Method for treating graphite in waste batteries in an integrated manner and graphite recovered material and applications

Abstract

This paper discloses a method for integrated processing of graphite from waste batteries, as well as the recycled graphite materials and their applications, belonging to the field of waste battery recycling technology. The method includes: heat-treating graphite material separated from waste batteries to obtain a first intermediate graphite material; subjecting the first intermediate graphite material to microwave treatment, followed by acid leaching and ball milling. Microwave treatment of the first intermediate graphite material increases the interlayer spacing; combined with acid leaching, it forms defective graphite; and ball milling further increases the defects in the graphite and increases the half-width at half-maximum (WHM) of the graphite material, transforming the graphite structure towards a hard carbon-like structure. This increases the migration dynamics of sodium ions, facilitating their storage and release.

Description

Technical Field

[0001] This disclosure relates to the field of waste battery recycling technology, specifically to a method for integrated processing of graphite in waste batteries across the entire chain, as well as the recycled graphite material and its applications. Background Technology

[0002] Sodium resources are abundant and widely distributed. The energy density and cycle life of sodium batteries are gradually narrowing the gap with lithium-ion batteries. Sodium batteries also have the characteristics of high rate capability, low temperature resistance and safe use, which has led many manufacturers to turn their attention to the development and production of sodium batteries.

[0003] However, the negative electrode materials used in sodium-ion batteries are currently expensive and have low sodium storage capacity, which is not conducive to obtaining sodium-ion batteries with high initial discharge specific capacity and high initial coulombic efficiency.

[0004] In view of this, this disclosure is hereby made. Summary of the Invention

[0005] The purpose of this disclosure is to provide a method for integrated processing of graphite in waste batteries across the entire supply chain, as well as graphite recycling materials and batteries, to solve or improve the aforementioned technical problems.

[0006] This disclosure can be implemented as follows:

[0007] In a first aspect, this disclosure provides a method for integrated processing of graphite from waste batteries across the entire supply chain, comprising the following steps: heat-treating graphite material separated from waste batteries to obtain a first intermediate graphite material; microwave-treating the first intermediate graphite material to obtain a second intermediate graphite material with increased interlayer spacing; acid-leaching the second intermediate graphite material to obtain a third intermediate graphite material with defects; and ball-milling the third intermediate graphite material to obtain a graphite recycling material with increased half-width at half-maximum.

[0008] In an optional implementation, the ball milling speed is 300 rpm to 1000 rpm, and the ball milling time is 20 min to 60 min.

[0009] In an optional implementation, the waste batteries include at least one of ternary lithium batteries, lithium iron phosphate batteries, and lithium cobalt oxide batteries.

[0010] In an optional embodiment, the preparation of graphite material includes: disassembling the waste battery after discharge treatment to separate the positive electrode sheet and the negative electrode sheet; and crushing and screening the negative electrode sheet.

[0011] In an optional implementation, the discharge treatment involves soaking the waste batteries to be treated in salt water.

[0012] In an optional embodiment, the brine includes at least one of sodium sulfate solution and sodium chloride solution.

[0013] In an optional implementation, the mesh size of the sieve used for sieving is 10-300 mesh.

[0014] In an optional embodiment, the heat treatment includes at least one of the following features:

[0015] Feature 1: The heat treatment is carried out in an inert atmosphere;

[0016] Feature 2: The heat treatment temperature is 300℃-750℃;

[0017] Feature 3: The heat treatment time is 1-5 hours;

[0018] Feature 4: The heating rate during the heat treatment process is 3℃ / min-20℃ / min.

[0019] In an optional implementation, the microwave processing power is 400W-1500W, and / or the microwave processing time is 15s-40s.

[0020] In an optional embodiment, the acid leaching treatment includes at least one of the following features:

[0021] Feature 1: The concentration of the acid used is 10g / L-300g / L;

[0022] Feature 2: The acid used is sulfuric acid;

[0023] Feature 3: The solid-liquid ratio of the acid leaching treatment is 1g:1mL-1g:10mL;

[0024] Feature 4: The acid leaching temperature is 40℃-100℃;

[0025] Feature 5: The acid leaching time is 30-400 minutes.

[0026] In an optional implementation, the third intermediate graphite material is further washed with water before ball milling.

[0027] In an optional implementation, the washing solution is washed until the pH value is ≥5.

[0028] In an optional implementation, the washed material is dried before ball milling.

[0029] In an optional embodiment, the drying temperature is 40°C-200°C, and / or the drying time is 8h-48h.

[0030] In an optional implementation, the ball-to-material ratio in the ball mill is 1:1 to 6:1.

[0031] Secondly, this disclosure provides a recycled graphite material obtained by processing it using any of the methods described in the foregoing embodiments.

[0032] In an optional embodiment, the interlayer spacing of the recycled graphite material is 0.390 mm to 0.412 mm, and / or the half-width at half-maximum (WHM) of the recycled graphite material is 0.293 to 0.488.

[0033] Thirdly, this disclosure provides an application of the graphite recycled material of the aforementioned embodiments, for example, in the preparation of batteries.

[0034] In an optional implementation, the battery is a sodium-ion battery.

[0035] Fourthly, this disclosure provides a battery in which the negative electrode material includes the recycled graphite material described in the foregoing embodiments.

[0036] In an optional implementation, the battery is a sodium-ion battery.

[0037] The beneficial effects of this disclosure include:

[0038] This disclosure creatively proposes a whole-chain integrated method for processing graphite from waste batteries. By using microwave heating to alter the interlayer spacing and pore size of the graphite material, combined with acid leaching, defective graphite is formed. Subsequent ball milling not only increases the defects in the graphite material but also enlarges its half-width at half-maximum (HWHM), transforming the graphite structure into a hard carbon-like structure. This increases the migration dynamics of sodium ions, facilitating their storage and release, and improving sodium storage capacity. The recycled graphite obtained by this method has a larger interlayer spacing, a wider HWHM, and a higher sodium storage capacity. Using it in battery manufacturing not only reduces manufacturing costs but also enables batteries to simultaneously possess high initial discharge specific capacity and initial coulombic efficiency. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a process flow diagram of Embodiment 1 of this disclosure. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] The following provides a detailed explanation of the integrated method for processing graphite in waste batteries across the entire supply chain, as well as the recycling and application of graphite materials.

[0043] Given the high cost and low sodium storage capacity of current sodium-ion battery anode materials, the inventors proposed recycling the anode active materials from spent lithium-ion batteries to prepare sodium-ion battery anode materials, thereby significantly reducing costs. However, directly using recycled graphite obtained through conventional recycling processes to prepare sodium-ion battery anode materials suffers from low sodium storage capacity. Therefore, the inventors creatively proposed a fully integrated, end-to-end method for processing graphite from spent batteries. This method utilizes microwave heating of the graphite material to alter the interlayer spacing and pore size; combined with acid leaching, it creates defective graphite; further ball milling not only increases the defects in the graphite material but also enlarges its half-width at half-maximum (HWHM), transforming the graphite structure into a hard carbon-like structure. This increases the migration dynamics of sodium ions, facilitating their storage and release, and improving sodium storage capacity.

[0044] For reference, the above-mentioned integrated whole-chain treatment method for graphite in waste batteries may include the following steps: heat-treating the graphite material separated from the waste batteries to obtain a first intermediate graphite material; microwave-treating the first intermediate graphite material to obtain a second intermediate graphite material with increased interlayer spacing; acid-leaching the second intermediate graphite material to obtain a third intermediate graphite material with defects; and ball-milling the third intermediate graphite material to obtain a graphite recycling material with increased half-width at half-maximum.

[0045] The waste batteries are waste lithium-ion batteries, which may include, for example but not exclusively, at least one of ternary lithium batteries, lithium iron phosphate batteries and lithium cobalt oxide batteries.

[0046] In this disclosure, the preparation of graphite materials may include: disassembling a waste battery after discharge treatment to separate positive and negative electrode sheets; and crushing and sieving the negative electrode sheets.

[0047] One example of the discharge treatment is soaking the used batteries in brine. The brine used may, by way of example but not by way of limitation, include at least one of sodium sulfate solution and sodium chloride solution.

[0048] After the negative electrode sheet is mechanically crushed, it can be screened using a sieve with a mesh size of 10-300 to obtain powdered graphite material, i.e., waste graphite powder.

[0049] In this disclosure, the heat treatment of the obtained graphite material is carried out in an inert atmosphere. The inert atmosphere may, by way of example, include at least one of nitrogen, helium, and argon.

[0050] The heat treatment temperature is 300℃-750℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃ or 750℃, or any other value within the range of 300℃-750℃.

[0051] If the heat treatment temperature is below 300℃, it is not conducive to the removal of volatiles in graphite materials; if the heat treatment temperature is above 750℃, on the one hand, the energy consumption is too high, and on the other hand, it is not easy to increase the FWHM, which is not conducive to the transformation of graphite into a hard carbon structure.

[0052] The heat treatment time is 1h-5h, such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, or any other value within the range of 1h-5h.

[0053] The heating rate during heat treatment can be between 3°C / min and 20°C / min, such as 3°C / min, 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, or 20°C / min, or any other value within the range of 3°C / min to 20°C / min. In some embodiments, the heating rate during heat treatment is between 3°C / min and 10°C / min.

[0054] By performing heat treatment under the above conditions, the volatiles in the graphite material can be effectively removed, and the binder attached to the graphite material can be decomposed.

[0055] After heat treatment, allow it to cool naturally to room temperature.

[0056] In this disclosure, the power used for microwave processing of the first intermediate graphite material is 400W-1500W, such as 400W, 500W, 600W, 700W, 800W, 900W, 1000W, 1100W, 1200W, 1300W, 1400W or 1500W, or any other value within the range of 400W-1500W.

[0057] If the microwave processing power is below 400W, it is not conducive to increasing the interlayer spacing of graphite powder and forming micropores. Since the graphite raw material used in this application is recycled graphite, this recycled graphite has undergone long-term lithium-ion intercalation and deintercalation in lithium-ion batteries, and its interlayer spacing is larger than that of new graphite, which can be considered as expanded graphite. With instantaneous microwave processing, the interlayers expand due to rapid heating, thus increasing the interlayer spacing. Under the instantaneous high temperature, impurities in the graphite interlayers will partially vaporize or form nano-oxide particles. After subsequent acid leaching, these impurities are removed, leaving vacancies, but defects are retained. However, if the microwave processing power is too low, it cannot effectively achieve the effect of rapid heating, and it is also difficult to vaporize the impurities in the graphite interlayers or form nano-oxide particles. Similarly, if the microwave processing power is higher than 1500W, it will cause excessive oxidation of graphite, resulting in too many defects, which is not conducive to sodium ion diffusion and structural stability during cycling.

[0058] The microwave processing time is 15s-40s, such as 15s, 20s, 25s, 30s, 35s or 40s, or any other value within the range of 15s-40s.

[0059] If the microwave treatment time is less than 15s, it is not conducive to increasing the interlayer spacing of graphite powder and forming micropores; if the microwave treatment time is longer than 40s, it will increase excessive defects, which is not conducive to the diffusion of sodium ions and the stability of the structure during the cycling process.

[0060] Microwave treatment under the above conditions, compared to traditional electric furnace heating, can produce instantaneous ultra-fast heating and cooling, increasing the interlayer spacing and pore size of waste graphite powder, which is beneficial for sodium ion diffusion and structural stability during cycling. It should be noted that traditional electric furnace heating follows a heating curve, requiring good furnace insulation. However, microwave heating can rapidly reach high temperatures, and after heating, the cooling rate is much higher because microwave equipment does not have the insulation requirements of traditional electric furnaces. Waste graphite powder treated with the above combined heat and microwave treatment can effectively decompose electrolyte residues in graphite, such as SEI (solid electrolyte interphase) impurities; simultaneously, a carbon shell can form around the graphite particles, preserving the inherent three-dimensional layered graphite core structure. Furthermore, the carbon shell derived from the solid electrolyte interphase interface on the graphite particle surface helps improve the initial specific capacity of the second intermediate graphite material, exhibiting superior rate performance and cycling stability; at the same time, the treated graphite effectively promotes the decomposition of organic binders and electrolyte residues. For example, heat treatment and microwave treatment generate high temperatures that cause organic binders to decompose and carbonize at high temperatures. At the same time, some electrolytes are salts, which reach their melting and boiling points under the high temperatures generated by microwaves and then vaporize and escape, thus achieving the effect of purifying graphite.

[0061] In this disclosure, the concentration of acid used for acid leaching treatment of the second intermediate graphite material is 10 g / L-300 g / L, such as 10 g / L, 50 g / L, 80 g / L, 100 g / L, 120 g / L, 150 g / L, 180 g / L, 200 g / L, 220 g / L, 250 g / L, 280 g / L, or 300 g / L, or any other value within the range of 10 g / L-300 g / L.

[0062] If the concentration of the acid used is less than 10 g / L, it will not be conducive to the leaching of impurities; if the concentration of the acid used is greater than 300 g / L, it will lead to increased corrosivity of the acid leaching solution and affect the service life of the equipment.

[0063] In some alternative embodiments, the acid used for the acid leaching treatment can be sulfuric acid. In other embodiments, the use of other commonly used acids is not excluded.

[0064] For reference, the solid-liquid ratio for acid leaching can be 1g:1mL-1g:10mL, such as 1g:1mL, 1g:2mL, 1g:3mL, 1g:4mL, 1g:5mL, 1g:6mL, 1g:7mL, 1g:8mL, 1g:9mL or 1g:10mL, or any other value within the range of 1g:1mL-1g:10mL.

[0065] If too little acid is used in the pickling process, it will not be enough to completely remove impurities; if too much acid is used, more water will be needed for rinsing.

[0066] The temperature for acid leaching is 40℃-100℃, such as 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, or any other value within the range of 40℃-100℃.

[0067] If the acid leaching temperature is below 40℃, the molecular kinetic energy is low, the diffusion rate of the solution and the solubility of the substances are both low, and the transport and reaction of substances are slow, which is not conducive to the leaching of impurities. If the acid leaching temperature is above 100℃, on the one hand, for substances with high activation energy, the increase in temperature may make it difficult for reactant molecules to overcome this energy barrier, thereby weakening the reaction rate. On the other hand, excessively high temperature may lead to increased liquid evaporation, thereby reducing the solution concentration and affecting the acid leaching effect. In addition, excessively high temperature may lead to a decrease in the solubility of some substances, affecting the acid leaching effect of graphite.

[0068] The acid leaching time is 30 min to 400 min, such as 30 min, 50 min, 100 min, 150 min, 200 min, 250 min, 300 min, 350 min or 400 min, or any other value within the range of 30 min to 400 min.

[0069] If the acid leaching time is less than 30 minutes, it is not conducive to the leaching of inorganic impurities; if the acid leaching time is more than 400 minutes, the energy consumption is too high.

[0070] Microwave treatment followed by acid leaching can form a third intermediate graphite material with defects (such as micropores). In particular, high-concentration, long-duration deep acid leaching can form a third intermediate graphite material with even more defects. Specifically, the thermal effect of microwave treatment can cause the decomposition of the interfacial continuous phase resistive layer (electrolyte residue SEI), forming inorganic salt and metal oxide nanoparticles (some salts in the electrolyte are instantaneously oxidized into metal oxides during rapid microwave treatment). These nanoparticles can be removed from the graphite bulk phase after acid washing, and the locations of the removed nanoparticles form micropores. The formation of micropores increases the active sites for sodium ion insertion / extraction.

[0071] Furthermore, the third intermediate graphite material obtained after acid treatment is washed with water.

[0072] For example, washing with water until the pH value of the washing solution is ≥5 is sufficient. Here, the washing solution refers to the liquid obtained after rinsing the third intermediate graphite material.

[0073] In some embodiments, the washed material is pressure filtered, and the resulting material is dried. In other embodiments, the washed material can be dried directly.

[0074] For example, the drying temperature can be between 40℃ and 200℃, such as 40℃, 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, or 200℃. The drying time can be between 8h and 48h, such as 8h, 14h, 20h, 26h, 32h, 38h, 42h, or 48h.

[0075] If the drying temperature exceeds 200℃, some volatile substances released during the drying process are easily oxidized and burned, which may pose safety risks.

[0076] In this disclosure, ball milling is carried out in a ball mill.

[0077] The ball mill speed is 300rpm-1000rpm, such as 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm or 1000rpm, or any other value within the range of 300rpm-1000rpm.

[0078] If the ball mill speed is below 300 rpm, it is not conducive to the increase of defects and the increase of the half-width at half-maximum (FWHM) of the graphite material; if the ball mill speed is above 1000 rpm, there will be too many defects in the graphite material, which is not conducive to the diffusion of sodium ions and the stability of the structure during the circulation process. At the same time, if the ball mill speed is too high, it is also not conducive to the stable operation of the ball mill equipment.

[0079] The ball milling time is 20min-60min, such as 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min, or any other value within the range of 20min-60min.

[0080] If the ball milling time is less than 20 minutes, it is not conducive to the formation of defects in graphite and the increase of the full width at half maximum (FWHM) of graphite material; if the ball milling time is too long, too many defects will be generated, which is not conducive to the diffusion of sodium ions and the stability of the structure during the cycling process.

[0081] The ball-to-material ratio in ball milling is 1:1 to 6:1, such as 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1, or any other value within the range of 1:1 to 6:1.

[0082] By further ball milling graphite materials after microwave treatment, the interlayer spacing of graphite can be increased. Ball milling alters both the graphite size distribution and the defect concentration (i.e., the number of defects or micropores), thus facilitating sodium ion storage in the electrolyte. Furthermore, with prolonged ball milling, the increased defects also increase the full width at half maximum (FWHM) of the graphite material, essentially transforming the graphite structure into a hard carbon-like structure. This enhances the migration dynamics of sodium ions, thereby promoting their storage and release. However, it is important to note that ball milling times exceeding 60 minutes can lead to excessive defects, which is detrimental to sodium ion storage and release, resulting in a sharp decline in capacity and initial efficiency.

[0083] As mentioned above, the processing method provided in this disclosure has a short cycle time, is easy to operate, and can reduce energy consumption and greenhouse gas emissions, making it environmentally friendly and energy-saving. Furthermore, this method can obtain graphite reclaimed material with large interlayer spacing, high half-width, and high sodium storage capacity.

[0084] Accordingly, this disclosure also provides a recycled graphite material obtained by the above method. The resulting recycled graphite material has a large interlayer spacing and half-width at half-maximum, and a high sodium storage capacity.

[0085] For reference, the interlayer spacing of the aforementioned recycled graphite material can be 0.390 mm to 0.412 mm. The half-width at half-maximum (WHM) of the recycled graphite material can be 0.293 to 0.488.

[0086] Furthermore, this disclosure also provides an application of the above-mentioned recycled graphite material, for example, it can be used to prepare batteries, especially sodium-ion batteries.

[0087] Accordingly, this disclosure also provides a battery in which the negative electrode material includes the aforementioned recycled graphite.

[0088] For example, the battery is a sodium-ion battery.

[0089] Batteries containing the aforementioned recycled graphite materials can simultaneously exhibit high initial discharge specific capacity and high initial coulombic efficiency.

[0090] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0091] Example 1

[0092] This embodiment provides a method for integrated processing of graphite from waste batteries across the entire supply chain. Please refer to [link / reference]. Figure 1 This includes the following steps:

[0093] Step (1): Soak the waste lithium battery (waste ternary NCM battery, recycled from CATL) in 30wt% sodium chloride brine for 48 hours to discharge it, then cut the shell and separate the core to obtain the positive electrode and negative electrode. Crush the negative electrode and pass it through a 100-mesh sieve to obtain waste graphite powder (i.e., graphite material).

[0094] Step (2): The above-mentioned waste graphite powder is heat-treated under N2 atmosphere. The heat treatment process is as follows: the temperature is raised to 550℃ at a heating rate of 5℃ / min, and held at 550℃ for 2 hours. After the holding period, the temperature is lowered to room temperature to obtain the first intermediate graphite material.

[0095] Step (3): The first intermediate graphite material was placed in a crucible, and then the entire crucible was placed in a microwave device for microwave treatment. The power used for microwave treatment was 800W, and the treatment time was 15s. After the microwave treatment was completed, the sample was cooled to room temperature to obtain the second intermediate graphite material.

[0096] Step (4): The second intermediate graphite material was subjected to deep acid leaching with 300 g / L concentrated sulfuric acid. The liquid-to-solid ratio for the acid leaching was 10 mL: 1 g, the acid leaching temperature was 60 °C, and the treatment time was 120 min, to obtain the third intermediate graphite material.

[0097] Step (5): The third intermediate graphite material is washed with water multiple times until the pH value of the washing solution is close to 7. Then, it is filtered by pressure. The filtered material is placed in an oven and dried at 80°C for 48 hours to obtain the purified graphite material.

[0098] Step (6): Place the purified graphite material into a ball mill for ball milling. The ball-to-material ratio is 1:1, the ball milling speed is 600 rpm, and the ball milling time is 20 h to obtain recycled graphite material (sodium electrode anode material).

[0099] Example 2

[0100] The difference between this embodiment and Embodiment 1 is that the microwave treatment time is 20 seconds and the ball milling time is 30 hours.

[0101] Example 3

[0102] The difference between this embodiment and Embodiment 1 is that the microwave treatment time is 30 seconds and the ball milling time is 40 hours.

[0103] Example 4

[0104] The difference between this embodiment and Embodiment 1 is that the microwave treatment time is 40 seconds and the ball milling time is 50 hours.

[0105] Example 5

[0106] The difference between this embodiment and Embodiment 1 is that the microwave treatment time is 50 seconds and the ball milling time is 60 hours.

[0107] Example 6

[0108] This embodiment provides a method for integrated processing of graphite from waste batteries across the entire supply chain, including the following steps:

[0109] Step (1): After soaking the waste lithium-ion battery (waste LCO battery, recycled from CATL) in a 30wt% sodium chloride solution for 48 hours to discharge it, cut the shell and separate the core to obtain the positive electrode and negative electrode. Crush the negative electrode and pass it through a 100-mesh sieve to obtain waste graphite powder (i.e., graphite material).

[0110] Step (2): The above-mentioned waste graphite powder is heat-treated under an argon atmosphere. The heat treatment process is as follows: the temperature is raised to 300℃ at a heating rate of 3℃ / min, and held at 300℃ for 5 hours. After the holding period, the temperature is lowered to room temperature to obtain the first intermediate graphite material.

[0111] Step (3): The first intermediate graphite material was placed in a crucible, and then the entire crucible was placed in a microwave device for microwave treatment. The power used for microwave treatment was 400W, and the treatment time was 40s. After the microwave treatment was completed, the sample was cooled to room temperature to obtain the second intermediate graphite material.

[0112] Step (4): The second intermediate graphite material was subjected to acid leaching treatment with 10 g / L concentrated sulfuric acid. The liquid-to-solid ratio used in the acid leaching treatment was 1 mL: 1 g, the acid leaching temperature was 40 °C, and the treatment time was 400 min, to obtain the third intermediate graphite material.

[0113] Step (5): The third intermediate graphite material is washed with water multiple times until the pH value of the washing solution is 5. Then, it is filtered by pressure. The filtered material is placed in an oven and dried at 40°C for 24 hours to obtain the purified graphite material.

[0114] Step (6): Place the purified graphite material into a ball mill for ball milling. The material-to-ball ratio used in the ball mill is 4:1, the ball milling speed is 300 rpm, and the ball milling time is 60 h to obtain recycled graphite material.

[0115] Example 7

[0116] This embodiment provides a method for integrated processing of graphite from waste batteries across the entire supply chain, including the following steps:

[0117] Step (1): After soaking the waste lithium-ion battery (waste LFP battery, recycled from CATL) in a 30wt% sodium sulfate solution for 48 hours to discharge it, cut the shell and separate the core to obtain the positive electrode and negative electrode. Crush the negative electrode and pass it through a 100-mesh sieve to obtain waste graphite powder (i.e., graphite material).

[0118] Step (2): The above-mentioned waste graphite powder is heat-treated in a helium atmosphere. The heat treatment process is as follows: the temperature is raised to 750℃ at a heating rate of 20℃ / min, and held at 750℃ for 1 hour. After the holding period, the temperature is lowered to room temperature to obtain the first intermediate graphite material.

[0119] Step (3): The first intermediate graphite material was placed in a crucible, and then the entire crucible was placed in a microwave device for microwave treatment. The power used for microwave treatment was 1500W, and the treatment time was 20s. After the microwave treatment was completed, the sample was cooled to room temperature to obtain the second intermediate graphite material.

[0120] Step (4): The second intermediate graphite material was subjected to acid leaching treatment with 150 g / L concentrated sulfuric acid. The liquid-to-solid ratio used in the acid leaching treatment was 5 mL: 1 g, the acid leaching temperature was 100 °C, and the treatment time was 30 min, to obtain the third intermediate graphite material.

[0121] Step (5): The third intermediate graphite material is washed with water multiple times until the pH value of the washing solution is 6. Then, it is filtered by pressure. The filtered material is placed in an oven and dried at 200℃ for 8 hours to obtain the purified graphite material.

[0122] Step (6): Place the purified graphite material into a ball mill for ball milling. The material-to-ball ratio used in the ball mill is 6:1, the ball milling speed is 1000 rpm, and the ball milling time is 40 h to obtain recycled graphite material.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is that step (2) was not performed, that is, microwave treatment was not performed, and the first intermediate graphite material obtained after heat treatment was directly subjected to acid leaching treatment.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that step (6) was not performed, that is, ball milling was not performed.

[0127] Comparative Example 3

[0128] The difference between this comparative example and Example 1 is that the microwave treatment time is 15s and the ball milling time is 70h.

[0129] Comparative Example 4

[0130] The difference between this comparative example and Example 1 is that step (2) was not performed, that is, no heat treatment was performed, and the obtained waste graphite powder was directly subjected to microwave treatment.

[0131] Comparative Example 5

[0132] The difference between this comparative example and Example 1 is that step (4) was not performed, that is, acid leaching was not performed, and the second intermediate graphite material obtained after microwave treatment was directly ball-milled.

[0133] Comparative Example 6

[0134] The difference between this comparative example and Example 1 is that the heat treatment temperature is 800°C.

[0135] Comparative Example 7

[0136] The difference between this comparative example and Example 1 is that the microwave processing power is 200W.

[0137] Comparative Example 8

[0138] The difference between this comparative example and Example 1 is that the microwave processing power is 2000W.

[0139] Comparative Example 9

[0140] The difference between this comparative example and Example 1 is that the microwave treatment time is 10 seconds.

[0141] Comparative Example 10

[0142] The difference between this comparative example and Example 1 is that the microwave treatment time is 50 seconds.

[0143] Comparative Example 11

[0144] The difference between this comparative example and Example 1 is that the concentration of the acid used in the acid leaching treatment is 400 g / L.

[0145] Comparative Example 12

[0146] The difference between this comparative example and Example 1 is that the acid leaching temperature is 30°C.

[0147] Comparative Example 13

[0148] The difference between this comparative example and Example 1 is that the acid leaching temperature is 120°C.

[0149] Comparative Example 14

[0150] The difference between this comparative example and Example 1 is that the acid leaching time is 20 minutes.

[0151] Comparative Example 15

[0152] The difference between this comparative example and Example 1 is that the ball milling time is 10 hours.

[0153] Comparative Example 16

[0154] The difference between this comparative example and Example 1 is that the ball milling speed is 1200 rpm.

[0155] Test case

[0156] The structural and electrochemical performance data of the graphite recycled materials obtained in Examples 1-7 and Comparative Examples 1-16 were compared, and the results are shown in Table 1.

[0157] The structural comparison included interlayer spacing and FWHM. The interlayer spacing and FWHM were determined by X-ray diffraction.

[0158] The electrochemical performance data comparison includes the initial discharge specific capacity and initial coulombic efficiency. Specifically, each graphite recycled material was prepared into a sodium-ion battery according to the following method, and then the initial discharge specific capacity and initial coulombic efficiency of the sodium-ion battery were measured under 0.1C conditions.

[0159] Table 1 Comparison Results

[0160]

[0161]

[0162] As shown in Table 1, among Examples 1-5, the graphite recycled material obtained in Example 4 has a larger interlayer spacing and a wider FWHM, which can accommodate more sodium ions. Consequently, its discharge specific capacity is higher and its first coulombic efficiency is also higher.

[0163] The interlayer spacing and initial discharge capacity of the graphite recycled materials in Examples 2 and 3 are not much different from those in Example 4, but the initial efficiency is lower than that in Example 4. The reasons may include: the ball milling time in Example 4 is longer than that in Examples 2 and 3. As the ball milling time increases, certain defects are added, which will increase the FWHM of the material, causing the material to transform into a structure similar to hard carbon, increasing the migration power of sodium ions, which is beneficial to the storage and release of sodium ions.

[0164] The interlayer spacing of the graphite recycled material obtained in Example 5 is not much different from that in Example 4. The FWHM is larger than that in Example 4, and the first coulomb efficiency is lower than that in Example 4. The reason may be that ball milling produces too many defects, which increases the irreversible capacity, thereby reducing the first coulomb efficiency of Example 5 compared to Example 4.

[0165] Comparative Example 1 was not microwave-treated, and Comparative Example 2 was not ball-milled. The interlayer spacing of the graphite was higher than that of the standard graphite, but its interlayer spacing was too small, which was still not conducive to the storage and release of sodium ions, resulting in low capacity and first-time efficiency. In Comparative Example 3, the ball-milling time was further increased, and the capacity and first-time efficiency dropped sharply, indicating that the excessive ball-milling time produced too many defects, which was not conducive to the storage and release of sodium ions.

[0166] As can be seen from Comparative Example 4-16, when the processing method or the processing conditions are inappropriate, it is impossible to obtain a sodium-ion battery with good electrochemical performance.

[0167] In summary, this disclosure creatively provides a method for recovering graphite materials from spent lithium-ion batteries using a specific processing method and using them to prepare sodium-ion batteries. This method has a short cycle time, is easy to operate, and can reduce energy consumption and greenhouse gas emissions, making it environmentally friendly and energy-saving. Furthermore, this method can effectively obtain graphite recycled materials with large interlayer spacing, half-width at half-maximum (HWHM), and high sodium storage capacity. Sodium-ion batteries with the aforementioned graphite recycled material as the anode material can simultaneously exhibit high initial discharge specific capacity and initial coulombic efficiency.

[0168] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for integrated processing of graphite in waste batteries across the entire supply chain, characterized in that, The process includes the following steps: heat-treating the graphite material obtained from the separation of waste batteries to obtain a first intermediate graphite material; microwave-treating the first intermediate graphite material to obtain a second intermediate graphite material with increased interlayer spacing; acid-leaching the second intermediate graphite material to obtain a third intermediate graphite material with defects; and ball-milling the third intermediate graphite material to obtain a graphite recycling material with increased half-width at half-maximum. The microwave processing power is 400W-1500W, and the microwave processing time is 15s-40s; The concentration of acid used in the acid leaching treatment is 10 g / L-300 g / L; the acid used in the acid leaching treatment is sulfuric acid; the solid-liquid ratio of the acid leaching treatment is 1 g:1 mL-1 g:10 mL; the temperature of the acid leaching treatment is 40℃-100℃; and the time of the acid leaching treatment is 30 min-400 min. The ball milling speed is 300rpm-1000rpm, and the ball milling time is 20h-60h.

2. The method according to claim 1, characterized in that, The preparation of the graphite material includes: disassembling the waste battery after discharge treatment and separating the positive electrode sheet and the negative electrode sheet; crushing and screening the negative electrode sheet.

3. The method according to claim 2, characterized in that, Discharge treatment involves soaking the used batteries in salt water.

4. The method according to claim 3, characterized in that, Salt water includes at least one of sodium sulfate solution and sodium chloride solution.

5. The method according to claim 2, characterized in that, The mesh size of the sieves used for screening is 10-300 mesh.

6. The method according to claim 1, characterized in that, Heat treatment includes at least one of the following characteristics: Feature 1: The heat treatment is carried out in an inert atmosphere; Feature 2: The heat treatment temperature is 300℃-750℃; Feature 3: The heat treatment time is 1-5 hours; Feature 4: The heating rate during the heat treatment process is 3℃ / min-20℃ / min.

7. The method according to claim 1, characterized in that, Prior to ball milling, the third intermediate graphite material is washed with water. Alternatively, before ball milling, the washed material may be dried.

8. The method according to claim 7, characterized in that, Wash with water until the pH of the washing solution is ≥5.

9. The method according to claim 7, characterized in that, The drying temperature is 40℃-200℃, and / or the drying time is 8h-48h.

10. The method according to claim 1, characterized in that, The ball-to-material ratio in ball mills is 1:1 to 6:

1.

11. A type of recycled graphite material, characterized in that, Obtained by processing according to any one of claims 1-10.

12. The recycled graphite material according to claim 11, characterized in that, The interlayer spacing of the recycled graphite material is 0.390mm-0.412mm, and / or the half-width at half-maximum (WHM) of the recycled graphite material is 0.293-0.

488.

13. An application of the recycled graphite material as described in claim 11 or 12, characterized in that, The recycled graphite material is used to manufacture batteries.

14. The application according to claim 13, characterized in that, The battery is a sodium-ion battery.

15. A battery, characterized in that, The negative electrode material of the battery includes the recycled graphite material as described in claim 11 or 12.

16. The battery according to claim 15, characterized in that, The battery is a sodium-ion battery.

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