CN114824213A - Composite graphite, preparation method thereof, negative plate and secondary battery - Google Patents

Composite graphite, preparation method thereof, negative plate and secondary battery Download PDF

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Publication number
CN114824213A
CN114824213A CN202210438880.5A CN202210438880A CN114824213A CN 114824213 A CN114824213 A CN 114824213A CN 202210438880 A CN202210438880 A CN 202210438880A CN 114824213 A CN114824213 A CN 114824213A
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graphite
composite graphite
carbon
mixing
solvent
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郭雅芳
陈杰
杨山
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Huizhou Liwinon Energy Technology Co Ltd
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Huizhou Liwinon Energy Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/21—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to composite graphite and a preparation method thereof, a negative plate and a secondary battery, which comprise the following steps: step S1, mixing the graphite material, the polar additive and the first solvent to obtain a first material; s2, placing the first material in an electromagnetic field, cooling, solidifying, heating and vaporizing to obtain a second material; step S3, mixing a nitrogen source, a carbon source and a second solvent to obtain a mixed solution; and step S4, adding the second material into the mixed solution, ultrasonically stirring, filtering, drying, heating and carbonizing in an inert atmosphere, and performing ball milling and filtering to obtain the composite graphite. The graphite material is processed to increase the interlayer spacing of the graphite material, which is beneficial to the rapid insertion and extraction of lithium ions, and then nitrogen doping and carbon coating are carried out to improve the capacity and form electronegativity stronger than carbon-carbon bonds, so that the composite graphite has stronger attraction to the lithium ions and is beneficial to the magnification improvement, and thus the composite graphite with capacity and magnification performance simultaneously is obtained.

Description

Composite graphite, preparation method thereof, negative plate and secondary battery
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to composite graphite, a preparation method thereof, a negative plate and a secondary battery.
Background
With the rapid development of the world economy, the problems of energy shortage, environmental pollution and the like become serious challenges which must be faced on the sustainable development roads of all countries. The rapid development of the lithium ion battery technology opens a brand-new energy age, the characteristics of high energy density, high working voltage, good cycle performance, safety, no pollution and the like of the lithium ion battery are generally applied to digital products, electric automobiles, military products and the like, the development of the lithium ion battery is as vigorous as possible, the requirement on the charging rate of the battery is higher and higher, and the existing material cannot have both capacity and multiplying power performance.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the preparation method of the composite graphite is provided, and the prepared composite graphite has capacity and rate capability.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of composite graphite comprises the following steps:
step S1, mixing the graphite material, the polar additive and the first solvent to obtain a first material;
s2, placing the first material in an electromagnetic field, cooling, solidifying, heating, vaporizing and cooling to obtain a second material;
step S3, mixing a nitrogen source, a carbon source and a second solvent to obtain a mixed solution;
and step S4, adding the second material into the mixed solution, ultrasonically stirring, filtering, drying, heating and carbonizing in an inert atmosphere, and performing ball milling and filtering to obtain the composite graphite.
Preferably, the preparation method of the graphite material comprises the following steps: crushing a carbon material, ball-milling, adding a binder, stirring and mixing, mechanically fusing, and heating for graphitization to obtain the graphite material.
Preferably, the particle size D50 after ball milling in the step S1 is 3-7 μm.
Preferably, the weight part ratio of the carbon material to the binder is 1-3: 0.1-0.5, the rotation speed of stirring and mixing is 500-1500rpm/min, and the time of stirring and mixing is 10-30 min.
Preferably, the graphitization temperature is 2400-3000 ℃, and the graphitization time is 20-60 h.
Preferably, the frequency of the electromagnetic field in the step S2 is 5-15 Hz, the solidification temperature is-150 to-10 ℃, the temperature reduction rate is 15-60 ℃/S, the vaporization temperature is 150 to 200 ℃, and the heating rate is 15 to 60 ℃/S.
Preferably, the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 1-3: 0.2-3: 5-12.
Preferably, in the step S4, the drying temperature is 40-150 ℃, the drying time is 10-50 h, the carbonization temperature is 400-1500 ℃, and the carbonization time is 1-10 h.
The second purpose of the invention is: aiming at the defects of the prior art, the composite graphite has good capacity, compaction density and rate capability.
In order to achieve the purpose, the invention adopts the following technical scheme:
the composite graphite is prepared by the preparation method of the composite graphite.
The third purpose of the invention is that: aiming at the defects of the prior art, the negative plate is provided and has good electrochemical performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a negative plate comprises the composite graphite.
The fourth purpose of the invention is that: aiming at the defects of the prior art, the secondary battery has good electrochemical performance, good cyclicity performance and good rapid charge and discharge performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a secondary battery comprises the negative plate.
Compared with the prior art, the invention has the beneficial effects that: the invention carries out quick freezing, cooling solidification and heating vaporization treatment on the graphite material in an electromagnetic field, increases the interlayer spacing of the graphite material, is beneficial to quick embedding and removing of lithium ions, carries out nitrogen doping and carbon coating, improves the capacity, forms stronger electronegativity than carbon-carbon bonds, has stronger attraction to the lithium ions, and is beneficial to multiplying power improvement, thereby obtaining the composite graphite which gives consideration to both the capacity and the multiplying power performance.
Drawings
Fig. 1 is an SEM image of the composite graphite of the present invention.
Fig. 2 is a graph of cycle retention at a magnification of 7C of the composite graphite prepared in example 1 of the present invention.
Detailed Description
A preparation method of composite graphite comprises the following steps:
step S1, mixing the graphite material, the polar additive and the first solvent to obtain a first material;
s2, placing the first material in an electromagnetic field, cooling, solidifying, heating, vaporizing and cooling to obtain a second material;
step S3, mixing a nitrogen source, a carbon source and a second solvent to obtain a mixed solution;
and step S4, adding the second material into the mixed solution, ultrasonically stirring, filtering, drying, heating and carbonizing in an inert atmosphere, and performing ball milling and filtering to obtain the composite graphite.
The graphite material is rapidly frozen in an electromagnetic field, the polar additive can be embedded into interlayer spacing of the graphite material together with a solvent, the graphite material is cooled and solidified, the volumes of the polar additive and the solvent are increased, the interlayer spacing of the graphite material is increased, heating vaporization treatment is carried out, the polar additive and the solvent are vaporized and removed, the obtained graphite material is favorable for rapid embedding and removing of lithium ions, nitrogen doping and carbon coating are carried out, the capacity is improved, electronegativity higher than that of a carbon-carbon bond is formed, the attraction force on the lithium ions is stronger, and the multiplying power is favorably improved, so that the composite graphite with capacity and multiplying power performance is obtained.
The polar additive takes benzene ring, naphthalene ring or pyridine as a main bracket, contains one or more hydroxyl or amino and carboxyl organic molecules, and is used as an interlayer distance expansion bracket after being frozen. The solvent is deionized water. The electromagnetic field has a low-frequency electromagnetic field of 6-9 Hz, so that water molecules and polar additives freely enter the graphite layer. And (3) solidifying rapidly after solidification to enable water to be solidified into ice, increasing the volume change, increasing the graphite interlayer spacing by 0.337-0.340, heating to enable moisture to be vaporized to obtain a graphite material after interlayer spacing expansion treatment, and mixing the graphite material with a nitrogen source, a carbon source and a second solvent for graphitization treatment to obtain the composite graphite material with large interlayer spacing coated by nitrogen-doped carbon. The second solvent is any one of ethanol, deionized water and propanol. The nitrogen source may be any one of glucosamine, urea, and protein. The carbon source may be any one of oxalic acid, citric acid, and stearic acid. Wherein, the weight part ratio of the second material to the mixed solution in the step S4 is 1-2: 0.4-0.8.
Preferably, the preparation method of the graphite material comprises the following steps: crushing the carbon material, ball milling, adding the binder, stirring and mixing, mechanically fusing, and heating and graphitizing to obtain the graphite material.
The carbon material can be one or more of needle coke, petroleum coke, pitch coke or natural graphite, can reduce the particle size of raw materials after the ball-milling, make the carbon material become the sphere by irregular shape such as triangle-shaped, multilateral shape, spherical carbon material can reduce ion transmission's span for the carbon material of other shapes, promotes the charge-discharge ability, and the tip edges and corners can be ground away to another direction, is favorable to the shape of later stage granulation. The binder is mixed with the material subjected to ball milling, so that the binder is fully coated on the surface of the material, mechanical fusion is carried out, the softened binder is adhered together for granulation, the isotropy of particles is increased, and the lithium intercalation end face is increased, so that the rapid charging and discharging speed is improved.
Preferably, the particle size D50 after ball milling in the step S1 is 3-7 μm. The ball-milling can reduce graphite precursor particle diameter on the one hand, reduces ion transport distance and promotes charging, and on the other hand can grind off most advanced edges and corners, is favorable to the shape of later stage granulation. The control of a certain particle size can not only improve the compaction density of the cathode material, but also improve the charge and discharge performance. The particle diameter D50 after ball milling was 3 μm, 4 μm, 5 μm, 6 μm, and 7 μm. The spherical graphite material is beneficial to the compaction density of the prepared composite graphite during coating, so that the cathode sheet has capacity, compaction density and rate capability.
Preferably, the weight part ratio of the carbon material to the binder is 1-3: 0.1-0.5, the rotation speed of stirring and mixing is 500-1500rpm/min, and the time of stirring and mixing is 10-30 min. Certain carbon material and adhesive are set to mix the adhesive with the carbon material and the adhesive is coated on the surface of the carbon material for pelletizing. And a certain stirring speed and stirring and mixing time are set, so that the mixing is more uniform. Preferably, the weight ratio of the carbon material to the binder is 1-3: 0.2-0.5, 1-3: 0.2-0.4, 1.5-3: 0.2-0.4, 2-3: 0.2-0.4. The rotation speed is 500rpm/min, 600rpm/min, 700rpm/min, 800rpm/min, 1200rpm/min, 1300rpm/min, and the stirring and mixing time is 10min, 12min, 16min, 18min, 20min, 25min, and 30 min.
Preferably, the graphitization temperature is 2400-3000 ℃, and the graphitization time is 20-60 h. Through graphitization treatment, carbon atoms distributed in disorder inside the material are arranged in order, so that the structure is more stable and the performance is better. Preferably, the graphitization temperature is 2400 deg.C, 2500 deg.C, 2600 deg.C, 2700 deg.C, 2800 deg.C, 2900 deg.C, 3000 deg.C. The graphitization time is 20h, 30h, 40h, 50h and 60 h.
Preferably, the frequency of the electromagnetic field in the step S2 is 5-15 Hz, the solidification temperature is-150 to-10 ℃, the temperature reduction rate is 15-60 ℃/S, the vaporization temperature is 150 to 200 ℃, and the heating rate is 15 to 60 ℃/S. Preferably, the frequency of the electromagnetic field is 6-9 Hz, and the frequency is matched with the interlayer spacing of the graphite material, so that the polar additive and the solvent can enter the graphite material more easily. When the temperature is reduced, a certain speed is needed, so that the solution is quickly solidified, the volume is increased, the interlayer spacing is increased, a certain temperature is kept, and the structure is more stable. The heating raises the temperature, thereby dissolving and vaporizing the polar additive and the solvent, thereby removing it. The frequencies of the electromagnetic field are 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, 10Hz, 11Hz, 12Hz, 13Hz, 14Hz, and 15 Hz. The solidification temperature is-150 ℃, 120 ℃, 100 ℃, 80 ℃, 60 ℃, 40 ℃ and 20 ℃. The vaporization temperature is 150 deg.C, 160 deg.C, 170 deg.C, 180 deg.C, 190 deg.C, and 200 deg.C. The cooling rate is 15 ℃/s, 20 ℃/s, 25 ℃/s, 30 ℃/s, 35 ℃/s, 40 ℃/s, 45 ℃/s, 50 ℃/s, 55 ℃/s and 60 ℃/s, and the heating rate is 15 ℃/s, 20 ℃/s, 25 ℃/s, 30 ℃/s, 35 ℃/s, 40 ℃/s, 45 ℃/s, 50 ℃/s, 55 ℃/s and 60 ℃/s.
Preferably, the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 1-3: 0.2-3: 5-12. And controlling certain weight parts of the nitrogen source, the carbon source and the second solvent to enable the nitrogen doping rate and the carbon coating rate to be within a certain range, wherein the carbon coating can increase the energy density, and the nitrogen doping can improve the attraction to lithium ions, so that the multiplying power is improved. Preferably, the weight ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 1-3: 0.5-3: 5-10, 1-3: 6-10, 2-3: 6-8, 1.5-3: 6-10.
Preferably, in the step S4, the drying temperature is 40-150 ℃, the drying time is 10-50 h, the carbonization temperature is 400-1500 ℃, and the carbonization time is 1-10 h. Preferably, the drying temperature is 60-120 ℃, 80-100 ℃, the drying time is 10-40 h, 20-40 h and 25-35 h, the carbonization temperature is 600-1500 ℃, 800-1500 ℃, 1000-1500 ℃, 1200-1500 ℃, and the carbonization time is 2-10 h, 4-8 h, 5-8 h and 6-8 h.
The second purpose of the invention is: aiming at the defects of the prior art, the composite graphite has good capacity, compaction density and rate capability.
In order to achieve the purpose, the invention adopts the following technical scheme:
the composite graphite is prepared by the preparation method of the composite graphite.
Compared with the traditional graphite, the composite graphite has larger interlayer spacing, is beneficial to charge-discharge cycle and improves the rate capability, the surface of the composite graphite has nitrogen doping, the composite graphite has stronger attraction to lithium ions, the rate capability is further improved, the energy density and stability of the material can be increased by carbon coating, the material has better cycle stability, energy density and rate capability, and 5-10C rate charge-discharge can be realized.
The third purpose of the invention is that: aiming at the defects of the prior art, the negative plate is provided and has good electrochemical performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a negative plate comprises the composite graphite.
The negative plate has good rate performance and energy density.
The fourth purpose of the invention is that: aiming at the defects of the prior art, the secondary battery has good electrochemical performance, good cyclicity performance and good rapid charge and discharge performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a secondary battery comprises the negative plate.
The secondary battery of the present invention has good rate capability and energy density. The secondary battery comprises a positive plate, an isolating membrane, a negative plate, electrolyte and a shell, wherein the positive plate and the negative plate are separated by the isolating membrane, and the shell is used for packaging the positive plate, the isolating membrane, the negative plate and the electrolyte.
The positive plate comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, the positive active material layer comprises a positive active material, and the positive active material can be a chemical formula including but not limited to Li a Ni x Co y M z O 2-b N b (wherein a is more than or equal to 0.95 and less than or equal to 1.2, x>0, y is more than or equal to 0, z is more than or equal to 0, and x + y + z is 1,0 is more than or equal to b and less than or equal to 1, M is selected from one or more of Mn and Al and N is selected from F, P, S), and the positive active material can also be selected from the group consisting of but not limited to LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 、Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4 、CuS 2 、FeS 2 、MoS 2 、NiS、TiS 2 And the like. The positive electrode active material may be further modified, and the method of modifying the positive electrode active material is known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, and the like, and the material used in the modification may be one or a combination of more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, and the like. And the positive electrode current collector is generally a structure or a part for collecting current, and the positive electrode current collector may be any material suitable for being used as a positive electrode current collector of a lithium ion battery in the field, for example, the positive electrode current collector may include, but is not limited to, a metal foil and the like, and more specifically, may include, but is not limited to, an aluminum foil and the like. The dispersant in the positive electrode is polyacrylonitrile or polystyrene.
The positive electrode active material layer further includes a conductive agent, which may be a carbon material, a metal-based material, a conductive polymer, or the like, and any conductive material may be used as the conductive agent as long as it does not cause chemical changes within the battery. Examples of the conductive agent include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanotubes, graphene, or the like; a metal-based material comprising metal powder or metal fibers containing one or more of copper, nickel, aluminum, or silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.
The positive electrode active material layer further includes a binder, which may be used to improve the binding properties of the positive electrode active materials to each other and to the current collector. Examples of the binder include one or more of synthetic rubber, a polymer material, and the like. Examples of the synthetic rubber include styrene-butadiene-based rubber, fluorine-based rubber, or ethylene propylene diene rubber. The binder may further include, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxymethyl methyl cellulose, hydroxydiacetyl cellulose, polyvinyl chloride, carboxy polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.
Preferably, the negative plate comprises a negative current collector and a negative active material layer coated on at least one surface of the negative current collector, the negative active material layer comprises a negative active material, a conductive agent, a binder and a dispersing agent, and the weight part ratio of the negative active material to the conductive agent to the binder to the dispersing agent is 85-99: 1-15: 1-5. The negative active material adopts the composite graphite.
The negative electrode active material layer further includes a binder. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. The negative electrode binder contains hydroxyalkyl methylcellulose because hydroxyalkyl methylcellulose has excellent binding properties and dispersibility to the carbon material. The hydroxyalkyl methyl cellulose comprises at least one of sodium hydroxyalkyl methyl cellulose or lithium hydroxyalkyl methyl cellulose, and the alkyl group comprises methyl, ethyl, propyl or butyl.
The anode active material layer further includes a conductive material. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanotubes, graphene, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
The present invention will be described in further detail with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.
Example 1
Step 1, carrying out coarse crushing and fine grinding on needle coke, and then carrying out ball milling and shaping treatment by using a ball mill to obtain a graphite precursor, wherein D50 is 6.5 mu m;
step 2, adding the graphite precursor and the binder pitch in a mechanical fusion machine according to the weight part of 1:0.25, and processing for 20min at the rotating speed of 1000rpm, wherein the softening point of the pitch is 120 ℃;
step 3, placing the spherical graphite precursor prepared in the step 2 in a graphitization furnace, heating to 2550 ℃, and treating for 48 hours to obtain spherical graphite;
step 4, mixing the spherical graphite, the polar additive p-hydroxybenzoic acid and the deionized water in a temperature-controllable container according to the proportion of 1:0.2:20, and uniformly stirring to obtain a first material;
step 5, a low-frequency electromagnetic field with the frequency of 8Hz is accessed to the first material, so that water molecules and polar additives freely enter the graphite layer;
step 6, rapidly cooling the container to-100 ℃ at the speed of 30 ℃/s, maintaining for 5 hours, and increasing the spacing between graphite layers by the volume change of water solidified into ice during the period;
step 7, raising the temperature of the container to 150 ℃ at a rate of 18 ℃/s, vaporizing the deionized water, and cooling to obtain a second material;
step 8, uniformly mixing melamine serving as a nitrogen source, citric acid serving as a carbon source and butanediol serving as a solvent in a weight ratio of 1:1.2:7 in an ultrasonic machine to prepare a mixed solution;
step 9, adding the second material (the second material) prepared in the step 7 into the mixed solution obtained in the step 8, and continuing to perform ultrasonic stirring to obtain uniform slurry;
step 10, filtering the uniform slurry obtained in the step 9, drying the slurry at 80 ℃ for 48 hours, and then moving the slurry to an inert atmosphere to carry out carbonization treatment at 1000 ℃ for 5 hours;
and 11, performing ball milling dispersion on the material prepared in the step 10, and sieving with a 500-mesh sieve to obtain the nitrogen-doped carbon-coated large-interlayer-distance graphite, namely the composite graphite, as shown in figure 1.
Example 2
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 1:0.4, the rotating speed of stirring and mixing is 600rpm/min, and the time of stirring and mixing is 10 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 1:0.5, the stirring and mixing speed is 800rpm/min, and the stirring and mixing time is 13 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 2:0.1, the stirring and mixing speed is 800rpm/min, and the stirring and mixing time is 18 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 3:0.1, the stirring and mixing speed is 1000rpm/min, and the stirring and mixing time is 24 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 3:0.2, the stirring and mixing rotating speed is 1500rpm/min, and the stirring and mixing time is 22 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 7
The difference from example 1 is that: the weight portion ratio of the carbon material to the binder is 3:0.5, the rotating speed of stirring and mixing is 1300rpm/min, and the time of stirring and mixing is 28 min.
The rest is the same as embodiment 1, and the description is omitted here.
Example 8
The difference from example 1 is that: in the step S2, the frequency of the electromagnetic field is 15Hz, the solidification temperature is-100 ℃, the cooling rate is 30 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S.
The rest is the same as embodiment 1, and the description is omitted here.
Example 9
The difference from example 1 is that: in the step S2, the frequency of the electromagnetic field is 5Hz, the solidification temperature is-100 ℃, the cooling rate is 30 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S.
The rest is the same as embodiment 1, and the description is omitted here.
Example 10
The difference from example 1 is that: in the step S2, the frequency of the electromagnetic field is 8Hz, the solidification temperature is-100 ℃, the cooling rate is 50 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S.
The rest is the same as embodiment 1, and the description is omitted here.
Example 11
The difference from example 1 is that: in the step S2, the frequency of the electromagnetic field is 8Hz, the solidification temperature is-100 ℃, the cooling rate is 20 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S.
The rest is the same as embodiment 1, and the description is omitted here.
Example 12
The difference from example 1 is that: in the step S2, the frequency of the electromagnetic field is 8Hz, the solidification temperature is-150 ℃, the cooling rate is 30 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S.
The rest is the same as embodiment 1, and the description is omitted here.
Example 13
The difference from example 1 is that: the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 1:0.2: 7.
The rest is the same as embodiment 1, and the description is omitted here.
Example 14
The difference from example 1 is that: the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 1:3: 7.
The rest is the same as embodiment 1, and the description is omitted here.
Example 15
The difference from example 1 is that: the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 3:1.2: 7.
The rest is the same as embodiment 1, and the description is omitted here.
Example 16
The difference from example 1 is that: the weight part ratio of the nitrogen source, the carbon source and the second solvent in the step S3 is 3:2: 7.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
The difference from example 1 is that: the preparation methods of the composite graphite are different:
step 1, mixing needle bananas, a polar additive p-hydroxybenzoic acid and deionized water in a temperature-controllable container in a ratio of 1:0.2:20, and uniformly stirring to obtain a first material;
step 2, a low-frequency electromagnetic field with the frequency of 8Hz is accessed to the first material, so that water molecules and polar additives freely enter the graphite layer;
step 3, rapidly cooling the container to-100 ℃ at the speed of 30 ℃/s, maintaining for 5 hours, and increasing the spacing between graphite layers by the volume change of water solidified into ice during the period;
step 4, raising the temperature of the container to 150 ℃ at a rate of 18 ℃/s, vaporizing the deionized water, and cooling to obtain a material II;
step 5, uniformly mixing melamine serving as a nitrogen source, citric acid serving as a carbon source and butanediol serving as a solvent in a weight ratio of 1:2:8 in an ultrasonic machine to prepare a mixed solution;
step 6, adding the material II prepared in the step 4 into the mixed solution in the step 5, and continuously performing ultrasonic stirring to obtain uniform slurry;
step 7, filtering the uniform slurry obtained in the step 6, drying the slurry at 80 ℃ for 48 hours, and then moving the slurry to an inert atmosphere to carry out carbonization treatment at 1000 ℃ for 5 hours;
and 8, performing ball milling dispersion on the material prepared in the step 7, and screening by using a 500-mesh sieve to obtain the nitrogen-doped carbon-coated graphite with large interlayer spacing, namely the negative electrode material.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 2
The difference from example 1 is that: the preparation methods of the composite graphite are different:
step 1, carrying out coarse crushing and fine grinding on needle coke, and then carrying out ball milling and shaping treatment by using a ball mill to obtain a graphite precursor, wherein D50 is 6.5 mu m;
step 2, adding the graphite precursor and the binder pitch in a mechanical fusion machine according to the weight part of 1:0.25, and processing for 20min at the rotating speed of 1000rpm, wherein the softening point of the pitch is 120 ℃;
step 3, placing the spherical graphite precursor prepared in the step 2 in a graphitization furnace, heating to 2550 ℃, and treating for 48 hours to obtain spherical graphite;
step 4, mixing the spherical graphite, the polar additive p-hydroxybenzoic acid and the deionized water in a temperature-controllable container according to the ratio of 1:0.2:20, and uniformly stirring to obtain a first material;
step 5, uniformly mixing melamine serving as a nitrogen source, citric acid serving as a carbon source and butanediol serving as a solvent in a weight ratio of 1:2:8 in an ultrasonic machine to prepare a mixed solution;
step 6, adding the material I prepared in the step 4 into the mixed solution in the step 5, and continuously performing ultrasonic stirring to obtain uniform slurry;
step 7, filtering the uniform slurry obtained in the step 6, drying the slurry at 80 ℃ for 48 hours, and then moving the slurry to an inert atmosphere to carry out carbonization treatment at 1000 ℃ for 5 hours;
and 8, performing ball milling dispersion on the material prepared in the step 7, and sieving with a 500-mesh sieve to obtain the nitrogen-doped carbon-coated large-interlayer-distance graphite, namely the composite graphite.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 3
The difference from example 1 is that: the preparation method of the composite graphite comprises the following steps:
step 1, carrying out coarse crushing and fine grinding on needle coke, and then carrying out ball milling and shaping treatment by using a ball mill to obtain a graphite precursor, wherein D50 is 6.5 mu m;
step 2, adding the graphite precursor and the binder pitch in a mechanical fusion machine according to the weight part of 1:0.25, and processing for 20min at the rotating speed of 1000rpm, wherein the softening point of the pitch is 120 ℃;
step 3, placing the spherical graphite precursor prepared in the step 2 in a graphitization furnace, heating to 2550 ℃, and treating for 48 hours to obtain spherical graphite;
step 4, mixing the spherical graphite, the polar additive p-hydroxybenzoic acid and the deionized water in a temperature-controllable container according to the ratio of 1:0.2:20, and uniformly stirring to obtain a first material;
step 5, a low-frequency electromagnetic field with the frequency of 8Hz is accessed to the first material, so that water molecules and polar additives freely enter the graphite layer;
step 6, rapidly cooling the container to-100 ℃ at the speed of 30 ℃/s, maintaining for 5 hours, and increasing the spacing between graphite layers by the volume change of water solidified into ice during the period;
and 7, raising the temperature of the container to 150 ℃ at a rate of 18 ℃/s, vaporizing the deionized water, and cooling to obtain the composite graphite.
The rest is the same as embodiment 1, and the description is omitted here.
And (3) performance testing: the composite graphite, the negative electrode sheet and the secondary battery prepared in the above examples 1 to 16 and comparative examples 1 to 3 were subjected to performance tests, and the test results are recorded in table 1.
TABLE 1
Figure BDA0003614230750000141
As can be seen from table 1, the composite graphite, the negative electrode material, and the secondary battery prepared in examples 1 to 16 of the present invention have better capacity retention rate and rate capability than those of comparative examples 1 to 3, and can realize rapid charge and discharge. The graphite material with smaller particle size is obtained by ball milling the carbon material, the graphite material is rapidly frozen in an electromagnetic field, the polar additive can be embedded into the interlayer spacing of the graphite material together with the solvent, the volume of the polar additive and the solvent is increased by cooling and solidification, the interlayer spacing of the graphite material is increased, the polar additive and the solvent are vaporized and removed by heating, and the obtained graphite material is beneficial to rapid embedding and separation of lithium ions, and then nitrogen doping and carbon coating are carried out, so that the capacity is improved, the electronegativity is stronger than that of a carbon-carbon bond, the composite graphite has stronger attraction to the lithium ions and is beneficial to the magnification improvement, and the composite graphite with both the capacity and the magnification performance is obtained. As shown in fig. 2, when the composite graphite prepared in example 1 is applied to a secondary battery and subjected to a 7C rate performance test, the capacity retention rate is still maintained at 85% or more after 1000 charge and discharge cycles, and the composite graphite has good performance.
The comparison of the embodiments 1 to 7 shows that when the weight ratio of the carbon material to the binder is set to be 1:0.25, the stirring and mixing speed is 1000rpm/min, and the stirring and mixing time is 20min, the prepared secondary battery has better performance, and the binder can be uniformly mixed with the carbon material and coated on the surface of the carbon material, so that a fully coated material is obtained during subsequent granulation, and the material has smaller particle size and better performance.
As shown by comparison of examples 1 and 8-12, when the frequency of the electromagnetic field in step S2 is set to be 8Hz, the solidification temperature is-100 ℃, the cooling rate is 30 ℃/S, the vaporization temperature is 150 ℃, and the heating rate is 18 ℃/S, the prepared secondary battery has better performance, the frequency with proper size can enable the polar additive and the solvent to be rapidly embedded into the interlayer spacing of the graphite material, the entering depth is increased, the interlayer spacing is increased, the solidification volume of the polar additive and the solvent in the interlayer spacing of the graphite material is increased only by the rapid cooling rate, the interlayer spacing of the graphite material is increased, and the structural stability of the graphite material is not damaged.
As shown by comparison of examples 1 and 13-16, when the weight part ratio of the nitrogen source, the carbon source, and the second solvent in step S3 is set to be 1:1.2:7, the prepared secondary battery has better capacity retention rate and rate capability, because nitrogen doping can improve the attraction to lithium ions, thereby improving the rate capability, and carbon coating can improve the energy density, and the two are combined to improve the capacity retention rate and the rate capability.
Compared with the comparative example 1, the method has the advantages that when the carbon material is subjected to ball milling to reduce the particle size, the ion transmission distance can be reduced, the rate capability is improved, and the capacity retention rate is suitable to be improved.
As is apparent from comparison between example 1 and comparative example 2, the rate capability of the graphite material can be improved by performing cooling solidification and heating vaporization treatment on the graphite material, the polar additive and the solvent, because the volume of the solvent embedded between the graphite material layers is increased by the cooling solidification, the interlayer spacing is enlarged, and the polar additive and the solvent are removed after heating vaporization, thereby obtaining the graphite material with the enlarged interlayer spacing, and further improving the rate capability of the graphite material.
The comparison between the embodiment 1 and the comparative example 3 shows that the rate capability and the capacity retention rate can be improved by carrying out nitrogen doping and carbon coating on the graphite material, because the graphite material after nitrogen doping has stronger attraction to lithium ions, the desorption of the lithium ions is facilitated, the rate capability is improved, the material structure is more stable after carbon coating, a certain capacity is provided, the capacity retention rate is improved, and the capacity retention rate and the rate capability are both synergistically improved by matching the nitrogen doping and the carbon coating.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious modifications, substitutions or alterations based on the present invention will fall within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (11)

1. The preparation method of the composite graphite is characterized by comprising the following steps:
step S1, mixing the graphite material, the polar additive and the first solvent to obtain a first material;
s2, placing the first material in an electromagnetic field, cooling, solidifying, heating, vaporizing and cooling to obtain a second material;
step S3, mixing a nitrogen source, a carbon source and a second solvent to obtain a mixed solution;
and step S4, adding the second material into the mixed solution, ultrasonically stirring, filtering, drying, heating and carbonizing in an inert atmosphere, and performing ball milling and filtering to obtain the composite graphite.
2. The method for preparing composite graphite according to claim 1, wherein the method for preparing the graphite material comprises: crushing the carbon material, ball milling, adding the binder, stirring and mixing, mechanically fusing, and heating and graphitizing to obtain the graphite material.
3. The method for preparing composite graphite according to claim 2, wherein the particle size D50 after ball milling in the step S1 is 3 to 7 μm.
4. The method for preparing composite graphite according to claim 3, wherein the weight portion ratio of the carbon material to the binder is 1-3: 0.1-0.5, the stirring and mixing speed is 500-1500rpm/min, and the stirring and mixing time is 10-30 min.
5. The method for preparing composite graphite according to claim 4, wherein the graphitization temperature is 2400-3000 ℃ and graphitization time is 20-60 h.
6. The method for preparing composite graphite according to claim 1, wherein the frequency of the electromagnetic field in step S2 is 5 to 15Hz, the solidification temperature is-150 to-10 ℃, the cooling rate is 15 to 60 ℃/S, the vaporization temperature is 150 to 200 ℃, and the heating rate is 15 to 60 ℃/S.
7. The method for preparing composite graphite according to claim 1, wherein the weight ratio of the nitrogen source, the carbon source and the second solvent in step S3 is 1-3: 0.2-3: 5-12.
8. The method for preparing composite graphite according to claim 1, wherein in step S4, the drying temperature is 40-150 ℃, the drying time is 10-50 h, the carbonization temperature is 400-1500 ℃, and the carbonization time is 1-10 h.
9. Composite graphite produced by the method for producing composite graphite according to any one of claims 1 to 8.
10. A negative electrode sheet, comprising the composite graphite according to claim 9.
11. A secondary battery comprising the negative electrode sheet according to claim 10.
CN202210438880.5A 2022-04-25 2022-04-25 Composite graphite, preparation method thereof, negative plate and secondary battery Pending CN114824213A (en)

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