Graphite-based silicon carbon negative electrode material and preparation method and application thereof

Abstract

The embodiment of the invention relates to a graphite-based silicon carbon negative electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a carbon source, biomass fine powder and porous graphite according to a certain mass ratio, carrying out hydrothermal heating treatment, and sintering in an inert atmosphere to obtain a sintered product; mixing the sintered product with hydroxide, activating, cooling, washing, filtering, and drying to obtain a graphite composite porous material; placing the graphite composite porous material in a tubular furnace for silicon deposition to obtain a silicon-carbon composite material; and carrying out carbon coating on the silicon-carbon composite material to obtain the graphite-based silicon-carbon negative electrode material. According to the preparation method disclosed by the embodiment of the invention, the biomass fine powder is nested in pores of the porous graphite, and the pores are modified by the carbon source, so that the pressure resistance of the material is improved.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a graphite-based silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Currently, commercial lithium-ion batteries mainly use graphite as the negative electrode material, but the theoretical specific capacity of graphite is low at only 372mAh / g, which can no longer meet the growing demand for high energy density. Silicon material is considered to be the most promising next-generation negative electrode material to replace graphite due to its theoretical specific capacity of up to 4200mAh / g. However, silicon will produce up to 300% volume expansion during the lithium insertion process, leading to problems such as material structure destruction, electrode pulverization, and decreased battery cycle performance, which seriously restricts its practical application.

[0003] To solve the above problems, researchers have proposed a variety of modification methods, such as nano-sizing of silicon, alloying of silicon with metals, and composites of silicon with active or inactive materials. Among them, silicon-carbon composite materials are considered to be more ideal composite materials due to the excellent electronic conductivity and structural stability of carbon materials. In the prior art, although porous graphite-based silicon-carbon materials have good structural stability and conductivity, their fast charging performance is poor and it is difficult to meet the requirements of high power density. For example, a silicon-carbon composite negative electrode material, a preparation method and an application disclosed in a Chinese patent with publication number CN114068901A, although the overall expansion rate of the composite negative electrode material is smaller and has better cycle stability, the fast charging performance of the silicon-carbon material is not improved, and the electrochemical performance needs to be further improved. A Chinese patent with publication number CN108565408A discloses a negative electrode material for a lithium-ion battery. Although it uses the soft and deformable characteristics of graphite to provide space for the volume expansion of silicon, it also uses carbon with a certain strength as a skeleton to further ensure the overall stability of the negative electrode material, but there is still a problem of poor pressure resistance due to unreasonable structural design.

[0004] Therefore, how to improve the fast charging performance of silicon-carbon composites while ensuring structural stability and electrical conductivity, and to construct silicon-carbon composites that have high compaction, high fast charging performance and high cycle stability, is a key issue that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a graphite-based silicon-carbon negative electrode material and its preparation method and application in view of the defects of the prior art. The preparation method allows biomass fine powder to be embedded in the pores of porous graphite, and the pores are modified by a carbon source to form a carbon connection between the biomass fine powder and the graphite matrix, thereby improving the pressure resistance of the material.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a graphite-based silicon-carbon negative electrode material, the preparation method comprising:

[0007] After mixing a carbon source, biomass fine powder and porous graphite according to a certain mass ratio, perform hydrothermal heating treatment, and then sinter in an inert atmosphere to obtain a sintered product;

[0008] Mix the sintered product with a hydroxide for activation treatment, and then obtain a graphite composite porous material through cooling, washing, filtering and drying treatments;

[0009] Place the graphite composite porous material in a tubular furnace for silicon deposition to obtain a silicon-carbon composite material;

[0010] Perform carbon coating on the silicon-carbon composite material to obtain a graphite-based silicon-carbon negative electrode material.

[0011] Preferably, the carbon source includes: one or more of glucose, sucrose, fructose, citric acid, polyvinylpyrrolidone, ascorbic acid, chitosan; the raw materials of the biomass fine powder include one or more of coconut shell, straw, rice husk, fruit shell, cotton fiber, fruit core, wheat straw, corn cob, wood chip, bamboo and water bamboo leaf; the certain mass ratio is [30-50]:[10-20]:[30-60].

[0012] Preferably, the conditions of the hydrothermal heating treatment are specifically: temperature 145°C - 155°C, time 1.5 hours - 2.5 hours.

[0013] Preferably, the sintering temperature is 300°C - 700°C, and the time is 2 hours - 4 hours.

[0014] Preferably, the ratio of the sintered product to the hydroxide is 1:3 - 1:1, the activation treatment temperature is 700°C - 900°C, and the time is 2 hours - 4 hours.

[0015] Preferably, the silicon deposition temperature is 480°C - 560°C, and the time is 5 hours - 7 hours.

[0016] Preferably, the carbon coating temperature is 500°C - 600°C, and the time is 1.5 hours - 2.5 hours.

[0017] In a second aspect, the present invention provides a graphite-based silicon-carbon negative electrode material, and the graphite-based silicon-carbon negative electrode material is prepared by the preparation method described in any one of the first aspects above.

[0018] In a third aspect, the present invention provides a negative electrode sheet, and the negative electrode sheet includes the graphite-based silicon-carbon negative electrode material described in the second aspect.

[0019] In a fourth aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes the negative electrode sheet described in the third aspect.

[0020] A preparation method of a graphite-based silicon-carbon anode material provided by an embodiment of the present invention nests biomass fine powder in (fills) the pores of porous graphite. On the one hand, it can reasonably fill the pores of the porous graphite, reduce the ineffective space in the pores, improve the overall density and structural stability of the material, solve the problem of poor fast charging performance of the existing porous graphite matrix silicon-carbon material, overcome the defects of low compaction density, poor fast charging performance and poor pressure resistance of the existing silicon-carbon composite material, and construct a silicon-carbon composite material that takes into account high compaction and high pressure resistance; on the other hand, the presence of the biomass fine powder improves the ion transport environment in the pores, makes the transport of lithium ions in the pores smoother, is conducive to the ion exchange between the silicon particles and the electrolyte, and improves the fast charging performance of the battery. After the carbon source is activated to form pores, it forms a composite structure with the graphite matrix, further optimizing the pore structure of the material, increasing the specific surface area of the material, providing more active sites, and being conducive to the adsorption and insertion of lithium ions. At the same time, the formed composite structure enables the deposited silicon particles to be better dispersed in the composite material, avoids the aggregation of the silicon particles, increases the contact area between the silicon particles and the electrolyte, and enhances the electrochemical activity of the silicon particles. The synergy of the carbon source and the biomass fine powder improves the utilization rate and electrochemical performance of the silicon particles; the carbon layer coating process is adopted to further improve the structural stability and cycle stability of the material; by increasing the silicon content, a higher specific capacity is achieved, meeting the requirements of high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of a preparation method of a graphite-based silicon-carbon anode material provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] The technical solutions of the present invention will be further described in detail below through the drawings and embodiments.

[0024] An embodiment of the present invention provides a preparation method of a graphite-based silicon-carbon anode material, and the process is as Figure 1 shown, including the following steps:

[0025] Step 110, after mixing a carbon source, biomass fine powder and porous graphite according to a certain mass ratio, performing hydrothermal heating treatment, and then sintering in an inert atmosphere to obtain a sintered product;

[0026] Specifically, the carbon source may include one or more of glucose, sucrose, fructose, citric acid, polyvinylpyrrolidone, ascorbic acid, and chitosan, and glucose is preferred.

[0027] The particle size D50 of the biomass fine powder is 100 nm to 500 nm. The raw materials of the biomass fine powder come from coconut shells, straw, rice husks, fruit shells, cotton fibers, fruit stones, wheat straws, corncobs, wood chips, bamboo, and water bamboo leaves, etc. The preparation of the biomass fine powder is achieved by conventional methods in the art: that is, the biomass raw materials are obtained through crushing, acid cooking, carbonization, and crushing and grading treatments.

[0028] The particle size D50 of the porous graphite is 3 μm - 35 μm, the specific surface area is 10 m 2 / g - 500 m 2 / g, the pore diameter of the pores is 200 nm - 1000 nm, and the porosity is 5% - 20%. The porous graphite can be obtained by etching porous graphite raw materials with strong acids. Specifically, porous graphite raw materials can be added to aqua regia, and the reaction is carried out at a temperature of 25°C - 100°C for 1 hour - 2 hours.

[0029] A certain mass ratio can be [30 - 50]:[10 - 20]:[30 - 60], and 50:20:30 is preferred.

[0030] The conditions of the hydrothermal heat treatment can specifically be: the temperature is 145°C - 155°C, preferably 150°C, and the time is 1.5 hours - 2.5 hours, preferably 2 hours.

[0031] During the hydrothermal heat treatment, the carbon source dissolves, wraps the biomass fine powder and the porous graphite, promotes the uniform mixing of the three, and initially forms a cross-linked structure. The pores of the porous graphite are filled with the biomass fine powder and the carbon source, and the hydrothermal process helps the uniform distribution of these components in the pores, providing a uniform precursor for subsequent sintering.

[0032] The inert atmosphere can specifically be nitrogen and / or argon. The sintering can specifically be carried out in a tube furnace, and the heating rate can be 4°C / min - 6°C / min, preferably 5°C / min. The temperature can be 300°C - 700°C, preferably 400°C, and the time can be 2 hours - 4 hours, preferably 2 hours.

[0033] During this process, the carbon source partially undergoes hydrolysis and dehydration reactions to form an amorphous carbon precursor, which initially fills the pores of the porous graphite or covers its surface.

[0034] The polysaccharides in the biomass fine powder can be partially decomposed into small molecule sugars, partially carbonized into carbonaceous materials or form volatile components, and the volatile components volatilize to form a microporous structure.

[0035] The porous graphite basically maintains its skeletal structure during the sintering process. However, at high temperatures, the active sites on its surface will undergo chemical bonding or physical adsorption with the amorphous carbon precursor generated by the decomposition of the carbon source and the carbonaceous material generated by the pyrolysis of the biomass fine powder, enabling the carbon source and the biomass fine powder to bind to the porous graphite.

[0036] The sintering process mainly densifies the material, stabilizes the microstructure inside the material, improves the mechanical strength and thermal stability of the material, and can also promote the graphitization of the amorphous carbon precursor. Sintering can also change the functional groups on the material surface and optimize its electrochemical properties.

[0037] Step 120: Mix the sintered product with a hydroxide for activation treatment, and then obtain the graphite composite porous material through cooling, washing, filtering, and drying processes.

[0038] Specifically, the hydroxide can include sodium hydroxide and / or potassium hydroxide. The ratio of the sintered product to the hydroxide can be 1:3 - 1:1, the activation temperature can be 700°C - 900°C, preferably 900°C, the time can be 2 hours - 4 hours, preferably 2 hours. The activation atmosphere can be nitrogen and / or argon.

[0039] As a preferred solution, the sintered product can also be crushed and classified using a ball mill before activation. During the activation process, the hydroxide reacts with the carbon material to open the already formed occluded pores, expand the original pores, or form new pore structures with the active sites. The carbon source completely undergoes thermal decomposition and carbonization reactions to generate amorphous carbon, which is deposited in the pores and on the surface of the porous graphite, thereby modifying and filling the porous graphite. All the biomass fine powder is pyrolyzed and converted into gas and escapes, and a carbonaceous material similar to coke is deposited and solidified in the pores of the porous graphite, thus achieving nesting in the porous graphite.

[0040] In summary, activation mainly etches the material through chemical reactions, thereby generating a large number of pores inside the material, increasing the specific surface area of the material, and providing more active sites.

[0041] Washing can be carried out using deionized water, filtration separates the solid and liquid, and drying is performed in a drying oven at no less than 60°C.

[0042] Step 130: Place the graphite composite porous material in a tube furnace for silicon deposition to obtain a silicon-carbon composite material.

[0043] Specifically, to ensure the uniformity of silicon deposition, first, the biomass / graphite porous composite material can be crushed and classified by a ball mill to obtain a powdery material. Second, under a protective atmosphere, it is heated to 480°C - 560°C, preferably 550°C, at a heating rate of 2°C / min - 4°C / min, preferably 3°C / min. Then, the silicon source gas and the protective gas are introduced into a tube furnace in a certain proportion and held for 5 - 7 hours, preferably 6 hours.

[0044] The silicon source gas can specifically include one or more of silane (SiH4), silicon tetrachloride (SiCl4), and dimethylsilane (CH3SiH3).

[0045] The protective atmosphere can be nitrogen and / or argon.

[0046] The ratio of the silane gas to the protective gas can be 1:2 - 2:1, preferably 1:1.

[0047] The nanosized silicon particles are deposited in the pores of the porous graphite. On the one hand, it can inhibit the volume expansion of silicon, and on the other hand, it can increase the specific capacity of the material, thereby enhancing the energy density of the battery.

[0048] The silicon content in the silicon-carbon composite material can specifically be 56wt% - 60wt%.

[0049] Step 140: Perform carbon coating on the silicon-carbon composite material to obtain a graphite-based silicon-carbon negative electrode material.

[0050] Specifically, the carbon source gas for carbon coating can specifically be methane, acetylene, propylene, etc. The temperature can be 500°C - 600°C, preferably 500°C, and the time can be 1.5 hours - 2.5 hours, preferably 2 hours.

[0051] Carbon coating can provide a continuous electron transport path, reduce the internal resistance of the electrode, thereby increasing the electronic conductivity. It can also further inhibit the expansion of silicon particles, prevent the electrode material from breaking due to expansion, and reduce the direct contact between the electrolyte and silicon, reducing side reactions and lithium loss.

[0052] In summary, for the preparation method of the graphite-based silicon-carbon anode material provided by the embodiments of the present invention, the biomass fine powder is nested (filled) in the pores of the porous graphite. On the one hand, it can reasonably fill the pores of the porous graphite, reduce the ineffective space in the pores, improve the overall density and structural stability of the material, solve the problem of poor fast charging performance of the existing porous graphite matrix silicon-carbon material, overcome the defects of low tap density, poor fast charging performance and poor pressure resistance of the existing silicon-carbon composite material, and construct a silicon-carbon composite material that takes into account high tap density and high pressure resistance; on the other hand, the presence of the biomass fine powder improves the ion transport environment in the pores, makes the lithium ions transport more smoothly in the pores, is conducive to the ion exchange between the silicon particles and the electrolyte, and improves the fast charging performance of the battery. After the carbon source is activated to form pores, it forms a composite structure with the graphite matrix, further optimizing the pore structure of the material, increasing the specific surface area of the material, providing more active sites, and being conducive to the adsorption and insertion of lithium ions. At the same time, the formed composite structure enables the silicon particles to be better dispersed in the composite material, avoids the agglomeration of the silicon particles, increases the contact area between the silicon particles and the electrolyte, and enhances the electrochemical activity of the silicon particles. The synergistic effect of the carbon source and the biomass fine powder improves the utilization rate and electrochemical performance of the silicon particles; the carbon layer coating process is adopted to further improve the structural stability and cycle stability of the material; by increasing the silicon content, a high specific capacity is achieved, meeting the requirements of high energy density.

[0053] The graphite-based silicon-carbon anode material provided by the embodiments of the present invention can be applied to lithium-ion batteries.

[0054] To better understand the technical solutions provided by the present invention, the following uses multiple specific examples to separately illustrate the specific process of preparing the graphite-based silicon-carbon anode material by using the method provided by the above embodiments of the present invention, and the electrochemical characteristics of the prepared graphite-based silicon-carbon anode material.

[0055] Example 1

[0056] Step 1, glucose, coconut shell (D50 = 300 nm) and porous graphite (D50 = 20 μm, pore diameter of 500 nm, porosity of 15%, specific surface area of 260 m 2 / g) are mixed according to a mass ratio of 50:20:30, and then hydrothermally heat-treated at 150 °C for 2 hours.

[0057] Step 2, under a nitrogen atmosphere, the product obtained in Step 1 is placed in a tube furnace, and then heated to 400 °C at a heating rate of 5 °C / min and held for 2 hours for sintering to obtain a sintered product.

[0058] Step 3: Mix the sintered product with sodium hydroxide in a mass ratio of 1:1, place the mixture in a tubular furnace, and under a nitrogen atmosphere, activate it at 900 °C for 2 hours. After cooling, wash it three times with deionized water, filter, and perform a drying treatment to obtain a graphite composite porous material.

[0059] Step 4: Crush and classify the graphite composite porous material to obtain a powdery graphite composite porous material. Then place it in a tubular furnace, and under a nitrogen atmosphere, heat it to 550 °C at a heating rate of 3 °C / min. Then, introduce a mixed gas of silane and nitrogen with a gas flow ratio of 1:1 and keep it warm for 6 hours to uniformly deposit silicon in the graphite composite porous material to obtain a silicon-carbon composite material.

[0060] Step 5: Under a nitrogen atmosphere, introduce acetylene and perform carbon coating at 500 °C for 2 hours to obtain a graphite-based silicon-carbon negative electrode material.

[0061] After that, use the prepared graphite-based silicon-carbon negative electrode material to prepare a pole piece, specifically as follows:

[0062] Add the graphite-based silicon-carbon negative electrode material, conductive agent carbon black, and binder to deionized water in a mass ratio of 8:1:1 and mix evenly. Among them, the binder is sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of the two is 1:0.8. Use a pulper to prepare a slurry, coat it on a copper foil with a coating thickness of 220 μm, place it in a blast drying oven and dry it at 55 °C for 2 hours, and cut it into a circle with a diameter of 14 mm, and vacuum dry it in a vacuum drying oven at 100 °C for 8 hours to obtain a pole piece.

[0063] First, assemble a button-type half-cell using the prepared pole piece and conduct tests: First, assemble the above-mentioned pole piece into a button-type half-cell in an argon-filled glove box. Among them, the electrolyte of the button-type half-cell is 1 mol / L lithium hexafluorophosphate LiPF6, and the solvent of the electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate. Among them, the volume ratio of EC, DMC, and DEC is 1:1:1. The counter electrode is metallic lithium. The separator is a polyethylene separator. Second, at room temperature, use a charge-discharge instrument to conduct a constant current charge-discharge mode test. The discharge cut-off voltage is 0.005 V, the charge cut-off voltage is 2 V, and test the first charge specific capacity, the first discharge specific capacity, the first cycle Coulomb efficiency, and the capacity retention rate after 200 cycles at a current density of 0.1 C. Then test the capacity retention rate after 50 cycles at a current density of 4 C. During this test process, the compaction density of the pole piece, that is, the normal compaction density, is 0.9 g / cm 3 。

[0064] Second, perform a withstand voltage test on the electrode sheet: Press the electrode sheet using a roll press. Specifically, use a pressure device to apply pressure at 40 Mpa for 5 minutes. After assembling the coin-type half-cell with the electrode sheet after the pressure treatment according to the above method, perform a constant current charge-discharge mode test. The discharge cut-off voltage is 0.005 V, and the charge cut-off voltage is 2 V. Test the initial charge specific capacity, initial discharge specific capacity, and first-cycle Coulomb efficiency at a current density of 0.1 C. During this test, the compaction density of the electrode sheet, that is, the post-compaction density, is 1.2 g / cm 3 。

[0065] Example 2

[0066] Step 1, mix glucose, coconut shell (D50 = 300 nm), and porous graphite (D50 = 20 μm, pore size of 500 nm, porosity of 15%, specific surface area of 260 m 2 / g) in a mass ratio of 50:10:50, and then perform hydrothermal heating treatment at 150 °C for 2 hours.

[0067] Steps 2-5 and the test process are the same as in Example 1.

[0068] Example 3

[0069] Step 1, mix glucose, coconut shell (D50 = 300 nm), and porous graphite (D50 = 20 μm, pore size of 500 nm, porosity of 15%, specific surface area of 260 m 2 / g) in a mass ratio of 50:20:50, and then perform hydrothermal heating treatment at 150 °C for 2 hours.

[0070] Steps 2-5 and the test process are the same as in Example 1.

[0071] Example 4

[0072] Step 1, mix glucose, coconut shell (D50 = 200 nm), and porous graphite (D50 = 20 μm, pore size of 500 nm, porosity of 15%, specific surface area of 260 m 2 / g) in a mass ratio of 50:20:30, and then perform hydrothermal heating treatment at 150 °C for 2 hours.

[0073] Steps 2-5 and the test process are the same as in Example 1.

[0074] Example 5

[0075] Step 1, mix glucose, coconut shell (D50 = 400 nm), and porous graphite (D50 = 20 μm, pore size of 500 nm, porosity of 15%, specific surface area of 260 m 2 / g) After mixing in a mass ratio of 50:20:30, hydrothermal heat treatment is carried out at 150 °C for 2 hours.

[0076] Steps 2-5 and the testing process are the same as in Example 1.

[0077] Example 6

[0078] Step 1, Glucose, coconut shell (D50 = 300 nm) and porous graphite (D50 = 10 μm, pore diameter 400 nm, porosity 20%, specific surface area 120 m 2 / g) After mixing in a mass ratio of 50:20:30, hydrothermal heat treatment is carried out at 150 °C for 2 hours.

[0079] Steps 2-5 and the testing process are the same as in Example 1.

[0080] Example 7

[0081] Step 1, Sucrose, rice husk (D50 = 100 nm) and porous graphite (D50 = 3 μm, pore diameter 200 nm, porosity 10%, specific surface area 100 m 2 / g) After mixing in a mass ratio of 30:10:60, hydrothermal heat treatment is carried out at 145 °C for 2.5 hours.

[0082] Step 2, Under an argon atmosphere, the product obtained in Step 1 is placed in a tube furnace, and then heated to 300 °C at a heating rate of 4 °C / min and kept at this temperature for 4 hours for sintering to obtain a sintered product.

[0083] Step 3, The sintered product and potassium hydroxide are mixed in a mass ratio of 1:2 and then placed in a tube furnace. Under an argon atmosphere, activation treatment is carried out at 700 °C for 4 hours. After cooling, it is washed three times with deionized water, filtered, and dried to obtain a graphite composite porous material.

[0084] Step 4, The graphite composite porous material is crushed and classified to obtain a powdery graphite composite porous material. Then it is placed in a tube furnace. Under an argon atmosphere, it is heated to 480 °C at a heating rate of 2 °C / min, and then a mixed gas of silicon tetrachloride and argon is introduced in a gas flow ratio of 1:2 and kept at this temperature for 7 hours to uniformly deposit silicon in the graphite composite porous material to obtain a silicon-carbon composite material.

[0085] Step 5, Under an argon atmosphere, methane is introduced and carbon coating is carried out at 550 °C for 2 hours to obtain a graphite-based silicon-carbon negative electrode material.

[0086] The specific testing process is the same as in Example 1.

[0087] Example 8

[0088] Step 1: After mixing fructose, corn cob (D50 = 200 nm), and porous graphite (D50 = 35 μm, pore size of 300 nm, porosity of 5%, specific surface area of 200 m 2 / g) according to a mass ratio of 40:15:30, perform hydrothermal heating treatment at 155 °C for 1.5 hours.

[0089] Step 2: Under a nitrogen atmosphere, place the product obtained in Step 1 into a tube furnace, then heat it up to 700 °C at a heating rate of 6 °C / min, and hold for 2 hours for sintering to obtain a sintered product.

[0090] Step 3: After mixing the sintered product and sodium hydroxide according to a mass ratio of 1:2.5, place them into a tube furnace. Under a nitrogen atmosphere, perform activation treatment at 800 °C for 3 hours. After cooling, wash three times with deionized water, filter, and perform drying treatment to obtain a graphite composite porous material.

[0091] Step 4: Crush and classify the graphite composite porous material to obtain a powdered graphite composite porous material. Then place it into a tube furnace. Under a nitrogen atmosphere, heat it up to 560 °C at a heating rate of 4 °C / min, and then introduce a mixed gas of silane and nitrogen with a gas flow ratio of 1:2 and hold for 5 hours to uniformly deposit silicon in the graphite composite porous material to obtain a silicon-carbon composite material.

[0092] Step 5: Under a nitrogen atmosphere, introduce propylene and perform carbon coating at 600 °C for 1.5 hours to obtain a graphite-based silicon-carbon anode material.

[0093] The specific testing process is the same as that in Example 1.

[0094] Example 9

[0095] Step 1: After mixing citric acid, wood chips (D50 = 300 nm), and porous graphite (D50 = 20 μm, pore size of 500 nm, porosity of 20%, specific surface area of 10 m 2 / g) according to a mass ratio of 35:20:40, perform hydrothermal heating treatment at 146 °C for 2 hours.

[0096] Step 2: Under an argon atmosphere, place the product obtained in Step 1 into a tube furnace, then heat it up to 500 °C at a heating rate of 5 °C / min, and hold for 4 hours for sintering to obtain a sintered product.

[0097] Step 3: After mixing the sintered product and potassium hydroxide according to a mass ratio of 1:3, place them into a tube furnace. Under an argon atmosphere, perform activation treatment at 850 °C for 3 hours. After cooling, wash three times with deionized water, filter, and perform drying treatment to obtain a graphite composite porous material.

[0098] Step 4: Crush and classify the graphite composite porous material to obtain a powdery graphite composite porous material, and then place it in a tube furnace. Under an argon atmosphere, heat it at a heating rate of 3 °C / min to 500 °C, and then introduce a mixed gas of dimethylsilane and argon at a gas flow ratio of 2:1 and keep it warm for 6 hours to uniformly deposit silicon in the graphite composite porous material, obtaining a silicon-carbon composite material.

[0099] Step 5: Under an argon atmosphere, introduce ethane and perform carbon coating at 550 °C for 2.5 hours to obtain a graphite-based silicon-carbon anode material.

[0100] The specific testing process is the same as that in Example 1.

[0101] Example 10

[0102] Step 1: Mix polyvinylpyrrolidone, fruit cores (D50 = 400 nm), and porous graphite (D50 = 25 μm, pore size of 1000 nm, porosity of 18%, specific surface area of 300 m 2 / g) according to a mass ratio of 45:10:50, and then perform hydrothermal heating treatment at 150 °C for 2.5 hours.

[0103] Step 2: Under an argon atmosphere, place the product obtained in Step 1 in a tube furnace, and then heat it at a heating rate of 5 °C / min to 600 °C and keep it warm for 2 hours for sintering to obtain a sintered product.

[0104] Step 3: Mix the sintered product and sodium hydroxide according to a mass ratio of 1:2, place them in a tube furnace, and under an argon atmosphere, perform activation treatment at 750 °C for 3.5 hours. After cooling, wash it three times with deionized water, filter, and perform drying treatment to obtain a graphite composite porous material.

[0105] Step 4: Crush and classify the graphite composite porous material to obtain a powdery graphite composite porous material, and then place it in a tube furnace. Under an argon atmosphere, heat it at a heating rate of 4 °C / min to 530 °C, and then introduce a mixed gas of silicon tetrachloride and argon at a gas flow ratio of 2:1 and keep it warm for 6.5 hours to uniformly deposit silicon in the graphite composite porous material, obtaining a silicon-carbon composite material.

[0106] Step 5: Under an argon atmosphere, introduce methane and perform carbon coating at 560 °C for 2 hours to obtain a graphite-based silicon-carbon anode material.

[0107] The specific testing process is the same as that in Example 1.

[0108] Comparative Example 1

[0109] Step 1: Place porous graphite (D50 = 20 μm, pore size 500 nm, porosity 15%, specific surface area 260 m 2 / g) in a tubular furnace. Under a nitrogen atmosphere, heat it at a heating rate of 3 °C / min to 550 °C, and then introduce a mixed gas of silane and nitrogen at a gas flow ratio of 1:1 and hold for 6 hours to uniformly deposit silicon in the porous graphite, obtaining a silicon-carbon composite material.

[0110] Step 2: Under a nitrogen atmosphere, introduce acetylene and perform carbon coating at 500 °C for 2 hours to obtain a graphite-based silicon-carbon anode material.

[0111] The testing process is the same as that in Example 1.

[0112] Comparative Example 2

[0113] Step 1: Mix coconut shell (D50 = 300 nm) and sodium hydroxide in a mass ratio of 1:1 and place them in a tubular furnace. Under a nitrogen atmosphere, perform activation treatment at 900 °C for 2 hours. After cooling, wash three times with deionized water, filter, and perform drying treatment to obtain a graphite composite porous material.

[0114] Step 2: Crush and classify the graphite composite porous material to obtain a powdered graphite composite porous material, and then place it in a tubular furnace. Under a nitrogen atmosphere, heat it at a heating rate of 3 °C / min to 550 °C, and then introduce a mixed gas of silane and nitrogen at a gas flow ratio of 1:1 and hold for 6 hours to uniformly deposit silicon in the graphite composite porous material, obtaining a silicon-carbon composite material.

[0115] Step 3: Under a nitrogen atmosphere, introduce acetylene and perform carbon coating at 500 °C for 2 hours to obtain a graphite-based silicon-carbon anode material.

[0116] The testing process is the same as that in Example 1.

[0117] Table 1 summarizes the test results of Examples 1-10 and Comparative Examples 1-2 of the present invention.

[0118]

[0119]

[0120] Table 1

[0121] As can be seen from the data in Table 1, for the graphite-based silicon-carbon anode materials prepared in Examples 1-10 of the present invention, at different compaction densities, the first-cycle Coulombic efficiency loss is within 1%, and the capacity loss is within 100 mAhg -1Within. While for the graphite-based silicon-carbon anode materials prepared in Comparative Examples 1 and 2, the Coulombic efficiency loss in the first cycle is above 3% and the capacity loss is above 200 mAhg -1 Above. The capacity retention rates of the graphite-based silicon-carbon anode materials prepared in Examples 1-10 of the present invention after 200 cycles and 50 cycles at a current density of 4C are also much higher than those of Comparative Examples 1 and 2. This shows that the graphite-based silicon-carbon anode materials of the present invention have good pressure resistance at high tap densities, and thus have excellent cycle retention rates and rate performance.

[0122] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a graphite-based silicon-carbon anode material, characterized in that, The preparation method includes: Mixing a carbon source, biomass fine powder, and porous graphite according to a certain mass ratio, followed by hydrothermal heat treatment, and then sintering under an inert atmosphere to obtain a sintered product; Mixing the sintered product with a hydroxide for activation treatment, and then cooling, washing, filtering, and drying to obtain a graphite composite porous material; Placing the graphite composite porous material in a tube furnace for silicon deposition to obtain a silicon-carbon composite material; Performing carbon coating on the silicon-carbon composite material to obtain a graphite-based silicon-carbon negative electrode material.

2. The preparation method according to claim 1, wherein The carbon source includes one or more of glucose, sucrose, fructose, citric acid, polyvinylpyrrolidone, ascorbic acid, and chitosan; the raw materials of the biomass fine powder include one or more of coconut shell, straw, rice husk, fruit shell, cotton fiber, fruit pit, wheat straw, corn cob, wood chips, bamboo, and water bamboo leaves; the certain mass ratio is [30-50]:[10-20]:[30-60].

3. The preparation method according to claim 1, characterized in that, The conditions of the hydrothermal heat treatment are specifically: temperature 145°C - 155°C, time 1.5 hours - 2.5 hours.

4. The preparation method according to claim 1, characterized in that, The sintering temperature is 300°C - 700°C, and the time is 2 hours - 4 hours.

5. The preparation method according to claim 1, wherein The ratio of the sintered product to the hydroxide is 1:3 - 1:1, the activation treatment temperature is 700°C - 900°C, and the time is 2 hours - 4 hours.

6. The preparation method according to claim 1, wherein The temperature of the silicon deposition is 480°C - 560°C, and the time is 5 hours - 7 hours.

7. The preparation method according to claim 1, characterized in that, The temperature of the carbon coating is 500°C - 600°C, and the time is 1.5 hours - 2.5 hours.

8. A graphite-based silicon-carbon anode material, characterized in that, The graphite-based silicon-carbon negative electrode material is prepared by the preparation method according to any one of claims 1 - 7 above.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes the graphite-based silicon-carbon negative electrode material according to claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet according to claim 9.

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