Graphite composite material, preparation method thereof, and lithium ion battery

Abstract

The present invention discloses a graphite composite material, a preparation method thereof, and a lithium-ion battery, relating to the technical field of battery material preparation. The preparation method of the graphite composite material comprises: obtaining amidated graphite, mixing the amidated graphite, lithium peroxide, hydrogen peroxide solution, and an organic acid reagent, and performing a cross-linking reaction to obtain an intermediate; mixing the intermediate with a curing agent and asphalt, and sequentially performing a curing reaction and a carbonization reaction to obtain the graphite composite material. The lithium peroxide and hydrogen peroxide solution, two oxidants, oxidatively cross-link the amidated graphite under acidic conditions, dissociating lithium ions from the lithium peroxide and entering the interlayer spaces of the graphite; the intermediate and the curing agent further cross-link to form a more complex three-dimensional network structure; and the carbonization process coats the graphite surface with soft carbon, thereby improving the stability, initial efficiency, fast-charging performance, and high-temperature performance of the graphite material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and in particular to a graphite composite material, a preparation method thereof, and a lithium ion battery. Background Art

[0002] Currently, the negative electrode material for commercial lithium batteries is primarily artificial graphite, which has relatively low initial efficiency. For example, when lithium iron phosphate is used as the positive electrode material, the initial efficiency of the positive electrode is around 96%, while the initial efficiency of artificial graphite is between 92% and 94%. Therefore, when using these two positive and negative electrodes to make lithium-ion batteries, the negative electrode becomes the key factor limiting the improvement of the energy density of lithium iron phosphate batteries. Summary of the Invention

[0003] The main purpose of the present invention is to provide a graphite composite material, a preparation method thereof and a lithium ion battery, aiming to solve the problem of low initial efficiency of artificial graphite materials in the prior art.

[0004] To achieve the above object, the present invention provides a method for preparing a graphite composite material, comprising the following steps:

[0005] S10, obtaining amidated graphite, mixing the amidated graphite, lithium peroxide, a hydrogen peroxide solution, and an organic acid reagent, and performing a cross-linking reaction to obtain an intermediate;

[0006] S20, mixing the intermediate with a curing agent containing an aldehyde group and asphalt, and sequentially performing a curing reaction and a carbonization reaction to obtain the graphite composite material.

[0007] In one embodiment, in step S10, the step of obtaining amidated graphite includes:

[0008] S01, obtaining carboxylated graphite, mixing the carboxylated graphite, an organic solvent, and an acyl chloride reagent, performing an acyl chloride reaction, and obtaining acyl chloride graphite;

[0009] S02. Mixing the acyl chloride graphite with a solution of an amino compound to perform an amide reaction to obtain amidated graphite.

[0010] In one embodiment, in step S01, the step of obtaining carboxylated graphite includes:

[0011] Graphite is mixed with a mixed acid solution and subjected to an oxidation reaction to obtain carboxylated graphite.

[0012] In one embodiment, the mass ratio of graphite to mixed acid is 100:(500-1000); and / or,

[0013] The mixed acid comprises sulfuric acid and nitric acid, wherein the volume ratio of sulfuric acid to nitric acid is (1-3):1, the mass percentage concentration of sulfuric acid is 70wt%-98wt%, and the mass percentage concentration of nitric acid is 50wt%-70wt%; and / or,

[0014] The oxidation reaction time is 12 to 72 hours.

[0015] In one embodiment, in step S01, the mass ratio of the carboxylated graphite, the organic solvent and the acyl chloride reagent is 100:(500-1000):(10-50); and / or,

[0016] In step S01, the organic solvent includes N-N dimethylformamide; and / or,

[0017] In step S01, the acyl chloride reagent includes thionyl chloride; and / or,

[0018] In step S01, the temperature of the acyl chlorination reaction is 50-100° C.; and / or,

[0019] In step S01, the acyl chlorination reaction time is 12 to 24 hours; and / or,

[0020] In step S02, the mass ratio of the graphite chloride to the solution of the amino compound is 100:(10-30); and / or,

[0021] In step S02, the mass percentage concentration of the amino compound in the amino compound solution is 3 wt% to 30 wt%; and / or,

[0022] In step S02, the amino compound in the amino compound solution includes at least one of aniline, dimethylamine and trimethylamine; and / or,

[0023] In step S02, the amide reaction time is 1 to 6 hours; and / or,

[0024] The temperature of the amide reaction is 0-10°C.

[0025] In one embodiment, in step S10:

[0026] The mass ratio of the amidated graphite, the lithium peroxide, the hydrogen peroxide solution and the organic acid reagent is 100:(10-30):(10-30):(5-15), and the mass percentage concentration of hydrogen peroxide in the hydrogen peroxide solution is 10wt% to 30wt%; and / or,

[0027] The organic acid reagent includes one of acetic acid, malic acid, oxalic acid or citric acid; and / or,

[0028] The cross-linking reaction temperature is 50-100° C.; and / or,

[0029] The cross-linking reaction time is 1 to 6 hours.

[0030] In one embodiment, in step S20:

[0031] The mass ratio of the intermediate, the aldehyde-containing curing agent and the asphalt is 100:(5-15):(5-15); and / or,

[0032] The aldehyde-containing curing agent includes at least one of p-hydroxybenzaldehyde, vanillin and syringaldehyde; and / or,

[0033] The curing reaction temperature is 400-600° C.; and / or,

[0034] The curing reaction time is 1 to 6 hours; and / or,

[0035] The temperature of the carbonization reaction is 1000-1400° C.; and / or,

[0036] The carbonization reaction time is 1 to 6 hours.

[0037] The present invention also provides a graphite composite material, which is prepared by the above-mentioned method for preparing the graphite composite material.

[0038] In one embodiment, the graphite composite material has a particle size of 10 to 15 μm.

[0039] The present invention also provides a lithium-ion battery, comprising the graphite composite material prepared by the aforementioned method for preparing the graphite composite material or the aforementioned graphite composite material.

[0040] In the technical solution of the present invention, in step S10, the amidated graphite has a multilayer structure and an amide group is connected to its surface. The amidated graphite is mixed with lithium peroxide, hydrogen peroxide solution, and an organic acid reagent. Part of the lithium peroxide in the system decomposes into lithium ions and hydrogen peroxide under an acidic environment at room temperature. The hydrogen peroxide is further decomposed into oxygen free radicals. The oxygen free radicals cross-link with part of the amide groups (-CONHOH) on the surface of the amidated graphite to form peroxyamide groups, which further undergo cross-linking reaction with nearby adjacent amide groups or peroxyamide groups to form a first three-dimensional network structure. In the cross-linking process, the generated lithium ions enter the interlayer spacing of the graphite, thereby expanding the interlayer spacing of the graphite. At the same time, other lithium-containing compounds generated by lithium peroxide exist in the three-dimensional network structure to obtain an intermediate, which is doped with nitrogen elements provided by the amide groups and lithium elements provided by the lithium peroxide. In step S20, the intermediate is mixed and ball-milled with a curing agent containing an aldehyde group and asphalt to make it uniformly dispersed, and then subjected to a curing treatment. During the process, the aldehyde groups (-CHO) in the organic curing agent containing aldehyde groups react with the uncrosslinked amide groups (-CONH2) to form a structure connected by methylene bridges (-CH2-). Multiple methylene bridges are connected to form a more complex three-dimensional cross-linked network, that is, the second three-dimensional network structure, which improves the structural stability of the graphite material; then a carbonization treatment is carried out to carbonize the organic matter in the asphalt and deposit it on the surface of the intermediate to form a dense soft carbon layer. Such a preparation process improves the cross-linking degree of the graphite surface, the interlayer spacing of the graphite and the stability of the graphite structure, thereby increasing the speed of lithium removal and lithium insertion of the graphite material, and the incorporation of lithium also makes up for the defects of the graphite itself, reducing the change in the volume of the graphite during the charge and discharge process, and the greater the degree of cross-linking, the larger the specific surface area of ​​the composite material, so that the graphite has the advantages of fewer defects and larger specific surface area; the soft carbon coating and lithium nitrogen doping jointly reduce the interfacial impedance of the graphite material, reduce the polarizability of the graphite material, and improve the first efficiency, fast charging performance and high temperature performance of the graphite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 the structures shown in these drawings without paying any creative work.

[0042] Figure 1 This is a scanning electron microscope (SEM) image of the graphite composite material in Example 1 provided by the present invention.

[0043] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] Currently, the negative electrode material for commercial lithium batteries is primarily artificial graphite, which has relatively low initial efficiency. For example, when lithium iron phosphate is used as the positive electrode material, the initial efficiency of the positive electrode is around 96%, while the initial efficiency of artificial graphite is between 92% and 94%. Therefore, when using these two positive and negative electrodes to make lithium-ion batteries, the negative electrode becomes the key factor limiting the improvement of the energy density of lithium iron phosphate batteries.

[0046] The main reasons for the low initial efficiency of artificial graphite are: (1) artificial graphite materials have a large specific surface area and many defects, which cause the loss of lithium ions during the initial charge and discharge process, thereby reducing the initial efficiency; (2) artificial graphite materials have large polarization, and lithium insertion and removal of the material are difficult, so the initial efficiency is low.

[0047] The current measures to improve the initial efficiency of graphite mainly include: (1) shaping the graphite material to reduce defects and specific surface area, but this method will reduce the dynamic performance of the material; (2) reducing the coating amount of the graphite material, but this method will cause the dynamic performance of the material to decrease and the high-temperature performance to deteriorate.

[0048] In view of this, the present invention proposes a method for preparing a graphite composite material, comprising the following steps:

[0049] S10, obtaining amidated graphite, mixing the amidated graphite, lithium peroxide, a hydrogen peroxide solution, and an organic acid reagent, and performing a cross-linking reaction to obtain an intermediate;

[0050] S20, mixing the intermediate with a curing agent containing an aldehyde group and asphalt, and sequentially performing a curing reaction and a carbonization reaction to obtain the graphite composite material.

[0051] In the technical solution of the present invention, in step S10, the amidated graphite has a multilayer structure and an amide group is connected to its surface. The amidated graphite is mixed with lithium peroxide, hydrogen peroxide solution, and an organic acid reagent. Part of the lithium peroxide in the system decomposes into lithium ions and hydrogen peroxide under an acidic environment at room temperature. The hydrogen peroxide is further decomposed into oxygen free radicals. The oxygen free radicals cross-link with part of the amide groups (-CONHOH) on the surface of the amidated graphite to form peroxyamide groups, which further undergo cross-linking reactions with nearby adjacent amide groups or peroxyamide groups to form a three-dimensional network structure. During the cross-linking process, the generated lithium ions enter the interlayer spacing of the graphite, thereby expanding the interlayer spacing of the graphite. At the same time, other lithium-containing compounds generated by the lithium peroxide exist in the three-dimensional network structure to obtain an intermediate, which is doped with nitrogen elements provided by the amide groups and lithium elements provided by the lithium peroxide. In step S20, the intermediate is mixed with an aldehyde-containing curing agent and asphalt and ball-milled to uniformly disperse them, and then cured. During the curing process, the aldehyde groups (-CHO) in the organic curing agent containing aldehyde groups undergo condensation reactions with the uncrosslinked amide groups (-CONH2) to generate a structure connected by methylene bridges (-CH2-). Multiple methylene bridges are connected to form a more complex three-dimensional cross-linked network, thereby improving the structural stability of the graphite material. Subsequently, a carbonization treatment is performed to carbonize the organic matter in the asphalt and deposit it on the surface of the intermediate to form a dense soft carbon layer. This preparation process improves the degree of cross-linking on the graphite surface, the interlayer spacing of the graphite, and the stability of the graphite structure, thereby increasing the speed of lithium removal and lithium insertion in the graphite material. The incorporation of lithium also compensates for the defects of the graphite itself and reduces the change in the volume of the graphite during charging and discharging. The greater the degree of cross-linking, the larger the specific surface area of ​​the composite material, so that the graphite has the advantages of fewer defects and a large specific surface area. The soft carbon coating and lithium-nitrogen doping jointly reduce the interfacial impedance of the graphite material, reduce the polarizability of the graphite material, and improve the initial efficiency, fast charging performance, and high-temperature performance of the graphite material.

[0052] That is, two oxidants, lithium peroxide and hydrogen peroxide solution, oxidize the amidated graphite under acidic conditions. On the one hand, the oxygen free radicals generated by hydrogen peroxide attack the amide groups on the surface of the graphite, causing it to be oxidized and cross-linked to form a three-dimensional network structure. On the other hand, lithium peroxide dissociates into lithium ions, which are doped into the interlayer gaps of the graphite to obtain an intermediate. The intermediate is cross-linked with the curing agent to form a more complex three-dimensional network structure. The carbonization treatment coats the graphite surface with soft carbon, thereby improving the stability, initial efficiency, fast charging performance and high-temperature performance of the graphite material.

[0053] In some embodiments of the present invention, in step S10, the step of obtaining amidated graphite includes: S01, obtaining carboxylated graphite, mixing the carboxylated graphite, an organic solvent, and an acyl chloride reagent, performing an acyl chloride reaction, and obtaining acyl chloride graphite; S02, mixing the acyl chloride graphite with a solution of an amino compound, performing an amide reaction, and obtaining amidated graphite.

[0054] In the technical solution of the present invention, the surface of the carboxylated graphite has a large number of carboxylic acid groups. The carboxylated graphite is mixed with an organic solvent and an acyl chloride reagent, so that the carboxylic acid groups on the graphite surface react with the acyl chloride reagent, converting the carboxylic acid groups into acyl chloride groups to obtain acyl chloride graphite; after the acyl chloride graphite is mixed with a solution of an amino compound, the amino group of the amino compound reacts with the acyl chloride groups of the graphite, converting the acyl chloride groups into amide groups to obtain amidated graphite. The surface of the amidated graphite obtained by the above method is relatively evenly doped with nitrogen, forming a stable covalent bond between nitrogen and carbon, thereby improving the thermal stability and conductivity of the graphite material.

[0055] In some embodiments of the present invention, in step S01, obtaining carboxylated graphite includes mixing graphite with a mixed acid solution and performing an oxidation reaction to obtain carboxylated graphite. Oxidation of the graphite with the mixed acid introduces oxygen-containing functional groups, primarily carboxylic acid groups, onto the graphite surface. These oxygen-containing functional groups significantly increase the hydrophilicity of the graphite, resulting in good dispersibility in water and other polar solvents. Furthermore, during the oxidation process, the π-π stacking effect between the graphite layers is weakened, increasing the interlayer spacing, which facilitates lithium ion insertion.

[0056] In some embodiments of the present invention, the mass ratio of the graphite to the mixed acid is 100:(500-1000). Within the above mass ratio range, the graphite can be fully oxidized, so that more carboxyl groups are formed on its surface.

[0057] In some embodiments of the present invention, the mixed acid includes sulfuric acid and nitric acid, wherein the volume ratio of sulfuric acid to nitric acid is (1-3):1, the mass percentage concentration of sulfuric acid is 70wt%-98wt%, and the mass percentage concentration of nitric acid is 50wt%-70wt%. Using nitric acid and sulfuric acid with these mass percentage concentrations can accelerate the oxidation rate of graphite and quickly form more carboxyl groups on the graphite surface.

[0058] In some embodiments of the present invention, the oxidation reaction time is 12 to 72 hours. The oxidation reaction time can be 12 hours, 36 hours, or 72 hours. The oxidation reaction time within the above range can ensure that more carboxyl groups are formed on the graphite surface.

[0059] In some embodiments of the present invention, in step S01, the mass ratio of the carboxylated graphite, the organic solvent, and the acyl chloride reagent is 100:(500-1000):(10-50). This mass ratio within the above range can ensure that the carboxyl groups on the graphite surface can be fully converted into acyl chloride groups.

[0060] In some embodiments of the present invention, in step S01, the organic solvent includes N-N-dimethylformamide. The organic solvent can improve the dispersibility and solubility of the carboxylated graphite, prevent graphite from agglomerating, and thus enable it to react more fully with the acyl chloride reagent.

[0061] In some embodiments of the present invention, in step S01, the acyl chloride reagent includes thionyl chloride. The acyl chloride reagent can quickly convert the carboxyl groups on the graphite surface into acyl chloride groups.

[0062] In some embodiments of the present invention, in step S01, the chlorination reaction temperature is 50-100° C. and / or the chlorination reaction time is 12-24 hours. The chlorination reaction time and temperature within these ranges ensure that the carboxyl groups on the surface of the carboxylated graphite undergo sufficient chlorination reaction and are converted into acyl chloride groups, thereby obtaining graphite with a high degree of chlorination.

[0063] In some embodiments of the present invention, in step S02, the mass ratio of the chlorinated graphite to the amino compound solution is 100:(10-30). The mass ratio within the above range can ensure that the acyl chloride groups in the chlorinated graphite are fully converted into amide groups.

[0064] In some embodiments of the present invention, in step S02, the mass percentage concentration of the amino compound in the amino compound solution is 3 wt % to 30 wt %. The mass percentage concentration within the above range can ensure that more amino groups are provided to react with the acyl chloride groups of the acyl chloride graphite for amide reaction.

[0065] In some embodiments of the present invention, in step S02, the amino compound in the solution of the amino compound includes at least one of aniline, dimethylamine, and trimethylamine. The amino compound can react well with the acyl chloride group of the acyl chloride graphite to quickly obtain amidated graphite.

[0066] In some embodiments of the present invention, in step S02, the amide reaction time is 1 to 6 hours; and / or the amide reaction temperature is 0 to 10° C. The amide reaction time and temperature within the above ranges can ensure a relatively complete amide reaction, so that the acyl chloride groups in the acyl chloride graphite are relatively fully converted into amide groups.

[0067] In some embodiments of the present invention, in step S10: In some embodiments of the present invention, the mass ratio of the amidated graphite, the lithium peroxide, the hydrogen peroxide solution, and the organic acid reagent is 100:(10-30):(10-30):(5-15), and the mass percentage concentration of hydrogen peroxide in the hydrogen peroxide solution is 10 wt% to 30 wt%. This mass ratio within the above range ensures that lithium peroxide can hydrolyze more lithium ions in an acidic environment, and hydrogen peroxide can decompose to generate more oxygen free radicals, thereby attacking the amide groups on the surface of the amidated graphite to form a cross-linked structure. The mass percentage concentration of hydrogen peroxide in the hydrogen peroxide solution within the above range ensures that more oxygen free radicals are generated, thereby increasing the rate of the cross-linking reaction.

[0068] In some embodiments of the present invention, in step S10, the organic acid reagent includes one of acetic acid, malic acid, oxalic acid, or citric acid. The organic acid reagent can quickly dissociate lithium peroxide into lithium ions.

[0069] In some embodiments of the present invention, in step S10, the cross-linking reaction temperature is 50-100° C. and / or the cross-linking reaction time is 1-6 hours. The cross-linking reaction temperature and time within these ranges allow oxygen free radicals to fully cross-link with amide groups on the surface of the amidated graphite, and the cross-linked products to further cross-link with adjacent groups, forming a well-cross-linked three-dimensional network structure.

[0070] In some embodiments of the present invention, in step S20, the mass ratio of the intermediate, the aldehyde-containing curing agent, and the asphalt is 100:(5-15):(5-15). This mass ratio within the above range ensures that the curing agent can provide more aldehyde groups to cross-link with the intermediate, forming a larger cross-linked network, and at the same time, ensures that the asphalt can more fully form a soft carbon layer covering the graphite surface during the carbonization process.

[0071] In some embodiments of the present invention, in step S20, the aldehyde-containing curing agent includes at least one of p-hydroxybenzaldehyde, vanillin, and syringaldehyde. The above curing agent can react well with the amide group in the intermediate to form a cross-linked structure.

[0072] In some embodiments of the present invention, in step S20, the curing reaction temperature is 400-600°C; and / or the curing reaction time is 1-6 hours. Curing time and temperature within these ranges ensure that the aldehyde groups of the curing agent fully react and crosslink with the groups of the intermediate, introducing more methylene groups into the first three-dimensional network structure to form a more strongly cross-linked three-dimensional network structure, thereby increasing the specific surface area and stability of the graphite material.

[0073] In some embodiments of the present invention, in step S20, the carbonization reaction temperature is 1000-1400°C; and / or the carbonization reaction time is 1-6 hours. The carbonization reaction time and temperature within these ranges ensure that hydrogen and other elements in the asphalt and even the second three-dimensional network structure are volatilized, leaving behind a denser, softer carbon layer and graphite with a larger specific surface area.

[0074] The present invention also provides a graphite composite material prepared by the aforementioned method for preparing the graphite composite material. The graphite composite material has all the beneficial effects of the aforementioned method for preparing the graphite composite material, which will not be described in detail here.

[0075] In some embodiments of the present invention, the particle size of the graphite composite material is 10-15 μm. The particle size of the graphite composite material can be 10 μm, 12 μm or 5 μm. The particle size within this range can ensure that subsequent processing is less difficult.

[0076] The present invention further provides a lithium-ion battery comprising the graphite composite material prepared by the aforementioned method for preparing the graphite composite material, or the aforementioned graphite composite material. Thus, the lithium-ion battery possesses all the beneficial effects of the aforementioned method for preparing the graphite composite material or the aforementioned graphite material, and no further details are given herein.

[0077] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0078] Example 1

[0079] A method for preparing a graphite composite material comprises the following steps:

[0080] S01-S02, adding 100 g of artificial graphite to 500 g of a mixed acid solution (concentrated sulfuric acid:concentrated nitric acid=1:1, the mass percentage concentration of sulfuric acid in the concentrated sulfuric acid is 90 wt %, and the mass percentage concentration of nitric acid in the concentrated nitric acid is 60 wt %), soaking for 48 h, filtering, washing with deionized water, and vacuum drying at 80° C. for 24 h to obtain carboxylated graphite;

[0081] 100 g of carboxylated graphite was added to 800 g of thionyl chloride and mixed evenly, followed by addition of 30 g of N,N-dimethylformamide, and the mixture was reacted at 80° C. for 18 h. The mixture was filtered, and the filter residue was washed with tetrahydrofuran and then dried under vacuum at 80° C. for 24 h to obtain chlorinated graphite.

[0082] 100 g of acyl chloride graphite was added to 20 g of aniline solution (the mass percentage concentration of aniline in the aniline solution was 3 wt%), followed by ultrasonic reaction at 4° C. for 3 h, filtration, and vacuum drying the filter residue at 80° C. for 24 h to obtain amidated graphite;

[0083] S10, adding 100 g of amidated graphite to 2000 g of anhydrous acetic acid and dispersing the mixture uniformly, then adding 20 g of 5 wt% lithium perhydride in N-methylpyrrolidone and 20 g of 30 wt% hydrogen peroxide, reacting at 80° C. for 3 h, filtering, and drying the filter residue in vacuum at 80° C. for 24 h to obtain an intermediate;

[0084] S20, adding 100 g of the intermediate, 10 g of p-hydroxybenzaldehyde and 10 g of asphalt into a ball mill and mixing them evenly, and then transferring them into a tube furnace, first heating them to 500° C. and curing them for 3 h, and then heating them to 1200° C. and carbonizing them for 3 h to obtain a graphite composite material.

[0085] Example 2

[0086] A method for preparing a graphite composite material comprises the following steps:

[0087] S01-S02, adding 100 g of artificial graphite to 1000 g of a mixed acid solution (concentrated sulfuric acid:concentrated nitric acid=3:1, the mass percentage concentration of sulfuric acid in the concentrated sulfuric acid is 70 wt %, and the mass percentage concentration of nitric acid in the concentrated nitric acid is 50 wt %), soaking for 12 h, filtering, washing with deionized water, and vacuum drying at 80° C. for 24 h to obtain carboxylated graphite;

[0088] 100 g of carboxylated graphite was added to 500 g of thionyl chloride and mixed evenly, followed by addition of 10 g of N,N-dimethylformamide, and the mixture was reacted at 50° C. for 24 h. The mixture was filtered, and the filter residue was washed with tetrahydrofuran and then dried under vacuum at 80° C. for 24 h to obtain chlorinated graphite.

[0089] 100 g of acyl chloride graphite was added to 10 g of dimethylamine solution (the mass percentage concentration of dimethylamine in the dimethylamine solution was 10 wt%), followed by ultrasonic reaction at 10° C. for 1 h, filtration, and vacuum drying the filter residue at 80° C. for 24 h to obtain amidated graphite;

[0090] S10, adding 100 g of amidated graphite to 2000 g of anhydrous acetic acid and dispersing the mixture uniformly, then adding 10 g of 10 wt% lithium perhydride in N-methylpyrrolidone and 10 g of 30 wt% hydrogen peroxide, reacting at 50° C. for 6 h, filtering, and drying the filter residue in vacuum at 80° C. for 24 h to obtain an intermediate;

[0091] S20, adding 100 g of the intermediate, 5 g of vanillin and 5 g of asphalt into a ball mill and mixing them evenly, and then transferring them into a tube furnace, first heating them to 400° C. and curing them for 6 h, and then heating them to 1000° C. and carbonizing them for 6 h to obtain a graphite composite material.

[0092] Example 3

[0093] A method for preparing a graphite composite material comprises the following steps:

[0094] S01-S02, adding 100 g of artificial graphite to 500 g of a mixed acid solution (concentrated sulfuric acid:concentrated nitric acid=2:1, the mass percentage concentration of sulfuric acid in the concentrated sulfuric acid is 95 wt %, and the mass percentage concentration of nitric acid in the concentrated nitric acid is 70 wt %), soaking for 72 h, filtering, washing with deionized water, and vacuum drying at 80° C. for 24 h to obtain carboxylated graphite;

[0095] 100 g of carboxylated graphite was added to 1000 g of thionyl chloride and mixed evenly, followed by addition of 50 g of N,N-dimethylformamide, and the mixture was reacted at 100° C. for 12 h. The mixture was filtered, and the filter residue was washed with tetrahydrofuran and then dried under vacuum at 80° C. for 24 h to obtain chlorinated graphite.

[0096] 100 g of acyl chloride graphite was added to 30 g of trimethylamine solution (the mass percentage concentration of trimethylamine in the trimethylamine solution was 30 wt%), followed by ultrasonic reaction at 0° C. for 6 h, filtration, and vacuum drying the filter residue at 80° C. for 24 h to obtain amidated graphite;

[0097] S10, adding 100 g of amidated graphite to 2000 g of anhydrous acetic acid and dispersing the mixture uniformly, then adding 30 g of a 1 wt% organic solution of lithium perhydride in N-methylpyrrolidone and 30 g of a 30 wt% hydrogen peroxide solution, reacting at 100° C. for 1 h, filtering, and drying the filter residue in vacuo at 80° C. for 24 h to obtain an intermediate;

[0098] S20, adding 100 g of the intermediate, 15 g of syringaldehyde and 15 g of asphalt into a ball mill and mixing them evenly, and then transferring them into a tube furnace, first heating them to 600° C. for curing for 1 h, and then heating them to 1400° C. for carbonization for 1 h to obtain a graphite composite material.

[0099] Comparative Example 1

[0100] Compared with Example 1, Comparative Example 1 is the same as Example 1 except that the amidated graphite in step S10 is replaced by artificial graphite.

[0101] Comparative Example 2

[0102] Compared with Example 1, Comparative Example 2 is the same as Example 1 except that lithium peroxide is not added in step S10.

[0103] Comparative Example 3

[0104] Comparative Example 3 is the same as Comparative Example 1 except that lithium peroxide is not added in step S10.

[0105] Comparative Example 4

[0106] Compared with Example 1, Comparative Example 4 is the same as Example 1 except that lithium peroxide and hydrogen peroxide are not added in step S10.

[0107] Comparative Example 5

[0108] Compared with Example 1, Comparative Example 5 is the same as Example 1 except that no curing agent is added in step S20.

[0109] Comparative Example 6

[0110] Comparative Example 6 is the same as Comparative Example 4 except that no curing agent is added in step S20.

[0111] Performance Testing

[0112] The graphite composite material prepared in Example 1 was tested by scanning electron microscopy (SEM), and the results were as follows: Figure 1 shown.

[0113] Depend on Figure 1 It can be seen that the material presents a secondary granular structure with a particle size ranging from 10 to 15 μm.

[0114] The properties of the graphite composite materials in Examples 1 to 3 and Comparative Examples 1 to 6 were characterized as follows:

[0115] The tap density and specific surface area of ​​the graphite composite material were tested according to the test method in the standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries";

[0116] The powder resistivity of graphite composite material was tested by four-probe tester;

[0117] The diffusion coefficient of graphite composites was tested by constant current intermittent titration technique (GITT);

[0118] The test results are shown in Table 1.

[0119] Table 1 Performance characteristics of negative electrode materials in Examples 1 to 3 and Comparative Examples 1 to 6

[0120]

[0121] As can be seen from Table 1, the resistivity of the graphite composite materials prepared in Examples 1 to 3 is significantly better than that of the comparative example. The reason is that the doping of heteroatoms in the graphite composite materials improves the electronic conductivity of the material and the lithium ion transport rate of the material, thereby improving the diffusion coefficient of the material and reducing the resistivity.

[0122] The graphite composite materials prepared in Examples 1 to 3 and the graphite composite materials prepared in Comparative Examples 1 to 6 were assembled into button batteries according to the following method:

[0123] The graphite composite negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-6 served as negative electrodes and were assembled into button-type batteries with a lithium sheet, electrolyte, and separator in a glove box maintained at an argon atmosphere and a water content below 0.1 ppm. The separator was Celebard 2400; the electrolyte was a LiPF6 solution with a LiPF6 concentration of 1 mol / L; and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a 1:1 weight ratio.

[0124] The performance of the 9 button batteries prepared was tested using a blue battery tester. The test conditions were as follows:

[0125] First discharge capacity: Charge and discharge at a rate of 0.1C, with a voltage range of 0.005-2V. Stop after 3 cycles, and then test the discharge capacity at 1C.

[0126] Cycling performance: 25±3℃, 0.2C / 0.2C, 100 cycles;

[0127] Rate performance: 2C / 0.1C;

[0128] The test results are shown in Table 2.

[0129] Table 2 Performance characteristics of button batteries corresponding to Examples 1 to 3 and Comparative Examples 1 to 6

[0130]

[0131] As can be seen in Table 2, the discharge capacity and initial efficiency of button-type batteries using the graphite composite materials of Examples 1 to 3 are significantly higher than those of Comparative Examples 1 to 6. The experimental results indicate that this is because lithium coating the graphite composite reduces its irreversible capacity and improves initial efficiency, while heteroatom doping increases the material's electronic conductivity and improves rate capability.

[0132] The graphite composite materials of Examples 1 to 3 and Comparative Examples 1 to 6 are used as negative electrode active materials and the positive electrode active materials are ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A 5Ah soft-pack battery was assembled using a mixture of celegard 2400 (Celegard 2400) and a LiPF6 solution (a 1:1 volume ratio mixture of EC and DEC, with a LiPF6 concentration of 1.1 mol / L). The resulting soft-pack battery was tested for cycle and rate performance. The test results are detailed in Table 3.

[0133] Cycle performance: The battery's 500-cycle performance is tested at a charge and discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3°C.

[0134] Rate performance: Charge the battery to 100% SOC at a rate of 2C using constant current + constant voltage mode. Calculate constant current ratio = constant current capacity / (constant current capacity + constant voltage capacity).

[0135] Table 3 Performance characteristics of soft-pack batteries corresponding to Examples 1 to 3 and Comparative Examples 1 to 6

[0136] Capacity retention rate after 500 cycles (%) Rate performance (%) Example 1 94.65 94.5 Example 2 94.38 93.7 Example 3 95.11 94.9 Comparative Example 1 89.34 90.6 Comparative Example 2 88.13 88.9 Comparative Example 3 86.65 86.5 Comparative Example 4 87.11 87.3 Comparative Example 5 85.23 84.9 Comparative Example 6 84.98 82.3

[0137] As can be seen from Table 3, the cycle performance of the battery of the embodiment is significantly better than that of the comparative example. The reason is that the lithium salt in the graphite composite material obtained in the embodiment reduces the consumption of lithium ions during the charge and discharge process and has high liquid retention performance, thereby improving its cycle performance; at the same time, the embodiment material has a high diffusion coefficient and low resistivity, thereby improving the fast charging performance.

[0138] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A method for preparing a graphite composite material, characterized in that: The following steps are involved: S10, obtaining amidated graphite, mixing the amidated graphite, lithium peroxide, a hydrogen peroxide solution, and an organic acid reagent, and performing a cross-linking reaction to obtain an intermediate; S20, mixing the intermediate with a curing agent containing an aldehyde group and asphalt, and sequentially performing a curing reaction and a carbonization reaction to obtain the graphite composite material.

2. The method for preparing the graphite composite material according to claim 1, wherein In step S10, the step of obtaining amidated graphite includes: S01, obtaining carboxylated graphite, mixing the carboxylated graphite, an organic solvent, and an acyl chloride reagent, performing an acyl chloride reaction, and obtaining acyl chloride graphite; S02. Mixing the acyl chloride graphite with a solution of an amino compound to perform an amide reaction to obtain amidated graphite.

3. The method for preparing the graphite composite material according to claim 2, wherein: In step S01, the step of obtaining carboxylated graphite includes: Graphite is mixed with a mixed acid solution and subjected to an oxidation reaction to obtain carboxylated graphite.

4. The method for preparing the graphite composite material according to claim 3, wherein: The mass ratio of the graphite to the mixed acid is 100:(500-1000); and / or, The mixed acid comprises sulfuric acid and nitric acid, wherein the volume ratio of sulfuric acid to nitric acid is (1-3):1, the mass percentage concentration of sulfuric acid is 70wt%-98wt%, and the mass percentage concentration of nitric acid is 50wt%-70wt%; and / or, The oxidation reaction time is 12 to 72 hours.

5. The method for preparing the graphite composite material according to claim 2, wherein: In step S01, the mass ratio of the carboxylated graphite, the organic solvent and the acyl chloride reagent is 100:(500-1000):(10-50); and / or, In step S01, the organic solvent includes N-N dimethylformamide; and / or, In step S01, the acyl chloride reagent includes thionyl chloride; and / or, In step S01, the temperature of the acyl chlorination reaction is 50-100° C.; and / or, In step S01, the acyl chlorination reaction time is 12 to 24 hours; and / or, In step S02, the mass ratio of the graphite chloride to the solution of the amino compound is 100:(10-30); and / or, In step S02, the mass percentage concentration of the amino compound in the amino compound solution is 3 wt% to 30 wt%; and / or, In step S02, the amino compound in the amino compound solution includes at least one of aniline, dimethylamine and trimethylamine; and / or, In step S02, the amide reaction time is 1 to 6 hours; and / or, The temperature of the amide reaction is 0-10°C.

6. The method for preparing the graphite composite material according to claim 1, wherein: In step S10: The mass ratio of the amidated graphite, the lithium peroxide, the hydrogen peroxide solution and the organic acid reagent is 100:(10-30):(10-30):(5-15), and the mass percentage concentration of hydrogen peroxide in the hydrogen peroxide solution is 10wt% to 30wt%; and / or, The organic acid reagent includes one of acetic acid, malic acid, oxalic acid or citric acid; and / or, The cross-linking reaction temperature is 50-100° C.; and / or, The cross-linking reaction time is 1 to 6 hours.

7. The method for preparing the graphite composite material according to claim 1, wherein: In step S20: The mass ratio of the intermediate, the aldehyde-containing curing agent and the asphalt is 100:(5-15):(5-15); and / or, The aldehyde-containing curing agent includes at least one of p-hydroxybenzaldehyde, vanillin and syringaldehyde; and / or, The curing reaction temperature is 400-600° C.; and / or, The curing reaction time is 1 to 6 hours; and / or, The temperature of the carbonization reaction is 1000-1400° C.; and / or, The carbonization reaction time is 1 to 6 hours.

8. A graphite composite material, characterized in that: The graphite composite material is prepared by the preparation method according to any one of claims 1 to 7.

9. The graphite composite material according to claim 8, wherein The particle size of the graphite composite material is 10 to 15 μm.

10. A lithium ion battery, characterized in that: The invention comprises a graphite composite material prepared by the method for preparing a graphite composite material according to any one of claims 1 to 7 or a graphite composite material according to any one of claims 8 to 9.

Images