WO2018153122A1 - 改性石墨负极材料及其制备方法及二次电池 - Google Patents

改性石墨负极材料及其制备方法及二次电池 Download PDF

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WO2018153122A1
WO2018153122A1 PCT/CN2017/108907 CN2017108907W WO2018153122A1 WO 2018153122 A1 WO2018153122 A1 WO 2018153122A1 CN 2017108907 W CN2017108907 W CN 2017108907W WO 2018153122 A1 WO2018153122 A1 WO 2018153122A1
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negative electrode
modified graphite
conductive agent
multilayer graphene
anode material
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English (en)
French (fr)
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崔航
陈泰强
谢远森
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology 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
    • H01M4/58—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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to the field of secondary batteries, and in particular to a modified graphite anode material, a preparation method thereof and a secondary battery.
  • the anode material becomes a key factor in the development of high energy density secondary batteries.
  • the volume of the negative electrode accounts for 40% to 50% of the volume of the entire secondary battery, especially at a high energy density
  • the increase in the compaction density of the negative electrode is an effective way to increase the energy density of the secondary battery.
  • the increase of the compaction density of the negative electrode is beneficial to increase the energy density of the secondary battery, but inevitably causes problems such as difficulty in electrolyte infiltration, increase in polarization, deterioration of interface, etc., thereby causing dynamic performance and circulation of the secondary battery.
  • the performance deteriorates.
  • the negative electrode is easy to be decomposed by lithium under high pressure and the capacity is attenuated rapidly after circulating at room temperature.
  • an object of the present invention is to provide a modified graphite anode material, a preparation method thereof and a secondary battery, which can achieve a higher compaction density of the anode.
  • a secondary battery When applied to a secondary battery, it is possible to effectively improve the lithium deposition of the negative electrode of the secondary battery while improving the cycle performance of the secondary battery.
  • the present invention provides a modified graphite anode material comprising graphite and a multilayer graphene.
  • the multilayer graphene is dispersed in the stone In the ink.
  • the multilayer graphene is loaded with a conductive agent by adhesion of a binder.
  • the invention provides a method for preparing a modified graphite anode material, which is used for preparing the modified graphite anode material according to the first aspect of the invention, comprising the steps of: under a protective gas atmosphere, The reactor of the mechanical fusion machine is filled with a plurality of layers of graphene, a conductive agent and a binder, and the rotation speed is set and raised, so that the multilayer graphene is loaded with a conductive agent through the bonding of the binder; the conductive agent is loaded The multi-layer graphite and the graphite are added to the mixing machine for mixing, and after the mixing is completed, the sieving and demagnetization are performed to obtain the modified graphite anode material.
  • the invention provides a secondary battery comprising the modified graphite anode material according to the first aspect of the invention.
  • the modified graphite negative electrode material of the present invention can achieve a higher compaction density of the negative electrode, and can effectively improve the lithium deposition of the negative electrode of the secondary battery when it is applied to the secondary battery, and at the same time improve the cycle performance of the secondary battery.
  • Example 1 is a FESEM image of a multilayer Pene loaded with Super P prepared in Example 1;
  • Example 2 is an SEM image of the modified graphite anode material obtained in Example 1;
  • Fig. 5 is a view showing the lithium deposition of the negative electrode of Example 1.
  • modified graphite anode material according to the present invention a preparation method thereof, and a secondary battery are explained in detail below.
  • the modified graphite anode material according to the first aspect of the invention includes graphite and a plurality of graphenes dispersed in the graphite.
  • the multilayer graphene is loaded with a conductive agent by adhesion of a binder.
  • the multilayer graphene has a very good lubricating effect, but its conductivity and electrolyte wettability are general, while the surface and interior of the multilayer graphene are With more voids, it is easy to adsorb or bond other substances.
  • the conductive agent has a small particle size, a relatively large specific surface area, and excellent electrical conductivity and electrolyte wettability (infiltration time of about 10 s).
  • a bonding agent to bond a conductive agent to a multilayer graphene (such as a surface of a multilayer graphene and an internal interlayer position, etc.)
  • conductivity and electrolyte wettability of the multilayer graphene can be improved.
  • the surface energy of the multilayer graphene is reduced, so that the surface can form a large-area excellent lubricating film.
  • the excellent lubricating effect of the multilayer graphene can greatly reduce the frictional resistance between the graphite particles during cold pressing, thereby causing the graphite particles to be between It can be better slipped to achieve higher compaction density and avoid the problem of difficult processing of single-layer graphene.
  • the use of multi-layer graphene can achieve rapid deintercalation of lithium, and the excellent conductivity and electrolyte wettability of the conductive agent can significantly reduce the risk of lithium deposition of the negative electrode under high-pressure solid density, and better maintain the excellent graphite negative electrode material.
  • the multilayer graphene may have a true density of 1.8 g/cm 3 to 2.15 g/cm 3 , and the true density multilayer graphene has Very good lubrication effect, in the process of cold compaction, the frictional resistance between the graphite particles can be reduced, and the graphite particles can be optimally packed, thereby increasing the compaction density of the negative electrode.
  • the true density of the multilayer graphene is further increased or decreased, the good lubricity of the graphene disappears, and the processing property of the graphene deteriorates, resulting in a large fluctuation of the viscosity of the anode slurry, and coating or graphene cannot be performed. It is difficult to disperse in the negative electrode slurry, causing a large fluctuation in the capacity of the secondary battery, and it is difficult to achieve mass production.
  • the number of layers of the multilayer graphene may be 10 to 20, and the multilayer graphene having the number of layers has a good lubricating effect and is low.
  • Specific surface area (BET) usually BET ⁇ 40 m 2 /g.
  • the number of layers of graphene used in the prior art is usually less than 10.
  • the graphene has good conductivity and high capacity, the specific surface area is sharply increased, resulting in an increase in irreversible capacity loss of the secondary battery, and due to the huge The specific surface area, graphene self-agglomeration phenomenon is significantly increased, resulting in processing difficulties, resulting in a large fluctuation of the viscosity of the anode slurry, can not be coated or graphene is difficult to disperse in the anode slurry, resulting in capacity fluctuation of the secondary battery Larger, it is more difficult to achieve mass production.
  • the number of layers of the multilayer graphene may be 10-15.
  • the conductive agent may include one or more of a carbon black conductive agent and a graphite conductive agent.
  • the conductive agent may be selected from one of Super-P, Super S, acetylene black, 350G, carbon fiber, carbon nanotube, Ketjen black, KS-6, KS-15, SFG-6, SFG-15. kind or several.
  • the binder may be selected from the group consisting of One or more of cyan, phenolic resin, polyurethane, polystyrene resin, polyacrylate, ethylene-vinyl acetate copolymer.
  • the mass ratio of the graphite to the multilayer graphene may be (99.9% to 85%): (0.1% to 15%). If the content of the multilayer graphene is too high, the first efficiency of the secondary battery is low, the capacity is low, and the energy density of the secondary battery is affected, and in addition, the excessive content of the multilayer graphene may cause The dispersibility of the negative electrode slurry is deteriorated, which in turn affects the compaction density of the negative electrode, which causes the negative electrode to be easily decomposed and affects the performance of the secondary battery. If the content of the multilayer graphene is too low, the conductivity and lubricity are relatively Poor, so that the improvement of the compaction density of the negative electrode is not obvious.
  • the mass ratio of the conductive agent, the binder to the multilayer graphene may be (10% to 40%): (5%) ⁇ 40%): (20% to 80%). If the content of the conductive agent is too high, it is difficult to uniformly disperse on the surface of the multilayer graphene, and the excellent lubricity of the multilayer graphene cannot be effectively exerted, thereby affecting the processing of the negative electrode sheet, resulting in the compaction density of the negative electrode.
  • the content of the conductive agent is too low, the active point of the surface of the multilayer graphene is not uniformly covered by the conductive agent, and the conductivity and electrolyte infiltration of the multilayer graphene cannot be effectively improved. In the circulation, a large amount of side reactions are generated, and a large amount of electrolyte is consumed, eventually causing deterioration of the cycle performance of the secondary battery.
  • the graphite may be selected from artificial graphite and/or natural graphite.
  • the multilayer graphene may have a median diameter D50 of from 6 ⁇ m to 24 ⁇ m.
  • the multilayer graphene having a larger median diameter D50 has a low synthesis yield, so increasing the median diameter D50 of the multilayer graphene leads to an increase in processing cost; if the median value of the multilayer graphene When the particle diameter D50 is low, it is difficult to form a continuous conductive network, thereby affecting the conductive effect.
  • the median diameter D50 of the multilayer graphene is too low or too high, which affects the distribution of the multilayer graphene in the graphite particles, affects the compaction density of the negative electrode, and affects the dispersibility of the negative electrode slurry.
  • the method for preparing a modified graphite anode material according to the second aspect of the present invention which is used for preparing the modified graphite anode material according to the first aspect of the present invention, comprising the steps of: (1) moving to a mechanical fusion machine under a protective gas atmosphere; The reactor is filled with a plurality of layers of graphene, a conductive agent and a binder, and the rotation speed is set and raised, so that the multilayer graphene is loaded with a conductive agent through the bonding of the binder; (2) the conductive agent is loaded.
  • the multi-layered graphite and graphite are added to the mixing machine for mixing, and after the mixing is completed, the sieving and demagnetization are performed to obtain the modified graphite anode material.
  • the multilayer graphene used in the step (1) is prepared by adding flake graphene to a mechanical fusion machine and setting the rotation speed for shaping. And granulation to obtain a granulated multilayer graphene, wherein the mechanical fusion machine can rotate at a speed of from 300 r/min to 1200 r/min.
  • the conductive agent is loaded onto the multilayer graphene by mechanical fusion
  • the principle is that each material is in the rotor.
  • High-speed rotation under the action of centrifugal force, close to the wall, passing between the rotor and the stator extrusion head at high speed.
  • the material is subjected to both the pressing force and the shearing force. Due to the high-speed rotation, the material is in the rotor.
  • the cycle is reciprocated with the stator, and is continuously subjected to a pressing force and a shearing force to load the conductive agent onto the multilayer graphene.
  • the rotation speed in the step (1) may be from 300 r/min to 1200 r/min, and the temperature rise temperature is not limited so that the selected binder is selected. Soften it.
  • the rotation speed in the step (2) may be from 100 r/min to 1200 r/min.
  • a secondary battery according to the third aspect of the invention will be described again.
  • a secondary battery according to a third aspect of the invention includes the modified graphite anode material according to the first aspect of the invention.
  • the secondary battery includes: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.
  • the separator is spaced between the positive electrode tab and the negative electrode tab.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on the positive electrode current collector, and the positive electrode film includes a positive electrode active material, a binder, and a conductive agent.
  • the negative electrode sheet includes a negative electrode current collector and an negative electrode film disposed on the negative electrode current collector, the negative electrode film including a negative electrode active material, a binder, and a conductive agent, wherein the negative electrode active material may include A modified graphite anode material according to the first aspect of the invention.
  • the separator may be any separator material used in the existing secondary battery, such as polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof. Composite membranes, but are not limited to these.
  • the secondary battery may be a lithium ion secondary battery, a sodium ion secondary battery, or a zinc ion secondary battery.
  • the electrolyte salt may be selected from a lithium salt, and the lithium salt may be selected from the group consisting of LiPF 6 , LiBF 4 , LiFSI, LiTFSI, LiClO 4 , LiAsF 6 , LiBOB, LiDFOB, LiPO.
  • LiPF 6 LiBF 4 , LiFSI, LiTFSI, LiClO 4 , LiAsF 6 , LiBOB, LiDFOB, LiPO.
  • LiPF 6 LiBF 4 , LiFSI, LiTFSI, LiClO 4 , LiAsF 6 , LiBOB, LiDFOB, LiPO.
  • LiTFOP LiN(SO 2 RF) 2
  • LiN(SO 2 F)(SO 2 RF)(SO 2 RF) LiN(SO 2 F)(SO 2 RF)
  • n is an integer within 1 to 10.
  • the lithium salt is LiPF 6 .
  • the positive electrode active material may be selected from lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), spinel-type LiMn 2 O 4 , olivine-type LiMPO 4 , one of ternary positive electrode materials LiNi x A y B (1-xy) O 2 and Li 1-x' (A' y' B' z' C 1-y'-z' ) O 2 or Several.
  • M is selected from one or more of Co, Ni, Fe, Mn, and V; and in the ternary positive electrode material LiNi x A y B (1-xy) O 2 , A and B are each independently selected from one of Co, Al, and Mn, and A and B are not the same, 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and x+y ⁇ 1; in the ternary positive electrode material Li 1 -x' (A' y' B' z' C 1-y'-z' ) In O 2 , A', B', and C are each independently selected from one of Co, Ni, Fe, and Mn, 0 ⁇ x' ⁇ 1, 0 ⁇ y' ⁇ 1, 0 ⁇ z' ⁇ 1 and y'+z' ⁇ 1, and A', B', and C are different.
  • the anode active material may be only the modified graphite anode material according to the first aspect of the invention.
  • the anode active material may further include a material in which lithium may be intercalated at ⁇ 2 V (vs. Li/Li + ), and specifically, the anode active material may further include mesophase micro-carbon spheres (abbreviated as MCMB), hard.
  • MCMB mesophase micro-carbon spheres
  • the secondary battery is a sodium ion secondary battery or a zinc ion secondary battery, it is only necessary to change the corresponding positive electrode active material, negative electrode active material, and electrolyte salt.
  • a flaky graphene having a layer of 10 layers and a true density of 2.1 g/cm 3 was placed in a mechanical fusion machine, and the rotation speed was 600 r/min and the rotation time was 1.5 h, and the sheet-like graphene was shaped and granulated.
  • a multilayer graphite having a morphology rule and a median diameter D50 of 14 ⁇ m was obtained.
  • the conductive carbon black Super P, the binder pitch and the above multilayer graphene were added into the vertical reaction kettle of the mechanical fusion machine at a mass ratio of 15:10:75, and the temperature rise temperature was set to 200 ° C to 280.
  • the surface modification of the multilayer graphene was carried out, and after completion of the reaction, a multilayer graphene loaded with Super P was obtained (see FIG. 1 for the morphology).
  • the graphite and the multi-layer graphene loaded with Super P are added to the V-type mixer at a mass ratio of 99.5:0.5 for mixing, and the rotation speed is set to 400 r/min. After the mixture is completed, the sieve is demagnetized and the modification is obtained. Graphite anode material.
  • the modified graphite anode material prepared above, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethylcellulose (CMC) are dissolved in deionized water at a mass ratio of 97.5:1.5:1.
  • the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and then dried at 85 ° C, followed by cold pressing, and the cold pressing pressure is 2000 T (ton), followed by trimming and cutting. And slitting, welding the tabs to obtain a negative electrode sheet, wherein the coating weight of the negative electrode slurry was 167 mg / 1540.25 mm 2 .
  • the positive electrode active material lithium cobaltate, the conductive agent Super P, the binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone at a mass ratio of 96:2:2, and uniformly mixed to form a positive electrode slurry, and then the positive electrode is prepared.
  • the slurry is uniformly coated on the positive electrode current collector aluminum foil, and then dried at 85 ° C, then cold pressed, trimmed, cut, stripped, and welded to the ear to obtain a positive electrode sheet, wherein the coating weight of the positive electrode slurry is 340 mg / 1540.25 mm 2 , and the compacted density of the positive electrode sheet was 4.1 g/cm 3 .
  • the positive electrode sheet, the negative electrode sheet, and the separator are formed into a battery core by a winding process, and then encapsulated with an aluminum plastic film, injected with an electrolyte, and then subjected to processes such as formation, capacity, and shaping.
  • the preparation of the lithium ion secondary battery is completed.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the number of layers of the flake graphene was 15 layers, and the true density was 2.09 g/cm 3 .
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the number of layers of the flake graphene was 20 layers, and the true density was 2.15 g/cm 3 .
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of graphite to multi-layer graphene loaded with Super P was 90:10.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of graphite to multi-layer graphene loaded with Super P was 85:15.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of Super P, asphalt and multilayer graphene is 10:5:85.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of Super P, asphalt and multilayer graphene is 40:40:20.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the multilayer graphene had a median diameter D50 of 6 ⁇ m.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the multilayer graphene had a median diameter D50 of 24 ⁇ m.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the conductive agent is selected from the group consisting of Ketchen Black.
  • the binder is selected from the group consisting of polystyrene resins, and the temperature rise temperature is controlled at 240 ° C to 250 ° C.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the number of layers of the flake graphene was 20 layers, and the true density was 1.8 g/cm 3 .
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of graphite to multi-layer graphene loaded with Super P was 80:20.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of Super P, asphalt and multilayer graphene is 5:5:90.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of Super P, asphalt and multilayer graphene is 45:45:10.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the multilayer graphene had a median diameter D50 of 3 ⁇ m.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the multilayer graphene had a median diameter D50 of 30 ⁇ m.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the mass ratio of graphite to multilayer graphene loaded with Super P was 99.9:0.1.
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the negative electrode material is selected from conventional artificial graphite without the addition of graphene.
  • the preparation process of the negative electrode sheet is as follows: artificial graphite, conductive agent Super P, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) are dissolved at a mass ratio of 96.5:1:1.5:1.
  • the anode slurry was uniformly mixed in deionized water, and then the anode slurry was uniformly coated on the anode current collector copper foil, and then dried at 85 ° C, followed by cold pressing, and the cold pressing pressure was 2000 T, followed by cutting. Edge, cut piece, slit, and solder tab, and a negative electrode sheet was obtained, in which the coating weight of the negative electrode slurry was 167 mg / 1540.25 mm 2 .
  • the preparation method of the lithium ion secondary battery is the same as that of the embodiment 1, except that
  • the modified graphite anode material is obtained by simply mixing graphite with graphene.
  • the lithium ion secondary battery was charged to 4.35 V at a constant current of 1.3 C at 25 ° C, then charged at a constant voltage to a current of 0.05 C, and then discharged to 3.0 V with a constant current of 1 C, which was a cycle charge and discharge process. After charging and discharging were repeated 10 times in this manner, the lithium ion secondary battery was disassembled, and the lithium deposition of the negative electrode was observed. Among them, the degree of lithium is divided into no lithium, slight lithium, moderate lithium and severe lithium. The slight lithium deposition indicates that the lithium deposition region on the surface of the negative electrode is 1/10 or less of the entire region, and the severe lithium deposition indicates that the lithium deposition region on the surface of the negative electrode exceeds 1/3 of the entire region.
  • the lithium ion secondary battery was charged to 4.35 V at a constant current of 1 C at 25 ° C, then charged to a current of 0.05 C at a constant voltage, and then discharged to 3.0 V with a constant current of 1 C, which was a cycle charge and discharge process.
  • the charging and discharging were repeated as described above, and the capacity retention ratio after the lithium ion secondary battery was cycled 350 times was calculated.
  • the negative electrode sheet of Comparative Example 1 showed severe lithium deposition, and the negative electrode of Example 1 did not exhibit lithium deposition.
  • FIG. 1 is a FESEM image of a Super P-loaded multilayer graphene prepared in Example 1;
  • FIG. 2 is an SEM image of the modified graphite negative electrode material obtained in Example 1;
  • FIG. 3 is a modified graphite obtained in Comparative Example 2.
  • SEM image of the negative electrode material It can be seen from Fig. 3 that graphene has agglomeration in the graphite particles, and the distribution is uneven, which leads to poor electrolyte wettability of the negative electrode sheet, low compaction density of the negative electrode, and easy lithium deposition, and lithium ion secondary battery. The cycle performance is also poor.
  • Fig. 3 shows that graphene has agglomeration in the graphite particles, and the distribution is uneven, which leads to poor electrolyte wettability of the negative electrode sheet, low compaction density of the negative electrode, and easy lithium deposition, and lithium ion secondary battery. The cycle performance is also poor.
  • Fig. 3 shows that graphene has agglomeration in the
  • the multilayer graphene loaded with the conductive agent can be relatively uniformly dispersed in the graphite particles, and a conductive network structure is formed. It can also be seen from Fig. 1 that the conductive agent is also uniformly dispersed on the multilayer graphite thinner, which improves the processing property of the multilayer graphite thinning and is advantageous for improving conductivity and electrolyte wettability.
  • Example 12-16 under the premise of not significantly reducing the compaction density of the negative electrode of the lithium ion secondary battery, the lithium deposition of the negative electrode, and the cycle performance, the compaction density of the negative electrode of the lithium ion secondary battery, the lithium deposition of the negative electrode, and the cycle performance are still There is an improvement.

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Abstract

一种改性石墨负极材料及其制备方法及二次电池。所述改性石墨负极材料包括石墨以及多层石墨烯。所述多层石墨烯分散在所述石墨中。所述多层石墨烯通过粘结剂的粘结作用负载有导电剂。所述改性石墨负极材料能够使负极实现更高的压实密度，当其应用到二次电池中后能够有效的改善二次电池的负极析锂情况，同时改善二次电池的循环性能。

Description

改性石墨负极材料及其制备方法及二次电池 技术领域
本发明涉及二次电池领域，尤其涉及一种改性石墨负极材料及其制备方法及二次电池。
背景技术
随着对二次电池能量密度的要求越来越高，负极材料成为高能量密度二次电池开发的关键因素。由于负极体积占整个二次电池体积的40％～50％，尤其在高能量密度下其所占比例更高，因此提高负极压实密度是提高二次电池能量密度的有效方式。负极压实密度的增加有利于提升二次电池的能量密度，但是不可避免的会带来电解液浸润困难、极化增大、界面变差等问题，从而导致二次电池的动力学性能及循环性能恶化，比如，高压实密度下负极易析锂及室温下循环后容量衰减较快。
石墨负极材料的综合性能比较好，尤其是循环性能比较好，但是提高石墨的压实密度则比较困难，因为石墨的辊压压力已经达到极限；且在高压实密度下，负极与电解液的界面比较差，导致负极析锂风险加大。单层石墨烯的导电性非常好，但是加工性能很差。现有技术中将石墨烯与石墨简单混合，由于石墨烯本身的特点其很难与石墨混合均匀，会造成二次电池的一致性太差，从而无法量产使用。
发明内容
鉴于背景技术中存在的问题，本发明的目的在于提供一种改性石墨负极材料及其制备方法及二次电池，所述改性石墨负极材料能够使负极实现更高的压实密度，当其应用到二次电池中后能够有效的改善二次电池的负极析锂情况，同时改善二次电池的循环性能。
为了达到上述目的，在本发明的第一方面，本发明提供了一种改性石墨负极材料，其包括石墨以及多层石墨烯。所述多层石墨烯分散在所述石 墨中。所述多层石墨烯通过粘结剂的粘结作用负载有导电剂。
在本发明的第二方面，本发明提供了一种改性石墨负极材料的制备方法，用于制备本发明第一方面所述的改性石墨负极材料，包括步骤：在保护气体气氛下，向机械融合机的反应釜中加入多层石墨烯、导电剂以及粘结剂，设置转速并升温，以使多层石墨烯通过粘结剂的粘结作用负载有导电剂；将负载有导电剂的多层石墨稀以及石墨加入混料机中进行混料，混料完成后过筛、去磁，即得到改性石墨负极材料。
在本发明的第三方面，本发明提供了一种二次电池，其包括根据本发明第一方面所述的改性石墨负极材料。
相对于现有技术，本发明的有益效果为：
本发明的改性石墨负极材料能够使负极实现更高的压实密度，当其应用到二次电池中后能够有效的改善二次电池的负极析锂情况，同时改善二次电池的循环性能。
附图说明
图1是实施例1制备得到的负载有Super P的多层石墨烯的FESEM图；
图2是实施例1得到的改性石墨负极材料的SEM图；
图3是对比例2得到的改性石墨负极材料的SEM图；
图4是对比例1的负极析锂情况；
图5是实施例1的负极析锂情况。
具体实施方式
下面详细说明根据本发明的改性石墨负极材料及其制备方法及二次电池。
首先说明根据本发明第一方面的改性石墨负极材料。
根据本发明第一方面的改性石墨负极材料包括石墨以及多层石墨烯，所述多层石墨烯分散在所述石墨中。所述多层石墨烯通过粘结剂的粘结作用负载有导电剂。
在根据本发明第一方面所述的改性石墨负极材料中，多层石墨烯具有非常好的润滑效果，但其导电性和电解液浸润性一般，同时多层石墨烯表面和内部 具有较多的空隙，很容易吸附或粘结其它物质。导电剂粒径小，比表面积比较大，具有优异的导电性和电解液浸润性(浸润时间在10s左右)。因此通过利用粘结剂的粘结作用将导电剂负载到多层石墨烯上(比如多层石墨烯的表面和内部层间位置等)，可以提升多层石墨烯的导电性和电解液浸润性，同时降低多层石墨烯的表面能，使其表面能够形成大面积成片的优良润滑膜。当将负载有导电剂的多层石墨烯与石墨混合得到改性石墨负极材料后，多层石墨烯优异的润滑效果可以大大降低冷压时石墨颗粒之间的摩擦阻力，从而使石墨颗粒之间可以更好的滑移以达到更高的压实密度，避免单层石墨烯加工困难的问题。同时利用多层石墨烯可以实现快速脱嵌锂，且利用导电剂优异的导电性和电解液浸润性，显著降低了高压实密度下负极的析锂风险，更好的保持了石墨负极材料优异的综合性能，尤其是循环性能。
在根据本发明第一方面所述的改性石墨负极材料中，所述多层石墨烯的真密度可为1.8g/cm3～2.15g/cm3，此种真密度的多层石墨烯具有非常好的润滑效果，在冷压压实过程中，可以减小石墨颗粒之间的摩擦阻力，使石墨颗粒达到最佳堆积状态，从而可提升负极的压实密度。若进一步增大或减小多层石墨烯的真密度，则石墨烯良好的润滑性消失，且石墨烯的加工性能变差，导致负极浆料的粘度波动较大，无法进行涂布或石墨烯在负极浆料中很难分散开，造成二次电池的容量波动较大，较难实现量产。
在根据本发明第一方面所述的改性石墨负极材料中，所述多层石墨烯的层数可为10～20，具有此层数的多层石墨烯具有较好的润滑效果和较低的比表面积(BET)(通常BET<40m2/g)。现有技术中使用的石墨烯的层数通常小于10，这种石墨烯虽然导电性很好、容量很高，但是比表面积会急剧增加，造成二次电池不可逆容量损失加大，而且由于巨大的比表面积，石墨烯自身团聚现象明显增加，从而造成加工困难，导致负极浆料的粘度波动较大，无法进行涂布或石墨烯在负极浆料中很难分散开，造成二次电池的容量波动较大，较难实现量产。优选地，所述多层石墨烯的层数可为10～15。
在根据本发明第一方面所述的改性石墨负极材料中，所述导电剂可包括碳黑导电剂、石墨导电剂中的一种或几种。优选地，所述导电剂可选自Super-P、Super S、乙炔黑、350G、碳纤维、碳纳米管、科琴黑、KS-6、KS-15、SFG-6、SFG-15中的一种或几种。
在根据本发明第一方面所述的改性石墨负极材料中，所述粘结剂可选自沥 青、酚醛树脂、聚氨酯、聚苯乙烯树脂、聚丙烯酸酯、乙烯-醋酸乙烯共聚物中的一种或几种。
在根据本发明第一方面所述的改性石墨负极材料中，所述石墨与所述多层石墨烯的质量比可为(99.9％～85％):(0.1％～15％)。若所述多层石墨烯的含量过高，则会造成二次电池的首次效率偏低，容量偏低，进而影响二次电池的能量密度，此外，多层石墨烯的含量过高还会导致负极浆料的分散性变差，反而影响负极的压实密度，导致负极容易析锂，影响二次电池的性能；若所述多层石墨烯的含量过低，则其导电性及润滑性相对较差，从而对负极的压实密度的改善不明显。
在根据本发明第一方面所述的改性石墨负极材料中，所述导电剂、所述粘结剂与所述多层石墨烯的质量比可为(10％～40％):(5％～40％):(20％～80％)。若所述导电剂的含量过高，则其较难均匀分散在所述多层石墨烯的表面，无法有效发挥多层石墨烯优良的润滑性，从而影响负极片的加工，导致负极压实密度偏低；若所述导电剂的含量过低，则所述多层石墨烯表面的活性点未能被所述导电剂均匀覆盖，无法有效改善多层石墨烯的导电性和电解液浸润性，在循环中会产生较多的副反应，消耗较多的电解液，最终导致二次电池的循环性能恶化。
在根据本发明第一方面所述的改性石墨负极材料中，所述石墨可选自人造石墨和/或天然石墨。
在根据本发明第一方面所述的改性石墨负极材料中，所述多层石墨烯的中值粒径D50可为6μm～24μm。中值粒径D50较大的多层石墨烯的合成优率低，因此增大所述多层石墨烯的中值粒径D50会导致加工成本升高；若所述多层石墨烯的中值粒径D50偏低，则较难形成连续的导电网络，从而影响导电效果。此外，多层石墨烯的中值粒径D50过低或过高，均会影响多层石墨烯在石墨颗粒中的分布，影响负极的压实密度，影响负极浆料的分散性。
其次说明根据本发明第二方面的改性石墨负极材料的制备方法。
根据本发明第二方面的改性石墨负极材料的制备方法，用于制备本发明第一方面所述的改性石墨负极材料，包括步骤：(1)在保护气体气氛下，向机械融合机的反应釜中加入多层石墨烯、导电剂以及粘结剂，设置转速并升温，以使多层石墨烯通过粘结剂的粘结作用负载有导电剂；(2)将负载有导电剂 的多层石墨稀以及石墨加入混料机中进行混料，混料完成后过筛、去磁，即得到改性石墨负极材料。
在根据本发明第二方面的改性石墨负极材料的制备方法中，步骤(1)中使用的多层石墨烯的制备过程为：将片状石墨烯加入到机械融合机中，设置转速进行整形和造粒，得到颗粒状的多层石墨烯，其中，机械融合机的转速可为300r/min～1200r/min。
在根据本发明第二方面的改性石墨负极材料的制备方法中，在步骤(1)中，采用机械融合的方式，将导电剂负载到多层石墨烯上，其原理是各物料在转子中高速旋转，在离心力的作用下紧贴器壁，在转子和定子挤压头之间高速穿过，在这个瞬间，物料同时受到挤压力和剪切力的作用，由于高速旋转，物料在转子和定子之间循环往复，不断地受到挤压力和剪切力的作用，从而将导电剂负载到多层石墨烯上。
在根据本发明第二方面所述的改性石墨负极材料的制备方法中，步骤(1)中的转速可为300r/min～1200r/min，升温温度不受限制，以使得所选粘结剂软化即可。
在根据本发明第二方面所述的改性石墨负极材料的制备方法中，步骤(2)中的转速可为100r/min～1200r/min。
再次说明根据本发明第三方面的二次电池。
根据本发明第三方面的二次电池包括根据本发明第一方面所述的改性石墨负极材料。
在根据本发明第三方面所述的二次电池中，所述二次电池包括：正极片、负极片、隔离膜以及电解液。所述隔离膜间隔于正极片和负极片之间。所述正极片包括正极集流体和设置于所述正极集流体上的正极膜片，所述正极膜片包括正极活性材料、粘结剂和导电剂。所述负极片包括负极集流体和设置于所述负极集流体上的负极膜片，所述负极膜片包括负极活性材料、粘结剂，也可以包括导电剂，其中所述负极活性材料可包括根据本发明第一方面所述的改性石墨负极材料。
在根据本发明第三方面所述的二次电池中，所述隔离膜可以是现有二次电池中使用的任何隔离膜材料，例如聚乙烯、聚丙烯、聚偏氟乙烯以及它们的多层复合膜，但不仅限于这些。
在根据本发明第三方面所述的二次电池中，所述二次电池可为锂离子二次电池、钠离子二次电池或锌离子二次电池。
当二次电池为锂离子二次电池时，所述电解质盐可选自锂盐，所述锂盐可选自LiPF6、LiBF4、LiFSI、LiTFSI、LiClO4、LiAsF6、LiBOB、LiDFOB、LiPO2F2、LiTFOP、LiN(SO2RF)2、LiN(SO2F)(SO2RF)中的一种或几种，其中，RF＝CnF2n+1，表示饱和全氟烷基，n为1～10内的整数。优选地，所述锂盐为LiPF6。
当二次电池为锂离子二次电池时，所述正极活性材料可选自钴酸锂(LiCoO2)、镍酸锂(LiNiO2)、尖晶石型的LiMn2O4、橄榄石型的LiMPO4、三元正极材料LiNixAyB(1-x-y)O2以及Li1-x’(A’y’B’z’C1-y’-z’)O2中的一种或几种。其中，在橄榄石型的LiMPO4中，M选自Co、Ni、Fe、Mn、V中的一种或几种；在三元正极材料LiNixAyB(1-x-y)O2中，A、B各自独立地选自Co、Al、Mn中的一种，且A和B不相同，0<x<1，0<y<1且x+y<1；在三元正极材料Li1-x’(A’y’B’z’C1-y’-z’)O2中，A’、B’、C各自独立地选自Co、Ni、Fe、Mn中的一种，0<x’<1，0≤y’<1，0≤z’<1且y’+z’<1，且A’、B’、C不相同。
当二次电池为锂离子二次电池时，所述负极活性材料可仅为根据本发明第一方面所述的改性石墨负极材料。但是所述负极活性材料还可包括在＜2V(vs.Li/Li+)时可以嵌入锂的材料，具体地，所述负极活性材料还可包括中间相微碳球(简称为MCMB)、硬碳、软碳、硅、硅-碳复合物、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO2、尖晶石结构的锂化TiO2-Li4Ti5O12、Li-Al合金中的一种或几种。
当二次电池为钠离子二次电池或锌离子二次电池时，仅需改变对应的正极活性材料、负极活性材料、电解质盐即可。
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。在实施例中仅示出二次电池为锂离子二次电池的情况，但本发明不限于此。
实施例1
(1)改性石墨负极材料的制备
将层数为10层、真密度为2.1g/cm3的片状石墨烯加入机械融合机中，设置转速为600r/min、旋转时间为1.5h，进行片状石墨烯的整形与造粒，得到形 貌规则、中值粒径D50为14μm的多层石墨稀。
在氮气气氛保护下，将导电碳黑Super P、粘结剂沥青以及上述多层石墨烯按质量比15:10:75加入机械融合机的立式反应釜中，设置升温温度为200℃～280℃、转速为300r/min，进行多层石墨烯的表面改性，反应结束后得到负载有Super P的多层石墨烯(形貌参见图1)。
将石墨及负载有Super P的多层石墨烯按质量比99.5:0.5加入V型混料机中进行混料，设置转速为400r/min，混料完成后过筛、去磁，即得到改性石墨负极材料。
(2)负极片的制备
将上述制备得到的改性石墨负极材料、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按质量比为97.5:1.5:1溶于去离子水中混合均匀制成负极浆料，之后将负极浆料均匀涂布在负极集流体铜箔上，随后在85℃下烘干后进行冷压，冷压的压力为2000T(吨)，之后经切边、裁片、分条、焊接极耳，得到负极片，其中负极浆料的涂布重量为167mg/1540.25mm2。
(3)正极片的制备
将正极活性材料钴酸锂、导电剂Super P、粘结剂聚偏氟乙烯(PVDF)按质量比96:2:2溶于N-甲基吡咯烷酮中混合均匀制成正极浆料，之后将正极浆料均匀涂布在正极集流体铝箔上，随后在85℃下烘干后进行冷压、切边、裁片、分条、焊接极耳，得到正极片，其中正极浆料的涂布重量为340mg/1540.25mm2、正极片的压实密度为4.1g/cm3。
(4)电解液的制备
电解液采用lM的LiPF6作为锂盐，有机溶剂采用EC/EMC＝3:7(体积比)。
(5)锂离子二次电池的制备
将正极片、负极片以及隔离膜(厚度为12μm的聚丙烯微孔膜)经过卷绕工艺制作成电芯，再用铝塑膜封装、注入电解液，之后经过化成、容量、整形等工序后，完成锂离子二次电池的制备。
实施例2
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述片状石墨烯的层数为15层、真密度为2.09g/cm3。
实施例3
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述片状石墨烯的层数为20层、真密度为2.15g/cm3。
实施例4
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
石墨与负载有Super P的多层石墨烯的质量比为90:10。
实施例5
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
石墨与负载有Super P的多层石墨烯的质量比为85:15。
实施例6
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
Super P、沥青以及多层石墨烯的质量比为10:5:85。
实施例7
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
Super P、沥青以及多层石墨烯的质量比为40:40:20。
实施例8
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述多层石墨烯的中值粒径D50为6μm。
实施例9
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述多层石墨烯的中值粒径D50为24μm。
实施例10
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述导电剂选自科琴黑。
所述粘结剂选自聚苯乙烯树脂，升温温度控制在240℃～250℃。
实施例11
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述片状石墨烯的层数为20层、真密度为1.8g/cm3。
实施例12
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
石墨与负载有Super P的多层石墨烯的质量比为80:20。
实施例13
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
Super P、沥青以及多层石墨烯的质量比为5:5:90。
实施例14
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
Super P、沥青以及多层石墨烯的质量比为45:45:10。
实施例15
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述多层石墨烯的中值粒径D50为3μm。
实施例16
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
所述多层石墨烯的中值粒径D50为30μm。
实施例17
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
石墨与负载有Super P的多层石墨烯的质量比为99.9:0.1。
对比例1
锂离子二次电池的制备方法同实施例1，区别在于，
负极材料选自常规人造石墨，不加入石墨烯。
负极片的制备过程为：将人造石墨、导电剂Super P、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按质量比为96.5:1:1.5:1溶于去离子水中混合均匀制成负极浆料，之后将负极浆料均匀涂布在负极集流体铜箔上，随后在85℃下烘干后进行冷压，冷压的压力为2000T，之后经切边、裁片、分条、焊接极耳，得到负极片，其中负极浆料的涂布重量为167mg/1540.25mm2。
对比例2
锂离子二次电池的制备方法同实施例1，区别在于，
(1)改性石墨负极材料的制备
改性石墨负极材料通过将石墨与石墨烯简单混合得到。
接下来说明锂离子二次电池的性能测试。
(1)负极析锂测试
在25℃下，将锂离子二次电池以1.3C恒流充电至4.35V，然后恒压充电至电流为0.05C，然后用1C恒电流放电至3.0V，此为一个循环充放电过程。如此反复进行充电和放电10次后，将锂离子二次电池拆解，观察负极析锂情况。其中，析锂程度分为不析锂、轻微析锂、中度析锂以及严重析锂。轻微析锂表示负极表面的析锂区域为整体区域的1/10以下，严重析锂表示负极表面的析锂区域超过整体区域的1/3。
(2)锂离子二次电池的循环性能测试
在25℃下，将锂离子二次电池以1C恒流充电至4.35V，然后恒压充电至电流为0.05C，然后用1C恒电流放电至3.0V，此为一个循环充放电过程。如此反复进行充电和放电，计算锂离子二次电池循环350次后的容量保持率。
表1 实施例1-17和对比例1-2的参数
Figure PCTCN2017108907-appb-000001
Figure PCTCN2017108907-appb-000002
表2 实施例1-17和对比例1-2的性能测试结果
Figure PCTCN2017108907-appb-000003
表3 实施例1与对比例1的不同冷压压力下的负极压实密度(g/cm3)
冷压压力(T) 500 750 1000 1500 2000
对比例1 1.443 1.519 1.593 1.677 1.751
实施例1 1.455 1.563 1.648 1.743 1.819
从表3中可以看出，与仅使用常规石墨作为负极材料的对比例1相比，实施例1的负极压实密度明显提高。
从图4和图5中可以看出，对比例1的负极片出现严重析锂，而实施例1的负极未出现析锂。
结合表1可知，对比例1的锂离子二次电池350个循环后的容量保持率仅为92％，而实施例1的锂离子二次电池350个循环后的容量保持率高达94％，显著延长了锂离子二次电池的使用寿命。
图1是实施例1制备得到的负载有Super P的多层石墨烯的FESEM图；图2是实施例1得到的改性石墨负极材料的SEM图；图3是对比例2得到的改性石墨负极材料的SEM图。从图3中可以看出，石墨烯在石墨颗粒中有团聚现象，分布不均匀，会导致负极片的电解液浸润性差，负极的压实密度较低，容易析锂，锂离子二次电池的循环性能也较差。从图2中可以看出，负载有导电剂的多层石墨烯能比较均匀地分散在石墨颗粒中，并且形成了导电网络结构。从图1中还可以看出，导电剂也均匀分散在多层石墨稀上，改善了多层石墨稀的加工性能，并且有利于提高导电性和电解液浸润性。
进一步结合表2可知，实施例1-11、17中采用本申请的改性石墨负极材料的锂离子二次电池的负极压实密度、负极析锂情况以及循环性能均得到了显著的改善，实施例12-16在未显著降低锂离子二次电池的负极压实密度、负极析锂情况以及循环性能的前提下，对锂离子二次电池的负极压实密度、负极析锂情况以及循环性能仍旧有改善的效果。

Claims (10)

  1. 一种改性石墨负极材料，包括：
    石墨；以及
    多层石墨烯，分散在所述石墨中；
    其特征在于，
    所述多层石墨烯通过粘结剂的粘结作用负载有导电剂。
  2. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述多层石墨烯的真密度为1.8g/cm3～2.15g/cm3。
  3. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述多层石墨烯的层数为10～20；优选地，所述多层石墨烯的层数为10～15。
  4. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述导电剂包括碳黑导电剂、石墨导电剂中的一种或几种。
  5. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述导电剂选自Super-P、Super S、乙炔黑、350G、碳纤维、碳纳米管、科琴黑、KS-6、KS-15、SFG-6、SFG-15中的一种或几种。
  6. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述粘结剂选自沥青、酚醛树脂、聚氨酯、聚苯乙烯树脂、聚丙烯酸酯、乙烯-醋酸乙烯共聚物中的一种或几种。
  7. 根据权利要求1所述的改性石墨负极材料，其特征在于，
    所述石墨与所述多层石墨烯的质量比为(85％～99.9％):(0.1％～15％)；所述导电剂、所述粘结剂与所述多层石墨烯的质量比为(10％～40％):(5％～40％):(20％～85％)。
  8. 根据权利要求1所述的改性石墨负极材料，其特征在于，所述多层石墨烯的中值粒径D50为6μm～24μm。
  9. 一种改性石墨负极材料的制备方法，用于制备权利要求1-8中任一项所述的改性石墨负极材料，其特征在于，包括步骤：
    在保护气体气氛下，向机械融合机的反应釜中加入多层石墨烯、导电剂以及粘结剂，设置转速并升温，以使多层石墨烯通过粘结剂的粘结作用负载有导电剂；
    将负载有导电剂的多层石墨稀以及石墨加入混料机中进行混料，混料完成后过筛、去磁，即得到改性石墨负极材料。
  10. 一种二次电池，其特征在于，包括根据权利要求1-8中任一项所述的改性石墨负极材料。
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