Microcrystal composite graphite, preparation method thereof and battery

Abstract

The invention provides microcrystalline composite graphite, a preparation method thereof and a battery, and relates to the field of new energy. The calcined coke and the microcrystalline graphite are etched, and etched calcined coke and etched microcrystalline graphite are obtained; the calcined coke after etching, the microcrystalline graphite after etching and asphalt are mixed, the obtained mixture is subjected to low-temperature granulation, and a granulation product is obtained; and carrying out high-temperature roasting on the granulation product to obtain the microcrystalline composite graphite. Low-cost microcrystalline graphite and high-capacity calcined coke are selected, so that the preparation cost is reduced, and meanwhile, the preparation of high-capacity microcrystalline composite graphite can be realized; and the specific surface area and the surface defects of the calcined coke and the microcrystalline graphite are increased through surface etching treatment, so that the oil absorption value is further increased, and a better composite granulation effect is achieved.

Description

Technical Field

[0001] The present application relates to the field of new energy, and particularly to a microcrystalline composite graphite, a preparation method thereof, and a battery. Background Art

[0002] Graphite is one of the most commonly used anode materials, and has advantages such as high bulk density, large capacity, and long cycle life. Graphite includes microcrystalline graphite and artificial graphite, and each of them has some unique advantages, but they also have obvious limitations. For example: Although microcrystalline graphite has good lithium intercalation ability and low cost, due to its low mechanical strength and uneven conductivity, it is difficult to be used alone in high-performance batteries; Although artificial graphite has a stable structure and good conductivity, its high cost and small specific surface area limit its wide application.

[0003] In addition, the compounding of artificial graphite and natural graphite is generally in the way of mixing finished products later. It is relatively difficult to granulate microcrystals or compound granulate the two. The traditional physical mixing method is difficult to achieve good compounding of the two materials and cannot give full play to their respective advantages.

[0004] Therefore, how to effectively combine microcrystalline graphite and artificial graphite to simultaneously improve the comprehensive performance of the material and reduce the cost has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of the present application is to provide a microcrystalline composite graphite, a preparation method thereof, and a battery to solve the above problems.

[0006] To achieve the above purpose, the first aspect of the present application provides a preparation method of a microcrystalline composite graphite, including:

[0007] Etching calcined coke and microcrystalline graphite to obtain etched calcined coke and etched microcrystalline graphite;

[0008] Mixing the etched calcined coke, the etched microcrystalline graphite and pitch, and subjecting the obtained mixture to low-temperature granulation to obtain a granulated product;

[0009] Subjecting the granulated product to high-temperature roasting to obtain microcrystalline composite graphite.

[0010] Optionally, the preparation method of the microcrystalline composite graphite satisfies at least one of the following conditions:

[0011] A. The D50 of the calcined coke and the microcrystalline graphite are each independently 9 μm - 10 μm;

[0012] B. The graphitization degree of the microcrystalline graphite > 96%, and the purity > 99.99%;

[0013] C. The softening point of the asphalt is 250°C - 300°C, the QI is 0 - 0.2%, the TI is 30% - 40%, and the coking value is 70 - 75.

[0014] Optionally, the etching in the method for preparing the microcrystalline composite graphite includes:

[0015] Under the environment of any one or more of CO2, air or water vapor, perform a first gradient temperature increase on the calcined coke and the microcrystalline graphite.

[0016] Optionally, the first gradient temperature increase includes: a first temperature increase, a second temperature increase, a third temperature increase, and a fourth temperature increase that are carried out in sequence;

[0017] The temperature of the first temperature increase is 300°C - 450°C;

[0018] The temperature of the second temperature increase is 500°C - 650°C;

[0019] The temperature of the third temperature increase is 700°C - 900°C;

[0020] The time of the first temperature increase, the second temperature increase, and the third temperature increase are each independently 1h - 2h;

[0021] The temperature of the fourth temperature increase is 1100°C - 1300°C, and the time is 1h - 4h.

[0022] Optionally, the mass ratio of the etched calcined coke to the etched microcrystalline graphite is 6 - 8:2 - 4;

[0023] The mass ratio of the total mass of the etched calcined coke and the etched microcrystalline graphite to the mass of the asphalt is 80 - 90:10 - 20.

[0024] Optionally, the low-temperature granulation includes:

[0025] Introduce nitrogen and perform a second gradient temperature increase during stirring.

[0026] Optionally, the method for preparing the microcrystalline composite graphite satisfies at least one of the following conditions:

[0027] A. The flow rate of the nitrogen is 1m 3 / min - 5m 3 / min;

[0028] B. The stirring rate is 20Hz - 40Hz;

[0029] C. The second gradient temperature increase includes a fifth temperature increase, a sixth temperature increase, and a seventh temperature increase that are carried out in sequence;

[0030] The temperature of the fifth temperature increase is 250°C - 300°C, the temperature of the sixth temperature increase is 350°C - 400°C, and the temperature of the seventh temperature increase is 700°C - 800°C;

[0031] The time of the fifth temperature increase, the sixth temperature increase, and the seventh temperature increase are each independently 1 h - 4 h.

[0032] Optionally, the temperature of the high-temperature calcination is 3000°C - 3200°C, and the time is 2 h - 4 h.

[0033] The second aspect of the present application provides a microcrystalline composite graphite, which is prepared by the preparation method of the microcrystalline composite graphite.

[0034] The third aspect of the present application provides a battery, the raw materials of which include the microcrystalline composite graphite.

[0035] Compared with the prior art, the beneficial effects of the present application include:

[0036] The preparation method of the microcrystalline composite graphite provided by the present application, by selecting low-cost microcrystalline graphite and high-capacity calcined coke, while reducing the preparation cost, can also realize the preparation of high-capacity microcrystalline composite graphite; and by surface etching treatment to increase the specific surface area and surface defects of the calcined coke and microcrystalline graphite, thereby further increasing the oil absorption value to achieve a better composite granulation effect.

[0037] The microcrystalline composite graphite provided by the present application, through the close combination of microcrystalline graphite and calcined coke, optimizes the ion diffusion dynamics and electron transport path at the composite interface of the microcrystalline composite graphite to achieve an improvement in rate performance; and the synergistic effect of microcrystalline graphite and calcined coke improves the reversible capacity and first Coulomb efficiency of the microcrystalline composite graphite; in addition, the microcrystalline composite graphite effectively inhibits the graphite layer peeling and volume expansion problems through the buffering effect of microcrystalline graphite and the mechanical support of calcined coke, and significantly improves the capacity, first Coulomb efficiency and rate performance of the microcrystalline composite graphite material.

[0038] The battery provided by the present application has excellent electrochemical performance, high capacity and good rate performance. Description of the Drawings

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.

[0040] Figure 1 It is the SEM diagram of the microcrystalline composite graphite provided for Example 1. Detailed Description of the Embodiments

[0041] As used herein, the terms:

[0042] "Prepared by..." is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing", or any other variation thereof, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises the listed elements does not have to be limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0043] The conjunctive "consisting of" excludes any unrecited element, step, or component. If used in a claim, this phrase will render the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause within the body of a claim rather than immediately following the subject, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0044] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 - 5" is disclosed, the described range should be interpreted to include the ranges "1 - 4", "1 - 3", "1 - 2", "1 - 2 and 4 - 5", "1 - 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0045] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0046] "Parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. Suppose we say that the mass part of component A is a parts and the mass part of component B is b parts, then it represents the mass ratio of component A to component B as a:b. Or, it represents that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0047] "And / or" is used to indicate that either or both of the stated circumstances may occur. For example, A and / or B includes (A and B) and (A or B).

[0048] It should be noted that microcrystalline graphite has advantages such as a large specific surface area and low cost, but its mechanical strength and conductivity are relatively low; while artificial graphite has excellent conductivity and structural stability, but has disadvantages such as high manufacturing cost and small specific surface area. Therefore, when artificial graphite and microcrystalline graphite are compounded, their respective advantages can be brought into play. In particular, the calcined coke in artificial graphite has the characteristic of high capacity and can match the high capacity of microcrystalline graphite. However, how to compound and granulate microcrystalline graphite and calcined coke well to give full play to their respective advantages is blank in the existing technology.

[0049] Based on this, the first aspect of this application provides a preparation method of microcrystalline composite graphite, including:

[0050] Etching the calcined coke and microcrystalline graphite to obtain etched calcined coke and etched microcrystalline graphite;

[0051] Mixing the etched calcined coke, the etched microcrystalline graphite and pitch, and performing low-temperature granulation on the obtained mixture to obtain a granulated product;

[0052] Performing high-temperature roasting on the granulated product to obtain microcrystalline composite graphite.

[0053] Preferably, the calcined coke includes calcined needle coke.

[0054] In some embodiments, the preparation method of the microcrystalline composite graphite satisfies at least one of the following conditions:

[0055] A. The D50 of the calcined coke and the microcrystalline graphite are each independently 9 μm - 10 μm;

[0056] Optionally, the D50 of the calcined coke and the microcrystalline graphite can each independently be 9 μm, 9.5 μm, 10 μm or any value between 9 μm - 10 μm;

[0057] B. The graphitization degree of the microcrystalline graphite > 96%, and the purity > 99.99%;

[0058] Optionally, the graphitization degree of the microcrystalline graphite can be 97%, 98%, 99% or any value > 96%, and the purity can be 99.999, 99.9999 or any value > 99.99%;

[0059] C. The softening point of the pitch is 250°C - 300°C, QI is 0 - 0.2%, TI is 30% - 40%, and the coking value is 70 - 75.

[0060] Optionally, the softening point of the pitch can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C or any value between 250°C and 300°C, the QI can be 0, 0.1%, 0.2% or any value between 0 and 0.2%, the TI can be 30%, 35%, 40% or any value between 30% and 40%, and the coking value can be 70, 71, 72, 73, 74, 75 or any value between 70 and 75.

[0061] It should be noted that the pitch is a high-capacity pitch with strong adhesiveness, and the carbonized organizational structure is a large-piece coarse fiber structure; it should also be noted that the high-capacity pitch with strong adhesiveness is beneficial to the composite of calcined coke and microcrystalline graphite;

[0062] In some embodiments, the etching in the method for preparing the microcrystalline composite graphite includes:

[0063] Under the environment of any one or more of CO2, air or water vapor, the calcined coke and the microcrystalline graphite are subjected to a first gradient temperature increase.

[0064] It should be noted that it is preferably to perform the first gradient temperature increase in water vapor. Under a high-temperature environment (usually between 800°C and 1200°C), water vapor reacts with the carbon atoms on the graphite surface to form carbon monoxide (CO) or carbon dioxide (CO). The reaction equations are as follows:

[0065] C + H2O(g) → CO(g) + H2(g);

[0066] C + 2H2O(g) → CO2(g) + 2H2(g);

[0067] Both of these two reactions are endothermic reactions and require a certain activation energy to start;

[0068] Water vapor has higher reactivity to the defects, edge sites or impurities on the graphite surface because the carbon atoms at these positions are more easily oxidized. Therefore, in this way, the defects and impurities in the graphite can be selectively removed, thus achieving the purpose of purification; temperature is one of the key factors determining the reaction rate. As the temperature increases, the reaction rate accelerates, and at the same time, the influence depth on the graphite structure will also increase; however, too high a temperature may cause excessive loss or structural damage of the graphite. Therefore, it is necessary to precisely control the reaction conditions; increasing the water vapor pressure in the system can also improve the reaction efficiency. A higher water vapor partial pressure means that more water molecules can contact the graphite surface, thereby accelerating the oxidation reaction.

[0069] Etching principle at each temperature: In the low-temperature range (about 350°C - 450°C), at lower temperatures, the reaction rate between water vapor and graphite is slow, and the etching effect is not obvious. At this time, there may only be slight surface oxidation, and it mainly occurs at the defect sites or edge positions of graphite; the etching in this temperature range is mainly used for preliminary cleaning of the graphite surface to remove some impurities that are easily oxidized; Medium-temperature range (about 500°C - 900°C): As the temperature rises to this range, the reaction between water vapor and graphite becomes more active, and the etching rate increases significantly. In this temperature range, water vapor can more effectively penetrate into the interlayer structure of graphite and start to effectively remove more impurities and defects. At this time, the etching curve may show a relatively obvious upward trend, indicating that the etching rate increases with the increase in temperature; High-temperature range (about 1100°C - 1300°C): When the temperature further increases, the etching rate reaches the maximum. At these higher temperatures, the reaction between water vapor and graphite becomes very intense, and the etching efficiency is the highest. At the same time, due to the enhanced reaction activity at high temperatures, the etching is not limited to the surface but may also penetrate deep into the graphite interior, resulting in a more thorough purification effect; however, too high a temperature may also cause the loss of graphite itself and even change its crystal structure. Therefore, in actual operation, a balance needs to be found to achieve the best etching effect without damaging the quality of graphite. Ultra-high temperature range (>1200°C): If the temperature continues to rise above 1200°C, although the etching rate will theoretically still increase, this situation should be avoided in practical applications because extreme high temperatures may lead to excessive consumption of the graphite material or generate unnecessary side reactions, such as the destruction of the graphite lattice structure.

[0070] In some embodiments, the first gradient temperature increase includes: a first temperature increase, a second temperature increase, a third temperature increase, and a fourth temperature increase that are carried out in sequence;

[0071] The temperature of the first temperature increase is 300°C - 450°C;

[0072] Optionally, the temperature of the first temperature increase can be 300°C, 350°C, 400°C, 450°C, or any value between 300°C - 450°C;

[0073] The temperature of the second temperature increase is 500°C - 650°C;

[0074] Optionally, the temperature of the second temperature increase can be 500°C, 550°C, 600°C, 650°C, or any value between 500°C - 650°C;

[0075] The temperature of the third temperature increase is 700°C - 900°C;

[0076] Optionally, the temperature of the third temperature increase can be 700°C, 800°C, 900°C, or any value between 700°C - 900°C;

[0077] The time of the first temperature rise, the second temperature rise, and the third temperature rise are each independently 1 h - 2 h;

[0078] The temperature of the fourth temperature rise is 1100°C - 1300°C, and the time is 1 h - 4 h.

[0079] Optionally, the temperature of the fourth temperature rise can be 1100°C, 1200°C, 1300°C, or any value between 1100°C - 1300°C, and the time can be 1 h, 2 h, 3 h, 4 h, or any value between 1 h - 4 h.

[0080] In some embodiments, the mass ratio of the calcined coke after etching to the microcrystalline graphite after etching is 6 - 8:2 - 4;

[0081] Optionally, the mass ratio of the calcined coke after etching to the microcrystalline graphite after etching can be 6:2, 7:2, 8:2, 6:3, 6:4, or any value between 6 - 8:2 - 4;

[0082] It should be noted that when the mass ratio of the calcined coke after etching to the microcrystalline graphite after etching is within the range of 6 - 8:2 - 4, the calcined coke as the main body will not affect the overall electrochemical performance, thus achieving the best cost - effective effect;

[0083] The mass ratio of the total mass of the calcined coke after etching and the microcrystalline graphite after etching to the mass of the pitch is 80 - 90:10 - 20.

[0084] Optionally, the mass ratio of the total mass of the calcined coke after etching and the microcrystalline graphite after etching to the mass of the pitch can be 80:10, 80:15, 80:20, 85:10, 90:10, or any value between 80 - 90:10 - 20.

[0085] In some embodiments, the low - temperature granulation includes:

[0086] Introducing nitrogen and performing a second - gradient temperature rise during stirring.

[0087] In some embodiments, the preparation method of the microcrystalline composite graphite satisfies at least one of the following conditions:

[0088] A. The flow rate of the nitrogen is 1 m 3 / min - 5 m 3 / min;

[0089] Optionally, the flow rate of the nitrogen can be 1 m 3 / min, 2 m 3 / min, 3 m 3 / min, 4 m 3 / min, 5 m 3 / min or 1 m 3 / min - 5 m 3 Any value between;

[0090] B. The rate of the stirring is 20 Hz - 40 Hz;

[0091] Optionally, the rate of the stirring can be 20 Hz, 30 Hz, 40 Hz or any value between 20 Hz - 40 Hz;

[0092] C. The second gradient temperature increase includes a fifth temperature increase, a sixth temperature increase, and a seventh temperature increase carried out in sequence;

[0093] The temperature of the fifth temperature increase is 250°C - 300°C, the temperature of the sixth temperature increase is 350°C - 400°C, and the temperature of the seventh temperature increase is 700°C - 800°C;

[0094] Optionally, the temperature of the fifth temperature increase can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C or any value between 250°C - 300°C, the temperature of the sixth temperature increase can be 350°C, 370°C, 400°C or any value between 350°C - 400°C, and the temperature of the seventh temperature increase can be 700°C, 750°C, 800°C or any value between 700°C - 800°C;

[0095] The time of the fifth temperature increase, the sixth temperature increase, and the seventh temperature increase are each independently 1 h - 4 h.

[0096] It should be noted that the calcined coke needs to go through high-temperature graphitization to become graphite. Through the second gradient temperature increase, the calcined coke reaches a high volume, and the microcrystalline graphite can be further purified, so that the capacity is higher and the performance is better.

[0097] In some embodiments, the temperature of the high-temperature roasting is 3000°C - 3200°C, and the time is 2 h - 4 h.

[0098] Optionally, the temperature of the high-temperature roasting can be 3000°C, 3100°C, 3200°C or any value between 3000°C - 3200°C, and the time can be 2 h, 3 h, 4 h or any value between 2 h - 4 h.

[0099] The second aspect of the present application provides a microcrystalline composite graphite prepared by the preparation method of the microcrystalline composite graphite.

[0100] The third aspect of the present application provides a battery, the raw materials of which include the microcrystalline composite graphite.

[0101] The implementation scheme of the present application will be described in detail below in conjunction with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0102] Example 1

[0103] This example provides a preparation method of microcrystalline composite graphite, and the specific steps are as follows:

[0104] S1: In an environment with a water vapor mass content of 15 wt%, the calcined acicular coke and microcrystalline graphite are heated at a gradient temperature, rising from room temperature of 25 °C to 400 °C, 600 °C, 800 °C, and 1100 °C in sequence, and kept at a constant temperature for 1 h at 400 °C, 600 °C, and 800 °C respectively, and kept at a constant temperature for 2 h at 1100 °C. After that, the temperature is decreased to obtain the etched calcined acicular coke and the etched microcrystalline graphite. Among them, the D50 of the raw material calcined acicular coke and microcrystalline graphite are 9 μm and 9 μm respectively, the graphitization degree of the microcrystalline graphite > 96%, the purity > 99.99%, the sulfur content of the calcined acicular coke of the coke type < 0.5, the ash content < 0.05, and the volatile content < 10;

[0105] S2: Mix the etched calcined acicular coke, the etched microcrystalline graphite and pitch. Among them, the mass ratio of the etched calcined acicular coke to the etched microcrystalline graphite is 6:4, and the mass ratio of the total mass of the etched calcined acicular coke and the etched microcrystalline graphite to the mass of pitch is 88:12. The softening point of the pitch is 260 °C, QI is 0.1%, TI is 35%, and the coking value is 73;

[0106] S3: Under the condition of a nitrogen flow rate of 2 m 3 / min, granulation is carried out by gradient temperature rising at a stirring rate of 40 Hz, rising from room temperature of 25 °C to 300 °C, 350 °C, and 700 °C in sequence, and kept at a constant temperature for 4 h at 300 °C, 350 °C, and 700 °C respectively. After that, the temperature is decreased to obtain the granulated product;

[0107] S4: The granulated product is subjected to high-temperature roasting at 3000 °C to obtain microcrystalline composite graphite.

[0108] The SEM of this microcrystalline composite graphite is as Figure 1 shown.

[0109] Example 2

[0110] The difference from Example 1 is that the mass ratio of the etched calcined acicular coke to the etched microcrystalline graphite is 7:3.

[0111] Example 3

[0112] The difference from Example 1 is that the mass ratio of etched calcined needle coke to etched microcrystalline graphite is 8:2.

[0113] Example 4

[0114] The difference from Example 1 is that etching is carried out in an air environment.

[0115] Example 5

[0116] The difference from Example 1 is that etching is carried out in a CO2 environment.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that the calcined needle coke is not etched and is directly mixed and granulated.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the microcrystalline graphite is not etched and is directly mixed and granulated.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that neither the calcined needle coke nor the microcrystalline graphite is etched and they are directly mixed and granulated.

[0123] Comparative Example 4

[0124] The difference from Example 1 is that the temperature is not increased gradually during the etching process, and it is directly heated to 1100 °C.

[0125] Comparative Example 5

[0126] The difference from Example 1 is that in step S1, the final temperature increase during etching is 750 °C.

[0127] Comparative Example 6

[0128] The difference from Example 1 is that in step S1, the etching environment is N2.

[0129] Comparative Example 7

[0130] The difference from Example 1 is that in step S3, the temperature is not increased gradually during the low-temperature granulation process, and it is directly heated to 700 °C.

[0131] Comparative Example 8

[0132] The difference from Example 1 is that in step S3, the final temperature increase during low-temperature granulation is 500 °C.

[0133] The microcrystalline composite graphite prepared in the above-mentioned examples and comparative examples was made into a CR2430 battery, specifically: mixing according to the mass ratio of graphite: CMC: SP: SBR = 95: 1.5: 1.5: 2, adding an appropriate amount of water to make it into a slurry, coating it on a copper foil, putting the coated electrode sheet into a vacuum drying oven at 110 °C for vacuum drying for 4 h for standby; the electrolyte was 1 mol / L LiPF6 / EC / DEC / DM, the lithium metal sheet was the counter electrode, and the polypropylene microporous membrane was the separator to assemble the battery. The batteries prepared in the above-mentioned examples and comparative examples were tested for product characteristics and performance (capacity, initial Coulombic efficiency, and rate), as shown in Table 1 specifically.

[0134] Among them, the test methods for capacity, initial Coulombic efficiency, and rate are as follows:

[0135] Battery capacity characterization test: First, charge the battery at a constant current of 0.2C to 4.2V, then charge it at a constant voltage until the current is 10 mA, then let it stand for 10 minutes, then discharge it at a constant current of 0.2C to 2.7V, and then let it stand for 10 minutes. The battery is charged and discharged in this program for 3 cycles to obtain the capacity of the battery.

[0136] Rate test: Charge and discharge the prepared button battery according to 0.1C, 0.5C, 1C, 2C, 0.1C for 10 cycles each to test the rate performance of the electrode material.

[0137] Kangta Tap: Test according to the national standard GB / T 21354-2008 "General Method for Determination of Tap Density of Powder Products".

[0138] Micromeritics SSA: Test according to the national standard GB / T 19587-2017, "Determination of Specific Surface Area of Solid Materials by Gas Adsorption BET Method".

[0139] Table 1 Product Characteristics and Performance

[0140]

[0141]

[0142] Analysis:

[0143] As can be seen from Table 1, the capacity, rate, and initial Coulombic efficiency of the examples of the present application are all superior to those of the comparative examples. From the examples, the reversible capacity of Examples 1-5 can be increased to more than 361 mAh / g; from the comparative examples, when etching is not carried out, the granulation effect is poor, the particle size of the prepared product is small and the tap density is insufficient, and the overall rate performance of the comparative example is significantly lower than that of the examples. When gradient heating is not carried out, it will affect various indicators. The specific analysis is as follows:

[0144] It can be seen from Comparative Examples 1-3 that when the calcined needle coke and microcrystalline graphite are not etched, the tap density of the obtained product will be significantly reduced, which will affect the subsequent processing performance.

[0145] It can be seen from Comparative Example 4 that when the etching process is not subjected to gradient temperature increase, the particle size of the final product does not meet the standard, the granulation is not ideal, and the tap density and specific surface area are significantly deteriorated.

[0146] It can be seen from Comparative Example 5 that when the final heating temperature of etching does not reach 1100° C.-1300° C., the granulation is not ideal and the indicators in various aspects are not as good as those in Example 1.

[0147] It can be seen from Comparative Example 6 that when the etching environment is not CO2, air or water vapor, the product has no etching effect, granulation effect, and compaction is not improved, and the final product is not ideal.

[0148] It can be seen from Comparative Example 7 that when the low-temperature granulation process is not subjected to gradient temperature increase, the granulation effect is affected to a certain extent, and the compaction is lost, as can be seen from the particle size and the tap density.

[0149] It can be seen from Comparative Example 8 that when the final heating temperature of low-temperature granulation is not within the range of 700°C-800°C, the etching effect affects the final composite granulation, and the granulation has a certain effect, but the final product has limited improvement in compaction.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0151] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present application and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing microcrystalline composite graphite, characterized in that: include: Etching the calcined coke and microcrystalline graphite to obtain etched calcined coke and etched microcrystalline graphite; The etched calcined coke, the etched microcrystalline graphite and asphalt are mixed, and the obtained mixture is subjected to low-temperature granulation to obtain a granulated product; The granulated product is calcined at high temperature to obtain microcrystalline composite graphite.

2. The method for preparing microcrystalline composite graphite according to claim 1, characterized in that: At least one of the following conditions is met: A. The D50 of the calcined coke and the microcrystalline graphite are independently 9 μm-10 μm; B. The graphitization degree of the microcrystalline graphite is greater than 96%, and the purity is greater than 99.99%; C. The softening point of the asphalt is 250°C-300°C, the QI is 0.05%-0.2%, the TI is 30%-40%, and the coking value is 70-75.

3. The method for preparing microcrystalline composite graphite according to claim 1, characterized in that: The etching comprises: In an environment of any one or more of CO2, air or water vapor, the calcined coke and the microcrystalline graphite are subjected to a first gradient temperature increase.

4. The method for preparing microcrystalline composite graphite according to claim 3, characterized in that: The first gradient temperature increase includes: a first temperature increase, a second temperature increase, a third temperature increase, and a fourth temperature increase performed in sequence; The first heating temperature is 300°C-450°C; The second heating temperature is 500°C-650°C; The third heating temperature is 700°C-900°C; The time for the first heating, the second heating, and the third heating is independently 1h-2h; The temperature of the fourth heating is 1100° C.-1300° C., and the time is 1 h-4 h.

5. The method for preparing microcrystalline composite graphite according to claim 1, characterized in that: The mass ratio of the etched calcined coke to the etched microcrystalline graphite is 6-7:2-4; The mass ratio of the total mass of the etched calcined coke and the etched microcrystalline graphite to the mass ratio of the asphalt is 80-90:10-20.

6. The method for preparing microcrystalline composite graphite according to claim 1, characterized in that: The low temperature granulation comprises: Nitrogen gas was introduced, and the second gradient temperature increase was performed during stirring.

7. The method for preparing microcrystalline composite graphite according to claim 6, characterized in that: At least one of the following conditions is met: A. The flow rate of the nitrogen is 1m 3 / min-5m 3 / min; B. the stirring rate is 20Hz-40Hz; C. The second gradient temperature increase includes a fifth temperature increase, a sixth temperature increase, and a seventh temperature increase performed sequentially; The fifth heating temperature is 250°C-300°C, the sixth heating temperature is 350°C-400°C, and the seventh heating temperature is 700°C-800°C; The time for the fifth temperature rise, the sixth temperature rise, and the seventh temperature rise are each independently 1 hour to 4 hours.

8. The method for preparing microcrystalline composite graphite according to any one of claims 1 to 7, characterized in that: The high temperature calcination temperature is 3000° C.-3200° C., and the time is 2 h-4 h.

9. A microcrystalline composite graphite, characterized in that: The microcrystalline composite graphite is prepared by the preparation method of any one of claims 1 to 8.

10. A battery, characterized in that: The raw material comprises the microcrystalline composite graphite as described in any one of claims 1-9.

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