Regenerated graphite negative electrode material, preparation method thereof, negative electrode and lithium ion battery

Abstract

The embodiment of the invention provides a regenerated graphite negative electrode material, a preparation method thereof, a negative electrode and a lithium ion battery. The preparation method of the regenerated graphite negative electrode material comprises the following steps: mixing waste graphite powder with coke ultrafine powder to obtain a precursor material; the precursor material and a binder are sequentially mixed, kneaded and granulated to obtain precursor particles, the precursor particles are graphitized, the precursor particles are converted into graphite particles, the regenerated graphite negative electrode material is obtained, and the regenerated graphite negative electrode material comprises the graphite particles. According to the preparation method of the regenerated graphite negative electrode material provided by the embodiment of the invention, not only is the recycling of the waste graphite powder realized, but also the resource utilization of the coke ultrafine powder is realized.

Description

Technical Field

[0001] This application relates to the field of battery materials, and in particular to a recycled graphite anode material and its preparation method, an anode, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as the most widely used rechargeable batteries, typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. During charge-discharge cycles, the conversion between electrical and chemical energy relies on the insertion and extraction of lithium ions between the positive and negative electrodes in the internal circuit, as well as the directional migration of electrons in the external circuit. The negative electrode plays a crucial role in storing and releasing lithium ions and conducting current, significantly impacting the battery's energy density, cycle performance, charge-discharge rate, and low-temperature discharge performance. Among numerous materials suitable for negative electrodes, graphite has become the mainstream negative electrode material for large-scale commercial applications due to its advantages such as low cost, high structural stability, non-toxicity, good conductivity, and excellent mechanical properties.

[0003] With the rapid development of new energy fields such as electric vehicles, the market demand for batteries is growing rapidly. At the same time, the stock of waste batteries is also increasing year by year. Therefore, the recycling and disposal of waste batteries has become urgent. However, graphite anodes are prone to structural degradation during battery cycling: long-term charge-discharge cycles can cause irreversible expansion and contraction of the graphite interlayer structure, resulting in problems such as lattice defects and particle breakage. This makes it difficult to directly reuse recycled graphite materials. Summary of the Invention

[0004] Based on this, embodiments of this application provide a recycled graphite anode material, its preparation method, an anode, and a lithium-ion battery.

[0005] In a first aspect, embodiments of this application provide a method for preparing a recycled graphite anode material, comprising:

[0006] Waste graphite powder is mixed with coke ultrafine powder to obtain precursor material;

[0007] The precursor material and binder are mixed and granulated sequentially to obtain precursor particles. The precursor particles are then graphitized to transform them into graphite particles, resulting in a recycled graphite anode material, wherein the recycled graphite anode material comprises graphite particles.

[0008] In some embodiments, the mass ratio of the waste graphite powder to the coke ultrafine powder is (60-80):(20-40); and / or,

[0009] The mass ratio of the binder to the precursor material is (5-8):100; and / or,

[0010] The process of mixing waste graphite powder with coke ultrafine powder to obtain precursor materials includes:

[0011] Modified coke ultrafine powder is obtained by mixing coke ultrafine powder with a dispersant, wherein the mass ratio of dispersant to coke ultrafine powder is (1-3):100; the modified coke ultrafine powder is then mixed with waste graphite powder to obtain a precursor material; the dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, fatty acid soap, sodium polyacrylate, polycarboxylate, hydroxyethyl cellulose, and polyacrylate; and / or,

[0012] Before mixing the waste graphite powder with the coke ultrafine powder, the waste graphite powder is placed in an air atmosphere and subjected to a first oxidation etching at a temperature of 300℃-480℃.

[0013] In some embodiments, the adhesive comprises at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylamide, polyvinyl alcohol, sodium alginate, polyurethane, emulsified asphalt, tar, solid coal tar pitch, petroleum asphalt, phenolic resin, epoxy resin, and polyacrylonitrile; and / or,

[0014] When graphitizing precursor particles, the graphitization temperature is 2800℃-3100℃, and the graphitization time is 70-90 hours; and / or,

[0015] The particle size D50 of the waste graphite powder is 7μm-10μm; and / or,

[0016] The particle size D50 of the coke ultrafine powder is 1μm to 5μm.

[0017] In some embodiments, after converting the precursor particles into graphite particles, the method for preparing the regenerated graphite anode material further includes: mixing the graphite particles with a coating agent to obtain a core-shell structure precursor, and carbonizing the core-shell structure precursor to obtain the regenerated graphite anode material, wherein the regenerated graphite anode material includes graphite particles and a coating layer wrapped around the outer surface of the graphite particles.

[0018] In some embodiments, the mass ratio of the coating agent to the graphite particles is (6-10):100; and / or,

[0019] The coating agent includes a hard carbon precursor and a soft carbon precursor, and the mass ratio of the hard carbon precursor to the soft carbon precursor in the coating agent is (0.4-0.6):(0.4-0.6).

[0020] In some embodiments, the hard carbon precursor comprises a resin, the resin comprising at least one selected from phenolic resin, epoxy resin, polyimide resin, furfural resin, and furfuryl alcohol resin; and / or,

[0021] The soft carbon precursor includes asphalt, the asphalt having a softening point above 150°C, and the asphalt including at least one of coal tar pitch and petroleum asphalt.

[0022] In some embodiments, the precursor particles undergo a second oxidation etching prior to graphitization; and / or,

[0023] During the carbonization process of the core-shell structure precursor, a third oxidation etching is performed on the core-shell structure precursor; and / or,

[0024] The carbonization of the core-shell structure precursor includes:

[0025] In an inert atmosphere, the core-shell structure precursor is heated from room temperature to a first temperature and held at the first temperature for 4 to 7 hours. The first temperature is 80°C to 150°C.

[0026] The core-shell structure precursor is heated from a first temperature to a second temperature and held at the second temperature for 3 to 6 hours. The second temperature is 250°C to 330°C.

[0027] The core-shell structure precursor is heated from the second temperature to the third temperature and held at the third temperature for 2 to 5 hours. The third temperature is 350℃ to 450℃.

[0028] The core-shell precursor is heated from the third temperature to the fourth temperature and held at the fourth temperature for 6-10 hours. The fourth temperature is 800℃-1200℃.

[0029] In some embodiments, the second oxidation etching of the precursor particles includes: placing the precursor particles in an air atmosphere and performing a second oxidation etching at a temperature of 200°C-300°C; and / or,

[0030] The third oxidation etching of the core-shell structure precursor during the carbonization process includes:

[0031] During the process of heating the core-shell structure precursor from the second temperature to the third temperature and / or during the holding process at the third temperature, the inert atmosphere around the core-shell structure precursor is switched to an air atmosphere, and the core-shell structure precursor is subjected to a third oxidation etching in the air atmosphere at a temperature of 370℃-450℃. After the etching is completed, the air atmosphere is switched back to an inert atmosphere.

[0032] Secondly, embodiments of this application provide a recycled graphite anode material prepared by the method described above.

[0033] In some embodiments, the recycled graphite anode material includes graphite particles and a coating layer covering the outer surface of the graphite particles, the coating layer including hard carbon and soft carbon; the hard carbon is infiltrated into the graphite particles;

[0034] From the inner surface to the outer surface of the coating layer, the mass percentage of hard carbon in the coating layer gradually decreases, while the mass percentage of soft carbon in the coating layer gradually increases.

[0035] Thirdly, embodiments of this application provide a negative electrode, including the recycled graphite negative electrode material as described above.

[0036] Fourthly, embodiments of this application provide a lithium-ion battery, including the negative electrode as described above.

[0037] The method for preparing recycled graphite anode material provided in this application involves mixing waste graphite powder with coke ultrafine powder to obtain a precursor material. After mixing, granulating, and graphitizing the precursor material with a binder, the recycled graphite anode material is obtained. This method not only realizes the recycling of waste graphite powder but also the resource utilization of coke ultrafine powder. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0039] Figure 1 A flowchart illustrating the preparation method of the recycled graphite anode material provided in this application embodiment. Detailed Implementation

[0040] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0041] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0042] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a+b, a+c, b+c, or a+b+c, where a, b, and c can be single or multiple.

[0043] "Parts by weight" is a basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit mass, such as 1g, 1kg, 2g, 2kg, etc. If we say that component A has "a" parts by weight and component B has "b" parts by weight, it means the mass ratio of component A to component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike parts by weight, the sum of the parts by weight of all components is not limited to 100 parts.

[0044] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0045] Please see Figure 1 This application provides a method for preparing a recycled graphite anode material, comprising:

[0046] S100, waste graphite powder is mixed with coke ultrafine powder to obtain precursor material.

[0047] For example, the particle size D50 of waste graphite powder is 7μm-10μm, such as 7μm, 8μm, 9μm, 10μm, etc.

[0048] For example, the particle size D50 of the coke ultrafine powder is 1μm to 5μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0049] For example, the mass ratio of waste graphite powder to coke ultrafine powder is (60-80):(20-40), such as 60:40, 70:30, 80:20, etc.

[0050] For example, the waste graphite powder is subjected to a first oxidation etching before being mixed with coke ultrafine powder.

[0051] It should be noted that by performing a first oxidation etching on the waste graphite powder before mixing it with the coke ultrafine powder, micropores can be formed on the surface of the waste graphite powder, thereby enhancing the bonding force between the waste graphite powder and the coke ultrafine powder.

[0052] For example, the first oxidation etching of waste graphite powder includes: placing the waste graphite powder in an air atmosphere and performing the first oxidation etching at a temperature of 300℃-480℃ (e.g., 300℃, 350℃, 400℃, 450℃, 480℃, etc.), and the time for the first oxidation etching is 2 minutes-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, 5 minutes, etc.).

[0053] For example, the process of mixing waste graphite powder with coke ultrafine powder to obtain the precursor material includes:

[0054] Modified coke ultrafine powder is obtained by mixing coke ultrafine powder with a dispersant, wherein the mass ratio of dispersant to coke ultrafine powder is (1-3):100; the modified coke ultrafine powder is then mixed with waste graphite powder to obtain a precursor material.

[0055] For example, a mechanical fusion machine is used to mix coking ultrafine powder and dispersant. The rotation speed of the mechanical fusion machine is 10Hz to 20Hz, and the mixing time is 3 hours to 6 hours.

[0056] It should be noted that by adding a dispersant to the coke ultrafine powder, the self-agglomeration and bridging phenomenon of the coke ultrafine powder can be improved, the flowability of the coke ultrafine powder can be increased, and thus the mixing uniformity of the coke ultrafine powder and waste graphite powder can be improved.

[0057] For example, the mass ratio of dispersant to coke ultrafine powder can be 1:100, 1.5:100, 2:100, 2.5:100, 3:100, etc.

[0058] For example, the dispersant includes at least one of sodium carboxymethyl cellulose (CMC), sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, fatty acid soap, sodium polyacrylate, polycarboxylate (PCE), hydroxyethyl cellulose, and polyacrylate (PAA).

[0059] For example, the raw coke pulverizer is obtained by pulverizing raw coke, which includes at least one of needle coke, petroleum coke, and pitch coke. For example, the pulverizing equipment for pulverizing the raw coke may include one or more of mechanical mills, roller mills, ring roller mills, air jet mills, and jet mills, and the pulverizing equipment is sourced from Hunan Zhongke Xingcheng Graphite Co., Ltd.

[0060] For example, the waste graphite powder is obtained from waste batteries through dismantling, crushing, acid washing, and heat treatment. For example, the waste batteries are at least one of retired 3C digital small batteries, automotive large battery packs, and tested waste batteries (mainly full batteries). For example, the heat treatment temperature is 600℃-950℃, the heat treatment time is 6 hours-12 hours, and after heat treatment, when the waste graphite powder cools to 300℃-480℃, it undergoes a first oxidation etching.

[0061] S200 involves sequentially mixing and granulating the precursor material and binder to obtain precursor particles, and then graphitizing the precursor particles to obtain graphite particles.

[0062] For example, a mechanical fusion machine is used to mix the precursor material and the binder. The rotation speed of the mechanical fusion machine is 20Hz to 30Hz, and the mixing time is 1 hour to 2 hours.

[0063] For example, the mass ratio of the binder to the precursor material is (5-8):100, such as 5:100, 6:100, 7:100, 8:100, etc.

[0064] For example, the adhesive includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate, polyurethane (WPU), emulsified asphalt, tar, solid coal tar pitch, petroleum asphalt, phenolic resin, epoxy resin, and polyacrylonitrile.

[0065] For example, when graphitizing the precursor particles, the graphitization temperature is 2800℃-3100℃ (e.g., 2800℃, 2900℃, 3000℃, 3100℃, etc.), and the graphitization time is 70 hours-90 hours (e.g., 70 hours, 75 hours, 80 hours, 85 hours, 90 hours, etc.).

[0066] For example, in step S200, after converting the precursor particles into graphite particles, the graphite particles can be mixed with a coating agent to obtain a core-shell structure precursor. The core-shell structure precursor is then carbonized to obtain a recycled graphite anode material. At this time, the recycled graphite anode material includes graphite particles and a coating layer wrapped around the outer surface of the graphite particles.

[0067] Understandably, core-shell precursors include graphite particles and coating agents that coat the surface of the graphite particles.

[0068] For example, the coating agent includes a hard carbon precursor and a soft carbon precursor, and the mass ratio of the hard carbon precursor to the soft carbon precursor in the coating agent is (0.4-0.6):(0.4-0.6), such as 0.4:0.6, 0.5:0.5, 0.6:0.4, etc.

[0069] It should be noted that by using a coating agent to coat graphite particles, the hard carbon precursor in the coating agent is carbonized to form hard carbon, and the soft carbon precursor is carbonized to form soft carbon. Since soft carbon has high electrical conductivity and good toughness, and hard carbon has more ion channels and better rigidity, hard carbon and soft carbon can work synergistically to improve the rate performance and cycle performance of the recycled graphite anode material.

[0070] For example, the hard carbon precursor includes a resin, which includes at least one of phenolic resin, epoxy resin, polyimide resin, furfural resin, and furfuryl alcohol resin.

[0071] For example, the soft carbon precursor includes asphalt, the asphalt having a softening point above 150°C, and the asphalt including at least one of coal tar pitch and petroleum asphalt.

[0072] For example, a mechanical fusion machine is used to mix graphite particles and coating agent. The rotation speed of the mechanical fusion machine is 30Hz to 40Hz, and the mixing time is 2 hours to 3 hours.

[0073] For example, the mass ratio of coating agent to graphite particles is (6-10):100, such as 6:100, 7:100, 8:100, 9:100, 10:100, etc.

[0074] For example, the precursor particles are subjected to a second oxidation etching before graphitization.

[0075] It should be noted that by performing a second oxidation etching on the precursor particles before graphitization, micropores can be formed on the surface of the precursor particles. This results in a large number of micropores on the surface of the graphite particles after graphitization. When the graphite particles are mixed with the coating agent, the adhesion between the coating agent and the graphite particles can be enhanced, thus allowing the coating agent to be stably coated on the surface of the graphite particles.

[0076] For example, the second oxidation etching of the precursor particles includes: placing the precursor particles in an air atmosphere and performing a second oxidation etching at a temperature of 200°C-300°C (e.g., 200°C, 230°C, 250°C, 280°C, 300°C, etc.), and the second oxidation etching time is 5 minutes-10 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.).

[0077] For example, during the carbonization of the core-shell structure precursor, the core-shell structure precursor is subjected to a third oxidation etching.

[0078] It should be noted that by performing a third oxidation etching on the core-shell structure precursor during the carbonization process, the hard carbon formed by resin carbonization and the soft carbon formed by pitch carbonization can be intercalated, thereby forming a coating layer on the surface of graphite particles composed of intercalated hard carbon and soft carbon.

[0079] For example, the carbonization of the core-shell structure precursor includes:

[0080] In an inert atmosphere, the core-shell structure precursor is heated from room temperature to a first temperature and held at the first temperature for 4 to 7 hours. The first temperature is 80°C to 150°C.

[0081] The core-shell structure precursor is heated from a first temperature to a second temperature and held at the second temperature for 3 to 6 hours. The second temperature is 250°C to 330°C.

[0082] The core-shell structure precursor is heated from the second temperature to the third temperature and held at the third temperature for 2 to 5 hours. The third temperature is 350℃ to 450℃.

[0083] The core-shell precursor is heated from the third temperature to the fourth temperature and held at the fourth temperature for 6-10 hours. The fourth temperature is 800℃-1200℃.

[0084] For example, the first temperature can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc., and the holding time at the first temperature can be 4 hours, 5 hours, 6 hours, 7 hours, etc.

[0085] For example, the core-shell precursor is heated from room temperature to a first temperature at a heating rate of 2°C to 6°C. For example, the room temperature is 20°C to 25°C.

[0086] For example, the second temperature can be 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, etc., and the holding time at the second temperature can be 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0087] For example, the core-shell precursor is heated from a first temperature to a second temperature at a heating rate of 2°C to 6°C.

[0088] For example, the third temperature can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc., and the holding time at the third temperature can be 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0089] For example, the core-shell precursor is heated from the third temperature to the fourth temperature at a heating rate of 1°C to 5°C.

[0090] For example, the fourth temperature can be 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc., and the holding time at the fourth temperature can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0091] For example, the core-shell precursor is heated from the third temperature to the fourth temperature at a heating rate of 8°C to 12°C.

[0092] It should be noted that the above carbonization process adopts a gradient heating method. When the temperature rises to the first temperature (80℃-150℃), the resin is basically in a completely molten state, uniformly coating the graphite particles with liquid phase. In addition, some of the liquid resin seeps into the interior of the graphite particles from the surface cracks. When the temperature rises to the second temperature (250℃-330℃), the resin initially solidifies but still has weak plasticity. At the same time, the asphalt begins to soften and melt. The asphalt that initially transforms into liquid phase penetrates into the carbon pores of the resin to form a co-intercalated structure. When the temperature rises to the third temperature (350℃-450℃), the asphalt is essentially in a fully molten state for asphalt coating. When the temperature rises to the fourth temperature (800℃-1200℃), the coating layer undergoes carbonization and its strength is enhanced. The carbonized coating layer includes hard carbon formed by resin carbonization and soft carbon formed by asphalt carbonization. The hard carbon penetrates into the graphite particles, and its mass percentage gradually decreases from the inner surface to the outer surface of the coating layer, while the mass percentage of soft carbon gradually increases. Because soft carbon has higher electrical conductivity and better toughness, while hard carbon has more ion channels and better rigidity, the hard and soft carbon can work synergistically to improve the rate performance and cycle performance of the recycled graphite anode material.

[0093] For example, the third oxidation etching of the core-shell structure precursor during the carbonization process includes:

[0094] During the process of heating the core-shell structure precursor from the second temperature to the third temperature and / or during the holding process at the third temperature, the inert atmosphere around the core-shell structure precursor is switched to an air atmosphere. The core-shell structure precursor is then subjected to a third oxidation etching in the air atmosphere at a temperature of 370℃-450℃ (e.g., 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc.). The time for the third oxidation etching is 3 minutes to 8 minutes (e.g., 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, etc.). After the etching is completed, the air atmosphere is switched back to an inert atmosphere.

[0095] It should be noted that during the process of heating the core-shell structure precursor from the second temperature to the third temperature, or during the process of holding at the third temperature, the asphalt is in a gradually melting state. By performing a third oxidation etching on the core-shell structure precursor at this stage, the resin coated on the surface of the graphite particles and already cured can be etched, so that micropores are generated on the surface and / or inside of the resin. This allows the asphalt to be embedded in the resin through the micropores, realizing the co-intercalation structure of resin and asphalt. In turn, after carbonization, the co-intercalation structure of hard carbon and soft carbon is realized.

[0096] For example, the inert atmosphere includes at least one of nitrogen, helium (He), neon (Ne), and argon (Ar).

[0097] The method for preparing recycled graphite anode material provided in this application involves mixing waste graphite powder with coke ultrafine powder to obtain a precursor material. After mixing, granulating, and graphitizing the precursor material with a binder, the recycled graphite anode material is obtained. This method not only realizes the recycling of waste graphite powder but also the resource utilization of coke ultrafine powder.

[0098] Furthermore, after converting the precursor particles into graphite particles, the graphite particles can be mixed with a coating agent to obtain a core-shell structured precursor. The core-shell structured precursor can then be carbonized to obtain a recycled graphite anode material. It should be noted that by using a coating agent to coat the graphite particles, the hard carbon precursor in the coating agent is carbonized to form hard carbon, and the soft carbon precursor is carbonized to form soft carbon. Since soft carbon has higher electrical conductivity and better toughness, while hard carbon has more ion channels and better rigidity, hard carbon and soft carbon can work synergistically to improve the rate performance and cycle performance of the recycled graphite anode material.

[0099] This application also provides a recycled graphite anode material, which is prepared by the above-described method for preparing recycled graphite anode materials.

[0100] For example, the recycled graphite anode material includes graphite particles and a coating layer covering the outer surface of the graphite particles, the coating layer including hard carbon and soft carbon. For example, the hard carbon is formed by resin carbonization, and the soft carbon is formed by pitch carbonization.

[0101] For example, the hard carbon is infiltrated into the graphite particles, and from the inner surface to the outer surface of the coating layer, the mass percentage of the hard carbon in the coating layer gradually decreases, while the mass percentage of the soft carbon in the coating layer gradually increases. Because the hard carbon has a porous structure, while the soft carbon is relatively dense, the coating layer has a structure with a porous inner layer and a dense outer layer, thereby enhancing its rate performance and cycle performance.

[0102] This application also provides a negative electrode, including the recycled graphite negative electrode material prepared by the above preparation method or the above-described recycled graphite negative electrode material.

[0103] This application also provides a lithium-ion battery, including the negative electrode as described above.

[0104] For example, the negative electrode includes a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer and the second negative electrode active material layer are respectively disposed on opposite sides of the negative electrode current collector, and at least one of the first negative electrode active material layer and the second negative electrode active material layer includes the recycled graphite negative electrode material as described above.

[0105] The recycled graphite anode material and its preparation method provided in this application will be described in detail below with reference to specific embodiments.

[0106] Example 1

[0107] A method for preparing a recycled graphite anode material includes:

[0108] Step 1: Provide ultrafine coke powder (particle size D50 of 3.5 μm), a byproduct of needle coke crushing. Simultaneously, obtain waste graphite powder (particle size D50 of 8.5 μm) from waste batteries through dismantling, crushing, acid washing, heat treatment at 850℃ for 8 hours, and cooling. Then, uniformly mix the waste graphite powder and ultrafine coke powder in a mechanical fusion machine to obtain the precursor material, wherein the mass ratio of waste graphite powder to ultrafine coke powder is 70:30.

[0109] Step 2: Add polyacrylic acid (binder) to the precursor material. The mass ratio of polyacrylic acid (binder) to the precursor material is 6.5:100. Knead the mixture at room temperature in a mechanical fusion machine at a kneading speed of 25 Hz for 1 hour. Then transfer it to a reaction vessel at a speed of 30 Hz, pass an inert gas through it, and heat-treat it at 550°C for 8 hours. After cooling to room temperature, send it to a graphitization furnace for graphitization at a graphitization temperature of 3000°C for 75 hours. After cooling, graphite particles are obtained. These graphite particles constitute the recycled graphite anode material.

[0110] Example 2

[0111] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0112] In step 1, waste graphite powder and modified coke ultrafine powder are uniformly mixed at a mass ratio of 60:40 to obtain precursor material.

[0113] Example 3

[0114] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0115] In step 1, waste graphite powder and modified coke ultrafine powder are uniformly mixed at a mass ratio of 80:20 to obtain precursor material.

[0116] Example 4

[0117] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0118] In step 2, the mass ratio of polyacrylic acid (binder) to precursor material is 5:100.

[0119] Example 5

[0120] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0121] In step 2, the mass ratio of polyacrylic acid (binder) to precursor material is 8:100.

[0122] Example 6

[0123] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0124] In step 1, the process of uniformly mixing waste graphite powder and coke ultrafine powder in a mechanical fusion machine includes: uniformly mixing coke ultrafine powder and sodium carboxymethyl cellulose (dispersant) in a mechanical fusion machine to obtain modified coke ultrafine powder, wherein the mass ratio of sodium carboxymethyl cellulose (dispersant) to ultrafine powder is 2:100; and uniformly mixing the modified coke ultrafine powder with waste graphite powder to obtain precursor material.

[0125] Example 7

[0126] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0127] In step 1, after heat treatment at 850℃ for 8 hours, the temperature is lowered to 350℃ and air is introduced for micro-oxidation for 3 minutes (first oxidation etching). After cooling, the oxidized and etched waste graphite powder (particle size D50 is 8.5μm) is obtained.

[0128] Example 8

[0129] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0130] Following step 2, the following is also included:

[0131] Step 3: Graphite particles and coating agent are added to a mechanical fusion machine at a mass ratio of 100:8 for uniform coating treatment. The coating agent includes resin (phenolic resin) and asphalt (coal tar pitch) at a mass ratio of 0.5:0.5. The rotation speed is 35 Hz and the time is 2.5 hours. Then, it is fed into a rotary kiln (with a wall scraper on the inner wall) and heated from room temperature to 100°C. It is heat-treated at 100°C for 5 hours at a rotation speed of 20 Hz, then heated to 280°C for 4 hours at a rotation speed of 25 Hz, then further heated to 400°C for 3 hours at a rotation speed of 30 Hz, and finally heated to 1100°C for 8 hours at a rotation speed of 25 Hz. Then, it is cooled to room temperature to obtain carbonized material. The carbonized material is then mixed, sieved, and demagnetized to obtain recycled graphite anode material. The recycled graphite anode material includes graphite particles and a coating layer wrapped around the outer surface of the graphite particles.

[0132] Example 9

[0133] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0134] In step 3, graphite particles and coating agent are added to a mechanical fusion machine at a mass ratio of 100:6 for uniform coating treatment.

[0135] Example 10

[0136] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0137] In step 3, graphite particles and coating agent are added to a mechanical fusion machine at a mass ratio of 100:10 for uniform coating treatment.

[0138] Example 11

[0139] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0140] In step 3, the coating agent comprises resin (epoxy resin) and pitch (coal tar pitch) in a mass ratio of 0.5:0.5.

[0141] Example 12

[0142] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0143] In step 3, the coating agent comprises resin (phenolic resin) and asphalt (petroleum asphalt) in a mass ratio of 0.5:0.5.

[0144] Example 13

[0145] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0146] In step 2, after heat treatment at 550℃ for 8 hours, when the temperature is reduced to 250℃, air is slowly introduced and maintained for 6 minutes (second oxidation etching). After etching is completed, the gas is switched to inert gas, and then cooled to room temperature before being sent to a graphitization furnace for graphitization.

[0147] Example 14

[0148] A recycled graphite anode material, the preparation method of which differs from that in Example 8, is as follows:

[0149] In step 3, air is introduced for the last 5 minutes of the 400℃ heat treatment for 3 hours to perform oxidation etching (third oxidation etching), and then the process is switched to inert gas.

[0150] Example 15

[0151] A recycled graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0152] In step 1, after heat treatment at 850℃ for 8 hours, the temperature is lowered to 350℃ and air is introduced for micro-oxidation for 3 minutes (first oxidation etching). After cooling, the oxidized and etched waste graphite powder (particle size D50 is 8.5μm) is obtained. The process of uniformly mixing the waste graphite powder and coke ultrafine powder in a mechanical fusion machine includes: uniformly mixing the coke ultrafine powder and sodium carboxymethyl cellulose (dispersant) in a mechanical fusion machine to obtain modified coke ultrafine powder, wherein the mass ratio of sodium carboxymethyl cellulose (dispersant) to ultrafine powder is 2:100; and uniformly mixing the modified coke ultrafine powder with the waste graphite powder to obtain the precursor material.

[0153] In step 2, after heat treatment at 550℃ for 8 hours, when the temperature is reduced to 250℃, air is slowly introduced and maintained for 6 minutes (second oxidation etching). After etching, the gas is switched to inert gas, and then cooled to room temperature before being sent to a graphitization furnace for graphitization.

[0154] Following step 2, the following is also included:

[0155] Step 3: Graphite particles and coating agent are added to a mechanical fusion machine at a mass ratio of 100:8 for uniform coating treatment. The coating agent includes resin (phenolic resin) and asphalt (coal tar pitch) at a mass ratio of 0.5:0.5. The rotation speed is 35 Hz and the time is 2.5 hours. Then, the mixture is fed into a rotary kiln (with a wall scraper on the inner wall) and heated from room temperature to 100°C. It is then heat-treated at 100°C for 5 hours at a rotation speed of 20 Hz, then heated to 280°C for 4 hours at a rotation speed of 25 Hz, then further heated to 400°C for 3 hours at a rotation speed of 30 Hz, and finally heated to 1100°C for 8 hours at a rotation speed of 25 Hz. The mixture is then cooled to room temperature to obtain a carbonized material. The carbonized material is then mixed, sieved, and demagnetized to obtain a recycled graphite anode material. The recycled graphite anode material includes graphite particles and a coating layer wrapped around the outer surface of the graphite particles.

[0156] In step 3, air is introduced for the last 5 minutes of the 400℃ heat treatment for 3 hours to perform oxidation etching (third oxidation etching), and then the process is switched to inert gas.

[0157] Comparative Example 1

[0158] A graphite anode material, the preparation method of which includes:

[0159] The ultrafine powder (particle size D50 of 3.5μm) by-product of needle coke pulverization is fed into a graphitization furnace for graphitization at a temperature of 3000℃ and an energization time of 75 hours. After cooling and exiting the furnace, the graphite anode material can be obtained.

[0160] Comparative Example 2

[0161] A graphite anode material, the preparation method of which differs from that in Example 1, is as follows:

[0162] Waste batteries are dismantled, crushed, acid-washed, and heat-treated at 850°C for 8 hours. After cooling, waste graphite powder (particle size D50 is 8.5μm) is obtained. The waste graphite powder is then sent to a carbonization furnace for carbonization at 1150°C for 16 hours. After cooling and exiting the furnace, graphite anode material is obtained.

[0163] Comparative Example 3

[0164] A graphite anode material, the preparation method of which includes:

[0165] Waste batteries are dismantled, crushed, and acid-washed, then heat-treated at 850℃ for 8 hours. After cooling, waste graphite powder (particle size D50 of 8.5μm) is obtained. The waste graphite powder and coal tar pitch are put into a mechanical fusion machine and kneaded at room temperature. The mass ratio of coal tar pitch to waste graphite powder is 6.5:100, the kneading speed is 25Hz, and the kneading time is 1 hour. Then, it is transferred to a reaction vessel, the speed is 30Hz, inert gas is introduced, and it is heat-treated at 550℃ for 8 hours. After cooling to room temperature, it is sent to a graphitization furnace for graphitization at 3000℃ for 75 hours. After cooling, the graphite anode material is obtained.

[0166] Comparative Example 4

[0167] A graphite anode material, the preparation method of which includes:

[0168] The ultrafine powder (particle size D50 of 3.5 μm) by-product of needle coke pulverization was mixed with coal tar pitch in a mechanical blender at room temperature. The mass ratio of coal tar pitch to aggregate powder was 6.5:100. The mixing speed was 25 Hz and the mixing time was 1 hour. Then, it was transferred to a reaction vessel and heat-treated at 550℃ for 8 hours with inert gas. After cooling to room temperature, it was sent to a graphitization furnace for graphitization at 3000℃ for 75 hours. After cooling, the graphite anode material was obtained.

[0169] Comparative Example 5

[0170] A graphite anode material, the preparation method of which includes:

[0171] The aggregate powder (particle size D50 of 9μm) after pulverizing needle coke was put into a mechanical fusion machine and kneaded at room temperature with coal tar pitch. The mass ratio of coal tar pitch to aggregate powder was 6.5:100, the kneading speed was 25Hz, and the kneading time was 1 hour. Then it was transferred to a reaction vessel, the speed was 30Hz, inert gas was introduced, and it was heat-treated at 550℃ for 8 hours. After cooling to room temperature, it was sent to a graphitization furnace for graphitization at 3000℃ for 75 hours. After cooling, the graphite anode material was obtained.

[0172] Material property testing:

[0173] The performance of the recycled graphite anode materials prepared in Examples 1-15 and the graphite anode materials prepared in Comparative Examples 1-5 was tested. The test parameters and methods are as follows:

[0174] Particle size: Tested using a Malvern Panaco Zetasizer Ultra dynamic scattering particle size analyzer;

[0175] Specific surface area (BET): Tested using a CANTA specific surface area meter;

[0176] Coating pore volume and pore diameter: tested using a Micrometer instrument;

[0177] Coating thickness: was measured using a JEM-ACE200F field emission transmission electron microscope.

[0178] Electrical conductivity: The T-8100 four-probe powder conductivity tester was used for testing.

[0179] The test results are shown in Table 1.

[0180] Table 1

[0181]

[0182] As can be seen from Table 1, the conductivity of the recycled graphite anode materials prepared in Examples 1-15 is greater than that of the graphite anode materials prepared in Comparative Examples 1-5, indicating that the recycled graphite anode materials prepared in this application have better electrical conductivity.

[0183] Button-to-full-circuit test:

[0184] The preparation method of the button cell is as follows: The negative electrode materials of the batteries prepared in Examples 1-15 and Comparative Examples 1-5 are mixed evenly with conductive agent (SP), CMC, and SBR irradiated in a ratio of 95:1.5:1.5:2, respectively, and coated onto copper foil with a compaction density of 1.60 g / cm³. 3After vacuum drying, it serves as the negative electrode, with lithium metal as the counter electrode. The electrolyte is a 1M LiPF6 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 mass ratio. The separator is a PE / PPPE composite membrane, forming a coin cell. The initial discharge capacity and efficiency are tested, with the charging voltage limited to 0.005-2V. The initial discharge capacity and efficiency are recorded. The capacity after 180 cycles is recorded simultaneously. The capacity retention rate after 180 cycles is 180% of the discharge capacity at 180 cycles / initial discharge capacity * 100%.

[0185] The preparation method of the all-electric soft-pack battery: the positive electrode formula is lithium iron phosphate:PVDF:SP in a ratio of 96%:2%:2%, and the negative electrode formula is fine powder composite graphite:CMC:SBR:SP in a ratio of 95.5%:1.5%:2%:1%. The soft-pack battery GRP8570156 is obtained through slurry preparation, coating, rolling, slitting, winding, assembly, and formation. The test conditions are: charge and discharge at a current density of 5C, charging voltage limited to 3.5-4V, 50 cycles at a single rate, and the rate capacity retention rate is the percentage of remaining capacity under the rate condition to the initial capacity.

[0186] The test results are shown in Table 2.

[0187] Table 2

[0188]

[0189]

[0190] As can be seen from Table 2, the initial discharge efficiency, initial discharge capacity, 180-cycle capacity retention, and 5C rate performance capacity retention of the regenerated graphite anode materials prepared in Examples 1-15 are all greater than those of the graphite anode materials prepared in Comparative Examples 1-5. The charge transfer resistance Rct of the regenerated graphite anode materials prepared in Examples 1-15 is also less than that of the graphite anode materials prepared in Comparative Examples 1-5. This indicates that the regenerated graphite anode materials prepared in this application have higher energy utilization efficiency, higher capacity, and better cycle performance and rate performance.

[0191] The foregoing has provided a detailed description of the recycled graphite anode material, its preparation method, the anode itself, and the lithium-ion battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a recycled graphite anode material, characterized in that, include: Waste graphite powder is mixed with coke ultrafine powder to obtain precursor material; The precursor material and binder are mixed and granulated sequentially to obtain precursor particles. The precursor particles are then graphitized to transform them into graphite particles, resulting in a recycled graphite anode material, wherein the recycled graphite anode material comprises graphite particles.

2. The method for preparing the recycled graphite anode material according to claim 1, characterized in that, The mass ratio of the waste graphite powder to the coke ultrafine powder is (60-80):(20-40); and / or, The mass ratio of the binder to the precursor material is (5-8):100; and / or, The process of mixing waste graphite powder with coke ultrafine powder to obtain precursor materials includes: Modified coke ultrafine powder is obtained by mixing coke ultrafine powder with a dispersant, wherein the mass ratio of dispersant to coke ultrafine powder is (1-3):100; the modified coke ultrafine powder is then mixed with waste graphite powder to obtain a precursor material; the dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, fatty acid soap, sodium polyacrylate, polycarboxylate, hydroxyethyl cellulose, and polyacrylate; and / or, Before mixing the waste graphite powder with the coke ultrafine powder, the waste graphite powder is placed in an air atmosphere and subjected to a first oxidation etching at a temperature of 300℃-480℃.

3. The method for preparing the recycled graphite anode material according to claim 1, characterized in that, The adhesive comprises at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylamide, polyvinyl alcohol, sodium alginate, polyurethane, emulsified asphalt, tar, solid coal tar pitch, petroleum asphalt, phenolic resin, epoxy resin, and polyacrylonitrile; and / or, When graphitizing precursor particles, the graphitization temperature is 2800℃-3100℃, and the graphitization time is 70-90 hours; and / or, The particle size D50 of the waste graphite powder is 7μm-10μm; and / or, The particle size D50 of the coke ultrafine powder is 1μm to 5μm.

4. The method for preparing the recycled graphite anode material according to claim 1, characterized in that, After converting the precursor particles into graphite particles, the preparation method of the regenerated graphite anode material further includes: mixing the graphite particles with a coating agent to obtain a core-shell structure precursor, and carbonizing the core-shell structure precursor to obtain the regenerated graphite anode material, wherein the regenerated graphite anode material includes graphite particles and a coating layer wrapped around the outer surface of the graphite particles.

5. The method for preparing the recycled graphite anode material according to claim 4, characterized in that, The mass ratio of the coating agent to the graphite particles is (6-10):100; and / or, The coating agent includes a hard carbon precursor and a soft carbon precursor, and the mass ratio of the hard carbon precursor to the soft carbon precursor in the coating agent is (0.4-0.6):(0.4-0.6).

6. The method for preparing the recycled graphite anode material according to claim 5, characterized in that, The hard carbon precursor comprises a resin, wherein the resin comprises at least one selected from phenolic resin, epoxy resin, polyimide resin, furfural resin, and furfuryl alcohol resin; and / or, The soft carbon precursor includes asphalt, the asphalt having a softening point above 150°C, and the asphalt including at least one of coal tar pitch and petroleum asphalt.

7. The method for preparing the recycled graphite anode material according to claim 4, characterized in that, Prior to graphitization, the precursor particles undergo a second oxidation etching; and / or, During the carbonization process of the core-shell structure precursor, the core-shell structure precursor undergoes a third oxidation etching. And / or, The carbonization of the core-shell structure precursor includes: In an inert atmosphere, the core-shell structure precursor is heated from room temperature to a first temperature and held at the first temperature for 4 to 7 hours. The first temperature is 80°C to 150°C. The core-shell structure precursor is heated from a first temperature to a second temperature and held at the second temperature for 3 to 6 hours. The second temperature is 250°C to 330°C. The core-shell structure precursor is heated from the second temperature to the third temperature and held at the third temperature for 2-5 hours. The third temperature is 350℃-450℃. The core-shell precursor is heated from the third temperature to the fourth temperature and held at the fourth temperature for 6-10 hours. The fourth temperature is 800℃-1200℃.

8. The method for preparing the recycled graphite anode material according to claim 7, characterized in that, The second oxidation etching of the precursor particles includes: placing the precursor particles in an air atmosphere and performing a second oxidation etching at a temperature of 200℃-300℃; and / or, The third oxidation etching of the core-shell structure precursor during the carbonization process includes: During the process of heating the core-shell structure precursor from the second temperature to the third temperature and / or during the holding process at the third temperature, the inert atmosphere around the core-shell structure precursor is switched to an air atmosphere, and the core-shell structure precursor is subjected to a third oxidation etching in the air atmosphere at a temperature of 370℃-450℃. After the etching is completed, the air atmosphere is switched back to an inert atmosphere.

9. A recycled graphite anode material prepared by the preparation method according to any one of claims 1-8.

10. The recycled graphite anode material according to claim 9, characterized in that, The recycled graphite anode material includes graphite particles and a coating layer covering the outer surface of the graphite particles. The coating layer includes hard carbon and soft carbon. The hard carbon is infiltrated into the graphite particles. From the inner surface to the outer surface of the coating layer, the mass percentage of hard carbon in the coating layer gradually decreases, while the mass percentage of soft carbon in the coating layer gradually increases.

11. A negative electrode, characterized in that, Including the recycled graphite anode material described in any one of 9-10.

12. A lithium-ion battery, characterized in that, Includes the negative electrode as described in claim 11.

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