Graphite particle granulation degree testing method and evaluation method

Abstract

The invention provides a test method and an evaluation method for the granulation degree of graphite particles, and relates to the technical field of material performance detection. The testing method comprises the following steps: (1) performing earlier stage treatment on aggregate to obtain single-particle aggregate, and performing granulation treatment on the single-particle aggregate to obtain granulated materials which comprise primary particles and secondary particles; (2) respectively testing the single-particle aggregate and the granulation material by adopting a particle size analyzer to obtain the particle size change rate B of the material before and after the granulation of the particle size Dv50 of the single-particle aggregate and after the granulation of the particle size Dv50 of the granulation material; counting the number of primary particles and the number of secondary particles in the granulation material by adopting a scanning electron microscope to obtain the number of the primary particles and the number of the secondary particles, and calculating the proportion A of the secondary particles; a dynamic particle size and particle shape analyzer is adopted to test the particle shape of the granulation material to obtain the convexity C and the length-width ratio F; and (3) calculating the granulation degree Gd value, wherein Gd = A * B * C / F. The test method is simple, and the granulation effect can be quantitatively evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of material property detection, and particularly relates to a test method and an evaluation method for the granulation degree of graphite particles. Background Art

[0002] With the continuous rise of new energy vehicles, the anode graphite material, one of the four major main materials in lithium-ion batteries, has attracted extensive attention. The anode active materials in lithium-ion battery materials are divided into single particles and secondary particles. The processing performance of traditional single-particle anode materials is poor, mainly manifested as low tap density and large baking rebound after compaction, which is easy to cause battery swelling, and the rate performance is average.

[0003] In this regard, those skilled in the art usually perform secondary granulation on single-particle anode materials, which is macroscopically isotropic. It can not only maintain the mass specific capacity of the anode material, but also solve the problems of low tap density and rebound of the electrode sheet, and enrich the number of channels for Li + intercalation and deintercalation in the crystal lattice, further improving the rate performance of the anode material and reducing swelling. However, for the granulation degree of single particles granulated into secondary particles, at present, only the granulation effect is qualitatively evaluated from electron microscope pictures, and there is a lack of a quantitative evaluation method for the granulation degree of graphite particles. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a test method and an evaluation method for the granulation degree of graphite particles. The test method of the present invention is simple and can quantitatively evaluate the quality of the granulation effect.

[0005] To achieve the above purpose, on the one hand, the present invention provides a test method for the granulation degree of graphite particles, including: (1) Prepare granulated material Perform preliminary treatment on the aggregate to obtain single-particle aggregate, and perform granulation treatment on the single-particle aggregate to obtain granulated material, where the granulated material includes primary particles and secondary particles; (2) Test basic parameters Use a particle size analyzer to test the single-particle aggregate and the granulated material respectively to obtain the particle size D v 50 造粒前 of the single-particle aggregate and the particle size D v 50 造粒后 of the granulated material, and calculate the particle size change rate B of the material before and after granulation; Use a scanning electron microscope to count the number of primary particles and the number of secondary particles in the granulated material to obtain the number of primary particles A1 and the number of secondary particles A2, and calculate the proportion A of secondary particles; Use a dynamic particle size and shape analyzer to test the particle shape of the granulated material to obtain the convexity C and the aspect ratio F; (3) Calculate the granulation degree Gd value Gd = A × B × C / F where A = A2 / (A1 + A2); B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 .

[0006] Compared with the prior art, the present invention comprehensively considers various situations that may occur during granulation, combines the bonding ratio of particles (i.e., the proportion of secondary particles) in the macroscopic granulation process and the particle size change rate before and after granulation with the microscopic morphology of the particles, and provides a test method for the granulation degree Gd of graphite particles, Gd = A × B × C / F. This test method is simple and can quantitatively evaluate the quality of the granulation effect. The larger the Gd value, the better the granulation effect. It can be used for quantitative comparison of the granulation effects of particles obtained from different raw materials and granulation processing technologies.

[0007] In some embodiments, the aggregate is selected from at least one of petroleum coke, coal coke, calcined coke, and needle coke.

[0008] In some embodiments, the pretreatment includes at least one of coarse crushing, pulverization, and shaping.

[0009] In some embodiments, the temperature of the granulation treatment is 550 °C to 750 °C.

[0010] In some embodiments, the single-particle aggregate particle size D v 50 造粒前 is 3 μm to 15 μm.

[0011] In some embodiments, the granulated material particle size D v 50 造粒后 is 10 μm to 35 μm.

[0012] In some embodiments, the proportion of secondary particles A is 0.2 to 1.0.

[0013] In some embodiments, the particle size change rate B is 0.3 to 1.5.

[0014] In some embodiments, the convexity C is 0.8 to 1.0.

[0015] In some embodiments, the aspect ratio F is 1 to 3.

[0016] In some embodiments, the granulation treatment is carried out in a granulation kettle.

[0017] In some embodiments, the granulation kettle is selected from at least one of a rotary kiln, a vertical granulation kettle, a horizontal granulation kettle, and a continuous granulation kettle.

[0018] In some embodiments, before the granulated material is subjected to SEM statistics, it further includes ultrasonically dispersing the granulated material in a solvent to obtain a test solution 1, taking a small amount of the test solution 1 and dropping it on a foil material and drying it to obtain a test sample, and placing the test sample under a scanning electron microscope for photographing and statistics.

[0019] In some embodiments, the mass fraction of the granulated material in the test solution 1 is 0.01% - 1.5%.

[0020] In some embodiments, the solvent is selected from ethanol or water.

[0021] In some embodiments, the foil material is selected from aluminum foil or copper foil.

[0022] In some embodiments, the time for ultrasonic dispersion is 3 min - 5 min.

[0023] In some embodiments, the drying is carried out in a drying oven.

[0024] In some embodiments, the drying temperature is 60 °C - 110 °C, and the drying time is 5 min - 15 min.

[0025] In some embodiments, the scanning electron microscope is selected from TSM - 7900F, and the magnification is 100 times - 3000 times.

[0026] In some embodiments, the number of granulated material particles in each picture taken by the scanning electron microscope ≥ 10.

[0027] In some embodiments, the particle size analyzer is selected from at least one of Malvern 2000 laser particle size analyzer or Malvern 3000 laser particle size analyzer.

[0028] In some embodiments, the obscuration of the particle size analyzer is 8% - 12%, the internal ultrasound is 1500 rpm - 3000 rpm, and the ultrasound time is 30 s - 120 s.

[0029] In some embodiments, the measurement of the convexity C and the aspect ratio F of the granulated material includes dispersing the granulated material in a liquid medium to form a test solution 2, and then placing the test solution 2 in the dynamic particle size and shape analyzer for measurement.

[0030] In some embodiments, the mass fraction of the granulated material in the test solution 2 is 0.1% - 5%; In some embodiments, the liquid medium is selected from ethanol or water.

[0031] In some embodiments, the number of measurements of the test solution 2 is at least 3.

[0032] In some embodiments, the dynamic particle size and shape analyzer is selected from QICPIC of Sympatec GmbH, Germany.

[0033] In some embodiments, the test range of the dynamic particle size and shape analyzer is 0.6 μm to 1126 μm.

[0034] In some embodiments, the data exchange frequency of the dynamic particle size and shape analyzer is 60 Hz to 100 Hz.

[0035] In some embodiments, the data processing mode of the dynamic particle size and shape analyzer is EQPC.

[0036] On the other hand, the present invention provides a method for evaluating the granulation degree of graphite particles. The granulation degree of graphite particles is detected by using the aforementioned test method for the granulation degree of graphite particles to obtain the Gd value, and the quality of graphite granulation is evaluated by the magnitude of the Gd value.

[0037] In some embodiments, if Gd ≥ 0.2, it indicates good granulation effect.

[0038] In some embodiments, if 0.1 ≤ Gd < 0.2, it indicates average granulation effect.

[0039] In some embodiments, if Gd < 0.1, it indicates poor granulation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 XRD patterns of graphite anode materials 1 and graphite anode materials 4 prepared from the granulated materials of Example 1 and Example 4 of the present invention; Figure 2 SEM image of graphite anode material 1 prepared from the granulated material of Example 1 of the present invention; Figure 3 SEM image of graphite anode material 4 prepared from the granulated material of Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The applicant of the present invention found during the production and research process that single-particle aggregates are transformed into secondary particles through the granulation process. Due to differences in raw materials, additives, granulation equipment or processes, the granulation effects vary greatly. In addition to achieving the expected granulation results, various unsatisfactory granulation results may also occur, such as failure to granulate, non-compliance with granulation particle size standards, or poor granulation morphology.

[0042] The following introduces several common granulation results. The first one is that most of the secondary particles are tightly spherical-like agglomerated and bonded by several large and small single particles. The proportion of secondary particles is high, the particle size changes greatly after granulation, and the granulation degree is high. The second one is that if the viscosity of the aggregate is poor or the addition amount of additives and auxiliary materials is small, the bonding between large particles is poor and it is easily sheared and separated during the stirring process. Most of the secondary particles are formed by several small single particles bonded to the surface of large particles. The proportion of secondary particles is very high, but the secondary particles are only bonded by a few particles, and the particle size after granulation cannot meet the requirements. The third one is that some single particles are agglomerated and bonded into secondary particles, and some still exist in the form of single particles, that is, partial granulation or incomplete granulation. The content of fine powder in the product is too high, which affects the powder indexes and battery performance. The fourth one is that some coke raw materials such as calcined coke tend to be flat and long and narrow after being crushed due to their own characteristics. After granulation in a vertical kettle, it is easy to form a laminated structure, and the particles are not firmly bonded and are easy to slide, resulting in a still large aspect ratio of the particles after granulation. There may be other results in granulation, which will not be elaborated here one by one.

[0043] If the granulation degree is only evaluated by the proportion A of secondary particles, there is a lack of monitoring of the particle size after granulation, and there are large deviations in the evaluation of the above various granulation situations; if the granulation degree is only evaluated by the change rate of the Dv50 particle size in the particle size test before and after granulation, there is a lack of control over the content of fine powder in partial granulation. The convexity and aspect ratio are used to describe the regularity degree of the particle shape, reflecting the uniformity and consistency of the shape of the material particles. The convexity of a particle specifically refers to the ratio of the projected area of the particle to the total area after filling the concave part, and is used to characterize the shape density degree of the particle. The maximum value of the convexity is 0.99. The larger the convexity, the fewer the concavities and convexities at the boundary of each particle, that is, the fewer the burrs; the aspect ratio specifically refers to the ratio of the maximum Feret value to the minimum Feret value, and is used to characterize the similarity degree of the projected shape of the particle to a circle. The minimum value of the aspect ratio is 1. The smaller the aspect ratio, the closer the particle is to a spherical or circular shape. Therefore, two indexes of convexity and aspect ratio can be used to characterize the morphology of the particles after granulation. The larger the convexity and the smaller the aspect ratio, the rounder and smoother the particles will be, and they will have higher tap density, bulk density, fluidity, etc. than the powder particles with other morphologies, and can significantly improve the electrochemical performance of the anode material, including specific capacity, first cycle efficiency, and cycle performance, etc.

[0044] Based on the above analysis and consideration, the applicant of the present invention comprehensively considers the particle morphology (convexity, aspect ratio) of the granulated material, the proportion of secondary particles, and the change rate of the particle size of the material before and after granulation, and provides a test method and an evaluation method for the granulation degree of graphite particles. The test method is simple and can quantitatively evaluate the quality of the granulation effect. The granulation degree is represented by Gd. The larger the Gd value, the better the granulation effect. Specifically, the evaluation method for the granulation degree of graphite particles of the present invention can be as follows: (1) If Gd≥0.2, it indicates that the granulation effect is good (2) If 0.1 ≤ Gd < 0.2, it indicates that the granulation effect is average; (3) If Gd < 0.1, it indicates that the granulation effect is poor.

[0045] Furthermore, the test method for the granulation degree of the graphite particles of the present invention includes the steps of: (1) preparing granulated materials; (2) testing basic parameters; (3) calculating the granulation degree Gd value.

[0046] Step (1) includes pre-treating the aggregate to obtain single-particle aggregate, and subjecting the single-particle aggregate to granulation treatment to obtain granulated materials.

[0047] Among them, the aggregate is selected from at least one of petroleum coke, coal coke, calcined coke, and needle coke. In some technical solutions, the aggregate is selected from petroleum coke; in some technical solutions, the aggregate is selected from calcined coke; in some technical solutions, the aggregate is selected from needle coke. The pre-treatment includes at least one of coarse crushing, pulverizing, and shaping. The aggregate is obtained as single-particle aggregate through at least one of the processes of coarse crushing, pulverizing, and shaping. The granulation treatment is carried out in a granulation kettle, and the granulation kettle is selected from at least one of a rotary kiln, a vertical granulation kettle, a horizontal granulation kettle, and a continuous granulation kettle. In some technical solutions, the granulation kettle is selected as a vertical granulation kettle; in some technical solutions, the granulation kettle is selected from a rotary kiln. The temperature of the granulation treatment is 550 °C to 750 °C. As an example, the temperature of the granulation treatment is 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 620 °C, 640 °C, 660 °C, 680 °C, 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C. The granulated materials include primary particles and secondary particles. Among them, the primary particles are the initial particles formed by the pre-treatment of the aggregate, and there are no structures such as stacking and continuous connection in the primary particles. The secondary particles refer to the particles that have undergone a certain degree of agglomeration and bonding after granulation treatment on the basis of single-particle aggregate.

[0048] Step (2) includes using a particle size analyzer to test the single-particle aggregate and the granulated materials respectively to obtain the particle size D v 50 造粒前 of the single-particle aggregate and the particle size D v 50 造粒后 of the granulated materials, and calculating the particle size change rate B of the material before and after granulation; using a scanning electron microscope to count the number of primary particles and the number of secondary particles in the granulated materials to obtain the number of primary particles A1 and the number of secondary particles A2, and calculating the proportion A of secondary particles; using a dynamic particle size and shape analyzer to test the particle shape of the granulated materials to obtain the convexity C and the aspect ratio F.

[0049] In the test calculation of the particle size change rate B, D v50 represents the median particle size of the particle size test particle size volume distribution curve, indicating that half of the particles have a particle size lower than this value, while the other half have a particle size greater than this value. Specifically, the particle size analyzer can be selected from at least one of the Malvern 2000 laser particle size analyzer or the Malvern 3000 laser particle size analyzer. In some technical solutions, the particle size analyzer is selected from the Malvern 2000 laser particle size analyzer; in some technical solutions, the particle size analyzer is selected from the Malvern 3000 laser particle size analyzer. The obscuration of the particle size analyzer is 8% - 12%. As an example, the obscuration of the particle size analyzer is 8%, 9%, 10%, 11%, 12%. The internal ultrasound of the particle size analyzer is 1500 rpm - 3000 rpm. In some technical solutions, the internal ultrasound is 2500 rpm. As an example, the internal ultrasound can be, but is not limited to, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2500 rpm, 2600 rpm, 2800 rpm, 3000 rpm. The ultrasound time is 30 s - 120 s. In some technical solutions, the ultrasound time is 60 s. As an example, the ultrasound time can be, but is not limited to, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s. The single-particle aggregate particle size D v 50 造粒前 is 3 μm - 15 μm. In some technical solutions, the single-particle aggregate particle size D v 50 造粒前 is 12 μm - 14 μm; in some technical solutions, the single-particle aggregate particle size D v 50 造粒前 is 12 μm - 14 μm; in some technical solutions, the single-particle aggregate particle size D v 50 造粒前 is 8 μm - 12 μm; as an example, the single-particle aggregate particle size D v 50 造粒前 can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm. The granulated material particle size D v 50 造粒后 is 10 μm - 35 μm. In some technical solutions, the granulated material particle size D v 50 造粒后 is 12 μm - 14 μm; in some technical solutions, the granulated material particle size D v 50 造粒后 is 20 μm - 25 μm; in some technical solutions, the granulated material particle size D v 50造粒后 is 15 μm to 19 μm; as an example, the particle size D of the granulated material v 50 造粒后 can be but is not limited to 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 33 μm, 35 μm. The particle size change rate B of the material before and after granulation can be calculated by the formula B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 . The particle size change rate B is 0.3 to 1.5. As an example, the particle size change rate B can be but is not limited to 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5. When the value of B is too small, it indicates that the number of particles in the secondary particles is generally small, the orientation improvement is limited, resulting in slow lithium ion transport. When the value of B is too large, it will cause too large particle size, too long ion transport path, the capacity cannot be exerted, and the volume expands during multiple charge and discharge cycles, and the buffer space is limited, so the particle structure is easily damaged.

[0050] In the test calculation of the secondary particle ratio A, the image analysis method is used to select multiple scanning electron microscope photos after each graphite sample is dispersed, and the area on each photo is as non-repetitive as possible, and then the number of single-particle aggregates A1 and the number of secondary particles A2 in each photo are counted, and the secondary particle ratio is calculated according to the formula A=A2 / (A1+A2), and the average value is the secondary particle ratio A. Specifically, before the scanning electron microscope statistics are performed, the granulated material also includes ultrasonically dispersing the granulated material in a solvent to obtain a test liquid 1, taking a small amount of the test liquid 1 and dropping it on a foil and drying it to obtain a test sample, and placing the test sample under a scanning electron microscope for photographing and statistics. Wherein, the mass fraction of the granulated material in the test liquid 1 is 0.01%~1.5%. As an example, the mass fraction of the granulated material in the test liquid can be, but not limited to, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%. The solvent can be selected from ethanol or water. The foil is selected from aluminum foil or copper foil. The time of ultrasonic dispersion is 3min~5min. As an example, the time of ultrasonic dispersion can be, but not limited to, 3 min, 4 min, 5 min. Drying can be carried out in a drying oven. The drying temperature is 60℃~110℃. As an example, the drying temperature can be, but not limited to, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃. The drying time is 5 min to 15 min. As an example, the drying time can be, but is not limited to, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, and 15 min. The scanning electron microscope can be selected from TSM-7900F, and the magnification is 100 times to 3000 times. The number of particles of the granulated material in each picture taken by the scanning electron microscope is ≥10, and the particles are not adhered to each other. The secondary particle ratio A is 0.2 to 1.0. As an example, the secondary particle ratio A can be, but is not limited to, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0. When the value of A is too small, it means that the primary particles in the granulated material account for too much, the pores between the particles increase, the surface area is too much, and the processing performance of the powder is deteriorated.

[0051] The measurement of the convexity C and the aspect ratio F of the granulated material includes dispersing the granulated material in a liquid medium to form a test solution 2, and then placing the test solution 2 in a dynamic particle size and shape analyzer for measurement. Specifically, the liquid medium is selected from ethanol or water. The test of the test solution 2 is performed at least 3 times. The dynamic particle size and shape analyzer is selected from QICPIC of Sympatec GmbH, Germany. The measurement range of the dynamic particle size and shape analyzer is 0.6 μm to 1126 μm, and the data exchange frequency of the dynamic particle size and shape analyzer is 60 Hz to 100 Hz. In some technical solutions, the data exchange frequency is 80 Hz. As an example, the data exchange frequency can be, but is not limited to, 60 Hz, 65 Hz, 70 Hz, 75 Hz, 80 Hz, 85 Hz, 90 Hz, 95 Hz, 100 Hz. The data processing mode of the dynamic particle size and shape analyzer is EQPC. Specifically, the convexity C is 0.8 to 1.0. As an example, the convexity C can be, but is not limited to, 0.8, 0.9, 1.0. When the value of C is too small, the surface of the granulated material is not smooth, with many concavities, convexities or burrs, which is not conducive to improving the tapped density and the compacted density of the finished product. At the same time, the surface area increases, affecting the charge and discharge efficiency of the battery. The aspect ratio F is 1 to 3. As an example, the aspect ratio F can be, but is not limited to, 1, 2, 3. When the value of F is too large, the particles tend to be long and narrow ellipsoids, which will result in too long lithium ion insertion paths, and during the rolling process, the particles are arranged flat, and the ion insertion direction is single.

[0052] In step (3), the Gd value is calculated according to the formula Gd = A × B × C / F. The larger the Gd value, the better the granulation effect.

[0053] To better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0054] Example 1 This example is a test method for the granulation degree of graphite particles, including the steps of: (1) Prepare granulated material The petroleum coke raw rubber is coarsely broken, pulverized and shaped to obtain single-particle aggregates. The single-particle aggregates are placed in a vertical granulation kettle and granulated at 600 °C to obtain granulated material, which includes primary particles and secondary particles; (2)Test basic parameters Use a particle size analyzer to measure the single-particle aggregate and the granulated material respectively to obtain the particle size D of the single-particle aggregate v 50 造粒前 and the particle size D of the granulated material v 50 造粒后, calculate the particle size change rate B of the material before and after granulation. Among them, the particle size analyzer is Malvern 2000 laser particle size analyzer, the obscuration is 12%, the internal ultrasonic is 2500 rpm, and the ultrasonic time is 60 s; Ultrasonically disperse the granulated material in ethanol for 5 min to obtain a test solution with a mass fraction of 1%. Take 0.2 mL of the test solution and drop it on the copper foil, and dry it in a blast dryer at 80 °C for 10 min to obtain a test sample. Place the test sample under a scanning electron microscope for photographing, and count the number of primary particles and secondary particles in the test solution sample, and calculate the proportion A of secondary particles. Among them, the scanning electron microscope is selected from TSM-7900F, 3 photos are taken, the number of granulated material particles in each picture taken by the scanning electron microscope ≥ 10, and the particles do not stick to each other; Disperse the granulated material in ethanol to form a test solution 2 with a mass fraction of 3%. Then place the test solution in a dynamic particle size and shape analyzer for testing to obtain the convexity C and the aspect ratio F. Among them, the dynamic particle size and shape analyzer is selected from QICPIC of German Sympatec, the test range is 0.6 μm - 1126 μm, the data exchange frequency is 80 Hz, the data processing mode is EQPC, the number of tests is 4, and the average value is taken; (3) Calculate the granulation degree Gd value Gd = A × B × C / F Among them, A = number of secondary particles / (number of primary particles + number of secondary particles); B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 .

[0055] Example 2 This example is a test method for the granulation degree of graphite particles, including the steps: (1) Prepare granulated material Crush, pulverize, and shape the calcined acicular coke pitch to obtain single-particle aggregates. Place the single-particle aggregates in a vertical granulation kettle and perform granulation treatment at 650 °C to obtain granulated material. The granulated material includes primary particles and secondary particles; (2)Test basic parameters Use a particle size analyzer to test the single-particle aggregates and the granulated material respectively to obtain the particle size D of the single-particle aggregates v 50 造粒前 and the particle size D of the granulated material v 50 造粒后 , calculate the particle size change rate B of the material before and after granulation. Among them, the particle size analyzer is Malvern 2000 laser particle size analyzer, the obscuration is 10%, the internal ultrasonic is 2500 rpm, and the ultrasonic time is 60 s; The granulated material was ultrasonically dispersed in ethanol for 3 min to prepare a test solution with a mass fraction of 1.5%. 0.2 mL of the test solution was taken and dropped on a copper foil, and then dried in a forced-air oven at 75 °C for 13 min to obtain a test sample. The test sample was placed under a scanning electron microscope for photographing, and the number of primary particles and secondary particles in the test solution sample was counted, and the proportion A of secondary particles was calculated. Among them, the scanning electron microscope was selected from TSM-7900F, 3 photos were taken, the number of granulated material particles in each picture taken by the scanning electron microscope was ≥10, and the particles were not adhered to each other; The granulated material was dispersed in ethanol to form a test solution with a mass fraction of 1%. Then the test solution was placed in a dynamic particle size and shape analyzer for testing to obtain the convexity C and the aspect ratio F. Among them, the dynamic particle size and shape analyzer was selected from QICPIC of Sympatec Germany, the test range was 0.6 μm - 1126 μm, the data exchange frequency was 80 Hz, the data processing mode was EQPC, the number of tests was 4, and the average value was taken; (3) Calculate the granulation degree Gd value Gd = A × B × C / F Among them, A = number of secondary particles / (number of primary particles + number of secondary particles); B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 .

[0056] Example 3 This example is a test method for the granulation degree of graphite particles, including the steps: (1) Prepare the granulated material The needle coke pitch was coarsely broken, crushed, and shaped to obtain single-particle aggregates. The single-particle aggregates were placed in a roller furnace and granulated at 650 °C to obtain the granulated material. The granulated material included primary particles and secondary particles; (2)Test basic parameters The particle size analyzer was used to test the single-particle aggregates and the granulated material respectively to obtain the particle size D v 50 造粒前 of the single-particle aggregates and the particle size D v 50 造粒后 of the granulated material, and the particle size change rate B of the material before and after granulation was calculated. Among them, the particle size analyzer was a Malvern 2000 laser particle size analyzer, the obscuration was 8%, the internal ultrasound was 2500 rpm, and the ultrasound time was 60 s; The granulated material was ultrasonically dispersed in ethanol for 5 min to prepare a test solution with a mass fraction of 0.5%. Take 0.2 mL of the test solution and drop it on a copper foil, then dry it in a blast dryer at 80 °C for 10 min to obtain a test sample. Place the test sample under a scanning electron microscope for photographing, and count the number of primary particles and secondary particles in the test solution sample, and calculate the proportion A of secondary particles. Among them, the scanning electron microscope is selected from TSM-7900F, 3 photos are taken, the number of granulated material particles in each picture taken by the scanning electron microscope is ≥10, and the particles do not adhere to each other; The granulated material was dispersed in ethanol to form a test solution 2 with a mass fraction of 5%. Then the test solution was placed in a dynamic particle size and shape analyzer for testing to obtain the convexity C and the aspect ratio F. Among them, the dynamic particle size and shape analyzer is selected from QICPIC of Sympatec GmbH in Germany, the test range is 0.6 μm - 1126 μm, the data exchange frequency is 80 Hz, the data processing mode is EQPC, the number of tests is 4, and the average value is taken; (3) Calculate the granulation degree Gd value Gd = A × B × C / F Among them, A = number of secondary particles / (number of primary particles + number of secondary particles); B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 .

[0057] Example 4 This example is a test method for the granulation degree of graphite particles, including the steps: (1) Prepare the granulated material The needle coke was coarsely broken, pulverized, and shaped to obtain single-particle aggregates. The single-particle aggregates were placed in a vertical granulation kettle and granulated at 650 °C to obtain the granulated material. The granulated material includes primary particles and secondary particles; (2)Test basic parameters Use a particle size analyzer to test the single-particle aggregates and the granulated material respectively to obtain the particle size D v 50 造粒前 and the particle size D v 50 造粒后 of the granulated material. Calculate the particle size change rate B of the material before and after granulation. Among them, the particle size analyzer is a Malvern 2000 laser particle size analyzer, the obscuration is 8%, the internal ultrasound is 2500 rpm, and the ultrasound time is 60 s; The granulated material was ultrasonically dispersed in ethanol for 5 min to obtain a test solution with a mass fraction of 1%. 0.2 mL of the test solution was taken and dropped on a copper foil, and then dried in a blast dryer at 80 °C for 10 min to obtain a test sample. The test sample was placed under a scanning electron microscope for photographing, and the number of primary particles and secondary particles in the test solution sample was counted, and the proportion A of secondary particles was calculated. Among them, the scanning electron microscope was selected from TSM-7900F, 3 photos were taken, the number of granulated material particles in each picture taken by the scanning electron microscope was ≥10, and the particles were not adhered to each other; The granulated material was dispersed in ethanol to form a test solution with a mass fraction of 0.5%. Then the test solution was placed in a dynamic particle size and shape analyzer for testing to obtain the convexity C and the aspect ratio F. Among them, the dynamic particle size and shape analyzer was selected from QICPIC of Sympatec Germany, the test range was 0.6 μm to 1126 μm, the data exchange frequency was 80 Hz, the data processing mode was EQPC, the number of tests was 4, and the average value was taken; (3) Calculate the granulation degree Gd value Gd = A × B × C / F Among them, A = number of secondary particles / (number of primary particles + number of secondary particles); B = (D v 50 造粒后 - D v 50 造粒前 ) / D v 50 造粒前 .

[0058] The results of the proportion A of secondary particles, the particle size change rate B, the convexity C of the granulated material, the aspect ratio F, and the granulation degree Gd value were tested and calculated for Examples 1 to 4 as shown in Table 1. At the same time, the tapped density and specific surface area of the granulated materials in Examples 1 to 4 were tested, and the results are shown in Table 1.

[0059] Table 1 Test results of Examples 1 to 4

[0060] Table 1 shows the test data of the granulated materials in Examples 1 to 4. Comparing Examples 1, 2, and 4, different coke raw materials were granulated using a vertical kettle, and there were significant differences in the granulation effects. The secondary particle projection near-circularity obtained from green petroleum coke was the highest, the particles were round, compact, had the smallest aspect ratio, and the largest convexity. Moreover, the raw material had a high volatile content, the proportion of particle bonding during the granulation process was good, the particle size changed significantly after granulation, the granulation size was the largest, the tapped density was relatively high, and the specific surface area was relatively low. In contrast, the granulation sizes of calcined coke and needle coke were slightly lower, and the tapped densities were also lower. Comparing Examples 3 and 4, the aspect ratio of the granulated material after granulation using a rotary kiln was slightly lower. The transverse shear force of the stirring paddle in the vertical granulation kettle easily caused the particles to slide off, resulting in a large aspect ratio of the secondary particles and a small proportion of the secondary particles. Correspondingly, the specific surface area was slightly larger and the tapped density was slightly lower. It can be seen that the granulation effect differences under different granulation processes can be effectively judged by this method.

[0061] To further verify the rationality of the test method for the granulation degree of the graphite particles of the present invention, the granulated materials prepared in Examples 1 to 4 were respectively shaped and then placed in a continuous graphitization furnace for high-temperature graphitization treatment. After cooling, they were dispersed, demagnetized, and screened to obtain graphite anode materials 1 to 4. Among them, the graphitization temperature curve was to heat up to 2300 °C at a heating rate of 18 °C / min, and then heat up to 3000 °C at a heating rate of 15 °C / min and hold for 3 h. After graphitization treatment, it was cooled to room temperature at a cooling rate of 20 °C / min. The graphite anode materials 1 to 4 were respectively made into half-cells for electrochemical performance testing, and the test results are shown in Table 2.

[0062] Fabrication of half-cell: A polyvinylidene fluoride solution with a mass fraction of 6 - 7% was prepared using N-methylpyrrolidone as the solvent. The graphite anode material (select one from the graphite anode materials 1 to 4 prepared from the granulated materials in Examples 1 to 4), polyvinylidene fluoride, and conductive carbon black were mixed uniformly in a mass ratio of 91:7:2 with N-methylpyrrolidone to obtain a slurry with a solid content of 40 - 46%. The slurry was coated on a copper foil to obtain a pole piece. The coated pole piece was placed in a forced-air drying oven at 110 °C and dried for 4 h, and then punched into small round pieces with a diameter of 14 mm. After vacuum drying, it was transferred to a glove box filled with argon for assembly into a 2032-type button cell. A ternary mixed solvent of 1 mol / L LiPF6 was mixed in a volume ratio of EC:DMC:EMC = 1:1:1 and added with vinylene carbonate (accounting for 1% of the electrolyte mass) as the electrolyte, a metal lithium sheet as the counter electrode, and a PE separator as the separator to assemble a half-cell.

[0063] The assembled half-cells were subjected to electrochemical performance testing on an electrochemical detection system.

[0064] 1. OI value of the electrode: Graphite has a hexagonal layered structure. During the preparation of the electrode, preferred orientation is likely to occur, and the degree of orientation will directly affect the diffusion rate of lithium ions. The orientation ratio (OI value) of the graphite layered structure can be rapidly characterized by the intensity ratio of the diffraction peaks of the graphite electrode (004) and (110). In this invention, an X-ray diffractometer was used to test the negative electrode graphite electrode with a compaction density of 1.55 - 1.60 g / cm 3 and the orientation ratio of the graphite electrode sample was calculated using the peak intensity ratio I(004) / I(110).

[0065] 2. Capacity test: Under normal temperature conditions, discharge at a constant current of 0.1C until the voltage reaches 0.01V, then discharge at a constant current of 0.02C until the voltage reaches 0.005V, and charge at a constant current of 0.1C until the voltage reaches 1.5V. The capacity charged to 1.5V is the first charge capacity at 0.1C.

[0066] 3. First efficiency test: The ratio of the first charge capacity to the first discharge capacity is the first Coulomb efficiency.

[0067] 4. Cycle test: Discharge at a constant current of 0.5C until the voltage reaches 0.01V, then discharge at a constant current of 0.02C until the voltage reaches 0.005V, and charge at a constant current of 0.5C until the voltage reaches 1.5V. The capacity charged to 1.5V is the charge capacity at 0.5C. After 100 cycles, the ratio of the charge capacity of the 100th cycle to the charge capacity at 0.5C is the cycle capacity retention rate.

[0068] 5. Swelling test: After vacuum drying, measure and record the thickness h1 of the small round piece. After assembling it into a half-cell, discharge at a constant current of 0.1C at room temperature until the voltage reaches 0.01V, then discharge at a constant current of 0.02C until the voltage reaches 0.005V. Then disassemble the battery and measure the thickness h2 of the electrode when fully inserted. The swelling rate of the negative electrode material is calculated by the formula (h2 - h1) / h1.

[0069] Table 2 Electrochemical performance test results of graphite negative electrode materials 1 - 4 prepared from the granulating materials of Examples 1 - 4

[0070] Table 2 shows the orientation degree test and electrochemical performance test of graphite anode materials 1-4 prepared from the granulated materials of Examples 1-4. It can be found that the higher the granulation degree, the better the granulation effect of the anode material, and the lower the orientation degree of the electrode sheet. This is mainly because the diffraction signal of the (004) plane comes from graphite with a layer structure parallel to the electrode sheet, and the diffraction signal of the (110) plane comes from graphite with a layer structure perpendicular to the electrode sheet. Granulation causes single particles with different crystal plane directions to bond into a secondary particle, resulting in a more abundant orientation of the inner end faces of the particles, an increase in the intensity of the (110) diffraction peak, a decrease in the OI value, and a higher isotropy of the particles. From Figure 1 It can be seen that the intensity of the (004) diffraction peak of the graphite material in Example 1 is significantly weaker than that of the graphite material in Example 4, while the intensity of the (110) diffraction peak is significantly stronger in Example 1 than that of the graphite material in Example 4, indicating that the graphite in Example 1 has a lower orientation degree ratio, more end face directions, and better isotropy.

[0071] The graphite anode materials in Examples 1-3 have good cycling performance, all above 96%. The cycling performance of the graphite anode material in Example 4 is slightly worse, and the capacity retention rate is only 94.5% after 100 cycles at 0.5C. The electrochemical expansion rate of the graphite anode material is the smallest in Example 1 and the largest in Example 4. This is because the better the isotropy of the particles, the more buffer directions there are for the volume expansion stress caused by the insertion of lithium ions after the material is made into a battery and undergoes charge-discharge testing, and the smaller the macroscopic expansion rate. During the cycling process, the SEI film rupture caused by volume swelling is less, and the cycling performance is better. In Example 4, some single-particle aggregates were not granulated successfully, and there were more fine powders (primary particles), and their particle aspect ratios were also larger, resulting in a large specific surface area of the particles. The formation of the SEI film on the particle surface during the first charge-discharge consumes more active lithium ions, resulting in a low efficiency.

[0072] From Figure 2 It can be seen that the particles of graphite material 1 in Example 1 are basically all secondary particles, and the particle sizes are relatively uniform, indicating that the bonding effect during the granulation process is good. This is consistent with the relatively large A value of the secondary particle ratio. Because the particles are bonded to each other, the particle size change rate before and after granulation is also relatively large. Figure 3 It can be seen that some primary particles in graphite material 4 of Example 4 did not bond to each other, and the powder is composed of primary particles and secondary particles, which is consistent with the calculated A value of 0.45.

[0073] Based on the above analysis, it can be known that the granulation effect of graphite secondary particles can be evaluated using the granulation degree Gd = A × B × C / F. The higher the granulation degree, the better the granulation effect.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for testing the granulation degree of graphite particles, characterized in that: include: (1) Preparation of granulated material The aggregate is pre-processed to obtain single-grain aggregate, and the single-grain aggregate is granulated to obtain granulated material, wherein the granulated material includes primary particles and secondary particles; (2) Test basic parameters The single-grain aggregate and the granulated material are tested by a particle size analyzer to obtain the single-grain aggregate particle size D v 50 造粒前 and granulation material particle size D v 50 造粒后 , calculate the particle size change rate B of the material before and after granulation; The number of the primary particles and the number of the secondary particles in the granulated material are counted by a scanning electron microscope to obtain the number of primary particles and the number of secondary particles, and the secondary particle ratio A is calculated; The particle shape of the granulated material is tested by a dynamic particle size and shape analyzer to obtain the convexity C and the aspect ratio F; (3) Calculation of granulation degree Gd value Gd=A×B×C / F Where A = secondary particle number / (primary particle number + secondary particle number); B = (D v 50 造粒后 -D v 50 造粒前 ) / D v 50 造粒前 .

2. The method for testing the granulation degree of graphite particles according to claim 1, characterized in that: The method comprises at least one of the following features (i) to (ix): (i) the aggregate is selected from at least one of petroleum coke, coal coke, calcined coke and needle coke; (ii) the preliminary treatment includes at least one of coarse crushing, pulverizing and shaping; (iii) the temperature of the granulation treatment is 550°C to 750°C; (iv) The particle size D of the single aggregate particle v 50 造粒前 3 μm~15 μm; (v) The particle size D of the granulated material v 50 造粒后 10 μm~35 μm; (vi) the secondary particles account for A of 0.2 to 1.0; (vii) the particle size change rate B is 0.3 to 1.5; (viii) the convexity C is 0.8 to 1.0; (ix) The aspect ratio F is 1 to 3.

3. The method for testing the granulation degree of graphite particles according to any one of claims 1 or 2, characterized in that: The granulation process is carried out in a granulation kettle, and the granulation kettle is selected from at least one of a drum furnace, a vertical granulation kettle, a horizontal granulation kettle and a continuous granulation kettle.

4. The method for testing the granulation degree of graphite particles according to claim 1 or 2, characterized in that: Before the scanning electron microscope statistics are performed on the granulated material, the granulated material is ultrasonically dispersed in a solvent to obtain a test liquid 1, a small amount of the test liquid 1 is dropped on a foil and dried to obtain a test sample, and the test sample is placed under a scanning electron microscope for photographing and statistics.

5. The method for testing the granulation degree of graphite particles according to claim 4, characterized in that: Includes at least one of the following features (a) to (h): (a) the mass fraction of the granulated material in the test solution 1 is 0.01% to 1.5%; (b) the solvent is selected from ethanol or water; (c) the foil is selected from aluminum foil or copper foil; (d) the ultrasonic dispersion time is 3 min to 5 min; (e) the drying is carried out in a drying oven; (f) the drying temperature is 60°C to 110°C, and the drying time is 5 min to 15 min; (g) The scanning electron microscope is selected from TSM-7900F, and the magnification is 100 times to 3000 times; (h) The number of particles of the granulated material in each picture taken by the scanning electron microscope is ≥ 10.

6. The method for testing the granulation degree of graphite particles according to claim 1 or 2, characterized in that: The particle size analyzer is selected from at least one of Malvern 2000 laser particle size analyzer and Malvern 3000 laser particle size analyzer.

7. The method for testing the granulation degree of graphite particles according to claim 1 or 2, characterized in that: The shading degree of the particle size analyzer is 8% to 12%, the internal ultrasound is 1500 rpm to 3000 rpm, and the ultrasound time is 30 s to 120 s.

8. The method for testing the granulation degree of graphite particles according to claim 1 or 2, characterized in that: The test of the convexity C and the aspect ratio F of the granulated material comprises dispersing the granulated material in a liquid medium to form a test liquid 2, and then placing the test liquid 2 in the dynamic particle size and shape analyzer for testing.

9. The method for testing the granulation degree of graphite particles according to claim 8, characterized in that: The invention comprises at least one of the following features (I) to (VII): (I) the mass fraction of the granulated material in the test solution 2 is 0.1% to 5%; (II) the liquid medium is selected from ethanol or water; (III) the number of tests of the test liquid 2 is at least 3; (IV) The dynamic particle size and shape analyzer is selected from QICPIC of Sympatec of Germany. (V) The test range of the dynamic particle size and shape analyzer is 0.6 μm to 1126 μm; (VI) the data exchange frequency of the dynamic particle size and shape analyzer is 60 Hz to 100 Hz; (VII) The data processing mode of the dynamic particle size and shape analyzer is EQPC.

10. A method for evaluating the degree of granulation of graphite particles, characterized in that: The method for testing the granulation degree of graphite particles according to any one of claims 1 to 9 is used to test the granulation degree of graphite particles to obtain the Gd value. (1) If Gd≥0.2, it indicates that the granulation effect is good (2) If 0.1≤Gd<0.2, it indicates that the granulation effect is average; (3) If Gd < 0.1, it indicates that the granulation effect is poor.

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