CN115312731A

CN115312731A - Graphite-based negative electrode active material, preparation method and application thereof, and secondary battery

Info

Publication number: CN115312731A
Application number: CN202211043818.2A
Authority: CN
Inventors: 余盛豪; 葛传长; 仰韻霖
Original assignee: Guangdong Kaijin New Energy Technology Co Ltd
Current assignee: Guangdong Kaijin New Energy Technology Co Ltd
Priority date: 2022-08-29
Filing date: 2022-08-29
Publication date: 2022-11-08

Abstract

The invention discloses a graphite-based negative active material and a preparation method and application thereof. The graphite-based negative active material includes a graphite core and a hard carbon coating layer. The surface of the graphite core is provided with holes, the hard carbon coating layer wraps the surface of the graphite core and is embedded into the holes, and the hard carbon coating layer is formed by oxidizing and carbonizing asphalt. The hard carbon layer formed by pre-oxidizing and carbonizing asphalt is used as a coating layer, so that the first charge and discharge performance, multiplying power and other performances of the material can be improved. On one hand, the hard carbon coating layer can improve the binding force between the graphite core and the hard carbon coating layer, and can effectively relieve the volume effect in the charging and discharging process of the secondary battery so as to avoid pulverization of the graphite-based negative active material in the circulating process. On the other hand, enough lithium embedding space can be provided in the hard carbon coating layer, so that the conductivity of the graphite-based negative electrode active material is effectively improved, and the high quick charging performance is kept.

Description

Graphite-based negative electrode active material, preparation method and application thereof, and secondary battery

Technical Field

The invention relates to the technical field of material preparation, in particular to a graphite-based negative active material, a preparation method and application thereof, and a secondary battery.

Background

The current commercialized negative electrode materials mainly comprise natural graphite, artificial graphite and intermediate equal graphite materials. In recent years, the upper limit of the energy density of artificial graphite negative electrodes has been rapidly developed, and the energy density has been increased from 350mAh/g to 365mAh/g, which is very close to the theoretical capacity value 372mAh/g of graphite. However, the current development of energy density also has a bottleneck, on one hand, the graphitization temperature is limited, and the benefit brought by further increase of the energy density is insufficient; on the other hand, the selection of the precursor has better orientation, which requires the raw material supplier to design the coking process and produce highly oriented coke.

Therefore, people's eyesight aims at the negative electrode material that high energy density and fast charge gradually, through reducing charge time, promotes the use of battery and experiences. In the current lithium battery market, the lithium battery has large capacity and is the most popular product at present due to quick charging. Among them, carbon coating of the material is one of the most effective methods for improving the quick charging performance. The carbon coating which is common at present mainly has the following two problems:

(1) The conventional carbon coating layer and the intermediate core have weak structural strength, so that the volume effect in the charging and discharging process is difficult to relieve, and the pulverization of the material in the circulating process is difficult to avoid;

(2) The coating layer is usually made of asphalt materials, the asphalt materials are carbonized to form a soft carbon layer, the first irreversible capacity is large, the charge-discharge potential platform is low, and the improvement of the quick charging performance of the composite material formed after coating is limited.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a graphite-based negative active material, which has a better coating property and a better fast charging property.

The second purpose of the present invention is to provide a method for preparing a graphite-based negative active material, which can form a hard carbon coating layer by oxidizing pitch and then carbonizing the oxidized graphite core to coat the oxidized graphite core, and improve the binding force between the graphite core and the hard carbon coating layer.

The invention also aims to provide application of the graphite-based negative electrode active material, and the graphite-based negative electrode active material has better quick charge performance.

In order to achieve the first object, a first aspect of the present invention provides a graphite-based negative active material including a graphite core having pores on a surface thereof, and a hard carbon coating layer wrapping the surface of the graphite core and embedded in the pores, the hard carbon coating layer being formed by oxidizing and carbonizing pitch.

The hard carbon coating layer formed by pre-oxidizing and carbonizing the asphalt is used as the coating layer, so that the first charge-discharge performance, the multiplying power and other performances of the material can be improved. On one hand, the hard carbon coating layer can improve the binding force between the graphite core and the hard carbon coating layer, and can effectively relieve the volume effect of the secondary battery in the charging and discharging process so as to avoid pulverization of the graphite-based negative active material in the circulating process. On the other hand, enough lithium embedding space can be provided inside the hard carbon coating layer, so that the conductivity of the graphite-based negative electrode active material is effectively improved, and the high quick charging performance is kept. Therefore, the graphite-based negative active material has better electrochemical performance, and is particularly suitable for being used as a negative active material in the field of quick charging.

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

In some embodiments, the graphite core has a D50 of 2 μm to 50 μm and a carbon content of 99% or greater.

In some embodiments, the hard carbon overcoat layer is one or more layers, and each layer independently has a thickness of 0.03 μm to 2.0 μm.

In some embodiments, BET is 1m ² G to 5m ² In terms of/g, or a compacted density of 1g/cm ³ To 2g/cm ³ The lithium separation window is more than or equal to 30 percent, or the first discharge specific capacity is not less than 350mAh/g, or the first coulombic efficiency is more than or equal to 88 percent.

In order to achieve the second object, a second aspect of the present invention provides a method for preparing a graphite-based negative active material, comprising the steps of:

(1) Asphalt pretreatment

Dispersing the asphalt in an organic solvent uniformly, and filtering to remove insoluble substances to obtain an asphalt mixed solution;

(2) Pretreatment of graphite

Sequentially carrying out surface acid pickling activation, drying and oxidation on graphite to obtain graphite oxide;

(3) Preparation of the precursor

Mixing the asphalt mixed solution, graphite oxide and an oxidant to obtain a precursor;

(4) Carbonizing by carbonization

And carbonizing the precursor.

In the preparation method of the graphite-based negative active material, the filtered asphalt mixed solution can better contact graphite with a solvent, so that asphalt is dispersed more uniformly, and the performance of the coating material is improved. The graphite can form defects, namely surface holes, on the surface of the graphite through acid activation and oxidation, the defects have high chemical activity, and the asphalt and the graphite oxide are easy to perform surface reaction and combine to improve the coating performance. The oxidant is added into the asphalt mixed liquor before the precursor is carbonized, so that part of active functional groups (such as olefin and the like) contained in the asphalt are oxidized to form chemical bonds, the asphalt generates defects, the oxidation degree is gradually increased along with the progress of the carbonization reaction, the defects formed in the asphalt are increased, the original short-range ordered soft carbon structure formed by the asphalt is damaged, the structure is gradually transited to hard carbon, and finally, a disordered hard carbon coating layer can be formed on the surface and the holes of the graphite core after carbonization.

In some embodiments, the bitumen is a solid phase bitumen or a liquid phase bitumen, and the coking value is from 10% to 70%.

In some embodiments, the organic solvent is at least one of an oil solvent, an alcohol solvent, a ketone solvent, a hydrocarbon solvent, and a heterocyclic organic compound.

In some embodiments, the filtration is by suction, centrifugation, or pressure filtration.

In some embodiments, the pitch comprises 1% to 8% by weight of the graphite.

In some embodiments, the solution used for acid cleaning activation is at least one of hydrochloric acid, nitric acid, and hydrofluoric acid.

In some embodiments, the oxidation is carried out by passing an oxidizing atmosphere at 200 ℃ to 500 ℃.

In some embodiments, the temperature of drying is 50 ℃ to 130 ℃ for 0.5h to 10h.

In some embodiments, the oxidizing agent is at least one of hydrogen peroxide, peracetic acid, sodium dichromate, potassium dichromate, chromic acid, nitric acid, potassium permanganate, ammonium persulfate, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate.

In some embodiments, the graphite oxide may be mixed after the asphalt mixture and the oxidant are mixed in step (3), or the oxidant may be added to the mixture of the asphalt mixture and the graphite oxide.

In some embodiments, the mixing is mechanical mixing at a speed of 300rpm to 800rpm for 10min to 30min.

In some embodiments, the carbonization comprises placing the precursor in a reactor, heating to 400 ℃ to 1400 ℃, and introducing a protective gas to carry out a heat preservation reaction.

In order to achieve the third object, the third aspect of the present invention provides the use of the graphite-based negative active material in a negative electrode material and a secondary battery. The secondary battery includes a positive electrode material, a negative electrode material, and an electrolyte. The secondary battery adopting the graphite-based negative active material as the negative active material has better quick charging performance.

Drawings

FIG. 1 is an SEM scanning electron micrograph of graphite oxide of example 1.

Fig. 2 is an SEM scanning electron micrograph of the artificial graphite in comparative example 1.

Detailed Description

The graphite-based negative active material has better electrochemical properties such as capacity, first coulombic efficiency, multiplying power and the like, and is suitable for being used as the negative active material in the field of quick charging. In the actual operation process, the graphite-based negative active material may be selected according to the use requirements of the secondary battery.

The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte.

Positive pole passing bagThe anode slurry containing the anode active material, the binder and the conductive agent is coated on an anode current collector and is dried, cold-pressed and die-cut to obtain the anode current collector. The mass ratio of the positive electrode active material, the binder and the conductive agent can be 85-99. The positive active material may be a lithium cobaltate material, a nickel cobalt manganese oxide, or a nickel cobalt aluminum oxide. Wherein the lithium cobaltate material is doped and coated modified lithium cobaltate, and the chemical formula of the nickel cobalt manganese oxide is LiNi _x Co _y Mn _z M _(1-x-y-z) O ₂ Wherein M is at least one of Mg, cu, zn, sn, B, ga, cr, sr, V and Ti, and x is more than or equal to 0.6<1，0<y<1，0<z<1, x + y + z is less than or equal to 1. The chemical formula of the nickel-cobalt-aluminum oxide is LiNi _x Co _y Al _z N _(1-x-y-z) O ₂ N is at least one of Mn, mg, cu, zn, sn, B, ga, cr, sr, V and Ti. The binder is at least one selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl pyrrolidone, styrene-butadiene rubber, acrylated styrene-butadiene rubber, and epoxy resin. The conductive agent is used for improving the conductivity of the positive electrode and can be selected from carbon-containing materials such as carbon black, acetylene black, ketjen black, carbon fiber and the like, or metal powder or metal fiber materials such as copper, nickel, aluminum, silver and the like, or conductive polymers such as polyphenylene derivatives, or mixtures thereof. The positive current collector may be an aluminum foil. The solvent of the positive electrode slurry may be N-methylpyrrolidone.

The electrolyte includes a nonaqueous organic solvent and a lithium salt. The non-aqueous organic solvent may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ -butyrolactone, delta-decalactone, γ -valerolactone, γ -caprolactone, dibutyl ether, tetraethylene glycol dimethyl ether, 1, 2-dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, cyclohexanone, isopropanol, and the like. The lithium salt may be LiPF ₆ 、LiBF ₄ 、LiSbF ₆ 、LiAsF ₆ 、LiC ₄ F ₉ SO ₃ 、LiClO ₄ 、LiAlO ₂ And LiB (C) ₂ O ₄ ) ₂ Of lithium salt in a concentration of 0.5M to 1.5M. Additives can also be added into the electrolyte to improve the performance of the battery, and the additives can account for at least 10% of the electrolyte by weight of 0.1%. Including but not limited to at least one of ethylene sulfite (GS), fluoroethylene carbonate (FEC), vinylene Carbonate (VC), vinyl Ethylene Carbonate (VEC), 1, 3-Propane Sultone (PS), and vinyl sulfate (DTD).

The separator may be a single layer or a combined multilayer of polyethylene and polypropylene, such as a polyethylene/polypropylene bilayer separator, a polyethylene/polypropylene/polyethylene trilayer separator, or a polypropylene/polyethylene/polypropylene trilayer separator. The separator may be provided with an insulating layer that allows ions to pass therethrough but prevents the secondary battery from being short-circuited when thermal shrinkage occurs.

The negative electrode is obtained by coating negative electrode slurry containing a negative electrode active material and a binder on a negative electrode current collector, drying, cold pressing and die cutting. The negative electrode active material may be the graphite-based negative electrode active material of the present invention alone, or may be a mixture of the graphite-based negative electrode active material and other negative electrode active materials (e.g., silicon-based negative electrode active material, soft carbon, hard carbon, etc.). The binder is used to improve the adhesion between the negative active material particles and the aluminum foil current collector. At least one selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene rubber, and acrylated styrene-butadiene rubber. The graphite-based negative active material of the present invention has good conductivity, and thus, a conductive agent may be optionally added or not added according to actual use. The solvent of the negative electrode slurry may be N-methylpyrrolidone. The negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and the like.

The graphite-based negative active material of the present invention includes a graphite core and a hard carbon coating layer. The surface of the graphite core is provided with holes, and the hard carbon coating layer wraps the surface of the graphite core and is embedded into the holes. The hard carbon coating is formed by oxidizing and carbonizing pitch.

The BET of the graphite-based negative active material is 1m ² G to 5m ² (iv) g, as an example, BET may be, but is not limited to, 1m ² /g、2m ² /g、3m ² /g、4m ² /g、5m ² (ii) in terms of/g. The compacted density is 1.3g/cm ³ To 1.5g/cm ³ By way of example, the compacted density may be, but is not limited to, 1g/cm ³ 、1.1g/cm ³ 、1.2g/cm ³ 、1.3g/cm ³ 、1.4g/cm ³ 、1.5g/cm ³ 、1.6g/cm ³ 、1.7g/cm ³ 、1.8g/cm ³ 、1.9g/cm ³ 、2g/cm ³ . The window of lithium extraction is 30% or more, and by way of example, the window of lithium extraction may be, but is not limited to, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%. The first discharge specific capacity is not less than 350mAh/g, and as an example, the first discharge specific capacity may be, but not limited to, 350mAh/g, 353mAh/g, 357mAh/g, 360 mAh/g. The first coulombic efficiency is greater than or equal to 88%, and as an example, the first coulombic efficiency may be, but is not limited to, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%.

In addition, the graphite core is natural graphite and/or artificial graphite, i.e., the graphite core may be natural graphite or artificial graphite, or a mixture of natural graphite and artificial graphite. As an example, the graphite core is artificial graphite, and the fast charging performance of the graphite-based negative active material prepared therefrom is better. The graphite core has a D50 of 2 μm to 50 μm, and the D50 may be, by way of example and not limitation, 2 μm, 5 μm, 9 μm, 14 μm, 19 μm, 24 μm, 30 μm, 36 μm, 41 μm, 45 μm, 50 μm. The carbon content of the graphite core is 99% or more, and as an example, the carbon content of the graphite core may be, but is not limited to, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%. The hard carbon coating layer is one or more layers, and each layer has a thickness of 0.03 μm to 2.0 μm independently. By way of example, the thickness may be, but is not limited to, 0.03 μm, 0.05 μm, 0.1 μm, 0.13 μm, 0.15 μm, 0.18 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.3 μm, 1.6 μm, 2.0 μm. The graphite core can be coated and dried for many times by the asphalt mixed solution, so that a plurality of hard carbon coating layers are formed on the surface of the graphite core.

The preparation method of the graphite-based negative active material comprises the following steps:

(1) Asphalt pretreatment

Dispersing asphalt in an organic solvent uniformly, and filtering to remove insoluble substances to obtain an asphalt mixed solution;

(2) Pretreatment of graphite

(3) Preparation of the precursor

(4) Carbonizing by carbonization

And carbonizing the precursor.

Wherein, in step (1), the asphalt is solid phase asphalt or liquid phase asphalt, and the coking value is 10% to 70%, further coking value can be 30% to 70%, further 50% to 70%, as an example, the coking value can be but is not limited to 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%. The asphalt can be coal tar asphalt, petroleum asphalt or natural asphalt, wherein the petroleum asphalt is liquid phase asphalt, and the coal tar asphalt and the natural asphalt are solid phase asphalt. Pitch comprises 1% to 8% by weight of the graphite, and by way of example and not limitation, pitch comprises 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% by weight of the graphite.

The organic solvent is at least one of oil solvent, alcohol solvent, ketone solvent, hydrocarbon solvent and heterocyclic organic compound. As an example, the oil solvent may be at least one of kerosene, mineral oil, and vegetable oil. The alcohol solvent can be at least one of ethanol, methanol, ethylene glycol, isopropanol, n-octanol, propylene alcohol and octanol. The ketone solvent may be at least one of acetone, methyl butanone, methyl isobutyl ketone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone and cyclohexanone. The alkane solvent may be at least one of cyclohexane, n-hexane, isoheptane, 3-dimethylpentane, and 3-methylhexane.

The filtration is performed by suction filtration, centrifugation or pressure filtration, and by way of example, suction filtration is used. The suction filtration can be realized by connecting and installing Buchner funnels, high-speed filter paper, 1000mL suction bottles, vacuum suction pumps and other equipment; starting a vacuum air pump, and introducing asphalt dispersed in an organic solvent into a funnel, wherein the volume of the solution poured each time is not more than 2/3 of that of the Buchner funnel; before the suction filtration is stopped, a connecting pipe between the suction filtration bottle and the vacuum pump is pulled down to prevent the solution from being sucked back; transferring the filtrate and washing the equipment. The suction filtration process is equivalent to the extraction of chain hydrocarbon, cyclic hydrocarbon, aromatic hydrocarbon and other macromolecules in the asphalt by an organic solvent, and insoluble components are removed.

The acid cleaning activation and oxidation in the step (2) can be used for pore-forming etching on the surface of graphite to form the defect of easy combination of the hard carbon coating layer. The solution adopted for acid cleaning activation is at least one of hydrochloric acid, nitric acid and hydrofluoric acid. In practice, a diluted solution obtained by diluting hydrochloric acid, nitric acid, and hydrofluoric acid may be used as the solution for the acid cleaning activation. Acid washing first can enhance the reactivity of the graphite surface to facilitate oxidation.

The oxidation is carried out by introducing oxidizing atmosphere at 200-500 ℃. The temperature of the oxidation reaction is, for example, but not limited to, 200 ℃, 230 ℃, 280 ℃, 300 ℃, 320 ℃, 350 ℃, 370 ℃, 400 ℃, 420 ℃, 440 ℃, 460 ℃, 480 ℃, 500 ℃. Further, the oxidation may be: placing the graphite after acid cleaning activation into a reactor, heating to 200-500 ℃ at the speed of 1-5 ℃/min, introducing oxidizing atmosphere at the speed of 0.5-20.0L/min, reacting for 0.5-20 h at the constant temperature, and naturally cooling to room temperature to obtain an oxidation product. The oxidizing atmosphere is oxygen or air. The temperature rise rate can be, for example, but not limited to, 1 deg.C/min, 1.5 deg.C/min, 2 deg.C/min, 2.5 deg.C/min, 3 deg.C/min, 3.5 deg.C/min, 4 deg.C/min, 4.5 deg.C/min, 5 deg.C/min. The rate of introduction of the oxidizing atmosphere may be, but is not limited to, 0.5L/min, 1L/min, 3L/min, 5L/min, 7L/min, 10L/min, 13L/min, 15L/min, 20L/min. The incubation reaction can be, but is not limited to, 0.5h, 1h, 3h, 5h, 10h, 13h, 18h, 20h.

The drying temperature is 50 ℃ to 130 ℃, and the temperature is exemplified by, but not limited to, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃,110 ℃, 120 ℃, 130 ℃. The time is 0.5h to 10h, and may be exemplified by, but not limited to, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h.

In the step (3), during mixing, the asphalt mixed solution and the oxidant may be mixed first and then the graphite oxide may be mixed, or the oxidant may be added to the mixture of the asphalt mixed solution and the graphite oxide. The mixing adopts a mechanical mixing mode, the rotating speed is 300rpm to 800rpm, and the time is 10min to 30min. Wherein the rotation speed can be selected from 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 660rpm, 700rpm, 750rpm and 800rpm. The time can be 10min, 13min, 15min, 17min, 20min, 23min, 25min, 28min, and 30min. The oxidant is at least one of hydrogen peroxide, peroxyacetic acid, sodium dichromate, potassium dichromate, chromic acid, nitric acid, potassium permanganate, ammonium persulfate, sodium hypochlorite, sodium percarbonate, sodium perborate and potassium perborate.

In the step (4), the carbonization comprises the steps of placing the precursor into a reactor, heating to 400-1400 ℃, and introducing protective gas for heat preservation reaction. The carbonization temperature is exemplified by, but not limited to, 400 ℃, 450 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 460 ℃, 480 ℃, 500 ℃. Further, the carbonization may be: and (2) placing the precursor into a reactor, heating to 400-1400 ℃ at the speed of 1-5 ℃/min, introducing protective gas at the speed of 0.5-20.0L/min, reacting for 0.5-20 h at a constant temperature, and naturally cooling to room temperature to obtain a carbonized product, wherein the protective gas is one or more of nitrogen, argon, helium, hydrogen and argon-hydrogen mixed gas. The temperature rise rate can be, for example, but is not limited to, 1 deg.C/min, 1.5 deg.C/min, 2 deg.C/min, 2.5 deg.C/min, 3 deg.C/min, 3.5 deg.C/min, 4 deg.C/min, 4.5 deg.C/min, 5 deg.C/min. The introducing rate of the protective gas can be but is not limited to 0.5L/min, 1L/min, 3L/min, 5L/min, 7L/min, 10L/min, 13L/min, 15L/min and 20L/min. The incubation reaction can be, but is not limited to, 0.5h, 1h, 3h, 5h, 10h, 13h, 18h, 20h.

The heat treatment condition is that the temperature is increased to 300-900 ℃, the temperature is kept for 1-12 h, and the temperature increasing rate is 1-10 ℃/min. The maximum temperature of the heat treatment may be, for example, but not limited to, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃. The incubation time may be, for example, but not limited to, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h. The temperature ramp rate can be, for example, but is not limited to, 1 deg.C/min, 2 deg.C/min, 3 deg.C/min, 4 deg.C/min, 5 deg.C/min, 6 deg.C/min, 7 deg.C/min, 8 deg.C/min, 9 deg.C/min, 10 deg.C/min. As an example, the heat treatment is carried out by raising the temperature to 400 ℃ at a rate of 5 ℃/min and reacting for 3 hours.

To better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to specific examples. It should be noted that the following implementation of the method is a further explanation of the present invention, and should not be taken as a limitation of the present invention.

Example 1

The embodiment is a graphite modified material, and the preparation method comprises the following steps:

(1) Asphalt pretreatment

After 10g of petroleum asphalt (coking value is 45%) is uniformly dispersed in 100g of tetrahydrofuran, insoluble substances are removed by suction filtration to obtain 107g of asphalt mixed solution;

(2) Pretreatment of graphite

Performing acid pickling and activating treatment on 100g of artificial graphite (the carbon content is 99.2%) with the D50 of 7 microns and nitric acid according to a mass ratio of 1;

(3) Preparation of the precursor

Uniformly mixing 50g of asphalt mixed solution and 2g of potassium dichromate, adding graphite oxide, and mechanically mixing to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(4) Carbonizing

And carbonizing the precursor under the condition of nitrogen protection atmosphere, wherein the heating rate is 5 ℃/min, the reaction temperature is 1100 ℃, preserving heat for 5h, and cooling to obtain the graphite-based negative active material.

The obtained graphite-based negative active material adopts a microphone specific surfaceThe BET measured by a product measuring instrument Tristar3020 is 2.41m ² (iv) g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 11.2 μm. The 50kN compaction density of the graphite cathode material of the lithium ion battery is measured to be 1.78g/cm by adopting the national standard GB/T243333-2019 graphite cathode material ³ . And (3) testing the surface morphology of the graphite oxide in the step (2) by using an SEM (scanning electron microscope), wherein the result is shown in the figure. Compared with the non-oxidized artificial graphite in fig. 2, the oxidized graphite in fig. 1 has a small number of pores, i.e., defects, on the surface thereof, thereby being beneficial to improving the capacity and the bonding force with the hard carbon coating layer. And performing Raman 3D scanning test on the graphite-based negative active material, wherein the thickness of the hard carbon coating layer is 0.5 mu m.

Example 2

(1) Asphalt pretreatment

After 8g of petroleum asphalt (coking value is 45%) is uniformly dispersed in 100g of tetrahydrofuran, insoluble substances are removed by suction filtration to obtain 105g of asphalt mixed solution;

(2) Pretreatment of graphite

Performing acid washing and activating treatment on 100g of artificial graphite (with a D50 of 7 microns, the carbon content of 99.2%) and nitric acid according to a mass ratio of 1;

(3) Preparation of the precursor

Uniformly mixing 50g of asphalt mixed liquor and 2g of potassium dichromate, adding graphite oxide, and mechanically mixing to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(4) Carbonizing

The BET of the obtained graphite-based negative active material is 2.23m by adopting a Mach specific surface area determinator Tristar3020 ² (iv) g. MS3000 measurement of Malvern laser particle size analyzerThe test particle diameter D50 was 10.7. Mu.m. The compacted density of the graphite anode material is 1.80g/cm measured by adopting the national standard GB/T243357-2019 lithium ion battery graphite anode material ³ 。

Example 3

(1) Asphalt pretreatment

Dispersing 6g of petroleum asphalt (coking value is 45%) in 100g of tetrahydrofuran uniformly, and removing insoluble substances by suction filtration to obtain 102g of asphalt mixed solution;

(2) Pretreatment of graphite

(3) Preparation of the precursor

(4) Carbonizing by carbonization

And carbonizing the precursor under the condition of nitrogen protection atmosphere, wherein the heating rate is 5 ℃/min, the reaction temperature is 1100 ℃, the temperature is kept for 5h, and cooling is carried out to obtain the graphite-based negative active material.

The BET of the obtained graphite-based negative active material is 2.02m measured by a Mach specific surface area determinator Tristar3020 ² (iv) g. The particle diameter D50 measured by a Malvern laser particle size Analyzer MS3000 is 10.4 μm. The tap density is 1.81g/cm by adopting the national standard GB/T243354-2019 graphite cathode material for lithium ion batteries ³ 。

Example 4

(1) Asphalt pretreatment

Uniformly dispersing 12g of petroleum asphalt (coking value is 45%) in 100g of tetrahydrofuran, and removing insoluble substances by suction filtration to obtain 109g of asphalt mixed solution;

(2) Pretreatment of graphite

(3) Preparation of the precursor

(4) Carbonizing

The BET of the obtained graphite-based negative active material is 2.57m by adopting a Tristar3020 measuring instrument of Michelia ² (ii) in terms of/g. The particle diameter D50 measured by a Malvern laser particle size Analyzer MS3000 was 11.7. Mu.m. The tap density is 1.77g/cm by adopting the national standard GB/T243354-2019 graphite cathode material for lithium ion batteries ³ 。

Example 5

(1) Asphalt pretreatment

Uniformly dispersing 14g of petroleum asphalt (coking value is 45%) in 100g of tetrahydrofuran, and removing insoluble substances by suction filtration to obtain 111g of asphalt mixed solution;

(2) Pretreatment of graphite

(3) Preparation of the precursor

(4) Carbonizing

The BET of the obtained graphite-based negative active material measured by a Mach specific surface area determinator Tristar3020 is 2.78m ² (iv) g. The particle diameter D50 measured by a Malvern laser particle size Analyzer MS3000 was 11.6. Mu.m. The tap density is measured to be 1.75g/cm by adopting the national standard GB/T243333-2019 lithium ion battery graphite cathode material ³ 。

Example 6

(1) Asphalt pretreatment

Dispersing 10g of coal tar pitch (coking value is 60%) in 100g of tetrahydrofuran uniformly, and removing insoluble substances by suction filtration to obtain 107g of pitch mixed liquor;

(2) Pretreatment of graphite

(3) Preparation of the precursor

(4) Carbonizing

The obtained graphite-based negative active material adoptsThe BET of the specific surface area determinator Tristar3020 for the Michel is 2.62m ² (ii) in terms of/g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 12.8 μm. The tap density is 1.78g/cm by adopting the national standard GB/T243354-2019 graphite cathode material for lithium ion batteries ³ 。

Example 7

(1) Asphalt pretreatment

(2) Pretreatment of graphite

Performing acid pickling and activating treatment on 100g of natural graphite (with a D50 of 7.5 microns, the carbon content of 99.9%) and nitric acid according to a mass ratio of 1;

(3) Preparation of the precursor

(4) Carbonizing by carbonization

The BET of the obtained graphite-based negative active material measured by a Mach specific surface area determinator Tristar3020 is 3.78m ² (ii) in terms of/g. The particle diameter D50 measured by a Malvern laser particle size Analyzer MS3000 is 8.9 μm. The compacted density of the graphite anode material is 1.91g/cm measured by adopting the national standard GB/T243357-2019 lithium ion battery graphite anode material ³ 。

Example 8

(1) Asphalt pretreatment

After 10g of petroleum asphalt (coking value is 45%) is uniformly dispersed in 120g of mineral oil, insoluble substances are removed by suction filtration to obtain 80g of asphalt mixed liquor;

(2) Pretreatment of graphite

Performing acid pickling and activating treatment on 100g of artificial graphite (the carbon content is 99.2%) with the D50 of 7 microns and concentrated hydrochloric acid according to a mass ratio of 1;

(3) Preparation of the precursor

(4) Carbonizing by carbonization

The BET of the obtained graphite-based negative active material measured by a Mach specific surface area determinator Tristar3020 is 1.59m ² (iv) g. The particle diameter D50 measured by a Malvern laser particle size analyzer MS3000 is 9.3. Mu.m. The tap density is measured to be 1.81g/cm by adopting the national standard GB/T243333-2019 lithium ion battery graphite cathode material ³ 。

Example 10

(1) Asphalt pretreatment

After 10g of petroleum asphalt (coking value is 45%) is uniformly dispersed in 100g of mineral oil, insoluble substances are removed by suction filtration to obtain 100g of asphalt mixed liquor;

(2) Pretreatment of graphite

80g of artificial graphite (with the carbon content of 99.2%) with the D50 of 7 microns and nitric acid are subjected to acid pickling and activating treatment according to the mass ratio of 1;

(3) Preparation of the precursor

Uniformly mixing 40g of asphalt mixed liquor and 2g of ammonium persulfate, adding graphite oxide, and mechanically mixing to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(4) Carbonizing

And carbonizing the precursor under the condition of nitrogen protection atmosphere, wherein the heating rate is 8 ℃/min, the reaction temperature is 1200 ℃, preserving heat for 5h, and cooling to obtain the graphite-based negative active material.

The BET of the obtained graphite-based negative active material is 1.98m by adopting a Mach specific surface area determinator Tristar3020 ² (ii) in terms of/g. The particle diameter D50 measured by a Malvern laser particle size Analyzer MS3000 is 10.5 μm. The tap density is measured to be 1.79g/cm by adopting the national standard GB/T243333-2019 lithium ion battery graphite cathode material ³ 。

Comparative example 1

This example used the same artificial graphite as in example 1, and its BET was measured to be 1.65m using a Mach specific surface area meter Tristar3020 ² (iv) g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 7.5 μm. The compacted density of the graphite anode material is 1.88g/cm measured by adopting the national standard GB/T243357-2019 lithium ion battery graphite anode material ³ The surface topography thereof is shown in FIG. 2 by SEM electron microscopy.

Comparative example 2

(1) Asphalt pretreatment

Dispersing 10g of petroleum asphalt (coking value is 45%) in 100g of tetrahydrofuran uniformly, and removing insoluble substances by suction filtration to obtain 107g of asphalt mixed liquor;

(2) Preparation of the precursor

Mechanically mixing 50g of asphalt mixed solution and 100g of artificial graphite (carbon content is 99.2%) with D50 of 7 mu m to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(3) Carbonizing

The BET of the obtained graphite-based negative active material is 1.08m by adopting a Mach specific surface area determinator Tristar3020 ² (ii) in terms of/g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 10.7 μm. The compacted density of the graphite anode material is 1.81g/cm measured by adopting the national standard GB/T243357-2019 lithium ion battery graphite anode material ³ 。

Comparative example 3

(1) Asphalt pretreatment

(2) Pretreatment of graphite

(3) Preparation of the precursor

Mechanically mixing 50g of asphalt mixed liquor and graphite oxide to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(4) Carbonizing

The BET of the obtained graphite-based negative active material measured by a Mach specific surface area meter Tristar3020 is 1.54m ² (ii) in terms of/g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 10.9 μm. The compacted density is measured to be 1.80g/cm by adopting the national standard GB/T243333-2019 lithium ion battery graphite cathode material ³

Comparative example 4

(1) Asphalt pretreatment

(2) Preparation of the precursor

Uniformly mixing 50g of asphalt mixed liquor and 2g of potassium dichromate, adding 100g of artificial graphite (the carbon content is 99.2%) with the D50 of 7 mu m, and mechanically mixing to obtain a precursor, wherein the rotating speed is 450rpm, and the time is 15min;

(3) Carbonizing

The BET of the obtained graphite-based negative active material is 2.03m measured by a Mach specific surface area determinator Tristar3020 ² (ii) in terms of/g. The particle diameter D50 of the Malvern laser particle size analyzer MS3000 is 11.3 μm. The compacted density is measured to be 1.81g/cm by adopting the national standard GB/T243333-2019 lithium ion battery graphite cathode material ³ 。

Electrochemical performance tests were performed on the graphite-based negative active materials obtained in examples 1 to 9 and comparative examples 1 to 4 using a half-cell test method, and the results are shown in table 1.

The test method comprises the following steps: the graphite-based negative electrode active materials obtained in examples 1 to 9 and comparative examples 1 to 4, polyvinylidene fluoride and SP were mixed according to a mass ratio of 70. A metallic lithium plate is used as a counter electrode, and 1mol/L LiPF is used ₆ As lithium salt, EC: DMC: EMC =1 (v/v) as solvent mixed electrolyte, and a polypropylene microporous membrane as a separator was assembled into a CR2032 type button cell in an inert gas filled glove box. The charge and discharge test of the button cell is carried out on a cell test system of blue-electricity electronic corporation of Wuhan city, and the constant current charge and discharge are carried out at 0.1C and the charge and discharge voltage is limited to 0.005V under the normal temperature conditionTo 1.5V.

TABLE 1 physical and electrochemical Properties of the materials obtained in the examples

As can be seen from table 1, the graphite-based negative active materials of examples 1 to 9 have a high lithium deposition window, which indicates that the electrochemical properties such as the rate and the rapid charging are good, and also have high first discharge specific capacity, compaction density, and first coulombic efficiency. The graphite can be subjected to acid cleaning activation and oxidation, and then pores are formed and etched on the surface of the graphite to form defects, namely surface holes, the defects have high chemical activity, and asphalt and graphite oxide are easy to perform surface reaction to combine to improve the coating performance, so that the cycle and quick filling performance of the graphite are improved. The asphalt is added with an oxidant for reaction before carbonization to form a coating layer, so that partial active functional groups (such as olefin and the like) contained in the asphalt are oxidized to form chemical bonds to generate defects in the asphalt, and the oxidation degree is gradually increased along with the progress of carbonization reaction, the defects formed in the asphalt are increased, and the original short-range ordered soft carbon structure formed by the asphalt is destroyed, the structure is gradually transited to hard carbon, and the quick filling performance of the asphalt is improved.

In comparative example 3, no oxidizing agent was added to oxidize the pitch, and the coating material formed by the pitch was still soft carbon, so the window for lithium precipitation was low. In comparative example 4, the graphite was not subjected to surface pickling activation and oxidation in advance, and even if an oxidizing agent was added before the carbonization reaction, the lithium precipitation window was low because the surface was hardly oxidized to form defects without pickling activation.

It should be finally noted that the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments, and it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. The graphite-based negative active material is characterized by comprising a graphite core and a hard carbon coating layer, wherein the surface of the graphite core is provided with holes, the hard carbon coating layer wraps the surface of the graphite core and is embedded into the holes, and the hard carbon coating layer is formed by oxidizing and carbonizing asphalt.

2. The graphite-based negative active material of claim 1, wherein the graphite core is natural graphite and/or artificial graphite.

3. The graphite-based negative active material according to claim 1, wherein the graphite core has a D50 of 2 to 50 μm and a carbon content of 99% or more.

4. The graphite-based anode active material according to claim 1, wherein the hard carbon coating layer is one or more layers, and each layer has a thickness of 0.03 μm to 2.0 μm independently.

5. The graphite-based anode active material according to claim 1, characterized by satisfying at least one of the following characteristics (1) to (5):

(1) BET of 1m ² G to 5m ² /g；

(2) The compacted density is 1g/cm ³ To 2g/cm ³ ；

(3) The lithium separating window is more than or equal to 30 percent;

(4) The first discharge specific capacity is not lower than 350mAh/g;

(5) The first coulombic efficiency is more than or equal to 88 percent.

6. The preparation method of the graphite-based negative active material is characterized by comprising the following steps:

(1) Asphalt pretreatment

(2) Pretreatment of graphite

Carrying out surface pickling activation, drying and oxidation on graphite in sequence to obtain graphite oxide;

(3) Preparation of the precursor

Mixing the asphalt mixed solution, the graphite oxide and an oxidant to obtain a precursor;

(4) Carbonizing

Carbonizing the precursor.

7. The method for producing a graphite-based negative active material according to claim 6, characterized by comprising at least one of the following features (1) to (11):

(1) The asphalt is solid-phase asphalt or liquid-phase asphalt, and the coking value is 10-70%;

(2) The organic solvent is at least one of an oil solvent, an alcohol solvent, a ketone solvent, a hydrocarbon solvent and a heterocyclic organic compound;

(3) The filtration mode is suction filtration, centrifugation or filter pressing;

(4) The pitch comprises 1% to 8% by weight of the graphite;

(5) The solution adopted for acid cleaning activation is at least one of hydrochloric acid, nitric acid and hydrofluoric acid;

(6) The oxidation is carried out by introducing oxidizing atmosphere at 200-500 ℃ for oxidation reaction;

(7) The drying temperature is 50-130 ℃, and the drying time is 0.5-10 h;

(8) The oxidant is at least one of hydrogen peroxide, peracetic acid, sodium dichromate, potassium dichromate, chromic acid, nitric acid, potassium permanganate, ammonium persulfate, sodium hypochlorite, sodium percarbonate, sodium perborate and potassium perborate;

(9) In the step (3), the asphalt mixed liquor and the oxidant may be mixed first and then the graphite oxide may be mixed, or the oxidant may be added to the mixture of the asphalt mixed liquor and the graphite oxide;

(10) The mixing adopts a mechanical mixing mode, the rotating speed is 300rpm to 800rpm, and the time is 10min to 30min;

(11) And the carbonization comprises the steps of placing the precursor in a reactor, heating to 400-1400 ℃, and introducing protective gas for heat preservation reaction.

8. Use of the graphite-based negative active material according to any one of claims 1 to 5, or the graphite-based negative active material prepared by the method for preparing the graphite-based negative active material according to claim 6 or 7, in a negative electrode material.

9. A secondary battery comprising a cathode material, an anode material and an electrolyte, wherein the anode material comprises the graphite-based anode active material according to any one of claims 1 to 5 or the graphite-based anode active material prepared by the method for preparing the graphite-based anode active material according to claim 6 or 7.