to obtain the Si/C composite fiber material.

Preferably, in the spinning solution, the mass fraction of the first polymer is 5-35%; the mass of the silicon particles is greater than 0, and the mass of the silicon particles is 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 that of the first polymer; further preferably, the other auxiliary agent is one or more of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, amino functional group silane, hexadecyl trimethyl ammonium bromide, 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; further preferably, the lignin comprises one or more of organic solvent lignin, hydrolyzed lignin and lignin extracted from papermaking black liquor.

Preferably, the solvent is a polar solvent which is favorable for dispersing the silicon particles 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), and polyimide PI (preferably PLA with molecular weight of 3000-60000 g/mol).

Preferably, the step of preparing the spinning solution comprises:

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; preferably, in the step of preparing the silicon dispersion, other auxiliaries are further added to the silicon dispersion;

blending: 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 a spinning solution; 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; more preferably, the spinning solution is placed in a vacuum state at 25 to 80 ℃ to be subjected to defoaming treatment (preferably defoaming treatment for 12 to 48 hours).

Preferably, the step of preparing the Si/C composite fiber strand includes:

step 1): the spinning solution enters a coagulating bath through a spinning trickle formed by a spinning pack to be coagulated and formed to obtain nascent composite fibers;

step 2): carrying out multi-stage water washing and hot drawing treatment on the nascent composite fiber;

step 3): drying the nascent composite fiber after the hot drawing treatment to obtain Si/C composite fiber protofilament;

preferably, in the step 1), the coagulation bath includes a solvent and water; wherein the volume ratio of the solvent to the water is 0:10-7: 3; further preferably, the solvent in the coagulation bath is the same type as the solvent in the spinning dope;

preferably, in the step 1), the temperature of the spinning solution is 30-65 ℃, and the temperature of the coagulation bath is 25-75 ℃;

preferably, in the step 1), the aperture of the spinneret plate in the spinneret assembly is 0.1-0.6 mm.

Preferably, the step 2) includes: sequentially carrying out primary washing treatment, secondary washing treatment and tertiary washing treatment on the nascent composite fiber; wherein the temperature of the first-stage water washing treatment is 38-42 ℃, the temperature of the second-stage water washing treatment is 48-52 ℃, and the temperature of the third-stage water washing treatment is 58-65 ℃; preferably, the time of each stage of water washing treatment is 1-30 min.

Preferably, in the step 2), the hot drawing treatment is carried out in water, the temperature of the hot drawing treatment is 60-95 ℃, and the drawing ratio of the hot drawing treatment is 1:1-5: 1;

preferably, in the step 3), the drying process is any one of a freeze drying process, a vacuum drying process and an atmospheric drying process.

Preferably, the step of pre-oxidation and carbonization includes:

pre-oxidation: heating the Si/C composite fiber precursor 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;

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 Si/C composite fiber material.

On the other hand, the Si/C composite fiber material is applied to a lithium ion battery cathode material.

Compared with the prior art, the Si/C composite fiber material and the preparation method and the application thereof have at least the following beneficial effects:

in the Si/C composite fiber material provided by the embodiment of the invention, Si particles are dispersed in a long fibrous carbon fiber matrix; unlike the core-shell structure and the like adopted in the past, the Si/C composite fiber material provided by the embodiment of the invention has the advantages of one-dimensional materials, such as directional electron and ion transmission paths, and excellent electrochemical reaction kinetics.

The Si/C composite material provided by the embodiment of the invention has high mechanical strength and abundant pore structures, so that when the Si/C composite fiber material is used as a lithium battery cathode material, the volume expansion of Si can be inhibited, a buffer space is provided for the volume expansion of Si, the cracking and pulverization of the material structure are avoided, and the structural stability of an SEI film is ensured.

The preparation method of the Si/C composite fiber material provided by the embodiment of the invention is different from the preparation method of the traditional Si/C composite material, and the Si/C composite nascent fiber material is prepared by a solution spinning technology based on a phase separation process, and then oxidized and carbonized to obtain the Si/C composite fiber material. 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, the fibers spontaneously form a pore structure upon phase separation during spinning. The introduction of lignin can become a pore-forming agent and a pore structure regulator, and a freeze drying treatment method is adopted, so that the pore structure of the Si/C composite fiber material can be further enriched.

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 a sample of the Si/C composite fiber material prepared in example 2 under nitrogen;

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

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

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 in the developed research method for fibrous Si/C cathode materials, the yield is not high, and the difficulty of large-scale batch production is high. In contrast, 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. However, there is currently no research related to the preparation of fibrous Si/C composites using this technique.

Based on the problems in the prior art, the invention provides a Si/C composite fiber material and a preparation method thereof for the first time, which specifically comprise the following steps:

on one hand, the embodiment of the invention provides a preparation method of a Si/C composite fiber material, which comprises the following steps:

1. the preparation method of the spinning solution specifically comprises the following steps:

(1) preparing a silicon dispersion liquid: dispersing silicon powder in solvent, and mechanically stirring at 25-80 deg.C (preferably 4-12 hr) to obtain uniformly dispersed silicon dispersion.

(2) Blending: and (2) mixing the silicon dispersion liquid obtained in the step (1), the first polymer or the first polymer solution and the solvent according to a certain proportion, and then uniformly mixing the mixture at a temperature of between 25 and 80 ℃ by adopting mechanical stirring to obtain a spinning solution with the mass fraction of the first polymer of between 5 and 35 percent.

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

Preferably, in the step of preparing the silicon dispersion, other auxiliaries may be further added to the silicon dispersion; wherein the mass of the other auxiliary agents is 0-10% of the mass of the first polymer. Preferably, the other auxiliary agent is one or more of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, amino functional group silane, hexadecyl trimethyl ammonium bromide, ethylene glycol, glycerol, F127, P123 or 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 other additives.

Preferably, in the blending step, the spinning solution further 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, a suitable porosity and pore size distribution in the material are critical for determining the material properties. After the lignin is added into the spinning solution, the skin layer of the fiber is weakened and a large number of holes are generated in the fiber forming process. Meanwhile, the environment-friendly and cheap lignin is used as a pore-forming agent 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.

Preferably, the mass of the silicon particles is greater than 0 and the mass of the silicon particles is 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.

2. Preparing Si/C composite fiber precursor: and solidifying the spinning solution to form nascent fiber by adopting a wet spinning method or a dry-jet wet spinning method, and then washing, hot-drawing and drying the nascent fiber to obtain the Si/C composite fiber precursor.

Dry-jet-wet spinning is distinguished from wet spinning in that the spinning jet of the wet spinning process is directed into the coagulation bath (i.e. the spinneret is located in the coagulation bath), whereas the spinning jet of the dry-jet-wet spinning process is passed through air and then into the coagulation bath (i.e. a certain air space is present between the spinneret and the coagulation bath). Here, the distance of the air section may be set to 1-20 cm.

Preferably, the step of preparing the Si/C composite fiber strand comprises:

(1) and (3) allowing the spinning solution to pass through spinning trickle formed by a spinning pack to enter a coagulating bath for coagulation and formation to obtain the nascent composite fiber.

Here, the coagulation bath includes a solvent and water; wherein the volume ratio of the solvent to the water is 0:10-7: 3; further preferably, the solvent in the coagulation bath is of the same type as the solvent in the spinning dope. Preferably, the draw down ratio of the fiber in the coagulation bath is 0.5 to 2 times.

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

The aperture of the spinneret plate in the spinneret pack is 0.1-0.6 mm.

(2) And carrying out multi-stage water washing and hot drawing treatment on the nascent composite fiber.

Specifically, the primary composite fiber is sequentially subjected to primary washing treatment, secondary washing treatment and tertiary washing treatment; wherein the temperature of the first water washing treatment is 38-42 ℃ (preferably 40 ℃), the temperature of the second water washing treatment is 48-52 ℃ (preferably 50 ℃), and the temperature of the third water washing treatment is 58-65 ℃ (preferably 60 ℃); preferably, the time of each stage of water washing treatment is 1-30 min.

The hot-drawing treatment is carried out in pure water, the temperature of the hot-drawing treatment is 60-95 ℃, and the drawing ratio of the hot-drawing treatment is 1:1-5: 1.

(3) And drying the nascent composite fiber after the hot drawing treatment to obtain the Si/C composite fiber precursor.

Here, the drying method is preferably a freeze-drying method. Unlike the preparation method of ordinary carbon fiber (the preparation of ordinary carbon fiber is dry densification for improving mechanical properties), the application firstly proposes to select a freeze-drying treatment method, and the freeze-drying treatment method is beneficial to keeping the pore structure in the fiber. And the high-temperature drying shrinkage is too large, so that the pore structure in the fiber is damaged (the drying densification in the prior art removes the pore structure of the fiber as much as possible to obtain the fiber with complete structure and excellent mechanical property). The pore structure of the fiber needs to be reserved, and a buffer space is provided for the volume expansion of Si, so that the porosity of the Si/C composite fiber material can be ensured, the Si/C composite fiber material has rich pore structures, and Si particles are coated in the pores of the fiber, so that when the Si/C composite fiber material is used as a lithium battery cathode material, the volume expansion of Si can be inhibited, and meanwhile, the buffer space is provided for the volume expansion of Si, and the cracking and pulverization of the material structure are avoided.

Of course, the fibers may be dried by methods such as vacuum drying, atmospheric drying, etc., without changing the structural properties of the fibers.

3. Pre-oxidation and carbonization treatment: and carrying out pre-oxidation and carbonization treatment on the Si/C composite fiber protofilament to obtain the Si/C composite fiber material.

Pre-oxidation: heating the Si/C composite fiber precursor 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;

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 Si/C composite fiber material.

On the other hand, the embodiment of the invention also provides a Si/C composite fiber material, the structure of which can be seen in fig. 1, fig. 2 and fig. 4, the Si/C composite fiber material is compounded by a carbon matrix and Si particles dispersed therein; the Si/C composite fiber material is fibrous, specifically, long-fiber (here, it is known to those skilled in the art that "long-fiber" refers to continuous fibers, i.e., continuous filaments are ejected during spinning, and not short fibers such as cotton); 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 greater than 0 and not more than 45%, preferably 5 to 30%. The silicon particles have a particle size of 20-200 nm. The diameter of the Si/C composite fiber material is 30-250 μm. Preferably, the Si/C composite fiber material provided by the embodiment of the present invention is prepared by the above-mentioned method for preparing a Si/C composite fiber material.

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 6min, then drawing 1 time in pure water at 80 ℃, and freeze-drying to obtain the Si/C composite fiber protofilament.

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 Si/C composite fiber material prepared in example 1 had a large number of pores in the cross section.

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 25 ℃ coagulation bath (volume ratio of DMSO/water in the coagulation bath: 20/80). the nascent fiber was washed in a multistage water bath at 40 ℃, 50 ℃ and 60 ℃ in this order 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 fiber precursor.

Heating the Si/C composite fiber precursor to 250 ℃ in the air at the heating rate of 5 ℃/min, and keeping the temperature of the Si/C composite fiber precursor 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 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 surface micro-morphology 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 cross-sectional micro-morphology 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 diameters, pore diameters and Si particle contents of the Si/C composite fiber materials prepared in examples 1 to 8 are shown in Table 3.

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

As can be seen from examples 1 to 8, fig. 1 to 4, and tables 1 to 3, the preparation method of the Si/C composite fiber material provided by the present invention can prepare a long fibrous Si/C composite fiber material, and the Si/C composite fiber material has a rich pore structure (the carbon matrix in the Si/C composite fiber material is in a honeycomb or sponge structure), such 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 fracture and pulverization of the material structure, and ensuring the structural stability of the SEI film.

In summary, the invention is different from the prior preparation method of the Si/C composite material, and the Si/C composite fiber material is prepared 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, during phase separation in the spinning process, a pore structure is formed in the fiber, 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 Si/C composite fiber material 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.