Silicon-carbon composite material, method for preparing the same, electrode, and battery

Abstract

This application belongs to the field of battery technology, and particularly relates to silicon-carbon composite materials and their preparation methods, electrodes, and batteries. The method includes: mixing asphalt with potassium hydroxide and dopants uniformly, heating to a first preset temperature, passing a crosslinking agent mixed gas at a first preset flow rate for first activation, cooling to obtain asphalt-based porous carbon; adding the asphalt-based porous carbon to an aldehyde compound solution, then adding a phenolic compound and a catalyst and mixing uniformly, performing a hydrothermal reaction, filtering, and performing a second activation to obtain a hard carbon-coated soft carbon porous carbon composite material; immersing the porous carbon composite material in a liquid silane solution and reacting under closed negative pressure to obtain an intermediate material; heating the asphalt to a molten state, then adding the intermediate material and an organoniobium compound and stirring uniformly to perform carbonization to obtain a silicon-carbon composite material; possessing low expansion, high pore volume, low impedance, and high compaction density, thus improving the electrochemical performance of the battery.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and in particular relates to silicon-carbon composite materials and their preparation methods, electrodes, and batteries. Background Technology

[0002] Current silicon-carbon composite materials are generally made from single raw materials (such as biomass, resin-based materials, and petroleum coke), with simple structures and corresponding disadvantages, which cannot meet the high-performance requirements of the market. For example, biomass porous carbon has low cost and low impedance, but low compaction density; resin-based porous carbon has strong compressive strength and low expansion, but high impedance; petroleum coke has low impedance and low cost, but low compaction density.

[0003] Existing silicon-carbon composite materials cannot simultaneously possess low expansion, high pore volume, low impedance, and high compaction density. Summary of the Invention

[0004] This application provides silicon-carbon composite materials and their preparation methods, electrodes, and batteries, aiming to solve to some extent the problem that silicon-carbon composite materials cannot simultaneously possess low expansion, high pore volume, low impedance, and high compaction density.

[0005] In a first aspect, this application provides a method for preparing silicon-carbon composite materials, including:

[0006] S1, mix asphalt with potassium hydroxide and dopants evenly, heat to a first preset temperature, pass crosslinking agent mixed gas through at a first preset flow rate for first activation, cool, and obtain asphalt-based porous carbon;

[0007] S2, add pitch-based porous carbon to an aldehyde compound solution, then add phenolic compounds and catalysts and mix evenly, carry out hydrothermal reaction, filter, and the resulting material undergoes a second activation to obtain a hard carbon-coated soft carbon porous carbon composite material.

[0008] S3, the hard carbon-coated soft carbon porous carbon composite material is immersed in a liquid silane solution, and then reacted under closed conditions and negative pressure to obtain an intermediate material;

[0009] S4. The asphalt is heated to a molten state, then intermediate materials and organoniobium compounds are added and stirred evenly to carbonize, thus obtaining a silicon-carbon composite material.

[0010] In one embodiment, in S1:

[0011] The ratio of the amount of asphalt, potassium hydroxide, dopant, and crosslinking agent mixed gas is 100g:(100~500)g:(1~5)g:(100~300)mL;

[0012] The volume ratio of crosslinking agent gas to carbon dioxide is (1~5):10;

[0013] The first preset temperature is 800℃~1000℃, the first preset flow rate is 10mL / min~50mL / min, and the first activation reaction time is 30min~300min;

[0014] The dopant is any one or a combination of tributyl phosphate, phytic acid, ammonium polyphosphate, pyrazole phosphorus, and parathion;

[0015] The crosslinking agent is any one or a combination of terephthalic acid, phthalic acid, isophthalic acid, pyromellitic dianhydride, and pyromellitic tricarboxylic acid.

[0016] In one embodiment, in S2:

[0017] The mass ratio of pitch-based porous carbon: aldehyde compound: phenol compound: catalyst is 100:(100~200):(100~200):(10~30);

[0018] The mass concentration of aldehyde compounds in the solution is 35wt%~40wt%, and the mass concentration of phenolic compounds is 10wt%~20wt%.

[0019] The hydrothermal reaction temperature is 100℃~200℃, the pressure is 1Mpa~5Mpa, and the reaction time is 1h~6h;

[0020] The second activation temperature is 800℃~1000℃, the water vapor flow rate is 100mL / min~500mL / min, and the activation time is 30 minutes~300 minutes.

[0021] In one embodiment, in S3:

[0022] The mass ratio of hard carbon-coated soft carbon porous carbon composite material to liquid silane is 100:(50~100);

[0023] The temperature of the closed negative pressure reaction is 500℃~700℃, the negative pressure is 0.01Mpa~0.05Mpa, and the reaction time is 2h~12h.

[0024] In one embodiment, in S4:

[0025] The mass ratio of intermediate material, bitumen, and organoniobium compound is 100:(5~10):(1~5);

[0026] The melting temperature is 200℃~300℃;

[0027] The carbonization heating rate is 1℃ / min to 10℃ / min, and the temperature is raised to 750℃ to 900℃ for 1h to 3h.

[0028] In one embodiment, the aldehyde compound is any one or a combination of benzaldehyde, phenylacetaldehyde, 3-phenylpropanal, 2,5-dihydroxybenzaldehyde, phenylpropenal, and p-methylbenzaldehyde;

[0029] The phenolic compounds are any one or a combination of p-aminophenol, 6-amino-p-phenol, 4-amino-3-methylphenol, 3-aminophenol, p-acetaminophenol, and 3-ethylamino-4-methylphenol;

[0030] The catalyst is any one or a combination of bismuth neodecanoate, bismuth isooctanoate, bismuth laurate, bismuth neodecanoate, and bismuth naphthenate;

[0031] The liquid silane is any one or a combination of dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, and dichlorovinylmethylsilane;

[0032] Asphalt is any one or a combination of coal tar pitch, petroleum asphalt, natural asphalt and mesophase asphalt, with a softening point ≤150℃.

[0033] The organoniobium compound is any one or a combination of niobium ethanol, niobium n-propoxide, niobium isopropoxide, and niobium pentanol.

[0034] In one embodiment, the silicon-carbon composite material has a powder resistivity ≤2.01 Ω·cm and a specific surface area of ​​1.5 m². 2 / g~2.5m 2 / g, gas production ≤0.029ml / mg.

[0035] Secondly, this application provides a silicon-carbon composite material prepared by the method for preparing silicon-carbon composite materials described in any one of the first aspects.

[0036] Thirdly, this application provides an electrode comprising a silicon-carbon composite material prepared by any of the methods for preparing silicon-carbon composite materials described in the first aspect or a silicon-carbon composite material as described in the second aspect.

[0037] Fourthly, this application provides a battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the electrode as described in the third aspect.

[0038] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0039] The advantages of this application compared to the prior art are:

[0040] The method for preparing silicon-carbon composite materials provided in this application includes the following steps: S1, mixing asphalt with potassium hydroxide and a dopant until uniform, heating to a first preset temperature, and then performing a first activation by introducing a crosslinking agent mixed gas at a first preset flow rate, followed by cooling to obtain asphalt-based porous carbon; S2, adding the asphalt-based porous carbon to an aldehyde compound solution, then adding a phenolic compound and a catalyst and mixing them uniformly, performing a hydrothermal reaction, filtering, and performing a second activation to obtain a hard carbon-coated soft carbon porous carbon composite material; S3, immersing the hard carbon-coated soft carbon porous carbon composite material in a liquid silane solution, and then reacting it under closed negative pressure to obtain an intermediate material; S4, heating the asphalt to a molten state, then adding the intermediate material and an organoniobium compound and stirring until uniform, and performing carbonization to obtain the silicon-carbon composite material. Compared with the prior art, this application has the following beneficial effects:

[0041] 1. By adding potassium hydroxide as an activator to the pitch-based porous carbon precursor for etching and pore creation, and then cross-linking with a cross-linking agent mixed with gas to increase the number of pores and increase the pore volume, and by activating to form hierarchical pores, the volume expansion buffer of silicon is reduced and the ion transport rate is improved.

[0042] 2. Phenolic resin-based porous carbon is coated on the surface of pitch-based porous carbon. Pitch-based porous carbon is soft carbon with high compaction density, good conductivity, low impedance, and high initial charge-discharge efficiency. Phenolic resin carbon is hard carbon with stable structure and strong compressive strength. It can inhibit the agglomeration and volume expansion of silicon particles and improve the ion storage capacity. It combines the advantages of soft carbon and hard carbon, thereby improving the comprehensive performance of silicon-carbon composite materials.

[0043] 3. Molten asphalt (carbon source) coats intermediate materials and organoniobium compounds, forming niobium carbide or niobium oxide after carbonization. Due to the large interlayer spacing, it is doped into the asphalt carbon layer, which improves conductivity, interfacial stability and structural stability, thereby increasing the lithium ion insertion and extraction rate during charging and discharging and improving the rate performance of the battery. At the same time, liquid silane coats phenolic resin-based porous carbon and asphalt-based porous carbon in the outer layer through liquid phase coating, which further improves the conductivity of silicon-carbon composite materials after carbonization.

[0044] 4. Compared with inorganic catalysts, organic bismuth catalysts have advantages such as high catalytic efficiency, low impurity content, and low catalytic temperature.

[0045] 5. The use of liquid-phase silane deposition in porous carbon has advantages such as high safety, good wettability, nanoscale dispersion of silicon in the pores, reduced risk of stress concentration, improved uniformity of nano-silicon in porous carbon, low cost, and simple process.

[0046] The silicon-carbon composite material of this application improves the compressive strength, power performance and reduces expansion through the synergistic effect of etching activation pore formation, organic niobium doping, hard carbon coating of soft carbon, liquid silane nanoscale dispersion deposition coating, and pitch carbon source re-carbonization coating, thereby improving the cycle performance and rate performance of the battery. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic flowchart of a method for preparing a silicon-carbon composite material according to an embodiment of this application;

[0049] Figure 2 This is a SEM image of the hard carbon-coated soft carbon porous carbon composite material prepared in Example 1;

[0050] Figure 3 This is a schematic diagram of the SEM test of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0051] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0052] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0053] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0054] The terms "first" and "second" are used only to describe the purpose and to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the provisions of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0055] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0056] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0057] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0058] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0059] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0060] Existing silicon-carbon composite materials cannot simultaneously possess low expansion, high pore volume, low impedance, and high compaction density.

[0061] To address the aforementioned problems to some extent, the first aspect of this application, such as Figure 1 As shown, this application provides a method for preparing silicon-carbon composite materials, including:

[0062] S1, mix asphalt with potassium hydroxide and dopants evenly, heat to a first preset temperature, pass crosslinking agent mixed gas through at a first preset flow rate for first activation, cool, and obtain asphalt-based porous carbon.

[0063] S2, add pitch-based porous carbon to an aldehyde compound solution, then add phenolic compounds and catalysts and mix evenly, carry out a hydrothermal reaction, filter, and the resulting material undergoes a second activation to obtain a hard carbon-coated soft carbon porous carbon composite material.

[0064] S3, a hard carbon-coated soft carbon porous carbon composite material is immersed in a liquid silane solution, and then reacted under closed conditions and negative pressure to obtain an intermediate material.

[0065] S4. The asphalt is heated to a molten state, then intermediate materials and organoniobium compounds are added and stirred evenly to carbonize, thus obtaining a silicon-carbon composite material.

[0066] Compared with existing technologies, in S1 of this application, potassium hydroxide is a strong alkali activator. At high temperature, potassium hydroxide reacts with pitch to etch and create pores, forming pitch-based porous carbon with a high specific surface area. Dopant introduces heteroatoms, enhancing the surface polarity or catalytic effect of the pitch-based porous carbon. The crosslinking agent mixture crosslinks with pitch molecules at high temperature, improving the stability of the carbon skeleton, increasing the number of pores, and increasing pore volume. Further activation forms hierarchical pores, reducing the volume expansion buffer of silicon and improving ion transport speed. In S2, aldehydes and phenols undergo a condensation reaction under hydrothermal conditions to generate phenolic resin, which coats the surface of the pitch-based porous carbon with phenolic resin-based porous carbon. After carbonization, a hard carbon-coated soft carbon structure is formed. The pitch-based porous carbon is soft carbon with high compaction density, good conductivity, low impedance, and high initial charge / discharge efficiency. The phenolic resin carbon, on the other hand, is hard carbon with defects and micropores, exhibiting structural stability and strong compressive strength, inhibiting silicon particle agglomeration and volume expansion, thus improving lithium-ion storage capacity. It combines the advantages of both soft and hard carbon, thereby improving… The overall performance of silicon-carbon composite materials is improved; S3, using liquid-phase silane deposition in porous carbon has high safety and good wettability. Under negative pressure, it is drawn into the interior of porous carbon and then generates silicon or silicon carbide deposited in the pores, realizing the nanoscale dispersion of silicon in the pores, reducing the risk of stress concentration, and improving the uniformity of nano-silicon in porous carbon. At the same time, the liquid silane on the outer layer coats phenolic resin-based porous carbon and pitch-based porous carbon in the liquid phase, which further improves the conductivity of silicon-carbon composite materials after carbonization, and has the advantages of low cost and simple process; S4, molten pitch (carbon source) coats intermediate materials and organoniobium compounds. After carbonization, the organoniobium compounds form niobium carbide or niobium oxide, which is doped in the pitch carbon layer. Due to the large interlayer spacing of the pitch carbon layer, the conductivity, interface stability and structural stability are improved, thereby improving the lithium ion insertion and extraction rate during charging and discharging, and improving the rate performance of the battery; and compared with inorganic catalysts, the use of organic bismuth catalysts has the advantages of high catalytic efficiency, low impurity content and low catalytic temperature. The silicon-carbon composite material of this application improves the compressive strength, power performance and reduces expansion through the synergistic effect of etching activation pore formation, organic niobium doping, hard carbon coating of soft carbon, liquid silane nanoscale dispersion deposition coating, and pitch carbon source re-carbonization coating, thereby improving the cycle performance and rate performance of the battery.

[0067] In one embodiment, in S1, the ratio of the amount of asphalt, potassium hydroxide, dopant, and crosslinking agent mixed gas is 100g:(100~500)g:(1~5)g:(100~300)mL; the volume ratio of crosslinking agent gas and carbon dioxide is (1~5):10; the first preset temperature is 800℃~1000℃, the first preset flow rate is 10mL / min~50mL / min, and the first activation reaction time is 30 minutes~300 minutes; the dopant is any one or a combination of tributyl phosphate, phytic acid, ammonium polyphosphate, pyrazole phosphorus, and parathion; the crosslinking agent is any one or a combination of terephthalic acid, phthalic acid, isophthalic acid, pyromellitic dianhydride, and pyromellitic tricarboxylic acid. In this embodiment, the ratio of asphalt, potassium hydroxide, dopant, and crosslinking agent mixed gas balances the amount of each raw material; phosphorus-containing dopant can further enhance surface polarity, and polycarboxylic acid can improve the crosslinking effect with asphalt molecules; the first preset temperature, the first preset flow rate, and the first activation reaction time can make the chemical activation, gas phase precipitation, and crosslinking reaction more complete, thereby improving the comprehensive performance of asphalt-based porous carbon.

[0068] In one embodiment, in step S2, the mass ratio of asphalt-based porous carbon: aldehyde compound: phenol compound: catalyst is 100:(100~200):(100~200):(10~30); the mass concentration of the aldehyde compound solution is 35wt%~40wt%, and the mass concentration of the phenol compound is 10wt%~20wt%; the hydrothermal reaction temperature is 100℃~200℃, the pressure is 1MPa~5MPa, and the reaction time is 1h~6h; the second activation temperature is 800℃~1000℃, the steam flow rate is 100mL / min~500mL / min, and the activation time is 30min~300min. In this embodiment, the hydrothermal reaction conditions allow for better condensation polymerization, and the second activation conditions further regulate the porosity.

[0069] In one embodiment, in step S3, the mass ratio of hard carbon-coated soft carbon porous carbon composite material to liquid silane is 100:(50~100); the temperature of the closed negative pressure reaction is 500℃~700℃, the negative pressure is 0.01Mpa~0.05Mpa, and the reaction time is 2h~12h. In this embodiment, the closed negative pressure reaction conditions allow the liquid silane to be distributed more evenly and to decompose and deposit better in the pores.

[0070] In one embodiment, in step S4, the mass ratio of the intermediate material, asphalt, and organoniobium compound is 100:(5~10):(1~5); the melting temperature is 200℃~300℃; and the carbonization heating rate is 1℃ / min~10℃ / min, heating to 750℃~900℃ for 1h~3h. In this embodiment, carbonizing the mixture of intermediate material, asphalt, and organoniobium compound allows for a more uniform niobium doping distribution, improving conductivity and interface stability.

[0071] In one embodiment, the aldehyde compound is any one or a combination of benzaldehyde, phenylacetaldehyde, 3-phenylpropanal, 2,5-dihydroxybenzaldehyde, phenylpropenal, and p-methylbenzaldehyde;

[0072] The phenolic compounds are any one or a combination of p-aminophenol, 6-amino-p-phenol, 4-amino-3-methylphenol, 3-aminophenol, p-acetaminophenol, and 3-ethylamino-4-methylphenol;

[0073] The catalyst is any one or a combination of bismuth neodecanoate, bismuth isooctanoate, bismuth laurate, bismuth neodecanoate, and bismuth naphthenate;

[0074] The liquid silane is any one or a combination of dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, and dichlorovinylmethylsilane;

[0075] Asphalt is any one or a combination of coal tar pitch, petroleum asphalt, natural asphalt and mesophase asphalt, with a softening point ≤150℃.

[0076] The organoniobium compound is any one or a combination of niobium ethanol, niobium n-propoxide, niobium isopropoxide, and niobium pentanol.

[0077] In one embodiment, the silicon-carbon composite material has a powder resistivity ≤ 2.01 Ω·cm and a specific surface area of ​​1.5 m². 2 / g~2.5m 2 / g, gas production ≤0.029ml / mg.

[0078] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0079] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0080] Example 1

[0081] Methods for preparing silicon-carbon composite materials include:

[0082] S1. Mix 100g of petroleum asphalt with 300g of potassium hydroxide and 3g of tributyl phosphate evenly, and heat to 900℃. Activate for 150 minutes by passing a mixture of terephthalic acid gas (volume ratio: terephthalic acid: carbon dioxide = 3:10) at a flow rate of 3mL / min. Cool to obtain asphalt-based porous carbon.

[0083] S2, 100g of pitch-based porous carbon was added to 150g of 35wt% benzaldehyde solution, along with 150g of 15wt% p-aminophenol solution and 20g of bismuth neodecanoate. The mixture was thoroughly mixed and transferred to a high-pressure reactor. The mixture was subjected to a hydrothermal reaction at 150℃ and 3MPa for 3 hours. After filtration, the resulting material was activated at 900℃ by introducing steam at a flow rate of 300mL / min for 150 minutes to obtain a porous carbon composite material with hard carbon coated with soft carbon.

[0084] S3, 100g of hard carbon coated soft carbon porous carbon composite material was immersed in 80g of dimethylchlorosilane solution, and then reacted for 6h under sealed conditions at a temperature of 600℃ and a negative pressure of 0.03Mpa to obtain intermediate material.

[0085] S4. 8g of coal tar pitch was heated to 250℃ to form a molten state. Then, 100g of intermediate material and 3g of niobium ethanol were added and stirred evenly. The temperature was increased to 850℃ at a rate of 5℃ / min and carbonized for 2 hours to obtain silicon-carbon composite material.

[0086] Example 2

[0087] Methods for preparing silicon-carbon composite materials include:

[0088] S1. Mix 100g of coal tar pitch with 100g of potassium hydroxide and 1g of ammonium polyphosphate evenly, and heat to 800℃. Activate for 300 minutes by passing a phthalic acid mixed gas (volume ratio: phthalic acid: carbon dioxide = 1:10) at a flow rate of 1mL / min. Cool to obtain pitch-based porous carbon.

[0089] S2, 100g of pitch-based porous carbon was added to 100g of 40wt% phenylacetaldehyde solution, along with 100g of 20wt% 6-amino-p-phenol and 10g of bismuth isooctanoate. The mixture was thoroughly mixed and transferred to a high-pressure reactor. The mixture was subjected to a hydrothermal reaction at 100℃ and 5MPa for 6 hours. After filtration, the resulting material was activated at 800℃ by introducing steam at a flow rate of 100mL / min for 300 minutes to obtain a hard carbon-coated soft carbon porous carbon composite material.

[0090] S3: 100g of hard carbon-coated soft carbon porous carbon composite material was immersed in 50g of trichloroethylsilane solution, and then reacted for 2h under sealed conditions at a temperature of 500℃ and a negative pressure of 0.01Mpa to obtain intermediate material.

[0091] S4. Heat 5g of petroleum asphalt to 200℃ to form a molten state, then add 100g of intermediate material and 1g of niobium n-propoxide, and stir evenly. Heat to 750℃ at a heating rate of 1℃ / min for 3 hours to obtain silicon-carbon composite material.

[0092] Example 3

[0093] Methods for preparing silicon-carbon composite materials include:

[0094] S1. Mix 100g of mesophase pitch with 500g of potassium hydroxide and 5g of pyrazole phosphorus evenly, and heat to 1000℃. Activate the mixture for 30 minutes by passing it through a phthalic acid mixed gas (volume ratio: phthalic acid: carbon dioxide = 5:10) at a flow rate of 5mL / min. Cool to obtain pitch-based porous carbon.

[0095] S2, 100g of pitch-based porous carbon was added to 200g of 35wt% 3-phenylpropanal solution, along with 200g of 20wt% 4-amino-3-methylphenol solution and 30g of bismuth laurate. The mixture was thoroughly mixed and transferred to a high-pressure reactor. The mixture was subjected to a hydrothermal reaction at 200℃ and 1MPa for 1 hour. After filtration, the resulting material was activated at 1000℃ by introducing steam at a flow rate of 500mL / min for 30 minutes to obtain a hard carbon-coated soft carbon porous carbon composite material.

[0096] S3, 100g of hard carbon-coated soft carbon porous carbon composite material was immersed in 100g of methyl vinyl dichlorosilane solution, and then reacted for 12h under sealed conditions at a temperature of 700℃ and a negative pressure of 0.05Mpa to obtain intermediate material.

[0097] S4. Heat 10g of mesophase pitch to 300℃ to form a molten state, then add 100g of intermediate material and 5g of niobium isopropoxide, stir evenly, and heat to 900℃ at a heating rate of 10℃ / min for 1 hour to obtain silicon-carbon composite material.

[0098] Comparative Example 1

[0099] Unlike Example 1, S1 does not contain the dopant tributyl phosphate, but is otherwise the same as Example 1.

[0100] Comparative Example 2

[0101] Unlike Example 1, S2 only activates the asphalt-based porous carbon obtained in S1 without hard carbon coating; specifically, the asphalt-based porous carbon is activated at 900°C by introducing water vapor at a flow rate of 300 mL / min for 150 minutes to obtain a soft carbon porous carbon composite material, and the other steps are the same as in Example 1.

[0102] Comparative Example 3

[0103] Unlike Example 1, S1 and S2 are omitted; only the hard carbon porous carbon composite material is prepared. Specifically, 150g of 35wt% formaldehyde solution, 150g of 15wt% resorcinol solution, and 20g of bismuth neodecanoate are mixed evenly and transferred to a high-pressure reactor. A hydrothermal reaction is carried out at 150°C and 3 MPa for 3 hours. After filtration, the resulting material is activated at 900°C by introducing steam at a flow rate of 300 mL / min for 150 minutes to obtain the hard carbon porous carbon composite material. S3 and S4 are the same as in Example 1.

[0104] Comparative Example 4

[0105] Unlike Example 1, the 80g dimethylchlorosilane solution in S3 was replaced with gaseous silane, and S4 was omitted. Specifically, the hard carbon-coated soft carbon porous carbon composite material in S2 of Example 1 was transferred to a fluidized bed, and then silane gas was introduced at a flow rate of 100mL / min for 150 minutes to obtain a silicon-carbon precursor material. Then, 8g of coal tar pitch was heated to 250°C to form a molten state, and then 100g of silicon-carbon precursor material was added and stirred evenly. The temperature was then increased to 850°C at a heating rate of 5°C / min for 2 hours to obtain a silicon-carbon composite material.

[0106] Performance / Data Testing:

[0107] 1. Scanning electron microscopy (SEM) test:

[0108] Figure 2 The image shows a SEM image of the hard carbon-coated soft carbon porous carbon composite material prepared in Example 1. As can be seen from the image, the material exhibits a blocky structure with uniform size distribution and reasonable particle size distribution. There are many micropores on its surface, and the particle size of the material is 5 micrometers to 10 micrometers. Figure 3 This is a schematic diagram of SEM testing of the silicon-carbon composite material prepared in Example 1. Figure 3 As can be seen from the results, the silicon-carbon composite material prepared in Example 1 exhibits a granular structure with fewer micropores, uniform size distribution, and particle size between 5 micrometers and 10 micrometers.

[0109] 2. Physicochemical property testing of porous carbon:

[0110] The pore volume and pore size of the porous carbon obtained in Examples 1-3 and Comparative Examples 1-3 were tested according to the national standard GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method". The specific surface area and tap density of the porous carbon in each example and comparative example were tested according to the national standard GB / T-38823-2020 "Silicon Carbon". The powder resistivity of the porous carbon in each example and comparative example was tested using a four-probe tester. At the same time, the disorder (ID / IG, where ID represents graphitized carbon and IG represents amorphous carbon) of the porous carbon in each example and comparative example was tested by XRD. A larger ID / IG indicates a smaller disorder and lower impedance, while a smaller ID / IG indicates a larger disorder and higher impedance. The test results are shown in Table 1.

[0111] 3. Physicochemical property testing of silicon-carbon composite materials:

[0112] The specific surface area and tap density of the silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-4 were tested according to the national standard GB / T-38823-2020 "Silicon-Carbon". The diffusion coefficient of the silicon-carbon composite materials prepared in each example and comparative example was tested by GITT. The powder resistivity of the silicon-carbon composite materials prepared in each example and comparative example was tested by a four-probe tester. The gas production of the powder material was also tested (m1g of powder material was added to deionized water to prepare a concentration of 10wt%, soaked at 45℃ for 48h, and the gas production V1 was tested and the gas production V1 / m1 was calculated). The test results are shown in Table 1.

[0113] Table 1. Physicochemical property test data of porous carbon and silicon-carbon composite materials in each embodiment and comparative example.

[0114]

[0115] Because Examples 1-3 coated the corresponding soft carbon pitch-based porous carbon with hard carbon porous carbon and didped it with phosphorus to reduce the electronic conductivity of the powder material, and improved the pore size and pore volume of the material through two activations to create pores, it was beneficial for the deposition of active materials and the improvement of their power. Comparative Example 1 did not dope with tributyl phosphate, so its impedance was too high, the pore-forming effect was poor, and the specific surface area was reduced. Comparative Examples 2 and 3 used soft carbon-based porous carbon or hard carbon-based porous carbon alone, which failed to achieve the synergistic effect between the materials, resulting in a lower tap density, higher carbon orientation (higher ID / IG), and higher powder resistivity of the corresponding porous carbon. Comparative Example 4 used gaseous silane to replace liquid silane. Although the impedance of the porous carbon did not change significantly, the dispersion uniformity of silane in the porous carbon was deviated, resulting in a larger local expansion of the silicon-carbon composite material and a higher gas production.

[0116] 4. Button cell battery performance test:

[0117] The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-4 were used as negative electrode materials for lithium-ion batteries to prepare coin cells according to the following methods:

[0118] A binder, conductive agent, and solvent are added to the corresponding silicon-carbon composite materials, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used is LA132, the conductive agent is SP (conductive carbon black), and the solvent is NMP. The ratio of composite material, SP, LA132, and NMP is 70g:15g:15g:300mL. The electrolyte is a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent is a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1. The lithium metal sheet is used as the counter electrode, and the separator is a polypropylene (PP) membrane.

[0119] Each coin cell was assembled in an argon-filled glove box, and then electrochemical performance was tested. Specifically, the electrochemical performance was tested on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 1.5V and a charge / discharge rate of 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cells were tested, and the charging DC resistance (DCR) of the corresponding coin cells (at 50% state of charge) was also tested. The test results are shown in Table 2.

[0120] Table 2 Electrochemical test data of batteries prepared using silicon-carbon composite materials from each embodiment and comparative example.

[0121]

[0122] Because each embodiment coats the porous carbon surface with phosphorus heteroatom compounds, it improves the electronic conductivity of the material, reduces the powder resistance, increases the diffusion coefficient, and reduces the corresponding DC charging resistance (DCR). Therefore, the silicon-carbon materials prepared by the embodiments in Tables 1 and 2 are superior to the comparative examples in terms of powder resistance, diffusion coefficient, and DCR. Compared with Example 1, Comparative Example 1 did not involve phosphorus doping, resulting in a higher powder resistance, higher polarization, reduced initial efficiency, and increased DCR. Compared with Comparative Example 3, Comparative Example 2 used either soft carbon-based porous carbon or hard carbon-based porous carbon alone, resulting in weak synergistic effects between the materials, higher polarization, reduced specific capacity, increased powder resistance, and increased the corresponding DCR. Comparative Example 4 used gaseous silane instead of liquid silane, leading to uniformity deviation and lower initial efficiency.

[0123] 5. Electrochemical performance testing of pouch batteries

[0124] With ternary materials (LiNi) 0.8 Co 0.1 Mn 0.1Using O2 as the positive electrode material, LiPF6 as the electrolyte, and a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as the solvent, 5Ah soft-pack batteries were prepared using Celgard 2400 membrane as the separator and silicon-carbon composite materials prepared in each example and comparative example as the negative electrode material. Electrode surface resistance and rate performance were then tested.

[0125] Electrode surface resistance: The electrode surface resistance was tested using a surface resistance tester; the test results are shown in Table 3 below.

[0126] Fast charging performance tests at different rates were conducted. Under a charging / discharging voltage range of 2.5-4.2V and a test temperature of 25±3.0℃, the battery was charged at 1.0C, 3.0C, and 5.0C, and discharged at 1.0C. The constant current ratio and electrode surface resistance of the battery were measured under different charging modes. The test results are shown in Table 3.

[0127] Table 3. Electrode surface resistance and rate performance test data of the silicon-carbon composite materials used in each embodiment and comparative example.

[0128]

[0129] The silicon-carbon composite materials prepared in the various embodiments of this application adopt a hard carbon-coated soft carbon structure. As can be seen from Table 3, compared with the comparative examples, the powder resistance is reduced, the diffusion coefficient of the silicon-carbon composite material is increased, thereby improving the constant current ratio of the silicon-carbon composite material and reducing the electrode surface resistance.

[0130] It should be understood that the order of the sequence numbers in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0131] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0132] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0133] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing silicon-carbon composite materials, characterized in that, include: S1, mix asphalt with potassium hydroxide and dopants evenly, heat to a first preset temperature, pass crosslinking agent mixed gas through at a first preset flow rate for first activation, cool, and obtain asphalt-based porous carbon; S2, add pitch-based porous carbon to an aldehyde compound solution, then add phenolic compounds and an organic bismuth catalyst and mix evenly, carry out a hydrothermal reaction, filter, and the resulting material undergoes a second activation to obtain a hard carbon-coated soft carbon porous carbon composite material. S3, the hard carbon-coated soft carbon porous carbon composite material is immersed in a liquid silane solution, and then reacted under closed conditions and negative pressure to obtain an intermediate material; S4. The asphalt is heated to a molten state, then intermediate materials and organoniobium compounds are added and stirred evenly to carbonize, thus obtaining a silicon-carbon composite material. The dopant is any one or a combination of tributyl phosphate, phytic acid, ammonium polyphosphate, pyrazole phosphorus, and parathion.

2. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, In S1: The ratio of the amount of asphalt, potassium hydroxide, dopant, and crosslinking agent mixed gas is 100g:(100~500)g:(1~5)g:(100~300)mL; The volume ratio of crosslinking agent gas to carbon dioxide is (1~5):10; The first preset temperature is 800℃~1000℃, the first preset flow rate is 10mL / min~50mL / min, and the first activation reaction time is 30min~300min; The crosslinking agent is any one or a combination of terephthalic acid, phthalic acid, isophthalic acid, pyromellitic dianhydride, and pyromellitic tricarboxylic acid.

3. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, In S2: The mass ratio of pitch-based porous carbon: aldehyde compound: phenol compound: organic bismuth catalyst is 100:(100~200):(100~200):(10~30); The mass concentration of aldehyde compounds in the solution is 35wt%~40wt%, and the mass concentration of phenolic compounds is 10wt%~20wt%. The hydrothermal reaction temperature is 100℃~200℃, the pressure is 1Mpa~5Mpa, and the reaction time is 1h~6h; The second activation temperature is 800℃~1000℃, the water vapor flow rate is 100mL / min~500mL / min, and the activation time is 30 minutes~300 minutes.

4. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, In S3: The mass ratio of hard carbon-coated soft carbon porous carbon composite material to liquid silane is 100:(50~100); The temperature of the closed negative pressure reaction is 500℃~700℃, the negative pressure is 0.01Mpa~0.05Mpa, and the reaction time is 2h~12h.

5. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, In S4: The mass ratio of intermediate material, bitumen, and organoniobium compound is 100:(5~10):(1~5); The melting temperature is 200℃~300℃; The carbonization heating rate is 1℃ / min to 10℃ / min, and the temperature is raised to 750℃ to 900℃ for 1h to 3h.

6. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, Aldehydes are any one or a combination of benzaldehyde, phenylacetaldehyde, 3-phenylpropanal, 2,5-dihydroxybenzaldehyde, phenylpropenal, and p-methylbenzaldehyde; The phenolic compounds are any one or a combination of p-aminophenol, 6-amino-p-phenol, 4-amino-3-methylphenol, 3-aminophenol, p-acetaminophenol, and 3-ethylamino-4-methylphenol; The organic bismuth catalyst is any one or a combination of bismuth isooctanoate, bismuth laurate, bismuth neodecanoate and bismuth naphthenate; The liquid silane is any one or a combination of dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, and dichlorovinylmethylsilane; Asphalt is any one or a combination of coal tar pitch, petroleum asphalt, natural asphalt and mesophase asphalt, with a softening point ≤150℃. The organoniobium compound is any one or a combination of niobium ethanol, niobium n-propoxide, niobium isopropoxide, and niobium pentanol.

7. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, The powder resistivity of the silicon-carbon composite material is ≤2.01 Ω·cm, and the specific surface area is 1.5 m². 2 / g~2.5m 2 / g, gas production ≤0.029ml / mg.

8. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared by the method described in any one of claims 1 to 7.

9. An electrode, characterized in that, This includes silicon-carbon composite materials prepared by any one of the methods for preparing silicon-carbon composite materials according to claims 1 to 7, or silicon-carbon composite materials as described in claim 8.

10. A battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The negative electrode is the electrode as described in claim 9.

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