A spherical graphite / porous silicon-carbon composite material, a preparation method and application thereof

Abstract

The application discloses a spherical graphite / porous silicon-carbon composite material and a preparation method and application thereof, and belongs to the technical field of new energy material preparation. The preparation method is as follows: first, pitch and fine flake graphite are subjected to first ball milling mixing to obtain a first precursor; second, spherical graphite is added into the first precursor for second ball milling mixing to obtain a second precursor; third, the second precursor is subjected to first calcination to obtain a third precursor; fourth, the third precursor is immersed in a diluted ethyl silicate solution, and then is subjected to filtration and drying to obtain a fourth precursor; fifth, the fourth precursor is subjected to second calcination to obtain the spherical graphite / porous silicon-carbon composite material; the first ball milling is carried out at a rotating speed of 500-800 rpm; the second ball milling is carried out at a rotating speed of 200-400 rpm; and the first ball milling and the second ball milling are both carried out in an air atmosphere. The preparation method can solve the technical problems of complex operation, non-uniform local oxidation of products and inconsistent silicon particle dispersion in the conventional pitch coating process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy material preparation, and particularly relates to a spherical graphite / porous silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] Graphite is the main source of lithium ion battery anodes, and commercial graphite is usually spherical graphite. Therefore, flake graphite needs to be granulated before use, which will result in nearly 40% of fine flake graphite being difficult to fully utilize, causing great waste of this resource. From the composition and structure, the spherical tailings can also be used for lithium ion batteries, such as a method for preparing lithium battery anodes from natural graphite spherical tailings provided in Chinese Patent No. CN115472832A, which realizes high value-added utilization of tailings.

[0003] From the energy point of view, in order to achieve the target of 500 Wh kg -1 of battery energy density, researchers usually need to modify the spherical graphite, and silicon-carbon composite material is undoubtedly one of the most promising directions. In order to fully mix silicon and graphite, ball milling is usually used for mixing, however, mechanical mixing can only achieve physical combination of silicon and graphite, and during the battery cycle process, it is easy to cause the free and agglomeration of silicon particles, resulting in local polarization and stress concentration, and finally destroying the structure of the electrode. Preparing porous silicon-carbon composite material is an effective method to improve the stability and performance of the material. From the industrialization point of view, pitch has the advantages of wide source and high carbon yield in pyrolysis process. If pitch is used to coat graphite, not only the surface of the spherical graphite can be modified to reduce possible side reactions, but also it is easy to be compounded with silicon, such as preparing pitch-based porous carbon material can realize the fixation and embedding of silicon particles by means of porous network structure, and improve the stability of the material. However, due to the conjugation effect of polycyclic aromatic hydrocarbons in pitch, pitch is easy to accumulate and agglomerate during pyrolysis, which is not conducive to complete coating on the surface of spherical graphite, and even more not conducive to the formation of porous network structure.

[0004] In order to solve the problem of pitch agglomeration, researchers usually use pre-oxidation to introduce oxygen-containing functional groups in pitch, thereby increasing the cross-linking structure of pitch molecules. However, due to the viscosity and easy agglomeration of pitch particles themselves, the uniformity problem of pre-oxidation is always difficult to solve. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a spherical graphite / porous silicon-carbon composite material and a preparation method and application thereof, which solve the technical problems of complex operation, local non-uniform oxidation of products and inconsistent dispersion of silicon particles in the process of traditional pitch coating.

[0006] In order to achieve the above object, the present application adopts the following technical solutions to achieve the above object:

[0007] The present application provides a preparation method of spherical graphite / porous silicon-carbon composite material, comprising the following steps:

[0008] S1: first ball-milling mixing of pitch and fine flake graphite to obtain a first precursor;

[0009] S2: second ball-milling mixing of spherical graphite into the first precursor to obtain a second precursor;

[0010] S3: first calcination of the second precursor to obtain a third precursor;

[0011] S4: immersion of the third precursor in a diluted solution of tetraethyl orthosilicate, followed by filtration and drying to obtain a fourth precursor;

[0012] S5: second calcination of the fourth precursor to obtain the spherical graphite / porous silicon-carbon composite material;

[0013] In the S1, the first ball-milling is carried out at a speed of 500-800 rpm; in the S2, the second ball-milling is carried out at a speed of 200-400 rpm; and the first ball-milling and the second ball-milling are carried out in an air atmosphere.

[0014] In an embodiment, in the S1, the mass ratio of the pitch to the fine flake graphite is 1:(0.4-1).

[0015] In an embodiment, in the S1, the fine flake graphite has a radial size of 2-10 μm.

[0016] In an embodiment, in the S2, the mass ratio of the spherical graphite to the first precursor is 1:(0.1-0.4).

[0017] In an embodiment, the first ball-milling is carried out for 0.5-2 h, and the ball-to-material ratio of the grinding balls to the grinding material composed of the pitch and the fine flake graphite is (30-50):1 during the first ball-milling;

[0018] The second ball-milling is carried out for 0.5-2 h, and the ball-to-material ratio of the grinding balls to the grinding material composed of the spherical graphite and the first precursor is (10-30):1 during the second ball-milling.

[0019] In an embodiment, in the S3, the first calcination is carried out at a temperature of 800-1200℃ for 1-3 h; and in the S5, the second calcination is carried out at a temperature of 600-850℃ for 1-3 h.

[0020] The first and second calcinations in the S3 and S5 are both carried out in an inert atmosphere, which is nitrogen or argon.

[0021] In an embodiment, in the S4, the diluted tetraethyl orthosilicate solution is a methanol-diluted tetraethyl orthosilicate solution.

[0022] The volume ratio of the tetraethyl orthosilicate solution to methanol is 1:(1-10).

[0023] The impregnation time is 1-3 hours.

[0024] In an embodiment, in the S4, the ratio of the third precursor to the diluted tetraethyl orthosilicate solution is 1g:(2.5-10)mL.

[0025] The application also provides a spherical graphite / porous silicon-carbon composite material prepared by the preparation method of the spherical graphite / porous silicon-carbon composite material.

[0026] The application also provides an application of the spherical graphite / porous silicon-carbon composite material in a lithium ion battery negative electrode.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application provides a preparation method of a spherical graphite / porous silicon-carbon composite material. The preparation method first mixes fine flaky graphite and pitch in an air atmosphere through a first ball milling mode (high-speed ball milling mode). In this process, the high-speed collision of the grinding balls in the air atmosphere not only realizes the pre-oxidation of the pitch and reduces the problems of foaming and agglomeration in the later calcination process, but also realizes the construction of a porous three-dimensional network structure of the fine flaky graphite and the pitch. In a later second ball milling mode (low-speed ball milling stage), the spherical graphite can be better coated, and the porous pitch-based coated spherical graphite material obtained can fully absorb silicon in a later impregnation process, so as to ensure the uniform and sufficient dispersion of silicon particles after calcination. The above method adopts a mechanical force activation mode of high-speed ball milling to pre-oxidize the pitch, avoids the problems of complex operation and uneven local oxidation of the product in the traditional pitch coating process, and realizes the uniform dispersion of the pitch and the fine flaky graphite in the high-speed ball milling process. Since the fine flaky graphite has the same texture as the spherical graphite, the low-speed ball milling stage can assist the coating of the spherical graphite, and a spherical graphite material with good uniformity is obtained. Meanwhile, since the pre-oxidation process of the pitch and the fine flaky graphite can also realize the construction of a porous three-dimensional network structure, the impregnation of the tetraethyl orthosilicate solution after the first calcination not only can fully absorb silicon by means of the porous structure, but also solves the problem of inconsistent dispersion of silicon particles in the traditional solid-state (silicon powder) mixing process, and has potential industrial application potential.

[0029] The present invention also provides a spherical graphite / porous silicon-carbon composite material prepared by the above-mentioned preparation method. The inner core of the spherical graphite / porous silicon-carbon composite material is mainly composed of traditional spherical graphite, and the outer shell is composed of a composite of porous silicon-carbon material and fine flake graphite. High-speed ball milling of asphalt and fine flake graphite ensures the uniformity of the network structure, the core-shell wrapping of fine flake graphite and spherical graphite ensures the stability of the material structure, and the impregnation method ensures the uniform and effective dispersion of silicon, thereby helping to improve the lithium storage capacity of the material.

[0030] On the other hand, the present invention provides the use of the spherical graphite / porous silicon-carbon composite material prepared by the above preparation method in the negative electrode of a lithium ion battery, which can obtain a higher specific capacity, stable cycle performance and good rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The spherical graphite / porous silicon-carbon composite material 0.2Ag prepared in Example 1 of the present invention -1 Cycle performance diagram;

[0032] Figure 2 The spherical graphite / porous silicon-carbon composite material 0.2Ag prepared in Example 2 of the present invention -1 Cycle performance diagram. DETAILED DESCRIPTION

[0033] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0034] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0035] Herein, all features such as values, amounts, amounts, and concentrations defined in numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0036] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0037] Herein, all possible combinations between technical features in various embodiments or examples are not described in order to simplify the description. Therefore, as long as there is no contradiction in the combination of technical features, various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations shall be considered as the scope described in the specification.

[0038] The application provides a spherical graphite / porous silicon-carbon composite material and a preparation method and application thereof.

[0039] In an aspect, a preparation method of a spherical graphite / porous silicon-carbon composite material is provided, comprising the following steps:

[0040] S1: first ball-milling mixing asphalt and fine flake graphite according to a mass ratio of 1:(0.4-1) to obtain a first precursor;

[0041] S2: adding spherical graphite into the first precursor according to a mass ratio of 1:(0.1-0.4) to obtain a second precursor;

[0042] S3: first calcining the second precursor to obtain a third precursor;

[0043] S4: impregnating the third precursor in a diluted solution of tetraethyl orthosilicate according to a use ratio of 1g:(2.5-10)mL, and then filtering and drying to obtain a fourth precursor;

[0044] S5: second calcining the fourth precursor to obtain the spherical graphite / porous silicon-carbon composite material;

[0045] In the S1, the first ball-milling is performed under a rotation speed of 500-800 rpm; in the S2, the second ball-milling is performed under a rotation speed of 200-400 rpm; and the first ball-milling and the second ball-milling are both performed in an air atmosphere.

[0046] In the specific implementation process, the specific steps of S1 are as follows:

[0047] S1: first ball-milling mixing asphalt and fine flake graphite according to a mass ratio of 1:(0.4-1) to obtain a first precursor, the fine flake graphite is derived from spherical graphite tailings remaining in a flake graphite granulation process, and the radial size is between 2-10 μm; the first ball-milling is high-energy ball-milling, the rotation speed is between 500-800 rpm, the ball-to-material ratio is (30-50):1, the ball-milling time is 0.5-2 h, and the ball-milling atmosphere is air.

[0048] In the specific implementation process, the specific steps of S2 are as follows:

[0049] S2: adding the spherical graphite into the first precursor according to a mass ratio of 1:(0.1-0.4) to obtain a second precursor by a second ball milling, the second ball milling is a low-speed ball milling, the rotation speed is between 200-400 rpm, the ball-to-material ratio is (10-30):1, the ball milling time is 0.5-2 h, and the ball milling atmosphere is air.

[0050] In the specific implementation process, the specific steps of S3 are as follows:

[0051] S3: performing a first calcination on the second precursor at a temperature of 800-1200℃ and in an inert atmosphere for 1-3 h to obtain a third precursor, the inert atmosphere can be nitrogen or argon.

[0052] In the specific implementation process, the specific steps of S4 are as follows:

[0053] immersing the third precursor in a diluted solution of tetraethyl orthosilicate according to a dosage ratio of 1 g:(2.5-10) mL, and then filtering and drying to obtain a fourth precursor, the diluted solution of tetraethyl orthosilicate is a methanol-diluted solution, the volume ratio of the tetraethyl orthosilicate solution to the methanol is 1:(1-10), and the immersion time is 1-3 h.

[0054] In the specific implementation process, the specific steps of S5 are as follows:

[0055] performing a second calcination on the fourth precursor at a temperature of 600-850℃ for 1-3 h to obtain a spherical graphite / porous silicon-carbon composite material, the second calcination is performed in an inert atmosphere, and the inert atmosphere can be nitrogen or argon.

[0056] The preparation method not only can improve the incomplete coating of the pitch-based carbon material on the surface of the spherical graphite by means of the fine flake graphite, but also can ensure the uniform dispersion of the silicon particles on the surface of the spherical graphite when the silicon material is compounded by means of the impregnation method in the later stage, and can improve the volume expansion and cycle performance decay of the graphite / silicon composite material in the charge and discharge process.

[0057] On the other hand, a spherical graphite / porous silicon-carbon composite material prepared by the above-mentioned preparation method of the spherical graphite / porous silicon-carbon composite material is provided, and the spherical graphite / porous silicon-carbon composite material has the advantages of good structural stability, high size consistency, and uniform component distribution.

[0058] In another aspect, the application provides an application of the spherical graphite / porous silicon-carbon composite material prepared by the above-mentioned preparation method in a lithium ion battery negative electrode, and the application can achieve good electrochemical performance, especially a specific capacity higher than 372 mAh g -1 , and good cycle stability.

[0059] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims.

[0060] The following examples use the instruments and equipment that are conventional in the art. The experimental methods in the following examples, if not specified, are generally carried out according to the conventional conditions, or according to the conditions suggested by the manufacturers. The following examples use various raw materials, unless otherwise specified, and the conventional commercially available products are used, and the specifications are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, "%" means weight percent, "parts" means weight parts, and the ratio means weight ratio.

[0061] Example 1

[0062] 100 g of pitch and 40 g of fine flake graphite were mixed and loaded into a ball mill tank under air conditions, and then high-speed ball milling was carried out at 500 rpm and a ball-to-material ratio of 30:1 for 0.5 h, to obtain a first precursor. The ball mill cover was opened, and spherical graphite was directly added, wherein the mass ratio of the spherical graphite to the above-mentioned first precursor (pitch + fine flake graphite) was 10:1, and then low-speed ball milling was carried out at 200 rpm and a ball-to-material ratio of 10:1 for 0.5 h, to obtain a second precursor. The second precursor was calcined at 800°C for 3 h under nitrogen to obtain a third precursor; the third precursor was placed in a tetraethyl orthosilicate (TEOS) methanol solution (1:1 by volume) for 1 h, and the mass-to-volume ratio of the third precursor to the TEOS dilute solution was 1 g:2.5 mL. Then, the dried fourth precursor was calcined at 600°C for 3 h under argon to obtain a spherical graphite / porous silicon-carbon composite material.

[0063] The composite material prepared in Example 1 was coated on a copper foil to prepare a negative electrode, and a PP separator, 1 mol / L LiPF6 (solvent: a mixture of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1) as an electrolyte, and a lithium sheet were assembled into a button cell for electrochemical performance testing. The specific capacity was 954 mAh g -1 at 0.2 A g -1 , and the specific capacity was 534 mAh g -1 after 300 cycles.

[0064] Example 2

[0065] 100g of pitch and 100g of fine flake graphite were mixed in air and placed in a ball mill. The mixture was then subjected to high-speed ball milling at 800 rpm and a ball-to-material ratio of 50:1 for 2 hours to produce the first precursor. Spherical graphite was added directly to the mill lid, with a mass ratio of spherical graphite to the first precursor (pitch + fine flake graphite) of 10:4. The second precursor was then subjected to low-speed ball milling at 400 rpm and a ball-to-material ratio of 30:1 for 2 hours. The second precursor was calcined at 1200°C under argon for 1 hour to produce the third precursor. The third precursor was then placed in a methanol solution of ethyl orthosilicate (TES) (a dilute TES solution) for 3 hours (the volume ratio of TES to methanol was 1:10). The mass-to-volume ratio of the third precursor to the dilute TES solution was 1g:10mL. The dried fourth precursor was then calcined at 850° C. for 1 h under nitrogen to obtain a spherical graphite / porous silicon-carbon composite material.

[0066] The composite material prepared in Example 2 was coated on copper foil to prepare the negative electrode, and PP was used as the separator, 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1) was used as the electrolyte, and the lithium sheet was assembled into a button cell for electrochemical performance testing. -1 The initial specific capacity is 1035 mAh g -1 , the specific capacity is 588mAhg after 300 cycles -1 .

[0067] like Figure 1 and Figure 2 As shown in the figure, the capacity of the lithium-ion battery negative electrode material obtained by this method can be much higher than the theoretical specific capacity of graphite (372mAhg -1 ) performance, after 300 cycles, it still has at least 56% and more than 500mAhg -1 It has good specific capacity and high specific energy characteristics.

[0068] The present invention is an improved ball milling method for preparing spherical graphite / porous silicon-carbon composite materials. First, asphalt and fine flake graphite are ball milled at high speed. During this process, the asphalt is pre-oxidized and evenly dispersed with the flake graphite. After the spherical graphite is added to the flake graphite / asphalt composite material at a later stage, a cross-linked network structure can be formed, which ensures the uniformity of the coating while further improving the capacity, rate and other performance of the graphite negative electrode with the help of asphalt carbonization.

[0069] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a spherical graphite / porous silicon-carbon composite material, characterized in that: The following steps are involved: S1: ball milling asphalt and fine flake graphite to obtain the first precursor; S2: adding spherical graphite to the first precursor and performing a second ball milling to obtain a second precursor; S3: calcining the second precursor for the first time to obtain a third precursor; S4: immersing the third precursor in a dilute solution of ethyl orthosilicate, and then filtering and drying to obtain a fourth precursor; S5: calcining the fourth precursor for a second time to obtain a spherical graphite / porous silicon-carbon composite material; In S1, the first ball milling is performed at a rotation speed of 500-800 rpm; in S2, the second ball milling is performed at a rotation speed of 200-400 rpm; the first ball milling and the second ball milling are performed in an air atmosphere; In S1, the mass ratio of the asphalt to the fine flake graphite is 1:(0.4-1); In S1, the radial size of the fine flake graphite is 2-10 μm; In S2, the mass ratio of the spherical graphite to the first precursor is 1:(0.1-0.4); In S3, the temperature of the first calcination is 800-1200° C., and the time of the first calcination is 1-3 hours; in S5, the temperature of the second calcination is 600-850° C., and the time of the second calcination is 1-3 hours; In S3 and S5, the first calcination and the second calcination are both performed under an inert atmosphere, and the inert atmosphere is nitrogen or argon.

2. The method for preparing the spherical graphite / porous silicon-carbon composite material according to claim 1, wherein: The time of the first ball milling is 0.5-2 hours; the ball-to-material ratio of the grinding balls to the abrasive composed of asphalt and fine flake graphite during the first ball milling is (30-50):1; The second ball milling time is 0.5-2 hours; during the second ball milling process, the ball-to-material ratio of the grinding balls to the abrasive consisting of spherical graphite and the first precursor is (10-30):

1.

3. The method for preparing the spherical graphite / porous silicon-carbon composite material according to claim 1, wherein: In S4, the dilute ethyl orthosilicate solution is a ethyl orthosilicate solution diluted with methanol; The volume ratio of the ethyl orthosilicate solution to methanol is 1:(1-10); The immersion time is 1 to 3 hours.

4. The method for preparing the spherical graphite / porous silicon-carbon composite material according to claim 1, wherein: In the above-mentioned S4, the usage ratio of the third precursor to the diluted ethyl orthosilicate solution is 1 g: (2.5-10) mL.

5. A spherical graphite / porous silicon-carbon composite material obtained by the method for preparing a spherical graphite / porous silicon-carbon composite material according to any one of claims 1 to 4.

6. Use of the spherical graphite / porous silicon-carbon composite material as claimed in claim 5 in a negative electrode of a lithium-ion battery.

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