Artificial graphite secondary particles and preparation method and application thereof

Abstract

The present application relates to an artificial graphite secondary particle and a preparation method and application thereof. The preparation method of the artificial graphite secondary particle comprises: crushing and screening artificial graphite to prepare primary particles; mixing and granulating the primary particles and a binder to prepare artificial graphite secondary particles; wherein the binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, lithium silicate, lithium phosphate and lithium carbonate solution; the particle size D10 of the artificial graphite secondary particle is 4 μm to 7 μm; the particle size D50 of the artificial graphite secondary particle is 12 μm to 16 μm; the particle size D90 of the artificial graphite secondary particle is 25 μm to 35 μm. The artificial graphite secondary particles prepared by the preparation method have good size uniformity and density.

Description

Technical Field

[0001] The present application relates to the technical field of artificial graphite negative electrode materials, and in particular to an artificial graphite secondary particle and a preparation method and application thereof. Background Art

[0002] Artificial graphite materials are divided into primary particles and secondary particles according to their different application fields and usage requirements, according to their structural differences. Secondary particles have the advantages of high compaction density, high capacity, and good cycle performance, and are especially suitable for negative electrode materials for lithium-ion batteries.

[0003] In the preparation of traditional artificial graphite secondary particles, usually the carbon source is first granulated into secondary particles, and then graphitized to obtain artificial graphite secondary particles. The size uniformity and density of the artificial graphite secondary particles prepared in this way are poor. Summary of the invention

[0004] Based on this, it is necessary to provide an artificial graphite secondary particle with good size uniformity and density, and a preparation method and application thereof.

[0005] In one aspect of the present application, a method for preparing artificial graphite secondary particles is provided, comprising the following steps:

[0006] The artificial graphite is crushed and sieved to prepare primary particles;

[0007] Mixing the primary particles and the binder to form granules to prepare the artificial graphite secondary particles;

[0008] Wherein, the binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, lithium silicate, lithium phosphate and lithium carbonate solution;

[0009] The particle size D10 of the artificial graphite secondary particles is 4 μm to 7 μm; the particle size D50 of the artificial graphite secondary particles is 12 μm to 16 μm; and the particle size D90 of the artificial graphite secondary particles is 25 μm to 35 μm.

[0010] In some embodiments, the mixing and granulation is performed using a spray dryer or a granulator; the mixing and granulation satisfies at least one of the conditions (1) to (4):

[0011] (1) The mixing and granulation time is 10s to 10min;

[0012] (2) During the mixing and granulation process, the relative humidity is 5% to 50%;

[0013] (3) The rotation speed of the spray dryer or the granulator is 10 rpm to 100 rpm;

[0014] (4) The pressure in the spray dryer or the granulator is 100 bar to 1000 bar.

[0015] In some embodiments, the average particle size of the primary particles is 1 μm to 20 μm.

[0016] In some embodiments, the method for preparing artificial graphite comprises the following steps:

[0017] crushing and sieving the carbon source to prepare powder;

[0018] Mixing the powder, adhesive and additive to prepare a mixture;

[0019] Sintering the mixture at a temperature of ≥2000° C. and cooling to prepare artificial graphite;

[0020] Wherein, the carbon source includes at least one of coal tar, petroleum coke and natural graphite; the adhesive includes at least one of phenolic resin, polyvinyl alcohol, acrylate and silica sol;

[0021] The additive includes at least one of a sintering aid, an antioxidant and a pore control agent;

[0022] The sintering aid includes at least one of metal powder and boron powder;

[0023] The antioxidant includes at least one of boron nitride and silicate.

[0024] In some embodiments, the sintering step further comprises:

[0025] Spraying a coating material on the surface of the mixture; the coating material comprises at least one of a metal organic compound, an organosilicon compound, a fluorinated compound, a carbon-based material, a porous material, and a polymer;

[0026] The metal organic compound includes at least one of titanate and zirconate;

[0027] The organosilicon compound includes at least one of silicone oil, methylsiloxane and silane;

[0028] The fluorinated compound includes at least one of hexafluoroacrylate and carbon fluoride;

[0029] The carbon-based material includes at least one of carbon nanotubes and carbon black;

[0030] The porous material includes at least one of molecular sieve and activated carbon;

[0031] The polymer includes at least one of polyethylene, polypropylene, polyester and polyurethane.

[0032] In some embodiments, the cooling step comprises:

[0033] Passing a protective gas to cool the artificial graphite to 800° C. at a first rate;

[0034] Using a condensation system to cool the artificial graphite to 800° C., so that the artificial graphite is cooled to ≤40° C. at a second rate;

[0035] Wherein, the first rate is 80-120°C / min; the second rate is 10-50°C / min.

[0036] In some of the embodiments, the method further comprises: modifying the surface of the artificial graphite secondary particles.

[0037] In a second aspect, the present application also provides an artificial graphite secondary particle, which is prepared according to the above-mentioned method for preparing the artificial graphite secondary particle.

[0038] In a third aspect, the present application also provides a negative electrode material, comprising the above-mentioned artificial graphite secondary particles.

[0039] In a fourth aspect, the present application also provides a negative electrode sheet, comprising the above-mentioned artificial graphite secondary particles or the above-mentioned negative electrode material.

[0040] The preparation method of the embodiment of the present application is different from the traditional process of first secondary granulation and then graphitization to generate artificial graphite. The primary particles of artificial graphite are first prepared and then mixed with a binder to granulate to prepare secondary particles. The obtained artificial graphite secondary particles have good size uniformity and density.

[0041] The artificial graphite secondary particles prepared according to the preparation method are used to prepare lithium-ion batteries and have good cycle stability, safety performance and high-temperature cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a scanning electron microscope photograph of artificial graphite secondary particles prepared in one embodiment of the present application;

[0043] Figure 2 This is a scanning electron microscope photograph of artificial graphite secondary particles prepared in one embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0045] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0046] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0047] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 800-850nm means that the units of the left endpoint "800" and the right endpoint "850" are both nm (nanometers).

[0048] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be used as a lower limit or upper limit, combined with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0049] The temperature parameters herein, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

[0050] In this article, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0054] In one aspect of the present application, a method for preparing artificial graphite secondary particles is provided, comprising the following steps S210 and S220.

[0055] Step S210: crushing and screening the artificial graphite to prepare primary particles.

[0056] In some embodiments, the average particle size of the primary particles is 1 μm to 20 μm. Optionally, the average particle size of the primary particles is 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any range of the above values. Further, the average particle size of the primary particles is 5 μm to 10 μm.

[0057] In some embodiments, in step S210, the artificial graphite is crushed by a pulverizer or a high-energy ball mill, and the crushed artificial graphite is screened by a sieve to obtain primary particles of suitable size.

[0058] Step S220: The primary particles and the binder are mixed and granulated to prepare artificial graphite secondary particles.

[0059] Wherein, the adhesive includes at least one of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), lithium silicate, lithium phosphate and lithium carbonate solution. Organic adhesives such as PVA and CMC have bonding properties, and can be decomposed at high temperatures, leaving a certain amount of residual carbon as a connecting material to bond secondary particles. Lithium silicate, lithium phosphate, etc. form a liquid phase at high temperatures to help particle bonding. In an embodiment of the present application, the adhesive uses a lithium carbonate solution, and the liquid lithium carbonate solution helps the bonding of secondary particles, and decomposes during the granulation process, and the remaining lithium element helps to improve the conductive properties of the artificial graphite secondary particles.

[0060] The particle size D10 of the artificial graphite secondary particles is 4 μm to 7 μm; the particle size D50 of the artificial graphite secondary particles is 12 μm to 16 μm; and the particle size D90 of the artificial graphite secondary particles is 25 μm to 35 μm.

[0061] The preparation method of the embodiment of the present application is different from the traditional process of first secondary granulation and then graphitization to generate artificial graphite. The artificial graphite is first prepared into primary particles, and then mixed with a binder to granulate to prepare secondary particles. The obtained artificial graphite secondary particles have good size uniformity and density.

[0062] In some embodiments, the mixed granulation in step S220 is carried out by a spray dryer or a granulator. In some embodiments, the rotation speed of the spray dryer or the granulator is 10rpm to 100rpm. Optionally, the rotation speed of the spray dryer or the granulator is 10rpm, 20rpm, 40rpm, 50rpm, 60rpm, 80rpm, 100rpm or any of the above numerical values. In some embodiments, the pressure in the spray dryer or the granulator is 100bar to 1000bar. Optionally, the pressure in the spray dryer or the granulator is 100bar, 200bar, 400bar, 500bar, 600bar, 800bar, 1000bar or any of the above numerical values.

[0063] In some embodiments, the mixing and granulation time is 10 s to 10 min. Optionally, the mixing and granulation time is 10 s, 30 s, 1 min, 2 min, 4 min, 5 min, 6 min, 8 min, 10 min or any range thereof.

[0064] In some embodiments, the relative humidity during the mixing and granulation process is 5% to 50%. Optionally, the relative humidity during the mixing and granulation process is 5%, 10%, 20%, 25%, 30%, 40%, 50% or any range of the above values.

[0065] In some embodiments, the method for preparing artificial graphite comprises the following steps:

[0066] Step S110: crushing and screening the carbon source to prepare powder, wherein the carbon source includes at least one of coal tar, petroleum coke and natural graphite, and the adhesive includes at least one of phenolic resin, polyvinyl alcohol, acrylate and silica sol.

[0067] In some embodiments, in step S110, the carbon source is crushed by a jaw crusher, a hammer crusher or a ball mill, and the crushed artificial graphite is sieved by a screen to obtain powder of suitable size.

[0068] In some embodiments, the average particle size of the powder is 10 μm to 100 μm.

[0069] Step S120: Mix the powder, adhesive and additives to prepare a mixture.

[0070] The additive includes at least one of a sintering aid, an antioxidant and a pore control agent.

[0071] The sintering aid can reduce the sintering temperature in step S130, accelerate the sintering process, and increase the density of the sintered product. In some embodiments, the sintering aid includes at least one of metal powder and boron powder.

[0072] The antioxidant can prevent the oxidation of graphite particles during the sintering process of step S130, thereby ensuring that the sintered product has good conductivity and chemical stability. In some embodiments, the antioxidant includes at least one of boron nitride and silicate.

[0073] The pore control agent can adjust the porosity and conductivity of graphite during the sintering process of step S130. Specifically, the pore control agent is an organic matter that is volatile at the sintering temperature or an inorganic salt that melts at the sintering temperature. In this way, the pore control agent generates gas during the sintering process, thereby obtaining artificial graphite with a microporous structure.

[0074] Step S130: sintering the mixture at a temperature of ≥2000° C., cooling, and preparing artificial graphite.

[0075] In some embodiments, the sintering temperature is 2000°C to 3000°C.

[0076] In some embodiments, the sintering step of S130 further includes:

[0077] Spraying a coating material on the surface of the mixture, wherein the coating material includes at least one of metal organic compounds, organosilicon compounds, fluorinated compounds, carbon-based materials, porous materials, and polymers.

[0078] The metal organic compound can form a stable metal oxide film on the graphite surface to improve thermal stability and electrochemical stability. In some embodiments, the metal organic compound includes at least one of titanate and zirconate.

[0079] The organosilicon compound can form a silicon film on the graphite surface, providing good thermal stability and electrolyte affinity. In some embodiments, the organosilicon compound includes at least one of silicone oil, methylsiloxane and silane.

[0080] The fluorinated compound can form a fluorinated film on the graphite surface, provide excellent chemical stability and prevent the electrolyte from reacting with the graphite, thereby avoiding the loss of the electrolyte. In some embodiments, the fluorinated compound includes at least one of hexafluoroacrylate and carbon fluoride.

[0081] The carbon-based material can form a carbonaceous film on the surface of graphite to improve the conductivity and thermal stability of graphite. In some embodiments, the carbon-based material includes at least one of carbon nanotubes and carbon black.

[0082] The porous material has a porous structure, and coating the surface of graphite can improve the ion transmission performance of the material. In some embodiments, the porous material includes at least one of a molecular sieve and activated carbon.

[0083] The polymer has a chain or mesh structure, and coating the graphite surface can improve the mechanical strength. In some embodiments, the polymer includes at least one of polyethylene, polypropylene, polyester and polyurethane.

[0084] In some embodiments, the cooling step in S130 includes:

[0085] (1) A protective gas is introduced to cool the artificial graphite to 800° C. at a first rate. The first rate is 80 to 120° C. / min. Optionally, the first rate is 80° C. / min, 90° C. / min, 100° C. / min, 110° C. / min, 120° C. / min, or any range thereof.

[0086] In some embodiments, the protective gas includes, but is not limited to, nitrogen and argon.

[0087] (2) Using a condensation system to cool the artificial graphite to 800°C, the artificial graphite is cooled to ≤40°C at a second rate. The second rate is 10-50°C / min. Optionally, the second rate is 10°C / min, 20°C / min, 30°C / min, 40°C / min, 50°C / min, or any range of the above values.

[0088] Through a two-stage cooling process, the artificial graphite formed by sintering is first cooled quickly in a protective gas atmosphere, and then cooled to near room temperature through a condensation system. This can prevent the artificial graphite from oxidizing during the cooling process and ensure the structural stability and good conductivity of the artificial graphite.

[0089] In some embodiments, the method further comprises: modifying the surface of the artificial graphite secondary particles. By modifying the surface of the artificial graphite secondary particles, the artificial graphite secondary particles have better electrolyte affinity.

[0090] In some embodiments, the surface modification specifically includes: mixing artificial graphite secondary particles and a surface modifier, wherein the surface modifier includes at least one of an organic silicon compound and a fluoride.

[0091] In a second aspect, the present application also provides an artificial graphite secondary particle, which is prepared according to the above-mentioned method for preparing the artificial graphite secondary particle. The particle size D10 of the artificial graphite secondary particle is 4 μm to 7 μm, the particle size D50 is 12 μm to 16 μm, and the particle size D90 is 25 μm to 35 μm.

[0092] In some embodiments, the tap density of the artificial graphite secondary particles is ≥1.05 g / cm 3 Optionally, the tap density of the artificial graphite secondary particles is 1.05 g / cm 3 ~1.15g / cm 3 Artificial graphite secondary particles have a high tap density and can be used to prepare negative electrode sheets with a high energy density.

[0093] In some embodiments, the specific surface area of ​​the artificial graphite secondary particles is ≤2.0 m 2 / g. Optionally, the specific surface area of ​​the artificial graphite secondary particles is 1.8m 2 / g~2.0m 2 / g.

[0094] In some embodiments, the gram capacity of the artificial graphite secondary particles is ≥345 mAh / g. Optionally, the gram capacity of the artificial graphite secondary particles is 345 mAh / g to 360 mAh / g.

[0095] See also Figure 1 , Figure 2 , is a scanning electron microscope photo of the artificial graphite secondary particles prepared in one embodiment of the present application. It can be seen that the artificial graphite secondary particles have good size uniformity, no obvious cracks on the particle surface, and good density.

[0096] In some embodiments, the artificial graphite secondary particles further include doping elements, including but not limited to nitrogen, sulfur, boron and lithium.

[0097] The embodiments of the present application also provide the use of the above-mentioned artificial graphite secondary particles in the preparation of secondary batteries.

[0098] In a third aspect, the present application also provides a negative electrode material, comprising the above-mentioned artificial graphite secondary particles.

[0099] In a fourth aspect, the present application further provides a negative electrode sheet. Generally, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector.

[0100] In an embodiment of the present application, the negative electrode active layer includes the artificial graphite secondary particles of the second aspect or the negative electrode material of the third aspect.

[0101] Furthermore, the negative electrode active layer also includes a conductive agent and a binder.

[0102] The negative electrode sheet includes the above-mentioned artificial graphite secondary particles. Compared with traditional natural graphite or artificial graphite, the prepared secondary battery has better cycle stability, safety performance and high-temperature cycle performance.

[0103] In a fifth aspect, the present application also provides a secondary battery, which includes the above-mentioned negative electrode sheet. The secondary battery also includes a positive electrode sheet, a separator and an electrolyte.

[0104] In order to make the purpose, technical solutions and advantages of the present application more concise and clear, the present application is described with the following specific embodiments, but the present application is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present application and can be used to describe the present application, and cannot be understood as limiting the scope of the present application. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

[0105] Example 1

[0106] The method for preparing the artificial graphite secondary particles of this embodiment comprises the following steps:

[0107] (1) Natural graphite is crushed by a ball mill and sieved to obtain a powder with an average particle size of 20 μm.

[0108] (2) 10 kg of powder is mixed evenly with 500 g of phenolic resin and 200 g of antioxidant so that the adhesive and additive are coated on the surface of the powder to form a mixture.

[0109] (3) The mixture is placed in a graphite furnace and sintered at 2500°C for 2 days to prepare artificial graphite.

[0110] (4) After sintering, nitrogen gas is introduced into the graphite furnace to purge the artificial graphite to 800°C at a rate of 80°C / min. Then, the graphite furnace is heat exchanged by a condensation system to cool the artificial graphite to 25°C at a rate of 20°C / min, and the artificial graphite is taken out.

[0111] (5) The artificial graphite is crushed by a high-energy ball mill and then sieved to obtain primary particles with an average particle size of 5 μm.

[0112] (6) Using a spray dryer to mix the primary particles and the lithium carbonate solution to form granules, and then collecting the secondary particles. The operating parameters of the spray dryer are: pressure 300 bar, temperature 200° C., relative humidity 20%, and rotation speed 50 rpm.

[0113] (7) Dry the collected secondary particles for later use.

[0114] The physical properties of the prepared artificial graphite secondary particles are recorded in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] Comparative Example 1

[0119] This comparative example uses natural graphite as the negative electrode active material. The average particle size of the natural graphite is 20 μm.

[0120] Comparative Example 2

[0121] The preparation method of the artificial graphite secondary particles of this comparative example comprises the following steps:

[0122] (1) Natural graphite and asphalt are mixed and granulated to prepare secondary particles, wherein the average particle size of the secondary particles is 20 μm.

[0123] (2) The secondary particles are placed in a graphite furnace and sintered at 3000° C. to prepare artificial graphite secondary particles.

[0124] Comparative Example 3

[0125] This comparative example uses silicon-based materials as negative electrode active materials.

[0126] Preparation of working electrode: The negative electrode active material of the above embodiment or comparative example, the conductive agent Super P and the binder PVDF are mixed in a mass ratio of 92:3:5 to prepare a slurry. The slurry is then coated on a copper foil to prepare a working electrode.

[0127] Battery preparation: lithium foil is used as the counter electrode; the electrolyte contains 1M LiPF6, and its solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The electrolyte also contains 1wt% of the additive vinylene carbonate (VC). The working electrode, diaphragm and counter electrode are stacked to prepare the battery cell, and then the electrolyte is injected to prepare the soft pack battery.

[0128] The prepared soft pack battery was subjected to electrochemical testing in the following manner. The test results are recorded in Table 2.

[0129] First discharge capacity: Charge the battery to the specified upper voltage limit at a rate of C / 10. Then discharge it to the specified lower voltage limit at a rate of C / 10. Record the discharge capacity, which is the first discharge capacity.

[0130] 100 cycle stability: The battery is charged and discharged 100 times, and the discharge capacity after the 100th cycle is compared with the initial discharge capacity. Capacity retention rate = (100th cycle discharge capacity / initial discharge capacity)*100%.

[0131] High temperature (55°C) cycle stability: Place the battery in a test box at 55°C. Perform 100 charge and discharge cycles and record the discharge capacity of each cycle. Analyze the change in discharge capacity as the number of cycles increases to evaluate the cycle stability at high temperature. High temperature (55°C) capacity retention rate = (100th cycle discharge capacity / first discharge capacity) * 100%.

[0132] Table 2

[0133] project Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 First discharge capacity (mAh / g) 358 340 352 420 100 cycles stability (%) 93 85 90 75 High temperature cycle stability (%) 91 80 88 80

[0134] It can be seen from the relevant data in Table 2 that the first discharge capacity of the artificial graphite secondary particles prepared in Example 1 is 358 mAh / g, which is higher than the natural graphite in Comparative Example 1 and the artificial graphite secondary particles prepared in Comparative Example 2. The negative electrode material of Comparative Example 3 is a silicon-based material, which has a higher first discharge capacity than that of Example 1 and Comparative Examples 1 to 2. However, due to the high volume expansion rate of the silicon-based material, the battery cycle stability and high-temperature cycle performance are poor. The 100 cycle stability and high-temperature cycle stability of Example 1 are significantly higher than those of Comparative Examples 1 to 3. As a negative electrode material, the artificial graphite secondary particles prepared in Example 1 have both high capacity and good cycle stability and high-temperature stability.

[0135] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0136] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solutions of the present application in detail, but cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the attached claims described in the present application. Therefore, the protection scope of the patent of this application shall be based on the contents of the attached claims, and the description and drawings can be used to explain the contents of the claims.

Claims

1. A method for preparing artificial graphite secondary particles, It is characterized in that The following steps are involved: The artificial graphite is crushed and sieved to prepare primary particles; Mixing the primary particles and the binder to form granules to prepare the artificial graphite secondary particles; Wherein, the binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, lithium silicate, lithium phosphate and lithium carbonate solution; The particle size D10 of the artificial graphite secondary particles is 4 μm to 7 μm; the particle size D50 of the artificial graphite secondary particles is 12 μm to 16 μm; the particle size D90 of the artificial graphite secondary particles is 25 μm to 35 μm; The preparation method of the artificial graphite comprises the following steps: crushing and sieving the carbon source to prepare powder; Mixing the powder, adhesive and additive to prepare a mixture; Sintering the mixture at a temperature of ≥2000° C. and cooling to prepare artificial graphite; Wherein, the carbon source includes at least one of coal tar, petroleum coke and natural graphite; the adhesive includes at least one of phenolic resin, polyvinyl alcohol, acrylate and silica sol; The additive includes at least one of a sintering aid, an antioxidant and a pore control agent; The sintering aid includes at least one of metal powder and boron powder; The antioxidant includes at least one of boron nitride and silicate; The sintering step further comprises: Spraying a coating material on the surface of the mixture; the coating material comprises at least one of a metal organic compound, an organosilicon compound, a fluorinated compound, a carbon-based material, a porous material, and a polymer; The metal organic compound includes at least one of titanate and zirconate; The organosilicon compound includes at least one of silicone oil, methylsiloxane and silane; The fluorinated compound includes at least one of hexafluoroacrylate and carbon fluoride; The carbon-based material includes at least one of carbon nanotubes and carbon black; The porous material includes at least one of molecular sieve and activated carbon; The polymer includes at least one of polyethylene, polypropylene, polyester and polyurethane.

2. The method for preparing the artificial graphite secondary particles according to claim 1, It is characterized in that The mixing and granulation is carried out by a spray dryer or a granulator; the mixing and granulation satisfies at least one of the conditions (1) to (4): (1) The mixing and granulation time is 10s to 10min; (2) During the mixing and granulation process, the relative humidity is 5% to 50%; (3) The rotation speed of the spray dryer or the granulator is 10 rpm to 100 rpm; (4) The pressure in the spray dryer or the granulator is 100 bar to 1000 bar.

3. The method for preparing the artificial graphite secondary particles according to claim 1, It is characterized in that The average particle size of the primary particles is 1 μm to 20 μm.

4. The method for preparing artificial graphite secondary particles according to claim 1, It is characterized in that The cooling step comprises: Passing a protective gas to cool the artificial graphite to 800° C. at a first rate; Using a condensation system to cool the artificial graphite to 800° C., so that the artificial graphite is cooled to ≤40° C. at a second rate; Wherein, the first rate is 80-120°C / min; the second rate is 10-50°C / min.

5. The method for preparing artificial graphite secondary particles according to claim 1, It is characterized in that Also includes: The surfaces of the artificial graphite secondary particles are modified.

6. A kind of artificial graphite secondary particles, It is characterized in that The method for preparing artificial graphite secondary particles according to any one of claims 1 to 5 is used.

7. A negative electrode material, It is characterized in that Comprising the artificial graphite secondary particles as described in claim 6.

8. A negative electrode sheet, It is characterized in that It includes the artificial graphite secondary particles according to claim 6 or the negative electrode material according to claim 7.

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