Graphite-modified material, graphite-based negative electrode active material, and preparation method and application thereof

Abstract

The application discloses a graphite modified material, a graphite-based negative electrode active material, and a preparation method and application thereof. The graphite modified material comprises graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersion solvent. The preparation method of the graphite modified material comprises the following steps: (1) preparing a mixed solution containing a surfactant; (2) preparing a mixture containing the mixed solution, an oxidizing agent and graphite; (3) preparing a dry mixture; and (4) preparing a heat treatment product. The surfactant produces a wetting effect on the surface of graphite particles, and is adsorbed on the surface of the graphite to prevent the aggregation of the graphite, thereby playing a dispersion role. The graphite can be fully contacted with the oxidizing agent, the graphite surface is uniformly and fully oxidized, defects are formed on the surface of the graphite, the lithium intercalation sites are increased, and thus the graphite modified material with high capacity is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, in particular to a graphite-based material, and more particularly to a graphite modified material, a graphite-based negative active material, and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of society, fossil energy such as oil and natural gas is rapidly consumed, and the ecology and environment caused by the exploitation and consumption of these resources are increasingly serious. Secondary batteries are favored by people due to their environmental friendliness, no memory effect, long service life, high working voltage and other advantages, and play a crucial role in the development of human beings.

[0003] Natural graphite and artificial graphite occupy the main market of secondary battery negative materials, and artificial graphite is more used in China. With the increasing demand of people for electric vehicles, mobile power sources and energy storage elements, the capacity and production capacity of artificial graphite negative materials cannot meet the needs of current life development. Therefore, we need to develop natural graphite negative materials with excellent performance. Natural graphite is obtained by flotation, purification, crushing, spheroidization and grading. The traditional natural graphite negative material is prepared by coating, high-temperature carbonization, screening and magnetic removal. Compared with artificial graphite, the natural graphite negative material prepared by this process has higher capacity, but still cannot meet the demand of high-capacity energy storage devices.

[0004] At present, the industry also uses oxidizing agents to modify graphite, and the surface of the graphite is modified by surface oxidation to improve the electrochemical performance of the graphite. However, the graphite is not easy to disperse in the solvent, and the oxidizing agent is difficult to fully contact with the graphite, so the modification of the surface of the graphite is limited, and it is difficult to make the graphite achieve the expected electrochemical performance. In order to solve this problem, some researchers first oxidize the graphite with concentrated sulfuric acid before mixing the graphite with the oxidizing agent. This method can solve the problem of the difficulty of dispersion of the graphite, but there is a great safety hazard, and it is difficult to popularize in industry.

[0005] Therefore, how to use a safe and effective way to oxidize and modify the graphite to obtain a graphite material with excellent electrochemical performance is still a difficult problem that needs to be solved by the industry. SUMMARY

[0006] In view of this, one of the purposes of the present application is to provide a graphite modified material, which has a high reversible capacity and is particularly suitable for the demand of high-capacity energy storage devices.

[0007] The second purpose of the present application is to provide a preparation method of a graphite modified material, which can generate defects on the surface of the graphite and increase the lithium intercalation sites by liquid phase oxidation modification, thereby improving the capacity of the graphite. This preparation method is simple in process and low in cost.

[0008] The third object of the present application is to provide a graphite-based negative electrode active material with higher reversible capacity and first coulombic efficiency, especially for the demand of high comprehensive performance energy storage devices.

[0009] The fourth object of the present application is to provide a preparation method of graphite-based negative electrode active material, which can improve the first coulombic efficiency while improving the capacity of graphite by coating carbon after modifying the graphite in liquid phase.

[0010] The fifth object of the present application is to provide the application of graphite modification material and graphite-based negative electrode active material, which has better capacity and first coulombic efficiency as negative electrode active material.

[0011] To achieve the first object, the first aspect of the present application provides a graphite modification material, which comprises graphite with defects on the surface formed by modifying the surface with surfactant as dispersing solvent.

[0012] The graphite modification material of the present application can avoid graphite agglomeration by modifying the surface with surfactant as dispersing agent, so that a small amount of defects are formed on the surface of each graphite particle to increase the lithium intercalation sites and improve the reversible capacity.

[0013] In some embodiments, the graphite is natural graphite, and the 0.1C reversible capacity after modification is ≥372 mAh / g.

[0014] In some embodiments, the graphite is artificial graphite, and the 0.1C reversible capacity after modification is ≥360 mAh / g.

[0015] In some embodiments, the surfactant is a cationic surfactant and / or a non-ionic surfactant.

[0016] In some embodiments, the graphite is modified by an oxidizing agent, and the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate or potassium permanganate.

[0017] In some embodiments, D50 is ≥17.7 μm, and the first coulombic efficiency is ≥90%.

[0018] To achieve the second object, the second aspect of the present application provides a preparation method of graphite modification material, which comprises the following steps:

[0019] (1) Preparation of mixed solution

[0020] Mixing the surfactant and water to obtain a mixed solution;

[0021] (2) Preparation of mixed material

[0022] The mixed solution is mixed with graphite and an oxidizing agent to obtain a mixture;

[0023] (3) preparing a dried mixture

[0024] The mixture is dried to obtain a dried mixture;

[0025] (4) preparing a heat-treated product

[0026] The dried mixture is heat-treated, and then crushed and sieved after cooling.

[0027] The surfactant is dissolved in water to form a microemulsion, which is mixed with an oxidizing agent and graphite. The surfactant in the microemulsion can wet the surface of the graphite particles and be adsorbed on the surface of the graphite to prevent the aggregation of the graphite, thereby playing a dispersion and stabilization role. The graphite and the oxidizing agent can be fully contacted, the graphite surface can be uniformly and fully oxidized, defects can be formed on the graphite surface, and the lithium intercalation sites can be increased, thereby obtaining a graphite modified material with high capacity.

[0028] In some embodiments, the graphite is natural graphite and / or artificial graphite.

[0029] In some embodiments, the mass ratio of the surfactant to the water is 1:20-100.

[0030] In some embodiments, the surfactant is a cationic surfactant and / or a non-ionic surfactant.

[0031] In some embodiments, the surfactant is at least one of polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide.

[0032] In some embodiments, the mass ratio of the mixed solution, the graphite, and the oxidizing agent is 100-1000:100:1-30.

[0033] In some embodiments, the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate, or potassium permanganate.

[0034] In some embodiments, the mixing conditions include that the stirring speed is not less than 400 rpm / min, and the stirring time is 1 h to 4 h.

[0035] In some embodiments, the dispersion is performed by stirring with a blender or a kneader.

[0036] In some embodiments, the rotation speed used for the dispersion is not less than 40 rpm / min, and the time is 0.5 h to 12 h.

[0037] In some embodiments, the drying device is an oven, a kneader or a dryer.

[0038] In some embodiments, the drying temperature is 60-160℃ and the drying time is 1-48h.

[0039] In some embodiments, the heat treatment is performed in a vacuum box furnace under a protective atmosphere of argon, nitrogen or helium.

[0040] In some embodiments, the heat treatment is performed at a temperature of 300-900℃ for 1-12h, and the heating rate is 1-10℃ / min.

[0041] In some embodiments, the crushing is performed by a mechanical crusher.

[0042] In some embodiments, the mesh size of the screening is greater than 200 mesh.

[0043] To achieve the above third object, the third aspect of the present application provides a graphite-based negative electrode active material, which comprises a graphite core and a carbon layer coated on the graphite core, and the first coulombic efficiency is ≥92%, and the graphite core is graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersion solvent.

[0044] The graphite core of the present application is graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersion solvent, which can avoid the agglomeration of graphite, and a small amount of defects is formed on the surface of each graphite particle to increase the lithium intercalation sites and have a better capacity. The carbon layer formed by carbonization after coating can further improve the first coulombic efficiency, so that the graphite-based negative electrode active material has a higher capacity and first coulombic efficiency, and can meet the use requirements of the negative electrode material of the energy storage device with high comprehensive performance.

[0045] In some embodiments, the graphite is natural graphite and / or artificial graphite.

[0046] In some embodiments, the graphite is oxidized and modified by an oxidizing agent, and the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate or potassium permanganate.

[0047] In some embodiments, D50≥20μm and BET≥1.5m 2 / g.

[0048] In some embodiments, the surfactant is a cationic surfactant and / or a non-ionic surfactant.

[0049] In some embodiments, the raw material for preparing the carbon layer comprises coal tar pitch, petroleum pitch or natural pitch.

[0050] To achieve the above fourth object, the fourth aspect of the present application provides a method for preparing a graphite-based negative electrode active material, comprising the steps of:

[0051] (1) preparing a mixed solution

[0052] mixing a surfactant and water to obtain a mixed solution;

[0053] (2) preparing a mixed material

[0054] adding graphite and an oxidizing agent to the mixed solution to obtain a mixed material;

[0055] (3) preparing a dried material

[0056] drying the mixed material to obtain a dried material;

[0057] (4) preparing a precursor

[0058] heat-treating the dried material in a high-temperature furnace, and then crushing and sieving the dried material after cooling to obtain a precursor;

[0059] (5) material coating

[0060] mixing the precursor with pitch and then carbonizing the mixture.

[0061] The present application first prepares a precursor through liquid-phase oxidation. The precursor is dispersed by a surfactant as a dispersion solvent, which prevents the agglomeration of graphite. Then, the graphite is modified through liquid-phase oxidation to uniformly and sufficiently oxidize the surface of the graphite, thereby forming defects on the surface of the graphite and increasing lithium intercalation sites. Finally, the graphite is coated with pitch and carbonized to improve the first coulombic efficiency and other electrochemical properties of the graphite.

[0062] In some embodiments, the graphite is natural graphite and / or artificial graphite.

[0063] In some embodiments, the mass ratio of the surfactant to water is 1:20-100.

[0064] In some embodiments, the surfactant is at least one of polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide.

[0065] In some embodiments, the mass ratio of the mixed solution, the graphite, and the oxidizing agent is 100-1000:100:1-30.

[0066] In some embodiments, the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate, or potassium permanganate.

[0067] In some embodiments, the mixing condition comprises: using a stirring speed of no less than 400 rpm / min and stirring for 1 h to 4 h.

[0068] In some embodiments, the dispersing is performed by using a blender or a kneader.

[0069] In some embodiments, the dispersing is performed by using a stirring speed of no less than 40 rpm / min and for 0.5 h to 12 h.

[0070] In some embodiments, the drying is performed by using an oven, a kneader or a dryer.

[0071] In some embodiments, the drying is performed at a temperature of 60℃ to 160℃ for 1 h to 48 h.

[0072] In some embodiments, the heat treatment is performed in a vacuum box furnace under a protective atmosphere of argon, nitrogen or helium.

[0073] In some embodiments, the heat treatment condition comprises: heating to 300℃ to 900℃ and maintaining for 1 h to 12 h, and the heating rate is 1℃ / min to 10℃ / min.

[0074] In some embodiments, the pulverizing is performed by using a mechanical pulverizer.

[0075] In some embodiments, the screening is performed by using a mesh size of more than 200 mesh.

[0076] In some embodiments, the pitch is coal tar pitch, petroleum pitch or natural pitch.

[0077] In some embodiments, the pitch has a softening point of 230℃ to 270℃ and a D50 of 3 μm to 10 μm.

[0078] In some embodiments, the mass ratio of the precursor to the pitch is 100:5-20.

[0079] In some embodiments, the precursor and the pitch are mixed by using a high-speed mixer, and the stirring speed is 400 rpm / min to 600 rpm / min and the stirring time is 10 min to 30 min.

[0080] In some embodiments, the carbonization is performed in a high-temperature vacuum furnace under a protective atmosphere of argon, nitrogen or helium.

[0081] In some embodiments, the carbonization condition comprises: heating to 900℃ to 1200℃ and maintaining for 1 h to 8 h, and the heating rate is 1℃ / min to 10℃ / min.

[0082] To achieve the above-mentioned fifth object, the fifth aspect of the present application provides the use of the aforementioned graphite modified material or graphite-based negative electrode active material in a negative electrode material and in a secondary battery. The secondary battery comprises a positive electrode material, a negative electrode material and an electrolyte. The secondary battery using the aforementioned graphite modified material modified by liquid-phase oxidation or the graphite-based negative electrode active material modified by liquid-phase oxidation and then carbon-coated as the negative electrode active material has better capacity and first coulombic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0083] Figure 1 SEM scanning electron microscope image of the graphite modified material of Example 1.

[0084] Figure 2 SEM scanning electron microscope image of the natural graphite of Comparative Example 1. DETAILED DESCRIPTION

[0085] The graphite modified material of the present application has better capacity, especially for natural graphite, the 0.1C reversible capacity after modification can be as high as 380mAh / g, which is significantly higher than the theoretical capacity of natural graphite (372mAh / g), and is mainly suitable for use in high-capacity energy storage device negative electrode materials. The capacity and first coulombic efficiency of the graphite-based negative electrode active material are both good, and it is suitable for use in high-comprehensive-performance energy storage device negative electrode materials. In actual operation, the graphite modified material or graphite-based negative electrode active material can be selected according to the use requirements of the secondary battery.

[0086] The secondary battery of the present application comprises a positive electrode material, a negative electrode material and an electrolyte. The positive electrode is obtained by coating a positive electrode slurry comprising a positive electrode active material, a binder and a conductive agent on a positive electrode current collector, drying and cold pressing. The positive electrode active material can be selected from lithium cobaltate-based positive electrode materials, lithium iron phosphate-based positive electrode materials, lithium manganate-based positive electrode materials, lithium nickel cobalt manganate-based positive electrode materials and lithium nickel cobalt manganate aluminum-based positive electrode materials. The binder is selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, epoxy ethylene-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber and epoxy resin. The conductive agent is used to improve the conductivity of the positive electrode and can be selected from carbon-containing materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or metal powder or metal fiber materials such as copper, nickel, aluminum, silver, or conductive polymers such as polyphenylene derivatives, or mixtures thereof. The solvent of the positive electrode slurry can be N-methylpyrrolidone. The positive electrode current collector can be an aluminum foil.

[0087] The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent functions as a medium for transporting ions involved in the electrochemical reactions of the battery. The non-aqueous organic solvent can include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, or an alcohol-based solvent. The carbonate-based solvent can be a linear carbonate and / or a branched carbonate, and specifically can include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, etc. The ester-based solvent can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, valerolactone, γ-valerolactone, γ-caprolactone, etc. The ether-based solvent can include dibutyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, 2-methyl tetrahydrofuran, tetrahydrofuran, etc. The ketone-based solvent can include cyclohexanone, etc. The alcohol-based solvent can include ethanol, isopropyl alcohol, etc. The lithium salt can be at least one of LiPF6, LiBF4, LiSbF6, LiAsF6, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(CxF2x+1)(CyF2y+1)(SO2)(Rf) (wherein x and y are natural numbers), and LiB(C2O4)2. Additives can also be added to the electrolyte to improve battery performance, including but not limited to at least one of vinyl sulfite, fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, and vinyl sulfate. x F 2x+1 SO2)(C y F 2y+1 SO2)(wherein x and y are natural numbers), and LiB(C2O4)2. Additives can also be added to the electrolyte to improve battery performance, including but not limited to at least one of vinyl sulfite, fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, and vinyl sulfate.

[0088] The separator film can be a single layer or a combined multi-layer of polyethylene, polypropylene, polyvinylidene fluoride, for example, a polyethylene / polypropylene double-layer separator film, a polyethylene / polypropylene / polyethylene three-layer separator film, or a polypropylene / polyethylene / polypropylene three-layer separator film. A ceramic layer can also be provided on the separator film to prevent short circuiting of the secondary battery when thermal shrinkage occurs.

[0089] The negative electrode can be obtained by coating a negative electrode slurry containing a negative electrode active material and a binder on a negative electrode current collector, drying, and cold-pressing. The negative electrode active material can use the graphite-modified material or the graphite-based negative electrode active material of the present application alone or in combination with other negative electrode active materials such as silicon-based negative electrode active materials, soft carbon, hard carbon, etc. The binder is used to improve the adhesion between the negative electrode active material particles and between the negative electrode active material particles and the aluminum foil current collector. The binder can be at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, epoxy ethylene-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, and epoxy resins. The graphite-modified material or the graphite-based negative electrode active material of the present application has conductivity by itself, and thus a conductive agent can be added or not added. The solvent of the negative electrode slurry can be N-methyl pyrrolidone. The negative electrode current collector can be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with a conductive metal, etc.

[0090] The graphite modified material of the present application includes graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersion solvent. The capacity of the graphite modified material of the present application is higher than that of conventional graphite of the same type (natural / artificial). As for natural graphite, the 0.1C reversible capacity after modification is ≥372 mAh / g. The 0.1C reversible capacity can be, but is not limited to, 372 mAh / g, 373 mAh / g, 374 mAh / g, 375 mAh / g, 376 mAh / g, 377 mAh / g, 378 mAh / g, 380 mAh / g, 381 mAh / g, 382 mAh / g, 383 mAh / g, 384 mAh / g, 385 mAh / g. As for artificial graphite, the 0.1C reversible capacity after modification is ≥360 mAh / g. The 0.1C reversible capacity can be, but is not limited to, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, 364 mAh / g, 365 mAh / g, 366 mAh / g, 367 mAh / g, 368 mAh / g, 369 mAh / g, 370 mAh / g, 371 mAh / g. The D50 of the graphite modified material is ≥17.7 μm, for example, but not limited to, 17.7 μm, 17.8 μm, 18 μm, 18.1 μm, 18.2 μm, 18.3 μm, 18.4 μm, 18.5 μm, 18.6 μm, 18.7 μm, 18.8 μm, 18.9 μm, 19 μm. The first coulombic efficiency is ≥90%, for example, but not limited to, 90%, 90.1%, 90.2%, 90.3%, 90.4%, 90.5%, 90.6%, 90.7%, 90.8%, 90.9%, 91%, 91.1%, 91.2%.

[0091] The preparation method of the graphite modified material of the present application includes the following steps:

[0092] (1) Preparation of a mixed solution

[0093] The surfactant and water are mixed to obtain a mixed solution;

[0094] (2) Preparation of a mixed material

[0095] The graphite and the oxidizing agent are added to the mixed solution for dispersion to obtain a mixed material;

[0096] (3) Preparation of a dried material

[0097] The mixed material is dried to obtain a dried material;

[0098] (4) Preparation of a heat-treated product

[0099] The dried material is heat-treated, and after cooling, is crushed and sieved.

[0100] In step (1), the surfactant is at least one of cationic surfactant and / or nonionic surfactant. The surfactant in the aqueous solution can produce a wetting effect on the surface of the graphite particles, and is adsorbed on the surface of the graphite to prevent aggregation of the graphite, thereby playing a dispersion stabilizing effect. The surfactant is at least one of polyoxyethylene sorbitan monolaurate (Tween 20), polyoxyethylene sorbitan monopalmitate (Tween 40), polyoxyethylene sorbitan monostearate (Tween 60), polyoxyethylene sorbitan monooleate (Tween 80), cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide. As an example, the surfactant is polyoxyethylene sorbitan monostearate (Tween 60), which has good emulsion system stability and emulsification effect.

[0101] The mass ratio of the surfactant to water is 1:20-100, which can be 1:20-80, 1:20-60, or 1:40-60. For example, but not limited to, the mass ratio can be 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100.

[0102] The mixing condition includes using a stirring speed of not less than 400 rpm / min and a stirring time of 1-4 h. For example, but not limited to, the stirring speed can be 400 rpm / min, 450 rpm / min, 500 rpm / min, 550 rpm / min, 600 rpm / min, 650 rpm / min, 700 rpm / min, 750 rpm / min, or 800 rpm / min. For example, but not limited to, the stirring time can be 1 h, 2 h, 3 h, or 4 h. As an example, the stirring speed can be 600 rpm / min and the stirring time can be 2 h.

[0103] In step (2), the graphite is natural graphite and / or artificial graphite, for example, natural graphite, which has better capacity performance.

[0104] The mass ratio of the mixed solution, the graphite, and the oxidizing agent is 100-1000:100:1-30, which can be, for example, but not limited to, 100:100:1, 100:100:30, 120:100:5, 1000:100:1, 1000:100:30, 150:100:15, 300:100:20, 500:100:25, 600:100:18, 700:100:23, 800:100:17, or 900:100:30. As an example, the mass ratio of the mixed solution, the graphite, and the oxidizing agent can be 120:100:5.

[0105] The oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate or potassium permanganate. As an example, the oxidizing agent is ammonium persulfate, which has strong oxidizing properties and does not affect the stability of the emulsion system.

[0106] The dispersion is performed by stirring with a blender or a kneader, and the rotation speed used for the dispersion is not less than 40 rpm / min, and the time is 0.5 h to 12 h. The rotation speed may, for example, but not limited to, be 40 rpm / min, 50 rpm / min, 60 rpm / min, 70 rpm / min, 80 rpm / min, 90 rpm / min. The rotation time may, for example, but not limited to, be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h. As an example, a kneader is selected for stirring, and the rotation speed is 60 rpm / min, and the time is 0.5 h.

[0107] In step (3), the drying is performed by using an oven, a kneader or a drying machine. The temperature used for the drying is 60℃ to 160℃, and the time is 1 h to 48 h. The temperature may, for example, but not limited to, be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃. The drying time may, for example, but not limited to, be 1 h, 2 h, 6 h, 9 h, 13 h, 20 h, 24 h, 30 h, 34 h, 40 h, 44 h, 48 h. As an example, a kneader is selected for drying, and the drying temperature is 110℃, and the time is 24 h, which not only makes the graphite surface oxidation uniform and sufficient, but also saves energy.

[0108] In step (4), the heat treatment is performed in a vacuum box furnace under a protective atmosphere of argon, nitrogen or helium. As an example, nitrogen is selected as the protective atmosphere.

[0109] The heat treatment is performed by heating to 300℃ to 900℃, and holding for 1 h to 12 h, and the heating rate is 1℃ / min to 10℃ / min. The maximum temperature of the heat treatment may, for example, but not limited to, be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃. The holding time may, for example, but not limited to, be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h. The heating rate may, for example, but not limited to, be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min. As an example, the heat treatment is performed by heating to 400℃ at a rate of 5℃ / min, and reacting for 3 h.

[0110] The pulverization is performed using a mechanical pulverizer, and the screening mesh number is greater than 200 meshes. As an example, the screening mesh number can be 325 meshes.

[0111] The graphite-based negative electrode active material of the present application comprises a graphite core and a carbon layer coated on the graphite core, and the first coulombic efficiency is ≥ 92%, and the graphite core is graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersion solvent. For natural graphite, the corresponding 0.1C reversible capacity of the graphite-based negative electrode active material is ≥ 365 mAh / g. The 0.1C reversible capacity may be, for example, but not limited to, 365 mAh / g, 366 mAh / g, 367 mAh / g, 368 mAh / g, 369 mAh / g, 370 mAh / g, 371 mAh / g, 372 mAh / g, 373 mAh / g, 374 mAh / g, 375 mAh / g. For artificial graphite, the corresponding 0.1C reversible capacity of the graphite-based negative electrode active material is ≥ 355 mAh / g. The 0.1C reversible capacity may be, for example, but not limited to, 355 mAh / g, 356 mAh / g, 357 mAh / g, 358 mAh / g, 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g. The first coulombic efficiency is ≥ 92%, for example, but not limited to, 92%, 92.1%, 92.2%, 92.3%, 92.4%, 92.5%, 92.6%, 92.7%, 92.8%, 92.9%, 93%, 93.1%, 93.2%, 93.3%, 93.4%, 93.5%. The BET is ≥ 1.5 m 2 / g, for example, but not limited to, 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g, 2.0 m 2 / g, 2.2 m 2 / g, 2.4 m 2 / g. The D50 of the graphite modified material is ≥ 20 μm, for example, but not limited to, 20 μm, 20.1 μm, 20.2 μm, 20.3 μm, 20.4 μm, 20.5 μm, 20.6 μm, 20.7 μm, 20.8 μm, 20.9 μm, 21 μm.

[0112] The preparation method of the graphite-based negative electrode active material of the present application comprises the following steps:

[0113] (1) Preparation of a mixed solution

[0114] The surfactant and water are mixed to obtain a mixed solution;

[0115] (2) Preparation of a mixed material

[0116] adding graphite and an oxidizing agent to the mixed solution to disperse the mixture;

[0117] (3) preparing the dry mixture

[0118] drying the mixture to obtain a dry mixture;

[0119] (4) preparing the precursor

[0120] heat-treating the dry mixture in a high-temperature furnace, crushing and sieving the mixture after cooling to obtain a precursor;

[0121] (5) coating the material

[0122] mixing the precursor with pitch and carbonizing the mixture.

[0123] In step (1), the surfactant is a cationic surfactant and / or a non-ionic surfactant. The surfactant can produce a wetting effect on the surface of the graphite particles in the aqueous solution, and is adsorbed on the surface of the graphite to prevent aggregation of the graphite, thereby playing a dispersion stabilizing role. The surfactant is at least one of polyoxyethylene sorbitan monolaurate (Tween 20), polyoxyethylene sorbitan monopalmitate (Tween 40), polyoxyethylene sorbitan monostearate (Tween 60), polyoxyethylene sorbitan monooleate (Tween 80), cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide. As an example, the surfactant is polyoxyethylene sorbitan monostearate (Tween 60), which has good emulsion system stability and emulsification effect.

[0124] The mass ratio of the surfactant to water is 1:20-100, which can be 1:20-80, 1:20-60, or 1:40-60. For example, but not limited to, the mass ratio can be 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100.

[0125] The mixing conditions include a stirring speed of not less than 400 rpm / min and a stirring time of 1-4 h. For example, but not limited to, the stirring speed can be 400 rpm / min, 450 rpm / min, 500 rpm / min, 550 rpm / min, 600 rpm / min, 650 rpm / min, 700 rpm / min, 750 rpm / min, or 800 rpm / min. For example, but not limited to, the stirring time can be 1 h, 2 h, 3 h, or 4 h. As an example, the stirring speed can be 600 rpm / min and the stirring time can be 2 h.

[0126] In step (2), the graphite is natural graphite and / or artificial graphite, for example, natural graphite, which has better capacity performance.

[0127] The mass ratio of the mixed solution, the graphite and the oxidizing agent is 100-1000:100:1-30, for example, but not limited to, 100:100:1, 100:100:30, 120:100:5, 1000:100:1, 1000:100:30, 150:100:15, 300:100:20, 500:100:25, 600:100:18, 700:100:23, 800:100:17, 900:100:30. As an example, the mass ratio of the mixed solution, the graphite and the oxidizing agent can be 120:100:5.

[0128] The oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate or potassium permanganate. As an example, the oxidizing agent is ammonium persulfate, which has strong oxidizing property and does not affect the stability of the emulsion system.

[0129] The dispersion is performed by using a stirring machine or a kneader, the rotation speed used for the dispersion is not less than 40 rpm / min, and the time is 0.5 h to 12 h. For example, but not limited to, the rotation speed can be 40 rpm / min, 50 rpm / min, 60 rpm / min, 70 rpm / min, 80 rpm / min, 90 rpm / min. For example, but not limited to, the rotation time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h. As an example, the kneader is selected for the stirring, and the rotation speed is 60 rpm / min, and the time is 0.5 h.

[0130] In step (3), the drying device is an oven, a kneader or a drying machine. The temperature used for the drying is 60-160°C, and the time is 1-48 h. For example, but not limited to, the temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C. For example, but not limited to, the drying time can be 1 h, 2 h, 6 h, 9 h, 10 h, 13 h, 20 h, 24 h, 30 h, 34 h, 40 h, 44 h, 48 h. As an example, the kneader is selected for the drying, and the drying temperature is 110°C, and the time is 24 h, which not only makes the graphite surface be oxidized uniformly and sufficiently, but also saves energy.

[0131] In step (4), the heat treatment is performed in a vacuum box furnace under a protective atmosphere, and the protective atmosphere is argon, nitrogen or helium. As an example, nitrogen is selected as the protective atmosphere.

[0132] The heat treatment is performed at a temperature of 300-900℃ for 1-12h at a heating rate of 1-10℃ / min. The maximum temperature of the heat treatment can be, for example, but is not limited to, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃. The holding time can be, for example, but is not limited to, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h. The heating rate can be, for example, but is not limited to, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min. As an example, the heat treatment is performed at a temperature of 400℃ for 3h at a heating rate of 5℃ / min.

[0133] The pulverization is performed using a mechanical pulverizer, and the screen size is greater than 200 mesh. As an example, the screen size can be 325 mesh.

[0134] In step (5), the raw material for the carbon layer includes coal tar pitch, petroleum pitch or natural pitch. For example, petroleum pitch is used, which has better coating performance.

[0135] The softening point of the pitch is 230-270℃, and the D50 is 3-10μm. The softening point can be, for example, but is not limited to, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃. As an example, the softening point of the pitch can be 250℃. The D50 can be, for example, but is not limited to, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm.

[0136] The mass ratio of the precursor to the pitch is 100:5-20, which can be, for example, but is not limited to, 100:5, 100:8, 100:10, 100:13, 100:15, 100:18, 100:20. As an example, the mass ratio of the precursor to the pitch can be 100:10.

[0137] The precursor and pitch are stirred and mixed by a high-speed mixer, and the stirring speed is 400 rpm / min to 600 rpm / min, and the stirring time is 10 min to 30 min. The stirring speed may be, for example but not limited to, 400 rpm / min, 420 rpm / min, 440 rpm / min, 460 rpm / min, 480 rpm / min, 500 rpm / min, 520 rpm / min, 540 rpm / min, 560 rpm / min, 580 rpm / min, 600 rpm / min. The stirring time may be, for example but not limited to, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min. As an example, the stirring speed may be 500 rpm / min, and the stirring time may be 20 min.

[0138] The carbonization is carried out in a high-temperature vacuum furnace under a protective atmosphere of argon, nitrogen or helium. As an example, nitrogen is selected as the protective atmosphere. The carbonization conditions are heating to 900°C to 1200°C, and holding for 1 h to 8 h, and the heating rate is 1°C / min to 10°C / min. The maximum temperature of carbonization may be, for example but not limited to, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C. The holding time may be, for example but not limited to, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h. The heating rate may be, for example but not limited to, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min. As an example, the carbonization is heating to 1000°C at a rate of 5°C / min, and reacting for 3 h.

[0139] For the purpose, technical solution and beneficial effects of the present application, the present application will be further described below in combination with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0140] Example 1

[0141] The present example is a graphite modified material, and the preparation method thereof comprises:

[0142] (1) Preparation of mixed solution

[0143] Tween 60 and water are mixed at a mass ratio of 1:50 in a blender at a speed of 600 rpm / min for 2 h to obtain a mixed solution;

[0144] (2) Preparation of mixed material

[0145] The kneader was warmed to 110°C, and the mixture was kneaded for 24 h and then dried to obtain a dry material;

[0146] (3) Preparation of dry material

[0147] The kneader was warmed to 110°C, and the mixture was kneaded for 24 h and then dried to obtain a dry material;

[0148] (4) Preparation of heat-treated product

[0149] The dry material was placed in a vacuum box furnace, and the vacuum box furnace was warmed to 400°C at a warming rate of 5°C / min under a nitrogen atmosphere and was kept at 400°C for 3 h. After cooling, the undersize material obtained by crushing with a crusher and passing through a 325-mesh sieve was the graphite-modified material.

[0150] The specific surface area of the obtained graphite-modified material was 6.8 m 2 / g, and the particle size D50 was 18.0 μm, which was measured by a Malvern laser particle size analyzer MS3000. The surface morphology of the graphite-modified material was tested by a scanning electron microscope SEM, as shown in Figure 1 , and Figure 2 compared with the unmodified natural graphite, Figure 1 a small amount of defects existed on the surface of the graphite-modified material, which was beneficial to improving the capacity.

[0151] Example 2

[0152] The graphite-modified material of the present example was prepared by the following method:

[0153] (1) Preparation of mixed solution

[0154] Tween 60 and water were mixed at a mass ratio of 1:50 in a blender at a speed of 600 rpm / min for 2 h to obtain a mixed solution;

[0155] (2) Preparation of mixture

[0156] The kneader was used to add artificial graphite secondary particle graphitized product (D50 = 17.6 μm, purity > 99.9%) and potassium permanganate to the mixed solution, and the mixture was mixed at room temperature at a speed of 60 rpm / min for 0.5 h to disperse, to obtain a mixture, wherein the mass ratio of the mixed solution, artificial graphite, and potassium permanganate was 120:100:5;

[0157] (3) Preparation of dry material

[0158] The kneader was warmed to 110°C, and the mixture was kneaded for 24 h and then dried to obtain dried material;

[0159] (4) Preparation of heat-treated product

[0160] The dried material was placed in a vacuum box furnace, and the vacuum box furnace was warmed to 400°C at a warming rate of 5°C / min under a nitrogen atmosphere and kept for 3 h. After cooling, the material was crushed by a crusher and then sieved through a 325 mesh sieve to obtain the graphite modified material.

[0161] The specific surface area of the obtained graphite modified material was 1.9 m 2 / g, and the particle size D50 was 17.9 μm, as measured by a Malvern laser particle size analyzer MS3000.

[0162] Example 3

[0163] The graphite modified material of the present example was prepared by the following method:

[0164] (1) Preparation of mixed solution

[0165] Hexadecyl trimethyl ammonium bromide and water were mixed in a mass ratio of 1:50 in a blender at a speed of 600 rpm / min for 2 h to obtain a mixed solution.

[0166] (2) Preparation of mixture

[0167] The mixed solution was mixed with natural graphite (D50 = 17.6 μm, purity > 99.9%) and potassium permanganate in a mass ratio of 120:100:5 at a speed of 60 rpm / min at room temperature for 0.5 h to obtain a mixture.

[0168] (3) Preparation of dried material

[0169] The kneader was warmed to 110°C, and the mixture was kneaded for 24 h and then dried to obtain dried material.

[0170] (4) Preparation of heat-treated product

[0171] The dried material was placed in a vacuum box furnace, and the vacuum box furnace was warmed to 400°C at a warming rate of 5°C / min under a nitrogen atmosphere and kept for 3 h. After cooling, the material was crushed by a crusher and then sieved through a 325 mesh sieve to obtain the graphite modified material.

[0172] The specific surface area of the obtained graphite modified material was 6.4 m 2 / g, and the particle size D50 was 17.7 μm, as measured by a Malvern laser particle size analyzer MS3000.

[0173] Example 4

[0174] The present example is a graphite modified material, and the preparation method thereof comprises:

[0175] (1) Preparation of a mixed solution

[0176] Tween 80 and water were mixed at a mass ratio of 1:80 in a blender at a speed of 600 rpm / min for 2 h to obtain a mixed solution;

[0177] (2) Preparation of a mixed material

[0178] A kneader was used to add natural graphite (D50 = 17.6 μm, purity > 99.9%) and potassium permanganate to the mixed solution, and the mixture was dispersed at room temperature at a speed of 60 rpm / min for 0.5 h to obtain a mixed material, wherein the mass ratio of the mixed solution, the natural graphite and the potassium permanganate was 450:100:25;

[0179] (3) Preparation of a dried material

[0180] The kneader was heated to 110°C, and the mixed material was kneaded for 24 h and then dried to obtain a dried material;

[0181] (4) Preparation of a heat-treated product

[0182] The dried material was placed in a vacuum box furnace, and the vacuum box furnace was heated to 700°C at a heating rate of 8°C / min under a nitrogen atmosphere and kept for 2 h. After cooling, the product was ground by a grinder and then sieved through a 325 mesh sieve to obtain a graphite modified material.

[0183] The specific surface area of the obtained graphite modified material was 7.0 m 2 / g as determined by a Micromeritics surface area analyzer Tristar 3020, and the particle size D50 was 18.1 μm as determined by a Malvern laser particle size analyzer MS3000.

[0184] Example 5

[0185] The present example is a graphite-based negative electrode active material, and the preparation method thereof comprises:

[0186] (1) Preparation of a mixed solution

[0187] Tween 60 and water were mixed at a mass ratio of 1:50 in a blender at a speed of 600 rpm / min for 2 h to obtain a mixed solution;

[0188] (2) Preparation of a mixed material

[0189] The mixing solution, natural graphite (D50=17.6 μm, purity >99.9%) and potassium permanganate are added into a kneader, and are mixed at room temperature for 0.5 h at a speed of 60 rpm / min to disperse, to obtain a mixture, wherein the mass ratio of the mixing solution, natural graphite and potassium permanganate is 120:100:5;

[0190] (3) Preparation of dry material

[0191] The kneader is heated to 110°C, and the mixture is kneaded for 24 h and then dried to obtain a dry material;

[0192] (4) Preparation of precursor

[0193] The dry material is placed in a vacuum box furnace, and the vacuum box furnace is heated to 400°C at a heating rate of 5°C / min under a nitrogen atmosphere and is kept for 3 h. After cooling, the undersize of a 325 mesh sieve is obtained by using a pulverizer to crush, to obtain a precursor;

[0194] (5) Material coating

[0195] The precursor and petroleum pitch with a softening point of 250°C and a D50 of 7 μm are put into a high-speed mixer at a weight ratio of 100:10, and are stirred at a speed of 500 rpm / min for 20 min to obtain a mixture. The mixture is heated to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere and is kept for 3 h. After cooling, the undersize of a 325 mesh sieve is obtained by using a pulverizer to crush, to obtain a graphite-based negative electrode active material.

[0196] The specific surface area of the obtained graphite-based negative electrode active material is 1.7 m2 / g, and the particle size D50 is 20.2 μm, which are measured by using a specific surface area tester Tristar 3020 and a Malvern laser particle size analyzer MS3000. 2

[0197] Example 6

[0198] The graphite-based negative electrode active material of the present example is prepared by the following method:

[0199] (1) Preparation of mixing solution

[0200] The Tween 60 and water are mixed in a blender at a mass ratio of 1:50 at a speed of 600 rpm / min for 2 h to obtain a mixing solution;

[0201] (2) Preparation of mixture

[0202] The mixing solution, natural graphite (D50=17.6 μm, purity >99.9%) and ammonium persulfate are added into a kneader, and are mixed at room temperature for 0.5 h at a speed of 60 rpm / min to disperse, to obtain a mixture, wherein the mass ratio of the mixing solution, natural graphite and ammonium persulfate is 120:100:5;​

[0203] (3) Preparation of dry material

[0204] The kneader was warmed to 110°C, and the mixture was kneaded for 24 h and then dried to obtain the dry material;

[0205] (4) Preparation of precursor

[0206] The dry material was placed in a vacuum box furnace, and the vacuum box furnace was warmed to 400°C at a warming rate of 5°C / min under a nitrogen atmosphere and was kept for 3 h. After cooling, the product was crushed by a crusher and was sieved through a 325 mesh sieve to obtain the precursor;

[0207] (5) Material coating

[0208] The precursor and petroleum pitch with a softening point of 250°C and a D50 of 7 μm were mixed in a high-speed mixer at a weight ratio of 100:10, and were stirred at 500 rpm / min for 20 min to obtain a mixture. The mixture was warmed to 1000°C at a warming rate of 5°C / min under a nitrogen atmosphere and was kept for 3 h. After cooling, the product was crushed and sieved through a 325 mesh sieve to obtain the graphite-based negative electrode active material.

[0209] The specific surface area of the obtained graphite-based negative electrode active material was 1.9 m2 / g, and the particle size D50 was 20.4 μm. 2

[0210] Example 7

[0211] The graphite-based negative electrode active material of the present example was prepared by the following method:

[0212] (1) Preparation of mixed solution

[0213] Tween 60 and water were mixed in a mass ratio of 1:80 in a blender at a speed of 450 rpm / min for 3 h to obtain the mixed solution;

[0214] (2) Preparation of mixture

[0215] The mixed solution, natural graphite (D50 = 17.6 μm, purity > 99.9%) and potassium permanganate were mixed in a kneader at a speed of 80 rpm / min at room temperature for 0.5 h to obtain the mixture, wherein the mass ratio of the mixed solution, natural graphite and potassium permanganate was 300:100:10;

[0216] (3) Preparation of dry material

[0217] The kneader was warmed to 150°C, and the mixture was kneaded for 10 h and then dried to obtain the dry material; ​

[0218] (4) Preparation of heat-treated product

[0219] The dry material was placed in a vacuum box furnace, and the vacuum box furnace was raised to 500°C at a temperature raising rate of 10°C / min under a nitrogen atmosphere and kept for 1 h. After cooling, the undersize of the pulverizer after crushing was obtained as the precursor;

[0220] (5) Material coating

[0221] The precursor and petroleum pitch with a softening point of 250°C and a D50 of 7 μm were put into a high-speed mixer at a weight ratio of 100:10, stirred at 500 rpm / min for 20 min to obtain a mixture. The mixture was heated to 1000°C at a temperature raising rate of 5°C / min under a nitrogen atmosphere and kept for 3 h. After crushing, the undersize of the 325 mesh sieve was obtained as the graphite-based negative electrode active material.

[0222] The specific surface area of the obtained graphite-based negative electrode active material was 1.8 m 2 / g, and the particle size D50 was 20.5 μm, which was tested by a Malvern laser particle size analyzer MS3000.

[0223] Comparative Example 1

[0224] This example was the same natural graphite as in Example 1. The specific surface area of the natural graphite was 5.6 m 2 / g, and the particle size D50 was 17.6 μm, which was tested by a Malvern laser particle size analyzer MS3000. The surface morphology thereof was shown in FIG. 1. Figure 2

[0225] Comparative Example 2

[0226] This example was a graphite-based negative electrode active material. The preparation method thereof included:

[0227] The natural graphite (D50 = 17.6 μm, purity > 99.9%) and petroleum pitch with a softening point of 250°C and a D50 of 7 μm were put into a high-speed mixer at a weight ratio of 100:10, stirred at 500 rpm / min for 20 min to obtain a mixture. The mixture was heated to 1000°C at a temperature raising rate of 5°C / min under a nitrogen atmosphere and kept for 3 h. After crushing, the undersize of the 325 mesh sieve was obtained as the graphite-based negative electrode active material.

[0228] The specific surface area of the obtained graphite-based negative electrode active material was 1.7 m 2 / g, and the particle size D50 was 20.0 μm, which was tested by a Malvern laser particle size analyzer MS3000.​

[0229] The materials obtained in Examples 1-7 and Comparative Examples 1-2 were subjected to 0.1C charge-discharge test by half-cell test method, and the results are shown in Table 1.

[0230] The test method was as follows: the materials obtained in Examples 1-7 and Comparative Examples 1-2, a 6% polyvinylidene fluoride solution in N-methyl pyrrolidone, and SP were mixed in a mass ratio of 92:4:4, and then uniformly coated on a copper foil. The electrode was then subjected to vacuum drying treatment at 105°C for 24h, and then assembled into a coin cell in a glove box. The electrolyte in the electrolyte was LiPF6, with a concentration of 1M, and the solvent was a mixture of dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1:1:1. The counter electrode was a lithium sheet, and the entire test was completed on an American Arbin electrochemical test system.

[0231] Table 1: Physical properties and electrochemical properties of the materials obtained in each group of examples

[0232]

[0233] As can be seen from Table 1, both the graphite modified materials obtained by liquid phase oxidation in Examples 1-4, and the graphite-based negative electrode active materials obtained by carbon coating after liquid phase oxidation in Examples 5-7, have high particle size D50 and specific surface area values, which is due to the large specific surface area caused by oxidation.

[0234] In addition, the graphite modified materials obtained by liquid phase oxidation in Examples 1-4, compared with the natural graphite of Comparative Example 1, not only have good physical properties, but also have a small amount of defects on the surface of each graphite particle after modification by oxidation using a surfactant as a dispersion solvent, which increases the lithium intercalation sites and has a better capacity, and is particularly suitable for negative electrode active materials for high-capacity energy storage devices.

[0235] Compared with the graphite-based negative electrode active material obtained by carbon coating of the natural graphite of Comparative Example 2, and the graphite-based negative electrode active material obtained by carbon coating after liquid phase oxidation in Examples 5-7, both of which use pitch for carbon coating, the first coulombic efficiency is high. In addition, the graphite core of Examples 5-7 is graphite with defects on the surface formed by oxidation using a surfactant as a dispersion solvent, which forms a small amount of defects on the surface of the graphite particles, increases the lithium intercalation sites, has a better capacity, and can meet the use requirements of negative electrode materials for high-comprehensive-performance energy storage devices.

[0236] As can be seen from Comparative Examples 1 and 3, when a surfactant of the Tween series is used, the reversible capacity and the first coulombic efficiency are high, which may be related to the stability of the emulsion system.

[0237] From Comparative Examples 5 and 6, it can be seen that the physical properties and electrochemical properties of the graphite-based negative active material obtained by using ammonium persulfate as the oxidizing agent are both better, which is probably due to the strong oxidizing property of ammonium persulfate and the fact that it does not affect the stability of the emulsion system.

[0238] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the examples listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. A method for producing a graphite-modified material, characterized by, comprising the steps of: (1) preparing a mixed solution mixing a surfactant and water to obtain a mixed solution; (2) preparing a mixed material adding graphite and an oxidizing agent to the mixed solution to obtain a mixed material; (3) preparing a dried material drying the mixed material to obtain a dried material, wherein the drying is performed at a temperature of 60-160°C; (4) preparing a heat-treated product heat-treating the dried material, and then crushing and sieving the heat-treated product after cooling, wherein the heat treatment is performed at a temperature of 300-900°C.

2. The method for producing a graphite-modified material according to claim 1, characterized by, comprising at least one of the following features (1) to (14): (1) the graphite is natural graphite and / or artificial graphite; (2) the mass ratio of the surfactant to the water is 1:20-100; (3) the surfactant is at least one of polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide; (4) the mass ratio of the mixed solution, the graphite, and the oxidizing agent is 100-1000:100:1-30; (5) the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate, or potassium permanganate; (6) the mixing is performed at a stirring speed of not less than 400 rpm / min for 1-4 h; (7) the dispersing is performed by stirring using a blender or a kneader; (8) the dispersing is performed at a speed of not less than 40 rpm / min for 0.5-12 h; (9) the drying is performed using an oven, a kneader, or a dryer; (10) the drying is performed for 1-48 h; (11) the heat treatment is performed in a vacuum box furnace under a protective atmosphere of argon, nitrogen, or helium; (12) the heat treatment is performed at a temperature of 300-900°C for 1-12 h at a heating rate of 1-10°C / min; (13) the crushing is performed using a mechanical crusher; and (14) the sieving is performed at a mesh size of more than 200 mesh.

3. The graphite-modified material produced by the method for producing a graphite-modified material according to claim 1 or 2, characterized by, The graphite is oxidized and modified on the surface by using a surfactant as a dispersing solvent to form defects on the surface.

4. The graphite-modified material according to claim 3, wherein comprising at least one of the following features (1) to (5): (1) the graphite is natural graphite, and the 0.1C reversible capacity after modification is ≥372 mAh / g; (2) the graphite is artificial graphite, and the 0.1C reversible capacity after modification is ≥360 mAh / g; (3) the surfactant is a cationic surfactant and / or a nonionic surfactant; (4) the graphite is oxidized and modified by using an oxidizing agent, wherein the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate, or potassium permanganate; (5) D50 is ≥17.7 μm, and the first coulombic efficiency is ≥90%.

5. Process for the preparation of a graphite-based negative electrode active material, characterized in that, comprising the steps of: (1) preparing a mixed solution mixing a surfactant and water to obtain a mixed solution; (2) preparing a mixed material adding graphite and an oxidizing agent to the mixed solution to obtain a mixed material; (3) preparing a dried material The mixture is dried to obtain a dried mixture, and the drying is performed at a temperature of 60-160℃; (4) Preparation of the precursor The dried mixture is heat-treated in a high-temperature furnace, and after cooling, the precursor is obtained by crushing and screening, and the heat-treatment condition is to heat to 300-900℃; (5) Material coating The precursor is mixed with pitch and then carbonized.

6. The method for producing a graphite-based negative electrode active material according to claim 5, characterized by, At least one of the following features (1) to (20) is included: (1) The graphite is natural graphite and / or artificial graphite; (2) The mass ratio of the surfactant to the water is 1:20-100; (3) The surfactant is at least one of polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cetyltrimethylammonium sulfate, cetyltrimethylammonium bromide, and tetradecyldimethylbenzylammonium bromide; (4) The mass ratio of the mixed solution, the graphite, and the oxidizing agent is 100-1000:100:1-30; (5) The oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate, or potassium permanganate; (6) The mixing condition includes using a stirring speed of no less than 400 rpm / min and stirring for 1-4 h; (7) The dispersing is performed by stirring with a blender or a kneader; (8) The dispersing is performed at a speed of no less than 40 rpm / min for 0.5-12 h; (9) The drying device is an oven, a kneader, or a dryer; (10) The drying time is 1-48 h; (11) The heat-treatment is performed in a vacuum box furnace under a protective atmosphere of argon, nitrogen, or helium; (12) The heat-treatment condition is to heat at a rate of 1-10℃ / min for 1-12 h; (13) The crushing is performed by a mechanical crusher; (14) The screening is performed with a mesh size of more than 200 mesh; (15) The pitch is coal tar pitch, petroleum pitch, or natural pitch; (16) The pitch has a softening point of 230-270℃ and a D50 of 5-10 μm; (17) The mass ratio of the precursor to the pitch is 100:5-20; (18) The precursor and the pitch are mixed by stirring with a high-speed mixer at a speed of 400-600 rpm / min for 10-30 min; (19) The carbonization is performed in a high-temperature vacuum furnace under a protective atmosphere of argon, nitrogen, or helium; (20) The carbonization condition is to heat to 900-1200℃ and heat for 1-8 h at a rate of 1-10℃ / min.

7. The graphite-based negative electrode active material produced by the production method of the graphite-based negative electrode active material according to claim 5 or 6, characterized by, The material includes a graphite core and a carbon layer coated on the graphite core, and the first coulombic efficiency is ≥92%, and the graphite core is graphite with defects formed on the surface by oxidation modification using a surfactant as a dispersing solvent.

8. Graphite-based negative electrode active material according to claim 7, characterized in that At least one of the following features (1) to (5) is included: (1) The graphite is natural graphite and / or artificial graphite; (2) the graphite is modified by an oxidizing agent, and the oxidizing agent is hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, ammonium persulfate or potassium permanganate; (3) D50 > 20 pm, BET > 1.5 m2 / g 2 / g; (4) the surfactant is a cationic surfactant and / or a non-ionic surfactant; (5) the raw material for preparing the carbon layer comprises coal tar pitch, petroleum pitch or natural pitch.

9. The graphite modified material according to claim 3 or 4, or the graphite-based negative electrode active material according to claim 7 or 8, for use in a negative electrode material.

10. A secondary battery comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized by, The negative electrode material comprises the graphite modified material according to claim 3 or 4, or the graphite-based negative electrode active material according to claim 7 or 8.

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