Regenerated graphite negative electrode material containing nitrogen and carbon layer and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a regenerated graphite negative electrode material containing a nitrogen-carbon layer and a preparation method and application thereof.The preparation method comprises the steps that waste graphite powder obtained by conducting microwave pretreatment on waste lithium ion battery negative electrode pieces and a nitrogen-containing organic sugar solution are mixed, and after a reaction, the regenerated graphite negative electrode material containing the nitrogen-carbon layer is obtained; a precursor of the coated graphite negative electrode material is obtained; and carrying out microwave heat treatment on the precursor of the coated graphite negative electrode material to obtain the regenerated graphite negative electrode material containing the nitrogen and carbon layer. In a microwave heat treatment process, graphite is rapidly heated under the action of microwaves, heat is directly conducted to a nitrogen-containing organic sugar coating layer on the surface of a precursor, in-situ carbonization of the nitrogen-containing organic sugar coating layer is rapidly and uniformly realized to form a nitrogen-containing carbon layer, and existence of nitrogen atoms on the surface of regenerated graphite reduces the adsorption energy of a negative electrode to Li < + > and promotes migration of Li < + >; and the nitrogen-containing carbon layer can effectively repair the surface defects and damage of the waste graphite, so that good rate capability is embodied.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a recycled graphite anode material containing a nitrogen-containing carbon layer, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, due to advantages such as high energy density, low self-discharge, and no memory effect, lithium-ion batteries have become the most promising secondary batteries and are widely used in the fields of electronic products, electric vehicles, aerospace, and large-scale power energy storage systems. However, lithium-ion batteries have a certain service life, generally 3 - 10 years. Limited by this, a large number of retired batteries will be generated. Therefore, effectively recycling waste lithium-ion batteries has important practical application value. Currently, in the field of battery recycling, the main focus is on recycling cathode materials with relatively high values such as lithium, nickel, cobalt, and manganese. Relatively mature technologies such as hydrometallurgy, pyrometallurgy, and bioleaching have been successfully applied to industrial production, while the recycling of waste graphite anode materials is relatively less.

[0003] Graphite dominates the lithium-ion battery anode market. The production of battery-grade graphite is complex. With the continuous increase in the number of waste lithium-ion batteries, the volume of waste graphite is huge. The direct disposal of waste graphite will also cause serious environmental pollution. In contrast, recycling waste graphite from waste lithium-ion batteries and further reusing it will be more economically beneficial and sustainable.

[0004] Currently, the main methods for repairing the anode graphite of retired lithium-ion batteries include surface coating, element doping, leaching and calcination, and preparing graphite-derived materials, etc. The surface coating method usually uses common carbon-based or metal-based materials as precursors to coat on waste graphite, and combines heat treatment to repair the surface structure defects of graphite, which has a very important impact on improving electrochemical performance. However, the conventional heating method has a long heating time and high energy consumption, and the conventional coating layer is mostly simple amorphous carbon, which can only play a role in repairing defects. The element doping method usually dopes waste graphite with B / N to regulate the local electronic structure and lithium-ion intercalation, but it is difficult to achieve precise regulation. The leaching and calcination method has problems such as leaching solution pollution and high energy consumption. Preparing graphite-derived materials is also an effective method for recycling waste graphite, and has certain potential advantages in synthesizing expanded graphite, graphene, and silicon-carbon composite materials, but the preparation process is often complex and difficult to industrialize.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a regenerated graphite anode material containing a nitrogen-containing carbon layer, its preparation method and application, aiming to solve the problems that the existing repair methods for the graphite anodes of waste lithium-ion batteries can only repair defects but cannot improve the electrochemical performance, etc.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a regenerated graphite anode material containing a nitrogen-containing carbon layer, comprising the steps of:

[0009] Performing microwave pretreatment on the negative electrode sheet of a waste lithium-ion battery to obtain waste graphite powder;

[0010] Mixing the waste graphite powder and a nitrogen-containing organic sugar solution, and after reaction, obtaining a precursor of a coated graphite anode material;

[0011] Performing microwave heat treatment on the precursor of the coated graphite anode material to obtain a regenerated graphite anode material containing a nitrogen-containing carbon layer.

[0012] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, the power of the microwave pretreatment is 0.2 kW - 0.6 kW, the temperature of the microwave pretreatment is 450°C - 550°C, and the time of the microwave pretreatment is 10 min - 60 min.

[0013] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, both the microwave pretreatment and the microwave heat treatment are carried out in an inert atmosphere; the inert atmosphere includes one or more of argon, helium, and nitrogen.

[0014] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, the mass fraction of the nitrogen-containing organic sugar solution is 2.5 wt% - 7.5 wt%.

[0015] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, the solid-liquid ratio of the waste graphite powder to the nitrogen-containing organic sugar solution is 5 g / L - 20 g / L.

[0016] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, the nitrogen-containing organic sugar in the nitrogen-containing organic sugar solution includes one or more of chitosan, chitin, glucosamine, and glycosaminoglycan.

[0017] In the preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer, the power of the microwave heat treatment is 0.2 kW - 0.6 kW, the temperature of the microwave heat treatment is 700°C - 900°C, and the time of the microwave heat treatment is 1 h - 5 h.

[0018] The preparation method of the regenerated graphite anode material with a nitrogen-containing carbon layer, wherein, before the microwave pretreatment of the waste lithium-ion battery anode sheet, the following steps are further included: after the waste lithium-ion battery is deeply discharged, it is disassembled to obtain the waste lithium-ion battery anode sheet;

[0019] The waste lithium-ion battery includes one or more of the lithium-ion batteries used in new energy vehicles, 3C consumer lithium-ion batteries, and lithium-ion batteries for energy storage.

[0020] A regenerated graphite anode material with a nitrogen-containing carbon layer is prepared by using the preparation method of the regenerated graphite anode material with a nitrogen-containing carbon layer.

[0021] The application of a regenerated graphite anode material with a nitrogen-containing carbon layer in a lithium-ion battery.

[0022] Beneficial effects: The present invention provides a regenerated graphite anode material with a nitrogen-containing carbon layer, its preparation method and application. The preparation method of the regenerated graphite anode material with a nitrogen-containing carbon layer includes the steps of: performing microwave pretreatment on the waste lithium-ion battery anode sheet to obtain waste graphite powder; mixing the waste graphite powder with a nitrogen-containing organic sugar solution, and after reaction, obtaining a precursor of the coated graphite anode material; performing microwave heat treatment on the precursor of the coated graphite anode material to obtain a regenerated graphite anode material with a nitrogen-containing carbon layer. The present invention uses microwave pretreatment for impurity removal combined with liquid-phase coating and microwave in-situ carbonization to repair waste graphite. In the microwave pretreatment process, organic impurities in the waste graphite anode material are effectively removed, and at the same time, the separation of the waste graphite anode powder from the current collector is achieved, avoiding the use of toxic solvents for leaching; subsequently, a coated precursor is obtained through liquid-phase coating with a nitrogen-containing organic sugar, and the precursor is heat-treated by using a microwave heating method with rapid heating and selective heating, so that the nitrogen-containing organic sugar is rapidly carbonized in-situ into a nitrogen-containing amorphous carbon layer, effectively repairing the surface defects and damages of the waste graphite anode material. And, during the microwave heat treatment process, the graphite rapidly heats up under the action of microwaves and directly conducts heat to the nitrogen-containing organic sugar coating layer on the surface of the precursor, rapidly and uniformly realizing the in-situ carbonization of the nitrogen-containing organic sugar coating layer to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the adsorption energy of the anode to Li + and promote the migration of Li + , and enhance the surface conductivity of the anode. The nitrogen-containing carbon layer effectively repairs the surface defects and damages of the waste graphite and exhibits good rate performance. Description of the Drawings

[0023] Figure 1 It is a process flow diagram of the preparation method of a regenerated graphite anode material with a nitrogen-containing carbon layer of the present invention;

[0024] Figure 2It is the thermogravimetric curve of waste graphite powder before the microwave pretreatment and impurity removal process in Example 1;

[0025] Figure 3 It is the thermogravimetric curve of waste graphite powder after the microwave pretreatment and impurity removal process in Example 1;

[0026] Figure 4 It is the Fourier transform infrared spectrum of waste graphite powder before and after the microwave pretreatment and impurity removal process in Example 1;

[0027] Figure 5 It is the scanning electron microscope image of waste graphite powder before and after the microwave pretreatment and impurity removal process in Example 1;

[0028] Figure 6 It is the scanning electron microscope image of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in Example 1;

[0029] Figure 7 It is the XPS (N1s) image of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in Example 1;

[0030] Figure 8 It is the conductivity image of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in Example 1;

[0031] Figure 9 It is the cycle performance image of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in Example 1;

[0032] Figure 10 It is the cycle performance image of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in Example 1 at a 2C rate;

[0033] Figure 11 It is the cycle performance image of the regenerated graphite anode material with a pure carbon layer after repair in Comparative Example 1 and Comparative Example 2. Detailed implementation manners

[0034] The present invention provides a regenerated graphite anode material with a nitrogen-containing carbon layer, its preparation method and application. To make the purpose, technical solution and effect of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Those skilled in the art of the present technology can understand that unless otherwise defined, all terms (including technical terms and scientific terms) used here have the same meaning as the general understanding of those of ordinary skill in the art in the field to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined as here.

[0036] As shown Figure 1 in the figure, the present invention provides a method for preparing a regenerated graphite anode material with a nitrogen-containing carbon layer, comprising the steps of:

[0037] Step S10: Microwave pretreat the waste lithium-ion battery anode sheet to obtain waste graphite powder;

[0038] Step S20: Mix the waste graphite powder and a nitrogen-containing organic sugar solution, and after reaction, obtain a precursor of the coated graphite anode material;

[0039] Step S30: Perform microwave heat treatment on the precursor of the coated graphite anode material to obtain a regenerated graphite anode material with a nitrogen-containing carbon layer.

[0040] In this embodiment, microwave pretreatment for impurity removal is combined with liquid-phase coating and microwave in-situ carbonization to repair waste graphite. During the microwave pretreatment process, organic impurities in the waste graphite anode material are effectively removed, and at the same time, the separation of the waste graphite anode powder from the current collector is achieved, avoiding the use of toxic solvents for leaching; subsequently, a coated precursor is obtained through liquid-phase coating with a nitrogen-containing organic sugar. The precursor is heat-treated by a microwave heating method with rapid heating and selective heating, enabling the nitrogen-containing organic sugar to be rapidly carbonized in-situ into a nitrogen-containing amorphous carbon layer, effectively repairing the surface defects and damages of the waste graphite anode material. Moreover, during the microwave heat treatment process, the graphite rapidly heats up under the action of microwaves and directly conducts heat to the nitrogen-containing organic sugar coating layer on the surface of the precursor, rapidly and uniformly realizing the in-situ carbonization of the nitrogen-containing organic sugar coating layer to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the adsorption energy of the anode for Li + ions, promote the migration of Li + ions, and enhance the surface conductivity of the anode. The nitrogen-containing carbon layer effectively repairs the surface defects and damages of the waste graphite and exhibits good rate performance. At the same time, this preparation method has a simple process, is green and pollution-free, has low energy consumption and high capacity, and the obtained regenerated graphite anode material has good cycle stability.

[0041] Specifically, compared with traditional heating, the microwave heat treatment adopted in the present invention has the advantages of rapid heating, selective heating of materials, energy transfer rather than heat transfer, etc. Graphite materials have good microwave absorption characteristics and can rapidly increase in temperature under the action of microwaves. During the microwave pretreatment process, the binder on the surface of waste graphite is rapidly heated and decomposed, effectively separating the waste graphite from the current collector. Using the graphite anode material repaired by this method as the anode material of a lithium-ion battery, it is measured that after the regenerated graphite anode material is cycled 100 times under the condition of 0.5C, the discharge specific capacity of the regenerated graphite anode material is as high as 372.79 mAh / g, which is better than the commercial graphite anode material sold on the market. Moreover, at a high rate of 2C, the discharge specific capacity of the regenerated graphite is as high as 310.6 mAh / g. Further, the preparation method of the present invention effectively repairs the surface damage of the waste graphite anode material, and at the same time introduces nitrogen atoms to construct a Li + fast transmission layer, which has the characteristics of simple process, low energy consumption, environmental protection, and excellent electrochemical performance, and its economic and social benefits are very significant.

[0042] In some embodiments, the power of the microwave pretreatment is 0.2 kW - 0.6 kW, the temperature of the microwave pretreatment is 450°C - 550°C, and the time of the microwave pretreatment is 10 min - 60 min. The binder on the surface of waste graphite can be rapidly heated and decomposed by microwave pretreatment, effectively separating the waste graphite from the current collector. Controlling the power, temperature, and time of the microwave pretreatment within the above ranges can enable the complete decomposition of the binder and the effective separation of the waste graphite from the current collector, obtaining waste graphite powder with a higher purity and simplifying the extraction process of the waste graphite powder. Traditional impurity removal methods generally use acid, alkali, or organic solvent leaching, often accompanied by pollution of the leaching solution.

[0043] In a preferred embodiment, the waste lithium-ion battery anode is placed in a microwave atmosphere tube furnace, rapidly heated to 450°C at a power of 0.2 kW, and kept at this temperature for 10 min to perform microwave treatment on the waste lithium-ion battery anode sheet, obtaining waste graphite powder.

[0044] In some embodiments, both the microwave pretreatment and the microwave heat treatment are carried out in an inert atmosphere; the inert atmosphere includes one or more of argon, helium, and nitrogen. Performing microwave pretreatment on the waste lithium-ion battery anode sheet in an inert atmosphere and performing microwave treatment on the precursor of the coated graphite anode material in an inert atmosphere can avoid oxidation reactions, resulting in performance differences in the graphite anode material.

[0045] In some embodiments, the mass fraction of the nitrogen-containing organic sugar solution is 2.5 wt% - 7.5 wt%. The nitrogen-containing organic sugar solution with this mass fraction can effectively coat the waste graphite powder to form a precursor, so as to achieve rapid in-situ carbonization to form a nitrogen-containing carbon layer under the condition of microwave heat treatment.

[0046] In a preferred embodiment, the mass fraction of the nitrogen-containing organic sugar solution is 2.5 wt%. The nitrogen-containing organic sugar solution with this mass fraction can better coat the waste graphite powder to obtain a precursor of the coated graphite anode material.

[0047] In some embodiments, the solid-liquid ratio of the waste graphite powder to the nitrogen-containing organic sugar solution is 5 g / L - 20 g / L. Controlling the solid-liquid ratio of the waste graphite powder and the nitrogen-containing organic sugar solution within the above range can make the nitrogen-containing organic sugar solution uniformly coat on the surface of the waste graphite powder.

[0048] In a preferred embodiment, the solid-liquid ratio of the waste graphite powder to the nitrogen-containing organic sugar solution is 10 g / L.

[0049] In some embodiments, the nitrogen-containing organic sugars in the nitrogen-containing organic sugar solution include one or more of chitosan, chitin, glucosamine, and glycosaminoglycan. Using nitrogen-containing organic sugars such as chitosan, chitin, glucosamine, and glycosaminoglycan as carbon sources to perform liquid-phase coating on the purified waste graphite powder, and selecting microwave heat treatment to achieve rapid in-situ carbonization to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the adsorption energy of the anode to Li + and promote the migration of Li + , and enhance the conductivity of the anode surface, thereby effectively repairing the surface defects and damages of the waste graphite, and showing good rate performance.

[0050] In some embodiments, the power of the microwave heat treatment is 0.2 kW - 0.6 kW, the temperature of the microwave heat treatment is 700 °C - 900 °C, and the time of the microwave heat treatment is 1 h - 5 h. Using the microwave heating method with rapid heating and selective heating to heat-treat the precursor, the nitrogen-containing organic sugar is rapidly carbonized in-situ into a nitrogen-containing amorphous carbon layer, effectively repairing the surface defects and damages of the waste graphite anode material.

[0051] In a preferred embodiment, the power of the microwave heat treatment is 0.2 kW, the temperature of the microwave heat treatment is 700 °C, and the time of the microwave heat treatment is 1 h.

[0052] In some embodiments, before the microwave pretreatment of the waste lithium-ion battery anode sheet, it further includes the steps of: after the waste lithium-ion battery is deeply discharged, it is disassembled to obtain the waste lithium-ion battery anode sheet.

[0053] In some embodiments, the waste lithium-ion battery includes, but is not limited to, one or more of the lithium-ion batteries used in new energy vehicles, 3C consumer lithium-ion batteries, and lithium-ion batteries for energy storage.

[0054] In addition, the present invention also provides a regenerated graphite anode material with a nitrogen-containing carbon layer, which is prepared by a preparation method of the regenerated graphite anode material with a nitrogen-containing carbon layer.

[0055] In this embodiment, in the process of microwave heat treatment in the preparation method, the graphite rapidly heats up under the action of microwaves, and directly conducts heat to the nitrogen-containing organic sugar coating layer on the surface of the precursor, rapidly and uniformly realizing the in-situ carbonization of the nitrogen-containing organic sugar coating layer to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the adsorption energy of the anode to Li + and promote the migration of Li + and enhance the conductivity of the anode surface. The nitrogen-containing carbon layer effectively repairs the surface defects and damages of the waste graphite, and exhibits good rate performance. The above preparation method effectively repairs the surface damage of the waste graphite anode material, and at the same time introduces nitrogen atoms to construct a Li + rapid transmission layer, which has the characteristics of simple process, low energy consumption, environmental protection, and excellent electrochemical performance, and its economic and social benefits are very significant.

[0056] In addition, an application of a regenerated graphite anode material with a nitrogen-containing carbon layer in a lithium-ion battery.

[0057] The following further gives examples to illustrate the present invention in detail. Similarly, it should be understood that the following examples are only used to further illustrate the present invention, and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all belong to the protection scope of the present invention.

[0058] Example 1

[0059] A used ternary lithium-ion battery from a new energy vehicle is deeply discharged and then disassembled. The negative electrode sheet of the used lithium-ion battery is taken out and placed into a microwave atmosphere tube furnace. It is quickly heated to 450 °C and maintained at this temperature for 10 min. The microwave power is set to 0.2 kW. Argon is introduced as a protective gas during the heating process. After natural cooling, used graphite powder and copper foil are obtained. Take 0.2 g of the used graphite powder after the microwave pretreatment process into a beaker, add 20 ml of a chitosan solution with a mass fraction of 2.5 wt%, stir at 750 rpm for 2 h. After the reaction is completed, the reaction solution is filtered, washed, and dried to obtain a precursor of the coated graphite negative electrode material. The precursor is placed into a microwave atmosphere tube furnace and quickly heated to 700 °C and maintained at this temperature for 1 h. The microwave power is set to 0.2 kW. Argon is introduced as a protective gas during the heating process. After natural cooling, a regenerated graphite negative electrode material with a nitrogen-containing carbon layer is obtained.

[0060] Figure 2 is the thermogravimetric curve of the used graphite powder before the microwave pretreatment impurity removal process. From Figure 2 it can be seen that the weight loss peaks at 75 °C, 130 °C, and 320 °C correspond to the decomposition of the electrolyte, SEI, and binder respectively, indicating that the used graphite powder before microwave pretreatment mainly contains impurities such as electrolyte, SEI, and binder. Figure 3 is the thermogravimetric curve of the used graphite after the microwave pretreatment impurity removal process. From Figure 3 it can be seen that there is no weight loss peak caused by the decomposition of substances in the used graphite powder after microwave pretreatment. Therefore, it indicates that the microwave pretreatment process has successfully removed the main impurities in the used graphite powder. Figure 4 is the Fourier transform infrared spectrum of the used graphite powder before and after the microwave pretreatment impurity removal process. From Figure 4 it can be seen that organic functional groups such as -COO and -CH 2 exist on the surface of the used graphite powder before microwave pretreatment, which belong to the organic impurities in the used graphite powder. However, there are no such functional groups on the surface of the used graphite powder after microwave pretreatment, indicating again that the microwave pretreatment process can successfully remove the main organic impurities in the used graphite powder. Figure 5 is the scanning electron microscope image of the used graphite powder before and after the microwave pretreatment impurity removal process. From Figure 5 it can be seen that there are many small impurities on the surface of the used graphite particles before microwave pretreatment, and the impurities on the surface of the graphite particles are removed after microwave pretreatment.

[0061] Figure 6 is the scanning electron microscope image of the regenerated graphite negative electrode material with a nitrogen-containing carbon layer repaired in this example. From Figure 6 it can be seen that the surface of the regenerated graphite is more flat and orderly after being repaired in this example, and the defects and surface damages exposed on the surface of the used graphite are successfully repaired. Figure 7XPS (N1s) spectrum of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in this example. It can be seen from Figure 7 that after repair in this example, there is nitrogen element on the surface of the regenerated graphite, indicating that a nitrogen-containing carbon coating layer has been successfully formed on the surface of the regenerated graphite. Figure 8 Conductivity spectrum of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in this example. It can be seen from Figure 8 that the conductivity of the waste graphite is only 0.31 S / cm, while the conductivity of the regenerated graphite is increased to 27.78 S / cm, indicating that the nitrogen-containing carbon layer significantly improves the conductivity of the graphite surface, which helps to promote the charge transfer on the surface of the graphite anode. Figure 9 Cycling performance spectrum of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in this example. It can be seen from Figure 9 that after 100 cycles at 0.5C, the discharge specific capacity of the regenerated graphite remains at 372.79 mAh / g, which is better than that of the commercial graphite anode material sold in the market. Figure 10 Cycling performance spectrum of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in this example at a rate of 2C. It can be seen from Figure 10 that at a high rate of 2C, the discharge capacity of the regenerated graphite is stable at 310.6 mAh / g, indicating that the surface of the regenerated graphite anode material with a nitrogen-containing carbon layer after repair in this example can effectively passivate the side reactions on the broken surface of the waste graphite, improve the interfacial stability, and accelerate the Li + transport rate.

[0062] Example 2

[0063] A waste ternary lithium-ion battery from a new energy vehicle is deeply discharged and then disassembled. The negative electrode sheet of the waste lithium-ion battery is taken out and placed into a microwave atmosphere tube furnace. It is quickly heated to 500 °C and maintained at this temperature for 30 min. The microwave power is set to 0.4 kW, and argon is introduced as a protective gas during the heating process. After natural cooling, waste graphite powder and copper foil are obtained; 0.2 g of the waste graphite powder after the microwave pretreatment process is taken in a beaker, 20 ml of a chitosan solution with a mass fraction of 5 wt% is added, and it is stirred at 750 rpm for 2 h. After the reaction is completed, the reaction solution is filtered, washed, and dried to obtain a precursor of the coated graphite anode material; the precursor is placed into a microwave atmosphere tube furnace and quickly heated to 800 °C and maintained at this temperature for 1 h. The microwave power is set to 0.4 kW, and argon is introduced as a protective gas during the heating process. After natural cooling, a regenerated graphite anode material with a nitrogen-containing carbon layer is obtained.

[0064] Example 3

[0065] A used lithium-ion battery from 3C consumer electronics is deeply discharged and then disassembled. The negative electrode sheet of the used lithium-ion battery is taken out and placed into a microwave atmosphere tube furnace. It is quickly heated to 500 °C and maintained at this temperature for 60 min. The microwave power is set to 0.2 kW. Argon is introduced as a protective gas during the heating process. After natural cooling, used graphite powder and copper foil are obtained; 0.2 g of the used graphite powder after the microwave pretreatment process is taken in a beaker, 20 ml of a chitosan solution with a mass fraction of 7 wt% is added, and it is stirred at 750 rpm for 2 h. After the reaction is completed, the reaction solution is filtered, washed, and dried to obtain a precursor of the coated graphite negative electrode material; the precursor is placed into a microwave atmosphere tube furnace and quickly heated to 900 °C and maintained at this temperature for 1 h. The microwave power is set to 0.2 kW. Argon is introduced as a protective gas during the heating process. After natural cooling, a regenerated graphite negative electrode material with a nitrogen-containing carbon layer is obtained.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that chitosan is replaced with glucose, and other operations and parameters are the same as those in Example 1. Figure 11 It is the cyclic performance graph of the regenerated graphite negative electrode material with a pure carbon layer repaired by this comparative example. From Figure 11 It can be seen that after 100 cycles under the condition of 0.5C, the discharge specific capacity of the regenerated graphite negative electrode material coated with a pure carbon layer repaired by this comparative example is 321.37 mAh / g, which is lower than that of the regenerated graphite negative electrode material with a nitrogen-containing carbon layer, and the cyclic stability of this comparative example is also poor. Its capacity begins to decay after 50 cycles.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that chitosan is replaced with sucrose, and other operations and parameters are the same as those in Example 1. Figure 11 It is the cyclic performance graph of the regenerated graphite negative electrode material with a pure carbon layer repaired by this comparative example. From Figure 11 It can be seen that after 100 cycles under the condition of 0.5C, the discharge specific capacity of the regenerated graphite negative electrode material coated with a pure carbon layer repaired by this comparative example is 316.73 mAh / g, which is lower than that of the regenerated graphite negative electrode material with a nitrogen-containing carbon layer.

[0070] In summary, the present invention provides a regenerated graphite anode material containing a nitrogen-containing carbon layer, its preparation method and application. The preparation method of the regenerated graphite anode material containing a nitrogen-containing carbon layer includes the steps of: subjecting the negative electrode sheet of a waste lithium-ion battery to microwave pretreatment to obtain waste graphite powder and a current collector; mixing the waste graphite powder with a nitrogen-containing organic sugar solution, and after reaction, obtaining a precursor of the coated graphite anode material; subjecting the precursor of the coated graphite anode material to microwave heat treatment to obtain a regenerated graphite anode material containing a nitrogen-containing carbon layer. The present invention realizes the repair of waste graphite by combining microwave pretreatment for impurity removal, liquid-phase coating and microwave in-situ carbonization. In the microwave pretreatment process, organic impurities in the waste graphite anode material are effectively removed, and at the same time, the separation of the waste graphite anode powder and the current collector is realized, avoiding the use of toxic solvents for leaching; subsequently, a coated precursor is obtained through liquid-phase coating with nitrogen-containing organic sugar, and the precursor is heat-treated by a microwave heating method with rapid heating and selective heating, so that the nitrogen-containing organic sugar is rapidly carbonized in-situ into a nitrogen-containing amorphous carbon layer, effectively repairing the surface defects and damages of the waste graphite anode material. Moreover, during the microwave heat treatment process, the graphite rapidly heats up under the action of microwave and directly conducts heat to the nitrogen-containing organic sugar coating layer on the surface of the precursor, rapidly and uniformly realizing the in-situ carbonization of the nitrogen-containing organic sugar coating layer to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the adsorption energy of the anode to Li + and promote the migration of Li + , and enhance the conductivity of the anode surface. The nitrogen-containing carbon layer effectively repairs the surface defects and damages of the waste graphite and exhibits good rate performance.

[0071] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer, characterized in that: Includes steps: The waste lithium-ion battery negative electrode sheet is subjected to microwave pretreatment to obtain waste graphite powder; The waste graphite powder and the nitrogen-containing organic sugar solution are mixed and reacted to obtain a precursor of a coated graphite negative electrode material; The precursor of the coated graphite negative electrode material is subjected to microwave heat treatment to obtain a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer.

2. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: The power of the microwave pretreatment is 0.2 kW-0.6 kW, the temperature of the microwave pretreatment is 450° C.-550° C., and the time of the microwave pretreatment is 10 min-60 min.

3. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: The microwave pretreatment and the microwave heat treatment are both carried out under an inert atmosphere; the inert atmosphere includes one or more of argon, helium and nitrogen.

4. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: The mass fraction of the nitrogen-containing organic sugar solution is 2.5wt%-7.5wt%.

5. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 4, characterized in that: The solid-to-liquid ratio of the waste graphite powder to the nitrogen-containing organic sugar solution is 5g / L-20g / L.

6. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: The nitrogen-containing organic sugar in the nitrogen-containing organic sugar solution includes one or more of chitosan, chitin, glucosamine, and glycosaminoglycan.

7. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: The power of the microwave heat treatment is 0.2 kW-0.6 kW, the temperature of the microwave heat treatment is 700° C.-900° C., and the time of the microwave heat treatment is 1 h-5 h.

8. The method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer according to claim 1, characterized in that: Before the negative electrode sheet of the waste lithium-ion battery is subjected to microwave pretreatment, the method further comprises the steps of: disassembling the waste lithium-ion battery after deep discharge to obtain the negative electrode sheet of the waste lithium-ion battery; The waste lithium-ion batteries include one or more of lithium-ion batteries used in new energy vehicles, 3C consumer lithium-ion batteries, and lithium-ion batteries used for energy storage.

9. A regenerated graphite negative electrode material containing a nitrogen carbon layer, characterized in that: The material is prepared by the method for preparing a regenerated graphite negative electrode material containing a nitrogen-containing carbon layer as described in any one of claims 1 to 8.

10. Use of the regenerated graphite negative electrode material containing nitrogen-containing carbon layer as claimed in claim 9 in a lithium-ion battery.

Images