A silicon-carbon composite material, a negative electrode and a battery

Abstract

This invention belongs to the field of batteries and provides a silicon-carbon composite material, a negative electrode, and a battery. The silicon-carbon composite material comprises a hierarchical porous carbon material, silicon nanoparticles dispersed in the pores of the hierarchical porous carbon material, and an amorphous carbon layer coating the surface of the hierarchical porous carbon material. The pore structure of the hierarchical porous carbon material includes micropores, mesopores, and macropores, with a pore volume of 0.4 cm³. 3 / g~1.5cm 3 / g, with micropore volume accounting for 60% to 92% of the total pore volume. This silicon-carbon composite material can effectively inhibit the aggregation of silicon nanoparticles and reduce stress concentration. When used as a negative electrode active material to prepare batteries, it can produce products with better initial efficiency, lower expansion rate, and higher cycle stability.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a silicon-carbon composite material, a negative electrode, and a lithium-ion battery. Background Technology

[0002] Graphite anode materials dominate the lithium-ion battery anode market due to their high conductivity, strong stability, and low cost. However, with continuous technological advancements, the actual capacity of graphite materials in practical applications is gradually approaching their theoretical capacity (372 mAh / g), which can no longer meet the demand for higher energy density lithium-ion batteries.

[0003] Silicon has a theoretical capacity of up to 4200 mAh / g and is considered the most promising candidate to replace graphite as the next-generation anode active material for lithium-ion batteries. However, silicon undergoes significant volume expansion (~300%) during lithium intercalation and cycling, leading to silicon particle fragmentation and failure.

[0004] Combining silicon with hierarchical porous carbon materials enables the uniform distribution of silicon nanoparticles within the material, preventing particle breakage due to stress concentration. However, silicon nanoparticles loaded within the micropores of the hierarchical porous carbon material still exhibit significant volume expansion after lithium insertion, and are prone to separation from the active carbon after delithiation, leading to material failure. Therefore, it is crucial to develop a negative electrode active material that offers better initial battery performance, lower expansion rate, and higher cycle stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a silicon-carbon composite material, a negative electrode, and a battery. This silicon-carbon composite material contains a hierarchical porous carbon material, in which silicon nanoparticles can be uniformly dispersed. Combined with the amorphous carbon on the surface, this effectively inhibits the aggregation of silicon nanoparticles and reduces stress concentration. The amorphous carbon on the surface of the silicon-carbon composite material can also prevent direct contact between silicon particles and electrolyte, reduce the occurrence of side reactions, and improve the structural stability of the material. This silicon-carbon composite material is beneficial to improving battery performance, resulting in lower initial efficiency, lower expansion rate, and higher cycle stability.

[0006] To achieve the above objectives, the first aspect of the present invention provides a silicon-carbon composite material comprising a hierarchical porous carbon material, silicon nanoparticles dispersed in the pores of the hierarchical porous carbon material, and an amorphous carbon layer coated on the surface of the hierarchical porous carbon material.

[0007] The pore structure of the hierarchical porous carbon material includes micropores, mesopores, and macropores;

[0008] The pore volume of the hierarchical porous carbon material is 0.4 cm³. 3 / g~1.5cm 3 / g;

[0009] In the hierarchical porous carbon material, the micropore volume accounts for 60-90% of the total pore volume.

[0010] Preferably, the silicon-carbon composite material further contains nitrogen (N) and phosphorus (P) elements.

[0011] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector, the negative electrode coating comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon composite material described in the first aspect.

[0012] A third aspect of the present invention provides a battery comprising the silicon-carbon composite material described in the first aspect and / or the negative electrode sheet described in the second aspect.

[0013] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0014] (1) The hierarchical porous carbon material in the silicon-carbon composite material provided by this invention comprises a hierarchical porous structure of micropores-mesopores-macropores. Silicon nanoparticles are dispersed in the micropores. At the same time, due to the confinement effect of the micropores, the aggregation phenomenon of silicon nanoparticles is significantly improved, thereby effectively inhibiting the aggregation of silicon nanoparticles and reducing stress concentration. In addition, the presence of mesopores and macropores in the hierarchical porous carbon material avoids the aggregation and blockage of silicon nanoparticles on the material surface, improving the expansion of silicon. On the other hand, mesopores and macropores have a large pore volume, which can provide more buffer space for the volume expansion caused by lithium intercalation of silicon particles, avoiding the problem of material failure caused by the separation of silicon particles from active carbon after delithiation, and further improving the structural stability of silicon-carbon composite materials.

[0015] (2) In the silicon-carbon composite material provided by this invention, the hierarchical porous carbon material as a substrate enables silicon nanoparticles to be uniformly dispersed in the material, buffering the volume expansion of silicon particles during lithium intercalation during charging. Elemental silicon has a high theoretical specific capacity, and depositing silicon nanoparticles in the hierarchical porous carbon material can significantly improve the electrochemical energy storage performance of the composite material. The amorphous carbon on the surface of the silicon-carbon composite material can prevent direct contact between silicon particles and electrolyte, reduce the occurrence of side reactions, and improve the structural stability of the material. At the same time, the amorphous carbon also plays an isolating role, inhibiting the agglomeration tendency of silicon particles, avoiding material failure caused by stress concentration, and improving the cycle stability of the negative electrode active material. In addition, since silicon is a semiconductor, the conductivity of porous carbon material is significantly reduced after being combined with it. The surface coating of amorphous carbon helps to improve the conductivity of the material, thereby improving the first-efficiency performance of the negative electrode active material.

[0016] (3) The silicon-carbon composite material provided by the present invention is preferably also doped with N and P elements, which can accelerate the electron transfer rate, improve the conductivity of the electrode material, and at the same time improve the wettability of the electrode material surface and increase the contact area between the electrode material and the electrolyte.

[0017] (4) When the silicon-carbon composite material provided by the present invention is used as the negative electrode active material to prepare negative electrode sheets and batteries, it exhibits advantages such as high specific capacity, high initial efficiency, small cycle expansion and high cycle stability.

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a hierarchical porous carbon material.

[0020] Figure 2 The N2 isothermal adsorption-desorption curves are for the hierarchical porous carbon materials of Example 1 and Comparative Example 1.

[0021] Figure 3 The diagram shows the pore size distribution of the hierarchical porous carbon materials in Example 1 and Comparative Example 1.

[0022] Figure 4 The images show the Raman spectra of the hierarchical porous carbon materials of Example 1 and Comparative Example 1.

[0023] Figure 5 The image shows the fine N1s energy spectrum of the hierarchical porous carbon material in Example 1.

[0024] Figure 6 This is a fine P2p energy spectrum of the hierarchical porous carbon material in Example 1.

[0025] Figure 7 The capacity retention rate curves of lithium-ion pouch batteries prepared using the negative electrode active materials of Example 1 and Comparative Example 1.

[0026] Figure 8 The thickness change rate curve of lithium-ion pouch batteries prepared using the negative electrode active materials of Example 1 and Comparative Example 1 at 1000T. Detailed Implementation

[0027] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0029] The first aspect of the present invention provides a silicon-carbon composite material comprising a hierarchical porous carbon material, silicon nanoparticles dispersed in the pores of the hierarchical porous carbon material, and an amorphous carbon layer coated on the surface of the hierarchical porous carbon material.

[0030] The pore structure of the hierarchical porous carbon material includes micropores, mesopores, and macropores;

[0031] The pore volume of the hierarchical porous carbon material is 0.4 cm³. 3 / g~1.5cm 3 / g;

[0032] In the hierarchical porous carbon material, the micropore volume accounts for 60-90% of the total pore volume.

[0033] In this invention, the term "micropore" is defined as a pore with a diameter less than 2 nm, "mesopore" is defined as a pore with a diameter in the range of 2-50 nm, and "macropore" is defined as a pore with a diameter greater than 50 nm (50 nm-200 nm).

[0034] In the hierarchical porous carbon material of the present invention, mesopores and macropores are located between micropores, forming an interconnected pore structure, for example, as shown in... Figure 1 As shown.

[0035] In some embodiments, the specific surface area of ​​the hierarchical porous carbon material is 500 m². 2 / g~2000m 2 / g, for example 500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1100m 2 / g、1150m 2 / g、1200m 2 / g、1250m 2 / g、1300m 2 / g, 1350m 2 / g, 1400m 2 / g, 1450m 2 / g1500m2 / g, 1600m 2 / g, 1700m 2 / g、1800m 2 / g、1900m 2 / g or 2000m 2 / g. A larger specific surface area indicates a greater number of micropores, which can support more silicon particles, providing more reaction sites for the silicon particles and electrolyte, improving wetting, and also helping to increase the specific capacity of silicon-carbon materials.

[0036] In some embodiments, the specific surface area of ​​the hierarchical porous carbon material is 1000 m². 2 / g~1500m 2 / g.

[0037] In some embodiments, the micropore specific surface area of ​​the hierarchical porous carbon material is 500 m². 2 / g~1400m 2 / g, for example 900m 2 / g, 1000m 2 / g、1100m 2 / g、1150m 2 / g、1200m 2 / g、1250m 2 / g、1300m 2 / g, 1350m 2 / g or 1400m 2 / g.

[0038] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 m². 2 / g~50m 2 / g, for example 0.1m 2 / g, 0.5m 2 / g、1m 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g or 50m 2 / g. Silicon particles fill most of the micropores in the hierarchical porous carbon material. The silicon-carbon composite material has a significantly lower specific surface area compared to the hierarchical porous carbon material. The low specific surface area of ​​the silicon-carbon composite material helps to reduce the contact between the negative electrode active material and the electrolyte, reduce the formation of the SEI film, and thus improve the battery's initial efficiency and capacity retention.

[0039] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g~6m 2 / g.

[0040] In some embodiments, the pore volume of the silicon-carbon composite material is 0.0001 cm³. 3 / g~0.02cm 3 / g, for example 0.0001cm 3 / g, 0.0005cm 3 / g, 0.001cm 3 / g, 0.002cm 3 / g, 0.004cm 3 / g, 0.006cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.015cm 3 / g or 0.02cm 3 / g.

[0041] In some embodiments, the pore volume of the silicon-carbon composite material is 0.001 cm³. 3 / g~0.015cm 3 / g.

[0042] The pore volume of the hierarchical porous carbon material of the present invention is 0.4 cm³. 3 / g~1.5cm 3 / g, for example, 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, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g. The larger the pore volume of hierarchical porous carbon materials, the more silicon can be deposited, which is beneficial to improving the specific capacity of silicon-carbon materials.

[0043] In some embodiments, the pore volume of the hierarchical porous carbon material is 0.7 cm³. 3 / g~1.2cm 3 / g.

[0044] In some embodiments, the micropore volume of the hierarchical porous carbon material is 0.6 cm³. 3 / g~1.4cm 3 / g, for example, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g or 1.4cm 3 / g. Micropores enable silicon particles to be uniformly distributed within the pore structure of carbon materials, improving stress concentration and mitigating material failure caused by the expansion and fragmentation of silicon particles.

[0045] In this invention, the micropore volume of the hierarchical porous carbon material accounts for 60% to 92% of the total pore volume, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 92%. In some embodiments, the micropore volume of the hierarchical porous carbon material accounts for 80% to 91% of the total pore volume.

[0046] In some embodiments, the mesopore volume in the hierarchical porous carbon material accounts for 5% to 30% of the total pore volume, for example, 5%, 8%, 10%, 12%, 15%, 20%, 25%, or 30%. When the carbon material is entirely composed of micropores, silicon particles are prone to clogging the material surface during silicon deposition, resulting in a reduction in the amount of silicon deposited inside the material. A certain amount of mesopores can improve this problem.

[0047] In some embodiments, the mesopore volume of the hierarchical porous carbon material accounts for 6% to 15% of the total pore volume.

[0048] In some embodiments, the macropore volume of the hierarchical porous carbon material accounts for 1% to 20% of the total pore volume, for example, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 14%, 16%, 18%, or 20%.

[0049] In some embodiments, in the hierarchical porous carbon material, the macropore volume accounts for 2% to 10% of the total pore volume.

[0050] In this invention, parameters such as the specific surface area, pore area, and pore volume of the material are determined by N2 isothermal adsorption-desorption and calculated by the BET method.

[0051] In some embodiments, the median particle size Dv50 of the silicon-carbon composite material is 5 μm to 15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0052] In some embodiments, the median particle size of the silicon-carbon composite material is 5 μm to 10 μm.

[0053] In some embodiments, the median particle size of the hierarchical porous carbon material is 5 μm to 15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0054] In some embodiments, the median particle size of the hierarchical porous carbon material is 5 μm to 10 μm.

[0055] Limiting the particle size of materials within a certain range is beneficial to improving the overall electrochemical performance of anode active materials. Specifically, smaller particle sizes mean a higher specific surface area, resulting in a larger contact area with the electrolyte. This leads to greater consumption of active lithium during the first charging cycle, resulting in a lower initial efficiency of the anode active material. Conversely, larger particle sizes result in a longer diffusion path for lithium ions within the material, leading to poorer kinetic performance of the anode active material. Furthermore, larger particle sizes result in greater spacing, lower packing density, and difficulty in obtaining anode sheets with higher compaction density, leading to a lower volumetric energy density of the battery.

[0056] In this invention, the particle size distribution of the material is determined by a laser particle size analyzer. The specific testing process is as follows: (1) the sample to be tested is added to the medium liquid and ultrasonically dispersed evenly; (2) the medium liquid containing the sample to be tested is poured into the measuring chamber; (3) the laser particle size analyzer is started, the laser beam is irradiated into the sample and scattered, and the intensity and angle of the scattered light are recorded, so that the particle size and distribution of the sample to be tested can be analyzed.

[0057] In some embodiments, the true density of the hierarchical porous carbon material is 1.9 cm³. 3 / g~2.6cm 3 / g, for example, 1.9cm 3 / g、2cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g, 2.4cm 3 / g, 2.5cm 3 / g or 2.6cm 3 / g. When the true density of hierarchical porous carbon materials falls within the above range, silicon-carbon composite materials with superior overall performance can be obtained. When the true density of hierarchical porous carbon materials is less than the above range, it indicates the presence of a large number of pore structures in the material, which is detrimental to the structural stability of the material, especially for mesopores and macropores. An excessive number of mesopores and macropores can easily lead to the collapse of the internal structure of the material. When the true density of hierarchical porous carbon materials is greater than the above range, it means that the number of pore structures in the material is relatively small. During the subsequent chemical vapor deposition of silicon nanoparticles, due to insufficient active sites, it is difficult to deposit more silicon particles, resulting in a lower silicon content and a lower specific capacity of the material.

[0058] In some embodiments, the true density of the hierarchical porous carbon material is 2 cm³. 3 / g~2.5cm 3 / g.

[0059] In some embodiments, the true density of the silicon-carbon composite material is 1.5 cm³. 3 / g~2.5cm 3 / g, for example, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g、2cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g, 2.5cm 3 / g. When the true density of the negative electrode active material is within the above range, it ensures that the silicon-carbon composite material, while having a high silicon content, provides sufficient buffer space for the expansion of silicon particles during charging, avoiding material failure due to excessive volume expansion. When the true density of the negative electrode active material is lower than the above range, it indicates that there are still many pores in the material, and the silicon particles are not fully deposited inside the material. The low silicon content leads to a low specific capacity of the material. When the true density of the negative electrode active material is higher than the above range, it means that there are fewer pore structures in the material. During charging, the silicon particles undergo volume expansion due to lithium intercalation. If the pore structure in the material is insufficient to support the volume expansion of the silicon particles, the material structure will be damaged and fail.

[0060] In some embodiments, the true density of the silicon-carbon composite material is 1.7 cm³. 3 / g~2.1cm 3 / g.

[0061] In this invention, the true density of the material is determined by the gas displacement method. For example, a certain mass of the sample to be tested is weighed using an analytical balance, and then the sample is sealed in a sample chamber of known volume. A certain amount of inert gas (helium, nitrogen, etc.) is introduced into the sample chamber and diffuses into the expansion chamber. The volume of the sample is obtained by the pressure difference before and after gas diffusion. Finally, the true density of the material can be calculated based on the mass and volume of the material.

[0062] In some embodiments, the thickness of the amorphous carbon layer in the silicon-carbon composite material is 1 nm to 20 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm or 20 nm.

[0063] In some embodiments, the thickness of the amorphous carbon layer in the silicon-carbon composite material is 5 nm to 10 nm. The uniform coating of amorphous carbon on the surface of the silicon-carbon composite material prevents direct contact between silicon and the electrolyte, reduces side reactions, and alleviates volume expansion caused by silicon intercalation, thereby improving the stability of the silicon-carbon material.

[0064] In some embodiments, the hierarchical porous carbon material I D / I G The value is between 0.5 and 1.5, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0065] In some embodiments, the hierarchical porous carbon material I D / I G It ranges from 0.8 to 1.5.

[0066] In the Raman curve of the hierarchical porous carbon material, I D / I G This refers to the intensity ratio of the D peak to the G peak in the Raman curve. In this invention, the Raman spectrum was obtained using an RM2000 microconfocal Raman spectrometer (Reinshaw product), with the following specifications: the excitation source was a He-Ne laser with a wavelength of 525 nm.

[0067] Typically, the Raman spectra of carbon materials are in the range of 1334–1346 cm⁻¹. -1 and 1581~1585cm -1 Characteristic peaks appear within the region, corresponding to the D (Defects and Disorder) band and G (Graphitic) band of the carbon material, respectively. The D band originates from sp2 in the carbon layer. 3 Defects or disordered expansion of structural domains, while G-bands and sp in the carbon lattice 2 It is related to the stretching vibration of the bond. The peak intensity ratio of the D band and G band is I D / I G It is commonly used to characterize the degree of order in the structures of amorphous carbon materials and graphitized carbon materials. When I D / I G A lower peak intensity indicates that there are more defects in the porous carbon material structure, which is beneficial for the capture and adsorption of silane molecules on the carbon matrix surface during subsequent chemical vapor deposition, thereby increasing the amount of silicon deposited.

[0068] In some embodiments, the silicon-carbon composite material further comprises N and / or P elements.

[0069] In some embodiments, the hierarchical porous carbon material in the silicon-carbon composite material includes at least one of the doping elements N and P.

[0070] The fine N1s energy spectrum of nitrogen, after Gaussian peak fitting, yielded three characteristic peaks corresponding to pyridinic nitrogen (~399 eV), pyrrolic nitrogen (~400.5 eV), and quaternary nitrogen (~405 eV). Pyridinic and pyrrolic nitrogen are located at the six-membered and five-membered ring carbon atom positions at the edges of the graphite carbon layer, respectively, while quaternary nitrogen is located at the six-membered ring carbon atom positions inside the graphite carbon layer. Different types of nitrogen atoms have different effects on improving the electrochemical performance of activated carbon materials. For example, pyridinic and pyrrolic nitrogen can undergo reversible redox reactions during charge and discharge, providing additional pseudocapacitance; quaternary nitrogen can increase the electron transfer rate and also improve the conductivity of the electrode material.

[0071] After peak fitting of the P2p characteristic peak curve of phosphorus, characteristic peaks appeared near the binding energies of 132.7 and 133.9 eV, corresponding to the PC and P=O groups, respectively. The P atoms in the PC group can provide additional electrons to the carbon lattice, improving the conductivity of the activated carbon material; the P=O group can improve the wettability of the electrode material surface, increasing the contact area between the electrode material and the electrolyte.

[0072] In some embodiments, the nitrogen (N) content in the silicon-carbon composite material is less than 6 wt%, for example, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or 6 wt%, and the phosphorus (P) content is between 0.05 wt% and 6 wt%, for example, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%. The nitrogen (N) and phosphorus (P) elements provide additional electrons to the valence and conduction bands of carbon atoms, which can accelerate the electron transfer rate, improve the conductivity of the electrode material, and also improve the wettability of the electrode material surface, increasing the contact area between the electrode material and the electrolyte.

[0073] In some embodiments, the content of nitrogen (N) in the silicon-carbon composite material is 2 wt% to 5 wt%, and the content of phosphorus (P) is 1 wt% to 5 wt%.

[0074] In some embodiments, the nitrogen (N) content in the hierarchical porous carbon material is less than 10 wt%, for example, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%; and the phosphorus (P) content is 0.05 wt% to 6 wt%, for example, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%.

[0075] In some embodiments, the content of nitrogen (N) in the hierarchical porous carbon material is 2 wt% to 7 wt%, and the content of phosphorus (P) is 1 wt% to 5 wt%. N and P elements can accelerate the electron transfer rate, improve the conductivity of the electrode material, and also improve the wettability of the electrode material surface, increasing the contact area between the electrode material and the electrolyte.

[0076] In some embodiments, the content of hierarchical porous carbon material in the silicon-carbon composite material is 35 wt% to 85 wt%, for example, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%. In some embodiments, the content of silicon nanoparticles in the silicon-carbon composite material is 10 wt% to 60 wt%, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, or 60 wt%. In some embodiments, the content of the amorphous carbon layer is 0.1 wt% to 5 wt%, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%. When the content of each substance in the silicon-carbon composite material is within the above range, the resulting silicon-carbon composite material exhibits superior overall performance, resulting in better initial efficiency, lower expansion rate, and higher cycle stability of the battery. The content of silicon nanoparticles is expressed as the content of silicon elemental.

[0077] In this invention, the content of each element is determined by XPS.

[0078] In some embodiments, the electrical conductivity of the silicon-carbon composite material is 10 S / cm to 500 S / cm, for example, 10 S / cm, 20 S / cm, 30 S / cm, 40 S / cm, 50 S / cm, 60 S / cm, 70 S / cm, 80 S / cm, 90 S / cm, 100 S / cm, 150 S / cm, 200 S / cm, 250 S / cm, 300 S / cm, 350 S / cm, 400 S / cm, 450 S / cm, or 500 S / cm.

[0079] In some embodiments, the electrical conductivity of the silicon-carbon composite material is 20 S / cm-320 S / cm. Materials with low electrical conductivity generate more heat during cell cycling, leading to energy loss. Increasing the material's electrical conductivity can reduce the rate of cell aging and damage, thereby extending the cell's lifespan.

[0080] In this invention, the electrical conductivity of the silicon-carbon particles can be tested according to the method of GB / T 24533-2019.

[0081] This invention also provides a method for preparing a silicon-carbon composite material, the method comprising:

[0082] (1) Mix N-containing biomass material with an organophosphorus source solution and then dry it to obtain a solid precursor;

[0083] (2) The solid precursor prepared in step (1) is subjected to carbonization treatment to obtain intermediate carbonized product;

[0084] (3) The intermediate carbonization product is activated by an activator to obtain a hierarchical porous carbon material;

[0085] (4) Silicon particles were deposited into hierarchical porous carbon materials by chemical vapor deposition to obtain nano-silicon@hierarchical porous carbon composite materials;

[0086] (5) An amorphous carbon layer was deposited onto the surface of nano-silicon@hierarchical porous carbon composite material by chemical vapor deposition to obtain silicon-carbon composite material.

[0087] The nitrogen-containing biomass material can be conventional nitrogen-containing biomass in the art. In some embodiments, the nitrogen-containing biomass material may include, but is not limited to, at least one of yeast powder, soybean meal, soybean residue, distiller's grains, vinegar residue, soy sauce residue, and mushroom substrate.

[0088] In some embodiments, the nitrogen content in the nitrogen-containing biomass material is 1 wt% to 20 wt%, for example, 1 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%.

[0089] The inventors discovered that when the nitrogen content of biomass raw materials is within 7 wt% (including when it is close to 0), the electrical performance of the prepared button cells and pouch cells generally shows a gradual decreasing trend as the nitrogen content decreases.

[0090] In some embodiments, the phosphorus content in the N-containing biomass material is less than 10 wt%, for example, 0 wt%, 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, or 10 wt%.

[0091] In some embodiments, the organophosphorus source includes at least one of phytic acid, ammonium formate, polycarboxylic acid, and sodium phosphate acetate.

[0092] In some embodiments, the organophosphorus source includes phytic acid.

[0093] In some embodiments, the concentration range of the organophosphorus source solution is 0.1 mol / L to 5 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0094] By controlling the ratio of organophosphorus source to nitrogen-containing biomass material within a certain range, intermediate carbonization products with a certain number of pore structures can be generated first, providing sufficient active sites for subsequent activation by activators.

[0095] In some embodiments, the mass ratio of the organophosphorus source to the N-containing biomass material is 0.1:1 to 4:1, for example, 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0096] In some embodiments, the mass ratio of the organophosphorus source to the nitrogen-containing biomass material is 0.3:1 to 0.7:1.

[0097] In step (1), the mixing process may be accompanied by stirring, and the drying can be a conventional drying method, such as freeze drying.

[0098] In step (2), the carbonization process can be carried out in a conventional apparatus, such as a tube furnace, and the temperature is increased to the carbonization temperature at a certain heating rate (e.g., 3℃ / min to 8℃ / min). In some embodiments, the conditions for the carbonization process in step (2) include: a temperature of 400 to 600℃, for example 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, or 600℃, a time of 2 to 4 hours, and an inert atmosphere.

[0099] In step (3), an activator is used to activate the intermediate carbonized product. In some embodiments, the activator includes, but is not limited to, KOH, ZnCl2, H3PO4, etc.

[0100] In some embodiments, the mass ratio of the activator to the intermediate carbonization product is 0.1:1 to 4:1, for example 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0101] In some embodiments, the mass ratio of the activator to the intermediate carbonization product is 0.5:1 to 2:1.

[0102] In some embodiments, the activation treatment conditions in step (3) include: a temperature of 600–1000°C, preferably 700–900°C, a time of 1–3 hours, and an inert atmosphere. The temperature can be increased to the activation temperature at a certain heating rate (e.g., 3°C / min–8°C / min).

[0103] In step (4), silicon particles are deposited into the hierarchical porous carbon material by chemical vapor deposition. In some embodiments, the silicon source used in the silicon particle chemical vapor deposition process includes silanes and / or chlorosilanes. The general formula for silanes is Si.n H 2n+2 n is a positive integer, such as 1, 2, 3, 4, 5, or 6. Chlorosilanes are silanes substituted with chlorine, such as dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0104] The silicon source can be mixed with an inert atmosphere to form a mixed gas that is introduced into the CVD deposition chamber. The flow rate of the mixed gas during the deposition process can be adjusted according to the actual situation, for example, within the range of 10-200 sccm.

[0105] In some embodiments, in step (4), the deposition conditions include: a temperature of 400–600°C, a time of 1–4 h, and an inert atmosphere. The temperature is increased to the deposition temperature at a certain heating rate (e.g., 3°C / min–8°C / min).

[0106] In step (5), an amorphous carbon layer is deposited onto the surface of the nano-silicon@hierarchical porous carbon composite material by chemical vapor deposition. In some embodiments, the carbon source used in the chemical vapor deposition process of the amorphous carbon layer includes at least one of C1-C4 alkanes (such as methane, ethane, etc.), C2-C4 olefins (such as ethylene, etc.), and C2-C4 alkynes (such as acetylene, etc.). The carbon source can be introduced into the CVD deposition chamber in gaseous form, and the flow rate of the carbon source gas during the deposition process can be adjusted according to the actual situation, for example, it can be adjusted in the range of 10-200 sccm.

[0107] In some embodiments, the deposition conditions in step (5) include: a temperature of 600–800°C, a time of 0.5–1.5 h, and an inert atmosphere. The temperature is increased to the deposition temperature at a certain heating rate (e.g., 3°C / min–8°C / min).

[0108] In some embodiments, the inert atmosphere includes at least one of nitrogen, argon, and helium.

[0109] In some embodiments, the amounts of each component are such that the content of nitrogen (N) in the silicon-carbon composite material is less than 6 wt% and the content of phosphorus (P) is between 1 wt% and 5 wt%.

[0110] In some embodiments, the amounts of each component are such that the content of hierarchical porous carbon material in the silicon-carbon composite material is 35wt% to 85wt%, the content of silicon nanoparticles is 10wt% to 60wt%, and the content of amorphous carbon layer is 0.1wt% to 5wt%.

[0111] In some embodiments, the amounts of each component are such that the content of N element in the hierarchical porous carbon material is 0.1wt% to 8wt%, and the content of P element is 0.05wt% to 6wt%.

[0112] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector, the negative electrode coating comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon composite material described in the first aspect.

[0113] In addition to the silicon-carbon composite material described in the first aspect of this invention, the negative electrode active material may also be mixed with other negative electrode active materials in the art, such as carbon materials (e.g., graphite) and / or silicon materials.

[0114] In some embodiments, the content of silicon-carbon composite material in the negative electrode active material is 3 wt% or more, for example, 3 wt%, 4 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or 100 wt%.

[0115] In some embodiments, where the negative electrode active material contains other carbon and / or silicon materials, the content of silicon-carbon composite material in the negative electrode active material is 3 wt% to 10 wt%, for example, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0116] In some embodiments, the content of silicon-carbon composite material in the negative electrode coating is 3wt% to 99wt%, for example, 3wt%, 4wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, or 99wt%.

[0117] The negative electrode coating may also include additives commonly used in coatings, such as conductive agents and binders.

[0118] In some embodiments, the negative electrode coating includes the negative electrode active material, the conductive agent, and the binder.

[0119] The conductive agent may include conductive agents conventionally used in the art, such as at least one selected from Super P, acetylene black, and Ketjen black.

[0120] The adhesive may include adhesives conventionally used in the art, for example, the adhesive is selected from at least one of sodium carboxymethyl cellulose, carboxymethyl cellulose, polyvinylidene fluoride and styrene-butadiene rubber.

[0121] In some embodiments, based on the total weight of the negative electrode coating, the content of the negative electrode active material can be 80-99 wt% (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt%), the content of the conductive agent can be 0.5-10 wt% (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt%), and the content of the binder can be 0.5-10 wt% (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt%).

[0122] In some embodiments, based on the total weight of the negative electrode coating, the content of the negative electrode active material is 95-99 wt%, the content of the conductive agent is 0.5-2.5 wt%, and the content of the binder is 0.5-2.5 wt%.

[0123] A third aspect of the present invention provides a battery comprising the silicon-carbon composite material described in the first aspect and / or the negative electrode sheet described in the second aspect.

[0124] The components of the battery, excluding the negative electrode (e.g., positive electrode, separator, electrolyte, aluminum-plastic film, etc.), can all be conventional choices in the art.

[0125] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer coated on at least one side surface of the positive current collector, wherein the positive active material layer includes a positive active material.

[0126] The positive electrode active material can be a conventionally selected material in the art. For example, the positive electrode active material is selected from at least one of lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganese oxide (LMO), lithium nickel oxide, lithium nickel manganese oxide binary material, lithium-rich manganese-based material, and lithium manganese iron phosphate.

[0127] The positive electrode active material may also include doped and / or coated positive electrode active materials.

[0128] The batteries can all be assembled in accordance with conventional methods in the field.

[0129] The battery can be a liquid electrolyte battery, a semi-solid battery, or an all-solid battery.

[0130] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0131] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0132] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0133] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0134] In the following examples, unless otherwise specified, all materials and reagents used are commercially available.

[0135] In the following examples, the specific surface area and pore structure information of the materials were determined by N2 isothermal adsorption-desorption and calculated by fitting models such as BET and NLDFT.

[0136] In the following example, the particle size distribution of the material is obtained by testing with a laser particle size analyzer. The specific testing process includes: (1) adding the sample to be tested into the medium liquid and dispersing it evenly by ultrasonication; (2) pouring the medium liquid containing the sample to be tested into the measuring chamber; (3) starting the laser particle size analyzer, irradiating the sample with the laser beam and causing scattering, recording the intensity and angle of the scattered light, and then analyzing the particle size and distribution of the sample to be tested.

[0137] Example 1

[0138] This embodiment illustrates the preparation of the silicon-carbon composite material described in this invention.

[0139] (1) Preparation of hierarchical porous carbon materials

[0140] Yeast powder (with an nitrogen content of approximately 7 wt%) was mixed with phytic acid solution to form a homogeneous precursor solution (the mass ratio of phytic acid to yeast powder was 0.5:1). The solution was refrigerated at -20°C for 8 hours. The solidified precursor was then rapidly transferred to a freeze dryer and dried at -80°C and 10 Pa vacuum for 12–20 hours to obtain a fluffy solid precursor.

[0141] The solid precursor was placed in a tube furnace and heated to 500°C at a rate of 5°C / min under a N2 atmosphere. After holding at this temperature for 3 hours, it was naturally cooled to room temperature to obtain an intermediate carbonization product. KOH was mixed evenly with the intermediate carbonization product (the mass ratio of KOH to the intermediate carbonization product was 1:1). The reactants were then placed in a tube furnace and activated at 800°C at a rate of 5°C / min under a N2 atmosphere. After holding at this temperature for 2 hours, it was naturally cooled to room temperature to obtain the hierarchical porous carbon material.

[0142] Figure 2 and Figure 3 The isothermal adsorption-desorption curves and pore size distribution diagrams of the obtained hierarchical porous carbon materials are shown respectively. Figure 4 Raman spectra of hierarchical porous carbon materials are shown. Figure 5 The image shows the fine N1s energy spectrum of the hierarchical porous carbon material. Figure 6 This is the fine P2p energy spectrum of the hierarchical porous carbon material.

[0143] (2) Preparation of nano-silicon@hierarchical porous carbon composite material

[0144] The multi-level porous carbon material is placed in a tube furnace and heated from room temperature to 500°C at a rate of 5°C / min in an N2 atmosphere. A SiH4-N2 mixed gas with a flow rate of 60 sccm and containing 20% ​​SiH4 is introduced and maintained at 500°C for 3 hours to obtain nano-silicon@multi-level porous carbon composite material.

[0145] (3) Preparation of silicon-carbon composite materials

[0146] The nano-silicon@hierarchical porous carbon composite material is placed in a tube furnace and heated from room temperature to 700°C at a rate of 5°C / min in a N2 atmosphere. Acetylene gas with a flow rate of 100 sccm is introduced and the temperature is maintained for 1 hour to obtain an amorphous carbon@nano-silicon@hierarchical porous carbon composite material with an amorphous carbon layer on the surface, which is the silicon-carbon composite material of the present invention.

[0147] The physicochemical characteristics of the hierarchical porous carbon material were determined (specific surface area, pore characteristics, median particle size, true density, Ig). D / I G The contents of nitrogen (N) and phosphorus (P) elements were measured, and the results are shown in Table 1.

[0148] The thickness of the amorphous carbon layer was measured, and the physicochemical characteristics (specific surface area, pore volume, true density, silicon content, N element content, and P element content) of the silicon-carbon composite material were measured. The results are shown in Table 2.

[0149] Example 2

[0150] Example 2a: This example is based on Example 1, except that the mass ratio of phytic acid to yeast powder in step (1) is adjusted to 0.25:1.

[0151] Example 2b: This example is based on Example 1, except that the mass ratio of phytic acid to carbon-containing precursor during the pre-activation process is adjusted to 1:1.

[0152] Example 2c: This example is based on Example 1, except that the mass ratio of phytic acid to carbon-containing precursor during the pre-activation process is adjusted to 2:1.

[0153] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0154] Example 3

[0155] Example 3a: This example is based on Example 1, except that the mass ratio of KOH to intermediate carbonization product in step (1) is adjusted to 0.5:1.

[0156] Example 3b: This example is based on Example 1, except that the mass ratio of KOH to intermediate carbonization product in step (1) is adjusted to 2:1.

[0157] Example 3c: This example is based on Example 1, except that the mass ratio of KOH to intermediate carbonization product in step (1) is adjusted to 3:1.

[0158] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0159] Example 4

[0160] Example 4a: This example is based on Example 1, except that the activation process temperature is set to 700°C.

[0161] Example 4b: This example is based on Example 1, except that the activation process temperature is set to 900°C.

[0162] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0163] Example 5

[0164] Example 5a: This example is based on Example 1, except that an equal weight of soybean meal (with an N content of about 5 wt%) is used instead of yeast powder.

[0165] Example 5b: This example is based on Example 1, except that an equal weight of distiller's grains (with an N content of about 3 wt%) is used instead of yeast powder.

[0166] Example 5c: This comparative example is based on Example 1, except that an equal weight of corn starch (with an N content of about 0 wt%) is used instead of yeast powder.

[0167] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0168] Example 6

[0169] Example 6a: This example is based on Example 1, except that the heat preservation time in the SiH4-N2 mixed atmosphere in step (2) is changed to 1 hour.

[0170] Example 6b: This example is based on Example 1, except that the flow rate of the SiH4-N2 mixed gas in step (2) is changed to 120 sccm.

[0171] The characterization results of the prepared amorphous carbon layer and silicon-carbon composite material are shown in Table 2.

[0172] Example 7

[0173] Example 7a: This example is based on Example 1, except that the holding time for depositing amorphous carbon in step (3) is changed to 0.5h, and the thickness of the amorphous carbon layer obtained is 1.22nm.

[0174] Example 7b: This example is based on Example 1, except that the flow rate of depositing amorphous carbon in step (3) is changed to 150 sccm, and the thickness of the amorphous carbon layer obtained is 5.53 nm.

[0175] Example 7c: This example is based on Example 1, except that the holding time for depositing amorphous carbon in step (3) is changed to 3h, and the thickness of the amorphous carbon layer is 15.2nm.

[0176] The characterization results of the prepared amorphous carbon layer and silicon-carbon composite material are shown in Table 2.

[0177] Comparative Example 1

[0178] This comparative example is based on Example 1, except that phytic acid and KOH are not added in step (1).

[0179] Figure 2 and Figure 3 The isothermal adsorption-desorption curves and pore size distribution of the hierarchical porous carbon material in Comparative Example 1 are shown respectively.

[0180] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0181] Comparative Example 2

[0182] This comparative example is based on Example 1, except that phytic acid is not added in step (1).

[0183] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0184] Comparative Example 3

[0185] This comparative example is based on Example 1, except that KOH is not added in step (1).

[0186] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0187] Comparative Example 4

[0188] This comparative example is based on Example 1, except that the nano-silicon@hierarchical porous carbon composite material is not subjected to amorphous carbon coating treatment. That is, the nano-silicon@hierarchical porous carbon composite material prepared in Example 1 is a silicon-carbon composite material.

[0189] The characterization results of the prepared hierarchical porous carbon materials, amorphous carbon layers, and silicon-carbon composite materials are shown in Table 1 and Table 2, respectively.

[0190] Table 1

[0191]

[0192]

[0193] Table 2

[0194]

[0195]

[0196] Test case

[0197] 1. Preparation and performance evaluation of button cells

[0198] (1) Preparation of negative electrode

[0199] The silicon-carbon composite materials prepared in the examples and comparative examples were mixed with conductive carbon black, carbon nanotubes, and polyacrylic acid at a mass ratio of 80:9:1:10. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry. This slurry was then uniformly coated onto copper foil, with the areal density controlled at 4–8 mg / cm³. 2 Within the range. Next, the copper foil is placed in an oven and dried at 80°C for 8-12 hours. After rolling and slitting, the negative electrode sheet can be obtained.

[0200] (2) Assembly of button cells

[0201] The negative electrode sheet is stamped into a 16mm diameter negative electrode disc using a stamping machine, and the lithium metal sheet is stamped into an 18mm diameter positive electrode disc. In a glove box, the spring, gasket, negative electrode disc, cellulose separator, and positive electrode disc are sequentially placed into the button cell casing. After adding an appropriate amount of electrolyte, the casing is pressed and sealed using a pressing machine to obtain the button cell battery.

[0202] (3) Performance Testing

[0203] The performance of the coin cell half-cells prepared above was tested at room temperature (25℃) using the LAND testing system. The specific test steps included:

[0204] (a) Discharge to 5mV at 0.025C and then let stand for 10 minutes;

[0205] (b) Discharge to 5mV at 0.01C and then let stand for 10 minutes;

[0206] (c) Charge to 1.5V at 0.02C and let stand for 10 minutes;

[0207] Repeat steps (a) to (c) 3 times.

[0208] The initial efficiency of the battery was obtained by using the discharge and charge curves, and the specific capacity of the negative electrode active material was calculated based on the mass of the negative electrode active material. The results are shown in Table 3.

[0209] Table 3

[0210] serial number First-time efficiency (%) Capacity (mAh / g) Example 1 90.5 1790 Example 2a 86.2 1509 Example 2b 87.5 1575 Example 2c 88.1 1588 Example 3a 88.3 1621 Example 3b 85.8 1539 Example 3c 82.5 1512 Example 4a 88.9 1664 Example 4b 88.3 1592 Example 5a 90.1 1770 Example 5b 90.4 1740 Example 5c 88.8 1658 Example 6a 87.7 1578 Example 6b 82.2 1499 Example 7a 87.0 1776 Example 7b 87.5 1773 Example 7c 88.2 1625 Comparative Example 1 75.1 819 Comparative Example 2 80.5 1361 Comparative Example 3 79.2 1169 Comparative Example 4 81.7 1763

[0211] 2. Preparation and performance evaluation of pouch cells

[0212] (1) Preparation of negative electrode

[0213] The silicon-carbon composite material, graphite, carbon black, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber prepared in the examples and comparative examples were mixed in a mass ratio of 4.86:92.34:0.05:1.4:0.35:1. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry. This slurry was then uniformly coated onto copper foil, with the areal density controlled at 4–8 mg / cm³. 2 Within the range. Next, the copper foil is placed in an oven and dried at 80°C for 8-12 hours. After rolling and slitting, the negative electrode sheet can be obtained.

[0214] (2) Preparation of positive electrode

[0215] Lithium cobalt oxide, PVDF, acetylene black, and carbon nanotubes were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. This slurry was then uniformly coated onto aluminum foil, with the areal density controlled at 8–15 mg / cm³. 2 Within the specified range. Next, the aluminum foil is placed in an oven and dried at 120°C for 8–12 hours. After rolling and slitting, the positive electrode sheet can be obtained.

[0216] (3) Assembly of pouch batteries

[0217] The negative electrode, separator, and positive electrode are stacked in sequence, and then the battery is obtained through processes such as winding, encapsulation, liquid injection, secondary sealing, formation, and sorting.

[0218] Examples R1-R3: The silicon-carbon composite material prepared in Example 1 was used to prepare soft-pack batteries according to the above method. The difference was that, with the total amount of silicon-carbon composite material and graphite remaining unchanged, the content of silicon-carbon composite material in the total mass of silicon-carbon composite material and graphite was adjusted from 5 wt% to 4 wt%, 7 wt%, and 10 wt%, respectively.

[0219] (4) Performance testing of the full battery

[0220] At room temperature (25℃), the performance of the prepared soft-pack battery was tested using the LAND test system. The specific test steps included: (1) charging to 4.53V with a constant current of 2C, cutting off current of 0.05C, and letting stand for 10 minutes; (2) discharging to 3.0V with a constant current of 0.7C and letting stand for 10 minutes; (1) to (2) were cycled 1000 times.

[0221] The battery's weekly capacity retention rate is calculated based on the initial discharge capacity and weekly discharge capacity. Before testing, the initial battery thickness is measured and recorded using a PPG battery thickness gauge. After every 100 cycles, the current battery thickness is measured and recorded using a PPG battery thickness gauge, and the battery thickness change rate is calculated.

[0222] The specific capacity, initial efficiency, capacity retention at 1000T, and thickness change rate of the prepared full cell were measured, and the results are shown in Table 4.

[0223] Figure 7 The capacity retention rate curves of lithium-ion pouch batteries prepared using the negative electrode active materials of Example 1 and Comparative Example 1.

[0224] Figure 8 The thickness change rate curve of lithium-ion pouch batteries prepared using the negative electrode active materials of Example 1 and Comparative Example 1 at 1000T.

[0225] Table 4

[0226] serial number Capacity (mAh / g) First-time efficiency (%) 1000T capacity retention rate (%) Thickness change rate (%) for 1000T Example 1 427 89.1 82.5 8.7 Example 2a 413 85.0 71.8 12.0 Example 2b 416 86.3 77.3 11.2 Example 2c 417 86.8 78.0 10.2 Example 3a 418 87.1 75.2 11.6 Example 3b 414 84.6 73.7 11.5 Example 3c 413 81.2 70.8 12.5 Example 4a 420 87.8 80.2 9.5 Example 4b 417 87.1 79.7 9.3 Example 5a 426 88.9 82.2 8.9 Example 5b 424 89.2 82.0 8.7 Example 5c 420 87.6 81.5 9.8 Example 6a 416 86.5 83.2 8.4 Example 6b 412 81.1 82.8 8.8 Example 7a 426 85.8 73.1 11.8 Example 7b 426 86.3 74.2 11.2 Example 7c 418 87.2 78.3 10.4 Example R1 410 89.4 83.7 8.4 Example R2 455 88.5 75.1 12.5 Example R3 498 88.1 73.0 13.7 Comparative Example 1 378 73.9 60.2 17.7 Comparative Example 2 405 79.2 58.7 18.2 Comparative Example 3 396 78.0 65.2 16.5 Comparative Example 4 425 80.5 56.1 20.8

[0227] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0228] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material comprises a hierarchical porous carbon material, silicon nanoparticles dispersed in the pores of the hierarchical porous carbon material, and an amorphous carbon layer coated on the surface of the hierarchical porous carbon material, wherein the thickness of the amorphous carbon layer is 1 nm to 20 nm. The pore structure of the hierarchical porous carbon material includes micropores, mesopores, and macropores; The pore volume of the hierarchical porous carbon material is 0.4 cm³. 3 / g ~1.5 cm 3 / g; In the hierarchical porous carbon material, the micropore volume accounts for 60% to 92% of the total pore volume; In the silicon-carbon composite material, the hierarchical porous carbon material includes doped elements N and P. The N1s fine energy spectrum of element N contains three characteristic peaks after Gaussian peak fitting. The three characteristic peaks correspond to pyridine nitrogen, pyrrole nitrogen and graphite-like nitrogen, respectively. The silicon-carbon composite material also contains N and P elements, wherein the content of N element is 2wt%~5wt% and the content of P element is 0.05wt%~6wt%.

2. The silicon-carbon composite material according to claim 1, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 0.1 m². 2 / g ~50 m 2 / g; and / or The specific surface area of ​​the hierarchical porous carbon material is 500 m². 2 / g ~2000m 2 / g.

3. The silicon-carbon composite material according to claim 2, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g ~6 m 2 / g; and / or The specific surface area of ​​the hierarchical porous carbon material is 1000 m². 2 / g ~1500 m 2 / g.

4. The silicon-carbon composite material according to claim 1, characterized in that, The pore volume of the silicon-carbon composite material is 0.0001 cm³. 3 / g ~0.02 cm 3 / g; and / or The pore volume of the hierarchical porous carbon material is 0.7 cm³. 3 / g ~1.2 cm 3 / g.

5. The silicon-carbon composite material according to claim 4, characterized in that, The pore volume of the silicon-carbon composite material is 0.001 cm³. 3 / g ~0.015 cm 3 / g.

6. The silicon-carbon composite material according to claim 1, characterized in that, In the hierarchical porous carbon material, the micropore volume accounts for 80% to 91% of the total pore volume; and / or In the hierarchical porous carbon material, the mesopore volume accounts for 5% to 30% of the total pore volume; and / or In the hierarchical porous carbon material, the volume of macropores accounts for 1% to 20% of the total pore volume.

7. The silicon-carbon composite material according to claim 6, characterized in that, In the aforementioned hierarchical porous carbon material, the mesopore volume accounts for 6% to 15% of the total pore volume.

8. The silicon-carbon composite material according to claim 7, characterized in that, In the hierarchical porous carbon material, the volume of macropores accounts for 2% to 10% of the total pore volume.

9. The silicon-carbon composite material according to claim 1, characterized in that, The median particle size of the silicon-carbon composite material is 5 μm to 15 μm; and / or The median particle size of the hierarchical porous carbon material is 5 μm to 15 μm.

10. The silicon-carbon composite material according to claim 1, characterized in that, The true density of the silicon-carbon composite material is 1.5 cm³. 3 / g ~2.5 cm 3 / g; and / or The true density of the hierarchical porous carbon material is 1.9 cm³. 3 / g ~2.6 cm 3 / g.

11. The silicon-carbon composite material according to claim 10, characterized in that, The true density of the silicon-carbon composite material is 1.7 cm³. 3 / g ~2.1 cm 3 / g; and / or The true density of the hierarchical porous carbon material is 2.2 cm³. 3 / g ~2.5 cm 3 / g.

12. The silicon-carbon composite material according to claim 1, characterized in that, In the silicon-carbon composite material, the thickness of the amorphous carbon layer is 5 nm to 10 nm; and / or I of the multi-level porous carbon material D / I G The value is 0.5~1.

5.

13. The silicon-carbon composite material according to claim 12, characterized in that, I of the multi-level porous carbon material D / I G The value ranges from 0.9 to 1.

4.

14. The silicon-carbon composite material according to claim 1, characterized in that, In the silicon-carbon composite material, the content of silicon nanoparticles is 10 wt% to 60 wt%.

15. The silicon-carbon composite material according to claim 14, characterized in that, The silicon-carbon composite material contains 1 wt% to 5 wt% of phosphorus.

16. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material according to any one of claims 1-15.

17. The negative electrode sheet according to claim 16, characterized in that, The content of silicon-carbon composite material in the negative electrode active material is more than 3 wt%.

18. A battery, characterized in that, The battery comprises the silicon-carbon composite material according to any one of claims 1-15 and / or the negative electrode sheet according to claim 16 or 17.

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