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

Abstract

The application belongs to 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 of the graphene-heteroatom doped porous carbon material, a negative electrode sheet and a lithium ion battery. The graphene-heteroatom doped porous carbon material is composed of porous carbon, graphene and heteroatoms distributed in the porous carbon. The content of the graphene is 0.5wt% to 2wt% in terms of mass percentage, the content of the heteroatoms is 0.5wt% to 2wt% in terms of mass percentage, and the rest is the porous carbon. The graphene-heteroatom doped porous carbon material has high electronic conductivity of the heteroatoms and high ductility of the graphene sheet structure, so that the compaction density of the porous carbon is improved. In addition, the alkaline groups on the surface of the heteroatom solution and the acidic groups of the graphene oxide can generate a carbon structure linked by chemical bonds through a hydrothermal reaction, so that the tap density and the electronic conductivity of the material are improved.

Description

Technical Field

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

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

[0003] Porous carbon, as a raw material for silicon-carbon materials, suffers from poor electronic conductivity due to its porous structure. While nano-silicon can be deposited within porous carbon, and amorphous carbon can be deposited on its surface at low temperatures, the poor electronic and ionic conductivity of amorphous carbon, despite its good isotropy, results in poor fast-charging and fast-discharging performance of silicon-carbon materials due to the combined effect of poor conductivity in both the core and outer shell. Summary of the Invention

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

[0005] To achieve the above technical objectives, the technical solution adopted by the present invention is 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] The graphene content is 0.5wt% to 2wt% by mass percentage, the heteroatom content is 0.5wt% to 2wt%, and the remainder is porous carbon.

[0008] In specific applications, the graphene content can be 0.5wt%, 0.7wt%, 0.9wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 1.9wt%, or 2wt%, etc., and the heteroatom content 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 by simultaneously doping porous carbon with heteroatoms and graphene, the compaction density of the porous carbon is improved by utilizing the poor electronic conductivity of heteroatoms and the high ductility of the graphene sheet structure. Simultaneously, the basic groups on the surface of the heteroatom solution and the acidic groups of graphene oxide can form chemically bonded carbon structures through a hydrothermal reaction, further enhancing the tap density and electronic conductivity.

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

[0011] S1. Mix porous carbon, heteroatoms and graphene oxide evenly, transfer to a high-pressure reactor for reaction and filtration to obtain a porous carbon material precursor;

[0012] S2. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace and process it with carbon dioxide gas to 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 compaction density, tap density, and electronic conductivity of the materials 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 uniform mixing of porous carbon, heteroatoms, and graphene oxide includes adding porous carbon to a heteroatom solution and dispersing it uniformly, followed by adding a graphene oxide solution and ultrasonically dispersing it uniformly; preferably, the concentration of the heteroatom solution is 1 wt% to 10 wt%; preferably, the heteroatom solution is obtained by mixing heteroatoms and a solvent, wherein the solvent is at least one selected from dichloromethane, dimethylformamide, tetrahydrofuran, and sulfoxide; preferably, the concentration of the graphene oxide solution is 1 wt% to 5 wt%.

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

[0017] It should be noted that when 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 material. When the amount of heteroatoms and graphene oxide added is too low, the improvement of the electronic conductivity of the material and the reduction of the expansion of the active material are limited. When the amount of graphene oxide added is too high, it will cause the graphene itself to agglomerate and increase the cost. When the amount of heteroatoms added is too high, the excessive heteroatoms will cause the tap density to decrease.

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

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

[0020] Alternatively, step S2 may satisfy one or both of the following conditions e to f:

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

[0022] f. In step S2, the temperature at which the carbon dioxide gas is introduced for treatment is 900℃~1100℃, the time is 30min~300min, and the flow rate of the carbon dioxide gas is 100SCCM~500SCCM.

[0023] A third aspect of the present invention provides a graphene-heteroatom-doped porous carbon material, which is prepared by the method for preparing 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 material's compaction density, tap density, and electronic conductivity.

[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, including a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0026] The 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, the outer layer is lithium titanate amorphous carbon composite, and the thickness ratio of the core, the middle layer and the outer shell is (80-95):(1-3):(2-19).

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

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

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

[0030] In one embodiment of the present invention, the silane gas is at least one of methanesilane, ethylsilane, dimethyldichlorosilane, and trichlorosilane.

[0031] The 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. The graphene-heteroatom-doped porous carbon material described in the first and third aspects is transferred to a fluidized bed device, and a silane mixed gas is first introduced for treatment, and then a carbon source gas is introduced for treatment to obtain a silicon carbide-coated silicon-carbon composite material.

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

[0034] It should be noted that the lithium titanate amorphous carbon-coated silicon-carbon composite material prepared by using the above-mentioned graphene-heteroatom-doped porous carbon materials, lithium titanate, pitch, etc. can improve the electronic conductivity by utilizing graphene and heteroatoms, and improve the ionic conductivity of the material by utilizing lithium titanate, 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 introducing the silane mixed gas for treatment, the pressure inside the fluidized bed equipment is set to 0.01 MPa to 0.1 MPa;

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

[0038] c. In step S1, the temperature at which the carbon source gas is introduced 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 includes silane gas and nitrogen gas; preferably, the volume ratio of the silane gas to the nitrogen gas is (1-5):10; preferably, the silane gas is at least one of methylsilane, dimethylsilane, dimethyldichlorosilane and monochlorotrihydrosilane.

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

[0041] Alternatively, step S2 may satisfy one or both of the following conditions f to h:

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

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

[0044] It should be noted that mixing lithium titanate, asphalt, and silicon carbide-coated silicon-carbon composite materials in a mass ratio of (1-3):(5-10):100 can effectively utilize the large interlayer spacing and zero expansion of lithium titanate to improve the fast charging and cycle performance of the material. When the amount of lithium titanate added is too low, the improvement on 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 will decrease due to the high voltage plateau of lithium titanate.

[0045] h. In step S2, the carbonization temperature is 1100℃~1300℃ and the time is 1h~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 method for preparing 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. Its application in lithium-ion batteries can improve power performance, initial efficiency and cycle performance.

[0048] A seventh aspect of the present invention provides a negative electrode sheet, 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 has better ionic and electronic conductivity.

[0050] An 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 using the above-mentioned negative electrode sheet, lithium-ion batteries have characteristics such as good power performance, high initial efficiency, and good cycle performance.

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

[0053] 1) By simultaneously doping porous carbon with heteroatoms and graphene, the compaction density of porous carbon is improved by utilizing the poor electronic conductivity of heteroatoms and the high ductility of graphene sheet structure. At the same time, the basic groups on the surface of heteroatom solution and the acidic groups of graphene oxide can generate chemically bonded carbon structures through hydrothermal reaction, which improves the tap density and electronic conductivity of the material.

[0054] 2) Lithium titanate and pitch are carbonized to obtain lithium titanate amorphous carbon coating on the surface of silicon carbon material. Taking advantage of the high ionic conductivity and large interlayer spacing of lithium titanate, as well as the high compatibility of amorphous carbon with electrolyte, the electronic and ionic conductivity of the material can be improved, and the rate capability and storage performance can be enhanced. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] in:

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

[0058] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other materials or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; the relevant operations can be fully understood based on the description in the specification and general technical knowledge in the art.

[0059] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[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] The graphene content is 0.5wt% to 2wt% by mass percentage, the heteroatom content is 0.5wt% to 2wt%, and the remainder is porous carbon.

[0062] By simultaneously doping porous carbon with heteroatoms and graphene, the compaction density of porous carbon is improved by utilizing the poor electronic conductivity of heteroatoms and the high ductility of graphene sheet structure. Simultaneously, the basic groups on the surface of the heteroatom solution and the acidic groups of graphene oxide can form chemically bonded carbon structures through a hydrothermal reaction, further enhancing the tap density and electronic conductivity of the material.

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

[0064] S1. Mix porous carbon, heteroatoms and graphene oxide evenly, transfer to a high-pressure reactor for reaction and filtration to obtain a porous carbon material precursor;

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

[0066] By mixing porous carbon, heteroatoms, and graphene oxide, graphene-heteroatom-doped porous carbon materials can be prepared, which can improve the compaction density, tap density, and electronic conductivity of the materials.

[0067] A third aspect of the present invention provides a graphene-heteroatom-doped porous carbon material, prepared using the method described in the second aspect. The graphene-heteroatom-doped porous carbon material prepared by the above method can improve the material's compaction density, tap 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, including a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0069] The 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, the outer layer is lithium titanate amorphous carbon composite, and the thickness ratio of the core, the middle layer and the outer shell is (80-95):(1-3):(2-19).

[0070] By utilizing graphene and heteroatoms to enhance electronic conductivity and lithium titanate to enhance ionic conductivity, lithium titanate amorphous carbon-coated silicon-carbon composite material exhibits superior ionic and electronic conductivity. Applying this lithium titanate amorphous carbon-coated silicon-carbon composite material to lithium-ion batteries improves power performance, initial efficiency, and cycle performance.

[0071] The 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. The graphene-heteroatom-doped porous carbon material described in the first and third aspects is transferred to a fluidized bed device, and a silane mixed gas is first introduced for treatment, and then a carbon source gas is introduced for treatment to obtain a silicon carbide-coated silicon-carbon composite material.

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

[0074] By employing the aforementioned graphene-heteroatom-doped porous carbon materials, lithium titanate, asphalt, etc., the prepared lithium titanate amorphous carbon-coated silicon-carbon composite material can utilize graphene and heteroatoms to enhance electronic conductivity, and utilize lithium titanate to enhance the ionic conductivity of the material, thus enabling the lithium titanate amorphous carbon-coated silicon-carbon composite material to have better ionic and electronic conductivity.

[0075] The sixth aspect of this invention provides a lithium titanate amorphous carbon-coated silicon-carbon composite material, prepared using the method described in the fifth aspect. The lithium titanate amorphous carbon-coated silicon-carbon composite material prepared by the above method exhibits superior 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 sheet, characterized in that it comprises the lithium titanate amorphous carbon-coated silicon-carbon composite material described in the fourth and sixth aspects. By employing the aforementioned lithium titanate amorphous carbon-coated silicon-carbon composite material, the negative electrode sheet exhibits superior ionic and electronic conductivity.

[0077] An eighth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the seventh aspect. By employing the aforementioned negative electrode sheet, the lithium-ion battery exhibits characteristics such as good power performance, high initial efficiency, and good cycle performance.

[0078] The present application will be further described in detail below through specific embodiments. These embodiments are only for further illustration and should not be construed as limiting the present application. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the product manufacturer shall apply; and any equipment or reagents used in the embodiments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0079] Example 1

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

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

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

[0083] Step S1:

[0084] Graphene-heteroatom-doped porous carbon material was transferred to a fluidized bed apparatus, evacuated to 0.05 MPa, then heated to 400°C, and a mixture of silane and nitrogen gas (volume ratio: silane:nitrogen = 3:10) was introduced at a flow rate of 300 SCCM for 150 min to deposit nano-silicon in the graphene-heteroatom-doped porous carbon material. After that, the introduction of the silane and nitrogen gas was stopped and replaced with ethylene gas. The temperature was raised to 800°C and the mixture was introduced at a flow rate of 30 SCCM for 150 min to form a silicon carbide protective film on its surface, thus 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℃ to obtain a liquid asphalt-lithium titanate composite. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly through a VC mixer. The mixture was then carbonized at 1200℃ for 3 hours to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0087] Example 2

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

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

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

[0091] Step S1:

[0092] Graphene-heteroatom-doped porous carbon material was transferred to a fluidized bed apparatus, evacuated to 0.01 MPa, heated to 300°C, and a silane-nitrogen mixture (volume ratio: silane:nitrogen = 1:10) was introduced. Deposition was carried out at a flow rate of 100 SCCM for 300 min to deposit nano-silicon in the graphene-heteroatom-doped porous carbon material. Then, the silane-nitrogen mixture 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 min to form a silicon carbide protective film on the surface, thus obtaining 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℃ to obtain a liquid asphalt-lithium titanate composite. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly through a VC mixer. The mixture was then carbonized at 1100℃ for 6 hours to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0095] Example 3

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

[0097] 100g of porous carbon was added to a 50g solution of 10wt% thiophene in tetrahydrofuran and dispersed evenly. Then, 100g of a 5wt% graphene oxide solution was added and ultrasonically dispersed evenly. The mixture was then transferred to a high-pressure reactor and reacted at 200℃ and 1MPa for 1h. After filtration, the resulting material was freeze-dried at -40℃ for 48h. The resulting material was then transferred to a tube furnace, heated to 1100℃, and carbon dioxide gas was introduced at a flow rate of 500SCCM for 30min to obtain graphene-heteroatom-doped porous carbon material.

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

[0099] Step S1:

[0100] Graphene-heteroatom-doped porous carbon material was transferred to a fluidized bed apparatus, evacuated to 0.1 MPa, heated to 500°C, and a mixture of dimethyldichlorosilane gas (volume ratio: dimethyldichlorosilane: nitrogen = 5:10) was introduced at a flow rate of 500 SCCM for 30 min to deposit nano-silicon in the graphene-heteroatom-doped porous carbon material. Then, the dimethyldichlorosilane was stopped and replaced with methane gas, and the temperature was raised to 900°C. The methane gas was introduced at a flow rate of 50 SCCM for 30 min to form a silicon carbide protective film on the surface, thus obtaining 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℃ to obtain a liquid asphalt-lithium titanate composite. Then, 100g of silicon carbide-coated silicon-carbon composite material was added and mixed evenly through a VC mixer. The mixture was then carbonized at 1300℃ for 1 hour to obtain a lithium titanate amorphous carbon-coated silicon-carbon composite material.

[0103] Comparative Example 1

[0104] Unlike Example 1, commercially available porous carbon (Kuraray Ltd., Japan, model YP-80F) was used to replace the graphene-heteroatom-doped porous carbon material in step S1, while the rest was the same as in Example 1.

[0105] Comparative Example 2

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

[0107] Comparative Example 3

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

[0109] Comparative Example 4

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

[0111] Comparative Example 5

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

[0113] Comparative Example 6

[0114] Unlike Example 1, in step S2 of preparing lithium titanate amorphous carbon-coated silicon-carbon composite material, 8g of lithium titanate and 8g of asphalt were mixed evenly, and the rest was the same as in Example 1.

[0115] Test case

[0116] 1) Scanning electron microscopy (SEM) morphology analysis:

[0117] SEM tests were performed on the lithium titanate amorphous carbon-coated silicon-carbon composite material (hereinafter referred to as silicon-carbon composite material) in Example 1. The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the material has a granular structure, the particle size is evenly distributed, and there is slight adhesion. The particle size is between 2μm and 5μm.

[0118] 2) Button cell battery test

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

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

[0121] The thickness D1 of the negative electrode sheet of the coin cell containing the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 after roll pressing was measured. Then, the full-charge thickness D2 of the negative electrode sheet was dissected at 100% SOC of the coin cell, and the expansion rate was calculated.

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

[0123] The specific surface area and tap density of silicon-carbon composite materials were tested in accordance with GB / T 38823-2020 "Silicon-Carbon"; the powder resistivity of silicon-carbon composite materials was tested using a four-probe tester, and the diffusion coefficient of the materials was tested using 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] As can be seen from the data in Table 1, the specific capacity, initial efficiency, powder resistivity, full-charge expansion, and rate performance of the silicon-carbon composite materials prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-6. This is because: by doping porous carbon with heteroatoms and graphene, the powder resistivity of the material is reduced, and the ductility of graphene is used to improve the tap density and compaction density of the material; simultaneously, the outer coating of lithium titanate improves the lithium-ion diffusion coefficient of the material, thereby improving the rate performance; and the outer coating of lithium titanate restricts the expansion of the material during charging and discharging.

[0128] 3) Pouch battery testing

[0129] Anode sheets were prepared by mixing 95% artificial graphite with the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 as the anode material. Ternary materials (LiNi) were also used. 1 / 3 Co 1 / 3 Mn 1 / 3 A 5Ah pouch cell was fabricated using lithium hexafluorophosphate (LiPF6) as the positive electrode and a 1:1 mixture of ethylene carbonate (EC) and methyl ethyl carbonate (DEC) as the solvent in the electrolyte, with an electrolyte concentration of 1.3 mol / L. A Celgard 2400 membrane was used as the separator. The liquid absorption capacity, gas generation, rate performance, and high-temperature storage performance of the negative electrode were tested.

[0130] a. Liquid absorption capacity test

[0131] A 1 mL burette was used to draw 1 mL of electrolyte and add one drop to the surface of the electrode. The time was recorded until the electrolyte was completely absorbed. The test results are shown in Table 2.

[0132] b. Electrode gas generation test

[0133] The electrode was weighed, and the weight of the active material was calculated as M1. The electrode was then placed in deionized water and soaked at 45℃ for 48 hours. The gas production rate V1 was calculated, and then the total gas production of the electrode was calculated.

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

[0135] Table 2

[0136]

[0137]

[0138] As can be seen from 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 in the comparative example. This may be because the silicon-carbon composite materials in the examples have a high specific surface area, which improves the liquid absorption and retention capacity of the material; simultaneously, the coating of lithium titanate on the material surface improves the integrity of the coating and reduces gas production.

[0139] c. Ratio Performance Testing

[0140] Rate performance tests were conducted on the silicon-carbon composite pouch cells of Examples 1-3 and Comparative Examples 1-6.

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

[0142] Table 3

[0143] 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 shown in 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 outer layer is coated with lithium titanate, which reduces the ion impedance, thus reducing the charging DCR.

[0145] d. High-temperature storage performance test

[0146] High-temperature storage tests were conducted on the silicon-carbon composite pouch cells of Examples 1-3 and Comparative Examples 1-6.

[0147] The battery's capacity at a full charge was tested at 60℃ and recorded as X1. After being placed at 60℃ for 7 days, the battery's capacity was tested again and recorded as X2. The charge retention was calculated as X2 / X1*100%. Then, the battery was fully charged to 100% SOC and its capacity was tested again and recorded as X3. The recovered capacity was calculated.

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

[0149] Table 4

[0150] 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] As can be seen from Table 4 above, the silicon-carbon composite materials of Examples 1-3 have better high-temperature storage performance than those of Comparative Examples 1-6. This is because the material surface is coated with lithium titanate and amorphous carbon, which improves the integrity of the coating, reduces gas production, reduces side reactions, and improves high-temperature storage performance.

[0152] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. 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, including a core, an outer shell, and an intermediate layer located between the core and the outer shell; The core is a silicon-carbon material obtained by reacting a silane mixed gas with graphene-heteroatom-doped porous carbon material, the intermediate layer is silicon carbide, and the outer shell is a lithium titanate amorphous carbon composite. The thickness ratio of the core, the intermediate layer and the outer shell is (80-95):(1-3):(2-19). The graphene-heteroatom-doped porous carbon material is composed of porous carbon and graphene and heteroatoms distributed in the porous carbon. By mass percentage, the content of graphene is 0.5wt% to 2wt%, the content of heteroatoms is 0.5wt% to 2wt%, and the remainder is the porous carbon. The graphene-heteroatom-doped porous carbon material is prepared by the following method, which includes the following steps: S1. Mix porous carbon, heteroatoms and graphene oxide evenly, transfer to a high-pressure reactor for reaction and filtration to obtain a porous carbon material precursor; S2. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace and process it with carbon dioxide gas to obtain the graphene-heteroatom-doped porous carbon material.

2. The lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 1, characterized in that, Step S1 satisfies one or more of the following conditions a to d: a. In step S1, the process of uniformly mixing porous carbon, heteroatoms, and graphene oxide includes adding porous carbon to a heteroatom solution and dispersing it uniformly, followed by adding a graphene oxide solution and ultrasonically dispersing it uniformly. b. In step S1, the porous carbon, the heteroatoms, 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℃~200℃, the pressure is 1Mpa~5Mpa, and the reaction time is 1h~6h; d. In step S1, the heteroatom is at least one of pyrrole, aniline, thiophene, dopamine, pyridine, and pyrimidine; Step S2 satisfies one or two of the following conditions e to f: e. In step S2, the freeze-drying temperature is -50℃ to -30℃, and the time is 24h to 48h; f. In step S2, the temperature at which the carbon dioxide gas is introduced for treatment is 900℃~1100℃, the time is 30min~300min, and the flow rate of the carbon dioxide gas is 100SCCM~500SCCM.

3. A method for preparing a lithium titanate amorphous carbon-coated silicon-carbon composite material, characterized in that, Includes the following steps: S1. Transfer graphene-heteroatom-doped porous carbon material to a fluidized bed device, first pass in a silane mixed gas for treatment, then pass in a carbon source gas for treatment, to obtain silicon carbide-coated silicon-carbon composite material. S2. Mix lithium titanate, asphalt and the silicon carbide-coated silicon-carbon composite material, and carbonize to obtain the lithium titanate amorphous carbon-coated silicon-carbon composite material. The graphene-heteroatom-doped porous carbon material is composed of porous carbon and graphene and heteroatoms distributed in the porous carbon. By mass percentage, the content of graphene is 0.5wt% to 2wt%, the content of heteroatoms is 0.5wt% to 2wt%, and the remainder is the porous carbon. The graphene-heteroatom-doped porous carbon material is prepared by the following method, which includes the following steps: S11. The porous carbon, heteroatoms and graphene oxide are mixed evenly and transferred to a high-pressure reactor for reaction and filtration to obtain a porous carbon material precursor. S12. After freeze-drying the porous carbon material precursor, transfer it to a tube furnace and process it with carbon dioxide gas to obtain the graphene-heteroatom-doped porous carbon material.

4. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 3, characterized in that, Step S1 satisfies one or more of the following conditions a to e: a. In step S1, before introducing the silane mixed gas for treatment, the pressure inside the fluidized bed equipment is set to 0.01 MPa to 0.1 MPa; b. In step S1, the temperature at which the silane mixed gas is introduced for treatment is 300℃~500℃, the time is 30min~300min, and the flow rate of the silane mixed gas is 100SCCM~500SCCM. c. In step S1, the temperature at which the carbon source gas is introduced 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 includes silane gas and nitrogen gas; e. In step S1, the carbon source gas is at least one of ethylene and methane; Step S2 satisfies one or two of the following conditions f to h: f. In step S2, the mixing of lithium titanate, asphalt and silicon carbide-coated silicon-carbon composite material includes mixing lithium titanate and asphalt evenly, heating to 300℃~500℃ to obtain liquid asphalt and lithium titanate composite, and then adding the silicon carbide-coated silicon-carbon composite material and mixing evenly. g. In step S2, the lithium titanate, the asphalt, and the silicon carbide-coated silicon-carbon composite material are mixed in a mass ratio of (1-3):(5-10):100; h. In step S2, the carbonization temperature is 1100℃~1300℃ and the time is 1h~6h.

5. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 3, characterized in that, Step S11 satisfies one or more of the following conditions a to d: a. In step S11, the process of uniformly mixing porous carbon, heteroatoms, and graphene oxide includes adding porous carbon to a heteroatom solution and dispersing it uniformly, followed by adding a graphene oxide solution and ultrasonically dispersing it uniformly. b. In step S11, the porous carbon, the heteroatoms, and the graphene oxide are mixed in a mass ratio of 100:(1-5):(1-5); c. In step S11, the reaction temperature is 100℃~200℃, the pressure is 1Mpa~5Mpa, and the reaction time is 1h~6h; d. In step S11, the heteroatom is at least one of pyrrole, aniline, thiophene, dopamine, pyridine, and pyrimidine; Step S12 satisfies one or two of the following conditions e to f: e. In step S12, the freeze-drying temperature is -50℃ to -30℃, and the time is 24h to 48h; f. In step S12, the temperature at which the carbon dioxide gas is introduced for treatment is 900℃~1100℃, the time is 30min~300min, and the flow rate of the carbon dioxide gas is 100SCCM~500SCCM.

6. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 5, characterized in that, The concentration of the heteroatom solution is 1 wt% to 10 wt%. Alternatively, the heteroatom and solvent are mixed to obtain the heteroatom solution, wherein the solvent is at least one of dichloromethane, dimethylformamide, tetrahydrofuran, and sulfoxide. Alternatively, the concentration of the graphene oxide solution is 1 wt% to 5 wt%.

7. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 2, characterized in that, The concentration of the heteroatom solution is 1 wt% to 10 wt%. Alternatively, the heteroatom and solvent are mixed to obtain the heteroatom solution, wherein the solvent is at least one of dichloromethane, dimethylformamide, tetrahydrofuran, and sulfoxide. Alternatively, the concentration of the graphene oxide solution is 1 wt% to 5 wt%.

8. The method for preparing the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 4, characterized in that, The volume ratio of the silane gas to the nitrogen gas is (1-5):10; Alternatively, the silane gas is at least one of methanesilane, ethylsilane, dimethyldichlorosilane, and trichlorosilane.

9. A lithium titanate amorphous carbon-coated silicon-carbon composite material, characterized in that, The lithium titanate amorphous carbon-coated silicon-carbon composite material was prepared by any one of the preparation methods described in claims 3 to 8.

10. A negative electrode sheet, characterized in that, Including the lithium titanate amorphous carbon-coated silicon-carbon composite material as described in claim 1, 2, or 9.

11. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 10.

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