A graphite critical water reaction treatment method

Abstract

The present invention belongs to the field of graphite material processing and specifically discloses a method for treating graphite by critical water reaction. A mixed solution containing graphite to be treated, additives A and B, and water is placed in a pressure-resistant container for a pre-reaction. The solution is then heated to a supercritical state of water for a supercritical reduction reaction. After the reaction, the treated graphite is collected. The additive A is at least one of an alcohol, ether, ester, nitrile, and ketone; the additive B is a F-containing compound. The pre-reaction temperature is 120 to 300°C and the pressure is 1 to 5 MPa. The method can effectively improve the fixed carbon content and degree of graphitization of the treated graphite. Furthermore, it can restructure its physical and chemical structure and improve its electrochemical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of high-value utilization of graphite, and in particular relates to a graphite critical water reaction treatment method. Background Art

[0002] Graphite is an important negative electrode active material, but the electrochemical performance of natural graphite directly used as negative electrode active material is limited. Existing technologies usually treat it through acid-base process to improve its electrochemical performance. However, the improvement of electrochemical performance in this aspect needs to be improved, and there is great environmental pressure.

[0003] Furthermore, with the widespread adoption of lithium-ion batteries, the amount of discarded batteries is increasing annually. Especially with the increasing use of lithium-ion batteries in electric vehicles, used lithium-ion batteries will become one of my country's major sources of municipal solid waste. Lithium-ion batteries primarily consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a metal casing. The positive electrode is primarily composed of a ternary positive electrode material, a positive electrode active material such as lithium cobalt oxide or lithium iron phosphate, conductive carbon, and aluminum foil; the negative electrode is primarily composed of a negative electrode active material such as artificial graphite or natural graphite, conductive carbon, and copper foil. Because the valuable metal content in used batteries is much higher than that of natural ores, and the impurity content is lower, used lithium-ion batteries are often referred to as "urban minerals." However, current research on the recycling of used lithium-ion batteries focuses on the positive electrode, while relatively little research is conducted on the recycling of graphite negative electrode materials.

[0004] At present, the negative electrodes, whether they are scraps generated in battery production or negative electrode plates obtained from battery disassembly, are mostly recovered by simple mechanical powdering to recover copper. After the copper is recovered, the carbon powder inevitably contains residual copper, conductive agents (such as acetylene black and other amorphous carbon), aqueous binders, and even residual electrolytes and diaphragms, so these waste carbon powders can only be disposed of as solid waste or used as fuel or reducing agents in the metallurgical industry at a low value. In addition, some scrapped negative electrode slurries are inevitably generated in battery production. Although the amount of such slurries is not too large, due to the high water content and the presence of binders and amorphous conductive carbon materials, there is currently no effective treatment method.

[0005] In fact, the main components of the negative electrodes of used lithium-ion batteries are currently high-value artificial graphite and natural graphite. If a fully wet process is used, the amorphous conductive carbon material in the resulting carbon powder cannot be separated, and organic matter (mainly binders and electrolytes) will inevitably remain. If a high-temperature process is used, inert gas and high temperatures are required, which not only increases the processing cost, but also the problem of the amorphous conductive carbon material in the carbon powder cannot be separated, resulting in low purity of the carbon powder. Reported graphite powder oxidation processes have uncontrollable oxidation levels, and the resulting carbon material often has a low degree of graphitization and many structural defects. Further conversion to graphite requires high reaction temperatures, high energy consumption, high costs, and no production advantages. Therefore, the development of low-cost, short-process technologies for recovering high-purity graphite from used lithium battery negative electrode powder is of great significance.

[0006] In summary, existing graphite recovery methods still have technical problems such as complex recovery process and unsatisfactory electrochemical properties of the recovered materials. Summary of the Invention

[0007] In view of the technical problems that the existing graphite processing process still has low purity of recycled materials and unsatisfactory electrochemical performance, the purpose of the present invention is to provide a graphite critical water reaction treatment method, aiming to improve the purity of the recovered graphite, restore and reconstruct its physical structure and chemical activity, and improve its electrochemical performance.

[0008] A graphite critical water reaction treatment method, wherein a mixed solution of a material to be treated containing graphite, an additive A, an additive B, and water is placed in a pressure-resistant container for pre-reaction, and then the temperature is continuously raised to a supercritical state of water to perform a supercritical reduction reaction, and the treated graphite is collected after the reaction is completed;

[0009] The auxiliary agent A is at least one of alcohol, ether, ester, nitrile and ketone;

[0010] The auxiliary agent B is a compound containing F;

[0011] The temperature of the preliminary reaction is 120-300° C., and the pressure is 1-5 MPa.

[0012] The present invention has found that, with the synergistic assistance of the additives A and B, and further in combination with the pretreatment and supercritical water reduction treatment, the waste graphite can be regenerated based on the supercritical water reduction mechanism, the purity of the graphite fixed carbon can be improved, and its structure can be restored, thereby improving the initial efficiency and cycle performance of the regenerated graphite.

[0013] In the present invention, the graphite is at least one of natural graphite and waste graphite.

[0014] In the present invention, the waste graphite can be any graphite material that is theoretically difficult to effectively utilize. For example, the waste graphite can be at least one of graphite negative electrode active material separated from waste batteries, graphite scraps from production, offcuts of graphite negative electrode sheets from lithium-ion batteries, and graphite crucible waste.

[0015] In the present invention, the material to be processed, in addition to graphite, may also contain at least one of a conductive agent, a binder, an electrolyte, a current collector, and a separator. In other words, the technical solution of the present invention can be used to simultaneously process a mixture of waste graphite containing at least one of these materials. This not only enables the simultaneous processing of multiple raw materials in one pot, but also creates a certain degree of synergy in the graphite recovery process, helping to further improve the purity and electrochemical properties of the recovered graphite.

[0016] In the present invention, the conductive agent, binder, current collector and separator can all be conventional components in the negative electrode of waste batteries, and the electrolyte can be electrolyte components adsorbed in the disassembled negative electrode.

[0017] In the present invention, the material to be processed is at least one of graphite negative electrode active materials, graphite negative electrode black powder, graphite negative electrode slurry, and graphite negative electrode sheets stripped from waste batteries. In the present invention, the graphite negative electrode black powder is a mixture mainly comprising graphite and a conductive agent after stripping the current collector. The graphite negative electrode sheet can be a negative electrode sheet obtained by direct stripping, which comprises a current collector and a negative electrode material composited on its surface. The negative electrode material includes graphite, a conductive agent, and a binder. In addition, the negative electrode sheet is allowed to adsorb electrolyte. The negative electrode sheet can be a broken or unbroken sheet. Considering the treatment process and effect, the negative electrode sheet is preferably a non-broken sheet.

[0018] The waste batteries mentioned above are theoretically allowed to be all batteries using graphite as negative electrode active material, for example, they can be waste lithium-ion batteries.

[0019] In the present invention, the synergistic assistance of the additives A and B and the combined synergy of the pretreatment and supercritical water reduction treatment are the key to improving the purity and electrochemical performance of waste graphite.

[0020] The auxiliary agent A is at least one of alcohol, ether, ester, nitrile and ketone having a carbon number of less than or equal to 20, preferably less than or equal to 10.

[0021] Preferably, the alcohol is at least one of C1-C6 units or polyols, for example, it can be at least one of methanol, ethanol, propanol, isopropanol, 1-butanol, propylene glycol, glycerol, etc.

[0022] Preferably, the ether is at least one of C2-C6 monoether, polyether or cyclic ether; for example, it can be at least one of dimethyl ether, diethyl ether, methyl ethyl ether, oxycyclopentane and oxycyclohexane.

[0023] Preferably, the ester is C2~C 10 Carboxylate C3~C 10 Carbonate At least one of the following; in addition, the ester may also be a carboxylic acid ester or a carbonate internal ester. In the structure, R1 is H, a C1-C6 alkyl group, or a C3-C6 cycloalkyl group; R2 and R3 are C1-C6 alkyl groups or C3-C6 cycloalkyl groups; or R1 and R2 are cyclized to form a five-membered or six-membered ring including C(O)-O; and R2 and R3 are cyclized to form a five-membered or six-membered ring including -OC(O)-O.

[0024] Preferably, the nitrile is a C2-C4 nitrile; for example, it can be at least one of acetonitrile, propionitrile, etc.

[0025] Preferably, the ketone is C3~C 10 At least one of monoketones, polyketones, and cyclic ketones; for example, it can be at least one of acetone, 2-butanone, 3-pentanone, cyclopentanone, cyclohexanone, etc.

[0026] More preferably, the auxiliary agent A is at least one of methanol, ethanol, carbonate, ether, acetonitrile and acetone.

[0027] Preferably, the auxiliary agent A is a combination of two or more of alcohol, ether, ester, nitrile and ketone.

[0028] The study found that the use of combined additives can help further achieve synergy with pre-reaction and supercritical reduction treatment methods, and help further improve the treatment effect.

[0029] Preferably, the auxiliary agent A is a combination of alcohol and ester, more preferably a combination of alcohol and carbonate; the ratio of the two is preferably 1-10:1-10.

[0030] Preferably, the weight ratio of the auxiliary agent A to the material to be treated is 0.5 to 10:100, preferably 2 to 5:100.

[0031] Preferably, the additive B is at least one of HF, alkali metal fluoride, alkaline earth metal fluoride, and ammonium fluoride. The alkali metal is, for example, at least one of Li, Na, and K; and the alkaline earth metal is, for example, at least one of Mg, Ca, and Ba.

[0032] Preferably, the weight ratio of the auxiliary agent B to the material to be treated is 0.05-1:100; preferably 0.2-0.5:100.

[0033] Preferably, in the mixed liquid, the solid-liquid ratio of the material to be treated to water is 0.1 to 40:100 (g:ml); preferably 10 to 30:100 (g:ml).

[0034] Preferably, with the assistance of the auxiliary agent A and the auxiliary agent B, and further in combination with the pretreatment and supercritical water reduction treatment, the purity of the graphite can be unexpectedly achieved based on the supercritical water fluid-mediated reduction mechanism, and the surface structure and active group dredging and reconstruction can be carried out, thereby significantly improving the electrochemical properties of the recovered graphite, such as the first efficiency and cycle performance.

[0035] Preferably, the temperature of the preliminary reaction is 150-250° C.; and the pressure is preferably 1-5 MPa.

[0036] Preferably, the pre-reaction time is 2-5 hours.

[0037] In the present invention, after the pre-reaction treatment, the temperature is continued to be raised to the supercritical state of water to carry out the reduction reaction mediated by supercritical water.

[0038] Preferably, the temperature of the supercritical reduction reaction stage is 400-800° C., and the pressure is 20-50 MPa; more preferably, the temperature is 400-600° C., and the pressure is 25-50 MPa.

[0039] Preferably, the supercritical reduction reaction stage is 15 minutes to 5 hours; more preferably, 0.5 to 2 hours.

[0040] In the present invention, existing means can be used to recover graphite from the supercritical reaction system.

[0041] Preferably, in the present invention, after supercritical treatment, the solution is directly subjected to solid-liquid separation, or is pre-screened and then subjected to solid-liquid separation, the slurry before solid-liquid separation and / or the solid after solid-liquid separation is subjected to acid treatment, and then washed with water and dried to obtain treated graphite.

[0042] For example, when the material to be processed contains a current collector, the supercritical reduction system can be pre-screened to separate the current collector, followed by solid-liquid separation. The size of the sieve can be determined based on the specific material, sufficient to separate the current collector and the treated graphite slurry. For example, the mesh size can be 200-400 mesh. If the material to be processed does not contain a current collector, screening is not required.

[0043] In the present invention, the slurry before solid-liquid separation (the slurry after screening or the supercritical reaction system without screening) or the solid after solid-liquid separation can be subjected to acid treatment. For example, acid treatment can be performed by adding an acid solution to the supercritical reaction system or the slurry after screening (the slurry before solid-liquid separation), followed by solid-liquid separation, and the separated solid is washed with water and dried to obtain the treated graphite; or the solid after solid-liquid separation is subjected to acid treatment, washing with water, and drying to obtain the recovered graphite.

[0044] The acid in the acid solution for acid treatment is, for example, at least one of hydrochloric acid, nitric acid, and sulfuric acid. There is no particular requirement for the concentration of the acid solution, and it can be, for example, 0.01 to 2M.

[0045] When the slurry before solid-liquid separation is subjected to acid treatment, the acid solution is directly added to the slurry before solid-liquid separation, and the amount of acid added is such that the pH of the solution is controlled to be less than or equal to 3, preferably less than or equal to 2. When the solid after solid-liquid separation is washed with acid solution, the amount of acid used is such that the solid is immersed.

[0046] The degree of water washing is, for example, until the pH of the filtrate is 5-7.

[0047] In the present invention, the recovered graphite can be dried based on existing graphite drying means.

[0048] A preferred treatment method of the present invention comprises the following steps:

[0049] In the first step, waste lithium-ion battery negative electrode powder is placed in a supercritical reactor, and appropriate amounts of water, additives A, and additive B (fluoride) are added. The temperature and pressure are adjusted to carry out each stage of the pretreatment reaction. The waste lithium-ion battery negative electrode refers to any of the following: scrap electrode sheets from battery production, the carbon powder after copper recovery from powdering, negative electrode sheets from battery disassembly, the carbon powder after copper recovery from powdering, and negative electrode slurry scrapped from lithium-ion battery production. The solid-liquid ratio of the waste lithium-ion battery negative electrode to water is 0.1 to 40:100 (g:ml); preferably, the solid-liquid ratio of the battery to water is 10 to 30:100 (g:ml). The auxiliary agent A is one or more selected from methanol, ethanol, carbonates, ether, acetonitrile, acetone, etc.; the mass ratio of auxiliary agent A to the negative electrode of the waste lithium-ion battery is 0.5-10:100 (preferably 2-5:100); the fluoride is one or more selected from LiPF6, metal fluoride, or non-metal fluoride (such as ammonium fluoride, hydrogen fluoride, etc.); the mass percentage of fluoride to the negative electrode of the waste lithium-ion battery is 0.05-1:100 (preferably 0.2-0.5:100). The pretreatment temperature is 120-300°C, the pressure is 1-5 MPa, and the reaction time is 2-5 hours.

[0050] The second step is to increase the reaction temperature and pressure so that the water therein is in a supercritical state and start a supercritical reduction reaction; the supercritical reaction conditions are: temperature of 400-800°C, pressure of 20-50 MPa, and supercritical reaction time of 15 min to 5 h; preferably, the supercritical reaction temperature is 400-600°C, pressure of 25-50 MPa, and supercritical reaction time is 0.5-2 h.

[0051] In the third step, after the supercritical reduction reaction is completed, the slurry is shaken and separated to obtain the oversize material (copper foil) and undersize slurry respectively;

[0052] In the fourth step, the undersize slurry is subjected to conventional acid leaching and water washing processes, followed by solid-liquid separation. The resulting filter cake is then dried and dispersed to obtain high-purity graphite powder. The acid leaching and water washing of the undersize slurry refers to adding 0.01-2M hydrochloric acid, nitric acid, or sulfuric acid to the slurry and reacting it at room temperature to 60°C for 0.5-2 hours. The water washing process involves washing the filter cake multiple times with deionized water until the filtrate has a pH of 5-7. The drying process involves drying the filter cake at 120-220°C for 8-24 hours.

[0053] The method of the present invention innovatively carries out a pre-reaction and a supercritical water reducing atmosphere with the assistance of the auxiliary agent A and the auxiliary agent B, which can produce synergy, obtain high-purity graphite, and obtain a graphite material with high electrochemical performance. The mechanism is mainly:

[0054] The pretreatment is carried out in cooperation with the auxiliary agent A and the auxiliary agent B, and the graphite can be subjected to controllable micro-oxidation and layer expansion treatment. The temperature is further raised to the supercritical condition of water, and a supercritical water-mediated reduction reaction can be carried out with the assistance of the auxiliary agent. For example, the auxiliary agent A will undergo the following gasification reaction, and in the critical reaction system, a reducing environment is formed (the hydrogen and carbon monoxide formed constitute a reducing system), and the graphite is reduced to a highly ordered graphite with a regular structure. At the same time, the impurity metal ions are separated and dissolved from the graphite material.

[0055] In the present invention, reducing gas is generated in the supercritical system, thereby reducing the metal impurities remaining in the negative electrode of the waste lithium-ion battery, creating conditions for subsequent low-acid leaching of related metal impurities and obtaining high-purity graphite. In addition, the supercritical reducing atmosphere helps to transform the structure and chemical properties of graphite, and helps to improve its electrochemical performance.

[0056] The present invention also provides a method for regenerating graphite negative electrodes of waste batteries. The treated graphite is obtained by the method and then used as a negative electrode active material for assembling batteries.

[0057] Beneficial effects:

[0058] ① The present invention provides a new waste graphite recovery method, which performs pre-reaction and supercritical water reduction treatment with the synergistic assistance of additives A and B. This can achieve synergy between materials and operations, help purify graphite, and promote the reconstruction of its physical structure and chemical activity; thereby improving the purity and electrochemical properties of the recovered graphite. In addition, the present invention can directly process leftover electrode sheets generated in the lithium-ion battery industry, negative electrode sheets obtained from battery disassembly, carbon powder after copper recovery from negative electrode sheet powdering, and negative electrode slurry scrapped in lithium-ion battery production, and is simple to operate.

[0059] ② The technical solution of the present invention can obtain high-purity, high-graphitization graphite materials; research has found that the processed graphite has a fixed carbon content of more than 99.92% and a graphitization degree of more than 90% high-purity graphite; in addition, the processed graphite has excellent electrochemical properties.

[0060] ③ According to the technical solution of the present invention, the negative electrode that has not been stripped can still be processed by the method of the present invention, and high-quality graphite materials can also be obtained. It can also achieve full recovery of valuable components such as copper in the negative electrode of waste batteries.

[0061] ④ The reaction conditions are easy to control, the treatment is simple, the process is short, and it is easy to produce on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 SEM images of the raw materials used in Example 1;

[0063] Figure 2 This is the SEM image of the graphite powder obtained after treatment in Example 1;

[0064] Figure 3 This is the XRD pattern of the graphite powder obtained after treatment in Example 1;

[0065] Figure 4 This is the SEM image of the graphite powder obtained in Comparative Example 1;

[0066] Figure 5 This is a macroscopic photograph of the raw materials used in Example 2;

[0067] Figure 6 This is the SEM image of the graphite powder in the raw materials used in Example 2;

[0068] Figure 7 This is the SEM image of the graphite powder obtained in Example 2;

[0069] Figure 8 This is the SEM image of the graphite powder obtained in Comparative Example 2.

[0070] Figure 9 This is the TEM image of the graphite powder obtained in Comparative Example 5.

[0071] Figure 10 This is the SEM image of the graphite powder obtained in Comparative Example 10. DETAILED DESCRIPTION

[0072] The present invention will be further described in detail below with reference to specific examples, but the present invention is not limited to the following examples.

[0073] In the following case, CR2025 button cells were assembled in an argon-filled dry glove box in accordance with GB / T 24533-2009, using the obtained graphite electrode as the working electrode, metallic lithium as the negative electrode, 1 mol / L LiPF6 in EC / EMC (volume ratio 1:1) as the electrolyte, and a PE-PP composite membrane as the separator. Electrochemical performance was tested at room temperature in the voltage range of 0.001-2.0 V, and the charge and discharge tests were performed at a current density of 0.2C.

[0074] The treatment objects used in the following cases are merely examples of the implementation of the technical solution of the present invention and do not constitute a limitation on the scope of protection of the present invention:

[0075] Example 1:

[0076] Using the negative electrode sheets produced in the production of lithium-ion batteries as raw materials, high-purity graphite powder is prepared based on the technology of the present invention:

[0077] The scraps in this case were prepared by dissolving graphite, binder (PVDF), and conductive carbon black in NMP at a mass ratio of 95:2.5:2.5, then coating the mixture on copper foil and dried electrode scraps. The scraps were ultrasonically dissolved in NMP, and the copper foil was separated to obtain dry carbon powder (main components: graphite, binder, and conductive carbon black). The separated carbon powder was processed as follows:

[0078] ① Place 8g of carbon powder recovered from the powdered copper of the negative electrode corners in a supercritical reactor. Add 1000mL of water, 0.32g of methanol, and 0.032g of hydrogen fluoride into the reactor, seal the reactor, and heat the reactor in a heating furnace. Maintain the reactor temperature at 150°C and the pressure at 2MPa. React under these conditions for 3h.

[0079] ②Then the temperature and pressure of the reactor were raised to 450℃ and 25MPa respectively, and the reaction was carried out under these conditions for 30 minutes;

[0080] ③ After the reactor is cooled, add 0.01M hydrochloric acid (to make the reaction liquid pH = 1) and stir the reaction at 30°C for 1 hour, then filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5, filter and dry at 180 degrees for 2 hours to obtain high-purity graphite powder.

[0081] The analysis found that:

[0082] ① The surface of the obtained graphite powder is clean, and no amorphous small particles of carbon and other impurities are found (see Figure 2 );

[0083] ② XRD showed that the obtained graphite powder had a complete graphite structure (see Figure 3 );

[0084] ③Electrochemical tests showed that the obtained material exhibited a first efficiency of 93.6% and a reversible specific capacity of 362mAh / g when used as the negative electrode of lithium-ion batteries.

[0085] ④ The obtained graphite powder has a fixed carbon content of 99.95% and a graphitization degree of 93%.

[0086] Example 2:

[0087] High-purity graphite powder is prepared based on the technology of the present invention using negative electrode sheets obtained from dismantling waste lithium-ion batteries (the waste lithium-ion batteries are mechanically dismantled and manually sorted to obtain waste negative electrode sheets, and the ratio of original graphite, conductive agent (conductive carbon black), and binder (PVDF) in the negative electrode sheets is 95:3:2; in addition, no additional electrolyte recovery treatment is performed on the dismantled negative electrode sheets).

[0088] ① Place 150g of the waste graphite negative electrode obtained by disassembling the above-mentioned waste battery in a supercritical reactor, introduce 1000mL of water, 7.5g of acetone, and 0.75g of lithium fluoride into the reactor, seal the reactor, turn on the heating furnace to heat the reactor, maintain the reactor temperature at 180°C and the pressure at 1MPa, and react under these conditions for 2h;

[0089] ②Then raise the temperature and pressure of the reactor to 500℃ and 30MPa respectively, and react under this condition for 1h;

[0090] ③ After the reactor is cooled, place it in a vibration separator and pass it through a 325-mesh sieve. The material on the sieve is copper powder;

[0091] ④ Add 0.02M sulfuric acid (control the pH of the solution to 2) to the slurry under the sieve, stir and react at 30°C for 0.5h, then filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 6.5, filter and dry at 200 degrees for 12h to obtain high-purity graphite powder.

[0092] The analysis found that:

[0093] ① Comparing the SEM images before and after treatment, it is found that the surface of the graphite powder obtained after treatment with the technology of the present invention is clean, and no small particles of conductive agent are found in the powder (comparison Figure 6 and Figure 7 );

[0094] ② XRD shows that the obtained graphite powder has a complete graphite structure. Figure 3 same;

[0095] ③Electrochemical tests showed that the obtained material exhibited a first efficiency of 92.6% and a reversible specific capacity of 358mAh / g when used as the negative electrode of lithium-ion batteries.

[0096] ④ The obtained graphite powder has a fixed carbon content of 99.94% and a graphitization degree of 94%.

[0097] Example 3:

[0098] Processing of negative electrode slurry from scraps:

[0099] The negative electrode slurry of the scraps is obtained by ultrasonically dissolving the negative electrode sheets (same as in Example 1) produced in the production of lithium-ion batteries with NMP and separating the copper foil.

[0100] ① Place 200g (solid content 70wt%) of negative electrode slurry in the reactor, introduce 1000mL of water, 6g of diethyl carbonate, and 0.6g of ammonium fluoride into the reactor, seal the reactor, turn on the heating furnace to heat the reactor, maintain the reactor temperature at 200℃ and the pressure at 2.5MPa, and react under these conditions for 4h;

[0101] ②Then the temperature and pressure of the reactor were raised to 550℃ and 35MPa respectively, and the reaction was carried out under these conditions for 1h;

[0102] ③ After the reactor is cooled, 0.05M nitric acid is added (to adjust the pH of the solution to 1) and the reaction is stirred at 40°C for 0.5h. Then, the solid-liquid separation is achieved by suction filtration. The filter cake is rinsed with deionized water to a pH of 5.5. After filtration, it is dried at 200 degrees for 12h to obtain high-purity graphite powder.

[0103] The analysis found that:

[0104] ① The fixed carbon content of the obtained graphite powder is 99.95% and the degree of graphitization is 95%;

[0105] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 94.6% and a reversible specific capacity of 356mAh / g when used as the negative electrode of lithium-ion batteries.

[0106] Example 4:

[0107] ① 250 g of carbon powder (same as in Example 1) obtained by recovering copper from the powdered corners of the negative electrode sheet was placed in a supercritical reactor. 1000 mL of water, 10 g of propanol, and 1 g of calcium fluoride were introduced into the reactor, and the reactor was sealed. The reactor was heated in a heating furnace, maintaining the reactor temperature at 250° C. and the pressure at 3 MPa. The reaction was carried out under these conditions for 2 h.

[0108] ②Then raise the temperature and pressure of the reactor to 600℃ and 20MPa respectively, and react under this condition for 2h;

[0109] ③ After the reactor is cooled, add 0.01M hydrochloric acid (to adjust the pH of the solution to 0.5) and stir the reaction at 50°C for 0.5h. Then, filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 7. After filtration, dry it at 220 degrees for 12h to obtain high-purity graphite powder.

[0110] The analysis found that:

[0111] ① The fixed carbon content of the obtained graphite powder is 99.98% and the degree of graphitization is 96%;

[0112] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 95.6% and a reversible specific capacity of 361mAh / g when used as the negative electrode of lithium-ion batteries.

[0113] Example 5:

[0114] ① 300 g of carbon powder (same as in Example 1) obtained by recovering copper from the powdered corners of the negative electrode sheet was placed in a supercritical reactor. 1000 mL of water, 7.5 g of methanol, and 0.75 g of hydrogen fluoride were introduced into the reactor, and the reactor was sealed. The reactor was heated in a heating furnace, and the reactor temperature was maintained at 300 ° C and the pressure was 5 MPa. The reaction was carried out under these conditions for 5 h.

[0115] ②Then the temperature and pressure of the reactor were raised to 650℃ and 40MPa respectively, and the reaction was carried out under these conditions for 30 minutes;

[0116] ③ After the reactor is cooled, add 1.5M hydrochloric acid (to adjust the pH of the solution to 1) and stir the reaction at 40°C for 1 hour. Then, filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5. After filtering, dry it at 120 degrees for 24 hours to obtain high-purity graphite powder.

[0117] The analysis found that:

[0118] ① The fixed carbon content of the obtained graphite powder is 99.97% and the degree of graphitization is 94%;

[0119] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 94.6% and a reversible specific capacity of 362mAh / g when used as the negative electrode of lithium-ion batteries.

[0120] Example 6:

[0121] The difference from Example 5 is that an auxiliary agent A incorporating methanol and diethyl carbonate is used. The different steps are as follows: ① 300 g of carbon powder recovered from copper powdered from the negative electrode edge (same as in Example 5) is placed in a supercritical reactor. 1000 mL of water, 2.5 g of methanol, 5 g of diethyl carbonate, and 0.75 g of hydrogen fluoride are introduced into the reactor, and the reactor is sealed. The reactor is heated in a heating furnace, maintaining the reactor temperature at 300° C. and the pressure at 5 MPa. The reaction is carried out under these conditions for 5 hours. Other conditions are the same as in Example 5.

[0122] The analysis found that:

[0123] ① The fixed carbon content of the obtained graphite powder is 99.98% and the degree of graphitization is 95%;

[0124] ②Electrochemical tests showed that the obtained material, when used as the negative electrode of lithium-ion batteries, exhibited a first efficiency of 95.8% and a reversible specific capacity of 365mAh / g.

[0125] The use of combined additives A can unexpectedly achieve synergy and further improve the purity and electrochemical performance of graphite.

[0126] Example 7:

[0127] The difference from Example 5 is that an auxiliary agent B of a combination of hydrogen fluoride and ammonium fluoride is used. The difference is that step ① is: 300 g of carbon powder obtained by recovering copper from the edge negative electrode sheet (same as in Example 5) is placed in a supercritical reactor, 1000 mL of water, 7.5 g of methanol, 0.25 g of hydrogen fluoride, and 0.5 g of ammonium fluoride are introduced into the reactor, and the reactor is sealed. The heating furnace is turned on to heat the reactor, and the reactor temperature is maintained at 300°C and the pressure is 5 MPa. The reaction is carried out under these conditions for 5 hours; the other steps are the same as in Example 5.

[0128] The analysis found that:

[0129] ① The fixed carbon content of the obtained graphite powder is 99.98% and the degree of graphitization is 96%;

[0130] ②Electrochemical tests showed that the obtained material, when used as the negative electrode of lithium-ion batteries, exhibited a first efficiency of 95.5% and a reversible specific capacity of 366mAh / g.

[0131] The use of combined additives A can unexpectedly achieve synergy and further improve the purity and electrochemical performance of graphite.

[0132] Example 8:

[0133] Compared with Example 5, the only difference is that the conditions of the pre-reaction are changed. The difference is ① that 300 g of carbon powder obtained by recovering copper from the powdered corner negative electrode sheet (same as Example 5) is placed in a supercritical reactor, 1000 mL of water, 7.5 g of methanol, and 0.75 g of hydrogen fluoride are introduced into the reactor, and the reactor is sealed. The heating furnace is turned on to heat the reactor, and the reactor temperature is maintained at 120°C and the pressure is 2 MPa. The reaction is carried out under these conditions for 2 hours; the other steps are the same as in Example 5.

[0134] The analysis found that:

[0135] ① The fixed carbon content of the obtained graphite powder is 99.92% and the degree of graphitization is 92%;

[0136] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 93.4% and a reversible specific capacity of 355mAh / g when used as the negative electrode of lithium-ion batteries.

[0137] Example 9:

[0138] Compared with Example 5, the only difference is that the conditions of the pre-reaction are changed. The difference is that step ① is to place 300 g of carbon powder obtained by powdering the negative electrode sheets from the corners and recovering copper (the same as in Example 5) in a supercritical reactor, and after 1000 mL of water, 7.5 g of methanol, and 0.75 g of hydrogen fluoride are passed into the reactor, the reactor is sealed, and the heating furnace is turned on to heat the reactor, maintaining the reactor temperature at 150°C and the pressure at 3 MPa, and reacting under these conditions for 3 hours; the rest is the same as in Example 5.

[0139] The analysis found that:

[0140] ① The fixed carbon content of the obtained graphite powder is 99.95% and the degree of graphitization is 93%;

[0141] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 94.2% and a reversible specific capacity of 358mAh / g when used as the negative electrode of lithium-ion batteries.

[0142] Example 10:

[0143] Using natural flake graphite (purity 89.3%, degree of graphitization 91%) as raw material, high-purity graphite powder is prepared based on the technology of the present invention.

[0144] ① Place 350g of natural flake graphite powder in a supercritical reactor, introduce 1000mL of water, 7.5g of methanol, and 1g of hydrogen fluoride into the reactor, seal the reactor, turn on the heating furnace to heat the reactor, maintain the reactor temperature at 150°C and the pressure at 3MPa, and react under these conditions for 3h;

[0145] ②Then the temperature and pressure of the reactor were raised to 650℃ and 40MPa respectively, and the reaction was carried out under these conditions for 30 minutes;

[0146] ③ After the reactor is cooled, add 50 ml of 1.5 M hydrochloric acid and stir the reaction at 40 ° C for 1 hour, then filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5, filter and dry at 120 degrees for 24 hours to obtain high-purity graphite powder.

[0147] ④ The obtained high-purity graphite powder is subjected to conventional spheroidization treatment to obtain spherical natural graphite with a median particle size d50 = 15 μm; the spherical graphite is then mixed with asphalt in a mass ratio of 95:5 and sintered (from room temperature to 1150°C under argon atmosphere and kept at this temperature for 2 hours) to obtain modified natural graphite.

[0148] The analysis found that:

[0149] ① The fixed carbon content of the obtained graphite powder is 99.95% and the degree of graphitization is 94%;

[0150] ②Electrochemical tests showed that the modified natural graphite exhibited a first efficiency of 93.8% and a reversible specific capacity of 353 mAh / g when used as the negative electrode of lithium-ion batteries.

[0151] Comparative Example 1:

[0152] Compared with Example 1, the main difference is that the pretreatment and supercritical reduction treatment assisted by A and B are not performed. The main difference is:

[0153] The carbon powder used in Example 1 was placed in a mixed acid of 1M hydrochloric acid solution and 0.2M nitric acid with a liquid-to-solid ratio of 3:1. After stirring at room temperature for 4 hours, the mixture was filtered to achieve solid-liquid separation. The filter cake was rinsed with deionized water to a pH of 5.5, filtered, and dried at 180 degrees for 2 hours to obtain graphite powder.

[0154] The analysis found that:

[0155] ① The surface of the obtained graphite powder has small carbon particles (see Figure 4 );

[0156] ②The fixed carbon content of the obtained material is 79.2% and the degree of graphitization is 60.3%;

[0157] ③Electrochemical tests showed that the obtained material had an initial efficiency of 61.2% and a reversible specific capacity of 208 mAh / g.

[0158] Comparative Example 2:

[0159] Compared with Example 2, the only difference is that the negative electrode sheet is not subjected to the pretreatment and supercritical reduction treatment assisted by A and B. The main reasons are:

[0160] The disassembled electrode (same as in Example 2) was directly placed in a 1M hydrochloric acid and 0.1M nitric acid solution with a liquid-to-solid ratio of 3:1. After stirring at room temperature for 6 hours, it was filtered to achieve solid-liquid separation. The filter cake was rinsed with deionized water to pH 6.5, filtered, and dried at 200 degrees for 12 hours to obtain graphite powder.

[0161] Figure 8 is the SEM picture of the graphite powder obtained in this comparative example, and Figure 7 Comparative analysis revealed the presence of small carbon particles on the surface of graphite powder obtained without supercritical treatment. The fixed carbon content was 82.1%, and the degree of graphitization was 62.4%. Electrochemical testing showed that the resulting material had an initial efficiency of 60.5% and a reversible specific capacity of 215 mAh / g.

[0162] Comparative Example 3:

[0163] Compared with Example 3, the only difference is that the negative electrode sheet is not subjected to the pretreatment and supercritical reduction treatment assisted by A and B. The main reasons are:

[0164] The scrapped negative electrode slurry (same as in Example 3) was directly placed in 1M hydrochloric acid with a liquid-to-solid ratio of 3:1. After stirring at 60 degrees for 2 hours, it was filtered to achieve solid-liquid separation. The filter cake was rinsed with deionized water to a pH of 5.5. After filtration, it was dried at 200 degrees for 12 hours to obtain graphite powder.

[0165] Tests show that its fixed carbon content is 80.1% and its graphitization degree is 61.2%. When the graphite powder is used as a lithium-ion battery, its initial efficiency is only 70.1% and its reversible specific capacity is 238 mAh / g. The main reason is that the conductive carbon is not removed.

[0166] Comparative Examples 1-3 show that conventional acid treatment cannot effectively improve the fixed carbon content and graphitization degree of the waste battery negative electrode material, that is, the obtained carbon material has low purity and low graphitization degree; when directly used as a negative electrode material for lithium-ion batteries, the electrochemical performance is poor.

[0167] Comparative Example 4:

[0168] Compared with Example 5, the only difference is that the additive A is not added. The difference is step ①: 300 g of carbon powder obtained by recovering copper from the negative electrode sheet by powdering (same as Example 5) is placed in a supercritical reactor, 1000 mL of water and 0.75 g of hydrogen fluoride are introduced into the reactor, and the reactor is sealed. The heating furnace is turned on to heat the reactor, and the reactor temperature is maintained at 300° C. and the pressure is 5 MPa. The reaction is carried out under these conditions for 5 hours. The other steps are the same as in Example 5, and the identification and performance measurement are carried out using the method of Example 5.

[0169] The analysis found that:

[0170] ① The fixed carbon content of the obtained graphite powder is 79.98%, and the degree of graphitization is 73%;

[0171] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 75.2% and a reversible specific capacity of 232mAh / g when used as the negative electrode of lithium-ion batteries.

[0172] Comparative Example 5:

[0173] Compared with Example 5, the only difference is that the additive B is not added. The difference is the following step: ① 300 g of carbon powder obtained by recovering copper from the edge negative electrode sheet (same as in Example 5) is placed in a supercritical reactor, 1000 mL of water and 7.5 g of methanol are introduced into the reactor, and the reactor is sealed. The heating furnace is turned on to heat the reactor, maintaining the reactor temperature at 300° C. and the pressure at 5 MPa, and reacting under these conditions for 5 hours; the other steps are the same as in Example 5, and the identification and performance measurement are carried out using the method of Example 5;

[0174] The analysis found that:

[0175] ① The fixed carbon content of the obtained graphite powder is 86.4% and the degree of graphitization is 72%;

[0176] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 74.6% and a reversible specific capacity of 212mAh / g when used as the negative electrode of lithium-ion batteries.

[0177] Without adding fluoride, the fixed carbon content of the obtained material reaches more than 80%, but its graphitization degree is also low. Figure 9 ) shows that when no fluoride is added, nano-scale conductive carbon remains in the obtained material, thereby reducing the degree of graphitization of the obtained carbon material.

[0178] It can be seen from Example 5, Comparative Example 4 and Comparative Example 5 that, with the assistance of additives A and B, they can work together and can be treated based on the auxiliary pre-oxidation and supercritical water reduction mechanism, which can achieve synergy, improve the purity of graphite, and unexpectedly reconstruct the physical and chemical structure, which helps to improve performance.

[0179] Comparative Example 6:

[0180] Compared with Example 5, the only difference is that the pretreatment reaction of the first step is not carried out, specifically:

[0181] ① 300 g of carbon powder (same as in Example 5) obtained by powdering and recovering copper from the negative electrode edge was placed in a supercritical reactor. 1000 mL of water, 7.5 g of methanol, and 0.75 g of hydrogen fluoride were introduced into the reactor, and the reactor was sealed. The heating furnace was turned on to heat the reactor, and the temperature and pressure of the reactor were maintained at 650 ° C and 40 MPa, respectively. The reaction was carried out under these conditions for 30 minutes. The other subsequent steps were the same as in Example 5.

[0182] The analysis found that:

[0183] ① The fixed carbon content of the obtained graphite powder is 72.8% and the degree of graphitization is 66%;

[0184] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 74.2% and a reversible specific capacity of 242mAh / g when used as the negative electrode of lithium-ion batteries.

[0185] It shows that if the material is directly subjected to supercritical reaction without the first step of pretreatment, the effect is not good, which is reflected in the high impurity content and low degree of graphitization of the obtained material; this shows that the layer expansion effect of pretreatment is a necessary prerequisite for achieving the supercritical reaction effect.

[0186] Comparative Example 7:

[0187] Compared with Example 5, the only difference is that the second step supercritical reaction is not performed, specifically:

[0188] ① Place 300g of carbon powder recovered from the powdered copper of the negative electrode corners in a supercritical reactor. Add 1000mL of water, 7.5g of methanol, and 0.75g of hydrogen fluoride into the reactor, seal the reactor, and heat the reactor in a heating furnace. Maintain the reactor temperature at 300℃ and the pressure at 5MPa. React under these conditions for 5h.

[0189] ② After the reactor is cooled, add 1.5M hydrochloric acid (to adjust the pH of the solution to 1) and stir the reaction at 40°C for 1 hour. Then, filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5. After filtration, dry it at 120 degrees for 24 hours to obtain high-purity graphite powder.

[0190] The analysis found that:

[0191] ① The fixed carbon content of the obtained graphite powder is 59.9% and the degree of graphitization is 53%;

[0192] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 61.6% and a reversible specific capacity of 182mAh / g when used as the negative electrode of lithium-ion batteries.

[0193] It shows that: without supercritical reaction, only pretreatment at low temperature and low pressure cannot achieve good treatment effect.

[0194] Comparative Example 8:

[0195] Compared with Example 5, the only difference is that the supercritical reaction conditions of the second step are not reached, specifically:

[0196] ① Place 300g of carbon powder recovered from the powdered copper of the negative electrode corners in a supercritical reactor. Add 1000mL of water, 7.5g of methanol, and 0.75g of hydrogen fluoride into the reactor, seal the reactor, and heat the reactor in a heating furnace. Maintain the reactor temperature at 300℃ and the pressure at 5MPa. React under these conditions for 5h.

[0197] ②Then the temperature and pressure of the reactor were raised to 650℃ and 5MPa respectively, and the reaction was carried out for 30 minutes under these conditions;

[0198] ③ After the reactor is cooled, place it in a vibration separator and pass it through a 325-mesh sieve. The material on the sieve is copper powder;

[0199] ④ Add 1.5M hydrochloric acid to the slurry under the sieve and stir the reaction at 40°C for 1 hour, then filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5, filter and dry at 120 degrees for 24 hours to obtain high-purity graphite powder.

[0200] The analysis found that:

[0201] ① The fixed carbon content of the obtained graphite powder is 62.1%, and the degree of graphitization is 64%;

[0202] ②Electrochemical tests showed that the obtained material exhibited a first efficiency of 65.6% and a reversible specific capacity of 202mAh / g when used as the negative electrode of lithium-ion batteries.

[0203] It shows that the second step did not reach the supercritical reaction conditions, the reaction system was difficult to reduce graphite well, and the various indicators of the obtained material were poor.

[0204] Comparative Example 9:

[0205] Compared with Example 5, the only difference is that the supercritical reaction in the oxidizing atmosphere is:

[0206] ① Place 300g of carbon powder recovered from the copper powder of the negative electrode edge in a supercritical reactor. After 1000mL of water, 10g of hydrogen peroxide, and 0.75g of hydrogen fluoride are introduced into the reactor, the reactor is sealed, and the heating furnace is turned on to heat the reactor. Oxygen is introduced into the system, and the reactor temperature is maintained at 300℃ and the pressure is 5MPa. The reaction is carried out under these conditions for 5h.

[0207] ②Then the temperature and pressure of the reactor were raised to 650℃ and 40MPa respectively, and the reaction was carried out under these conditions for 30 minutes;

[0208] ③ After the reactor is cooled, place it in a vibration separator and pass it through a 325-mesh sieve. The material on the sieve is copper powder;

[0209] ④ Add 1.5M hydrochloric acid to the slurry under the sieve and stir the reaction at 40°C for 1 hour, then filter to achieve solid-liquid separation. Rinse the filter cake with deionized water to pH 5.5, filter and dry at 120 degrees for 24 hours to obtain high-purity graphite powder.

[0210] The results show that:

[0211] ① The slurry obtained in step ④ is relatively viscous and very difficult to filter, and has a strong affinity for water; the material after drying is relatively fluffy and has a low tap density.

[0212] ② The obtained graphite powder has a fixed carbon content of 77.2%, an oxygen content of 20.1%, and a degree of graphitization of 54%;

[0213] ③Electrochemical tests showed that the obtained material exhibited a first efficiency of 44.1% and a reversible specific capacity of 232mAh / g when used as the negative electrode of lithium-ion batteries.

[0214] This indicates that the supercritical reaction under oxidizing conditions will cause the material to be strongly oxidized, and the surface of the material will show strong hydrophilicity, with a low fixed carbon content, a high oxygen content, and a low degree of graphitization.

[0215] Comparative Example 10: Using supercritical carbon dioxide system

[0216] Compared with Example 5, the only difference is that a supercritical carbon dioxide reaction system is used, specifically:

[0217] ① 300 g of carbon powder (same as in Example 5) obtained by powdering and recovering copper from the corner negative electrode sheet was placed in a supercritical reactor. 1000 ml of carbon dioxide (the carbon dioxide was cooled to a liquid state using a refrigerator and then pumped into the reactor), 10 g of hydrogen peroxide, and 0.75 g of hydrogen fluoride were introduced into the reactor. The reactor was sealed and heated in a heating furnace. Carbon dioxide gas was introduced into the system while maintaining the reactor temperature at 300°C and the pressure at 5 MPa. The reaction was continued for 5 h.

[0218] ② Cool the system and adjust the temperature and pressure to 40°C and 20 MPa respectively, and react for 30 minutes;

[0219] ③ After the reactor is cooled and the pressure is reduced, a solid is obtained. Then, 1.5 M hydrochloric acid is added and stirred at 40°C for 1 hour, and then filtered to achieve solid-liquid separation. The filter cake is rinsed with deionized water to pH 5.5, filtered, and dried at 120 degrees for 24 hours to obtain a powder.

[0220] The results show that:

[0221] ① The obtained powder material is relatively fluffy and has a low tap density; and from its SEM image ( Figure 10 ) It can be seen that the graphite has undergone a certain degree of exfoliation, resulting in the appearance of flakes.

[0222] ② The obtained graphite powder has a fixed carbon content of 81.4%, an oxygen content of 10.5%, and a degree of graphitization of 62%;

[0223] ③Electrochemical tests showed that the obtained material exhibited a first efficiency of 51% and a reversible specific capacity of 312mAh / g when used as the negative electrode of lithium-ion batteries.

[0224] This shows that in the supercritical carbon dioxide system, the obtained material has a higher specific surface area, lower fixed carbon content, higher oxygen content and lower degree of graphitization.

Claims

1. A graphite critical water reaction treatment method, characterized in that, A mixed solution of the material to be treated containing graphite, additive A, additive B, and water is placed in a pressure-resistant container for pre-reaction, and then the temperature is continuously raised to the supercritical state of water to perform a supercritical reduction reaction, and the treated graphite is collected after the reaction is completed; The auxiliary agent A is at least one of alcohol, ether, ester, nitrile and ketone; The auxiliary agent B is a compound containing F; The temperature of the pre-reaction is 120-300° C., and the pressure is 1-5 MPa.

2. The graphite critical water reaction treatment method according to claim 1, wherein The graphite is at least one of natural graphite and waste graphite.

3. The graphite critical water reaction treatment method according to claim 2, wherein The waste graphite is at least one of graphite negative electrode active materials separated from waste batteries, graphite scraps from production, cuttings of graphite negative electrode sheets of lithium-ion batteries, and graphite crucible waste.

4. The graphite critical water reaction treatment method according to claim 1, wherein The material to be processed may also contain at least one of a conductive agent, a binder, an electrolyte, a current collector, and a separator.

5. The graphite critical water reaction treatment method according to claim 1, wherein The material to be processed is at least one of graphite negative electrode active materials stripped from waste batteries, graphite negative electrode black powder, graphite negative electrode slurry, and graphite negative electrode sheets.

6. The graphite critical water reaction treatment method according to claim 5, wherein The waste batteries are waste lithium-ion batteries.

7. The graphite critical water reaction treatment method according to claim 1, wherein The auxiliary agent A is at least one of alcohol, ether, ester, nitrile and ketone with a carbon number less than or equal to 20.

8. The graphite critical water reaction treatment method according to claim 7, wherein: The auxiliary agent A is at least one of alcohol, ether, ester, nitrile and ketone with a carbon number less than or equal to 10.

9. The graphite critical water reaction treatment method according to claim 8, wherein The alcohol is at least one of a C1 to C6 unit or a polyol; The ether is at least one of a C2-C6 monoether, polyether or cyclic ether; The ester is C2~C 10 Carboxylic acid esters, C3~C 10 At least one of the carbonates; The nitrile is a C2~C4 nitrile; The ketone is C3~C 10 At least one of monoketones, polyketones, and cyclic ketones.

10. The graphite critical water reaction treatment method according to claim 9, wherein The auxiliary agent A is at least one of methanol, ethanol, carbonate, ether, acetonitrile and acetone.

11. The graphite critical water reaction treatment method according to any one of claims 1, 7 to 10, wherein: The weight ratio of the auxiliary agent A to the material to be treated is 0.5-10:

100.

12. The graphite critical water reaction treatment method according to claim 11, wherein The weight ratio of the auxiliary agent A to the material to be treated is 2-5:

100.

13. The graphite critical water reaction treatment method according to claim 1, wherein The auxiliary agent B is at least one of HF, alkali metal fluoride, alkaline earth metal fluoride and ammonium fluoride.

14. The graphite critical water reaction treatment method according to claim 1 or 13, wherein: The weight ratio of the auxiliary agent B to the material to be treated is 0.05~1:

100.

15. The graphite critical water reaction treatment method according to claim 14, wherein: The weight ratio of the auxiliary agent B to the material to be treated is 0.2-0.5:

100.

16. The graphite critical water reaction treatment method according to claim 1, wherein: In the mixed liquid, the solid-liquid ratio of the material to be treated to water is 0.1~40g / 100ml.

17. The graphite critical water reaction treatment method according to claim 16, wherein: In the mixed liquid, the solid-liquid ratio of the material to be treated and water is 10~30g / 100ml.

18. The graphite critical water reaction treatment method according to claim 1, wherein: In the mixed solution, the pre-reaction time is 2-5 hours.

19. The graphite critical water reaction treatment method according to claim 1, wherein: The temperature of the supercritical reduction reaction stage is 400-800° C. and the pressure is 20-50 MPa.

20. The graphite critical water reaction treatment method according to claim 19, wherein: The supercritical reduction reaction stage is 15 minutes to 5 hours.

21. The graphite critical water reaction treatment method according to claim 19, wherein: After supercritical treatment, the solution is directly subjected to solid-liquid separation, or is pre-screened and then subjected to solid-liquid separation. The slurry before solid-liquid separation and / or the solid after solid-liquid separation are subjected to acid treatment, and then washed with water and dried to obtain treated graphite.

22. A method for regenerating graphite negative electrodes of waste batteries, characterized in that: The treated graphite is obtained by the method according to any one of claims 1 to 21, and then used as a negative electrode active material for assembling a battery.

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