A method for modifying and recycling waste graphite box plates to prepare lithium ion battery negative materials

Abstract

The present application belongs to the field of waste regeneration, and particularly relates to a modification method of waste graphite box plate, which obtains mixed powder containing waste graphite box plate and petroleum coke, and then the mixed powder is heated to T1 temperature at a heating rate of V1, and then heated to T2 temperature at a heating rate of V2 for heat preservation modification treatment to prepare the modified graphite box plate; the weight ratio of the waste graphite box plate and the petroleum coke is 1:0.5-10; the v1 is 1-10 ℃ / min; the T1 temperature is 400-500 ℃; the v2 is 1-3.5 ℃ / min; and the T2 temperature is 550-700 ℃. The present application also relates to a method for calcining the modified box plate to obtain active material. The method can obtain high-performance active material based on waste box plate.

Description

Technical Field

[0001] This invention relates to the field of waste carbon material recycling, specifically to the field of waste box panel recycling. Background Technology

[0002] Lithium-ion batteries, as a new type of rechargeable battery, are widely used in electric vehicles, aerospace, and smart mobile devices. In these applications, the performance requirements for lithium-ion batteries are becoming increasingly stringent, including energy density, power density, safety performance, and cycle life. Among these, the negative electrode material, as a key component for transferring charge and storing electrical energy, has a significant impact on the overall performance of the battery.

[0003] Existing anode materials are mainly composed of graphite or graphite-like materials, which possess excellent electrochemical and electrical properties, thus enjoying widespread adoption. However, with the continuous expansion of lithium-ion battery applications and the increasing demand, traditional anode materials such as graphite are no longer sufficient to meet market needs. Furthermore, lithium-ion battery anode materials not only have high manufacturing costs but also require improved stability. Simultaneously, the processing and recycling of large quantities of waste graphite anode materials is a significant bottleneck restricting the sustainable development of the lithium-ion battery industry.

[0004] During the graphitization furnace production process, a material called waste graphite furnace plates is generated. This material, used as a carbon raiser, has low secondary utilization value. After crushing, the surface morphology of the waste graphite furnace plates is poor, and its specific surface area, tap density, capacity, and initial efficiency are all relatively low, making it unsuitable as a negative electrode material. Therefore, processing waste graphite furnace plates into negative electrode materials while simultaneously improving their capacity, rate capability, and lifespan has gradually become a research hotspot. Compared to other waste graphite materials, waste graphite furnace plates face two unique challenges when used to prepare negative electrodes. First, due to the fixed shape and large size of the waste graphite slabs from graphitization furnaces, traditional crushing methods are inefficient and produce poor particle morphology. New crushing technologies are needed to enhance crushing efficiency and improve particle morphology, thereby increasing material dispersibility and flowability. Second, the control parameters for waste graphite slab raw materials from graphitization furnaces differ from those of widely used low-sulfur coke and other anode graphite raw materials, such as sulfur content, ash content, and volatile matter. Therefore, the control and processing of raw materials need optimization and improvement to fully realize their performance potential while improving material reliability and stability. Thus, it is necessary to develop specific process flows and equipment suitable for waste graphite slab materials, and to conduct in-depth research and optimization of key technologies such as preparation conditions and raw material selection to achieve the goal of converting waste graphite slabs into high-performance anode materials. Developing a low-cost, high-performance pre-coating granulation modification method for waste graphite slab lithium-ion battery anode materials is of great significance for promoting the development of the lithium-ion battery industry and the resource reuse of waste graphite slabs from graphitization furnaces. Summary of the Invention

[0005] To address the problem of existing technologies lacking the ability to recycle waste graphite sheets and prepare negative electrode active materials, the primary objective of this invention is to provide a modification method (also known as a regeneration and repair method) for waste graphite sheets, aiming to repair defects and structures in waste graphite sheets to facilitate the preparation of high-performance negative electrode active materials.

[0006] The second objective of this invention is to prepare a negative electrode active material using the repaired waste box plate.

[0007] The third objective of this invention is to provide the negative electrode active material prepared from the aforementioned waste packaging plates and its application in lithium-ion batteries.

[0008] The fourth objective of this invention is to provide a lithium-ion battery comprising the negative electrode material prepared from the aforementioned waste packaging plate, as well as its negative electrode and negative electrode material.

[0009] Waste graphite linerboard is a waste material generated during the graphitization process in a graphitization furnace. The main industry approach to treating this waste is to use it as a carbon raiser. However, the recycling value of this approach is not ideal. In response to this industry situation, this invention is the first in the industry to propose a method for recycling waste graphite linerboard to prepare active materials. However, it was previously discovered that to fill this industry gap and successfully implement this novel approach, it is necessary to overcome the problems caused by the high surface defects and interlayer structure damage resulting from multiple rounds of graphitization in waste graphite linerboard, which are detrimental to the electrochemical performance (especially high-temperature cycling performance) of the recycled materials. To address this problem, this invention, after in-depth research, provides the following improvement solutions:

[0010] A method for modifying waste graphite box panels involves obtaining a mixed powder comprising waste graphite box panels and petroleum coke, then preheating the mixed powder to a temperature T1 at a heating rate of V1, and then heating it to a temperature T2 at a heating rate of V2 for heat preservation modification treatment to obtain the modified graphite box panels.

[0011] The petroleum coke contains 10%–20% volatile matter, ≤3% sulfur, and ≤2% ash.

[0012] The weight ratio of the waste graphite box plate and petroleum coke is 1:0.5 to 10;

[0013] The speed of v1 is 1 to 10 °C / min; the temperature of T1 is 400 to 500 °C.

[0014] The v2 is 1 to 3.5℃ / min; the temperature of T2 is 550 to 700℃.

[0015] This invention innovatively provides a method for repairing and regenerating waste graphite slabs without carbon source (such as asphalt or polymer) additives. It innovatively combines waste graphite slabs with petroleum coke, utilizing the physicochemical properties of petroleum coke, and coordinating the control of two-stage heat treatment (T1 and T2 stages) and the heating mechanism. This synergistic approach solves the problems of difficult repair and regeneration of waste graphite slabs due to high surface defects and interlayer breakage, thus hindering the attainment of high electrochemical performance. Research shows that the process described in this invention can achieve the reuse of waste graphite slabs and co-produce materials with high electrochemical performance, particularly high-temperature cycling stability.

[0016] In this invention, the additive-free treatment method of waste graphite box plates-petroleum coke, along with the combination of the physicochemical properties of petroleum coke, the two-stage heat treatment mechanism, and parameters, are key to synergistically solving the problem of difficult regeneration and repair of box plates, which is not conducive to the preparation of high-performance regenerated anodes.

[0017] In this invention, the waste graphite box plate is the box plate material from the decommissioned graphitization furnace.

[0018] Preferably, the waste graphite box plates are pretreated, and the pretreatment process includes acid immersion treatment and low temperature heat treatment.

[0019] The acid solution is an inorganic strong acid solution with a concentration of 0.1 to 5 M (such as an aqueous solution of at least one of sulfuric acid and hydrochloric acid); the temperature of the low-temperature heat treatment stage is 50 to 100°C.

[0020] This invention has discovered that the innovative combination of acid treatment and low-temperature heat treatment for pretreatment of waste graphite boxes, along with subsequent processes, can achieve synergy and help further improve the electrochemical properties of the materials from which the boxes are sourced, especially their high-temperature cycling performance.

[0021] In this invention, waste graphite sheets and petroleum coke are crushed separately and then mixed, or mixed and crushed together, to obtain the aforementioned mixed powder.

[0022] Preferably, the weight ratio of the waste graphite box plate and the petroleum coke is 1:1 to 4;

[0023] Preferably, v1 is 5–10 °C / min;

[0024] Preferably, T1 is 450–500℃;

[0025] Preferably, the heat preservation time at temperature T1 is less than or equal to 3 hours, and more preferably 0.5 to 1.5 hours.

[0026] Preferably, v2 is 2-3℃ / min;

[0027] Preferably, T2 is 600–650°C;

[0028] Preferably, the heat preservation time at temperature T2 is 3 to 10 hours.

[0029] Further preferably, the modification treatment is carried out on the mixture under negative pressure. A typical operating method is as follows: the mixed powder is placed in a reactor, the system pressure is pre-set to negative pressure, and then the reaction system is sealed for subsequent heat treatment. This invention demonstrates that modification under negative pressure can further improve the properties of the prepared material, particularly contributing to improved high-temperature cycling stability.

[0030] The negative pressure is, for example, a pressure less than or equal to 0.5 atm, preferably a pressure of 0.01 to 0.2 atm.

[0031] This invention also provides a method for modifying and regenerating waste graphite boxes to prepare negative electrode active materials. The modified graphite boxes are obtained by using the modification method of the waste graphite boxes described in this invention, and the graphite boxes are calcined to obtain the regenerated negative electrode active materials.

[0032] In this invention, the calcination temperature is not particularly required; for example, it can be 900–2800°C, or more specifically, 2000–2500°C.

[0033] In this invention, there are no special requirements for the calcination time, for example, it can be 0.5 to 5 hours.

[0034] The present invention also provides a method for preparing negative electrode active materials by modifying and regenerating the aforementioned waste graphite box plates.

[0035] In this invention, thanks to the combination of the aforementioned processes, the regenerated negative electrode active material can be endowed with special physicochemical properties. Moreover, the negative electrode active material obtained by the method can unexpectedly exhibit excellent electrochemical performance.

[0036] The present invention also provides an application of the negative electrode active material prepared by the method described above, for the preparation of lithium-ion batteries;

[0037] Preferably, it is used to prepare the negative electrode of a lithium-ion battery;

[0038] Further optimization will allow it to be used as a negative electrode material for lithium-ion batteries;

[0039] Further optimization involves combining it with binders and conductive agents to prepare negative electrode materials for lithium-ion batteries.

[0040] In this invention, lithium-ion batteries and their negative electrodes and materials can be prepared from the recycled negative electrode active material using known processes. For example, the negative electrode active material obtained in this invention is combined with a binder and selectively with a conductive agent to form a negative electrode material. Further, the negative electrode material is slurried and coated onto a current collector using known methods to form a negative electrode. Even further, the negative electrode is combined with a separator and a positive electrode to form a lithium-ion battery. The binder, conductive agent, separator, current collector, and positive electrode described in this invention can all be conventionally available in the industry.

[0041] The present invention also provides a negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material comprises a negative electrode active material prepared by regeneration according to the present invention.

[0042] The present invention also provides a lithium-ion battery comprising a negative electrode, a separator, and a positive electrode sequentially composited, wherein the negative electrode is the negative electrode of the present invention containing the regenerated negative electrode active material.

[0043] The beneficial effects of this invention are:

[0044] This invention fills the gap in the preparation of negative electrode active materials by regenerating waste graphite plates.

[0045] This invention innovatively provides a method for repairing and regenerating waste graphite box panels without carbon source (such as asphalt or polymer) additives. It innovatively combines waste graphite box panels with petroleum coke, and combines the physicochemical properties of petroleum coke with the combined control of T1 and T2 two-stage heat treatment and heating mechanism. This can achieve synergy and solve the problems of difficulty in repairing and regenerating waste graphite box panels with high electrochemical performance caused by high surface defects and interlayer breakage.

[0046] Compared with existing technologies, the method provided by this invention has the advantages of low preparation cost, abundant and reliable raw material sources, and simple and easy production process. It can also effectively solve the problem of processing and recycling large quantities of waste graphite anode materials, thus contributing to the sustainable development of the lithium-ion battery industry. Attached Figure Description

[0047] Figure 1 The image shown is a scanning electron microscope (SEM) image of the product prepared in step A4 of Example 1.

[0048] Figure 2 Scanning electron microscope image of the product prepared in step A4 of Example 2. Detailed Implementation

[0049] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the present invention; however, the implementation of the present invention is not limited thereto.

[0050] The waste graphite box plate mentioned in this invention is a graphite box plate waste material decommissioned from a conventional graphitization furnace. It has poor surface morphology, high hardness, and is difficult to crush. The volatile matter content of the graphite box plate is ≤5%, and the crushed particle size is 5-20um.

[0051] This invention is the first in the industry to propose repairing and regenerating waste graphite sheets to form negative electrode active materials. For example, the typical steps of the repair method for waste graphite sheets in this invention are as follows:

[0052] Step 1: Waste graphite slabs and petroleum coke are crushed and shaped to obtain primary granules; the petroleum coke is raw petroleum coke, with volatile matter of 10% to 20%, sulfur content of ≤3%, and ash content of ≤2%. The average particle size D50 of the primary granules is 5-20 μm.

[0053] Step 2: The primary granules of waste graphite box plates and the primary granules of petroleum coke are mixed in a certain proportion using a mixer to obtain a mixture; the mixer is, for example, a VC high-speed mixer. The speed of the mixer is 300-400 r / min, and the mixing time is 10-60 min.

[0054] Step 3: Add the mixture to a vertical reactor, preheat it to temperature T1 at a heating rate of V1, and then heat it to temperature T2 at a heating rate of V2 for heat preservation modification treatment to obtain the modified graphite box plate; wherein, v1 is 1~10℃ / min; temperature T1 is 400~500℃; and the heat preservation time at temperature T1 is less than or equal to 3h;

[0055] The v2 is 1 to 3.5 °C / min; the temperature of T2 is 550 to 700 °C; preferably, the holding time at temperature T2 is 3 to 10 hours; in this invention, unless otherwise stated, the atmosphere during the heat treatment stage is a protective atmosphere, such as an inert gas (e.g., typical Ar), and the starting pressure of the heat treatment process is atmospheric pressure.

[0056] The lithium-ion battery anode material prepared by this invention has the characteristics of good surface morphology, few defects, and excellent electrochemical performance, which can meet the high requirements of lithium-ion batteries. Meanwhile, the waste packaging materials used in this method are abundant as raw materials, and the preparation cost is low, which conforms to the concept of waste resource reuse and energy conservation, and has broad market application prospects.

[0057] This invention innovatively employs a novel crushing technology to pulverize waste graphite sheet materials from graphitization furnaces, improving the particle morphology and enhancing the material's dispersibility and flowability. Furthermore, it innovatively incorporates a specific proportion of petroleum coke containing volatiles for negative electrodes, utilizing the petroleum coke's volatiles to surface-modify the graphite sheet powder, thereby obtaining a graphite sheet lithium-ion battery negative electrode material with superior performance. Additionally, the invention employs specialized control over the heating curve, holding time, and other conditions during the synergistic heat treatment stage to obtain a graphite sheet lithium-ion battery negative electrode material with good surface morphology, few defects, and a stable secondary particle structure.

[0058] This invention utilizes crushing technology and process control, combined with petroleum coke surface modification and further combined with synergistic heat treatment process control technology, to enable the effective application of waste graphitization furnace plate materials in the preparation of lithium-ion battery anode materials. This reduces the waste of waste resources and also plays a positive role in the environment.

[0059] In a further typical embodiment of the present invention, the repaired plate material can be subjected to conventional calcination treatment to obtain a high-performance negative electrode active material. In this invention, the calcination treatment can be performed using conventional equipment and process conditions.

[0060] Example 1

[0061] A1. Waste graphite box plates and petroleum coke are crushed and shaped to obtain primary granules; wherein, the properties of petroleum coke are volatile matter: 15%, sulfur content: ≤3%, ash content: ≤2%, and the average particle size D50 of the primary granules is 8μm;

[0062] A2. The primary granules of waste graphite box plates and primary granules of petroleum coke are mixed in a weight ratio of 2:8 using a mixer to obtain a mixture; the mixer is a VC high-speed mixer. The mixer speed is 350 r / min, and the mixing time is 30 min.

[0063] A3. Add the mixture to a vertical reactor, seal the reactor, and then heat it from room temperature to 500℃ (marked as T1) at 5℃ / min (marked as v1), hold it at that temperature for 30 min (marked as t1), then heat it to 650℃ (marked as T2) at 3℃ / min (marked as v2), hold it at that temperature for 5 h (marked as t2), and finally cool it down to below 50℃, discharge the material, and obtain the recycled box panel material;

[0064] A4. The recycled graphite plate material prepared in A3 is placed in a graphitization furnace for calcination (graphitization); wherein the graphitization temperature is 2200℃, the graphitization time is 2h, and the recycled graphite plate anode material is obtained by cooling to room temperature.

[0065] Example 2

[0066] Compared with Example 1, the only difference is that in step A1, the volatile matter of petroleum coke is 10%, and in step A2, the weight ratio of graphite waste box material to petroleum coke is 4:6. Other operations and parameters are the same as in Example 1.

[0067] Example 3

[0068] Compared with Example 1, the only difference is that in step A1, the volatile matter of petroleum coke is 20%, and in step A2, the weight ratio of graphite waste box material to petroleum coke is 5:5. Other operations and parameters are the same as in Example 1.

[0069] Example 4

[0070] Compared with Example 1, the only difference is that in step A3, v1 is 10℃ / min, T1 is 450℃, and t1 is 40min; v2 is 2℃ / min, T2 is 600℃, and t2 is 6h; other operations and parameters are the same as in Example 1.

[0071] Example 5

[0072] Compared to Example 1, the only difference is that before A1, the waste graphite box panels are pre-modified. The steps are as follows: first, the waste graphite box panels are immersed in a 2M sulfuric acid solution for acid treatment, followed by solid-liquid separation, washing with water until neutral, and then heat treatment at a temperature of 80-85°C to obtain pre-modified graphite box panels. Subsequently, the modified graphite box panels are processed sequentially according to steps A1-A4, and all other operations and parameters are the same as in Example 1.

[0073] Example 6

[0074] Compared to Example 5, the only difference is that in A3, the mixture is added to a vertical reactor, the system pressure is reduced to 0.1 atm (0.1 atmospheres) beforehand, and the reactor is sealed before subsequent processing. All other operations and parameters are the same as in Example 5.

[0075] Comparative Example 1

[0076] Compared with Example 1, the only difference is that the petroleum coke is petroleum coke with 5% volatile matter, while the other steps and parameters are the same as in Example 1.

[0077] Comparative Example 2

[0078] Compared with Example 1, the only difference is that the heat treatment process in A3 is a single-stage heat treatment that only performs T2 and does not perform T1 treatment. That is, the heating process is: heating from room temperature to 650°C at 3°C / min, holding at that temperature for 5 hours, and finally cooling down and discharging.

[0079] Comparative Example 3

[0080] Compared with Example 1, the only difference is that the heating rate v2 of the second heat treatment in the A3 process is controlled at 5℃ / min, while all other operations and parameters are performed in accordance with Example 1.

[0081] Comparative Example 4

[0082] Compared with Example 1, the only difference is that the box plate and petroleum coke are not processed in step A2. Instead, the box plate and petroleum coke in the same proportion as in Example 1 are processed in step A3, then mixed according to step A2, and then processed in step A4.

[0083] Comparative Example 5

[0084] Compared with Example 1, the only difference is that the mixture of A2 was not processed in step A3, but was directly processed in step A4. All other operations and parameters were performed in accordance with Example 1.

[0085] The physicochemical properties of the modified boxes in Examples 1-6 and Comparative Examples 1-5 were tested respectively, and the test results are shown in Table 1.

[0086] Half-cell testing method: Using the graphite box plate electrode (the weight ratio of the final prepared recycled graphite box plate negative electrode active material, acetylene black, and PVDF in each case is 90:5:5) as the working electrode, lithium metal as the negative electrode, 1 mol / L LiPF6 EC / EMC (volume ratio 1:1) as the electrolyte, and PE-PP composite membrane as the separator, CR2025 coin cells were assembled in an argon-filled dry glove box. The cells were charged and discharged at a current density of 74 mA / g in a voltage range of 0.001-2V at a temperature of 40℃.

[0087] Full cell testing method: A 1Ah soft-pack full cell was prepared using the graphite box plate electrode (the weight ratio of the final prepared recycled graphite box plate negative electrode active material, SP, CMC, and SBR in each case was 95.8:1.0:1.2:2.0) as the negative electrode, lithium iron phosphate as the positive electrode, conventional electrolyte for lithium iron phosphate power batteries, and PE-PP composite membrane as the separator. Cyclic performance was tested under a charge-discharge regime of 0.5C and 1.0C, with a temperature of 45℃, a voltage range of 2.5-3.65V, and a charge rate of 0.5C.

[0088] The test results of the electrochemical performance are shown in Table 1;

[0089] Table 1

[0090]

[0091] This invention modifies and composites the surface defects of petroleum coke, especially waste graphite box plate particles, using petroleum coke volatiles, to obtain surface-coated secondary particles. These composite particles have fewer surface defects, paving the way for the preparation of products that simultaneously achieve excellent kinetic and lifespan performance of the secondary particle materials.

[0092] The above embodiments only illustrate several implementation methods of the present invention. The descriptions are relatively specific and detailed, but they should not be construed as allowing for various modifications and improvements to be made based on the concept of the present invention. These modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the claims used.

Claims

1. A method for modifying waste graphite box plates, characterized in that, A mixed powder containing waste graphite box plates and petroleum coke is obtained. The mixed powder is then preheated to temperature T1 at a heating rate of V1, and then heated to temperature T2 at a heating rate of V2 for heat preservation modification treatment to obtain the modified graphite box plate. The petroleum coke contains 10%~20% volatile matter, ≤3% sulfur, and ≤2% ash. The weight ratio of the waste graphite box plate to the petroleum coke is 1:0.5~10; The V1 is 1~10℃ / min; the T1 temperature is 400~500℃; The V2 is 1~3.5℃ / min; the T2 temperature is 550~700℃.

2. The modification method for waste graphite box plates as described in claim 1, characterized in that, The waste graphite box plates are pre-treated, and the pre-treatment process includes acid immersion treatment and low temperature heat treatment. The acid solution is an inorganic strong acid solution with a concentration of 0.1~5M; the temperature of the low-temperature heat treatment stage is 50~100℃.

3. The method for modifying waste graphite box plates as described in claim 1, characterized in that, The waste graphite box plate and petroleum coke are crushed separately and then mixed, or mixed and crushed, to obtain the mixed powder.

4. The method for modifying waste graphite box plates as described in claim 1, characterized in that, The D50 particle size of the mixed powder is 5-12 μm.

5. The method for modifying waste graphite box plates as described in claim 1, characterized in that, The weight ratio of the waste graphite box plate to the petroleum coke is 1:1~4.

6. The method for modifying waste graphite box plates as described in claim 1, characterized in that, V1 is 5~10℃ / min; T1 is 450~500℃; The holding time at temperature T1 is 0.5~1.5h.

7. The method for modifying waste graphite box plates as described in claim 1, characterized in that, V2 is 2~3℃ / min; T2 is 600~650℃; The heat preservation time at T2 temperature is 3~10 hours.

8. The method for modifying waste graphite box plates as described in any one of claims 1 to 7, characterized in that, The modification process is carried out under negative pressure.

9. A method for modifying and regenerating waste graphite plates to prepare negative electrode active materials, characterized in that, A modified graphite plate is obtained by the modification method described in any one of claims 1 to 7, and the graphite plate is calcined to obtain a regenerated negative electrode active material.

10. The method for modifying and regenerating waste graphite plates to prepare negative electrode active materials as described in claim 9, characterized in that, The calcination temperature is 900~2800℃; The calcination time is 0.5 to 5 hours.

11. A negative electrode active material prepared by the method of claim 9 or 10.

12. An application of the negative electrode active material according to claim 11, characterized in that, It is used to prepare lithium-ion batteries.

13. The application of the negative electrode active material as described in claim 12, characterized in that, It is used to prepare the negative electrode of a lithium-ion battery.

14. The application of the negative electrode active material as described in claim 13, characterized in that, It was used to prepare the negative electrode material for lithium-ion batteries.

15. The application of the negative electrode active material as described in claim 14, characterized in that, It was combined with binders and conductive agents to prepare negative electrode materials for lithium-ion batteries.

16. A negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composited thereon, characterized in that, The negative electrode material includes the negative electrode active material as described in claim 11.

17. A lithium-ion battery, comprising a negative electrode, a separator, and a positive electrode sequentially laminated together, characterized in that, The negative electrode is the negative electrode as described in claim 16.

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