Carbon material taking graphite recovered from waste lithium ion battery as raw material and preparation method of carbon material

Abstract

The invention relates to solid waste resource utilization and carbon material preparation, and discloses a carbon material with graphite recycled from waste lithium ion batteries as a raw material and a preparation method of the carbon material. The method comprises the following steps: S1, dispersing graphite powder recovered from the waste lithium ion battery into absolute ethyl alcohol to obtain a graphite suspension; the preparation method comprises the following steps: dispersing graphene oxide powder in ultrapure water, and carrying out ultrasonic treatment to obtain graphene oxide dispersion liquid; mixing the two mixtures; s2, drying the mixed slurry; adding a binder phenolic resin and absolute ethyl alcohol into the dried powder, and carrying out ball milling; s3, performing vacuum drying, crushing and sieving on the ball-milled slurry to obtain composite powder; the composite powder is firstly subjected to mold pressing preforming and then subjected to isostatic pressing forming, and a green body is obtained; and S4, curing and roasting the green body, carrying out graphitization treatment at the temperature of 2000 DEG C or above, and cooling to obtain the carbon material. According to the method, deep repair of the surface and interlayer defects of the recycled graphite is realized.

Description

Technical Field

[0001] This application relates to the resource utilization of solid waste and the preparation of carbon materials, specifically to a carbon material made from recycled graphite from waste lithium-ion batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries (LIBs) have become the mainstream electrochemical energy storage devices due to their high energy density and long cycle life, and are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems. With the surge in consumption and accelerated replacement cycles, a large number of lithium-ion batteries are gradually entering their retirement period. Therefore, achieving efficient and green recycling of retired LIBs has become a key link and an inevitable requirement for the sustainable development of the new energy industry.

[0003] Currently, research and practice in the recycling of waste LIBs in industry and academia mainly focus on the extraction and regeneration of cathode materials rich in valuable metals such as cobalt, nickel, manganese, and lithium. In contrast, the recycling value of graphite, which is widely used in anode materials (accounting for more than 90% of anode materials), is often overlooked. In conventional hydrometallurgical recycling processes, after the cathode metals are extracted through steps such as acid leaching, the remaining waste graphite is often treated as low-value fuel or solid waste. This not only results in a serious waste of carbon resources, but also directly produces greenhouse gases such as carbon dioxide during incineration, exacerbating environmental pressure.

[0004] From a microscopic perspective, the crystal structure of the graphite anode in waste LIBs has deteriorated significantly after long-term charge-discharge cycles. During the repeated insertion and extraction of lithium ions, fatigue and damage to the graphite layer structure are caused, specifically: (1) Some lithium ions are trapped between graphite layers due to kinetic or thermodynamic reasons, forming irreversible "dead lithium", which leads to the expansion of the graphite lattice and the interplanar spacing (d) in the c-axis direction (002). 002 (1) The density of graphite crystals increases significantly, far exceeding the 0.3354 nm of ideal graphite crystals; (2) the van der Waals forces between graphite sheets weaken, the stacking becomes loose and disordered, and the degree of order decreases; (3) a large number of microcracks, pores and dangling bonds are generated on the surface and edges of graphite particles, and the defect concentration increases significantly. These structural degradations seriously damage the high electrical conductivity, high thermal conductivity and structural stability that graphite materials should possess, making the performance of recycled graphite for direct utilization low and difficult to meet the application requirements of high-end carbon materials.

[0005] Therefore, how to improve the performance of carbon materials prepared from recycled graphite from waste lithium-ion batteries is an urgent problem to be solved. Summary of the Invention

[0006] In view of the above problems, this application provides a carbon material made from recycled graphite from waste lithium-ion batteries and a method for preparing the same, which improves the performance of the carbon material made from recycled graphite from waste lithium-ion batteries.

[0007] According to one aspect of the embodiments of this application, a method for preparing carbon material using recycled graphite from waste lithium-ion batteries as raw material is provided, comprising the following steps: S1. Disperse graphite powder from recycled waste lithium-ion batteries in anhydrous ethanol to obtain a graphite suspension; disperse graphene oxide powder in ultrapure water and sonicate to obtain a graphene oxide dispersion; under stirring conditions, add the graphene oxide dispersion to the graphite suspension and mix evenly to obtain a mixed slurry; wherein, the mass percentage of the recycled graphite powder from waste lithium-ion batteries to the graphene oxide powder is (95%~99.9%):(0.1%~5.0%). S2. The mixed slurry is heat-treated at 150~180℃ for 4~6 hours to obtain dried powder; phenolic resin and anhydrous ethanol are added to the dried powder, and ball milling is performed to obtain ball-milled slurry; wherein, based on the total mass of the dried powder, the amount of phenolic resin added is 10~25 wt.%; S3. The ball-milled slurry is vacuum dried, crushed, and sieved to obtain a composite powder; the composite powder is first pre-molded by molding, and then isostatically pressed to obtain a green body; S4. The blank is cured at 150~180℃ for 4~6 hours; then calcined at 800~1200℃ under inert gas protection; finally, graphitized at a temperature above 2000℃ for 1~2 hours, and then cooled to obtain carbon material.

[0008] In one alternative approach, in step S1, the frequency of the ultrasonic treatment is 20-40 kHz, the power is 200-600 W, and the treatment time is 30-45 minutes.

[0009] In one alternative approach, in step S1, the mass percentage of the recycled graphite powder from the waste lithium-ion battery to the graphene oxide powder is (95.0%~99%):(1.0%~5.0%).

[0010] In an alternative approach, during step S2, the amount of anhydrous ethanol added during ball milling is 50% to 80% of the mass of the dried powder.

[0011] In one alternative approach, in step S3, the pressure of the compression molding preforming is 5~10MPa; and the pressure of the isostatic pressing is 100~150MPa.

[0012] In an alternative approach, in step S4, the temperature of the graphitization treatment is 2400~2700℃.

[0013] In one alternative approach, the specific procedure for roasting in step S4 is as follows: the temperature is increased to 980°C at a heating rate of 2~5°C / min, and then held at that temperature for 2 hours.

[0014] According to another aspect of the embodiments of this application, a carbon material is provided, which is prepared by the method of any one of claims 1 to 7.

[0015] In one alternative approach, the intensity ratio of the D peak to the G peak in the Raman spectrum of the carbon material is I. D / I G Below 0.5.

[0016] In one alternative embodiment, the carbon material has a volume resistivity of less than 20 μΩ·m and an in-plane thermal conductivity of more than 60 W / (m·K).

[0017] This application involves mixing recycled graphite powder from waste lithium-ion batteries with graphene oxide dispersion in a specific ratio (95%~99.9%:0.1%~5.0%), adding phenolic resin binder (10~25 wt.%), and then ball-milling and molding the mixture. Following this process, the mixture undergoes curing, medium-temperature calcination, and crucial ultra-high temperature (above 2000℃) graphitization treatment, thereby transforming recycled graphite from waste lithium-ion batteries into high-performance carbon materials. Through the dual synergistic repair mechanism of phenolic resin and graphene oxide, the recycled graphite is repaired from the surface to the crystal lattice. The resulting carbon material exhibits a complete graphite crystal structure and excellent electrical conductivity (low resistivity) and thermal conductivity. This not only achieves high-value resource utilization of waste graphite but also possesses promising industrialization prospects.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the carbon material preparation method in the embodiments of this application; Figure 2 This is a high-magnification transmission electron microscope (TEM) image of the sample (ungraphitized) prepared in Comparative Example 1 of this application; Figure 3 This is a high-magnification transmission electron microscope (TEM) image of the sample prepared in Comparative Example 2 of this application (without graphene oxide addition); Figure 4 This is a high-magnification transmission electron microscope (TEM) image of the sample prepared in Example 5 of this application; Figure 5 The images show a comparison of the Raman spectra of the samples prepared in Comparative Examples 1, 2, 3, and 5 of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer and more specific, the application will be described in more detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not constitute any limitation on the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0021] Unless otherwise specified, all raw materials and reagents used in this application are commercially available conventional products or can be prepared by methods known in the art.

[0022] The inventors discovered that to improve or repair the performance of carbon materials, they can use polymers (such as phenolic resin and asphalt) for coating followed by carbonization, or combine them with nanomaterials (such as carbon nanotubes and graphene). However, for recycled graphite from waste lithium batteries with special damaged structures, if only precursors such as phenolic resin are used for coating and carbonization, it mainly fills macroscopic surface defects and is insufficient in its ability to deeply repair interlayer lattice expansion. If only graphene or graphene oxide is used for physical composite, although a conductive network can be built, the cost is high, and the interfacial bonding strength with the matrix graphite and the repair effect on internal defects are limited, resulting in insufficient process stability.

[0023] This application aims to overcome the shortcomings of waste lithium-ion battery graphite anode recycling technology, such as resource waste, low performance and difficulty in high-value utilization, and provides a method for preparing high-performance carbon materials using recycled graphite from waste lithium-ion batteries as raw materials, as well as the high-conductivity and high-thermal-conductivity carbon materials prepared by the above method, thereby expanding the application of recycled graphite in thermal management, conductive components and other fields.

[0024] (a) Raw material description Graphite powder from recycled waste lithium-ion batteries can be obtained through commercial recycling channels or prepared in-house using the following typical laboratory method: Disassembled waste LIB anode sheets (mainly composed of graphite, conductive carbon black, and binders PVDF or SBR / CMC) are heat-treated at 500-700℃ in an inert atmosphere to remove organic binders; the heat-treated material is then ground and soaked in dilute acid (such as 1M HCl) to dissolve residual lithium salts (such as LiF, Li2CO3) and trace metal impurities; subsequently, it is washed with water until neutral, dried, and sieved to obtain recycled graphite powder with a particle size D50 of approximately 10-30 μm. Its typical characteristics are d... 002 0.340 nm, with micropores and cracks on the surface.

[0025] Graphene oxide (GO) powder: can be prepared using methods such as the modified Hummers method or the Brodie method, or commercially available products can be purchased directly. The GO powder used in the embodiments of this application has a sheet size of approximately 1-10 μm, a high rate of monolayers or few layers, and good dispersibility in aqueous solution.

[0026] Thermosetting phenolic resin: This is a type A phenolic resin (resol type), with a solid content of approximately 50%-80%, soluble in organic solvents such as ethanol and acetone. As a binder and carbon precursor, it can undergo cross-linking curing and pyrolytic carbonization under heating conditions.

[0027] Anhydrous ethanol and ultrapure water: both are of analytical grade or higher and are used as solvents and dispersion media.

[0028] (II) Description of Instruments and Equipment and Alternative Methods The instruments and equipment used in the following embodiments are examples only. Those skilled in the art can select other devices with equivalent functions according to actual conditions.

[0029] Dispersion and mixing: In the examples, a mechanical stirrer (such as a cantilever mixer) was used to prepare the suspension. Alternatively, a high-speed shear disperser, planetary mixer, etc., can be used to achieve a similar mixing effect. Ultrasonic dispersion was performed using a probe-type or tank-type ultrasonic cleaner; the power and frequency could be adjusted within a reasonable range to achieve GO dispersion.

[0030] Heat treatment and drying: Blow-air drying ovens and vacuum drying ovens can be used for heat treatment and drying of slurries. Spray drying, rotary evaporation, and other equipment can also be used for rapid solvent removal and preliminary heat treatment.

[0031] Ball milling: In this example, a planetary ball mill is used, with the grinding jar made of polyurethane and the grinding balls being zirconia (ZrO2) balls. Alternatively, the grinding jar can be made of nylon, stainless steel (lined with polyurethane), etc.; the grinding balls can be agate balls, alumina balls, stainless steel balls, etc., with the selection mainly considering avoiding the introduction of impurities for contamination and achieving the required grinding efficiency. Vibratory mills, stirred mills, etc., can also be used for ball milling.

[0032] Molding: Compression molding preforming uses a single-axis hydraulic press. Alternatively, a mechanical press or powder tablet press can be used. Isostatic pressing uses a cold isostatic press (CIP) with water or oil as the pressure transmission medium. If isostatic pressing equipment is unavailable, higher-pressure bidirectional molding or multi-axis pressing can be used as a near-substitute, but the uniformity may be slightly inferior.

[0033] Heat treatment furnace: Curing and calcination can be performed using ordinary box-type resistance furnaces or tube furnaces. Ultra-high temperature graphitization requires a specialized graphitization furnace, such as an Atchison furnace (resistance heating) using a graphite heating element, or a medium-frequency induction graphitization furnace using induction coil heating. In addition to argon, high-purity nitrogen or helium can also be used as a protective atmosphere within a certain temperature range. (III) Specific Implementation Examples The following Examples 1-5 and Comparative Examples 1-2 are all in accordance with Figure 1 The process flow shown is as described in Table 1, and the specific parameters are shown in Table 1.

[0035] Example 1 S1. Raw Material Preparation and Mixing: Accurately weigh 99.9 g of recycled graphite powder from waste lithium-ion batteries and place it in a 500 mL beaker. Add 200 mL of anhydrous ethanol. Place the beaker on a magnetic stirrer and stir continuously at 800 rpm for 30 minutes until a uniform graphite suspension without significant sedimentation is formed. Separately weigh 0.1 g of graphene oxide powder and add it to 100 mL of ultrapure water. Place the mixture in an ultrasonic cell disruptor and sonicate for 45 minutes at 400 W and 28 kHz to obtain a uniform, clear, and transparent GO dispersion (concentration 1 mg / mL). While maintaining the graphite suspension at 600 rpm, add the GO dispersion dropwise using a constant flow pump at a rate of approximately 5 mL / min. After the addition is complete, continue stirring for 2 hours to ensure sufficient contact and adsorption between the GO and graphite particles, obtaining mixed slurry A1.

[0036] S2. Preliminary Heat Treatment and Ball Milling: Transfer slurry A1 to a petri dish and place it in a forced-air drying oven. Set the temperature to 180℃ and heat-treat for 4 hours. After heat treatment, a dry, blocky mixed powder B1 is obtained. Crush B1 and weigh it to calculate its total mass. Weigh phenolic resin (70% solid content) at 10% of the mass of B1. Place the B1 powder, phenolic resin, and anhydrous ethanol equivalent to 50% of the mass of B1 into a 500mL polyurethane planetary ball mill jar, and add zirconia grinding balls with a diameter of 5mm (grinding ball to material mass ratio of 3:1). Fix the ball mill jar on a planetary ball mill, set the revolution speed to 300 rpm and the rotation speed to 600 rpm, and ball mill for 4 hours. After ball milling, a slurry C1 with moderate viscosity and uniform dispersion is obtained.

[0037] S3. Drying, Granulation, and Molding: Pour slurry C1 into an enamel pan and place it in a vacuum drying oven. Dry at 80℃ for 12 hours until constant weight is achieved. The dried hardened material is initially crushed using a mortar and pestle, then granulated through a 100-mesh sieve to obtain a free-flowing composite powder D1. A certain amount of D1 powder is weighed and placed into a cylindrical stainless steel mold with an inner diameter of 20mm. It is then pre-molded on a single-shaft hydraulic press at a pressure of 8 MPa for 30 seconds to obtain a pre-compacted green blank E1. The E1 green blank is carefully wrapped and sealed with a latex sleeve and placed in the high-pressure cylinder of a cold isostatic press. The isostatic pressure is set to 140 MPa, and the holding time is 5 minutes. After depressurization, a dense, regularly shaped cylindrical green blank F1 is obtained.

[0038] S4. Curing, Calcination, and Graphitization: The preform F1 is placed in a box-type resistance furnace and heated to 180°C at a rate of 2°C / min under an air atmosphere, and cured at this temperature for 4 hours. After curing, the sample is transferred to an atmosphere tube furnace, and argon gas (flow rate 200 mL / min) is introduced as a protective gas. The temperature is increased to 980°C at a rate of 3°C / min and held at this temperature for 2 hours to complete the carbonization (calcination) of the phenolic resin. Then, the calcined sample is placed in a graphite crucible in a high-temperature graphitization furnace (Acheson furnace), surrounded by graphite coke. Under argon protection, the temperature is increased to 2400°C at a rate of approximately 10°C / min and held at 2400°C for 2 hours. After holding, heating is stopped, and the furnace is allowed to cool naturally to below room temperature (approximately 24-48 hours). The sample is then removed, yielding the final graphitized carbon material sample.

[0039] Example 2 The difference from Example 1 is as follows: in step S1, the amount of recycled graphite powder is 99.5g and GO powder is 0.5g; in step S2, the amount of phenolic resin added is 15% of the mass of dried powder B2; in step S4, the graphitization temperature is 2400℃ and held for 2 hours. The remaining steps, equipment, and detailed operating parameters are exactly the same as in Example 1, and a carbon material sample is obtained.

[0040] Example 3 The difference from Example 1 is as follows: in step S1, 99.0 g of graphite powder and 1.0 g of GO powder are recovered; in step S2, the amount of phenolic resin added is 20% of the mass of dried powder B3; in step S4, the graphitization process is to heat to 2700℃ and hold for 1 hour. The remaining steps, equipment, and detailed operating parameters are exactly the same as in Example 1, and a carbon material sample is obtained.

[0041] Example 4 The difference from Example 1 is as follows: in step S1, 98.0 g of graphite powder and 2.0 g of GO powder are recovered; in step S2, the amount of phenolic resin added is 25% of the mass of the dried powder B4; in step S4, the graphitization process is to heat to 2700℃ and hold for 1 hour. The remaining steps, equipment, and detailed operating parameters are exactly the same as in Example 1, and a carbon material sample is obtained.

[0042] Example 5 The difference from Example 1 is that in step S1, 95.0 g of graphite powder and 5.0 g of GO powder were recovered; in step S4, the graphitization process involved heating to 2700°C and holding at that temperature for 1 hour. The remaining steps, equipment, and detailed operating parameters were exactly the same as in Example 1, and a carbon material sample was obtained.

[0043] Comparative Example 1 The steps S1, S2, and S3 are exactly the same as in Example 3. In step S4, after the blank F1 is cured at 180°C for 4 hours, it is directly calcined at 980°C (argon protection, holding for 2 hours), and then cooled in the furnace without graphitization treatment above 2000°C.

[0044] Comparative Example 2 The difference from Example 3 is that in step S1, no graphene oxide powder is added; only 100.0g of recycled graphite powder is mixed with ethanol to form a suspension, and no GO dispersion is subsequently added or mixed. That is, the mixed slurry is only an ethanol suspension of graphite. Subsequent steps S2-S4 are exactly the same as in Example 3, including graphitization treatment at 2700℃.

[0045] (iv) Performance testing, characterization and result analysis The carbon samples prepared in all the above embodiments and comparative examples were subjected to the following tests and characterization: Volume resistivity testing: Measured at room temperature using a four-probe resistivity meter (such as the RTS-9). The sample is processed into a flat surface, and four probes are arranged at equal intervals and pressed firmly onto the sample surface. Resistivity is calculated by measuring current and voltage. Five different points are measured for each sample, and the average value is taken.

[0046] Thermal conductivity testing: A laser flash thermal conductivity meter (such as LFA 467 HyperFlash) was used. Samples were processed into discs with diameters of 12.7 mm and 25.4 mm, and a thickness of 2 mm. The thermal diffusivity (α) of the samples at room temperature was measured. Simultaneously, the specific heat capacity (Cp) was measured using differential scanning calorimetry (DSC), and the geometric density (ρ) was measured using Archimedes' displacement method. Thermal conductivity (λ) was calculated using the formula λ = α * ρ * Cp, and the thermal conductivity in both the through-plane and in-plane directions (for anisotropic samples) was reported.

[0047] Microstructure characterization: Transmission electron microscopy (TEM): The sample was ground into an ultrafine powder, dispersed in ethanol, dropped onto an ultrathin carbon film copper grid, dried, and then the edge morphology and stacking state of the graphite sheets were observed using a high-resolution transmission electron microscope (such as JEM-2100F). The results of Comparative Examples 1 and 2, as well as Example 5, are as follows: Figure 2-4 As shown.

[0048] Raman spectroscopy: A microconfocal Raman spectrometer (such as the Renishaw inVia) was used with a laser wavelength of 532 nm. Spectra were acquired at multiple random locations, and the D peak (~1350 cm⁻¹) was calculated. -1 ) and G peak (~1580 cm) -1 The ratio of the strength of (I) D / I G This ratio is a commonly used indicator to characterize the disorder and defect concentration of carbon materials; a lower value indicates a higher degree of graphitization and fewer defects. Typical spectra of Comparative Example 1, Comparative Example 2, Example 3, and Example 5 are shown below. Figure 5 As shown in the figure, from top to bottom, they are Comparative Example 1, Comparative Example 2, Example 3, and Example 5.

[0049] Table 1: Preparation parameters of the examples and comparative examples

[0050] Table 2: Performance Results of Examples and Comparative Examples

[0051] *Note: The amount of phenolic resin added is calculated based on the mass of the dried and mixed powder in step S2.

[0052] (V) Results Analysis and Mechanism Discussion Analysis based on the data in Tables 1 and 2 and the attached figures: The key role of ultra-high temperature graphitization: Taking Example 3 and Comparative Example 1 as examples, both have the exact same raw material ratios and preliminary processes. The only difference lies in the final heat treatment temperature: Example 3 underwent graphitization at 2700℃, while Comparative Example 1 only reached calcination at 980℃. Performance data show that the resistivity of Example 3 (19.3 μΩ·m) is much lower than that of Comparative Example 1 (48.3 μΩ·m), and its thermal conductivity is several times higher.

[0053] Taking Example 5 and Comparative Example 1 as examples, TEM images ( Figure 2 and Figure 4The comparison also clearly shows that the ungraphitized material in Comparative Example 1 has a loose structure and disordered carbon layers; while Example 5 (also treated at 2700°C) shows clear, flat and tightly stacked graphite sheets.

[0054] This verifies the effectiveness of high-temperature graphitization treatment above 2000℃. At this temperature, carbon atoms gain sufficient kinetic energy, undergoing violent thermal motion and rearrangement. The amorphous carbon generated from the pyrolysis of phenolic resin and the defective structure of the recycled graphite itself are reconstructed. 2 As the hybrid carbon network continues to expand and improve, the turbostratic carbon structure transforms into an ideal graphite crystal structure with three-dimensional long-range order, thereby fundamentally enhancing the intrinsic electrical and thermal conductivity properties of the material.

[0055] Synergistic repair and enhancement effects of graphene oxide (GO): Taking Example 3 and Comparative Example 2 as examples, both underwent complete graphitization at 2700℃. The key difference was that Example 3 added 1% GO, while Comparative Example 2 did not. The results showed that Example 3, with the addition of GO, was superior to Comparative Example 2 in both resistivity and thermal conductivity.

[0056] Taking Example 5 and Comparative Example 2 as examples, TEM images ( Figure 3 and Figure 4 The comparison also clearly shows that in Comparative Example 2 without GO, the typical layered structure of graphite material can be observed, but the interlayer stacking is loose; while Example 5 (with 5.0 wt.% GO added, i.e., high GO content) shows clear, flat and tightly stacked graphite sheets.

[0057] Raman spectroscopy ( Figure 5 This provides more direct evidence of microstructure: Example 5 (high GO content) I D / I G The ratio (0.13) was significantly lower than that of Comparative Example 1 (0.78) and Comparative Example 2 (0.53), indicating that the defect concentration of the material in Example 5 was lower and the graphite lattice was more complete. This is because GO is not only a simple conductive additive, but also plays the role of a seed or template in the high-temperature graphitization process. The GO sheets themselves have a good graphite microcrystalline structure. At ultra-high temperatures, the active sites at their edges can capture and guide the surrounding free carbon atoms or small carbon clusters to arrange themselves in an orderly manner, promoting the improvement of the lateral growth (La direction) and longitudinal stacking (Lc direction) of graphite crystals. At the same time, the flexible GO sheets can bridge adjacent graphite particles, constructing an efficient three-dimensional thermal and electrical conductive network inside the material. Therefore, the introduction of GO is the key to achieving deep repair rather than simple composite. In addition, the I in Example 3 D / I GThe ratio (0.19) was also significantly lower than that of Comparative Example 2 (0.53), further validating the effect of GO. Moreover, the I in Comparative Example 3... D / I G The ratio (0.19) was significantly lower than that of the ungraphitized Comparative Example 1 (I). D / I G The ratio of 0.78 indicates that high-temperature graphitization at temperatures above 2000℃ has a good effect on carbon atom reconstruction.

[0058] Synergistic effect of phenolic resin and GO and influence of formulation ratio (Analysis of Examples 1-5): From Examples 1 to 5, as the GO content increased from 0.1% to 5.0% (while the amount of phenolic resin was adjusted within a certain range), the performance of the prepared carbon material showed a regular optimization. The main functions of phenolic resin are: (1) as a binder to ensure the plasticity of the powder and the strength of the blank during the molding process; (2) its pyrolytic carbon fills surface defects to form a dense protective layer; (3) its pyrolytic carbon can serve as an additional carbon source at high temperatures and undergo graphitization under the induction of GO. GO focuses on guiding the repair of crystal structure and the construction of long-range conductive pathways. The two complement each other and work synergistically. When the GO content is low (e.g., 0.1% in Examples 2 to 5), its induced repair effect has a limited coverage; as the GO content increases (Examples 2-5), its repair effect and network construction ability are continuously enhanced, thus the performance is continuously improved. In particular, within the range of GO content of 0.5%-2.0% (Examples 2-4), the material has achieved very excellent comprehensive performance and a good balance between cost and performance.

[0059] The carbon material prepared according to the preferred embodiment (Example 5) of this application has a resistivity as low as 17.1 μΩ·m and an in-plane thermal conductivity as high as 98.3 W / (m·K). Its performance far exceeds that of original recycled graphite and is comparable to some mid-to-high-end isostatic graphite products. This fully demonstrates that this application has successfully prepared low-value waste lithium battery graphite into a high-value-added functional carbon material.

[0060] In summary, this application has the following beneficial effects: By combining phenolic resin amorphous carbon filling repair with graphene oxide-induced graphitization repair, the phenolic resin solution, with its excellent wettability and fluidity, can penetrate and fill the cracks and pores on the surface of recycled graphite particles. The amorphous carbon generated by its pyrolysis forms a dense shell, achieving physical sealing and initial strengthening of surface defects. The abundant oxygen-containing functional groups (such as -COOH, -OH) on the graphene oxide sheets can generate strong interactions with the graphite surface, ensuring its tight adhesion. Furthermore, during the subsequent ultra-high temperature graphitization process, the two-dimensional lattice structure of graphene oxide can serve as a template, guiding the surrounding disordered carbon atoms (including pyrolyzed carbon from phenolic resin and carbon at graphite defects) to arrange themselves in an ordered manner, promoting their transformation into an ideal graphite crystal structure, thereby deeply repairing bulk defects such as interlayer expansion. The synergy of these two methods achieves comprehensive repair from the surface to the core, from morphology to lattice.

[0061] In terms of process flow, firstly, graphene oxide dispersion is mixed with graphite in liquid phase to ensure uniform dispersion and adhesion of nano-scale graphene oxide; then, the initial structure is stabilized by medium-temperature heat treatment; next, phenolic resin is introduced for secondary coating and as a molding binder; finally, through a two-stage heat treatment of medium-temperature calcination carbonization and ultra-high temperature graphitization, the conversion of organic precursors and the final ordering of carbon structure are gradually realized. The carbon material prepared by this process has its graphite crystal structure effectively restored, showing a significant reduction in the (002) interplanar spacing and Raman spectroscopy. D / I G The resistivity is significantly reduced. Correspondingly, the intrinsic properties of the material achieve a leap forward, with a substantial decrease in resistivity and a significant increase in thermal conductivity. Its performance indicators are comparable to some artificial graphite products, greatly expanding its application fields.

[0062] The main operational units involved in this application (such as stirring, ultrasonication, ball milling, drying, pressing, and heat treatment) are all common processes in the field of material preparation. The required equipment (such as mixers, ultrasonic instruments, ball mills, ovens, presses, and high-temperature furnaces) is mature and widely available. The process parameters have a clear range and strong controllability, which is conducive to industrial-scale production and has good prospects for industrialization.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing carbon material using recycled graphite from waste lithium-ion batteries as raw material, characterized in that, The method comprises the following steps: S1, dispersing the graphite powder recycled from waste lithium ion batteries in anhydrous ethanol to obtain a graphite suspension; dispersing graphene oxide powder in ultrapure water, and ultrasonic treatment to obtain a graphene oxide dispersion; under stirring, adding the graphene oxide dispersion into the graphite suspension, and uniformly mixing to obtain a mixed slurry; wherein the mass percentage of the graphite powder recycled from waste lithium ion batteries and the graphene oxide powder is (95%-99.9%):(0.1%-5.0%); S2, heat treating the mixed slurry at 150-180 ℃ for 4-6 hours to obtain a dried powder; adding a binder phenolic resin and anhydrous ethanol to the dried powder, and performing ball milling treatment to obtain a ball-milled slurry; wherein the addition amount of the phenolic resin is 10-25 wt.% based on the total mass of the dried powder; S3, vacuum drying, crushing and sieving the ball-milled slurry to obtain a composite powder; first performing die pressing preforming on the composite powder, and then performing isostatic pressing forming to obtain a green body; S4, solidifying the green body at 150-180 ℃ for 4-6 hours; then performing roasting at 800-1200 ℃ under inert gas protection; finally, performing graphitization treatment at a temperature above 2000 ℃ for 1-2 hours, and obtaining carbon material after cooling.

2. The method of claim 1, wherein, In step S1, the ultrasonic treatment has a frequency of 20-40 kHz, a power of 200-600 W, and a treatment time of 30-45 minutes.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass percentage of the graphite powder recycled from waste lithium ion batteries and the graphene oxide powder is (95.0%-99%):(1.0%-5.0%).

4. The method of claim 1, wherein, In step S2, when performing ball milling treatment, the addition amount of the anhydrous ethanol is 50%-80% of the mass of the dried powder.

5. The preparation method according to claim 1, characterized in that, In step S3, the pressure of the die pressing preforming is 5-10 MPa; and the pressure of the isostatic pressing forming is 100-150 MPa.

6. The method of claim 1, wherein, In step S4, the temperature of the graphitization treatment is 2400-2700 ℃.

7. The production method according to claim 1 or 6, characterized by, In step S4, the specific procedure of the roasting is as follows: increasing the temperature to 980 ℃ at a temperature increasing rate of 2-5 ℃ / min, and maintaining the temperature for 2 hours.

8. A carbon material, characterized by, The carbon material is prepared by the method in any one of claims 1-7.

9. The carbon material according to claim 8, characterized by The intensity ratio I D / I G of the D peak and the G peak of the Raman spectrum of the carbon material is lower than 0.

5.

10. The carbon material according to claim 8 or 9, characterized in that, The volume resistivity of the carbon material is less than 20 μΩ·m, and the in-plane thermal conductivity is higher than 60 W / (m·K).

Images