Composite material and method for producing the same, secondary battery

Abstract

This application relates to composite materials, their preparation methods, and secondary batteries. The composite material comprises a stacked carbon matrix, with graphite particles filling the spaces between the carbon matrix layers. The ratio of the D90 of the carbon matrix to the D90 of the graphite particles is greater than or equal to 10. In the composite material of this application, the stacked carbon matrix exhibits extremely high electrical conductivity, forming conductive pathways and improving the conductivity of the composite material. The graphite particles filling the spaces between the carbon matrix layers increase the number of conductive contact points, enhancing the connectivity of the conductive pathways. Furthermore, ensuring that the ratio of the D90 of the carbon matrix to the D90 of the graphite particles is greater than or equal to 10 guarantees sufficient contact between the carbon matrix layers and the graphite particles, ensuring the integrity of the conductive network, thereby improving the conductivity and capacity of the composite material.

Description

Technical Field

[0001] This application belongs to the field of energy storage materials technology, specifically relating to composite materials and their preparation methods, and secondary batteries. Background Technology

[0002] Graphite-based thermal conductive films are generally prepared through seven processes: homogenization and dispersion, coating and drying, pretreatment, carbonization, graphitization, calendering and compaction, and die-cutting. In the die-cutting process, to meet the space, safety, and durability requirements of components, the film needs to be cut and bonded with additional polymer-based double-sided adhesive, substrate, and protective film. Inevitably, some unusable waste is generated during die-cutting. Because graphite-based die-cutting waste contains multiple components, including polymer adhesive materials, substrate, and graphite film, it is difficult to process and results in significant waste.

[0003] Currently, existing technologies for preparing carbon-containing anode materials or conductive agents require the purchase of raw materials, which have a simple structure and are difficult to form a conductive network, resulting in low conductivity and capacity, as well as high cost. In addition, since anode materials or conductive agents generally need to be processed in heat treatment or pulverization equipment, impurity elements are introduced into the material through these devices, thereby reducing the purity of the material.

[0004] Therefore, there is an urgent need to provide a material that is inexpensive and has high conductivity and capacity. Summary of the Invention

[0005] In order to overcome the above-mentioned defects, this application provides a composite material and its preparation method, as well as a secondary battery. The composite material of this application can obtain a material with high conductivity and capacity, and can be used in the negative electrode material or conductive agent of a secondary battery.

[0006] In a first aspect, this application provides a composite material comprising a carbon matrix stacked in layers, wherein graphite particles are filled between the carbon matrix layers, and the ratio of the D90 of the carbon matrix to the D90 of the graphite particles is greater than or equal to 10.

[0007] In some embodiments, the ratio of the D90 of the carbon matrix to the D90 of the graphite particles is 10 to 100.

[0008] In some embodiments, the graphite particles are dispersed on at least a portion of the surface of the carbon matrix.

[0009] In some embodiments, the raw materials for the composite material include waste thermally conductive film.

[0010] In some embodiments, the thermal conductive film waste includes at least one of graphene thermal conductive film, natural graphite thermal conductive film, and artificial graphite thermal conductive film.

[0011] In some embodiments, the graphite particles account for 0.1% to 30% of the mass of the composite material.

[0012] In some embodiments, the carbon matrix includes at least one of graphene and graphite.

[0013] In some embodiments, the median particle size D50 of the carbon matrix is ​​less than 5 μm.

[0014] In some embodiments, the D90 of the carbon matrix is ​​less than 10 μm.

[0015] In some embodiments, the median particle size D50 of the graphite particles is less than 0.5 μm.

[0016] In some embodiments, the D90 of the graphite particles is less than 1 μm.

[0017] In some embodiments, the fixed carbon content of the composite material is greater than 99.9%.

[0018] In some embodiments, the moisture content of the composite material is less than 0.1%.

[0019] In some embodiments, the ash content of the composite material is less than 0.1%.

[0020] In some embodiments, the composite material further includes a dopant element, wherein the dopant element accounts for 0 ppm to 0.2 ppm by mass in the composite material, and wherein the dopant element includes at least one of Fe, Co, Cu, Ni, Cr, Zn and Mn.

[0021] In some embodiments, the mass percentage of sulfur in the composite material is less than or equal to 100 ppm.

[0022] In some embodiments, the graphitization degree of the composite material is greater than or equal to 99%.

[0023] In some embodiments, the median particle size D90 of the composite material is less than or equal to 10 μm.

[0024] In some embodiments, the powder compaction density of the composite material is 1.75 g / cm³. 3 ~1.85g / cm 3 .

[0025] In some embodiments, the tap density of the composite material is 0.08 g / cm³. 3 ~0.18g / cm 3 .

[0026] In some embodiments, the powder conductivity of the composite material is greater than or equal to 300 S / cm.

[0027] Secondly, this application provides a method for preparing a composite material, comprising the following steps:

[0028] The waste thermal conductive film is carbonized to obtain a first precursor, and the carbonization is carried out in a first protective atmosphere;

[0029] The first precursor is graphitized to obtain the second precursor, wherein the carbonization temperature is less than or equal to the graphitization temperature.

[0030] The second precursor is crushed to obtain a composite material.

[0031] In some embodiments, the waste thermal conductive film is derived from graphite-based thermal conductive films.

[0032] In some embodiments, the waste thermal conductive film is derived from graphite-based thermal conductive films, which are composed of a substrate, a graphite film, and a polymer adhesive material.

[0033] In some embodiments, the waste thermal conductive film is derived from graphite-based thermal conductive films, which include at least one of graphene thermal conductive films, natural graphite thermal conductive films, and artificial graphite thermal conductive films.

[0034] In some embodiments, the first precursor comprises a mixture of a carbon matrix and amorphous carbon.

[0035] In some embodiments, the first precursor comprises a mixture of a carbon matrix and amorphous carbon, wherein the carbon matrix comprises at least one of graphene and graphite.

[0036] In some embodiments, the carbonization temperature is 900°C to 1500°C.

[0037] In some embodiments, the heating rate of the carbonization is 0.5°C / min to 2°C / min.

[0038] In some embodiments, the carbonization holding time is 5h to 10h.

[0039] In some embodiments, the first protective atmosphere includes at least one of nitrogen, helium, and argon.

[0040] In some embodiments, the graphitization temperature is 2700°C to 3000°C.

[0041] In some embodiments, the heating rate of the graphitization is 0.5°C / min to 3°C / min.

[0042] In some embodiments, the heating time for graphitization is 20h to 50h.

[0043] In some embodiments, the graphitization holding time is 5h to 10h.

[0044] In some embodiments, the graphitization is carried out in a second protective atmosphere, which includes at least one of nitrogen, helium, and argon.

[0045] In some embodiments, the median particle size D90 of the composite material is less than or equal to 10 μm.

[0046] In some embodiments, the second precursor is subjected to a first crushing and a second crushing to obtain a composite material.

[0047] In some embodiments, the pressure in the grinding chamber of the first pulverizer is 0.3 MPa to 0.6 MPa.

[0048] In some embodiments, the first pulverizing classifier rotates at a speed of 5000 rpm to 6500 rpm.

[0049] In some embodiments, the induced draft speed of the first pulverizer is 2000 rpm to 2500 rpm.

[0050] In some embodiments, the pressure in the grinding chamber of the second pulverizer is 0.6 MPa to 0.8 MPa.

[0051] In some embodiments, the second crushing classifier rotates at a speed of 6500 rpm to 7500 rpm.

[0052] In some embodiments, the induced draft speed of the second pulverizer is 2500 rpm to 3000 rpm.

[0053] Thirdly, this application provides a secondary battery, wherein the secondary battery comprises the composite material described in the first aspect or the composite material described in the second aspect.

[0054] The technical solution of this application has at least the following beneficial effects: In the composite material of this application, the stacked carbon matrix has ultra-high conductivity, which can form a conductive path and improve the conductivity of the composite material; the graphite particles filled between the carbon matrix layers can increase the conductive contact points and enhance the connectivity of the conductive path. Furthermore, by making the ratio of D90 of the carbon matrix to D90 of the graphite particles greater than or equal to 10, it is possible to ensure sufficient contact between the carbon matrix layers and the graphite particles, ensure the integrity of the conductive network, and thus improve the conductivity and capacity of the composite material.

[0055] This application involves subjecting waste thermal conductive film materials to two heat treatments. The first, carbonization, is conducted in a protective atmosphere, causing the polymer adhesive and substrate in the waste material to undergo high-temperature pyrolysis and carbonization, forming amorphous carbon. The graphitization temperature is higher than the carbonization temperature. Graphitization graphitizes the carbon materials (graphite film or graphene film) originally present in the waste material, and simultaneously, the amorphous carbon also graphitizes to form graphite particles. Since the carbon matrix within the thermal conductive film is already graphitized during its preparation, graphitization leads to a further graphitization of the carbon matrix, resulting in a higher degree of orientation and graphitization, thereby improving the material's conductivity and capacity. Compared to traditional graphite conductive agents, the graphitization process is also a purification process, resulting in a composite material with higher purity and superior performance. Attached Figure Description

[0056] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0057] Figure 1 Here is a SEM image of the composite material of this application;

[0058] Figure 2 This is a flowchart illustrating the preparation process of the composite material in this application;

[0059] Figure 3 This is an XRD pattern of the composite material after carbonization and graphitization in Example 1 of this application. Detailed Implementation

[0060] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0061] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0062] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0063] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0064] This application provides a composite material, such as Figure 1 and Figure 2 As shown, the composite material includes a carbon matrix stacked in layers, with graphite particles filling the spaces between the carbon matrix layers, and the ratio of the D90 of the carbon matrix to the D90 of the graphite particles is greater than or equal to 10.

[0065] In the above-described scheme, the composite material of this application features a stacked carbon matrix with extremely high conductivity, which can form conductive pathways and improve the conductivity of the composite material. The graphite particles filling the spaces between the carbon matrix layers increase the number of conductive contact points and enhance the connectivity of the conductive pathways. Furthermore, ensuring that the ratio of the D90 of the carbon matrix to the D90 of the graphite particles is greater than or equal to 10 guarantees sufficient contact between the carbon matrix layers and the graphite particles, ensuring the integrity of the conductive network, thereby improving the conductivity and capacity of the composite material.

[0066] In this application, the ratio of D90 of the carbon matrix to D90 of the graphite particles is greater than or equal to 10. Specifically, the ratio can be 10, 12, 13, 15, 18, 20, 25, and 30, or other values ​​within the above range, which are not limited here. If the ratio of D90 of the carbon matrix to D90 of the graphite particles is less than 10, the particle size difference between the carbon matrix and the graphite particles is too small, making it difficult for the graphite particles to fill into the carbon matrix sheets, thus affecting the formation of the conductive network. It is understood that D90 refers to the particle size corresponding to a cumulative particle size distribution of 90% in the carbon matrix. Preferably, the ratio of D90 of the carbon matrix to D90 of the graphite particles is 10 to 100.

[0067] In some embodiments, the carbon matrix is ​​in the form of sheets, specifically meaning that the sheet diameter is 1 μm to 10 μm and the thickness is 5 nm to 30 nm.

[0068] In some embodiments, at least a portion of the surface of the carbon matrix is ​​dispersed with graphite particles.

[0069] In some embodiments, the raw materials for the composite material include waste thermal conductive film, which is derived from graphite-based thermal conductive film. The components of graphite-based thermal conductive film include a substrate, a graphite film, and a polymer adhesive material.

[0070] In some embodiments, when the thermal conductive film die-cutting waste is graphene thermal conductive film die-cutting waste, the carbon matrix is ​​graphene; when the thermal conductive film die-cutting waste is natural graphite thermal conductive film die-cutting waste or artificial graphite thermal conductive film die-cutting waste, the carbon matrix is ​​graphite.

[0071] In some embodiments, the mass percentage of graphite particles in the composite material is 0.1% to 30%. Specifically, the mass percentage of graphite particles in the composite material can be 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, and 30%, etc., or other values ​​within the above range, which are not limited here. If the mass percentage of graphite particles in the composite material is less than 0.1%, the gaps between the carbon matrix layers cannot be effectively filled, affecting the integrity of its conductive network; if the mass percentage of graphite particles in the composite material is greater than 30%, the conductivity of the material is relatively low, because the conductivity of the composite material is mainly due to the carbon matrix material. Preferably, the mass percentage of graphite particles in the composite material is 0.2% to 10%.

[0072] In some embodiments, the median particle size of the carbon matrix is ​​less than 5 μm. Specifically, the median particle size of the carbon matrix can be 1 μm, 2 μm, 3 μm, and 4 μm, or other values ​​within the above range, which are not limited here.

[0073] In some embodiments, the D90 of the carbon matrix is ​​less than 10 μm. Specifically, the D90 of the carbon matrix can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and 9 μm, or other values ​​within the above range, which are not limited here. If the D90 of the carbon matrix is ​​greater than or equal to 10 μm, the carbon matrix sheets are too large, resulting in insufficient contact between the sheets and easy bridging, which leads to insufficient contact and dispersion with the active material, affecting the formation of the conductive network.

[0074] In some embodiments, the median particle size of the graphite particles is less than 0.5 μm. Specifically, the median particle size of the graphite particles can be 0.1 μm, 0.2 μm, 0.3 μm, and 0.4 μm, etc., or other values ​​within the above range, which are not limited here.

[0075] In some embodiments, the D90 of the graphite particles is less than 1 μm. Specifically, the D90 of the graphite particles can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, and 0.9 μm, or other values ​​within the above range, which are not limited here. If the D90 of the graphite particles is greater than or equal to 1 μm, the graphite particles cannot fill the carbon matrix sheets, affecting the contact with the active material and the conductive network.

[0076] In some embodiments, the fixed carbon content of the composite material is greater than 99.99%, indicating that the graphite in the composite material of this application is high-purity graphite, which has excellent electrical conductivity.

[0077] In some embodiments, the moisture content of the composite material is less than 0.1%. Specifically, the moisture content of the composite material can be 0.09%, 0.07%, 0.05%, 0.03%, and 0.01%, etc., or other values ​​within the above range, which are not limited here. The moisture content within the above range in the composite material of this application indicates that the composite material has a stable structure and is not prone to cracking when heated.

[0078] In some embodiments, the ash content of the composite material is less than 0.1%. Specifically, the ash content of the composite material can be 0.09%, 0.07%, 0.05%, 0.03%, and 0.01%, etc., or other values ​​within the above range, which are not limited here. Ash content refers to the content of solid elements other than carbon matrix in the composite material. The ash content within the above range in the composite material of this application indicates that the composite material has fewer impurities and higher purity.

[0079] In some embodiments, the composite material further includes dopant elements, the mass percentage of which is 0 ppm to 0.2 ppm. Specifically, the mass percentage of the dopant elements in the composite material can be 0.2 ppm, 0.15 ppm, 0.1 ppm, 0.75 ppm, and 0.05 ppm, or other values ​​within the above range, which are not limited here. The dopant elements in the composite material of this application include at least one of Fe, Co, Cu, Ni, Cr, Zn, and Mn. Controlling the mass percentage of the dopant elements in the composite material within the above range can avoid the problem of reduced specific capacity and energy density of the material due to excessive dopant elements, further stabilizing the self-discharge of the battery and preventing short circuits.

[0080] In some embodiments, the mass percentage of sulfur in the composite material is less than or equal to 100 ppm. Specifically, the mass percentage of sulfur in the composite material can be 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, and 100 ppm, or other values ​​within the above range, which are not limited here. Controlling the sulfur content in the composite material within the above range helps to reduce side reactions when the composite material is used in secondary batteries and improves the electrochemical performance of the composite material.

[0081] In some embodiments, the graphitization degree of the composite material is greater than or equal to 99%. Specifically, the graphitization degree of the composite material can be 99.1%, 99.3%, 99.5%, 99.7%, and 99.9%, etc., or other values ​​within the above range, which are not limited here. The composite material of this application has a high degree of graphitization, which can effectively improve the conductivity of the material.

[0082] In some embodiments, the D90 of the composite material is less than or equal to 10 μm. Specifically, the D90 of the composite material can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm, etc., or other values ​​within the above range, which are not limited here.

[0083] In some embodiments, the powder compaction density of the composite material is 1.75 g / cm³. 3 ~1.85g / cm 3 Specifically, the powder compaction density of the composite material can be 1.75 g / cm³. 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 1.80g / cm 3 1.81 g / cm 3 1.82g / cm 3 1.83g / cm 3 1.84 g / cm 3 and 1.85g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. In the composite material of this application, since the graphite particles are filled between the carbon matrix layers, they can fill the pores between the carbon matrix, so that the powder compaction density of the material is controlled within the above range, thereby improving the volumetric energy density of the composite material.

[0084] In some embodiments, the tap density of the composite material is 0.08 g / cm³. 3 ~0.18g / cm 3 Specifically, the tap density of the composite material can be 0.08 g / cm³. 3 0.10 g / cm 3 0.12g / cm 3 0.14 g / cm 3 0.16 g / cm 3 and 0.18 g / cm 3 Of course, it can also be other values ​​within the above range, and is not limited here. The test method for tapped density is as follows: a certain amount of powder is filled into a tapped density tester, and the sample is continuously vibrated and rotated by a vibration device until the volume of the sample no longer decreases. Finally, the tapped density is obtained by dividing the mass of the sample by the volume after tapping.

[0085] In some embodiments, the powder conductivity of the composite material is greater than or equal to 300 S / cm. Specifically, the powder conductivity of the composite material can be 300 S / cm, 350 S / cm, 400 S / cm, 450 S / cm, 500 S / cm, 600 S / cm, 700 S / cm, and 800 S / cm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0086] This application also provides a method for preparing the above-mentioned composite material, such as... Figure 2 The diagram shown is a flowchart of the preparation process of the composite material of this application, including the following steps:

[0087] The waste thermal conductive film is carbonized to obtain the first precursor. The carbonization is carried out in the first protective atmosphere.

[0088] The first precursor is graphitized to obtain the second precursor, wherein the graphitization temperature is greater than the carbonization temperature.

[0089] The second precursor is crushed to obtain a composite material.

[0090] In the above-mentioned solutions, the waste thermal conductive film contains multiple components such as polymer adhesive materials, substrates, graphite films or graphene films, which are difficult to process and directly discarding them results in a large amount of waste. This application uses the aforementioned waste thermal conductive film as a raw material for composite materials, which is then processed into high-value-added products, solving the problem that the current waste thermal conductive film die-cutting cannot be recycled and reused, and further reducing the cost of thermal conductive films. Specifically, this application performs two heat treatments on the waste thermal conductive film. Carbonization is carried out in a first protective atmosphere, causing the polymer adhesive materials and substrates in the waste thermal conductive film to undergo high-temperature pyrolysis and carbonization to form amorphous carbon. The graphitization temperature is higher than the carbonization temperature. Graphitization causes the carbon materials (graphite films or graphene films) originally present in the waste thermal conductive film to graphitize, and at the same time, the amorphous carbon also undergoes graphitization to form graphite particles. Since the carbon materials in the thermal conductive film have already been graphitized during the preparation process, graphitization will cause the carbon materials to undergo graphitization again, resulting in a higher degree of orientation and graphitization of the carbon matrix, thereby improving the conductivity and capacity of the material. Compared to traditional graphite conductive agents, and because graphitization is also a purification process, the composite material has higher purity and better performance. The preparation process of the composite material in this application is simple and low-cost. The polymer adhesive material in the waste thermal conductive film of this application is already adhered to the surface and interlayer of the thermal conductive film. During the graphitization process, the graphite particles converted from the polymer adhesive material can be well dispersed between the graphene sheets. Compared with the material obtained by directly mixing carbon matrix and graphite particles, it is more efficient, more stable, and more uniform. Furthermore, the composite material prepared in this application has better conductivity and capacity, and the carbon matrix and graphite particles are more evenly distributed, making the composite material more stable. Compared to directly mixing a carbon matrix and polymeric adhesive materials for carbonization and graphitization to obtain composite materials, there are two main drawbacks. First, not all polymeric adhesive materials can be used to prepare graphite particles; they must be graphitizable materials capable of being converted into soft carbon. The polymeric adhesive material used in this application originates from waste thermal conductive films, which can be converted into soft carbon, thus yielding graphite particles. Second, the ratio of polymeric adhesive material to graphite film needs to be strictly considered. Adding too much or too little polymeric adhesive material will lead to a decrease in the conductivity and capacity of the composite material. Using waste thermal conductive films directly as raw materials eliminates these considerations. Furthermore, the graphitization process of waste thermal conductive films is equivalent to a secondary graphitization, further repairing its crystal structure, resulting in a higher degree of graphitization and orientation, and superior performance. Simultaneously, the graphitization process is a further purification process, with minimal doping elements.

[0091] The preparation method of this application is described in detail below with reference to the embodiments:

[0092] Step S100: Carbonize the waste thermal conductive film to obtain the first precursor.

[0093] In this step, the thermal conductive film waste is die-cutting waste, which is the residual waste generated during the preparation of the thermal conductive film. It mainly includes multiple components such as polymer adhesive materials, substrate, graphite film and graphene film. The thermal conductive film die-cutting waste is carbonized, which causes the polymer adhesive material to undergo high-temperature pyrolysis and carbonization, decomposing and releasing small molecules (such as H2O, CH4, CO2 and CO, etc.) to form amorphous carbon. Thus, the first precursor is a mixture including carbon matrix and amorphous carbon, wherein the carbon matrix includes at least one of graphene and graphite.

[0094] In some embodiments, the waste thermal conductive film originates from graphite-based thermal conductive films, which include at least one of graphene thermal conductive films, natural graphite thermal conductive films, and artificial graphite thermal conductive films. The components of the graphite-based thermal conductive film include a substrate, a graphite film, and a polymer adhesive material. The substrate includes thermoplastic polymers such as PET (polyethylene terephthalate) and PP (polypropylene). The graphite film includes at least one of artificial graphite film, natural graphite film, and graphene film. The polymer adhesive material includes acrylic resin, etc.

[0095] In some embodiments, the carbonization temperature is 900℃ to 1500℃. Specifically, the carbonization temperature can be 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃ and 1500℃, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0096] In some embodiments, the heating rate of carbonization is 0.5℃ / min to 2℃ / min. Specifically, the heating rate of carbonization can be 0.5℃ / min, 1℃ / min, 1.5℃ / min and 2℃ / min, etc., or other values ​​within the above range, which are not limited here.

[0097] In some embodiments, the carbonization holding time is 5h to 10h. Specifically, the carbonization holding time can be 5h, 6h, 7h, 8h, 9h and 10h, etc., or other values ​​within the above range, which are not limited here.

[0098] In some embodiments, carbonization is carried out in a first protective atmosphere, which includes at least one of nitrogen, helium, and argon. If the carbonization process is not carried out in a protective atmosphere, the polymer adhesive material in the waste is easily vaporized by combustion with oxygen in the air, making it impossible to obtain amorphous carbon material, form a conductive network, and further reduce the material's capacity and initial efficiency.

[0099] In some implementations, a filtration device is installed during the carbonization process. The carbonization of the polymer adhesive material in the thermal conductive film waste produces tar, which needs to be removed by a filtration device.

[0100] Step S200: Graphitize the first precursor to obtain the second precursor.

[0101] In this step, the carbon matrix in the first precursor undergoes graphitization treatment, which gives the carbon matrix a higher degree of graphitization and conductivity. During the graphitization process, the amorphous carbon in the first precursor gradually evolves into a graphite structure, forming an ordered graphite structure. In addition, during the graphitization process, the metallic impurities in the first precursor volatilize and sublimate, improving the purity of the composite material.

[0102] In some embodiments, the graphitization temperature is 2700℃~3000℃. Specifically, the graphitization temperature can be 2700℃, 2800℃, 2900℃, and 3000℃, or other values ​​within the above range, which are not limited here. A graphitization temperature higher than the carbonization temperature ensures that during the carbonization process, organic materials such as polymer adhesives are first carbonized into carbon, and then graphitized to convert the carbon into graphite. Controlling the graphitization temperature within the above range can effectively improve the graphitization degree, orientation degree, and purity of the composite material.

[0103] In some embodiments, the heating rate of graphitization is 0.5℃ / min to 3℃ / min. Specifically, the heating rate of graphitization is 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min and 3℃ / min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0104] In some implementations, the graphitization heating time is 20h to 50h. Specifically, the graphitization heating time can be 20h, 25h, 30h, 35h, 40h, 45h and 50h, etc., or other values ​​within the above range, which are not limited here.

[0105] In some embodiments, graphitization is carried out in a second protective atmosphere, which includes at least one of nitrogen, helium, and argon.

[0106] In some methods, the graphitization equipment includes at least one of an Atchison graphitization furnace, an internal series graphitization furnace, a box-type graphitization furnace, and a continuous graphitization furnace.

[0107] Step S300: The second precursor is pulverized to obtain the composite material. Specifically, step S300 includes the following steps:

[0108] The second precursor is subjected to a first crushing and a second crushing to obtain a third precursor.

[0109] In some embodiments, the first pulverizing device may be an air jet mill, including but not limited to any one of a fluidized bed air jet mill and a cyclone air jet mill. It is understood that the inner wall of the aforementioned pulverizing device should be coated or fitted with non-metallic or stainless steel materials, such as ceramic zirconium oxide, alumina, or polytetrafluoroethylene, to avoid introducing excessive doping elements.

[0110] In some embodiments, the pressure of the first grinding chamber is 0.3MPa to 0.6MPa. Specifically, the pressure of the first grinding chamber can be 0.3MPa, 0.4MPa, 0.5MPa and 0.6MPa, etc., or other values ​​within the above range, which are not limited here.

[0111] In some embodiments, the rotation speed of the first crushing and classifying wheel is 5000 rpm to 6500 rpm. Specifically, the rotation speed of the first crushing and classifying wheel is 5000 rpm, 5800 rpm, 6000 rpm, and 6500 rpm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0112] In some embodiments, the speed of the first pulverizing fan is 2000 rpm to 2500 rpm, specifically 2000 rpm, 2200 rpm, 2400 rpm, 2500 rpm, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0113] Controlling the speed of the classifying wheel and the speed of the induced draft fan in the first crushing process within the above range is beneficial to obtaining coarsely crushed materials with uniform particle size, which facilitates the high efficiency and high output of the second crushing process and ensures the uniformity of the material particle size.

[0114] In some implementations, after the first crushing, the resulting material is collected by a collection device, and the dust is separated by a dust removal device before a second crushing is performed.

[0115] In some embodiments, this application does not limit the material collection equipment. For example, the material collection equipment may be a cyclone collector, which is powered by a high-pressure centrifuge.

[0116] In some embodiments, this application does not limit the dust removal equipment; for example, the dust removal equipment may be a pulse bag filter.

[0117] In some embodiments, the pressure of the grinding chamber of the second pulverizer is 0.6MPa to 0.8MPa. Specifically, the pressure of the grinding chamber of the first pulverizer can be 0.6MPa, 0.7MPa, and 0.8MPa, etc., or other values ​​within the above range, which are not limited here.

[0118] In some embodiments, the rotational speed of the second crushing classifier wheel is 6500 rpm to 7500 rpm, specifically 6500 rpm, 6800 rpm, 7000 rpm and 7500 rpm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0119] In some embodiments, the speed of the induced draft fan for the second crusher is 2500 rpm to 3000 rpm, specifically 2500 rpm, 2800 rpm and 3000 rpm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0120] In some embodiments, after the second crushing in step S302, the obtained material is collected by a collection device and the dust is separated by a dust removal device to obtain a composite material.

[0121] In some embodiments, the D90 of the composite material is less than or equal to 10 μm. Specifically, the median particle size of the composite material can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm, etc., or other values ​​within the above range, which are not limited here.

[0122] This application also discloses a secondary battery, which comprises a composite material as described in this application or a composite material prepared by the method described in this application.

[0123] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The negative electrode includes a current collector and a negative active material layer. The negative active material layer includes a negative active material, a conductive agent, and a binder. The negative active material includes the aforementioned composite material, or the conductive agent includes the aforementioned composite material.

[0124] The present application will be further described below through specific embodiments.

[0125] Example 1

[0126] (1) The die-cut waste of graphene thermal conductive film was placed in a crucible, protected by nitrogen gas, and heated to 1000℃ at a rate of 1℃ / min for carbonization treatment for 15 hours. Then the reaction product was cooled to room temperature to obtain amorphous carbon composite graphene mixture.

[0127] (2) The amorphous carbon composite graphene mixture is transferred to a graphitization furnace, protected by nitrogen, and graphitized at 3000℃ for 48 hours at a rate of 1℃ / min to obtain a graphitized graphite mixture.

[0128] (3) The graphitized mixture is pulverized by an air jet mill. Specifically, the compressed air is transported into the pulverizing chamber under a high pressure of 0.6 MPa. After being accelerated into a supersonic airflow, the compressed air is injected into the pulverizing zone to fluidize the material. The accelerated particles collide with each other for primary pulverization and shaping. The pulverized material is collected by a cyclone separator with a classifying wheel of 6000 rpm and an induced draft fan of 2000 rpm. After dust is separated by a pulse bag filter, the material is sent into the second-stage pulverizing chamber by a high-pressure centrifugal fan feeding device. The pressure inside the chamber is 0.7 MPa. The pulverized material is screened by a classifying wheel of 7000 rpm and an induced draft fan of 2500 rpm to remove the powder that meets the particle size requirements. The powder is then collected by the rear collection device to obtain the composite material.

[0129] The composite material in this embodiment includes stacked graphene sheets with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in the table. Figure 3 The images show the XRD patterns of the carbonized and graphitized materials of this application. Figure 3 The results show that after carbonization, the composite material has a characteristic peak of amorphous carbon at around 20°, which originates from the soft carbon converted from polymer adhesive materials in the die-cutting waste, and a characteristic peak of graphite at around 26°, which originates from graphene. After graphitization, the characteristic peak of amorphous carbon at around 22° disappears and is completely transformed into the characteristic peak of graphite at around 26°, indicating that the soft carbon is transformed into a graphite structure, that is, the composite material has a complete graphite structure.

[0130] Example 2

[0131] Unlike Example 1, the graphene thermal conductive film in step (1) is replaced with a "natural graphene thermal conductive film".

[0132] The composite material obtained in this embodiment includes stacked graphite layers with graphite particles filling the spaces between the graphite sheets. Its physicochemical properties are shown in Table 1.

[0133] Example 3

[0134] Unlike Example 1, the graphene thermal conductive film in step (1) is replaced with an "artificial graphite thermal conductive film".

[0135] The composite material obtained in this embodiment includes stacked graphite layers with graphite particles filling the spaces between the graphite sheets. Its physicochemical properties are shown in Table 1.

[0136] Example 4

[0137] Unlike Example 1, the carbonization temperature in step (1) is 900°C.

[0138] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0139] Example 5

[0140] Unlike Example 1, the carbonization temperature in step (1) is 1500°C.

[0141] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0142] Example 6

[0143] Unlike Example 1, the graphitization temperature in step (2) is 2700°C.

[0144] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0145] Example 7

[0146] Unlike Example 1, the heating rate of graphitization in step (2) is 0.5 °C / min.

[0147] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0148] Example 8

[0149] Unlike Example 1, the graphitization process in step (2) was not protected by nitrogen.

[0150] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0151] Example 9

[0152] Unlike Example 1, the graphitization temperature in step (1) is 2600°C.

[0153] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0154] Example 10

[0155] Unlike Example 1, the heating rate of graphitization in step (1) is 4°C / min.

[0156] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0157] Example 11

[0158] Unlike Example 1, the carbonization temperature in step (1) is 800°C.

[0159] The composite material obtained in this embodiment includes stacked graphene with graphite particles filling the spaces between the graphene sheets. Its physicochemical properties are shown in Table 1.

[0160] Comparative Example 1

[0161] Comparative Example 1 involves directly pulverizing the die-cut waste of graphene thermal conductive film using an air jet mill to obtain a composite material.

[0162] Comparative Example 2

[0163] Unlike Example 1, step (2) is omitted.

[0164] Comparative Example 3

[0165] Unlike Example 1, the carbonization process in step (1) was not protected by nitrogen.

[0166] Performance testing

[0167] (1) Electron microscopy test: The morphology of the material is confirmed by using a scanning electron microscope.

[0168] (2) In accordance with the specifications and procedures in Appendix A of GB / T 24533-2019, the median particle size of the material D50 and D90 was tested using a Malvern 3000 laser particle size analyzer. Pure water was used as the dispersion liquid, the pump speed was 2500 r / min, and the ultrasonic frequency was 20 Hz.

[0169] (3) Powder tap density: The tap density of the sample was tested using a tap density tester according to the test standard and procedures specified in Appendix M of GB / T 24533. The amplitude was 3 mm, the vibration frequency was 100-300 times per minute, and the vibration was repeated 1000 times. The tap density ρ = (m2-m1) / V, where ρ is the tap density (g / cm³). 3 m1 - mass of graduated cylinder (g); m2 - weight of graduated cylinder and total mass of sample after compaction (g); V - volume after compaction (cm³) 3 ).

[0170] (4) Powder compaction density: The compaction density of the sample was tested using a powder compaction density tester according to the test standard and procedures specified in Appendix L of GB / T 24533. ρ = 10 m / (S × H), where ρ is the compaction density (g / cm³). 3 m - sample weight (g); H - sample thickness after compaction (mm); S - cross-sectional area of ​​the top column (cm²) 2 ).

[0171] (5) Moisture test: The moisture content in the sample was measured by a Karl Fischer coulometric titrator according to the standard and procedure specified in Appendix B of GB / T 24533-2019. The desiccant was 3A molecular sieve, and the electrolyte was a diaphragmless electrolyte. The analytical results were rounded to 0.001% according to GB / T8170.

[0172] (6) Degree of graphitization: The interlayer spacing d of the sample was measured using an X-ray diffractometer in accordance with the specifications and procedures in Appendix E of GB / T 24533. 002 Single-crystal silicon powder, after grinding and passing through a 325-mesh standard sieve, was used as the internal standard material for X-ray diffraction. The interlayer spacing was calculated according to the Bragg equation, and the graphitization degree was calculated as follows: (3.44 - d...). 002 The degree of graphitization is calculated as 3.44-3.353)×100%.

[0173] (7) Doping element test: In accordance with the standard and procedure specified in Appendix H of GB / T 24533, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to test the iron, cadmium, nickel, copper, zinc, manganese and cobalt elements in the sample. The reagent used was aqua regia (concentrated nitric acid: concentrated hydrochloric acid volume ratio of 1:3). The test results were rounded to two decimal places in accordance with GB / T 8170. In accordance with the standard and procedure specified in Appendix J of GB / T 24533, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to test the sulfur content in the sample.

[0174] (8) Powder conductivity: The sample was tested using an eLiPMS-2000plus fully automatic powder resistivity tester with an electrode spacing of 3 mm, an electrode radius of 0.75 mm, a sample radius of 10 mm, and test pressures of 2 kN, 4 kN, 6 kN, 8 kN, and 10 kN.

[0175] (9) Electrochemical test: The test shall be conducted in accordance with the standard and procedure specified in Appendix G of GB / T 24533. The conductive agent is SP, the binder is styrene-butadiene rubber powder, and CMC is used as the dispersant. The specific test ratio is set as sample: CMC: SP: SBR = 95:1.5:1.5:2. The electrochemical performance of the half cell is tested on the Blue Battery Test System.

[0176] Examples 1 to 11 and Comparative Examples 1 to 3 were tested in accordance with the above method, and the results are shown in Table 1 and Table 2.

[0177] Table 1. Performance parameters of each embodiment and comparative example

[0178]

[0179] Table 2. Performance parameters of each embodiment and comparative example

[0180]

[0181]

[0182] As shown in Tables 1 and 2, the composite materials prepared in Examples 1 to 11 of this application include: a carbon matrix with ultra-high conductivity, which can form a conductive path and improve the conductivity of the composite material; graphite particles filled between the carbon matrix layers, which can increase the conductive contact points and enhance the connectivity of the conductive path; and a ratio of D90 of the carbon matrix to D90 of the graphite particles greater than or equal to 10, which can ensure sufficient contact between the carbon matrix layers and the graphite particles, ensure the integrity of the conductive network, and thus improve the conductivity and capacity of the composite material.

[0183] In Example 8, the graphitization process was not protected by nitrogen, which resulted in the graphene and graphite particles not being fully graphitized during the graphitization process. This meant that the ash and volatiles generated during the graphitization process could not be discharged in time, affecting the production of graphite crystals and resulting in low electrical conductivity of the composite material, thus leading to a reduction in capacity and initial efficiency.

[0184] In Example 9, the graphitization temperature was below 2700°C, resulting in low graphitization degree and low electrical conductivity of graphene and graphite particles, which reduced the capacity and initial efficiency of the composite material.

[0185] In Example 10, the graphitization rate was higher than 3°C / min, which led to a decrease in the orderliness of graphite crystal growth during the graphitization process of soft carbon particles and incomplete defect repair, resulting in a decrease in the capacity and first-pass efficiency of the composite material.

[0186] In Example 11, the carbonization temperature was below 900°C, which prevented the polymer adhesive material in the die-cutting waste from being completely carbonized and forming soft carbon. This affected the transformation of soft carbon into an ordered graphite crystal structure during the graphitization stage, resulting in a decrease in the capacity and first-pass efficiency of the composite material.

[0187] Comparative Example 1 directly pulverizes the die-cut waste of graphene thermal conductive film through an air jet mill to obtain a composite material. The material has a large particle size range and the medium particle size is difficult to control, resulting in poor particle size uniformity.

[0188] In Comparative Example 2, no graphitization process was performed, which prevented graphene and soft carbon from being graphitized, thus preventing the formation of graphite and a complete conductive network, resulting in reduced conductivity of the material.

[0189] In Comparative Example 3, the carbonization process was not protected by nitrogen. The polymer adhesive material in the die-cutting waste was burned and vaporized with oxygen in the air, which could not form amorphous carbon material. Therefore, a mixture including graphene and amorphous carbon could not be obtained, let alone graphene and graphite composite material. The lack of graphite particles affected the formation of the conductive network of the composite material system, thus leading to a decrease in capacity and initial efficiency.

[0190] The above provides a detailed description of a composite material, its preparation method, and a secondary battery provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A composite material, characterized in that, The composite material includes a carbon matrix stacked in layers, with graphite particles filling the spaces between the carbon matrix layers. The ratio of the D90 of the carbon matrix to the D90 of the graphite particles is 10.33 to 21.

3. The D90 of the carbon matrix is ​​less than 10 μm, and the D90 of the graphite particles is less than 1 μm. The median particle size D50 of the carbon matrix is ​​less than 5 μm.

2. The composite material according to claim 1, characterized in that, The composite material includes at least one of the following features (1) to (6): (1) The graphite particles are dispersed on at least a portion of the surface of the carbon matrix; (2) The raw materials for the composite material include waste thermally conductive film; (3) The raw materials of the composite material include waste thermal conductive film, which includes at least one of graphene thermal conductive film, natural graphite thermal conductive film and artificial graphite thermal conductive film; (4) The graphite particles account for 0.1% to 30% of the mass of the composite material; (5) The carbon matrix includes at least one of graphene and graphite; (6) The median particle size D50 of the graphite particles is less than 0.5 μm.

3. The composite material according to claim 1, characterized in that, The composite material includes at least one of the following features (1) to (5): (1) The fixed carbon content of the composite material is greater than 99.9%; (2) The moisture content of the composite material is less than 0.1%; (3) The ash content of the composite material is less than 0.1%; (4) The composite material further includes doping elements, wherein the mass percentage of the doping elements in the composite material is 0 ppm to 0.2 ppm, wherein the doping elements include at least one of Fe, Co, Cu, Ni, Cr, Zn and Mn; (5) The mass percentage of sulfur in the composite material is less than or equal to 100 ppm.

4. The composite material according to claim 1, characterized in that, The composite material includes at least one of the following features (1) to (5): (1) The graphitization degree of the composite material is greater than or equal to 99%; (2) The median particle size D90 of the composite material is less than or equal to 10 μm; (3) The compacted density of the composite material is 1.75 g / cm³. 3 ~1.85g / cm 3 ; (4) The tap density of the composite material is 0.08 g / cm³. 3 ~0.18 g / cm 3 ; (5) The powder conductivity of the composite material is greater than or equal to 300 S / cm.

5. A method for preparing the composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: The waste thermal conductive film is carbonized to obtain a first precursor, and the carbonization is carried out in a first protective atmosphere. The first precursor is graphitized to obtain the second precursor, wherein the carbonization temperature is less than or equal to the graphitization temperature. The second precursor is crushed to obtain a composite material.

6. The preparation method according to claim 5, characterized in that, The method includes at least one of the following features (1) to (9): (1) The waste thermal conductive film is derived from graphite-based thermal conductive films; (2) The waste thermal conductive film is derived from graphite thermal conductive film, and the components of the graphite thermal conductive film include substrate, graphite film and polymer adhesive material; (3) The waste thermal conductive film is derived from graphite thermal conductive film, which includes at least one of graphene thermal conductive film, natural graphite thermal conductive film and artificial graphite thermal conductive film; (4) The first precursor comprises a mixture of a carbon matrix and amorphous carbon; (5) The first precursor comprises a mixture of a carbon matrix and amorphous carbon, wherein the carbon matrix comprises at least one of graphene and graphite; (6) The carbonization temperature is 900℃~1500℃; (7) The heating rate of the carbonization is 0.5℃ / min to 2℃ / min; (8) The heat preservation time for carbonization is 5h~10h; (9) The first protective atmosphere includes at least one of nitrogen, helium and argon.

7. The preparation method according to claim 5, characterized in that, The method includes at least one of the following features (1) to (6): (1) The graphitization temperature is 2700℃~3000℃; (2) The heating rate of the graphitization is 0.5℃ / min to 3℃ / min; (3) The heating time for graphitization is 20h~50h; (4) The heat preservation time for graphitization is 5h~10h; (5) The graphitization is carried out in a second protective atmosphere, which includes at least one of nitrogen, helium and argon; (6) The median particle size D90 of the composite material is less than or equal to 10 μm.

8. The preparation method according to claim 5, characterized in that, The method includes at least one of the following features: The second precursor is subjected to a first crushing and a second crushing process to obtain a composite material.

9. The preparation method according to claim 8, characterized in that, The preparation method includes at least one of the following features (1) to (8): (1) The first pulverizing equipment includes an air jet mill; (2) The pressure in the grinding chamber of the first pulverizer is 0.3 MPa to 0.6 MPa; (3) The rotation speed of the first crushing classifier wheel is 5000 rpm to 6500 rpm; (4) The induced draft speed of the first pulverizer is 2000 rpm to 2500 rpm; (5) The second pulverizing equipment includes an air jet mill; (6) The pressure in the grinding chamber of the second pulverizer is 0.6 MPa to 0.8 MPa; (7) The rotation speed of the second crushing classifier wheel is 6500 rpm to 7500 rpm; (8) The induced draft speed of the second crusher is 2500 rpm to 3000 rpm.

10. A secondary battery, characterized in that, The secondary battery comprises the composite material according to any one of claims 1 to 4 or the composite material prepared by the preparation method according to any one of claims 5 to 9.

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