A method for detecting the tap density of a carbon negative electrode material

Abstract

This invention relates to a method for detecting the tap density of carbon anode materials, comprising the following steps: 1) taking a sample and testing the effective density d of the sample. t 2) The samples were divided into sample A and sample B. Sample A was sieved into coarse, medium, and small particles, and the tap density was tested sequentially to obtain d1, d2, and d3. The tap density d under ideal packing conditions was calculated as follows: d = d1 + d2 + d3 - d1 * d2 / d t -d1*d3 / d t -d3*d2 / d t +d1*d2*d3 / (d t ^2); 3) Test the tapped density of sample B to obtain d0; 4) Calculate the particle flow performance evaluation index D1 and the gradation optimization evaluation index D2: D1=(d2 / d t -0.4)*10; D2=d0 / ((D1-0.8)*d). This application can be used to analyze and study the flow properties and gradation optimization degree of the negative electrode material separately, which is conducive to making targeted improvements to the corresponding process based on the changes of the above indicators, thereby improving the effectiveness of the quality control of the negative electrode material.

Description

Technical Field

[0001] This invention relates to a method for detecting the tap density of carbon anode materials, belonging to the field of lithium-ion battery anode material preparation technology. Background Technology

[0002] Currently, the most widely used anode material for lithium-ion batteries is carbon anode material with artificial or natural graphite structures. The tap density of carbon anode materials is a key quality indicator that directly affects the volumetric energy density of the battery. According to the standard for graphite anode materials for lithium-ion batteries (GB / T 24533-2009), the tap density is tested according to the method for determining the tap density of metal powders in GB / T 5162.

[0003] The tap density of anode materials is related not only to the inherent properties of the material (degree of graphitization and porosity) but also to the particle size, particle size distribution, agglomeration, and particle shape. The corresponding process flow for quality control includes graphitization, shaping, and grading. However, current tap density testing methods cannot accurately determine the specific factors affecting the tap density, thus hindering targeted quality control measures. Summary of the Invention

[0004] To address the above problems, this invention provides a method for detecting the tap density of carbon anode materials, the specific solution of which is as follows:

[0005] A method for detecting the tap density of carbon anode materials includes the following steps:

[0006] 1) Sampling and testing the effective density d of the sample. t ;

[0007] 2) The samples were evenly divided into sample A and sample B. Sample A was sieved into coarse, medium, and small particles, and the tapped density was tested sequentially to obtain d1, d2, and d3; the tapped density d under ideal packing conditions was calculated:

[0008] d = d1 + d2 + d3 - d1 * d2 / d t -d1*d3 / d t -d3*d2 / d t +d1*d2*d3 / (d t ^2);

[0009] 3) Sample B was subjected to a tap density test to obtain d0;

[0010] 4) Calculate the particle flow performance evaluation index D1 and the gradation optimization evaluation index D2: D1=(d2 / d t -0.4)*10; D2=d0 / ((D1-0.8)*d).

[0011] Furthermore, d t The detection method is the liquid drainage method.

[0012] Furthermore, the coarse particles have a diameter >18 micrometers, the medium particles have a diameter between 12 and 18 micrometers, and the small particles have a diameter <12 micrometers.

[0013] Furthermore, d1, d2, d3, and d0 are all tested using a tap density meter. The tap density meter is equipped with four graduated cylinders. The graduated cylinders used to test d1 and d2 are equipped with a first counterweight and a second counterweight in sequence. During the test, the sample to be tested is first loaded into the graduated cylinder, and then the first or second counterweight is placed on top of the sample before the tap density is tested.

[0014] Furthermore, the weights of the first or second counterweight are m1 and m2 respectively. After sieving sample A, the coarse, medium, and small particles are weighed sequentially to obtain m. 11 m 12 m 13 If the sample weight during tap density testing is m0, then M1 = m0 * (m 12 +m 13 ) / m 11 M2 = m0 * m 13 / m 12 .

[0015] Furthermore, the tap density meter has four testing stations, and the vibration mechanism of each testing station is synchronously driven.

[0016] Furthermore, the tapped density meter includes a base on which four graduated cylinders are movably arranged in a straight line. A cam is provided below each graduated cylinder and is connected to the same rotating shaft, which is driven by a motor. Two of the graduated cylinders are equipped with counterweights, and the other two graduated cylinders are equipped with pads. Both the counterweights and pads are cylindrical. A crossbeam is rotatably arranged above the base, and four distance sensors are provided at the lower part of the crossbeam, corresponding to the four graduated cylinders respectively, for testing the height of the upper surface of the counterweights and pads.

[0017] The areal density of the coated and compacted negative electrode material determines its volumetric energy ratio. In existing technologies, tapped density and compacted density can be used to evaluate this indicator, with tapped density being more commonly used. Negative electrode material is a powder material, and the main factors affecting its tapped density include the density properties of the powder particles themselves, the flow properties of the powder, and the degree of optimization of the particle gradation. Higher particle density, better flow properties, and better gradation all contribute to improving the tapped density of the negative electrode material. In existing technologies, the indicators used to evaluate the density properties of the particles themselves are true density and effective density. True density is the density calculated after excluding all pores, including closed and open pores, while effective density is the density calculated after excluding closed pores.

[0018] Existing technologies use the ratio of compacted density to vibratory density to evaluate the flow properties of powders. However, the test results for compacted density are greatly affected by the pressure applied, requiring high-performance testing equipment, and the testing process is relatively complex, resulting in significant data fluctuations. Furthermore, compacted density itself is also significantly influenced by particle size distribution and cannot solely reflect flow properties.

[0019] Apart from this, there are no indicators to reflect the degree of gradation optimization of the anode material.

[0020] This application improves the detection and calculation methods for the flow performance evaluation indicators of anode materials, minimizing the influence of other factors, and introduces an indicator to evaluate the degree of gradation optimization of anode materials. This indicator can be used to analyze and study the flow performance and gradation optimization degree of anode materials independently. This facilitates targeted improvements to the corresponding processes based on changes in these indicators, thereby enhancing the effectiveness of anode material quality control. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the tap density meter in this invention. Detailed Implementation

[0022] The following detailed explanation of the invention patent solution, using specific examples, illustrates the invention patent in detail.

[0023] Example 1

[0024] This embodiment of a method for detecting the tap density of carbon anode materials includes the following steps:

[0025] 1) Sampling and testing the effective density d of the sample. t ;

[0026] 2) The samples were evenly divided into sample A and sample B. Sample A was sieved into coarse, medium, and small particles, and the tapped density was tested sequentially to obtain d1, d2, and d3; the tapped density d under ideal packing conditions was calculated:

[0027] d = d1 + d2 + d3 - d1 * d2 / d t -d1*d3 / d t -d3*d2 / d t +d1*d2*d3 / (d t ^2).

[0028] In an ideal packing state, the gaps between large particles are completely filled by medium-sized particles, and the gaps between medium-sized particles are completely filled by small particles. Based on this packing model, the following equation can be derived:

[0029] d1v = m1;

[0030] d2(v-m1 / dt ) = m2;

[0031] d3(v-(m1+m2) / d t ) = m3;

[0032] d0=(m1+m2+m3) / v

[0033] =[(d1v+d2v-m1 / d t *d2+d3v-m1 / d t *d3-m2 / d t *d3)] / v=d1+d2+d3-d2 / d t *(m1 / v)-d3 / d t *(m1 / v)-d3 / d t *(m2 / v)

[0034] =d1+d2+d3-d1*d2 / d t -d1*d3 / d t -d3 / d t *(d2(v-m1 / d t ) / v)

[0035] =d1+d2+d3-d1*d2 / d t -d1*d3 / d t -d3*d2 / d t +d1*d2*d3 / (dt^2).

[0036] Where m1, m2, and m3 are the masses of coarse, medium, and small particles under ideal packing conditions, and v is the volume of the ideal packing conditions.

[0037] 2) Sample B was subjected to a tap density test to obtain d0;

[0038] 3) Calculate the particle flow performance evaluation index D1 and the gradation optimization evaluation index D2: D1=(d2 / d t -0.4)*10; D2=d0 / ((D1-0.8)*d).

[0039] Among them, the larger the value of D1, the better the particle flowability, and the larger the value of D2, the better the gradation.

[0040] d t The detection method is the liquid displacement method. The effective volume of the sample is measured using the liquid displacement method, and then the effective density of the sample is calculated. This effective density is not affected by particle shape or particle size distribution.

[0041] In this method, coarse particles have a diameter >18 micrometers, medium particles have a diameter between 12 and 18 micrometers, and small particles have a diameter <12 micrometers. Among them, medium particles have the smallest particle size distribution range, and the measured values ​​are less affected by the particle size distribution.

[0042] d1, d2, d3, and d0 were all measured using a tap density meter. The tap density meter has four graduated cylinders. The cylinders used for measuring d1 and d2 are equipped with a first counterweight and a second counterweight, respectively. During testing, the sample to be tested is first placed into the graduated cylinder, and then the first or second counterweight is placed on top of the sample before the tap density is measured. During tap density measurement, smaller particles are compressed by the gravity of larger particles. The purpose of the counterweights is to simulate this compressive force, making the tap density of a sample testing a specific particle size range more closely resemble the conditions under which a mixed sample is tested.

[0043] Specifically, the weights of the first or second counterweight are M1 and M2 respectively. After sieving sample A, the coarse, medium, and small particles are weighed sequentially to obtain m. 11 m 12 m 13 If the sample weight during tap density testing is m0, then M1 = m0 * (m 12 +m 13 ) / m 11 M2 = m0 * m 13 / m 12 .

[0044] The mass of the counterweight is selected based on a calculated value accurate to 10g.

[0045] In this method, the tap density meter has four testing stations, and the vibration mechanism of each testing station is synchronously driven. Using synchronous drive ensures consistent conditions for tap density testing of all samples.

[0046] Specifically, such as Figure 1 The tapped density meter includes a base 1, on which four graduated cylinders 2 are movably mounted in a straight line. A cam 3 is located below each graduated cylinder, connected to a rotating shaft 4 driven by a motor. Two graduated cylinders have counterweights 5, and the other two have pads 6. Both the counterweights and pads are cylindrical. A crossbeam is rotatably mounted above the base, with four distance sensors 7 located at the bottom of the crossbeam, corresponding to the four graduated cylinders, used to measure the height of the upper surfaces of the counterweights and pads. The counterweights and pads ensure that the upper part of the sample is flat during tapping, preventing reading errors caused by uneven surfaces. Combined with the distance sensors, automatic detection can be achieved, avoiding errors caused by visual readings.

[0047] Table 1 shows the weights of the counterweights selected for testing samples numbered 1-9, with the unit of weight being g.

[0048] Table 1: Weight Configuration of Counterweights

[0049]

[0050]

[0051] Table 2 shows the sampling test results for samples numbered 1-9, with the tap density unit being g / cm³. 3 .

[0052] Table 2: Results of tap density test

[0053] dt d1 d2 d3 d d0 D1 D2 1 1.52 0.90 0.93 0.83 1.41 1.03 2.12 0.55 2 1.53 0.90 0.91 0.82 1.41 1.05 1.95 0.65 3 1.50 0.88 0.91 0.81 1.39 1.02 2.07 0.58 4 1.54 0.85 0.89 0.79 1.40 0.90 1.78 0.66 5 1.55 0.82 0.92 0.85 1.42 0.89 1.94 0.55 6 1.55 0.85 0.88 0.83 1.41 0.93 1.68 0.75 7 1.54 0.92 0.95 0.82 1.43 1.13 2.17 0.58 8 1.52 0.91 0.96 0.83 1.42 1.11 2.32 0.52 9 1.51 0.92 0.94 0.85 1.41 1.03 2.23 0.51

[0054] As can be seen from Table 2, the D1 values ​​of items 4 and 6 are relatively small, and quality analysis and improvement can be carried out on the shaping process to further improve the tap density of the product; while the D2 values ​​of items 1, 5, 8, and 9 are relatively small, and quality analysis and improvement can be carried out on the particle size distribution to further improve the tap density of the product.

Claims

1. A method for detecting the tap density of carbon anode materials, characterized in that, Includes the following steps: 1) Sampling, testing the effective density d of the sample t ; 2) The samples were evenly divided into sample A and sample B. Sample A was sieved into coarse, medium, and small particles, and the tapped density was tested sequentially to obtain d1, d2, and d3; the tapped density d under ideal packing conditions was calculated: d = d1+d2+d3-d1 d2 / d t -d1 d3 / d t - d3 d2 / d t +d1 d2 d3 / (d t ^2) ; 3) Sample B was subjected to a tap density test to obtain d0; 4) Calculate the particle flow performance evaluation index D1 and the gradation optimization evaluation index D2: D1=(d2 / d t -0.4) 10; D2 = d0 / (( D1 - 0.8) d).

2. The method for detecting the tap density of carbon anode materials according to claim 1, characterized in that: d t The detection method is the drainage method.

3. The method for detecting the tap density of carbon anode materials according to claim 1, characterized in that: Coarse particles have a diameter >18 micrometers, medium particles have a diameter between 12 and 18 micrometers, and small particles have a diameter <12 micrometers.

4. The method for detecting the tap density of carbon anode materials according to claim 1, characterized in that: The values ​​d1, d2, d3, and d0 are all measured by a tap density meter. The tap density meter has four graduated cylinders. The graduated cylinders used to measure d1 and d2 are equipped with a first counterweight and a second counterweight in sequence. During the test, the sample to be tested is first loaded into the graduated cylinder, and then the first or second counterweight is placed on top of the sample before the tap density is measured.

5. The method for detecting the tap density of carbon anode materials according to claim 4, characterized in that: The weights of the first or second counterweight are M1 and M2 respectively. After sieving sample A, the coarse, medium, and small particles are weighed sequentially to obtain m. 11 m 12 m 13 If the sample weight during tap density testing is m0, then M1 = m0. (m 12 +m 13 ) / m 11 M2 = m0 m 13 / m 12 .

6. The method for detecting the tap density of carbon anode materials according to claim 5, characterized in that: The tap density meter has four testing stations, and the vibration mechanism of each testing station is synchronously driven.

7. The method for detecting the tap density of carbon anode materials according to claim 6, characterized in that: The tapped density meter includes a base on which four graduated cylinders are movably arranged in a straight line. A cam is provided below each graduated cylinder and is connected to the same rotating shaft, which is driven by a motor. Two of the graduated cylinders are equipped with counterweights, and the other two graduated cylinders are equipped with pads. Both the counterweights and pads are cylindrical. A crossbeam is rotatably arranged above the base, and four distance sensors are provided at the lower part of the crossbeam, corresponding to the four graduated cylinders respectively, for measuring the height of the upper surface of the counterweights and pads.

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