Rapid evaluation method for performance of artificial graphite raw material

Abstract

The application discloses a kind of quick evaluation methods of artificial graphite raw material performance, it is applicable to ordinary petroleum coke and needle coke and other soft carbon raw materials, by quantitative analysis to microstructure of sample after crushing, heat treatment, and comprehensive structure data are calculated by combining contribution factor of different microstructure;At the same time, the soft carbon raw material is graphitized to obtain graphite powder and is assembled into battery, and the capacity of finished battery is tested, finally, the comprehensive structure data calculated is associated with the capacity of finished battery, the capacity performance of the corresponding graphitized product of soft carbon raw material is predicted, the purpose of quickly evaluating artificial graphite raw material is achieved, the method is simple and fast, the accuracy is high, time and labor are saved, and the efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of raw material evaluation technology for artificial graphite, and to a rapid evaluation method for the properties of artificial graphite raw materials. Background Technology

[0002] It is widely acknowledged in the industry that the global new energy vehicle market has entered a period of rapid development. Over the next 3-5 years, the new energy vehicle industry will experience high-speed growth, with global production expected to exceed 10 million vehicles by 2025. Lithium-ion batteries offer advantages such as high energy density, long cycle life, excellent charge / discharge performance, high operating voltage, no memory effect, lower pollution, and higher safety. Furthermore, compared to various fuel cells, air batteries, and supercapacitors, lithium-ion battery technology is significantly more mature.

[0003] Currently, lithium-ion battery anode materials are generally divided into carbon-based anodes and non-carbon-based anodes. Carbon-based anodes can be further divided into graphite, hard carbon, and soft carbon anodes, with graphite itself further divided into artificial graphite, natural graphite, and mesophase carbon microspheres. Non-carbon-based anodes include lithium titanate, tin alloy anodes, and silicon anodes. In 2021, the shipment volume of lithium-ion battery anodes in China reached 720,000 tons, a year-on-year increase of 97%, of which artificial graphite accounted for 84%, while natural graphite accounted for 14%. The reason why artificial graphite has become the main lithium storage material is that its raw material sources are abundant, it has a layered structure suitable for lithium-ion intercalation and deintercalation, and it can form lithium-graphite interlayer compounds, which have advantages such as low voltage plateau and small volume change during intercalation and deintercalation.

[0004] There are three lithium storage mechanisms in graphite materials: interlayer lithium storage, end-face lithium storage, and surface lithium storage. The more developed the graphite layers, the more lithium is inserted, and the greater the lithium storage capacity. The carbon atoms exposed at the edges of graphite sheets are in an amorphous state with high energy, serving as active sites for lithium ions, i.e., end-face lithium storage. The bonding between carbon atoms and lithium ions on the graphite surface is similar to that at the edges, i.e., surface lithium storage. However, most lithium ions begin to embed within the layers and form different levels of graphite interlayer compounds when the voltage is below 0.25V, meaning that interlayer lithium storage contributes more than 93% of the capacity. Generally, soft carbon (such as pitch coke, petroleum coke, etc.) must undergo graphitization to transform into a graphite structure. Therefore, graphitization is one of the most critical processes in the preparation of anodes using soft carbon as raw material, accounting for 50% of the cost of graphite anodes and being the most expensive part. Graphitization furnaces mainly include Atchison resistance furnaces (crucible or box type), internal series furnaces, and continuous furnaces. The graphitization process typically takes 40 days (loading, heating, cooling, and unloading).

[0005] Currently, the intrinsic relationship between heat treatment temperature and the graphite microcrystal parameters of materials has been systematically studied. For example, Chinese patent document CN111766173A discloses a method of drying raw coke samples, coarsely crushing them, and then sieving them through a 4mm sieve to obtain primary coke powder. After heat treatment at 700-800℃ in a nitrogen atmosphere, the powder is pulverized to a 0.071mm sieve to obtain secondary coke powder. The secondary coke powder is then vacuum dried at 110-140℃, and thermogravimetric analysis is performed in an air atmosphere at a rate of 2-5℃ / min from 50℃ to 900℃ to determine the reaction initiation temperature of graphitization degree change and the reaction initiation temperature of reversible capacity change.

[0006] Chinese patent document CN107764681A discloses a method of taking at least two groups of coke raw materials, such that the particle size D50 deviation between each group of coke raw materials is ≤2μm, and the specific surface area deviation within each group of coke raw materials is ≤2m². 2 / g, volatile matter deviation ≤2%; thermogravimetric analysis was performed on each coke raw material sample from at least two groups under an oxidizing atmosphere to obtain the onset temperature of weight loss in the oxidation reaction; graphitized coke raw material samples were used as negative electrode active materials to prepare electrode sheets, and the capacity of the finished product after graphitization of coke raw materials was tested; finally, a graph was plotted based on the data of the onset temperature of weight loss in the oxidation reaction and the capacity of the finished product after graphitization of coke raw materials to obtain the relationship between the capacity of the finished product after graphitization of coke raw materials and the onset temperature of weight loss in the oxidation reaction.

[0007] The above thermogravimetric analyses were performed on soft carbon coke samples, demonstrating the thermal stability of fixed carbon. These analyses are relatively macroscopic and cannot distinguish differences in crystal growth or disappearance caused by variations in microcrystalline structure. The correlation between capacity and temperature points is also low. However, the correlation between the microcrystalline structure of soft carbon and the microcrystalline parameters after graphitization has not yet been established. Therefore, to determine the electrochemical performance of the final anode material made from soft carbon raw materials, graphitization processing is necessary, followed by battery assembly and electrochemical performance testing. From obtaining the raw materials to obtaining electrochemical data, at least 3-4 months are required.

[0008] Given that graphitization involves the ordered arrangement of graphite crystallites along the radial and axial directions, the disappearance of grain boundaries, the formation of six-ring CC structures at crystal interfaces, and crystal growth, as well as the catalytic reactions of unsaturated carbon atoms at graphite layer boundaries, thermal vibrations of carbon atoms or gas molecules, the anisotropic properties of graphite crystallites, and van der Waals forces between graphite layers, all of these are related to the microcrystalline structure of the raw material. Therefore, if the correlation between the microstructure characteristics of the raw material and the electrochemical performance of the graphitized material can be established, the capacity performance data of the finished artificial graphite can be predicted more quickly and conveniently.

[0009] However, directly using soft carbon for structural analysis and subsequent electrochemical correlation presents a complex relationship. This is because most petroleum coke, pitch coke, and needle coke are produced through delayed coking processes. The thermal reaction of coke samples in the upper part of the reactor is incomplete, especially for petroleum coke products, where a large amount of unreacted heavy aromatic components remain in the coke during production. The degree of coking reaction is uneven, and some carbon microcrystalline structures are unstable. In the typical artificial graphite processing, the carbonization and graphitization processes can transform or eliminate these structures. Therefore, rapid heat treatment or modification of the soft carbon structure is necessary to ensure that the preserved structure is more representative and the data is more accurate. Summary of the Invention

[0010] In view of this, the present invention provides a rapid evaluation method for the performance of artificial graphite raw materials, which can guide the selection of raw materials and product design of lithium battery anode materials. This evaluation method uses quantitative analysis data of the polarized microstructure of artificial graphite raw materials and combines this with contribution factors of different microstructures to calculate comprehensive structural data, thereby rapidly evaluating the electrochemical performance of artificial graphite raw materials and predicting the capacity of the graphitized product. This solves the problem of low efficiency in the traditional anode industry, which requires 3-4 months to obtain the capacity of the graphitized product from artificial graphite raw materials. It significantly shortens the evaluation cycle, saves manpower and resources, and improves production efficiency.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A rapid evaluation method for the properties of artificial graphite raw materials includes the following steps:

[0013] Crushing: The soft carbon material is dried and crushed to 0.071-1 mm to obtain the crushed soft carbon material;

[0014] Heat treatment: The pulverized soft carbon material is heat-treated in a nitrogen atmosphere containing water vapor to obtain heat-treated soft carbon material.

[0015] Microstructure testing: 4-5g of the heat-treated soft carbon material was statically cured and polished with metallographic sample preparation epoxy resin and curing agent. The resulting optical sheet was examined by a polarizing microscope to obtain the content of each optical structure.

[0016] Capacity testing: The soft carbon material is dried, initially crushed, and classified to obtain soft carbon powder. After carbonization, graphitization, pulverization, and classification, graphite powder is obtained. The graphite powder is then used for battery assembly and charge-discharge testing to obtain the capacity of the finished battery after graphitization of the soft carbon material.

[0017] Constructing correlation curves: Correlation curves are obtained by correlating the content of each optical tissue with the capacity of the finished battery;

[0018] Evaluation: The finished capacity of the soft carbon material to be evaluated is evaluated by the correlation curve (i.e., by testing the content of each optical structure in the soft carbon material to be tested and combining the correlation curve, the finished battery capacity of the soft carbon material to be tested is predicted).

[0019] In the process of constructing the correlation curve, the capacity testing step uses the same soft carbon material as the pulverizing step, and there are at least 10 types.

[0020] When evaluating the soft carbon material under test using the correlation curve, the capacity testing step and the step of constructing the correlation curve are omitted.

[0021] Optionally, in the pulverizing step of the rapid evaluation method for the properties of artificial graphite raw materials provided by the present invention, the moisture content of the dried soft carbon material is less than 0.1%, and the true density is 1.362–1.425 g / cm³. 3 The volatile matter content is 3%–20%, the ash content is 0.01%–0.5%, and the sulfur content is 0.1%–5%.

[0022] The soft carbon material is selected from at least one of petroleum coke, needle coke, and pitch coke.

[0023] The soft carbon materials are at least 16 types.

[0024] Optionally, in the heat treatment step of the rapid evaluation method for the properties of artificial graphite raw materials provided by the present invention, the heat treatment temperature is 1100–1300℃, and the time is 0.5–2 hours; the volume content of water vapor in the nitrogen atmosphere containing water vapor is 8%–12%. The specific heat treatment device can be a tube furnace or a furnace of any shape with controllable atmosphere, as long as the device is equipped with a steam generator and can adjust the flow rate. Specifically, the heat treatment step can be carried out in the following manner:

[0025] The pulverized soft carbon material is placed in the device, and then nitrogen gas is introduced into the device. Water vapor is then introduced in addition to the nitrogen gas, while the flow rate of water vapor is controlled to be 8% to 12% of the volume flow rate of nitrogen gas. Then, in the nitrogen atmosphere containing water vapor, the material is heated from room temperature to 1100 to 1300°C at a rate of 60 to 80°C / min. The nitrogen flow rate is set according to the volume of the furnace (90 to 120 ml of nitrogen gas / L of furnace volume).

[0026] Optionally, in the microstructure testing step of the rapid evaluation method for the properties of artificial graphite raw materials provided by the present invention, the content of each optical structure is calculated according to the following formula.

[0027] The total number of effective points for each optical structure is at least 500;

[0028] In the microstructure testing step, the classification of various optical structures in the carbon material is shown in the table below:

[0029] Table 1

[0030]

[0031] The contents of small mosaic, medium mosaic, coarse mosaic, small flakes, large flakes, fine short fibers, coarse fibers, and long fibers are calculated using A1, A2, A3, A4, A5, A6, A7, and A8, respectively, in %; in Table 1 above, a1, a2, a3, a4, a5, a6, a7, and a8 represent the structural contribution factors of each optical structure, that is, the contribution rate of different optical structure to the capacity of the finished battery. This is to accurately express the relationship between the capacity of soft carbon materials with different structures and artificial graphite.

[0032] Optionally, in the rapid evaluation method for the properties of the above-mentioned artificial graphite raw materials provided by the present invention, in the microstructure testing step, the pulverized soft carbon material is cured with epoxy resin and curing agent in a mold for 24 hours to form a luminous film. The luminous film is then polished to obtain a smooth, pit-free, and scratch-free film. The film is then analyzed under a polarizing microscope. The step size of the measuring scale is adjusted to ensure that more than 500 effective measurement points are evenly distributed across the entire film. Starting from one end of the sample, the optical structure of the substance under the cross-shaped points is determined. The content of each optical structure is expressed as the percentage of the number of statistical points to the number of effective points. The mold used for curing, as well as the types of epoxy resin and curing agent, are not specifically limited; any conventional mold capable of curing the soft carbon material with epoxy resin and curing agent is acceptable. The specific crushing and microstructure testing steps for preparing the optical sheet can be referred to in sections 6.1, 6.2 and 6.3 of YB / T077-2017. The specific method for testing with a polarizing microscope can be referred to in YBT 4822-2020.

[0033] Optionally, in the capacity testing step of the rapid evaluation method for the properties of artificial graphite raw materials provided by the present invention, the primary crushing can be performed by jaw crusher or hammer crusher, and after graphitization, it can be pulverized by mechanical pulverizer, air jet mill or ball mill.

[0034] The soft carbon powder has a D50 of 15–18 μm; a D10 of 3–4 μm and a D90 of 25–27 μm; the particle size deviation of different samples does not exceed ±2 μm. Larger particle size differences will cause particle size effects, resulting in data deviation.

[0035] The parameters for carbonization and graphitization during the graphitization process are not specifically limited; industry-standard parameters can be used. For example, the following carbonization and graphitization parameters can be adopted:

[0036] The carbonization temperature is 700–1500℃, the time is 0.5–3h, and the heating rate is 1–10℃ / min; preferably, the carbonization temperature is 800–1200℃, the time is 1–2h, and the heating rate is 3–4℃ / min.

[0037] The graphitization temperature is 2800–3100℃ and the time is 1–20h; preferably, the graphitization temperature is 2950–3050℃ and the time is 5–10h; however, once the heating program and final temperature and time for carbonization and graphitization are selected, they need to be consistent between each sample, with a deviation of no more than ±5℃ and a time of no more than ±5min.

[0038] The graphite powder has a D50 of 14–16 μm and a specific surface area of ​​less than 2 cm². 3 / g, with a magnetic material content of less than 1ppm; an excessively high specific surface area may be caused by improper operation of the graphitization process, unreasonable temperature control, or the material being exposed to air before it has been sufficiently cooled, etc., and must be kept strictly consistent.

[0039] The battery assembly and charge / discharge testing methods are not specifically limited; any industry-standard methods may be used. For example, a battery assembly and charge / discharge testing method including the following steps may be adopted:

[0040] Using the graphitized product of each of the aforementioned soft carbon materials as the negative electrode active material, a slurry was prepared by mixing graphite, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2. The slurry was then coated onto copper foil and dried to obtain an areal density of 70 g / m³. 2 The compacted density is 1.75 g / cm³. 3 Electrodes;

[0041] Using the aforementioned electrode as the working electrode, a lithium sheet as the counter electrode, and 1 mol / L LiPF6 as the electrolyte, the electrolyte is a mixed solvent composed of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC in a volume ratio of 1:1:1. Charge-discharge tests are performed. Preferably, the voltage range of the charge-discharge test is 0.001–2.5V, and the initial delithiation capacity obtained is the capacity of the finished battery after graphitization of the soft carbon material.

[0042] Optionally, the construction of the correlation curve step in the rapid evaluation method for the performance of artificial graphite raw materials provided by the present invention further includes calculating a comprehensive structural parameter X by combining the content of each optical structure with the structural contribution factor of the optical structure, and then correlating the comprehensive structural parameter X with the capacity of the finished battery.

[0043] The comprehensive structural parameter X is calculated according to the following formula:

[0044] X=(a1×A1+a2×A2+a3×A3+a4×A4+a5×A5+a6×A6+a7×A7+a8×A8) / 100;

[0045] The correlation curve is Y = βX + γ, that is, Y = β(1×A1 + 2×A2 + 5×A3 + 10×A4 + 90×A5 + 20×A6 + 50×A7 + 100×A8) / 100 + γ; where Y is the capacity of the finished battery, γ is the intercept, and β is the slope.

[0046] Optionally, in the rapid evaluation method for the properties of the above-mentioned artificial graphite raw materials provided by the present invention, the correlation curve, after calibration, is Y = 0.6035X + 327.54, where the unit of Y is mAh / g.

[0047] The rapid evaluation method for the performance of the above-mentioned artificial graphite raw materials provided by this invention involves obtaining the content A1 to A8 of each optical structure of the soft carbon material to be tested according to the above-mentioned crushing and microstructure testing steps, then calculating the comprehensive structural parameter X, and substituting the comprehensive structural parameter X into the correlation curve to obtain the predicted battery capacity of the graphitized finished product of the soft carbon material to be tested. It should be noted that when evaluating the soft carbon material to be tested, the predicted battery capacity result is based on the capacity testing method used when constructing the correlation curve (i.e., the predicted battery capacity is the same capacity testing method used when constructing the correlation curve).

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] 1. The rapid evaluation method for the performance of artificial graphite raw materials provided by this invention is applicable to soft carbon raw materials such as ordinary petroleum coke and needle coke. It involves quantitative analysis of the microstructure of pulverized and heat-treated samples, and calculation of comprehensive structural data based on the contribution factors of different microstructures. Simultaneously, the soft carbon raw materials are graphitized to obtain graphite powder, which is then used for battery assembly. The capacity of the finished batteries is tested. Finally, the calculated comprehensive structural data is correlated with the capacity of the finished batteries to predict the capacity performance of the graphitized products corresponding to the soft carbon raw materials. This achieves the goal of rapidly evaluating artificial graphite raw materials. The method is simple, fast, accurate, time-saving, labor-saving, and highly efficient.

[0050] 2. The rapid evaluation method for the properties of artificial graphite raw materials provided by this invention, compared with existing methods, is based on microstructure analysis. It involves treating and modifying the structure in a water vapor atmosphere, and studying the stable microcrystalline structure retained after treatment. Furthermore, it correlates the structure with the electrochemical performance tested after graphitization, thus solving the problem that the relationship between some soft carbon structures and electrochemical performance is complex and not linear in existing methods. Attached Figure Description

[0051] Figure 1 This invention provides a calibration diagram of the comprehensive structural parameters obtained quantitatively from the microstructure of a soft carbon raw material and the capacity of the resulting artificial graphite. Detailed Implementation

[0052] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0053] Example 1

[0054] This embodiment provides a rapid evaluation method for the properties of artificial graphite raw materials, including the following steps:

[0055] Crushing: Ten different soft carbon materials were selected, dried to a moisture content of less than 0.1%, crushed to about 1 mm using a jaw crusher, and then passed through 200-mesh and 16-mesh molecular sieves in sequence to obtain soft carbon materials with a particle size range of 0.071 to 1 mm. The specific properties of each soft carbon material after drying are shown in Table 2 below.

[0056] Heat treatment: The pulverized soft carbon material is placed in a tube furnace, nitrogen is introduced, and water vapor is introduced on the basis of nitrogen. The flow rate of water vapor is controlled to be 10% of the volume flow rate of nitrogen. Then, in the nitrogen atmosphere containing water vapor, the temperature is heated from room temperature to 1200℃ at a rate of 70℃ / min for 1 hour.

[0057] Microstructure testing: Weigh 4.5g of the heat-treated soft carbon material and place it at the bottom of the mold. Then, pour a mixture of epoxy resin (CER1000 for metallographic sample preparation) and curing agent (CEH500) mixed at a mass ratio of 2:1 into the mold containing the crushed soft carbon material until it reaches 3 / 4 full. Allow the sample to cure at room temperature for 24 hours. After curing, use an automatic polishing machine to polish the sample with sandpaper from coarse to fine, and then polish it with alumina polishing liquid until it becomes a mirror-like sheet with a smooth surface free of pits and scratches. After rinsing with water, observe the sample under a polarizing microscope. Select appropriate parameters to collect polarized photographs, obtaining 520 valid photographs. Starting from one end of the sample, determine the optical structure of the substance under the crosshairs. The content of each optical structure is expressed as the percentage of the statistical points to the valid points. The content of each optical structure is calculated according to the following formula:

[0058]

[0059] The microstructure of all 10 pulverized soft carbon materials was tested using the above method. The test results of the content of various optical structures in each soft carbon material are shown in Table 3 below.

[0060] Capacity testing: Soft carbon materials were dried, jaw crushed, and finely ground and sieved by air jet mill to obtain soft carbon powder. Then, the powder was heated to 1100℃ at a rate of 4℃ / min and held at this temperature for 2 hours for carbonization. Then, it was graphitized at 3000℃ for 10 hours. After graphitization, it was crushed and graded to obtain graphite powder with a magnetic material content of less than 1ppm. The specific properties of soft carbon powder and graphite powder obtained from various soft carbon materials are shown in Table 2 below.

[0061] Using the above-mentioned graphite powder as the negative electrode active material, a slurry was prepared by mixing graphite powder, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder at a mass ratio of 95:1.5:1.5:2. The slurry was then coated onto copper foil and dried to obtain an areal density of 70 g / m³. 2 The compacted density is 1.75 g / cm³. 3 The electrode was used as the working electrode, the lithium sheet as the counter electrode, and 1 mol / L LiPF6 as the electrolyte. The solvent in the electrolyte was a mixed solvent composed of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC in a volume ratio of 1:1:1. Charge and discharge tests were performed. The specific voltage range for the charge and discharge test was 0.001V to 2.5V. The first delithiation capacity obtained was the capacity of the finished battery after graphitization of the soft carbon material.

[0062] The microstructure of all 10 soft carbon materials was tested using the above method, and these 10 soft carbon materials were the same as the 10 soft carbon materials in the pulverization step. The specific test results are shown in Table 3 below.

[0063] Table 2

[0064]

[0065]

[0066] Table 3

[0067]

[0068] Constructing correlation curves: The content of each optical tissue obtained from the above microstructure testing steps is combined with the structural contribution factor of each corresponding optical tissue to obtain the comprehensive structural parameter X.

[0069] X=(a1×A1+a2×A2+a3×A3+a4×A4+a5×A5+a6×A6+a7×A7+a8×A8) / 100;

[0070] Then, substituting X and the finished capacity batteries of each soft carbon material into the correlation curve Y=βX+γ, we get: 336=β(a1×50+a2×10+a3×5+a4×15+a5×5+a6×10+a7×3+a8×2) / 100+γ 338=β(a1×45+a2×7+a3×8+a4×10+a5×6+a6×9+a7×10+a8×5) / 100+γ 341=β (a1×42+a2×8+a3×10+a4×10+a5×8+a6×6+a7×11+a8×5) / 100+γ345=β(a1×34+a2×5+a3×10+ a4×7+a5×20+a6×6+a7×11+a8×7) / 100+γ350=β(a1×25+a2×8+a3×13+a4×7+a5×15+a6×5+a7× 14+a8×13) / 100+γ354=β(a1×20+a2×7+a3×15+a4×5+a5×18+a6×6+a7×14+a8×15) / 100+γ35 7=β(a1×17+a2×5+a3×20+a4×5+a5×15+a6×5+a7×15+a8×18) / 100+γ360=β(a1×10+a2×4+a3× 18+a4×9+a5×18+a6×6+a7×16+a8×19) / 100+γ362=β(a1×8+a2×5+a3×15+a4×6+a5×22+a6×4 +a7×12+a8×28) / 100+γ365=β(a1×5+a2×4+a3×10+a4×8+a5×24+a6×7+a7×12+a8×30) / 100+γ

[0071] After solving the equations and calibrating, we can obtain: a1 = 1, a2 = 2, a3 = 5, a4 = 10, a5 = 95, a6 = 20, a7 = 50, a8 = 100, β = 0.6035, γ = 327.54;

[0072] Therefore, the formula for calculating the comprehensive structural parameter X is:

[0073] X=(1×A1+2×A2+5×A3+10×A4+95×A5+20×A6+50×A7+100×A8) / 100;

[0074] The formula for calculating the capacity of a finished battery is:

[0075] Y = 0.6035(1×A1+2×A2+5×A3+10×A4+95×A5+20×A6+50×A7+100×A8) / 100+327.54, or Y = 0.6035X+327.54. (See details below.) Figure 1 As shown.

[0076] evaluate:

[0077] After drying the petroleum coke A to a moisture content of less than 0.1%, its true density was measured to be 1.3751 g / cm³. 3 The volatile matter content is 20%, the ash content is 0.15%, and the sulfur content is 0.3%. Then, it is crushed to about 1 mm using a jaw crusher, and then passed through 200 mesh and 16 mesh sieves in sequence to obtain petroleum coke A with a particle size range of 0.071 to 1 mm.

[0078] The crushed petroleum coke A was placed in a tubular furnace, nitrogen gas was introduced into the tubular furnace, and water vapor was introduced on the basis of nitrogen gas. At the same time, the flow rate of water vapor was controlled to be 10% of the volume flow rate of nitrogen gas. Then, in the nitrogen atmosphere containing water vapor, it was heated from room temperature to 1200℃ at a rate of 70℃ / min for 1 hour to obtain heat-treated petroleum coke A.

[0079] Weigh 4.5g of the heat-treated petroleum coke A and place it at the bottom of the mold. Pour the metallographic epoxy resin and curing agent, mixed in a 2:1 mass ratio, into the mold containing the pulverized soft carbon material until it reaches 3 / 4 full. Let it stand at room temperature for 24 hours to cure. After the sample has cured, use an automatic polishing machine to polish it with sandpaper from coarse to fine, and then polish it with alumina polishing liquid until it reaches a mirror finish with a smooth surface free of pits and scratches. After rinsing with water, observe it under a polarizing microscope. Select appropriate parameters to collect polarized photographs, obtaining 520 valid photographs. Starting from one end of the sample, determine the type of optical structure of the substance under the cross intersection. Express the content of each optical structure as a percentage of the number of statistical points to the number of valid points. Substitute the content of each optical structure into the calculation formula of the comprehensive structural parameter X to obtain X. Then substitute X into the calculation formula of the finished battery capacity to obtain the predicted finished battery capacity of the petroleum coke A. The specific results are shown in Table 4 below.

[0080] Verification Example 1

[0081] Petroleum coke A to be tested was dried, jaw crushed, finely ground by air jet milling, and sieved to obtain coke powder with particle sizes D50 = 19.5 μm, D10 = 5.08 μm, and D90 = 29 μm. Then, it was carbonized by heating to 1100 °C at a rate of 4 °C / min and holding at that temperature for 2 hours. Following this, it was graphitized at 3000 °C for 10 hours. After graphitization, it was pulverized and graded to obtain a powder with D50 = 16 μm and a specific surface area of ​​1.59 g / cm³. 3 Graphite powder with a magnetic material content of less than 1 ppm.

[0082] Capacity determination: Using the above-mentioned graphite powder as the negative electrode active material, a slurry was prepared by mixing graphite powder, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2. The slurry was then coated onto copper foil and dried to obtain a surface density of 70 g / m³. 2 Compacted to 1.75 g / cm³ 3 The electrode was used as the working electrode, and a lithium sheet as the counter electrode. A 1 mol / L LiPF6 electrolyte was used, with the solvent being a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio. Charge-discharge tests were conducted within the voltage range of 0.001V to 2.5V. The initial delithiation capacity obtained was the capacity of the finished battery after graphitization of petroleum coke A. The specific results are shown in Table 4 below.

[0083] Example 2

[0084] After drying the needle coke B to a moisture content of less than 0.1%, its true density was measured to be 1.4116 g / cm³. 3 The volatile matter content is 5.62%, the ash content is 0.04%, and the sulfur content is 0.27%. It is then crushed to about 1 mm using a jaw crusher, and then passed through 200 mesh and 16 mesh sieves in sequence to obtain needle coke B with a particle size range of 0.071 to 1 mm.

[0085] The pulverized needle coke B was placed in a tube furnace, nitrogen gas was introduced into the tube furnace, and water vapor was introduced on the basis of nitrogen gas. At the same time, the flow rate of water vapor was controlled to be 10% of the volume flow rate of nitrogen gas. Then, in the nitrogen atmosphere containing water vapor, it was heated from room temperature to 1200℃ at a rate of 70℃ / min for 1 hour to obtain heat-treated needle coke B.

[0086] Weigh 4.5g of the heat-treated needle coke B and place it at the bottom of the mold. Pour the metallographic epoxy resin and curing agent, mixed in a 2:1 mass ratio, into the mold containing the pulverized soft carbon material until it reaches 3 / 4 full. Let it stand at room temperature for 24 hours to cure. After the sample has cured, use an automatic polishing machine to polish it with sandpaper from coarse to fine, and then polish it with alumina polishing liquid until it reaches a mirror finish, with a smooth surface free of pits and scratches. After rinsing with water, observe it under a polarizing microscope. Select appropriate parameters to collect polarized light photographs, obtaining 520 valid photographs. Starting from one end of the sample, determine the optical structure of the substance below the cross intersection.

[0087] The content of each optical structure is expressed as the percentage of its statistical points to the effective points. The content of each optical structure is then substituted into the formula for calculating the comprehensive structural parameter X obtained in the correlation curve construction step of Example 1: X = (1×A1 + 2×A2 + 5×A3 + 10×A4 + 95×A5 + 20×A6 + 50×A7 + 100×A8) / 100 to obtain X. Then, X is substituted into the formula for calculating the finished battery capacity Y = 0.6035X + 327.54 obtained in the correlation curve construction step of Example 1 to obtain the predicted finished battery capacity of the above needle coke B. The specific results are shown in Table 4 below.

[0088] Verification Example 2

[0089] The needle-shaped coke B to be tested was dried, jaw crushed, finely ground by air jet milling, and sieved to obtain coke powder with particle sizes D50 = 18 μm, D10 = 4.08 μm, and D90 = 30 μm. Then, it was carbonized by heating to 1100 °C at a rate of 4 °C / min and holding at that temperature for 2 hours. Following this, it was graphitized at 3000 °C for 10 hours. After graphitization, it was pulverized and graded to obtain a powder with D50 = 16 μm and a specific surface area of ​​1.89 g / cm³. 3 Graphite powder with a magnetic material content of less than 1 ppm.

[0090] Capacity determination: Using the above-mentioned graphite powder as the negative electrode active material, a slurry was prepared by mixing graphite powder, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2. The slurry was then coated onto copper foil and dried to obtain a surface density of 70 g / m³. 2 Compacted to 1.75 g / cm³ 3 The electrode was used as the working electrode, and a lithium sheet as the counter electrode. A 1 mol / L LiPF6 electrolyte was used, with the solvent being a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio. Charge-discharge tests were conducted within the voltage range of 0.001V to 2.5V. The initial delithiation capacity obtained was the final battery capacity after graphitization of the needle-shaped coke B. The specific results are shown in Table 4 below.

[0091] Example 3

[0092] After drying the asphalt coke C to a moisture content of less than 0.1%, its true density was measured to be 1.39 g / cm³. 3 The volatile matter content is 7.47%, the ash content is 0.11%, and the sulfur content is 0.4%. It is then crushed to about 1 mm using a jaw crusher, and then passed through 200 mesh and 16 mesh sieves in sequence to obtain asphalt coke C with a particle size range of 0.071 to 1 mm.

[0093] The crushed pitch coke C was placed in a tube furnace, nitrogen was introduced into the tube furnace, and water vapor was introduced on the basis of nitrogen. At the same time, the flow rate of water vapor was controlled to be 10% of the volume flow rate of nitrogen. Then, in the nitrogen atmosphere containing water vapor, it was heated from room temperature to 1200℃ at a rate of 70℃ / min for 1 hour to obtain heat-treated pitch coke C.

[0094] Weigh 4.5g of the heat-treated pitch coke C and place it at the bottom of the mold. Pour the epoxy resin and curing agent, mixed in a 2:1 mass ratio, into the mold containing the pulverized soft carbon material until it reaches 3 / 4 full. Let it stand at room temperature for 24 hours to cure. After the sample has cured, use an automatic polishing machine to polish it with sandpaper from coarse to fine, and then polish it with alumina polishing liquid until it reaches a mirror finish, with a smooth surface free of pits and scratches. After rinsing with clean water, observe it under a polarizing microscope. Select appropriate parameters to collect polarized light photographs, obtaining 520 valid photographs. Starting from one end of the sample, determine the optical structure of the substance below the cross intersection.

[0095] The content of each optical structure is expressed as the percentage of its statistical points to the effective points. The content of each optical structure is then substituted into the formula for calculating the comprehensive structural parameter X obtained in the correlation curve construction step of Example 1: X = (1×A1 + 2×A2 + 5×A3 + 10×A4 + 95×A5 + 20×A6 + 50×A7 + 100×A8) / 100 to obtain X. Then, X is substituted into the formula for calculating the finished battery capacity Y = 0.6035X + 327.54 obtained in the correlation curve construction step of Example 1 to obtain the predicted finished battery capacity of the above-mentioned pitch coke C. The specific results are shown in Table 4 below.

[0096] Verification Example 3

[0097] The asphalt coke C to be tested was dried, jaw crushed, finely ground by air jet milling, and sieved to obtain coke powder with particle sizes D50 = 17 μm, D10 = 6.1 μm, and D90 = 27.5 μm. Then, it was carbonized by heating to 1100℃ at a rate of 4℃ / min and holding at that temperature for 2 hours, followed by graphitization at 3000℃ for 10 hours. After graphitization, it was pulverized and graded to obtain a particle size of D50 = 15 μm and a specific surface area of ​​1.59 g / cm³. 3 Graphite powder with a magnetic material content of less than 1 ppm.

[0098] Capacity determination: Using the above-mentioned graphite powder as the negative electrode active material, a slurry was prepared by mixing graphite powder, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2. The slurry was then coated onto copper foil and dried to obtain a surface density of 70 g / m³. 2 Compacted to 1.75 g / cm³ 3The electrode was used as the working electrode, and a lithium sheet as the counter electrode. A 1 mol / L LiPF6 electrolyte was used, with the solvent being a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio. Charge-discharge tests were conducted within the voltage range of 0.001V to 2.5V. The initial delithiation capacity obtained was the capacity of the finished battery after graphitization of pitch coke C. The specific results are shown in Table 4 below.

[0099] Table 4

[0100]

[0101] As shown in the table above, the contents of various optical structures A1-A8 of different types of coke tested according to the evaluation method provided by this invention are substituted into the calculation formula of the comprehensive structural parameter X to quickly predict the capacity of artificial graphite. The results are similar to those obtained by assembling batteries after 3-4 months of graphitization treatment, indicating that the evaluation method provided by this invention is accurate and reliable. Moreover, the prediction time of the evaluation method provided by this invention is only about 2-3 days, which not only greatly saves the manpower and resources of anode companies in screening raw materials, but also provides a basis for coke production units and research institutes to adjust operating conditions and change test conditions, which has significant economic and social benefits.

[0102] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A rapid evaluation method for the properties of artificial graphite raw materials, characterized in that, Includes the following steps: Crushing: Dry and crush the soft carbon material to 0.071-1 mm to obtain crushed soft carbon material; Heat treatment: The pulverized soft carbon material is heat-treated in a nitrogen atmosphere containing water vapor to obtain heat-treated soft carbon material. Microstructure testing: The heat-treated soft carbon material was statically cured with epoxy resin and curing agent, polished, and the resulting optical sheet was examined by a polarizing microscope to obtain the content of each optical structure. Capacity testing: Soft carbon material is carbonized and graphitized to obtain graphite powder; the graphite powder is tested to obtain the capacity of the finished battery after graphitization of the soft carbon material. Constructing correlation curves: Correlation curves are obtained by correlating the content of each optical tissue with the capacity of the finished battery; Evaluation: The battery capacity of the soft carbon material under test is evaluated using the correlation curve. In the process of constructing the correlation curve, the capacity testing step uses the same soft carbon material as the pulverizing step, and there are at least 10 types. When evaluating the soft carbon material under test using the correlation curve, the capacity testing step and the step of constructing the correlation curve are omitted.

2. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 1, characterized in that, In the pulverization step, the dried soft carbon material has a moisture content of less than 0.1%, a true density of 1.362~1.425 g / cm3, a volatile matter content of 3%~20%, an ash content of 0.01%~0.5%, and a sulfur content of 0.1%~5%; and / or The soft carbon material is selected from at least one of petroleum coke, needle coke, and pitch coke; and / or The soft carbon materials are at least 16 types.

3. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 1, characterized in that, In the heat treatment step, the temperature of the heat treatment is 1100~1300℃, and the time is 0.5-2h; The volume content of water vapor in the nitrogen atmosphere containing water vapor is 8% to 12%.

4. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 1, characterized in that, In the microstructure testing step, the content of each optical tissue is calculated according to the following formula. Wherein, the total number of effective points of each optical tissue is at least 500; and / or The classification of optical structures in the microstructure testing steps is shown in the table below: The contents of small mosaic, medium mosaic, coarse mosaic, small piece, large piece, fine short fiber, coarse fiber and long fiber are calculated using A1, A2, A3, A4, A5, A6, A7 and A8 respectively; a1, a2, a3, a4, a5, a6, a7 and a8 are the structural contribution factors of each optical structure.

5. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 4, characterized in that, In the capacity testing step, the soft carbon powder has a D50 of 8~22μm, a D10 of 2~5μm, and a D90 of 25~30μm. The carbonization temperature is 700~1500℃, the time is 0.5~3h, and the heating rate is 1~10℃ / min; The graphitization temperature is 2800~3100℃, and the time is 1~20h; The graphite powder has a D50 of 14~16 μm and a specific surface area of ​​less than 2 cm². 3 / g, with magnetic material content less than 1ppm; Battery assembly and charge / discharge testing include the following steps: Using the graphite powder as the negative electrode active material, a slurry was prepared by mixing graphite, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder in a mass ratio of 95:1.5:1.5:

2. The slurry was then coated onto copper foil and dried to obtain an areal density of 70 g / m³. 2 The compacted density is 1.75 g / cm³. 3 Electrodes; Using the aforementioned electrode as the working electrode, a lithium sheet as the counter electrode, and 1 mol / L LiPF6 as the electrolyte, the electrolyte is a mixed solvent composed of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC in a volume ratio of 1:1:

1. Charge-discharge tests are performed; the voltage range of the charge-discharge test is 0.001–2.5V, and the initial delithiation capacity obtained is the capacity of the finished battery after graphitization of the soft carbon material.

6. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 5, characterized in that, In the capacity testing step, the soft carbon powder has a D50 of 15~18μm, a D10 of 3~4μm, and a D90 of 25~27μm.

7. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 5, characterized in that, The carbonization temperature is 800~1200℃, the time is 1~2h, and the heating rate is 3~4℃ / min.

8. The rapid evaluation method for the properties of artificial graphite raw materials as described in claim 5, characterized in that, The graphitization temperature is 2950~3050℃, and the time is 5~10h.

9. The rapid evaluation method for the properties of artificial graphite raw materials as described in any one of claims 5-8, characterized in that, The step of constructing the correlation curve further includes combining the content of each optical tissue with the structural contribution factor of the optical tissue to obtain a comprehensive structural parameter X, and then correlating the comprehensive structural parameter X with the capacity of the finished battery. The comprehensive structural parameter X is calculated according to the following formula: X=(a1×A1+a2×A2+a3×A3+a4×A4+a5×A5+a6×A6+a7×A7+a8×A8) / 100; The correlation curve is Y = βX + γ; where Y is the finished battery capacity, γ is the intercept, and β is the slope.

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