Asphalt solid-phase composition for coating, modified asphalt-coated natural graphite negative electrode material and preparation therefor, and lithium ion battery

Abstract

An asphalt solid-phase composition for coating, a modified asphalt-coated natural graphite negative electrode material, preparation therefor, and a lithium ion battery. The asphalt solid-phase composition for coating is used for forming an amorphous carbon coating layer covering the surface of natural graphite, and comprises asphalt for coating use and a modification additive, wherein the mass ratio of the natural graphite, the asphalt for coating use and the modification additive is 1000:45-80:3-12; and the modification additive comprises a saturated long-chain component, a wax component having a low molecular weight and a component containing a modification group which are in a mass ratio of 2-10:0.5-5:0.5-7. In the present invention, by adding the modification additive, the softening point and viscosity of asphalt are reduced, thereby improving the wetting contact property of asphalt with graphite, improving the density and uniformity of coating layers, and further improving the electrochemical properties of a natural graphite negative electrode material. The negative electrode material of the present invention exhibits higher first-cycle Coulombic efficiency, better cycle performance, lower impedance and lower specific surface area under low asphalt dosage conditions.

Description

Coating Pitch Solid Phase Composition, Modified Pitch Coating Natural Graphite Anode Material and Its Preparation and Lithium-ion Battery

[0001] This application claims priority to Chinese Patent Application No. 202411859468.6, filed on December 17, 2024, entitled "Coating Pitch Solid Composition, Modified Pitch Coating Natural Graphite Anode Material and its Preparation and Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to a coating asphalt solid phase composition, modified asphalt-coated natural graphite anode material, its preparation, and lithium-ion batteries, belonging to the field of materials technology, particularly electrode materials technology. Background Technology

[0003] Lithium-ion rechargeable batteries, with their significant advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness, are widely used in smartphones, laptops, electric vehicles, and energy storage systems. They achieve the storage and release of electrical energy through the reversible insertion and extraction of lithium ions between the positive and negative electrode materials. The core components of a lithium-ion rechargeable battery include positive electrode materials, negative electrode materials, a separator, and an electrolyte. The negative electrode material is the carrier of lithium ions during charging, and its performance directly affects key indicators such as energy density, cycle life, and safety performance of the lithium-ion battery. A negative electrode material with good cycle stability can extend the battery's lifespan.

[0004] Lithium-ion battery anode materials are one of the most important applications of graphite materials. Battery manufacturers use either natural or synthetic graphite as the anode material. Synthetic graphite faces development bottlenecks due to its processing from fossil fuel raw materials with extremely high energy consumption and carbon emissions; in contrast, natural graphite has significant resource advantages. However, although natural graphite anode materials have high specific capacity, they suffer from defects such as bulk / surface defects, large expansion effects, anisotropy, and poor compatibility with electrolytes, leading to poor cycle stability. To address this, the most mature anode material production process is the solid-solid mixing of common pitch-based coating materials and spherical graphite, followed by carbonization under a protective atmosphere. This process forms an amorphous carbon layer on the graphite surface, repairing surface defects and reducing the co-intercalation of lithium ions and electrolyte molecules, thereby significantly improving the electrochemical performance of natural graphite anode materials. Besides the bulk properties of spherical graphite, the performance of the coating material is a decisive factor in the anode material's performance.

[0005] For example, CN113991076A uses polyurethane and ZnO to modify asphalt, densifying the carbonized layer by increasing the softening point of the asphalt, reducing the content of light components in the asphalt matrix, and enhancing the stability of the asphalt. CN115093874A uses stripping treatment on oxidized asphalt to obtain petroleum-based coated asphalt with low quinoline insolubles and high softening point.

[0006] It is evident that current technologies for modifying coated asphalt mainly focus on increasing coking value and reducing the content of light components in asphalt. The modification process often involves cross-linking reactions, pre-oxidation, dissolution and extraction of components, making the preparation process quite complex. However, few researchers have paid attention to the wetting process of graphite by asphalt during carbonization and have modified the asphalt based on this wetting process to obtain anode materials with better performance.

[0007] Therefore, providing a novel asphalt solid composition for coating, modified asphalt-coated natural graphite anode material and its preparation, and lithium-ion batteries have become urgent technical problems to be solved in this field. Summary of the Invention

[0008] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a coating asphalt solid-phase composition, a modified asphalt-coated natural graphite anode material, its preparation, and a lithium-ion battery. The present invention uses modifying additives in the preparation of the modified asphalt-coated natural graphite anode material, which can improve its electrochemical performance and enhance its various electrochemical properties in a balanced manner.

[0009] To achieve the above objectives, on the one hand, the present invention provides a coating bitumen solid composition for forming an amorphous carbon coating layer on the surface of natural graphite, wherein the coating bitumen solid composition comprises coating bitumen and modifying additives, wherein the mass ratio of natural graphite, coating bitumen and modifying additives is 1000:45-80:3-12; the modifying additives comprise saturated long-chain components, low-molecular-weight wax components and components containing modifying groups in a mass ratio of 2-10:0.5-5:0.5-7.

[0010] In one specific embodiment of the coating bitumen solid composition of the present invention, the mass ratio of natural graphite, coating bitumen and modifying additive is 1000:45-60:4.5-9.

[0011] In one specific embodiment of the asphalt solid composition for coating described above in this invention, the mass ratio of the saturated long-chain component, the low-molecular-weight wax component, and the component containing modified groups is 3-8:1-4:1-6.

[0012] In one specific embodiment of the asphalt solid composition for coating described above in this invention, the modified additive is a powder with a median particle size D50 of 3-20 μm, preferably 5-10 μm. The median particle size of the modified additive is highly correlated with the uniformity of the mixture; obviously, the smaller the median particle size, the more uniform the modified additive is in the mixture. However, since most modified additives are organic components or contain special groups, an excessively low median particle size can lead to severe static electricity on the surface of the modified additive powder, which is detrimental to the transportation and processing of the powder.

[0013] In one specific embodiment of the coating bitumen solid composition of the present invention, the carbon number of the saturated long-chain component is 15-200.

[0014] As a specific embodiment of the asphalt solid composition for coating described above in this invention, the saturated long-chain component includes one or a combination of stearic acid, stearamide, eicosanoic acid, and Sasobit.

[0015] The saturated long-chain components used in this invention are saturated long-chain aliphatic compounds or their modified products. These substances are easily soluble in asphalt, have a melting point between 80-115℃, can enhance the fluidity of asphalt, and improve the melting and dripping characteristics of asphalt. Furthermore, these substances preferentially gasify and decompose during the carbonization process of asphalt, and leave no residue after carbonization. They are safe and non-toxic, making them suitable as the main agent in modifying additives.

[0016] In one specific embodiment of the asphalt solid composition for coating described above in this invention, the molecular weight of the low molecular weight wax component ranges from 100 to 5000.

[0017] As a specific embodiment of the asphalt solid phase composition for coating described above in this invention, the low molecular weight wax component includes one or a combination of several of the following: synthetic Fischer-Tropsch wax, polyethylene wax, Honeywell wax powder, microcrystalline wax, and lignite wax.

[0018] The low-molecular-weight wax component used in this invention has good compatibility with asphalt and can significantly reduce the viscosity of asphalt at high temperatures. However, because it is a light component, excessive addition may be detrimental to the performance of the potential negative electrode material. Polyethylene wax is the most common type. Polyethylene waxes from different sources have different synthesis routes, compositions, and melting points, resulting in varying modification effects on asphalt. Those skilled in the art can rationally select the appropriate polyethylene wax source based on the desired modification effect. For example, in some specific embodiments of this invention, the polyethylene wax may be BASF polyethylene wax, etc.

[0019] As a specific embodiment of the asphalt solid composition for coating described above in this invention, the modified groups include one or a combination of several of amino, sulfonic acid, maleic anhydride and carboxyl groups.

[0020] As a specific embodiment of the asphalt solid phase composition for coating described above in this invention, the component containing the modified group includes one or a combination of several of the following: p-aminobenzenesulfonic acid, maleic anhydride-grafted polyethylene wax, benzenesulfonic anhydride, and sulfobenzoic acid.

[0021] The components containing modified groups used in this invention all have high melting and decomposition points, allowing them to contact and react with the components in asphalt, ensuring surface modification during asphalt softening. Specifically, p-aminobenzenesulfonic acid, with its amino and sulfonic acid groups, acts as an amphiphilic surfactant, improving the wetting and contact properties between asphalt and the graphite matrix; maleic anhydride-grafted polyethylene wax, with its maleic anhydride group and both polar and non-polar groups / segments, serves as an organic / inorganic compatibilizer and coupling agent, providing good asphalt compatibility to the polyethylene wax matrix and promoting better coupling effects of the maleic anhydride group; benzenesulfonic anhydride, with its disulfonic acid group, and sulfobenzoic acid, possessing both sulfonic acid and carboxyl groups, provide a denser three-dimensional network structure during asphalt melting, reducing voids between graphite and the carbonized layer, thereby densifying the carbonized layer.

[0022] As a specific embodiment of the coating asphalt solid phase composition of the present invention, the coating asphalt is a high-temperature coating asphalt with a softening point of 200-285℃, preferably 240-285℃; and a coking value of ≥50%, preferably ≥60%.

[0023] The quinoline insoluble content in the coated asphalt is ≤0.3wt%, and the ash content is ≤0.1wt%, and both the quinoline insoluble content and the ash content are calculated based on the total weight of the coated asphalt as 100%.

[0024] The median particle size D50 of the coated asphalt is 1-8 μm, preferably 2-4 μm.

[0025] In the coating asphalt solid composition provided by the present invention, all components are solid phases. The modifiers therein achieve uniform dispersion and modify the asphalt through melting during the heating and carbonization process and the dripping melting characteristics of the asphalt itself. This can avoid the use of various solvents, reduce processing costs and operation difficulty, and the amount of modifiers added is low, which has little impact on the residual carbon rate of the coating material. Compared with conventional processes, the increase in material costs is small.

[0026] On the other hand, the present invention also provides a method for preparing a modified bitumen-coated natural graphite anode material, wherein the preparation method includes:

[0027] S1: Under the protection of inert gas, natural graphite and the above-mentioned coating asphalt solid phase composition are mixed evenly to obtain a mixture;

[0028] S2: Under the protection of inert gas, the mixture is carbonized to obtain the modified asphalt-coated natural graphite anode material.

[0029] As a specific embodiment of the preparation method described above in this invention, in S1, the natural graphite is spherical graphite with a median particle size D50 of 16-18 μm and a fixed carbon content ≥99.95 wt%, and the fixed carbon content is calculated based on the total weight of the spherical graphite as 100%.

[0030] The tap density of the spherical graphite is ≥0.96 g / cm³. 3 Preferably, it is ≥0.98g / cm³. 3 ;

[0031] The specific surface area of ​​the spherical graphite is ≤6.5cm². 2 / g, preferably ≤6.0cm 2 / g.

[0032] The natural graphite and coated bitumen used in this invention can both be obtained through conventional means in the art, such as commercial purchase or acquisition.

[0033] As a specific embodiment of the preparation method described above in this invention, in S1, the powder temperature is ≤50℃ during the mixing process / the entire mixing process.

[0034] As a specific embodiment of the preparation method described above in this invention, in S1, the mixing process is carried out in a mixer.

[0035] As a specific embodiment of the preparation method described above in this invention, in S2, the carbonization includes heating to 1050-1350°C at a heating rate of 1-10°C / min and holding at that temperature for 1-6 hours.

[0036] In a specific embodiment of the preparation method described above in this invention, in S2, the carbonization is carried out in an atmosphere furnace.

[0037] As a specific embodiment of the preparation method described above in this invention, in S2, after carbonization, the carbonized product is first subjected to natural cooling, and then subjected to operations such as dispersing, sieving and demagnetizing to obtain the modified asphalt-coated natural graphite anode material.

[0038] The preparation method of the modified bitumen-coated natural graphite anode material provided by the present invention has a simple process, no complicated operation steps, and does not involve liquid phase treatment.

[0039] In another aspect, the present invention also provides a modified bitumen-coated natural graphite anode material, wherein the modified bitumen-coated natural graphite anode material is prepared by the above-described method for preparing modified bitumen-coated natural graphite anode material, comprising natural graphite and an amorphous carbon coating layer coated on the surface of the natural graphite.

[0040] In the modified bitumen-coated natural graphite anode material provided by this invention, the amorphous carbon coating layer plays a role in repairing surface defects of natural graphite, reducing specific surface area, isolating the electrolyte from the natural graphite body, and reducing the co-intercalation of lithium ions and electrolyte molecules, thereby significantly improving the electrochemical performance of the natural graphite anode material, such as its first-efficiency performance and long-cycle performance.

[0041] In another aspect, the present invention also provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the modified asphalt-coated natural graphite negative electrode material described above.

[0042] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0043] This invention adds a modifying agent during the preparation of modified bitumen-coated natural graphite anode material. The modifying agent includes saturated long-chain components, low-molecular-weight wax components, and components containing modifying groups. The components in the modifying agent complement each other and work synergistically to reduce the softening point and viscosity of bitumen during carbonization, change the surface tension between bitumen and graphite, enhance the wettability of bitumen to graphite, allow bitumen to penetrate into the pores inside graphite particles, repair cracks on the graphite surface, and improve the uniformity and density of the amorphous carbon coating layer. This effectively improves the electrochemical performance of the anode material, such as the first-cycle coulombic efficiency and long-cycle performance, while reducing the specific surface area and AC impedance of the anode material.

[0044] This invention achieves superior performance of natural graphite anode material products by combining different modifying agents with low addition amounts of coating material (coating asphalt + modifying agents). Furthermore, the preparation process is simple and the products offer high cost-effectiveness. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figures 1a and 1b are scanning electron microscope images of the modified bitumen-coated natural graphite anode material provided in Embodiment 1 of the present invention.

[0047] Figures 1c and 1d are scanning electron microscope images of the modified bitumen-coated natural graphite anode material provided in Embodiment 2 of the present invention.

[0048] Figures 1e and 1f are scanning electron microscope images of the modified bitumen-coated natural graphite anode material provided in Embodiment 3 of the present invention.

[0049] Figure 2 shows the infrared transmission spectra of the modified bitumen-coated natural graphite anode materials provided in Examples 1-3 of this invention.

[0050] Figure 3 is a diagram of the softening process of the coating material (coated asphalt + modified additives) provided in Embodiment 1 and Comparative Examples 1-3 of the present invention.

[0051] Figure 4 shows the wetting contact angles of the coating materials (coated asphalt + modified additives) provided in Embodiment 1 and Comparative Examples 1-3 of the present invention.

[0052] Figure 5 shows the AC impedance spectra of the negative electrode materials provided in Examples 1-3 and Comparative Examples 1-7 of the present invention.

[0053] Figure 6 is a 1C / 1C cycle diagram of the negative electrode materials provided in Examples 1-3 and Comparative Examples 1-7 of the present invention. Detailed Implementation

[0054] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0055] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0056] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0057] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0058] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0059] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying tables, drawings, and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0061] Example 1

[0062] This embodiment provides a modified bitumen-coated natural graphite anode material, which is prepared by a method including the following specific steps:

[0063] S1: Natural graphite, coated asphalt, and modified additives are mixed evenly in a mixer equipped with a cooling water jacket. High-purity nitrogen is introduced for protection throughout the mixing process. The temperature of the material before mixing is 25.5℃ and the temperature after discharge is 26.4℃, which is the result of the mixture.

[0064] The natural graphite mentioned is spherical graphite, a commercially available conventional product, with a median particle size D50 of 16.71 μm, a fixed carbon content of 99.96 wt%, and a tap density of 0.98 g / cm³. 3 The specific surface area is 5.85 cm². 2 / g; The coated asphalt is also a commercially available conventional product, with a measured softening point of 251℃, a coking value of 68.9%, a quinoline insoluble content of 0.17wt%, an ash content of 0.04wt%, and a median particle size D50 of 3.22μm;

[0065] The modifying additives include stearic acid, BASF polyethylene wax, and p-aminobenzenesulfonic acid, with median particle sizes D50 of 7.22 μm, 8.98 μm, and 8.16 μm, respectively; the mass ratio of each raw material is spherical graphite: coated pitch: stearic acid: BASF polyethylene wax: p-aminobenzenesulfonic acid = 1000:48:4.8:1.2:1.2;

[0066] S2: The above mixture is placed in an atmosphere furnace and heated to 1150°C at a heating rate of 5°C / min under the protection of high-purity nitrogen. The mixture is then held at this temperature for 2 hours for carbonization. After carbonization, the resulting product is allowed to cool naturally, and then dispersed, sieved, and demagnetized to obtain the modified asphalt-coated natural graphite anode material.

[0067] Example 2

[0068] This embodiment provides a modified bitumen-coated natural graphite anode material, which is prepared by a method including the following specific steps:

[0069] S1: Natural graphite, coated asphalt, and modified additives are mixed evenly in a mixer equipped with a cooling water jacket. High-purity nitrogen is introduced for protection throughout the mixing process. The temperature of the material before mixing is 25.0℃ and the temperature after discharge is 25.5℃, which is used to measure the temperature of the material.

[0070] The natural graphite is spherical graphite, and the spherical graphite and coated bitumen used are the same as in Example 1; the modifying additives include Sasobit, synthetic Fischer-Tropsch wax, maleic anhydride-grafted polyethylene wax, and benzenesulfonic anhydride, with median particle sizes D50 of 8.50 μm, 6.99 μm, 5.30 μm, and 8.14 μm, respectively; the mass ratio of each raw material is spherical graphite: coated bitumen: Sasobit: synthetic Fischer-Tropsch wax: maleic anhydride-grafted polyethylene wax: benzenesulfonic anhydride = 1000:48:4.8:1.2:1.2:1.2;

[0071] S2: The above mixture is placed in an atmosphere furnace and heated to 1150°C at a heating rate of 5°C / min under the protection of high-purity nitrogen. The mixture is then held at this temperature for 2 hours for carbonization. After carbonization, the resulting product is allowed to cool naturally, and then dispersed, sieved, and demagnetized to obtain the modified asphalt-coated natural graphite anode material.

[0072] Example 3

[0073] This embodiment provides a modified bitumen-coated natural graphite anode material, which is prepared by a method including the following specific steps:

[0074] S1: Natural graphite, coated asphalt, and modified additives are mixed evenly in a mixer equipped with a cooling water jacket. High-purity nitrogen is introduced for protection throughout the mixing process. The temperature of the material before mixing is 23.0℃ and the temperature after discharge is 23.5℃, which is measured by a laser temperature gun to obtain the mixture.

[0075] The natural graphite used is spherical graphite, and the spherical graphite and coated bitumen used are the same as in Example 1. The modifying additives include stearic acid, stearamide, Honeywell wax powder, sulfobenzoic acid, and maleic anhydride-grafted polyethylene wax, with median particle sizes D50 of 7.22 μm, 5.61 μm, 9.75 μm, 8.87 μm, and 5.30 μm, respectively. The mass ratio of each raw material is spherical graphite: coated bitumen: stearic acid: stearamide: Honeywell wax powder: sulfobenzoic acid: maleic anhydride-grafted polyethylene wax = 1000:60:2.4:1.2:1.2:1.2:1.2;

[0076] S2: The above mixture is placed in an atmosphere furnace and heated to 1300°C at a heating rate of 5°C / min under the protection of high-purity nitrogen. The mixture is then held at this temperature for 2 hours for carbonization. After carbonization, the resulting product is allowed to cool naturally, and then dispersed, sieved, and demagnetized to obtain the modified asphalt-coated natural graphite anode material.

[0077] Comparative Example 1

[0078] This comparative example provides an asphalt-coated natural graphite anode material, which differs from Example 1 only in that no modifying additives are added.

[0079] Comparative Example 2

[0080] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that the modifying agent is stearic acid, and the mass ratio of each raw material is spherical graphite:coated bitumen:stearic acid = 1000:48:7.2.

[0081] Comparative Example 3

[0082] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that the modifying agent is p-aminobenzenesulfonic acid, and the mass ratio of each raw material is spherical graphite: coated bitumen: p-aminobenzenesulfonic acid = 1000:48:7.2.

[0083] Comparative Example 4

[0084] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that:

[0085] The modifying agents are stearic acid and p-aminobenzenesulfonic acid, and the mass ratio of each raw material is spherical graphite: coated pitch: stearic acid: p-aminobenzenesulfonic acid = 1000:48:4.8:2.4.

[0086] Comparative Example 5

[0087] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that:

[0088] The modifying agent is stearic acid and BASF polyethylene wax, and the mass ratio of each raw material is spherical graphite: coated pitch: stearic acid: BASF polyethylene wax = 1000:48:4.8:2.4.

[0089] Comparative Example 6

[0090] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that:

[0091] The mass ratio of each raw material is spherical graphite: coated pitch: stearic acid: BASF polyethylene wax: p-aminobenzenesulfonic acid = 1000:48:4.8:6:1.2.

[0092] Comparative Example 7

[0093] This comparative example provides a modified bitumen-coated natural graphite anode material, which differs from Example 1 only in that:

[0094] The mass ratio of each raw material is spherical graphite: coated pitch: stearic acid: BASF polyethylene wax: p-aminobenzenesulfonic acid = 1000:48:4.8:1.2:8.

[0095] Test Example 1

[0096] This test example uses a ZEISS SUPRA55 microscope and performs field emission scanning electron microscopy (SEM) analysis on the modified bitumen-coated natural graphite anode materials provided in Examples 1-3 of this invention under standard testing conditions. The obtained SEM images are shown in Figures 1a-1f. Figures 1a and 1b are SEM images of the modified bitumen-coated natural graphite anode material provided in Example 1 of this invention. Figures 1c and 1d are SEM images of the modified bitumen-coated natural graphite anode material provided in Example 2 of this invention. Figures 1e and 1f are SEM images of the modified bitumen-coated natural graphite anode material provided in Example 3 of this invention.

[0097] As can be seen from Figures 1a-1f, the modified bitumen-coated natural graphite anode material particles provided in Examples 1-3 of the present invention are potato-shaped or roughly circular, and an amorphous carbon coating layer can be observed on their surface and in the gaps between the graphite sheets.

[0098] Test Example 2

[0099] In this test example, the modified bitumen-coated natural graphite anode materials provided in Examples 1-3 of this invention were analyzed by infrared transmission spectroscopy using a Bruker INVENIO-R under standard testing conditions. The obtained infrared transmission spectra are shown in Figure 2. As can be seen from Figure 2, the modified bitumen-coated natural graphite anode materials provided in Examples 1-3 of this invention do not have obvious characteristic peak signals in the fingerprint region, indicating that there are no residual modifying agents after carbonization.

[0100] Test Example 3

[0101] In this test case, the coating materials (coating bitumen + modified additives) provided in Example 1 and Comparative Examples 1-3 were used as the substrate. The softening of the coating materials and their wetting of the graphite were continuously recorded under the conditions of room temperature to 500°C, heating rate of 5°C / min and inert atmosphere. The softening process diagram and wetting contact angle diagram are shown in Figure 3 and Figure 4, respectively.

[0102] As shown in Figure 3, compared with Comparative Example 1 without any modifiers, the softening point temperature of the coating material in Comparative Example 2 decreased by approximately 40°C. This indicates that saturated long-chain components such as stearic acid, as modifiers, can lower the softening point of the coated asphalt, allowing it to enter a state of good wetting with the spherical graphite more quickly. As shown in Figure 4, compared with Comparative Example 1 without any modifiers, the wetting contact angle in Comparative Example 3 under the wetting state significantly decreased from approximately 70° to 18°, and remained at 53° even after further heating and curing. This indicates that components containing modifying groups, such as p-aminobenzenesulfonic acid, as modifiers can significantly improve the wetting performance of the coated asphalt on the graphite groups.

[0103] As can be seen from Figures 3 and 4, compared with Comparative Examples 1-3, in Example 1 of the present invention, by using a compound of saturated long-chain components, low-molecular-weight wax components and components containing modified groups as modifying agents, the softening point can be reduced and the wettability of the coated asphalt can be improved. This prolongs the wetting time of the coated asphalt on the spherical graphite during the heating process, making it easier for the coated asphalt to penetrate into the pores inside the spherical graphite particles and better repair the cracks on the surface of the spherical graphite.

[0104] Test Example 4

[0105] In this test example, Bettersize2600 and Micromeritics TriStar II 3020 were used to test the particle size and specific surface area of ​​the negative electrode materials provided in each embodiment and comparative example under normal test conditions. CHI660E was also used to test the AC impedance spectra of the negative electrode materials provided in each embodiment and comparative example under normal test conditions. The obtained AC impedance spectra are shown in Figure 5, and the obtained particle size and specific surface area data are shown in Table 1 below.

[0106] This test case also tested the electrochemical performance of the negative electrode materials provided in each embodiment and comparative example, including:

[0107] The natural graphite anode materials provided in each embodiment and each comparative example were used as anode active materials. The three materials were mixed evenly according to the mass ratio of anode active material:LA133:SuperP=94:3:3 and then coated on copper foil current collector. After drying, cutting and rolling, anode sheets were obtained for later use.

[0108] The negative electrode sheets obtained above were assembled into 2032 coin cells, and the first charge capacity and first-week coulombic efficiency were tested. The counter electrode was a lithium sheet, the electrolyte solute was LiPF6, and the solvent was a mixture of DEC, DMC and EC in a volume ratio of 1:1:1 with a solute concentration of 1 mol / L. The separator was a commercially available Celgard 2320. The tests were conducted on a battery testing instrument CT300A1U, with a charge and discharge voltage of 0.005-1.5V. The first week was subjected to deep discharge (0.1C-0.01C) and 0.1C charge. The first charge capacity and first-week coulombic efficiency obtained are listed in Table 1 below.

[0109] For the cycling performance of the negative electrode material, the active material:LA133:SuperP was charged and discharged under 1C / 1C conditions according to the mass ratio of active material:LA133:SuperP=90:5:5. The other test conditions were the same as the test process for the first charge capacity and the first cycle coulombic efficiency. The obtained 1C / 1C cycle diagram is shown in Figure 6. The 1C / 1C 500-cycle capacity retention rate results are also listed in Table 1 below.

[0110] Table 1. Comparison of the first-week charging specific capacity, first-cycle efficiency, particle size, and specific surface area of ​​the negative electrode materials provided in Examples 1-3 and Comparative Examples 1-7.

[0111] Note: This invention tests the negative electrode material by fabricating a coin cell. Under normal circumstances, an improvement of 0.2%-0.3% in the first-cycle efficiency is considered effective, and an improvement of more than 0.4% in the first-cycle efficiency is considered significant. An improvement of 3%-5% in the 1C / 1C 500-cycle capacity retention rate is considered effective, and an improvement of more than 5% in the 1C / 1C 500-cycle capacity retention rate is considered significant.

[0112] As can be seen from Table 1 and Figures 5-6, compared with the asphalt-coated natural graphite anode material provided in Comparative Example 1, the specific surface area and AC impedance of the modified asphalt-coated natural graphite anode material prepared by adding only stearic acid as a modifier in Comparative Example 2 are significantly reduced, but the first-time efficiency is basically not improved, and the cycle performance is reduced, with the 1C / 1C 500-cycle capacity retention rate decreasing from 86.1% to 85.4%.

[0113] Compared to the asphalt-coated natural graphite anode material provided in Comparative Example 1, the first efficiency of the modified asphalt-coated natural graphite anode material prepared by Comparative Example 3 after adding only p-aminobenzenesulfonic acid as a modifier increased from 93.45% to 93.66%. Although the first efficiency was improved to a certain extent, the specific surface area and AC impedance also decreased slightly, but the cycle performance deteriorated, and the overall performance could not meet the requirements.

[0114] Compared to the pitch-coated natural graphite anode material provided in Comparative Example 1, the modified pitch-coated natural graphite anode material prepared in Comparative Example 4, which only added stearic acid and p-aminobenzenesulfonic acid as modifying agents, has a lower AC impedance and improved long-cycle performance, and its specific surface area is also reduced to a certain extent. However, the initial efficiency is only improved by 0.15%, and the 1C / 1C 500-cycle capacity retention rate is only improved by 0.6%, and the improvement effect is not significant.

[0115] Compared to the bitumen-coated natural graphite anode material provided in Comparative Example 1, the modified bitumen-coated natural graphite anode material prepared in Comparative Example 5 by adding only stearic acid and BASF polyethylene wax as modifiers has a significantly reduced specific surface area, but its initial efficiency is slightly reduced, and its overall performance also fails to meet the requirements.

[0116] In Examples 1 and 2 of this invention, modified bitumen-coated natural graphite anode materials were prepared by compounding modified additives under the same conditions as Comparative Examples 1-5, where the amount of bitumen used and the firing regime were the same.

[0117] Compared with the anode material provided in Comparative Example 1, the modified pitch-coated natural graphite anode materials provided in Examples 1 and 2 of this invention exhibit balanced electrochemical performance and physical properties, with first-cycle efficiency increased by 0.44% and 0.58% respectively, and 1C / 1C 500-cycle capacity retention increased by 5.6% and 4.1% respectively, with significant improvements. Furthermore, the specific surface area and AC impedance both decreased significantly.

[0118] Compared with the anode material provided in Comparative Example 2, the modified pitch-coated natural graphite anode materials provided in Examples 1 and 2 of this invention exhibit balanced electrochemical performance and physical properties, with first-cycle efficiency increased by 0.41% and 0.55% respectively, and 1C / 1C 500-cycle capacity retention increased by 6.3% and 4.8% respectively, with significant improvements. Furthermore, the specific surface area and AC impedance both decreased significantly.

[0119] Compared with the anode material provided in Comparative Example 3, the modified pitch-coated natural graphite anode materials provided in Examples 1 and 2 of this invention exhibit balanced electrochemical performance and physical properties, with first-cycle efficiency increased by 0.23% and 0.37% respectively, and 1C / 1C 500-cycle capacity retention increased by 7.0% and 5.5% respectively, with significant improvements. Furthermore, the specific surface area and AC impedance both decreased significantly.

[0120] Compared with the anode material provided in Comparative Example 4, the modified pitch-coated natural graphite anode materials provided in Examples 1 and 2 of this invention exhibit balanced electrochemical performance and physical properties, with first-cycle efficiency increased by 0.29% and 0.43% respectively, and 1C / 1C 500-cycle capacity retention increased by 5.0% and 3.5% respectively, with significant improvements. Furthermore, the specific surface area and AC impedance both decreased significantly.

[0121] Compared with the anode material provided in Comparative Example 5, the modified pitch-coated natural graphite anode materials provided in Examples 1 and 2 of this invention exhibit balanced electrochemical performance and physical properties, with first-cycle efficiency increased by 0.48% and 0.62% respectively, and 1C / 1C 500-cycle capacity retention increased by 4.7% and 3.2% respectively, with significant improvements. Furthermore, the specific surface area and AC impedance both decreased.

[0122] Compared to Example 1, Comparative Example 6 increased the amount of low-molecular-weight wax component. As shown in Table 1 and Figures 5-6, the test results indicate that, compared to the modified bitumen-coated natural graphite anode material provided in Example 1, the performance of the anode material provided in Comparative Example 6 significantly decreased. Specifically, the initial efficiency decreased by 0.80%, and the 1C / 1C 500-cycle capacity retention decreased by 9.9%. This indicates that excessive low-molecular-weight wax component severely affected the performance improvement effect of the modifying additives on the anode material.

[0123] Compared to Example 1, Comparative Example 7 increased the amount of components containing modified groups. As shown in Table 1 and Figures 5-6, the test results show that compared to the modified bitumen-coated natural graphite anode material provided in Example 1, the performance of the anode material provided in Comparative Example 7 is significantly reduced. Specifically, the initial efficiency decreased by 0.51%, the 1C / 1C 500-cycle capacity retention decreased by 7.3%, and the AC impedance and specific surface area did not achieve good improvement. This indicates that excessive components containing modified groups are detrimental to the performance improvement of the anode material.

[0124] Furthermore, the softening and wetting results of the coating material shown in Figures 3 and 4 above are sufficient to prove that the components in the compound modified additive used in this invention complement each other and work synergistically, thereby improving the electrochemical performance and physical properties of the negative electrode material by reducing the softening point of the coating asphalt and improving the wettability of the coating asphalt.

[0125] In Example 3 of this invention, by increasing the amount of coating asphalt and the carbonization temperature, and further adapting the modifying additives according to the preparation conditions, a negative electrode material product with better initial efficiency and cycle performance, and lower impedance and specific surface area was obtained. This demonstrates that this invention can produce natural graphite negative electrode materials with different properties, allowing for the selection of negative electrode products with different performance and production costs according to customer customization needs.

[0126] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of the present invention should still fall within the scope of the present invention. Furthermore, the technical features, technical features and technical inventions, and technical inventions in the present invention can be freely combined and used.

Claims

1. A coating bitumen solid composition for forming an amorphous carbon coating layer on the surface of natural graphite, wherein, The coating asphalt solid composition comprises coating asphalt and modifying additives, wherein the mass ratio of natural graphite, coating asphalt and modifying additives is 1000:45-80:3-12; the modifying additives comprise saturated long-chain components, low-molecular-weight wax components and components containing modifying groups in a mass ratio of 2-10:0.5-5:0.5-7. The saturated long-chain component includes one or a combination of stearic acid, stearamide, and Sasobit. The molecular weight of the low molecular weight wax component ranges from 100 to 5000, and the low molecular weight wax component includes one or a combination of several of synthetic Fischer-Tropsch wax, polyethylene wax and Honeywell wax powder. The component containing the modified group includes one or a combination of several of the following: p-aminobenzenesulfonic acid, maleic anhydride-grafted polyethylene wax, benzenesulfonic anhydride, and sulfobenzoic acid.

2. The coating bitumen solid composition according to claim 1, wherein, The modified additive is a powder with a median particle size D50 of 3-20 μm.

3. The coating bitumen solid composition according to claim 1 or 2, wherein, The mass ratio of natural graphite, coated bitumen, and modifying additives is 1000:45-60:4.5-9.

4. The coating bitumen solid composition according to claim 1 or 2, wherein, The softening point of the coated asphalt is 200-285℃, and the coking value is ≥50%. The quinoline insoluble content in the coated asphalt is ≤0.3wt%, and the ash content is ≤0.1wt%. The median particle size D50 of the coated asphalt is 1-8 μm.

5. The coating bitumen solid composition according to claim 4, wherein, The softening point of the coated asphalt is 240-285℃, and the coking value is ≥60%. The quinoline insoluble content in the coated asphalt is ≤0.3wt%, and the ash content is ≤0.1wt%. The median particle size D50 of the coated asphalt is 2-4 μm.

6. The coating bitumen solid composition according to claim 1 or 2, wherein, The mass ratio of the saturated long-chain component, the low-molecular-weight wax component, and the component containing modified groups is 3-8:1-4:1-6.

7. A method for preparing a modified bitumen-coated natural graphite anode material, wherein, The preparation method includes: S1: Under the protection of an inert gas, natural graphite and the coating asphalt solid phase composition according to any one of claims 1-6 are mixed evenly to obtain a mixture; S2: Under the protection of inert gas, the mixture is carbonized to obtain the modified asphalt-coated natural graphite anode material.

8. The preparation method according to claim 7, wherein, In S1, the natural graphite is spherical graphite with a median particle size D50 of 16-18 μm and a fixed carbon content of ≥99.95 wt%. The tap density of the spherical graphite is ≥0.96 g / cm³. 3 ; The specific surface area of ​​the spherical graphite is ≤6.5cm². 2 / g.

9. The preparation method according to claim 8, wherein, In S1, the natural graphite is spherical graphite with a median particle size D50 of 16-18 μm and a fixed carbon content of ≥99.95 wt%. The tap density of the spherical graphite is ≥0.98 g / cm³. 3 ; The specific surface area of ​​the spherical graphite is ≤6.0 cm². 2 / g.

10. The preparation method according to any one of claims 7-9, wherein, In S1, the powder temperature during the mixing process is ≤50℃.

11. The preparation method according to any one of claims 7-9, wherein, In S2, the carbonization includes heating to 1050-1350°C at a heating rate of 1-10°C / min and holding at that temperature for 1-6 hours.

12. A modified bitumen-coated natural graphite anode material, wherein, The modified bitumen-coated natural graphite anode material is prepared by the preparation method of the modified bitumen-coated natural graphite anode material according to any one of claims 7-11, comprising natural graphite and an amorphous carbon coating layer coated on the surface of the natural graphite.

13. A lithium-ion battery, wherein, The negative electrode of the lithium-ion battery comprises the modified bitumen-coated natural graphite negative electrode material as described in claim 12.

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