Porous carbon material, silicon-carbon composite material and preparation method and application thereof

Abstract

The invention is suitable for the technical field of lithium ion battery materials, and discloses a graphene-heteroatom doped porous carbon material, a lithium titanate amorphous carbon coated silicon carbon composite material, a preparation method thereof, a negative pole piece and a lithium ion battery. The graphene-heteroatom doped porous carbon material is prepared from porous carbon, graphene and heteroatoms, the graphene and the heteroatoms are distributed in the porous carbon, and in percentage by mass, the content of the graphene is 0.5 wt%-2wt%, the content of the heteroatoms is 0.5 wt%-2wt%, and the balance is the porous carbon. According to the graphene-heteroatom doped porous carbon material disclosed by the invention, the compaction density of porous carbon is improved by utilizing high electron conductivity of heteroatoms and high ductility of a graphene lamellar structure; in addition, a basic group on the surface of the heteroatom solution and an acidic group of the graphene oxide can generate a chemical bond linked carbon structure through a hydrothermal reaction, and the tap density and the electronic conductivity of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to a graphene-heteroatom doped porous carbon material, a lithium titanate amorphous carbon-coated silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] Silicon-carbon materials are composed of porous carbon, nano-silicon deposited in the pores of the porous carbon, and amorphous carbon coated on the surface of the porous carbon.

[0003] Porous carbon, the raw material for silicon-carbon materials, has a porous structure that results in poor electronic conductivity. Nanosilicon is deposited within the porous carbon, and amorphous carbon is deposited on its surface at low temperatures. While amorphous carbon exhibits good isotropic properties, it exhibits poor electronic and ionic conductivity. This poor conductivity between the core and shell of the silicon-carbon material results in poor fast-charge and fast-discharge performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a graphene-heteroatom doped porous carbon material, a lithium titanate amorphous carbon-coated silicon-carbon composite material and its preparation method, a negative electrode plate and a lithium ion battery, aiming to solve the technical problem of poor electronic conductivity of existing porous carbon materials.

[0005] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0006] A first aspect of the present invention provides a graphene-heteroatom doped porous carbon material, comprising porous carbon and graphene and heteroatoms distributed in the porous carbon;

[0007] In terms of mass percentage, the content of the graphene is 0.5wt% to 2wt%, the content of the heteroatoms is 0.5wt% to 2wt%, and the rest is the porous carbon.

[0008] In specific applications, the content of the graphene can be 0.5wt%, 0.7wt%, 0.9wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 1.9wt% or 2wt%, etc., and the content of the heteroatoms can be 0.5wt%, 0.7wt%, 0.9wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 1.9wt% or 2wt%, etc.

[0009] It should be noted that the simultaneous doping of heteroatoms and graphene into porous carbon improves the tap density of the porous carbon by leveraging the poor electronic conductivity of the heteroatoms and the high ductility of the graphene sheet structure. Furthermore, the basic groups on the surface of the heteroatom solution and the acidic groups of graphene oxide react hydrothermally to form a chemically bonded carbon structure, increasing both the tap density and electronic conductivity.

[0010] A second aspect of the present invention provides a method for preparing a graphene-heteroatom-doped porous carbon material, comprising the following steps:

[0011] S1, mixing porous carbon, heteroatoms and graphene oxide uniformly, transferring the mixture to a high-pressure reactor for reaction, and filtering to obtain a porous carbon material precursor;

[0012] S2. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace, introduce carbon dioxide gas for treatment, and obtain the graphene-heteroatom doped porous carbon material.

[0013] It should be noted that by mixing porous carbon, heteroatoms and graphene oxide to prepare graphene-heteroatom-doped porous carbon materials, the compacted density, tap density and electronic conductivity of the material can be improved.

[0014] In one implementation of the present invention, step S1 satisfies one or more of the following conditions a to d:

[0015] a. In step S1, the mixing of the porous carbon, heteroatoms and graphene oxide comprises adding the porous carbon to the heteroatom solution and dispersing the porous carbon uniformly, and then adding the graphene oxide solution and ultrasonically dispersing the porous carbon uniformly; preferably, the concentration of the heteroatom solution is 1 wt% to 10 wt%; preferably, the heteroatom solution is obtained by mixing the heteroatoms with a solvent, and the solvent is at least one of dichloromethane, dimethylformamide, tetrahydrofuran and thionyl chloride; preferably, the concentration of the graphene oxide solution is 1 wt% to 5 wt%;

[0016] b. In the step S1, the porous carbon, the heteroatom and the graphene oxide are mixed in a mass ratio of 100:(1-5):(1-5);

[0017] It should be noted that porous carbon, heteroatoms and graphene oxide are mixed in a mass ratio of 100:(1~5):(1~5). Heteroatoms and graphene oxide can effectively improve the electronic conductivity of the material and restrain the expansion of the active substance. When the amount of added heteroatoms and graphene oxide is too low, the effect on improving the electronic conductivity of the material and reducing the expansion of the active substance is limited. When the amount of added graphene oxide is too high, it will cause the graphene itself to agglomerate and the cost will increase. When the amount of added heteroatoms is too high, too many heteroatoms will cause the tap density to decrease.

[0018] c. In step S1, the reaction temperature is 100°C to 200°C, the pressure is 1Mpa to 5Mpa, and the reaction time is 1h to 6h;

[0019] d. In step S1, the heteroatom is at least one of pyrrole, aniline, thiophene, dopamine, pyridine, and pyrimidine;

[0020] Alternatively, step S2 satisfies one or two of the following conditions e to f:

[0021] e. In step S2, the freeze-drying temperature is -50°C to -30°C, and the time is 24h to 48h;

[0022] f. In step S2, the temperature of the carbon dioxide gas for treatment is 900°C to 1100°C, the time is 30min to 300min, and the flow rate of the carbon dioxide gas is 100SCCM to 500SCCM.

[0023] The third aspect of the present invention provides a graphene-heteroatom doped porous carbon material, which is prepared using the preparation method of the graphene-heteroatom doped porous carbon material described in the second aspect.

[0024] It should be noted that the graphene-heteroatom doped porous carbon material prepared by the above method can improve the compaction density, tap density and electronic conductivity of the material.

[0025] A fourth aspect of the present invention provides a lithium titanate amorphous carbon-coated silicon-carbon composite material, wherein the lithium titanate amorphous carbon-coated silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0026] The inner core is a silicon-carbon material obtained by reacting a silane mixed gas with the graphene-heteroatom-doped porous carbon material described in the first and third aspects, the middle layer is silicon carbide, and the outer layer is a lithium titanate amorphous carbon composite. The thickness ratio of the inner core, the middle layer and the outer shell is (80-95): (1-3): (2-19).

[0027] It should be noted that by using graphene and heteroatoms to improve electronic conductivity, and using lithium titanate to improve the ionic conductivity of the material, the lithium titanate amorphous carbon-coated silicon-carbon composite material has better ionic and electronic conductivity. The lithium titanate amorphous carbon-coated silicon-carbon composite material is applied to lithium-ion batteries, which improves power performance, initial efficiency and cycle performance.

[0028] In one implementation of the present invention, the silane mixed gas includes silane gas and nitrogen gas.

[0029] In one implementation of the present invention, the volume ratio of the silane gas to the nitrogen gas is (1-5):10.

[0030] In one implementation of the present invention, the silane gas is at least one of monosilane, disilane, dimethyldichlorosilane and monochlorotrihydrogensilane.

[0031] A fifth aspect of the present invention provides a method for preparing a lithium titanate amorphous carbon-coated silicon-carbon composite material, comprising the following steps:

[0032] S1. Transferring the graphene-heteroatom-doped porous carbon material described in the first and third aspects to a fluidized bed apparatus, first introducing a silane mixed gas for treatment, and then introducing a carbon source gas for treatment to obtain a silicon carbide-coated silicon-carbon composite material;

[0033] S2. Evenly mix lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material, and carbonize the mixture to obtain the lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0034] It should be noted that by adopting the above-mentioned graphene-heteroatom doped porous carbon material, lithium titanate, asphalt, etc., the lithium titanate amorphous carbon-coated silicon-carbon composite material prepared can utilize graphene and heteroatoms to improve the electronic conductivity, and utilize lithium titanate to improve the ionic conductivity of the material, so that the lithium titanate amorphous carbon-coated silicon-carbon composite material has better ionic and electronic conductivity.

[0035] In one implementation of the present invention, step S1 satisfies one or more of the following conditions a to d:

[0036] a. In step S1, before the silane mixed gas is introduced for treatment, the pressure within the fluidized bed apparatus is set to 0.01 MPa to 0.1 MPa;

[0037] b. In step S1, the temperature of the silane mixed gas for treatment is 300 ℃ ~ 500 ℃, the time is 30min ~ 300min, and the flow rate of the silane mixed gas is 100 SCCM ~ 500 SCCM;

[0038] c. In step S1, the temperature of the carbon source gas for treatment is 700 ℃ ~ 900 ℃, the time is 30min ~ 300min, and the flow rate of the carbon source gas is 10SCCM ~ 50SCCM;

[0039] d. In step S1, the silane mixed gas comprises silane gas and nitrogen; preferably, the volume ratio of the silane gas to the nitrogen is (1-5):10; preferably, the silane gas is at least one of monosilane, disilane, dimethyldichlorosilane and monochlorotrihydrogensilane;

[0040] e. In step S1, the carbon source gas is at least one of ethylene and methane;

[0041] Alternatively, step S2 satisfies one or two of the following conditions f to h:

[0042] f. In step S2, the mixing of lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material includes mixing lithium titanate and asphalt evenly, heating to 300°C to 500°C to obtain a liquid asphalt and lithium titanate complex, and then adding the silicon carbide-coated silicon-carbon composite material and mixing evenly;

[0043] g. In the step S2, the lithium titanate, the asphalt and the silicon carbide-coated silicon-carbon composite material are mixed in a mass ratio of (1 to 3): (5 to 10): 100;

[0044] It should be noted that by mixing lithium titanate, asphalt and silicon carbide-coated silicon-carbon composite materials in a mass ratio of (1-3): (5-10): 100, the large interlayer spacing and zero expansion of lithium titanate itself can be effectively utilized to improve the fast charging and cycle performance of the material; when the amount of lithium titanate added is too low, the effect on improving the fast charging performance of the material is limited; when the amount of lithium titanate added is too high, the energy density of the composite material is reduced due to the high voltage platform of lithium titanate itself.

[0045] h. In step S2, the carbonization temperature is 1100°C to 1300°C, and the time is 1h to 6h.

[0046] The sixth aspect of the present invention provides a lithium titanate amorphous carbon-coated silicon-carbon composite material, which is prepared by the preparation method of the lithium titanate amorphous carbon-coated silicon-carbon composite material described in the fifth aspect.

[0047] It should be noted that the lithium titanate amorphous carbon-coated silicon-carbon composite material prepared by the above method has better ionic and electronic conductivity. Applying it to lithium-ion batteries can improve power performance, initial efficiency and cycle performance.

[0048] The seventh aspect of the present invention provides a negative electrode plate, characterized in that it comprises the lithium titanate amorphous carbon-coated silicon-carbon composite material described in the fourth and sixth aspects.

[0049] It should be noted that by using the above-mentioned lithium titanate amorphous carbon-coated silicon-carbon composite material, the negative electrode plate has better ionic and electronic conductivity.

[0050] The eighth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the seventh aspect.

[0051] It should be noted that by adopting the above-mentioned negative electrode plate, the lithium-ion battery has the characteristics of good power performance, high initial efficiency and good cycle performance.

[0052] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0053] 1) By simultaneously doping heteroatoms and graphene into porous carbon, the compaction density of the porous carbon is improved by taking advantage of the poor electronic conductivity of heteroatoms and the high ductility of the graphene sheet structure. At the same time, the basic groups on the surface of the heteroatom solution and the acidic groups of graphene oxide can form a chemically bonded carbon structure through hydrothermal reaction, thereby improving the material's tap density and electronic conductivity.

[0054] 2) Lithium titanate and asphalt are carbonized to obtain lithium titanate amorphous carbon, which is coated on the surface of the silicon-carbon material. The high ionic conductivity and large interlayer spacing of lithium titanate itself, as well as the high compatibility of amorphous carbon with the electrolyte, can be used to enhance the electronic and ionic conductivity of the material, and improve the rate and storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0056] in:

[0057] Figure 1 This is an SEM image of the lithium titanate amorphous carbon-coated silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. In the following embodiments, many detailed descriptions are intended to enable the present application to be better understood. However, those skilled in the art can readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other materials or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid overwhelm the core of the present application with excessive descriptions, and for those skilled in the art, it is not necessary to describe these related operations in detail. The related operations can be fully understood based on the description in the specification and the general technical knowledge in the art.

[0059] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various embodiments. Furthermore, the steps or actions in the method description may be reordered or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various sequences in the specification and drawings are provided solely for the purpose of clearly describing a particular embodiment and are not intended to be mandatory, unless otherwise specified.

[0060] A first aspect of the present invention provides a graphene-heteroatom doped porous carbon material, comprising porous carbon and graphene and heteroatoms distributed in the porous carbon;

[0061] In terms of mass percentage, the content of the graphene is 0.5wt% to 2wt%, the content of the heteroatoms is 0.5wt% to 2wt%, and the rest is the porous carbon.

[0062] By simultaneously doping porous carbon with heteroatoms and graphene, the team leveraged the poor electronic conductivity of heteroatoms and the high ductility of graphene sheet structures to increase the compaction density of the porous carbon. Furthermore, the hydrothermal reaction between the basic groups on the surface of the heteroatom solution and the acidic groups of graphene oxide generated a chemically bonded carbon structure, increasing the material's tap density and electronic conductivity.

[0063] A second aspect of the present invention provides a method for preparing a graphene-heteroatom-doped porous carbon material, comprising the following steps:

[0064] S1, mixing porous carbon, heteroatoms and graphene oxide uniformly, transferring the mixture to a high-pressure reactor for reaction, and filtering to obtain a porous carbon material precursor;

[0065] S2. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace, introduce carbon dioxide gas for treatment, and obtain the graphene-heteroatom doped porous carbon material.

[0066] By mixing porous carbon, heteroatoms and graphene oxide to prepare graphene-heteroatom-doped porous carbon materials, the compacted density, tap density and electronic conductivity of the materials can be improved.

[0067] A third aspect of the present invention provides a graphene-heteroatom-doped porous carbon material, produced using the method for preparing a graphene-heteroatom-doped porous carbon material described in the second aspect. The graphene-heteroatom-doped porous carbon material produced using the above method can improve the material's compacted density, tapped density, and electronic conductivity.

[0068] A fourth aspect of the present invention provides a lithium titanate amorphous carbon-coated silicon-carbon composite material, wherein the lithium titanate amorphous carbon-coated silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0069] The inner core is a silicon-carbon material obtained by reacting a silane mixed gas with the graphene-heteroatom-doped porous carbon material described in the first and third aspects, the middle layer is silicon carbide, and the outer layer is a lithium titanate amorphous carbon composite. The thickness ratio of the inner core, the middle layer and the outer shell is (80-95): (1-3): (2-19).

[0070] By using graphene and heteroatoms to improve electronic conductivity, and using lithium titanate to improve the ionic conductivity of the material, the lithium titanate amorphous carbon-coated silicon-carbon composite material has better ionic and electronic conductivity. The lithium titanate amorphous carbon-coated silicon-carbon composite material is applied to lithium-ion batteries, which improves power performance, initial efficiency and cycle performance.

[0071] A fifth aspect of the present invention provides a method for preparing a lithium titanate amorphous carbon-coated silicon-carbon composite material, comprising the following steps:

[0072] S1. Transferring the graphene-heteroatom-doped porous carbon material described in the first and third aspects to a fluidized bed apparatus, first introducing a silane mixed gas for treatment, and then introducing a carbon source gas for treatment to obtain a silicon carbide-coated silicon-carbon composite material;

[0073] S2. Evenly mix lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material, and carbonize them to obtain the lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0074] By adopting the above-mentioned graphene-heteroatom doped porous carbon material, lithium titanate, asphalt, etc., the lithium titanate amorphous carbon-coated silicon-carbon composite material is prepared. The electronic conductivity can be improved by using graphene and heteroatoms, and the ionic conductivity of the material can be improved by using lithium titanate, so that the lithium titanate amorphous carbon-coated silicon-carbon composite material has better ionic and electronic conductivity.

[0075] A sixth aspect of the present invention provides a lithium titanate amorphous carbon-coated silicon-carbon composite material, produced using the method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material described in the fifth aspect. The lithium titanate amorphous carbon-coated silicon-carbon composite material produced using the above method has excellent ionic and electronic conductivity. Its application in lithium-ion batteries can improve power performance, initial efficiency, and cycle performance.

[0076] A seventh aspect of the present invention provides a negative electrode plate, characterized by comprising the lithium titanate amorphous carbon-coated silicon-carbon composite material described in the fourth and sixth aspects. By using the lithium titanate amorphous carbon-coated silicon-carbon composite material, the negative electrode plate has excellent ionic and electronic conductivity.

[0077] The eighth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the seventh aspect. By adopting the negative electrode sheet, the lithium-ion battery has the characteristics of good power performance, high initial efficiency and good cycle performance.

[0078] The present application is further described in detail below through specific examples. The following examples are only provided to further illustrate the present application and should not be construed as limiting the present application. It should be noted that if specific conditions are not specified in the examples, the process is carried out according to conventional conditions or the conditions recommended by the product manufacturer; the equipment and reagents used in the examples, for which the manufacturer is not specified, are all conventional products that can be purchased through commercial channels.

[0079] Example 1

[0080] A method for preparing a graphene-heteroatom doped porous carbon material comprises the following steps:

[0081] 100 g of porous carbon was added to 100 g of a 5 wt% pyridine dichloromethane solution and dispersed evenly. Then, 100 g of a 3 wt% graphene oxide solution was added and ultrasonically dispersed evenly. The mixture was transferred to a high-pressure reactor, reacted at a temperature of 150 ° C and a pressure of 3 MPa for 3 hours, filtered, and the obtained material (i.e., a porous carbon material precursor) was freeze-dried at -40 ° C for 36 hours. The obtained material was then transferred to a tubular furnace, heated to 1000 ° C, and carbon dioxide gas was introduced at a flow rate of 300 SCCM for 150 minutes to obtain a graphene-heteroatom-doped porous carbon material.

[0082] The preparation method of lithium titanate amorphous carbon-coated silicon-carbon composite material comprises the following steps:

[0083] Step S1:

[0084] The graphene-heteroatom doped porous carbon material was transferred to a fluidized bed device, evacuated to 0.05 MPa, and then heated to 400°C. A disilane mixed gas (volume ratio, disilane: nitrogen = 3:10) was introduced at a flow rate of 300 SCCM for 150 minutes to deposit nanosilicon in the graphene-heteroatom doped porous carbon material. The introduction of the disilane mixed gas was then stopped and replaced with ethylene gas. The temperature was raised to 800°C and introduced at a flow rate of 30 SCCM for 150 minutes to form a silicon carbide protective film on its surface, thereby obtaining a silicon carbide-coated silicon-carbon composite material.

[0085] Step S2:

[0086] 2g of lithium titanate and 8g of asphalt were mixed evenly and heated to 400°C to obtain a liquid asphalt and lithium titanate complex. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly using a VC mixer. The mixture was carbonized at 1200°C for 3h to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0087] Example 2

[0088] A method for preparing a graphene-heteroatom doped porous carbon material comprises the following steps:

[0089] 100 g of porous carbon was added to 100 g of a 1 wt% aniline dimethylformamide solution and dispersed evenly. Then, 100 g of a 1 wt% graphene oxide solution was added and ultrasonically dispersed evenly. The carbon was transferred to a high-pressure reactor, reacted at a temperature of 100 ° C and a pressure of 5 MPa for 6 hours, filtered, and the obtained material was freeze-dried at -40 ° C for 24 hours. The obtained material was then transferred to a tubular furnace, heated to 900 ° C, and carbon dioxide gas was introduced at a flow rate of 100 SCCM for 300 minutes to obtain a graphene-heteroatom doped porous carbon material.

[0090] The preparation method of lithium titanate amorphous carbon-coated silicon-carbon composite material comprises the following steps:

[0091] Step S1:

[0092] The graphene-heteroatom doped porous carbon material was transferred to a fluidized bed device, evacuated to 0.01 MPa, and then heated to 300°C. A silane mixed gas (volume ratio, silane: nitrogen = 1:10) was introduced, and deposition was carried out at a flow rate of 100 SCCM for 300 minutes to deposit nanosilicon in the graphene-heteroatom doped porous carbon material. After that, the introduction of the silane mixed gas was stopped and acetylene gas was introduced instead. The temperature was raised to 700°C and deposition was carried out at a flow rate of 10 SCCM for 300 minutes to generate a silicon carbide protective film on its surface to obtain a silicon carbide-coated silicon-carbon composite material.

[0093] Step S2:

[0094] 1g of lithium titanate and 5g of asphalt were mixed evenly and heated to 300°C to obtain a liquid asphalt and lithium titanate complex. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly using a VC mixer. The mixture was carbonized at 1100°C for 6h to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0095] Example 3

[0096] A method for preparing a graphene-heteroatom doped porous carbon material comprises the following steps:

[0097] 100 g of porous carbon was added to 50 g of a 10 wt% thiophene tetrahydrofuran solution and dispersed evenly. Then 100 g of a 5 wt% graphene oxide solution was added and ultrasonically dispersed evenly. The mixture was transferred to a high-pressure reactor and reacted at a temperature of 200 ° C and a pressure of 1 MPa for 1 hour. The obtained material was filtered and freeze-dried at -40 ° C for 48 hours. The obtained material was then transferred to a tubular furnace, heated to 1100 ° C, and carbon dioxide gas was introduced at a flow rate of 500 SCCM for 30 minutes to obtain a graphene-heteroatom doped porous carbon material.

[0098] The preparation method of lithium titanate amorphous carbon-coated silicon-carbon composite material comprises the following steps:

[0099] Step S1:

[0100] The graphene-heteroatom doped porous carbon material was transferred to a fluidized bed apparatus, evacuated to 0.1 MPa, and then heated to 500°C. A dimethyldichlorosilane mixed gas (volume ratio, dimethyldichlorosilane: nitrogen = 5:10) was introduced at a flow rate of 500 SCCM for 30 minutes to deposit nanosilicon in the graphene-heteroatom doped porous carbon material. The introduction of dimethyldichlorosilane was then stopped and replaced with methane gas, which was heated to 900°C and introduced at a flow rate of 50 SCCM for 30 minutes to form a silicon carbide protective film on its surface to obtain a silicon carbide-coated silicon-carbon composite material.

[0101] Step S2:

[0102] 3g of lithium titanate and 10g of asphalt were mixed evenly and heated to 500°C to obtain a liquid asphalt and lithium titanate complex. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly using a VC mixer, and carbonized at 1300°C for 1h to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that commercially available porous carbon (Kuraray Co., Ltd., Japan, model YP-80F) is used to replace the graphene-heteroatom doped porous carbon material in step S1, and the rest is the same as Example 1.

[0105] Comparative Example 2

[0106] Different from Example 1, in the step of preparing graphene-heteroatom-doped porous carbon material, 100 g of porous carbon was added to 300 g of 15 wt% pyridine dichloromethane solution and dispersed evenly, and then 300 g of 15 wt% graphene oxide solution was added and ultrasonically dispersed evenly, and then transferred to a high-pressure reactor. The rest was the same as Example 1.

[0107] Comparative Example 3

[0108] Different from Example 1, in the step of preparing graphene-heteroatom-doped porous carbon material, 100 g of porous carbon was added to 100 g of dichloromethane solution and dispersed evenly, and then 100 g of 3 wt% graphene oxide solution was added, mixed and ultrasonically dispersed evenly, and then transferred to a high-pressure reactor. The rest was the same as Example 1.

[0109] Comparative Example 4

[0110] Different from Example 1, in the step of preparing graphene-heteroatom-doped porous carbon material, 100 g of porous carbon was added to 100 g of 5 wt% pyridine dichloromethane solution and dispersed evenly, then 100 g of water was added and dispersed evenly, and then transferred to a high-pressure reactor. The rest was the same as Example 1.

[0111] Comparative Example 5

[0112] The difference from Example 1 is that in step S2 of preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material, lithium titanate is not added. The rest is the same as Example 1.

[0113] Comparative Example 6

[0114] The difference from Example 1 is that in step S2 of preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material, 8 g of lithium titanate and 8 g of asphalt are evenly mixed. The rest is the same as Example 1.

[0115] Test Case

[0116] 1) Scanning electron microscope (SEM) test:

[0117] The lithium titanate amorphous carbon coated silicon carbon composite material (hereinafter referred to as silicon carbon composite material) in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the material has a granular structure, and the particle size of the material is evenly distributed and slightly bonded, and the particle size is between 2μm and 5μm.

[0118] 2) Button battery test

[0119] The silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 were used as negative electrode materials for lithium-ion batteries to prepare button-type cells. The preparation method was as follows: a binder, a conductive agent, and a solvent were added to the composite material, stirred to form a slurry, coated on copper foil, and dried and rolled to produce a negative electrode sheet. The binder used was polyvinylidene fluoride (PVDF), the conductive agent was conductive carbon black (SP), and the solvent was N-methylpyrrolidone (NMP). The ratio of the composite material, SP, PVDF, and NMP used was 90g:4g:6g:250mL. The electrolyte solution consisted of lithium hexafluorophosphate (LiPF6) and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio as the solvent, with an electrolyte concentration of 1 mol / L. A metal lithium sheet served as the counter electrode, and a polypropylene (PP) film was used as the separator. The button-type cells were assembled in an argon-filled glove box.

[0120] Electrochemical performance tests were performed on button cells containing the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 using a Wuhan Blue Power CT2001A battery tester with a charge and discharge voltage range of 0.005 V to 2.0 V and a charge and discharge rate of 0.1 C. The rate performance of the material was also tested (1 C / 0.1 C).

[0121] The thickness D1 of the negative electrode sheet of the button cell containing the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 after rolling was measured. The button cell was then dissected to measure the full-charge thickness D2 of the negative electrode sheet when fully charged to 100% SOC, and the expansion rate was calculated:

[0122] The expansion ratio is = (D1-D2) / D1;

[0123] The specific surface area and tap density of silicon-carbon composite materials were tested with reference to GB / T 38823-2020 "Silicon-Carbon"; the powder resistivity of the silicon-carbon composite materials was tested using a four-probe tester, and the diffusion coefficient of the material was tested by GITT; at the same time, the specific surface area and powder resistivity of graphene-heteroatom doped porous carbon materials (hereinafter referred to as porous carbon materials) were tested.

[0124] The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] The data in Table 1 show that the specific capacity, initial efficiency, powder resistivity, full-charge expansion, and rate performance of the silicon-carbon composites prepared in Examples 1-3 are significantly superior to those in Comparative Examples 1-6. This is due to the following: doping the porous carbon with heteroatoms and graphene reduces the powder resistance of the material, while utilizing the ductility of graphene to increase the tap density and compacted density of the material; simultaneously, the lithium titanate coating increases the lithium ion diffusion coefficient of the material, thereby improving the material's rate performance; and the lithium titanate coating in the outer layer constrains the material's expansion during charge and discharge.

[0128] 3) Soft pack battery test

[0129] The silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 were mixed with 95% artificial graphite as negative electrode materials to prepare negative electrode sheets. 1 / 3 Co 1 / 3 Mn 1 / 3 A 5Ah soft-pack battery was fabricated using lithium hexafluorophosphate (LiPF6) as the positive electrode, a 1:1 volume ratio mixture of ethylene carbonate (EC) and ethyl methyl carbonate (DEC) as the solvent, and a 1.3 mol / L electrolyte concentration. Celgard 2400 membrane was used as the separator. The negative electrode was tested for its liquid absorption capacity, gas generation, rate capability, and high-temperature storage performance.

[0130] a. Liquid absorption capacity test

[0131] Use a 1mL burette and draw 1mL of electrolyte. Add one drop of electrolyte to the electrode surface and time until the electrolyte is completely absorbed. Record the time t. The test results are shown in Table 2.

[0132] b. Pole gas production test

[0133] Weigh the electrode and calculate the weight of the active material as M1. Then place the electrode in deionized water and soak it at 45℃ for 48h. Calculate the gas production V1. Then calculate the gas production of the electrode.

[0134] =V1 / M1, see Table 2 for details.

[0135] Table 2

[0136]

[0137]

[0138] As can be seen in Table 2, the liquid absorption capacity and electrode gas production of the silicon-carbon composite materials obtained in Examples 1-6 are significantly lower than those of the comparative example. This may be due to the high specific surface area of ​​the silicon-carbon composite materials in the examples, which improves the material's liquid absorption and retention capacity. Furthermore, the lithium titanate coating on the surface of the material improves the material's coating integrity and reduces gas production.

[0139] c. Rate performance test

[0140] The rate performance test was performed on the soft-pack batteries of the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6.

[0141] HPPC tests were performed at different SOCs (5%, 10%, 30%, 50%, 70%, 90%, and 95%) according to 3C, and the charging DCR was tested. The test results are shown in Table 3.

[0142] Table 3

[0143] SOC 95％ 90％ 70％ 50％ 30％ 10％ 5％ Example 1 14.33 13.77 13.97 13.84 17.84 21.18 23.87 Example 2 15.44 14.58 14.90 14.75 18.80 22.31 25.10 Example 3 13.41 12.58 12.88 12.72 16.59 18.76 22.53 Comparative Example 1 17.58 17.28 17.76 17.36 21.93 26.82 30.54 Comparative Example 2 16.97 16.55 16.89 16.65 20.98 25.76 29.12 Comparative Example 3 18.87 18.32 18.56 18.23 22.21 27.87 32.11 Comparative Example 4 20.34 20.65 20.98 20.45 24.87 29.76 35.01 Comparative Example 5 18.97 18.21 18.84 18.51 22.72 27.40 31.76 Comparative Example 6 17.88 17.43 17.89 17.77 22.03 26.98 30.89

[0144] As can be seen from Table 3, the charging DCR of the soft-pack lithium-ion battery prepared using the silicon-carbon composite material of the present invention is better than that of the comparative example. The reason is that the silicon-carbon composite material of the present invention has a low powder resistivity, which reduces the resistance, and the lithium titanate is coated on the outer layer, which reduces the ionic impedance, thereby reducing the charging DCR.

[0145] d. High temperature storage performance test

[0146] A high-temperature storage test was performed on the soft-pack batteries of the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6.

[0147] The capacity of the battery under full charge is X1 when tested at 60℃. After 7 days at 60℃, the capacity of the battery is tested again and the value is X2. The charge retention is calculated as X2 / X1*100%. After that, the battery is fully charged to 100% SOC and the capacity of the battery is tested as X3. The recovery capacity is calculated as

[0148] =X3 / X1*100%; the test results are shown in Table 4.

[0149] Table 4

[0150] Charge retention Capacity recovery Example 1 96.4％ 98.7％ Example 2 97.3％ 99.3％ Example 3 96.1％ 98.1％ Comparative Example 1 94.2％ 96.7％ Comparative Example 2 93.2％ 96.1％ Comparative Example 3 93.0％ 95.8％ Comparative Example 4 92.5％ 95.4％ Comparative Example 5 93.4％ 96.2％ Comparative Example 6 94.1％ 96.5％

[0151] It can be seen from Table 4 above that the high-temperature storage performance of the silicon-carbon composite materials of Examples 1-3 is better than that of Comparative Examples 1-6. The reason is that the surface of the material is coated with lithium titanate and amorphous carbon, which improves the coating integrity of the material, reduces gas production, reduces side reactions, and improves the high-temperature storage performance.

[0152] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A graphene-heteroatom doped porous carbon material, characterized in that: The invention comprises porous carbon and graphene and heteroatoms distributed in the porous carbon; In terms of mass percentage, the content of the graphene is 0.5wt% to 2wt%, the content of the heteroatoms is 0.5wt% to 2wt%, and the rest is the porous carbon.

2. A method for preparing a graphene-heteroatom doped porous carbon material, characterized in that: The following steps are involved: S1, mixing porous carbon, heteroatoms and graphene oxide uniformly, transferring the mixture to a high-pressure reactor for reaction, and filtering to obtain a porous carbon material precursor; S2. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace, introduce carbon dioxide gas for treatment, and obtain the graphene-heteroatom doped porous carbon material.

3. The method for preparing a graphene-heteroatom-doped porous carbon material according to claim 2, wherein: Step S1 satisfies one or more of the following conditions a to d: a. In step S1, the mixing of the porous carbon, heteroatoms and graphene oxide comprises adding the porous carbon to the heteroatom solution and dispersing the porous carbon uniformly, and then adding the graphene oxide solution and ultrasonically dispersing the porous carbon uniformly; preferably, the concentration of the heteroatom solution is 1 wt% to 10 wt%; preferably, the heteroatom solution is obtained by mixing the heteroatoms with a solvent, and the solvent is at least one of dichloromethane, dimethylformamide, tetrahydrofuran and thionyl chloride; preferably, the concentration of the graphene oxide solution is 1 wt% to 5 wt%; b. In the step S1, the porous carbon, the heteroatom and the graphene oxide are mixed in a mass ratio of 100:(1-5):(1-5); c. In step S1, the reaction temperature is 100°C to 200°C, the pressure is 1Mpa to 5Mpa, and the reaction time is 1h to 6h; d. In step S1, the heteroatom is at least one of pyrrole, aniline, thiophene, dopamine, pyridine, and pyrimidine; Alternatively, step S2 satisfies one or two of the following conditions e to f: e. In step S2, the freeze-drying temperature is -50°C to -30°C, and the time is 24h to 48h; f. In step S2, the temperature of the carbon dioxide gas for treatment is 900°C to 1100°C, the time is 30min to 300min, and the flow rate of the carbon dioxide gas is 100SCCM to 500SCCM.

4. A graphene-heteroatom doped porous carbon material, characterized in that: The method for preparing the graphene-heteroatom-doped porous carbon material is used as claimed in claim 2 or 3.

5. A lithium titanate amorphous carbon-coated silicon-carbon composite material, characterized in that: The lithium titanate amorphous carbon-coated silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell; The inner core is a silicon-carbon material obtained by reacting a silane mixed gas and the graphene-heteroatom-doped porous carbon material as described in claim 1 or 4, the middle layer is silicon carbide, and the outer layer is a lithium titanate amorphous carbon composite. The thickness ratio of the inner core, the middle layer and the outer shell is (80-95): (1-3): (2-19).

6. A method for preparing a lithium titanate amorphous carbon-coated silicon-carbon composite material, characterized in that: The following steps are involved: S1. Transferring the graphene-heteroatom-doped porous carbon material according to claim 1 or 4 to a fluidized bed apparatus, first introducing a silane mixed gas for treatment, and then introducing a carbon source gas for treatment to obtain a silicon carbide-coated silicon-carbon composite material; S2. Evenly mix lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material, and carbonize the mixture to obtain the lithium titanate amorphous carbon-coated silicon-carbon composite material.

7. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material according to claim 6, wherein: Step S1 satisfies one or more of the following conditions a to d: a. In step S1, before the silane mixed gas is introduced for treatment, the pressure within the fluidized bed apparatus is set to 0.01 MPa to 0.1 MPa; b. In step S1, the temperature of the silane mixed gas for treatment is 300 ℃ ~ 500 ℃, the time is 30min ~ 300min, and the flow rate of the silane mixed gas is 100 SCCM ~ 500 SCCM; c. In step S1, the temperature of the carbon source gas for treatment is 700 ℃ ~ 900 ℃, the time is 30min ~ 300min, and the flow rate of the carbon source gas is 10SCCM ~ 50SCCM; d. In step S1, the silane mixed gas comprises silane gas and nitrogen; preferably, the volume ratio of the silane gas to the nitrogen is (1-5):10; preferably, the silane gas is at least one of monosilane, disilane, dimethyldichlorosilane and monochlorotrihydrogensilane; e. In step S1, the carbon source gas is at least one of ethylene and methane; Alternatively, step S2 satisfies one or two of the following conditions f to h: f. In step S2, the mixing of lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material includes mixing lithium titanate and asphalt evenly, heating to 300°C to 500°C to obtain a liquid asphalt and lithium titanate complex, and then adding the silicon carbide-coated silicon-carbon composite material and mixing evenly; g. In the step S2, the lithium titanate, the asphalt and the silicon carbide-coated silicon-carbon composite material are mixed in a mass ratio of (1 to 3): (5 to 10): 100; h. In step S2, the carbonization temperature is 1100°C to 1300°C, and the time is 1h to 6h.

8. A lithium titanate amorphous carbon-coated silicon-carbon composite material, characterized in that: The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material is adopted as claimed in claim 6 or 7.

9. A negative electrode plate, characterized in that: It comprises the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 5 or 8.

10. A lithium ion battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 9.

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