A silicon-carbon composite material, its preparation method, a secondary battery, and an electrical device thereof.

Abstract

This application relates to a silicon-carbon composite material, comprising a carbon nanotube / porous carbon composite matrix and a silicon-based material, wherein the porous carbon and carbon nanotubes in the carbon nanotube / porous carbon composite matrix are interconnected through connecting units. Utilizing the high electrical conductivity and strong mechanical properties of carbon nanotubes, the overall electrical conductivity, compressive strength, and expansion resistance of the silicon-carbon composite material can be improved, thereby enhancing the cycle performance, electrode cycle expansion performance, and rate performance of secondary batteries.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to a silicon-carbon composite material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Rechargeable batteries are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. With the continuous development of the new energy industry, customers are placing higher demands on the use of rechargeable batteries.

[0003] Silicon-based anode materials have attracted widespread attention due to their high capacity; however, silicon-based materials suffer from severe volume effects, resulting in significant volume expansion during charging. Furthermore, existing silicon-based anode materials exhibit poor compressive strength and conductivity, failing to meet the electrochemical performance requirements of batteries.

[0004] Therefore, it is necessary to develop a silicon-based anode material that can enable batteries to have better cycle performance, electrode cycle expansion performance, and rate performance. Summary of the Invention

[0005] In view of the problems existing in the background technology, this application provides a silicon-carbon composite material that can enable the battery to have better cycle performance, electrode cycle expansion performance and rate performance.

[0006] The silicon-carbon composite material provided in the first aspect of this application includes a carbon nanotube / porous carbon composite matrix and a silicon-based material. The porous carbon and carbon nanotubes in the carbon nanotube / porous carbon composite matrix are interconnected through connecting units.

[0007] In the technical solution of this application embodiment, carbon nanotubes and porous carbon are interconnected through connecting units, stably bonded together. The high conductivity of carbon nanotubes improves the poor conductivity of porous carbon, reducing the resistivity of the silicon-carbon composite material and improving its overall conductivity. The strong mechanical properties of carbon nanotubes enable composite reinforcement, giving the silicon-carbon composite material better compressive strength and expansion resistance, thereby improving its structural stability and preventing deterioration of cycle performance caused by particle breakage due to expansion and contraction during electrode cold pressing and charging / discharging. This application can effectively improve the cycle performance, electrode cycle expansion performance, and rate performance of secondary batteries containing this silicon-carbon composite material.

[0008] In some embodiments, according to the first aspect, a first example of the first aspect is provided, wherein the connecting unit includes at least one of carbon-carbon bond, benzene ring, ester group, and carbonyl group.

[0009] Optimizing the types of connecting units can enhance the bonding between carbon nanotubes and porous carbon, thereby improving the compressive strength of silicon-carbon composite materials.

[0010] In some embodiments, according to the first aspect, a second example of the first aspect is proposed, wherein at least a portion of the silicon-based material is distributed in the pores of the carbon nanotube / porous carbon composite matrix.

[0011] At least a portion of the silicon-based material is distributed within the pores of the carbon nanotube / porous carbon composite matrix. The pores of the carbon nanotube / porous carbon composite matrix provide expansion space, effectively mitigating the expansion of the silicon-based material. Simultaneously, by limiting the pore size of the porous carbon composite matrix, the silicon-based material can be restricted to a smaller particle size (average particle size ≤ 50 nm). Furthermore, the porous carbon composite matrix isolates the silicon-based material from the electrolyte, effectively improving its cycling performance.

[0012] In some embodiments, according to the first aspect, a third example of the first aspect is proposed, wherein at least a portion of the carbon nanotubes extends one end out of the surface of the silicon-carbon composite material.

[0013] Having at least a portion of the carbon nanotubes extend one end out of the silicon-carbon composite material surface is beneficial for fully utilizing the high conductivity of the carbon nanotubes, thereby improving the conductivity of the silicon-carbon composite material.

[0014] In some embodiments, according to the first aspect, a fourth example of the first aspect is proposed, wherein the diameter of the carbon nanotubes is 0.5-20 nm. Optionally, the diameter of the carbon nanotubes is 0.7-10 nm.

[0015] The smaller the diameter of carbon nanotubes, the better their electrical conductivity and mechanical properties, but if they are too small, they will be difficult to synthesize and costly.

[0016] In some embodiments, according to the first aspect, a fifth example of the first aspect is proposed, wherein the length of the carbon nanotube is denoted as L, and the volume distribution particle size Dv50 of the silicon-carbon composite material is denoted as D0, then the silicon-carbon composite material satisfies: L≥3D0. Optionally, the silicon-carbon composite material satisfies: 3D0≤L≤7D0.

[0017] Ensuring that the length of carbon nanotubes meets the above formula ensures that carbon nanotubes are distributed throughout the entire particle of the silicon-carbon composite material, fully utilizing the electrical conductivity and mechanical properties of carbon nanotubes, thereby improving the overall electrical conductivity and compressive strength of the silicon-carbon composite material.

[0018] In some embodiments, according to the first aspect, a sixth example of the first aspect is proposed, wherein the aspect ratio of the carbon nanotubes is greater than or equal to 900, and can be selected as 2500-25000.

[0019] In some embodiments, according to the first aspect, a seventh example of the first aspect is proposed, wherein the content of carbon nanotubes in the silicon-carbon composite material is ≤8%; optionally 0.2%-5.0%.

[0020] If the carbon nanotube content is too low, it cannot effectively improve the conductivity of silicon-carbon composite materials; if the content is too high, the cost will be too high, and it will affect the dispersion and processing effect.

[0021] In some embodiments, according to the first aspect, an eighth example of the first aspect is proposed, wherein the carbon nanotube / porous carbon composite matrix meets at least one of the following conditions (1)-(4):

[0022] (1) The carbon nanotube / porous carbon composite matrix contains mesopores, optionally with a pore volume ≥ 0.1 cm³. 3 / g, preferably 0.2-2.5cm 3 / g;

[0023] (2) The carbon nanotube / porous carbon composite matrix contains micropores, optionally with a pore volume ≤ 0.3 cm³. 3 / g, preferably 0.05-0.2cm 3 / g;

[0024] (3) The carbon nanotube / porous carbon composite matrix contains macropores, optionally with a pore volume ≤ 0.5 cm³. 3 / g, preferably 0.05-0.4cm 3 / g;

[0025] (4) The carbon nanotube / porous carbon composite matrix includes mesopores and micropores. Optionally, the ratio of the pore volume of the mesopores to the pore volume of the micropores is ≥2, preferably 3-15.

[0026] By optimizing the pore size within the carbon nanotube / porous carbon composite matrix, it is beneficial to limit the silicon-based material to a smaller particle size (average particle size ≤ 50 nm), while also helping to isolate the composite material from the electrolyte. Furthermore, limiting the micropores / mesopores / macropores to a certain range allows for sufficient expansion space. Through these beneficial effects, the expansion and cycling performance of silicon-carbon composite materials can be improved.

[0027] In some embodiments, according to the first aspect, a ninth example of the first aspect is provided, wherein the silicon-based material is nano-silicon-based particles. Optionally, the average particle size of the nano-silicon-based particles is ≤50 nm, more preferably 3-20 nm.

[0028] Excessive particle size of silicon nanoparticles can lead to excessive localized charging expansion, affecting the structural stability of silicon-carbon composite materials and consequently their cycling performance.

[0029] In some embodiments, according to the first aspect, a tenth example of the first aspect is proposed, wherein the silicon-based material includes at least one of elemental silicon, silicon oxide (such as silicon suboxide), silicon-carbon composite, silicon-nitrogen composite, silicon alloy, and pre-lithiated silicon oxide.

[0030] Further optimization of the types of silicon-based materials can help improve the capacity of silicon-carbon composite materials, thereby increasing the energy density of batteries.

[0031] In some embodiments, according to the first aspect, an eleventh example of the first aspect is provided, wherein the silicon-based material comprises amorphous silicon. Optionally, the silicon-based material comprises a mixture of amorphous silicon and crystalline silicon.

[0032] Optimizing the types of silicon-based materials can improve the capacity of silicon-carbon composite materials, thereby increasing the energy density of batteries.

[0033] In some embodiments, according to the first aspect, a twelfth example of the first aspect is provided, wherein the carbon nanotube / porous carbon composite matrix is ​​formed by carbonization of a resin precursor and carbon nanotubes grafted with functional groups and / or polymers. Both the functional groups and / or polymers are capable of chemically reacting with the resin precursor, thereby linking the carbon nanotubes to the resin precursor and forming connecting units after carbonization.

[0034] Functional groups and / or polymers can chemically react with resin precursors, causing carbon nanotubes to chemically link with the resin precursors and form connecting units after carbonization, thereby enhancing the interfacial bonding between carbon nanotubes and resin and improving the compressive strength of silicon-carbon composite materials.

[0035] In some embodiments, according to the first aspect, a thirteenth example of the first aspect is provided, wherein infrared spectroscopy is used to test a silicon-carbon composite material or a carbon nanotube / porous carbon composite matrix, the silicon-carbon composite material or carbon nanotube / porous carbon composite matrix containing at least one of the following linking units: an ester carbonyl group, the absorption peak of which is 1750–1735 cm⁻¹. -1 The carbonyl group of the ketone has an absorption peak at 1725–1705 cm⁻¹. -1 ; Benzene ring group, with an absorption peak of 1620–1450 cm⁻¹ -1 ; and carbon-carbon bonds, with absorption peaks at 2400–1950 cm⁻¹. -1 ; and / or,

[0036] Transmission electron microscopy tests on silicon-carbon composite materials or carbon nanotube / porous carbon composite matrices showed that the proportion of regions in which the distance between the carbon atoms surrounding the carbon nanotubes and the outermost carbon atoms of the carbon nanotubes was ≤0.35 nm was ≥50%.

[0037] Infrared spectroscopy revealed the presence of connecting units in the silicon-carbon composite or carbon nanotube / porous carbon composite matrix, while transmission electron microscopy showed that the porous carbon and carbon nanotubes were interconnected. These characterization results indicate that the porous carbon and carbon nanotubes are linked together as a whole through connecting units, resulting in enhanced interfacial bonding.

[0038] In some embodiments, according to the first aspect, a fourteenth example of the first aspect is proposed, defining the compressive strength index of the silicon-carbon composite material as P = D0 / (D0-D1), then P ≥ 3, where D0 is the volume distribution particle size Dv50 of the silicon-carbon composite material, and D1 is the volume distribution particle size Dv50 of the silicon-carbon composite material after being compressed, and the compression conditions are holding the pressure at 300MPa for 30s and repeatedly compressing 50 times.

[0039] A compressive strength index P≥3 indicates that silicon-carbon composite materials have good compressive strength, which can effectively improve the expansion problem of silicon-based materials, thus giving silicon-carbon composite materials excellent cycle performance.

[0040] In some embodiments, according to the first aspect, a fifteenth example of the first aspect is proposed, wherein the resistivity ρ of the silicon-carbon composite material at a pressure of 4 MPa is ≤0.4 Ω·cm, and optionally, 0.05 Ω·cm ≤ ρ ≤0.3 Ω·cm.

[0041] The lower the resistivity of silicon-carbon composite materials under 4 MPa pressure, the better their electrical conductivity. Optimizing the resistivity of silicon-carbon composite materials is beneficial for improving their electrical conductivity.

[0042] In some embodiments, according to the first aspect, a sixteenth example of the first aspect is proposed, wherein the silicon-carbon composite material satisfies at least one of the following conditions (I)-(V):

[0043] (I) The volume distribution particle size Dv50 of the silicon-carbon composite material is ≤8μm, and can be selected as 3-7μm;

[0044] (II) The porosity of silicon-carbon composite materials is ≤20%, and can be selected as 5%-15%;

[0045] (III) The specific surface area (SSA) of silicon-carbon composite materials is ≤ 5.0 m². 2 / g, selectable from 0.8-4.0m 2 / g;

[0046] (IV) The silicon-carbon composite material contains mesopores, optionally with a pore volume ≤ 0.3 cm³. 3 / g, preferably 0.05-0.1cm 3 / g;

[0047] (V) The mass ratio of elements in the silicon-carbon composite material is Si:C:O = (20-55):(40-70):(3-10).

[0048] Optimizing the particle size of silicon-carbon composite materials can prevent poor cycle performance due to excessively small particle size and poor conductivity due to excessively large particle size. By reserving a certain porosity within the silicon-carbon composite material, expansion space can be accommodated for the silicon-based material during charging, buffering expansion and improving the material's cycle performance. A specific surface area that is too high for silicon-carbon composite materials will affect material performance, while a specific surface area that is too low is difficult to achieve in porous carbon materials. If the pore volume of the mesopores in the silicon-carbon composite material is too low, the reserved expansion space for the silicon-based material will be insufficient, affecting the cycle performance of the silicon-carbon composite material. If the pore volume of the mesopores in the silicon-carbon composite material is too high, the volumetric energy density of the silicon-carbon composite material will be too low, reducing its practicality. Furthermore, an excessively high pore volume of the mesopores in the silicon-carbon composite material will affect its compressive strength, leading to poor pressure resistance. Optimizing the silicon content ensures the capacity requirements of the silicon-carbon composite material; optimizing the carbon content ensures the effective formation of porous carbon and effectively isolates the subsequently deposited silicon-based material; optimizing the oxygen content ensures the flexibility of the porous carbon and the stability of the connection between the porous carbon and the silicon-based material and carbon nanotubes.

[0049] In some embodiments, according to the first aspect, a seventeenth example of the first aspect is provided, wherein the surface of the silicon-carbon composite material is further provided with a coating layer. Optionally, the coating layer includes at least one selected from a carbon coating layer, a polymer coating layer, an inorganic salt coating layer, and a metal oxide coating layer.

[0050] By forming a coating layer on the surface of silicon-carbon composite material, it is beneficial to further isolate the direct contact between the electrolyte and silicon-carbon composite material, improve cycle performance, and the coating layer has a certain buffering effect, further buffering expansion and reducing the impact of expansion on the electrode. In particular, the carbon coating layer can further improve the conductivity of silicon-carbon material.

[0051] A second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0052] Modified carbon nanotubes are obtained by grafting functional groups and / or polymers onto carbon nanotubes.

[0053] The modified carbon nanotubes are mixed with the resin precursor solution to obtain a mixed solution. The functional groups and polymers on the modified carbon nanotubes can react chemically with the resin precursor to connect the modified carbon nanotubes with the resin precursor.

[0054] The mixed solution was cured to obtain a composite matrix precursor;

[0055] Carbonization of the composite matrix precursor yields a porous carbon / carbon nanotube composite matrix; and

[0056] Silicon-based materials are deposited on a porous carbon / carbon nanotube composite matrix to obtain silicon-carbon composite materials.

[0057] In the technical solution of this application embodiment, a silicon-carbon composite material with good compressive strength and electrical conductivity can be obtained through this method. This method is simple to operate, highly repeatable, and beneficial for large-scale industrial production.

[0058] In some embodiments, according to the second aspect, a first example of the second aspect is provided, wherein the mixed solution further comprises 0.5% to 30% of a catalyst by mass percentage. Optionally, the catalyst comprises one or more of hexamethylenetetramine, ammonium bicarbonate, ammonium carbonate, ammonia, zinc salt, copper salt, and chromium salt.

[0059] Optimizing reaction conditions can shorten the reaction time between modified carbon nanotubes and resin precursors, thereby improving the reaction conversion rate.

[0060] In some embodiments, according to the second aspect, a second example of the second aspect is provided, wherein mixing includes: stirring at 20–60°C for 1–10 h. The modified carbon nanotubes undergo one or more of the following reactions: esterification, addition, polymerization, and condensation polymerization.

[0061] In some embodiments, according to the second aspect, a third example of the second aspect is proposed, wherein the functional group includes one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl groups; and / or, the polymer includes one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate.

[0062] By optimizing the types of functional groups and / or polymers grafted onto carbon nanotubes, it is beneficial to form more stable connecting units between carbon nanotubes and porous carbon, thereby enhancing interfacial bonding and improving the compressive strength of silicon-carbon composite materials.

[0063] In some embodiments, according to the second aspect, a fourth example of the second aspect is provided, wherein the curing process includes: pre-curing and full curing. Optionally, the curing process includes: pre-curing, pulverization, and full curing.

[0064] Optimizing the curing process can improve the curing effect and enhance the internal uniformity of silicon-carbon composite materials.

[0065] In some embodiments, according to the second aspect, a fifth example of the second aspect is provided, wherein the pre-curing temperature is 70-140°C, optionally 80-130°C; and / or the pre-curing time is 3-12 hours, optionally 5-10 hours.

[0066] Optimizing the pre-curing temperature and time can improve the internal uniformity of silicon-carbon composite materials and enhance the uniformity of pore distribution and size.

[0067] In some embodiments, according to the second aspect, a sixth example of the second aspect is proposed, wherein the curing temperature is 150-220°C, optionally 160-200°C; and / or the curing time is 8-20h, optionally 10-15h.

[0068] Optimizing the temperature and time for full curing can improve the curing effect and enhance the internal uniformity of silicon-carbon composite materials.

[0069] In some embodiments, according to the second aspect, a seventh example of the second aspect is provided, wherein the carbonization temperature is 900-3000°C, optionally 1000-2000°C; and / or the carbonization time is 2-6 hours, optionally 3-5 hours.

[0070] Optimizing the temperature and time of carbonization treatment helps to form more stable connecting units between carbon nanotubes and porous carbon, thereby enhancing the interfacial bonding and improving the compressive strength of silicon-carbon composite materials.

[0071] In some embodiments, according to the second aspect, an eighth example of the second aspect is proposed, wherein deposition is performed by chemical vapor deposition. Optionally, the deposition gas includes a mixture of at least one or more of H2, N2, and Ar with a silane gas.

[0072] Silicon deposition via chemical vapor deposition is advantageous for achieving uniform deposition of silicon-based materials in porous carbon / carbon nanotube composite matrices. Furthermore, the growth of silicon particles is limited by the pore size of porous carbon, which can restrict silicon particles to a smaller size range, such as an average particle size ≤50nm. On the other hand, it can achieve a tight bond between porous carbon and the deposited silicon-based material, which can better limit the expansion of silicon materials to a certain extent.

[0073] A third aspect of this application provides a secondary battery, including a negative electrode sheet, which comprises a silicon-carbon composite material according to the first aspect of this application or a silicon-carbon composite material obtained according to the preparation method of the second aspect of this application.

[0074] In the technical solutions of this application embodiment, since the silicon-carbon composite material of the first aspect of this application or the silicon-carbon composite material obtained according to the preparation method of the second aspect of this application is used, the secondary battery of this application has improved cycle performance.

[0075] A fourth aspect of this application provides an electrical device including a secondary battery as described in the third aspect of this application.

[0076] In the technical solutions of this application embodiment, since the silicon-carbon composite material of the first aspect of this application or the silicon-carbon composite material obtained according to the preparation method of the second aspect of this application is used, the electrical device of this application has improved cycle performance.

[0077] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0078] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0079] Figure 1 This is a schematic diagram of the silicon-carbon composite material of this application.

[0080] Figure 2 This is a scanning electron microscope (SEM) image of the silicon-carbon composite material of this application.

[0081] Figure 3 This is a schematic diagram of one embodiment of a secondary battery.

[0082] Figure 4 yes Figure 3 The exploded diagram.

[0083] Figure 5 This is a schematic diagram of one embodiment of the battery module.

[0084] Figure 6 This is a schematic diagram of one embodiment of the battery pack.

[0085] Figure 7 yes Figure 6 The exploded diagram.

[0086] Figure 8 This is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source.

[0087] Explanation of reference numerals in the attached figures:

[0088] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0089] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0090] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing description of the drawings, are intended to cover non-exclusive inclusion.

[0091] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0092] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more (including two).

[0093] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical term "connection" refers to the combination of two chemical substances through a connecting unit. Those skilled in the art can understand the specific meaning of the above term in the embodiments of this application according to the specific circumstances.

[0094] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0095] Silicon-based anode materials have attracted widespread attention due to their high capacity; however, silicon-based materials suffer from severe volume effects, resulting in significant volume expansion during charging. To address this, researchers have developed silicon-carbon anode materials. However, existing silicon-carbon anode materials exhibit poor compressive strength, and their structure is easily damaged during actual cold pressing of the electrode, thus affecting their electrochemical performance. Furthermore, their high resistivity and poor conductivity fail to meet the requirements for electrochemical performance. Therefore, there is an urgent need to develop a silicon-based anode material that can enable batteries to possess better cycle performance, electrode cycle expansion performance, and rate performance.

[0096] After in-depth research, the inventors designed a silicon-carbon composite material, referencing... Figure 1 It comprises a carbon nanotube / porous carbon composite matrix and silicon-based materials. The porous carbon and carbon nanotubes in the carbon nanotube / porous carbon composite matrix are interconnected through connecting units.

[0097] In the technical solution of this application embodiment, carbon nanotubes and porous carbon are interconnected through connecting units, stably bonded together. The high conductivity of carbon nanotubes improves the poor conductivity of porous carbon, reducing the resistivity of the silicon-carbon composite material and improving its overall conductivity. The strong mechanical properties of carbon nanotubes enable composite reinforcement, giving the silicon-carbon composite material better compressive strength and thus better anti-expansion properties. This improves the structural stability of the silicon-carbon composite material and prevents particle breakage during cold pressing of the electrode, which could lead to deterioration in cycle performance. This application can effectively improve the cycle performance, electrode cycle expansion performance, and rate performance of secondary batteries containing this silicon-carbon composite material.

[0098] In some embodiments, the connecting unit includes at least one of carbon-carbon bonds, benzene rings, ester groups, and carbonyl groups.

[0099] Optimizing the types of connecting units can enhance the bonding between carbon nanotubes and porous carbon, thereby improving the compressive strength of silicon-carbon composite materials.

[0100] Of course, the types of connecting units are not limited to the above-mentioned types. Any connecting unit that can chemically connect carbon nanotubes and porous carbon is included in the scope of this application and will not be listed here.

[0101] In some embodiments, at least a portion of the silicon-based material is distributed within the pores of the carbon nanotube / porous carbon composite matrix.

[0102] At least a portion of the silicon-based material is distributed within the pores of the carbon nanotube / porous carbon composite matrix. The pores of the carbon nanotube / porous carbon composite matrix provide expansion space, effectively mitigating the expansion of the silicon-based material. Simultaneously, by limiting the pore size of the porous carbon composite matrix, the silicon-based material can be restricted to a smaller particle size (e.g., average particle size ≤ 50 nm). Furthermore, the porous carbon composite matrix isolates the silicon-based material from the electrolyte, effectively improving its cycling performance.

[0103] In some embodiments, reference Figure 2 At least one end of a portion of the carbon nanotubes extends out of the surface of the silicon-carbon composite material.

[0104] At least one end of the carbon nanotubes extends beyond the surface of the silicon-carbon composite material. This design facilitates contact between the carbon nanotubes and the electrolyte, fully utilizing the high conductivity of the carbon nanotubes and thus improving the conductivity of the silicon-carbon composite material. If the carbon nanotubes are completely encased within the porous carbon, they cannot make good contact with the electrolyte, and their conductivity cannot be fully utilized, which is detrimental to improving the conductivity of the silicon-carbon composite material.

[0105] In some embodiments, the diameter of the carbon nanotubes can be 0.5-20 nm. Optionally, the diameter of the carbon nanotubes can be 0.7-10 nm.

[0106] The smaller the diameter of carbon nanotubes, the better their electrical conductivity and mechanical properties, but if they are too small, they will be difficult to synthesize and costly.

[0107] In some specific embodiments, the diameter of the carbon nanotubes can be 0.5 nm, 0.7 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm. Optionally, the diameter of the carbon nanotubes can be 0.7-6 nm. The diameter of the carbon nanotubes can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0108] In some embodiments, the length of the carbon nanotubes is denoted as L, and the volume distribution particle size Dv50 of the silicon-carbon composite material is denoted as D0. Then, the silicon-carbon composite material satisfies: L ≥ 3D0. Optionally, the silicon-carbon composite material satisfies: 3D0 ≤ L ≤ 7D0.

[0109] Ensuring the carbon nanotube length conforms to the above formula guarantees that carbon nanotubes are distributed throughout the entire particle of the silicon-carbon composite material, fully utilizing their electrical and mechanical properties, thereby improving the overall conductivity and compressive strength of the silicon-carbon composite material. Furthermore, ensuring the carbon nanotube length is greater than the volumetric particle size of the silicon-carbon composite material also facilitates that at least one end of each carbon nanotube extends beyond the surface of the composite material. If the carbon nanotubes are too short, they are easily encased within the porous carbon, making it difficult for them to contact the electrolyte and hindering their conductivity.

[0110] In some specific embodiments, L can be 3D0, 3.5D0, 4D0, 4.5D0, 5D0, 5.5D0, 6D0, 6.5D0 or 7D0.

[0111] In some embodiments, the aspect ratio of the carbon nanotubes is greater than or equal to 900, and can be selected as 2500-25000.

[0112] In some specific embodiments, the aspect ratio of the carbon nanotubes can be 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, or 25000. The aspect ratio of the carbon nanotubes can be within a range formed by using any two of the values ​​listed above as endpoints.

[0113] In some embodiments, the content of carbon nanotubes in the silicon-carbon composite material is ≤8%; optionally, it is 0.2%-5.0%.

[0114] If the carbon nanotube content is too low, it cannot effectively improve the conductivity of silicon-carbon composite materials; if the content is too high, the cost will be too high, and it will affect the dispersion and processing effect.

[0115] In some specific embodiments, the content of carbon nanotubes in the silicon-carbon composite material can be 0.2%, 0.3%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, or 8.0%. The content of carbon nanotubes in the silicon-carbon composite material can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0116] In some embodiments, the carbon nanotube / porous carbon composite matrix includes mesopores; optionally, the pore volume of the mesopores is ≥0.1 cm³. 3 / g, for example, can be 0.2-2.5cm 3 / g.

[0117] In some specific embodiments, the pore volume of the mesopore can be 0.1 cm³. 3 / g, 0.2cm 3 / g, 0.5cm 3 / g, 1.0cm 3 / g, 1.5cm 3 / g, 2.0cm 3 / g or 2.5cm 3 / g. The pore volume of mesopores can be within a range of values ​​formed by taking any two of the values ​​listed above as endpoints.

[0118] In some embodiments, the carbon nanotube / porous carbon composite matrix includes micropores; optionally, the pore volume of the micropores is ≤0.3 cm³. 3 / g, for example, can be 0.05-0.2cm 3 / g.

[0119] In some specific embodiments, the pore volume of the micropores can be 0.05 cm³. 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g or 0.3cm 3 / g. The pore volume of the micropores can be within a range of values ​​formed by taking any two of the values ​​listed above as endpoints.

[0120] In some embodiments, the carbon nanotube / porous carbon composite matrix includes macropores; optionally, the pore volume of the macropores is ≤0.5 cm³. 3 / g, for example, can be 0.05-0.4cm 3 / g.

[0121] In some specific embodiments, the volume of the macropore can be 0.05 cm³. 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g, 0.3cm 3 / g, 0.35cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g or 0.5cm 3 / g. The pore volume of macropores can be within a range of values ​​formed by taking any two of the values ​​listed above as endpoints.

[0122] In some embodiments, the carbon nanotube / porous carbon composite matrix includes mesopores and micropores; optionally, the ratio of the pore volume of the mesopores to the pore volume of the micropores is ≥2, for example, it can be 3-15.

[0123] In some specific embodiments, the ratio of the pore volume of mesopores to the pore volume of micropores can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. The ratio of the pore volume of mesopores to the pore volume of micropores can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0124] In some embodiments, the porosity of the porous carbon / carbon nanotube composite matrix is ​​≥20%, optionally 20% to 60%.

[0125] In some embodiments, the average pore size of the porous carbon / carbon nanotube composite matrix is ​​1–100 nm, and can be selected as 5–50 nm.

[0126] By optimizing the pore size within the carbon nanotube / porous carbon composite matrix, it is beneficial to limit the silicon-based material to a smaller particle size (e.g., average particle size ≤ 50 nm), while also helping to isolate the composite material from the electrolyte. Furthermore, limiting the micropores / mesopores / macropores to a certain range allows for sufficient expansion space. Through these beneficial effects, the expansion and cycling performance of silicon-carbon composite materials can be improved.

[0127] In some embodiments, the mass percentage of carbon nanotubes in the carbon nanotube / porous carbon composite matrix can be 0.05%-16%, preferably 0.1%-10%, for example, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The mass percentage of carbon nanotubes in the carbon nanotube / porous carbon composite matrix can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0128] In some embodiments, the silicon-based material is nano-silicon-based particles. Optionally, the average particle size of the nano-silicon-based particles is ≤50nm, and more preferably 3-20nm.

[0129] The inventors discovered that excessively large particle size of nano-silicon-based particles can lead to excessive localized charging expansion, affecting the structural stability of silicon-carbon composite materials and consequently impacting their cycle performance.

[0130] In some specific embodiments, the average particle size of the silicon nanoparticles can be 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm. The average particle size of the silicon nanoparticles can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0131] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide (such as silicon suboxide), silicon-carbon composite, silicon-nitrogen composite, silicon alloy, and pre-lithiated silicon oxide.

[0132] In some embodiments, the silicon-based material comprises amorphous silicon. Optionally, the silicon-based material comprises a mixture of amorphous silicon and crystalline silicon.

[0133] Further optimization of the types of silicon-based materials can help improve the capacity of silicon-carbon composite materials, thereby increasing the energy density of batteries.

[0134] In some embodiments, the carbon nanotube / porous carbon composite matrix is ​​formed by carbonizing a resin precursor and carbon nanotubes grafted with functional groups and / or polymers. The functional groups and / or polymers can chemically react with the resin precursor, linking the carbon nanotubes to the resin precursor and forming connecting units after carbonization.

[0135] Functional groups and / or polymers can chemically react with resin precursors, causing carbon nanotubes to chemically link with the resin precursors and form connecting units after carbonization, thereby enhancing the interfacial bonding between carbon nanotubes and resin and improving the compressive strength of silicon-carbon composite materials.

[0136] In some specific embodiments, the functional group may be one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl groups. The polymer may be one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate.

[0137] In some embodiments, infrared spectroscopy is used to test the silicon-carbon composite material or carbon nanotube / porous carbon composite matrix, wherein the silicon-carbon composite material or carbon nanotube / porous carbon composite matrix contains at least one of the following connecting units: ester carbonyl group, with an absorption peak of 1750–1735 cm⁻¹. -1 The carbonyl group of the ketone has an absorption peak at 1725–1705 cm⁻¹. -1 ; Benzene ring group, with an absorption peak of 1620–1450 cm⁻¹ -1 ; and carbon-carbon bonds, with absorption peaks at 2400–1950 cm⁻¹. -1 .

[0138] In some embodiments, transmission electron microscopy (TEM) tests are performed on silicon-carbon composite materials or carbon nanotube / porous carbon composite matrices. The proportion of regions in the silicon-carbon composite material or carbon nanotube / porous carbon composite matrix where the distance between the carbon atoms surrounding the carbon nanotubes and the outermost carbon atoms of the carbon nanotubes is ≤0.35 nm is ≥50%. This indicates that the porous carbon and the carbon nanotubes are connected together. Here, "regional proportion" refers to the ratio of the length of the carbon nanotube with a distance between the carbon atoms surrounding the carbon nanotubes and the outermost carbon atoms of the carbon nanotubes ≤0.35 nm to the actual length of the carbon nanotube. The regional proportion signifies the percentage of the connection area between the carbon nanotubes and porous carbon with connecting units within the overall length of the carbon nanotube. The larger the value, the tighter the connection between the carbon nanotubes and porous carbon. A regional proportion >50% indicates that the carbon nanotubes and porous carbon are effectively connected by connecting units.

[0139] Infrared spectroscopy revealed the presence of connecting units in the silicon-carbon composite or carbon nanotube / porous carbon composite matrix. Transmission electron microscopy showed that the porous carbon and carbon nanotubes were linked together. These characterization results indicate that the porous carbon and carbon nanotubes are connected into a unified whole through connecting units, resulting in enhanced interfacial bonding and effectively improving the overall compressive strength of the silicon-carbon composite.

[0140] In some embodiments, the compressive strength index of the silicon-carbon composite material is defined as P = D0 / (D0-D1), then P ≥ 3, where D0 is the volume distribution particle size Dv50 of the silicon-carbon composite material, and D1 is the volume distribution particle size Dv50 of the silicon-carbon composite material after being compressed. The compression conditions are to hold the pressure at 300MPa for 30s and repeat the compression 50 times.

[0141] A compressive strength index P≥3 indicates that silicon-carbon composite materials have good compressive strength, which can effectively improve the expansion problem of silicon-based materials, thus giving silicon-carbon composite materials excellent cycle performance.

[0142] Optionally, 5≤P≤100. The larger the P value, the smaller the impact of compression on the particle size of the material, and the more resistant the silicon-carbon composite material is to compression.

[0143] In some specific embodiments, P can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100. The value of P can be within a range of values ​​formed by using any two of the values ​​listed above as endpoints.

[0144] In some embodiments, the resistivity ρ of the silicon-carbon composite material at a pressure of 4 MPa is ≤0.4 Ω·cm, and optionally, 0.05 Ω·cm ≤ ρ ≤0.3 Ω·cm.

[0145] The lower the resistivity of silicon-carbon composite materials under 4 MPa pressure, the better their electrical conductivity. Optimizing the resistivity of silicon-carbon composite materials is beneficial for improving their electrical conductivity.

[0146] In some specific embodiments, ρ can be 0.05 Ω·cm, 0.1 Ω·cm, 0.15 Ω·cm, 0.2 Ω·cm, 0.25 Ω·cm, 0.3 Ω·cm, 0.35 Ω·cm, or 0.4 Ω·cm. The resistivity ρ can be within a range formed by using any two of the values ​​listed above as endpoints.

[0147] In some embodiments, the volumetric particle size distribution Dv50 of the silicon-carbon composite material is ≤8 μm, and can be selected as 3-7 μm. In some specific embodiments, the volumetric particle size distribution Dv50 of the silicon-carbon composite material can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, or 8 μm. The volumetric particle size distribution Dv50 of the silicon-carbon composite material can be within the numerical range formed by any two of the values ​​listed above as endpoints. By optimizing the particle size of the silicon-carbon composite material, it is possible to avoid the deterioration of cycle performance due to excessively small particle size and the deterioration of conductivity due to excessively large particle size.

[0148] In some embodiments, the porosity of the silicon-carbon composite material is ≤20%, optionally 5%-15%. In some specific embodiments, the porosity of the silicon-carbon composite material can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. The porosity of the silicon-carbon composite material can be within a numerical range formed by using any two of the values ​​listed above as endpoints. By reserving a certain porosity within the silicon-carbon composite material, expansion space can be reserved for the silicon-based material during charging, buffering expansion and improving the material's cycle performance.

[0149] In some embodiments, the specific surface area (SSA) of the silicon-carbon composite material is ≤ 5.0 m². 2 / g, selectable from 0.8-4.0m 2 / g. In some specific embodiments, the specific surface area (SSA) of the silicon-carbon composite material can be 0.8 m². 2 / g, 1.0m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g. The specific surface area (SSA) of silicon-carbon composites can be within a range formed by using any two of the values ​​listed above as endpoints. Too high a specific surface area will affect the material properties of silicon-carbon composites, while too low a specific surface area is difficult to achieve in silicon-carbon composites.

[0150] In some embodiments, the silicon-carbon composite material includes mesopores; optionally, the pore volume of the mesopores is ≤0.3 cm³. 3 / g, for example, can be 0.05-0.1cm 3 / g. In some specific embodiments, the pore volume of the mesopores can be 0.05cm³. 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g or 0.3cm 3 / g. The pore volume of the mesopores can be within a range formed by taking any two of the values ​​listed above as endpoints. If the pore volume of the mesopores in the silicon-carbon composite material is too low, the reserved expansion space for the silicon-based material will be insufficient, which will affect the cycle performance of the silicon-carbon composite material. If the pore volume of the mesopores in the silicon-carbon composite material is too high, the volumetric energy density of the silicon-carbon composite material will be too low, reducing its practicality. Furthermore, an excessively high pore volume of the mesopores in the silicon-carbon composite material will affect its compressive strength, resulting in the material being not pressure-resistant.

[0151] In some embodiments, the elemental mass ratio in the silicon-carbon composite material is Si:C:O = (20-55):(40-70):(3-10).

[0152] In some specific embodiments, the elemental mass ratio of Si:C:O in the silicon-carbon composite material can be 20:70:10, 30:65:5, 40:55:5, 55:42:3, or 55:40:5. The elemental mass ratio of Si:C:O in the silicon-carbon composite material can be within a numerical range formed by using any two of the values ​​listed above as endpoints. Optimizing the silicon content ensures the capacity requirements of the silicon-carbon composite material. Optimizing the carbon content ensures the effective formation of porous carbon and effectively isolates the subsequently deposited silicon-based material. Optimizing the oxygen content ensures the flexibility of the porous carbon and the stability of the connection between the porous carbon and the silicon-based material and carbon nanotubes.

[0153] In some embodiments, the surface of the silicon-carbon composite material is further provided with a coating layer. Optionally, the coating layer includes at least one of a carbon coating layer, a polymer coating layer, an inorganic salt coating layer, and a metal oxide coating layer.

[0154] By forming a coating layer on the surface of silicon-carbon composite material, it is beneficial to further isolate the direct contact between the electrolyte and silicon-carbon composite material, improve cycle performance, and the coating layer has a certain buffering effect, further buffering expansion and reducing the impact of expansion on the electrode. In particular, the carbon coating layer can further improve the conductivity of silicon-carbon material.

[0155] A second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0156] Modified carbon nanotubes are obtained by grafting functional groups and / or polymers onto carbon nanotubes.

[0157] The modified carbon nanotubes are mixed with the resin precursor solution to obtain a mixed solution. The functional groups and polymers on the modified carbon nanotubes can react chemically with the resin precursor to connect the modified carbon nanotubes with the resin precursor.

[0158] The mixed solution was cured to obtain a composite matrix precursor;

[0159] Carbonization of the composite matrix precursor yields a porous carbon / carbon nanotube composite matrix; and

[0160] Silicon-based materials are deposited on a porous carbon / carbon nanotube composite matrix to obtain silicon-carbon composite materials.

[0161] This method can yield silicon-carbon composite materials with good compressive strength and electrical conductivity. The method is simple to operate, highly repeatable, and conducive to large-scale industrial production.

[0162] In some embodiments, the mixed solution further comprises 0.5% to 30% of a catalyst by mass percentage. Optionally, the catalyst comprises one or more of hexamethylenetetramine, ammonium bicarbonate, ammonium carbonate, ammonia, zinc salt, copper salt, and chromium salt. In some specific embodiments, the mass ratio of modified carbon nanotubes, catalyst, and phenolic resin precursor solution may be (0.05-8):(3-7):(83-96.95).

[0163] Optimizing reaction conditions can shorten the reaction time between modified carbon nanotubes and resin precursors, thereby improving the reaction conversion rate.

[0164] In some embodiments, mixing includes stirring at 20–60°C for 1–10 h. The modified carbon nanotubes undergo one or more of the following reactions with the resin precursor: esterification, addition, polymerization, and condensation.

[0165] In some embodiments, the functional group includes one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl groups. The polymer includes one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate.

[0166] By optimizing the types of functional groups and / or polymers grafted onto carbon nanotubes, it is beneficial to form more stable connecting units between carbon nanotubes and porous carbon, thereby enhancing interfacial bonding and improving the compressive strength of silicon-carbon composite materials.

[0167] Functional groups grafted onto carbon nanotubes can serve as curing agents for resin precursors. Optionally, the functional groups can be acidic or basic.

[0168] In some embodiments, the curing process includes: pre-curing and full curing. Optionally, the curing process includes: pre-curing, pulverization, and full curing.

[0169] Optimizing the curing process can improve the curing effect and enhance the internal uniformity of silicon-carbon composite materials.

[0170] In some specific implementations, the volume distribution particle size Dv50 of the powder obtained after pulverization can be 3 to 15 μm, and can be selected as 5 to 10 μm.

[0171] In some embodiments, the pre-curing temperature is 70-140°C, optionally 80-130°C; and / or, the pre-curing time is 3-12 hours, optionally 5-10 hours.

[0172] Optimizing the pre-curing temperature and time can improve the internal uniformity of silicon-carbon composite materials and enhance the uniformity of pore distribution and size.

[0173] In some embodiments, the curing temperature is 150-220°C, optionally 160-200°C; and / or the curing time is 8-20 hours, optionally 10-15 hours.

[0174] Optimizing the temperature and time for full curing can improve the curing effect and enhance the internal uniformity of silicon-carbon composite materials.

[0175] In some specific embodiments, the complete curing is carried out under an inert atmosphere. The inert atmosphere can be nitrogen, argon, etc.

[0176] In some embodiments, the carbonization temperature is 900-3000℃, optionally 1000-2000℃; and / or, the carbonization time is 2-6h, optionally 3-5h.

[0177] Optimizing the temperature and time of carbonization treatment helps to form more stable connecting units between carbon nanotubes and porous carbon, thereby enhancing the interfacial bonding and improving the compressive strength of silicon-carbon composite materials.

[0178] In some specific embodiments, the carbonization process is carried out under an inert atmosphere. The inert atmosphere may be nitrogen, argon, etc.

[0179] In some embodiments, deposition is performed by chemical vapor deposition. Optionally, the deposition gas includes a mixture of at least one or more of H2, N2, and Ar with a silane gas.

[0180] Silicon deposition via chemical vapor deposition is advantageous for achieving uniform deposition of silicon-based materials in porous carbon / carbon nanotube composite matrices. Furthermore, the growth of silicon particles is limited by the pore size of porous carbon, which can restrict silicon particles to a smaller size range, such as ≤50nm. On the other hand, it can achieve a tight bond between porous carbon and the deposited silicon-based material, which can better limit the expansion of silicon materials to a certain extent.

[0181] In some specific embodiments, the silane gas includes at least one of methylsilane, disilane, propane, monochlorosilane, dichlorosilane, and trichlorosilane.

[0182] In some specific embodiments, the volume percentage of silane gas in the gas mixture can be 5%-80%, for example, 5%, 15%, 25%, 35%, 45%, 55%, 65% or 80%. The volume percentage of silane gas can be within a range of values ​​formed by using any two of the values ​​listed above as endpoints.

[0183] In some specific embodiments, the flow rate of the mixed gas can be 100-400 mL / min, for example, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, 300 mL / min, 350 mL / min, or 400 mL / min. The flow rate of the mixed gas can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0184] In some specific embodiments, the deposition temperature can be 400-1000℃, for example, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃. The deposition temperature can be within a numerical range formed by using any two of the values ​​listed above as endpoints. The deposition time can be 2-10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. The deposition time can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0185] In some embodiments, the resin precursor may be any one of furan resin precursor, urea-formaldehyde resin precursor, pyrimidine resin precursor, phenolic resin precursor, epoxy resin precursor, polyoxymethylene acrylate resin precursor, and polyacrylonitrile resin precursor.

[0186] The ratio of carbon nanotubes to resin precursors can be adjusted according to material design requirements.

[0187] In some embodiments, the grafting method includes acid washing or alkaline washing with one or more of nitric acid, sulfuric acid, acetic acid, ammonia, and oxalic acid. Acid washing with an organic acid is preferred. Acid washing can graft carboxyl groups, etc., onto the carbon nanotubes. For example, alkaline washing with ammonia can be used to graft hydroxyl groups. Of course, other known methods can also be used to graft functional groups and / or polymers onto carbon nanotubes, such as grafting polymethyl methacrylate.

[0188] In some embodiments, the preparation method further includes forming a coating layer on the resulting silicon-carbon composite material.

[0189] In some specific embodiments, a carbon coating layer can be formed by chemical vapor deposition (CVD). The deposition gas in CVD can be a mixture of C2H2 and N2. The volume percentage of C2H2 in the mixture can be 2%-40%. The flow rate of the mixture can be 100-300 mL / min. The deposition temperature can be 800-1000℃, and the deposition time can be 0.5-2 h.

[0190] [Rechargeable Battery]

[0191] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be activated and the battery to continue to be used.

[0192] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0193] [Negative electrode plate]

[0194] In a secondary battery, the negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, wherein the negative electrode film layer includes the silicon-carbon composite material provided in this application.

[0195] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can be a copper foil.

[0196] The negative electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0197] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0198] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0199] As an example, other optional additives may be thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0200] [Positive electrode plate]

[0201] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector, the positive electrode film layer including a positive active material.

[0202] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0203] The specific type of positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0204] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0205] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0206] The positive electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0207] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P(SP), graphene, and carbon nanofibers.

[0208] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0209] [Isolation membrane]

[0210] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0211] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0212] Electrolyte

[0213] A secondary battery may include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0214] As an example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0215] As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0216] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0217] In some embodiments, the secondary battery of this application is a lithium-ion secondary battery.

[0218] Secondary batteries can be prepared according to conventional methods in the field, such as winding (or stacking) the positive electrode, separator, and negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, thus obtaining a battery cell. The battery cell is placed in an outer package, electrolyte is injected and the package is sealed to obtain a secondary battery.

[0219] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 3 This is an example of a square-structured secondary battery 5.

[0220] In some embodiments, the secondary battery may include an outer packaging. The outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0221] In some embodiments, refer to Figure 4 The outer packaging may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed on the opening to close the receiving cavity.

[0222] The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 can contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0223] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0224] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0225] Figure 5 This is an example of a battery module 4. In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0226] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0227] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0228] Figure 6 and Figure 7 This is an example of a battery pack 1. The battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery compartment.

[0229] [Electrical appliances]

[0230] This application also provides an electrical device, which includes at least one of the aforementioned secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0231] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0232] Figure 8 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density in its secondary batteries, a battery pack or battery module can be used.

[0233] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0234] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0235] Example

[0236] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0237] All materials used in the embodiments of this application are commercially available.

[0238] Preparation of silicon-carbon composite materials

[0239] Example 1

[0240] (1) Preparation of modified carbon nanotubes

[0241] Prepare carbon nanotube raw materials, using single-walled carbon nanotubes with a diameter of 2 nm and a length of 35 μm;

[0242] Carbon nanotubes were acid-washed with acetic acid to graft carboxyl functional groups onto them, thus obtaining modified carbon nanotubes.

[0243] (2) Preparation of carbon nanotube / porous carbon composite matrix

[0244] The prepared modified carbon nanotubes, ammonium bicarbonate catalyst and phenolic resin precursor solution were mixed at a mass ratio of 2%:5%:93% (expressed as raw material mass ratio in Table 1). After stirring at 60°C for 1 hour, mixed solution A was obtained. In this solution, the carboxyl functional groups on the modified carbon nanotubes can chemically react with the phenolic resin precursor, thereby connecting the modified carbon nanotubes with the phenolic resin precursor.

[0245] Mixture solution A was pre-cured in an 80℃ oven for 10 hours. The pre-cured material was then crushed to obtain powder B. The crushing intensity was controlled as follows: air jet mill: airflow velocity 1m. 3 / min, classifier wheel frequency 45HZ, induced draft fan frequency 40HZ, pulverizing air pressure 0.8MPa, feeding speed 1kg / h, control the volume distribution particle size Dv50 of powder B to 7μm;

[0246] Powder B was placed in an oven and protected with nitrogen gas. It was then fully cured at 160°C for 15 hours to obtain powder C.

[0247] Powder C was placed in a high-temperature furnace and protected with nitrogen gas. It was carbonized at 1100℃ for 4 hours to form powder D, namely carbon nanotube / porous carbon composite matrix.

[0248] (3) Deposition of nano-silicon-based particles

[0249] Powder D was deposited with silicon using chemical vapor deposition (CVD). The deposition gas was a mixture of silane and H2, with silane comprising 20% ​​by volume. The flow rate of the mixed gas was 400 mL / min, the deposition temperature was 500 °C, and the deposition time was 10 h. The deposited silicon nanoparticles had a volume distribution particle size (Dv50) of 10 nm. After this step, a silicon-carbon composite material was obtained.

[0250] (4) Preparation of the coating layer

[0251] A carbon coating layer was formed on a silicon-carbon composite material using chemical vapor deposition (CVD). The deposition gas was a mixture of C₂H₂ and N₂, with C₂H₂ accounting for 20% of the volume. The gas flow rate was 300 mL / min, the deposition temperature was 800 °C, and the deposition time was 0.5 h. After this step, a silicon-carbon composite material with a carbon coating layer was obtained.

[0252] Example 2-18

[0253] Examples 2-18 are performed according to the method described in Example 1, except that the parameters listed in Table 1 below are different from those in Example 1.

[0254] Comparative Example 1

[0255] Comparative Example 1 is basically the same as the scheme described in Example 1, except that carbon nanotubes are not added during the carbon matrix synthesis process. Instead, phenolic resin precursor is directly used for reaction, pre-curing, crushing, full curing, carbonization, and deposition of nano-silicon-based particles to obtain the silicon-carbon composite material of Comparative Example 1.

[0256] Comparative Example 2

[0257] Nano-silicon powder (volume distribution particle size Dv50 of 50nm) and modified carbon nanotubes were added to a phenolic resin precursor for polymerization reaction, followed by pre-curing, crushing, full curing, and carbonization to obtain the silicon-carbon composite material of Comparative Example 2. The relevant process conditions were the same as those of Example 1, except that nano-silicon powder was used instead of deposited nano-silicon-based particles.

[0258] Comparative Example 3

[0259] The silicon-carbon composite material obtained in Comparative Example 1, carbon nanotubes (2 nm in diameter and 25 μm in length), and a small amount of phenolic resin precursor solution were mixed at a ratio of 92.05%:1.95%:6%, and then pre-cured, crushed, fully cured, and carbonized. The process was the same as in Example 1, resulting in a silicon-carbon composite material with CNT coating on the surface, namely the silicon-carbon composite material of Comparative Example 3. Comparative Example 3 is based on Comparative Example 1, with further modification of carbon nanotube coating to obtain the silicon-carbon composite material.

[0260] Table 1

[0261]

[0262]

[0263] Using the silicon-carbon composite materials prepared in the above examples and comparative examples, secondary batteries were prepared according to the general preparation method described below.

[0264] Preparation of secondary batteries

[0265] Negative electrode preparation:

[0266] The silicon-carbon composite material, artificial graphite, styrene-butadiene rubber (SBR) binder, polyacrylic acid (PAA) binder, dispersant (CMC-Na), conductive carbon black (Super-P, SP), and carbon nanotubes (CNT) prepared in the above embodiments and comparative examples were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 10%:85%:2%:1%:1%:0.7%:0.3% to prepare a negative electrode slurry. The negative electrode slurry was coated onto the current collector copper foil using a coating device, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0267] Preparation of the positive electrode: The positive electrode active material LiNi... 0.8 Co 0.1 Mn 0.1 O2 (NCM811), binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97%:1.5%:1.5% and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0268] Electrolyte preparation: Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in the mixture to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0269] Preparation of secondary battery: The above positive electrode sheet, separator and negative electrode sheet are stacked and wound in sequence to obtain electrode assembly; the electrode assembly is placed in outer packaging, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation and aging, secondary battery is obtained.

[0270] Characterization and testing of porous carbon / carbon nanotube composite matrix (i.e., powder D)

[0271] 1. Pore volume testing of micropores, mesopores, and macropores within carbon nanotube / porous carbon composite matrices:

[0272] The pore volume assessment method can refer to GB / T 19587-2017 and GB / T 21650.2-2008. A TriStarII 3020 pore size analyzer was used for testing. At a constant temperature, adsorbed gas was adsorbed onto the test material under a series of progressively increasing pressures. The pore size and pore volume distribution of the porous carbon / carbon nanotube composite matrix material can be characterized by the curves of the volume of each pore size versus the corresponding partial pressure. Further calculations can yield the average pore size. The test results are shown in Table 2 below.

[0273] 2. Mass percentage test of carbon nanotubes in carbon nanotube / porous carbon composite matrix:

[0274] The carbon nanotube content in a carbon nanotube / porous carbon composite matrix can be determined as follows: The carbon nanotube / porous carbon composite matrix powder is placed in an ion polisher (e.g., IB-19500CP). Under vacuum conditions, the ion source ionizes argon gas to generate argon ions. After acceleration and focusing, the high-speed argon ions bombard atoms or molecules on the sample surface, achieving ion polishing and enabling cross-sectional detection. The resulting cross-section is then tested using a scanning electron microscope (e.g., ZEISS Sigma 300). Thirty carbon nanotube / porous carbon composite matrix particles are selected, and the area ratio of carbon nanotubes within the carbon material (excluding the cross-sectional pore area) is measured. Since the true density of carbon nanotubes is comparable to that of porous carbon materials, the mass ratio of carbon nanotubes in the composite matrix can be assessed based on the area ratio. The average value can be used as the equivalent carbon nanotube content in the carbon nanotube / porous carbon composite matrix.

[0275] Table 2

[0276]

[0277] Characterization and testing of silicon-carbon composite materials

[0278] 1. Volumetric distribution particle size Dv50 test of materials

[0279] According to standard GB / T 19077.1-2016, Dv50 can be obtained by measuring with a laser particle size analyzer (e.g., Malvern Master Size3000). Dv50 is physically defined as the particle size corresponding to a material’s cumulative volume distribution percentage of 50%.

[0280] 2. Testing of the volumetric particle size Dv50 after the material is compressed.

[0281] After pressing the material under certain pressing conditions (for example, in this application, it can be: holding the pressure at 300MPa for 30s and pressing repeatedly 50 times), the volume distribution particle size Dv50 of the pressed material is tested according to the above method.

[0282] 3. Measurement of the length L of carbon nanotubes in silicon-carbon composite materials

[0283] The length L of carbon nanotubes can be measured by cross-sectional SEM. For example, the procedure can be as follows: Place the silicon-carbon composite powder in an ion polisher (e.g., IB-19500CP). Under vacuum conditions, the ion source ionizes argon gas to generate argon ions. After acceleration and focusing, the high-speed argon ions bombard atoms or molecules on the sample surface, achieving ion polishing and thus enabling cross-sectional detection. The obtained cross-section is then tested using a scanning electron microscope (e.g., ZEISS Sigma 300). Thirty carbon nanotubes are selected for length measurement, and the average value is taken as the carbon nanotube length L. The test results are shown in Table 3 below.

[0284] 4. Testing of carbon nanotube content in silicon-carbon composite materials

[0285] The carbon nanotube content in silicon-carbon composite materials can be determined as follows: The silicon-carbon composite powder is placed in an ion polisher (e.g., IB-19500CP). Under vacuum conditions, the ion source ionizes argon gas to generate argon ions. After acceleration and focusing, the high-speed argon ions bombard atoms or molecules on the sample surface, achieving ion polishing and enabling cross-sectional detection. The resulting cross-section is then tested using a scanning electron microscope (e.g., ZEISS Sigma 300). Thirty silicon-carbon composite particles are selected, and the area ratio of carbon nanotubes within the particles is measured. Since the true densities of silicon and carbon are similar, the area ratio of carbon nanotubes in the silicon-carbon composite particles can be approximated as the carbon nanotube content in the silicon-carbon composite material. The average value is then taken as the carbon nanotube content in the silicon-carbon composite material.

[0286] 5. Test of the elemental mass ratio Si:C:O in silicon-carbon composite materials

[0287] The oxygen content in silicon-carbon composite materials is assessed based on the "Quantitative Analysis by Microbeam Analysis Energy Dispersive Spectroscopy" standard in GB / T 17359-2012. Cross-sectional EDS energy dispersive spectroscopy is used for evaluation. The specific procedure is as follows: The powder to be tested is placed in an ion polisher (e.g., IB-19500CP model). Under vacuum conditions, the ion source ionizes argon gas to generate argon ions. After acceleration and focusing, the high-speed argon ions bombard atoms or molecules on the sample surface, achieving ion polishing and thus enabling cross-sectional detection. The obtained powder cross-section is then placed in an energy dispersive spectroscopy analyzer (e.g., OXFORD model) to test the oxygen content at various points on the material cross-section. The average value of 10 test points is used to obtain the material's oxygen content.

[0288] The silicon content in silicon-carbon composite materials was evaluated using inductively coupled plasma optical emission spectrometry (ICP) in accordance with the U.S. Environmental Protection Agency standard EPA 6010D-2018. The specific procedure was as follows: the powder to be tested was placed in a microwave digester (e.g., CEM-Mars6) for digestion, and the digested solution was passed into an ICP analyzer (e.g., ICAP7400). The silicon content in the material was calculated by comparing it with the silicon concentration in the standard solution.

[0289] The carbon content in silicon-carbon composite materials was tested using a carbon-sulfur analyzer (e.g., the DEK HCS-140 infrared carbon-sulfur analyzer) according to GB / T 20123-2006 / ISO 15350:200. The principle is as follows: the sample is heated and burned at high temperature in a high-frequency furnace under oxygen-rich conditions, causing carbon to oxidize into carbon dioxide. This gas enters the absorption cell, absorbs the corresponding infrared radiation, and is then converted into a corresponding signal by a detector. The carbon content in the material is calculated. The test results are shown in Table 3 below.

[0290] 6. Porosity testing of materials

[0291] The true density of a material is obtained by testing it with a true density meter (e.g., AccuPyc II1340). The specific procedure is as follows: a certain mass of sample is weighed and placed in the true density meter. The testing system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and expansion chamber, and then applying Bohr's Law (PV = nRT), the true volume Vr can be calculated, and the true density ρr = m / Vr. The apparent density of a material can be obtained by loading a certain mass of powder into a cylindrical mold with an inner diameter of 10 mm, applying a pressure of 200 MPa, and obtaining the corresponding apparent volume V0 of the powder. The apparent density of the material is then ρ0 = m / V0.

[0292] Material porosity P = 1 - ρ0 / ρr × 100%.

[0293] The test results are shown in Table 3 below.

[0294] 7. Specific surface area SSA test of silicon-carbon composite materials

[0295] The specific surface area (SSA) of silicon-carbon composite materials was determined according to GB / T 19587-2017 "Gas Adsorption BET Method for Determining Specific Surface Area of ​​Solid Substances". A specific surface area analyzer (e.g., TriStar II3020) was used. Under constant temperature and low temperature conditions, the amount of gas adsorbed on the solid surface at different relative pressures was measured. Based on the Brownauer-Etter-Taylor (BET) multilayer adsorption theory, the monolayer adsorption amount of the sample was calculated, thereby determining the specific surface area of ​​the solid. The test results are shown in Table 3 below.

[0296] 8. Test of the average particle size of nano-silicon-based particles in silicon-carbon composites

[0297] The average particle size of the silicon-based nanoparticles in the silicon-carbon composite material was determined by measuring the particle size of 100 silicon-based nanoparticles using a transmission electron microscope (e.g., Thermo Fisher F200i S / TEM) (TEM test). The average particle size was obtained by averaging the measured values. For irregularly shaped particles, the particle size at the maximum particle size was used as the standard. The test results are shown in Table 3 below.

[0298] 9. Resistivity test of silicon-carbon composite materials under 4 MPa pressure

[0299] Using a resistivity meter (e.g., Suzhou Jinglü Electronics ST2722), take 1g of powder sample, place the sample between the electrodes of the meter, and use an electronic pressure machine to maintain constant pressure at different intensities for 15-25s. Record the sample height h (cm), voltage U, current I, resistance R (KΩ), and the area S of the compressed powder sheet (1cm²). 2 The resistivity of the powder was calculated using the formula δ=S*R*1000 / h, with units of Ω·cm. The test results are shown in Table 3 below.

[0300] Table 3

[0301]

[0302]

[0303]

[0304]

[0305] Electrical performance characterization of secondary batteries

[0306] 45℃ Cyclic Performance Test:

[0307] The prepared secondary battery was charged at a constant current rate of 1C to a voltage of 4.25V under a constant temperature environment of 45℃, and then charged at a constant voltage of 4.25V until the current was less than or equal to 0.05mA. After that, it was allowed to stand for 5 minutes, and then discharged at a constant current rate of 1C to a voltage of 2.5V, and allowed to stand for 5 minutes. This is one cycle of charge and discharge. The discharge capacity of this cycle is recorded as the discharge capacity of the secondary battery in the first cycle. The secondary battery was subjected to 300 charge and discharge cycles according to the above method, and the discharge capacity of the 300th cycle was recorded.

[0308] The capacity retention rate CR45℃ (%) of the secondary battery after 300 cycles at 45℃ is calculated as: discharge capacity of the 300th cycle / discharge capacity of the 1st cycle × 100%. The test results are shown in Table 4 below.

[0309] Electrode cyclic expansion performance test of secondary batteries at 45℃:

[0310] The thickness of the negative electrode sheet after the cold pressing process is recorded as h0. Following the cycle performance test method for secondary batteries at 45°C, the secondary battery is cycled for 300cls, charged at a constant current rate of 1C to a voltage of 4.25V, and then charged at a constant voltage of 4.25V until the current is less than or equal to 0.05mA. Afterward, it is allowed to stand for 5 minutes. The cycled cell is disassembled in a drying room, and the thickness of the negative electrode sheet after 300cls of cycling is recorded as h300. The electrode sheet expansion rate of the secondary battery at 45°C after 300cls of cycling is Δh300.

[0311] Δh300(%)=(h300-h0) / h0*100%. The test results are shown in Table 4 below.

[0312] Ratio performance testing method:

[0313] At 25℃, the prepared secondary battery was charged at a constant current of 0.33C (i.e., the current value at which the theoretical capacity is completely discharged within 3 hours) to the charging cutoff voltage of 4.25V. Then, it was charged at a constant voltage to the current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.5V. Its actual capacity was recorded as C0.

[0314] Then, the battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.25V, followed by constant voltage charging to a current of 0.05C. After resting for 5 minutes, it was discharged at a constant current of 3C to the discharge cutoff voltage of 2.5V. Its actual capacity was recorded as C3.

[0315] The rate performance of a secondary battery can be characterized by DR = C3 / C0 × 100%. A higher DR value indicates better rate performance of the material. The test results are shown in Table 4 below.

[0316] The test results are shown in Table 4 below.

[0317] Table 4

[0318]

[0319]

[0320] As shown in Table 4, the silicon-carbon composite materials of Examples 1-18 exhibited a capacity retention of 93.4%-97.3% after 300 cycles at 45°C, a cycle expansion rate Δh300 of 33.8%-37.7%, and a rate performance (DR) of 80.2%-84.7%. These secondary batteries demonstrated good cycle stability, minimal cycle expansion, and good kinetic performance. The silicon-carbon composite material of Comparative Example 1, which did not contain CNTs, maintained a capacity retention of 88.3% after 300 cycles at 45°C, a cycle expansion rate Δh300 of 42.7%, and a rate performance (DR) of 75.8%. The silicon-carbon composite material of Comparative Example 2 used 50nm silicon nanoparticles, representing a superior level of nano-silicon powder, and did not contain deposited nano-silicon particles. After 300 cycles at 45°C, it maintained a capacity retention of 82.5%, a cycle expansion rate Δh300 of 47.2%, and a rate performance (DR) of 77.4%. The silicon-carbon composite material of Comparative Example 3, coated with CNTs on the silicon-carbon material substrate of Comparative Example 1, retained 89.5% of its capacity after 300 cycles at 45°C, with a cycle expansion rate Δh300 of 40.5% and a rate performance (DR) of 78.1%. The cycle performance, cycle expansion, and kinetic performance of Comparative Examples 1-3 were all inferior to those of Examples 1-18. This shows that by depositing nano-silicon-based materials in a carbon nanotube / porous carbon composite matrix through interconnecting units of porous carbon and carbon nanotubes, the secondary battery can achieve both good cycle performance and low cycle expansion, and also has an advantage in rate performance.

[0321] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A silicon-carbon composite material, comprising a carbon nanotube / porous carbon composite matrix and a silicon-based material, wherein the porous carbon in the carbon nanotube / porous carbon composite matrix is connected with the carbon nanotube through a connecting unit, and the connecting unit comprises at least one of a carbon-carbon bond, a benzene ring, an ester group, and a carbonyl group.

2. The silicon-carbon composite material of claim 1, wherein, At least a portion of the silicon-based material is distributed in the pores of the carbon nanotube / porous carbon composite matrix.

3. The silicon-carbon composite material of any one of claims 1-2, wherein, At least a portion of one end of the carbon nanotube protrudes from the surface of the silicon-carbon composite material.

4. The silicon-carbon composite material of any one of claims 1-3, wherein, The carbon nanotube has a tube diameter of 0.5-20 nm.

5. The silicon-carbon composite material of any one of claims 1-3, wherein, The carbon nanotube has a tube diameter of 0.7-10 nm.

6. The silicon-carbon composite material of any one of claims 1-5, wherein, The length of the carbon nanotube is denoted as L, the volume distribution particle size Dv50 of the silicon-carbon composite material is denoted as D0, and the silicon-carbon composite material satisfies: L ≥ 3D0.

7. The silicon-carbon composite of claim 6, wherein, The silicon-carbon composite material satisfies: 3D0≤L≤7D0.

8. The silicon-carbon composite material of any one of claims 1-7, wherein, The aspect ratio of the carbon nanotube is greater than or equal to 900.

9. The silicon-carbon composite material of claim 8, wherein, The aspect ratio of the carbon nanotube is 2500-25000.

10. The silicon-carbon composite material of any one of claims 1-9, wherein, The content of the carbon nanotube in the silicon-carbon composite material is ≤8%.

11. The silicon-carbon composite material of claim 10, wherein, The content of the carbon nanotube in the silicon-carbon composite material is 0.2%-5.0%.

12. The silicon-carbon composite material of any one of claims 1-11, wherein, The carbon nanotube / porous carbon composite matrix satisfies at least one of the following (1)-(4): (1) The carbon nanotube / porous carbon composite matrix comprises mesopores inside; (2) The carbon nanotube / porous carbon composite matrix comprises micropores inside; (3) The carbon nanotube / porous carbon composite matrix comprises macropores inside; (4) The carbon nanotube / porous carbon composite matrix comprises mesopores and micropores inside.

13. The silicon-carbon composite material of claim 12, wherein, The mesopores have a pore volume > 0.1 cm3 / g 3 / g.

14. The silicon-carbon composite of claim 12, wherein, The micropores have a pore volume of < 0.3 cm3 / g 3 / g.

15. The silicon-carbon composite of claim 12, wherein, The micropores have a pore volume of 0.05 to 0.2 cm3 / g. 3 / g.

16. The silicon-carbon composite of claim 12, wherein, the macropores have a pore volume of < 0.5 cm3 / g 3 / g.

17. The silicon-carbon composite of claim 12, wherein, The macropores have a pore volume of 0.05 to 0.4 cm3 / g. 3 / g.

18. The silicon-carbon composite of claim 12, wherein, The ratio of the pore volume of the mesopores to the pore volume of the micropores is ≥2.

19. The silicon-carbon composite of claim 12, wherein, The ratio of the pore volume of the mesopores to the pore volume of the micropores is 3-15.

20. The silicon-carbon composite material of any one of claims 1-19, wherein, The silicon-based material is a nano-silicon-based particle.

21. The silicon-carbon composite of claim 20, wherein, The average particle size of the nano-silicon-based particle is ≤50 nm.

22. The silicon-carbon composite of claim 20, wherein, The average particle size of the nano-silicon-based particle is 3-20 nm.

23. The silicon-carbon composite material of any one of claims 1-22, wherein, The silicon-based material comprises at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, silicon alloy, and pre-lithiated silicon oxide.

24. The silicon-carbon composite of claim 23, wherein, The silicon-based material comprises silicon monoxide.

25. The silicon-carbon composite material of any one of claims 1-24, wherein, The silicon-based material comprises amorphous silicon.

26. The silicon-carbon composite of claim 25, wherein, The silicon-based material comprises a mixture of amorphous silicon and crystalline silicon.

27. The silicon-carbon composite material of any one of claims 1-26, wherein, The carbon nanotube / porous carbon composite matrix is formed by carbonization of a resin precursor and carbon nanotubes grafted with functional groups and / or polymers, wherein the functional groups and / or the polymers can chemically react with the resin precursor, so that the carbon nanotubes are connected with the resin precursor, and the connecting unit is formed after carbonization.

28. The silicon-carbon composite material of any one of claims 1-27, wherein, The silicon-carbon composite or the carbon nanotube / porous carbon composite matrix containing at least one of the following connecting units: an ester carbonyl group with an absorption peak of 1750~1735cm -1 ; a ketone carbonyl group with an absorption peak of 1725~1705cm -1 ; a benzene ring group with an absorption peak of 1620~1450cm -1 ; and a carbon-carbon bond with an absorption peak of 2400~1950cm -1 ; and / or, The silicon-carbon composite material or the carbon nanotube / porous carbon composite matrix is tested by transmission electron microscopy, and the proportion of the area where the distance between the carbon atoms on the periphery of the carbon nanotube and the outermost layer of carbon atoms of the carbon nanotube is ≤0.35 nm is ≥50%.

29. The silicon-carbon composite material of any one of claims 1-28, wherein, The compression index P of the silicon-carbon composite material is defined as P=D0 / (D0-D1), wherein P≥3, D0 is the volume distribution particle size Dv50 of the silicon-carbon composite material, and D1 is the volume distribution particle size Dv50 of the silicon-carbon composite material after compression, and the compression condition is 300 MPa pressure for 30 s and repeated compression for 50 times.

30. The silicon-carbon composite material of any one of claims 1-29, wherein, The resistivity of the silicon-carbon composite material under a pressure of 4 MPa is ρ≤0.4 Ω·cm.

31. The silicon-carbon composite of claim 30, wherein, 0.05 Ω·cm≤ ρ ≤ 0.3 Ω·cm.

32. The silicon-carbon composite material of any one of claims 1-31, wherein, The silicon-carbon composite material satisfies at least one of the following conditions (I)-(V): (I) The volume distribution particle size Dv50 of the silicon-carbon composite material is ≤8 μm; (II) The porosity of the silicon-carbon composite material is ≤20%; (III) the silicon-carbon composite material has a specific surface area SSA < 5.0 m2 / g 2 / g; (IV) The silicon-carbon composite material comprises mesopores inside; (V) The mass ratio of elements in the silicon-carbon composite material is Si:C:O=(20-55):(40-70):(3-10).

33. The silicon-carbon composite of claim 32, wherein, The volume distribution particle size Dv50 of the silicon-carbon composite material is 3-7 μm.

34. The silicon-carbon composite of claim 32, wherein, The porosity of the silicon-carbon composite material is 5%-15%.

35. The silicon-carbon composite of claim 32, wherein, The specific surface area SSA of the silicon-carbon composite material is 0.8-4.0 m 2 / g.

36. The silicon-carbon composite of claim 32, wherein, the mesopores have a pore volume of < 0.3 cm3 / g 3 / g.

37. The silicon-carbon composite of claim 32, wherein, The mesopores have a pore volume of 0.05-0.1 cm 3 / g.

38. The silicon-carbon composite of any one of claims 1-37, wherein, The silicon-carbon composite material further comprises a coating layer on the surface.

39. The silicon-carbon composite of claim 38, wherein, The coating layer comprises at least one of a carbon coating layer, a polymer coating layer, an inorganic salt coating layer, and a metal oxide coating layer.

40. A method of making a silicon-carbon composite material, wherein, The method comprises the following steps: grafting functional groups and / or polymers on the carbon nanotubes to obtain modified carbon nanotubes, wherein the functional groups comprise one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl, and the polymers comprise one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate; mixing the modified carbon nanotubes with a resin precursor solution to obtain a mixed solution, wherein the functional groups and the polymers on the modified carbon nanotubes can chemically react with the resin precursor, so that the modified carbon nanotubes are connected to the resin precursor; performing a curing treatment on the mixed solution to obtain a composite matrix precursor; performing a carbonization treatment on the composite matrix precursor to obtain a porous carbon / carbon nanotube composite matrix; and depositing a silicon-based material on the porous carbon / carbon nanotube composite matrix to obtain a silicon-carbon composite material.

41. The method of manufacturing according to claim 40, wherein, The mixed solution further comprises 0.5%-30% of a catalyst by mass percentage.

42. The method of manufacturing according to claim 41, wherein, The catalyst comprises one or more of hexamethylenetetramine, ammonium bicarbonate, ammonium carbonate, aqueous ammonia, a zinc salt, a copper salt, and a chromium salt.

43. The method of manufacturing according to claim 40, wherein, The mixing comprises stirring at 20-60°C for 1-10 h, and the modified carbon nanotubes and the resin precursor undergo one or more of esterification, addition reaction, polyaddition, and polycondensation.

44. The preparation method according to any one of claims 40-43, wherein The curing treatment comprises pre-curing and full-curing.

45. The method of making according to any one of claims 40-43, wherein, The curing treatment comprises pre-curing, crushing, and full-curing.

46. The preparation method according to claim 44 or 45, wherein The temperature of the pre-curing is 70-140°C; and / or The time of the pre-curing is 3-12 h.

47. The method of manufacturing according to claim 46, wherein, The temperature of the pre-curing is 80-130°C.

48. The method of manufacturing according to claim 46, wherein, The pre-curing time is 5-10 h.

49. The production method according to claim 44 or 45, wherein, The full-curing temperature is 150-220 °C; and / or, The full-curing time is 8-20 h.

50. The method of manufacturing according to claim 49, wherein, The full-curing temperature is 160-200.

51. The method of manufacturing according to claim 49, wherein, The full-curing time is 10-15 h.

52. The production method according to any one of claims 40-51, wherein, The carbonization treatment temperature is 900-3000 °C; and / or, The carbonization treatment time is 2-6 h.

53. The method of manufacturing according to claim 52, wherein, The carbonization treatment temperature is 1000-2000.

54. The method of manufacturing according to claim 52, wherein, The carbonization treatment time is 3-5 h.

55. The method of making according to any one of claims 40-54, wherein, The deposition is performed by a chemical vapor deposition method.

56. The method of manufacturing according to claim 55, wherein, The deposition gas includes a mixed gas of at least one of H2, N2, and Ar and a silane gas.

57. A secondary battery comprising a negative electrode sheet comprising the silicon-carbon composite material according to any one of claims 1-39 or obtained by the production method according to any one of claims 40-56.

58. An electrical device, comprising: A secondary battery comprising the secondary battery according to claim 57.

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