Silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a silicon-carbon negative electrode material which comprises a porous petroleum-based carbon material, hard carbon distributed on the surface and in pores of the porous petroleum-based carbon material, and a nano silicon-based material and a carbon nano material embedded in the porous petroleum-based carbon material. According to the silicon-carbon negative electrode material, a porous petroleum-based carbon material is taken as a matrix, and a nano silicon-based material and a carbon nano material are embedded into the porous petroleum-based carbon material, so that the problems of material pulverization, electrode failure and the like in charging and discharging processes can be inhibited; the hard carbon layer is distributed in pores of the porous petroleum-based carbon material, so that contact between the silicon-based material and electrolyte can be effectively inhibited, and repeated formation of an SEI film is prevented; the conductivity of the silicon-based negative electrode is enhanced, and the cycle performance of the silicon-based material is effectively improved; therefore, the application of the silicon-carbon material in the lithium ion battery is realized. The preparation method of the silicon-carbon negative electrode material has the advantages of no pollution, simple operation, green and easily available raw materials, cheap equipment and easy realization of continuous production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a silicon-carbon anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries (LIBs) have become the most important energy supply device supporting the normal operation of portable devices such as mobile phones, laptops, and cameras. However, with the development of technology, new electrode materials with high rate performance are imperative. For anode materials, silicon-based anode materials are favored due to their ultra-high theoretical specific capacity (4200 mA hg). -1 It is considered one of the most promising candidate materials for next-generation high-energy-density lithium-ion batteries, with a theoretical specific capacity that is currently higher than that of commercially available graphite-based carbon materials (372 mAh g⁻¹). -1 It is 11 times more efficient than lithium. However, due to its inherent limitations, several issues need to be addressed before it can be practically applied. For example, silicon-based materials experience severe volume expansion during lithium insertion / extraction, leading to electrode pulverization; repeated growth of the solid electrolyte interface (SEI) degrades conductivity and reduces cycle performance. Solving the problem of repeated SEI growth can be achieved by nano-sizing silicon-based materials, controlling their structure, and preparing silicon-based composite materials to maintain their electrochemical performance.

[0003] To address the severe volume expansion problem, the most direct approach is to reduce the volume of silicon itself; decreasing the particle size of silicon can effectively alleviate this expansion. Huang et al., through in-situ transmission electron microscopy and other studies, discovered a strong particle size-dependent fracture behavior in silicon nanoparticles during the initial alloying process. This means that particle diameter plays a significant role in the cycling stability of nano-Si. The study suggests that 150 nm is the critical value for the fracture behavior of silicon nanoparticles; below this value, cracking does not occur, while above it, particle breakage occurs. Therefore, nanostructuring of Si materials can serve as a fundamental approach. Further introduction of other methods can not only achieve the advantage of low volume expansion brought about by nanostructuring but also eliminate the adverse effects of secondary agglomeration. Designing composite materials is also a very good approach for improving the performance of silicon-based anode materials, as it combines the advantages of several materials into a single composite, greatly enhancing the material's electrochemical performance. Silicon offers high specific capacity, while carbon has good electrical conductivity and mechanical strength, is widely available and diverse, and both have low charge / discharge plateaus, belong to the same group, have good compatibility, and can be synthesized in many ways, making them economical and environmentally friendly. Therefore, they are regarded by the industry as the best candidates for realizing the commercialization of high-energy-density lithium-ion batteries.

[0004] Currently, the most studied carbon materials combined with silicon include graphite, graphene, carbon nanotubes, and pyrolytic carbon. Researchers have designed silicon-based materials with special structures, such as core-shell structures and porous structures, to improve their lithium storage performance. Wen et al. designed a core-shell structured Si@C. Starting with SiO2 nanoparticles, they coated a polymer film with resorcinol-formaldehyde resin, calcined it at high temperature to form the SiO2@C coated structure, and then used a hydrothermal method to remove some of the silica, forming a so-called core-shell (yolk-shell) structure. Finally, they used a magnesothermic reduction method to give the core a porous structure, further improving the material's cycling performance. To address the issues of volume expansion and poor conductivity and ion conduction properties of silicon during lithium insertion and extraction, researchers have proposed many solutions from different perspectives. Among these, using various structures of nano-silicon materials, structural control of silicon-based materials, and combining them with other materials have significantly improved the electrochemical performance of silicon materials.

[0005] For example, Chinese patent document CN111348647A reports a multi-layered coated silicon-carbon composite material and its preparation method, the preparation process including ball milling, spray drying, and high-temperature encapsulation in a reaction vessel. Although this method yields coated silicon-carbon anode material, the multi-layered coating may lead to slow lithium-ion transport, resulting in poor rate performance. Furthermore, the method is overly complex, uneconomical, environmentally unfriendly, and costly, hindering industrial production. Chinese patent document CN102683649A discloses a method for preparing a carbon-silicon anode material for lithium-ion batteries, using a sol formed from resorcinol and formaldehyde to mix and coat nano-silicon powder and ultrafine graphite powder before carbonization. While this improves the surface structure and cycle performance of the silicon-carbon material, its large specific surface area and low initial efficiency limit its application in lithium batteries.

[0006] Although methods for controlling silicon-based materials can solve some problems of silicon-based anodes to a certain extent, none of them can completely solve the negative impacts caused by the inherent properties of silicon-based anodes, such as cycle stability. Therefore, more in-depth research is still needed. At the same time, for silicon-based composite materials to be commercialized, more mature and simple preparation methods are still needed. Summary of the Invention

[0007] In view of this, the present invention provides a silicon-carbon anode material and its preparation method. This silicon-carbon anode material uses a porous petroleum-based carbon material as a matrix. By embedding nano-silicon and carbon nanomaterials into the porous petroleum-based carbon material, problems such as material pulverization and electrode failure during charge and discharge can be suppressed. By distributing a hard carbon layer on the surface and in the pores of the porous petroleum-based carbon material, the contact between the silicon-based material and the electrolyte can be effectively suppressed, preventing repeated formation of the SEI film. This enhances the conductivity of the silicon-based anode and effectively improves the cycle performance of the silicon-based material, thereby enabling the application of silicon-carbon materials in lithium-ion batteries. The preparation method of this silicon-carbon anode material is pollution-free, simple to operate, uses readily available and environmentally friendly raw materials, requires inexpensive equipment, and is easy to implement for continuous production.

[0008] To achieve the above objectives, the present invention provides a silicon-carbon anode material, comprising a porous petroleum-based carbon material, hard carbon distributed in the surface pores of the porous petroleum-based carbon material, and nano-silicon-based material and carbon nanomaterial embedded in the porous petroleum-based carbon material.

[0009] Of which, based on the mass of the silicon-carbon anode material as 100%, the content of the porous petroleum-based carbon material is 55%-90%, the content of the hard carbon is 3%-20%, the content of the nano-silicon-based material is 4%-20%, and the content of the carbon nanomaterial is 1%-5%.

[0010] This invention also provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0011] S1: Mix micron-sized silicon-based material, carbon nanomaterial, activator, binder and solvent until the binder dissolves, and then mill (mill until the micron-sized silicon-based material becomes nano-sized silicon-based material) to obtain a first mixture;

[0012] S2: The first mixture is ultrasonically mixed with petroleum coke material to obtain a second mixture;

[0013] S3: The second mixture is ball-milled to obtain a precursor of silicon-carbon anode material; after carbonization, acid washing, drying, grinding and sieving, the silicon-carbon anode material is obtained.

[0014] The mass ratio of the activator to the petroleum coke material is 1:(5-25);

[0015] The Hardgrove Grindability Index of the petroleum coke material is greater than 70, and no specific requirements are made for the particle size.

[0016] The activator is selected from alkaline alkali metal salts;

[0017] The carbon nanomaterial is selected from at least one of graphite microsheets, graphene, carbon nanotubes, and carbon fibers;

[0018] The shape of the silicon-based material is selected from at least one of spherical, near-spherical, sheet-like, linear, and tubular shapes;

[0019] Based on the mass of the micron-sized silicon-based material, the carbon nanomaterial, the binder, and the petroleum coke material as 100%, the amount of the micron-sized silicon-based material is 3%-19%; the amount of the carbon nanomaterial is 0.5%-4.5%; the amount of the binder is 5-22%; and the amount of the petroleum coke material is 56%-91%.

[0020] In one optional embodiment, the grinding and sieving steps do not specifically limit the particle size or the mesh size of the sieve. Different mesh sizes of sieves can be selected as needed to obtain materials with different particle sizes.

[0021] In one alternative embodiment, the purpose of the acid washing is to remove the activator.

[0022] In an optional embodiment, the present invention does not specify the type of silicon-based material, and a suitable silicon-based material can be selected according to the needs of on-site operations. For example, the silicon-based material can be selected from silicon particles, silicon suboxide (SiO2), etc. x At least one of the following: preferably, the silicon-based material has a size of 1-20 μm.

[0023] In one optional embodiment, the spherical silicon-based material has a diameter of less than 5 μm and greater than 1 μm, the near-spherical silicon-based material has a particle size of greater than 1 μm and less than 5 μm, the sheet-like silicon-based material has a thickness of less than 5 μm and greater than 1 μm, and the tubular silicon-based material has a diameter of greater than 1 μm and less than 5 μm.

[0024] In one optional embodiment, the carbon nanomaterial has a size of 1-200 nm; preferably, the graphite microsheets have a thickness of less than 50 nm and a sheet diameter of 0.2-1 μm; the graphene has a thickness of less than 10 nm and a sheet diameter of 0.2-1 μm; and the carbon nanotubes have a diameter of 1-50 nm.

[0025] In one alternative embodiment, the adhesive is selected from water-based adhesives, preferably at least one of carboxymethyl cellulose (CMC), chitosan (CS), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and alginate (ALG).

[0026] In one alternative embodiment, the solvent is selected from deionized water.

[0027] In one optional embodiment, the activator is selected from at least one of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, and KHCO3.

[0028] In one optional embodiment, the mass-to-volume ratio of the adhesive to the solvent is (0.5-4) g: 100 mL.

[0029] In one optional embodiment, in step S1, mixing is performed under stirring conditions at a stirring rate of 100-250 r / min.

[0030] In one optional embodiment, the carbonization temperature is 600-1500℃, preferably 600-1300℃; the carbonization time is 1-6h; and the carbonization heating rate is 3-10℃ / min, preferably 2-7℃ / min.

[0031] In one alternative implementation, the ball milling time is 2-6 hours.

[0032] In one alternative embodiment, the ultrasonic mixing time is 0.5-2 hours.

[0033] In this invention, conventional equipment such as sand mills, ball mills, and high-temperature tube furnaces are used for sand milling, ball milling, and carbonization. Furthermore, this invention does not have special requirements for stirring; achieving the desired dispersion effect is sufficient.

[0034] Specifically, the method for preparing the silicon-carbon anode material provided by the present invention includes the following steps:

[0035] (1) Mix the micron-sized silicon-based material, carbon nanomaterial, binder (add at a rate of 0.5-4g per 100ml of solvent), activator and solvent; stir until the binder is fully dissolved to form a homogeneous mixture, and set aside;

[0036] (2) The above mixture is transferred to a sand mill for sand milling to obtain a homogeneous colloid containing nanoscale silicon-based materials and carbon nanomaterials, which is referred to as the first mixture. The sand milling action realizes the nano-scale silicon-based materials, and at the same time, the liquid phase sand milling realizes the homogeneous mixing of nanoscale silicon-based materials and carbon nanomaterials, and realizes the uniform dispersion of nanoscale silicon-based materials and carbon nanomaterials, and at the same time obtains the mixture colloid.

[0037] (3) Add petroleum coke material to the first mixture and perform ultrasonic treatment to fully mix the petroleum coke material with the first mixture to obtain a second mixture; wherein, based on the total mass of micron-sized silicon-based material, carbon nanomaterial, petroleum coke material and binder as 100%, the amount of micron-sized silicon-based material is 3%-19%, the amount of carbon nanomaterial is 0.5%-4.5%, the amount of binder is 5%-22%, the amount of petroleum coke material is 56%-91%, and the mass ratio of activator to petroleum coke material is 1:5-1:25;

[0038] (4) The second mixture is subjected to high-energy ball milling. The local high temperature generated between the particles by the high-energy ball milling and the activator under the local high temperature generated by the high-energy ball milling realize the in-situ activation and pore formation of the petroleum coke material, transforming the petroleum coke material into a porous material. Combined with the extrusion pressure and high pressure generated by the high-energy ball milling, the nano-silicon-based material and carbon nanomaterial are uniformly embedded in the pores and interior of the petroleum coke porous material with a high Hastelloy grindability index. Simultaneously, the in-situ composite of silicon-carbon material (carbon nanomaterial and nano-silicon-based material) and carbon matrix precursor material - petroleum coke material is realized, thereby obtaining the precursor of silicon-carbon anode material in which carbon nanomaterial and nano-silicon-based material are uniformly distributed on the surface and interior of micron-sized petroleum coke by the binder.

[0039] (5) The silicon-carbon anode material precursor obtained above is placed in a high-temperature furnace for high-temperature carbonization treatment; after carbonization is completed, the material is taken out and acid washed with dilute hydrochloric acid to remove unreacted alkaline activator. After drying, grinding and sieving, silicon-carbon anode material that meets the particle size requirements is obtained.

[0040] Beneficial effects

[0041] 1. The silicon-carbon anode material provided by the present invention uses porous petroleum-based carbon material as the matrix material, embeds nano-silicon-based materials and carbon nanomaterials into the surface and pores of the matrix material, and coats the surface and pores of the matrix material with hard carbon. Combined with the limitation of the content of each material, the specific capacity, structural stability and cycle life of the silicon-carbon anode material are significantly improved, thereby improving the energy density of the battery while ensuring the service life.

[0042] 2. The method for preparing silicon-carbon anode materials provided by this invention involves using micron-sized silicon-based materials and carbon nanomaterials of specific shapes, mixing them with specific amounts of alkaline metal activators and binders in a solvent, and milling them to form nano-silicon-based materials, thereby forming a homogeneous colloid. This colloid is then ultrasonically mixed with petroleum coke material of a specific hardness. Compared to the micron-sized petroleum coke material, the homogeneous colloid formed by the nano-silicon-based materials, carbon nanomaterials, activators, and binders in the solvent has a smaller volume, and the petroleum coke material serves as the main matrix material. Therefore, the binders and activators in the homogeneous colloid can uniformly embed the nano-silicon-based materials and carbon nanomaterials into the surface and pores of the petroleum coke material. After ball milling and high-temperature carbonization, the petroleum coke material is activated by the activator and transformed into a porous petroleum-based carbon material. Multidimensional carbon nanomaterials can be further uniformly distributed in the pores and surface of the porous petroleum-based carbon material, while simultaneously stitching the nano-silicon-based materials into the interior of the porous petroleum-based carbon material. Meanwhile, the binder, acting as a bridge between petroleum coke and nanomaterials, forms a thin, uniform hard carbon layer on the surface of porous petroleum-based carbon material after high-temperature carbonization, adhering to the surfaces of carbon nanomaterials and nano-silicon-based materials. This coated hard carbon layer improves the compatibility between the anode material and the electrolyte, effectively preventing capacity loss caused by the co-intercalation of solvent macromolecules during lithium intercalation, and also preventing the repeated formation of the SEI film during the contact between the anode material and the electrolyte. The binder, after high-temperature carbonization, forms a hard carbon network; its larger interlayer spacing and porous structure provide more lithium storage sites, promoting Li-... + Embedding significantly improves the overall conductivity and cycle stability of the anode material. Therefore, the hard carbon formed by binder carbonization, porous petroleum-based carbon materials, and carbon nanomaterials form a three-dimensional framework structure that can effectively alleviate the volume expansion or agglomeration of silicon-based materials during charging and discharging, improve problems such as electrode material crushing and internal short circuits in the battery, enhance electronic conductivity, and ensure the structural stability, thermal stability, overall mechanical strength, and cycle life of the anode material, thereby improving the energy density of the battery while ensuring safety.

[0043] In summary, the method for preparing silicon-carbon anode materials provided by this invention, on the one hand, utilizes the localized high temperature generated by ball milling to in-situ activate micron-sized petroleum coke materials to form petroleum-based porous materials. This successfully embeds nano-silicon-based materials and carbon nanomaterials uniformly into the surface and pores of the porous petroleum-based carbon material. Combined with the hard carbon formed after the binder is carbonized, a three-dimensional silicon-carbon composite anode material with stable structure and excellent conductivity is formed. This structure not only improves the specific capacity of the anode material but also significantly enhances its cycle stability and rate performance, extends battery life, and improves battery energy density and power density. On the other hand, the binder is uniformly distributed on the surface of the petroleum coke material. The three-dimensional carbon skeleton formed after high-temperature carbonization improves the compatibility between the silicon-carbon anode material and the electrolyte, effectively alleviating problems such as volume expansion and electrode material pulverization of silicon-based materials during charging and discharging, and enhancing electronic conductivity. Simultaneously, carbon nanomaterials are also uniformly distributed in the hard carbon network on the surface of the silicon-based material. The rich porous structure between the hard carbon layers is Li + The transmission provides more lithium storage sites and transmission channels, significantly improving the rate performance, fast charging performance and cycle performance of lithium batteries.

[0044] 3. The method for preparing silicon-carbon anode materials provided by the present invention avoids complex chemical reaction processes by using sand milling and ball milling to prepare precursors of silicon-carbon anode materials, ensuring the uniformity and consistency of materials. Moreover, the raw materials and solvent water used in the entire preparation process are all environmentally friendly materials, and the waste generated in the preparation process is small. It is environmentally friendly, green and efficient, with mature technology, low cost, and can be prepared and applied on a large scale, which is in line with the concept of green chemistry and sustainable development.

[0045] 4. The method for preparing silicon-carbon anode material provided by the present invention controls the thickness of the hard carbon layer by further adjusting the amount of binder added in the solvent. The carbon layer formed by combining carbon nanomaterials can ensure the lithium-ion transport rate, improve the compatibility between the anode material and the electrolyte, prevent co-intercalation and decomposition of organic solvents, and avoid electrode structure breakage and peeling during cycling. Attached Figure Description

[0046] Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention;

[0047] Figure 2 This is a particle size distribution diagram of the silicon-carbon anode material prepared in Example 1 of the present invention;

[0048] Figure 3 The BET curve of the silicon-carbon anode material prepared in Example 1 of this invention;

[0049] Figure 4 This is a cross-sectional SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention;

[0050] Figure 5 This is a SEM image of the silicon-carbon anode material prepared in Comparative Example 1 of this invention. Detailed Implementation

[0051] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0052] For any experimental steps or conditions not specified in the following examples and comparative examples, the procedures and conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0053] For ease of comparison, petroleum coke particles with a Hastings grindability index of 80 are used in all the following examples.

[0054] Example 1

[0055] S1: 10g of micron-sized silicon particles (D50 approximately 10μm), 4.5g of carbon nanotubes (diameter approximately 15nm), 10g of NaOH solid activator, and 18.5g of binder (carboxymethyl cellulose, CMC) were mixed in 1000mL of deionized water under stirring at 200r / min until the CMC was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 8h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture was designated as the first mixture.

[0056] S2: Add 70g of petroleum coke particles to the first mixture above and sonicate for 30 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0057] S3: The above second mixture is ball-milled in a ball mill for 2 hours to obtain a precursor of silicon-carbon anode material. The precursor is carbonized in a high-temperature furnace at a heating rate of 5℃ / min, a temperature of 1200℃, and a carbonization time of 2 hours. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0058] Figure 1 The SEM image of the silicon-carbon anode material shows that carbon nanotubes are uniformly distributed on the surface of the silicon-carbon anode material. At the same time, due to the local high temperature generated during the ball milling process, NaOH activates and etches the surface of the petroleum-based carbon material, making the surface of the silicon-carbon anode material uneven.

[0059] Figure 2The particle size distribution curve of the silicon-carbon anode material shows that the particle size is relatively uniform, around 6.5 μm.

[0060] Figure 3 The nitrogen adsorption-desorption curve (BET curve) of this silicon-carbon anode material shows a typical H3-type hysteresis ring, indicating that the silicon-carbon anode material has a porous structure, which can also be observed in the SEM image.

[0061] To observe the internal structure of the silicon-carbon anode material, it was cut with an argon ion beam and then subjected to SEM analysis. The cross-sectional SEM image of the silicon-carbon anode material is shown below. Figure 4 As shown, a porous structure appears at the edge of the composite material due to the activation effect of NaOH. The nano-silicon and carbon nanomaterials are uniformly and orderly embedded on the surface of the porous petroleum-based carbon material, indicating the successful preparation of the porous silicon-carbon anode material.

[0062] Example 2

[0063] S1: 8g of micron-sized silicon material (D50 approximately 8μm), 2g of graphite microsheets (D50 approximately 200nm), 5g of activator KOH solid, and 10g of binder (chitosan, CS) are mixed in 800mL of deionized water under stirring at 250r / min until CS is completely dissolved. The mixture is then transferred to a sand mill and sand-milled to grind the micron-sized silicon material to the nanoscale and form a homogeneous slurry with the other raw materials. This is referred to as the first mixture.

[0064] S2: Add 85g of petroleum coke particles to the first mixture above and sonicate for 45 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0065] S3: The above second mixture is ball-milled in a ball mill for 3 hours to obtain a precursor of silicon-carbon anode material. The precursor is carbonized in a high-temperature furnace at a heating rate of 3℃ / min, a temperature of 900℃, and a carbonization time of 3h. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0066] Example 3

[0067] S1: 19g of micron-sized SiOx material (D50 approximately 40μm), 0.4g of graphene oxide (sheet size 200nm), 10g of Na2CO3 solid activator, and 22.6g of binder (polyacrylic acid, PAA) were mixed in 3400mL of deionized water under stirring at 150r / min until PAA was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 6h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture was designated as the first mixture.

[0068] S2: Add 63g of petroleum coke particles to the first mixture above and sonicate for 60 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0069] S3: The above second mixture is ball-milled in a ball mill for 4 hours to obtain a precursor of silicon-carbon anode material. The precursor is carbonized in a high-temperature furnace at a heating rate of 10℃ / min, a temperature of 1450℃, and a carbonization time of 1h. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0070] Example 4

[0071] S1: 1.5g of micron-sized silicon particles and 2.0g of SiOx material (both materials have a D50 of approximately 40μm), 2g of carbon fiber (approximately 1μm in diameter), 2g of NaOH and 2g of KOH solids, and 5.5g of binder (polyvinyl alcohol, PVA) are mixed in 138mL of deionized water under stirring at 100r / min until the PVA is completely dissolved. The mixture is then transferred to a sand mill and sand-milled to grind the micron-sized silicon material to the nanoscale and form a homogeneous slurry with the other raw materials. This mixture is referred to as the first mixture.

[0072] S2: Add 94g of petroleum coke particles to the first mixture above and sonicate for 90 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0073] S3: The above second mixture is ball-milled in a ball mill for 6 hours to obtain a precursor of silicon-carbon anode material. The precursor is carbonized in a high-temperature furnace at a heating rate of 8℃ / min, a temperature of 650℃, and a carbonization time of 5h. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0074] Comparative Example 1

[0075] S1: 10g of micron-sized silicon particles (D50 approximately 10μm), 4.5g of carbon nanotubes (diameter approximately 15nm), 10g of NaOH solid activator, and 18.5g of binder (carboxymethyl cellulose, CMC) were mixed in 1000mL of deionized water under stirring at 200r / min until the CMC was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 8h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture was designated as the first mixture.

[0076] S2: Add 70g of petroleum coke particles to the first mixture above and sonicate for 30 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0077] S3: The second mixture above is carbonized in a high-temperature furnace at a heating rate of 5℃ / min, a temperature of 1200℃, and a carbonization time of 2h. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0078] Figure 5 The image shows the SEM image of the silicon-carbon anode material prepared in this comparative example. It can be observed from the image that, due to the lack of ball milling-induced activation and extrusion, the petroleum coke cannot effectively combine with the activator, and even after carbonization, no effective porous structure is formed. At the same time, the nanoscale silicon and carbon nanomaterials cannot be effectively embedded into the petroleum-based carbon material. Under the carbonization process, the hard carbon material formed with the binder is randomly distributed around the petroleum-based carbon material.

[0079] Comparative Example 2

[0080] S1: 10g of micron-sized silicon particles (D50 approximately 10μm), 4.5g of carbon nanotubes (diameter approximately 15nm), and 18.5g of binder (carboxymethyl cellulose, CMC) were mixed in 1000mL of deionized water under stirring at 200r / min until the CMC was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 8h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture is referred to as the first mixture.

[0081] S2: Add 70g of petroleum coke particles to the first mixture above and sonicate for 30 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0082] S3: The second mixture above is carbonized in a high-temperature furnace at a heating rate of 5℃ / min, a temperature of 1200℃, and a carbonization time of 2h. After carbonization, it is ground and sieved to obtain silicon-carbon anode material.

[0083] Comparative Example 3

[0084] S1: 10g of micron-sized silicon particles (D50 approximately 10μm), 4.5g of carbon nanotubes (diameter approximately 15nm), 10g of NaOH solid activator, and 18.5g of binder (carboxymethyl cellulose, CMC) were mixed in 1000mL of deionized water under stirring at 200r / min until the CMC was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 8h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture was designated as the first mixture.

[0085] S2: Add 70g of coconut shell material particles to the first mixture above and sonicate for 30 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0086] S3: The second mixture above is carbonized in a high-temperature furnace at a heating rate of 5℃ / min, a temperature of 1200℃, and a carbonization time of 2h. After carbonization, it is ground and sieved to obtain silicon-carbon anode material.

[0087] Comparative Example 4

[0088] S1: 10g of micron-sized silicon particles (D50 approximately 10μm), 4.5g of carbon nanotubes (diameter approximately 15nm), 3g of NaOH solid activator, and 18.5g of binder (carboxymethyl cellulose, CMC) were mixed in 1000mL of deionized water under stirring at 200r / min until the CMC was completely dissolved. The mixture was then transferred to a sand mill and sand-milled for 8h to grind the micron-sized silicon material to the nanoscale and form a homogeneous colloid with the other raw materials. This mixture was designated as the first mixture.

[0089] S2: Add 70g of petroleum coke particles to the first mixture above and sonicate for 30 minutes to obtain a homogeneous mixture, which is referred to as the second mixture.

[0090] S3: The second mixture above is carbonized in a high-temperature furnace at a heating rate of 5℃ / min, a temperature of 1200℃, and a carbonization time of 2h. After carbonization, the activator is removed by washing with hydrochloric acid aqueous solution. After drying, grinding and sieving, silicon-carbon anode material is obtained.

[0091] The silicon-carbon anode materials obtained in the above embodiments and comparative examples were used to prepare lithium-ion battery anode electrode sheets according to the following methods: the obtained silicon-carbon anode material was used as the active material, carbon black as the conductive agent, and polyvinylpyrrolidone (PVP) as the binder. They were mixed evenly at a mass ratio of 8:1:1, and pure water was used as the solvent to prepare the slurry. The slurry was coated on a 10μm thick copper foil to form an electrode sheet of 5cm×15cm. After drying in an oven at 80℃, the electrode sheet was rolled to the required thickness and dried under vacuum at 120℃ for 12h to obtain the lithium-ion battery anode electrode sheet. Then, a coin cell was assembled using a lithium metal sheet as the counter electrode, a Celgard 2300 membrane as the separator, and 1mol / L LiPF6 / EC+DEC+DMC (volume ratio 1:1:1) as the electrolyte. The electrochemical performance of coin cells was tested using a charge / discharge tester from Shenzhen Xinwei Electronics Co., Ltd. The charge / discharge voltage range was 0.005-1.5V, and the charge / discharge current density was 50mA / g. The capacity retention rate of the battery after 100 cycles was measured at C. 100 / C1, the test results are shown in Table 1.

[0092] Table 1

[0093] Initial lithium insertion capacity / mAh / g Capacity retention rate after 100 cycles / % Example 1 1480 75 Example 2 1372 65 Example 3 721 81 Example 4 873 71 Comparative Example 1 1212 23 Comparative Example 2 1317 42 Comparative Example 3 1275 33 Comparative Example 4 1140 40

[0094] As can be seen from the data in the table above, the lithium-ion battery made from the silicon-carbon anode material provided by this invention exhibits excellent initial lithium intercalation capacity and cycle stability.

[0095] Of course, the present invention may have other embodiments and variations. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and variations according to the present invention, but these corresponding changes and variations should all fall within the protection scope of the claims of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, It includes porous petroleum-based carbon materials, hard carbon distributed on the surface and in the pores of the porous petroleum-based carbon materials, and nano-silicon-based materials and carbon nanomaterials embedded in the porous petroleum-based carbon materials; Of which, based on the mass of the silicon-carbon anode material as 100%, the content of the porous petroleum-based carbon material is 55%-90%, the content of the hard carbon is 3%-20%, the content of the nano-silicon-based material is 4%-20%, and the content of the carbon nanomaterial is 1%-5%.

2. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: S1: Micron-sized silicon-based material, carbon nanomaterial, activator, binder and solvent are mixed until the binder is dissolved, and then milled to obtain a first mixture; S2: The first mixture is ultrasonically mixed with petroleum coke material to obtain a second mixture; S3: The second mixture is ball-milled to obtain a precursor of silicon-carbon anode material; the precursor is carbonized, acid-washed, dried, ground and sieved to obtain the silicon-carbon anode material. The mass ratio of the activator to the petroleum coke material is 1:(5-25); The Hastelloy Grindability Index of the petroleum coke material is greater than 70; The activator is selected from alkaline alkali metal salts; The carbon nanomaterial is selected from at least one of graphite microsheets, graphene, carbon nanotubes, and carbon fibers; The shape of the silicon-based material is selected from at least one of spherical, near-spherical, sheet-like, linear, and tubular shapes; Based on the mass of the micron-sized silicon-based material, the carbon nanomaterial, the binder, and the petroleum coke material as 100%, the amount of the micron-sized silicon-based material is 3%-19%; the amount of the carbon nanomaterial is 0.5%-4.5%; the amount of the binder is 5%-22%; and the amount of the petroleum coke material is 56%-91%.

3. The preparation method according to claim 2, characterized in that, The silicon-based material is selected from at least one of silicon particles and silicon suboxide; preferably, the size of the silicon-based material is 1-20 μm. In the silicon-based material, the diameter of the sphere is less than 5 μm, the size of the near-spherical shape is less than 5 μm, the thickness of the sheet is less than 5 μm, and the diameter of the tubular shape is less than 5 μm.

4. The preparation method according to claim 2 or 3, characterized in that, The carbon nanomaterials have a size of 1-200 nm; preferably, the graphite microsheets have a thickness of less than 50 nm and a sheet diameter of 0.2-1 μm; the graphene has a thickness of less than 10 nm and a sheet diameter of 0.2-1 μm; and the carbon nanotubes have a diameter of 1-50 nm.

5. The preparation method according to claim 2 or 3, characterized in that, The adhesive is selected from water-based adhesives, preferably at least one of carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, chitosan, and alginate; The solvent is selected from deionized water.

6. The preparation method according to claim 2 or 3, characterized in that, The activator is selected from at least one of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, and KHCO3.

7. The preparation method according to claim 2 or 3, characterized in that, The mass-to-volume ratio of the binder to the solvent is (0.5-4) g: 100 mL.

8. The preparation method according to claim 2 or 3, characterized in that, In step S1, the mixture is stirred at a speed of 100-250 r / min.

9. The preparation method according to claim 2 or 3, characterized in that, The carbonization temperature is 600-1500℃, the time is 1-6h, and the heating rate of the carbonization is 3-10℃ / min.

10. The preparation method according to claim 2 or 3, characterized in that, The ball milling time is 2-6 hours; The ultrasonic mixing time is 0.5-2 hours.

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