Method for preparing negative electrode regenerated graphite from waste graphite

Abstract

The invention relates to a method for preparing negative electrode regenerated graphite from waste graphite, and the method comprises the following steps: mixing a waste graphite negative electrode with a vulcanizing agent, and carrying out primary impurity removal to obtain graphite; oxidizing and acid-leaching the graphite to obtain a leaching solution and leaching residues; the leached residues are sequentially subjected to first acid leaching and second acid leaching, and high-purity graphite is obtained; the high-purity graphite is subjected to coating modification and carbonization regeneration, and the negative electrode regenerated graphite is obtained. According to the method, the vulcanizing agent is adopted for impurity removal, impurities in the waste graphite negative electrode can be deeply removed, and finally high-purity graphite with the purity reaching 99.95% or above is obtained; meanwhile, the whole recovery process has small damage to the layered crystal structure of the graphite, the original complete graphite structure can be maintained, the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in a traditional recovery method is solved, and the negative electrode regenerated graphite meets the requirements of a lithium ion battery negative electrode material with high capacity and long cycle life.

Description

Technical Field

[0001] The invention belongs to the technical field of resource recovery and relates to a method for recovering waste graphite, in particular to a method for preparing negative electrode regenerated graphite from waste graphite. Background Art

[0002] As the global energy structure shifts toward a low-carbon economy, lithium-ion batteries, with their advantages such as high energy density and long cycle life, have gained widespread application in portable electronic devices, electric vehicles, and large-scale energy storage systems. As a core component of lithium-ion batteries, the anode material directly influences the battery's electrochemical performance. Natural and artificial graphite, with their stable layered structure and reversible lithium-ion insertion and extraction, currently dominate the anode material market.

[0003] With the rapid expansion of the lithium-ion battery market, the number of retired batteries has exploded. Failure to effectively recycle these batteries not only wastes valuable resources like graphite, lithium, cobalt, and nickel, but can also lead to heavy metal pollution and electrolyte leakage. Therefore, the recycling of spent lithium-ion batteries has become a key component of the sustainable development of the new energy industry. The recycling of spent negative electrode graphite has garnered significant attention due to its cost-effectiveness and environmental friendliness.

[0004] In the recycling process of spent negative electrode graphite, purity and structural integrity are key indicators that determine whether the recycled graphite can be reused in high-performance lithium-ion batteries. Retired negative electrode sheets often contain residues consisting of binders, metal impurities, electrolyte decomposition products, and other organic contaminants. The presence of these impurities significantly reduces the conductivity of graphite and the efficiency of lithium ion diffusion, leading to a significant decrease in the electrochemical performance of the recycled graphite, such as the initial charge and discharge efficiency and cycle stability. Therefore, a purification process must be used to remove these impurities and achieve a purity of over 99.9% for the recycled graphite. Graphite's layered crystal structure is the foundation for achieving high reversible capacity and long cycle life. When the graphite structure is intact, lithium ions can be rapidly inserted and removed through the interlayer gaps, and the crystal structure is not easily collapsed during charge and discharge. However, existing recycling technologies often struggle to achieve a balance between purity and structural integrity during the purification process.

[0005] Therefore, it is necessary to provide a method for preparing negative electrode regenerated graphite from waste graphite while ensuring the structural integrity and purity of the negative electrode regenerated graphite. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing negative electrode regenerated graphite from waste graphite, which can deeply remove impurities in the waste graphite negative electrode, and ultimately obtain high-purity graphite with a purity of more than 99.95%; at the same time, the entire recycling process causes little damage to the layered crystal structure of the graphite, and can maintain the original intact graphite structure, thus solving the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in traditional recycling methods, so that the negative electrode regenerated graphite meets the requirements of high-capacity and long cycle life lithium-ion battery negative electrode materials.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing negative electrode regenerated graphite from waste graphite, the method comprising the following steps:

[0009] (1) mixing the waste graphite negative electrode with a sulfiding agent and performing preliminary impurity removal to obtain graphite;

[0010] (2) oxidizing and acid leaching the graphite in step (1) to obtain a leachate and a leach residue;

[0011] (3) The leached residue in step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite;

[0012] (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain the negative electrode regenerated graphite.

[0013] The method provided by the present invention can deeply remove impurities in waste graphite negative electrodes, and ultimately obtain high-purity graphite with a purity of more than 99.95%. At the same time, the entire recycling process causes little damage to the layered crystal structure of the graphite, and can maintain the original complete graphite structure, thus solving the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in traditional recycling methods, and ensuring that the negative electrode regenerated graphite meets the requirements of lithium ion battery negative electrode materials with high capacity and long cycle life.

[0014] In one embodiment of the present invention, the median particle size D50 of the waste graphite negative electrode in step (1) is 2 μm to 10 μm.

[0015] In one embodiment of the present invention, the vulcanizing agent in step (1) includes sublimed sulfur and / or sulfur.

[0016] In one embodiment of the present invention, the mass ratio of the waste graphite negative electrode to the vulcanizing agent in step (1) is 10:1 to 40:1.

[0017] In one embodiment of the present invention, the preliminary impurity removal method in step (1) comprises dynamic vulcanization.

[0018] In one embodiment of the present invention, the dynamic vulcanization includes a first vulcanization and a second vulcanization performed sequentially.

[0019] The temperature of the first vulcanization is 150°C to 300°C, and the time is 2h to 4h;

[0020] The temperature of the second vulcanization is 500° C. to 800° C., and the time is 2 hours to 4 hours.

[0021] In one embodiment of the present invention, protective gas is continuously introduced during the dynamic vulcanization.

[0022] In one embodiment of the present invention, the leachate used in the oxidative acid leaching in step (2) includes an oxidant and an inorganic acid.

[0023] In one embodiment of the present invention, the oxidant includes any one of H2O2, NaClO or ammonium persulfate, or a combination of at least two thereof.

[0024] In one embodiment of the present invention, the inorganic acid includes any one of HCl, H2SO4 or HNO3, or a combination of at least two of them.

[0025] In one embodiment of the present invention, the temperature of the oxidative acid leaching in step (2) is 25°C to 50°C.

[0026] In one embodiment of the present invention, the oxidative acid leaching time in step (2) is 30 min to 90 min.

[0027] In one embodiment of the present invention, the volume-to-mass ratio of the leachate to the graphite is 5:1 to 10:1, and the unit of the volume-to-mass ratio is mL / g.

[0028] In one embodiment of the present invention, the oxidative acid leaching method in step (2) comprises countercurrent acid leaching.

[0029] In one embodiment of the present invention, the first acid leaching in step (3) is performed using a first acid solution; the first acid solution comprises 3 wt% to 8 wt% of HF and 5 wt% to 15 wt% of HNO3.

[0030] In one embodiment of the present invention, the liquid-to-solid ratio of the first acid leaching is 8:1 to 15:1, expressed in mL / g.

[0031] In one embodiment of the present invention, the temperature of the first acid leaching is 40° C. to 60° C., and the time is 40 min to 60 min.

[0032] In one embodiment of the present invention, the second acid leaching in step (3) is performed using a second acid solution; the second acid solution comprises 3 wt% to 8 wt% of H2SO4.

[0033] In one embodiment of the present invention, the liquid-to-solid ratio of the second acid leaching is 5:1 to 8:1, expressed in mL / g.

[0034] In one embodiment of the present invention, the temperature of the second acid leaching is 30° C. to 50° C., and the time is 30 min to 45 min.

[0035] In one embodiment of the present invention, the first acid leaching and the second acid leaching methods each independently include countercurrent acid leaching.

[0036] In one embodiment of the present invention, the coating agent used for the coating modification in step (4) includes an organic carbon source.

[0037] In one embodiment of the present invention, the organic carbon source comprises any one or a combination of at least two of dopamine, asphalt, glucose, polytetrafluoroethylene or polyacrylonitrile;

[0038] In one embodiment of the present invention, the amount of the coating agent is 5 wt% to 10 wt% of the high-purity graphite.

[0039] In one embodiment of the present invention, the heating rate of the carbonization regeneration in step (4) is 4°C / min to 8°C / min.

[0040] In one embodiment of the present invention, the temperature of the carbonization regeneration in step (4) is 1000° C. to 1200° C., and the time is 1 hour to 3 hours.

[0041] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The method provided by the present invention can deeply remove impurities in waste graphite negative electrodes, and ultimately obtain high-purity graphite with a purity of more than 99.95%. At the same time, the entire recycling process causes little damage to the layered crystal structure of the graphite, and can maintain the original complete graphite structure, thus solving the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in traditional recycling methods, and ensuring that the negative electrode regenerated graphite meets the requirements of lithium ion battery negative electrode materials with high capacity and long cycle life. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] When existing technologies are used to regenerate waste graphite, it is difficult to strike a balance between purity and the structural integrity of the graphite. For example, when chemical purification methods such as strong acid leaching are used, although metal impurities can be effectively dissolved, strong acids will corrode the interlayer structure of the graphite, resulting in an increase in the interlayer spacing or the appearance of irreversible defects; when high-temperature calcination is used to remove impurities, it may cause the graphite particles to sinter and oxidatively decompose through the layered structure, destroying their original crystal morphology; when auxiliary purification methods such as mechanical grinding are used, excessive mechanical force will cause the graphite particles to break and increase edge defects, reducing their structural stability during the recycling process.

[0046] It can be seen from this that if the focus is on improving the purity of the negative electrode recycled graphite, it will easily lead to damage to the graphite structure, causing the cycle performance of the negative electrode recycled graphite to decay faster; if the focus is on retaining the structural integrity, the impurities in the waste graphite will be difficult to completely remove, resulting in insufficient purity of the recycled graphite, which cannot meet the use requirements of high-performance batteries, which seriously limits the high-value recycling of waste graphite.

[0047] Therefore, in order to address the problem of difficulty in balancing purity and structural integrity in the recycling process of waste graphite in the existing technology, a recycling method has been developed that can not only achieve high-purity purification but also effectively retain the original layered crystal structure of graphite, thereby ensuring the electrochemical properties of the regenerated graphite such as cyclic stability. This method has important theoretical significance and practical application value.

[0048] Specifically, the present invention provides a method for preparing negative electrode regenerated graphite from waste graphite, the method comprising the following steps:

[0049] (1) mixing the waste graphite negative electrode with a sulfiding agent and performing preliminary impurity removal to obtain graphite;

[0050] (2) oxidizing the graphite from step (1) to obtain a leachate and a leach residue;

[0051] (3) The leached residue from step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite;

[0052] (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain negative electrode regenerated graphite.

[0053] The method provided by the present invention can deeply remove impurities in waste graphite negative electrodes, and ultimately obtain high-purity graphite with a purity of more than 99.95%. At the same time, the entire recycling process causes little damage to the layered crystal structure of the graphite, and can maintain the original complete graphite structure, thus solving the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in traditional recycling methods, and ensuring that the negative electrode regenerated graphite meets the requirements of lithium ion battery negative electrode materials with high capacity and long cycle life.

[0054] The present invention mixes the waste graphite negative electrode with a vulcanizing agent for preliminary impurity removal, with the purpose of utilizing the vulcanizing agent to chemically react with the metal impurities and organic pollutants remaining in the waste graphite negative electrode to generate volatile sulfides while reducing damage to the graphite layered structure.

[0055] In one embodiment of the present invention, the median particle size D50 of the waste graphite negative electrode in step (1) is 2 μm to 10 μm, for example, it can be 2 μm, 4 μm, 5 μm, 6 μm, 8 μm or 10 μm, but is not limited to the listed values, and the remaining values ​​not listed within the numerical range are also applicable.

[0056] Exemplarily, the waste graphite negative electrode of the present invention is obtained by mechanically stripping the waste negative electrode sheet and then screening it. By controlling the median particle size of the waste graphite negative electrode, the treatment effect of the sulfiding agent on the waste graphite negative electrode is improved.

[0057] In one embodiment of the present invention, the vulcanizing agent in step (1) includes sublimed sulfur and / or sulfur.

[0058] In one embodiment of the present invention, the mass ratio of the waste graphite negative electrode to the sulfiding agent in step (1) is 10:1 to 40:1, for example, it can be 10:1, 15:1, 20:1, 25:1, 30:1, 35:1 or 40:1, but is not limited to the listed values, and the remaining values ​​within the numerical range not listed are also applicable.

[0059] In one embodiment of the present invention, the method for preliminary impurity removal in step (1) comprises dynamic vulcanization.

[0060] Optionally, to improve the effectiveness of the preliminary impurity removal, the waste graphite negative electrode and the vulcanizing agent are uniformly mixed before the preliminary impurity removal. For example, mixing can be performed using a planetary ball mill or a twin-screw mixer. This is not specifically limited in the present invention, as long as the waste graphite negative electrode and the vulcanizing agent are uniformly mixed.

[0061] In one embodiment of the present invention, the dynamic vulcanization includes a first vulcanization and a second vulcanization performed sequentially; the temperature of the first vulcanization is 150°C to 300°C, and the time is 2h to 4h; the temperature of the second vulcanization is 500°C to 800°C, and the time is 2h to 4h.

[0062] Dynamic vulcanization is a simple process suitable for continuous production, but requires strict temperature control to avoid local overheating that damages the graphite structure. In one embodiment of the present invention, the temperature and time of the first vulcanization process are controlled to allow the vulcanizing agent to react with the binder in the waste graphite negative electrode, promoting its decomposition. The temperature and time of the second vulcanization process are controlled to allow impurities such as metals and silicon in the waste graphite negative electrode to react with the vulcanizing agent, causing them to vaporize and decompose, thereby promoting the removal of impurity elements.

[0063] The temperature of the first vulcanization is 150°C to 300°C, for example, 150°C, 160°C, 180°C, 200°C, 240°C, 250°C, 280°C or 300°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0064] The time of the first vulcanization is 2 hours to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] The temperature of the second vulcanization is 500°C to 800°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] The second vulcanization time is 2 hours to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] In one embodiment of the present invention, a protective gas is continuously introduced during dynamic vulcanization to prevent graphite from being oxidized. The protective gas includes nitrogen and / or an inert gas.

[0068] Exemplarily, the inert gas includes any one of helium, neon or argon, or a combination of at least two of them. Typical but non-limiting combinations include a combination of argon and neon, a combination of helium and neon, a combination of neon and argon, or a combination of helium, neon and argon.

[0069] In one embodiment of the present invention, the leachate used in the oxidative acid leaching in step (2) comprises an oxidant and an inorganic acid.

[0070] In one embodiment of the present invention, the oxidizing agent includes any one or a combination of at least two of H2O2, NaClO or ammonium persulfate. Typical but non-limiting combinations include a combination of H2O2 and NaClO, a combination of NaClO and ammonium persulfate, a combination of H2O2 and ammonium persulfate, or a combination of H2O2, NaClO and ammonium persulfate.

[0071] In one embodiment of the present invention, the inorganic acid includes any one of HCl, H2SO4 or HNO3, or a combination of at least two of them, for example, a combination of HCl and H2SO4, a combination of HCl and HNO3, a combination of H2SO4 and HNO3, or a combination of HCl, H2SO4 and HNO3.

[0072] Among them, H2O2 can oxidize metal impurities; HNO3 can provide an acidic environment and assist in dissolution; NaClO has a mild oxidizing ability, reducing damage to the graphite layer structure; H2SO4 can inhibit Cl - Interference with metal complexation; the oxidizing property of ammonium persulfate is controllable.

[0073] As a preferred technical solution, the leachate used in the oxidative acid leaching in step (2) includes 5wt% to 10wt% of H2O2 and 5wt% to 10wt% of HNO3; or, the leachate used in the oxidative acid leaching in step (2) includes 2wt% to 5wt% of NaClO and 5wt% to 8wt% of H2SO4; or, the leachate used in the oxidative acid leaching in step (2) includes 1wt% to 2wt% of ammonium persulfate and 5wt% to 10wt% of HCl.

[0074] Too high a temperature for oxidative acid leaching will destroy the graphite structure and affect the interlayer spacing of graphite. Therefore, in one embodiment of the present invention, the temperature for oxidative acid leaching in step (2) is 25°C to 50°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values, and the remaining values ​​within the numerical range not listed are also applicable.

[0075] In one embodiment of the present invention, the time for oxidative acid leaching in step (2) is 30 min to 90 min, for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0076] In one embodiment of the present invention, the volume mass ratio of the leachate to the graphite is 5:1 to 10:1, and the unit of the volume mass ratio is mL / g. For example, it can be 5:1, 6:1, 8:1, 9:1 or 10:1, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0077] In one embodiment of the present invention, the oxidative acid leaching method in step (2) comprises countercurrent acid leaching.

[0078] The present invention performs oxidative acid leaching by a countercurrent acid leaching method, which can effectively remove impurities in the graphite and reduce the damage to the graphite structure caused by the oxidative acid leaching.

[0079] After oxidative acid leaching, the residual metal impurities in the waste graphite are significantly reduced, but trace amounts of insoluble metal oxides and sulfide residues may still be present. The present invention further improves graphite purity through the step-by-step treatment of the first and second acid leaching processes. It also enables surface etching and functional group manipulation of the graphite, facilitating subsequent coating and modification.

[0080] In one embodiment of the present invention, the first acid leaching in step (3) is performed using a first acid solution; the first acid solution comprises 3 wt% to 8 wt% of HF and 5 wt% to 15 wt% of HNO3.

[0081] The first acid solution includes 3 wt% to 8 wt% of HF, for example, 3 wt%, 4 wt%, 5 wt%, 6 wt% or 8 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0082] The first acid solution includes 5wt% to 15wt% HNO3, for example, it can be 5wt%, 6wt%, 8wt%, 10wt%, 12wt% or 15wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0083] The acid leaching used in the first acid leaching of the present invention adopts a strong acid system, which can treat insoluble oxide impurities and achieve deep impurity removal.

[0084] In one embodiment of the present invention, the liquid-to-solid ratio of the first acid leaching is 8:1 to 15:1, expressed in mL / g, for example, 8:1, 9:1, 10:1, 12:1, or 15:1, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0085] In one embodiment of the present invention, the temperature of the first acid leaching is 40° C. to 60° C., and the time is 40 min to 60 min.

[0086] The temperature of the first acid leaching is 40°C to 60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0087] The time of the first acid leaching is 40 min to 60 min, for example, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0088] In one embodiment of the present invention, the second acid leaching in step (3) is performed using a second acid solution; the second acid solution comprises 3 wt% to 8 wt% of H2SO4.

[0089] The second acid solution includes 3wt% to 8wt% of H2SO4, for example, 3wt%, 4wt%, 5wt%, 6wt% or 8wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0090] The second acid leaching in the present invention gently etches the graphite surface, increases surface defects and roughness without destroying the main layered structure, and improves the coating modification effect.

[0091] In one embodiment of the present invention, the liquid-to-solid ratio of the second acid leaching is 5:1 to 8:1, expressed in mL / g, for example, 5:1, 6:1, 7:1 or 8:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0092] In one embodiment of the present invention, the temperature of the second acid leaching is 30° C. to 50° C., and the time is 30 min to 45 min.

[0093] The temperature of the second acid leaching is 30°C to 50°C, for example, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0094] The time of the second acid leaching is 30 min to 45 min, for example, 30 min, 35 min, 40 min or 45 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0095] In one embodiment of the present invention, the first acid leaching and the second acid leaching methods each independently include countercurrent acid leaching.

[0096] The present invention performs the first acid leaching and / or the second acid leaching by a countercurrent acid leaching method, which can effectively remove impurities in the graphite and reduce the damage to the graphite structure caused by oxidative acid leaching.

[0097] The present invention forms a modified layer on the surface of high-purity graphite through coating modification, fills the defects caused by treatments such as oxidative acid leaching, first acid leaching and second acid leaching, and repairs the integrity of the graphite layered structure; then, through carbonization regeneration, the coating layer is converted into a carbon layer that matches the graphite lattice, thereby improving the conductivity, cycle stability and compatibility of the graphite with the electrolyte.

[0098] In one embodiment of the present invention, the coating agent used in step (4) coating modification includes an organic carbon source.

[0099] In one embodiment of the present invention, the organic carbon source includes any one of dopamine, asphalt, glucose, polytetrafluoroethylene or polyacrylonitrile, or a combination of at least two thereof.

[0100] In one embodiment of the present invention, the amount of the coating agent is 5wt% to 10wt% of the high-purity graphite, for example, it can be 5wt%, 6wt%, 8wt%, 9wt% or 10wt%, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable; if the amount of the coating agent is too small, the ability to repair defects is insufficient; if the amount of the coating agent is too much, the conductivity of the negative electrode regenerated graphite will decrease.

[0101] Exemplarily, the coating modification method includes: uniformly dispersing high-purity graphite, and then adding a coating agent to the dispersion to uniformly coat the high-purity graphite with the coating agent.

[0102] In one embodiment of the present invention, the heating rate of carbonization regeneration in step (4) is 4°C / min to 8°C / min, for example, it can be 4°C / min, 5°C / min, 6°C / min, 7°C / min or 8°C / min, but is not limited to the listed values, and the remaining values ​​not listed within the numerical range are also applicable.

[0103] In one embodiment of the present invention, the temperature of the carbonization regeneration in step (4) is 1000° C. to 1200° C., and the time is 1 hour to 3 hours.

[0104] The temperature of carbonization regeneration is 1000°C to 1200°C, for example, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0105] The carbonization regeneration time is 1 hour to 3 hours, for example, 1 hour, 2 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0106] In one embodiment of the present invention, the carbonization regeneration in step (4) is carried out in a protective atmosphere, and the gas used in the protective atmosphere includes nitrogen and / or an inert gas.

[0107] One embodiment of the present invention thermally decomposes the coating agent into a carbon layer through carbonization regeneration. By controlling the heating rate and temperature, the carbon layer and high-purity graphite form an outer disordered carbon layer and an inner ordered carbon layer. The outer disordered carbon layer can alleviate electrolyte erosion, and the inner ordered carbon layer matches the graphite lattice; at the same time, residual impurities can be further removed by high-temperature volatilization.

[0108] The method provided by the present invention also includes necessary steps such as washing and drying, which are not specifically limited in the present invention and those skilled in the art can make reasonable arrangements according to needs.

[0109] Example 1

[0110] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, comprising:

[0111] (1) Waste graphite negative electrode with a median particle size D50 of 5 μm is mixed with a vulcanizing agent (sulfur) and preliminarily removed to obtain graphite;

[0112] The mass ratio of waste graphite negative electrode to vulcanizing agent is 20:1;

[0113] The method for preliminary impurity removal is dynamic vulcanization, during which nitrogen is continuously introduced; dynamic vulcanization includes the first vulcanization and the second vulcanization performed in sequence; the temperature of the first vulcanization is 250°C and the time is 3 hours; the temperature of the second vulcanization is 650°C and the time is 3 hours;

[0114] (2) oxidizing and acid leaching the graphite in step (1) to obtain a leachate and a leach residue;

[0115] The leaching solution used in the oxidative acid leaching includes 4 wt% NaClO and 6 wt% H2SO4, and the volume mass ratio of the leaching solution to the graphite is 8:1. The unit of the volume mass ratio is mL / g.

[0116] The temperature of oxidizing acid leaching was 40°C, the time was 60 min, and the method was countercurrent acid leaching;

[0117] (3) The leached residue in step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite; the first acid leaching and the second acid leaching are independently performed by countercurrent acid leaching;

[0118] The first acid leaching was performed using a first acid solution comprising 5 wt% HF and 10 wt% HNO3; the first acid leaching had a liquid-to-solid ratio of 12:1 (unit: mL / g); a temperature of 50°C and a time of 50 min;

[0119] The second acid leaching was performed using a second acid solution comprising 5 wt% H2SO4; the second acid leaching had a liquid-to-solid ratio of 6:1, expressed in mL / g; the temperature was 40°C, and the time was 40 min;

[0120] (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain the negative electrode regenerated graphite;

[0121] The coating agent used for coating modification is asphalt, and the amount used is 8wt% of high-purity graphite;

[0122] Carbonization regeneration was performed by heating the sample to 1100°C at a heating rate of 6°C / min and keeping the temperature for 2 h.

[0123] Example 2

[0124] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, comprising:

[0125] (1) Waste graphite negative electrode with a median particle size D50 of 2 μm is mixed with a vulcanizing agent (sulfur) and preliminarily removed to obtain graphite;

[0126] The mass ratio of waste graphite negative electrode to vulcanizing agent is 10:1;

[0127] The method for preliminary impurity removal is dynamic vulcanization, during which nitrogen is continuously introduced; the dynamic vulcanization includes a first vulcanization and a second vulcanization performed in sequence; the temperature of the first vulcanization is 150°C and the time is 4 hours; the temperature of the second vulcanization is 500°C and the time is 4 hours;

[0128] (2) oxidizing and acid leaching the graphite in step (1) to obtain a leachate and a leach residue;

[0129] The leaching solution used in the oxidative acid leaching includes 2 wt% NaClO and 8 wt% H2SO4, and the volume mass ratio of the leaching solution to the graphite is 5:1. The unit of the volume mass ratio is mL / g;

[0130] The oxidizing acid leaching temperature was 25°C, the time was 90 min, and the method was countercurrent acid leaching;

[0131] (3) The leached residue in step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite; the first acid leaching and the second acid leaching are independently performed by countercurrent acid leaching;

[0132] The first acid leaching was performed using a first acid solution comprising 3 wt% HF and 15 wt% HNO3; the first acid leaching had a liquid-to-solid ratio of 8:1 (unit: mL / g); the temperature was 40°C; and the time was 60 min;

[0133] The second acid leaching was performed using a second acid solution comprising 3 wt% H2SO4; the second acid leaching had a liquid-to-solid ratio of 5:1, expressed in mL / g; the temperature was 30°C, and the time was 45 min;

[0134] (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain the negative electrode regenerated graphite;

[0135] The coating agent used for coating modification is asphalt, and the amount used is 5wt% of high-purity graphite;

[0136] Carbonization regeneration was performed by heating the sample to 1000°C at a heating rate of 4°C / min and keeping the temperature for 3 h.

[0137] Example 3

[0138] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, comprising:

[0139] (1) Waste graphite negative electrode with a median particle size D50 of 10 μm is mixed with a vulcanizing agent (sulfur) and preliminarily removed to obtain graphite;

[0140] The mass ratio of waste graphite negative electrode to vulcanizing agent is 40:1;

[0141] The method for preliminary impurity removal is dynamic vulcanization, during which nitrogen is continuously introduced; dynamic vulcanization includes the first vulcanization and the second vulcanization performed in sequence; the temperature of the first vulcanization is 300°C and the time is 2 hours; the temperature of the second vulcanization is 800°C and the time is 2 hours;

[0142] (2) oxidizing and acid leaching the graphite in step (1) to obtain a leachate and a leach residue;

[0143] The leaching solution used in the oxidative acid leaching includes 5 wt% NaClO and 5 wt% H2SO4, and the volume mass ratio of the leaching solution to the graphite is 10:1. The unit of the volume mass ratio is mL / g;

[0144] The temperature of oxidizing acid leaching was 50°C, the time was 30 min, and the method was countercurrent acid leaching;

[0145] (3) The leached residue in step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite; the first acid leaching and the second acid leaching are independently performed by countercurrent acid leaching;

[0146] The first acid leaching was performed using a first acid solution comprising 8 wt% HF and 5 wt% HNO3; the first acid leaching had a liquid-to-solid ratio of 15:1 (unit: mL / g); the temperature was 60°C, and the time was 40 min;

[0147] The second acid leaching was performed using a second acid solution comprising 8 wt % H2SO4; the second acid leaching had a liquid-to-solid ratio of 8:1, expressed in mL / g; the temperature was 50°C, and the time was 30 min;

[0148] (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain the negative electrode regenerated graphite;

[0149] The coating agent used for coating modification is asphalt, and the amount used is 10wt% of high-purity graphite;

[0150] Carbonization regeneration was performed by heating the sample to 1200°C at a heating rate of 8°C / min and keeping the temperature for 1 h.

[0151] Example 4

[0152] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the mass ratio of the waste graphite negative electrode to the vulcanizing agent is 5:1.

[0153] Example 5

[0154] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the mass ratio of the waste graphite negative electrode to the vulcanizing agent is 45:1.

[0155] Example 6

[0156] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as that of Example 1 except that the temperature of the first sulfurization is 100°C.

[0157] Example 7

[0158] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite. Except that the temperature of the first sulfurization is 350° C., the rest is the same as that of Example 1.

[0159] Example 8

[0160] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the temperature of the second sulfurization is 450°C.

[0161] Example 9

[0162] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the oxidative acid leaching is downstream acid leaching.

[0163] Example 10

[0164] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite. Except that the first acid leaching is a downstream acid leaching, the rest is the same as that of Example 1.

[0165] Example 11

[0166] This embodiment provides a method for preparing negative electrode regenerated graphite from waste graphite. Except that the second acid leaching is a downstream acid leaching, the rest is the same as Example 1.

[0167] Comparative Example 1

[0168] This comparative example provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the second acid leaching is not performed and the time of the first acid leaching is extended to 90 minutes.

[0169] Comparative Example 2

[0170] This comparative example provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that the first acid leaching is not performed and the second acid leaching time is extended to 90 minutes.

[0171] Comparative Example 3

[0172] This comparative example provides a method for preparing negative electrode regenerated graphite from waste graphite, which is the same as Example 1 except that no preliminary impurity removal is performed and oxidative acid leaching is performed directly.

[0173] Performance Characterization

[0174] The purity of the negative electrode regenerated graphite obtained in the above examples and comparative examples was measured.

[0175] In addition, the negative electrode regenerated graphite obtained in each embodiment and comparative example was used as the negative electrode active material, and was mixed in a mass ratio of negative electrode active material: conductive carbon black: CMC: SBR = 95.3:1.5:1.4:1.8. After mixing with deionized water as a solvent, the slurry was coated on a copper foil with a coating surface density of 6.5±0.1 mg / cm2. After vacuum drying at 90°C, a negative electrode sheet was obtained, and the negative electrode sheet was rolled to a compaction density of 1.65±0.02 g / cc; a lithium sheet was used as the counter electrode.

[0176] The negative electrode sheet, lithium sheet, electrolyte (1 mol / L LiPF6, EC:EMC=1:1) and Celgard 2400 separator were assembled into a button battery.

[0177] The obtained button battery was tested for capacity and cycle performance at 25±2℃.

[0178] Capacity test: Under 25±2℃ environment, the voltage range is 0.005V~2V, and the capacity test is carried out at a charge and discharge rate of 0.05C;

[0179] Cycling test: At 25±2°C, ① charge at a constant current of 1C to a charge cutoff voltage of 4.2V. Then, charge at a constant voltage to a current of 0.05C and let it rest for 10 minutes. ② Discharge at a constant current of 1C to a discharge cutoff voltage of 3V. Record the initial capacity as C0. Repeat ①-②, recording the discharge capacity Cn of each cycle, until the cycle capacity retention rate (Cn / C0×100%) reaches 80%. Record the number of cycles.

[0180] The results are shown in Table 1.

[0181] Table 1

[0182]

[0183]

[0184] In summary, the method provided by the present invention can deeply remove impurities in waste graphite negative electrodes, and ultimately obtain high-purity graphite with a purity of more than 99.95%; at the same time, the entire recycling process causes little damage to the layered crystal structure of the graphite, and can maintain the original complete graphite structure, solving the problem of electrochemical performance degradation caused by insufficient graphite purity or structural damage in traditional recycling methods, so that the negative electrode regenerated graphite meets the requirements of high-capacity and long cycle life lithium-ion battery negative electrode materials.

[0185] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing negative electrode regenerated graphite from waste graphite, characterized in that: The method comprises the following steps: (1) mixing the waste graphite negative electrode with a sulfiding agent and performing preliminary impurity removal to obtain graphite; (2) oxidizing and acid leaching the graphite in step (1) to obtain a leachate and a leach residue; (3) The leached residue in step (2) is subjected to a first acid leaching and a second acid leaching in sequence to obtain high-purity graphite; (4) The high-purity graphite in step (3) is subjected to coating modification and carbonization regeneration to obtain the negative electrode regenerated graphite.

2. The method according to claim 1, characterized in that The median particle size D50 of the waste graphite negative electrode in step (1) is 2 μm to 10 μm; and / or, the vulcanizing agent in step (1) comprises sublimed sulfur and / or sulfur; And / or, the mass ratio of the waste graphite negative electrode to the vulcanizing agent in step (1) is 10:1 to 40:

1.

3. The method according to claim 1, characterized in that The method for preliminary impurity removal in step (1) includes dynamic vulcanization.

4. The method according to claim 3, characterized in that The dynamic vulcanization includes a first vulcanization and a second vulcanization performed sequentially; The temperature of the first vulcanization is 150°C to 300°C, and the time is 2h to 4h; The temperature of the second vulcanization is 500° C. to 800° C., and the time is 2 hours to 4 hours.

5. The method according to claim 3, characterized in that During the dynamic vulcanization, protective gas is continuously introduced.

6. The method according to claim 1, characterized in that The leaching solution used in the oxidative acid leaching in step (2) includes an oxidant and an inorganic acid; and / or, the oxidant comprises any one or a combination of at least two of H2O2, NaClO or ammonium persulfate; And / or, the inorganic acid includes any one of HCl, H2SO4 or HNO3, or a combination of at least two of them.

7. The method according to claim 6, characterized in that The temperature of the oxidative acid leaching in step (2) is 25° C. to 50° C.; And / or, the oxidative acid leaching time in step (2) is 30 min to 90 min; And / or, the volume mass ratio of the leachate to the graphite is 5:1 to 10:1, and the unit of the volume mass ratio is mL / g; And / or, the oxidative acid leaching method in step (2) comprises countercurrent acid leaching.

8. The method according to claim 1, characterized in that Step (3) the first acid leaching is performed using a first acid solution; the first acid solution comprises 3 wt% to 8 wt% of HF and 5 wt% to 15 wt% of HNO3; and / or, the liquid-to-solid ratio of the first acid leaching is 8:1 to 15:1, expressed in mL / g; And / or, the temperature of the first acid leaching is 40°C to 60°C, and the time is 40min to 60min; and / or, the second acid leaching in step (3) is performed using a second acid solution; the second acid solution comprises 3 wt% to 8 wt% of H2SO4; and / or, the liquid-to-solid ratio of the second acid leaching is 5:1 to 8:1, expressed in mL / g; And / or, the temperature of the second acid leaching is 30°C to 50°C, and the time is 30min to 45min; And / or, the first acid leaching and the second acid leaching methods each independently comprise countercurrent acid leaching.

9. The method according to claim 1, characterized in that The coating agent used for the coating modification in step (4) includes an organic carbon source; And / or, the organic carbon source includes any one or a combination of at least two of dopamine, asphalt, glucose, polytetrafluoroethylene or polyacrylonitrile; And / or, the amount of the coating agent is 5wt% to 10wt% of the high-purity graphite.

10. The method according to claim 1, characterized in that The heating rate of the carbonization regeneration in step (4) is 4°C / min to 8°C / min; And / or, the temperature of the carbonization regeneration in step (4) is 1000° C. to 1200° C., and the time is 1 hour to 3 hours.

Images