Artificial graphite and recycled graphite composite negative electrode material, preparation method thereof and battery

Abstract

The present application belongs to the technical field of lithium ion battery negative electrode material, and particularly relates to a kind of artificial graphite and recycled graphite composite negative electrode material, its preparation method and battery.The method comprises the following steps: 1) pretreatment of recycled graphite;2) mixing the purified recycled graphite with carbon source precursor, and carrying out medium temperature pyrolysis treatment under inert atmosphere;3) mixing the surface repair recycled graphite with artificial graphite precursor, adding binder for granulation, to obtain composite precursor particles;4) carbonization treatment of the composite precursor particles;5) high temperature graphitization treatment of the carbonization product under inert atmosphere, and sieving after cooling.The present application solves the problem of insufficient performance of recycled graphite when used alone by synergistically compounding recycled graphite with artificial graphite precursor, while reducing the production cost of artificial graphite negative electrode material, and realizing high-value utilization of waste graphite resources.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a composite anode material of artificial graphite and recycled graphite, its preparation method and battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high specific energy, long cycle life, and no memory effect, have been widely used in consumer electronics, new energy vehicles, and large-scale energy storage. Graphite materials, as the main anode material for commercial lithium-ion batteries, have seen their usage continuously increase with the expansion of the lithium battery industry. In lithium-ion batteries, graphite anode materials account for 12%-21% of the battery mass, making them a crucial component. Currently, the market mainly offers two types of anode graphite: natural graphite and artificial graphite. Artificial graphite dominates the mid-to-high-end power battery market due to its excellent cycle stability and rate performance. However, the production process of artificial graphite requires high-temperature graphitization treatment at 2300-3000℃, resulting in huge energy consumption, long production cycles, and high manufacturing costs. Furthermore, the impact of raw material and energy costs during graphitization has led to a year-on-year increase in the price of high-performance artificial graphite.

[0003] Meanwhile, with the explosive growth of the new energy vehicle industry, a large number of lithium-ion batteries are entering their retirement period. In 2024, the global scale of waste batteries reached 115 GWh, and it is projected that the global recycling scale will reach approximately 1 TWh by 2035. Currently, mainstream recycling technologies and capital in the industry are mostly focused on extracting high-value metals such as cobalt, nickel, and lithium from cathode materials. However, graphite materials for the anode, which account for nearly 15% of the battery weight and about 10% of the cost, have long been neglected due to uneconomical recycling technologies and relatively low recycling value, often being downgraded or directly discarded. This not only results in a huge waste of graphite resources but also brings potential environmental pollution risks.

[0004] In recent years, the recycling and regeneration of waste graphite anode materials has gradually attracted attention from academia and industry. Professor Zhou Xiangyang's team at Central South University proposed a new approach to the green recycling and high-value utilization of waste graphite, involving "component analysis-structural reconstruction-performance improvement," forming innovative technologies such as multi-level synergistic dissociation and efficient impurity removal, microstructure repair and defect passivation. BTR New Materials Group released a flexible regeneration technology for anode materials, solving problems such as impurities and structural defects in anode material recycling through an industry-first regeneration process, and launched its first R-graphite product with significant carbon emission advantages. Song Xiaohui's team at Hefei University of Technology used a "one-pot" Joule heating technology to construct a stable artificial solid electrolyte interface layer in situ on the surface of waste graphite. The regenerated graphite still provides a specific capacity of 101 mAh / g after 3000 cycles at a high rate of 3C. Furthermore, the recycling and regeneration of waste graphite has also been applied to functional applications such as the preparation of graphene-based adsorbent materials. However, the above studies mainly focus on the individual recycling of waste graphite. In industrial applications, there are still problems such as insufficient batch stability of recycled graphite, rapid degradation of high-rate performance, and insufficient integration with the existing anode material production system.

[0005] Currently, there is a lack of technical solutions for the synergistic utilization of recycled graphite and artificial graphite. Existing research on graphite-based composite anode materials mainly focuses on the composite of artificial and natural graphite (such as the composite technology of artificial and natural graphite disclosed in patent CN202310285XXX), or the composite of artificial graphite and hard carbon materials (such as the preparation of secondary graphite / hard carbon material particles by combining biomass hard carbon and artificial graphite). These technologies mainly aim to improve the overall electrochemical performance by complementing the advantages of different carbonaceous materials, but none of them involve the dimension of resource utilization of waste graphite, and fail to solve the dual needs of waste graphite disposal and cost reduction of anode materials.

[0006] In summary, how to organically combine the recycling and regeneration of waste graphite with the production system of artificial graphite to develop a composite anode material with high electrochemical performance, low production cost and good process compatibility is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a composite anode material of artificial graphite and recycled graphite, its preparation method, and a battery. This invention addresses the performance limitations of recycled graphite when used alone by synergistically combining recycled graphite with an artificial graphite precursor, while simultaneously reducing the production cost of the artificial graphite anode material and achieving high-value utilization of waste graphite resources.

[0008] The technical solution provided by this invention is as follows: A method for preparing a composite negative electrode material of artificial graphite and recycled graphite includes the following steps: 1) The recycled graphite is pretreated to obtain purified recycled graphite; 2) The purified and recovered graphite obtained in step 1) is mixed with a carbon source precursor and subjected to medium-temperature pyrolysis under an inert atmosphere to obtain surface-repaired recovered graphite. 3) Mix the surface-repaired recycled graphite obtained in step 2) with the artificial graphite precursor, add a binder and granulate to obtain composite precursor particles; 4) The composite precursor particles obtained in step 3) are subjected to carbonization treatment; 5) The carbonized product obtained in step 4) is subjected to high-temperature graphitization treatment under an inert atmosphere, cooled and sieved to obtain the composite anode material of artificial graphite and recycled graphite.

[0009] The above technical solution first purifies and repairs the surface of recycled graphite, then mixes it with an artificial graphite precursor in a certain proportion, and prepares a core-shell structured composite anode material through an integrated process of granulation, carbonization, and graphitization. This invention provides a high-capacity, high-efficiency matrix support using artificial graphite, fills the gaps between particles with recycled graphite, reduces material costs, and simultaneously achieves resource recycling.

[0010] The composite anode material made from artificial graphite and recycled graphite prepared by the above technical solution has a unique core-shell structure. The artificial graphite, after graphitization, forms a highly crystalline core, while the recycled graphite, after repair, fills the interparticle gaps and coats the core surface, forming a stable secondary particle structure. This structural design combines the high capacity and high first-efficiency characteristics of artificial graphite with the low cost and resource utilization advantages of recycled graphite.

[0011] Specifically, in step 1): the recycled graphite is crushed and sieved, and then acid-washed or alkali-washed to remove metal impurities. After washing and drying, purified recycled graphite is obtained, wherein: The pickling process uses one or more of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1-3 mol / L; The alkaline washing uses a sodium hydroxide or potassium hydroxide solution with a concentration of 1~4 mol / L; The washing process involves washing with deionized water until neutral, and the drying temperature is 80~120℃ for 6~24 hours.

[0012] The above technical solutions can effectively remove metallic impurities such as iron, cobalt, nickel, and copper, or separate some inorganic salts and oxides.

[0013] Specifically, in step 2): The carbon source precursor is one or more of asphalt, phenolic resin, polyacrylonitrile, glucose, or sucrose. The intermediate-temperature pyrolysis treatment is performed at a temperature of 400~800℃ for 2~6 h, with a heating rate of 2~5℃ / min. The amount of the carbon source precursor added is 5-15 wt% of the mass of purified and recovered graphite.

[0014] The above technical solutions can effectively restore the surface structural integrity of recycled graphite (recycled graphite often has defects, cracks, holes, or exfoliated layers on its surface after recycling) or improve initial coulombic efficiency and cycle life. They also enhance interfacial stability and electrochemical performance.

[0015] Specifically, in step 3): The surface-repairing recycled graphite and the artificial graphite precursor are mixed at a mass ratio of (20~50):(50~80); The artificial graphite precursor is one or more of needle coke, petroleum coke, coal tar pitch coke or mesophase carbon microspheres. The binder is asphalt or a polymer binder, and its addition amount is 5-15 wt% of the total mass of the surface-repaired recycled graphite and the artificial graphite precursor; The granulation process employs high-speed mixing granulation or spray granulation, with the particle size Dv50 controlled between 8 and 20 μm.

[0016] Based on the above technical solution, recycled graphite can be fully utilized, with a maximum usage of up to 50%.

[0017] Specifically, in step 4): The inert atmosphere is nitrogen or argon; The carbonization temperature is 600~1000℃, the time is 2~6 h, and the heating rate is 2~8℃ / min.

[0018] Based on the above technical solution, the carbonization process causes the binder and the coated carbon layer to undergo pyrolysis and carbonization, which firmly combines the recycled graphite with the artificial graphite precursor to form a stable secondary particle structure.

[0019] Specifically, in step 5): The inert atmosphere for graphitization is argon; the graphitization temperature is 2600~3000℃, the time is 24~72 h, and the heating rate is 5~15℃ / min. The particle size Dv50 of the composite anode material made from artificial graphite and recycled graphite is 10~18 μm, and the specific surface area is 1.5~4.0 m². 2 / g.

[0020] Based on the above technical solution, the high-temperature graphitization process rearranges the carbon atoms in the artificial graphite precursor from a disordered structure into a regular hexagonal layered graphite crystal structure, endowing the material with excellent conductivity and lithium-ion storage capacity. At the same time, the crystallinity of recycled graphite is further improved under this temperature condition, and surface defects are further healed, achieving synergy between recycled graphite and artificial graphite at the crystal structure level.

[0021] The recycled graphite used in the above technical solution originates from graphite sheets dismantled from the negative electrodes of retired lithium-ion batteries or graphite scraps generated during electrode production, with a graphite content of 70-80%. According to the method of the present invention, the utilization rate of graphite in the recycled graphite can reach 85%~95%.

[0022] The present invention also provides a graphite composite anode material prepared by the above method.

[0023] The present invention also provides a lithium-ion battery negative electrode sheet, comprising the aforementioned graphite composite negative electrode material.

[0024] The present invention also provides a lithium-ion secondary battery, including the lithium-ion battery negative electrode sheet, wherein the lithium-ion secondary battery is a power battery, energy storage battery or consumer electronics battery, and has good application effects in the fields of power batteries, energy storage batteries or consumer electronics batteries.

[0025] The recycled graphite used in this invention is waste graphite, generally derived from power batteries and consumer waste batteries. After more than 1000 cycles of use, its performance drops to below 30%. It is made by sieving graphite negative electrode powder to remove copper foil, and its main components are graphite, carbon black, binder, residual electrolyte, and SEI membrane components.

[0026] This invention achieves the high-value recycling of waste graphite and the synergistic effect of artificial graphite performance. The prepared composite anode material has high specific capacity, excellent cycle stability and low production cost, with a first-cycle coulombic efficiency ≥92%, a 0.1C reversible specific capacity ≥350 mAh / g, and a capacity retention rate ≥88% after 500 cycles at 1C. Attached Figure Description

[0027] Figure 1 This is an electron microscope image of the composite negative electrode material prepared in Example 1. Detailed Implementation

[0028] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] Unless otherwise specified, the test methods used in the embodiments are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0030] Example 1 The preparation method of the composite anode material of artificial graphite and recycled graphite includes the following steps: (1) Pretreatment of recycled graphite: Take 100 g of negative electrode graphite sheets obtained from the dismantling of retired lithium iron phosphate batteries, crush them, pass them through a 200-mesh sieve, add 300 mL of 2 mol / L hydrochloric acid solution, stir and acid wash at 60℃ for 2 h, filter and wash with deionized water until neutral, and dry at 100℃ for 12 h to obtain 95 g of purified recycled graphite.

[0031] (2) Surface repair of recycled graphite: Take 90 g of purified recycled graphite obtained in step (1), add 9 g of medium-temperature asphalt powder (accounting for 10 wt% of the mass of purified recycled graphite), mix thoroughly and place in a tube furnace, heat to 600℃ at 3℃ / min under nitrogen atmosphere, keep warm for 4 h, and obtain 96 g of surface repaired recycled graphite after natural cooling.

[0032] (3) Mixing and granulation: Take 30 g of surface repair and recycled graphite obtained in step (2), mix it with 70 g of needle coke, add 10 g of medium-temperature asphalt as a binder, and granulate it using a high-speed mixing granulator. Control the particle size Dv50 to be 12~15 μm to obtain composite precursor particles.

[0033] (4) Carbonization treatment: The composite precursor particles obtained in step (3) are placed in an atmosphere furnace and heated to 800°C at 5°C / min under nitrogen protection, held for 4 h, and then cooled naturally.

[0034] (5) Graphitization treatment: The carbonized product obtained in step (4) is placed in a graphitization furnace and heated to 2800℃ at 10℃ / min under argon protection. The temperature is maintained for 48 h. After cooling, it is passed through a 325-mesh sieve to obtain the composite negative electrode material.

[0035] Electrochemical performance testing: Using the composite negative electrode material obtained in this embodiment as the active material, a negative electrode sheet was prepared according to the mass ratio of active material: conductive agent (Super P): binder (PVDF) = 90:5:5. A CR2032 coin cell was assembled using a lithium sheet as the counter electrode for testing. The measured coulombic efficiency for the first cycle was 92.5%, the reversible specific capacity at 0.1C was 358 mAh / g, and the capacity retention rate after 500 cycles at 1C was 89.2%.

[0036] like Figure 1 The image shown is an electron microscope image of the composite negative electrode material, which shows that the material is uniform.

[0037] Example 2 The preparation method of the composite anode material of artificial graphite and recycled graphite includes the following steps: (1) Pretreatment of recycled graphite: 150 g of negative electrode graphite sheets obtained from the dismantling of ternary lithium-ion batteries were crushed, passed through a 200-mesh sieve, and 400 mL of 2 mol / L sulfuric acid solution was added. The mixture was stirred and acid-washed at 70°C for 3 h. After filtration, the mixture was washed with deionized water until neutral and dried at 110°C for 10 h to obtain 142 g of purified recycled graphite.

[0038] (2) Surface repair of recycled graphite: Take 120 g of purified recycled graphite obtained in step (1), add phenolic resin (12 wt% of the mass of purified recycled graphite based on carbon content), mix thoroughly with ethanol as the dispersion medium, dry and place in a tube furnace, heat to 700℃ at 4℃ / min under nitrogen atmosphere, keep warm for 3 h, and after natural cooling, obtain 128 g of surface repaired recycled graphite.

[0039] (3) Mixing and granulation: Take 40 g of the surface repair recycled graphite obtained in step (2), mix it with 60 g of petroleum coke, add 12 g of high temperature asphalt as a binder, and use spray granulation to control the particle size Dv50 to be 10~14 μm.

[0040] (4) Carbonization treatment: Under nitrogen atmosphere, the temperature is increased to 900℃ at 5℃ / min and held for 3 h.

[0041] (5) Graphitization treatment: Under an argon atmosphere, the temperature is increased to 2900℃ at 12℃ / min, held for 36 h, and then sieved after cooling.

[0042] Electrochemical performance: The first-cycle coulombic efficiency is 92.1%, the reversible specific capacity at 0.1C is 355 mAh / g, and the capacity retention rate after 500 cycles at 1C is 88.5%.

[0043] Example 3 The preparation method of the composite anode material of artificial graphite and recycled graphite includes the following steps: (1) Pretreatment of recycled graphite: Take 200 g of waste graphite generated during the production of graphite anode, remove surface impurities by alkaline washing (2 mol / L NaOH solution, 70℃, 3 h), and obtain 190 g of purified recycled graphite after washing and drying.

[0044] (2) Surface repair of recycled graphite: Take 150 g of purified recycled graphite, add glucose (8 wt% of the mass of purified recycled graphite based on carbon content), soak and dry, heat to 500℃ at 2℃ / min under nitrogen atmosphere, keep warm for 5 h, and obtain surface repaired recycled graphite.

[0045] (3) Mixing and granulation: Take 50 g of surface-repaired recycled graphite, mix it with 50 g of coal tar pitch coke, add 15 g of medium-temperature pitch, mix and granulate at high speed, and control Dv50 to be 14~18 μm.

[0046] (4) Carbonization treatment: Under nitrogen atmosphere, the temperature is increased to 700℃ at 4℃ / min and held for 6 h.

[0047] (5) Graphitization treatment: Under an argon atmosphere, the temperature is increased to 2700℃ at 8℃ / min, held for 60 h, and then sieved after cooling.

[0048] Electrochemical performance: The first-cycle coulombic efficiency is 91.8%, the reversible specific capacity at 0.1C is 352 mAh / g, and the capacity retention rate after 500 cycles at 1C is 87.6%.

[0049] Comparative Example 1 (pure artificial graphite) Using 100 g of needle coke as raw material, 10 g of medium-temperature pitch was added, and pure artificial graphite anode material was prepared by granulation, carbonization and graphitization processes in the same manner as in Example 1.

[0050] Electrochemical performance: The first-cycle coulombic efficiency is 93.2%, the reversible specific capacity at 0.1C is 362 mAh / g, and the capacity retention after 500 cycles at 1C is 90.1%.

[0051] Comparative Example 2 (pure recycled graphite, without composites) Using the surface-repaired recycled graphite obtained in step (2) of Example 1 as raw material, pure recycled graphite anode material was prepared by granulation, carbonization and graphitization processes in the same manner as in Example 1 (but without mixing with artificial graphite precursor).

[0052] Electrochemical performance: The first-cycle coulombic efficiency is 86.5%, the reversible specific capacity at 0.1C is 345 mAh / g, and the capacity retention after 500 cycles at 1C is 79.3%.

[0053] Comparative Example 3 (Pure recycled graphite without post-processing) The surface-repaired recycled graphite obtained in step (2) of Example 1 is used directly without granulation, carbonization and graphitization processes.

[0054] Electrochemical performance: The first-cycle coulombic efficiency is 80.2%, the reversible specific capacity at 0.1C is 293 mAh / g, and the capacity retention after 500 cycles at 1C is 66.4%.

[0055] Performance Comparison Analysis of Examples and Comparative Examples The electrochemical performance data of Examples 1-3 were compared with those of Comparative Examples 1-3, and the results are shown in the table below: The above comparison shows that: (1) The composite anode materials of Examples 1 to 3 are significantly better than pure recycled graphite anode materials in terms of first efficiency, specific capacity and cycle retention (Comparative Example 2), indicating that the synergistic composite of recycled graphite and artificial graphite precursor effectively makes up for the performance defects of recycled graphite when used alone.

[0056] (2) Compared with pure artificial graphite anode material (Comparative Example 1), when the proportion of recycled graphite is controlled at 30%~40% (Examples 1~2), the difference in first-time efficiency and specific capacity is only 1~2 percentage points, and the difference in cycle retention rate is within 2 percentage points. The performance is close to that of pure artificial graphite. This fully demonstrates that the composite strategy of the present invention achieves a large proportion of recycled graphite utilization while ensuring electrochemical performance.

[0057] (3) As the proportion of recycled graphite increases from 30% to 50% (Example 1 → Example 3), the overall performance of the material shows a moderate downward trend. However, the performance indicators of Example 3 are still significantly better than those of Comparative Example 2, and fully meet the requirements of commercial anode materials. Therefore, the proportion of recycled graphite can be flexibly adjusted within the range of 20% to 50% according to the actual application scenario: for power battery scenarios with high performance requirements, a lower proportion of 20% to 35% can be used; for energy storage battery scenarios that are cost-sensitive and have moderate performance requirements, a higher proportion of 35% to 50% can be used.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite negative electrode material of artificial graphite and recycled graphite, characterized in that, Includes the following steps: 1) The recycled graphite is pretreated to obtain purified recycled graphite; 2) The purified and recovered graphite obtained in step 1) is mixed with a carbon source precursor and subjected to medium-temperature pyrolysis under an inert atmosphere to obtain surface-repaired recovered graphite. 3) Mix the surface-repaired recycled graphite obtained in step 2) with the artificial graphite precursor, add a binder and granulate to obtain composite precursor particles; 4) The composite precursor particles obtained in step 3) are subjected to carbonization treatment; 5) The carbonized product obtained in step 4) is subjected to high-temperature graphitization treatment under an inert atmosphere, cooled and sieved to obtain the composite anode material of artificial graphite and recycled graphite.

2. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to claim 1, characterized in that, In step 1): the recycled graphite is crushed and sieved, and then acid-washed or alkali-washed to remove metal impurities. After washing and drying, purified recycled graphite is obtained, wherein: The pickling process uses one or more of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1-3 mol / L; The alkaline washing uses a sodium hydroxide or potassium hydroxide solution with a concentration of 1~4 mol / L; The washing process involves washing with deionized water until neutral, and the drying temperature is 80~120℃ for 6~24 hours.

3. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to claim 1, characterized in that, In step 2): The carbon source precursor is one or more of asphalt, phenolic resin, polyacrylonitrile, glucose, or sucrose. The intermediate-temperature pyrolysis treatment is performed at a temperature of 400~800℃ for 2~6 h, with a heating rate of 2~5℃ / min. The amount of the carbon source precursor added is 5-15 wt% of the mass of purified and recovered graphite.

4. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to claim 1, characterized in that, In step 3): The surface-repairing recycled graphite and the artificial graphite precursor are mixed at a mass ratio of (20~50):(50~80); The artificial graphite precursor is one or more of needle coke, petroleum coke, coal tar pitch coke or mesophase carbon microspheres. The binder is asphalt or a polymer binder, and its addition amount is 5-15 wt% of the total mass of the surface-repaired recycled graphite and the artificial graphite precursor; The granulation process employs high-speed mixing granulation or spray granulation, with the particle size Dv50 controlled between 8 and 20 μm.

5. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to claim 1, characterized in that, In step 4): The process is carried out under an inert atmosphere, which is either nitrogen or argon. The carbonization temperature is 600~1000℃, the time is 2~6 h, and the heating rate is 2~8℃ / min.

6. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to claim 1, characterized in that, In step 5): The inert atmosphere for graphitization is argon; the graphitization temperature is 2600~3000℃, the time is 24~72 h, and the heating rate is 5~15℃ / min. The particle size Dv50 of the composite anode material made from artificial graphite and recycled graphite is 10–18 μm, and the specific surface area is 1.5–4.0 m². 2 / g.

7. The method for preparing the composite negative electrode material of artificial graphite and recycled graphite according to any one of claims 1 to 6, characterized in that: The recycled graphite comes from graphite sheets dismantled from the negative electrodes of retired lithium-ion batteries or graphite scraps generated during electrode production. The recycled graphite anode powder contains 70-80% graphite.

8. A graphite composite anode material prepared by the method according to any one of claims 1 to 7.

9. A negative electrode sheet for a lithium-ion battery, characterized in that: Including the graphite composite anode material as described in claim 8.

10. A lithium-ion secondary battery, characterized in that: The lithium-ion battery includes the negative electrode sheet as described in claim 9, wherein the lithium-ion secondary battery is a power battery, an energy storage battery, or a consumer electronics battery.

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