Method for recovering graphite from waste secondary battery, graphite and secondary battery

Abstract

The embodiment of the invention provides a method for recycling graphite from a waste secondary battery, the graphite and the secondary battery. The method comprises the following steps: obtaining acid leaching residues of black powder in the waste secondary battery; the acid leaching residues are smashed, and smashed materials are obtained; carrying out flotation treatment on the crushed material to obtain graphite concentrate; carrying out segmented pyrolysis treatment on the graphite concentrate to remove a flotation solvent and a flotation reagent in the graphite concentrate so as to obtain purified graphite; and calcining the purified graphite to obtain recycled graphite. According to the embodiment of the invention, the purity and the crystal quality of the recycled graphite obtained by the embodiment of the invention can be improved, the recycling of the graphite in the waste secondary battery is realized, and the pollution of the graphite in the waste secondary battery to the environment and the waste of graphite resources are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of battery recycling, and particularly to a method for recycling graphite from waste secondary batteries, graphite, and secondary batteries. Background Art

[0002] With the rapid increase in the production of lithium-ion batteries, the subsequent issue is the recycling of a large number of lithium-ion batteries at the end of their service life.

[0003] In related technologies, the recycling of waste lithium-ion batteries mainly focuses on the recovery of valuable metal elements in the black powder. However, the remaining graphite in the black powder is directly buried or incinerated, which not only causes serious environmental pollution but also greatly wastes the graphite resources in the lithium-ion batteries. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for recycling graphite from waste secondary batteries, graphite, and secondary batteries, so as to solve the problems of environmental pollution and waste of graphite resources caused by directly burying or incinerating the graphite in waste batteries in related technologies.

[0005] To solve the above problems, the present invention is implemented through the following technical solutions:

[0006] The present invention provides a method for recycling graphite from waste secondary batteries, the method comprising:

[0007] Obtaining the acid leaching residue of the black powder in the waste secondary battery;

[0008] Crushing the acid leaching residue to obtain a crushed material;

[0009] Performing flotation treatment on the crushed material to obtain graphite concentrate; the graphite concentrate includes a flotation solvent and a flotation reagent;

[0010] Performing staged pyrolysis treatment on the graphite concentrate to remove the flotation solvent and the flotation reagent in the graphite concentrate, thereby obtaining purified graphite;

[0011] Performing calcination treatment on the purified graphite to obtain recycled graphite.

[0012] Further, in the method, the performing staged pyrolysis treatment on the graphite concentrate to remove the flotation solvent and the flotation reagent in the graphite concentrate, thereby obtaining purified graphite, includes:

[0013] Raising the temperature of the graphite concentrate to a first temperature and maintaining the graphite concentrate at the first temperature for a first duration, so that the flotation solvent in the graphite concentrate volatilizes, thereby obtaining a first concentrate;

[0014] Raise the temperature of the first concentrate from the first temperature to a second temperature, and keep the first graphite concentrate at the second temperature for a second period of time, so that the flotation reagent in the first concentrate volatilizes, obtaining a second concentrate, and determine the second concentrate as purified graphite.

[0015] Further, in the method, the method further includes:

[0016] During the process of keeping the graphite concentrate at the first temperature for a first period of time, collect the flotation solvent volatilized from the graphite concentrate;

[0017] During the process of keeping the first graphite concentrate at the second temperature for a second period of time, collect the flotation reagent volatilized from the first concentrate.

[0018] Further, in the method, the first temperature is 100°C to 120°C, and the first period of time is 50 min to 200 min; the second temperature is 220°C to 260°C, and the second period of time is 30 min to 60 min.

[0019] Further, in the method, the temperature for calcining the purified graphite is 2600°C to 3000°C, and the duration for calcining the purified graphite is 4 h to 24 h.

[0020] Further, in the method, the step of crushing the acid leaching residue to obtain a crushed material includes:

[0021] Based on the acid leaching residue and the ball milling solvent, prepare a ball milling slurry; in the ball milling slurry, the mass ratio of the acid leaching residue is 65 wt% to 85 wt%;

[0022] Perform ball milling on the ball milling slurry to obtain a crushed material; in the crushed material, the mass ratio of the particles with a particle size smaller than the target size is 80 wt% to 95 wt%.

[0023] Further, in the method, the rotation speed for ball milling the ball milling slurry is 100 rpm to 500 rpm, and the duration for ball milling the ball milling slurry is 0.5 h to 4 h.

[0024] Further, in the method, the flotation treatment includes roughing treatment and cleaning treatment;

[0025] The step of performing flotation treatment on the crushed material to obtain graphite concentrate includes:

[0026] Perform at least one roughing treatment on the crushed material to obtain a rougher concentrate;

[0027] Performing at least one beneficiation treatment on the roughly selected concentrate to obtain graphite concentrate;

[0028] Wherein, the duration of the roughing treatment is greater than that of the beneficiation treatment, and the mass ratio of the flotation reagent in the flotation system during the roughing treatment is greater than that of the flotation reagent in the flotation system during the beneficiation treatment.

[0029] Furthermore, in the method, the flotation reagent includes a collector and a frother;

[0030] During the roughing treatment, the mass ratio of the collector in the flotation system is 50 g / t to 200 g / t, and the mass ratio of the frother in the flotation system is 30 g / t to 100 g / t;

[0031] During the beneficiation treatment, the mass ratio of the collector in the flotation system is 5 g / t to 50 g / t, and the mass ratio of the frother in the flotation system is 0 g / t to 20 g / t.

[0032] Furthermore, in the method, after performing flotation treatment on the crushed material to obtain graphite concentrate, the method further includes:

[0033] Performing filtration treatment on the graphite concentrate to reduce the moisture content of the graphite concentrate to 10% - 20%.

[0034] The present invention also provides a kind of graphite, wherein, the graphite is obtained by recycling through the method for recycling graphite from waste secondary batteries as described above.

[0035] The present invention also provides a secondary battery, which includes a positive electrode plate and a negative electrode plate. The negative electrode plate includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, and the negative active material includes the graphite as described above.

[0036] Compared with the related art, the embodiments of the present invention have the following advantages:

[0037] The method for recovering graphite from waste secondary batteries provided by the embodiments of the present invention can disperse the graphite and metal elements in the acid leaching residue of the black powder in the waste secondary batteries by pulverizing the acid leaching residue to obtain a pulverized material, which is beneficial to separating the graphite and metal elements in the pulverized material by flotation treatment of the pulverized material, thereby facilitating reducing the residual amount of metal elements in the graphite concentrate obtained by flotation treatment. Furthermore, by performing segmented pyrolysis treatment on the graphite concentrate, the flotation solvent and flotation reagent in the graphite concentrate can be removed, reducing the residual amount of the flotation solvent and flotation reagent in the purified graphite and increasing the purity of graphite in the purified graphite; further, by performing calcination treatment on the purified graphite, not only can the residual metal elements in the purified graphite be removed, but also the lattice structure of the purified graphite can be repaired, increasing the crystallinity of the purified graphite, thereby increasing the purity and crystal quality of the recovered graphite obtained by the embodiments of the present invention, realizing the recycling of graphite in waste secondary batteries, and avoiding the pollution to the environment caused by graphite in waste secondary batteries and the waste of graphite resources.

[0038] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1 is the step flow of a method for recovering graphite from waste secondary batteries provided by the present invention Figure 1 ;

[0041] Figure 2 is the step flow of a method for recovering graphite from waste secondary batteries provided by the present invention Figure 2 ;

[0042] Figure 3 is Comparative Image 1 of the scanning electron microscopes of the graphite materials obtained in Example 1 and Comparative Example 1 provided by the present invention;

[0043] Figure 4 is Comparative Image 2 of the scanning electron microscopes of the graphite materials obtained in Example 1 and Comparative Example 1 provided by the present invention;

[0044] Figure 5 is the transmission electron microscope image of the graphite material obtained in Comparative Example 1 provided by the present invention;

[0045] Figure 6This is a transmission electron microscope image of the graphite material obtained in Example 1 provided by the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] With the rapid increase in the production of lithium-ion batteries, the problem of recycling a large number of lithium-ion batteries at the end of their life has also arisen. Waste lithium-ion batteries contain rich non-ferrous metal resources such as cobalt, nickel, manganese, copper, and aluminum, as well as harmful substances such as lithium hexafluorophosphate and carbonates. If they are not properly recycled and treated, it will not only lead to a waste of resources, but also pose a threat to the environment. In related technologies, the recycling of waste lithium-ion batteries mainly focuses on the recovery of valuable metal elements in black powder, while there is less research on the resource utilization of acid leaching residue of black powder. Usually, the acid leaching residue of black powder is directly buried or incinerated, which not only causes serious pollution to the environment, but also greatly wastes the graphite resources in lithium-ion batteries.

[0049] In order to solve the above problems, the present invention provides a method for recovering graphite from waste secondary batteries. Figure 1 , showing the steps of a method for recovering graphite from waste secondary batteries provided by an embodiment of the present invention Figure 1 , the method may specifically include steps S101 to S105:

[0050] Step S101: Obtain acid leaching residue of black powder in waste secondary batteries.

[0051] Step S102: crushing the acid leaching residue to obtain a crushed product.

[0052] Step S103: flotation treatment is performed on the crushed material to obtain graphite concentrate.

[0053] Step S104: performing a staged pyrolysis treatment on the graphite concentrate to remove the flotation solvent and flotation reagent in the graphite concentrate to obtain purified graphite.

[0054] Step S105: calcining the purified graphite to obtain recovered graphite.

[0055] The method for recovering graphite from waste secondary batteries provided in the embodiment of the present invention can be applied to the recovery of graphite from any type of secondary batteries, including but not limited to lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries.

[0056] In step S101, acid leaching residue of black powder in waste secondary batteries is obtained, which may specifically include steps S1011 to S1014:

[0057] Step S1011: discharging the used secondary batteries.

[0058] Step S1012: dismantle the used secondary batteries after the discharge process to obtain black powder from the used secondary batteries.

[0059] Specifically, first, the waste secondary batteries after discharge treatment are disassembled to separate the positive electrode active materials, negative electrode active materials, diaphragms, electrolytes and other components of the waste secondary batteries; then, the disassembled and separated components are sorted by physical methods (for example, magnetic separation, air separation, etc.), and the mixture of the positive electrode active materials and the negative electrode active materials obtained by sorting is determined as the black powder of the waste secondary batteries.

[0060] Step S1013: performing acid leaching on the black powder to obtain acid leaching slurry.

[0061] Specifically, the black powder obtained in step S1012 is placed in an acid leaching tank, and a leaching agent is added to the acid leaching tank so that the valuable metals in the black powder are dissolved by the leaching agent to obtain an acid leaching slurry.

[0062] The acid leaching slurry includes a leachate formed by dissolving valuable metals in the black powder into the leaching agent and solid components in the black powder that are insoluble in the leaching agent.

[0063] The leaching agent is an inorganic acid or an organic acid; the inorganic acid includes sulfuric acid and / or hydrochloric acid, and the organic acid includes citric acid and / or oxalic acid; the concentration of the leaching agent is 2 mol / L to 3 mol / L.

[0064] In the acid leaching tank, the mass ratio of the leaching agent to the black powder is 4:1 to 6:1.

[0065] The temperature for acid leaching of the black powder is 80° C. to 95° C.; the time for acid leaching of the black powder is 2 hours to 4 hours.

[0066] Step S1014: performing solid-liquid separation on the acid leaching slurry to obtain acid leaching residue.

[0067] Specifically, first, the acid leaching slurry obtained in step S1013 is subjected to solid-liquid separation to obtain solid components in the black powder that are insoluble in the leaching agent; then, the solid components are washed and dried to obtain acid leaching residue of the black powder in the waste secondary battery.

[0068] In step S1012, the comminution treatment may include, but is not limited to, ball milling, grinding, rod milling, etc. By subjecting the acid leaching residue to comminution treatment, the graphite and the residual metal elements in the graphite in the acid leaching residue can be comminuted and dispersed, reducing the degree of mutual encapsulation of the graphite and the metal elements in the comminuted material, which is beneficial to reducing the residual amount of metal elements in the graphite concentrate obtained by subjecting the comminuted material to flotation treatment in step S103, and thus improving the purity of the recovered graphite.

[0069] In step S103, a flotation system can be constructed based on the comminuted material, the flotation solvent, and the flotation reagent obtained in step S102, so as to perform flotation separation on the graphite and metal elements in the comminuted material through the flotation system, and determine the part with a relatively high proportion of graphite obtained by flotation as the graphite concentrate, and determine the part with a relatively high proportion of metal elements obtained by flotation as the metal impurities.

[0070] The graphite concentrate obtained through step S103 can be further purified through the operations corresponding to step S104 and step S105 to obtain the recovered graphite; it can be understood that the graphite concentrate obtained through step S103 includes the flotation solvent and the flotation reagent, and the flotation solvent and the flotation reagent included in the graphite concentrate are the residues of the flotation solvent and the flotation reagent in the flotation system in the graphite.

[0071] For the metal impurities obtained through step S103, the metal elements in the metal impurities can be recovered by the methods in the art for recovering valuable metal elements from waste secondary batteries, and the recovery process of the metal elements in the embodiments of the present invention will not be elaborated.

[0072] In the embodiments of the present invention, the flotation solvent is pure water, and the flotation reagent may include, but is not limited to, collectors and frothers, etc.

[0073] Among them, the collector can selectively adsorb on the surface of the graphite, enhancing the hydrophobicity of the graphite, making the graphite more likely to adhere to the bubbles generated by the frother and float to the surface of the flotation system, thereby realizing the flotation separation of the graphite and metal elements in the comminuted material; the frother is used to reduce the surface tension of the flotation solvent in the flotation system, promote the dispersion of air into small and stable bubbles, and improve the stability of the foam layer to prevent the merger and rupture of the bubbles.

[0074] Specifically, the collector includes at least one of n-undecane, n-dodecane, and n-tridecane; the frother includes at least one of methyl isobutyl carbinol (MIBC), sec-octanol, and isooctanol.

[0075] In step S104, by performing a staged pyrolysis treatment on the graphite concentrate, the flotation solvent and flotation reagent remaining in the graphite concentrate can be removed in sequence, thereby improving the purity of the purified graphite.

[0076] The staged pyrolysis process includes at least two treatment stages with different temperatures. During each treatment stage, the graphite concentrate can be kept warm at the temperature corresponding to that stage to volatilize the target impurities remaining in the graphite concentrate. The temperature corresponding to each treatment stage can be determined based on the boiling points of the flotation solvent and flotation reagent. The duration of the holding period can be determined based on the removal effect of the target impurities to be removed in that treatment stage. The target impurities include either the flotation solvent or the flotation reagent.

[0077] As an optional embodiment, the staged pyrolysis treatment includes two treatment stages with different temperatures, namely a first treatment stage and a second treatment stage; in step S104, the third temperature can be determined according to the boiling point of the flotation solvent or the flotation agent with a lower boiling point, and the fourth temperature can be determined according to the boiling point of the flotation solvent or the flotation agent with a higher boiling point; then, in the first treatment stage, the graphite concentrate is kept warm at the third temperature to remove target impurities with a lower boiling point in the graphite concentrate; finally, in the second treatment stage, the graphite concentrate is kept warm at the fourth temperature to remove target impurities with a higher boiling point in the graphite concentrate, thereby obtaining purified graphite.

[0078] As another optional embodiment, when the flotation reagent includes at least two reagent components, the staged pyrolysis treatment includes (n+1) treatment stages with different temperatures, where n is the total number of reagent components in the flotation reagent; in step S104, the temperatures corresponding to the (n+1) treatment stages in the staged pyrolysis treatment can be determined according to the boiling points of the flotation solvent and each reagent component in the flotation reagent; then, in each treatment stage, the graphite concentrate is kept warm at the temperature corresponding to the treatment stage to remove the target impurities corresponding to the treatment stage in the graphite concentrate, until the flotation solvent and flotation reagent in the graphite concentrate are removed to obtain purified graphite.

[0079] Optionally, when the flotation agent includes at least two agent components, the boiling point of each agent component in the flotation agent is less than 300°C.

[0080] In step S105 , the purified graphite may be calcined to further remove residual metal elements in the purified graphite, repair the lattice structure of the purified graphite, improve the crystallinity of the purified graphite, and thereby improve the crystal quality of the regenerated graphite.

[0081] It should be noted that the temperature of the calcination treatment in step S105 is higher than the highest temperature of the staged pyrolysis treatment in step S104.

[0082] The method for recovering graphite from waste secondary batteries provided by an embodiment of the present invention comprises the following steps: pulverizing the acid leaching residue of black powder in the waste secondary batteries to obtain a pulverized material; the graphite and metal elements in the acid leaching residue can be dispersed, which is beneficial for separating the graphite and metal elements in the pulverized material by flotation treatment of the pulverized material, thereby facilitating reducing the residual amount of metal elements in the graphite concentrate obtained by the flotation treatment; and further, by performing a staged pyrolysis treatment on the graphite concentrate, the flotation solvent and flotation agent in the graphite concentrate can be removed, the residual amount of the flotation solvent and flotation agent in the purified graphite can be reduced, and the purity of the graphite in the purified graphite can be improved; further, by calcining the purified graphite, not only can the residual metal elements in the purified graphite be removed, but the lattice structure of the purified graphite can also be repaired, and the crystallinity of the purified graphite can be improved, thereby improving the purity and crystal quality of the recovered graphite obtained by the embodiment of the present invention, thereby realizing the recycling of graphite from waste secondary batteries and avoiding the pollution of the environment caused by the graphite in the waste secondary batteries and the waste of graphite resources.

[0083] In addition, in the method for recovering graphite from waste secondary batteries provided by the embodiment of the present invention, each step has high operability and repeatability, and is easy to implement industrial production.

[0084] Optionally, the step S104 of performing a segmented pyrolysis treatment on the graphite concentrate to remove the flotation solvent and the flotation reagent in the graphite concentrate to obtain purified graphite includes steps S1041 to S1042:

[0085] Step S1041: Raise the temperature of the graphite concentrate to a first temperature, and keep the graphite concentrate at the first temperature for a first time period, so as to volatilize the flotation solvent in the graphite concentrate, thereby obtaining a first concentrate.

[0086] Step S1042: Raise the temperature of the first concentrate from the first temperature to a second temperature, and keep the first graphite concentrate at the second temperature for a second time period to volatilize the flotation agent in the first concentrate, thereby obtaining a second concentrate, and determine the second concentrate as purified graphite.

[0087] In an embodiment of the present invention, the segmented pyrolysis treatment includes two treatment stages with different temperatures, namely a first treatment stage and a second treatment stage; and in a scenario where the flotation solvent is pure water and the flotation reagent includes a collector and a frother, the boiling point of the flotation solvent is lower than the boiling point of the flotation reagent, then the first temperature can be determined according to the boiling point of the flotation solvent, and the second temperature can be determined according to the boiling point of the flotation reagent.

[0088] Specifically, in the process of performing segmented pyrolysis on graphite concentrate to obtain purified graphite, step S1041 and step S1042 may be sequentially performed to remove the flotation solvent and flotation reagent in the graphite concentrate.

[0089] In step S1041, the temperature of the graphite concentrate can be increased to a first temperature, and the graphite concentrate can be kept warm at the first temperature for a first period of time to volatilize the flotation solvent remaining in the graphite concentrate, thereby removing the flotation solvent in the graphite concentrate and obtaining a first concentrate; it can be understood that the first concentrate is the product obtained from the graphite concentrate after the flotation solvent is removed.

[0090] In step S1042, the temperature of the first concentrate obtained in step S1041 can be increased from the first temperature to the second temperature, and the first graphite concentrate can be kept warm at the second temperature for a second period of time to volatilize the flotation agent remaining in the first concentrate, thereby removing the flotation agent in the graphite concentrate to obtain a second concentrate, and the second concentrate is determined to be purified graphite; it can be understood that purified graphite is the product obtained from the graphite concentrate after removing the flotation solvent and flotation agent.

[0091] In some embodiments, the first temperature may be equal to the boiling point of the flotation solvent, and the second temperature may be equal to the boiling point of the flotation reagent; in other embodiments, the first temperature may be selected from a first temperature range determined based on the boiling point of the flotation solvent, and the second temperature may be selected from a second temperature range determined based on the boiling point of the flotation reagent.

[0092] The first duration may be determined based on the removal effect of the flotation solvent in step S1041 , and the second duration may be determined based on the removal effect of the flotation reagent in step S1042 , which is not specifically limited in the embodiment of the present invention.

[0093] It should be noted that, when the flotation reagent includes at least two reagent components, the second temperature can be determined according to the maximum boiling point of each reagent component.

[0094] When the flotation reagent includes at least two reagent components, the difference between the boiling points of the reagent components is less than or equal to the first threshold value, which can prevent the flotation reagent with a large difference in boiling points from decomposing and becoming ineffective at a higher temperature.

[0095] Optionally, the method further includes steps A11 and A12:

[0096] Step A11: During the process of keeping the graphite concentrate at the first temperature for a first period of time, collecting the flotation solvent volatilized from the graphite concentrate.

[0097] Step A12: During the process of keeping the first graphite concentrate at the second temperature for the second duration, collect the flotation reagent volatilized from the first concentrate.

[0098] In an embodiment of the present invention, during the process of keeping the graphite concentrate at the first temperature for the first duration through step S1041 to volatilize the flotation solvent in the graphite concentrate, step A11 can be simultaneously executed to collect the flotation solvent volatilized from the graphite concentrate, and the collected flotation solvent can be applied to the subsequent step S103 to achieve the recycling of the flotation solvent. Specifically, when the flotation solvent is pure water, the flotation solvent collected through step A11 is distilled water.

[0099] Correspondingly, during the process of keeping the first graphite concentrate at the second temperature for the second duration through step S1042 to volatilize the flotation reagent in the first concentrate, step A12 can be simultaneously executed to collect the flotation reagent volatilized from the first concentrate, and the collected flotation reagent can be applied to the subsequent step S103 to achieve the recycling of the flotation reagent.

[0100] In an embodiment of the present invention, during the process of performing segmented pyrolysis treatment on the graphite concentrate to remove the flotation solvent and flotation reagent in the graphite concentrate, step A11 can be executed to collect the flotation solvent volatilized from the graphite concentrate during the process of keeping the graphite concentrate at the first temperature for the first duration, and step A12 can be executed to collect the flotation reagent volatilized from the first concentrate during the process of keeping the first graphite concentrate at the second temperature for the second duration, which is beneficial to realizing the recycling of the flotation solvent and flotation reagent, improving the utilization rate of the flotation solvent and flotation reagent in the embodiment of the present invention, and further beneficial to reducing the cost of recovering graphite from waste secondary batteries in the embodiment of the present invention.

[0101] Optionally, the first temperature is 100°C to 120°C, and the first duration is 50 min to 200 min; specifically, the first temperature can be one of 100°C, 105°C, 110°C, 112°C, 118°C, and 120°C or the range value of any two of them, and the first duration can be one of 50 min, 80 min, 100 min, 150 min, and 200 min or the range value of any two of them.

[0102] In the embodiment of the present invention, the first temperature is controlled within the range of 100°C to 120°C, which can improve the volatilization efficiency of the flotation solvent while avoiding the volatilization of the flotation reagent along with the flotation solvent. While reducing the residual amount of the flotation solvent in the first concentrate, it can also improve the purity of the flotation solvent collected through step A11; further, in the embodiment of the present invention, the first duration is controlled within the range of 50 min to 200 min, which can enable the flotation solvent in the graphite concentrate to volatilize sufficiently, further reduce the residual amount of the flotation solvent in the first concentrate, and improve the purity of the flotation solvent collected through step A11.

[0103] Optionally, the second temperature is 220°C to 260°C, and the second duration is 30 min to 60 min; specifically, the second temperature can be one of 220°C, 230°C, 240°C, 250°C, and 260°C or the range value of any two of them, and the second duration can be one of 30 min, 40 min, 45 min, 50 min, 55 min, and 60 min or the range value of any two of them.

[0104] In the embodiment of the present invention, controlling the second temperature within the range of 220°C to 260°C can improve the volatilization efficiency of the flotation reagent; further, in the embodiment of the present invention, controlling the second duration within the range of 30 min to 60 min can enable the flotation reagent in the graphite concentrate to volatilize sufficiently. While reducing the residual amount of the flotation reagent in the purified graphite, it can also increase the amount of the flotation reagent collected through step A12, thereby improving the recycling rate of the flotation reagent.

[0105] Optionally, in step S105, the temperature for calcining the purified graphite is 2600°C to 3000°C, and the duration for calcining the purified graphite is 4 h to 24 h. Specifically, in step S105, the temperature for calcining the purified graphite can be one of 2600°C, 2700°C, 2750°C, 2800°C, 2950°C, and 3000°C or the range value of any two of them; the duration for calcining the purified graphite can be one of 4 h, 10 h, 15 h, 20 h, and 24 h or the range value of any two of them.

[0106] In the embodiment of the present invention, by controlling the temperature of the calcination treatment within the range of 2600°C to 3000°C and controlling the duration of the calcination treatment within the range of 4 h to 24 h, the metal elements remaining in the purified graphite can be better removed, thereby improving the purity of the recovered graphite, and the repair process of the lattice structure in the purified graphite can be promoted, improving the crystallinity of the purified graphite, and further improving the crystal quality of the recovered graphite.

[0107] Optionally, the step of crushing the acid leaching residue in step S102 to obtain a crushed product includes steps S1021 to S1022:

[0108] Step S1021: Prepare a ball milling slurry based on the acid leaching residue and a ball milling solvent.

[0109] Step S1022: Ball mill the ball milling slurry to obtain a crushed product.

[0110] In the embodiment of the present invention, the method of crushing the acid leaching residue is ball milling.

[0111] In step S1021, first prepare a ball milling slurry based on the acid leaching residue and a ball milling solvent. In the embodiment of the present invention, the ball milling solvent and the flotation solvent are the same, both being pure water, which can avoid the introduction of more impurity components and improve the effect of flotation treatment on the crushed product in step S103.

[0112] The crushed product obtained through step S1022 can be a dried product after removing the ball milling solvent, or a slurry containing both the crushed acid leaching residue and the ball milling solvent.

[0113] Among them, in the ball milling slurry, the mass ratio of the acid leaching residue is 65wt% - 85wt%. Within this range, during the ball milling process in step S1022, the effective collisions between the acid leaching residues in the ball milling slurry and between the acid leaching residue and the ball milling medium can be increased, enabling the acid leaching residue to be crushed more quickly, and making the mass ratio of the particles with a particle size smaller than the target size in the crushed product be 80wt% - 95wt%, which is beneficial to improving the efficiency of ball milling the acid leaching residue.

[0114] Among them, the ball milling medium is a zirconia ball, and the tank body of the ball milling tank is an agate tank.

[0115] Specifically, in the ball milling slurry, the mass ratio of the acid leaching residue can be one of 65wt%, 70wt%, 75wt%, 80wt% and 85wt%, or a range value between any two of them.

[0116] In the pulverized material obtained through step S1022, the mass percentage of particles with a particle size smaller than the target size can be one of 80wt%, 82wt%, 85wt%, 90wt%, 93wt%, and 95wt% or a range value between any two of them; in the pulverized material, controlling the mass percentage of particles with a particle size smaller than the target size within the range of 80wt% - 95wt% is beneficial to reducing the overall particle size of the particles in the pulverized material, thereby reducing the degree of mutual encapsulation between graphite and metal elements in the pulverized material and the residual amount of metal elements in the graphite concentrate obtained through step S103; in addition, reducing the overall particle size of the particles in the pulverized material can also reduce the layer spacing of the recovered graphite, improve the graphitization degree of the recovered graphite, and increase the diffusion rate of ions in the secondary battery prepared from the recovered graphite obtained according to the embodiments of the present invention. Further, reducing the overall particle size of the particles in the pulverized material can also shorten the migration path of ions in the secondary battery, which is beneficial to further increasing the diffusion rate of ions in the secondary battery, and thus improving the electrochemical performance of the secondary battery.

[0117] In the embodiments of the present invention, the target size can be 20μm.

[0118] Optionally, in step S1022, the rotation speed of ball-milling the ball-milling slurry is 100rpm - 500rpm, and the duration of ball-milling the ball-milling slurry is 0.5h - 4h; specifically, the rotation speed of ball-milling the ball-milling slurry can be one of 100rpm, 200rpm, 300rpm, 400rpm, and 500rpm or a range value between any two of them; the duration of ball-milling the ball-milling slurry can be one of 0.5h, 1h, 2h, 2.5h, 3.5h, and 4h or a range value between any two of them.

[0119] In the embodiments of the present invention, controlling the rotation speed of ball-milling the ball-milling slurry within the range of 100rpm - 500rpm and controlling the duration of ball-milling the ball-milling slurry within the range of 0.5h - 4h is beneficial to reducing the overall particle size of the particles in the pulverized material, such that the mass percentage of particles with a particle size smaller than the target size in the pulverized material is 80wt% - 95wt%, thereby reducing the residual amount of metal elements in the graphite concentrate obtained through step S103, improving the graphitization degree of the recovered graphite, and improving the electrochemical performance of the secondary battery prepared from the recovered graphite obtained according to the embodiments of the present invention.

[0120] Optionally, the flotation treatment includes rougher treatment and cleaner treatment; the step S103 of subjecting the pulverized material to flotation treatment to obtain graphite concentrate includes steps S1031 to S1032:

[0121] Step S1031: Subject the pulverized material to at least one rougher treatment to obtain a rougher concentrate.

[0122] Step S1032: performing at least one concentration treatment on the rougher concentrate to obtain graphite concentrate.

[0123] In an embodiment of the present invention, the flotation treatment of the pulverized material includes at least one roughing treatment and at least one fine treatment; wherein the roughing treatment is used to improve the recovery rate of graphite concentrate recovered from the pulverized material, and the fine treatment is used to improve the purity of the recovered graphite concentrate.

[0124] In order to improve the recovery rate of graphite concentrate from the crushed material, in an embodiment of the present invention, the duration of the roughing treatment is greater than that of the cleaning treatment, and the mass proportion of the flotation reagent in the flotation system during the roughing treatment is greater than the mass proportion of the flotation reagent in the flotation system during the cleaning treatment.

[0125] As an example, in step S1031, the number of times the crushed material is subjected to roughing treatment is 1; in step S1032, the number of times the roughing concentrate is subjected to flotation treatment is 3. While improving the recovery rate of graphite concentrate and the purity of graphite concentrate, the efficiency of flotation treatment of the crushed material to obtain graphite concentrate can also be improved.

[0126] Optionally, each roughing process lasts 3 minutes to 5 minutes, and each fine processing lasts 1 minute to 3 minutes.

[0127] Optionally, during the roughing treatment of step S1031, the mass proportion of the collector in the flotation system is 50g / t to 200g / t, and the mass proportion of the frother in the flotation system is 30g / t to 100g / t. Within this range, the effects of the collector and the frother in improving the recovery rate of the graphite concentrate can be fully exerted.

[0128] Specifically, during the roughing treatment process, the mass proportion of the collector in the flotation system can be within the range of one or any two of 50 g / t, 100 g / t, 150 g / t, 180 g / t and 200 g / t; the mass proportion of the frother in the flotation system can be within the range of one or any two of 30 g / t, 40 g / t, 50 g / t, 70 g / t, 90 g / t and 100 g / t.

[0129] Optionally, during the concentration treatment process of step S1032, the mass proportion of the collector in the flotation system is 5g / t to 50g / t, and the mass proportion of the frother in the flotation system is 0g / t to 20g / t. Within this range, the effects of the collector and the frother in improving the purity of the graphite concentrate can be fully exerted.

[0130] Specifically, during the beneficiation process, the mass ratio of the collector in the flotation system can be one of 5 g / t, 10 g / t, 20 g / t, 35 g / t, 40 g / t, and 50 g / t or a range value between any two of them; the mass ratio of the frother in the flotation system can be one of 0 g / t, 5 g / t, 10 g / t, 15 g / t, 18 g / t, and 20 g / t or a range value between any two of them.

[0131] Optionally, after performing the flotation treatment on the pulverized material in step S103 to obtain graphite concentrate, the method further includes step B11:

[0132] Step B11: Filter the graphite concentrate to reduce the moisture content of the graphite concentrate to 10% - 20%.

[0133] In the embodiment of the present invention, after obtaining the graphite concentrate by performing step S103 and before performing the stepwise pyrolysis treatment on the graphite concentrate in step S104, the graphite concentrate can also be filtered through step B11 to reduce the moisture content of the graphite concentrate to 10% - 20%, which is beneficial to shortening the duration of the stepwise pyrolysis treatment of the graphite concentrate in step S104. While reducing the energy consumption during the stepwise pyrolysis treatment, it can also improve the efficiency of the stepwise pyrolysis treatment.

[0134] As an example, the waste secondary battery is a lithium-ion battery; refer to Figure 2 , which shows the step flow of a method for recovering graphite from waste secondary batteries provided by the embodiment of the present invention Figure 2 , the method may include steps S201 to S204:

[0135] Step S201: Ball milling.

[0136] Specifically, first, based on the acid leaching residue of lithium-ion battery black powder and pure water as the ball milling solvent, prepare a ball milling slurry; then, perform ball milling on the ball milling slurry to obtain a pulverized material.

[0137] Step S202: Flotation treatment.

[0138] Specifically, use pure water as the flotation solvent, and perform flotation treatment and filtration treatment on the pulverized material obtained through step S201 with pure water and the flotation solvent to obtain graphite concentrate and metal impurities.

[0139] Step S203: Stepwise pyrolysis treatment.

[0140] Specifically, the graphite concentrate obtained in step S202 is subjected to a segmented pyrolysis treatment, which not only removes the pure water and flotation agent in the graphite concentrate to obtain purified graphite, but also collects the pure water and flotation agent in the graphite concentrate to obtain distilled water and flotation agent, and the collected flotation agent is repeatedly applied to the flotation treatment process of step S202.

[0141] Step S204: calcination treatment.

[0142] Specifically, the purified graphite obtained in step S203 is calcined to obtain the recycled graphite recovered in the embodiment of the present invention.

[0143] The present invention also provides graphite, wherein the graphite is recovered by any of the above methods for recovering graphite from waste secondary batteries.

[0144] The present invention also proposes a secondary battery, wherein the secondary battery includes a positive electrode sheet and a negative electrode sheet, the negative electrode sheet includes a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes the graphite as described above.

[0145] The present invention is described in detail below by way of examples.

[0146] Example 1

[0147] (1) Obtaining acid leaching residue of black powder in waste lithium-ion batteries

[0148] First, the waste lithium-ion batteries are discharged; then, the waste lithium-ion batteries after the discharge treatment are disassembled to separate the positive electrode active material, negative electrode active material, separator, electrolyte and other components of the waste lithium-ion batteries, and the disassembled and separated components are sorted by magnetic separation, and the mixture of the positive electrode active material and the negative electrode active material obtained by the sorting is determined as the black powder of the waste lithium-ion batteries; then, the black powder is placed in an acid leaching tank, and sulfuric acid with a concentration of 3 mol / L is added to the acid leaching tank, and the black powder is acid-leached at 90° C. for 3 hours so that the valuable metals in the black powder are dissolved by the leaching agent to obtain an acid leaching slurry, wherein the mass ratio of sulfuric acid to black powder is 5:1; then, the acid leaching slurry is solid-liquid separation to obtain solid components in the black powder that are insoluble in the leaching agent, and the solid components are washed and dried to obtain acid leaching residue (SG) of the black powder in the waste lithium-ion batteries.

[0149] (2) Obtaining crushed material

[0150] First, prepare a ball-milling slurry by mixing the acid-leaching residue obtained in step (1) with pure water, where the mass percentage of the acid-leaching residue in the ball-milling slurry is 75 wt%. Then, ball-mill the ball-milling slurry at a rotation speed of 300 rpm for 2 h to obtain a pulverized material.

[0151] (3) Obtain graphite concentrate

[0152] First, prepare a first flotation system by mixing the pulverized material obtained in step (2), pure water, n-undecane, and methyl isobutyl carbinol. In the first flotation system, the mass percentage of n-undecane is 100 g / t, and the mass percentage of methyl isobutyl carbinol is 60 g / t. Then, conduct a rough flotation treatment on the pulverized material once using the first flotation system to obtain a rough concentrate, and the duration of the rough flotation treatment is 4 min. Then, prepare a second flotation system by mixing the rough concentrate, pure water, n-undecane, and methyl isobutyl carbinol. In the second flotation system, the mass percentage of n-undecane is 30 g / t, and the mass percentage of methyl isobutyl carbinol is 10 g / t. Then, conduct a cleaning flotation treatment on the rough concentrate three times using the second flotation system to obtain graphite concentrate, and the duration of each cleaning flotation treatment is 2 min. Finally, conduct a filtration treatment on the graphite concentrate to reduce the water content rate of the graphite concentrate to 15%.

[0153] (4) Obtain purified graphite

[0154] First, raise the temperature of the graphite concentrate obtained in step (3) to the first temperature of 110 °C and keep it at the first temperature of 110 °C for the first duration of 120 min to volatilize the pure water in the graphite concentrate and obtain a first concentrate. Then, raise the temperature of the first concentrate from the first temperature of 110 °C to the second temperature of 240 °C and keep it at the second temperature of 240 °C for the second duration of 50 min to volatilize the n-undecane and methyl isobutyl carbinol in the first graphite concentrate and obtain a second concentrate, and determine the second concentrate as purified graphite.

[0155] (5) Obtain recycled graphite

[0156] Calcine the purified graphite obtained in step (4) at 2800 °C for 15 h to obtain recycled graphite (RG).

[0157] Examples 2 - 3

[0158] The differences between Examples 2 - 3 and Example 1 are that in step (2), the mass percentages of the acid-leaching residue in the ball-milling slurry are 65 wt% and 85 wt% respectively.

[0159] Examples 4 - 5

[0160] Examples 4-5 are different from Example 1 in that in step (2), the ball-milling slurry is ball-milled at a speed of 100 rpm for 4 h, and the ball-milling slurry is ball-milled at a speed of 500 rpm for 0.5 h.

[0161] Examples 6-7

[0162] Examples 6-7 are different from Example 1 in that in step (3), in the first flotation system, the mass ratio of n-undecane is 50 g / t and the mass ratio of methyl isobutyl carbinol is 30 g / t, and in the first flotation system, the mass ratio of n-undecane is 200 g / t and the mass ratio of methyl isobutyl carbinol is 100 g / t.

[0163] Examples 8-9

[0164] Examples 8-9 are different from Example 1 in that in step (3), in the second flotation system, the mass ratio of n-undecane is 5 g / t and the mass ratio of methyl isobutyl carbinol is 0 g / t, and in the second flotation system, the mass ratio of n-undecane is 50 g / t and the mass ratio of methyl isobutyl carbinol is 20 g / t.

[0165] Examples 10-11

[0166] Examples 10-11 are different from Example 1 in that in step (4), the first temperature is 100 °C and the first duration is 200 min, and the first temperature is 120 °C and the first duration is 50 min.

[0167] Examples 12-13

[0168] Examples 12-13 are different from Example 1 in that in step (4), the second temperature is 220 °C and the second duration is 60 min, and the second temperature is 260 °C and the second duration is 30 min.

[0169] Examples 14-15

[0170] Examples 14-15 are different from Example 1 in that in step (5), the purified graphite is calcined at 2600 °C for 24 h, and the purified graphite is calcined at 3000 °C for 4 h.

[0171] Comparative Example 1

[0172] Comparative Example 1 is different from Example 1 in that it only includes step (1).

[0173] Comparative Example 2

[0174] Comparative Example 2 is different from Example 1 in that it does not include steps (1) to (5), and uses the techniques well-known in the art to obtain battery-grade graphite.

[0175] The process parameters of the graphite materials obtained through each example and comparative example are shown in Table 1; among them, the graphite materials include recycled graphite obtained through Examples 1 to 15, acid leaching residue obtained through Comparative Example 1, and battery-grade graphite obtained through Comparative Example 2.

[0176] Table 1

[0177]

[0178]

[0179] Test method:

[0180] (1) Scanning Electron Microscope (SEM) test of graphite materials: Use SEM to characterize the surface morphology of the graphite materials obtained through the above examples and comparative examples, and the magnification range is 500 times to 30,000 times.

[0181] (2) Transmission electron microscope (TEM) test of graphite: Use TEM to characterize the microstructure of the graphite materials obtained through the above examples and comparative examples. The graphite material sample is dissolved in an ethanol solvent to prepare a dispersion liquid with a certain concentration, and the test is carried out after the solvent volatilizes.

[0182] (3) Cycle performance test of secondary batteries: In an environment of 25 ± 3 °C, Step 1. Leave it standing for 30 min; Step 2. Constant current charge at a rate of 1.0 C until the upper cut-off voltage is reached; Step 3. Leave it standing for 30 min; Step 4. Constant current discharge at a rate of 1.0 C until the lower cut-off voltage; Repeat the cycle of Steps 1 to 4, and stop charging and discharging when the number of cycles is equal to 300 times.

[0183] The graphite materials obtained through Example 1 and Comparative Example 1 are subjected to the above SEM test, and the test results are as Figure 3 and Figure 4 shown; referring to Figure 3 , compared with the acid leaching residue obtained through Comparative Example 1, the size of the recycled graphite obtained through Example 1 is significantly reduced, and as Figure 4 shown, the shape of the recycled graphite obtained through Example 1 is more regular and the surface is smoother and flatter.

[0184] The graphite materials obtained through Example 1 and Comparative Example 1 are subjected to the above TEM test, and the test results are as Figure 5 and Figure 6 shown; referring to Figure 5 , the layer spacing of the acid leaching residue obtained through Comparative Example 1 is 3.737 nm, referring toFigure 6 The interlayer spacing of the recycled graphite obtained through Example 1 is 3.678 nm. It can be seen therefrom that the embodiments of the present invention can reduce the interlayer spacing of the recycled graphite and improve the graphitization degree of the recycled graphite.

[0185] The graphite materials obtained through the above various examples and comparative examples were used as the negative electrode active materials to prepare secondary batteries respectively. Among the secondary batteries prepared based on the graphite materials obtained through the above examples and comparative examples, except for the different negative electrode active materials, other components were the same. The cycle performance tests of the above various secondary batteries were carried out at a 1C rate, and the test results are shown in Table 2.

[0186] Table 2

[0187]

[0188] According to the test data in Table 2, when the secondary battery prepared based on the recycled graphite obtained through the embodiments of the present invention was cycled 300 times at a 1C / 1C charge-discharge rate, the reversible capacity and capacity retention rate of the secondary battery were significantly higher than those of the secondary battery prepared based on the acid leaching residue obtained through Comparative Example 1, and the reversible capacity and capacity retention rate of the secondary battery prepared based on the recycled graphite obtained through the embodiments of the present invention were basically the same as those of the secondary battery prepared based on the battery-grade graphite obtained through Comparative Example 2. It can be seen therefrom that the purity and quality of the recycled graphite recovered through the embodiments of the present invention can reach the same level as that of the battery-grade graphite.

[0189] In summary, the method for recovering graphite from waste secondary batteries provided by the embodiments of the present invention can disperse the graphite and metal elements in the acid leaching residue by pulverizing the acid leaching residue of the black powder in the waste secondary battery to obtain a pulverized material, which is beneficial to separating the graphite and metal elements in the pulverized material by flotation treatment of the pulverized material, and further beneficial to reducing the residual amount of metal elements in the graphite concentrate obtained by flotation treatment. Then, by subjecting the graphite concentrate to staged pyrolysis treatment, the flotation solvent and flotation reagent in the graphite concentrate can be removed, and the residual amount of the flotation solvent and flotation reagent in the purified graphite can be reduced, and the purity of the graphite in the purified graphite can be improved; further, by calcining the purified graphite, not only the residual metal elements in the purified graphite can be removed, but also the lattice structure of the purified graphite can be repaired, and the crystallinity of the purified graphite can be improved, thereby improving the purity and crystal quality of the recycled graphite recovered through the embodiments of the present invention, realizing the recycling of graphite in waste secondary batteries, and avoiding the environmental pollution and waste of graphite resources caused by the graphite in waste secondary batteries.

[0190] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the claims are intended to be construed as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0191] The above has introduced in detail a method for recovering graphite from waste secondary batteries, graphite, and secondary batteries provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for recovering graphite from waste secondary batteries, characterized in that, The method includes: Obtaining the acid leaching residue of the black powder in the waste secondary battery; Crushing the acid leaching residue to obtain a crushed material; Performing flotation treatment on the crushed material to obtain graphite concentrate; the graphite concentrate includes a flotation solvent and a flotation reagent; Performing segmented pyrolysis treatment on the graphite concentrate to remove the flotation solvent and the flotation reagent in the graphite concentrate, and obtaining purified graphite; Performing calcination treatment on the purified graphite to obtain recycled graphite.

2. The method according to claim 1, wherein The performing segmented pyrolysis treatment on the graphite concentrate to remove the flotation solvent and the flotation reagent in the graphite concentrate, and obtaining purified graphite includes: Raising the temperature of the graphite concentrate to a first temperature, and keeping the graphite concentrate at the first temperature for a first duration, so that the flotation solvent in the graphite concentrate volatilizes, and obtaining a first concentrate; Raising the temperature of the first concentrate from the first temperature to a second temperature, and keeping the first graphite concentrate at the second temperature for a second duration, so that the flotation reagent in the first concentrate volatilizes, and obtaining a second concentrate, and determining the second concentrate as purified graphite.

3. The method according to claim 2, wherein The method further includes: During the process of keeping the graphite concentrate at the first temperature for the first duration, collecting the flotation solvent volatilized from the graphite concentrate; During the process of keeping the first graphite concentrate at the second temperature for the second duration, collecting the flotation reagent volatilized from the first concentrate.

4. The method according to claim 2 or 3, characterized in that, The first temperature is 100°C to 120°C, and the first duration is 50 min to 200 min; the second temperature is 220°C to 260°C, and the second duration is 30 min to 60 min.

5. The method according to claim 1, wherein The temperature for performing the calcination treatment on the purified graphite is 2600°C to 3000°C, and the duration for performing the calcination treatment on the purified graphite is 4 h to 24 h.

6. The method according to claim 1, characterized in that, The crushing the acid leaching residue to obtain a crushed material includes: Formulating a ball milling slurry based on the acid leaching residue and a ball milling solvent; in the ball milling slurry, the mass ratio of the acid leaching residue is 65 wt% to 85 wt%; Performing ball milling on the ball milling slurry to obtain a crushed material; in the crushed material, the mass ratio of the particles with a particle size smaller than the target size is 80 wt% to 95 wt%.

7. The method according to claim 6, characterized in that, The rotation speed for performing ball milling on the ball milling slurry is 100 rpm to 500 rpm, and the duration for performing ball milling on the ball milling slurry is 0.5 h to 4 h.

8. The method according to claim 1, wherein The flotation treatment includes roughing treatment and cleaning treatment; The performing flotation treatment on the crushed material to obtain graphite concentrate includes: Performing at least one roughing treatment on the crushed material to obtain a rougher concentrate; Performing at least one cleaning treatment on the rougher concentrate to obtain graphite concentrate; n 9. The method according to claim 8, characterized in that Wherein, the duration of the roughing treatment is longer than the duration of the cleaning treatment, and the mass ratio of the flotation reagent in the flotation system during the roughing treatment is greater than the mass ratio of the flotation reagent in the flotation system during the cleaning treatment. The flotation reagent includes a collector and a frother; During the rough selection process, the mass ratio of the collector in the flotation system is 50 g / t to 200 g / t, and the mass ratio of the frother in the flotation system is 30 g / t to 100 g / t; During the cleaning process, the mass ratio of the collector in the flotation system is 5 g / t to 50 g / t, and the mass ratio of the frother in the flotation system is 0 g / t to 20 g / t.

10. The method according to claim 1, wherein After the flotation treatment of the crushed material to obtain graphite concentrate, the method further includes: Filtering the graphite concentrate to reduce the water content of the graphite concentrate to 10% to 20%.

11. A kind of graphite, characterized in that, The graphite is obtained by recycling the graphite from waste secondary batteries according to any one of claims 1 to 10.

12. A secondary battery, characterized in that, It includes a positive electrode plate and a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes the graphite according to claim 11.

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