A recycling method of graphite negative electrode, negative electrode material and lithium ion battery

Abstract

The present application relates to a kind of preparation methods of lithium ion battery graphite negative electrode, the processing method includes the following steps: (1) waste graphite negative electrode is carried out in sodium persulfate aqueous solution and is immersed in advance, after filtration, obtain pretreated graphite;(2) the pretreated graphite is mixed with sulfuric acid and phosphoric acid mixed acid and then calcined, obtain calcined graphite;(3) the calcined graphite is carried out in aqueous solution and is immersed in, after filtration, drying, obtain harmless graphite.This method can realize the harmless and resource of waste lithium ion battery graphite negative electrode material, waste graphite negative electrode can become solid waste after harmless, graphite negative electrode can continue to be used in lithium ion battery negative electrode material after repair, process flow is simple, energy consumption is low, recovery efficiency is high, application prospect is relatively broad.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resource recycling, and relates to a waste lithium ion battery material recycling and reusing technology, in particular to a graphite negative electrode recycling method, a negative electrode material and a lithium ion battery. BACKGROUND

[0002] The new energy electric vehicle industry is developing rapidly, and the production of lithium ion batteries, as an important part of new energy electric vehicles, also shows an increasing trend year by year. At present, the service life of lithium ion batteries is about 3-5 years, and after the service life, they will face the problem of scrap. The scrapped lithium ion batteries contain harmful substances such as heavy metal elements and fluorine elements, and recycling them can alleviate the problems of resource shortage and environmental pollution.

[0003] At present, the main field of battery recycling is to recycle waste positive electrode materials, because waste positive electrode materials are rich in valuable metal elements such as Li, Ni, Co and Mn, and have a larger recycling value. Compared with the positive electrode material, the valuable metal content in the negative graphite material is relatively low, and the reserves of the graphite raw material are relatively abundant, so the profit of recycling waste graphite is low, which leads to the slow development of related recycling technologies.

[0004] The recycling method of waste negative graphite material can be roughly divided into two categories: pyrometallurgical process and hydrometallurgical process. The hydrometallurgical process mainly uses acid leaching, and the obtained graphite is relatively pure. However, in the acid leaching process, a high acid concentration is required, and there is a problem of low acid utilization rate. The high-acid waste liquid needs to be further treated, and the environmental protection cost is relatively high, which further compresses the profit space of recycled graphite. The pyrometallurgical process is relatively simple, but the energy consumption is high, and the loss rate of the negative electrode in the recycling process is relatively large, which leads to a decrease in the profit of recycled graphite.

[0005] The existing technology discloses the following methods for recycling waste negative graphite by hydrometallurgical process:

[0006] (1) The method of recycling lithium battery graphite negative electrode by using oxidation acid leaching, reduction acid leaching and microwave calcination is as follows: first, using hydrochloric acid + NaClO for oxidation acid leaching, then adding Na2SO3 for reduction acid leaching, and finally using microwave calcination to heat to 1200℃ under nitrogen atmosphere to recycle the graphite material. In this method, chlorine ions exist in the recycling process, which seriously corrodes the equipment during treatment. For enterprises that use sulfuric acid leaching to recycle positive electrode materials at the front end, the waste liquid after purification cannot be returned to the front end for use, and the treatment cost of chlorine-containing waste liquid is high.

[0007] (2) The waste graphite negative electrode is recovered by acid leaching, ball milling, and high-temperature roasting in air atmosphere and nitrogen atmosphere. First, the positive and negative electrode mixture is subjected to acid leaching, and the leached residue is made into granular filter residue of a certain particle size for spraying. The sprayed filter residue is subjected to ball milling, and the fine powder filter residue obtained by ball milling is first roasted at 200-500 DEG C in air atmosphere, and then roasted at 800-1100 DEG C in nitrogen atmosphere. Finally, the graphite negative electrode material is recovered. In the recovery process, the impurity elements affecting the performance of the graphite negative electrode material cannot be completely removed, and the regenerated graphite cannot meet the battery grade standard.

[0008] The above two methods have the defects that the treated waste liquid cannot be recycled, the waste liquid treatment cost is high, and the finally prepared graphite negative electrode material cannot meet the battery grade standard, which affects the market prospect of recycling waste graphite. SUMMARY

[0009] In view of the above problems existing in the prior art, the purpose of the present application is to provide a graphite negative electrode recovery method, which can change the hazardous waste graphite negative electrode into solid waste after treatment, and the graphite negative electrode can be used for lithium ion battery negative electrode material after repair. The process flow is simple, the energy consumption is low, the recovery efficiency is high, and the application prospect is relatively broad.

[0010] Another object of the present application is to provide a negative electrode material.

[0011] In addition, the present application also provides a lithium ion battery.

[0012] In order to achieve the above purpose, the present application provides the following specific technical solutions.

[0013] Firstly, the present application provides a graphite negative electrode recovery method, comprising the following steps:

[0014] (1) The waste graphite negative electrode is subjected to pre-dipping treatment in a sodium persulfate aqueous solution, and after filtration, a pretreated graphite is obtained;

[0015] (2) The pretreated graphite obtained in step (1) is uniformly mixed with a mixed acid of sulfuric acid and phosphoric acid, and then roasted at low temperature to obtain a roasted graphite;

[0016] (3) The roasted graphite is subjected to leaching treatment in an aqueous solution, and after filtration and drying, a harmless graphite is obtained.

[0017] When the waste graphite negative electrode is immersed in the sodium persulfate aqueous solution, the reaction is as follows:

[0018] Na2S2O8+Me→MeSO4+Na2SO4

[0019] Wherein Me represents impurity metal, MeSO4 represents metal sulfate. After sodium persulfate is dissolved in water, the aqueous solution is acidic, and the pH of the aqueous solution in the pretreatment process is adjusted to preliminarily dissolve the impurity elements in the waste graphite negative electrode. After sodium persulfate is dissolved in water, it has strong oxidizing property and can provide the required oxidation atmosphere for impurity removal.

[0020] As preferred, in step (1), the concentration of the aqueous sodium persulfate solution is 13-450 g / L; further preferably, the concentration of the aqueous sodium persulfate solution is 100-250 g / L. The inventors found that in this preferred case, the elemental impurity elements in the graphite can be better oxidized, thereby significantly improving the removal effect of the impurity elements.

[0021] As preferred, in step (1), the temperature of the pre-impregnation treatment is 35-95°C; the pre-impregnation treatment time is 30-360 min.

[0022] The temperature of the pre-impregnation treatment is too low to affect the pre-impregnation effect and reduce the removal effect of the impurities in the waste graphite during the pre-impregnation treatment; the temperature of the pre-impregnation treatment is too high to accelerate the decomposition of sodium persulfate, resulting in unsatisfactory oxidation effect during the pre-impregnation treatment, which also reduces the removal effect of the impurity elements in the graphite, and the temperature is too high to increase energy consumption. However, the inventors found during the research that by setting the temperature of the pre-impregnation treatment in the range of 35-95°C, a significant impurity removal effect can be obtained under the condition of low energy consumption.

[0023] As preferred, the waste graphite negative electrode material in step (1) is a waste graphite negative electrode obtained after disassembling waste lithium ion batteries of the same type or different types, and the lithium ion batteries include ternary lithium ion batteries, lithium iron phosphate batteries, lithium cobaltate batteries and other commonly seen lithium ion batteries in the market.

[0024] As preferred, in step (1), the concentration of the aqueous sodium persulfate solution is 13-450 g / L; the solid-liquid ratio of the waste graphite negative electrode to the aqueous sodium persulfate solution is 1:4-15 g / ml.

[0025] As preferred, in step (2), the molar ratio of phosphoric acid to sulfuric acid in the mixed acid of sulfuric acid and phosphoric acid is 0.50-12:1.

[0026] As preferred, in step (2), the solid-liquid ratio of the pretreated graphite to the mixed acid is 1-20:1 g / ml.

[0027] Further preferably, the solid-liquid ratio of the pretreated graphite to the mixed acid is 1-10:1 g / ml.

[0028] Further preferably, the solid-liquid ratio of the pretreated graphite to the mixed acid is 3-8:1 g / ml.

[0029] The application adopts a mixed mode of sulfuric acid and phosphoric acid to remove impurities from pretreated graphite, and the mixed acid of sulfuric acid and phosphoric acid has stronger dissolving capacity for impurity elements in the graphite during roasting, so that the impurity elements are more easily converted into metal salts that are easily soluble in water, thereby achieving the purpose of deep impurity removal of the graphite.

[0030] Preferably, in step (3), the solid-liquid ratio of the roasting graphite and water is 1:3-20 g / ml; the temperature of the leaching treatment is 40-95 DEG C; and the time of the leaching treatment is 120-720 min.

[0031] The temperature of the leaching treatment is set to 40-95 DEG C to avoid that the impurities in the roasting graphite are not dissolved ideally at too low temperature, and to avoid that the energy consumption is increased at too high temperature, thereby causing the cost to rise.

[0032] In order to obtain a material with better electrochemical activity and cycle stability, preferably, the harmless graphite is coated with pitch in liquid phase, and then calcined to obtain a resource graphite; the pitch includes one or two or more of coal pitch, low-temperature pitch, modified pitch, and mesophase pitch. The inventors of the present application find that the electrochemical performance of the material can be significantly improved by further coating the harmless graphite obtained by the recycling method provided in the present application with pitch in liquid phase, and in particular, the cycle performance of the material can be improved.

[0033] Preferably, the amount of the pitch is 1-15% of the mass of the harmless graphite; and the heating temperature during the liquid phase coating is 25-80 DEG C.

[0034] Preferably, the calcination temperature is 800-1200 DEG C; the heating rate is 1-5 DEG C / min; and the holding time is 30-360 min.

[0035] Secondly, based on the same inventive concept, the present application provides a negative electrode material, which uses the graphite obtained by the recycling method of the waste graphite negative electrode.

[0036] Finally, based on the same inventive concept, the present application provides a lithium ion battery, which uses the negative electrode material.

[0037] Compared with the prior art, the present application has the following obvious beneficial technical effects:

[0038] (1) The waste graphite negative electrode is immersed in a sodium persulfate aqueous solution, and the sodium persulfate is dissolved in water to form an acidic aqueous solution, thereby adjusting the pH of the aqueous solution in the pretreatment process. The sodium persulfate has strong oxidizing property after being dissolved in water, and can provide an oxidizing atmosphere required for impurity removal. The use of sodium persulfate for leaching treatment of the waste graphite reduces the process of acid leaching, avoids the introduction of chloride ions, and reduces the material cost and the subsequent treatment cost of waste liquid.

[0039] (2) roasting, pretreated graphite only mixed with sulfuric acid, unable to remove aluminum, calcium and other impurity elements in graphite. Pretreated graphite only mixed with phosphoric acid, phosphoric acid as a strong acid, if the amount of phosphoric acid is too small, the acidity is not enough, and metal phosphate precipitates are easily produced in the roasting process, which is not conducive to the removal of impurities in graphite; if the amount of phosphoric acid is too much, the cost will increase, and it is not conducive to the removal of phosphorus element. Pretreated graphite mixed with hydrochloric acid, hydrochloric acid is volatile in roasting, and the impurity removal effect is not ideal, which cannot remove impurity elements in depth, and hydrogen chloride or chlorine gas is produced in the roasting process, which is strong pollution to the environment, and hydrochloric acid has strong corrosiveness to the roasting equipment.

[0040] The application adopts the mixed mode of sulfuric acid and phosphoric acid to remove impurities from pretreated graphite, and the mixed acid of sulfuric acid and phosphoric acid has stronger dissolving ability for impurity elements in graphite during roasting, so that the impurity elements are more easily converted into water-soluble metal salts, and the deep removal of impurities from graphite is facilitated.

[0041] (3) Sodium persulfate can oxidize elemental impurity elements in graphite into corresponding oxides, and the dissolving ability of sulfur-phosphorus mixed acid for oxides is stronger than that for elemental substances. After pretreated by sodium persulfate, the removal effect of sulfur-phosphorus mixed acid on impurity elements can be improved, and the content of impurity elements in graphite can be reduced after pretreated by sodium persulfate, so that the amount of subsequent sulfur-phosphorus mixed acid can be reduced, and the cost can be reduced.

[0042] (4) The content of impurity elements Li, Al, Cu, Ni, Co, Mn and Mg in the treated waste graphite negative electrode material can be reduced to less than 5 ppm, the content of impurity element Fe can be reduced to less than 20 ppm, and the ash content is less than 0.08%. The waste liquid produced in the purification process can be returned to the front end and used as leaching bottom liquid to recover valuable metals such as Ni, Co, Mn and Li. The harmless graphite is coated with asphalt liquid phase and calcined to prepare negative electrode material again, realizing the harmless and resource utilization of waste lithium ion battery graphite negative electrode.

[0043] (5) A layer of asphalt is coated on the surface of the harmless graphite to reconstruct the surface, and the added asphalt fills the defects and pores formed in the waste graphite due to long-term charge and discharge cycle, reduces the specific surface area, and thus improves the electrochemical activity and cycle stability of the material. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The process flow chart of the graphite recycling method of the application;

[0045] Figure 2 The SEM photo of the waste lithium ion battery graphite negative electrode material;

[0046] Figure 3 The SEM photo of the harmless graphite in Example 1;

[0047] Figure 4 SEM photograph of the graphite prepared by the graphite recovery method used in Comparative Example 1;

[0048] Figure 5 SEM photograph of the graphite prepared by the graphite recovery method used in Comparative Example 1;

[0049] Figure 6 SEM photograph of the graphite prepared by the graphite recovery method used in Comparative Example 1; DETAILED DESCRIPTION

[0050] To make the technical problems, technologies and advantages of the present application clearer, specific examples will be described in detail below, but the protection scope of the present application is not limited to the following specific examples.

[0051] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing specific examples and are not intended to limit the protection scope of the present application.

[0052] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0053] Example 1:

[0054] A graphite recovery method, comprising the following steps:

[0055] (1) The graphite obtained after disassembling ternary lithium batteries was used as raw material, 20 g of the raw material (the content of metal elements in the raw material was Li: 0.20 wt%, Ni: 0.99 wt%, Co: 0.86 wt%, Mn: 1.21 wt%, Al: 0.48 wt%, Fe: 1.01 wt%, Cu: 0.48 wt%, Mg: 0.03 wt%) was weighed, and was leached with a 200 g / L sodium persulfate solution, the solid-liquid ratio of leaching was 1:12 g / ml, the reaction temperature was 85℃, and the leaching time was 350 min. After filtration, pretreated graphite was obtained. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the pretreated graphite were 507 ppm, 159 ppm, 127 ppm, 128 ppm, 1536 ppm, 4709 ppm, 140 ppm and 101 ppm, respectively.

[0056] (2) The above pretreated graphite was uniformly mixed with a mixed acid of concentrated sulfuric acid and concentrated phosphoric acid, and was subjected to low-temperature roasting, the molar ratio of phosphoric acid to sulfuric acid in the mixed acid was 6:1, 4 ml of the mixed acid was used, the roasting temperature was 245℃, and the holding time was 480 min, to obtain the roasted graphite.

[0057] (3) The above calcined graphite is subjected to water immersion, the reaction temperature is 90°C, the reaction time is 600 min, after water immersion, filtration is performed, and after being fully dried at 110°C, harmless graphite is obtained, and the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite are 1.4 ppm, 1.9 ppm, 1.8 ppm, 2.4 ppm, 1.5 ppm, 13.6 ppm, 1.5 ppm, and 1.5 ppm respectively.

[0058] (4) The above harmless graphite is added to a coal pitch solution fully dissolved in chloroform, and during coating, the temperature is controlled at 70°C, and stirring is performed for 45 min, so that the coal pitch coats the above harmless graphite in a liquid phase, and the coating amount of the coal pitch is 12% of the mass of the above harmless graphite. Then, calcination is performed under a nitrogen atmosphere, the calcination temperature is 1100°C, the heating rate is 5°C / min, and the holding time is 350 min, to obtain resource graphite. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the finally obtained resource graphite are 1.0 ppm, 1.8 ppm, 2.2 ppm, 0 ppm, 1.3 ppm, 13.2 ppm, 0 ppm, and 1.3 ppm respectively.

[0059] Comparative Example 1

[0060] A method for recycling graphite, comprising the following steps:

[0061] (1) Graphite obtained after disassembling a ternary lithium battery is used as raw material, 20 g of the raw material (the content of metal elements in the raw material is Li: 0.20 wt%, Ni: 0.99 wt%, Co: 0.86 wt%, Mn: 1.21 wt%, Al: 0.48 wt%, Fe: 1.01 wt%, Cu: 0.48 wt%, and Mg: 0.03 wt%) is weighed, and oxidation acid immersion is performed using concentrated hydrochloric acid + NaClO, the addition amount of concentrated hydrochloric acid is 16.67 ml, the concentration of hydrochloric acid is 2 mol / L, the addition amount of NaClO is 2 g, the concentration of NaClO is 20 g / L, the reaction temperature is 85°C, and the leaching time is 350 min. After filtration, oxidized graphite is obtained. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the oxidized graphite are 712 ppm, 360 ppm, 152 ppm, 213 ppm, 1966 ppm, 6709 ppm, 140 ppm, and 101 ppm respectively.

[0062] (2) The above pretreated graphite is reduced and acid leached with Na2SO3, the Na2SO3 addition amount is 2 g, the Na2SO3 concentration is 20 g / L, the leaching solid-liquid ratio is 1:5 g / ml, the reaction temperature is 85°C, and the leaching time is 350 min. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the reduced graphite obtained after filtration are 94 ppm, 100 ppm, 68 ppm, 84 ppm, 197 ppm, 298 ppm, 56 ppm, and 35 ppm, respectively.

[0063] (3) The above harmless graphite is added to a coal pitch solution fully dissolved in chloroform, and the coal pitch is stirred at 70°C for 45 min to perform liquid phase coating on the above harmless graphite. The coal pitch coating amount is 12% of the mass of the above harmless graphite. Then, calcination is performed under a nitrogen atmosphere, the calcination temperature is 1100°C, the heating rate is 5°C / min, and the holding time is 350 min to obtain a resource graphite. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the final obtained resource graphite are 90 ppm, 98 ppm, 65 ppm, 79 ppm, 195 ppm, 293 ppm, 52 ppm, and 30 ppm, respectively.

[0064] Comparative Example 2

[0065] A graphite recycling method, comprising the following steps:

[0066] (1) The graphite obtained after disassembling a ternary lithium battery is used as a raw material, 20 g of the raw material (the content of metal elements in the raw material is Li: 0.20 wt%, Ni: 0.99 wt%, Co: 0.86 wt%, Mn: 1.21 wt%, Al: 0.48 wt%, Fe: 1.01 wt%, Cu: 0.48 wt%, and Mg: 0.03 wt%) is weighed, and the raw material is leached with a sodium persulfate solution, the leaching solid-liquid ratio is 1:12 g / ml, the sodium persulfate concentration is 200 g / L, the reaction temperature is 85°C, and the leaching time is 350 min. After filtration, pretreated graphite is obtained. The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the pretreated graphite are 607 ppm, 259 ppm, 187 ppm, 258 ppm, 1736 ppm, 5709 ppm, 240 ppm, and 121 ppm, respectively.

[0067] (2) The above pretreated graphite is mixed with 4 mL of sulfuric acid with a concentration of 18.4 mol / L, and low-temperature calcination is performed, the calcination temperature is 245°C, and the holding time is 480 min to obtain calcined graphite.

[0068] (3) The above calcined graphite is subjected to water immersion, the reaction temperature is 90°C, the reaction time is 600 min, after water immersion, filtration is performed, and after being fully dried at 110°C, harmless graphite is obtained, and the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite are 68 ppm, 75 ppm, 95 ppm, 74 ppm, 156 ppm, 198 ppm, 76 ppm, and 38 ppm, respectively.

[0069] (4) The above harmless graphite is added to a coal pitch solution fully dissolved in chloroform, the temperature is controlled at 70°C, and stirring is performed for 45 min, so that the coal pitch coats the above harmless graphite in a liquid phase, and the coating amount of the pitch is 12% of the mass of the above harmless graphite. Then, calcination is performed under a nitrogen atmosphere, the calcination temperature is 1100°C, the heating rate is 5°C / min, and the holding time is 350 min, to obtain resource graphite. The impurity contents of the impurity elements Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the finally obtained resource graphite are 60 ppm, 71 ppm, 89 ppm, 70 ppm, 152 ppm, 193 ppm, 71 ppm, and 34 ppm, respectively.

[0070] Comparative Example 3

[0071] The difference from Comparative Example 2 is that the pretreated graphite is uniformly mixed with concentrated hydrochloric acid with a concentration of 12 mol / L, 4 mL of hydrochloric acid is used, and low-temperature calcination is performed, the calcination temperature is 245°C, and the holding time is 480 min, to obtain calcined graphite.

[0072] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite are 98 ppm, 85 ppm, 98 ppm, 65 ppm, 199 ppm, 186 ppm, 88 ppm, and 54 ppm, respectively.

[0073] The impurity contents of the impurity elements Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the resource graphite are 96 ppm, 83 ppm, 96 ppm, 64 ppm, 198 ppm, 186 ppm, 85 ppm, and 51 ppm, respectively.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that in step (1), the graphite raw material obtained after the ternary lithium battery is disassembled is not pretreated by using sodium persulfate, and the contents of the metal elements in the raw material are Li: 0.20 wt%, Ni: 0.99 wt%, Co: 0.86 wt%, Mn: 1.21 wt%, Al: 0.48 wt%, Fe: 1.01 wt%, Cu: 0.48 wt%, and Mg: 0.03 wt%.

[0076] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the harmless graphite obtained after mixed acid roasting + water leaching are 251 ppm, 79 ppm, 64 ppm, 68 ppm, 756 ppm, 2014 ppm, 81 ppm and 56 ppm respectively.

[0077] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the resource graphite obtained after calcination under a nitrogen atmosphere after being coated with coal pitch are 248 ppm, 77 ppm, 64 ppm, 67 ppm, 751 ppm, 2012 ppm, 79 ppm and 54 ppm respectively.

[0078] Comparative Example 5:

[0079] The difference from Example 1 is that the harmless graphite is not coated with pitch.

[0080] Comparative Example 6:

[0081] The difference from Comparative Example 2 is that the pretreated graphite is mixed uniformly with phosphoric acid with a concentration of 14.63 mol / L, 4 mL of phosphoric acid is used, low-temperature roasting is performed, the roasting temperature is 245°C, and the holding time is 480 min to obtain the roasted graphite.

[0082] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the harmless graphite are 98 ppm, 65 ppm, 99 ppm, 89 ppm, 195 ppm, 188 ppm, 93 ppm and 58 ppm respectively.

[0083] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the resource graphite are 95 ppm, 63 ppm, 99 ppm, 88 ppm, 195 ppm, 188 ppm, 93 ppm and 58 ppm respectively.

[0084] Example 2:

[0085] A method for harmless treatment and resource utilization of graphite negative electrodes of waste lithium ion batteries, the difference between the steps of which and Example 1 is that the concentration of sodium persulfate is 100 g / L, and pitch coating is not used.

[0086] The concentration of sodium persulfate is 100 g / L, and the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu and Mg in the pretreated graphite obtained are 598 ppm, 359 ppm, 167 ppm, 158 ppm, 1836 ppm, 5809 ppm, 210 ppm and 131 ppm respectively.

[0087] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite obtained after mixed acid roasting and water leaching are 2.4 ppm, 2.7 ppm, 2.5 ppm, 1.4 ppm, 3.5 ppm, 10.6 ppm, 2.5 ppm, and 4.5 ppm, respectively.

[0088] Example 3

[0089] A method for harmless treatment and resource utilization of graphite negative electrodes of waste lithium ion batteries, which is different from that in Example 1 in that the concentration of sodium persulfate is 150 g / L, and no coal pitch coating is used.

[0090] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the pretreated graphite obtained are 588 ppm, 369 ppm, 154 ppm, 162 ppm, 1731 ppm, 5609 ppm, 205 ppm, and 111 ppm, respectively.

[0091] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite obtained after mixed acid roasting and water leaching are 3.4 ppm, 1.7 ppm, 3.2 ppm, 4.2 ppm, 1.6 ppm, 15.4 ppm, 2.4 ppm, and 3.1 ppm, respectively.

[0092] Example 4

[0093] A method for harmless treatment and resource utilization of graphite negative electrodes of waste lithium ion batteries, which is different from that in Example 1 in that the concentration of sodium persulfate is 13 g / L, and the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the pretreated graphite obtained are 688 ppm, 269 ppm, 204 ppm, 212 ppm, 2031 ppm, 6609 ppm, 185 ppm, and 101 ppm, respectively.

[0094] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the harmless graphite obtained after mixed acid roasting and water leaching are 4.4 ppm, 4.7 ppm, 4.2 ppm, 3.2 ppm, 3.6 ppm, 16.4 ppm, 1.4 ppm, and 4.9 ppm, respectively.

[0095] After being coated with coal pitch and calcined in a nitrogen atmosphere, the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the resource graphite obtained are 4.2 ppm, 4.5 ppm, 4.0 ppm, 3.1 ppm, 3.5 ppm, 16.2 ppm, 1.1 ppm, and 4.7 ppm, respectively.

[0096] Example 5:

[0097] A method for harmless treatment and resource utilization of graphite negative electrode of waste lithium ion battery, the difference between the steps and example 1 is that the concentration of sodium persulfate is 450 g / L, the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, Mg in the pretreated graphite obtained are 518 ppm, 269 ppm, 194 ppm, 205 ppm, 1753 ppm, 5800 ppm, 241 ppm, 131 ppm respectively.

[0098] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, Mg in the harmless graphite obtained after mixed acid roasting and water leaching are 2.4 ppm, 3.8 ppm, 3.2 ppm, 3.8 ppm, 3.6 ppm, 19.4 ppm, 2.0 ppm, 4.8 ppm respectively.

[0099] After being wrapped by coal pitch and calcined in a nitrogen atmosphere, the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, Mg in the resource graphite obtained are 2.2 ppm, 3.6 ppm, 3.2 ppm, 3.7 ppm, 3.6 ppm, 19.2 ppm, 1.9 ppm, 4.6 ppm respectively.

[0100] Example 6:

[0101] A method for harmless treatment and resource utilization of graphite negative electrode of waste lithium ion battery, the difference between the steps and example 1 is that in step (2), the molar ratio of phosphoric acid to sulfuric acid in the mixed acid is 12:1.

[0102] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, Mg in the harmless graphite obtained after mixed acid roasting and water leaching are 3.4 ppm, 1.7 ppm, 3.2 ppm, 4.2 ppm, 1.6 ppm, 15.4 ppm, 2.4 ppm, 3.1 ppm respectively.

[0103] After being wrapped by coal pitch and calcined in a nitrogen atmosphere, the impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, Mg in the resource graphite obtained are 3.1 ppm, 1.5 ppm, 2.9 ppm, 4.1 ppm, 1.3 ppm, 15.1 ppm, 2.2 ppm, 3.0 ppm respectively.

[0104] Example 7:

[0105] A method for harmless treatment and resource utilization of waste lithium ion battery graphite negative electrode, the difference between the steps and embodiment 1 is that in step (2), the molar ratio of phosphoric acid and sulfuric acid in the mixed acid is 1:2;

[0106] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the graphite obtained after mixed acid roasting + water leaching are 3.1 ppm, 1.8 ppm, 3.7 ppm, 4.4 ppm, 1.9 ppm, 17.4 ppm, 4.4 ppm, and 3.2 ppm, respectively.

[0107] After being wrapped in coal pitch and calcined in a nitrogen atmosphere, the impurity elements Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the resource graphite obtained have impurity contents of 3.0 ppm, 1.7 ppm, 3.7 ppm, 4.2 ppm, 1.9 ppm, 17.3 ppm, 4.2 ppm, and 3.2 ppm, respectively.

[0108] Embodiment 8:

[0109] A method for harmless treatment and resource utilization of waste lithium ion battery graphite negative electrode, the difference between the steps and embodiment 1 is that in step (2), the solid-liquid ratio of pretreated graphite and mixed acid is 10:1 g / ml, and the amount of mixed acid used is 1 ml.

[0110] The impurity contents of Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the graphite obtained after mixed acid roasting + water leaching are 2.4 ppm, 3.6 ppm, 1.8 ppm, 2.9 ppm, 2.3 ppm, 14.3 ppm, 2.9 ppm, and 1.9 ppm, respectively.

[0111] After being wrapped in coal pitch and calcined in a nitrogen atmosphere, the impurity elements Li, Ni, Co, Mn, Al, Fe, Cu, and Mg in the resource graphite obtained have impurity contents of 2.3 ppm, 3.6 ppm, 1.7 ppm, 2.6 ppm, 2.2 ppm, 14.1 ppm, 2.9 ppm, and 1.8 ppm, respectively.

[0112] The graphite obtained after disassembling the above ternary lithium battery, the pretreated graphite, the water leaching residue, and the resource graphite are all detected by ICP. The ICP is an inductively coupled plasma emission spectrometer (ICP-OES) produced by CEM Company in the United States, model Optima8000DA. Before detection, the graphite is subjected to microwave digestion to completely dissolve it before detection.

[0113] The graphite obtained from Example 1 to Example 8, Comparative Example 1 to Comparative Example 6 was assembled into a battery in the following manner: 0.092 g of the graphite material was weighed, 0.003 g of acetylene black was added as a conductive agent and 0.005 g of polyvinylidene fluoride was added as a binder, N-methyl pyrrolidone was added as a dispersant, the mixture was mixed uniformly and then coated on an aluminum foil to form a positive electrode sheet, a lithium sheet was used as a negative electrode in a vacuum glove box, a composite film of PE and PP was used as a separator, 1 mol / L LiPF6 / DMC:EC (volume ratio 1:1) was used as an electrolyte, and a CR2032 button cell was assembled.

[0114] The cycle performance curve of the button cell was tested, and the capacity retention rate of the battery after 100 cycles of the battery prepared using the graphite in Example 1 to Example 8, Comparative Example 1 to Comparative Example 6 as a negative electrode was as follows: Figure 6 .

[0115] Table 1 Capacity retention rate of the battery after 100 cycles of the battery prepared using the graphite in Example 1 to Example 8, Comparative Example 1 to Comparative Example 6 as a negative electrode

[0116]

[0117] It should be noted that the above only describes the preferred embodiments of the present application, and for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for recovering graphite anodes, characterized in that, Includes the following steps: (1) The waste graphite negative electrode is pre-impregnated in sodium persulfate aqueous solution to obtain pre-treated graphite; (2) The pretreated graphite is mixed with a mixture of sulfuric acid and phosphoric acid and then calcined to obtain calcined graphite; (3) The calcined graphite is leached in water, filtered and dried to obtain harmless graphite.

2. The method for recycling graphite anodes according to claim 1, characterized in that, In step (1), the concentration of the sodium persulfate aqueous solution is 13~450g / L; the solid-liquid ratio of the waste graphite negative electrode to the sodium persulfate aqueous solution is 1:4~15g / mL.

3. The method for recycling a graphite negative electrode according to claim 2, characterized in that, In step (1), the concentration of the sodium persulfate aqueous solution is 100~250 g / L.

4. The method for recycling graphite negative electrodes according to claim 1, characterized in that, In step (1), the temperature of the pre-soaking treatment is 35~95℃; the time of the pre-soaking treatment is 30~360min.

5. The method for recycling a graphite negative electrode according to claim 4, characterized in that, In step (1), the temperature of the pre-soaking treatment is 50~95℃; the time of the pre-soaking treatment is 100~350min.

6. The method for recycling a graphite negative electrode according to claim 1, characterized in that, In step (2), the molar ratio of phosphoric acid to sulfuric acid in the mixed acid of sulfuric acid and phosphoric acid is 0.50~12:

1.

7. The method for recycling a graphite negative electrode according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the pretreated graphite to the mixed acid is 1~20:1g / mL.

8. The method for recycling a graphite negative electrode according to claim 7, characterized in that, In step (2), the solid-liquid ratio of the pretreated graphite to the mixed acid is 1~10:1g / mL.

9. A method for recycling a graphite negative electrode according to claim 7 or 8, characterized in that, In step (2), the solid-liquid ratio of the pretreated graphite to the mixed acid is 3~8:1g / mL.

10. A method for recycling a graphite negative electrode according to claim 1, characterized in that, In step (3), the leaching temperature is 40~95℃; the leaching time is 120~720min.

11. The method for recycling a graphite negative electrode according to claim 1, characterized in that, Also includes: The harmless graphite is obtained by liquid-phase coating with asphalt and then calcining.

12. The method for recycling a graphite negative electrode according to claim 11, characterized in that, The asphalt includes one or more of coal tar pitch, low-temperature asphalt, modified asphalt, and mesophase asphalt.

13. The method for recycling a graphite negative electrode according to claim 11, characterized in that, The amount of asphalt used is 1-15% of the mass of the harmless graphite; the heating temperature during liquid phase coating is 25-80℃.

14. A negative electrode material, characterized in that, The graphite material recovered by the method for recovering graphite anodes according to any one of claims 1 to 13.

15. A lithium-ion battery, characterized in that, Includes the negative electrode material as described in claim 14.

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