Graphite negative electrode material and preparation method therefor, negative electrode sheet, and lithium-ion battery

Abstract

A graphite negative electrode material and a preparation method therefor, a negative electrode sheet, and a lithium-ion battery, relating to the technical field of secondary batteries. According to the preparation method for the graphite negative electrode material, a graphite material is coated with amorphous carbon, and carbon coating is carried out in two steps; in a low-temperature mixing process, a graphitized product and a coating agent are uniformly mixed, and in a high-temperature dynamic coating process, in addition to completing further mixing, most of light components are removed by means of high-temperature heat treatment, the coating agent undergoes polycondensation and cross-linking, a surface coating layer with high isotropic degree and good coating effect is formed after carbonization, uncontrollable agglomeration in the subsequent carbonization process is avoided, and the graphite negative electrode material capable of realizing fast charging and considering energy density is prepared.

Description

Graphite negative electrode material and preparation method thereof, negative electrode sheet and lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311870361.7 and invention name “A graphite negative electrode material and its preparation method, negative electrode sheet and lithium-ion battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of secondary batteries, and specifically relates to a graphite negative electrode material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery. Background Art

[0004] In recent years, lithium-ion batteries have captured a significant market share in electric vehicles. With increasing demand for shorter charging times in the consumer electronics and power battery markets, fast-charging technology has become a key trend in lithium-ion battery technology development. As a crucial component of lithium-ion batteries, anode materials significantly impact their performance. Traditional graphite-based anode materials, with their low lithium insertion / deinsertion potential, suitable reversible capacity, abundant resources, and low cost, have consistently dominated the anode market.

[0005] Therefore, the preparation of graphite negative electrode materials with good fast charging performance has become a research hotspot. In the existing technology, graphite materials are coated with coating agents such as asphalt to improve the kinetic and cycle performance of the materials. However, the current coating methods either cause particle agglomeration during the carbonization process after coating, which is manifested as a large increase in Dv50, usually ≥2μm, and the subsequent depolymerization process will destroy the coating layer, resulting in poor coating effect; or volatile gases will escape during the carbonization process, which may damage the equipment furnace and even pose safety risks. There are also technologies in the existing technology that use particle size distribution control to improve fast charging performance, but the particle size distribution needs to be controlled within a very narrow range, which is difficult to achieve in actual operation, or the yield is very low and not practical.

[0006] Summary of the Invention

[0007] Therefore, the technical problem to be solved by this application is to overcome the above-mentioned problems existing in the prior art in improving the fast charging performance of graphite negative electrode materials, thereby providing a graphite negative electrode material and its preparation method, a negative electrode plate and a lithium-ion battery.

[0008] To this end, this application provides the following technical solutions:

[0009] The present application provides a method for preparing a graphite negative electrode material, characterized in that it comprises the following steps:

[0010] S1, mixing graphite and a coating agent to obtain a mixed material, wherein the mixing temperature is 30-200° C.;

[0011] S2, coating the mixed material at a temperature of 200-800° C. to obtain a coated material;

[0012] S3, carbonizing the coated material to obtain a graphite negative electrode material.

[0013] Optionally, the particle sizes of the graphite negative electrode material in step S3 and the coating material in step S2 satisfy the following relationship: D1-D2≤1.5μm; wherein D1 is the D V 50, D2 is the D of the coating material V 50.

[0014] In the present application, when the particle size of the graphite negative electrode material in step S3 and the coating material in step S2 satisfies the relationship D1-D2≤1.5μm, it indicates that the degree of agglomeration of the negative electrode material in the carbonization process is low, and no subsequent deep depolymerization is required, which effectively improves the problem of deterioration of the fast charging performance of the graphite negative electrode material caused by the destruction of the carbon coating layer due to subsequent deep depolymerization.

[0015] Optionally, the graphite in step S1 is one or more of artificial graphite, natural graphite or recycled graphite;

[0016] In this application, artificial graphite is a man-made graphite-like substance, generally including single artificial graphite particles and secondary artificial graphite particles. Natural graphite is naturally occurring graphite, generally occurring as ores such as graphite schist, graphite gneiss, graphite-containing schist, and metamorphic shale. Recycled graphite is derived from waste residues, waste liquids, and waste gases generated during the production of natural and artificial graphite, as well as from recycled waste batteries.

[0017] Optionally, the graphite is artificial graphite secondary particles;

[0018] Optionally, the method for preparing the secondary graphite particles comprises the steps of: crushing the coke-like material, mixing the crushed coke-like material with a binder, granulating, and finally graphitizing;

[0019] In the present application, there is no special requirement for the pulverization equipment. For example, an impact mill or a ring roller mill can be used for pulverization.

[0020] In the present application, there is no special requirement for the granulation equipment. For example, intermittent vertical, intermittent horizontal or continuous horizontal granulation equipment can be used for granulation.

[0021] In the present application, there is no special requirement for the graphitization equipment. For example, graphitization can be carried out in a crucible graphitization furnace, a box graphitization furnace, or an inner string graphitization furnace.

[0022] And / or, the coke-like material includes at least one of petroleum coke, pitch coke, and needle coke;

[0023] and / or, the sulfur content of the coke-like material is 0.2-5wt%;

[0024] Optionally, when the coke material is petroleum coke, its sulfur content is 0.5-5wt%;

[0025] Optionally, when the coke-like material is needle coke, its sulfur content is 0.2-2 wt%.

[0026] In the present application, the raw material is preferably petroleum coke or needle coke with a specific sulfur content. Since the raw material has a high degree of isotropy and the porosity of the material after graphitization is high, the transmission path of lithium ions can be shortened during the charge and discharge process, which is beneficial to the improvement of the fast charging performance of the graphite negative electrode material.

[0027] And / or, the binder is at least one of organic compounds such as petroleum asphalt, coal tar, phenolic resin, epoxy resin, starch, etc., and the amount of the binder accounts for 2-20% of the total mass of the raw materials;

[0028] and / or, the granulation temperature is 300-650° C., and the granulation time is 4-12 h;

[0029] And / or, the graphitization temperature is 2500-3500° C., and the graphitization power transmission time is 5-60 hours;

[0030] And / or, the D of the pulverized coke material v 50 is 4-10μm; (D v 90-D v 10) / D v 50=1.0-1.5;

[0031] And / or, D of the granulated material v 50 is 8-18μm; (D v 90-D v 10) / D v 50=1.0-1.4;

[0032] And / or, the graphitization degree of the graphitized material is 90%-95%.

[0033] Optionally, the coating agent in step S1 is a coal-based liquid-phase coating agent or a petroleum-based liquid-phase coating agent;

[0034] Optionally, the coating agent has a dynamic viscosity of 20-1000 mPa·s at 60°C.

[0035] Optionally, the coal-based liquid coating agent is a coal chemical liquid by-product with different distillation ranges and different residual carbon values, including at least one of coal tar, phenol oil, naphthalene oil, wash oil, and anthracene oil;

[0036] Optionally, the petroleum-based liquid coating agent is a petrochemical liquid by-product with different distillation ranges and different residual carbon values, including at least one of residual oil, slurry oil, heavy oil, and liquid asphalt.

[0037] And / or, in step S1, the amount of coating agent added is calculated based on the mass of the coated carbon residue, and the amount of liquid coating agent added accounts for 0.1-3% of the total mass of the coating carbon residue and the graphitized product.

[0038] In this application, the particle size of the raw materials and the granulated materials, especially the particle size distribution, is controlled within a specific range, which is conducive to achieving a balance between fast charging performance and energy density. Compared with the existing method of simply controlling the particle size distribution, the particle size distribution of this application is wider and has more practical application value.

[0039] In this application, the calculation formula for the proportion of coated residual carbon is: coking mass of coating agent / (coking mass of coating agent + mass of graphite) × 100%, coking mass of coating agent = coking value of coating agent × mass of coating agent.

[0040] and / or, in step S1, the mixing time of the graphite and the coating agent is 0.1-12 hours;

[0041] Optionally, in step S2, the coating is performed under stirring or rotating conditions;

[0042] Optionally, the stirring or rotating speed is 5-500 rpm and the time is 1-12 h.

[0043] Optionally, the coating material in step S2 includes at least one of the following (a) to (e):

[0044] (a) the oxygen content of the coating material is 100-10000 ppm;

[0045] (b) The true density of the coating material is 1.80-2.26 g / cm 3 ;

[0046] (c) the residual volatile matter of the coating material is 0.5% to 3%;

[0047] (d) Particle size D of the coating material v 50 is 7-16μm;

[0048] (e) the coating material (D v90-D v 10) / D v 50 is 0.9-1.3.

[0049] In this application, the oxygen content of the coating material is controlled within the range of 100-10000ppm, which is conducive to the formation of a highly disordered carbon layer structure after carbonization, thereby improving the fast charging performance of the graphite negative electrode material. However, when the oxygen content is too high, the coating material will also have more structural defects after carbonization, and more defects will lead to a low first efficiency of the graphite negative electrode and deterioration of the cycle performance. When the oxygen content is too low, it is not conducive to the formation of a highly disordered carbon layer structure, which is not conducive to the improvement of the fast charging performance of the graphite negative electrode.

[0050] In this application, (Dv90-Dv10) / Dv50 (i.e., particle size distribution) reflects the degree to which the particle sizes of larger and smaller particles in the graphite anode material deviate from the volume average particle size (i.e., Dv50). Controlling the (Dv90-Dv10) / Dv50 ratio of the coating material within the range of 0.9-1.3 is beneficial for increasing the porosity of the electrode sheet and, in turn, improving the fast-charging performance of the graphite anode material.

[0051] Optionally, the carbonization temperature in step S3 is 1000-1500° C., and the carbonization time is 2-24 hours.

[0052] In the present application, there is no special requirement for the carbonization equipment. For example, the carbonization can be carried out in a push plate kiln, a roller kiln, a tunnel kiln or a rotary kiln.

[0053] The present application provides a graphite negative electrode material, whose Raman Id / Ig is 0.1-0.4; (D v 90-D v 10) / D v 50 is 0.9-1.3;

[0054] Optionally, the oxygen content of the graphite negative electrode material is 100-5000ppm; D v 50 is 12-16μm.

[0055] In this application, Id / Ig is the characteristic peak of Raman spectrum at 1300cm -1 The D peak and characteristic peak near 1580cm -1 The ratio of the G peak intensities near

[0056] The present application also provides a negative electrode plate, comprising the above-mentioned graphite negative electrode material or the graphite negative electrode material prepared by the above-mentioned preparation method.

[0057] The present application also provides a lithium-ion battery comprising the above-mentioned negative electrode plate.

[0058] In this application, the lithium-ion secondary battery system, when used with nickel-cobalt-manganese ternary materials, lithium iron phosphate materials, and lithium cobalt oxide materials, has a fast charging capability of 3C-6C charging rate without lithium deposition.

[0059] In the present application, the preparation method of the negative electrode sheet is conventional in the field. Typically, but not limitatively, the preparation method of the negative electrode sheet includes fully stirring and mixing the above-prepared graphite negative electrode material, negative electrode conductive agent, and negative electrode binder to form a uniform negative electrode slurry; coating the negative electrode slurry on the surface of the negative electrode collector, and obtaining the negative electrode sheet after drying and cold pressing.

[0060] The negative electrode conductive agent may be a conductive material commonly used in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, the negative electrode conductive agent may be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), graphene, and composite conductive agents thereof.

[0061] The negative electrode binder can be a binder commonly used in the art, and can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0062] Other additives may be added to the above process for preparing the negative electrode sheet, such as a thickener, such as sodium carboxymethyl cellulose (CMC-Na), etc. The weight ratio of the other additives in the negative electrode active layer is 0 to 15 wt % based on the total weight of the negative electrode active layer.

[0063] The current collector in the negative electrode plate can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0064] The composition and preparation method of the lithium-ion battery include: a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are all selected by conventional technology, and the preparation method thereof is also conventional technical means.

[0065] The preparation method of the positive electrode sheet in the lithium-ion battery comprises fully stirring and mixing the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in an appropriate amount of solvent to form a uniform positive electrode slurry; coating the positive electrode slurry on the surface of the positive electrode current collector aluminum foil, and obtaining the positive electrode sheet after drying and cold pressing.

[0066] The positive electrode active material may include layered lithium cobalt oxide LiCoO2 material (LCO), spinel lithium manganese oxide LiMn2O4 material (LMO), olivine lithium iron phosphate LiFePO4 material (LFP), olivine lithium manganese iron phosphate LiMn 0.8 Fe 0.2 PO4 material (LMFP), layered ternary material LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 material (NMC333), layered ternary material LiNi 0.4 Mn 0.4 Co 0.2 O2(NMC442),LiNi 0.5 Mn 0.4 Co 0.2 O2(NMC532),LiNi 0.6 Mn 0.4 Co 0.2 O2(NMC622),LiNi 0.7 Mn 0.4 Co 0.2 O2(NMC721), LiNi 0.8 Mn 0.4 Co 0.2 O2(NMC811) and layered high nickel material LiNi 0.8 Co 0.15 Al 0.05 O2(NCA), etc.

[0067] The positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0068] The positive electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0069] The technical solution of this application has the following advantages:

[0070] The preparation method of the graphite negative electrode material provided in this application uses amorphous carbon to coat the graphite material. The carbon coating is carried out in two steps. The low-temperature mixing process uniformly mixes the graphitized product and the coating agent. In the high-temperature dynamic coating process, in addition to further mixing, the high-temperature heat treatment removes most of the lightweight components, and the coating agent completes polycondensation and cross-linking. After carbonization, it is conducive to forming a surface coating layer with a high degree of isotropy and good coating effect, avoiding uncontrollable agglomeration in the subsequent carbonization process. A graphite negative electrode material that can achieve both fast charging and energy density is prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0072] FIG1 is a flow chart of the preparation process of the graphite negative electrode material in Example 1 of the present application;

[0073] FIG2 is a SEM electron microscope image of the graphite negative electrode material provided in Example 1 of the present application. DETAILED DESCRIPTION

[0074] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0075] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0076] Example 1

[0077] This embodiment provides a graphite negative electrode material, the preparation process flow chart of which is shown in FIG1 , and the preparation method and specific operating parameters are as follows:

[0078] S1, mixing 85% by mass of graphite with 15% by mass of a petroleum-based liquid coating agent having a dynamic viscosity of 100 mPa·s at 60° C. (coking value of 10.3%) to obtain a mixed material, the mixing temperature being 50° C. and the mixing time being 6 h;

[0079] S2, dynamically coating the mixed material at a temperature of 600°C, with a stirring speed of 80 rpm and a stirring time of 6 h to obtain a coated material;

[0080] S3, carbonizing the coated material at a temperature of 1200° C. for 12 h to obtain a graphite negative electrode material. FIG2 is a SEM image of the obtained product.

[0081] Among them, the preparation steps of graphite are: crushing needle coke with a sulfur content of 0.6% to a Dv50 of 7μm, (Dv90-Dv10) / Dv50=1.15, then mixing the crushed coke particles with 10% asphalt, granulating at a temperature of 600°C, the granulation time is 8h, the Dv50 of the granulated material is 13.4μm, (Dv90-Dv10) / Dv50=1.12, and finally graphitizing at a temperature of 3000°C, and the graphitization power supply time is 48h.

[0082] Example 2

[0083] This embodiment provides a graphite negative electrode material, and its preparation method and specific operating parameters are as follows:

[0084] S1, mixing 95% by mass of graphite with 5% by mass of a petroleum-based liquid coating agent having a dynamic viscosity of 20 mPa·s at 60° C. and a coking value of 6.4% to obtain a mixed material, the mixing temperature being 30° C. and the mixing time being 6 h;

[0085] S2, dynamically coating the mixed material at a temperature of 200°C, with a stirring speed of 300 rpm and a stirring time of 6 h to obtain a coated material;

[0086] S3, carbonizing the coated material at a temperature of 1200° C. for 12 hours to obtain a graphite negative electrode material.

[0087] The preparation steps of graphite are as follows: crushing green coke with a sulfur content of 0.3% to a Dv50 of 10 μm, (Dv90-Dv10) / Dv50=1.13, then mixing the crushed green coke particles with 5% asphalt, and granulating at a temperature of 600°C for 8 hours. The Dv50 of the granulated material is 13.2 μm, (Dv90-Dv10) / Dv50=1.13. v 90-D v 10) / D v 50=1.10, and finally graphitized at a temperature of 3000°C, and the graphitization power supply time is 48h.

[0088] Example 3

[0089] This embodiment provides a graphite negative electrode material, and its preparation method and specific operating parameters are as follows:

[0090] S1, mixing 80% by mass of graphite with 20% by mass of a petroleum-based liquid coating agent having a dynamic viscosity of 1000 mPa·s at 60°C (coking value of 12.0%) to obtain a mixed material, the mixing temperature being 200°C and the mixing time being 10 hours;

[0091] S2, dynamically coating the mixed material at a temperature of 800°C, with a stirring speed of 100 rpm and a stirring time of 6 h to obtain a coated material;

[0092] S3, carbonizing the coated material at a temperature of 1200° C. for 12 hours to obtain a graphite negative electrode material.

[0093] Among them, the preparation steps of graphite are: crushing needle coke with a sulfur content of 1.8% to a Dv50 of 6μm, (Dv90-Dv10) / Dv50=1.22, then mixing the crushed coke particles with 10% asphalt, granulating at a temperature of 600°C, the granulation time is 8h, the Dv50 of the granulated material is 12.6μm, (Dv90-Dv10) / Dv50=1.1, and finally graphitizing at a temperature of 3000°C, and the graphitization power supply time is 48h.

[0094] Example 4

[0095] This embodiment provides a graphite negative electrode material, and its preparation method and specific operating parameters are as follows:

[0096] S1, mixing 90% by mass of graphite with 10% by mass of tar having a dynamic viscosity of 500 mPa·s at 60° C. (coking value of 15.2%) to obtain a mixed material, the mixing temperature being 100° C. and the mixing time being 8 h;

[0097] S2, dynamically coating the mixed material at a temperature of 500°C, a stirring speed of 300 rpm, and a stirring time of 6 h to obtain a coated material;

[0098] S3, carbonizing the coated material at a temperature of 1200° C. for 12 hours to obtain a graphite negative electrode material.

[0099] The preparation steps of graphite are as follows: crushing green coke with a sulfur content of 1% to a Dv50 of 8 μm, (Dv90-Dv10) / Dv50=1.14, then mixing the crushed green coke particles with 5% asphalt, and granulating at a temperature of 500°C for 8 hours. The Dv50 of the granulated material is -11.8 μm, (D v 90-D v 10) / D v50=1.11, and finally graphitized at a temperature of 3200°C, and the graphitization power supply time is 60h.

[0100] Example 5

[0101] This embodiment provides a graphite negative electrode material. Compared with Example 1, the difference is that the needle coke with a sulfur content of 0.6% in the preparation process of graphite is replaced by petroleum coke with a sulfur content of 2.5%.

[0102] The preparation steps of graphite are as follows: crushing petroleum coke with a sulfur content of 2.5% to a Dv50 of 7 μm, (D v 90-D v 10) / D v 50=1.21, then the crushed coke particles are mixed with 10% asphalt and granulated at a temperature of 600℃ for 8 hours. The D v 50 is 13.1μm, (D v 90-D v 10) / D v 50=1.16 Finally, graphitization is carried out at a temperature of 3000°C, and the graphitization power supply time is 48h.

[0103] Comparative Example 1

[0104] This comparative example provides a graphite negative electrode material, which differs from Example 1 in that the coating step S2 is not performed.

[0105] Comparative Example 2

[0106] This comparative example provides a graphite negative electrode material. Compared with Example 1, the difference is that the processing step of step S1 is not performed, and the high-temperature dynamic coating step is directly performed after the materials are mixed.

[0107] Comparative Example 3

[0108] This comparative example provides a graphite negative electrode material. Compared with Example 2, the difference is that the mixing temperature in step S1 is 20°C, and the coating temperature in step S2 is 150°C.

[0109] Test Case

[0110] The specific testing methods for the performance of the intermediate materials and final products obtained in the following examples and comparative examples are as follows:

[0111] The test method for graphitization degree is as follows: Graphitization degree is an indicator to measure the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure. XRD is used to test the 004 interplanar spacing d 004 , calculated according to the following formula: graphitization degree = (3.440-d 004×2) / (3.440-3.354)×100%.

[0112] The oxygen content can be tested using methods known in the art, such as Chongqing Yanrui / RO-330 oxygen analyzer.

[0113] The sulfur content can be tested using methods known in the art, such as a sulfur analyzer for sulfur and oxygen content testing.

[0114] The test method for the coking value of the coating agent is as follows: the coking value can be tested using methods known in the art, with reference to "GB / T 8727-2008 Determination of the coking value of coal tar pitch products".

[0115] The test method for dynamic viscosity is: it can be tested by methods known in the art, with reference to "GB / T 265-1988 Petroleum Products Kinematic Viscosity Determination and Dynamic Viscosity Calculation Method Reference".

[0116] The true density test method involves weighing a sample (1g to 5g) and placing it in a true density tester. The test system is sealed, and helium or nitrogen is introduced according to the procedure. The pressure of the gas in the sample chamber and expansion chamber is measured, and the true volume, and thus the true density, is calculated using the ideal gas law (PV = nRT).

[0117] The test method for particle size is: In this application, D v 50 represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%; D v 90 represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 90%; D v 10 represents the particle size corresponding to a 10% cumulative volume distribution percentage of the material; this can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0118] The test method for residual volatile matter is: heat in an airtight container under specified conditions, and the mass loss after moisture correction is the volatile matter. This test is based on the "SHT0026-1990 - Petroleum Coke Volatile Matter Determination Method."

[0119] The test method of Id / Ig is as follows: the graphite negative electrode material is measured by Raman spectroscopy at 1340 cm -1 to 1380cm -1 The peak intensity Id and at 1560 cm -1 to 1600cm-1 Id / Ig is the calculated ratio of the D peak intensity Id to the G peak intensity Ig.

[0120] The electrical properties of the graphite negative electrode materials obtained in each embodiment and comparative example were tested, and the specific testing methods are as follows:

[0121] Preparation method of lithium-ion battery (button battery): The preparation method of button lithium-ion battery can be tested by methods known in the art. The graphite negative electrode material, conductive agent (Super P), binder (SBR), and thickener (CMC-Na) prepared above are fully stirred and mixed in an appropriate amount of deionized water at a mass ratio of 96.2:0.8:1.8:1.2 to form a uniform negative electrode slurry, and then the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained. The coating thickness of the negative electrode sheet is 200μm. Using the above-mentioned negative electrode sheet, the lithium sheet is used as the counter electrode, the polyethylene (PE) film is used as the separator, and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) with a volume ratio of 1:1:1 is used as the electrolyte to assemble a button lithium-ion battery.

[0122] Preparation method of lithium-ion battery (soft pack full battery): Lithium nickel cobalt manganese oxide LiNi 0.5 Mn 0.3 Co 0.2 O2 (NMC532) material, conductive agent (Super P), and binder (PVDF) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 to form a uniform positive electrode slurry. The positive electrode slurry is then coated on the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained. The coating surface density of the positive electrode sheet is 18.0 mg / cm 2 The graphite negative electrode material of the above embodiment and comparative example, the conductive agent (Super P), the binder (SBR), and the thickener (CMC-Na) were fully stirred and mixed in an appropriate amount of deionized water at a mass ratio of 95.5:1.0:2.0:1.5 to form a uniform negative electrode slurry. The negative electrode slurry was coated on the surface of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating surface density of the negative electrode sheet was 9.0 mg / cm 2 A soft-pack lithium-ion full battery was assembled using the above-mentioned negative electrode sheet, positive electrode sheet, polyethylene (PE) film as a separator, and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 as an electrolyte.

[0123] Reversible specific capacity test method: Place the button cell in a constant temperature chamber of a 25°C blue electric test cabinet (T-3002A-5V 1mA) and let it rest for 6 hours. Discharge the button cell at 0.1C to 1.0mV, let it rest for 10 minutes, discharge it at 0.01C to 1.0mV, and then charge it at 0.05C to 1.5V. Record the capacity of the button cell at this time and record it as the reversible specific capacity.

[0124] The first cycle efficiency test method is as follows: Place the button cell in a 25°C blue electric test cabinet (T-3002A-5V 1mA) constant temperature box and let it rest for 6 hours. Discharge the button cell at 0.1C to 1.0mV, let it rest for 10 minutes, and then discharge it at 0.01C to 1.0mV, and record the discharge capacity D. Charge it at 0.05C to 1.5V, and record the charge capacity of the button cell at this time, which is recorded as the specific capacity C.

[0125] The first-cycle efficiency is calculated by the following formula: first-cycle efficiency (%) = C / D × 100%.

[0126] Charging Window: The batteries of the above-mentioned embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the batteries were charged at a constant current rate of 1C to a voltage of 4.4V, then charged at a constant voltage to a current of ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.5V. The actual capacity was recorded as C0. The battery is then charged with a constant current of 1.0C0, 2.0C0, 3.0C0, 4C0, 5C0, and 6C0 in sequence to a full battery charge cut-off voltage of 4.4V or a negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is discharged with 1C0 to a full battery discharge cut-off voltage of 2.5V. The state of charge (SOC) at different charge rates is recorded. When the battery is charged to 100% SOC (State of Charge, when "SOC=0" indicates that the battery is fully discharged, when "SOC=100%" indicates that the battery is fully charged), the rate range in which lithium plating does not occur on the negative electrode sheet is the fast charge window.

[0127] Cycling performance test: The soft pack full battery is placed in a constant temperature box of a Xinwei test cabinet (BTS-5V6A) at 25℃. The battery is left to stand for 1 hour, and then charged to 4.3V at a constant current of 1C. Then, it is charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged to 2.8V at a constant current of 1C. The initial capacity is recorded as C0. Then, the charge and discharge cycle is carried out according to the above process, and the discharge capacity C of each cycle is recorded. n , until the cycle capacity retention rate (C n / C0×100%) is 80%, and the number of cycles is recorded.

[0128] The specific test results are shown in the table below:

[0129] Table 1

[0130] Table 2

[0131] From the data of Examples 1-5 and Comparative Examples 1-3 in the above table, it can be seen that when the reversible specific capacity and the first coulombic efficiency are comparable, the charging window and cycle life of the examples are generally better than those of the comparative examples, indicating that the graphite negative electrode material obtained by the preparation method of the present application can achieve both improved fast charging performance and balanced capacity. From the data of Example 2 and Comparative Example 3, it can be seen that if the coating temperature is too low, the D1-D2 of the material will be too large, which is not conducive to improving the fast charging performance and cycle performance.

[0132] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A preparation method of a graphite anode material, characterized in that, It includes the following steps: S1. Mix graphite with a coating agent to obtain a mixed material, and the mixing temperature is 30 - 200 °C; S2. Coating the mixed material at a temperature of 200 - 800 °C to obtain a coated material; S3. Carbonize the coated material to obtain a graphite anode material.

2. The preparation method of the graphite anode material according to claim 1, wherein, In step S3, the particle sizes of the graphite anode material and the coating material in step S2 satisfy the following relational expression: D1 - D2 ≤ 1.5 μm; where D1 is the D V 50 of the graphite anode material, and D2 is the D V 50 of the coating material.

3. The preparation method of the graphite anode material according to claim 1 or 2, characterized in that, The graphite is one or more of artificial graphite, natural graphite or recycled graphite; Preferably, the graphite is artificial graphite secondary particles; Preferably, the preparation method of the artificial graphite secondary particles includes: crushing coke substances, then mixing the crushed coke substances with a binder, granulating, and finally graphitizing; Preferably, the sulfur content of the coke-like substance is 0.2-5 wt%; the D v 50 of the pulverized coke-like substance is 4-10 μm; (D v 90 - D v 10) / D v 50 = 1.0 - 1.5; Preferably, the D of the material after granulation v 50 is 8 - 18 μm; Preferably, (D v 90 - D v 10) / D v 50 = 1.0 - 1.

4.

4. The preparation method of the graphite anode material according to claim 3, wherein, In step S2, the coating is carried out under a stirring or rotating state; Optionally, the rotation speed of stirring or rotating is 5 - 500 rpm, Optionally, the stirring or rotating time is 1 - 12 h.

5. The preparation method of the graphite negative electrode material according to claim 3, characterized in that, Meet at least one of the following (1) - (10): (1) The coating agent is a coal-based liquid coating agent or a petroleum-based liquid coating agent; Optionally, the coal-based liquid coating agent is a coal chemical liquid by-product with different distillation ranges and different residual carbon values, including at least one of coal tar, phenol oil, naphthalene oil, wash oil, anthracene oil; Optionally, the petroleum-based liquid coating agent is a petrochemical liquid by-product with different distillation ranges and different residual carbon values, including at least one of residue oil, slurry oil, heavy oil, liquid asphalt; (2) The dynamic viscosity of the coating agent at 60 °C is 20 - 1000 mPa·s; (3) The addition amount of the coating agent is calculated by the mass of the coating residual carbon, and the addition amount of the liquid coating agent accounts for 0.1 - 3% of the total mass of the coating residual carbon and the graphitized product; (4) The mixing time of graphite and the coating agent is 0.1 - 12 h; (5) The coke substances include at least one of petroleum coke, pitch coke, needle coke; (6) The binder is at least one of petroleum asphalt, coal asphalt, phenolic resin, epoxy resin, starch; (7) The dosage of the binder accounts for 2 - 20% of the total mass of the raw materials; (8) The granulation temperature is 300 - 650 °C; the heating time is 4 - 12 h; (9) The graphitization temperature is 2500 - 3500 °C; the graphitization power-on time is 5 - 60 h; (10) The graphitization degree of the material after graphitization is 90% - 95%.

6. The preparation method of the graphite anode material according to any one of claims 1 or 5, characterized in that, In step S2, the coated material meets at least one of the following (a) - (e): (a) The oxygen content of the coated material is 100 - 10000 ppm; (b) The true density of the coating material is 1.80 - 2.26 g / cm 3 ; (c) The residual volatile matter of the coated material is 0.5% - 3%; (d) The particle size D of the coating material v is 7 - 16 μm for 50; (e) The (D of the coated material v 90 - D v (10) / D v 50 is 0.9 - 1.

3.

7. The preparation method of the graphite anode material according to claim 1, characterized in that, In step S3, the carbonization temperature is 1000 - 1500 °C; the carbonization time is 2 - 24 h.

8. A graphite anode material, characterized in that, The Id / Ig of the graphite anode material is 0.1 - 0.4; (D v 90 - D v (10) / D v 50 is 0.9 - 1.

3.

9. The graphite negative electrode material according to claim 8, characterized in that The oxygen content of the graphite anode material is 100 - 5000 ppm; D v The 50 is 12 - 16 μm.

10. A negative electrode plate, characterized in that, It includes the graphite anode material described in claim 8.

11. A lithium-ion battery, characterized in that, It includes the negative electrode plate described in claim 10.

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