Method for recycling graphite negative electrode material

Abstract

To overcome the low recycling rate of waste graphite negative electrodes and the environmental pollution caused by the incineration of waste PVC in the prior art, the present invention provides a method for recycling and reusing graphite negative electrode materials. The method comprises discharging and disassembling waste batteries to obtain graphite powder; coating the waste graphite powder with ultrafine powder; heat treating the coated waste graphite powder; washing the waste graphite powder and leaching metal ions; removing impurities from the leachate and recovering lithium carbonate; and heat treating the waste graphite. The method for recycling and reusing graphite negative electrode materials provided by the present invention reduces graphite loss and energy consumption, and has a short recovery cycle and high efficiency. Furthermore, by using the recovered untreated polyvinyl chloride as an auxiliary agent for recycling waste graphite negative electrodes, lithium recovery is achieved, while simultaneously reducing acid usage, wastewater generation, and treatment costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery material recycling, and in particular relates to a method for recycling and reusing graphite negative electrode materials. Background Art

[0002] Currently, used batteries are typically disassembled and sorted for recycling. However, due to the low added value of graphite, the negative electrode material, many factories resort to landfilling and incineration to dispose of used graphite negative electrode materials, resulting in a waste of resources. Current purification technologies for used graphite negative electrodes can be broadly divided into high-temperature calcination, acid leaching, and electrochemical methods. High-temperature calcination produces toxic gases and requires high temperatures, resulting in high energy consumption and increased recycling costs. Furthermore, high calcination temperatures produce numerous oxygen-containing functional groups on the graphite surface. As the temperature rises, the graphite loss rate and surface roughness also increase, further exacerbating graphite loss. Acid leaching typically involves calcination to separate copper foil from the used graphite, followed by inorganic acid leaching to remove metallic impurities from the used graphite. This method allows for efficient recovery of valuable metals from all components, but the waste liquid generated by acid leaching can pollute the environment. Electrochemical methods can only separate the current collector copper foil from the graphite active material, leaving the recovery of valuable metals unresolved. Some patent documents attempt to use chlorine gas at 1000-1100°C to convert high-boiling-point metals and oxides into low-boiling-point chlorides, thereby lowering the reaction temperature and saving energy. However, the chlorides produced by the reaction are toxic and can corrode equipment.

[0003] PVC and other materials have advantages such as light weight, waterproofness, moisture resistance, flame retardancy, and heat insulation, making them widely used in building materials, industrial products, and daily necessities. However, when treating waste plastics, especially chlorine-containing plastics, the incineration of PVC, which contains over 50% chlorine, releases large amounts of HCl gas and other chlorine-containing toxic pollutants, causing environmental damage. Currently, much plastic waste is disposed of similarly to other solid waste, primarily through landfill and incineration. Failure to promptly and properly treat waste plastics in landfills generates acidic and alkaline organic matter, and in severe cases, dissolves heavy metals from the waste. Thermal degradation is a PVC cracking technology. Under certain conditions or catalysis, in the absence or absence of oxygen, the material is heated to 350-900°C, converting it into gas, coke, and water. The HCl produced by pyrolysis catalyzes the thermal degradation reaction.

[0004] Scrapped lithium-ion battery anode materials contain not only copper and graphite, but also a high level of lithium. Typically, the lithium content in scrap graphite is 31 mg / g. The lithium in scrap graphite primarily exists in the form of Li2CO3, Li2O, LiF, ROCO2Li, and CH3OLi, which can be divided into water-soluble and water-insoluble lithium salts. Some components can be directly leached in deionized water, while others are embedded in the graphite layers and require acid reaction to recover the lithium from the intercalation. The metal ion content of the graphite anode after a single water wash is 0.1% to 2%, and the ash content is 1% to 5% by weight. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for recycling and reusing graphite negative electrode materials with high economic recovery value, energy saving and environmental protection, in order to address the problems of low recycling rate of waste graphite negative electrodes and environmental pollution caused by incineration of waste PVC in the prior art.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] A method for recycling and reusing graphite negative electrode materials is provided, comprising the following steps:

[0008] Coating of waste graphite negative electrode powder and PVC ultrafine powder;

[0009] Heat treatment of the coated waste graphite powder causes the metal elements to react with the chlorine element produced by thermal decomposition of PVC to obtain metal chloride salts;

[0010] Washing of waste graphite powder and leaching of metal ions;

[0011] Recovery and heat treatment of waste graphite powder.

[0012] Optionally, before the “coating of the waste graphite negative electrode powder with the PVC ultrafine powder”, the waste graphite negative electrode powder is heat treated at a heat treatment temperature of 150° C. to 350° C. and a heat treatment time of 0.5 to 3 hours.

[0013] Optionally, the particle size range of the ultrafine PVC powder is ≤1 μm.

[0014] Optionally, the mass proportion of the PVC ultrafine powder in the coated waste graphite powder is 0.5 to 10 wt%.

[0015] Optionally, the heating rate of the heat treatment of the coated waste graphite powder is 2 to 5° C. / min, the heat treatment temperature is 100 to 220° C., and the treatment time is 20 to 120 min.

[0016] Optionally, the coated waste graphite powder is heat-treated in a protective gas, where the protective gas is one or more of Ar, N2, and Kr.

[0017] Optionally, an impurity remover is added to the waste graphite powder washing leachate to remove impurities; and a lithium ion precipitant is added to the impurity-removed leachate to enrich the metal elements.

[0018] Optionally, the impurity remover is one or more of Na2S, K2S, NaHS, H2S, and BaS.

[0019] Optionally, the lithium ion precipitant is one or more of CO2, Na2CO3, K2CO3, NaHCO3

[0020] Optionally, the protective gas used in the heat treatment of the recycled waste graphite is one or more of Ar, N2, and Kr.

[0021] According to the method for recycling and reusing graphite negative electrode materials provided by the present invention, polyvinyl chloride plastic is initially thermally degraded to produce chlorine element, which is fused and coated with graphite after oxidative heat treatment. Lithium and other metal elements in the graphite negative electrode react with the chlorine element produced by the thermal degradation of polyvinyl chloride in a hot environment to convert metal and metal salt impurities in the graphite into easily soluble and soluble salts, which are then washed with water to remove impurities to obtain lithium carbonate. At the same time, the graphite is subjected to a short-term heat treatment to restore its layered structure, and the heat-treated graphite is then ground and sieved to obtain a recycled graphite product with uniform particle size. The preparation method of the present invention can realize the recovery of lithium element with good recovery effect, and also reduces the use of acid, reduces the generation of wastewater and saves costs. In addition, the method provided by the present invention can avoid long-term high-temperature calcination of waste graphite, reduce graphite loss, shorten the recovery cycle and achieve high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a charge and discharge curve diagram of a half-button battery prepared in Example 2 of the present invention;

[0023] Figure 2 This is a flow chart for recycling and reusing graphite negative electrode materials provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] An embodiment of the present invention provides a method for recycling and reusing graphite negative electrode materials, comprising the following steps:

[0026] Coating of waste graphite negative electrode powder and PVC ultrafine powder;

[0027] Heat treatment of the coated waste graphite powder causes the metal elements to react with the chlorine element produced by thermal decomposition of PVC to obtain metal chloride salts;

[0028] Washing of waste graphite powder and leaching of metal ions;

[0029] Recovery and heat treatment of waste graphite powder.

[0030] Specifically, the method for recycling and reusing graphite negative electrode materials utilizes chlorine generated by the initial thermal degradation of polyvinyl chloride plastic to fuse and coat graphite after oxidation and calcination. In a hot environment, metal elements such as lithium in the waste graphite negative electrode react with the chlorine generated by the thermal degradation of polyvinyl chloride to convert metal and metal salt impurities in the waste graphite into easily soluble and dissolvable salts. Lithium carbonate is then obtained by washing, leaching and removing impurities with water. At the same time, the graphite is subjected to a short-term heat treatment to restore its layered structure, effectively reducing recovery losses.

[0031] In an embodiment of the present invention, before the "coating of waste graphite negative electrode powder with PVC ultrafine powder" is performed, the waste graphite negative electrode powder is heat treated at a heat treatment temperature of 150° C. to 350° C. and a heat treatment time of 0.5 to 3 hours.

[0032] The calcination temperature is 300° C. and the calcination time is 1 hour. Long-term high-temperature calcination will aggravate the graphite recovery loss.

[0033] In an embodiment of the present invention, the particle size range of the ultrafine PVC powder is ≤1 μm.

[0034] The small particles in the PVC ultrafine powder can fully fill the gaps in the waste graphite negative electrode powder, making the coating denser, and helping the lithium and other metal elements in the waste graphite negative electrode powder to fully react with the chlorine element generated by the thermal degradation of polyvinyl chloride under a heating environment.

[0035] In the embodiment of the present invention, the mass proportion of the PVC ultrafine powder in the coated waste graphite powder is 0.5 to 10 wt%.

[0036] The solid content of the PVC is 5 wt %.

[0037] In the embodiment of the present invention, the heating rate of the heat treatment of the coated waste graphite powder is 2-5° C. / min, the heat treatment temperature is 100-220° C., and the treatment time is 20-120 min.

[0038] In an embodiment of the present invention, the coated waste graphite powder is heat-treated in a protective gas, and the protective gas is one or more of Ar, N2, and Kr.

[0039] The protective gas is N2. When the coated waste graphite powder is heat-treated, N2 is first introduced into the tetrafluoroethylene tank to exhaust other gases originally in the tank.

[0040] In an embodiment of the present invention, an impurity remover is added to the waste graphite powder washing leachate to remove impurities; and carbonate is added to the impurity-removed leachate to enrich metal elements.

[0041] In an embodiment of the present invention, the impurity remover in step five is one or more of Na2S, K2S, NaHS, H2S, and BaS.

[0042] The impurity remover is Na2S, which can remove trace copper impurities in the metal-rich leaching solution.

[0043] In an embodiment of the present invention, the lithium ion precipitant is one or more of CO2, Na2CO3, K2CO3, and NaHCO3.

[0044] The lithium ion precipitant is CO2, which enriches lithium elements to obtain lithium carbonate.

[0045] In an embodiment of the present invention, the protective gas used in the heat treatment of the recycled waste graphite is one or more of Ar, N2, and Kr.

[0046] Specifically, the protective gas Ar is introduced during the heat treatment of the recycled waste graphite. Ar can prevent S-Gra (graphene negative electrode powder) from reacting with other substances during the heating process, restore the graphite layered structure, effectively reduce the recovery loss, and achieve good recovery effect. In addition, Ar is an inert gas that is economical and readily available. The present invention is further illustrated by the following examples:

[0047] Example 1

[0048] This embodiment is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, comprising the following steps:

[0049] Waste graphite powder is obtained by discharging and dismantling waste batteries:

[0050] The waste lithium battery is placed in a 1.5 mol / L sodium chloride aqueous solution for discharge. When the battery voltage is lower than 1.5 V, the discharged battery is disassembled to obtain a negative electrode sheet. A certain mass of the negative electrode sheet is cut into pieces and placed in a ceramic crucible and then loaded into a box-type resistance furnace. The furnace temperature is raised to 300° C. at a heating rate of 3° C. / min at room temperature and kept warm for 1 hour. The calcined negative electrode sheet is sieved through a 20-mesh sieve. The material above the sieve is the copper current collector, and the material below the sieve is the waste graphite negative electrode material.

[0051] Coating of waste graphite negative electrode powder and ultrafine powder:

[0052] The PVC plastic was jet-milled into ultrafine powder with a particle size of 0.1 μm, and a certain amount of PVC ultrafine powder was weighed and blended with waste graphite negative electrode powder at a mixing speed of 2500 rpm / min and a mixing time of 15 min. The mass proportion of the PVC ultrafine powder was 3 wt%, and S-Gra@PVC mixed powder was obtained.

[0053] Heat treatment of waste graphite powder after coating:

[0054] The S-Gra@PVC mixed powder was placed in a tetrafluoroethylene tank, N2 gas was introduced, and the furnace temperature was raised to 150°C at a heating rate of 3°C / min at room temperature, and kept at this temperature for 40 minutes. The mixture was then taken out after cooling to room temperature.

[0055] Washing of waste graphite powder and leaching of metal ions:

[0056] The waste graphite powder to be heat-treated is taken out after cooling to room temperature, and deionized water is added at a solid-liquid ratio of -g / mL 1:15, and mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 20 minutes, and the first metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:10, mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the second metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:5, stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the third metal-rich washing liquid is obtained by filtering.

[0057] Leachate impurity removal and lithium carbonate recovery:

[0058] The three washing solutions in step 4 were enriched, and a certain amount of Na2S was added thereto, and the mixture was stirred continuously until all the metal impurity ions were converted into precipitates. After removing the precipitated impurities, the pH value of the solution was adjusted, and CO2 gas was introduced into the solution at room temperature for 0.5 h with stirring. The CO2 flow rate was 0.25 L / min, and then heated in a 90°C water bath with stirring for 0.5 h. Li2CO3 was filtered while hot.

[0059] Recycling and heat treatment of waste graphite powder:

[0060] The S-Gra filter residue was dried at 100°C for 3 hours, and the dried waste graphite S-Gra was placed in a ceramic crucible and loaded into a box-type resistance furnace. Ar protective gas was introduced throughout the process, with a heating rate of 5°C / min, a sintering temperature of 800°C, and a holding time of 0.5 hours. After cooling to room temperature, the recycled graphite P-Gra was obtained by grinding and screening.

[0061] Example 2

[0062] This embodiment is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, comprising the following steps:

[0063] Waste graphite powder is obtained by discharging and dismantling waste batteries:

[0064] The waste lithium battery is placed in a 1.5 mol / L sodium chloride aqueous solution for discharge. When the battery voltage is lower than 1.5 V, the discharged battery is disassembled to obtain a negative electrode sheet. A certain mass of the negative electrode sheet is cut into pieces and placed in a ceramic crucible and then loaded into a box-type resistance furnace. The furnace temperature is raised to 300° C. at a heating rate of 3° C. / min at room temperature and kept warm for 1 hour. The calcined negative electrode sheet is sieved through a 20-mesh sieve. The material above the sieve is the copper current collector, and the material below the sieve is the waste graphite negative electrode material.

[0065] Coating of waste graphite negative electrode powder and ultrafine powder:

[0066] The PVC plastic was jet-milled into ultrafine powder with a particle size of 0.3 μm, and a certain amount of PVC ultrafine powder was weighed and blended with waste graphite negative electrode powder at a mixing speed of 2500 rpm / min and a mixing time of 15 min, wherein the mass proportion of the PVC ultrafine powder was 5 wt%, to obtain S-Gra@PVC mixed powder.

[0067] Heat treatment of waste graphite powder after coating:

[0068] The S-Gra@PVC mixed powder was placed in a tetrafluoroethylene tank, N2 gas was introduced, and the furnace temperature was raised to 180°C at a heating rate of 3°C / min at room temperature, and kept at this temperature for 1 hour. The mixture was then taken out after cooling to room temperature.

[0069] Washing of waste graphite powder and leaching of metal ions:

[0070] The waste graphite powder to be heat-treated is taken out after cooling to room temperature, and deionized water is added at a solid-liquid ratio of -g / mL 1:15, and mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 20 minutes, and the first metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:10, mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the second metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:5, stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the third metal-rich washing liquid is obtained by filtering.

[0071] Leachate impurity removal and lithium carbonate recovery:

[0072] The three washing solutions in step 4 were enriched, and a certain amount of Na2S was added thereto, and the mixture was stirred continuously until all the metal impurity ions were converted into precipitates. After removing the precipitated impurities, the pH value of the solution was adjusted, and CO2 gas was introduced into the solution at room temperature for 0.5 h with stirring. The CO2 flow rate was 0.25 L / min, and then heated in a 90°C water bath with stirring for 0.5 h. Li2CO3 was filtered while hot.

[0073] Recycling and heat treatment of waste graphite powder:

[0074] The S-Gra filter residue was dried at 100°C for 3 hours, and the dried waste graphite S-Gra was placed in a ceramic crucible and loaded into a box-type resistance furnace. Ar protective gas was introduced throughout the process, with a heating rate of 5°C / min, a sintering temperature of 800°C, and a holding time of 0.5 hours. After cooling to room temperature, the recycled graphite P-Gra was obtained by grinding and screening.

[0075] Example 3

[0076] This embodiment is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, comprising the following steps:

[0077] Waste graphite powder is obtained by discharging and dismantling waste batteries:

[0078] The waste lithium battery is placed in a 1.5 mol / L sodium chloride aqueous solution for discharge. When the battery voltage is lower than 1.5 V, the discharged battery is disassembled to obtain a negative electrode sheet. A certain mass of the negative electrode sheet is cut into pieces and placed in a ceramic crucible and then loaded into a box-type resistance furnace. The furnace temperature is raised to 300° C. at a heating rate of 3° C. / min at room temperature and kept warm for 1 hour. The calcined negative electrode sheet is sieved through a 20-mesh sieve. The material above the sieve is the copper current collector, and the material below the sieve is the waste graphite negative electrode material.

[0079] Coating of waste graphite negative electrode powder and ultrafine powder:

[0080] The PVC plastic was jet-milled into ultrafine powder with a particle size of 0.5 μm, and a certain amount of PVC ultrafine powder was weighed and blended with waste graphite negative electrode powder at a mixing speed of 2500 rpm / min and a mixing time of 15 min, wherein the mass proportion of the PVC ultrafine powder was 8 wt%, to obtain S-Gra@PVC mixed powder.

[0081] Heat treatment of waste graphite powder after coating:

[0082] The S-Gra@PVC mixed powder was placed in a tetrafluoroethylene tank, N2 gas was introduced, and the furnace temperature was raised to 200°C at a heating rate of 3°C / min at room temperature, and kept at this temperature for 90 minutes. The mixture was then taken out after cooling to room temperature.

[0083] Washing of waste graphite powder and leaching of metal ions:

[0084] The waste graphite powder to be heat-treated is taken out after cooling to room temperature, and deionized water is added at a solid-liquid ratio of -g / mL 1:15, and mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 20 minutes, and the first metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:10, mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the second metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:5, stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the third metal-rich washing liquid is obtained by filtering.

[0085] Leachate impurity removal and lithium carbonate recovery:

[0086] The three washing solutions in step 4 were enriched, and a certain amount of Na2S was added thereto, and the mixture was stirred continuously until all the metal impurity ions were converted into precipitates. After removing the precipitated impurities, the pH value of the solution was adjusted, and CO2 gas was introduced into the solution at room temperature for 0.5 h with stirring. The CO2 flow rate was 0.25 L / min, and then heated in a 90°C water bath with stirring for 0.5 h. Li2CO3 was filtered while hot.

[0087] Recycling and heat treatment of waste graphite powder:

[0088] The S-Gra filter residue was dried at 100°C for 3 hours, and the dried waste graphite S-Gra was placed in a ceramic crucible and loaded into a box-type resistance furnace. Ar protective gas was introduced throughout the process, with a heating rate of 5°C / min, a sintering temperature of 800°C, and a holding time of 0.5 hours. After cooling to room temperature, the recycled graphite P-Gra was obtained.

[0089] Example 4

[0090] This embodiment is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, comprising the following steps:

[0091] Waste graphite powder is obtained by discharging and dismantling waste batteries:

[0092] The waste lithium battery is placed in a 1.5 mol / L sodium chloride aqueous solution for discharge. When the battery voltage is lower than 1.5 V, the discharged battery is disassembled to obtain a negative electrode sheet. A certain mass of the negative electrode sheet is cut into pieces and placed in a ceramic crucible and then loaded into a box-type resistance furnace. The furnace temperature is raised to 300° C. at a heating rate of 3° C. / min at room temperature and kept warm for 1 hour. The calcined negative electrode sheet is sieved through a 20-mesh sieve. The material above the sieve is the copper current collector, and the material below the sieve is the waste graphite negative electrode material.

[0093] Coating of waste graphite negative electrode powder and ultrafine powder:

[0094] The PVC plastic was jet-milled into ultrafine powder with a particle size of 1 μm, and a certain amount of PVC ultrafine powder was weighed and blended with waste graphite negative electrode powder at a mixing speed of 2500 rpm / min and a mixing time of 15 min, wherein the mass proportion of the PVC ultrafine powder was 10 wt%, to obtain S-Gra@PVC mixed powder.

[0095] Heat treatment of waste graphite powder after coating:

[0096] The S-Gra@PVC mixed powder was placed in a tetrafluoroethylene tank, N2 gas was introduced, and the furnace temperature was raised to 220°C at a heating rate of 3°C / min at room temperature, and kept at this temperature for 2 hours. The mixture was then taken out after cooling to room temperature.

[0097] Washing of waste graphite powder and leaching of metal ions:

[0098] The waste graphite powder to be heat-treated is taken out after cooling to room temperature, and deionized water is added at a solid-liquid ratio of -g / mL 1:15, and mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 20 minutes, and the first metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:10, mechanical stirring is performed at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the second metal-rich washing liquid is obtained by filtering; deionized water is then added to the filter residue at a solid-liquid ratio of -g / mL 1:5, stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and the third metal-rich washing liquid is obtained by filtering.

[0099] Leachate impurity removal and lithium carbonate recovery:

[0100] The three washing solutions in step 4 were enriched, and a certain amount of Na2S was added thereto, and the mixture was stirred continuously until all the metal impurity ions were converted into precipitates. After removing the precipitated impurities, the pH value of the solution was adjusted, and CO2 gas was introduced into the solution at room temperature for 0.5 h with stirring. The CO2 flow rate was 0.25 L / min, and then heated in a 90°C water bath with stirring for 0.5 h. Li2CO3 was filtered while hot.

[0101] Recycling and heat treatment of waste graphite powder:

[0102] The S-Gra filter residue was dried at 100°C for 3 hours, and the dried waste graphite S-Gra was placed in a ceramic crucible and loaded into a box-type resistance furnace. Ar protective gas was introduced throughout the process, with a heating rate of 5°C / min, a sintering temperature of 800°C, and a holding time of 0.5 hours. After cooling to room temperature, the recycled graphite P-Gra was obtained.

[0103] Comparative Example 1

[0104] This comparative example is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, and includes some of the operating steps in Example 1, except that:

[0105] This comparative example is used to illustrate a method for recycling and reusing graphite negative electrode materials disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

[0106] The waste graphite negative electrode powder is directly used for subsequent battery preparation without coating.

[0107] Electrochemical performance test:

[0108] The graphite P-Gra recovered from Examples 1 to 4 and Comparative Example 1 was mixed with a binder of polyvinylidene fluoride (PVDF) and a conductive agent of carbon black (super-P) in a mass ratio of 93:4:3, and N-methylpyrrolidone (NMP) was used as a dispersant to prepare a negative electrode slurry, which was evenly coated on an 8 μm copper foil and rolled and dried for use; a metal lithium sheet was used as a counter electrode, and a three-component mixed solvent of 1 mol / L LiPF6 was used according to V EC :V DMC :V EMC =1:1:1 volume ratio to prepare an electrolyte, and a 12 μm polyethylene microporous membrane is used as a separator, and button batteries are assembled in a glove box.

[0109] The button cell prepared above was subjected to the following performance tests:

[0110] The test results are entered in Table 1.

[0111] Table 1 Test results

[0112]

[0113] From the test results of Examples 1 to 3 in Table 1, it can be seen that the capacity retention rate of the button battery after 100 cycles at 1C is not less than 85%; in Example 2, when PVC ultrafine powder with a particle size of 0.3 μm is coated with waste graphite negative electrode powder, and the coated PVC ultrafine powder accounts for 5wt%, the first charge and discharge efficiency reaches 93.5%, and the charge and discharge effect is good ( Figure 1 ); The test results in Example 4 show that a higher coating amount of PVC ultrafine powder is not conducive to improving the battery capacity retention rate.

[0114] Comparing the test results of Examples 1 to 3 with those of Comparative Example 1, it can be seen that the cycle performance of the button battery prepared according to the method of Comparative Example 1 is significantly reduced.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recycling and reusing graphite negative electrode materials, characterized in that: The following steps are involved: Coating of waste graphite negative electrode powder and PVC ultrafine powder: PVC plastic was jet-milled into ultrafine powder with a particle size of ≤1 μm. A certain amount of PVC ultrafine powder was weighed and blended with waste graphite negative electrode powder, where the mass proportion of PVC ultrafine powder was 0.5-10 wt %, to obtain S-Gra@PVC mixed powder. The heat treatment of the coated waste graphite powder causes the metal elements to react with the chlorine element produced by the thermal decomposition of PVC to obtain metal chloride salts: The S-Gra@PVC mixed powder is placed in a tetrafluoroethylene tank, and a protective gas is introduced. The furnace temperature is raised to 100-220°C at a heating rate of 2-5°C / min at room temperature, and the temperature is kept at this temperature for 20-120 minutes. The mixture is then taken out after cooling to room temperature. Washing of waste graphite powder and leaching of metal ions: The waste graphite powder to be heat-treated was taken out after cooling to room temperature, and deionized water was added at a solid-liquid ratio of -g / mL 1:15, and mechanically stirred at room temperature at a stirring rate of 250 rpm / min for 20 minutes, and filtered to obtain the first metal-rich washing liquid; deionized water was then added to the filter residue at a solid-liquid ratio of -g / mL 1:10, mechanically stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and filtered to obtain the second metal-rich washing liquid; deionized water was then added to the filter residue at a solid-liquid ratio of -g / mL 1:5, stirred at room temperature at a stirring rate of 250 rpm / min for 10 minutes, and filtered to obtain the third metal-rich washing liquid; Recycling and heat treatment of waste graphite powder: The S-Gra filter residue was dried at 100°C for 3 hours, and then the dried waste graphite S-Gra was placed in an environment with Ar protective gas throughout the process, with a heating rate of 5°C / min, a sintering temperature of 800°C, and a holding time of 0.5 hours. After cooling to room temperature, it was ground and sieved to obtain recycled graphite P-Gra.

2. The method for recycling and reusing graphite negative electrode materials according to claim 1, wherein: Before "coating the waste graphite negative electrode powder with the PVC ultrafine powder", the waste graphite negative electrode powder is heat treated at a heat treatment temperature of 150°C to 350°C and a heat treatment time of 0.5 to 3 hours.

3. The method for recycling and reusing graphite negative electrode materials according to claim 1, wherein: The coated waste graphite powder is heat-treated in a protective gas, wherein the protective gas is one or more of Ar, N2, and Kr.

4. The method for recycling and reusing graphite negative electrode materials according to claim 1, wherein: An impurity remover is added to the waste graphite powder washing leaching solution to remove impurities; and a lithium ion precipitant is added to the impurity-removed leaching solution to enrich metal elements.

5. The method for recycling and reusing graphite negative electrode materials according to claim 4, characterized in that: The impurity remover is one or more of Na2S, K2S, NaHS, H2S, and BaS.

6. The method for recycling and reusing graphite negative electrode materials according to claim 4, characterized in that: The lithium ion precipitant is one or more of CO2, Na2CO3, K2CO3, and NaHCO3.

7. The method for recycling and reusing graphite negative electrode materials according to claim 1, characterized in that: The protective gas used in the heat treatment of the recycled waste graphite is one or more of Ar, N2, and Kr.

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