CN103305965B - Si-C composite material with nanometer micropore gap and preparation method thereof and purposes - Google Patents

Abstract

The invention discloses a silicon-carbon composite material with nano-micropores and its preparation method and application. The material includes nano-silicon particles and a nano-carbon fiber matrix, and the nano-silicon particles are dispersed in the nano-carbon fiber matrix. Nano-holes and micro-pores connecting the nano-holes are distributed in the nano-carbon fiber matrix. The method includes dissolving nano-silicon (Si) particles and polyacrylonitrile (PAN) in a solvent to prepare a mixed spinning solution, and then electrospinning the mixed spinning solution, and the spinning fine stream is solidified and formed in a coagulation bath The multi-void PAN-Si nanocomposite fiber is obtained; then oxidation treatment and carbonization treatment are carried out sequentially to obtain the aforementioned silicon-carbon composite material with nano-microporous structure. The use is the application of the material in the preparation of negative electrode materials for lithium ion batteries. Compared with the prior art, the invention reserves a buffer space for the expansion of the nano-silicon particles, and at the same time ensures the overall electron transport capability of the material.

Description

Silicon-carbon composite material with nano-micropores and its preparation method and application

technical field

The invention relates to a nanocomposite material, in particular to a silicon-carbon composite material with nanometer pores and its preparation method and application.

Background technique

Lithium-ion battery anode materials are generally carbon materials, such as graphite, needle coke, mesocarbon microspheres, carbon fibers, nano-carbon fibers, etc. At present, the theoretical reversible lithium storage specific capacity of graphite anode materials that have been commercially applied is 372mAh/g. Improving the capacity of lithium-ion batteries mainly depends on the lithium intercalation ability of negative electrode materials. The research and development of high-capacity negative electrode materials has become the key to improving the performance of lithium-ion batteries. The theoretical lithium storage capacity of silicon (Si) material is 4200mAh/g, which is an ideal material for increasing the negative electrode capacity. However, the volume expansion of Si materials during the lithium intercalation process can reach 300%, which will lead to the destruction of the material structure and mechanical crushing, resulting in the separation between the conductive network and the silicon particles. The poor conductivity of silicon materials, low initial charge and discharge efficiency, fast energy decay, and extremely poor cycle performance are key scientific issues that need to be solved urgently for this type of material to be used in high specific energy lithium-ion batteries. In order to alleviate the volume expansion of alloy materials during the charging process and improve their cycle stability, it is more effective to prepare nanoscale silicon particles or carbon/silicon nanocomposites.

Jung et al. used silane cracking to prepare a 50nm amorphous silicon film. The initial capacity can reach more than 3000mAh/g, but after 20 cycles, the capacity rapidly decays to 400mAh/g [H.Jung, M.Park, Y.Yoon , et al. Journal of Power Sources, 2003, 115:346.]. Bourderau prepared a 1.2μm Si film by CVD method, and found that the capacity can reach 1000mAh/g for the first time, but after 20 cycles, the capacity rapidly decays to about 200mAh/g [S.Bourderau, T.Brousse.Journal of Power Sources, 1999,81:233.]. While preparing Si nanowires, Cui introduced a core-shell structure. The core is a Si wire with a good crystal form, which plays a stable structure; the shell is a layer of amorphous Si film, which plays the role of capacity storage [L. Cui, Y. Cui. Nano Letters, 2009, 9: 491.].

The compounding of silicon and carbon for the preparation of negative electrode materials has become a research hotspot in recent years. The researchers also studied the application of composite materials of Si and graphite, mesocarbon microspheres, carbon nanotubes, graphene, porous carbon, amorphous carbon, carbon aerogel, etc. in lithium-ion battery anode materials. Electrospinning technology is an effective method for preparing nanofibers. The polymer precursor of electrospun carbon, after oxidative carbonization, can prepare nanocarbon fibers with unique microstructures, such as porous structure, hollow structure, embedded nanoparticles, and core-shell structure. , Surface irregularities, etc. [M.Inagani, Y.Yang, F.Kang. Advanced Materials, 2012,24:2547.]. Li et al. performed electrospinning of polyacrylonitrile (PAN) solution mixed with nano-silicon particles. After oxidative carbonization, nano-carbon fibers with silicon particles embedded in carbon matrix were obtained, and this was used as the negative electrode material of lithium-ion batteries. The initial capacity It can reach 1000mAh/g, and after 50 cycles, the capacity decays to less than 700mAh/g, mainly because there is no buffer space reserved for the expansion of silicon in the carbon matrix, which limits the improvement of the cycle performance of the material; The agglomeration of a large number of silicon particles is exposed on the surface of carbon nanofibers [Y.Li, B.Guo, L.Ji, et al.Carbon, 2013,51:185.]. Patent CN102623680A discloses a silicon-carbon composite anode material with a three-dimensional reserved hole structure and its preparation method. In the carbon matrix, silicon dioxide is used as a template to coat silicon particles, and finally the silicon dioxide is etched with hydrofluoric acid. In order to obtain the reserved void structure on the surface of silicon particles, the first reversible capacity of the material can reach 1190mAh/g, the Coulombic efficiency is 78.2%, the reversible capacity after 100 cycles is 1056mAh/g, and the capacity retention rate is 88.7%. However, in this patent, since the reserved pores are formed by etching silicon dioxide, after the silicon dioxide is etched away, the silicon particles are located in the pores as a whole and cannot fully contact the carbon matrix (only point contact due to gravity ), resulting in poor electron transport performance.

Contents of the invention

The technical problem to be solved by the present invention is to provide a silicon-carbon composite material with nano-micropores, while reserving a buffer space for the expansion of nano-silicon particles, while ensuring the overall electron transport capability of the material.

The present invention also provides the preparation method of the composite material and its use in the preparation of lithium ion negative electrode materials.

After research, the inventor of this patent believes that all silicon-carbon composite materials can not completely solve the problem of silicon expansion during charging and discharging. The key is that the carbon matrix in it does not really play a role in stabilizing the structure; Covering effect, to suppress the expansion stress of silicon; but does not provide sufficient buffer space for the expansion of silicon. After many times of charge and discharge, the carbon matrix will eventually destroy its own structure due to the expansion stress of silicon, thereby reducing the protective effect on silicon and its own electrochemical performance. Therefore, the study of silicon-carbon nanocomposites that provide a buffer space for the volume expansion of silicon will greatly promote the development of silicon-based negative electrode materials for high-capacity lithium-ion batteries. This patent is based on the theory of non-solvent-induced phase separation of polymer solutions. Electrospinning technology is used to electrospin the PAN (polyacrylonitrile) solution doped with nano-silicon particles. The coagulant is double-diffused and solidified, and the coagulation conditions are controlled to obtain primary fibers with a porous structure; after the primary nanofibers are oxidized and carbonized, nano-carbon fibers containing rich nano-micropores and nano-silicon embedded in the carbon matrix are obtained, and It is used as an anode material for lithium-ion batteries.

Specifically, the present invention solves the above-mentioned technical problems through the following technical means:

As shown in Figure 1, a silicon-carbon composite material with a nano-microporous structure includes nano-silicon particles and a nano-carbon fiber matrix, the nano-silicon particles are dispersed in the nano-carbon fiber matrix, and the nano-carbon fiber matrix is distributed with Nanoholes and micropores connecting the nanoholes.

Preferably: the average diameter of the nano-carbon fibers in the nano-carbon fiber matrix is 100-600 nm, and the average diameter of the nano-silicon particles is 10-60 nm.

Preferably: the mass fraction of the silicon particles is 3-67%, and the mass fraction of the carbon nanofiber matrix is 33-97%. If the content of silicon particles is less than 3%, the effect of improving the lithium storage capacity of the material is not significant, and if it is greater than 67%, the formation and distribution of the aforementioned structures in the material will not be ideal.

Compared with the prior art, the present invention uses non-solvent-induced solidification to form holes for electrospun fibers, and finally obtains porous nano-silicon-carbon composite fibers. The silicon-carbon composite material of the present invention encapsulates silicon in porous nano-carbon fibers. The embedding of silicon improves the overall lithium storage capacity of the material. The carbon matrix can help silicon particles to carry out charge transmission. Effectively accommodate the volume expansion of silicon during charging and discharging, and the micropores also provide convenient channels for the transmission of ions and charges. The composite material combines the advantages of silicon and carbon, and effectively suppresses the disadvantages of the two, thereby improving the electrochemical performance of the material.

The present invention also provides a method for preparing a silicon-carbon composite material with a nanovoid structure, comprising the following steps:

S1, configure the polyacrylonitrile spinning solution containing nano-silicon particles;

S2. Put the polyacrylonitrile spinning solution obtained in step S1 into a syringe, and perform electrospinning under a high-voltage electrostatic field, and the spinning fine stream enters a liquid coagulation bath to solidify and form after a 2-10 cm spinning process in the air The nascent polyacrylonitrile nanofibers are obtained, and the nascent polyacrylonitrile nanofibers are placed in a liquid coagulation bath for 1-3 hours, and then vacuum-dried to obtain polypropylene nanofibers, wherein the voltage of the high-voltage electrostatic field is 5-30kV, and the spinning The liquid flow rate is 0.1-1.0mL/h;

S3, oxidizing the polyacrylonitrile nanofibers obtained in step S2 to obtain nanofiber oxides;

S4. Carbonizing the nanofiber oxide to form the silicon-carbon composite material.

Preferably, the step S1 includes: adding polyacrylonitrile powder into an organic solvent and stirring to dissolve, then adding nano-silicon particles to continue stirring for more than 24 hours, and ultrasonically dispersing for more than 1 hour to obtain the polyacrylonitrile spinning polyacrylonitrile containing nano-silicon particles solution.

Preferably, said step S2 includes:

Preferably, the step S3 includes: the oxidation treatment is carried out in air, the oxidation temperature is controlled to gradually increase from room temperature to 250-300°C at a temperature increase rate of 1-10°C/min, and the temperature is kept constant for 1-3 hours to obtain the obtained nanofiber oxides.

Preferably, the carbonization is carried out in a high-temperature carbonization furnace. In an argon atmosphere, the temperature is gradually increased from room temperature to 600-1500 °C at a rate of 1-20 °C/min, and kept at a constant temperature for 1-3 hours. After cooling to room temperature, take it out The silicon-carbon composite material is obtained.

Preferably, the solvent of the polyacrylonitrile spinning solution is dimethylformamide.

Preferably, the mass fraction of polyacrylonitrile in the dimethylformamide solution of polyacrylonitrile is 6-15wt%, and the mass ratio of nano-silicon particles to polyacrylonitrile is 1:50-1:1.

Compared with the prior art, the method of the present invention carries out electrospinning molding to the polyacrylonitrile mixed solution doped with nano-silicon particles, and the spinning thin stream is solidified and shaped due to non-solvent-induced phase separation during solidification, forming PAN -Si nanofibers. During the curing process, the fiber skin is first cured, and the solvent gradually diffuses outward from the inside of the fiber, forming a large number of hole structures inside the fiber. After the subsequent oxidation and carbonization process, PAN gradually forms a carbon network structure, nano-silicon particles are coated in the carbon matrix, and the large pore structure is retained in the carbon matrix. In addition, an interconnected microporous structure is formed in the carbon matrix, and finally a silicon-carbon nanocomposite material with a built-in porous structure is obtained. The invention has simple preparation process and wide source of raw materials, and the prepared silicon-carbon nanocomposite material has stable structure and size, high reversible specific capacity and excellent cycle performance when used as negative electrode material of lithium ion battery.

The application of the silicon-carbon composite material with a nano-microporous structure described in any one of the foregoing in the preparation of lithium-ion battery negative electrode materials can improve the reversible capacity and cycle stability of the negative electrode material during charge and discharge.

Description of drawings

FIG. 1 is a schematic structural view of a silicon-carbon composite material in Example 1 of the present invention.

detailed description

The present invention will be further described below with reference to the accompanying drawings and in combination with preferred embodiments.

A silicon-carbon composite material with a nano-microporous structure, comprising nano-silicon particles and a nano-carbon fiber matrix, the nano-silicon particles are dispersed in the nano-carbon fiber matrix, and nano-holes are distributed in the nano-carbon fiber matrix. Nanoporous micropores. The average diameter of the carbon nanofibers in the carbon nanofiber matrix is 100-600nm, and the average diameter of the silicon particles is 10-60nm. The mass content of the nano-silicon particles is 3-67%, the mass content of the nano-carbon fiber matrix is 33-97%, and the aperture of the nanopore is preferably 50-100nm, and the aperture of the micropore is preferably less than 10nm . The above-mentioned silicon-carbon composite material can be prepared by the following method:

Dissolving nano-silicon particles and polyacrylonitrile in a solvent to prepare a mixed spinning solution, then electrospinning the mixed spinning solution, and solidifying the spinning fine stream in a coagulation bath to obtain multi-void PAN-Si nanocomposite fibers; Then oxidation treatment and carbonization treatment are carried out in sequence to obtain the aforementioned silicon-carbon composite material with nano-microporous structure. Wherein, the electric field voltage of electrospinning is preferably 5-30kV, and the flow velocity of spinning liquid is preferably 0.1-1.0Ml/h, preferably adopts the PAN that molecular weight _Mw is 15-200,000 as carbon source, polyacrylonitrile solution polyacrylonitrile The mass fraction of acrylonitrile is preferably 6-15wt%, and the mass ratio of nano-silicon particles to polyacrylonitrile is preferably 1:50-1:1. Oxidation treatment is preferably carried out in air, the oxidation temperature is controlled to gradually increase from room temperature to 250-300°C at a rate of 1-10°C/min, and the nanofiber oxide is obtained after keeping the temperature for 1-3h. The carbonization treatment is preferably carried out in a high-temperature carbonization furnace. In an argon atmosphere, the temperature is gradually increased from room temperature to 600-1500 °C at a rate of 1-20 °C/min, and kept at a constant temperature for 1-3 hours. After cooling to room temperature, the product is obtained. Silicon carbon composites.

The technical solution of the present invention is explained below in conjunction with more specific embodiments:

Comparative example 1

Step 1: Preparation of spinning solution. Weigh 9g of PAN powder with a molecular weight of _Mw =150000, add it to 96mL of DMF, stir at 65°C for 24h to dissolve, and prepare a PAN-DMF solution with a mass fraction of 9%; weigh 2.25g of nano The silicon particles were added to the DMF solution of PAN, stirred at 65° C. for 24 h, and ultrasonically dispersed for 1 h to obtain a mixed solution of Si uniformly dispersed in the DMF solution of PAN.

The second step: electrospinning to prepare Si-doped PAN nanofibers. Put the mixed solution prepared in the first step into a syringe, extrude the spinning solution at a flow rate of 0.3mL/h, and perform electrospinning under a high-voltage electric field of 18kV. The distance from the spinneret to the receiver is 15cm. The thin filaments were solidified and formed by removing the solvent in the air, and the nascent fibers were collected on aluminum foil to obtain PAN-Si composite nanofibers.

The third step: oxidation treatment of primary nanofibers. The nanofibers obtained in the second step are oxidized in a temperature-programmed oxidation furnace, the oxidation atmosphere is air, and the temperature is raised from room temperature to 200°C at a heating rate of 5°C/min, and then raised to 270°C at a rate of 2°C/min. Take it out after constant temperature for 1h, and prepare for high temperature carbonization treatment.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The oxidized nanofibers were carbonized in a high-temperature carbonization furnace. Under the protection of high-purity argon (purity>99.999%), the temperature was gradually raised from room temperature to 800°C at a rate of 10°C/min, and kept at a constant temperature for 1h, then cooled to After room temperature, the samples were taken out to obtain silicon-carbon nanocomposite fibers.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. According to the mass ratio of silicon-carbon nanocomposite material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) at 80:10:10, the electrode sheet is evenly mixed, and the metal lithium sheet is used as the counter electrode and reference electrode. , Clegard2500 as the diaphragm, the electrolyte is ethylene carbonate (EC) + diethyl carbonate (DMC) solution of 1mol/L LiPF6 (the volume ratio of EC to DMC is 1:1), in a glove box filled with high-purity argon Assembled into a 2032-type button battery. The Land battery test system was used to test the constant current charge and discharge performance of the above half-cell at room temperature, the charge and discharge rate was 100mA/g, and the charge and discharge voltage range was 0.01-3.0V.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 1074mAh/g, the Coulombic efficiency is 77%, the reversible capacity after 50 cycles is 698mAh/g, and the capacity retention rate is 65%.

Comparative example 2

Step 1: Preparation of spinning solution. Weigh 9g of PAN powder with a molecular weight of M _w =150000, add it to 96mL of DMF, stir at 65°C for 24h to dissolve, and prepare a PAN-DMF solution with a mass fraction of 9%; weigh 0.47g of nano The silicon particles were added to the DMF solution of PAN, stirred at 65° C. for 24 h, and ultrasonically dispersed for 1 h to obtain a mixed solution of Si uniformly dispersed in the DMF solution of PAN.

The second step: electrospinning to prepare Si-doped PAN nanofibers. The spinning conditions were the same as in the second step in Comparative Example 1.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions were the same as in the third step in Comparative Example 1.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The carbonization conditions are the same as the fourth step of Comparative Example 1.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Comparative Example 1.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 605mAh/g, the Coulombic efficiency is 83%, the reversible capacity after 50 cycles is 466mAh/g, and the capacity retention rate is 77%.

Comparative example 3

Step 1: Preparation of spinning solution. Weigh 9g of PAN powder with a molecular weight of M _w =150000, add it to 96mL of DMF, stir at 65°C for 24h to dissolve, and prepare a PAN-DMF solution with a mass fraction of 9%; weigh 6.0g of nano The silicon particles were added to the DMF solution of PAN, stirred at 65° C. for 24 h, and ultrasonically dispersed for 1 h to obtain a mixed solution of Si uniformly dispersed in the DMF solution of PAN.

The second step: electrospinning to prepare Si-doped PAN nanofibers. The spinning conditions were the same as in the second step in Comparative Example 1.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions were the same as in the third step in Comparative Example 1.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The carbonization conditions are the same as the fourth step of Comparative Example 1.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Comparative Example 1.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 1463mAh/g, the Coulombic efficiency is 67%, the reversible capacity after 50 cycles is 717mAh/g, and the capacity retention rate is 49%.

Example 1

Compared with Comparative Example 1.

Step 1: Preparation of spinning solution. The preparation method and conditions of the spinning solution were the same as the first step in Comparative Example 1, and a mixed solution in which Si was uniformly dispersed in the DMF solution of PAN was obtained.

The second step: electrospinning to prepare Si-doped PAN nanofibers. Put the mixed solution prepared in the first step into a syringe, extrude the spinning solution at a flow rate of 0.3mL/h, and perform electrospinning under a high-voltage electric field of 18kV. After passing through the air for a certain distance, the spinning solution enters the solidification Cured in a bath to form. The air section distance between the spinneret and the coagulation bath was 3 cm, the coagulation bath was a water bath at room temperature, and the coagulation time was 2 h. The as-spun fibers were vacuum-dried at 60 °C for 12 h to obtain porous PAN-Si composite nanofibers.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions are the same as the third step in Example 1.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The carbonization conditions are the same as the fourth step of Comparative Example 1. As shown in Figure 1, a nano-silicon-carbon composite material with a rich micropore structure, a nano-carbon fiber 100 as a matrix, and a nano-silicon particle 200 embedded therein is obtained, and nano-holes 300 of 50-100 nm are distributed in the material and interconnected. Micropores 400 having a pore diameter of less than 10 nm.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Comparative Example 1.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 1124mAh/g, the Coulombic efficiency is 81%, the reversible capacity after 50 cycles is 934mAh/g, and the capacity retention rate is 83%.

Example 2

Compared with Comparative Example 1.

Step 1: Preparation of spinning solution. The preparation method and conditions of the spinning solution were the same as the first step in Example 1, and a mixed solution in which Si was uniformly dispersed in the DMF solution of PAN was obtained.

The second step: electrospinning to prepare PAN nanofibers doped with Si and PVC. Put the mixed solution prepared in the first step into a syringe, extrude the spinning solution at a flow rate of 0.3mL/h, and perform electrospinning under a high-voltage electric field of 18kV. After passing through the air for a certain distance, the spinning solution enters the solidification Cured in a bath to form. The air section distance between the spinneret and the coagulation bath was 3 cm, the coagulation bath was absolute ethanol at room temperature, the coagulation time was 2 h, and the as-spun fibers were vacuum-dried at 60 °C for 12 h to obtain porous PAN-Si composite nanofibers.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions are the same as the third step in Example 1.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. Carbonization treatment conditions are the same as the fourth step in Example 1.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Example 1.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 1166mAh/g, the Coulombic efficiency is 84%, the reversible capacity after 50 cycles is 991mAh/g, and the capacity retention rate is 85%.

Example 3

Compared with Comparative Example 2.

Step 1: Preparation of spinning solution. The preparation method and conditions of the spinning solution are the same as the first step in Comparative Example 2.

The second step: electrospinning to prepare Si-doped PAN nanofibers. The spinning conditions were the same as the second step in Example 1.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions were the same as the third step in Comparative Example 2.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The carbonization conditions were the same as in the fourth step of Comparative Example 2.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Comparative Example 2.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 625mAh/g, the Coulombic efficiency is 86%, the reversible capacity after 50 cycles is 546mAh/g, and the capacity retention rate is 87%.

Example 4

Compared with Comparative Example 3.

Step 1: Preparation of spinning solution. The preparation method and conditions of the spinning solution are the same as the first step in Comparative Example 3.

The second step: electrospinning to prepare Si-doped PAN nanofibers. The spinning conditions were the same as the second step in Example 2.

The third step: oxidation treatment of primary nanofibers. The oxidation treatment conditions were the same as in the third step in Comparative Example 3.

The fourth step: carbonization of nanofibrous oxide and formation of nano-silicon-carbon composite material. The carbonization conditions were the same as in the fourth step of Comparative Example 3.

Step 5: Preparation and electrochemical performance testing of silicon-carbon nanocomposite anode materials. The material preparation and testing methods are the same as the fifth step in Comparative Example 3.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 625mAh/g, the Coulombic efficiency is 86%, the reversible capacity after 50 cycles is 546mAh/g, and the capacity retention rate is 87%.

According to the above steps, the first reversible capacity of the silicon-carbon composite nano-anode material is 1638mAh/g, the Coulombic efficiency is 75%, the reversible capacity after 50 cycles is 1113mAh/g, and the capacity retention rate is 68%.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art to which the present invention belongs, without departing from the concept of the present invention, several equivalent substitutions or obvious modifications can be made, and the same performance or use should be considered as belonging to the protection scope of the present invention.

Claims (9)

1. A silicon-carbon composite material with a nano-microporous structure, characterized in that: it comprises nano-silicon particles and a nano-carbon fiber matrix, the nano-silicon particles are dispersed in the nano-carbon fiber matrix, and the nano-carbon fiber matrix is distributed with nanopores and nanomicropores connected to the nanopores, the nanopores and nanomicropore structures in the carbon nanofiber matrix can effectively accommodate the volume expansion of silicon during charging and discharging, and the nanomicropores are also ions, The transport of charge provides a convenient channel. 2. The silicon-carbon composite material according to claim 1, characterized in that: the average diameter of the nano-carbon fibers in the nano-carbon fiber matrix is 100-600 nm, and the average diameter of the nano-silicon particles is 10-60 nm. 3. The silicon-carbon composite material according to claim 1, characterized in that: the mass fraction of the nano-silicon particles is 3-67%, and the mass fraction of the nano-carbon fiber matrix is 33-97%. 4. a method for preparing a silicon-carbon composite material with a nano-microporous structure as claimed in claim 1, characterized in that, comprising the following steps: S1. Configure a polyacrylonitrile spinning solution containing nano-silicon particles, the mass fraction of polyacrylonitrile in the polyacrylonitrile solution is 6-15wt%, and the mass ratio of nano-silicon particles and polyacrylonitrile added in the solution is 1 :50-1:1; S2. Put the polyacrylonitrile spinning solution obtained in step S1 into a syringe, and carry out electrospinning under a high-voltage electrostatic field. Nascent polyacrylonitrile nanofibers are obtained by non-solvent-induced phase separation and curing. During the curing process, the fiber skin is first cured, and the solvent gradually diffuses from the inside of the fiber to form a large number of hole structures inside the fiber. The nascent polyacrylonitrile nanofibers Place in a liquid coagulation bath for 1-3 hours, and then vacuum-dry to obtain polyacrylonitrile nanofibers, wherein the voltage of the high-voltage electrostatic field is 5-30kV, and the flow rate of the spinning solution is 0.1-1.0mL/h; S3, oxidizing the polyacrylonitrile nanofibers obtained in step S2 to obtain nanofiber oxides; S4. Carbonizing the nanofiber oxide to form the silicon-carbon composite material. 5. The preparation method according to claim 4, characterized in that: said step S1 comprises: Adding polyacrylonitrile powder into an organic solvent, stirring and dissolving, adding nano-silicon particles, continuing to stir for more than 24 hours, and ultrasonically dispersing for more than 1 hour to obtain the polyacrylonitrile spinning solution containing nano-silicon particles. 6. The preparation method according to claim 4, characterized in that: said step S3 comprises: The oxidation treatment is carried out in the air, and the oxidation temperature is controlled to gradually increase from room temperature to 250-300° C. at a temperature increase rate of 1-10° C./min, and the nanofiber oxide is obtained after keeping the temperature for 1-3 hours. 7. The preparation method according to claim 4, characterized in that: said step S4 comprises: The carbonization is carried out in a high-temperature carbonization furnace. In an argon atmosphere, the temperature is gradually increased from room temperature to 600-1500 °C at a rate of 1-20 °C/min, and kept at a constant temperature for 1-3 hours. After cooling to room temperature, the product is obtained. Silicon carbon composites. 8. The preparation method according to any one of claims 4-5, characterized in that: the solvent of the polyacrylonitrile spinning solution is dimethylformamide. 9. The application of the silicon-carbon composite material with nano-microporous structure as described in any one of claims 1-3 in the preparation of negative electrode materials for lithium-ion batteries.