A carbon material, its preparation method, and its applications

Abstract

This invention discloses a carbon material, its preparation method, and its applications, belonging to the field of anode material technology. The carbon material includes: a carbon substrate and a reinforcing carbon layer covering at least a portion of the surface of the carbon substrate; the reinforcing carbon layer is composed of at least two stacked carbon coating layers with different lattice orientations, with adjacent carbon coating layers having different lattice orientations. In this invention, the preferred lattice orientations of adjacent carbon coating layers are different, causing cracks to deflect, branch, or stop propagating at the interlayer interface, significantly improving the fracture toughness of the carbon layer; this multi-orientation stacked structure can uniformly disperse the anisotropic stress generated by silicon volume expansion into interlayer shear strain, avoiding local stress concentration; simultaneously, the three-dimensional conductive network constructed by multi-orientation microcrystals overcomes the defects of single-orientation coating layers in terms of conductive anisotropy and insufficient rate performance, ultimately providing stronger and more uniform physical constraints for repeated silicon expansion.

Description

Technical Field

[0001] This invention belongs to the field of negative electrode material technology, specifically relating to a carbon material and its preparation method and application. Background Technology

[0002] Currently, graphite is the primary anode material for commercial lithium-ion batteries, but its theoretical specific capacity is only 372 mAh / g, which is insufficient to meet the development requirements of high-energy-density batteries. Silicon, with a theoretical specific capacity as high as 4200 mAh / g, is more than ten times that of graphite. Therefore, silicon-carbon anode materials are considered key materials for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes massive volume expansion and contraction exceeding 300% during charging and discharging, leading to the pulverization of active particles and damage to the electrode structure. Simultaneously, the solid electrolyte interfacial film repeatedly ruptures and regenerates, continuously consuming electrolyte and lithium sources, resulting in rapid capacity decay and a significantly shortened cycle life. Furthermore, silicon has low intrinsic conductivity, affecting rate performance. Therefore, effectively suppressing silicon volume expansion, maintaining interfacial stability, and constructing a highly efficient conductive network are the core challenges for the commercialization of silicon-carbon anode materials.

[0003] Conventional methods for suppressing volume expansion mainly involve controlling the pore structure of porous carbon and its surface carbon layer. On one hand, the pore space within the porous carbon absorbs and buffers the volumetric strain generated by silicon during cycling. On the other hand, a carbon layer is further coated onto the surface of the silicon-carbon particles to ensure the strength of the porous carbon. However, the surface carbon layers used in existing technologies often suffer from problems such as a single or random orientation of carbon microcrystals. Specifically: First, when the carbon microcrystal orientation is single or disordered, there is a lack of effective control over the crack propagation direction. Under the cyclic stress generated by the repeated volume expansion of silicon, cracks can easily penetrate the entire coating layer rapidly along the arrangement direction of the carbon microcrystals, leading to early failure of the protective layer. Second, a single-oriented carbon layer exhibits significant anisotropy, resulting in uneven resistance to expansion stress in different directions. Stress tends to concentrate in weaker directions, accelerating localized damage. Third, the microcrystal growth direction is difficult to control precisely during the traditional carbon layer preparation process, leading to high residual stress within and between layers, insufficient interfacial bonding strength, and a tendency for interlayer delamination to occur during long-term cycling, further weakening the protective effect. Summary of the Invention

[0004] To address the above problems, the purpose of this invention is to provide a carbon material, its preparation method, and its applications.

[0005] In a first aspect, the present invention provides a carbon material comprising: a carbon substrate and a reinforcing carbon layer covering at least a portion of the surface of the carbon substrate; the reinforcing carbon layer is composed of at least two carbon coating layers having lattice orientations stacked together, wherein adjacent carbon coating layers have different lattice orientations, i.e., the preferred lattice orientations of two adjacent carbon coating layers are different from each other.

[0006] Secondly, the present invention provides a method for preparing a carbon material, comprising the following steps: S1. Disperse the carbon-based material in a mesophase pitch solution and transfer it to a template to prepare a sheet-like preform. Place the preform in a shearing device, heat it to the softening temperature, and then apply shear force along the X direction at a set speed for orientation. While maintaining the shearing conditions, introduce air and heat it to the crosslinking temperature to perform oxidative crosslinking to fix the pitch orientation direction. After cooling while maintaining the shearing conditions, perform graphitization treatment to obtain a carbon material with a first layer of oriented carbon coating on the surface. S2. The carbon material with a first oriented carbon coating layer on its surface is mixed with the mesophase pitch and heated until the pitch melts. A magnetic field perpendicular to the liquid surface is applied, and air is introduced at the same time and the temperature is raised to the crosslinking temperature to carry out oxidative crosslinking to fix the pitch orientation direction. After cooling under the magnetic field conditions, graphitization treatment is carried out to obtain the carbon material with a second oriented carbon coating layer on its surface. S3. When it is necessary to prepare two or more oriented carbon coating layers, alternately execute S1 and / or S2 until the designed number of layers is obtained to obtain carbon material.

[0007] Thirdly, the present invention provides a silicon-carbon material, comprising a carbon skeleton and silicon particles deposited in and / or on the surface of the carbon skeleton; the carbon skeleton is the aforementioned carbon material or porous carbon material, and the silicon-carbon material has a reinforcing carbon layer; the reinforcing carbon layer is composed of at least two carbon layers with lattice orientations stacked together, and adjacent carbon layers have different lattice orientations.

[0008] Fourthly, the present invention provides a negative electrode sheet comprising the aforementioned silicon-carbon material.

[0009] Fifthly, the present invention provides a battery comprising the aforementioned negative electrode.

[0010] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: This invention, by setting the preferred lattice orientations of adjacent carbon coating layers to be different, causes cracks to continuously deflect, branch, or terminate at the interlayer interface, thereby preventing through-cracks in the carbon shell along a single lattice orientation direction and significantly improving the fracture toughness and crack resistance of the carbon shell. Silicon-carbon materials obtained by depositing silicon using this carbon material exhibit a stacked structure with different lattice orientations, which uniformly disperses the multidirectional stress generated by silicon volume expansion and converts it into interlayer shear strain, avoiding structural damage caused by excessive local stress. The aforementioned multilayered lattice-oriented carbon coating effectively suppresses side reactions and capacity decay caused by carbon shell cracking during cycling, thus significantly improving the coulombic efficiency and cycling stability of the material. Furthermore, this multilayered structure constructs a three-dimensional conductive network through multi-oriented microcrystals, compensating for the anisotropic conductivity defects present in single-lattice-oriented coating layers, while avoiding rate performance degradation due to increased diffusion paths, achieving stable electrochemical performance at high rates.

[0011] The "cross-layout" structure of this invention (with different lattice orientations of adjacent layers) provides stronger and more uniform physical constraints on the repeated expansion of silicon, fundamentally suppressing particle pulverization and electrode structure damage. Attached Figure Description

[0012] Figure 1 This is a TEM image of the porous carbon coated with multilayer carbon prepared in Example 1.

[0013] Figure 2 TEM image of porous carbon coated with single-oriented carbon prepared for Comparative Example 2. Detailed Implementation

[0014] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0015] As previously stated, the present invention provides a carbon material comprising: a carbon substrate and a reinforcing carbon layer covering at least a portion of the surface of the carbon substrate; the reinforcing carbon layer is composed of at least two carbon coating layers having lattice orientations stacked together, and adjacent carbon coating layers having different lattice orientations, i.e., the preferred lattice orientations of two adjacent carbon coating layers are different from each other.

[0016] To address the problem of carbon shells easily cracking through a single lattice orientation, this invention employs adjacent carbon coating layers with different preferred lattice orientations. This causes cracks to deflect, branch, or stop propagating at the interlayer interface, significantly improving the fracture toughness of the carbon shell. This multi-orientation stacked structure can uniformly disperse the anisotropic stress generated by silicon volume expansion into interlayer shear strain, avoiding local stress concentration. Simultaneously, the three-dimensional conductive network constructed by multi-orientation microcrystals overcomes the defects of single-orientation coating layers in terms of conductive anisotropy and insufficient rate performance, ultimately providing stronger and more uniform physical constraints on the repeated expansion of silicon, fundamentally suppressing particle pulverization and electrode structure damage.

[0017] In some embodiments, the lattice orientation angle between adjacent carbon coating layers is 30 to 90°.

[0018] In some embodiments, the thickness of each orientation coating layer is 1~50nm, including but not limited to: 1nm, 10nm, 20nm, 30nm, 40nm, 50nm, etc.; the thickness of the reinforcing carbon layer is 10~200nm, including but not limited to: 10nm, 20nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, etc.

[0019] In some embodiments, the enhanced carbon layer is composed of 2 to 10 layers of carbon coating with lattice orientation.

[0020] In some embodiments, the pore volume of the carbon material is 0.2–1.0 cm³. 3 / g, including but not limited to: 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1cm 3 / g etc.

[0021] As the framework of silicon-carbon anodes, carbon materials directly determine the ability to accommodate silicon particles by their pore size; the larger the pore size, the more silicon particles can be accommodated.

[0022] Secondly, the present invention provides a method for preparing a multilayer carbon-coated carbon material, comprising the following steps: S1. Disperse the carbon-based material in a mesophase pitch solution and transfer it to a template to prepare a sheet-like preform. Place the preform in a shearing device, heat it to the softening temperature, and then apply shear force along the X direction at a set speed for orientation. While maintaining the shearing conditions, introduce air and heat it to the crosslinking temperature to perform oxidative crosslinking to fix the pitch orientation direction. After cooling while maintaining the shearing conditions, perform graphitization treatment to obtain a carbon material with a first layer of oriented carbon coating on the surface. S2. The carbon material with a first layer of oriented carbon coating on its surface is mixed with mesophase pitch and heated until the pitch melts. A magnetic field perpendicular to the liquid surface is applied, and air is introduced at the same time and the temperature is raised to the crosslinking temperature to carry out oxidative crosslinking to fix the pitch orientation direction. After cooling under the magnetic field condition, graphitization treatment is carried out to obtain the carbon material with a second layer of oriented carbon coating on its surface. S3. When it is necessary to prepare two or more oriented carbon coating layers, alternately execute S1 and / or S2 until the designed number of layers is obtained to obtain carbon material.

[0023] This invention utilizes alternating physical fields of shear orientation and magnetic field orientation, which are orthogonal or in different directions, to precisely control the preferred lattice orientation of each carbon coating layer and easily achieve multilayer structures with different orientations for adjacent layers. Shear orientation can achieve in-plane orientation along the X direction, while magnetic field orientation can achieve vertical orientation perpendicular to the liquid surface. The two are orthogonal, avoiding the limitation of alternating rotation with a single orientation method. This method can ultimately construct multilayer carbon shells in a "cross-layout" manner, significantly improving the material's crack resistance, stress dispersion ability, and comprehensive electrochemical performance.

[0024] In some embodiments, in step S1, the carbon substrate material is selected from one or more of activated carbon, carbon molecular sieve, template carbon, carbon aerogel, and carbon fiber.

[0025] In some embodiments, in step S1, the median particle size D50 of the carbon substrate material is 1~100μm; including but not limited to: 1μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc.; preferably 2~20μm.

[0026] In some embodiments, in step S1, the pore volume of the carbon substrate material is 1.2~1.6 cm³. 3 / g; including but not limited to: 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g etc.

[0027] The pore volume of the porous carbon substrate directly affects the pore size of the carbon material, which in turn affects the deposition of silicon particles. After the carbon material is graphitized at high temperature, the pore volume is further reduced. Therefore, the pore volume of the porous carbon substrate used should be large enough.

[0028] In some embodiments, in step S1, the average pore size of the carbon substrate material is 1.6~10.0 nm, including but not limited to: 1.6 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc., preferably 2~5 nm.

[0029] In some embodiments, in step S1, the specific surface area of ​​the carbon substrate material is 300~3000 m². 2 / g, including but not limited to: 300m 2 / g、500m 2 / g、600m 2 / g、800m 2 / g, 1000m 2 / g, 1500m 2 / g、2000m 2 / g、2500m 2 / g、3000m 2 / g, etc., preferably 500~2500m 2 / g.

[0030] In some embodiments, in step S1, the template is selected from square, round or other shaped molds according to actual needs. Its main function is to shape the mixture to facilitate subsequent processes.

[0031] In some embodiments, in step S1, the solvent of the mesophase pitch solution is tetrahydrofuran, and the concentration of the solution is 10~30wt%, including but not limited to: 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, etc.; the mass ratio of carbon matrix to mesophase pitch is 100:(0.2~2), including but not limited to: 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, etc.

[0032] In some embodiments, in step S1, the method for transferring the material to the template to prepare the sheet-like preform is the solvent removal method by evaporation.

[0033] In some embodiments, in step S1, the softening temperature is 150~170℃, including but not limited to: 150℃, 155℃, 160℃, 165℃, 170℃, etc.; the shearing speed is set to 5~20mm / s, including but not limited to: 5mm / s, 8mm / s, 10mm / s, 12mm / s, 15mm / s, 18mm / s, 20mm / s, etc.

[0034] In some embodiments, in step S1, the crosslinking temperature is 250~300℃, including but not limited to: 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the oxidative crosslinking time is 30~90min, including but not limited to: 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc.

[0035] In some embodiments, in step S2, the mass ratio of the carbon material with the first oriented carbon coating layer to the mesophase pitch is 100:(0.2~2), including but not limited to: 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, etc.

[0036] In some embodiments, in step S2, the strength of the magnetic field is 0.5~2T, including but not limited to: 0.5T, 0.8T, 1T, 1.2T, 1.5T, 1.8T, 2T, etc.

[0037] In some embodiments, in step S2, the crosslinking temperature is 250~300℃, including but not limited to: 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the oxidative crosslinking time is 30~90min, including but not limited to: 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc.

[0038] In some embodiments, in steps S1 and S2, the temperature of the graphitization treatment is independently 1600~2500°C, and the time of the graphitization treatment is independently 1~5h.

[0039] In some embodiments, the specific process of alternately executing S1 and / or S2 until the designed number of layers in step S3 is as follows: if the required total number of layers is odd, S1 is executed once first, and then S2 and S1 are executed alternately until the designed number of layers is reached; if the required total number of layers is even, S1 and S2 are executed alternately until the designed number of layers is reached.

[0040] In some embodiments, the preparation method further includes step S4: further activating and pore-forming the carbon material obtained in step S3 to obtain a porous carbon material.

[0041] In some embodiments, the pore-forming activation is performed using physical or chemical activation, and the pore volume of the porous carbon material is increased to 0.2–1.0 cm³. 3 / g, including but not limited to: 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g etc.

[0042] In some embodiments, the activating gas used in the physical activation pore-forming process is one or more of H2O, CO2, air, and oxygen; the etching agent used in the chemical activation pore-forming process is one or more of KOH, NaOH, ZnCl2, Na2CO3, and NaHCO3.

[0043] In some embodiments, the activation temperature for pore formation is 500~1200℃, including but not limited to: 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc.; the activation time for pore formation is 2~10h, including but not limited to: 2h, 2.5h, 3h, 3.5h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0044] In some embodiments, the activation pore-forming process does not affect the lattice orientation of the oriented carbon coating.

[0045] Thirdly, the present invention provides a silicon-carbon material comprising a carbon skeleton and silicon particles deposited in and / or on the surface of the carbon skeleton, wherein the carbon skeleton is the carbon material provided in the first aspect of the present invention or a carbon material prepared by the method for preparing the carbon material provided in the second aspect of the present invention.

[0046] The resulting silicon-carbon material continues the surface structure of the carbon material used, that is, it includes a reinforcing carbon layer, which is composed of at least two carbon layers with lattice orientations stacked together, and adjacent carbon layers have different lattice orientations.

[0047] In some embodiments, the method for preparing the silicon-carbon material includes the following steps: placing a carbon skeleton in a vapor deposition apparatus, introducing a silicon source gas and a carrier gas, and then performing vapor deposition to obtain the silicon-carbon material.

[0048] In some embodiments, the silicon source gas is one or more of SiH4, Si2H6, SiCl4, and SiHCl3, the carrier gas is nitrogen, and the volume ratio of silicon source gas to carrier gas is 1:(2~10), including but not limited to: 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.; the silane partial pressure in the reaction system is 1~5 kPa, including but not limited to: 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, etc.; the vapor deposition temperature is 450~600℃, including but not limited to: 450℃, 500℃, 550℃, 600℃, etc.; the vapor deposition time is 2~15h, including but not limited to: 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0049] By controlling the partial pressure of silane, the pyrolysis rate can be slowed down, which is conducive to the diffusion and nucleation of silicon atoms into the pores of carbon materials, avoiding accumulation only on the surface. Controlling the partial pressure of silane can maintain the stability of the precursor concentration and prevent it from being carried away by the gas flow before it has fully reacted. The deposition temperature can ensure the effective pyrolysis of silane and protect the stability of the carbon skeleton structure. By coordinating the deposition time with the temperature, the amount of silicon filling in the pores can be precisely controlled, so that the ratio of silicon volume to the total pore volume of carbon materials is maintained at 0.3~0.7. This ensures high capacity while reserving sufficient expansion buffer space, providing a structural basis for subsequent multi-stage stress control.

[0050] In some embodiments, the silicon content of the silicon-carbon material is 20-70 wt%.

[0051] In some embodiments, the specific surface area of ​​the silicon-carbon material is 0.5~10 m². 2 / g.

[0052] Fourthly, the present invention provides a negative electrode sheet comprising the aforementioned silicon-carbon material.

[0053] Fifthly, the present invention provides a battery comprising the aforementioned negative electrode.

[0054] Example 1 S1. Commercially available porous carbon was provided as the carbon substrate. The D50 of this carbon substrate was measured to be 8 μm, and the pore volume was 1.2 cm³. 3 / g, with an average pore size of 2.3nm and a specific surface area of ​​2087m². 2 / g. The carbon substrate was dried at 150°C for 0.5 h under a nitrogen atmosphere to obtain a dried porous carbon substrate; the mesophase pitch was dissolved in tetrahydrofuran solvent to prepare a 25 wt% mesophase pitch solution; the dried porous carbon substrate was placed in the mesophase pitch solution and stirred to disperse evenly to obtain a mixture, wherein the mass ratio of porous carbon substrate to mesophase pitch was 100:1; the mixture was placed in a sheet mold, and the solvent was evaporated at 90°C to obtain a sheet preform; the sheet preform was preheated to 160°C, The sheet-like preform is placed in a device capable of applying parallel shear force and continuously subjected to shear force at a shear rate of 10 mm / s along the X direction to orient it. During the orientation process, air is continuously introduced and the preform is heated to 280°C. The cross-linking orientation is maintained at 280°C for 60 min to fix the orientation structure through oxidative cross-linking. Then, it is cooled to room temperature while maintaining the orientation to obtain an oriented preform. The oriented preform is graphitized at 2200°C under a nitrogen atmosphere for 2 h to obtain a carbon material with a first layer of oriented carbon coating on its surface.

[0055] S2. A carbon material with a first-layer oriented carbon coating is mixed with mesophase pitch at a mass ratio of 100:1 and heated to 160°C to completely melt the mesophase pitch, resulting in a suspension of carbon material particles. The suspension is placed in a heating device with a magnetic field, and a magnetic field perpendicular to the liquid surface with a strength of 1T is applied. Under an air atmosphere, the suspension is heated to 280°C and cross-linked under the magnetic field for 60 minutes to fix the oriented structure through oxidative cross-linking. Then, it is cooled to room temperature while maintaining a constant magnetic field strength to obtain a secondary-oriented intermediate product. The secondary-oriented intermediate product is graphitized at 2200°C under a nitrogen atmosphere for 2 hours to obtain a carbon material with two layers of oriented carbon coating.

[0056] TEM image of carbon material with two oriented carbon coating layers as shown Figure 1 As shown, the thickness of the first-oriented carbon coating layer is about 5 nm, the thickness of the second-oriented carbon coating layer is about 6 nm, and the angle between the lattice orientation of the first-oriented carbon coating layer and the lattice orientation of the second-oriented carbon coating layer is between 30 and 90°.

[0057] S3. The carbon material containing two oriented carbon coating layers is placed in a mixed atmosphere of water vapor, carbon dioxide and nitrogen with a volume ratio of 15:20:65, and the temperature is raised to 1000℃ for activation treatment for 5 hours to obtain porous carbon material.

[0058] In this embodiment, the obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption amount at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.60 cm³. 3 / g.

[0059] Comparative Example 1 The same commercially available porous carbon as in Example 1 was used.

[0060] S1. First, graphitize the porous carbon in a nitrogen atmosphere at 2200℃ for 4 hours to obtain graphitized porous carbon.

[0061] S2. The graphitized porous carbon is placed in a mixed atmosphere of water vapor, carbon dioxide and nitrogen in a volume ratio of 15:20:65, and the temperature is raised to 1000℃ for activation treatment for 5 hours to obtain porous carbon material.

[0062] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.59 cm³. 3 / g.

[0063] Comparative Example 2 The difference from Example 1 is that only the orientation step S1 is performed; the specific preparation method is as follows: S1. The carbon substrate is dried at 150°C for 0.5 h under a nitrogen atmosphere to obtain a dried carbon substrate; the mesophase pitch is dissolved in tetrahydrofuran solvent to prepare a 25 wt% mesophase pitch solution; the dried carbon substrate is placed in the mesophase pitch solution and stirred to disperse evenly to obtain a mixture, wherein the mass ratio of carbon substrate to mesophase pitch is 100:2; the mixture is placed in a sheet mold, and the solvent is removed by evaporation at 90°C to obtain a sheet preform; the sheet preform is preheated to 160°C. Then, it is placed in a device that applies parallel shear force, and shear force is continuously applied along the X direction at a shear rate of 10 mm / s to orient the sheet-like preform; air is introduced during the orientation process, and the preform is heated to 280°C and maintained at 280°C for 60 min to fix the orientation structure through oxidative crosslinking. Then, it is cooled to room temperature while maintaining the orientation to obtain an oriented preform; the oriented preform is graphitized in a nitrogen atmosphere at 2200°C for 2 h to obtain a carbon material with a single-oriented carbon coating layer.

[0064] TEM images of the prepared carbon materials coated with carbon of a single orientation are shown below. Figure 2 As shown, the thickness of the single-oriented carbon coating layer is approximately 12 nm.

[0065] S2, same as step S3 in Example 1. The difference is that a carbon material with a single-oriented carbon coating layer is used instead of a carbon material with two-oriented carbon coating layers.

[0066] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.62 cm³. 3 / g.

[0067] Comparative Example 3 The difference from Example 1 is that only the orientation step S2 is performed; the specific preparation method is as follows: S1. A carbon matrix and mesophase pitch are mixed at a mass ratio of 100:2 and heated to 160°C to completely melt the mesophase pitch, resulting in a suspension of carbon-containing material particles. The suspension is placed in a heating device with a magnetic field, and a magnetic field perpendicular to the liquid surface with a strength of 1T is applied. Under air atmosphere, the suspension is heated to 280°C and subjected to oriented crosslinking under the magnetic field for 60 minutes to fix the oriented structure through oxidative crosslinking. Subsequently, it is cooled to room temperature while maintaining a constant magnetic field strength to obtain a secondary oriented intermediate product. This secondary oriented intermediate product is graphitized at 2200°C under a nitrogen atmosphere for 2 hours to obtain a carbon material with a single-oriented carbon coating layer. The thickness of the carbon coating layer in the prepared carbon material with a single-oriented carbon coating layer is 11 nm.

[0068] S2, same as step S3 in Example 1. The difference is that a carbon material with a single-oriented carbon coating layer is used instead of a carbon material with two-oriented carbon coating layers.

[0069] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.60 cm³. 3 / g.

[0070] Example 2 The difference from Example 1 is that in step S1, the shearing speed is 20 mm / s.

[0071] Example 3 The difference from Example 1 is that in step S1, the shearing speed is 5 mm / s.

[0072] Example 4 The difference from Example 1 is that in step S2, the magnetic field strength is 2T.

[0073] Example 5 The difference from Example 1 is that in step S2, the magnetic field strength is 0.5T.

[0074] Example 6 The difference from Example 1 is that the activation time in step S3 is 10 hours.

[0075] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.97 cm³. 3 / g.

[0076] Example 7 The difference from Example 1 is that the activation time in step S3 is 2 hours.

[0077] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.40 cm³. 3 / g.

[0078] Example 8 The difference from Example 1 is that the graphitization temperature in steps S1 and S2 is 2500°C.

[0079] In step S3, the activation time is 8 hours.

[0080] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.62 cm³. 3 / g.

[0081] Example 9 The difference from Example 1 is that the graphitization temperature in steps S1 and S2 is 1600°C.

[0082] In step S3, the activation time is 3 hours.

[0083] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.59 cm³. 3 / g.

[0084] Example 10 S1. Porous carbon (using the same commercially available porous carbon as in Example 1) was dried at 150°C under a nitrogen atmosphere for 0.5 h to obtain a dried carbon substrate. Mesophase pitch was dissolved in tetrahydrofuran solvent to prepare a 30 wt% mesophase pitch solution. The dried porous carbon was placed in the mesophase pitch solution and stirred until evenly dispersed to obtain a mixture, wherein the mass ratio of carbon substrate to mesophase pitch was 100:2. The mixture was placed in a sheet mold, and the solvent was removed by evaporation at 90°C to obtain a sheet preform. The sheet preform was preheated. After reaching 150°C, the material is placed in a device capable of applying parallel shear force, and shear force is continuously applied along the X direction at a shear rate of 8 mm / s to orient the sheet-like preform. During the orientation process, air is continuously introduced, and the preform is heated to 300°C. The cross-linking orientation is maintained at 300°C for 30 min to fix the orientation structure through oxidative cross-linking. Subsequently, the preform is cooled to room temperature while maintaining the orientation to obtain an oriented preform. The oriented preform is then graphitized at 2000°C under a nitrogen atmosphere for 5 h to obtain a carbon material with a first layer of oriented carbon coating on its surface.

[0085] S2. The carbon material with a first oriented carbon coating layer on its surface is mixed with mesophase pitch at a mass ratio of 100:0.5 and heated to 160°C to completely melt the mesophase pitch, resulting in a suspension of carbon material particles. The suspension is placed in a heating device with a magnetic field, and a magnetic field perpendicular to the liquid surface with a strength of 0.8T is applied. Under an air atmosphere, the suspension is heated to 300°C and cross-linked under the magnetic field for 30 minutes to fix the oriented structure through oxidative cross-linking. Then, it is cooled to room temperature while maintaining a constant magnetic field strength to obtain a secondary oriented intermediate product. The secondary oriented intermediate product is graphitized at 2200°C under a nitrogen atmosphere for 2 hours to obtain a carbon material with a second oriented carbon coating layer on its surface.

[0086] S3. Repeat the S1 (shear orientation) and S2 (magnetic field orientation) operations in sequence to obtain a carbon material with 4 oriented carbon coating layers.

[0087] The carbon material coated with four oriented carbon coating layers has the following thicknesses from the inside out: the first oriented carbon coating layer has a thickness of 11 nm, the second oriented carbon coating layer has a thickness of 3 nm, the third oriented carbon coating layer has a thickness of 12 nm, and the fourth oriented carbon coating layer has a thickness of 3 nm.

[0088] S4. The carbon material containing four oriented carbon coating layers is placed in a mixed atmosphere of water vapor, carbon dioxide and nitrogen with a volume ratio of 15:20:65, and the temperature is raised to 1000℃ for activation treatment for 6 hours to obtain porous carbon material.

[0089] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.58 cm³. 3 / g.

[0090] Example 11 S1. Porous carbon (using the same commercially available porous carbon as in Example 1) was dried at 150°C under a nitrogen atmosphere for 0.5 h to obtain a dried carbon substrate. Mesophase pitch was dissolved in tetrahydrofuran solvent to prepare a 10 wt% mesophase pitch solution. The dried carbon substrate was placed in the mesophase pitch solution and stirred until evenly dispersed to obtain a mixture, wherein the mass ratio of carbon substrate to mesophase pitch was 100:0.5. The mixture was placed in a sheet mold, and the solvent was removed by evaporation at 90°C to obtain a sheet preform. The sheet preform... After preheating to 170°C, the material is placed in a device capable of applying parallel shear force. Shear force is continuously applied along the X direction at a shear rate of 8 mm / s to orient the sheet-like preform. Air is introduced during the orientation process, and the preform is heated to 250°C. The cross-linking orientation is maintained at 250°C for 90 min to fix the orientation structure through oxidative cross-linking. The preform is then cooled to room temperature while maintaining the orientation to obtain an oriented preform. The oriented preform is graphitized in a nitrogen atmosphere at 2500°C for 1 h to obtain a carbon material with a first layer of oriented carbon coating on its surface.

[0091] S2. The carbon material with a first-layer oriented carbon coating is mixed with mesophase pitch at a mass ratio of 100:2 and heated to 160°C to completely melt the mesophase pitch, resulting in a suspension of carbon material particles. The suspension is placed in a heating device with a magnetic field, and a magnetic field perpendicular to the liquid surface with a strength of 1.5T is applied. Under an air atmosphere, the suspension is heated to 250°C and cross-linked under the magnetic field for 90 minutes (to fix the oriented structure through oxidative cross-linking). Then, it is cooled to room temperature while maintaining a constant magnetic field strength to obtain a secondary-oriented intermediate product. The secondary-oriented intermediate product is graphitized at 2500°C under a nitrogen atmosphere for 1 hour to obtain a carbon material with a second-layer oriented carbon coating.

[0092] S3. Repeat the S1 (shear orientation) and S2 (magnetic field orientation) operations in sequence for a total of 2 orientation coating cycles to obtain a carbon material with 6 oriented carbon coating layers.

[0093] The carbon material coated with six oriented carbon coating layers has the following thicknesses from the inside out: the first oriented carbon coating layer has a thickness of 3 nm, the second oriented carbon coating layer has a thickness of 13 nm, the third oriented carbon coating layer has a thickness of 2 nm, the fourth oriented carbon coating layer has a thickness of 13 nm, the fifth oriented carbon coating layer has a thickness of 3 nm, and the sixth oriented carbon coating layer has a thickness of 14 nm.

[0094] S4. The carbon material containing 6 oriented carbon coating layers is placed in a mixed atmosphere of water vapor, carbon dioxide and nitrogen with a volume ratio of 15:20:65, and the temperature is raised to 1200℃ for activation treatment for 5 hours to obtain porous carbon material.

[0095] The obtained porous carbon material was subjected to N2 static adsorption tests. Based on the adsorption capacity at the maximum partial pressure (p / p0>0.99), the pore volume was calculated to be 0.63 cm³. 3 / g.

[0096] Preparation of silicon-carbon materials: Silicon-carbon materials were prepared from the carbon materials obtained in Examples 1-5, Examples 8-11, and Comparative Examples 1-3 using the following process. The specific preparation method is as follows: The porous carbon material was placed in a tube furnace and heated from room temperature to 500°C at a rate of 2°C / min in a N2 atmosphere. Then, a mixed gas consisting of 20 vol% SiH4 and 80 vol% N2 was introduced, and the silane partial pressure in the reaction system was controlled at 3 kPa for vapor deposition for 8 hours. Finally, the material was allowed to cool naturally in a N2 atmosphere to obtain the silicon-carbon material. The silicon content in the silicon-carbon material was approximately 33 wt%.

[0097] The carbon material prepared in Example 6 was used to prepare silicon-carbon material using the following process. The specific preparation method is as follows: The porous carbon material was placed in a tube furnace and heated from room temperature to 500°C at a rate of 2°C / min in a N2 atmosphere. Then, a mixed gas consisting of 20 vol% SiH4 and 80 vol% N2 was introduced, and the silane partial pressure in the reaction system was controlled at 3 kPa for vapor deposition for 15 h. Finally, the material was allowed to cool naturally in a N2 atmosphere to obtain the silicon-carbon material. The silicon content in the silicon-carbon material was approximately 42 wt%.

[0098] The carbon material prepared in Example 7 was used to prepare silicon-carbon material using the following process. The specific preparation method is as follows: The porous carbon material was placed in a tube furnace and heated from room temperature to 500°C at a rate of 2°C / min in a N2 atmosphere. Then, a mixed gas consisting of 20 vol% SiH4 and 80 vol% N2 was introduced, and the silane partial pressure in the reaction system was controlled at 3 kPa for vapor deposition for 5 h. Finally, the material was allowed to cool naturally in a N2 atmosphere to obtain the silicon-carbon material. The silicon content in the silicon-carbon material was approximately 22 wt%.

[0099] The silicon-carbon materials prepared in Examples 1-11 and Comparative Examples 1-3 were subjected to BET tests, and their specific surface areas are shown in Table 1.

[0100] The following electrochemical performance tests were performed on the silicon-carbon materials prepared in Examples 1-11 and Comparative Examples 1-3: 1. Electrochemical testing Half-cell preparation and electrochemical performance testing: (1) Half-cell assembly: Silicon carbon material, conductive agent SuperP, binder polyacrylic acid and solvent deionized water are mixed evenly in a mass ratio of 95:1:4:120 and then evenly coated on the negative electrode current collector. The mixture is then dried at 100°C to obtain the negative electrode sheet. CR2032 coin cells are assembled in a glove box, with the negative electrode sheet as the working electrode, a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), where the LiPF6 concentration is 1 mol / L.

[0101] The battery was tested for charge and discharge using the LAND battery testing system.

[0102] (2) Cyclic specific capacity and initial efficiency test: After the CR2032 button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C and then discharged to 0.005V at 0.01C; after standing for 5 minutes, it was charged to 1.5V at a constant current of 0.05C; the initial delithiation specific capacity of 0.8V is the specific capacity (or mass specific capacity) of the electrode material, and the ratio of the initial delithiation capacity of 0.8V to the initial lithium insertion capacity is the initial coulombic efficiency of the battery at 0.8V.

[0103] (3) Ratio testing method: After the coin cell battery completes the cycle capacity and initial efficiency tests, it undergoes the following charge-discharge cycles at different rates: (1) Discharge at 0.1C to 0.005V and then charge at 0.1C to 1.5V, repeating 3 times, and recording the discharge and charge capacities for each cycle; (2) Discharge at 0.5C to 0.005V and then charge at 0.5C to 1.5V, repeating 3 times, and recording the discharge and charge capacities for each cycle; (3) Discharge at 1C to 0.005V and then charge at 1C to 1.5V, repeating 3 times, and recording the discharge and charge capacities for each cycle. The 1C / 0.1C rate is obtained by dividing the 1C and 1.5V charge capacity of the third cycle by the 0.1C and 1.5V charge capacity of the third cycle.

[0104] 2. Full cell preparation and electrochemical performance testing: Using silicon-carbon materials further prepared from the carbon materials of Examples 1-11 and Comparative Examples 1-3 as the negative electrode active material, pouch cells were fabricated using conventional methods with electrode sheets containing the negative electrode active material, and their electrical performance was tested. The pouch cells were fabricated in a dehumidified room at a dew point of -45°C. Charge-discharge cycle tests were performed on the cells using the LANBTS battery testing system. The specific test method is as follows: (1) Preparation of positive electrode sheet: The positive electrode active material LiCoO2, conductive agent SuperP, binder PVDF and solvent NMP are mixed evenly in a mass ratio of 92:3:5:150 and then evenly coated on the positive electrode current collector. Then, it is dried at 80℃ to obtain the positive electrode sheet.

[0105] (2) Preparation of negative electrode sheet: Silicon carbon material, conductive agent SuperP, binder polyacrylic acid and solvent deionized water are mixed evenly in a mass ratio of 95:1:4:120 and then evenly coated on the negative electrode current collector. Then it is dried at 100℃ to obtain the negative electrode sheet.

[0106] (3) The positive and negative electrode sheets are stacked in a square and separated by a polypropylene separator to form a battery cell, which is then packaged into an aluminum-plastic bag. An electrolyte of the appropriate capacity is injected into the aluminum-plastic bag, and the bag is vacuum sealed to obtain a soft-pack battery. The electrolyte is a mixture of LiPF6 EC and DEC, wherein the concentration of LiPF6 is 1 mol / L and the volume ratio of EC to DEC is 1:1.

[0107] (4) Formation and Capacity Testing: After liquid injection and sealing, the battery begins formation. It is placed in a constant temperature chamber at 25°C for 12 hours, then charged at a constant current of 0.02C to 3.3V, placed for 30 minutes, charged at a constant current of 0.025C to 3.8V, placed for 10 minutes, and charged at a constant current of 0.33C to 4.2V. After formation, the battery is vacuum-sealed and then subjected to capacity testing. It is charged at a constant current of 0.33C to 4.45V, placed for 10 minutes, discharged at a constant current of 1C to 3V, placed for 10 minutes, and discharged at a constant current of 0.33C to 3V. The capacity testing is then completed. The ratio of the discharge capacity to the charge capacity during the formation and capacity testing of the pouch battery is the initial efficiency of the battery.

[0108] (5) 25℃ Cyclic Test: Place the battery in a 25℃ constant temperature chamber, charge it to 4.45V with a constant current of 1C, and then charge it to 0.1C with a constant voltage of 4.45V. After standing for 10 minutes, discharge it to 3.0V with a constant current of 1C and stand for 10 minutes. Repeat the above charging and discharging steps until the discharge capacity is lower than 80% of the discharge capacity of the first cycle. The number of cycles obtained at this time is the cycle life of the soft pack battery. Record the capacity retention rate after 100 cycles.

[0109] The test data for the above tests are shown in Table 1.

[0110] Table 1 As can be seen from the data in Table 1, the batteries assembled from silicon-carbon materials prepared by the porous carbon materials prepared in Examples 1 to 11 exhibit excellent specific capacity, initial efficiency, capacity retention rate, and rate performance.

[0111] Comparative Example 1 used a graphitization process similar to that of Example 1 without coating to obtain a porous carbon material without an oriented carbon layer, and silicon was directly deposited on it. The first-efficiency, capacity retention, and rate performance of the battery assembled from this material were significantly lower than those of Example 1. This may be because the lack of physical constraint from the oriented carbon coating layer caused silicon volume expansion, leading to carbon shell cracking and repeated growth of the SEI film, resulting in irreversible capacity loss.

[0112] In Comparative Example 2, only a single layer of shear-oriented carbon coating and in Comparative Example 3, only a single layer of magnetic field-oriented carbon coating, the first-effect, capacity retention, and rate performance were all better than those of the uncoated Comparative Example 1. However, the capacity retention and rate performance were worse than those of the double-layer cross-oriented carbon coating in Example 1. This may be because: although a single-oriented carbon layer can provide some protection, its lattice orientation is singular, and cracks are prone to propagate through the orientation direction; while in Example 1, the lattice orientations of adjacent layers are different, which forces the cracks to deflect and branch at the interlayer interface, significantly improving crack resistance and cycle stability.

[0113] Adjusting the shear rate in Examples 1-3 resulted in some fluctuations in the electrochemical performance of the prepared materials. Among them, Example 1 showed the best overall performance, indicating that there is an optimization window for the shear rate.

[0114] In Example 4, increasing the magnetic field strength further improved the initial efficiency and capacity retention of the battery corresponding to the prepared material. This is likely because a stronger magnetic field facilitates the formation of a more complete oriented cross-linked network, enhancing the constraint on silicon volume expansion. In Example 5, decreasing the magnetic field strength did not result in superior performance of the battery corresponding to the prepared material, indicating that excellent results can be achieved within an appropriate range of magnetic field strength.

[0115] Examples 6 and 7 were prepared using carbon materials with different pore capacities. It can be seen that the size of the pore capacity directly determines the capacity of the silicon-carbon anode. The larger the pore capacity, the more silicon particles it can accommodate, which in turn leads to a higher specific capacity.

[0116] In Example 8, increasing the graphitization temperature significantly improved the first-stage efficiency, and the prepared material resulted in a battery with high rate performance. This was attributed to the improved conductivity of the carbon coating layer due to high-temperature graphitization, whose three-dimensional conductive network effectively compensated for the rate loss caused by the extended lithium-ion diffusion path. In Example 9, decreasing the graphitization temperature resulted in a battery with relatively low rate performance, indicating that the conductivity advantage of the cross-layout structure was not fully utilized when the degree of graphitization was insufficient.

[0117] The materials prepared in Examples 10 (4-layer cross-orientation) and 11 (6-layer cross-orientation) showed further improvements in initial efficiency and capacity retention compared to Example 1, with continued improvement in rate performance. This indicates that increasing the number of cross-orientation layers can more uniformly disperse the multidirectional stress generated by silicon volume expansion, converting it into interlayer shear strain. At the same time, the more complete three-dimensional conductive network constructed through multilayer microcrystals overcomes the defect of anisotropic conductivity in single-orientation coating layers.

[0118] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A carbon material, characterized in that, include: A carbon substrate and a reinforcing carbon layer covering at least a portion of the surface of the carbon substrate; The enhanced carbon layer is composed of at least two carbon coating layers with different lattice orientations, and adjacent carbon coating layers have different lattice orientations.

2. The carbon material according to claim 1, characterized in that, The lattice orientation angle between adjacent carbon coating layers is 30–90°.

3. The carbon material according to claim 1 or 2, characterized in that, The thickness of each coating layer is 1~50nm; And / or, the thickness of the enhanced carbon layer is 10~200nm; And / or, the enhanced carbon layer is composed of 2 to 10 layers of carbon coating with lattice orientation.

4. The carbon material according to claim 1 or 2, characterized in that, The carbon material has a pore volume of 0.2~1.0 cm³. 3 / g.

5. A method for preparing carbon materials, characterized in that, Includes the following steps: S1. Disperse the carbon-based material in a mesophase pitch solution and transfer it to a template to prepare a sheet-like preform. Place the preform in a shearing device, heat it to the softening temperature, and then apply shear force along the X direction at a set speed for orientation. While maintaining the shearing conditions, introduce air and heat it to the crosslinking temperature to perform oxidative crosslinking to fix the pitch orientation direction. After cooling while maintaining the shearing conditions, perform graphitization treatment to obtain a carbon material with a first layer of oriented carbon coating on the surface. S2. The carbon material with a first oriented carbon coating layer on its surface is mixed with the mesophase pitch and heated until the pitch melts. A magnetic field perpendicular to the liquid surface is applied, and air is introduced at the same time and the temperature is raised to the crosslinking temperature to carry out oxidative crosslinking to fix the pitch orientation direction. After cooling under the magnetic field conditions, graphitization treatment is carried out to obtain the carbon material with a second oriented carbon coating layer on its surface. S3. When it is necessary to prepare two or more oriented carbon coating layers, alternately execute S1 and / or S2 until the designed number of layers is obtained to obtain carbon material.

6. The method for preparing carbon materials according to claim 5, characterized in that, The carbon substrate material is selected from one or more of activated carbon, carbon molecular sieves, template carbon, carbon aerogel, and carbon fiber.

7. The method for preparing carbon materials according to claim 5, characterized in that, The median particle size D50 of the carbon matrix material is 1~100 μm; and / or, the pore volume of the carbon matrix material is 1.2~1.6 cm³. 3 / g; and / or, the average pore size of the carbon substrate material is 1.6~10.0 nm; and / or, the specific surface area of ​​the carbon substrate material is 300~3000 m². 2 / g.

8. The method for preparing carbon materials according to claim 5, characterized in that, In step S1, the solvent of the mesophase pitch solution is tetrahydrofuran, the concentration of the solution is 10~30wt%, and the mass ratio of carbon matrix to mesophase pitch is 100:(0.2~2). And / or, the softening temperature is 150~170℃; the shearing speed is set to 5~20mm / s; And / or, the crosslinking temperature is 250~300℃; the oxidative crosslinking time is 30~90min.

9. The method for preparing carbon materials according to claim 5, characterized in that, In step S2, the mass ratio of the carbon material with the first oriented carbon coating layer to the mesophase pitch is 100:(0.2~2); And / or, the strength of the magnetic field is 0.5~2T; And / or, the crosslinking temperature is 250~300℃, and the oxidative crosslinking time is 30~90min.

10. The method for preparing carbon materials according to claim 5, characterized in that, In steps S1 and S2, the graphitization temperature is independently 1600~2500℃ and the graphitization time is independently 1~5h.

11. The method for preparing carbon materials according to claim 5, characterized in that, It also includes step S4, which further pores the carbon material obtained in step S3 to obtain a porous carbon material; the pore-forming method is at least one of chemical activation pore-forming and physical activation pore-forming.

12. A silicon-carbon material, characterized in that, It includes a carbon skeleton and silicon particles deposited in and / or on the surface of the carbon skeleton, wherein the carbon skeleton is the carbon material according to any one of claims 1 to 4, or the carbon material prepared by the method according to any one of claims 5 to 11.

13. The silicon-carbon material according to claim 12, characterized in that, The silicon-carbon material has a reinforced carbon layer; the reinforced carbon layer is composed of at least two carbon layers with different lattice orientations, and adjacent carbon layers have different lattice orientations.

14. A negative electrode sheet, characterized in that, Includes the silicon-carbon material as described in claim 12 or 13.

15. A battery, characterized in that, Includes the negative electrode sheet as described in claim 14.

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