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

Abstract

The application provides a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode sheet and a battery. The silicon-carbon negative electrode material comprises a core and a carbon coating layer coated on the core; the core comprises a porous carbon framework and silicon particles, and the silicon particles are arranged in the pores of the porous carbon framework; there is a gap between the silicon particles and the surface of the pores of the porous carbon framework; in the core, the volume of the gap is V1, the volume of the silicon particles is V2, and V1 / V2 is 0.04-0.9. The silicon-carbon negative electrode material provided by the application has a buffer cavity reserved between the silicon particles and the pores of the porous carbon framework for silicon expansion, and can realize a silicon-carbon negative electrode material with low expansion and excellent electrical performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a silicon-carbon anode material and its preparation method, anode sheet and battery. Background Technology

[0002] Lithium-ion batteries, with their excellent energy density and power density, have become core energy storage devices in popular fields such as electric vehicles and portable electronic devices. However, existing commercial graphite anodes (with a theoretical specific capacity of only 372 mAh g⁻¹) -1 However, this makes it difficult to meet the market's urgent demand for higher energy density. Silicon materials, with their extremely high theoretical specific capacity (approximately 4200 mAh g⁻¹), are a better choice. -1 With its high energy density (approximately 10 times that of graphite), suitable operating potential, and abundant crustal reserves, it is considered the most promising next-generation high-energy-density lithium-ion battery anode material.

[0003] However, the commercial application of silicon anodes faces a severe challenge: during charge and discharge, they undergo alloying / dealloying reactions with lithium, accompanied by volume changes exceeding 300%. This leads to the pulverization of the active material particles and the loss of electrical contact with the conductive network, resulting in rapid capacity decay. Furthermore, the unstable electrode surface triggers continuous rupture and regeneration of the solid electrolyte interphase (SEI), a process that irreversibly consumes limited electrolyte and lithium sources, thus reducing coulombic efficiency and cycle life. In addition, silicon's inherently poor conductivity further restricts its commercial application.

[0004] Currently, most patents involve depositing silicon particles using chemical vapor deposition (CVD) on a porous carbon substrate, followed by surface carbon coating to obtain silicon-carbon composite materials. This approach leverages the high conductivity and mechanical strength of carbon materials to address the issues of poor conductivity and silicon volume expansion. However, the vapor-phase reaction is difficult to precisely control, resulting in a synchronous and homogeneous occurrence within all pores. Consequently, the effective pore filling rate of porous carbon is low, failing to maximize the buffering capacity of the carbon framework.

[0005] Another existing approach involves heat-treating chemically deposited iron hydroxide on silicon nanoparticles followed by annealing to obtain uniformly coated Fe2O3 / Fe3O4 / Si particles. These particles are then carbonized at 700°C after in-situ polymerization with resorcinol-formaldehyde. Finally, acid washing removes the Fe2O3 / Fe3O4, creating voids between the silicon particles and the surface carbon layer to provide space for subsequent silicon expansion. However, processes like etching the template with strong acids or bases are relatively complex and environmentally unfriendly, and it's difficult to control the volume of these voids.

[0006] Therefore, how to further achieve both low expansion and electrochemical performance of silicon-carbon materials is an urgent technical problem to be solved. Summary of the Invention

[0007] This application provides a silicon-carbon anode material and its preparation method, anode sheet and battery, which can obtain a silicon-carbon anode material with both low expansion and high electrochemical performance.

[0008] In a first aspect, this application provides a silicon-carbon anode material, comprising a core and a carbon coating layer covering the core; the core comprises a porous carbon framework and silicon particles; the silicon particles are disposed within the pores of the porous carbon framework; and there is a gap between the surfaces of the silicon particles and the pores of the porous carbon framework.

[0009] In the core, the volume of the gap is V1, the volume of the silicon particle is V2, and the ratio of V1 to V2 is 0.04-0.9.

[0010] In one possible implementation, the surface of the pores of the porous carbon framework is further provided with a nitrogen-doped carbon layer.

[0011] In one possible implementation, the mass percentage of nitrogen in the silicon-carbon anode material is 0.5-10%.

[0012] In one possible implementation, the silicon element in the silicon-carbon anode material accounts for 10-65% by mass.

[0013] In one possible implementation, the pore volume of the porous carbon framework is 0.4-1.5 cm³. 3 / g;

[0014] The pores in the porous carbon framework have an average pore diameter D, 0 <D≤10nm;

[0015] The specific surface area of ​​the porous carbon framework is 400-2500 m². 2 / g.

[0016] In one possible implementation, the pores in the porous carbon framework have an average pore size D, 1 <D≤2nm;

[0017] The specific surface area of ​​the porous carbon framework is 1000-2500 m². 2 / g.

[0018] In one possible implementation, the D of the silicon-carbon anode material v 50 represents 5.0-10.0 μm;

[0019] And / or; the specific surface area of ​​the silicon-carbon anode material is less than 20 m². 2 / g;

[0020] And / or; the tap density of the silicon-carbon anode material is 0.7-1.2 g / cm³. 3 .

[0021] In one possible implementation, the D of the silicon-carbon anode material v 50 is 6.5-8.0 μm;

[0022] And / or; the specific surface area of ​​the silicon-carbon anode material is 3.5-5.5 m². 2 / g;

[0023] And / or; the mass percentage of nitrogen in the silicon-carbon anode material is 0.5-6.5%;

[0024] And / or; the mass percentage of silicon in the silicon-carbon anode material is 25-55%.

[0025] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 500-2000 mAh / g.

[0026] And / or; after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is greater than or equal to 90%;

[0027] And / or; after the silicon-carbon anode material is assembled into a battery, the expansion rate of the battery is less than 120%;

[0028] And / or; after the silicon-carbon anode material is assembled into a battery, the capacity retention rate of the battery after 500 cycles is greater than 80%;

[0029] And / or; after the silicon-carbon anode material is assembled into a battery, the charge transfer impedance of the battery is 30-120Ω;

[0030] And / or; after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 is the peak intensity near 0.25V-0.30V; I2 is the peak intensity near 0.43V-0.50V; and I2 / I1 is less than or equal to 0.7.

[0031] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 1300-2000 mAh / g.

[0032] And / or; after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is 90%-92%;

[0033] And / or; after the silicon-carbon anode material is assembled into a battery, the expansion rate of the battery is 25-90%;

[0034] And / or; after the silicon-carbon anode material is assembled into a battery, the capacity retention rate of the battery after 500 cycles is 80%-95%;

[0035] And / or; after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 is the peak intensity near 0.25V-0.30V; I2 is the peak intensity near 0.43V-0.50V; satisfying I2 / I1 is 0.6-0.7.

[0036] Secondly, this application provides a method for preparing a silicon-carbon anode material, the method comprising:

[0037] S1: Impregnate the polyethylene polyamine into the pores of the porous carbon skeleton, and crosslink the polyethylene polyamine with an aliphatic epoxy compound to form a crosslinked product in the pores of the porous carbon skeleton.

[0038] S2: Under the protection of an inert gas, silane is introduced to deposit silicon particles on the cross-linked product in the pores of the porous carbon skeleton obtained in S1.

[0039] S3: Under the protection of an inert gas, a carbon source is introduced, and a carbon coating layer is deposited on the surface of the product obtained in S2 to obtain the silicon-carbon anode material.

[0040] In one possible embodiment, the polyethylene polyamine includes at least one of polyethyleneimine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; the aliphatic epoxy compound includes at least one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerol triglycidyl ether.

[0041] And / or; the mass ratio of the porous carbon to the polyethylene polyamine is 40:1-40:7;

[0042] And / or; the mass ratio of the polyethylene polyamine and the aliphatic epoxy compound is 20:1-20:7.

[0043] In one possible implementation, the polyethyleneimine comprises branched polyethyleneimine and / or linear polyethyleneimine;

[0044] And / or; the weight-average molecular weight of the polyethyleneimine is 600-1200 g / mol.

[0045] In one possible implementation, the volume ratio of the silane to the inert gas is 15:1 to 1:2;

[0046] And / or; in step S2, the temperature for silicon particle deposition is 350-460°C;

[0047] And / or; in step S3, the volume ratio of the carbon source to the inert gas is 10:1-1:4;

[0048] And / or; in step S3, the temperature at which the carbon coating layer is deposited is 480-560°C.

[0049] In one possible implementation, the silicon source includes at least one of silane, disilane, dichlorosilane, and trichlorosilane; the carbon source includes alkane gases.

[0050] Thirdly, this application provides a negative electrode sheet comprising the aforementioned silicon-carbon negative electrode material.

[0051] Fourthly, this application provides a battery including the aforementioned negative electrode.

[0052] This application provides a silicon-carbon anode material, its preparation method, an anode sheet, and a battery. The silicon particles and the porous carbon skeleton of this application have gaps on their surfaces. The volume of the gaps in the core is V1, and the volume of the silicon particles is V2, with a V1 / V2 ratio of 0.04-0.9. This means that a buffer cavity is reserved between the silicon particles and the pores of the porous carbon skeleton in the silicon-carbon anode material of this application to provide buffer space for silicon expansion. This has the following advantages: First, the reserved cavity provides "breathing space" for silicon expansion, allowing silicon to expand within a limited space without generating excessive lateral pressure on the porous carbon skeleton, significantly reducing the fracture rate of silicon particles and protecting the structural integrity of the anode material. Second, the buffer cavity can buffer the expansion force, maintaining good continuity and mechanical strength of the carbon skeleton and ensuring electrical contact between silicon and the porous carbon skeleton. Third, the buffer cavity allows silicon to expand within a fixed space, reducing overall particle deformation and surface cracking of the silicon-carbon anode material, constraining the expansion direction of silicon, and making volume changes more controllable. Finally, the buffer cavity retains channels for ion transport, maintaining a certain degree of pore connectivity even after silicon expansion, thus improving the battery's electrical performance. Therefore, this application yields a silicon-carbon anode material that combines low expansion with high electrochemical performance. Attached Figure Description

[0053] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0054] Figure 1 This is a schematic diagram of the synthesis process of the silicon-carbon anode material of Example 1 provided in this application.

[0055] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0056] To enable those skilled in the art to better understand the present invention, this application will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the invention and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0057] In a first aspect, this application provides a silicon-carbon anode material, including a core and a carbon coating layer covering the core; the core includes a porous carbon framework and silicon particles; the silicon particles are disposed within the pores of the porous carbon framework; and there is a gap between the surfaces of the silicon particles and the pores of the porous carbon framework.

[0058] In the core, the volume of the gap is V1, the volume of the silicon particle is V2, and the ratio of V1 to V2 is 0.04-0.9.

[0059] It is understandable that V1 / V2 is 0.04-0.9, such as 0.04, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range of two of the above values.

[0060] The silicon particles and the porous carbon skeleton of this application have a gap between their surfaces. The volume of the gap in the core is V1, and the volume of the silicon particle is V2, with V1 / V2 being 0.04-0.9. This means that the silicon-carbon anode material of this application has a buffer cavity between the silicon particles and the porous carbon skeleton to provide for silicon expansion. This has the following advantages: First, the reserved cavity provides "breathing space" for silicon expansion, allowing silicon to expand within a limited space without exerting excessive lateral pressure on the porous carbon skeleton, significantly reducing the fracture rate of silicon particles and protecting the structural integrity of the anode material. Second, the buffer cavity can buffer the expansion force, maintaining good continuity and mechanical strength of the carbon skeleton and ensuring electrical contact between silicon and the porous carbon skeleton. Third, the buffer cavity allows silicon to expand within a fixed space, reducing overall particle deformation and surface cracking of the silicon-carbon anode material, constraining the expansion direction of silicon, and making volume change more controllable. Finally, the buffer cavity retains a channel for ion transport, maintaining a certain degree of pore connectivity even after silicon expansion, improving the electrical performance of the battery. Therefore, this application provides a silicon-carbon anode material that combines low expansion and high electrochemical performance.

[0061] In one possible implementation, a nitrogen-doped carbon layer is further disposed on the surface of the pores of the porous carbon framework.

[0062] This application provides active sites through nitrogen-doped carbon, optimizes the electrical conductivity of carbon materials, and enhances lithium-ion transport kinetics through the electronic effect of nitrogen atoms, reducing charge transfer resistance. In addition, there is a nitrogen-doped carbon layer between the pores of the porous carbon skeleton and the silicon particles, which can further improve the structural stability. Finally, the silicon-carbon anode material has excellent cycle stability and rate performance while having a high specific capacity.

[0063] In a possible implementation, the mass percentage of nitrogen element in the silicon-carbon anode material is 0.5 - 10%. When the nitrogen content is within the above range, the doping of nitrogen can significantly enhance the electronic conductivity of the carbon skeleton and reduce the internal resistance of the electrode; excessive nitrogen doping will instead lead to excessive disorder of the structure and an increase in irreversible capacity.

[0064] It can be understood that the mass percentage of nitrogen element in the silicon-carbon anode material is 0.5 - 10%, such as 0.5%, 1.0%, 1.5%, 2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0% or the range composed of any two of the above values.

[0065] In a possible implementation, the mass percentage of silicon element in the silicon-carbon anode material is 10 - 65%. When the silicon element is within the above range, compared with graphite, the specific capacity of the material can be greatly improved; at the same time, its tap density and compaction density are higher than those of pure carbon materials, which can improve the volume energy density of the electrode sheet.

[0066] It can be understood that the mass percentage of silicon element in the silicon-carbon anode material is 10 - 65%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or the range composed of any two of the above values.

[0067] In a possible implementation, the pore volume of the pores in the porous carbon skeleton is 0.4 - 1.5 cm 3 / g, the pores in the porous carbon skeleton have an average pore diameter D, 0 < D ≤ 10 nm, and the specific surface area of the porous carbon skeleton is 400 - 2500 m 2 / g. When the pore volume, pore diameter, and specific surface area are within the above range, it can ensure the uniform deposition of nano-silicon and ensure that there is still corresponding space to buffer the volume expansion of silicon after depositing a certain amount of silicon.

[0068] It can be understood that the pore volume of the pores in the porous carbon skeleton is 0.4 - 1.5 cm 3 / g, such as 0.4 cm 3 / g, 0.6 cm 3 / g, 0.8 cm 3 / g, 1.0 cm 3 / g, 1.2 cm 3 / g, 1.5 cm 3 / g or a range composed of any two of the above values.

[0069] It can be understood that 0 < D ≤ 10 nm, such as 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm or a range composed of any two of the above values.

[0070] It can be understood that the specific surface area of the porous carbon skeleton is 400 - 2500 m 2 / g, for example, 400 m 2 / g, 700 m 2 / g, 1000 m 2 / g, 1300 m 2 / g, 1600 m 2 / g, 1900 m 2 / g, 2200 m 2 / g, 2500 m 2 / g or a range composed of any two of the above values.

[0071] It should be noted that the specific surface area of the porous carbon skeleton in this application refers to the specific surface area of the porous carbon skeleton when there are no silicon particles and nitrogen-doped carbon layers in the pores of the porous carbon skeleton.

[0072] In a possible implementation, 1 < D ≤ 2 nm.

[0073] In a possible implementation, the specific surface area of the porous carbon skeleton is 1000 - 2500 m 2 / g.

[0074] It can be understood that the D of the porous carbon skeleton v 50 is 7.20 - 8.95 μm, such as 7.20 μm, 7.50 μm, 7.80 μm, 8.10 μm, 8.40 μm, 8.70 μm, 8.95 μm or a range composed of any two of the above values.

[0075] In a possible implementation, the D v 50 of the silicon-carbon negative electrode material is 5.0 - 10.0 μm.

[0076] It can be understood that the D of the silicon-carbon negative electrode material v50 represents 5.0-10.0 μm, such as 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, or any range of two of the above values.

[0077] In one possible implementation, the specific surface area of ​​the silicon-carbon anode material is less than 20 m². 2 / g.

[0078] In one possible implementation, the tap density of the silicon-carbon anode material is 0.7-1.2 g / cm³. 3 For example, 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 Or a range consisting of any two of the above values.

[0079] In one possible implementation, the D of the silicon-carbon anode material v 50 represents 6.5-8.0 μm, such as 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, or any combination of two of the above values.

[0080] In one possible implementation, the specific surface area of ​​the silicon-carbon anode material is 3.5-5.5 m². 2 / g, for example 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g, 5.5m 2 / g or a range consisting of any two of the above values.

[0081] In one possible implementation, the mass percentage of nitrogen in the silicon-carbon anode material is 0.5-6.5%, for example, 0.5%, 1.0%, 1.5%, 2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, or any range of two of the above values.

[0082] In one possible implementation, the mass percentage of silicon in the silicon-carbon anode material is 25-55%, for example, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or any combination of two of the above values.

[0083] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 500-2000 mAh / g; for example, 500 mAh / g, 800 mAh / g, 1000 mAh / g, 1200 mAh / g, 1500 mAh / g, 1800 mAh / g, 2000 mAh / g, or any range of two of the above values.

[0084] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is greater than or equal to 90%.

[0085] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the battery's expansion rate is less than 120%.

[0086] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the battery capacity is greater than 80% after 500 cycles.

[0087] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the charge transfer impedance of the battery is 30-120Ω; for example, 30Ω, 50Ω, 70Ω, 100Ω, 120Ω or any two of the above values.

[0088] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 is the peak intensity near 0.25V-0.30V; I2 is the peak intensity near 0.43V-0.50V; satisfying: I2 / I1 is less than or equal to 0.7; for example, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7 or any range of two of the above values.

[0089] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 1300-2000 mAh / g; for example, 1300 mAh / g, 1400 mAh / g, 1500 mAh / g, 1600 mAh / g, 1700 mAh / g, 1800 mAh / g, 1900 mAh / g, 2000 mAh / g, or any range of two of the above values.

[0090] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is 90%-92%; for example, 90%, 91%, 92% or any two of the above values.

[0091] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the battery expansion rate is 25-90%; for example, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any two of the above values.

[0092] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, the capacity retention rate of the battery after 500 cycles is 80%-95%; for example, 80%, 85%, 90%, 95% or any two of the above values.

[0093] In one possible implementation, after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 has a peak intensity near 0.25V-0.30V; I2 has a peak intensity near 0.43V-0.50V; and I2 / I1 satisfies a range of 0.6-0.7, such as 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, or any two of the above values. Secondly, this application provides a method for preparing a silicon-carbon anode material, comprising:

[0094] S1: Impregnate polyethylene polyamines into the pores of a porous carbon skeleton, and cross-link the polyethylene polyamines with aliphatic epoxy compounds to form cross-linked products in the pores of the porous carbon skeleton.

[0095] S2: Under the protection of an inert gas, silane is introduced to deposit silicon particles on the cross-linked product in the pores of the porous carbon skeleton obtained in S1.

[0096] S3: Under the protection of an inert gas, a carbon source is introduced, and a carbon coating layer is deposited on the surface of the product obtained in S2 to obtain a silicon-carbon anode material.

[0097] First, this application allows polyethylene polyamines to fully penetrate the pores of a porous carbon framework through impregnation, increasing the pore filling rate of the porous carbon framework and providing a uniform substrate for subsequent silicon deposition. Subsequently, the polyethylene polyamines undergo a cross-linking reaction under the action of aliphatic epoxy compounds, forming a cross-linked polyethylene polyamine layer with enhanced thermal stability. The cross-linking reaction increases the thermal decomposition temperature of the polyethylene polyamines, causing them to decompose only in the carbon coating stage (S3), avoiding premature failure in the silicon deposition stage (S2). Second, CVD technology is used to achieve in-situ deposition of silicon particles within the pores of the porous carbon framework, ensuring close contact between silicon and the porous carbon framework while avoiding silicon floating. Finally, the carbon source decomposes to form a carbon coating layer, and the cross-linked polyethylene polyamine layer decomposes at high temperature to generate a nitrogen-rich residual carbon layer and voids; the carbon coating layer isolates silicon from the electrolyte, improving mechanical strength and conductivity; the thermal decomposition of the cross-linked polyethylene polyamines simultaneously forms expansion buffer voids, and the electronic structure of the carbon layer is optimized through nitrogen doping. That is, the cross-linked polyethylene polyamine material of this application serves as both an in-situ sacrificial template and a nitrogen source, achieving pore formation and nitrogen doping simultaneously through one-step pyrolysis. The cross-linked polyethylene polyamine material also constructs a synergistic structure of porous carbon framework and expansion buffer voids, systematically improving the electrochemical performance of the anode material.

[0098] In one possible implementation, the polyethylene polyamine includes at least one of polyethyleneimine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; the aliphatic epoxy compound includes at least one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerol triglycidyl ether.

[0099] In one possible implementation, the polyethyleneimine includes branched polyethyleneimine and / or linear polyethyleneimine. Branched polyethyleneimine and / or linear polyethyleneimine have relatively small molecular sizes, which facilitates better entry of polyethyleneimine into the pores of the porous carbon framework, reduces the likelihood of clogging the pore openings of the porous carbon framework, and promotes subsequent silicon particle deposition, thereby reducing silicon float phenomena.

[0100] In one possible implementation, the polyethyleneimine is branched polyethyleneimine, which has a smaller molecular size than linear polyethyleneimine and can enter the pores of the porous carbon framework more smoothly and completely.

[0101] In one possible implementation, the weight-average molecular weight of polyethyleneimine is 600-1200 g / mol, for example, 600 g / mol, 700 g / mol, 800 g / mol, 900 g / mol, 1000 g / mol, 1100 g / mol, 1200 g / mol, or any range of two of the above values.

[0102] Understandably, low molecular weight polyethyleneimine can be uniformly and fully impregnated in the pores without easily clogging the pore openings of the porous carbon framework, which is beneficial for the subsequent deposition of silicon nanoparticles, reduces the occurrence of silicon floating phenomenon, and the reserved expansion space can play a role in reducing expansion.

[0103] In one possible implementation, the mass ratio of porous carbon to polyethylene polyamine is 40:1 to 40:7, for example, 40:1, 40:2, 40:3, 40:4, 40:5, 40:6, 40:7 or any range of two of the above values.

[0104] When the mass ratio of porous carbon to polyethylene polyamines is within the above range, the amount of polyethylene polyamines impregnated can be appropriate, thereby generating suitable expansion buffer voids and nitrogen doping amount in the subsequent high-temperature stage of carbon coating, improving the expansion rate and charge transfer impedance performance of silicon-carbon anode materials.

[0105] In one possible implementation, the mass ratio of the polyethylene polyamine to the aliphatic epoxy compound is 20:1 to 20:7, for example, 20:1, 20:2, 20:3, 20:4, 20:5, 20:6, 20:7 or any range of two of the above values.

[0106] The mass ratio of polyethylene polyamines to aliphatic epoxy compounds is within the aforementioned range, ensuring that the aliphatic epoxy compound crosslinking agent does not over-crosslink or achieve insufficient crosslinking with the polyethylene polyamines. This guarantees that the thermal decomposition temperature window of the crosslinked polyethylene polyamines coincides with the carbon deposition temperature window in S3, allowing the crosslinked polyethylene polyamines to decompose completely at the preset carbon coating temperature. This avoids the blockage of the porous carbon skeleton by undecomposed polymers due to incomplete decomposition of the crosslinked polyethylene polyamines, reducing the amount of silicon deposited. Furthermore, complete decomposition of the crosslinked polyethylene polyamines ensures the formation of sufficient buffer cavities between the silicon particles and the porous carbon skeleton pores. Additionally, complete decomposition of the crosslinked polyethylene polyamines prevents the resulting residual carbon layer from becoming overly brittle, avoiding easy breakage during cycling, thus effectively accommodating the volume expansion of silicon; improving the initial coulombic efficiency and expansion rate of the silicon-carbon anode material. Finally, the complete decomposition of cross-linked polyethylene polyamines can improve the charge transfer impedance of the anode material; the complete decomposition of cross-linked polyethylene polyamines to generate nitrogen-containing residual carbon can effectively improve the charge transfer impedance of the anode material.

[0107] In one possible implementation, in step S1, a polyethylene polyamine is dissolved in a solvent to form a polyethylene polyamine solution, and the polyethylene polyamine solution is then impregnated into the pores of the porous carbon framework. Specifically, the solvent can be water and / or an alcohol solvent.

[0108] In one possible implementation, in step S1, the porous carbon skeleton is placed in a vacuum environment, and a solution of polyethylene polyamine is impregnated into the pores of the porous carbon skeleton, followed by pressure maintenance at 1-10 MPa for 4-6 hours.

[0109] In one possible implementation, in step S1, the porous carbon skeleton is placed in a vacuum environment, and a solution of polyethylene polyamine is impregnated into the pores of the porous carbon skeleton, followed by pressure maintenance at 2-4 MPa for 4-6 hours.

[0110] In this application, the porous carbon skeleton is first vacuum-evacuated to ensure that the gas in the pores of the porous carbon skeleton is fully expelled so that the polyethylene polyamine solution can completely immerse the porous carbon skeleton. Then, the pressure is increased to 1-10 MPa and maintained for 4-6 hours, forcing the polyethylene polyamine solution to fully penetrate into the pores of the porous carbon skeleton under high pressure.

[0111] In one possible implementation, in step S1, an aliphatic epoxy compound is dropped into a porous carbon skeleton impregnated with a solution of polyethylene polyamines, stirred, filtered, and vacuum dried at 40-60°C for 12-24 hours to allow the aliphatic epoxy compound and polyethylene polyamines to undergo a crosslinking reaction.

[0112] In one possible implementation, the aliphatic epoxy compound is added at a rate of 0.01-0.10 g / min.

[0113] In one possible implementation, the volume ratio of silane to inert gas is 15:1 to 1:2, for example, 15:1, 12:1, 9:1, 6:1, 3:1, 1:1, 1:2 or any range of two of the above values.

[0114] In one possible implementation, in step S2, the temperature for silicon particle deposition is 350-460°C, for example, 350°C, 370°C, 400°C, 430°C, 450°C, 460°C, or any combination of two of the above values.

[0115] In one possible implementation, in step S3, the volume ratio of carbon source to inert gas is 10:1 to 1:4, for example, 10:1, 8:1, 6:1, 4:1, 2:1, 1:1, 1:2, 1:4 or any range of two of the above values.

[0116] In one possible implementation, in step S3, the temperature for depositing the carbon coating layer is 480-560°C, for example, 480°C, 500°C, 520°C, 540°C, 560°C, or any combination of two of the above values.

[0117] In one possible implementation, the silicon source includes at least one of silane, disilane, dichlorosilane, and trichlorosilane.

[0118] In one possible implementation, the carbon source in step S3 includes alkane gases.

[0119] In one possible implementation, the carbon source in step S3 includes a gaseous carbon source and / or a liquid carbon source. The gaseous carbon source includes at least one of propylene and acetylene; the liquid carbon source includes at least one of benzene and n-hexane. The liquid carbon source can be introduced into the furnace via atomized carrier flow.

[0120] In one possible implementation, the inert gas in steps S2 and S3 independently includes at least one of nitrogen and argon.

[0121] In one possible implementation, the porous carbon framework is prepared as follows: a carbon material precursor is sintered at high temperature to remove impurities, and then pores are formed to obtain a porous carbon framework.

[0122] In one possible implementation, pore formation includes methods such as strong alkali corrosion, carbon dioxide activation, or water vapor activation.

[0123] In one possible implementation, the type of carbon material precursor is not particularly limited and may include, but is not limited to, pitch-based carbon material precursors, pitchene-based carbon material precursors, coal-based carbon material precursors, coke-based carbon material precursors, biochar-based carbon material precursors, carbon black-based carbon material precursors, oil-based carbon material precursors, tar-based carbon material precursors, polymer-based carbon material precursors, protein-based carbon material precursors, carbohydrate-based carbon material precursors, cotton-based carbon material precursors, fat-based carbon material precursors, waste-based carbon material precursors, graphite-based carbon material precursors, melamine-based carbon material precursors, wood-based carbon material precursors, porous graphene, porous graphene oxide, activated carbon, and combinations thereof.

[0124] Carbon material precursors of this type can easily produce porous carbon materials that meet the aforementioned particle size, specific surface area, tap density, and compaction density. Thirdly, this application provides a negative electrode sheet comprising the aforementioned silicon-carbon negative electrode material.

[0125] The negative electrode sheet of this application specifically includes a negative electrode current collector and a negative electrode active layer formed of silicon-carbon negative electrode material disposed on the surface of the negative electrode current collector.

[0126] In the specific preparation of the negative electrode, the silicon-carbon negative electrode material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained.

[0127] In one possible implementation, the negative electrode active layer comprises, by weight percentage, 70-99 wt% silicon-carbon negative electrode material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder; more specifically, it comprises 80-98 wt% silicon-carbon negative electrode material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0128] In one possible implementation, the material of the negative electrode current collector layer can be at least one of copper foil, nickel foam, and copper foam; the conductive agent can be at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; and the binder can be at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0129] Fourthly, this application provides a battery including the aforementioned negative electrode.

[0130] It is conceivable that, in addition to the aforementioned negative electrode, the lithium-ion battery of this application also includes a positive electrode, an electrolyte, and a separator.

[0131] This application does not strictly limit the positive electrode active material in the positive electrode sheet, and can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium nickel manganese oxide, lithium-rich manganese-based materials, etc.

[0132] This application does not strictly limit the choice of electrolyte, which may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0133] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0134] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0135] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0136] Example 1

[0137] Figure 1 This is a schematic diagram of the synthesis process of the silicon-carbon anode material in Embodiment 1 of this application, with reference to... Figure 1 The preparation method of the silicon-carbon anode material in this embodiment is as follows:

[0138] S1: Dissolve 1.0 g of anhydrous branched polyethyleneimine (Mw=600 g / mol, manufacturer: Thermo Fisher Scientific (China) Co., Ltd., CAS No. 9002-98-6; item number: 040527-22) in ethanol by mechanical stirring to form a branched polyethyleneimine solution. The mass ratio of anhydrous branched polyethyleneimine to ethanol is 1:20.

[0139] 10.0 g of porous carbon framework (average pore size 1.85 nm, specific surface area 2035 m²) was used. 2 / g, pore volume 0.94cm 3 / g,D v The porous carbon skeleton (7.85 μm) was placed in a vacuum impregnation tank, and the air inside the tank was evacuated using a vacuum pump to stabilize the vacuum at -0.1 MPa for 2 hours. Then, the inlet pipe of the impregnation tank was inserted into a beaker containing a branched polyethyleneimine solution, and the inlet valve was opened. The solution was drawn in and completely impregnated using negative pressure. After closing the valve, the tank was pressurized to 2 MPa and maintained at that pressure for 5 hours, forcing the branched polyethyleneimine solution to fully penetrate the pores of the porous carbon skeleton under high pressure.

[0140] S2: While maintaining a mechanical stirring speed of 100 rpm, 0.2 g of ethylene glycol diglycidyl ether was slowly added dropwise to the dispersion obtained in S1 at a rate of 0.05 g / min. After the addition was complete, mechanical stirring was continued for 18 h. Subsequently, the mixture was filtered, and the product was vacuum dried at 50 °C for 24 h to allow the ethylene glycol diglycidyl ether and branched polyethyleneimine to undergo a crosslinking reaction, resulting in a crosslinked polyethyleneimine layer.

[0141] The product obtained in step S2 was subjected to nitrogen adsorption-desorption testing. The average thickness of the impregnated layer (the thickness of the cross-linked polyethyleneimine layer) was obtained by dividing the decrease in pore volume of the porous carbon skeleton before and after impregnation by the specific surface area of ​​the porous carbon. In this embodiment, the average thickness of the impregnated layer is approximately 0.12 nm.

[0142] S3: The composite material obtained in S2 was placed in a chemical vapor deposition furnace and heated by introducing nitrogen gas at a flow rate of 0.3 L / min for 1 h and a heating temperature of 380 °C. Subsequently, nitrogen gas was continuously introduced and the temperature was kept constant while silane was introduced at a flow rate of 0.6 L / min to deposit nano-silicon (i.e., the volume ratio of silane to nitrogen was 2:1) for 15 h.

[0143] S4: Then, nitrogen gas is continuously introduced (nitrogen flow rate is 0.3 L / min), and heating continues at a temperature of 490°C. At the same time, acetylene gas with a flow rate of 0.3 L / min is introduced to perform carbon coating deposition (i.e., the volume ratio of carbon source to nitrogen gas is 1:1). The deposition time is 20 h, and the silicon-carbon anode material of this embodiment can be obtained.

[0144] The porous carbon framework preparation method in this embodiment is as follows:

[0145] Mix 20.0g of phenol, 24.0g of 40% formaldehyde solution and 0.4g of NaOH, reflux at 80℃ for 2 hours, neutralize with dilute hydrochloric acid, and dehydrate under reduced pressure to obtain methyl phenolic resin.

[0146] 20.0 g of methyl phenolic resin, 25.8 g of hexadecyltrimethylammonium bromide, 12.4 g of sodium chloride, 258.1 mL of anhydrous ethanol, and 129 mL of deionized water were mixed and stirred to dissolve. The solution was placed in a reaction vessel and heated to 120 °C at a rate of 3 °C / min, and held at that temperature for 18 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was washed with ethanol and deionized water and then dried to obtain the phenolic resin.

[0147] The phenolic resin was placed in a carbonization furnace and heated to 700°C at a rate of 3°C / min, under nitrogen protection at a rate of 100 mL / min throughout the process. The reaction was carried out for 3 hours, and after natural cooling, the carbonized material was obtained. Then, using water vapor at a flow rate of 1 mL / min and nitrogen at a rate of 50 mL / min, the temperature was increased to 800°C and activated for 5 hours. This was followed by a second activation under the same conditions. After drying, pulverizing, and classifying, the corresponding porous carbon framework was obtained.

[0148] Example 2

[0149] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the anhydrous branched polyethyleneimine (Mw=600g / mol) used in S1 is replaced with anhydrous linear polyethyleneimine (Mw=600g / mol, manufacturer: Shanghai McLean Biochemical Technology Co., Ltd.; item number: E808878).

[0150] Example 3

[0151] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the anhydrous branched polyethyleneimine (Mw=600g / mol) used in S1 is replaced with anhydrous branched polyethyleneimine (Mw=800g / mol, manufacturer: Shanghai McLean Biochemical Technology Co., Ltd.; item number: P871833).

[0152] Example 4

[0153] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of anhydrous branched polyethyleneimine used in S1 is changed to 0.125g.

[0154] Example 5

[0155] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of anhydrous branched polyethyleneimine used in S1 is changed to 2.0g.

[0156] Example 6

[0157] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of anhydrous branched polyethyleneimine used in S1 is changed to 2.5g.

[0158] Example 7

[0159] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of ethylene glycol diglycidyl ether used in S2 is changed to 0.025g.

[0160] Example 8

[0161] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of ethylene glycol diglycidyl ether used in S2 is changed to 0.4g.

[0162] Example 9

[0163] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the mass of ethylene glycol diglycidyl ether used in S2 is changed to 0.8g.

[0164] Example 10

[0165] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the nitrogen flow rate and acetylene flow rate in S4 are both 0.2 L / min, and the deposition time is 30 h.

[0166] Example 11

[0167] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the nitrogen flow rate and acetylene flow rate in S4 are both 0.5 L / min, and the deposition time is 12 h.

[0168] Example 12

[0169] The preparation method of the silicon-carbon anode material in this embodiment is basically the same as that in Example 1, except that the anhydrous branched polyethyleneimine (Mw=600g / mol) used in S1 is replaced with anhydrous branched polyethyleneimine (Mw=1200g / mol, manufacturer: Shanghai Anaiji Chemical Co., Ltd.; product number: D110145).

[0170] Example 13

[0171] The preparation method of the silicon-carbon anode material in this embodiment is as follows:

[0172] S1: Dissolve 0.25g of diethylenetriamine (manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; product number: D806302) in ethanol by mechanical stirring to form a diethylenetriamine solution. The mass ratio of diethylenetriamine to ethanol is 1:20.

[0173] 10.0 g of porous carbon framework (average pore size 1.07 nm, specific surface area 1000 m²) was used. 2 / g, pore volume 0.4cm 3 / g,D vThe porous carbon skeleton (7.20 μm) was placed in a vacuum impregnation tank. Air was evacuated from the tank using a vacuum pump to stabilize the vacuum at -0.1 MPa for 0.5 hours. Then, the inlet pipe of the impregnation tank was inserted into a beaker containing diethylenetriamine solution, and the inlet valve was opened. The solution was drawn in and completely submerged using negative pressure. After closing the valve, the tank was pressurized to 2 MPa and maintained at that pressure for 4 hours, forcing the diethylenetriamine solution to fully penetrate the pores of the porous carbon skeleton under high pressure.

[0174] S2: Maintaining a mechanical stirring speed of 100 rpm, slowly add 0.0125 g of 1,4-butanediol diglycidyl ether dropwise to the dispersion obtained in S1 at a rate of 0.1 g / min. After the addition is complete, continue mechanical stirring for 12 h. Then filter and vacuum dry the product at 40 °C for 12 h to allow the 1,4-butanediol diglycidyl ether and diethylenetriamine to undergo a crosslinking reaction, obtaining a crosslinked diethylenetriamine layer.

[0175] S3: The composite material obtained in S2 was placed in a chemical vapor deposition furnace and heated by introducing nitrogen gas at a flow rate of 0.3 L / min for 0.5 h. The heating temperature was 350 °C. Subsequently, nitrogen gas was continuously introduced and the temperature was kept constant while silane was introduced at a flow rate of 4.5 L / min for the deposition of nano-silicon (i.e., the volume ratio of silane to nitrogen was 15:1) for 1 h.

[0176] S4: Then, nitrogen gas is continuously introduced (nitrogen flow rate is 0.3 L / min), and heating continues at a temperature of 480°C. At the same time, acetylene gas with a flow rate of 3 L / min is introduced to perform carbon coating deposition (i.e., the volume ratio of carbon source to nitrogen gas is 10:1). The deposition time is 1 hour, and the silicon-carbon anode material of this embodiment can be obtained.

[0177] The porous carbon framework preparation method in this embodiment is as follows:

[0178] Mix 20.0g of phenol, 24.0g of 40% formaldehyde solution and 0.4g of NaOH, reflux at 80℃ for 2 hours, neutralize with dilute hydrochloric acid, and dehydrate under reduced pressure to obtain methyl phenolic resin.

[0179] 20.0 g of methyl phenolic resin, 25.8 g of hexadecyltrimethylammonium bromide, 12.4 g of sodium chloride, 258.1 mL of anhydrous ethanol, and 129 mL of deionized water were mixed and stirred to dissolve. The solution was placed in a reaction vessel and heated to 120 °C at a rate of 3 °C / min, and held at that temperature for 18 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was washed with ethanol and deionized water and then dried to obtain the phenolic resin.

[0180] Phenolic resin was placed in a carbonization furnace and heated to 700°C at a rate of 3°C / min, under nitrogen protection at a rate of 100 mL / min throughout the process. The reaction was carried out for 2 hours, and the carbonized material was obtained after natural cooling. Then, water vapor at a flow rate of 1 mL / min and nitrogen at a rate of 50 mL / min were used to heat the material to 800°C, and the process was activated for 3 hours. After drying, pulverizing, and classifying, the corresponding porous carbon framework was obtained.

[0181] Example 14

[0182] The preparation method of the silicon-carbon anode material in this embodiment is as follows:

[0183] S1: Dissolve 1.75g ​​of pentaethylenehexamine (manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; product number: P830660) in ethanol by mechanical stirring to form a pentaethylenehexamine solution. The mass ratio of pentaethylenehexamine to ethanol is 1:20.

[0184] 10.0 g of porous carbon framework (average pore size 2.00 nm, specific surface area 2500 m²) was used. 2 / g, pore volume 1.5cm 3 / g,D v The porous carbon skeleton (50 μm, 8.95 μm) was placed in a vacuum impregnation tank. Air was evacuated from the tank using a vacuum pump, stabilizing the vacuum at -0.1 MPa for 3.5 hours. Then, the inlet pipe of the impregnation tank was inserted into a beaker containing pentaethylenehexamine solution, and the inlet valve was opened. The solution was drawn in and completely submerged using negative pressure. After closing the valve, the tank was pressurized to 4 MPa and maintained at that pressure for 6 hours, forcing the pentaethylenehexamine solution to fully penetrate the pores of the porous carbon skeleton under high pressure.

[0185] S2: Maintaining a mechanical stirring speed of 100 rpm, slowly add 0.6125 g of glycerol triglycidyl ether dropwise to the dispersion obtained in S1 at a rate of 0.01 g / min. After the addition is complete, continue mechanical stirring for 24 h. Then filter and vacuum dry the product at 60 °C for 18 h to allow the glycerol triglycidyl ether and pentaethylenehexamine to undergo a crosslinking reaction, obtaining a crosslinked pentaethylenehexamine layer.

[0186] S3: The composite material obtained in S2 was placed in a chemical vapor deposition furnace and heated by introducing nitrogen gas at a flow rate of 0.3 L / min for 3 hours and a heating temperature of 460 °C. Subsequently, nitrogen gas was continuously introduced and the temperature was kept constant while silane was introduced at a flow rate of 0.15 L / min for the deposition of nano-silicon (i.e., the volume ratio of silane to nitrogen was 1:2) for 20 hours.

[0187] S4: Then, nitrogen gas is continuously introduced (nitrogen flow rate is 4L / min), and heating continues at a temperature of 560℃. At the same time, acetylene gas with a flow rate of 1L / min is introduced to perform carbon coating deposition (i.e., the volume ratio of carbon source to nitrogen gas is 1:4). The deposition time is 25h, and the silicon-carbon anode material of this embodiment can be obtained.

[0188] The porous carbon framework preparation method in this embodiment is as follows:

[0189] Mix 20.0g of phenol, 24.0g of 40% formaldehyde solution and 0.4g of NaOH, reflux at 80℃ for 2 hours, neutralize with dilute hydrochloric acid, and dehydrate under reduced pressure to obtain methyl phenolic resin.

[0190] 20.0 g of methyl phenolic resin, 25.8 g of hexadecyltrimethylammonium bromide, 12.4 g of sodium chloride, 258.1 mL of anhydrous ethanol, and 129 mL of deionized water were mixed and stirred to dissolve. The solution was placed in a reaction vessel and heated to 120 °C at a rate of 3 °C / min, and held at that temperature for 18 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was washed with ethanol and deionized water and then dried to obtain the phenolic resin.

[0191] Phenolic resin was placed in a carbonization furnace and heated to 700°C at a rate of 3°C / min, under nitrogen protection at a rate of 100 mL / min throughout the process. The reaction was carried out for 4 hours, and the carbonized material was obtained after natural cooling. Then, using steam at a flow rate of 2 mL / min and nitrogen at a rate of 50 mL / min, the temperature was increased to 800°C and activated for 12 hours. This was followed by a second activation under the same conditions. After drying, pulverizing, and classifying, the corresponding porous carbon framework was obtained.

[0192] Comparative Example 1

[0193] The preparation method of the silicon-carbon anode material in this comparative example is basically the same as that in Example 1, except that steps S1 and S2 are not performed, that is, the porous carbon framework in S1 is directly processed by steps S3 and S4.

[0194] Comparative Example 2

[0195] The preparation method of the silicon-carbon anode material in this comparative example is basically the same as that in Example 1, except that S2 is not performed, i.e., ethylene glycol diglycidyl ether is not added.

[0196] Test case

[0197] 1) Silicon-carbon anode material test example: The silicon-carbon anode material was tested as follows, and the test results are shown in Tables 1 to 4.

[0198] Pore ​​volume and average pore size testing of silicon-carbon anode materials and porous carbon framework: The specific surface area fully automatic pore size distribution tester of Beijing Jingwei Gaobo Science and Technology Co., Ltd. was used for testing using the nitrogen adsorption-desorption method.

[0199] Specific surface area of ​​silicon-carbon anode material and porous carbon framework: measured using a Microt TriStar 3020 specific surface area and pore size analyzer.

[0200] Particle size D of silicon-carbon anode materials and porous carbon framework v 50: Tested using Mastersizer 3000 laser diffraction technology.

[0201] Tap density of silicon-carbon anode material: tested by a tap density meter, with 3000 vibrations, a vibration height of 17.5 cm, and a vibration frequency of 260 times / min.

[0202] Silicon content testing: The ash content method was used for determination. The specific procedure was as follows: The silicon-carbon anode material was calcined at 950℃ in an air atmosphere. During the high-temperature calcination process, the carbon in the material reacted with oxygen to produce carbon monoxide (CO) and / or carbon dioxide (CO2) gases, which escaped. Nitrogen was converted into nitrogen gas (N2) and other gaseous products and discharged, while silicon was converted into solid silicon dioxide (SiO2). Ultimately, the material was completely converted into silicon dioxide. By measuring the mass after calcination, the mass content of silicon in the original material could be calculated.

[0203] Nitrogen content testing: This was performed using an oxygen-nitrogen analyzer. The material, encased in a tin / nickel bladder, was placed in a graphite crucible and completely melted at 2500℃. All nitrogen elements in the material were converted into nitric oxide. Subsequently, this nitric oxide was catalytically reduced back to nitrogen gas, and the mass percentage of nitrogen in the material was quantitatively analyzed using a thermal conductivity detector. By comparing with a standard curve, the mass percentage of nitrogen in the material could be directly obtained.

[0204] V 间隙 / V 硅 Test: The volume of silicon is obtained by multiplying the silicon content by the mass of the silicon-carbon anode material and dividing it by the silicon density; the volume of the gap in the silicon-carbon anode material is obtained by subtracting the weight of the silicon-carbon anode material before thermogravimetric analysis (TGA) from its true density and the weight of the silicon-carbon anode material after thermogravimetric analysis (TGA) from its true density.

[0205] Thermogravimetric analysis (TGA) of silicon-carbon anode materials: The silicon-carbon anode materials obtained in each embodiment and comparative example were used as measurement samples, with a sample mass of 50 mg. The programmed temperature was as follows: nitrogen gas flow rate of 0.3 L / min was used to raise the temperature from room temperature to 380°C at a rate of 10°C / min and hold it at that temperature for 60 min; the nitrogen gas flow rate was increased to 0.9 L / min and the temperature was maintained at 380°C for 120 min; the nitrogen gas flow rate was adjusted back to 0.3 L / min and the temperature was raised from 380°C to 490°C at a rate of 5°C / min and held at that temperature for 180 min; the nitrogen gas flow rate was increased to 0.6 L / min and the temperature was maintained at 490°C for 240 min.

[0206] True density testing of silicon-carbon anode materials before or after thermogravimetric analysis (TGA): The silicon-carbon anode materials obtained in each embodiment and comparative example were used as measurement samples. The true density of the silicon-carbon anode materials was accurately calculated by measuring the volume of helium gas replaced by the measurement sample. The dry measurement sample was placed into a sample chamber of known volume, and the pressure in the cavity and the sample chamber was measured sequentially during helium filling. The volume of the silicon-carbon anode material in the sample was calculated based on the pressure difference, and thus the true density was obtained.

[0207] True density test of porous carbon framework: The products obtained in step S2 of each embodiment and comparative example are used as measurement samples. The true density of the material framework is accurately calculated by measuring the volume of helium gas replaced by the measurement sample. The dry measurement sample is placed into a sample chamber of known volume, and the pressure in the cavity and the sample chamber is measured successively during helium filling. The volume of the porous carbon framework of the sample is calculated based on the pressure difference, and thus the true density is obtained.

[0208] Thermogravimetric analysis (TGA) of the porous carbon framework: The products obtained in step S2 of each example and comparative example were used as measurement samples, with a sample mass of 50 mg. The programmed temperature was as follows: nitrogen gas was introduced at a flow rate of 0.3 L / min, and the temperature was increased from room temperature to 380°C at a rate of 10°C / min, and held at this temperature for 60 min; the nitrogen gas flow rate was increased to 0.9 L / min, and the temperature was held at 380°C for 120 min; the nitrogen gas flow rate was adjusted back to 0.3 L / min, and the temperature was increased from 380°C to 490°C at a rate of 5°C / min, and held at this temperature for 180 min; the nitrogen gas flow rate was increased to 0.6 L / min, and the temperature was held at 490°C for 240 min. The purpose of this TGA test was to simulate the thermal decomposition of the crosslinked polyethylene polyamine layer at the carbon-coated temperature. After thermogravimetric analysis, the degree of decomposition of the crosslinking product = (1 - thermogravimetric residual mass ratio) * (mass of polyethylene polyamine + mass of aliphatic epoxy compound + mass of porous carbon) / (mass of polyethylene polyamine + mass of aliphatic epoxy compound) * 100%.

[0209] The thermogravimetric residual mass ratio is: the mass of the product obtained in step S2 of each embodiment and comparative example after thermogravimetric analysis / the mass of the product obtained in step S2 of each embodiment and comparative example before thermogravimetric analysis.

[0210] The quality test of the crosslinked product in step S2 is obtained by weighing the product obtained in step S2 and subtracting the mass of the porous carbon skeleton.

[0211] Battery performance test

[0212] The silicon-carbon anode materials of the examples and comparative examples were placed in an agate mortar with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was ground until a uniform slurry was formed. This slurry was then uniformly coated onto the surface of a copper foil current collector. After drying and rolling, the slurry was cut into circular electrode sheets to obtain the working electrode. The coating thickness was 300 μm, and the compaction density was 1.0 g / cm³. Finally, in a glove box, using a lithium metal sheet as the counter electrode, a solution of 1M LiPF6, EC, and DMC (EC and DMC volume ratio 1:1) as the electrolyte, and a polyethylene film as the separator, a CR2016 type button cell was assembled. During the process, the mass of the copper foil before coating (M1), the mass of the copper foil and the dried coating after drying (M2), and the mass of the electrode sheet after rolling and cutting (M3) were weighed. The mass of active material on each electrode sheet can be calculated as M3*(M2-M1) / M2.

[0213] 2) Battery test example: The above half-cells were tested as follows, and the test data are detailed in Table 3.

[0214] First Coulomb efficiency, reversible specific capacity, and 500-cycle capacity retention rate tests: Use the button cell clamps on the test cabinet to clamp the battery and perform the following tests.

[0215] Step 1: Let it stand for 2 hours;

[0216] Step 2: Perform a stepped constant current discharge from 0.1C to 0.01V, 0.08C to 0.005V, 0.05C to 0.005V, and 0.02C to 0.005V. Specifically, the stepped constant current discharge is performed by discharging from 0.1C to 0.01V, 0.08C to 0.005V, 0.05C to 0.005V, and 0.02C to 0.005V. Then let it stand for 10 minutes. Perform a constant current charge from 0.1C to 1.5V. Finally, let it stand for 10 minutes. This completes one cycle, and 500 cycles are added (step 2 is repeated 500 times).

[0217] After the test is completed, the initial charge capacity, initial discharge capacity, discharge capacity after 2 cycles, and discharge capacity after 500 cycles are read from the software. Initial coulombic efficiency = initial discharge capacity / initial charge capacity; reversible specific capacity = discharge capacity after 2 cycles / mass of active material on each electrode; 500-cycle capacity retention = discharge capacity after 500 cycles / discharge capacity after 2 cycles * 100%.

[0218] Expansion Rate Test: After the working electrode (negative electrode) is prepared, the working electrode and copper foil are weighed and their thickness measured. In a glove box, using lithium metal sheets as the counter electrode, electrolyte (1M LiPF6 and EC and DMC, EC and DMC volume ratio 1:1), and polyethylene film as the separator, the battery is assembled in a clean fixture. The assembled fixture is then subjected to cabinet testing. The testing software is set to constant pressure mode with an initial pressure of 1 kg; the battery is allowed to stand for 5 hours; constant current charging is performed from 0.1C to 4.2V; the battery is allowed to stand for 10 minutes; constant current discharging is performed from 0.1C to 2.75V; and finally, the battery is allowed to stand for 10 minutes. After the test, all battery thickness data can be read from the software. All thickness data are normalized by subtracting the first thickness; expansion rate = battery thickness change / (rolled electrode thickness - copper foil thickness) * 100%; the maximum expansion rate is taken as the final expansion rate of the material.

[0219] Electrochemical impedance and charge transfer impedance tests: The same test procedures as the above button batteries were followed, i.e., the batteries were clamped using the button battery clamps on the test cabinet. First, the batteries were allowed to stand for 2 hours; then, a stepped constant current discharge was performed from 0.1C to 0.01V, 0.08C to 0.005V, 0.05C to 0.005V, and 0.02C to 0.005V. Specifically, the stepped constant current discharge was performed at 0.1C to 0.01V, 0.08C to 0.005V, 0.05C to 0.005V, and 0.02C to 0.005V; then the batteries were allowed to stand for 10 minutes; next, a constant current charge was performed from 0.1C to 1.5V; finally, the batteries were allowed to stand for 10 minutes; this was repeated for one and a half charge-discharge cycles to activate and form a stable SEI film. Then, testing was conducted. During the test, the battery was set to 50% SOC, and a small sinusoidal perturbation (typically 5mV) was applied to the battery. The scanning frequency ranged from 0.01Hz to 100kHz, and the impedance spectrum was recorded. The corresponding charge transfer impedance was obtained by fitting the equivalent circuit diagram of its corresponding characteristics.

[0220] In the dQ / dV curve of the silicon-carbon anode material, I1 has a peak intensity near 0.25V-0.30V; I2 has a peak intensity near 0.43V-0.50V; satisfying: I2 / I1=0.60-0.70. Test conditions: CR2016 button cell, left to stand for 2 hours; constant current discharge: 0.1C to 0.01V; 0.08C to 0.005V; 0.05C to 0.005V; 0.02C to 0.005V; left to stand for 10 minutes; constant current charging: 0.03C to 1.5V; left to stand for 10 minutes to obtain the dQ / dV curve.

[0221] Table 1

[0222]

[0223] Table 2

[0224]

[0225] Table 3

[0226]

[0227] Table 4

[0228]

[0229] As shown by the data from Example 1 and Comparative Examples 1-2, using polyethyleneimine crosslinked with ethylene glycol diglycidyl ether as a template not only creates voids that allow for silicon volume expansion but also enables nitrogen doping, improving the initial coulombic efficiency and cycle stability. Simultaneously, it reduces the expansion rate and charge transfer impedance, and secondly, ensures that the reversible specific capacity does not decrease significantly (i.e., achieving both low expansion and good electrochemical performance). Furthermore, the crosslinking of ethylene glycol diglycidyl ether is necessary; crosslinking increases the thermal decomposition temperature of polyethyleneimine, ensuring that it only decomposes and forms a nitrogen-rich residual carbon layer during the higher-temperature carbon coating stage, thus successfully achieving carbon doping.

[0230] Data from Examples 1-3 and Example 12 show that branched polyethyleneimine of the same molecular weight has a smaller molecular size than linear polyethyleneimine, allowing it to enter the pores of porous carbon more smoothly and completely. Furthermore, the lower molecular weight (Mw = 600-1200 g / mol) also facilitates the complete entry of polyethyleneimine into the pores of porous carbon. Therefore, low-molecular-weight branched polyethyleneimine can uniformly and fully impregnate the pores without easily clogging the pore openings, which is beneficial for the subsequent deposition of silicon nanoparticles, reduces silicon floating, and the reserved expansion space helps to reduce expansion.

[0231] Data from Examples 1 and 4-6 show that increasing the amount of polyethyleneimine impregnation can increase the reserved expansion space volume and nitrogen doping content, thereby reducing the expansion rate and charge transfer impedance. However, the amount of silicon deposited subsequently will decrease accordingly, thus reducing the reversible specific capacity of the battery.

[0232] Data from Examples 1 and 7-9 show that increasing the amount of the crosslinking agent ethylene glycol diglycidyl ether leads to excessively high thermal decomposition temperature or a wider thermal decomposition window for the crosslinked polyethyleneimine. This results in a reduced degree of decomposition at the preset carbon coating temperature, and the generated residual carbon layer becomes brittle due to the excessive rigidity of the precursor, making it prone to cracking during cycling. Consequently, it cannot effectively accommodate the volume expansion of silicon, leading to a decrease in the initial coulombic efficiency and an increase in the expansion rate. Furthermore, the residual, insufficiently carbonized nitrogen-rich material has poor conductivity, resulting in increased charge transfer impedance.

[0233] Data from Examples 1 and 10-11 show that the silicon content, initial coulombic efficiency, expansion rate, and other indicators of the three are similar, proving that cross-linked polyethyleneimine can be completely decomposed at the carbon coating temperature and time set in this application.

[0234] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A silicon-carbon anode material, characterized in that, It includes a core and a carbon coating layer covering the core; the core includes a porous carbon framework and silicon particles; The silicon particles are disposed within the pores of the porous carbon skeleton; there is a gap between the surfaces of the silicon particles and the pores of the porous carbon skeleton. In the core, the volume of the gap is V1, the volume of the silicon particle is V2, and the ratio of V1 to V2 is 0.04-0.

9.

2. The silicon-carbon anode material according to claim 1, characterized in that, The surface of the pores in the porous carbon framework is also provided with a nitrogen-doped carbon layer.

3. The silicon-carbon anode material according to claim 2, characterized in that, The mass percentage of nitrogen in the silicon-carbon anode material is 0.5-10%.

4. The silicon-carbon anode material according to claim 2, characterized in that, The silicon element in the silicon-carbon anode material accounts for 10-65% of the total mass.

5. The silicon-carbon anode material according to claim 1 or 2, characterized in that, The total pore volume of the porous carbon framework is 0.4-1.5 cm³. 3 / g; The pores in the porous carbon framework have an average pore diameter D, 0 <D≤10nm; The specific surface area of ​​the porous carbon framework is 400-2500 m². 2 / g.

6. The silicon-carbon anode material according to claim 5, characterized in that, The pores in the porous carbon framework have an average pore size D,1 <D≤2nm; The specific surface area of ​​the porous carbon framework is 1000-2500 m². 2 / g.

7. The silicon-carbon anode material according to claim 1 or 2, characterized in that, The silicon-carbon anode material D v 50 represents 5.0-10.0 μm; And / or; the specific surface area of ​​the silicon-carbon anode material is less than 20 m². 2 / g; And / or; the tap density of the silicon-carbon anode material is 0.7-1.2 g / cm³. 3 .

8. The silicon-carbon anode material according to claim 1 or 2, characterized in that, The silicon-carbon anode material D v 50 is 6.5-8.0 μm; And / or; the specific surface area of ​​the silicon-carbon anode material is 3.5-5.5 m². 2 / g; And / or; the mass percentage of nitrogen in the silicon-carbon anode material is 0.5-6.5%; And / or; the mass percentage of silicon in the silicon-carbon anode material is 25-55%.

9. The silicon-carbon anode material according to claim 1 or 2, characterized in that, After the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 500-2000 mAh / g; And / or; after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is greater than or equal to 90%; And / or; after the silicon-carbon anode material is assembled into a battery, the expansion rate of the battery is less than 120%; And / or; after the silicon-carbon anode material is assembled into a battery, the capacity retention rate of the battery after 500 cycles is greater than 80%; And / or; after the silicon-carbon anode material is assembled into a battery, the charge transfer impedance of the battery is 30-120Ω; And / or; after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 is the peak intensity near 0.25V-0.30V; I2 is the peak intensity near 0.43V-0.50V; and I2 / I1 is less than or equal to 0.

70.

10. The silicon-carbon anode material according to claim 1 or 2, characterized in that, After the silicon-carbon anode material is assembled into a battery, the reversible specific capacity of the battery is 1300-2000mAh / g; And / or; after the silicon-carbon anode material is assembled into a battery, the initial coulombic efficiency of the battery is 90%-92%; And / or; after the silicon-carbon anode material is assembled into a battery, the expansion rate of the battery is 25-90%; And / or; after the silicon-carbon anode material is assembled into a battery, the capacity retention rate of the battery after 500 cycles is 80%-95%; And / or; after the silicon-carbon anode material is assembled into a battery, in the dQ / dV curve of the silicon-carbon anode material, I1 is the peak intensity near 0.25V-0.30V; I2 is the peak intensity near 0.43V-0.50V; satisfying: I2 / I1=0.60-0.

70.

11. A method for preparing a silicon-carbon anode material according to any one of claims 1-10, characterized in that, The method includes: S1: Impregnate the polyethylene polyamine into the pores of the porous carbon skeleton, and crosslink the polyethylene polyamine with an aliphatic epoxy compound to form a crosslinked product in the pores of the porous carbon skeleton. S2: Under the protection of an inert gas, a silicon source is introduced, and silicon particles are deposited on the cross-linked products in the pores of the porous carbon skeleton obtained in S1. S3: Under the protection of an inert gas, a carbon source is introduced, and a carbon coating layer is deposited on the surface of the product obtained in S2 to obtain the silicon-carbon anode material.

12. The preparation method according to claim 11, characterized in that, The polyethylene polyamines include at least one of polyethyleneimine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; the aliphatic epoxy compounds include at least one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerol triglycidyl ether. And / or; the mass ratio of the porous carbon to the polyethylene polyamine is 40:1-40:7; And / or; the mass ratio of the polyethylene polyamine and the aliphatic epoxy compound is 20:1-20:

7.

13. The preparation method according to claim 12, characterized in that, The polyethyleneimine includes branched polyethyleneimine and / or linear polyethyleneimine; And / or; the weight-average molecular weight of the polyethyleneimine is 600-1200 g / mol.

14. The preparation method according to claim 11, characterized in that, In step S2, the volume ratio of the silicon source to the inert gas is 15:1 to 1:

2. And / or; in step S2, the temperature for silicon particle deposition is 350-460°C; And / or; in step S3, the volume ratio of the carbon source to the inert gas is 10:1-1:4; And / or; in step S3, the temperature at which the carbon coating layer is deposited is 480-560°C.

15. The preparation method according to claim 11, characterized in that, The silicon source includes at least one of silane, disilane, dichlorosilane, and trichlorosilane; the carbon source includes alkane gases.

16. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material according to any one of claims 1-10.

17. A battery, characterized in that, Includes the negative electrode sheet according to claim 16.

Images