Preparation method of asphalt-based porous carbon with adjustable pore volume ratio, product and application thereof

Abstract

The application discloses a preparation method of pitch-based porous carbon with adjustable pore volume ratio, a product thereof and application of the porous carbon to preparation of a silicon-carbon negative electrode material, and the preparation of the porous carbon comprises the following steps: S1, dissolving cellulose in an alkali / urea / water solution, sufficiently hydrolyzing to obtain a uniform solution, adding pitch, sufficiently mixing, and then heating and drying to obtain a cellulose@pitch composite material; S2, heating the cellulose@pitch composite material to perform pre-oxidation crosslinking, and then performing pre-carbonization treatment in a protective atmosphere to obtain carbonized material; and S3, performing activation treatment on the carbonized material to obtain pitch-based porous carbon with adjustable pore volume ratio. The pitch-based porous carbon prepared by the method disclosed by the application has extremely high particle strength, and the microporosity and the micropore-mesopore ratio are adjustable; and the silicon-carbon negative electrode material prepared by taking the pitch-based porous carbon as a substrate has excellent cycle stability, high reversible specific capacity and high first coulomb efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of pitch-based porous carbon with adjustable pore volume ratio, a product thereof and application. BACKGROUND

[0002] Porous carbon is considered as one of the most potential carbon materials due to its developed internal pores, and has been widely used in the preparation of deposition type silicon-carbon negative materials. Developing high economic benefit porous carbon products has strong attraction for existing scientific research fields and enterprises. Pitch is a cheap petroleum chemical byproduct, and has high potential for producing porous carbon.

[0003] Pitch molecules contain a large number of conjugated structures, which are easy to form graphite-like structures during carbonization, reducing the skeleton strength of pitch-based porous carbon, which does not meet the production needs of deposition type silicon-carbon negative materials. In addition, the pore structure size of porous carbon seriously affects the uniformity of silane deposition. For example, a high-performance pitch-based porous carbon material and a preparation method thereof are disclosed in Chinese patent document CN118206115A, which comprises the following steps: step one, mixing coal pitch and carbon nanotubes to obtain a precursor; step two, pretreating and crushing the precursor; step three, adding graphene and drying; step four, pre-oxidation treatment; and step five, carbonization and activation treatment. The technical solution prepares porous carbon by adopting the processes of pre-oxidation, carbonization and activation, and carbon nanotubes and graphene are also added as modifiers, finally obtaining porous carbon particles with high hardness. However, graphene and carbon nanotubes are expensive to prepare, and large-scale production is not easy. In addition, there is a problem of physical mixing unevenness in the addition process of carbon materials, which leads to large local pore distribution fluctuation during activation, affecting the silane deposition efficiency and uniformity.

[0004] Therefore, in order to improve the cycle performance of deposition type silicon-carbon negative materials and alleviate the volume expansion of silicon, it is urgent to solve the coordination problem of the skeleton strength and pore structure of pitch-based porous carbon particles. SUMMARY

[0005] In view of the above problems, the present application discloses a preparation method of pitch-based porous carbon with adjustable pore volume ratio. The pitch-based porous carbon prepared by the method has extremely high particle strength, and the microporosity and micropore-mesopore ratio are adjustable. The silicon-carbon negative material prepared by using the pitch-based porous carbon as a substrate has excellent cycle stability, high reversible specific capacity and high first coulomb efficiency.

[0006] To achieve the above-mentioned purposes, the specific technical solutions of the present application are as follows:

[0007] In a first aspect, the present application provides a preparation method of pitch-based porous carbon with adjustable pore volume ratio, comprising:

[0008] S1: cellulose is dissolved in alkali / urea / water solution to obtain a uniform solution after sufficient hydrolysis, then pitch is added, and after sufficient mixing, cellulose pitch composite material is obtained by heating and drying;

[0009] S2: the cellulose pitch composite material is heated for pre-oxidation and cross-linking, and then pre-carbonization treatment is carried out in a protective atmosphere to obtain carbonized material;

[0010] S3: the carbonized material is activated to obtain pitch-based porous carbon with adjustable pore volume ratio.

[0011] The present application fully hydrolyzes cellulose in an alkali / urea / water solution system to obtain a uniform solution, so as to fully mix with pitch powder, so as to uniformly introduce cellulose long chains into the pitch matrix, and then the cellulose is used as a structure enhancer and cross-linking agent of the pitch matrix for carbonization treatment, which significantly improves the particle strength of the finally prepared pitch-based porous carbon, thereby effectively resisting the charge and discharge expansion of silicon nanoparticles.

[0012] In an optional embodiment, in step S1, at least one of the following features (1) to (7) is included:

[0013] (1) the alkali is selected from one or more of LiOH, NaOH, KOH;

[0014] Optionally, the alkali is selected from LiOH and NaOH; further optionally, the alkali is selected from LiOH.

[0015] (2) the cellulose includes but is not limited to one or more of alpha-cellulose, beta-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, and the number average molecular weight is 2000-15000;

[0016] Optionally, the cellulose is selected from alpha-cellulose and / or beta-cellulose;

[0017] Optionally, the number average molecular weight of the fiber is 5000-15000; further optionally, the number average molecular weight is 10000-15000.

[0018] (3) the mass ratio of cellulose, alkali, urea and water is (0.1-2.0):(0.2-5.0):3:(1-10);

[0019] Optionally, the mass ratio of cellulose, alkali, urea and water is (0.5-1.5):(0.5-2.0):3:(4-8);

[0020] Further optionally, the mass ratio of cellulose, alkali, urea and water is (1.0-1.5):(0.5-2.0):3:6.

[0021] (4) the preparation of the uniform solution is carried out at a low temperature of -20 to -10°C;

[0022] (5) the asphalt is in a powder form, and the particle size D 50 is 2 to 8 μm, and D max ≤ 50 μm;

[0023] Optionally, the asphalt is selected from the conventional types in the art, such as petroleum asphalt, coal pitch, mesophase pitch, naphthalene pitch, etc.; further optionally, the asphalt is selected from petroleum asphalt or coal pitch.

[0024] (6) the mass ratio of cellulose to asphalt is 1:(5 to 20);

[0025] Optionally, the mass ratio of cellulose to asphalt is 1:(5 to 10).

[0026] (7) the heating and drying is carried out at a temperature of 60 to 90°C.

[0027] The drying is to remove the solvent in the system to obtain a fully mixed composite solid.

[0028] In the optional embodiment, in step S2:

[0029] The pre-oxidation cross-linking produces cross-linking between the asphalt molecules and additional cross-linking between the cellulose molecules and the asphalt molecules through bridging oxygen, thereby forming a double cross-linking structure and improving the overall strength of the material; the pre-oxidation cross-linking also decomposes and removes the urea in the raw materials.

[0030] Optionally, the pre-oxidation cross-linking is carried out at a temperature of 250 to 350°C.

[0031] Optionally, the pre-oxidation cross-linking is carried out for 1 to 5 hours.

[0032] Optionally, the pre-oxidation cross-linking is carried out at a temperature increasing rate of 0.5 to 10°C / min.

[0033] Optionally, the pre-oxidation cross-linking is carried out in a rotary furnace, and the air flow is controlled at 0.5 to 10 L / min, and the rotation speed of the rotary furnace is controlled at 5 to 10 rpm.

[0034] Optionally, the protective atmosphere used in the pre-carbonization treatment includes one or more of nitrogen, argon, and helium.

[0035] The uniformly dispersed alkali in the cellulose@asphalt composite also has a certain activation function, and the residual alkali also simultaneously performs a pre-activation treatment on the carbon material during the pre-carbonization treatment.

[0036] Optionally, the pre-carbonization treatment is carried out at a temperature of 600 to 800°C.

[0037] Optionally, the pre-carbonization treatment has a time of 4-10 hours.

[0038] Optionally, the pre-carbonization treatment has a temperature rising rate of 0.5-20℃ / min.

[0039] In optional embodiments, the activation treatment in step S3 comprises at least one of the following features (a)-(d):

[0040] (a) the activation treatment is selected from physical activation, and the activation agent is selected from one or more of CO, CO2, water vapor, and oxygen;

[0041] Optionally, the activation agent is selected from one or more of CO, CO2, and water vapor.

[0042] (b) the activation treatment has a temperature of 700-1000℃;

[0043] Optionally, the temperature is 800-900℃.

[0044] (c) the activation treatment has a time of 2-15 hours;

[0045] (d) the activation treatment has a flow rate of the activation agent of 0.01-10 kg / h.

[0046] Optionally, the activation treatment has a flow rate of the activation agent of 0.1-5.0 kg / h.

[0047] Optionally, the activation treatment has a temperature rising rate of 0.5-20℃ / min.

[0048] Optionally, the activation treatment is performed in a rotary furnace, and the rotary speed of the rotary furnace is controlled to be 0.5-10 rpm.

[0049] In a second aspect, the present application further provides a pitch-based porous carbon with adjustable pore volume ratio, which has a particle strength of not less than 4.6 GPa, a microporosity of 85-90%, and a micropore-mesopore ratio of 4-7.

[0050] In a third aspect, the present application further provides a preparation method of a silicon-carbon negative electrode material, which is prepared by sequentially performing silicon deposition and carbon coating on the pitch-based porous carbon with adjustable pore volume ratio as a substrate.

[0051] In optional embodiments, the silicon deposition comprises at least one of the following features (1)-(7):

[0052] (1) the silicon deposition uses a raw material gas comprising a silicon source gas;

[0053] Optionally, the silicon source gas is selected from the conventional types in the art, including one or more of monosilane, disilane, dichlorodisilane, trichlorosilane.

[0054] (2) the flow rate of the raw gas is 1-50 L / h;

[0055] (3) the temperature for the silicon deposition is 300-800℃;

[0056] (4) the time for the silicon deposition is 1-40 h;

[0057] (5) the raw gas further comprises a carrier gas;

[0058] (6) the carrier gas is selected from nitrogen and / or argon;

[0059] (7) the volume fraction of the carrier gas is 1-30% based on 100% of the total volume of the raw gas.

[0060] In optional embodiments, the carbon coating comprises at least one of the following features (1)-(6):

[0061] (1) the raw gas for the carbon coating comprises a carbon-containing gas;

[0062] (2) the carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes;

[0063] Optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butylene, and 1,3-butadiene; and optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0064] (3) the flow rate of the raw gas for the carbon coating is 1-10 L / h;

[0065] (4) the temperature for the carbon coating is 400-1200℃;

[0066] (5) the time for the carbon coating is 1-10 h;

[0067] (6) the raw gas for the carbon coating further comprises an inert gas.

[0068] Optionally, the inert gas is selected from the conventional types in the art, such as nitrogen and argon.

[0069] In a fourth aspect, the present application further provides a silicon-carbon negative electrode material prepared according to the above method.

[0070] In a fifth aspect, the present application further provides a lithium ion battery comprising the above silicon-carbon negative electrode material.

[0071] Compared with the prior art, the present application has the following beneficial results:

[0072] The application discloses a preparation method of pitch-based porous carbon with adjustable pore volume ratio, and the pitch-based porous carbon is prepared by the following steps: a uniform solution is prepared by sufficiently hydrolyzing cellulose in an alkali / urea / water solution system, the solution is mixed with pitch powder, cellulose long chains are uniformly introduced into a pitch matrix, the cellulose is used as a structure enhancer and a crosslinking agent of the pitch matrix to perform carbonization treatment, and the particle strength of the pitch-based porous carbon prepared finally is significantly improved, so that the pitch-based porous carbon can effectively resist the charge and discharge expansion of silicon nanoparticles; a small amount of alkali contained in the raw material solution can be used as an activation seed to pre-activate the carbon material and participate in the subsequent physical activation process, so that the activation efficiency is improved; meanwhile, the existence of the alkali improves the microporosity, and the synergistic effect of the physical activation can accurately control the micropore and mesopore ratio of the pitch-based porous carbon, and the adaptability to the subsequent silane deposition process is enhanced; in addition, metal elements in the alkali exist in the pores of the porous carbon and are in close contact with the deposited nanosilicon interface, so that the content of irreversible lithium in the battery charge and discharge is effectively reduced, and the first coulomb efficiency of the negative electrode material is improved. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 Structure diagram of the alpha-cellulose used for the example 1. DETAILED DESCRIPTION

[0074] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0075] In the description of the present application, it should be noted that the specific meanings of the above-mentioned terms in the present application can be understood according to specific conditions by those skilled in the art. The embodiments of the present application will be described below according to the overall structure of the present application. Unless otherwise specified, the raw materials in the embodiments of the present application are purchased through commercial channels.

[0076] In a first aspect, the present application provides a preparation method of pitch-based porous carbon with adjustable pore volume ratio, comprising:

[0077] S1: cellulose is dissolved in an alkali / urea / water solution, and a uniform solution is obtained after sufficient hydrolysis, then pitch is added, and a cellulose@pitch composite material is obtained after sufficient mixing and heating and drying;

[0078] S2: the cellulose@pitch composite material is heated to perform pre-oxidation and crosslinking, and then is subjected to pre-carbonization treatment in a protective atmosphere to obtain carbonized material;

[0079] S3: activating the carbonized material to obtain pitch-based porous carbon with adjustable pore volume ratio.

[0080] The present application fully hydrolyzes cellulose in an alkali / urea / water solution system to prepare a uniform solution, so as to fully mix with pitch powder, thereby uniformly introducing long chains of cellulose into the pitch matrix, and then performing carbonization treatment on the cellulose as a structure enhancer and crosslinking agent of the pitch matrix, thereby significantly improving the particle strength of the finally prepared pitch-based porous carbon, and effectively resisting the charge / discharge expansion of silicon nanoparticles.

[0081] In optional embodiments, in step S1, at least one of the following features (1) to (7) is included:

[0082] (1) the alkali is selected from one or more of LiOH, NaOH, KOH;

[0083] Optionally, the alkali is selected from LiOH and NaOH; further optionally, the alkali is selected from LiOH.

[0084] (2) the cellulose includes, but is not limited to, one or more of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, and the number average molecular weight is 2000 to 15000;

[0085] Optionally, the cellulose is selected from α-cellulose and / or β-cellulose;

[0086] It has been found through experiments that, compared with α-cellulose, β-cellulose, and microcrystalline cellulose, the solution viscosity of carboxymethyl cellulose is higher, the uniformity of liquid phase mixing is lower, and the particle strength of the prepared pitch-based porous carbon is slightly decreased.

[0087] Further optionally, the cellulose is selected from α-cellulose.

[0088] The number average molecular weight of the cellulose can be specifically 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, or any value within the above range; optionally, the number average molecular weight of the cellulose is 5000 to 15000; further optionally, the number average molecular weight is 10000 to 15000.

[0089] It has been found through experiments that the particle strength of the prepared pitch-based porous carbon is related to the number average molecular weight of the cellulose used.

[0090] (3) the mass ratio of cellulose, alkali, urea, and water is (0.1 to 2.0):(0.2 to 5.0):3:(1 to 10);

[0091] Optionally, the mass ratio of cellulose, alkali, urea and water is (0.5-1.5):(0.5-2.0):3:(4-8);

[0092] Further optionally, the mass ratio of cellulose, alkali, urea and water is (1.0-1.5):(0.5-2.0):3:6.

[0093] It has been found through experiments that, with the optimization of the mass ratio of the above raw materials, the particle strength of the prepared pitch-based porous carbon is higher.

[0094] (4) The preparation of the uniform solution is carried out at a low temperature of -20 to -10°C; specifically, it can be -20°C, -19°C, -18°C, -17°C, -16°C, -15°C, -14°C, -13°C, -12°C, -11°C, -10°C, or any value within the above range.

[0095] (5) The pitch is in powder form, and the particle size D 50 is 2-8 μm; specifically, it can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or any value within the above range. max ≤ 50 μm; specifically, it can be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 3 μm, 4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any value within the above range.

[0096] Optionally, the pitch is selected from the conventional types in the art, such as petroleum pitch, coal pitch, mesophase pitch, naphthalene pitch, etc.; further optionally, the pitch is selected from petroleum pitch or coal pitch.

[0097] (6) The mass ratio of cellulose to pitch is 1:(5-20); specifically, it can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, or any ratio within the above range; optionally, the mass ratio of cellulose to pitch is 1:(5-10).

[0098] It has been found through experiments that, with the optimization of the mass ratio of the above cellulose and pitch, the particle strength of the prepared pitch-based porous carbon is higher.

[0099] (7) The heating and drying is carried out at a temperature of 60-90°C; specifically, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any value within the above range.

[0100] The drying aims to remove the solvent in the system to obtain a fully mixed composite solid.

[0101] In an optional embodiment, in step S2:

[0102] The pre-oxidation cross-linking forms a double cross-linking structure by cross-linking between pitch molecules and additional cross-linking between cellulose molecules and pitch molecules through bridging oxygen, thereby improving the overall strength of the material; the pre-oxidation cross-linking also decomposes and removes urea in the raw materials.

[0103] Optionally, the pre-oxidation cross-linking has a temperature of 250-350°C, and specifically can be 250°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or any value within the above range.

[0104] Optionally, the pre-oxidation cross-linking has a time of 1-5h, and specifically can be 1h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, or any value within the above range.

[0105] Optionally, the pre-oxidation cross-linking has a heating rate of 0.5-10°C / min, and specifically can be 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any value within the above range.

[0106] Optionally, the pre-oxidation cross-linking is performed in a rotary furnace, and the air flow is controlled to be 0.5-10L / min, and specifically can be 0.5L / min, 1L / min, 2L / min, 3L / min, 4L / min, 5L / min, 6L / min, 7L / min, 8L / min, 9L / min, 10L / min, or any value within the above range; the rotation speed of the rotary furnace is controlled to be 5-10rpm, and specifically can be 5rpm, 6rpm, 7rpm, 8rpm, 9rpm, 10rpm, or any value within the above range.

[0107] Optionally, the protective atmosphere used in the pre-carbonization treatment includes one or more of nitrogen, argon, and helium.

[0108] The uniformly dispersed alkali in the cellulose-pitch composite also has a certain activation function, and the residual alkali also simultaneously performs a pre-activation treatment on the carbon material during the pre-carbonization treatment.

[0109] Optionally, the pre-carbonization treatment has a temperature of 600-800 °C, specifically, 600 °C, 620 °C, 640 °C, 660 °C, 680 °C, 700 °C, 720 °C, 740 °C, 760 °C, 780 °C, 800 °C, or any value within the range.

[0110] Optionally, the pre-carbonization treatment has a time of 4-10 h, specifically, 4.0 h, 4.5 h, 5.0 h, 5.5 h, 6.0 h, 6.5 h, 7.0 h, 7.5 h, 8.0 h, 8.5 h, 9.0 h, 9.5 h, 10 h, or any value within the range.

[0111] Optionally, the pre-carbonization treatment has a temperature ramping rate of 0.5-20 °C / min, specifically, 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 15 °C / min, 20 °C / min, or any value within the range.

[0112] In optional embodiments, the activation treatment in step S3 comprises at least one of the following features (a)-(d):

[0113] (a) the activation treatment is selected from physical activation, and the activation agent is selected from one or more of CO, CO2, water vapor, oxygen;

[0114] Optionally, the activation agent is selected from one or more of CO, CO2, water vapor.

[0115] (b) the activation treatment has a temperature of 700-1000 °C, specifically, 700 °C, 720 °C, 740 °C, 760 °C, 780 °C, 800 °C, 820 °C, 840 °C, 860 °C, 880 °C, 900 °C, 950 °C, 1000 °C, or any value within the range; optionally, the temperature is 800-900 °C.

[0116] (c) the activation treatment has a time of 2-15 h, specifically, 2 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, or any value within the range.

[0117] (d) the activation treatment, the flow rate of the activating agent is 0.01-10 kg / h, specifically, it can be 0.01 kg / h, 0.05 kg / h, 0.1 kg / h, 0.5 kg / h, 1 kg / h, 1.5 kg / h, 2 kg / h, 2.5 kg / h, 3 kg / h, 3.5 kg / h, 4 kg / h, 4.5 kg / h, 5 kg / h, 6 kg / h, 7 kg / h, 8 kg / h, 9 kg / h, 10 kg / h or any value within the above range; optionally, the flow rate of the activating agent is 0.1-5.0 kg / h.

[0118] Optionally, the activation treatment, the heating rate is 0.5-20 ℃ / min, specifically, it can be 0.5 ℃ / min, 1 ℃ / min, 2 ℃ / min, 3 ℃ / min, 4 ℃ / min, 5 ℃ / min, 6 ℃ / min, 7 ℃ / min, 8 ℃ / min, 9 ℃ / min, 10 ℃ / min, 11 ℃ / min, 12 ℃ / min, 13 ℃ / min, 14 ℃ / min, 15 ℃ / min, 16 ℃ / min, 17 ℃ / min, 18 ℃ / min, 19 ℃ / min, 20 ℃ / min or any value within the above range.

[0119] Optionally, the activation treatment is carried out in a rotary furnace, and the rotation speed of the rotary furnace is controlled to be 0.5-10 rpm, specifically, it can be 0.5 rpm, 1 rpm, 2 rpm, 3 rpm, 4 rpm, 5 rpm, 6 rpm, 7 rpm, 8 rpm, 9 rpm, 10 rpm or any value within the above range.

[0120] In the second aspect, the present application further provides a pitch-based porous carbon with adjustable pore volume ratio, which is prepared according to the above method, and has a particle strength of no less than 4.6 GPa and a microporosity of 85-90%, and a micropore-mesopore ratio of 4-7.

[0121] In the third aspect, the present application further provides a preparation method of a silicon-carbon negative electrode material, which is prepared by sequentially depositing silicon and coating carbon on the pitch-based porous carbon with adjustable pore volume ratio.

[0122] In the optional embodiment, the silicon deposition comprises at least one of the following features (1)-(7):

[0123] (1) the silicon deposition, the raw gas used comprises a silicon source gas;

[0124] Optionally, the silicon source gas is selected from the conventional types in the art, including one or more of monosilane, disilane, dichlorodisilane and trichlorosilane.

[0125] (2) the flow rate of the raw gas is 1-50 L / h, and specifically can be 1 L / h, 2 L / h, 3 L / h, 5 L / h, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h, or any value within the above range;

[0126] (3) the temperature of the silicon deposition is 300-800°C, and specifically can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or any value within the above range.

[0127] (4) the time of the silicon deposition is 1-40 h, and specifically can be 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, or any value within the above range.

[0128] (5) the raw gas further comprises a carrier gas;

[0129] (6) the carrier gas is selected from nitrogen and / or argon;

[0130] (7) the volume fraction of the carrier gas is 1-30% based on 100% of the total volume of the raw gas, and specifically can be 1%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 28%, 30%, or any value within the above range.

[0131] In optional embodiments, the carbon coating comprises at least one of the following features (1)-(6):

[0132] (1) the carbon coating uses a raw gas comprising a carbon-containing gas;

[0133] (2) the carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes;

[0134] Optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butylene, and 1,3-butadiene; and optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0135] (3) the flow rate of the raw gas for the carbon coating is 1-10 L / h, and specifically can be 1 L / h, 2 L / h, 3 L / h, 4 L / h, 5 L / h, 6 L / h, 7 L / h, 8 L / h, 9 L / h, 10 L / h, or any value within the above range.

[0136] (4) The carbon coating temperature is 400-1200℃, and can be specifically 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any value within the above range.

[0137] (5) The carbon coating time is 1-10h, and can be specifically 1h, 1.5h, 2h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 6h, 7h, 8h, 9h, 10h or any value within the above range.

[0138] (6) The carbon coating raw gas further comprises an inert gas.

[0139] Optionally, the inert gas is selected from the conventional types in the art, such as nitrogen, argon and the like.

[0140] In a fourth aspect, the present application further provides a silicon-carbon negative electrode material prepared according to the above method.

[0141] In a fifth aspect, the present application further provides a lithium ion battery comprising the above silicon-carbon negative electrode material.

[0142] Example 1

[0143] S1, 10kg of α-cellulose (number average molecular weight is 12000) is dissolved in a LiOH / urea / water solution (the mass ratio of LiOH, urea and water is 10kg:30kg:60kg) at -15℃ to obtain a uniform solution under strong stirring, 100kg of petroleum pitch powder with a particle size D 50 of 5μm is put into the uniform solution, and after 10h of continuous stirring and mixing, it is dried at 80℃ to obtain a cellulose@pitch composite material;

[0144] S2, 50kg of the cellulose@pitch composite material is placed in a tube furnace, air with a flow rate of 5L / min is introduced, and the temperature is raised to 300℃ at a rate of 5℃ / min and kept for 4h to realize pre-oxidation of the pitch and removal of urea, and then nitrogen is switched in, and when the oxygen content is reduced to below 50ppm, the temperature is raised to 700℃ at a rate of 5℃ / min to realize pre-carbonization and pre-activation of the composite material, and the time is 6h to obtain a pre-carbonized material.

[0145] S3, 30kg of the above pre-carbonized material is placed in a rotary furnace, the rotary rate is set to 5r / min, the temperature is raised to 800℃ at a rate of 10℃ / min to realize steam activation to obtain a pitch-based porous carbon, the steam flow rate is 1.0kg / h, and the activation time is 9h.

[0146] Example 2

[0147] The preparation process is basically the same as that of Example 1, except that in step S1, the mass of LiOH added is replaced by 5 kg.

[0148] Example 3

[0149] The preparation process is basically the same as that of Example 1, except that in step S1, the mass of LiOH added is replaced by 20 kg.

[0150] Example 4

[0151] The preparation process is basically the same as that of Example 1, except that in step S1, the mass of α-cellulose added is replaced by 5 kg.

[0152] Example 5

[0153] The preparation process is basically the same as that of Example 1, except that in step S1, the mass of α-cellulose added is replaced by 15 kg.

[0154] Example 6

[0155] The preparation process is basically the same as that of Example 1, except that in step S1, LiOH is replaced by an equal mass of NaOH.

[0156] Example 7

[0157] The preparation process is basically the same as that of Example 1, except that in step S1, α-cellulose is replaced by an equal mass of carboxymethyl cellulose (number average molecular weight of 2200).

[0158] Example 8

[0159] The preparation process is basically the same as that of Example 1, except that in step S1, α-cellulose is replaced by an equal mass of β-cellulose (number average molecular weight of 5000).

[0160] Comparative Example 1

[0161] 50 kg of powdered petroleum pitch with a particle size D 50 The 50 kg of powdered petroleum pitch with a particle size D

[0162] The 30 kg of the above pre-carbonized material was placed in a rotary furnace, the rotary rate was set to 5 r / min, and the temperature was raised to 800℃ at a rate of 10℃ / min to perform steam activation to obtain pitch-based porous carbon, the steam flow rate was 1.0 kg / h, and the activation time was 9 h.

[0163] Comparative Example 2

[0164] S1, 10 kg of aqueous epoxy resin (Shanghai Guangyan Chemical Technology Co., Ltd., brand: 618, model: ZZZF04031) was dissolved in 60 kg of water solution at -15°C to obtain a uniform solution under strong stirring, and 100 kg of powdered petroleum pitch with a particle size D 50 of 5 μm was added into the above solution, and after 10 h of continuous stirring and mixing, it was dried at 80°C to obtain an epoxy resin-pitch composite material.

[0165] Steps S2-S3 were the same as in Example 1.

[0166] Comparative Example 3

[0167] The preparation process was basically the same as in Example 1, except that in step S1, no LiOH was added.

[0168] The performance data of the pitch-based porous carbon prepared in each example and comparative example are shown in Table 1 below, wherein the specific surface area and pore distribution were obtained by a precise high-bo nitrogen adsorption-desorption test system, and similar particle sizes were selected for the strength test of the particles, and the strength was measured by a strength tester.

[0169] Table 1

[0170]

[0171] Comparing Examples 1-3 and Comparative Example 3 in Table 1, the pitch-based porous carbon prepared in Example 1 has better comprehensive physical indexes and excellent comprehensive electrochemical performance; the microporosity, micropore-mesopore ratio and particle strength of the pitch-based porous carbon prepared in Example 2 slightly decrease with the decrease of the amount of LiOH; the microporosity, micropore-mesopore ratio and particle strength of the pitch-based porous carbon prepared in Example 3 slightly increase with the increase of the amount of LiOH. In Comparative Example 3, since the a-cellulose cannot be dissolved, the particle strength of the pitch-based porous carbon prepared is significantly reduced, and the alkaline activation is not assisted, which leads to a significant decrease in the micropore content of the prepared porous carbon.

[0172] Comparing Examples 1, 4 and 5, the particle strength of the pitch-based porous carbon prepared in Example 4 decreases with the decrease of the cellulose content, and the particle strength of the pitch-based porous carbon prepared in Example 5 increases with the increase of the cellulose content; the microporosity and micropore-mesopore ratio of the pitch-based porous carbon prepared in both Examples 4 and 5 have no obvious difference from those in Example 1.

[0173] Comparative Example 1, 6, in Example 6 with sodium hydroxide as a base instead of lithium hydroxide, the prepared pitch-based porous carbon particles strength decreased, and the microporosity and micropore mesopore ratio also decreased; this may be because relative to lithium hydroxide, sodium hydroxide will lead to insufficient dissociation of cellulose, and is not conducive to the generation of micropores.

[0174] Comparative Example 1, 7~8, the particle strength of the pitch-based porous carbon prepared in Example 7 is slightly lower than that of Example 1, which may be due to the high viscosity of the carboxymethyl cellulose solution, the low liquid phase mixing uniformity, resulting in the decrease of the pitch-based porous carbon particle strength; the particle strength of the pitch-based porous carbon prepared in Example 8 is also slightly lower than that of Example 1, which may be due to the number average molecular weight of cellulose is lower than that of Example 1.

[0175] Comparative Example 1 and Comparative Examples 1~2, in Comparative Example 1, no cellulose is added, and the prepared pitch-based porous carbon has very low particle strength; in Comparative Example 2, other common reinforcing agent epoxy resin is used instead of cellulose, and the reinforcing effect is not ideal.

[0176] Application Example

[0177] 10kg of pitch-based porous carbon prepared in each example and comparative example is placed as a substrate in a rotary furnace, under the condition of 500℃, a raw gas composed of silane gas and nitrogen gas is introduced, the flow rate of the raw gas is 8L / h, the nitrogen gas accounts for 2% in the raw gas, and the deposition time is 30h. The carbon coating process is to put the above-mentioned silicon-carbon material into the rotary furnace, introduce acetylene gas, and perform under the condition of nitrogen protection and 700℃ high temperature, the flow rate of the acetylene gas is 8L / h, and the carbon coating time is 5h.

[0178] The product prepared in each example and each comparative example is assembled as a negative electrode material to form a battery.

[0179] (1) Preparation of positive electrode sheet: the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), conductive agent SuperP, carbon nanotube, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:0.5:1.5 with N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry (solid content of 70wt%), which is coated on the positive and negative double sides of the current collector aluminum foil, dried at 100℃, then cold-pressed at room temperature under 4MPa, followed by edge cutting, sheet cutting, striping, and welding of the tabs to form a positive electrode sheet.

[0180] (2) Preparation of negative electrode sheet: under a nitrogen protection atmosphere, the solvent N-methyl pyrrolidone (NMP) is stirred and mixed uniformly with the binder PVDF, then the conductive agent SuperP is stirred and mixed uniformly, followed by the addition of the final product prepared in each example and each comparative example as a negative electrode active material to be stirred and mixed uniformly, to prepare a negative electrode slurry (solid content of 50wt%).

[0181] The above negative electrode slurry is coated on both sides of the current collector copper foil, dried at 100°C, cold-pressed at room temperature under 4 MPa, then trimmed, cut, striped, and welded to form a negative electrode sheet.

[0182] (3) Assembly of lithium ion battery

[0183] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets, and wound to obtain a bare cell. The bare cell is placed in an aluminum plastic shell package, dried at 100°C under a relative vacuum pressure of -0.95 x 105 Pa until the moisture content is below 100 ppm. An electrolyte is injected into the dried bare cell, wherein the electrolyte is composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) (EC: EMC: DEC volume ratio = 1:1:1) and LiPF6 (1.0 M), and the battery is packaged, rested, formed (0.02C constant current charging for 2h, 0.1C constant current charging for 2h), shaped, and tested for capacity (binning) to form a soft-packaged liquid lithium ion battery. During battery assembly, five batteries are prepared for each test, and five sets of data are tested. The final performance is the average of the five sets of data.

[0184] The battery cycle performance is tested on a blue light device. Specifically, at 25°C, first discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, discharge at 0.02C to 0.001V, and rest for 10 min; then charge at 0.1C to 1.5V and rest for 10 min. The charge and discharge capacities after the first cycle are recorded, and the first coulombic efficiency is calculated. After 100 cycles according to the above method, the charge and discharge capacities after 100 cycles are recorded, and the capacity retention rate after 100 cycles is calculated. The expansion test is performed after the battery is cycled by comparing the thickness of the electrode sheet before and after cycling. The specific test / calculated results are shown in Table 2 below.

[0185] Table 2

[0186]

[0187] Comparing Examples 1-8 in Table 2, the silicon-carbon negative electrode materials prepared in each example all have excellent cycle stability and low expansion rate, but the product prepared in Example 1 has the best electrochemical performance. Due to slight differences in the pore volume, microporosity, micropore-mesopore ratio, and other parameters of the porous carbon substrate in the other examples, the reversible specific capacity, initial efficiency, cycle retention rate, and expansion rate of the silicon-carbon negative electrode materials prepared in the other examples are slightly different.

[0188] Comparative Example 1 and Comparative Examples 1-2, the silicon-carbon negative electrode materials prepared in Comparative Examples 1-2 respectively have poor cycle stability and large expansion rate, which is related to the low particle strength of the porous carbon substrate itself.

[0189] Comparative Example 1 and Comparative Example 3, the capacity, retention rate and initial efficiency of the silicon-carbon negative electrode material prepared in Comparative Example 3 significantly decrease, and the expansion rate significantly increases, which is related to the low pore volume and low micropore-mesopore ratio of the porous carbon substrate itself.

[0190] The above discloses the preferred embodiments, but the protection scope of the present application is not limited thereto, and those skilled in the art can easily understand the spirit of the present application according to the above embodiments, and make different inferences and changes, as long as they do not deviate from the spirit of the present application, they are within the protection scope of the present application.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized by, A pore volume ratio adjustable asphalt-based porous carbon is used as a substrate, and silicon deposition and carbon coating are sequentially performed to prepare the same; The pore volume ratio adjustable asphalt-based porous carbon has a particle strength of not less than 4.5 GPa, a micropore rate of 85-90%, and a micropore-mesopore ratio of 4-7; The preparation method of the pore volume ratio adjustable asphalt-based porous carbon comprises: S1: cellulose is dissolved in an alkali / urea / water solution, and is sufficiently hydrolyzed to obtain a uniform solution, and then asphalt is added, and after being sufficiently mixed, heating and drying are performed to obtain a cellulose@asphalt composite material; S2: the cellulose@asphalt composite material is heated for pre-oxidation crosslinking, and then is subjected to pre-carbonization treatment in a protective atmosphere to obtain carbonized material; S3: the carbonized material is subjected to activation treatment to obtain the pore volume ratio adjustable asphalt-based porous carbon.

2. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S1, at least one of the following features (1)-(7) is included: (1) the alkali is selected from one or more of LiOH, NaOH and KOH; (2) the cellulose includes but is not limited to one or more of α-cellulose, β-cellulose, microcrystalline cellulose and carboxymethyl cellulose, and has a number average molecular weight of 2000-15000; (3) the mass ratio of cellulose, alkali, urea and water is (0.1-2.0):(0.2-5.0):3:(1-10); (4) the preparation of the uniform solution is performed at a low temperature of -20 to -10℃; (5) the asphalt is in powder form, particle size D 50 2-8 μm, D max ≤ 50 μm; (6) the mass ratio of cellulose to asphalt is 1:(5-20); (7) the heating and drying are performed at a temperature of 60-90℃.

3. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S2: the pre-oxidation crosslinking is performed at a temperature of 250-350℃ for 1-5h; the pre-carbonization treatment is performed in a protective atmosphere including one or more of nitrogen, argon and helium at a temperature of 600-800℃ for 4-10h.

4. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S3, the activation treatment includes at least one of the following features (a)-(d): (a) the activation treatment is selected from physical activation, and the activation agent is selected from one or more of CO, CO2, water vapor and oxygen; (b) the activation treatment is performed at a temperature of 700-1000℃; (c) the activation treatment is performed for 2-15h; (d) the activation treatment is performed at a flow rate of the activation agent of 0.01-10kg / h.

5. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The silicon deposition includes at least one of the following features (1)-(5): (1) the silicon deposition is performed using raw material gas including a silicon source gas; (2) the flow rate of the raw material gas is 1-50L / h; (3) the silicon deposition is performed at a temperature of 300-800℃; (4) the silicon deposition is performed for 1-40h; (5) the raw material gas further includes a carrier gas selected from nitrogen and / or argon; the volume ratio of the carrier gas to the total volume of the raw material gas is 1-30%.

6. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The carbon coating includes at least one of the following features (1)-(5): (1) the carbon coating is performed using raw material gas including a carbon-containing gas; the carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes and C2-C4 alkynes; (2) the flow rate of the raw material gas for the carbon coating is 1-10L / h; (3) the carbon coating is at a temperature of 400-1200℃; (4) the carbon coating is for a time of 1-10h; (5) the carbon coating is in a raw material gas further comprising an inert gas.

7. A silicon-carbon negative electrode material prepared according to the method of any one of claims 1-6.

8. A lithium-ion battery, characterized by A silicon-carbon negative electrode material as claimed in claim 7.

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