High-capacity dense anode material and its preparation method

Abstract

A high-capacity, dense anode material and its preparation method are disclosed. The preparation includes: mixing graphite micropowder with a first forming agent, such as asphalt, and a second additive, such as ammonium dihydrogen carbonate, to form a mixture; pressing the mixture into a blank; heat-treating the blank under a protective atmosphere to form a sinter; pulverizing the sinter into powder; mixing the powder with a third coating agent, such as phenolic resin, to form a homogenized material; and carbonizing the homogenized material to form, for example, a lithium-ion battery anode material. The anode material prepared by this invention can effectively shorten the migration distance during lithium-ion diffusion, greatly improve the rate performance of the material, effectively reduce defects on the surface and in the bulk of the graphite anode, ensure the formation of a smooth and stable specific surface area, further ensure the stable formation of the SEI film and structural stability during cycling, and effectively guarantee the material's high initial efficiency, high capacity, and long cycle performance.

Description

Technical Field

[0001] This invention relates to the recycling and preparation of battery negative electrode materials. Background Technology

[0002] The graphite anode material for batteries is mainly composed of natural graphite and artificial graphite. Both processes generate a significant amount of graphite powder during production. Taking natural graphite as an example, its production involves processing natural flake graphite, followed by purification, flotation, drying, crushing, and shaping. The powder generation rate during crushing alone exceeds 30%. Related research indicates that 15% of the total powder is of a larger particle size and can be recycled after classification, for example, in the preparation of graphite coatings and conductive pastes. However, graphite powder with smaller flake diameters (D50≤4µm) generally cannot be effectively utilized. Similarly, the synthesis of artificial graphite still generates a large amount of needle-shaped coke powder and graphite powder. These large quantities of generated graphite powder are usually difficult to handle effectively and can only be stored in stockpiles.

[0003] Small-diameter graphite powder, due to its small particle size, large specific surface area, low tap, high impurity content, and numerous surface defects, ultimately leads to problems such as low initial coulombic efficiency, poor rate performance, and cycle degradation in lithium batteries.

[0004] There are generally two solutions for the secondary utilization of graphite powder: one is to re-granulate the graphite powder to synthesize graphite anode materials with low tap density; the other is to modify and expand the graphite powder to prepare graphene materials for secondary utilization. However, the modification and expansion process uses strong acids and strong oxidants such as potassium permanganate, which is less environmentally friendly. Therefore, the industry generally prefers granulation to prepare anode materials for effective utilization.

[0005] CN 114804095 A discloses a graphite anode active material prepared from spheroidized graphite micropowder waste, its preparation method, and its application: the spheroidized graphite micropowder waste is subjected to ultrasonic pretreatment in an acid solution, then thermally fused with a carbon source, subsequently pressed into shape, and after carbonization and gas cooling, the anode material is obtained. This method can reconstruct defects in spheroidized graphite micropowder, and the obtained material has a reversible capacity of 355 mAh / g at 0.2C, a coulombic efficiency of 95.8%, and a rate performance of 5C / 0.2C = 96.1%. However, this method uses strong acids such as hydrofluoric acid as defect removal agents, resulting in significant environmental pollution.

[0006] CN113526956A discloses a low-cost, long-cycle graphite anode material, its preparation method, and its applications: A molding method is used to fill the internal pores of graphite micropowder with asphalt, simultaneously forming an asphalt coating layer on its surface. This method not only rapidly densifies the internal pores of the graphite micropowder, increasing the tap density of the anode material, but also uniformly coats it with a dense carbon coating layer, reducing the specific surface area of ​​the anode material and improving the battery's initial efficiency and cycle performance. The material has an initial discharge capacity of 349.8 mAh / g, an initial efficiency of 91.2%, and a retention rate of 83.1% after 1000 cycles at 1C. However, the molding process relies on pressure applied at both ends, making it difficult to achieve uniform molding and ultimately affecting product consistency. Furthermore, the use of a single asphalt solid phase coating method also suffers from uneven coating. Summary of the Invention

[0007] The purpose of this invention is to provide a feasible method for preparing battery anode materials using graphite micropowder.

[0008] According to a first aspect of the present invention, a method for preparing a battery negative electrode material is provided, comprising:

[0009] We provide graphite micro powder with a particle size D50 of less than 4 μm;

[0010] Provide a first molding agent, which is selected from at least one of asphalt, liquid-phase urea-formaldehyde resin, phenolic resin, resorcinol-formaldehyde resin, polyethylene, polypropylene, polystyrene and polyurethane;

[0011] A second additive is provided, which is selected from at least one of ammonium dihydrogen carbonate, melamine, urea, ammonium dihydrogen phosphate and boric acid;

[0012] Graphite micro powder is mixed with a first forming agent and a second additive to form a mixture, wherein the mass ratio of the first forming agent, the second additive and the graphite micro powder is (0.03~0.3):(0.005~0.03):1;

[0013] The mixture is pressed into a blank, wherein the pressing pressure ranges from 100 to 600 MPa and the pressing time is from 3 minutes to 2 hours;

[0014] The billet is heat-treated under a protective atmosphere, wherein the heat treatment adopts a staged heating method. First, the temperature is raised to 150-350℃ at a rate of 3-7℃ / min and held for 0.5-2.5h. Then, the temperature is raised to 300-1100℃ at a rate of 5-15℃ / min and held for 0.5-1.5h. Finally, the temperature is raised to 2300-3200℃ at a rate of 15-55℃ / min and held for 1-6h. After cooling to room temperature, a sintered material is formed.

[0015] The sintered material is crushed into powder with a particle size D50 of 6-16 μm;

[0016] Provide a third coating agent for particle size, which is selected from at least one of asphalt, phenolic resin, polyurethane, resorcinol formaldehyde resin, polyacrylamide, polypyrrole, polyketone and polyethylene;

[0017] The powder and the third coating agent are mixed to form a homogeneous material, wherein the mass ratio of the third coating agent to the powder is 0.1-10%; and

[0018] The homogeneous material formed by carbonization treatment is formed by heating the material to 200-1100℃ at a rate of 3-7℃ / min and holding it at that temperature for 1-5 hours, and then cooling it to room temperature.

[0019] According to the method of the present invention, the graphite powder may be waste graphite powder comprising at least one of natural flake graphite, spherical graphite powder, needle-shaped coke powder, coke powder, artificial graphite powder, and hard carbon powder.

[0020] According to the method of the present invention, the first molding agent may be selected from at least one of (low-temperature) asphalt, liquid-phase urea-formaldehyde resin and polyethylene.

[0021] According to the method of the present invention, the second additive may be selected from at least one of ammonium dihydrogen carbonate, melamine and urea.

[0022] According to the method of the present invention, the third coating agent may be selected from at least one of (high temperature) asphalt, phenolic resin, polyurethane and resorcinol formaldehyde resin.

[0023] According to another aspect of the present invention, an electrode negative electrode material prepared according to the above method is also provided.

[0024] The battery anode material according to the present invention has a particle size D50 of 8–20 μm. Furthermore, it possesses a homogeneous mesoporous pore structure with a pore size of 1–20 nm. In addition, its specific surface area (SSA) can reach 0.5–5 m². 2 / g, tap density can reach 1.0~1.3g / cm³ 3 The content of carbon (C) is 90-99.5% by mass, oxygen (O) is 0.1-5% by mass, nitrogen (N) is 0.1-5% by mass, and other metallic impurities are ≤200ppm.

[0025] According to another aspect of the present invention, a lithium-ion battery negative electrode is also provided, which is made of the aforementioned negative electrode material.

[0026] The negative electrode material prepared according to the present invention exhibits a core-shell structure, with its core being a graphite-like composite containing mesoporous structures, and its shell being a densely coated carbon layer with no pores on its outer surface. The present invention effectively controls the high impurity content in the raw materials through temperature regulation treatment. Through a combination of molding, nitrogen doping, and dense coating, the tap density of the material is significantly improved, the particle surface condition is enhanced, ensuring the electrode material possesses high initial efficiency and high capacity. Furthermore, the impedance of the material is significantly reduced, and the lithium-ion migration rate is increased, ultimately improving the rate performance of the battery. Attached Figure Description

[0027] Figure 1 SEM image of the negative electrode material prepared according to Example 1 of the present invention;

[0028] Figure 2 The charge-discharge curve of the negative electrode material prepared according to Example 1 of the present invention is shown.

[0029] Figure 3 The image shows the SEM image of the graphite micropowder sintered material in Comparative Example 1. Detailed Implementation

[0030] The present invention will be further explained and illustrated below through specific embodiments, comparative examples and accompanying drawings.

[0031] Example 1

[0032] (1) Weigh 1000g of flake graphite powder with D50=3.4um, 200g of low-temperature asphalt (D50=3um), and 20g of melamine, and disperse them uniformly in a fusion machine at 150℃ and 5000rpm for 3h to form a fusion material;

[0033] (2) Press 1000g of fused material through a cold isostatic press at 300MPa for 5min to form a cylinder with φ=600mm and a height of 800mm, thus forming a green billet;

[0034] (3) The green billet is placed in a box-type graphitization furnace and high-purity nitrogen gas with a flow rate of 2L / min is introduced as a protective gas; the green billet is treated by staged heating: heating to 200℃ at 5℃ / min and holding for 1h, heating to 1000℃ at 10℃ / min and holding for 1h, then heating to 2500℃ at 20℃ / min and holding for 2h, and then cooling to room temperature to form a sintered billet;

[0035] (4) 1000g of sintered billet is crushed by a jaw crusher with a jaw plate spacing of 1mm; the material after jaw crushing is ground by an air jet mill with a grinding and crushing power of 38Hz and a grading frequency of 58Hz. The particle size after crushing is D50 = 7um.

[0036] (5) Take 200g of powder and 10g of phenolic resin (D50=15um) and mix them evenly in a high-speed mixer at 500rpm for 5min. Place the mixed material in a box-type carbonization furnace and heat it to 900℃ at 5℃ / min. Keep it at 900℃ for 4h. After cooling to room temperature, sieve it to obtain the negative electrode material. The material has D50=8um.

[0037] SEM images of the prepared anode material are shown below. Figure 1 The charge / discharge curves are shown below. Figure 2 .

[0038] Example 2

[0039] (1) Weigh 2000g of natural graphite powder with D50=2.5um, 200g of liquid urea-formaldehyde resin, and 20g of ammonium dihydrogen carbonate, and knead them in a kneader at 500rpm for 1h to form a mixture;

[0040] (2) Press 1000g of the mixture in a hot press at 500MPa for 1h to form a cylinder with φ=100mm and a height of 200mm, thus forming a green blank;

[0041] (3) The green billet was placed in a small experimental furnace and high-purity argon gas with a flow rate of 2L / min was introduced as a protective gas. The process was carried out by staged heating: heating to 300℃ at 5℃ / min and holding for 2h, heating to 1400℃ at 10℃ / min and holding for 1h, then heating to 2700℃ at 50℃ / min and holding for 4h, and then cooling to room temperature to form a sintered billet.

[0042] (4) 1000g of sintered billet was coarsely crushed by a rotary mill with the torque adjusted to 20Hz. The coarse material after crushing was 1mm. The coarsely crushed material was then ground by an impact mill with the grinding chamber power at 50Hz and the classifier frequency at 60Hz. The particle size after crushing was D50 = 9um.

[0043] (5) Take 200g of powder and 10g of polyurethane (D50=15um) and mix them evenly in a food processor at 1000rpm for 5min. Place the mixed material in a tube furnace and heat it to 800℃ at 5℃ / min and keep it at that temperature for 4h. After cooling to room temperature, sieve it to obtain the negative electrode material with D50=10um.

[0044] Example 3

[0045] (1) Weigh 2000g of needle-shaped coke powder with D50=2um and polyethylene (D50=15um).

[0046] 100g of urea was mixed in a mixer at 500rpm for 20 minutes, then 200g of isopropanol containing 50g of urea was sprayed on, and the mixture was kneaded in a kneader at 500rpm for 1 hour and then evaporated at 100℃ to form a kneaded material.

[0047] (2) Press 1000g of kneaded material through a hot isostatic press at 150MPa for 20min to form a cylindrical blank with φ=100mm and a height of 30mm, thus forming a green blank;

[0048] (3) Place the green billet into a muffle furnace and introduce high-purity argon gas with a flow rate of 1L / min as a protective gas; use a staged heating process, heating to 200℃ at 5℃ / min and holding for 2h, then heating to 1000℃ at 10℃ / min and holding for 1h, then heating to 3000℃ at 50℃ / min and holding for 5h before cooling to form a sintered billet;

[0049] (4) 1000g of sintered billet was crushed by a universal crusher at a speed of 5000rpm for 20min to obtain a particle size of D50 = 15um after crushing;

[0050] (5) Take 500g of powder and 50g of resorcinol formaldehyde resin (D50=20um) and mix them evenly in a VC mixer at 1000rpm for 5min. Place the mixed material in a rotary kiln and heat it to 1000℃ at 5℃ / min and keep it at that temperature for 2h. After cooling to room temperature, sieve the material to obtain the negative electrode material, which has a D50=17um.

[0051] Comparative Example 1

[0052] (1) Weigh 1000g of flake graphite powder with D50=3um, and pass high-purity nitrogen gas with a flow rate of 2L / min as a protective gas; use staged heating to process the material, heat to 200℃ at 5℃ / min, hold for 1h, then heat to 1000℃ at 10℃ and hold for 1h, then heat to 2500℃ at 20℃ / min, hold for 2h and cool to room temperature to form a sintered material with D50=3um.

[0053] SEM images of the prepared graphite micropowder sintered material are shown below. Figure 3 .

[0054] Comparative Example 2

[0055] (1) Weigh 2000g of natural graphite powder with D50=3um, 200g of mesophase pitch (D50=5um), and 20g of ammonium dihydrogen carbonate, and mix them in a mixer at 1500rpm for 1h to form a mixture;

[0056] (2) The mixture was placed in a small test furnace and high-purity argon gas with a flow rate of 2L / min was introduced as a protective gas. The process was carried out by staged heating: heating to 300℃ at 5℃ / min and holding for 2h, then heating to 1400℃ at 10℃ and holding for 1h, then heating to 2700℃ at 50℃ / min and holding for 4h, and then cooling to room temperature to form a billet.

[0057] (3) 1000g of billet is coarsely crushed by a rotary mill with the torque adjusted to 20Hz. The coarse material after crushing is 1mm. The coarsely crushed material is then ground by an impact mill with the grinding chamber power at 50Hz and the classifier frequency at 60Hz. The particle size after crushing is D50 = 9um.

[0058] (4) Take 200g of powder and 10g of polyurethane (D50=15um) and mix them evenly in a food processor at 1000rpm for 5min. Place the mixed material in a tube furnace and heat it to 800℃ at 5℃ / min and keep it at that temperature for 4h. After cooling to room temperature, sieve it to obtain the negative electrode material with D50=5um.

[0059] Comparative Example 3

[0060] (1) Weigh 2000g of needle coke powder with D50=3um and 100g of polyethylene (D50=15um). Mix them in a mixer at 500rpm for 20min. Then spray 200g of isopropanol containing 50g of urea. Mix them in a kneader at 500rpm for 1h and evaporate them at 100℃ to form a kneaded material.

[0061] (2) Press 1000g of kneaded material through a hot isostatic press at 150MPa for 20min to form a cylindrical blank with φ=100mm and a height of 30mm, thus forming a green blank;

[0062] (3) Place the green billet into a muffle furnace and introduce high-purity argon gas with a flow rate of 1L / min as a protective gas; use a staged heating process, heat up to 200℃ at 5℃ / min, hold for 2h, then heat up to 1000℃ at 10℃ and hold for 1h, then heat up to 3000℃ at 50℃ / min, hold for 5h and cool to room temperature to form the billet.

[0063] (4) 1000g of billet was crushed by a universal crusher at a speed of 5000rpm for 20min to obtain a crushed particle size D50 = 15um.

[0064] The negative electrode materials of Examples 1-3 and Comparative Examples 1-3 were tested using the following method: A negative electrode material (CMC:SBR = 95:2:3) was slurried, with a solid content controlled at 55%. The slurry was then coated onto a copper foil current collector using a coating machine. The electrode sheets were obtained by blast drying at 100°C and roller pressing, with a compaction density controlled at 1.7 g / cm³. 3 Using lithium metal sheets as the counter electrode and 1 mol / L LiPF6 as the electrolyte, coin cells were used to test the initial efficiency, specific capacity, and first charge-discharge curves. A 2.5 Ah 18650 battery was constructed using commercial ternary 523 as the positive electrode material and a prepared material as the negative electrode material for rate performance and cycle performance testing (1C = 2.5A).

[0065] Tables 1 and 2 show the characterization parameters and electrochemical performance parameters of the anode materials prepared in each embodiment and comparative example, respectively.

[0066] Table 1: Characterization parameters of negative electrode materials

[0067]

[0068] Table 2: Electrochemical performance parameters of negative electrode materials

[0069]

[0070] Note: A sudden drop in battery capacity during cycling, often referred to as a "plummeting" capacity, indicates unstable battery performance.

[0071] contrast Figure 1 and Figure 3 It can be seen that, after processing by the method of the present invention, the morphology of the graphite micro powder material changes from flake-like ( Figure 3 The particles (approximately 3.43 μm in diameter) transformed into spherical particles, indicating a significant molding effect. From... Figure 2 As can be seen, the charge-discharge curve of the synthesized anode material is similar to that of ordinary graphite anode materials, with an initial efficiency of 94.6% and a reversible capacity of 347.1 mAh / g, which can fully meet the application requirements of existing graphite anode materials.

[0072] As shown in Tables 1 and 2, compared with Comparative Example 1, the anode material prepared by Example 1 after a series of treatments meets the application requirements (fixed carbon ≥ 95%, specific gravity ≤ 3m). 2 / g, metallic impurities ≤100ppm), specific surface area reaches 1.61m² 2 The carbon content was reduced to 98.88% per gram, the oxygen content decreased to 0.38% (oxygen content represents the amount of hydroxyl and carboxyl group defects), and the metal impurities decreased to 58 ppm. This indicates that the present invention has effectively utilized natural graphite powder to obtain high-performance electrode materials. A comparison of the data from Examples 2 and 3 demonstrates the universality of the synthesis method of the present invention; that is, under the same conditions, needle-shaped coke powder and flake graphite powder can also be used to effectively prepare anode materials that meet the requirements.

[0073] A comparison of the data from Example 2 and Comparative Example 2 shows that the material prepared in Example 2 exhibits a lower expansion rate, higher initial efficiency, and reversible capacity, ultimately ensuring a higher rate retention at 8C and better cycle performance. This indicates that the dense manufacturing process of the present invention not only ensures that the material maintains a higher tap density but also ensures a lower specific surface area, thereby ensuring a more stable formation of the SEI film during the charging and discharging process of the graphite anode. A comparison of Example 3 and Comparative Example 3 shows that the double-layer carbon coating process of the present invention can effectively reduce side reactions during the lithium intercalation process, ensuring that the material has better cycle performance.

[0074] In summary, this invention synthesizes a high-capacity, dense anode material using a simple process. This material utilizes the short-range ordered microcrystalline structure of graphite microparticles and the doping of atoms such as nitrogen to effectively shorten the migration distance during lithium-ion diffusion, significantly improving the material's rate performance. Through a combination of densification and coating processes, defects on the graphite anode surface and within the bulk phase are effectively reduced, ensuring the formation of a smooth and stable specific surface area. This further ensures the stable formation of the SEI film and structural stability during cycling, effectively guaranteeing the material's high initial efficiency, high capacity, and long cycle life. The preparation method of this invention is simple, convenient, low-cost, and environmentally friendly, enabling efficient industrial production of the anode material.

Claims

1. A method for preparing a battery negative electrode material, comprising: We provide graphite micro powder with a particle size D50 of less than 4 μm; A first molding agent is provided, which is selected from at least one of asphalt, liquid-phase urea-formaldehyde resin and polyethylene; A second additive is provided, which is selected from at least one of ammonium dihydrogen carbonate, melamine, and urea; Graphite micro powder is mixed with a first forming agent and a second additive to form a mixture, wherein the mass ratio of the first forming agent, the second additive and the graphite micro powder is (0.03 ~ 0.3): (0.005 ~ 0.03): 1; The mixture is pressed into a blank, wherein the pressing pressure ranges from 100 to 600 MPa and the pressing time is from 3 minutes to 2 hours; The billet is heat-treated under a protective atmosphere, wherein the heat treatment adopts a staged heating method. First, the temperature is raised to 150~350℃ at a rate of 3~7℃ / min and held for 0.5~2.5h. Then, the temperature is raised to 300~1100℃ at a rate of 5~15℃ / min and held for 0.5~1.5h. Finally, the temperature is raised to 2300~3200℃ at a rate of 15~55℃ / min and held for 1~6h. After cooling to room temperature, a sintered material is formed. The sintered material is crushed into powder with a particle size D50 of 6~16um; A third coating agent for particle size is provided, which is selected from at least one of phenolic resin, polyurethane and resorcinol-formaldehyde resin; The powder and the third coating agent are mixed to form a homogeneous material, wherein the mass ratio of the third coating agent to the powder is 0.1~10%; as well as The mixed material formed by carbonization treatment is formed by heating the material to 200-1100℃ at a rate of 3-7℃ / min and holding it at that temperature for 1-5 hours, and then cooling it to room temperature.

2. The method according to claim 1, wherein the graphite powder is waste graphite powder comprising at least one of natural flake graphite, spherical graphite powder, needle-shaped coke powder, coke powder, artificial graphite powder, and hard carbon powder.

3. An electrode negative electrode material prepared according to the method of claim 1 or 2.

4. The battery negative electrode material according to claim 3 has a particle size D50 of 8~20um.

5. The battery negative electrode material according to claim 4, having a homogeneous mesoporous pore structure with a pore size of 1~20 nm.

6. A lithium-ion battery negative electrode, made of a negative electrode material according to any one of claims 3-5.

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