Method for recycling and regenerating negative electrode graphite of waste battery

Abstract

The application discloses a recycling method of waste battery negative graphite, and relates to the field of lithium ion battery material recycling. The application uniformly mixes lithium carbonate fine powder and graphite to obtain preliminary prelithiation graphite, and then activates lithium atoms in the waste graphite through calcination to realize double prelithiation. Lithium oxide generated in the high-temperature calcination process of lithium carbonate becomes a fluxing agent, and the surface tension generated when the lithium oxide shrinks during slow cooling is used to gather small-particle-size graphite together, thereby providing necessary conditions for increasing the particle size of the graphite and reducing the specific surface area. Finally, a carbon source is used for coating and heat treatment on the surface of the graphite to realize high-value utilization of the retired lithium ion battery negative material. The method organically integrates the double prelithiation, high-temperature calcination and carbon coating processes, simultaneously repairs the internal structure of the damaged graphite negative material and the surface coating layer, and the first charge-discharge efficiency of the regenerated graphite material is obviously improved, and the regenerated graphite material is easy to be prepared and produced in a large scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery material recycling, in particular to a method for recycling and regenerating waste battery negative graphite. BACKGROUND

[0002] In recent years, energy and environmental problems have become increasingly prominent, and the development of new energy has become the trend of energy strategy. Among them, electrochemical energy storage has been widely used in the world due to its high energy storage efficiency, less dependence on external environment, relatively mature technology and wide application range. With the support of the country, new energy vehicles have developed rapidly in China. However, as the "heart" of new energy vehicles, the service life of power batteries is only 4-6 years. At present, the power batteries on the first batch of new energy vehicles in China have fully entered the "retirement period", and it is estimated that by 2025, the cumulative retired amount of domestic power lithium batteries will be close to 800,000 tons. Power lithium batteries contain many metal elements and organic substances, and if they are not effectively treated after retirement, they will cause serious resource waste and environmental pollution. Based on this, the state has introduced a series of policies to regulate and guide the healthy development of lithium battery recycling industry, and relevant research and industrialization promotion have been highly valued.

[0003] At present, the material recycling of lithium batteries mainly focuses on valuable metals such as lithium, cobalt, nickel, manganese and metal current collectors such as aluminum and copper in the positive active material. Because the negative graphite has a wide source and low recycling added value, the recycling technology and industrial development of the negative electrode are still in the initial stage. As an important strategic resource of the country, graphite has limited reserves and has very important economic value. With the increasing amount of retired power batteries year by year, it is urgent to recycle and reuse the retired graphite.

[0004] Currently, some recycling manufacturers can recycle waste graphite to obtain graphite material as lithium ion battery negative electrode material. However, the first coulombic efficiency of the recycled graphite negative electrode material is lower than that of the fresh graphite negative electrode material in actual application. The reason is that the bulk phase and surface of the retired graphite are damaged to different degrees after a long time of cycling, so it needs to be repaired by structure regeneration means. Chinese patent CN 109524736 A discloses a recycling method of graphite in waste batteries and its use: graphite slag recovered from waste batteries is used as a raw material, and after acid washing, the graphite is preliminarily purified, and then the preliminarily purified graphite is oxidized in a reaction kettle to obtain secondary purified graphite, and finally the secondary purified graphite is coated with pitch to obtain regenerated graphite material. Coating the surface of graphite with a carbon source to some extent improves and reconstructs the surface electron / ion transmission channel, and reduces the generation of SEI. However, only surface coating cannot effectively repair the internal crystal structure defects of the retired graphite, and the degree of graphitization of the graphite is not effectively improved. At the same time, acid washing removes lithium in the activated negative electrode powder to some extent, ignoring the positive role of lithium in the repair process of the retired graphite. Chinese patent CN 111924836 A discloses a recycling method of retired lithium ion battery negative electrode graphite: the organic components in the retired graphite are converted into amorphous carbon by calcination, and the prelithiation of the retired graphite is realized by using the migration characteristics of lithium atoms at different temperatures. However, on the one hand, the prelithiation of the retired graphite by relying only on a small amount of residual lithium cannot meet the subsequent use requirements. On the other hand, due to the co-embedding of solvated lithium ions into the graphite layer during the early battery cycling process, the crystal structure is damaged, and the negative electrode particles are easily damaged during the separation of the current collector and the active material, resulting in small particle size of the retired graphite, thereby increasing the contact area between the regenerated graphite and the electrolyte, increasing the side reaction, and finally reducing the first charge-discharge efficiency. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a recycling method of waste battery negative electrode graphite. The present application first mixes lithium carbonate powder with graphite uniformly for prelithiation, and then activates the lithium in the SEI of the original waste graphite at high temperature and re-applies it to the graphite to realize double prelithiation. In addition, a small amount of lithium oxide is generated as a fluxing agent at high temperature, and the surface tension generated during the slow cooling process can gather the broken small particle size graphite together, thereby creating the necessary conditions for increasing the particle size of the graphite and reducing the specific surface area. Finally, the surface of the graphite is coated with a carbon source and heat treated, and finally the retired lithium ion battery negative electrode material is used in a high-value way. This method integrates double prelithiation, high-temperature calcination and carbon coating processes, and repairs the internal structure and surface structure of the damaged graphite negative electrode material at the same time, and the regenerated graphite material obtained has good consistency and is easy to mass produce.

[0006] To solve the above technical problems, the application adopts the following technical solutions:

[0007] (1) The graphite mixture obtained by disassembling retired batteries of different sources is used as raw material, and the retired graphite powder and copper foil are separated through current collector stripping pretreatment;

[0008] (2) The retired graphite powder obtained in step (1) is classified by screening through an electric vibrating screen machine, and the intermediate particle size sample obtained by classification is recovered to obtain a crude graphite product;

[0009] (3) The crude graphite product is uniformly mixed with lithium carbonate powder to obtain pre-lithiated graphite;

[0010] (4) Calcination is carried out in an inert atmosphere, and after calcination is completed, it is cooled to room temperature to obtain double pre-lithiated graphite;

[0011] (5) The carbon source material is mixed with the double pre-lithiated graphite obtained in step (4) to perform carbon coating, and then the carbonization of the coating layer is carried out in a rotary furnace to obtain a regenerated graphite negative electrode material.

[0012] Preferably, the current collector stripping pretreatment in step (1) adopts one or more of crushing-gas sorting, calcination, and solvent leaching.

[0013] Preferably, the screen mesh of the electric vibrating screen machine in step (2) is 300-2500 mesh.

[0014] Preferably, the particle size of the crude graphite product in step (2) is 5-50 microns.

[0015] Preferably, the inert atmosphere in steps (4) and (5) is one or more of nitrogen, argon, etc.

[0016] Preferably, the particle size of the lithium carbonate powder in step (3) is 100 nm-1000 nm, and the addition amount is 0.5%-10% of the mass of the crude graphite product.

[0017] Preferably, in step (4), the calcination process is first heated at a heating rate of 0.5-10℃ / min to 900-1200℃, and then slowly cooled to room temperature at a rate of 0.5-10℃ / min after maintaining the calcination temperature for 1-12h.

[0018] Preferably, in step (5), the carbon source is one or more of coal tar pitch, petroleum pitch, emulsified pitch, citric acid, phenolic resin, chitosan, sucrose, polyvinyl alcohol, polypropylene alcohol, or polyaniline, and the addition amount of the carbon source is 0.1%-5% of the mass of the twice-treated graphite.

[0019] Preferably, the rotation speed of the rotary furnace in step (5) is 25-150 r / min, and the calcination process in the rotary furnace is completed in two stages: the first-stage calcination temperature is 300-600 DEG C, and the holding time is 0.5-2.5 h; the second-stage calcination temperature is 900-1300 DEG C, and the calcination time is 0.5 h-12 h; and the heating rate during the calcination process is 1-10 DEG C / min.

[0020] Preferably, the mixing mode of the materials in step (3) and step (5) is one or more of mechanical mixing, pneumatic mixing and impulsive mixing.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) In one aspect, the present application adopts fine lithium carbonate powder and graphite to uniformly disperse and pre-lithiate, and in another aspect, the lithium in the SEI of the waste graphite is activated and re-applied to the graphite according to the migration characteristics of lithium atoms at different temperatures, thereby realizing double pre-lithiation;

[0023] (2) In the present application, part of the lithium oxide produced in the calcination process of lithium carbonate becomes a fluxing agent, and in the slow cooling process, the surface tension generated when the lithium oxide shrinks gathers the broken small-particle-size graphite together, thereby providing necessary conditions for increasing the particle size of the graphite and reducing the specific surface area;

[0024] (3) In the present application, the internal defects of the graphite can be effectively repaired in the two high-temperature heat treatment processes, and the graphitization degree can also be effectively improved;

[0025] (4) In the present application, the surface of the graphite is coated with a carbon source, which can effectively improve and reconstruct the surface electron / ion transmission channel, reduce the generation of SEI, and ultimately realize the high-value utilization of the retired negative electrode material of the lithium ion battery;

[0026] (5) The preparation process of the present application is simple and easy to implement, and is easy to realize large-scale production. The entire double pre-lithiation process is very simple, the regenerated negative electrode material prepared has good consistency, can effectively improve the first charge / discharge efficiency of the regenerated graphite, and is worthy of market promotion. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application is a process flow diagram of the recycling method of the waste battery negative graphite. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the present application, the present application will be described clearly and completely in conjunction with the description and preferred embodiments below, but the protection scope of the present application is not limited to the following specific embodiments.

[0029] Example 1

[0030] The method for recycling and regenerating the negative electrode graphite of the waste battery of the present embodiment is as follows:

[0031] (1) The negative electrode sheet obtained by disassembling the waste lithium ion battery of Company A was used as the raw material, and was treated by a hammer crusher and a universal pulverizer, with the treatment time being 10 min and 15 min respectively. The obtained crushed material was subjected to screening treatment to separate the retired graphite from the copper foil, and a crude graphite product was obtained.

[0032] (2) The nanoscale lithium carbonate powder (200 nm) and the crude graphite product were fully ball-milled and dispersed in a planetary ball mill at a mass ratio of 1:50, and a pre-lithiated graphite material with good dispersibility was obtained.

[0033] (3) The pre-lithiated graphite was calcined, first at a heating rate of 5°C / min to 500°C, then slowly increased to 1100°C at a heating rate of 1°C / min, with a holding time of 5 h, and then slowly cooled to 50°C at a rate of 1°C / min, to obtain double pre-lithiated graphite.

[0034] (4) The coal pitch and the double pre-lithiated graphite were ball-mixed uniformly at a mass ratio of 1:100, and were placed in a rotary furnace at a rotation speed of 100 r / min, and were first heated at a rate of 1°C / min to 500°C and held for 2 h, and then heated at a rate of 1°C / min to 1200°C and held for 1 h, to obtain a regenerated graphite negative electrode material.

[0035] Example 2

[0036] The method for recycling and regenerating the negative electrode graphite of the waste battery of the present embodiment is as follows:

[0037] (1) The negative electrode sheet obtained by disassembling the waste lithium ion battery of Company A was used as the raw material, and was treated by a hammer crusher and a universal pulverizer, with the treatment time being 10 min and 15 min respectively. The obtained crushed material was subjected to screening treatment to separate the retired graphite from the copper foil, and a crude graphite product was obtained.

[0038] (2) The nanoscale lithium carbonate powder (200 nm) and the crude graphite product were fully ball-milled and dispersed in a planetary ball mill at a mass ratio of 1:50, and a pre-lithiated graphite material with good dispersibility was obtained.

[0039] (3) The pre-lithiated graphite was calcined, first at a heating rate of 5°C / min to 500°C, then slowly increased to 1100°C at a heating rate of 1°C / min, with a holding time of 5 h, and then slowly cooled to 50°C at a rate of 1°C / min, to obtain double pre-lithiated graphite.

[0040] (4) The phenolic resin and the double pre-lithiated graphite are mixed uniformly according to a mass ratio of 3:97, and in a rotary furnace at 120 r / min, a temperature rising rate of 2 ℃ / min is adopted, first, the temperature is kept at 600 ℃ for 2 h, and then the temperature is kept at 1000 ℃ for 1 h, to obtain the regenerated graphite negative electrode material.

[0041] Example 3

[0042] The waste battery negative electrode graphite recycling method of the present embodiment has the following steps:

[0043] (1) The negative electrode sheet obtained by disassembling the waste lithium ion battery of company A is used as raw material, and is treated by a hammer crusher and a universal pulverizer for 15 min and 20 min respectively, and the obtained crushed material is subjected to screening treatment to separate the retired graphite from the copper foil, to obtain a graphite crude product.

[0044] (2) The nanoscale lithium carbonate powder (200 nm) and the graphite crude product are fully stirred and dispersed in a ball mill according to a mass ratio of 1:50, to obtain a pre-lithiated graphite material with good dispersibility.

[0045] (3) The pre-lithiated graphite is calcined, first, the temperature is raised to 600 ℃ at a temperature rising rate of 5 ℃ / min, then the temperature is slowly raised to 1050 ℃ at a temperature rising rate of 1 ℃ / min, the holding time is 9 h, and then the temperature is slowly lowered to 50 ℃ at a rate of 1 ℃ / min, to obtain a double pre-lithiated graphite.

[0046] (4) The petroleum pitch and the double pre-lithiated graphite are mixed uniformly in a mixer according to a mass ratio of 1:50, and in a rotary furnace at 150 r / min, a temperature rising rate of 1 ℃ / min is adopted, first, the temperature is kept at 300 ℃ for 2 h, and then the temperature is kept at 1100 ℃ for 2 h, to obtain a regenerated graphite negative electrode material.

[0047] Example 4

[0048] The waste battery negative electrode graphite recycling method of the present embodiment has the following steps:

[0049] (1) The negative electrode sheet obtained by disassembling the waste lithium ion battery of company A is used as raw material, and is treated by a hammer crusher and a universal pulverizer for 15 min and 20 min respectively, and the obtained crushed material is subjected to screening treatment to separate the retired graphite from the copper foil, to obtain a graphite crude product.

[0050] (2) The nanoscale lithium carbonate powder (200 nm) and the graphite crude product are fully stirred and dispersed in a ball mill according to a mass ratio of 1:40, to obtain a pre-lithiated graphite material with good dispersibility.

[0051] (3) The pre-lithiated graphite is calcined, first raised to 600°C at a heating rate of 5°C / min, then slowly raised to 1100°C at a heating rate of 1°C / min, the holding time is 12h, and then slowly cooled to 50°C at a rate of 2°C / min, to obtain double pre-lithiated graphite.

[0052] (4) Citric acid and double pre-lithiated graphite are mixed uniformly at a mass ratio of 3:97, in a rotary furnace at 100 r / min, first at 450°C for 1h, then at 1100°C for 1h, to obtain the regenerated graphite negative electrode material.

[0053] Example 5

[0054] The method for recycling and regenerating the waste battery negative graphite in this example is as follows:

[0055] (1) The negative electrode sheet obtained by disassembling the waste lithium ion battery of company A is used as raw material, and is treated by hammer crusher and universal pulverizer respectively, the treatment time is 8min and 15min respectively, the obtained crushed material is screened to separate the retired graphite from the copper foil, to obtain the graphite crude product.

[0056] (2) Nanoscale lithium carbonate powder (200nm) and the graphite crude product are mixed and dispersed in a ball mill at a mass ratio of 1:35, to obtain pre-lithiated graphite material with good dispersibility.

[0057] (3) The pre-lithiated graphite is calcined, first raised to 500°C at a heating rate of 5°C / min, then raised to 1200°C at a heating rate of 1°C / min, the holding time is 5h, and then cooled to 50°C at a rate of 1°C / min, to obtain double pre-lithiated graphite.

[0058] (4) Sucrose and double pre-lithiated graphite are mixed uniformly in a mixer at a mass ratio of 1:50, in a rotary furnace at 120 r / min, first at 400°C for 1h, then at 1100°C for 3h, to obtain the regenerated graphite negative electrode material.

[0059] Comparative Example 1

[0060] The negative electrode sheet obtained by disassembling the waste lithium ion battery of company A is used as raw material, and is treated by hammer crusher and universal pulverizer respectively, the treatment time is 10min and 15min respectively, the obtained crushed material is screened to separate the retired graphite from the copper foil, to obtain the graphite crude product.

[0061] The crude graphite is calcined, first, the temperature is raised to 500℃ at a rate of 5℃ / min, the organic components in the retired graphite are converted into amorphous carbon, then the temperature is raised to 1100℃ at a rate of 1℃ / min, the holding time is 5h, then the temperature is lowered to 50℃ at a rate of 1℃ / min, the pre-lithiated graphite is obtained.

[0062] Then the coal pitch and the pre-lithiated graphite are ball-milled uniformly according to a mass ratio of 1:100, in a rotary furnace at 100r / min, the temperature is first raised to 500℃ at a rate of 1℃ / min, then the temperature is held for 2h, then the temperature is raised to 1200℃ at a rate of 1℃ / min, the holding time is 1h, the regenerated single pre-lithiated graphite negative electrode material is obtained.

[0063] Comparative Examples 2-5

[0064] The difference between the examples 2-5 and the comparative examples is that the pre-lithiation of the fine lithium carbonate and the crude graphite is not performed (the steps are the same as those of the comparative example 1).

[0065] The following table is the particle size test results and the electrochemical performance table of the double pre-lithiated regenerated graphite prepared in the above examples 1-5 and the single pre-lithiated graphite negative electrode material prepared in the comparative examples 1-5.

[0066]

[0067] As can be seen from the above table, the particle size of the double pre-lithiated regenerated graphite prepared in the examples of the present application is larger than that of the graphite material prepared in the comparative examples, and the corresponding first discharge specific capacity and first charge-discharge efficiency are also significantly higher than those of the single pre-lithiated graphite negative electrode material prepared in the comparative examples.

[0068] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, the above examples and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for recycling and regenerating a negative electrode graphite of a waste battery, characterized by The method comprises the following steps: (1) taking the negative plate obtained by disassembling the retired battery as raw material, and separating the retired graphite powder and copper foil through current collector stripping pretreatment; (2) screening and grading the retired graphite powder obtained in step (1) through an electric vibrating screen machine, recovering the intermediate particle size sample obtained in the grading, and obtaining a graphite crude product; (3) uniformly mixing the obtained graphite crude product with lithium carbonate fine powder to obtain prelithiated graphite; (4) calcining the prelithiated graphite in an inert atmosphere, cooling to room temperature after calcination is completed, and obtaining double prelithiated graphite; (5) mixing a carbon source material with the double prelithiated graphite obtained in step (4), then performing carbon coating, and then performing carbonization of the coating layer in a rotary furnace inert atmosphere to obtain a regenerated graphite negative electrode material; The screen mesh of the electric vibrating screen machine in step (2) is 300-2500 meshes; the particle size of the graphite crude product is 5-50 microns; The particle size of the lithium carbonate fine powder in step (3) is 100-1000 nm, and the addition amount is 0.5%-10% of the mass of the graphite crude product; In step (4), the calcination process is first heated at a heating rate of 0.5-10 ℃ / min to 900-1200 ℃, maintained at the calcination temperature for 1-12 h, and then reduced to room temperature at a rate of 0.5-10 ℃ / min.

2. The method for recycling and regenerating a negative electrode graphite of a waste battery according to claim 1, characterized by: The current collector stripping pretreatment in step (1) adopts one or more of crushing-gas sorting, calcination, and solvent leaching.

3. The method of claim 1, wherein the method is characterized by: The inert atmosphere in step (4) and step (5) is one or more of nitrogen and argon.

4. The method of claim 1, wherein the method is characterized by: The carbon source material in step (5) is one or more of coal tar pitch, petroleum pitch, emulsified asphalt, citric acid, phenolic resin, chitosan, sucrose, polyvinyl alcohol, polypropylene alcohol, or polyaniline, and the addition amount of the carbon source material is 0.1%-5% of the mass of the double prelithiated graphite.

5. The method of claim 1, wherein the method is characterized by: The rotation speed of the rotary furnace in step (5) is 25-150 r / min, and the calcination process in the rotary furnace is completed in two stages: the first stage calcination temperature is 300-600 ℃, and the holding time is 0.5-2.5 h; the second stage calcination temperature is 900-1300 ℃, and the calcination time is 0.5 h-12 h; the heating rate during calcination is 1-10 ℃ / min.

6. The method of claim 1, wherein the method is characterized by: The mixing method of the materials in step (3) and step (5) is one or more of mechanical mixing, pneumatic mixing, and impulsive mixing.

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