Graphite silicon-based composite material, preparation method and application

Abstract

The invention discloses a graphite silicon-based composite material, and a preparation method and application thereof. According to the invention, the graphite silicon-based composite material with a median particle size of 9-20 [mu] m and a sphericity degree of greater than 0.9 is prepared by means of homogenization and spray drying; and meanwhile, the dosage and process parameters of each component in the preparation process can be adjusted according to the particle size of the required graphite silicon-based composite material, so that the graphite silicon-based composite material with relatively good cycle performance and relatively high capacity can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and more particularly to a graphite-silicon composite material, a preparation method and an application thereof. Background Art

[0002] With the development of society, people's requirements for batteries are getting higher and higher. Among them, graphite anode materials are widely used due to their good cycle performance, high initial efficiency, and weak volume expansion during the cycle. However, its theoretical capacity is only 372 mAh / g, which can no longer meet the growing capacity demand of people. Therefore, researchers are eager to develop new anode materials. Silicon (Si) is considered a very promising anode material due to its high theoretical capacity (4200 mAh / g). However, it has problems such as large volume expansion, low initial efficiency, and low lithium-ion / electron conductivity, which seriously hinder its development.

[0003] In order to obtain a lithium battery anode material with stable cycle performance, higher initial efficiency, higher capacity and lower expansion, researchers physically mix graphite and silicon-based anode materials to obtain composite materials or confine silicon materials in the graphite framework. However, these methods still have some problems, such as poor uniformity, poor particle contact resulting in poor particle electrical contact, and the capacity of the composite material cannot be too high. The existence of these problems will affect the conductivity and electrochemical performance stability of the composite material, and at the same time, its effect of suppressing expansion is poor. At the same time, during the material preparation process, a part of "fine powder" will inevitably be generated, and these fine powders cannot be effectively utilized, and at the same time, it will increase the cost of lithium batteries.

[0004] In view of this, it is particularly necessary to develop a graphite-silicon composite material with good cycle performance and high capacity. Summary of the Invention

[0005] The purpose of the present invention is to provide a graphite-silicon composite material, a preparation method and an application thereof, so as to solve the problem of poor cycle performance of existing silicon-carbon anode materials.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a graphite-silicon composite material. The median particle size of the graphite-silicon composite material is 9-20 μm. The preparation of the graphite-silicon composite material includes: performing a first homogenization on a first mixture including graphite, a silicon-based material, a binder and water to obtain a second mixture, diluting the second mixture and then performing a second homogenization to obtain a slurry, and performing spray granulation and drying on the slurry to obtain the graphite-silicon composite material. The parameters of the slurry and spray granulation steps satisfy the requirements of Formula I:

[0008] D50 (Composite Material) = 2 × [D50 (①) * A1 + D50 (②) * A2] × [0.62 + A3] × (0.2 + 50X 1 ) × (0.9 + 6X 2 ) × (1

[0009] + 0.05 / X 3 ) Equation I

[0010] Wherein, D50 (①) is the median particle size of graphite in the first mixture, in μm;

[0011] D50 (②) is the median particle size of the silicon-based material in the first mixture, in μm;

[0012] A1 is the ratio of the mass of graphite to the total mass of graphite and silicon-based material, in %;

[0013] A2 is the ratio of the mass of silicon-based to the total mass of graphite and silicon-based material, in %;

[0014] A3 = 0.3 × min[D50 (①), D50 (②)] / max[D50 (①), D50 (②)], dimensionless;

[0015] X 1 is the ratio of the mass of the binder in the slurry to the total mass of graphite and silicon-based material, in %;

[0016] X 2 is the mass fraction of solids in the slurry, in %;

[0017] X 3 is the atomization pressure during spray granulation, in MPa.

[0018] In an alternative embodiment, the slurry satisfies at least one of the following characteristics:

[0019] a. The D50 (①) is 1 - 10 μm;

[0020] b. The D50 (②) is 1 - 10 μm;

[0021] c. The mass ratio of graphite and silicon-based material in the slurry is 1:99 to 99:1;

[0022] d. The ratio of the total mass of graphite and silicon-based material in the slurry to the mass of water is 15:85 to 75:25;

[0023] e. The ratio of the mass of the binder in the slurry to the total mass of graphite and silicon-based material is 1% - 25%;

[0024] f. The mass fraction of solids in the slurry is 1% - 60%.

[0025] In an alternative embodiment, the atomization pressure during spray granulation is 0.1 to 2.5 MPa;

[0026] and / or, the first mixture further comprises a conductive material selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerenes; the ratio of the mass of the conductive material to the total mass of graphite and silicon-based material is 0.01%-10%;

[0027] and / or, the sphericity of the graphite-silicon composite material is greater than 0.9.

[0028] In a second aspect, the present invention provides a method for preparing a graphite-silicon composite material, comprising:

[0029] Performing a first homogenization on a first mixture comprising graphite, a silicon-based material, a binder, and water to obtain a second mixture, diluting the second mixture and then performing a second homogenization to obtain a slurry, and performing spray granulation and drying on the slurry to obtain the graphite-silicon composite material, wherein the parameters of the slurry and spray granulation steps satisfy the requirements of Formula I:

[0030] D50 (composite material) = 2 × [D50(①) * A1 + D50(②) * A2] × [0.62 + A3] × (0.2 + 50X 1 ) × (0.9 + 6X 2 ) × (1

[0031] + 0.05 / X 3 ) Formula I

[0032] wherein, D50(①) is the median particle size of graphite in the first mixture, in μm;

[0033] D50(②) is the median particle size of the silicon-based material in the first mixture, in μm;

[0034] A1 is the ratio of the mass of graphite to the total mass of graphite and silicon-based material, in %;

[0035] A2 is the ratio of the mass of silicon-based to the total mass of graphite and silicon-based material, in %;

[0036] A3 = 0.3 × min[D50(①), D50(②)] / max[D50(①), D50(②)], dimensionless;

[0037] X 1 is the ratio of the mass of the binder in the slurry to the total mass of graphite and silicon-based material, in %;

[0038] X 2 is the mass fraction of solids in the slurry, in %;

[0039] X 3 X is the atomization pressure during spray granulation, with the unit of MPa;

[0040] D50 (composite material) is 9 - 20 μm.

[0041] In an alternative embodiment, a first homogenization is performed on a mixture including graphite, silicon-based material, binder, and water to obtain a solid-liquid mixture with a solid content of 15% - 75%;

[0042] The slurry is obtained by mixing the solid-liquid mixture with water and then performing a second homogenization.

[0043] In an alternative embodiment, the first homogenization time is 1 - 30 h, and the homogenization rotation speed is 500 - 6000 rpm;

[0044] And / or, the second homogenization time is 1 - 30 h, and the homogenization rotation speed is 500 - 6000 rpm;

[0045] And / or, the first mixture further includes a conductive material, and the conductive material is selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerenes; the ratio of the mass of the conductive material to the total mass of graphite and silicon-based material is 0.01% - 10%.

[0046] In an alternative embodiment, after the slurry is prepared, it is placed in a low-speed stirring tank and then transported through a pipeline to a spray granulation device for spray granulation, and the rotation speed of the stirring paddle in the low-speed stirring tank is 50 - 2000 rpm.

[0047] In an alternative embodiment, in the spray granulation step, the feeding rate is 0.15 - 5.0 kg / h, the inlet air temperature is 180 - 250 °C, the outlet air temperature is 95 - 125 °C, and the atomization pressure of the atomizer is 0.1 - 2.5 MPa.

[0048] In an alternative embodiment, the drying temperature is 120 - 200 °C, and the drying time is 1 - 9 h.

[0049] In an alternative embodiment, the sphericity of the graphite-silicon-based composite material obtained by spray granulation is greater than 0.9.

[0050] In a third aspect, the present invention provides a secondary battery including the graphite-silicon-based composite material according to any one of the foregoing embodiments.

[0051] The present invention has the following beneficial effects:

[0052] In this application, a graphite-silicon composite material with a median particle size of 9-20 μm and a sphericity greater than 0.9 is prepared by homogenization and spray drying. At the same time, the dosage of each component and process parameters in the preparation process can be adjusted according to the required particle size of the graphite-silicon composite material, which is beneficial to obtaining a graphite-silicon composite material with good cycle performance and high capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0054] Figure 1 SEM image of the graphite-silicon composite material prepared in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0056] An embodiment of the present invention provides a graphite-silicon composite material, the median particle size of the graphite-silicon composite material is 9-20 μm, and the sphericity is greater than 0.9. The preparation of the graphite-silicon composite material includes: performing a first homogenization on a first mixture including graphite, a silicon-based material, a binder, and water to obtain a second mixture, diluting the second mixture and then performing a second homogenization to obtain a slurry, and performing spray granulation and drying on the slurry to obtain the graphite-silicon composite material. The parameters of the slurry and spray granulation steps satisfy the requirements of Equation I:

[0057] D50 (composite material) = 2 × [D50 (①) * A1 + D50 (②) * A2] * [0.62 + A3] * (0.2 + 50X 1 ) * (0.9 + 6X 2 ) * (1

[0058] + 0.05 / X 3 ) Equation I

[0059] Wherein, D50 (①) is the median particle size of graphite in the first mixture, in μm;

[0060] D50 (②) is the median particle size of the silicon-based material in the first mixture, in μm;

[0061] A1 is the ratio of the mass of graphite to the total mass of graphite and silicon-based materials, in %;

[0062] A2 is the ratio of the mass of silicon-based to the total mass of graphite and silicon-based materials, in %;

[0063] A3 = 0.3 * min[D50(①), D50(②)] / max[D50(①), D50(②)], dimensionless;

[0064] X 1 is the ratio of the mass of the binder in the slurry to the total mass of graphite and silicon-based materials, in %;

[0065] X 2 is the mass fraction of solids in the slurry, in %;

[0066] X 3 is the atomization pressure during spray granulation, in MPa.

[0067] In the embodiments of the present application, the sphericity of the graphite-silicon composite material is greater than 0.9, specifically, it can be 0.9, 0.92, 0.94, 0.96, 0.98 or any value greater than 0.9. Under the same conditions, the improvement of sphericity can effectively reduce the particle breakage phenomenon in the rolling process, which is beneficial to reducing the specific surface area, thereby reducing side reactions and being beneficial to the improvement of cycle performance.

[0068] The D50 (composite material) of the graphite-silicon composite material is 9 - 20 μm, specifically, it can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 μm or any value between 9 - 20 μm; under the same conditions, the increase of D50 (composite material) is beneficial to reducing side reactions, but at the same time it also means a decrease in active sites, resulting in a reduction in the electrochemical reaction area and being not conducive to the improvement of the battery specific capacity; when D50 (composite material) decreases, the lithium ion transport path inside the particles is shorter, which is beneficial to improving the lithium ion diffusion rate, and the active sites increase, which is beneficial to the improvement of the battery specific capacity, but at the same time it is accompanied by an increase in side reactions, which is not conducive to the improvement of the battery cycle performance. Therefore, it is appropriate that D50 (composite material) is 9 - 20 μm.

[0069] In summary, D50 (composite material) has a great influence on the properties of the material. However, during the preparation of graphite-silicon-based composite materials, it is difficult to estimate the particle size of the product. Multiple attempts and continuous exploration are required, and the preparation steps and parameters need to be continuously adjusted to obtain a product with a preset median particle size. Furthermore, a composite material with good cycle performance and high capacity can be obtained. At the same time, if adjustments need to be made to the raw material composition, etc., the median particle size of the composite material product may change, and thus the preparation method needs to be readjusted, greatly increasing the time cost and costs of raw materials, consumables, etc. Therefore, a large amount of research has been conducted in this application to obtain Formula I, that is, the relationship between the median particle size of the composite material product and the key parameters, raw material composition, etc. during the preparation process. According to Formula I, the preparation method can be guided to obtain a composite material product with a preset median particle size.

[0070] In an alternative embodiment, the slurry satisfies at least one of the following characteristics:

[0071] a. The D50 (①) is 1 - 10 μm, specifically it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 μm or any value between 1 - 10 μm.

[0072] b. The D50 (②) is 1 - 10 μm, specifically it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 μm or any value between 1 - 10 μm.

[0073] c. The mass ratio of graphite to silicon-based material in the slurry is 1:99 to 99:1, specifically it can be 1:99, 5:95, 15:85, 25:75, 35:65, 45:55, 55:45, 65:35, 75:25, 85:15, 99:1 or any value between 1:99 to 99:1; the mass ratio of graphite to silicon-based material not only affects the median particle size of the composite material product, but also has a greater impact on the capacity and cycle performance of the composite material product. The increase in the proportion of the silicon-based material is beneficial to improving the capacity, but at the same time it will reduce the cycle performance. Therefore, the proportion of the silicon-based material should not be too high.

[0074] d. The ratio of the total mass of graphite and silicon-based material in the slurry to the mass of water is 15:85 to 75:25, specifically it can be 15:85, 25:75, 35:65, 45:55, 55:45, 65:35, 75:25 or any value between 15:85 to 75:25;

[0075] e. The mass fraction of the binder in the slurry is 1% - 15%, specifically it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or any value between 1% - 15%;

[0076] f. The mass fraction of solids in the slurry is 1% - 60%, specifically it can be 1%, 10%, 20%, 30%, 40%, 50%, 60% or any value between 1% and 60%.

[0077] The composition of the slurry will affect the viscosity, fluidity, etc. of the slurry, and further affect the median particle size of the product obtained after spray granulation. Therefore, a reasonable selection is required.

[0078] It should be noted that in the embodiments of the present application, the binder can be selected from at least one of liquid asphalt, waterborne epoxy resin, waterborne polyurethane, waterborne phenolic resin, polyacrylic acid and its derivatives, polyacrylonitrile and its derivatives, polyacrylamide and its derivatives, polyvinylpyrrolidone, sodium carboxymethyl cellulose, and styrene-butadiene rubber; the silicon-based material can be selected from at least one of silicon-carbon materials, silicon-oxygen materials, and silicon alloy materials.

[0079] In an alternative embodiment, the atomization pressure during spray granulation is 0.1 - 2.5 MPa, specifically it can be 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5 MPa or any value between 0.1 and 2.5 MPa.

[0080] Increasing the atomization pressure is beneficial to reducing the particle size of the composite material, and decreasing the atomization pressure is beneficial to increasing the particle size of the composite material. Therefore, the atomization pressure needs to be limited within a reasonable range to obtain composite material particles with the desired particle size.

[0081] In an alternative embodiment, a conductive material can also be added to the slurry. The conductive material is selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerenes. The ratio of the mass of the conductive material to the total mass of graphite and the silicon-based material is 0.01% - 10%. The addition of the conductive material is beneficial to improving the electrical conductivity of the composite material, thereby improving the first efficiency, etc. of the composite material.

[0082] The embodiments of the present invention also provide a method for preparing a graphite-silicon-based composite material, including:

[0083] Performing a first homogenization on a first mixture including graphite, a silicon-based material, a binder, and water to obtain a second mixture, diluting the second mixture and then performing a second homogenization to obtain a slurry, and performing spray granulation and drying on the slurry to obtain the graphite-silicon-based composite material. The parameters of the slurry and spray granulation steps satisfy the requirements of formula I:

[0084] D50 (composite material) = 2 × [D50 (①) * A1 + D50 (②) * A2] * [0.62 + A3] * (0.2 + 50X 1 ) * (0.9 + 6X 2 ) * (1

[0085] +0.05 / X 3 ) Formula I

[0086] Wherein, D50(①) is the median particle size of graphite in the first mixture, in μm;

[0087] D50(②) is the median particle size of the silicon-based material in the first mixture, in μm;

[0088] A1 is the ratio of the mass of graphite to the total mass of graphite and the silicon-based material, in %;

[0089] A2 is the ratio of the mass of silicon-based to the total mass of graphite and the silicon-based material, in %;

[0090] A3 = 0.3 * min[D50(①), D50(②)] / max[D50(①), D50(②)], dimensionless;

[0091] X 1 is the ratio of the mass of the binder in the slurry to the total mass of graphite and the silicon-based material, in %;

[0092] X 2 is the mass fraction of solids in the slurry, in %;

[0093] X 3 is the atomization pressure during spray granulation, in MPa;

[0094] D50 (composite material) is 9 - 20 μm.

[0095] This application has conducted a large number of studies and obtained Formula I, that is, the relationship between the median particle size of the composite material product and the key parameters and raw material composition in the preparation process. According to Formula I, the preparation method can be guided to obtain a composite material product with a preset median particle size.

[0096] In an alternative embodiment, a conductive material can be further added to the slurry. The conductive material is selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerenes. The ratio of the mass of the conductive material to the total mass of graphite and the silicon-based material is 0.01% - 10%. The addition of the conductive material is beneficial to improving the conductivity of the composite material, thereby improving the first efficiency, etc. of the composite material.

[0097] In an alternative embodiment, a first homogenization is performed on a mixture including graphite, a silicon-based material, a binder, and water to obtain a solid-liquid mixture with a solid content of 15% - 75%;

[0098] The solid-liquid mixture is mixed with water and then subjected to a second homogenization to obtain the slurry.

[0099] In the state of a relatively thick solid-liquid mixture, the interaction force between particles is stronger, and it is easier to achieve uniform dispersion of the particles. During the first homogenization process, the particles have been able to be dispersed relatively sufficiently. After dilution with water and then homogenization again, it can effectively prevent the particles from re-aggregating. The two homogenizations are beneficial to improving the uniformity of the slurry.

[0100] In an alternative embodiment, the first homogenization time is 1 to 30 h, specifically it can be 1, 5, 10, 15, 20, 25, 30 h or any value between 1 and 30 h; the homogenization speed is 500 - 6000 rpm, specifically it can be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000 rpm or any value between 500 and 6000 rpm.

[0101] In an alternative embodiment, the second homogenization time is 1 to 30 h, specifically it can be 1, 5, 10, 15, 20, 25, 30 h or any value between 1 and 30 h; the homogenization speed is 500 - 6000 rpm, specifically it can be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000 rpm or any value between 500 and 6000 rpm.

[0102] Appropriately extending the homogenization time and increasing the speed during homogenization are beneficial to improving the uniformity of the slurry.

[0103] In an alternative embodiment, after the slurry is prepared, it is placed in a low-speed stirring tank, and then transported through a pipeline to a spray granulation device for spray granulation. The rotation speed of the stirring paddle in the low-speed stirring tank is 50 - 2000 rpm. Keeping the slurry in the low-speed stirring tank is beneficial to preventing the particles in the slurry from settling and beneficial to ensuring the uniformity of the slurry entering the spray granulation device.

[0104] In an alternative embodiment, in the spray granulation step, the feeding rate is 0.15 - 5.0 kg / h, specifically it can be 0.15, 0.25, 0.50, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 kg / h or any value between 0.15 - 5.0 kg / h; the inlet air temperature is 180 - 250 °C, specifically it can be 180, 200, 220, 240, 250 °C or any value between 180 - 250 °C; the outlet air temperature is 95 - 125 °C, specifically it can be 95, 105, 115, 125 °C or any value between 95 - 125 °C; the atomization pressure of the atomizer is 0.1 - 2.5 MPa, specifically it can be 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5 MPa or any value between 0.1 - 2.5 MPa.

[0105] The reasonable setting of the parameters in the spray granulation step can, while obtaining a composite material product with a preset particle size, improve the sphericity of the composite material product and achieve the preliminary drying of the composite material product.

[0106] In an alternative embodiment, the drying temperature is 120 - 200 °C and the drying time is 1 - 9 h to further dry the composite material.

[0107] In a third aspect, the present invention provides a secondary battery, including the graphite-silicon-based composite material described in any one of the foregoing embodiments.

[0108] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0109] Example 1

[0110] This example provides a preparation method of a graphite-silicon-based composite material, which specifically includes the following steps:

[0111] 1) Take 800 g of graphite with a D50 of 3.4 μm, 200 g of silicon-carbon material with a D50 of 3.3 μm, 3000 g of water and 20 g of polyacrylic acid and place them in a homogenizer to homogenize for 5 h at 1100 rpm to obtain a mixture with a solid content of 25 wt%.

[0112] 2) Homogenize the 25 wt% mixture and water at a ratio of 1:4 at 1100 rpm for 2 h to obtain a slurry with a solid content of 5 wt%.

[0113] 3) Place the slurry in a low-speed stirring tank and continuously stir at 200 rpm.

[0114] 4) The slurry placed in the low-speed stirring tank is spray granulated under the conditions of a feeding speed of 1 kg / h, an inlet air temperature of 180 °C, an outlet air temperature of 100 °C, and an atomization pressure of the atomizer of 0.4 MPa.

[0115] 5) The granulated sample is dried at 180 °C for 6 h and then ground to obtain the graphite-silicon-based composite material. The SEM image is as Figure 1 shown.

[0116] 6) Then, 46 g of the composite material is added to 150 mL of deionized water, and then 3 g of a conductive agent (SP) and 5 g of SBR are added, followed by stirring for 1 h to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated on the current collector, dried, roll-pressed, and punched to obtain the battery negative electrode sheet.

[0117] In an argon atmosphere glove box, a 1 mol / L lithium hexafluorophosphate solution is used as the electrolyte, a polypropylene microporous membrane is used as the separator, and a sodium sheet is used as the positive electrode sheet to assemble a button cell, and the electrochemical performance is tested at 0.1C.

[0118] The test conditions for testing at 0.1C include: a test temperature of 25 °C, a charge-discharge rate of 0.1C, and a voltage range of 0.005 V - 2 V.

[0119] Example 2

[0120] This example provides a method for preparing a graphite-silicon-based composite material, which is only different from Example 1 in that the graphite D50 in step 1) is 6.5 μm.

[0121] Example 3

[0122] This example provides a method for preparing a graphite-silicon-based composite material, which is only different from Example 1 in that the amount of water added in step 2) is reduced so that the solid content of the diluted slurry is 10 wt%.

[0123] Example 4

[0124] This example provides a method for preparing a graphite-silicon-based composite material, which is only different from Example 1 in that the atomization pressure of the atomizer in step 4) is 0.3 MPa.

[0125] Example 5

[0126] This example provides a method for preparing a graphite-silicon-based composite material, which is only different from Example 1 in that the ratio of graphite to silicon-based material in step 1) is changed from 4:1 to 3:2.

[0127] Example 6

[0128] This embodiment provides a method for preparing a graphite-silicon composite material, which is different from that of Example 1 only in that 10 g of carbon nanotubes with a length of 0.1 - 30 μm and a tube diameter of 2 - 20 nm are added in step 1).

[0129] Comparative Example 1

[0130] This comparative example provides a method for preparing a graphite-silicon composite material, which is different from that of Example 1 only in that step 1) is omitted, and the types and compositions of the raw materials used remain unchanged: 800 g of graphite with a D50 of 3.4 μm, 200 g of silicon-based material with a D50 of 3.3 μm, 20 g of binder and 19000 g of water are mixed and placed in a homogenizer for homogenization at 1100 rpm for 2 h to obtain a slurry with a solid content of 5 wt%.

[0131] Comparative Example 2

[0132] This comparative example provides a method for preparing a graphite-silicon composite material, which is different from that of Example 1 only in that step 4) is omitted.

[0133] Comparative Example 3

[0134] This comparative example provides a method for preparing a graphite-silicon composite material, which is different from that of Example 1 only in that the drying in step (5) is omitted.

[0135] According to Equation I, the D50 of the graphite-silicon composite materials prepared in the above examples and comparative examples was predicted, and the prediction results are shown in Table 1.

[0136] Table 1

[0137]

[0138]

[0139] The test results of the graphite-silicon composite materials prepared in the above examples and comparative examples are shown in Table 2.

[0140] Table 2

[0141]

[0142] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A graphite silicon-based composite material, characterized in that: The median particle size of the graphite silicon-based composite material is 9-20 μm. The preparation of the graphite silicon-based composite material includes: homogenizing a first mixture including graphite, silicon-based material, binder and water for the first time to obtain a second mixture, diluting the second mixture and homogenizing it for the second time to obtain a slurry, spray granulating and drying the slurry to obtain the graphite silicon-based composite material, and the parameters of the slurry and spray granulation steps meet the requirements of formula I: D50(composite material)=2×[D50(①)*A1+D50(②)*A2]*[0.62+A3]*(0.2+50X1)*(0.9+6X2)*(1+0.05 / X3) Formula I Wherein, D50(①) is the median particle size of graphite in the first mixture, in μm; D50(②) is the median particle size of the silicon-based material in the first mixture, in μm; A1 is the ratio of the mass of graphite to the total mass of graphite and silicon-based materials, unit: %; A2 is the ratio of the mass of silicon-based materials to the total mass of graphite and silicon-based materials, in %; A3=0.3*min[D50(①),D50(②)] / max[D50(①),D50(②)], no unit; X1 is the ratio of the mass of the binder in the slurry to the total mass of the graphite and silicon-based materials, in %; X2 is the mass fraction of solids in the slurry, in %; X3 is the atomization pressure during spray granulation, unit: MPa.

2. The graphite silicon-based composite material according to claim 1, characterized in that: The slurry meets at least one of the following characteristics: a. The D50 (①) is 1-10 μm; b. The D50 (②) is 1-10 μm; c. The mass ratio of graphite to silicon-based material in the slurry is 1:99 to 99:1; d. The total mass ratio of graphite and silicon-based material in the slurry to water is 15:85 to 75:25; e. The ratio of the mass of the binder in the slurry to the total mass of graphite and silicon-based materials is 1% to 25%; f. The mass fraction of solid in the slurry is 1%-60%.

3. The graphite silicon-based composite material according to claim 1, characterized in that: The atomization pressure during the spray granulation is 0.1-2.5 MPa; And / or, the first mixture further comprises a conductive material, wherein the conductive material is selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerene; the ratio of the mass of the conductive material to the total mass of graphite and silicon-based materials is 0.01%-10%; And / or, the sphericity of the graphite silicon-based composite material is greater than 0.

9.

4. A method for preparing a graphite silicon-based composite material, characterized in that: include: A first mixture including graphite, a silicon-based material, a binder and water is homogenized for the first time to obtain a second mixture, the second mixture is diluted and then homogenized for the second time to obtain a slurry, and the slurry is spray granulated and dried to obtain the graphite silicon-based composite material, and the parameters of the slurry and spray granulation steps meet the requirements of formula I: D50(composite material)=2×[D50(①)*A1+D50(②)*A2]*[0.62+A3]*(0.2+50X1)*(0.9+6X2)*(1+0.05 / X3) Formula I Wherein, D50(①) is the median particle size of graphite in the first mixture, in μm; D50(②) is the median particle size of the silicon-based material in the first mixture, in μm; A1 is the ratio of the mass of graphite to the total mass of graphite and silicon-based materials, unit: %; A2 is the ratio of the mass of silicon-based materials to the total mass of graphite and silicon-based materials, in %; A3=0.3*min[D50(①),D50(②)] / max[D50(①),D50(②)], no unit; X1 is the ratio of the mass of the binder in the slurry to the total mass of the graphite and silicon-based materials, in %; X2 is the mass fraction of solids in the slurry, in %; X3 is the atomization pressure during spray granulation, unit: MPa; D50 (composite material) is 9-20 μm.

5. The method for preparing the graphite silicon-based composite material according to claim 3, characterized in that: The slurry preparation method comprises: first homogenizing a mixture including graphite, silicon-based material, binder and water to obtain a solid-liquid mixture with a solid content of 15% to 75%; The solid-liquid mixture is mixed with water and then homogenized for the second time to obtain the slurry.

6. The method for preparing the graphite silicon-based composite material according to claim 3, characterized in that: The first homogenization time is 1 to 30 hours, and the homogenization speed is 500-6000 rpm; And / or, the second homogenization time is 1 to 30 hours, and the homogenization speed is 500-6000 rpm; And / or, the first mixture further comprises a conductive material, the conductive material is selected from one or more of carbon nanotubes, conductive carbon black, graphene, and fullerene; the ratio of the mass of the conductive material to the total mass of graphite and silicon-based materials is 0.01%-10%.

7. The method for preparing the graphite silicon-based composite material according to claim 3, characterized in that: After the slurry is prepared, it is placed in a low-speed stirring tank and then transported to a spray granulation device through a pipeline for spray granulation. The rotation speed of the stirring paddle in the low-speed stirring tank is 50-2000 rpm.

8. The method for preparing the graphite silicon-based composite material according to claim 3, characterized in that: In the spray granulation step, the feed rate is 0.15-5 kg / h, the air inlet temperature is 180-250° C., the air outlet temperature is 95-125° C., and the atomization pressure of the atomizer is 0.1-2.5 MPa.

9. The method for preparing the graphite silicon-based composite material according to claim 3, characterized in that: The drying temperature is 120-200°C and the drying time is 1-9h; And / or, the graphite silicon-based composite material obtained after spray granulation has a sphericity greater than 0.

9.

10. A secondary battery, characterized in that: The invention comprises the graphite silicon-based composite material as described in any one of claims 1 to 3.

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