CN112909228B - Modified negative pole piece and preparation method and application thereof - Google Patents

Modified negative pole piece and preparation method and application thereof Download PDF

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CN112909228B
CN112909228B CN202110041391.1A CN202110041391A CN112909228B CN 112909228 B CN112909228 B CN 112909228B CN 202110041391 A CN202110041391 A CN 202110041391A CN 112909228 B CN112909228 B CN 112909228B
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graphite
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lithium
negative pole
lithium sheet
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CN112909228A (en
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冯建林
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Zhongke Ma'anshan New Material Science Park Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a modified negative pole piece and a preparation method and application thereof, wherein the negative pole piece comprises a lithium piece, and a first coating layer and a second coating layer which are sequentially coated on the surface of the lithium piece; the first coating layer comprises graphite and the second coating layer comprises alumina. According to the invention, the metal lithium sheet is used as the negative pole piece, and is subjected to two times of coating modification treatment, so that the problem of battery safety caused by the existence of lithium dendrite, negative pole precipitation and negative pole side reaction can be solved, and the energy density and the cyclicity of the lithium ion battery are also improved.

Description

Modified negative pole piece and preparation method and application thereof
Technical Field
The invention belongs to the field of new energy power batteries, and relates to a modified negative pole piece and a preparation method and application thereof.
Background
In order to meet the demand of practical lithium ion applications, it is necessary to develop a secondary battery having high energy/power density and long charge-discharge life. Lithium metal is considered to be an ideal lithium negative electrode material because of its extremely high theoretical specific capacity (3860mAh/g) and low redox potential. However, from the viewpoint of practical use of the battery, the metallic lithium negative electrode needs to be significantly improved in terms of rate, specific capacity and charge-discharge stability. On the one hand, a surface capacity of more than 10mAh/cm for the lithium negative electrode is required2The energy density of the battery can reach 500 Wh/kg; on the other hand, next generation battery applications require lithium negative electrodes at greater than 10mAh/cm2And rapid charge and discharge is realized at the current density of (2). However, lithium metal is susceptible to uncontrolled dendrite growth, volume expansion of the electrode, and instability of the solid electrolyte interfacial film during charge and discharge cycles, which are limited by safety and cyclability issues. The problems are more serious under the conditions of high current density and high-capacity charge and discharge, and the cycling stability and the service life of the battery are greatly influencedIts life is long.
CN108417800A discloses a graphene coated graphite/metal composite powder negative electrode material and a preparation method thereof, the method includes: firstly, doping an oxidized modified graphite material by metal to obtain graphite/metal composite powder, then uniformly mixing thermally oxidized polyacrylonitrile oligomer solid and the graphite/metal composite powder, and then baking and calcining to obtain the graphene-coated graphite/metal composite powder cathode material. The prepared graphene-coated graphite/metal composite powder negative electrode material.
CN106486653A discloses a liquid phase coating modified graphite cathode material and a preparation method thereof, wherein the liquid phase coating modified graphite cathode material is prepared from 800-1200 parts of graphite fine powder and a liquid coating agent, the graphite fine powder and the liquid coating agent are subjected to heat preservation and high-speed mixing in a high-speed mixer, are added into a continuous coating machine for coating to obtain a precursor, are subjected to high-temperature heat treatment under the protection of inert gas in a tube furnace, are subjected to heat preservation, and are cooled to room temperature, so that the liquid phase coating modified graphite cathode material is obtained.
The above scheme has the problems of low energy density or poor safety of the battery, and the like, so that the development of a safe and high-energy-density negative pole piece is necessary.
Disclosure of Invention
The invention aims to provide a modified negative pole piece and a preparation method and application thereof, wherein the negative pole piece comprises a lithium piece, and a first coating layer and a second coating layer which are sequentially coated on the surface of the lithium piece; wherein the first cladding layer comprises graphite and the second cladding layer comprises alumina. According to the invention, the metal lithium sheet is used as the negative pole piece, and is subjected to coating modification treatment twice, so that the problem of battery safety caused by the phenomena of lithium dendrite, negative pole precipitation and negative pole side reaction can be solved, and the energy density and the cyclicity of the lithium ion battery are also improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a modified negative pole piece, which comprises a lithium piece, and a first coating layer and a second coating layer which are sequentially coated on the surface of the lithium piece; wherein the first cladding layer comprises graphite and the second cladding layer comprises alumina.
According to the invention, the first coating layer and the second coating layer are coated on the surface of the lithium sheet, so that the phenomena of lithium dendrite, negative electrode precipitation and negative electrode side reaction are solved, the safety problem of the battery is improved, and the energy density and the cyclicity of the lithium ion battery are also improved.
Preferably, the first coating layer further comprises a coating agent.
Preferably, the capping agent comprises Li6Si2And/or Li2S。
The invention is achieved by using Li6Si2Or Li2S coats the graphite material, which is beneficial to improving the lithium ion exchange capacity when the metal lithium sheet is used as a negative electrode and improving the lithium ion insertion and extraction, and the more lithium ions are inserted, the higher the charge capacity is. Graphite is stable, and stability of the metal lithium sheet is improved in the embedding and separating process.
In a second aspect, the invention provides a preparation method of the modified negative electrode plate in the first aspect, and the preparation method comprises the following steps:
(1) mixing and heating graphite and a coating agent to obtain coated graphite;
(2) mixing the coated graphite obtained in the step (1) with a silane coupling agent solution to obtain a pretreatment solution, immersing a lithium sheet into the pretreatment solution, stirring, and performing activation treatment to obtain a modified lithium sheet containing a first coating layer;
(3) and (3) depositing an aluminum source on the modified lithium sheet obtained in the step (2), and drying to obtain the modified negative pole piece.
Preferably, the mass ratio of the graphite to the coating agent in the step (1) is 1 (0.8-1.5), such as: 1:0.8, 1:0.9, 1:1, 1:1.2, 1:1.5, etc.
Preferably, the time of the mixing and heating treatment is 3-5 h, for example: 3h, 3.2h, 3.5h, 3.8h, 4h, 4.3h, 4.5h, 4.7h or 5h and the like.
Preferably, the temperature of the mixing and heating treatment is 60-80 ℃, for example: 60 ℃, 62 ℃, 64 ℃, 66 ℃, 68 ℃, 70 ℃, 75 ℃ or 80 ℃ and the like.
Preferably, the silane coupling agent of step (2) comprises 3-aminopropyltriethoxysilane (KH-550) and/or 3-glycidyloxypropyltrimethoxysilane (KH-560).
The invention utilizes the crosslinking polycondensation effect of KH-550 and KH-560 to couple two substances with large polarity difference together, so that the coating with Li can be realized6Si2And/or Li2The graphite material of the S and the metal lithium sheet are organically crosslinked, so that the capacity density and other properties of the lithium ion battery are improved together.
Preferably, the solvent of the silane coupling agent solution includes anhydrous ethanol and/or methanol.
Preferably, the mass of the silane coupling agent is 1.0 to 1.5% of the mass of the graphite, for example: 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.
Preferably, the stirring speed of the step (2) is 100-120 rpm, for example: 100rpm, 102rpm, 105rpm, 110rpm, 116rpm, 120rpm, or the like.
Preferably, the stirring time is 1.5-3 h, such as: 1.5h, 1.8h, 2h, 2.4h, 2.8h or 3h and the like.
In the stirring process, the silane coupling agent can perform crosslinking polycondensation reaction, and the coating is coated with Li6Si2And/or Li2The graphite material of S is firmly crosslinked with the lithium sheet, so that the coating modification of the graphite material on the lithium sheet is realized.
Preferably, the means for activation treatment comprises a vacuum drying oven.
Preferably, the temperature of the activation treatment is 105-120 ℃, for example: 105 deg.C, 110 deg.C, 112 deg.C, 116 deg.C, 118 deg.C or 120 deg.C, etc.
Preferably, the time of the activation treatment is 1.5-3 h, for example: 1.5h, 1.8h, 2h, 2.4h, 2.8h or 3h and the like.
Preferably, the aluminium source of step (3) comprises aluminium nitrate and/or aluminium silicate.
Preferably, the mass of the aluminum source is 0.5 to 1.0% of the mass of the lithium sheet, for example: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%, etc.
Preferably, the method of deposition comprises electrostatic spray deposition.
The invention can atomize the mixed solution of the aluminum source to form tiny droplets by utilizing the electrostatic spray deposition technology, so the tiny droplets can be uniformly deposited on the modified lithium sheet containing the first coating layer to form a second coating layer, and further the effect of protecting the lithium sheet is achieved.
Preferably, the device for drying treatment in step (3) comprises a drying oven.
Preferably, the temperature of the drying treatment is 70-100 ℃, for example: 70 deg.C, 75 deg.C, 80 deg.C, 85 deg.C, 90 deg.C, 95 deg.C or 100 deg.C.
Preferably, the drying time is 1.5-3 h, for example: 1.5h, 1.8h, 2h, 2.4h, 2.8h or 3h and the like.
In the drying process, the aluminum source can be converted into the aluminum oxide, and the aluminum oxide has a tetrahedral network structure, so that the problem of stress generated in the embedding and extracting processes of ions of the lithium sheet can be solved, the structural collapse of the lithium sheet can be prevented, and the cyclicity can be improved.
As a preferable scheme of the invention, the preparation method comprises the following steps:
(1) mixing graphite and a coating agent at the temperature of 60-80 ℃, and heating for 3-5 h to obtain coated graphite;
(2) mixing the coated graphite obtained in the step (1) with a silane coupling agent solution to obtain a pretreatment solution, immersing a lithium sheet into the pretreatment solution, stirring at 100-120 rpm for 1.5-3 h, and activating at 105-120 ℃ for 1.5-3 h to obtain a modified lithium sheet containing a first coating layer;
(3) and (3) depositing an aluminum source on the modified lithium sheet obtained in the step (2), and drying at 70-100 ℃ for 1.5-3 h to obtain the modified negative pole piece.
In a third aspect, the invention further provides a lithium ion battery, where the lithium ion battery includes the modified negative electrode tab of the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) the inventionBy using Li6Si2And/or Li2S coats the graphite material, which is beneficial to improving the lithium ion exchange capacity when the metal lithium sheet is used as a negative electrode and improving the lithium ion intercalation and deintercalation, and the more the intercalated lithium ions are, the higher the charge capacity is; in addition, the graphite is stable, and the stability of the metal lithium sheet can be improved in the embedding and separating processes.
(2) After two times of coating modification treatment, the invention solves the phenomena of lithium dendrite, cathode precipitation and cathode side reaction, improves the safety problem of the battery, and also improves the energy density and the cyclicity of the lithium ion battery.
(3) The modified negative pole piece is applied to a lithium ion battery, the first discharge capacity of the modified negative pole piece can reach more than 161mAh/g, the 100-time cyclic discharge capacity can reach more than 141.1mAh/g, and the capacity retention rate can reach more than 87.6%.
Drawings
Fig. 1 is a flow chart of a preparation process of the modified negative electrode tab in embodiment 1 of the present invention.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a modified negative pole piece, a flow chart of a preparation process of the modified negative pole piece is shown in fig. 1, and a specific preparation method is as follows:
(1) firstly, graphite and Li are mixed6Si2Mixing at a mass ratio of 1:1 for 4h, heating to 70 deg.C to obtain Li-coated product6Si2The graphite material of (a);
(2) 3-aminopropyltriethoxysilane (KH-550) and absolute ethanol are selected to prepare a mixed solution, the addition amount of the 3-aminopropyltriethoxysilane is 1.3 percent of the mass of graphite, and then a graphite material is added into the solution and stirred to fully disperse the graphite in the solution; immersing the lithium sheet in the solution, fully stirring for 2h, taking out, transferring to a vacuum drying oven, drying for 2h at 100 ℃ and under the vacuum degree of 0.5Mpa, fully discharging redundant absolute ethyl alcohol and a very small amount of moisture, and obtaining a primary coated modified lithium sheet;
(3) mixing Al (NO)3)3Adding 0.8% of lithium sheet into anhydrous ethanol, dissolving to obtain solution, and performing electrostatic spray deposition to obtain Al (NO)3)3And (3) forming atomized liquid drops by the solution, spraying and depositing the atomized liquid drops on the primary coated modified lithium sheet in the step (2), and then transferring the lithium sheet to a drying oven to dry for 2 hours at the temperature of 80 ℃ to obtain the modified negative pole piece.
Example 2
The embodiment provides a modified negative pole piece, which is prepared by the following method:
(1) firstly, graphite and Li are mixed2S is mixed according to the mass ratio of 1:1 for 4h, the heating temperature is 80 ℃, and the Li-coated lithium iron phosphate is prepared2A graphite material of S;
(2) 3-glycidoxypropyltrimethoxysilane (KH-560) and absolute ethyl alcohol are selected to prepare a solution, the adding amount of the 3-glycidoxypropyltrimethoxysilane is 1.5 percent of the mass of the graphite, and then a graphite material is added into the solution to be stirred, so that the graphite is fully dispersed in the solution; immersing the lithium sheet in the solution, fully stirring for 2h, taking out, transferring to a vacuum drying oven, drying for 2h at 100 ℃ and under the vacuum degree of 0.7Mpa, fully discharging redundant absolute ethyl alcohol and a very small amount of moisture, and obtaining a primary coated modified lithium sheet;
(3) mixing Al (NO)3)3Adding 0.8% of lithium sheet into anhydrous ethanol, dissolving to obtain solution, and performing electrostatic spray deposition to obtain Al (NO)3)3And (3) forming atomized liquid drops by the solution, spraying and depositing the atomized liquid drops on the primary coated modified lithium sheet in the step (2), and then transferring the lithium sheet to a drying oven to dry for 2 hours at the temperature of 80 ℃ to obtain the modified negative pole piece.
Example 3
The embodiment provides a modified negative pole piece, which is prepared by the following method:
(1) firstly, graphite and Li are mixed2S are mixed according to the mass ratio of 1:1 for 4 hours at the heating temperature of 80 ℃ to obtain the Li-coated lithium secondary battery2A graphite material of S;
(2) 3-glycidoxypropyltrimethoxysilane (KH-560) and absolute ethyl alcohol are selected to prepare a solution, the adding amount of the 3-glycidoxypropyltrimethoxysilane is 1.0 percent of the mass of the graphite, and then a graphite material is added into the solution to be stirred, so that the graphite is fully dispersed in the solution; immersing the lithium sheet in the solution, fully stirring for 2h, taking out, transferring to a vacuum drying oven, drying for 2h at 100 ℃ and under the vacuum degree of 0.4Mpa, fully discharging redundant absolute ethyl alcohol and a very small amount of moisture, and obtaining a primary coated modified lithium sheet;
(3) mixing Al (NO)3)3Adding 0.5% of lithium sheet into anhydrous ethanol, dissolving to obtain solution, and performing electrostatic spray deposition to obtain Al (NO)3)3And (3) forming atomized liquid drops by the solution, spraying and depositing the atomized liquid drops on the primary coated modified lithium sheet in the step (2), and then transferring the lithium sheet to a drying oven to dry for 2 hours at the temperature of 80 ℃ to obtain the modified negative pole piece.
Example 4
The present example is different from example 1 only in that the heating temperature in step (1) is 60 ℃, and other conditions and parameters are completely the same as example 1.
Example 5
This example is different from example 1 only in that the heating temperature in step (1) is 50 ℃, and other conditions and parameters are completely the same as example 1.
Example 6
This example is different from example 1 only in that the heating temperature in step (1) is 90 ℃, and other conditions and parameters are exactly the same as those in example 1.
Comparative example 1
The negative electrode sheet of this comparative example was only a lithium sheet.
Comparative example 2
This comparative example differs from example 1 only in that the treatment of step (3) was not conducted, and other conditions and parameters were exactly the same as those of example 1.
And (3) performance testing:
the negative electrode sheets described in examples 1 to 6 and comparative examples 1 to 2 were subjected to the first discharge capacity and 100-cycle discharge capacity test: constant current charging and discharging were performed at a current of 0.05C with respect to the theoretical capacity of the battery. The cut-off voltage is 3.0V-4.2V. Subsequently, the cycle was repeated 100 times at a low magnification of 0.5C. The first discharge capacity and the 100 th cycle discharge capacity were recorded, and the capacity retention rate was calculated as 100 cycle discharge capacity/first discharge capacity. The results are shown in table 1:
TABLE 1
Figure BDA0002895995750000091
As can be seen from Table 1, the first discharge capacity of the modified negative electrode piece disclosed by the invention can reach more than 161mAh/g, the 100-time cycle discharge capacity can reach more than 141.1mAh/g, and the capacity retention rate can reach more than 87.6% in examples 1-6.
Compared with the embodiment 1 and the embodiment 4-6, the performance of the prepared negative pole piece can be influenced by the heating temperature of the mixture of the graphite and the coating agent, and the graphite and the coating agent can be better mixed by optimizing the temperature at 60-80 ℃, so that the performance of the prepared negative pole piece is improved.
Compared with the comparative example 1, the invention can solve the battery safety problem caused by the phenomena of lithium dendrite, negative electrode precipitation and negative electrode side reaction by performing coating modification treatment on the metal lithium sheet twice, also improves the energy density and the cyclicity of the lithium ion battery, and utilizes Li6Si2And/or Li2S coats the graphite material, which is beneficial to improving the lithium ion exchange capacity of the metal lithium sheet as a negative electrode and improving the lithium ion insertion and extraction, and the more lithium ions are inserted, the higher the charge capacity is. Graphite is stable, and stability of the metal lithium sheet is improved in the embedding and separating processes.
As can be seen from comparison of example 1 and comparative example 2, the present invention can uniformly deposit Al (NO) using the electrostatic spray deposition technique3)3Deposition on metallic lithium sheetsIn addition, the nitrate of aluminum can be converted into aluminum oxide, and the aluminum oxide has a tetrahedral network structure, which is beneficial to improving the stress problem generated in the embedding and removing processes of ions of the lithium sheet, preventing the collapse of the lithium sheet structure and improving the cyclicity.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (23)

1. A modified negative pole piece is characterized by comprising a lithium piece, and a first coating layer and a second coating layer which are sequentially coated on the surface of the lithium piece;
wherein the first cladding layer comprises graphite and the second cladding layer comprises alumina;
the modified negative pole piece is prepared by the following method:
(1) mixing and heating graphite and a coating agent to obtain coated graphite;
(2) mixing the coated graphite obtained in the step (1) with a silane coupling agent solution to obtain a pretreatment solution, immersing a lithium sheet into the pretreatment solution, stirring, and performing activation treatment to obtain a modified lithium sheet containing a first coating layer;
(3) and (3) depositing an aluminum source on the modified lithium sheet obtained in the step (2), and drying to obtain the modified negative pole piece.
2. The modified negative electrode tab of claim 1, wherein the first coating layer further comprises a coating agent.
3. The modified negative electrode tab of claim 2, wherein the coating agent comprises Li6Si2And/or Li2S。
4. The preparation method of the modified negative electrode plate as claimed in any one of claims 1 to 3, characterized in that the preparation method comprises the following steps:
(1) mixing and heating graphite and a coating agent to obtain coated graphite;
(2) mixing the coated graphite obtained in the step (1) with a silane coupling agent solution to obtain a pretreatment solution, immersing a lithium sheet into the pretreatment solution, stirring, and performing activation treatment to obtain a modified lithium sheet containing a first coating layer;
(3) and (3) depositing an aluminum source on the modified lithium sheet obtained in the step (2), and drying to obtain the modified negative pole piece.
5. The preparation method according to claim 4, wherein the mass ratio of the graphite to the coating agent in the step (1) is 1 (0.8-1.5).
6. The method according to claim 4, wherein the mixing and heating treatment is carried out for 3 to 5 hours.
7. The method according to claim 4, wherein the temperature of the mixing and heating treatment is 60 to 80 ℃.
8. The method according to claim 4, wherein the silane coupling agent of the step (2) comprises 3-aminopropyltriethoxysilane and/or 3-glycidoxypropyltrimethoxysilane.
9. The method according to claim 4, wherein the solvent of the silane coupling agent solution comprises absolute ethanol and/or methanol.
10. The method according to claim 4, wherein the silane coupling agent is present in an amount of 1.0 to 1.5% by mass based on the mass of the graphite.
11. The method according to claim 4, wherein the stirring speed in the step (2) is 100 to 120 rpm.
12. The method according to claim 4, wherein the stirring time is 1.5 to 3 hours.
13. The method of claim 4, wherein the means for activating comprises a vacuum oven.
14. The method according to claim 4, wherein the temperature of the activation treatment is 105 to 120 ℃.
15. The method according to claim 4, wherein the activation treatment is carried out for 1.5 to 3 hours.
16. The method of claim 4, wherein the aluminum source of step (3) comprises aluminum nitrate and/or aluminum silicate.
17. The method according to claim 4, wherein the mass of the aluminum source is 0.5 to 1.0% of the mass of the lithium sheet.
18. The method of claim 4, wherein the depositing comprises electrostatic spray deposition.
19. The method according to claim 4, wherein the drying apparatus in the step (3) comprises a drying oven.
20. The method according to claim 4, wherein the temperature of the drying treatment is 70 to 100 ℃.
21. The method according to claim 4, wherein the drying time is 1.5 to 3 hours.
22. The method of claim 4, comprising the steps of:
(1) mixing graphite and a coating agent at the temperature of 60-80 ℃, and heating for 3-5 h to obtain coated graphite;
(2) mixing the coated graphite obtained in the step (1) with a silane coupling agent solution to obtain a pretreatment solution, immersing a lithium sheet into the pretreatment solution, stirring at 100-120 rpm for 1.5-3 h, and activating at 105-120 ℃ for 1.5-3 h to obtain a modified lithium sheet containing a first coating layer;
(3) and (3) depositing an aluminum source on the modified lithium sheet obtained in the step (2), and drying at 70-100 ℃ for 1.5-3 h to obtain the modified negative pole piece.
23. A lithium ion battery comprising the modified negative electrode sheet of any one of claims 1 to 3.
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