Silicon-carbon negative electrode material, preparation method thereof and battery

Abstract

The invention discloses a silicon-carbon negative electrode material, a preparation method thereof and a battery, and belongs to the technical field of negative electrode materials. The compaction density of the silicon-carbon negative electrode material is greater than or equal to 1.1 g / cm < 3 >, and the NLDFT total pore volume is less than or equal to 0.005 cm < 3 > / g; and in the NLDFT total pore volume of the silicon-carbon negative electrode material, the pore volume not exceeding 10% is provided by pores with the pore diameter not less than 50nm. The silicon-carbon negative electrode material has relatively high compaction density and first efficiency, and is beneficial to improving the volume energy density of the battery. The preparation method comprises the following steps: carrying out silicon deposition on a porous carbon raw material, carrying out high-pressure impregnation on a precursor obtained after primary carbon deposition by using an organic carbon source, and then carrying out secondary carbon deposition. The method is simple to operate, the silicon-carbon negative electrode material with relatively high compaction density can be prepared, and the prepared silicon-carbon negative electrode material can be further used for preparing a battery, so that the volume energy density of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and more particularly, to a silicon-carbon anode material, a preparation method thereof, and a battery. Background Art

[0002] In recent years, with the development of technology, the industry has made great progress in solving the swelling problem of silicon when used as the anode of lithium-ion batteries. For example, a method of filling nano-silicon by chemical vapor infiltration of a silicon source gas into the pores of porous carbon is adopted to avoid the swelling of the battery anode during use. However, the materials obtained by the above scheme have a low tap density and cannot meet the requirements of high volumetric energy density application fields.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a silicon-carbon anode material, a preparation method thereof, and a battery to solve or improve the above technical problems.

[0005] The present application can be implemented as follows:

[0006] In a first aspect, the present application provides a silicon-carbon anode material, whose tap density ≥ 1.1 g / cm 3 , and the total pore volume of NLDFT ≤ 0.005 cm 3 / g; and, in the total pore volume of NLDFT of the silicon-carbon anode material, no more than 10% of the pore volume is provided by pores with a pore diameter of not less than 50 nm.

[0007] In an optional embodiment, the silicon-carbon anode material further includes at least one of the following characteristics:

[0008] Characteristic 1: The specific surface area of the silicon-carbon anode material ≤ 5 m 2 / g;

[0009] Characteristic 2: The carbon content in the silicon-carbon anode material is 50 - 55 wt%.

[0010] In a second aspect, the present application provides a preparation method of a silicon-carbon anode material as described in the foregoing embodiment, including the following steps: impregnating the precursor obtained by silicon deposition and first carbon deposition of a porous carbon raw material with an organic carbon source under high pressure, and then performing second carbon deposition.

[0011] In an optional embodiment, the porous carbon raw material has at least one of the following characteristics:

[0012] Characteristic 1: The specific surface area of the porous carbon raw material ≥ 1500 m 2 / g;

[0013] Characteristic 2: The total pore volume of the porous carbon raw material ≥ 0.6 cm3 / g;

[0014] Feature Three: In the total pore volume of the porous carbon raw material, at least 70% of the pore volume is provided by micropores with a pore diameter not exceeding 2 nm;

[0015] Feature Four: The Dv of the porous carbon raw material 50 is between 2 - 4 μm and Span ≥ 1.3.

[0016] In an alternative embodiment, the silicon deposition includes at least one of the following features:

[0017] Feature One: The pressure of the silicon deposition does not exceed 1000 Pa, preferably 100 - 1000 Pa;

[0018] Feature Two: The temperature of the silicon deposition is 460 - 560 °C;

[0019] Feature Three: A first mixed gas containing a silicon source and an inert gas is introduced during the silicon deposition. In the first mixed gas, the volume percentage of the silicon source is 3 - 80%.

[0020] In an alternative embodiment, the first carbon deposition includes at least one of the following features:

[0021] Feature One: The temperature of the first carbon deposition is 550 - 650 °C;

[0022] Feature Two: The pressure of the first carbon deposition does not exceed 111.3 Kpa, preferably 102.3 - 111.3 Kpa;

[0023] Feature Three: A second mixed gas containing a carbon source and an inert gas is introduced during the first carbon deposition. In the second mixed gas, the volume percentage of the carbon source is 5 - 25%.

[0024] In an alternative embodiment, the high-pressure impregnation includes at least one of the following features:

[0025] Feature One: The organic carbon source includes at least one of modified pitch, phenolic resin, and low-sulfur slurry;

[0026] Feature Two: The mass of the organic carbon source is 5 - 10 wt% of the precursor;

[0027] Feature Three: The pressure of the high-pressure impregnation is not less than 0.5 MPa, preferably 0.5 - 5 MPa;

[0028] Feature Four: The temperature of the high-pressure impregnation is 60 - 300 °C.

[0029] In an alternative embodiment, it further includes: calcining the material obtained after high-pressure impregnation;

[0030] The calcining includes at least one of the following features:

[0031] Feature 1: The calcination is carried out in an inert gas atmosphere;

[0032] Feature 2: The calcination temperature is 580 - 650 °C;

[0033] Feature 3: The calcination time is 1 - 5 h.

[0034] In an optional embodiment, it further includes: performing a second carbon deposition on the calcined material;

[0035] The second carbon deposition includes at least one of the following features:

[0036] Feature 1: The temperature of the second carbon deposition is 550 - 650 °C;

[0037] Feature 2: The pressure of the second carbon deposition does not exceed 106.3 Kpa, preferably 102.3 - 106.3 Kpa;

[0038] Feature 3: A third mixed gas containing a carbon source and an inert gas is introduced during the second carbon deposition. In the third mixed gas, the volume percentage of the carbon source is 10 - 50%.

[0039] In a third aspect, the present application provides a battery, which includes the silicon-carbon anode material of the foregoing embodiment.

[0040] The beneficial effects of the present application include:

[0041] The tap density of the silicon-carbon anode material provided by the present application is ≥ 1.1 g / cm 3 , and the total pore volume of NLDTF ≤ 0.005 cm 3 / g; moreover, in the total pore volume of NLDFT of the silicon-carbon anode material, no more than 10% of the pore volume is provided by pores with a pore diameter of not less than 50 nm. This silicon-carbon anode material has a relatively high tap density and initial efficiency, which is beneficial to improving the volumetric energy density of the battery. This silicon-carbon anode material fully fills the micropores and some mesopores in the porous carbon by low-pressure chemical vapor deposition of silicon, fills the macropores and some mesopores in the porous carbon by high-pressure impregnation, and further densifies the material by chemical vapor deposition of carbon after calcination, and realizes particle grading by matching with a relatively wide particle size distribution. This preparation method is simple in operation and can be industrially promoted. The prepared silicon-carbon anode material can be further used to prepare a battery, which is beneficial to improving the volumetric energy density and initial efficiency of the battery, etc. Description of the Drawings

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0043] Figure 1 SEM mapping diagram of the silicon-carbon anode material prepared in Example 1;

[0044] Figure 2 Particle size distribution curve of the silicon-carbon anode material prepared in Example 1;

[0045] Figure 3 NLDFT pore size distribution curve of the silicon-carbon anode material prepared in Example 1. Detailed implementation manners

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0047] The silicon-carbon anode material provided by the present application, its preparation method, and the battery will be specifically described below.

[0048] The present application provides a silicon-carbon anode material with a tap density ≥ 1.1 g / cm 3 , and the total pore volume of NLDFT ≤ 0.005 cm 3 / g; moreover, among the total pore volume of NLDFT of the silicon-carbon anode material, no more than 10% of the pore volume is provided by pores with a pore diameter of not less than 50 nm.

[0049] The test method for the above tap density is as follows: A certain mass of powder sample is loaded into a mold with a fixed area, compacted under a pressure of 5 t, and the instrument automatically measures the height of the powder body, thereby calculating the tap density of the powder body. The instrument used is Shenzhen Sansi UTM7305.

[0050] The test method for the total pore volume of NLDFT is as follows: Using nitrogen as the adsorption gas for a static isothermal adsorption and desorption experiment to obtain the adsorption and desorption curve, and using the non-local density functional theory to fit the curve to obtain the total pore volume and pore size distribution curve. The instrument used is Micromeritics 2460.

[0051] The above silicon-carbon anode material has a high tap density and initial efficiency, which is beneficial to improving the volumetric energy density of the battery.

[0052] Furthermore, in some embodiments, the specific surface area of the above silicon-carbon anode material is ≤ 5 m 2 / g.

[0053] The test method for the above specific surface area is as follows: using nitrogen as the adsorption gas to conduct a static isothermal adsorption and desorption experiment to obtain the adsorption and desorption curve, and calculating the specific surface area using the BET equation.

[0054] If the specific surface area of the silicon-carbon anode material is too large, it is likely to cause excessive loss of the first-cycle capacity; if the specific surface area of the silicon-carbon anode material is too small, the reaction area is too small, the material utilization rate is low, and the capacity and rate performance will be reduced.

[0055] In some embodiments, the carbon content in the above silicon-carbon anode material is 50-55 wt%, such as 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt% or 55 wt%, etc. Under the condition of the above carbon content, most of the pores inside the material can be filled, which is beneficial to improving the tap density.

[0056] It should be noted that the tap density of the current conventional silicon-carbon anode material is relatively low. The reason may be that after chemical vapor deposition, there are still many unfilled mesopores and macropores in the material. In the silicon-carbon anode material provided by the present application, the pores (including micropores, mesopores and macropores) inside the material are basically completely filled, and it can have a relatively high tap density. Among them, the pore diameter of the "micropore" is less than 2 nm, the pore diameter of the "macropore" is greater than 50 nm, and the pore diameter of the "mesopore" is 2-50 nm.

[0057] Correspondingly, the present application also provides a preparation method of the above silicon-carbon anode material, which may include the following steps: impregnating the precursor obtained by silicon deposition and the first carbon deposition of the porous carbon raw material with an organic carbon source under high pressure, and then performing the second carbon deposition.

[0058] As a reference, the specific surface area of the porous carbon raw material used in the present application is ≥ 1500 m 2 / g, and the total pore volume is ≥ 0.6 cm 3 / g. Among the total pore volume of the porous carbon raw material, the pore volume provided by micropores with a pore diameter not exceeding 2 nm is not less than 70%. The Dv 50 of the porous carbon raw material is 2-4 μm, and Span ≥ 1.3. Using the above porous carbon as the raw material is beneficial to preparing a silicon-carbon anode material with a relatively high tap density.

[0059] Span refers to the diameter distance: Span = (Dv 90 -Dv 10 ) / Dv 50 , and its test method is: using a laser particle size analyzer to conduct a particle size distribution test to obtain Dv 90 , Dv50 、Dv 10 , Span was calculated using Mastersizer 3000.

[0060] In the present application, the silicon deposition process can be carried out in the following manner: a porous carbon raw material with a mass of M1 is put into a reactor, an inert gas is introduced for replacement, the pressure of the reactor is reduced to P1 through the reactor's own vacuum system, and then the temperature is raised to T1, and a first mixed gas with a silicon source gas concentration of C1 is introduced, and the pressure is maintained unchanged for low-pressure chemical vapor infiltration.

[0061] The pressure P1 of silicon deposition does not exceed 1000 Pa, and may be, for example, 1000 Pa, 900 Pa, 800 Pa, 600 Pa, 500 Pa, 450 Pa, 400 Pa, 350 Pa, 300 Pa, 250 Pa, 200 Pa, 150 Pa, 100 Pa or 50 Pa, or any other value within the range of not more than 1000 Pa. In some preferred embodiments, the pressure of silicon deposition is 100-1000 Pa.

[0062] If the pressure of silicon deposition is too high, it will easily lead to too fast adsorption and deposition rates, which will cause pore sealing and make it impossible to fully fill the micropores and small mesopores.

[0063] The temperature T1 of silicon deposition may be 460-560°C, such as 460°C, 480°C, 500°C, 520°C, 540°C or 560°C, or any other value within the range of 460-560°C.

[0064] The first mixed gas contains a silicon source and an inert gas, wherein the volume percentage C1 of the silicon source can be 3-80%, such as 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc., or any other value within the range of 3-80%.

[0065] The silicon source may be silane by way of example but not limitation, and the inert gas may be helium, argon or nitrogen by way of example but not limitation.

[0066] Through the above-mentioned low-pressure chemical vapor infiltration, silicon deposition can be more effectively carried out in the micropores and small mesopores of the porous carbon raw material, avoiding pore sealing caused by too fast adsorption and deposition, and obtaining a material with almost completely filled micropores.

[0067] In some typical embodiments, after silicon deposition, a material with at least 95% of the micropores filled can be obtained.

[0068] In this application, the first carbon deposition can be carried out in the following manner: raise the temperature of the reactor to T2, stop evacuating, control the reactor pressure to be P2, introduce a second mixed gas with a carbon source gas concentration of C2, and perform atmospheric pressure chemical vapor deposition.

[0069] Among them, the temperature T2 of the first carbon deposition can be 550 - 650 °C, such as 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C or 650 °C, etc., or can also be any other value within the range of 550 - 650 °C.

[0070] The pressure of the first carbon deposition does not exceed 111.3 Kpa, such as 101.3 Kpa, 102.3 Kpa, 103.3 Kpa, 104.3 Kpa, 105.3 Kpa, 106.3 Kpa, 107.3 Kpa, 108.3 Kpa, 109.3 Kpa, 110.3 Kpa or 111.3 Kpa, etc., or can also be any other value within the range of 102.3 - 111.3 Kpa.

[0071] The second mixed gas contains a carbon source and an inert gas. Among them, the volume percentage C2 of the carbon source can be 5 - 25%, such as 5%, 10%, 15%, 20% or 25%, etc., or can also be any other value within the range of 5 - 25%.

[0072] The above carbon source can be, by way of example but not limitation, acetylene, and the inert gas can be, by way of example but not limitation, helium, argon or nitrogen, etc.

[0073] Through the first carbon deposition, a relatively dense carbon coating layer can be formed on the surface of the deposited silicon, realizing the passivation of the porous carbon after silicon deposition.

[0074] In this application, high-pressure impregnation can be carried out in the following manner: after cooling the reactor, take out the material obtained after the first carbon deposition, and carry out high-pressure impregnation of it together with an organic carbon source in a high-pressure autoclave, controlling the pressure of the autoclave to be P3 and the temperature to be T3.

[0075] Among them, the organic carbon source used for high-pressure impregnation can include, by way of example but not limitation, at least one of modified asphalt, phenolic resin and low-sulfur slurry.

[0076] In some preferred embodiments, the asphalt is a low-molecular-weight modified asphalt. By using a low-molecular-weight modified asphalt, it is more conducive to fully filling the macropores and some mesopores of the material.

[0077] The mass of the above-mentioned organic carbon source can be 5-10 wt% of the precursor, such as 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt% or 10 wt%, etc., or any other value within the range of 5-10 wt%.

[0078] If the mass of the organic carbon source is too small, it cannot effectively fill the macropores in the material; if the mass of the organic carbon source is too large, it is not conducive to controlling the carbon content of the material and easily leads to a decrease in the material capacity.

[0079] The pressure of the above-mentioned high-pressure impregnation is not less than 0.5 MPa, such as 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, etc. In some preferred embodiments, the pressure of the high-pressure impregnation is 0.5-5 MPa.

[0080] If the pressure of the high-pressure impregnation is too low, it cannot effectively promote the impregnation of the organic carbon source into the mesopores and macropores of the material.

[0081] The temperature of the high-pressure impregnation can be 60-300 °C, such as 60 °C, 80 °C, 100 °C, 150 °C, 200 °C, 250 °C or 300 °C, etc., or any other value within the range of 60-300 °C.

[0082] By performing the high-pressure impregnation treatment in the above manner, it is possible to effectively fill the remaining unfilled macropores and some mesopores in the material obtained by the first carbon deposition.

[0083] Furthermore, the material obtained after high-pressure impregnation is calcined.

[0084] In this application, the calcination can be carried out in the following manner: the material after high-pressure impregnation is calcined in a reactor under the condition of a temperature of T4.

[0085] The above-mentioned calcination process can be carried out in an inert gas atmosphere.

[0086] The calcination temperature T4 can be 550-650 °C, such as 550 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C or 650 °C, etc., or any other value within the range of 550-650 °C.

[0087] The calcination time can be 1-5 h, such as 1 h, 2 h, 3 h, 4 h or 5 h, etc., or any other value within the range of 1-5 h.

[0088] Through the above-mentioned calcination process, the organic carbon source can be carbonized and non-carbon substances can be removed.

[0089] Further, the calcined material is subjected to a second carbon deposition.

[0090] In this application, the second carbon deposition can be carried out in the following manner: after the volatiles in the material have completely overflowed during the calcination process, a third mixed gas with a carbon source concentration of C3 is introduced into the reactor, and the reactor pressure is set to P4 for atmospheric pressure chemical vapor deposition.

[0091] Among them, the temperature of the second carbon deposition can be 550 - 650 °C, such as 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C or 650 °C, etc., or any other value within the range of 550 - 650 °C. In some embodiments, the temperature of the second carbon deposition is the same as the calcination temperature.

[0092] The pressure of the second carbon deposition does not exceed 106.3 Kpa, such as 101.3 Kpa, 102.3 Kpa, 103.3 Kpa, 104.3 Kpa, 105.3 Kpa or 106.3 Kpa, etc., or any other value within the range of 102.3 - 106.3 Kpa.

[0093] During the second carbon deposition process, a third mixed gas containing a carbon source and an inert gas is introduced. In the third mixed gas, the volume percentage of the carbon source can be 10 - 50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., or any other value within the range of 10 - 50%.

[0094] Similarly, the carbon source in the third mixed gas can be acetylene by way of example but not limitation, and the inert gas can be helium, argon or nitrogen, etc. by way of example but not limitation.

[0095] Since during the calcination process, the space originally occupied by the non - carbon substances that volatilize or are removed will correspondingly form small pores, through the second carbon deposition, the pore structure formed after the carbonization of the organic carbon source can be further filled, thereby further increasing the compacted density of the material.

[0096] Further, under the protection of an inert gas, the reactor is cooled, and after discharging, it is sieved to remove magnetism, and then the negative electrode material can be obtained.

[0097] In addition, this application also provides a battery, which includes the above - mentioned silicon - carbon negative electrode material, and this battery has a relatively high volumetric energy density.

[0098] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0099] Example 1

[0100] This example provides a silicon - carbon negative electrode material, and its preparation method includes:

[0101] S1: Screening surface area is 1700m 2 / g, total pore volume is 0.75cm 3 / g、Dv 50 =3.05 μm, Span=1.65 porous carbon as raw material, wherein the pore volume contributed by micropores with a pore diameter not exceeding 2 nm is 72%.

[0102] S2: Put 2 kg of the porous carbon raw material into the reactor, introduce nitrogen for replacement, and then reduce the pressure of the reactor to P1 = 200 Pa through the reactor's own vacuum system, and increase the temperature to T1 = 520°C. At this time, introduce the first mixed gas (a mixture of silane and nitrogen, wherein the volume percentage of silane C1 is 50%), maintain the pressure unchanged, and carry out low-pressure chemical vapor infiltration to obtain precursor A.

[0103] S3: Raise the reactor temperature to T2 = 600°C, stop evacuating, control the reactor pressure P2 = 103.3 Kpa, introduce the second mixed gas (a mixture of acetylene and nitrogen, wherein the volume percentage of acetylene C2 is 20%) to perform atmospheric pressure chemical vapor deposition to obtain precursor B.

[0104] S4: Put the precursor B and the modified asphalt into a high-pressure reactor for high-pressure impregnation, and control the pressure of the reactor to P3 = 4MPa and the temperature to T3 = 280° C. The mass of the modified asphalt is 8wt% of the precursor B.

[0105] S5: The material after high pressure impregnation is loaded into a reactor and calcined in a nitrogen atmosphere at a calcination temperature of T4 = 640°C and a calcination time of 4 hours.

[0106] S6: After the volatile components have completely overflowed, a third mixed gas (a mixed gas of acetylene and nitrogen, wherein the volume percentage C3 of acetylene is 30%) is introduced into the reactor at a temperature of 620° C. and a reactor pressure P4=103.3 KPa to perform atmospheric pressure chemical vapor deposition.

[0107] S7: Cooling the reactor under the protection of nitrogen, screening and demagnetizing the discharged material to obtain the negative electrode material.

[0108] Example 2

[0109] This embodiment provides a silicon-carbon negative electrode material, and the preparation method thereof includes:

[0110] S1: Same as Example 1.

[0111] S2: Put 2 kg of the porous carbon raw material into the reactor, introduce nitrogen for replacement, and then reduce the pressure of the reactor to P1 = 300 Pa through the reactor's own vacuum system, and increase the temperature to T1 = 480°C. At this time, introduce the first mixed gas (a mixture of silane and nitrogen, wherein the volume percentage of silane C1 is 30%), maintain the pressure unchanged, and carry out low-pressure chemical vapor infiltration to obtain precursor A.

[0112] S3: Raise the reactor temperature to T2 = 580°C, stop evacuating, control the reactor pressure P2 = 104.3Kpa, introduce the second mixed gas (a mixture of acetylene and nitrogen, wherein the volume percentage C2 of acetylene is 10%) to perform atmospheric pressure chemical vapor deposition to obtain precursor B.

[0113] S4: Put the precursor B and the phenolic resin into a high-pressure reactor for high-pressure impregnation, and control the pressure of the reactor P3 = 2MPa and the temperature T3 = 240° C. The mass of the phenolic resin is 9wt% of the precursor B.

[0114] S5: The material after high pressure impregnation is loaded into a reactor and calcined in a nitrogen atmosphere at a calcination temperature of T4 = 620°C and a calcination time of 3 hours.

[0115] S6: After the volatiles have completely overflowed, the third mixed gas (a mixed gas of acetylene and nitrogen, wherein the volume percentage C3 of acetylene is 20%) is introduced into the reactor at a temperature of 600° C. and a reactor pressure P4=104.3 KPa to perform atmospheric pressure chemical vapor deposition.

[0116] S7: Cooling the reactor under the protection of nitrogen, screening and demagnetizing the discharged material to obtain the negative electrode material.

[0117] Example 3

[0118] This embodiment provides a silicon-carbon negative electrode material, and the preparation method thereof includes:

[0119] S1: Same as Example 1.

[0120] S2: Put 2 kg of the porous carbon raw material into the reactor, introduce nitrogen for replacement, and then reduce the pressure of the reactor to P1 = 600 Pa through the reactor's own vacuum system, and increase the temperature to T1 = 540°C. At this time, introduce the first mixed gas (a mixture of silane and nitrogen, wherein the volume percentage of silane C1 is 60%), maintain the pressure unchanged, and carry out low-pressure chemical vapor infiltration to obtain precursor A.

[0121] S3: Raise the reactor temperature to T2 = 620°C, stop evacuating, control the reactor pressure P2 = 108.3 Kpa, introduce the second mixed gas (a mixture of acetylene and nitrogen, wherein the volume percentage of acetylene C2 is 15%) to perform atmospheric pressure chemical vapor deposition to obtain precursor B.

[0122] S4: Put the precursor B and the low-sulfur oil slurry into a high-pressure reactor for high-pressure impregnation, and control the pressure of the reactor P3 = 1 MPa and the temperature T3 = 170° C. The mass of the phenolic resin is 7 wt % of the precursor B.

[0123] S5: The material after high pressure impregnation is loaded into a reactor and calcined in a nitrogen atmosphere at a calcination temperature of T4 = 630°C and a calcination time of 2 hours.

[0124] S6: After the volatiles have completely overflowed, the third mixed gas (a mixed gas of acetylene and nitrogen, wherein the volume percentage C3 of acetylene is 40%) is introduced into the reactor at a temperature of 640°C and a reactor pressure P4=105.3 KPa to perform atmospheric pressure chemical vapor deposition.

[0125] S7: Cooling the reactor under the protection of nitrogen, screening and demagnetizing the discharged material to obtain the negative electrode material.

[0126] Example 4

[0127] This embodiment provides a silicon-carbon negative electrode material, and the preparation method thereof includes:

[0128] S1: Screening surface area is 1500m 2 / g, total pore volume is 0.6cm 3 / g、Dv 50 =2μm, Span=1.3 porous carbon as raw material, wherein the pore volume contributed by micropores with pore diameter not exceeding 2nm is 70%.

[0129] S2: Put 2 kg of the porous carbon raw material into the reactor, introduce nitrogen for replacement, and then reduce the pressure of the reactor to P1 = 100 Pa through the reactor's own vacuum system, and increase the temperature to T1 = 460°C. At this time, introduce the first mixed gas (a mixture of silane and nitrogen, wherein the volume percentage of silane C1 is 3%), maintain the pressure unchanged, and carry out low-pressure chemical vapor infiltration to obtain precursor A.

[0130] S3: Raise the reactor temperature to T2 = 550°C, stop evacuating, control the reactor pressure P2 = 102.3 Kpa, introduce the second mixed gas (a mixture of acetylene and nitrogen, wherein the volume percentage C2 of acetylene is 5%) to perform atmospheric pressure chemical vapor deposition to obtain precursor B.

[0131] S4: Put the precursor B and the modified asphalt into a high-pressure reactor for high-pressure impregnation, and control the pressure of the reactor to P3 = 0.5 MPa and the temperature to T3 = 100° C. The mass of the asphalt is 5 wt% of the precursor B.

[0132] S5: The material after high pressure impregnation is loaded into a reactor and calcined in a nitrogen atmosphere at a calcination temperature of T4 = 580°C and a calcination time of 1 hour.

[0133] S6: After the volatile components have completely overflowed, a third mixed gas (a mixed gas of acetylene and nitrogen, wherein the volume percentage C3 of acetylene is 10%) is introduced into the reactor at a temperature of 550° C. and a reactor pressure P4=102.3 KPa to perform atmospheric pressure chemical vapor deposition.

[0134] S7: Cooling the reactor under the protection of nitrogen, screening and demagnetizing the discharged material to obtain the negative electrode material.

[0135] Example 5

[0136] This embodiment provides a silicon-carbon negative electrode material, and the preparation method thereof includes:

[0137] S1: Screening surface area is 1800m 2 / g, total pore volume is 0.8cm 3 / g、Dv 50 =4μm, Span=1.52 porous carbon as raw material, wherein the pore volume contributed by micropores with a pore diameter not exceeding 2nm is 80%.

[0138] S2: Put 2 kg of the porous carbon raw material into the reactor, introduce nitrogen for replacement, and then reduce the pressure of the reactor to P1 = 1000 Pa through the reactor's own vacuum system, and increase the temperature to T1 = 560°C. At this time, introduce the first mixed gas (a mixture of silane and nitrogen, wherein the volume percentage of silane C1 is 80%), maintain the pressure unchanged for low-pressure chemical vapor infiltration, and obtain precursor A.

[0139] S3: Raise the reactor temperature to T2 = 650°C, stop evacuating, control the reactor pressure P2 = 113.3 Kpa, introduce the second mixed gas (a mixture of acetylene and nitrogen, wherein the volume percentage C2 of acetylene is 25%) to carry out normal pressure chemical vapor deposition to obtain precursor B.

[0140] S4: Put the precursor B and the modified asphalt into a high-pressure reactor for high-pressure impregnation, and control the pressure of the reactor to P3 = 5MPa and the temperature to T3 = 300° C. The mass of the modified asphalt is 10wt% of the precursor B.

[0141] S5: Load the material after high-pressure impregnation into a reactor and calcine it in a nitrogen atmosphere at a calcination temperature T4 = 650 °C for 5 h.

[0142] S6: After the volatiles have completely overflowed, introduce the third mixed gas (a mixed gas of acetylene and nitrogen, where the volume percentage C3 of acetylene is 50%) into the reactor at a temperature of 650 °C and a reactor pressure P4 = 106.3 KPa for atmospheric pressure chemical vapor deposition.

[0143] S7: Cool down the reactor under the protection of nitrogen, and after discharging, screen and demagnetize to obtain the anode material.

[0144] Comparative Example 1

[0145] The difference between this comparative example and Example 1 is that: the total pore volume of the porous carbon raw material is 0.55 cm 3 / g, the pore volume contributed by micropores with a pore diameter not exceeding 2 nm is 65%, and Span = 1.1.

[0146] Comparative Example 2

[0147] The difference between this comparative example and Example 1 is that: S4 and S5 were not carried out.

[0148] Comparative Example 3

[0149] The difference between this comparative example and Example 1 is that: S6 was not carried out.

[0150] Comparative Example 4

[0151] The difference between this comparative example and Example 1 is that: in S2, P1 is 2000 Pa.

[0152] Comparative Example 5

[0153] The difference between this comparative example and Example 1 is that: in S4, P3 is 0.4 MPa.

[0154] Test Example 1

[0155] Perform performance tests on the silicon-carbon anode materials prepared in Examples 1-5 and Comparative Examples 1-5, and the results are shown in Table 1 and Figures 1 to 3 as follows.

[0156] Among them, the test method for the tap density is: load a powder sample of a certain mass into a mold with a fixed area, compact it under a pressure of 5 t, and the instrument automatically measures the height of the powder body, so as to calculate the tap density of the powder body. The instrument used is Shenzhen Sansi UTM7305.

[0157] The test method for the total pore volume is as follows: A static isothermal adsorption and desorption experiment is carried out using nitrogen as the adsorption gas to obtain the adsorption and desorption curve. The non-local density functional theory is used to fit the curve to obtain the total pore volume and the pore size distribution curve. The instrument used is Micromeritics 2460.

[0158] The pore volume contribution rate can be obtained from the pore size distribution curve.

[0159] The test method for the specific surface area is as follows: A static isothermal adsorption and desorption experiment is carried out using nitrogen as the adsorption gas to obtain the adsorption and desorption curve. The BET equation is used to calculate the specific surface area. The instrument used is Micromeritics 2460.

[0160] The test method for the carbon content is as follows: The sample is heated under oxygen-rich conditions to completely oxidize the carbon element in it into carbon dioxide. The amount of carbon dioxide is calibrated by infrared absorption, and then the carbon content of the sample is converted. The instrument used is a carbon and sulfur analyzer.

[0161] Table 1 Test Results

[0162]

[0163] Test Example 2

[0164] The silicon-carbon anode materials prepared in Examples 1-5 and Comparative Examples 1-5 were prepared into lithium-ion coin half-cells and soft-pack full-cells according to the following method and subjected to performance tests. The results are shown in Table 2.

[0165] Preparation method of the coin half-cell: According to the ratio of 8:1:1, the anode material, the anode binder PAA, and the anode conductive agent SP are mixed and then diluted with deionized water to form an anode slurry and stirred evenly.

[0166] Then, the anode slurry is coated on the surface of the anode current collector using a coating device and dried to obtain a pole piece. Here, the anode current collector uses copper foil.

[0167] The preparation method of the electrolyte is as follows: A mixed solvent of 4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC) is prepared according to the volume ratio of 1:2:7, and the electrolyte salt lithium hexafluorophosphate is dissolved at a ratio of 1.2 mol / kg.

[0168] The above-mentioned pole piece is cut into a suitable shape and assembled into a coin half-cell together with a lithium sheet, a separator, and the electrolyte in a glove box filled with argon.

[0169] Preparation method of soft-pack full battery: The ternary 811 cathode material, conductive agent SP, binder PVDF, and single-walled carbon nanotubes are uniformly dispersed in the dispersant NMP according to the ratio of 96.5:1:1.5:0.5. Then, the slurry is uniformly coated on the aluminum foil, transferred to a vacuum oven for drying, and then rolled, cut, and weighed to obtain the cathode electrode sheet. The above-mentioned silicon-carbon anode material and artificial graphite are mixed according to the ratio of 1.5:8.5 to prepare a composite material. The composite material, conductive agent SP, binders CMC, SBR, and single-walled carbon nanotubes are uniformly dispersed in deionized water according to the ratio of 96:0.5:1.8:1.6:0.1. Then, the slurry is uniformly coated on the copper foil, transferred to a vacuum oven for drying, and then rolled, cut, and weighed to obtain the anode electrode sheet. The CB values of the anode and cathode electrode sheets are matched to be about 1.1, and processes such as winding, tab welding, liquid injection, and encapsulation are carried out to obtain the soft-pack full battery.

[0170] Test conditions: The test temperature of the coin-type half battery is 25 ± 1°C, the cut-off voltage is between 0.005 and 2V, and charge and discharge are carried out at a current density of 0.1C. Calculate the first efficiency at 0.8V = (lithium deintercalation capacity at 0.8V for the first time / lithium intercalation capacity at 2V for the first time) × 100%; The capacity of the soft-pack full battery is 1Ah, the test temperature is 25 ± 1°C, charge and discharge are carried out at a current density of 1C to obtain the average voltage, and the volume of the battery is obtained by the drainage method, so as to calculate the volume energy density.

[0171] Table 2 Test results

[0172]

[0173]

[0174] It can be seen from Table 2 that the silicon-carbon anode material provided by the embodiment of the present application can obtain a lithium-ion battery with better volume energy density and first efficiency compared to the silicon-carbon anode material provided by the comparative example.

[0175] In summary, the silicon-carbon anode material provided by the present application has a high tap density, which is beneficial to improving the volume energy density of the battery. Its preparation method is simple in operation, and a silicon-carbon anode material with a high tap density can be prepared. The prepared silicon-carbon anode material can be further used to prepare a battery, which is further beneficial to improving the volume energy density of the battery.

[0176] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The tap density of the silicon-carbon negative electrode material is ≥ 1.1 g / cm 3 , and the total pore volume of NLDFT is ≤ 0.005 cm 3 / g; moreover, among the total pore volume of NLDFT of the silicon-carbon negative electrode material, the pore volume provided by pores with a pore diameter of not less than 50 nm accounts for no more than 10%.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that The silicon-carbon negative electrode material further includes at least one of the following features: Feature 1: The specific surface area of the silicon-carbon negative electrode material ≤ 5m 2 / g; Feature 2: The carbon content in the silicon-carbon negative electrode material is 50-55 wt%.

3. A method for preparing the silicon-carbon anode material as described in claim 1 or 2, characterized in that, It includes the following steps: The precursor obtained by silicon deposition and the first carbon deposition of the porous carbon raw material is subjected to high-pressure impregnation with an organic carbon source, and then the second carbon deposition is carried out.

4. The preparation method according to claim 3, characterized in that, The porous carbon raw material has at least one of the following features: Feature 1: The specific surface area of the porous carbon raw material ≥ 1500 m 2 / g; Feature 2: The total pore volume of the porous carbon raw material ≥ 0.6 cm 3 / g; Feature 3: In the total pore volume of the porous carbon raw material, at least 70% of the pore volume is provided by micropores with a pore diameter not exceeding 2 nm; Feature Four: The Dv of the porous carbon raw material 50 is 2 - 4 μm, and Span ≥ 1.

3.

5. The preparation method according to claim 3, characterized in that, The silicon deposition includes at least one of the following features: Feature 1: The pressure of silicon deposition does not exceed 1000 Pa, preferably 100-1000 Pa; Feature 2: The temperature of silicon deposition is 460-560 °C; Feature 3: A first mixed gas containing a silicon source and an inert gas is introduced during the silicon deposition process. In the first mixed gas, the volume percentage of the silicon source is 3-80%.

6. The preparation method according to claim 3, characterized in that, The first carbon deposition includes at least one of the following features: Feature 1: The temperature of the first carbon deposition is 550-650 °C; Feature 2: The pressure of the first carbon deposition does not exceed 111.3 Kpa, preferably 102.3-111.3 Kpa; Feature 3: A second mixed gas containing a carbon source and an inert gas is introduced during the first carbon deposition process. In the second mixed gas, the volume percentage of the carbon source is 5-25%.

7. The preparation method according to claim 3, characterized in that, The high-pressure impregnation includes at least one of the following features: Feature 1: The organic carbon source includes at least one of modified pitch, phenolic resin, and low-sulfur slurry; Feature 2: The mass of the organic carbon source is 5-10 wt% of the precursor; Feature 3: The pressure of high-pressure impregnation is not less than 0.5 MPa, preferably 0.5-5 MPa; Feature 4: The temperature of high-pressure impregnation is 60-300 °C.

8. The preparation method according to claim 3, wherein It also includes: Calcining the material obtained after high-pressure impregnation; The calcining includes at least one of the following features: Feature 1: The calcining is carried out in an inert gas atmosphere; Feature 2: The calcining temperature is 580-650 °C; Feature 3: The calcining time is 1-5 h.

9. The preparation method according to claim 8, wherein It also includes: Carrying out the second carbon deposition on the calcined material; The second carbon deposition includes at least one of the following features: Feature 1: The temperature of the second carbon deposition is 550-650 °C; Feature 2: The pressure of the second carbon deposition does not exceed 106.3 Kpa, preferably 102.3-106.3 Kpa; Feature 3: A third mixed gas containing a carbon source and an inert gas is introduced during the second carbon deposition process. In the third mixed gas, the volume percentage of the carbon source is 10-50%.

10. A battery, characterized in that, The battery includes the silicon-carbon negative electrode material described in claim 1 or 2.

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