CN115275416B - Method for recycling graphite from waste lithium-ion batteries and high-capacity fast-charging negative electrode materials - Google Patents

Abstract

The invention discloses a method for recovering graphite in a waste lithium ion battery and a high-capacity quick-charge anode material, wherein the method comprises the following steps: pretreating a negative pole piece in a waste lithium ion battery to obtain graphite powder; detecting the interlayer spacing D002, the median D50 of particle size distribution and the specific surface area S of the graphite powder; judging whether the graphite powder meets the recovery condition according to the detection result; wherein, the recovery condition is that the interlayer spacing D002, the median D50 of the particle size distribution and the specific surface area S respectively meet a specific relational expression; if yes, recycling the graphite powder; if not, carrying out secondary treatment on the graphite powder until the graphite powder meets the recovery condition, and then recovering the graphite powder. The invention not only can ensure that the recycled graphite powder can be used for preparing the high-capacity quick-charge anode material with low cost and stable performance, but also can promote the recycling of the waste lithium ion battery.

Description

Method for recycling graphite from waste lithium-ion batteries and high-capacity fast-charging negative electrode materials

Technical Field

The invention relates to the technical field of lithium ion batteries, and in particular to a method for recovering graphite from waste lithium ion batteries and a high-capacity fast-charging negative electrode material.

Background technique

With the development and popularization of electric vehicles, lithium-ion batteries are widely used, and the output of lithium-ion batteries has also increased rapidly. Since the service life of lithium-ion batteries will gradually decrease with the increase of usage time, a large number of waste batteries will inevitably be generated. If they are not recycled, it will cause serious environmental pollution and waste of resources. Therefore, recycling them is of great significance and can also achieve certain economic benefits.

At present, the negative electrode of common waste lithium-ion batteries is mainly graphite, whose main component is carbon and has a relatively simple composition. Although the interlayer spacing of graphite will become larger after repeated cyclic embedding and extraction of lithium ions, which will be beneficial to the improvement of fast charging capacity during recycling, and compared with existing fast charging materials such as mesophase carbon microspheres, the cost is reduced by about 30%, but if the interlayer spacing of graphite is too large, it will not only lead to too small particle size, but also lead to too large specific surface area, which will reduce the energy density of the battery and deteriorate the stability of the material interface.

Therefore, how to recycle the graphite negative electrode materials of waste lithium-ion batteries to obtain low-cost, stable performance, high-capacity and fast-charging negative electrode materials has become one of the technical problems that technicians in this field need to solve urgently.

The above information is presented as background information only to assist with understanding the present disclosure and no determination or admission is made as to whether any of the above may be used as prior art with respect to the present disclosure.

Summary of the invention

The invention provides a method for recovering graphite from waste lithium-ion batteries and a high-capacity fast-charging negative electrode material to solve the deficiencies of the prior art.

To achieve the above object, the present invention provides the following technical solutions:

In a first aspect, an embodiment of the present invention provides a method for recovering graphite from waste lithium-ion batteries, the method comprising:

Pre-treating the negative electrode sheets in the waste lithium-ion batteries to obtain graphite powder;

Detecting the interlayer spacing d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder;

According to the test results, it is judged whether the graphite powder meets the recycling conditions; wherein the recycling conditions are that the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S respectively satisfy the following relationship:

0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m ² /g<S<4.0m ² /g;

If yes, the graphite powder is recycled;

If not, the graphite powder is subjected to secondary treatment until the graphite powder meets the recycling conditions, and then the graphite powder is recycled.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, the step of pre-treating the negative electrode plates from the waste lithium-ion batteries to obtain graphite powder is as follows:

The negative electrode sheets in the waste lithium-ion batteries are pickled, washed with water, filtered and dried at high temperature to obtain graphite powder.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, the step of detecting the interlayer spacing d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder comprises:

The interlayer spacing d002 of the graphite powder is detected by X-ray diffraction test method;

The particle size distribution median D50 of the graphite powder is detected by a particle size test method;

The specific surface area S of the graphite powder is detected by nitrogen adsorption method.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, before the step of recovering the graphite powder, the method further comprises:

The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions:

3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5.

Furthermore, in the method for recycling graphite from waste lithium-ion batteries, the graphite powder is subjected to secondary treatment until the graphite powder meets the recycling conditions, and then the recycling step is:

The graphite powder is subjected to a particle size control treatment and/or a coating modification treatment until the graphite powder meets the recycling conditions and then recycled.

Furthermore, in the method for recycling graphite from waste lithium-ion batteries, the recycling conditions are that the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S respectively satisfy the following relationship:

0.3365nm<d002<0.3370nm, 6.0um<D50<12.5um, 1.5m ² /g<S<3.0m ² /g.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, the step of screening out the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship from the graphite powder that meets the recovery conditions: 3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5 is:

The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions:

6.9<(0.021/(d002-0.336)+15.3/S)*0.04*D50<24.3.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, the steps of acid-washing, water-washing, filtering and high-temperature drying the negative electrode sheets from the waste lithium-ion batteries to obtain graphite powder are as follows:

The negative electrode plates in the waste lithium-ion batteries are acid-washed three times, water-washed twice, filtered and dried at high temperature to obtain graphite powder.

Furthermore, in the method for recovering graphite from waste lithium-ion batteries, the particle size control process includes one or more of crushing, granulation, shaping, grading, and fusion;

The coating modification treatment includes one or more of liquid phase coating, solid phase coating and gas phase coating.

In a second aspect, an embodiment of the present invention provides a high-capacity fast-charging negative electrode material, wherein the high-capacity fast-charging negative electrode material comprises graphite powder, and the graphite powder is obtained by the method for recovering graphite from waste lithium-ion batteries as described in the first aspect above.

Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

The embodiments of the present invention provide a method for recycling graphite in waste lithium-ion batteries and a high-capacity, fast-charging negative electrode material. The negative electrode plates in the waste lithium-ion batteries are first pretreated into graphite powder, and then the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations is recycled. This not only ensures that the recycled graphite powder can be used to prepare a high-capacity, fast-charging negative electrode material with low cost and stable performance, but also promotes the recycling and reuse of waste lithium-ion batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic flow diagram of a method for recovering graphite from waste lithium-ion batteries provided in Example 1 of the present invention;

FIG2 is a schematic flow diagram of a method for recovering graphite from waste lithium-ion batteries provided in Example 2 of the present invention;

FIG3 is a schematic flow chart of a method for recovering graphite from waste lithium-ion batteries provided in Embodiment 3 of the present invention.

Detailed ways

In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

In the description of the present invention, it is to be understood that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally disposed component. When a component is considered to be "disposed on" another component, it may be directly disposed on the other component or there may be a centrally disposed component.

In addition, terms such as "long", "short", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention. They do not indicate or imply that the device or component referred to must have this specific direction or operate with a specific direction structure, and should not be understood as a limitation of the present invention.

The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

Embodiment 1

In view of the defects of the existing technology for recycling graphite from waste lithium-ion batteries, the applicant, based on many years of rich practical experience and professional knowledge in the design and manufacture of such products, and in conjunction with the application of theory, actively conducts research and innovation in the hope of creating a technology that can solve the defects in the existing technology and make the graphite recycling technology more practical. After continuous research and design, and after repeated trial samples and improvements, the present invention with real practical value was finally created.

Please refer to Figure 1, which is a schematic diagram of a process for recycling graphite from waste lithium-ion batteries provided in Example 1 of the present invention. The method is applicable to the scenario of recycling graphite from lithium-ion batteries. The method specifically comprises the following steps:

S101, pre-treating the negative electrode plates in the waste lithium-ion batteries to obtain graphite powder.

It should be noted that the negative electrode plates in the currently common waste lithium-ion batteries are mainly graphite. After pre-treatment of the negative electrode plates, the negative electrode plates can be changed from sheets to powder.

In this embodiment, step S101 can be further refined into the following steps:

The negative electrode sheets in the waste lithium-ion batteries are pickled, washed with water, filtered and dried at high temperature to obtain graphite powder.

It should be noted that the pretreatment of the negative electrode sheet in this step is intended to process the negative electrode sheet into graphite powder. Specifically, when recycling waste lithium-ion batteries, the waste lithium-ion batteries are first disassembled, and then the negative electrode sheet is taken out, and then the negative electrode sheet is subjected to a series of pretreatments such as acid washing, water washing, filtering and high-temperature drying.

It is understandable that, depending on the actual situation, each pretreatment of the negative electrode plate may be performed more than once. For example, the negative electrode plate in the waste lithium-ion battery may be acid-washed three times, washed with water twice, filtered and dried at high temperature to obtain graphite powder.

S102, detecting the interlayer distance d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder.

It should be noted that when recycling graphite, if you want to use the recycled graphite to prepare negative electrode materials that take into account the performance of capacity, life and fast charging, it is crucial to select graphite powder with suitable interlayer spacing d002, particle size distribution median D50 and specific surface area S. Therefore, this step requires the interlayer spacing d002, particle size distribution median D50 and specific surface area S of the graphite powder to be tested.

In this embodiment, step S102 can be further refined to include the following steps:

The interlayer spacing d002 of the graphite powder is detected by X-ray diffraction test method;

The particle size distribution median D50 of the graphite powder is detected by a particle size test method;

The specific surface area S of the graphite powder is detected by nitrogen adsorption method.

It should be noted that when detecting the interlayer spacing d002, the graphite powder is subjected to X-ray diffraction, and the interlayer spacing d002 of the graphite powder is calculated according to the general rules for X-ray diffraction test methods JB/T4220-2011. If the interlayer spacing d00 is small, the resistance to rapid embedding of lithium ions into the graphite is large and the fast charging capability is weak. If the interlayer spacing d00 is large, it may cause a significant decrease in the density of the material and an increase in capacity loss.

When detecting the median particle size distribution D50, the median particle size distribution D50 of the graphite powder is obtained by a particle size tester according to the general rules of GBT24533-2019. If the particle size is too large, the lithium ion embedding path is long and fast charging is not utilized. If the particle size is too small, the electrode density is small and the energy density is low. For the recycled graphite powder, the particle size distribution is relatively dispersed.

When detecting the specific surface area S, the specific surface area S of the recovered graphite powder is obtained by nitrogen adsorption-desorption specific surface area testing equipment according to the general rules of GBT19587-2017. If the specific surface area is too small, the interfacial reaction activity is low. If the specific surface area is large, there are many side reactions, which sacrifices the battery life.

S103, judging whether the graphite powder meets the recycling conditions according to the test results; wherein the recycling conditions are that the interlayer spacing d002, the median of the particle size distribution D50 and the specific surface area S respectively meet the following relationship: 0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m2 ^/ g<S<4.0m2 ^/ g. If yes, execute step S104, if no, execute step S105.

It should be noted that in order to ensure the high-value utilization and performance improvement of recycled graphite powder and at the same time reduce the cost of existing fast-charging battery materials, the applicant found after research that when the interlayer spacing d002, particle size distribution median D50 and specific surface area S of the graphite powder respectively meet the conditions of 0.3363nm<d002<0.3375nm, 4um<D50<14um, 0.6m2/g<S<4m2/g, the performance of the graphite powder is very excellent, and it is possible to prepare a low-cost, stable and high-capacity fast-charging negative electrode material.

In this embodiment, the recycling conditions in step S103 can be further refined as follows:

The interlayer spacing d002, the median particle size distribution D50 and the specific surface area S respectively satisfy the following relationship:

0.3365nm<d002<0.3370nm, 6.0um<D50<12.5um, 1.5m ² /g<S<3.0m ² /g.

It can be seen that the recycling conditions are adjusted in this embodiment, specifically, the ranges that the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S need to meet are narrowed, thereby ensuring that the performance of the recycled graphite powder is better.

S104, recovering the graphite powder.

It should be noted that in this embodiment, the graphite powder that meets the recycling conditions can be directly recycled to prepare negative electrode materials that take into account both fast charging and high capacity.

S105, performing secondary processing on the graphite powder until the graphite powder meets the recycling conditions, and then executing step S104.

It should be noted that in this embodiment, for graphite powder that does not meet the recycling conditions, it is necessary to perform secondary treatment on it. The purpose of the secondary treatment is to process the graphite powder to meet the recycling conditions and then recycle it.

It can be understood that if the interlayer spacing d002 does not meet the recycling conditions, it is necessary to adopt a secondary treatment method that can make the interlayer spacing d002 meet the recycling conditions, that is, satisfy the relationship of 0.3363nm<d002<0.3373nm; if the median particle size distribution D50 does not meet the recycling conditions, it is necessary to adopt a secondary treatment method that can make the median particle size distribution D50 meet the recycling conditions, that is, satisfy the relationship of 4.0um<D50<14.5um; if the specific surface area S does not meet the recycling conditions, it is necessary to adopt a secondary treatment method that can make the specific surface area S meet the recycling conditions, that is, satisfy the relationship of ^0.6m2/ g<S< ^4.0m2 /g.

A method for recovering graphite from waste lithium-ion batteries provided in an embodiment of the present invention comprises pre-treating the negative electrode plates in the waste lithium-ion batteries into graphite powder, and then recovering the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations. This not only ensures that the recovered graphite powder can be used to prepare a low-cost and stable high-capacity and fast-charging negative electrode material, but also promotes the recycling and reuse of waste lithium-ion batteries.

Embodiment 2

Please refer to Figure 2, which is a schematic flow chart of a method for recycling graphite from waste lithium-ion batteries disclosed in an embodiment of the present invention. Based on the technical solution provided in Example 1, this embodiment further optimizes the method before step S104 "recycling the graphite powder". The explanations of the terms that are the same or corresponding to the above embodiments are not repeated here. Specifically, the method provided in this embodiment may also include the following steps:

The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions:

3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5.

Based on the above optimization, as shown in FIG2 , the present embodiment provides a method for recovering graphite from waste lithium-ion batteries, which may specifically include the following steps:

S201, pre-treating the negative electrode plates in the waste lithium-ion batteries to obtain graphite powder.

S202, detecting the interlayer spacing d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder.

S203, judging whether the graphite powder meets the recycling conditions according to the test results; wherein the recycling conditions are that the interlayer distance d002, the median value of the particle size distribution D50 and the specific surface area S respectively meet the following relationship: 0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m2 ^/ g<S<4.0m2 ^/ g. If yes, execute step S204, then execute step S205, if no, execute step S206.

S204. Filter out the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship from the graphite powder that meets the recycling conditions: 3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5.

It should be noted that since the interlayer spacing d002, the median particle size distribution D50 and the specific surface area S of the graphite powder, their respective changes are not independent. For example, when the median particle size distribution D50 decreases, the specific surface area S will increase accordingly. In view of this, the applicant found after further research that when the relationship between the three satisfies 3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5, the obtained graphite powder has further excellent comprehensive performance in terms of energy, life and fast charging capability.

In this embodiment, the step S204 can be further refined as follows:

The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions:

6.9<(0.021/(d002-0.336)+15.3/S)*0.04*D50<24.3.

It can be seen that this embodiment adjusts the relationship between the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S, specifically narrowing the numerical range, thereby ensuring that the performance of the recycled graphite powder is better.

S205, recovering the graphite powder.

S206, performing secondary processing on the graphite powder until the graphite powder meets the recycling conditions, and then performing steps S204 and S205 in sequence.

A method for recovering graphite from waste lithium-ion batteries provided in an embodiment of the present invention comprises pre-treating the negative electrode plates in the waste lithium-ion batteries into graphite powder, and then recovering the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations. This not only ensures that the recovered graphite powder can be used to prepare a low-cost and stable high-capacity and fast-charging negative electrode material, but also promotes the recycling and reuse of waste lithium-ion batteries.

Embodiment 3

Please refer to Figure 3, which is a schematic flow chart of a method for recycling graphite from waste lithium-ion batteries disclosed in an embodiment of the present invention. Based on the technical solution provided in Example 1, this embodiment further optimizes step S105 "subjecting the graphite powder to secondary treatment until the graphite powder meets the recycling conditions". The explanations of the terms that are the same or corresponding to the above embodiments are not repeated here, namely:

The graphite powder is subjected to a particle size control treatment and/or a coating modification treatment until the graphite powder meets the recycling conditions and then recycled.

Based on the above optimization, as shown in FIG3 , the present embodiment provides a method for recovering graphite from waste lithium-ion batteries, which may specifically include the following steps:

S301, pre-treating the negative electrode plates in the waste lithium-ion batteries to obtain graphite powder.

S302, detecting the interlayer spacing d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder.

S303, judging whether the graphite powder meets the recycling conditions according to the test results; wherein the recycling conditions are that the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S respectively meet the following relationship: 0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m2 ^/ g<S<4.0m2 ^/ g. If yes, execute step S304, if no, execute step S305.

S304, recovering the graphite powder;

S305, performing a particle size control process and/or a coating modification process on the graphite powder until the graphite powder meets the recycling conditions, and then executing step S304.

In this embodiment, the particle size control process includes one or more of crushing, granulation, shaping, classification, and fusion;

The coating modification treatment includes one or more of liquid phase coating, solid phase coating and gas phase coating.

It should be noted that if the particle size is too large, the particle size can be reduced by crushing, while for graphite powder with too small particle size, the particle size can be increased by granulation. Of course, the particle size control process is not limited to the above methods, such as shaping, grading, fusion, etc. are also included.

The coating agent used in the coating modification treatment is one or a mixture of various types of asphalt, resin, and polymer materials. The coating carbonization temperature is between 700 and 1600° C., and the time is within 1-24 hours.

A method for recovering graphite from waste lithium-ion batteries provided in an embodiment of the present invention comprises pre-treating the negative electrode plates in the waste lithium-ion batteries into graphite powder, and then recovering the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations. This not only ensures that the recovered graphite powder can be used to prepare a low-cost and stable high-capacity and fast-charging negative electrode material, but also promotes the recycling and reuse of waste lithium-ion batteries.

Embodiment 4

Embodiment 4 of the present invention provides a high-capacity fast-charging negative electrode material, wherein the high-capacity fast-charging negative electrode material comprises graphite powder, and the graphite powder is obtained by the method for recovering graphite from waste lithium-ion batteries as described in any of the above embodiments.

In order to verify the feasibility of the graphite recovery method provided by the present invention, this embodiment first recovers graphite from waste lithium-ion batteries, then uses the recovered graphite to prepare negative electrode materials, and then uses the negative electrode materials to prepare lithium-ion batteries. Finally, a verification experiment is carried out, as follows:

(1) Pretreatment of waste lithium-ion batteries

Dismantle the waste lithium-ion battery, take out the negative electrode plate, mix it with 0.6 mol/L sulfuric acid at a solid-liquid ratio of 50 g/L, and immerse and wash it at 25°C for 0.5 h. Then take out the copper foil current collector, filter the immersion mother liquor to obtain the filter residue, then wash the filter residue with water twice, filter it again, and dry the filter residue at high temperature to obtain the pretreated graphite powder, and test its interlayer spacing d002, particle size distribution median D50 and specific surface area S;

(2) Preparation of negative electrode materials

If necessary, the pretreated graphite powder can be crushed or granulated, and coated and modified at the same time to obtain a graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations.

(3) Negative electrode sheet preparation

The recycled negative electrode graphite: sodium carbon methyl cellulose (CMC): styrene butadiene rubber (SBR): conductive carbon black = 96wt%: 1wt%: 1.5wt%: 1.5wt% by mass ratio are mixed, deionized water is added, stirred evenly to obtain a slurry, and then coated on a copper foil, dried, cold pressed, and slit to obtain a negative electrode sheet;

(4) Preparation of positive electrode sheet

NCM: PVDF: conductive carbon black = 96.5wt%: 1.0wt%: 3.5wt% are mixed, NMP is added, stirred evenly to obtain a slurry, and then coated on an aluminum foil, dried, cold pressed, and slit to obtain a positive electrode sheet;

(5) Preparation of electrolyte

EC:EMC:DMC=1:1:1 volume ratio is mixed to obtain an organic solvent, and lithium hexafluorophosphate is dissolved therein to obtain a 1 mol/L electrolyte;

(6) Diaphragm preparation

Choose polyethylene membrane diaphragm;

(7) Lithium-ion battery preparation

The positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell and encapsulated in an aluminum-plastic film, dried, and then injected with an electrolyte, aged, formed, sealed, and divided to obtain a lithium-ion soft-pack battery;

(8) Performance characterization test of lithium-ion batteries

8-1: Energy test, the lithium-ion battery is fully charged at 1C and fully discharged at 1C in the voltage range of 2.8V-4.3V at 25℃, and the discharge amount is recorded. The battery weight is weighed with a balance, and the energy density of the battery is obtained by dividing the actual discharge amount of 1C by the battery mass. The actual energy density is considered to be low if it is less than 90% of the design value, moderate if it is between 90% and 110% of the design value, and high if it is higher than 110% of the design value;

8-2: Fast charge and lithium deposition rate test. Under 25°C conditions, the prepared lithium-ion battery is fully charged at 1C in the voltage range of 2.8V-4.3V, fully discharged at 1C, and then charged to 4.3V at 2.5C. When the negative electrode interface is normal, it is judged as no lithium deposition. When the lithium deposition area is between 0%-5%, it is judged as slight lithium deposition. When the negative electrode lithium deposition area is higher than 5%, it is judged as lithium deposition.

8-3: Cycle test: At 25°C, the prepared lithium-ion battery is fully charged at 1C in the voltage range of 2.8V-4.3V, and fully discharged at 1C. When the capacity decays to 80% of the rated capacity, the number of cycles is recorded.

The specific experimental data of sixteen groups of examples, namely, Examples 1 to 16, and twelve groups of comparative examples, namely, Comparative Examples 1 to 12, are shown in Table 1 below:

Table 1:

It can be seen from Table 1 that when the interlayer spacing d002, the median particle size distribution D50 and the specific surface area S respectively satisfy 0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m2 ^/ g ^<S<4.0m2 /g, the performance of the graphite powder is very excellent, and a low-cost and stable high-capacity fast-charging negative electrode material can be prepared.

A high-capacity and fast-charging negative electrode material provided in an embodiment of the present invention is prepared by first pre-treating the negative electrode plates in waste lithium-ion batteries into graphite powder, and then recovering the graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S respectively satisfy corresponding specific relationship equations. This not only ensures that the recovered graphite powder can be used to prepare a high-capacity and fast-charging negative electrode material with low cost and stable performance, but also promotes the recycling and reuse of waste lithium-ion batteries.

Thus far, the description of the above-described embodiments is provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a specific embodiment are generally not subject to the limitations of the specific embodiment, but when applicable, they can be interchanged and used for selected embodiments even if not specifically shown or described. In many respects, the same element or feature can also be changed. This variation is not considered to be a departure from the present disclosure, and all such modifications are intended to be included in the scope of the present disclosure.

Example embodiments are provided so that the present disclosure will be thorough and the scope will be fully conveyed to those skilled in the art. In order to thoroughly understand the embodiments of the present disclosure, numerous details are set forth, such as examples of specific parts, devices, and methods. Obviously, for those skilled in the art, it is not necessary to use specific details, the example embodiments can be implemented in many different forms, and neither should be construed as limiting the scope of the present disclosure. In certain example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

Here, specialized vocabulary is used only for the purpose of describing specific example embodiments, and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a" and "the" used herein may be intended to include plural forms as well. The terms "including" and "having" are inclusive, and therefore specify the presence of the claimed features, wholes, steps, operations, elements and/or components, but do not exclude the presence or additional presence of one or more other features, wholes, steps, operations, elements, components and/or combinations thereof. Unless the order of execution is clearly indicated, the method steps, processing and operations described herein are not interpreted as necessarily needing to be performed in the specific order discussed and shown. It should also be understood that additional or optional steps may be adopted.

When an element or layer is referred to as being "on ...", "engaged with ...", "connected to" or "coupled to" another element or layer, it may be directly on another element or layer, engaged with another element or layer, connected to or coupled to another element or layer, or there may be an intervening element or layer. In contrast, when an element or layer is referred to as being "directly on ...", "directly engaged with ...", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening element or layer. Other words used to describe element relationships should be interpreted in a similar manner (e.g., "between ..." and "directly between ...", "adjacent" and "directly adjacent", etc.). The term "and/or" used herein includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or parts, these elements, components, regions, layers and/or parts are not limited by these terms. These terms may only be used to distinguish one element, component, region or part from another element, component, region or part. Unless clearly indicated by the context, the use of terms such as "first", "second" and other numerical terms herein does not imply sequence or order. Therefore, the first element, component, region, layer or part discussed below can adopt the terminology of the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

Spatially relative terms, such as "inside", "outside", "below", "below...", "lower", "above", "upper", etc., may be used herein for ease of description to describe the relationship between one element or feature and one or more other elements or features as shown in the figure. Spatially relative terms may be meant to include different orientations of the device in addition to the orientation depicted in the figure. For example, if the device in the figure is flipped, the elements described as "below other elements or features" or "below elements or features" will be oriented as "above other elements or features". Therefore, the example term "below..." may include both upward and downward orientations. The device can be oriented in other ways (rotated 90 degrees or other orientations) and interpreted with the spatially relative descriptions herein.

Claims (10)

1. A method for recovering graphite from waste lithium-ion batteries, characterized in that the method comprises: Pre-treating the negative electrode sheets in the waste lithium-ion batteries to obtain graphite powder; Detecting the interlayer spacing d002, the median value D50 of the particle size distribution and the specific surface area S of the graphite powder; According to the test results, it is judged whether the graphite powder meets the recycling conditions; wherein the recycling conditions are that the interlayer spacing d002, the median value of the particle size distribution D50 and the specific surface area S respectively satisfy the following relationship: 0.3363nm<d002<0.3373nm, 4.0um<D50<14.5um, 0.6m ² /g<S<4.0m ² /g; If yes, the graphite powder is recycled; If not, the graphite powder is subjected to secondary treatment until the graphite powder meets the recycling conditions, and then the graphite powder is recycled. 2. The method for recovering graphite from waste lithium-ion batteries according to claim 1, wherein the step of pretreating the negative electrode sheet in the waste lithium-ion batteries to obtain graphite powder is: The negative electrode plates in the waste lithium-ion batteries are pickled, washed with water, filtered and dried at high temperature to obtain graphite powder. 3. The method for recovering graphite from waste lithium-ion batteries according to claim 1, wherein the step of detecting the interlaminar spacing d002, the particle size distribution median D50 and the specific surface area S of the graphite powder comprises: The interlayer spacing d002 of the graphite powder is detected by X-ray diffraction test method; The particle size distribution median D50 of the graphite powder is detected by a particle size test method; The specific surface area S of the graphite powder is detected by nitrogen adsorption method. 4. The method for recovering graphite from waste lithium-ion batteries according to claim 1, characterized in that before the step of recovering the graphite powder, the method further comprises: The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions: 3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5. 5. The method for recycling graphite from waste lithium-ion batteries according to claim 1, characterized in that the graphite powder is subjected to secondary treatment until the graphite powder meets the recycling conditions, and then the steps of recycling are: The graphite powder is subjected to a particle size control treatment and/or a coating modification treatment until the graphite powder meets the recycling conditions and then recycled. 6. The method for recovering graphite from waste lithium-ion batteries according to claim 1, wherein the recovery condition is that the interlaminar spacing d002, the particle size distribution median D50 and the specific surface area S satisfy the following relationship respectively: 0.3365nm<d002<0.3370nm, 6.0um<D50<12.5um, 1.5m ² /g<S<3.0m ² /g. 7. The method for recovering graphite from waste lithium-ion batteries according to claim 4, characterized in that the step of screening out the graphite powder whose interlaminar spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship from the graphite powder that meets the recovery condition: 3.8<(0.021/(d002-0.336)+15.3/S)*0.04*D50<44.5 is: The graphite powder whose interlayer spacing d002, particle size distribution median D50 and specific surface area S satisfy the following relationship is selected from the graphite powder that meets the recycling conditions: 6.9<(0.021/(d002-0.336)+15.3/S)*0.04*D50<24.3. 8. The method for recovering graphite from waste lithium-ion batteries according to claim 2, characterized in that the steps of acid-washing, washing, filtering and high-temperature drying the negative electrode sheets from the waste lithium-ion batteries to obtain graphite powder are: The negative electrode plates in the waste lithium-ion batteries are acid-washed three times, water-washed twice, filtered and dried at high temperature to obtain graphite powder. 9. The method for recovering graphite from waste lithium-ion batteries according to claim 5, characterized in that the particle size control process comprises one or more of crushing, granulation, shaping, grading, and fusion; The coating modification treatment includes one or more of liquid phase coating, solid phase coating and gas phase coating. 10. A high-capacity fast-charging negative electrode material, comprising graphite powder, characterized in that the graphite powder is obtained by the method for recovering graphite from waste lithium-ion batteries as described in any one of claims 1 to 9.