CN115275176B

CN115275176B - Preparation method of silicon-carbon composite material and lithium battery

Info

Publication number: CN115275176B
Application number: CN202211205598.9A
Authority: CN
Inventors: 蒋世用; 钟宽; 詹世英; 张正; 姚骏; 丁坤鹏; 吴瑞华
Original assignee: Hebei Gree Titanium New Energy Co ltd; Chongqing University; Zhuhai Guangtong Automobile Co Ltd; Gree Altairnano New Energy Inc
Current assignee: Hebei Gree Titanium New Energy Co ltd; Chongqing University; Zhuhai Guangtong Automobile Co Ltd; Gree Altairnano New Energy Inc
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2023-03-07
Anticipated expiration: 2042-09-30
Also published as: CN115275176A

Abstract

The invention provides a preparation method of a silicon-carbon composite material and a lithium battery. Mixing nanoscale silicon slurry obtained by wet ball milling with nanoscale carbon precursor slurry to obtain mixed slurry; adding a micron-sized graphite matrix and a nano-sized conductive agent into the mixed slurry to obtain a silicon-carbon composite precursor; dissolving a carbon precursor in a silicon-carbon composite precursor by using a solvent to obtain a silicon-carbon composite material, wherein the silicon-carbon composite material is of a core-shell structure, and the outer layer of the silicon-carbon composite material is a carbon coating layer with a carbon coating auxiliary agent; the secondary layer is a porous intermediate layer and is made of a composite layer of a nano-scale conductive agent and nano-scale silicon with carbon coated on the surface; the inner core is a micron-sized graphite matrix. According to the silicon-carbon composite material obtained by the method, the porous structure of the silicon-carbon composite material is formed by dissolving the nanoscale carbon precursor, so that a space is provided for volume expansion of nano silicon in charging and discharging, the crushing phenomenon of the silicon-based composite material is avoided, and the stability of the material is improved.

Description

Preparation method of silicon-carbon composite material and lithium battery

Technical Field

The invention relates to the technical field of vehicle batteries, in particular to a preparation method of a silicon-carbon composite material and a lithium battery.

Background

The lithium ion battery is mainly developed in the direction of high energy density, the current main flow direction is that a high nickel anode is matched with a silicon-based cathode, and the energy density reaches 300-400Wh/kg. Lithium-rich product Li generated by alloying silicon cathode with lithium at normal temperature of silicon-based cathode material _3.75 The capacity of the Si phase is up to 3572mAh/g, which is far higher than 372mAh/g of the theoretical specific capacity of the graphite cathode. However, si and Li in the repeated charge-discharge process of the silicon-based negative electrode material _3.75 Si phase transformation can produce huge volume expansion (up to 270%), which can lead to structural pulverization of the electrode material and rapid capacity degradation. And the conductivity of silicon is poor. The industry mainly improves the performance of the silicon-based negative electrode material through technologies such as nanocrystallization, carbon coating, loading on a carrier with good conductivity, pore-forming, pre-lithiation and the like.

Disclosure of Invention

The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiment(s) of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:

fig. 1 shows a schematic structural view of a first embodiment of a silicon carbon composite according to the invention.

Wherein the figures include the following reference numerals:

1. a graphite negative electrode core; 2. silicon nanoparticles; 3. a nanoscale conductive agent; 4. a porous carbon structure; 5. and a carbon coating layer.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Exemplary embodiments according to the present application will now be described in more detail with reference to the accompanying drawings. These exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to only the embodiments set forth herein. It is to be understood that these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art, in the drawings, it is possible to enlarge the thicknesses of layers and regions for clarity, and the same devices are denoted by the same reference numerals, and thus the description thereof will be omitted.

Referring to fig. 1, according to an embodiment of the present application, a method for preparing a silicon-carbon composite material is provided.

Specifically, the preparation method of the silicon-carbon composite material comprises the following steps: and mixing the nanoscale silicon slurry obtained by wet ball milling with the nanoscale carbon precursor slurry to obtain mixed slurry. And adding a micron-sized graphite matrix and a nano-sized conductive agent into the mixed slurry, grinding, dispersing, and spray drying to obtain the silicon-carbon composite precursor. And dissolving a carbon precursor in the silicon-carbon composite precursor by using a solvent, then carrying out liquid phase coating under the action of a carbon coating auxiliary agent, and then drying and carbonizing in sequence to obtain the silicon-carbon composite material. Wherein, the silicon-carbon composite material is in a core-shell structure, and the outer layer of the silicon-carbon composite material is a carbon coating layer 5 with a carbon coating auxiliary agent. The secondary layer is a porous intermediate layer and is made of a composite layer of a nano-scale conductive agent and nano-scale silicon with carbon coated on the surface. The inner core is a micron-sized graphite matrix.

In this embodiment, as shown in fig. 1, the porous silicon-carbon material is prepared by mixing nano silicon slurry obtained by wet ball milling and carbon precursor slurry obtained by wet ball milling, adding a micron-sized graphite matrix and a nanoscale conductive agent 3, spray-drying, dissolving the carbon precursor with a solvent, performing liquid phase coating, adding a carbon coating auxiliary agent, drying, and carbonizing to obtain the silicon-carbon composite material with the porous structure coated graphite matrix. The porous structure is formed by dissolving a nano-scale carbon precursor, so that the pore-forming effect is obvious, a space is provided for the volume expansion of nano-silicon in charging and discharging, the crushing phenomenon of the silicon-based composite material is avoided, and the stability of the material is improved. The graphite is at least one of natural graphite, crystalline flake graphite, artificial graphite and mesocarbon microbeads. The particle size of the micron-sized graphite matrix is 1-50 microns. The silicon-carbon composite material comprises: the graphite cathode comprises a graphite cathode core 1, silicon nanoparticles 2, a nanoscale conductive agent 3, a porous carbon structure 4 and a carbon coating layer 5.

Further, micron-sized silicon ball milling is adopted in wet ball milling to obtain the nano-sized silicon slurry, wherein the particle size of micron-sized silicon is 1-20 microns, and the particle size of the ball-milled silicon nanoparticles 2 is 10-150 nm. The arrangement ensures that micron-sized silicon can enter the porous middle layer, prevents the crushing phenomenon and improves the stability of the material.

Furthermore, the particle size of the powdery carbon precursor after ball milling is between 10 and 500 nanometers. This arrangement makes the carbon precursor more uniformly dissolved.

In one embodiment of the present application, the method comprises: adding micron-sized silicon powder into a solvent for ball milling dispersion, stirring to wet and mix the silicon powder, and adding the mixture into a ball milling tank of zirconia balls for ball milling to obtain the nanoscale silicon slurry. And weighing a millimeter-scale carbon precursor, grinding and crushing the millimeter-scale carbon precursor, adding the millimeter-scale carbon precursor into a ball milling tank with zirconia balls, and then adding a ball milling dispersing solvent for ball milling to obtain the nanoscale carbon precursor slurry. And adding the nanoscale silicon slurry and the carbon precursor slurry into a transfer tank of a grinding tank, and pre-stirring uniformly to obtain mixed slurry. And adding the conductive agent into the grinding tank, mixing with the mixed slurry, and uniformly stirring. Dissolving the adhesive into the solvent dispersed by ball milling, then adding into a grinding tank, and uniformly stirring. Adding the graphite matrix into a grinding tank, uniformly stirring, and then carrying out grinding dispersion operation; after grinding and dispersing are finished, spray drying is carried out to obtain a silicon-carbon composite precursor; adding a carbon-coated auxiliary agent and a ball-milling dispersion solvent according to a preset value of spray drying weight, uniformly stirring in a planetary stirring tank, carrying out vacuum baking at a preset temperature value for a preset time, and carrying out carbonization treatment; and taking out the sample after carbonization, crushing the sample, and sieving the sample by a 400-mesh sieve to obtain the silicon-carbon composite material.

Wherein the weight ratio of the silicon powder to the graphite substrate is 40%, the conductive agent is vapor grown carbon fiber, the vapor grown carbon fiber accounts for 4% of the total solids, the carbon precursor is polyurethane, the polyurethane accounts for 15% of the total solids, the adhesive is styrene butadiene rubber, the styrene butadiene rubber accounts for 7% of the total solids, and the total solids accounts for 18%. The arrangement makes the grinding of the silicon powder and the graphite substrate more uniform, so that the finally formed silicon-carbon composite material product has higher purity, the preparation process is simplified, and the large-scale preparation is easy.

In the present embodiment, the carbonization treatment includes: carbonizing in the atmosphere of nitrogen, argon, neon or argon as inert gas, wherein the nitrogen flow is 1.5L/min-2.5L/min, heating to 200 ℃ to 600 ℃ at the heating rate of 2 ℃/min-10 ℃/min, preserving heat for 0.5 h-5.5 h, then heating to 700 ℃ to 1000 ℃ at the heating rate of 1.5 ℃/min-5 ℃/min, carbonizing for 0.5 h-5.5 h, and naturally cooling to below 100 ℃ to obtain the sample. After carbonization is set, a carbon coating layer is formed outside the porous carbon structure 4, so that the contact between the whole silicon-based composite material and electrolyte is reduced, and the stability of the material is improved.

Further, the conductive agent is at least one of SP conductive carbon black, silver nanoparticles, copper nanoparticles, gold nanoparticles, silver nanowires, copper nanowires, carbon nanotubes, vapor grown carbon fibers, zinc oxide nanorods, silicon carbide nanowires, and boron nitride nanowires; the carbon-coated auxiliary agent is at least one of SP conductive carbon black, nano aluminum oxide, nano silicon oxide, nano magnesium oxide, nano boehmite and nano titanium dioxide, and the particle size of the carbon-coated auxiliary agent is 10-100 nm; the carbon precursor is at least one of polyethylene, polypropylene, polystyrene, phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, epoxy resin, asphalt, unsaturated polyester resin and polyurethane; the solvent for ball milling dispersion is at least one of ethanol, acetone, N-methyl pyrrolidone, N-dimethylformamide, isopropanol, ethyl acetate, deionized water, toluene, xylene, tetrahydrofuran and acetonitrile. The arrangement makes the outer carbon coating, the carbon coating on the surface of the nano silicon and the conductive agent between the nano silicon form a multidimensional conductive network structure, which is beneficial to improving the overall conductivity of the silicon-based composite material.

The solvent for dissolving the carbon precursor is at least one of ethanol, methanol, acetone, diethyl ether, ethyl acetate, N-methylpyrrolidone, N-dimethylformamide, toluene, xylene, tetrahydrofuran and acetonitrile; the adhesive dissolved in the dispersing solvent is at least one of sodium alginate, sodium carboxymethylcellulose, polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polyethylene glycol, styrene butadiene rubber, methyl cellulose, ethyl cellulose and chitosan. This arrangement allows the carbon precursor to be sufficiently dissolved.

The silicon material accounts for 10 to 80 percent of the total mass of the silicon and the graphite, the added carbon precursor accounts for 5 to 50 percent of the total added solid, the added conductive agent accounts for 1 to 10 percent of the total added solid, and the added carbon coating auxiliary agent accounts for 1 to 10 percent of the coated material. The arrangement ensures that the obtained porous structure is prepared without extra removal, is a self-composition material of the silicon-carbon composite material, does not introduce extra substances, improves the product purity, simplifies the preparation process, and is easy for large-scale preparation.

Example 1

1000g of silicon powder with the D50 of 5 microns is added with 2000g of NMP, the silicon powder is wetted and preliminarily mixed by manual pre-stirring, and then the mixture is added into a ball milling tank with zirconia balls with the diameter of 0.3mm, ball milling is carried out for 24 hours, and the stirring speed is 1500r/min, so that nano silicon slurry with the D50 particle size of 105nm is obtained. 344g of millimeter-sized block asphalt is weighed, manually ground and crushed by a mortar, added into a ball milling tank with zirconia balls with the diameter of 1mm, then 1947g of NMP is added, and ball milling is carried out for 8 hours at the stirring speed of 1000r/min. And then transferring the mixture into a zirconia ball milling tank with the diameter of 0.3mm, and carrying out ball milling for 4h at the rotating speed of 1000r/min to obtain the asphalt slurry with the D50 of 60 nm. Adding the nano silicon slurry and the asphalt slurry into a transfer tank of a dispersion grinding tank, and pre-stirring uniformly. 51.5g of conductive nanoparticles SP were added to the milling jar, mixed with the jar slurry and pre-stirred uniformly. 51.5g of colloidal PVDF was dissolved in 2393g of NMP, and the solution was added to a milling jar and stirred with the jar contents. 667g of artificial graphite having a D50 of 10 μm were added to the jar and pre-stirred with the contents of the jar. In the above slurry, the ratio of silicon to graphite was 60%, the conductive nanoparticles SP accounted for 3% of the total solids (without gums and asphalts), the asphalts accounted for 20% of the total solids, the gums accounted for 3% of the total solids, and the solids content was 25%. Then grinding dispersion is carried out, the grinding rotating speed is 2000r/min, and the grinding time is 5h. After the polishing, the mixture was spray-dried to obtain 1.96kg of a silicon-carbon composite precursor. 1000g of spray drying is taken, simultaneously 50g of 5% carbon-coated auxiliary agent nano alumina with the particle size of 30nm is weighed, 1500g of solvent tetrahydrofuran is added, and the mixture is uniformly stirred in a planetary stirring tank. Tetrahydrofuran dissolves the pitch dispersed on the surface of the graphite matrix, and the dissolved pitch and the nano-alumina form slurry together with the sprayed powder. Then baking the mixture for 4 hours at 80 ℃ in vacuum, and finally performing carbonization treatment. The carbonization is performed under an atmosphere of an inert gas, nitrogen. The nitrogen flow is 2L/min, the temperature is raised to 350 ℃ at the temperature rise rate of 3 ℃/min, and the temperature is kept for 2h; then heating to 800 ℃ at the heating rate of 2 ℃/min, carbonizing for 4h, naturally cooling to below 100 ℃, and taking out a sample. And (3) crushing the sample, and sieving the crushed sample with a 400-mesh sieve to obtain the silicon-carbon material. And performing a power-on half-cell test on the obtained porous silicon-carbon composite material, wherein the gram volume is 1005mAh/g, and the highest first effect is 91.2%.

Example 2

1000g of silicon powder with the D50 of 2 microns is added with 2500g of ethyl acetate, the silicon powder is wetted and preliminarily mixed by manual pre-stirring, and then the mixture is added into a ball milling tank with zirconia balls with the diameter of 0.3mm, the ball milling is carried out for 12 hours, the stirring speed is 1500r/min, and the nano silicon slurry with the D50 particle size of 95nm is obtained. 526g of millimeter-sized bulk polyethylene is weighed, manually ground and crushed by a mortar, added into a ball milling tank with zirconia balls with the diameter of 1mm, then 4737g of ethyl acetate is added, and ball milling is carried out for 8 hours at the stirring speed of 1000r/min. And then transferring the mixture into a zirconia ball milling tank with the particle size of 0.3mm, and carrying out ball milling for 3h at the rotating speed of 1000r/min to obtain polyethylene particles with the D50 particle size of 50 nm. Adding the nano silicon slurry and the polyethylene slurry into a transfer tank of a dispersion grinding tank, and pre-stirring uniformly. 105g of nanowire BN was added to the milling tank, mixed with the slurry in the tank and pre-stirred uniformly. 168g of PAA was dissolved in 2690g of ethyl acetate, added to a milling jar and pre-stirred with the contents of the jar. 1000g of flake graphite having a D50 of 15 μm was put into a grinding pot and pre-stirred with the contents of the pot. In the slurry, the proportion of silicon in silicon-graphite is 50%, the nanowire BN accounts for 5% of the total solid (without glue and polyethylene), the polyethylene accounts for 25% of the total solid, the glue accounts for 8% of the total solid, and the solid content is 22%. Then grinding dispersion is carried out, the grinding rotating speed is 2000r/min, and the grinding time is 5h. After the polishing, the slurry was spray-dried to obtain 2.63kg of a silicon-carbon composite precursor. Adding 78.9g of carbon coating auxiliary agent SP with the particle size of 50nm according to 3% of the weight of spray drying, adding 4675g of solvent acetone, and uniformly stirring in a planetary stirring tank. The acetone can dissolve the polyethylene nano-particles dispersed on the surface of the graphite matrix, and the dissolved polyethylene nano-particles and SP form slurry with spray powder. Then baking the mixture for 4 hours at 80 ℃ in vacuum, and finally performing carbonization treatment. The carbonization is performed under an atmosphere of an inert gas, nitrogen. The nitrogen flow is 2L/min, the temperature is raised to 250 ℃ at the temperature rise rate of 3 ℃/min, and the temperature is kept for 2h; then heating to 820 ℃ at the heating rate of 2 ℃/min, carbonizing for 4h, naturally cooling to below 100 ℃, and taking out the sample. Crushing the sample, and sieving with a 400-mesh sieve to obtain the silicon-carbon material

Example 3

1000g of silicon powder with the D50 of 3 microns is added with 4500g of isopropanol, the silicon powder is wetted and preliminarily mixed by manual pre-stirring, and then the mixture is added into a ball milling tank with zirconia balls with the diameter of 0.2mm, the ball milling is carried out for 16h, the stirring speed is 1500r/min, and the nano silicon slurry with the D50 particle size of 90nm is obtained. Weighing 390g of millimeter-sized blocky polyurethane, manually grinding and crushing by using a mortar, adding the material into a ball milling tank with zirconia balls with the diameter of 1mm, adding 2865g of isopropanol, carrying out ball milling for 6 hours at the stirring speed of 1000r/min, transferring the material into a zirconia ball milling tank with the particle size of 0.2mm, carrying out ball milling for 3 hours at the rotating speed of 1000r/min, and obtaining polyurethane particles with the D50 particle size of 40 nm. Adding the nano silicon slurry and the polyurethane slurry into a transfer tank of a dispersion grinding tank, and pre-stirring uniformly. 104g VGCF was added to the grind pot, mixed with the slurry in the pot and pre-stirred to homogeneity. 182g of ethyl cellulose gum is dissolved in 7108g of isopropanol and added into a grinding tank to be pre-stirred with the materials in the tank uniformly. 1500g of artificial graphite having a D50 of 16 μm were added to the milling jar and pre-stirred with the jar contents. Then grinding dispersion is carried out, the grinding rotating speed is 2000r/min, and the grinding time is 5h. After the polishing, the slurry was spray-dried to obtain 2.96kg of a silicon-carbon composite precursor. Adding carbon-coated auxiliary agent nano boehmite (148 g) with the particle size of 60nm in an amount of 5% of the weight of spray drying, adding solvent DMF 4662g, and stirring uniformly in a planetary stirring tank. DMF can dissolve the polyurethane nanoparticles dispersed on the surface of the graphite matrix, and forms slurry with boehmite and the spray powder after the polyurethane nanoparticles are dissolved. Then baking the mixture for 4 hours at 80 ℃ in vacuum, and finally performing carbonization treatment. And (4) crushing the sample, and sieving the crushed sample with a 400-mesh sieve to obtain the silicon-carbon composite material. The carbon coating material source which is used for carbon coating of nano silicon and external carbon coating of a porous structure is arranged, extra removal is not needed, the carbon coating material source is a self-composition material of the silicon-carbon composite material, extra substances are not introduced, the product purity is improved, the preparation process is simplified, and the large-scale preparation is easy.

Comparative example 1

In example 1, 500g of the spray-dried sample was directly mixed with 750g of tetrahydrofuran solvent, and the subsequent steps were the same as in example. The product obtained after carbonization has no coating auxiliary agent, and the coating layer is only coated on the silicon-carbon particles by the dissolved asphalt. The obtained porous silicon-carbon composite material is subjected to a power-on half-cell test, the gram volume is 924mAh/g, and the highest first effect is 86.2%.

Comparative example 2

In example 1, 400g of the spray-dried sample was directly carbonized. The product obtained after carbonization has no further pore-forming treatment and coating treatment. And (3) performing a power-on half-cell test on the obtained silicon-carbon composite material, wherein the gram volume is 905mAh/g, and the highest first effect is 84.1%.

Comparative example 3

In example 3, a silicon carbon composite porous material having no VGCF in the silicon porous layer was obtained in the same manner as in example 3 except that the nano-conductive agent VGCF was not added in the polish dispersion stage. And (3) performing a buckling electricity half-cell test on the obtained porous silicon-carbon composite material, wherein the gram volume is 992mAh/g, and the highest first effect is 87.2%.

Further, by adding a nano conductive agent, dissolving the carbon-coated precursor and carrying out secondary coating treatment under the coating auxiliary agent, the porous silicon-carbon composite material with a porous silicon layer and a carbon-coated and three-dimensional conductive network can be obtained. The prepared porous structure is formed by dissolving the nano-scale carbon precursor, the pore-forming effect is obvious, the silicon nano-material is distributed in the porous structure, a space is reserved for the volume expansion of the silicon-based material, the materials are prevented from being extruded and crushed, and the stability of the materials is facilitated. The composite material is coated with carbon on the outer layer, the nano conductive agent and the carbon coating layer on the surface of the nano silicon, so that the conductivity of the material is improved, and the gram volume and the first effect of the material are improved. The gram volume and the first effect of the material can be reduced without a nano conductive agent, a carbon-free coating auxiliary agent and coating treatment. The preparation of the porous structure, the dissolved carbon precursor is used as a carbon coating material source of carbon coating of nano silicon and external carbon coating of the porous structure while realizing pore forming, does not need to be additionally removed, is a self-component material of a silicon-carbon composite material, does not introduce additional substances, improves the product purity, simplifies the preparation process, and is easy for large-scale preparation.

In another embodiment of the present application, a lithium battery is provided, where a negative electrode of the lithium battery includes a silicon-carbon composite material, and the silicon-carbon composite material is prepared by the above preparation method of the silicon-carbon composite material.

For ease of description, spatially relative terms such as "above … …", "above … …", "above … … upper surface", "above", etc. may be used herein to describe the spatial positional relationship of one device or feature to other devices or features as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

In addition to the foregoing, it should be noted that reference throughout this specification to "one embodiment," "another embodiment," "an embodiment," or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment described generally throughout this application. The appearances of the same phrase in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the scope of the invention to effect such feature, structure, or characteristic in connection with other embodiments.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon composite material is characterized by comprising the following steps:

mixing the nanoscale silicon slurry obtained by wet ball milling with the nanoscale carbon precursor slurry to obtain mixed slurry;

adding a micron-sized graphite matrix and a nano-sized conductive agent into the mixed slurry, grinding, dispersing, and spray drying to obtain a silicon-carbon composite precursor;

dissolving the carbon precursor in the silicon-carbon composite precursor by using a solvent, then carrying out liquid phase coating under the action of a carbon coating auxiliary agent, and then sequentially drying and carbonizing to obtain a silicon-carbon composite material;

the silicon-carbon composite material is of a core-shell structure, and the outer layer of the silicon-carbon composite material is a carbon coating layer with the carbon coating auxiliary agent; the secondary layer is a porous intermediate layer and is made of a composite layer of the nano-scale conductive agent and the nano-scale silicon with carbon coated on the surface; the inner core is the micron-sized graphite matrix;

the carbon-coated auxiliary agent is at least one of SP conductive carbon black, nano aluminum oxide, nano silicon oxide, nano magnesium oxide, nano boehmite and nano titanium dioxide, and the particle size of the carbon-coated auxiliary agent is 10-100 nm;

the silicon material accounts for 10-80% of the total mass of the silicon and the graphite, the amount of the added carbon precursor accounts for 5-50% of the total amount of the added solid, the amount of the added conductive agent accounts for 1-10% of the total amount of the added solid, and the amount of the added carbon coating auxiliary agent accounts for 1-10% of the coated material.

2. The method as claimed in claim 1, wherein the nanoscale silicon slurry is obtained by using micron-sized silicon ball milling in wet ball milling, wherein the particle size of micron-sized silicon is between 1 and 20 microns, and the particle size of the silicon nanoparticles after ball milling is between 10 and 150 nm.

3. The method of claim 1 or 2, wherein the particle size of the ball-milled powdered carbon precursor is between 10 and 500 nm.

4. The method according to claim 1, characterized in that it comprises:

weighing the millimeter-scale carbon precursor, grinding and crushing the carbon precursor, adding the carbon precursor into a ball milling tank with zirconia balls, and then adding a ball milling dispersed solvent for ball milling to obtain nanoscale carbon precursor slurry;

adding the nanoscale silicon slurry and the nanoscale carbon precursor slurry into a transfer tank of a grinding tank, and pre-stirring uniformly to obtain mixed slurry;

adding the conductive agent into a grinding tank, mixing with the mixed slurry, and uniformly stirring;

dissolving the adhesive into a ball-milling dispersed solvent, then adding the solvent into a grinding tank, and uniformly stirring;

adding the graphite matrix into a grinding tank, uniformly stirring, and then carrying out grinding dispersion operation;

after grinding and dispersing are finished, spray drying is carried out to obtain the silicon-carbon composite precursor;

adding the carbon-coated auxiliary agent and the ball-milling dispersion solvent according to a preset value of spray drying weight, uniformly stirring in a planetary stirring tank, carrying out vacuum baking at a preset temperature value for a preset time, and carrying out carbonization treatment;

and taking out the sample after carbonization, crushing the sample, and sieving the sample with a 400-mesh sieve to obtain the silicon-carbon composite material.

5. The method of claim 4, wherein the carbonizing treatment comprises:

carbonizing in the atmosphere of nitrogen, argon, neon or argon as inert gas, wherein the nitrogen flow is 1.5L/min-2.5L/min, heating to 200 ℃ to 600 ℃ at the heating rate of 2 ℃/min-10 ℃/min, preserving heat for 0.5 h-5.5 h, then heating to 700 ℃ to 1000 ℃ at the heating rate of 1.5 ℃/min-5 ℃/min, carbonizing for 0.5 h-5.5 h, and naturally cooling to below 100 ℃ to obtain the sample.

6. The method according to claim 1 or 4,

the conductive agent is at least one of SP conductive carbon black, silver nanoparticles, copper nanoparticles, gold nanoparticles, silver nanowires, copper nanowires, carbon nanotubes, vapor-grown carbon fibers, zinc oxide nanorods, silicon carbide nanowires and boron nitride nanowires;

the carbon precursor is at least one of polyethylene, polypropylene, polystyrene, phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, epoxy resin, asphalt, unsaturated polyester resin and polyurethane;

the solvent for ball milling dispersion is at least one of ethanol, acetone, N-methyl pyrrolidone, N-dimethylformamide, isopropanol, ethyl acetate, deionized water, toluene, xylene, tetrahydrofuran and acetonitrile.

7. The method according to claim 1 or 4,

the solvent for dissolving the carbon precursor is at least one of ethanol, methanol, acetone, diethyl ether, ethyl acetate, N-methylpyrrolidone, N-dimethylformamide, toluene, xylene, tetrahydrofuran and acetonitrile;

the adhesive dissolved in the dispersing solvent is at least one of sodium alginate, sodium carboxymethylcellulose, polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polyethylene glycol, styrene butadiene rubber, methyl cellulose, ethyl cellulose and chitosan.

8. A lithium battery, the negative electrode of which comprises a silicon-carbon composite material, characterized in that the silicon-carbon composite material is prepared by the method for preparing a silicon-carbon composite material according to any one of claims 1 to 7.