Composite pyrobase graphite negative electrode active material and preparation and application thereof

Abstract

The present application belongs to the field of negative electrode material, and particularly relates to a preparation method of composite pyrocarbon-based graphite negative electrode active material. The composite material containing high-sulfur petroleum coke, composite treatment agent and binder A is pre-treated in a protective atmosphere at T1 temperature for first-stage heat preservation, and then treated at P1 pressure and T2 temperature for second-stage heat preservation to obtain high-sulfur pyrocarbon; the composite treatment agent comprises (NH4 + )nX and M a Y b ; X is anion, T1 is 250-550 DEG C, T2 is 700-1200 DEG C; P1 is less than or equal to 0.1 atm; the acicular coke and binder B are compounded and treated in a heat preservation atmosphere at T3 temperature for heat preservation to obtain acicular coke-based carbon; the high-sulfur pyrocarbon-based carbon and the acicular coke-based carbon are compounded and formed, and then subjected to graphitization treatment, followed by cooling to T4 temperature and quenching treatment with a cooling medium to obtain the composite pyrocarbon-based graphite negative electrode active material; wherein T4 is 1200-750 DEG C. The present application also includes the material prepared by the preparation method and the application thereof. The material has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrode material technology, and specifically relates to a negative electrode material. Background Technology

[0002] Lithium-ion batteries are a typical representative of new green rechargeable battery systems, and due to their excellent performance, they are widely used in many fields. The comprehensive performance of lithium-ion battery anode materials is key to achieving long cycle life and high energy density. Graphite materials, due to their advantages such as low delithiation potential, high theoretical lithium intercalation capacity, good cycle stability, and good reversibility, are crucial for the commercialization of lithium-ion batteries. Currently, commercially available lithium-ion battery anode materials are still mainly graphite, including natural graphite and artificial graphite. Natural graphite ore is abundant, but the purification process of natural graphite requires sophisticated equipment. The abundant active groups on the surface of natural graphite lead to side reactions with the electrolyte, resulting in lithium source loss. In addition, the anisotropy of natural graphite requires optimization through special processes to improve its performance, resulting in high processing costs and poor fast-charging performance. Artificial graphite is generally modified by coating coke (petroleum coke, needle coke, etc.) with pitch. Currently, there is an imbalance in the supply of petroleum coke in China, with increased production of high-sulfur petroleum coke and a severe shortage of low-sulfur petroleum coke. Therefore, the development of high-sulfur petroleum coke-based carbon anode materials is of great significance for expanding the application fields of lithium-ion batteries and reducing the production cost of anode materials. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a method for preparing composite coke-based graphite anode active materials, aiming to obtain high-performance anode active materials, particularly those with super-fast charging performance and high-temperature resistance, based on low-cost coke preparation.

[0004] The second objective of this invention is to provide an artificial graphite anode material with high compaction, high capacity, and fast charging performance prepared by the aforementioned method.

[0005] The third objective of this invention is to provide the application of the artificial graphite anode material prepared by the aforementioned method in fast-charging lithium secondary batteries, and the resulting lithium secondary battery.

[0006] High-sulfur coke refers to coke with a sulfur content of 3% or higher. Due to its high sulfur content, primarily in the form of organic sulfur, its conversion and reuse are difficult. When preparing anode materials from high-sulfur coke using conventional low-sulfur coke preparation processes, it is difficult to effectively convert the high organic sulfur content, which is detrimental to the performance of the prepared anode material, particularly its rate capability and cycle performance under extreme conditions. To address this problem, this invention provides the following solution:

[0007] A method for preparing a composite coke-based graphite anode active material involves pre-treating a composite material containing high-sulfur petroleum coke, a composite treatment agent, and a binder A under a protective atmosphere and at a temperature of T1, followed by a second stage of heat preservation treatment under a pressure of P1 and at a temperature of T2 to obtain high-sulfur coke-based carbon.

[0008] The composite treatment agent includes (NH4) + )nX and M a Y b X is an anion, n is the absolute value of the oxidation state of X, M is a transition metal element, Y is an anionic element, a is the absolute value of the oxidation state of Y, and b is the absolute value of the oxidation state of M.

[0009] T1 is 250–550℃, T2 is 700–1200℃; P1 is less than or equal to 0.1 atm;

[0010] Needle coke and binder B are combined and kept in a heat-insulating atmosphere at a temperature of T3 to obtain needle coke-based carbon.

[0011] The composite coke-based graphite anode active material is prepared by graphitizing high-sulfur coke-based carbon and needle-shaped coke-based carbon, then cooling it to T4 temperature and quenching it with a cooling medium.

[0012] Among them, T4 is 1200~750℃.

[0013] To address the unsatisfactory lithium-ion compatibility, lithium storage, and transport performance of anode active materials prepared from high-sulfur coke, this invention innovatively involves a combined T1 and P1-T2 modification treatment of high-sulfur coke with the assistance of a composite treatment agent. This effectively converts excess electrochemically harmful sulfur in the high-sulfur coke and modifies the physical and chemical properties of the material through the conversion process, making it suitable for lithium-ion insertion, extraction, and transport. Furthermore, the combination with needle coke and subsequent quenching treatment improves the physical and chemical bonding compatibility between coke particles, further enhancing the lithium-ion and electron transport network, pathways, and structural stability. The method described in this invention achieves synergy, enabling the preparation of anode active materials from high-sulfur coke. Moreover, it significantly improves the super-fast charging capability and cycle stability under extreme conditions (such as high-temperature storage conditions) of the prepared materials.

[0014] In this invention, the modification treatment of T1 and P1~T2 with the assistance of a combined treatment agent, the compounding of needle coke, and the quenching treatment are the key to synergistically solving the problem of preparing high-sulfur coke-based negative electrodes and improving the material properties.

[0015] In this invention, the high-sulfur petroleum coke is a byproduct obtained from crude oil residue through coking during the crude oil refining process.

[0016] The particle size of the high-sulfur coke primary particles is not particularly required, for example, it is 5 to 15 μm, and more preferably 5 to 8 μm.

[0017] Preferably, the sulfur content of the high-sulfur coke is greater than or equal to 3 wt%, preferably 4 to 10 wt.%, and can be further preferred to be 5 to 9 wt. considering the preparation effect and cost.

[0018] In this invention, based on the synergistic control of the components of the combined treatment agent, and further combined with the control of T1, P1, and T2 parameters, MNC active bonds can be formed, which can effectively convert harmful sulfur in high-sulfur coke, and simultaneously remodel and modify the physical and chemical structure of the material. This can unexpectedly improve the compatibility of the prepared material with lithium ions.

[0019] Preferably, in the composite treatment agent, X is Cl-, F-, HCO3-, Ac-, or CO3-. 2- At least one of them;

[0020] Preferably, M is at least one of iron, cobalt, and nickel, and nickel is preferred;

[0021] Preferably, Y is at least one of Cl, NO3, O, and C2O4, and more preferably NO3.

[0022] Preferably, in the composite treatment agent, (NH4) + )nX and M a Y b The weight ratio is 1-20:1-5, preferably 3-6:1.

[0023] In this invention, the adhesive A can be an organic compound with adhesive properties known in the industry. Preferably, the adhesive A is at least one of asphalt, phenolic resin, glucose, sucrose, polyphenylene nitrate, polypyrrole, and polydopa.

[0024] Preferably, the weight ratio of high-sulfur petroleum coke, composite treatment agent, and binder A is 100:1 to 25:5 to 15; more preferably, it is 100:5 to 20:5 to 10; and even more preferably, it is 100:10 to 15:8 to 10.

[0025] Preferably, the high-sulfur petroleum coke, composite treatment agent, and binder A are spheroidized to form secondary particles with a D50 of 13-18 μm before subsequent processing.

[0026] In this invention, the protective atmosphere is at least one of nitrogen and an inert gas; preferably, it may also contain hydrogen.

[0027] Preferably, the T1 heat preservation process is carried out under normal pressure;

[0028] Preferably, the temperature of T1 is 300–500°C, and more preferably 450–550°C. Under negative pressure and the preferred temperature of T1, the modification effect can be unexpectedly further improved synergistically, thereby improving the material properties.

[0029] Preferably, the heat preservation time at temperature T1 is 1 to 3 hours.

[0030] In this invention, under the synergistic control of the combined treatment agent components, and further combined with the T1 and T2 stage heat preservation treatment under negative pressure P1, the conversion of harmful sulfur in high sulfur coke can be synergistically promoted, and the physicochemical properties of the material can be reconstructed and modified, so that it can unexpectedly adapt to the application requirements of lithium ions and improve the super-fast charging capability of the prepared negative electrode.

[0031] Preferably, P1 is less than or equal to 0.01 atm (standard atmospheric pressure), more preferably less than or equal to 0.005 atm, and considering the processing cost, it can preferably be 0.00001 to 0.005 atm;

[0032] Preferably, the temperature of T2 is 800–1100°C, and more preferably 1000–1100°C.

[0033] Preferably, the heat preservation time at temperature T2 is 1 to 5 hours.

[0034] In this invention, the adhesive B can be a conventional organic compound with adhesive properties in the industry, preferably at least one of asphalt, phenolic resin, glucose, sucrose, polyphenylene oxide, polypyrrole, and polydopa.

[0035] Preferably, the weight ratio of needle coke to binder B is 100:2 to 8; more preferably, it is 100:5 to 6.

[0036] Preferably, the temperature of T3 is 650–1050°C; more preferably, it is 900–1000°C.

[0037] Preferably, the heat preservation time at temperature T3 is 2 to 6 hours.

[0038] In this invention, high-sulfur-based carbon and needle-shaped coke are graphitized and then subjected to quenching treatment. This process unexpectedly achieves synergy, improves the particle suitability between coke particles, improves electron-ion transport pathways and kinetics, and thus improves super-fast charging capability and stability under extreme conditions.

[0039] In this invention, high-sulfur-based carbon and needle-shaped coke can be compounded using existing methods, for example, high-sulfur coke-based carbon and needle-shaped coke-based carbon can be compounded and mixed and then pressed into shape.

[0040] Preferably, the weight ratio of high-sulfur coke-based carbon to needle-shaped coke-based carbon is 100:20 to 180, and more preferably 100:30 to 50;

[0041] Preferably, the graphitization temperature is 2700–3000℃;

[0042] Preferably, the graphitization holding time is 8 to 26 hours, and more preferably 15 to 20 hours;

[0043] Preferably, after the graphitized material is cooled to T4, the material is placed directly into the cooling medium system while it is still hot, or the cooling medium is sprayed onto the material.

[0044] Preferably, the cooling medium is an aqueous solution, liquid nitrogen, or dry ice; the aqueous solution is at least one of water, a water-organic solvent mixture, or an aqueous solution of an organic acid; the organic solvent is a solvent miscible with water. The organic acid is, for example, a C1-C4 carboxylic acid. This invention has found that rapid cooling in an acid-organic acid system helps to further synergistically improve performance, particularly improving fast charging and high-temperature stability.

[0045] Preferably, when the cooling medium is an aqueous solution, its initial temperature is less than or equal to 60°C.

[0046] A preferred preparation method of the present invention includes the following steps:

[0047] Step (1): Crush the high-sulfur petroleum coke into primary particles with a particle size of 5-8 μm, and then crush the primary particles of high-sulfur petroleum coke and (NH4) into primary particles. + )nX、M a Y b Asphalt is mixed evenly in a certain proportion and then granulated to obtain secondary particles with a particle size of 13-18 μm. The secondary particles are then subjected to a two-stage heat treatment. The first stage heat treatment is carried out under normal pressure at a temperature of 250-550℃; the second stage heat treatment is carried out under negative pressure at a pressure of 1-50 Pa and a temperature of 700-1200℃. The resulting product is labeled GLJ-C. X is Cl- or NO3-; M is iron, cobalt, or nickel; Y is Cl- or NO3-; and the high-sulfur petroleum coke is mixed with (NH4+). + The mass ratio of nX is 100:1~20, and the high-sulfur graphite coke is mixed with M. a Y b The mass ratio of high-sulfur petroleum coke to pitch is 100:1 to 5, and the mass ratio of high-sulfur petroleum coke to pitch is 100:5 to 15.

[0048] Step (2): Crush needle coke into particles with a particle size of 5-10 μm, mix these particles with asphalt (mass ratio of 100:2-8) evenly, and then perform heat treatment under normal pressure to obtain the product labeled ZZJ-C.

[0049] Step (3): Mix GLJ-C and ZZJ-C at a mass ratio of 100:20 to 180, press them into blocks, and then perform graphitization treatment. During the cooling process, when the temperature drops to 1200 to 750°C, place the graphitized material in a cooling medium while it is still hot to quench it. Finally, after solid-liquid separation, drying, and dispersing, the final negative electrode material can be obtained.

[0050] The present invention also provides a composite coke-based graphite anode active material prepared by the aforementioned preparation method.

[0051] The method described in this invention can endow materials with special physical and chemical properties. In addition, the materials prepared by the method have excellent lithium-ion compatibility and excellent lithium storage and lithium transport capabilities, and can exhibit excellent capacity, rate capability, cycle stability and high temperature stability.

[0052] The present invention also provides an application of the composite coke-based graphite anode active material prepared by the above preparation method, which is used as an anode active material for lithium secondary batteries.

[0053] In a preferred application, it is used as a negative electrode active material, and is compounded with conductive agents and binders to obtain a negative electrode material. The conductive agents and binders are both materials known in the industry.

[0054] In a further preferred application, the negative electrode material is applied to the surface of the negative electrode current collector to form the negative electrode. Existing conventional methods can be used, such as a coating method, to apply the negative electrode material of this invention onto the current collector to form the negative electrode. The current collector can be any material known in the industry.

[0055] In a further preferred application, the negative electrode, positive electrode, separator, and electrolyte are assembled into a lithium secondary battery.

[0056] A lithium secondary battery comprising the composite coke-based graphite anode active material prepared by the aforementioned method.

[0057] The lithium secondary battery, wherein the negative electrode sheet comprises the graphite negative electrode material.

[0058] Preferably, the lithium secondary battery is a lithium-ion battery.

[0059] The beneficial effects of the technical solution of this invention are as follows:

[0060] This invention innovatively employs a combined T1 and P1-T2 modification treatment on high-sulfur coke with the assistance of a composite treatment agent. This effectively converts excess electrochemically harmful sulfur in the high-sulfur coke and modifies the physical and chemical properties of the material through the behavior of the conversion process, making it suitable for lithium-ion insertion, extraction, and transport. Furthermore, the combination with needle coke and subsequent quenching treatment improves the physical and chemical compatibility between coke particles, further enhancing the lithium-ion and electron transport network, pathways, and structural stability. The method described in this invention achieves synergy, enabling the preparation of negative electrode active materials from high-sulfur coke. Moreover, it significantly improves the super-fast charging capability and cycle stability under extreme conditions of the prepared materials. Attached Figure Description

[0061] Appendix Figure 1 The image shows the SEM image of the final sample obtained in Example 1.

[0062] Appendix Figure 2 This is a TEM image of the final sample obtained in Example 1. Detailed Implementation

[0063] The following examples illustrate the specific steps of the present invention. It should be understood that these examples are merely illustrative and not intended to limit the scope of the invention in any way. Various processes and methods not described in detail in this invention are conventional methods known in the art.

[0064] Example 1

[0065] Step (1): Crush high-sulfur petroleum coke (sulfur content 7.58 wt.%) into primary particles with a particle size of 5 μm. Mix the primary particles of high-sulfur petroleum coke, the combined treatment agent (containing ammonium fluoride (labeled as component a) and nickel nitrate (labeled as component b) in a weight ratio of 10:2) and asphalt in a mass ratio of 100:12:10. Place the mixture in a fusion granulator for granulation to obtain powder with a particle size of 15 μm. Place the obtained powder in an atmosphere furnace for the following heat treatment: introduce nitrogen into the atmosphere furnace, heat to 500℃ (T1) at 5℃ / min, hold for 2h, then evacuate the system to make the negative pressure of the system 20Pa (labeled as P1), then heat to 1000℃ (labeled as T2) at 5℃ / min, hold for 2h, and cool to room temperature to obtain product GLJ-C.

[0066] Step (2): The needle coke is crushed into particles with a particle size of 8 μm. The particles are mixed with asphalt at a mass ratio of 100:5 and then placed in an atmosphere furnace. Under nitrogen protection, the temperature is increased to 1000℃ (marked as T3) at 5℃ / min. After holding at this temperature for 2 hours, the mixture is cooled to room temperature to obtain the product ZZJ-C.

[0067] Step (3): Mix GLJ-C and ZZJ-C at a mass ratio of 100:50, and then press them in an isostatic press at a pressure of 80MPa and a holding time of 5min. Perform conventional graphitization treatment on the pressed block at a temperature of 3000℃ for 18h. During the cooling process, when the temperature drops to 800℃ (marked as T4), place the material in ice water (quenching medium, solid-liquid ratio of 1g / 10~30mL) while it is still hot. Finally, after solid-liquid separation, drying and dispersing, the final negative electrode material can be obtained.

[0068] Physicochemical tests showed that the compacted density of the obtained material was 1.853 g / cm³. 3 .

[0069] According to GB / T 24533-2009, the prepared active material and sodium alginate were slurried at a weight ratio of 90:10 and coated onto a current collector, then cured and dried to prepare a graphite electrode. Using the graphite electrode as the working electrode, lithium metal as the negative electrode, 1 mol / L LiPF6 EC / EMC (volume ratio 1:1) as the electrolyte, and a PE-PP composite membrane as the separator, CR2025 coin cells were assembled in an argon-filled dry glove box. Electrochemical performance was tested at room temperature in the voltage range of 0.001-2.0V, with a charge / discharge test current density of 0.2C. The initial reversible capacity was recorded as 358 mAh / g, with a coulombic efficiency of 92.1% and a capacity retention of 98.9% after 500 cycles (newly prepared cycling performance); the reversible specific capacity at 10C was 341 mAh / g, and the reversible specific capacity at 20C was 321 mAh / g; the capacity retention after 7 days of storage at 0.2C and 500 cycles at room temperature was 92.4% (high-temperature storage performance; the retention rates after 7 days of storage at 55°C in the following cases are all test results under those conditions).

[0070] Example 2

[0071] Compared to Example 1, the only difference is that the composition and ratio of the combined treatment agent are changed. The experimental group includes:

[0072] Group a: In the combined treatment agent, component a is NH4HCO3; component b is Co3O4; other operations and parameters are the same as in Example 1;

[0073] Group b: In the combined treatment agent, component a is NH4F; component b is Ni2C2O4; (preferred ammonium salts and transition metal salts) other operations and parameters are the same as in Example 1;

[0074] Group C: High-sulfur petroleum coke grade 1 granules, combined treatment agent, and asphalt in a mass ratio of 100:20:15; other operations and parameters are the same as in Example 1;

[0075] Group d: High-sulfur petroleum coke grade 1 granules, combined treatment agent, and asphalt in a mass ratio of 100:7:5. Other operations and parameters are the same as in Example 1;

[0076] Electrochemical tests were performed according to the method in Example 1, and the results were as follows:

[0077] Group A: Initial reversible capacity was 352 mAh / g, coulombic efficiency was 91.3%, and capacity retention after 500 cycles was 98.3%; reversible specific capacity at 10C was 337 mAh / g, and reversible specific capacity at 20C was 314 mAh / g; capacity retention after 7 days of storage at 55℃ was 90.6%.

[0078] Group B: Initial reversible capacity was 353 mAh / g, coulombic efficiency was 91.8%, and capacity retention after 500 cycles was 98.5%; reversible specific capacity at 10C was 336 mAh / g, and reversible specific capacity at 20C was 314 mAh / g; capacity retention after 7 days of storage at 55℃ was 91.1%.

[0079] Group C: Initial reversible capacity was 355 mAh / g, coulombic efficiency was 92.0%, and capacity retention after 500 cycles was 98.6%; reversible specific capacity at 10C was 339 mAh / g, and reversible specific capacity at 20C was 315 mAh / g; capacity retention after 7 days of storage at 55℃ was 91.2%.

[0080] Group d: Initial reversible capacity was 352 mAh / g, coulombic efficiency was 91.8%, and capacity retention after 500 cycles was 98.2%; reversible specific capacity at 10C was 335 mAh / g, and reversible specific capacity at 20C was 317 mAh / g; capacity retention after 7 days of storage at 55℃ was 91.7%.

[0081] As can be seen from Examples 1 and 2, using NH4F and nickel nitrate yields a better synergistic effect, and further controlling their dosage to a mass ratio of high-sulfur petroleum coke, combined treatment agent, and asphalt of 100:5 to 20:5 to 10, especially 100:10 to 15:8 to 10, can achieve even better performance.

[0082] Example 3

[0083] Compared with Example 1, the only difference is that T1 / P1 and T2 are changed, respectively:

[0084] Group a: T1 is 500℃, and the holding time at T1 is 1h; T2 is 1100℃, and the holding time at T2 is 1h; P1 is 100Pa; other operations and parameters are the same as in Example 1;

[0085] Group b: T1 is 300℃, and the holding time at T1 is 3h; T2 is 800℃, and the holding time at T2 is 5h; P1 is 20Pa; other operations and parameters are the same as in Example 1.

[0086] Group C: T1 is 450℃, and the holding time at T1 is 2h; T2 is 900℃, and the holding time at T2 is 3h; P1 is 50Pa; other operations and parameters are the same as in Example 1.

[0087] Electrochemical tests were performed according to the method in Example 1, and the results were as follows:

[0088] a: Initial reversible capacity is 354 mAh / g, coulombic efficiency is 92.2%, and capacity retention is 98.9% after 500 cycles; reversible specific capacity at 10C is 338 mAh / g, and reversible specific capacity at 20C is 321 mAh / g; capacity retention after 7 days of storage at 55℃ is 92.3%.

[0089] b: The initial reversible capacity is 348 mAh / g, the coulombic efficiency is 91.5%, and the capacity retention rate after 500 cycles is 98.3%; the reversible specific capacity at 10C is 329 mAh / g, and the reversible specific capacity at 20C is 317 mAh / g; the capacity retention rate after 7 days of storage at 55℃ is 90.8%.

[0090] c: Initial reversible capacity is 355 mAh / g, coulombic efficiency is 92.3%, and capacity retention after 500 cycles is 99.3%; reversible specific capacity at 10C is 333 mAh / g, and reversible specific capacity at 20C is 312 mAh / g; capacity retention after 7 days of storage at 55℃ is 91.7%.

[0091] Example 4

[0092] Compared with Example 1, the only difference is that in step (2), the needle coke and pitch are in a mass ratio of 100:6, and the temperature of T3 is 900℃;

[0093] The initial reversible capacity was 351 mAh / g, the coulombic efficiency was 91.4%, and the capacity retention after 500 cycles was 98.2%; the reversible specific capacity at 10C was 335 mAh / g, and the reversible specific capacity at 20C was 317 mAh / g; the capacity retention after 7 days of storage at 55℃ was 92.3%.

[0094] Example 5

[0095] Compared with Example 1, the only difference is that in step (3), the mass ratio of GLJ-C to ZZJ-C is 100:30. Other operations and parameters are the same as in Example 1.

[0096] The initial reversible capacity was 351 mAh / g, the coulombic efficiency was 91.3%, and the capacity retention after 500 cycles was 98.2%; the reversible specific capacity at 10C was 332 mAh / g, and the reversible specific capacity at 20C was 311 mAh / g; the capacity retention after 7 days of storage at 55℃ was 92.1%.

[0097] Example 6

[0098] Compared with Example 1, the only difference is that the quenching medium and conditions are changed, namely:

[0099] Group A: The quenching medium is a 30% v% aqueous ethanol solution;

[0100] Group b: The quenching medium is a 0.01M aqueous solution of acetic acid;

[0101] Group C: The temperature of T4 is 900℃;

[0102] Electrochemical tests were performed according to the method in Example 1, and the results were as follows:

[0103] a: Initial reversible capacity was 361 mAh / g, coulombic efficiency was 93.8%, and capacity retention was 99.4% after 500 cycles; reversible specific capacity at 10C was 348 mAh / g, and reversible specific capacity at 20C was 327 mAh / g; capacity retention was 93.2% after 7 days of storage at 55℃.

[0104] b: The initial reversible capacity is 363 mAh / g, the coulombic efficiency is 94.4%, and the capacity retention rate after 500 cycles is 99.6%; the reversible specific capacity at 10C is 349 mAh / g, and the reversible specific capacity at 20C is 329 mAh / g; the capacity retention rate after 7 days of storage at 55℃ is 93.5%.

[0105] c: Initial reversible capacity was 345 mAh / g, coulombic efficiency was 91.2%, and capacity retention was 98.2% after 500 cycles; reversible specific capacity at 10C was 326 mAh / g, and reversible specific capacity at 20C was 313 mAh / g; capacity retention was 92.1% after 7 days of storage at 55℃.

[0106] Compared with Example 1, it can be seen that rapid cooling in the preferred medium (organic solvent-water and weak acid aqueous solution) can obtain better performance.

[0107] Comparative Example 1:

[0108] Compared with Example 1, the only difference is that in step (1), ammonium chloride was not added to the combined treatment agent, and the amount of the combined treatment agent remained unchanged, while other conditions were the same.

[0109] The determination was performed according to the method in Example 1, and the results are as follows:

[0110] The obtained material has a reversible capacity of 313 mAh / g at 0.2C, a coulombic efficiency of 72%, and a capacity retention of 61% after 500 cycles; the reversible specific capacity at 10C is 126 mAh / g, and the reversible specific capacity at 20C is 67 mAh / g.

[0111] Comparative Example 2

[0112] Compared with Example 1, the only difference is that in step (1), the ammonium fluoride in the combined treatment agent is replaced by an equal mass of sodium fluoride, while other conditions remain the same.

[0113] The obtained material has a reversible capacity of 327 mAh / g at 0.2C, a coulombic efficiency of 73%, and a capacity retention of 66% after 500 cycles; the reversible specific capacity at 10C is 137 mAh / g, and the reversible specific capacity at 20C is 62 mAh / g.

[0114] Comparative Example 3

[0115] Compared with Example 1, the only difference is that in step (1), no transition metal salts are added to the composite treatment agent, and the total amount of the combined treatment agent remains unchanged, while other conditions are the same.

[0116] The obtained material has a reversible capacity of 321 mAh / g at 0.2C, a coulombic efficiency of 71%, and a capacity retention of 65% after 500 cycles; the reversible specific capacity at 10C is 103 mAh / g, and the reversible specific capacity at 20C is 55 mAh / g.

[0117] Comparative Example 4

[0118] Compared with Example 1, the only difference is that in step (1), nickel nitrate in the combined treatment agent is replaced by an equal amount of lithium nitrate, while other conditions are the same.

[0119] The obtained material has a reversible capacity of 305 mAh / g at 0.2C, a coulombic efficiency of 68%, and a capacity retention of 42% after 500 cycles; the reversible specific capacity at 10C is 129 mAh / g, and the reversible specific capacity at 20C is 62 mAh / g.

[0120] Comparative Example 5

[0121] Compared with Example 1, the only difference is that the temperature of T1 is changed to 150°C; other operations and parameters are the same as in Example 1.

[0122] Electrochemical tests were performed according to the method in Example 1, and the results are as follows:

[0123] The reversible capacity at 0.2C is 322 mAh / g, the coulombic efficiency is 71%, and the capacity retention after 500 cycles is 74%; the reversible specific capacity at 10C is 174 mAh / g, and the reversible specific capacity at 20C is 78 mAh / g.

[0124] Comparative Example 6

[0125] Compared with Example 1, the difference is that step (1) does not use negative pressure treatment, that is, P1 is 1 atm (that is, standard atmospheric pressure), and other conditions are the same.

[0126] The obtained material has a reversible capacity of 305 mAh / g at 0.2C, a coulombic efficiency of 72%, and a capacity retention of 62% after 500 cycles; the reversible specific capacity at 10C is 171 mAh / g, and the reversible specific capacity at 20C is 84 mAh / g.

[0127] Comparative Example 7

[0128] Compared with Example 1, the difference is that step (3) does not use rapid cooling, but uses natural cooling with the furnace, while other conditions are the same.

[0129] The obtained material has an initial reversible capacity of 321 mAh / g at 0.2C, a coulombic efficiency of 87.7%, and a capacity retention of 71% after 500 cycles; the reversible specific capacity at 10C is 233 mAh / g, and the reversible specific capacity at 20C is 117 mAh / g.

[0130] As can be seen from Example 1 and Comparative Examples 1-8, without the combined synergistic process described in this invention, the capacity and fast-charging performance of the material decrease significantly, so there is no need to conduct high-temperature storage tests.

Claims

1. A method for preparing a composite coke-based graphite negative electrode active material, characterized in that, a composite material containing high-sulfur petroleum coke, a composite treatment agent, and a binder A is pre-treated in a protective atmosphere at a T1 temperature for a first holding process, and then treated at a P1 pressure and a T2 temperature for a second holding process to obtain high-sulfur coke-based carbon; the high-sulfur petroleum coke has a sulfur content of greater than or equal to 3 wt%; T1 is 250-550℃, and T2 is 700-1200℃; P1 is less than or equal to 0.1 atm; needle coke and a binder B are compounded and treated in a holding atmosphere at a T3 temperature to obtain needle coke-based carbon; the binder B is at least one of pitch, phenolic resin, glucose, sucrose, polyaniline, polypyrrole, and polydopamine; the high-sulfur coke-based carbon and the needle coke-based carbon are compounded and formed, and then subjected to graphitization treatment, followed by cooling to a T4 temperature and quenching treatment using a cooling medium to obtain the composite coke-based graphite negative electrode active material; and T4 is 1200-750℃. The high-sulfur petroleum coke has a sulfur content of 4-8 wt%. The high-sulfur petroleum coke has a D50 of 5-8 μm. The composite treatment agent comprises (NH4 + )nX and M a Y b ; X is anion of at least one of Cl - , F - , HCO3 - , Ac - , CO3 2- , n is absolute value of valence of X; M is transition metal element of at least one of iron, cobalt and nickel; Y is anion of at least one of Cl, NO3, O and C2O4; a is absolute value of valence of Y, b is absolute value of valence of M; and the binder A is at least one of asphalt, phenol formaldehyde resin, glucose, sucrose, polyaniline, polypyrrole and polydopamine. The weight ratio of the high-sulfur petroleum coke, the composite treatment agent, and the binder A is 100:1-25:5-15. The high-sulfur petroleum coke, the composite treatment agent, and the binder A are spheroidized to form secondary particles with a D50 of 13-18 μm, and then subjected to subsequent treatment. The protective atmosphere is at least one of nitrogen and an inert gas. The protective atmosphere further contains hydrogen.

2. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, In the complex treatment agent, the weight ratio of (NH4 + nX and M a Y b is 1-20: 1-5.

3. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, The T1 holding process is performed at normal pressure.

4. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, The holding time at the T1 temperature is 1-3 h.

5. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, P1 is less than or equal to 0.01 atm.

6. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, P1 is less than or equal to 0.005 atm.

7. The preparation method of the composite coke-based graphite anode active material as described in claim 1, characterized in that, The holding time at the T2 temperature is 1-5 h.

8. The method of claim 7, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The weight ratio of the needle coke and the binder B is 100:2-8. ​ 9. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: T3 is 650-1050℃. ​ 10. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The holding time at the T3 temperature is 2-6 h. ​ 11. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The high-sulfur coke-based carbon and the needle coke-based carbon are compounded and formed. ​ 12. The method of producing a complex pyrobase graphite negative electrode active material according to claim 11, characterized by, The weight ratio of the high-sulfur coke-based carbon and the needle coke-based carbon is 100:20-180.

13. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The graphitization temperature is 2700-3000℃. ​ 14. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The holding time for graphitization is 8-26 h. ​ 15. The method for preparing the composite coke-based graphite anode active material as described in claim 1, characterized in that, After the graphitized material is cooled to T4, the material is directly placed in a cooling medium system while hot, or the cooling medium is sprayed onto the material.

16. The method of claim 1, wherein the composite pyrobase graphite negative active material is prepared by the steps of: The cooling medium is an aqueous solution, liquid nitrogen, or dry ice; the aqueous solution is at least one of water, a water-organic solvent mixture, and an aqueous organic acid solution; and the organic solvent is a solvent that is miscible with water. ​ 17. The method for preparing the composite coke-based graphite anode active material as described in claim 1, characterized in that, When the cooling medium is an aqueous solution, the initial temperature thereof is less than or equal to 60℃.

18. The method of producing a complex pyrobase graphite negative electrode active material according to claim 17, wherein 24.A composite coke-based graphite negative electrode active material prepared by the method of any one of claims 1-23.

19. The method for preparing the composite coke-based graphite anode active material as described in claim 1, characterized in that, The composite coke-based graphite negative electrode active material is used as a negative electrode active material to prepare a negative electrode material for a lithium secondary battery.

20. The method for preparing the composite coke-based graphite anode active material as described in claim 1, characterized in that, The composite coke-based graphite negative electrode active material is used as a negative electrode active material to prepare a lithium secondary battery.

21. The method for preparing the composite coke-based graphite anode active material as described in claim 1, characterized in that, The composite coke-based graphite negative electrode active material is used as a negative electrode active material to prepare a lithium secondary battery.

22. The method of producing a complex pyrobase graphite negative electrode active material according to claim 21, wherein ​ 23. The method of producing a complex pyrobase graphite negative electrode active material according to claim 22, wherein ​ ​ 25. Use of a composite coke-based graphite negative electrode active material produced according to the production process of any one of claims 1 to 23, characterized in that ​ 26. The use of claim 25, wherein, ​ 27. The use of claim 26, wherein, ​ 28. A lithium secondary battery, characterized by comprising: The negative electrode comprises the composite pyrobase graphite negative electrode active material prepared by the preparation method in any one of claims 1-23.

Images