WO2021108996A1 - 复合石墨材料及其制备方法、二次电池和装置 - Google Patents

复合石墨材料及其制备方法、二次电池和装置 Download PDF

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WO2021108996A1
WO2021108996A1 PCT/CN2019/122743 CN2019122743W WO2021108996A1 WO 2021108996 A1 WO2021108996 A1 WO 2021108996A1 CN 2019122743 W CN2019122743 W CN 2019122743W WO 2021108996 A1 WO2021108996 A1 WO 2021108996A1
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composite graphite
graphite material
composite
polymer
cyclizable
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PCT/CN2019/122743
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English (en)
French (fr)
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梁成都
赵玉珍
温严
黄起森
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宁德时代新能源科技股份有限公司
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Priority to KR1020227011947A priority Critical patent/KR20220064385A/ko
Priority to EP19954825.6A priority patent/EP3913708A4/en
Priority to PCT/CN2019/122743 priority patent/WO2021108996A1/zh
Priority to CN201980066188.0A priority patent/CN114245942A/zh
Priority to JP2022520243A priority patent/JP2022550944A/ja
Publication of WO2021108996A1 publication Critical patent/WO2021108996A1/zh
Priority to US17/475,365 priority patent/US20220002160A1/en

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    • H—ELECTRICITY
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    • 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
    • H01M4/362—Composites
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    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • H01M4/602—Polymers
    • H01M4/606—Polymers containing aromatic main chain polymers
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/622—Binders being polymers
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    • 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
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    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/74—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by peak-intensities or a ratio thereof only
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    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
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    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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    • H—ELECTRICITY
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    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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

Definitions

  • This application relates to the field of energy storage materials, in particular to the field of secondary batteries. Specifically, the present application relates to composite graphite materials and preparation methods thereof, secondary batteries and devices.
  • the first aspect of the present application provides a composite graphite material, including a core material and a coating layer covering at least a part of the surface of the core material, the core material includes graphite, and the coating layer includes a segment having a ring structure
  • the weight loss rate of the composite graphite material is 0.1% to 0.55%.
  • the composite graphite material of the present application can increase the gram capacity and reduce the expansion rate of the pole piece, and more preferably can also improve the cycle performance and/or dynamic performance of the battery.
  • the second aspect of the present application provides a method for preparing a composite graphite material, including the following steps:
  • the composite graphite material includes a core material and a coating layer covering at least a part of the surface of the core material, the core material includes graphite, and the coating layer includes a coating material having a ring structure segment, wherein
  • the weight loss rate of the composite graphite material is 0.1% to 0.55%.
  • a third aspect of the present application provides a secondary battery, including a negative pole piece, the negative pole piece includes a negative active material, and the negative active material includes the composite graphite material described in the first aspect of the present application.
  • a fourth aspect of the present application provides a device, and the device includes the secondary battery provided in the third aspect of the present application.
  • the composite graphite material with the coating layer with ring structure fragments of the present application not only improves the gram capacity of the negative electrode active material, but also reduces the expansion rate of the negative electrode piece containing the composite graphite material; further, the battery is made Time can also improve the dynamic performance and/or cycle performance of the battery.
  • the method of the second aspect of the present application by strictly controlling the degree of cyclization and carbonization of the polymer in the coating layer, a composite graphite material with the above-mentioned excellent properties is obtained. This is unpredictable by those skilled in the art.
  • Figure 1 is a schematic reaction formula illustrating the cyclization and partial carbonization of polyacrylonitrile.
  • FIG. 2 is a Raman spectrum of the composite graphite material of Example 2 and Comparative Example 1 of the present application.
  • FIG. 3 is a TG diagram of the composite graphite material of Example 2 and Comparative Example 1 of the present application.
  • Fig. 4 is an infrared spectrum of a polymer material with cyclic structure fragments.
  • Fig. 5 is a schematic diagram of a secondary battery provided by an embodiment of the present application.
  • Fig. 6 is a schematic diagram of a battery module provided by an embodiment of the present application.
  • Fig. 7 is a schematic diagram of a battery pack provided by an embodiment of the present application.
  • Fig. 8 is an exploded view of the battery pack of Fig. 7.
  • Fig. 9 is a schematic diagram of a device provided by an embodiment of the present application.
  • 10a-10b are SEM (scanning electron microscope) pictures of composite graphite materials provided by embodiments of the present application.
  • FIG. 11 is a schematic structural diagram of a composite graphite material provided by an embodiment of the present application.
  • composition is described as including or including specific components, it is expected that the composition does not exclude optional components not covered by the present invention, and it is expected that the composition may consist of or consist of the involved components, or Where a method is described as including or including specific process steps, it is expected that the method does not exclude optional process steps not involved in the present invention, and it is expected that the method can be constituted or composed of the involved process steps.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit in combination with any other point or single numerical value or in combination with other lower or upper limits to form an unspecified range.
  • the first aspect of the present application provides a composite graphite material, including a core material and a coating layer covering at least a part of the surface of the core material, the core material includes graphite, and the coating layer includes a segment having a ring structure
  • the weight loss rate of the composite graphite material is 0.1% to 0.55%.
  • the weight loss rate of the composite graphite material when the composite graphite material is heated from 40°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the composite graphite material is 0.1%-0.4%; more preferably 0.1%-0.3 %.
  • the weight loss rate of the composite graphite material is less than 0.1%, the coating integrity of the coating layer on the surface of the graphite core material is greatly reduced, so that on the one hand, the effect of the coating layer itself in increasing the capacity of the material is reduced; The effect between the coating and the adhesive is weakened, so that the adhesion and cohesion of the pole piece are low, and the expansion rate of the pole piece becomes larger during the cycle.
  • the weight loss rate of the composite graphite material is greater than 0.55%, which will cause the material to consume too much active ions during the cycle, which will make the cycle performance of the battery core worse; at the same time, the more active ions are consumed, the thicker the side reaction layer on the surface of the composite material. It will also cause the pole piece to expand.
  • the inert non-oxidizing gas may be selected from one or more of nitrogen, carbon dioxide, ammonia, helium, and argon.
  • nitrogen can be used as an inert non-oxidizing gas.
  • the heating rate of the weight loss process may be 10°C/min or lower, preferably 5°C/min or lower.
  • the weight loss rate is measured from 40°C to 800°C at a rate of 10°C/min in an inert non-oxidizing gas (for example, nitrogen) atmosphere.
  • the composite graphite material of the present application at least a part of the surface of the core material is covered by a coating layer.
  • the composite graphite material includes a core material and a coating layer covering at least 80% of the surface of the core material. More preferably, the composite graphite material includes a core material and a coating layer covering at least 90% of the surface of the core material. In some preferred embodiments, the composite graphite material includes a core material and a coating layer covering the surface of the core material.
  • the coating layer includes a coating material having a nitrogen heterocyclic structure fragment, and at least part of the nitrogen heterocyclic structure has a carbon-nitrogen double bond.
  • the hydrophilicity of the graphite material is greatly improved.
  • the composite graphite is more stable in the slurry, and the contact with the binder is more uniform.
  • the adhesion and cohesion of the pole pieces are therefore Upgrade, which can improve the cycle expansion performance of the battery.
  • the coating layer with the above-mentioned structural fragments itself can participate in the deintercalation of active ions, and provides more channels for deintercalation of active ions, providing the graphite material with extra capacity besides the core, thereby increasing its gram capacity.
  • This is unexpected by those skilled in the art, because in general, coating other coatings (such as amorphous carbon coatings, conventional polymer coatings) on the surface of graphite materials will result in the effective active substance of the material. Reduce, thereby reducing the gram capacity of the material.
  • the coating modification of the present application shows more important significance and technological progress for the improvement of the gram capacity of the graphite material.
  • the coating layer with the above-mentioned structural fragments provides more channels suitable for active ion deintercalation, the active ion transmission efficiency of the material is improved.
  • the coating layer also has good electronic conductivity. Therefore, the graphite material has better kinetic characteristics, which improves the kinetic performance and cycle performance of the battery using the graphite material.
  • the nitrogen heterocyclic ring structure segment can be a fused ring or a non-fused ring.
  • the nitrogen heterocyclic ring structure fragment includes an aza fused ring structure fragment, in which at least part of the nitrogen heterocyclic ring has a carbon-nitrogen double bond.
  • the nitrogen heterocycle also has a carbon-carbon double bond.
  • the conductivity of the coating layer is further improved.
  • the nitrogen heterocycle is a five-membered ring or a six-membered ring.
  • the coating layer has higher elasticity and toughness, can better adapt to the expansion and contraction of repeated de-nucleation/intercalation of lithium, isolates the contact between the surface of the material and the electrolyte, and reduces the capacity loss of the material due to the erosion of the electrolyte. Can improve the cycle performance of the battery.
  • the nitrogen heterocyclic ring structure fragment may include one or more of a pyridine ring, an imidazole ring, a quinoline ring, and a pyrimidine ring.
  • the nitrogen heterocyclic ring structure fragment includes one or more of the aza condensed ring structure fragments in Formula 1 to Formula 3.
  • the nitrogen heterocyclic structure fragment includes a combination of at least two of Formula 1 to Formula 3. More preferably, the nitrogen heterocyclic ring structure fragment includes a combination of three of Formula 1 to Formula 3.
  • the core material of the composite graphite material can be selected from one or more of artificial graphite and natural graphite.
  • the core material is selected from artificial graphite
  • the composite graphite material when the composite graphite material also satisfies one or more of the following parameters, the performance of the material can be further improved.
  • the ratio I D /I G of the D peak intensity I D to the G peak intensity I G of the composite graphite material is 0.4 to 1.0.
  • Peak D and Peak G are Raman characteristic peaks of graphite materials.
  • the intensity of peak D and peak G can be measured using laser Raman spectroscopy, for example, a LabRAM HR Evolution type Raman spectrometer.
  • D is the position of the peak in 1300cm -1 ⁇ 1400cm -1
  • G is the peak position of 1550cm -1 to 1620cm -1.
  • the I D /I G of the composite graphite material is 0.4 to 1.0.
  • the I D /I G of the composite graphite material can be 0.4 to 0.95, 0.45 to 0.9, 0.5 to 0.8.
  • I D / I G at the time within a given range can further improve the stability of the material surface, and thus possible to further reduce the volume of the negative electrode tab of the battery during the expansion cycle.
  • the I D /I G of the composite graphite material is 0.5 to 0.8.
  • the orientation index OI value of the composite graphite material in the pole piece is ⁇ 15, Preferably it is 8-12.
  • the OI value is within the given range, and the composite graphite material has a higher degree of isotropy, so the composite graphite material expands in the pole piece during the battery cycle It is dispersed in all directions, which can further reduce the expansion of the pole piece during the cycle.
  • the orientation index OI value of the composite graphite material C 004 /C 110 .
  • the peak area of the diffraction peak attributable to the (004) crystal plane is C 004
  • the peak area of the diffraction peak attributable to the (110) crystal plane is C 110 .
  • X-ray diffraction analysis can refer to the standard JISK 0131-1996, and use an X-ray diffractometer (for example, Bruker D8 Discover X-ray diffractometer) for testing.
  • X-ray diffraction analysis can refer to the standard JISK 0131-1996, and use an X-ray diffractometer (for example, Bruker D8 Discover X-ray diffractometer) for testing.
  • a copper target can be used as an anode target, and a Ni filter with a thickness of 0.02mm is used to filter CuK ⁇ , and CuK ⁇ rays are used as the radiation source, and the ray wavelength (Take the weighted average of K ⁇ 1 and K ⁇ 2 ), the scanning 2 ⁇ angle range is 20° ⁇ 80°, and the scanning rate is 4°/min.
  • An exemplary preparation method of the pole piece for testing the orientation index OI of the above-mentioned composite graphite material is as follows:
  • the composite graphite material of the present application and the binder styrene butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent conductive carbon black (Super P) are in accordance with the mass ratio of 96.2:1.8:1.2 : 0.8 dispersed in solvent deionized water, mixed uniformly to prepare a slurry; the slurry is uniformly coated on the copper foil current collector, and the surface density of the coating can be 10mg/cm 2 ⁇ 11mg/cm 2 (for example, 10.5mg/ cm 2 ), after the pole pieces are dried, they are cold pressed using a cold press, and the compacted density after cold pressing is 1.6 g/cm 3 to 1.7 g/cm 3 (for example, 1.65 g/cm 3 ).
  • SBR styrene butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • Super P conductive agent conductive carbon black
  • the prepared pole piece is placed in an X-ray diffractometer, and the peak area C 004 of the (004) crystal plane diffraction peak of the composite graphite material in the pole piece and the peak of the (110) crystal plane diffraction peak of the composite graphite material are obtained by X-ray diffraction analysis.
  • Area C 110 , the orientation index OI value of the composite graphite material C 004 / C 110 .
  • the Dv50 of the composite graphite material is 15 ⁇ m to 20 ⁇ m, preferably 15 ⁇ m to 18 ⁇ m.
  • the D v 50 of the composite graphite material is suitable for making it have high active ion and electron transport performance, and at the same time it can reduce the side reaction of the electrolyte in the negative electrode.
  • the composite graphite material with an appropriate volume average particle size D v 50 is also beneficial to increase its powder compaction density.
  • the volume average particle size D v 10 of the composite graphite material is greater than or equal to 6 ⁇ m.
  • the D v 10 of the composite graphite material may be 6 ⁇ m or more, 6.5 ⁇ m or more, 7 ⁇ m or more, or 7.5 ⁇ m or more.
  • the active specific surface area is small, and the side reactions in the secondary battery can be further reduced.
  • the D v 10 of the artificial graphite may be 11 ⁇ m or less, 10.5 ⁇ m or less, 10 ⁇ m or less, 9.5 ⁇ m or less, and 9 ⁇ m or less.
  • the Dn10 of the composite graphite material is 1.0 ⁇ m to 3.0 ⁇ m, preferably 1.2 to 2.0 ⁇ m, and more preferably 1.3 ⁇ m to 1.8 ⁇ m.
  • the Dn10 of the composite graphite material may be about 1.3 ⁇ m, 1.4 ⁇ m, 1.5 ⁇ m, 1.6 ⁇ m, 1.7 ⁇ m, or 1.8 ⁇ m.
  • the D n 10 of the composite graphite material is appropriate, there are fewer side reactions between it and the electrolyte.
  • the composite graphite material and additives such as the binder can be uniformly dispersed, and the overall adhesion force of the pole piece is relatively high. Therefore, the cycle performance and anti-swelling performance of the battery are further reduced.
  • the proper D n 10 of the composite graphite material can also make it have a higher gram capacity.
  • the D n 10, D v 10, and D v 50 of the composite graphite material can be measured with a laser particle size analyzer (such as Malvern Master Size 3000) with reference to the standard GB/T 19077.1-2016.
  • a laser particle size analyzer such as Malvern Master Size 3000
  • D n 10, D v 10, and D v 50 are as follows:
  • D n 10 the particle size corresponding to when the cumulative number distribution percentage of the material reaches 10%
  • D v 10 The particle size when the cumulative volume distribution percentage of the material reaches 10%
  • D v 50 The particle size when the cumulative volume distribution percentage of the material reaches 50%.
  • the specific surface area of the composite graphite material (SSA) of 0.5m 2 /g ⁇ 1.3m 2 / g, preferably 0.6m 2 /g ⁇ 1.0m 2 / g.
  • the composite graphite material has an appropriate specific surface area, can reduce the side reaction of the electrolyte on the surface, and reduce the gas production, thereby reducing the volume expansion of the secondary battery during the cycle. At the same time, the composite graphite material can have higher electrochemical reaction activity, so that the secondary battery has higher dynamic performance, which is beneficial to meet the power demand of the device.
  • a proper specific surface area can also make the composite graphite material and the binder have a strong bonding force, which can improve the cohesion and bonding force of the pole piece, thereby further reducing the cyclic expansion of the pole piece.
  • the specific surface area can be tested using methods known in the art. For example, you can refer to GB/T 19587-2017, use the nitrogen adsorption specific surface area analysis test method to test, and use the BET (Brunauer Emmett Teller) method to calculate, in which the nitrogen adsorption specific surface area analysis test can pass the Tri-Star 3020 type of the American Micromeritics company The specific surface area pore size analysis tester was carried out.
  • BET Brunauer Emmett Teller
  • the compacted density of the composite graphite material measured under a pressure of 5 tons is 1.80 g/cm 3 to 2.10 g/cm 3 , preferably 1.93 g/cm 3 to 2.05 g/cm 3 .
  • the composite graphite material itself can have a higher gram capacity.
  • the negative pole piece using the composite graphite material also has a higher compaction density, so that the battery has a higher energy density.
  • the powder compaction density can be tested by methods known in the art. For example, refer to GB/T 24533-2009, use an electronic pressure testing machine (such as UTM7305) to test: put a certain amount of powder on a special compaction mold, set different pressures, and read the thickness of the powder under different pressures on the device Calculate the compacted density under different pressures.
  • UTM7305 electronic pressure testing machine
  • the tap density of the composite graphite material is 0.8 g/cm 3 to 1.15 g/cm 3 , preferably 0.9 g/cm 3 to 1.05 g/cm 3 .
  • the negative pole piece can have a suitable porosity to ensure that the pole piece has better electrolyte infiltration performance, so that the battery has a higher cycle performance.
  • the tap density of the composite graphite material is conducive to obtaining a higher gram capacity.
  • the compaction density of the negative pole piece using the composite graphite material is also higher, so that the energy density of the battery can be improved.
  • the tap density of the composite graphite material can be tested using methods known in the art. For example, you can refer to the standard GB/T 5162-2006 and use a powder tap density tester (such as Dandong Baxter BT-301) for testing.
  • a powder tap density tester such as Dandong Baxter BT-301
  • the sulfur content of the composite graphite material is less than 0.02 wt%.
  • the presence of sulfur in the coating layer may affect the stability of the aforementioned structural fragments, making it difficult to control the degree of cyclization and carbonization of the polymer in the coating layer.
  • the sulfur content can be determined by elemental analysis methods.
  • the composite graphite material of the present application can be prepared by the method of the second aspect of the present application. Therefore, the present application also describes the composite graphite material obtained by the method of the second aspect of the present application.
  • the second aspect of the present application provides a method for preparing a composite graphite material, which is characterized in that it comprises the following steps:
  • the powder is heat-treated at a temperature of 300-400°C to obtain the composite graphite material.
  • the composite graphite material includes a core material and a coating layer covering at least a part of the surface of the core material, the core material includes graphite, and the coating layer includes a coating material having a ring structure segment.
  • the weight loss rate of the composite graphite material is 0.1% to 0.55%.
  • the cladding layer may have the structure discussed above.
  • Figure 4 shows the infrared spectrum obtained after the above-mentioned drying and heat treatment of the polymer material. In Figure 4, the absorption peaks of carbon-nitrogen double bonds and carbon-carbon double bonds in the ring structure fragments can be clearly observed.
  • the coating layer includes The covering material of the ring structure segment.
  • coating layers include coating materials having one or more structural segments in the following formula:
  • the coating layer has at least two of the above-mentioned structural segments. More preferably, the coating layer has at least two of the above-mentioned structural segments. Even more preferably, the cladding layer has a combination of the aforementioned structural fragments.
  • the graphite core material in step (1) can be obtained commercially.
  • the content of the coating layer in the composite graphite can be controlled by adjusting the amount of polymer added.
  • the degree of cyclization and carbonization of the polymer can be controlled.
  • the inventors of the present application have found a more preferable amount of raw materials, temperature and time of the heat treatment step.
  • the advantages of adjusting the content of the coating layer within a certain range are as discussed above, and will not be repeated here.
  • the mass ratio m G :m P of graphite to cyclizable polymer is 40:1 to 200:1, more preferably 50:1 to 150:1.
  • the mass ratio m G :m P of graphite to cyclizable polymer may be 70:1 to 120:1, more preferably 80:1 to 110:1.
  • the mass ratio of graphite to cyclizable polymer m G :m P is 100:1.
  • the cyclizable polymer includes polyacrylonitrile (PAN) or a copolymer thereof.
  • the cyclizable polymer includes polyacrylonitrile or copolymers of acrylonitrile and olefins. More preferably, the cyclizable polymer includes polyacrylonitrile or copolymers of acrylonitrile and acrylic, acrylamide, and itaconic acid monomers.
  • cyclizable polymers include polyacrylonitrile or acrylonitrile and one of itaconic acid (IA), vinyl acetate (Vac), acrylic acid (AA), methyl acrylate (MA) and acrylamide (AM)kind or several kinds of copolymers.
  • the cyclizable polymer is or includes polyacrylonitrile.
  • the number average molecular weight of the cyclizable polymer is 50,000 to 150,000 Da, preferably 80,000 to 120,000 Da.
  • the solution including the cyclizable polymer may include water, N-dimethylformamide, N,N-dimethylacetamide, N-methyl One or more of pyrrolidone and dimethyl sulfoxide. More preferably, the solution including the cyclizable polymer may be or include N-dimethylformamide.
  • the solution including the cyclizable polymer in step (1) can be obtained by a method known in the art.
  • a solution including the cyclizable polymer can be obtained by dissolving the cyclizable polymer in a solvent and stirring until dissolved.
  • drying methods include, but are not limited to, spray drying, flash evaporation, rotary evaporation, freeze drying, and the like.
  • spray drying is used.
  • the drying temperature can be adjusted according to the solvent used in the solution or slurry.
  • the drying is spray drying performed at 180-210°C. More preferably, the drying is spray drying performed at 190°C to 205°C.
  • the heat treatment is performed in an inert non-oxidizing gas.
  • inert non-oxidizing gases include, but are not limited to, nitrogen, carbon dioxide, ammonia, and inert gases (eg, helium, argon), and combinations thereof.
  • nitrogen can be used as an inert non-oxidizing gas.
  • the heat treatment is performed at a temperature of 350°C to 400°C.
  • the temperature of the heat treatment has a key influence on the cyclization and carbonization of the polymer.
  • a large number of studies have found that the polymer coating has not been thermally cracked and is still in the state of polymer when heat treatment is performed at a temperature of 200°C or lower.
  • the polymer itself has no gram capacity, so the gram capacity of the coated material is reduced. .
  • the temperature rises from 300°C to 400°C. As the temperature rises, the coating layer begins to decompose, the gram capacity of the material increases, and the anti-expansion performance is also improved to the maximum.
  • the degree of polymer cyclization and carbonization can be adjusted by strictly controlling the temperature of the heat treatment.
  • the temperature of the above-mentioned preferred heat treatment it is possible to better control the partial carbonization of the cyclizable polymer (especially polyacrylonitrile) while maintaining the cyclic structure fragments discussed above.
  • the heat treatment time is 3-6 hours; preferably, the heat treatment time is 3.5-5 hours.
  • FIG. 1 shows a schematic reaction formula for cyclization and partial carbonization of polyacrylonitrile.
  • polyacrylonitrile mainly undergoes intramolecular cyclization below 220°C (as shown in Figure 1(a)), and intermolecular cyclization occurs at about 300°C (as shown in Figure 1(b)) ).
  • the cyclic structure fragments begin to be partially carbonized to form cyclic structure fragments with carbon-nitrogen double bonds and carbon-carbon double bonds, or have ⁇ cyclic structure fragments.
  • a coating material having one or more structural fragments in the following formula is formed:
  • the carbonization process also affects the weight loss rate of the composite graphite material from 40°C to 800°C in an inert non-oxidizing gas atmosphere. If the degree of carbonization is too high, so that most of the ring structure fragments are decomposed, the weight loss rate of the obtained composite graphite material will be significantly reduced. For example, when the carbonization process is carried out at 1000°C for 4 hours, the weight loss rate of the obtained composite graphite material from 40°C to 800°C is extremely small, indicating that most (or even almost all) of the coating layer can be cyclized The polymer is converted into amorphous carbon, so that the gram capacity is reduced and the anti-swelling performance of the battery is reduced.
  • the obtained composite graphite material will have a low temperature during the process from 40°C to 800°C.
  • the weight loss rate is increased, and the obtained composite graphite material has very limited improvement in battery performance, for example, the battery's dynamic performance is insufficient, the maximum charge rate is reduced, or a slight lithium evolution occurs.
  • the graphite core material in step (1) can also be prepared by the following steps:
  • step S20 shaping the product obtained in step S10.
  • step S30 Granulate the product obtained in step S20, wherein the amount of binder added in the granulation process does not exceed 5% of the total weight of the raw coke raw material.
  • step S40 Perform graphitization treatment on the product obtained in step S30 at a temperature of 2800° C. to 3200° C. to obtain the graphite.
  • the graphite is artificial graphite.
  • the raw coke raw material may be selected from one or more of raw petroleum coke and raw pitch coke, and preferably includes raw petroleum coke.
  • the raw coke raw material is non-needle coke.
  • the non-needle coke can be selected from one or more of non-needle green petroleum coke and non-needle green pitch coke.
  • the non-needle coke includes non-needle green petroleum coke.
  • the volatile content of the raw coke raw material is 6%-12% (weight percentage); preferably, the volatile content of the raw coke raw material is 7%-10%.
  • the volatile content of the raw coke raw material is appropriate, which can make it have higher self-adhesiveness in the granulation process of step S20, improve the bonding strength between the primary particles in the graphite, and make the artificial graphite have higher structural strength And higher gram capacity.
  • the sulfur content of the raw coke raw material may be 2% or less, 1.5% or less, 1% or less, or 0.5% or less.
  • the raw coke raw material has a lower sulfur content, which can prevent the specific surface area of the graphite material from increasing due to the escape of more sulfur components in the subsequent process.
  • the sulfur content of the raw coke raw material is ⁇ 1%.
  • step S20 further includes removing fine powder after shaping.
  • the D n 10 of the precursor after shaping is adjusted to be in an appropriate range through the fine powder treatment, so that the D n 10 of the obtained artificial graphite is in the desired range.
  • step S20 After a lot of research, it has been found that the fine powder removal treatment after shaping in step S20 is beneficial to further increase the gram capacity of artificial graphite.
  • step S30 preferably, the granulation process is performed without adding a binder.
  • the amount of the binder is controlled within the given range, the gram capacity of graphite can be further increased; especially, in the absence of a binder, the self-adhesive properties of the green coke can be used for granulation. Improve the overall structural strength of artificial graphite particles.
  • the artificial graphite is used as the core of the graphite material of this application, the corresponding properties of the graphite material are also improved.
  • the step S30 can granulate the granular product obtained in step S20 without adding a binder.
  • the volatile content of raw coke raw materials should not be too high, otherwise it will significantly reduce the gram capacity of graphite and affect its processing performance during subsequent use.
  • the volume average particle size D v 50 of the granulated product can be within the required range, or the D v 10, D v 50 and D v 90 of the granulated product can be all within the required range. Need to be within range.
  • the D v 50 and D v 10 of the final composite graphite material can be within the required range.
  • the temperature for graphitization in step S40 is 2900°C to 3100°C.
  • a third aspect of the present application provides a secondary battery, including a negative pole piece, and the negative pole piece includes a negative active material, characterized in that the negative active material includes the composite graphite material described in the first aspect of the present application.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode membrane that is disposed on at least one surface of the negative electrode current collector and includes a negative electrode active material
  • the negative electrode active material includes the composite material described in the first aspect of the present application. Graphite material.
  • the secondary battery of the present application has higher energy density and excellent anti-expansion performance, so that the battery has both higher energy density and better cycle performance.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film is laminated on either or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector can be made of materials with good electrical conductivity and mechanical strength.
  • copper foil is used as the negative electrode current collector.
  • the negative electrode membrane may also optionally include other negative electrode active materials that can be used in the negative electrode of the secondary battery.
  • the other negative electrode active materials can be one or more of other graphite materials, mesophase micro-carbon spheres (MCMB), hard carbon and soft carbon.
  • the negative electrode membrane further includes a binder.
  • the binder may be selected from polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), sodium alginate (SA), polymethacrylic acid (PMAA) And one or more of carboxymethyl chitosan (CMCS).
  • the negative electrode membrane optionally further includes a thickener.
  • the thickener may be sodium carboxymethyl cellulose (CMC-Na).
  • the negative electrode membrane optionally further includes a conductive agent.
  • the conductive agent used for the negative electrode membrane can be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers .
  • the secondary battery may also include a positive electrode tab.
  • active ions are inserted and extracted back and forth between the positive pole piece and the negative pole piece.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode membrane provided on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film is laminated on either or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector can be made of materials with good electrical conductivity and mechanical strength.
  • the positive electrode current collector may be an aluminum foil.
  • the positive pole piece may include a positive active material.
  • This application does not specifically limit the specific types of positive electrode active materials, and materials known in the art that can be used for secondary battery positive electrodes can be used, and those skilled in the art can make selections according to actual needs.
  • the positive electrode active material may be selected from one or more of lithium transition metal oxides and modified compounds thereof.
  • the modification compound may be doping modification and/or coating modification of the lithium transition metal oxide.
  • the lithium transition metal oxide can be selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structures.
  • the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
  • the cathode active material of the secondary battery may be selected from LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 (LFP) and LiMnPO 4 One or more.
  • the positive electrode membrane may also optionally include a binder.
  • a binder There is no specific restriction on the type of binder, and those skilled in the art can make a selection according to actual needs.
  • the binder used for the positive electrode membrane may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
  • a conductive agent is optionally included in the positive electrode film.
  • the type of conductive agent is not specifically limited, and those skilled in the art can make a selection according to actual needs.
  • the conductive agent used for the positive electrode film may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the secondary battery further includes an electrolyte.
  • the electrolyte conducts ions between the positive pole piece and the negative pole piece.
  • the type of electrolyte in this application and it can be selected according to requirements.
  • the electrolyte may be selected from at least one of solid electrolytes and liquid electrolytes (ie, electrolytes).
  • the electrolyte uses an electrolytic solution.
  • the electrolyte includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (difluorosulfonate) Lithium imide), LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate), LiBOB (lithium bisoxalate), LiPO 2 F 2 (Lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate) one or more.
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate Ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , Ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) one
  • the electrolyte may also optionally include additives.
  • the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. Additives, etc.
  • the isolation film is arranged between the positive pole piece and the negative pole piece to play a role of isolation.
  • the type of isolation membrane in this application, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multilayer composite film. When the isolation film is a multilayer composite film, the materials of each layer can be the same or different.
  • Some embodiments of the present application also provide a method for preparing a secondary battery, which includes the step of using any one or several composite graphite materials of the present application to prepare a negative pole piece.
  • the step of using the composite graphite material of the present application to prepare a negative pole piece may include: combining the negative electrode active material including the composite graphite material of the first aspect of the present application with a binder, and an optional thickener and The conductive agent is dispersed in a solvent, and the solvent can be deionized water to form a uniform negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode pole piece is obtained.
  • the preparation method of the secondary battery may further include a step of preparing a positive electrode piece.
  • the positive electrode active material, conductive agent, and binder can be dispersed in a solvent (for example, N-methylpyrrolidone, NMP for short) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector On the fluid, after drying, cold pressing and other processes, the positive pole piece is obtained.
  • a solvent for example, N-methylpyrrolidone, NMP for short
  • the preparation method of the secondary battery further includes the step of assembling the negative pole piece, the positive pole piece and the electrolyte to form a secondary battery.
  • the positive pole piece, the separator film, and the negative pole piece can be wound or laminated in order, so that the separator film is located between the positive pole piece and the negative pole piece to isolate the battery cell;
  • the electric core is placed in the outer package, and the electrolyte is injected and sealed to obtain the secondary battery of the present application.
  • the secondary battery may be a lithium ion secondary battery.
  • the secondary battery may include an outer package and a battery cell encapsulated in the outer package.
  • the number of battery cells in the secondary battery can be one or several, which can be adjusted according to requirements.
  • the outer packaging of the secondary battery may be a soft bag (for example, a bag type, and the material may be plastic, such as polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate One or more of esters, PBS, etc.), or hard shell (such as aluminum shell, etc.).
  • a soft bag for example, a bag type
  • the material may be plastic, such as polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate One or more of esters, PBS, etc.), or hard shell (such as aluminum shell, etc.).
  • FIG. 5 shows a secondary battery 5 with a square structure as an example.
  • the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 6 shows the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodating space, and a plurality of secondary batteries 5 are accommodated in the accommodating space.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3.
  • the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4.
  • a plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the fourth aspect of the present application provides a device.
  • the device includes the secondary battery of the third aspect of the present application.
  • the secondary battery may be used as a power source of the device or an energy storage device.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.
  • Figure 9 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, and the like.
  • the device is generally required to be thin and light, and a secondary battery can be used as a power source.
  • the nuclear materials used in the following examples of this application can be obtained commercially, or can be obtained according to the following preparation method:
  • step 2 2) Add artificial graphite A to the polymer solution obtained in step 1, stir and mix uniformly to obtain a mixed slurry;
  • step 3 The mixed slurry obtained in step 2 is transferred to a spray drying equipment using a peristaltic pump, and dried in a nitrogen atmosphere to obtain a dry powder, wherein the rotation speed of the peristaltic pump is 20 rpm and the spray drying temperature range is 190°C;
  • step 3 The dry powder obtained in step 3 is heat-treated in a nitrogen atmosphere, the temperature of the heat treatment is 400° C., and the time of the heat treatment is 4 hours, to obtain a composite graphite material.
  • the composite graphite material prepared above, the conductive agent Super P, the binder styrene-butadiene rubber (SBR), and the thickener CMC-Na are fully stirred and mixed in an appropriate amount of deionized water at a mass ratio of 96.2:0.8:1.8:1.2.
  • a uniform negative electrode slurry is formed; the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode pole piece is obtained.
  • the compacted density of the negative pole piece is 1.65 g/cm 3 , and the areal density is 10.7 mg/cm 2 .
  • the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), the conductive agent Super-P, and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2. ) Is mixed uniformly to form a positive electrode slurry, and then the positive electrode slurry is uniformly coated on the aluminum foil of the current collector, and after drying and cold pressing, a positive electrode sheet is obtained.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • PE polyethylene
  • a STA449F3 model of synchronous thermal analyzer was used to determine the negative electrode active material in each example and comparative example. Among them, the atmosphere is nitrogen, the test temperature range is 40°C to 800°C, and the heating rate is 10°C/min. Record the mass percentage of the material mass measured at different temperatures relative to the initial material mass.
  • the button cell was discharged to 0.005V at a constant current with a current of 0.05C, left for 10 minutes, and then discharged at a constant current to 0.005V with a current of 50 ⁇ A, and then discharged to 0.005V at a current of 50 ⁇ A.
  • the current is then discharged to 0.005V at a constant current; then charged to 2V at a constant current with a current of 0.1C, and the charge capacity is recorded.
  • the ratio of the charging capacity to the mass of the composite graphite material is the gram capacity of the prepared artificial graphite.
  • the blue battery test system LAND CT2001A can be used to test the button battery, and the gram capacity of the composite graphite material can be calculated.
  • the lithium-ion secondary battery At 25°C, charge the lithium-ion secondary battery with a constant current of 1C to 4.3V, then charge at a constant voltage until the current is less than or equal to 0.05C, and then discharge at a constant current of 1C to 2.8V, which is a charge and discharge Cycle, the discharge capacity this time is the discharge capacity of the first cycle.
  • the lithium ion secondary battery was subjected to 1400 charge-discharge cycles according to the above method, the discharge capacity of the 1400th cycle was recorded, and the capacity retention rate of the lithium ion secondary battery after 1400 1C/1C cycles was calculated.
  • the capacity retention rate (%) of the lithium ion secondary battery after 1400 1C/1C cycles discharge capacity at the 1400th cycle/discharge capacity at the first cycle ⁇ 100%.
  • the thickness of the negative pole piece after cold pressing is recorded as H 0 .
  • the cold-pressed negative pole piece, positive pole piece, separator and electrolyte are made into a secondary battery.
  • the secondary battery is subjected to a 1C/1C cycle of 100% DOD (100% depth of discharge, that is, fully charged and then fully discharged) in a Xinwei charging and discharging machine.
  • a full charge and discharge cycle is recorded as one circle.
  • the cycle stops.
  • SOC State of Charge
  • the cyclic expansion rate of the negative pole piece is: (H 1 /H 0 -1) ⁇ 100%.
  • the batteries prepared in the examples and comparative examples were fully charged at x C and fully discharged at 1C for 10 times, then the battery was fully charged at x C, and then the negative pole piece was disassembled and the negative electrode was observed. Lithium evolution on the surface of the pole piece. If no lithium is deposited on the surface of the negative electrode, the charge rate x C is tested again with a gradient of 0.1C until lithium is deposited on the surface of the negative electrode, and the test is stopped. At this time, the charge rate (x-0.1)C is the maximum charge rate of the battery. .
  • Comparing Comparative Example 7 with Example 4 it can be seen that, compared with the polymer-coated graphite material without carbonization, the partially carbonized composite graphite material can significantly improve the gram capacity, and significantly improve the cycle performance and resistance of the battery. Expansion performance. Comparing Comparative Example 5 with Example 4, it can be seen that when the heat treatment temperature reaches 1000°C, the degree of carbonization is too high, the desired ring structure fragments in the coating layer are gradually destroyed, the gram capacity is reduced, and the expansion rate is obvious Elevated.
  • Comparing Comparative Examples 1 and 8 with Example 4 it can be seen that compared with conventional coating materials, when polyacrylonitrile is used as the cyclizable polymer, the gram capacity is significantly increased, and the anti-expansion performance is obtained. Effectively improve.
  • the inventor also surprisingly found that when the core material uses artificial graphite A, the expansion rate of the pole pieces in the battery is significantly reduced, and the battery performance is improved. Cycle performance. This can be confirmed from the comparison between Example 4 and Example 11.
  • the ratio I D /I G of the D peak intensity I D to the G peak intensity I G of the composite graphite of Example 2 is 0.82, which is in the range of 0.4 to 1.0.
  • Comparative Example D and the peak intensity I D G I G 1 peak intensity ratio I D / I G was 0.21, not in the range of 0.4 to 1.0.
  • D is the position of the peak in 1300cm -1 ⁇ 1400cm -1
  • G is the peak position of 1550cm -1 to 1620cm -1.

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Abstract

本申请提供了一种复合石墨材料及其制备方法、二次电池和装置。本申请的复合石墨材料包括核材料和包覆在所述核材料表面至少一部分的包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，其中，当将所述复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。本申请的复合石墨材料可以改善克容量和降低极片膨胀率，更优选地还可以改善电池的循环性能和动力学性能。

Description

复合石墨材料及其制备方法、二次电池和装置 技术领域
本申请涉及储能材料领域，尤其涉及二次电池领域。具体地，本申请涉及复合石墨材料及其制备方法、二次电池和装置。
背景技术
二次电池由于具有能量密度高、循环寿命长、安全可靠、无记忆效应等优点，已广泛应用于各类数码产品、便携式设备、电动汽车、储能电源等。
目前，在商业上常用的二次电池中，通常采用碳质材料作为负极活性材料。在碳质材料中，石墨因其较高的理论克容量(372mA·h/g)和环境友好等优势，广泛应用于二次电池中。在实际使用的产品中，石墨材料的克容量通常难以达到其理论克容量。现有的一些提高石墨材料克容量的方法往往会使电池的其它电化学性能受到影响。
因此，亟需提供一种具有高克容量且可以兼顾其它性能的材料。
发明内容
本申请的第一方面提供一种复合石墨材料，包括核材料和包覆在所述核材料表面至少一部分的包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，并且当将复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。本申请的复合石墨材料可以提高克容量和降低极片膨胀率，更优选地还可以改善电池的循环性能和/或动力学性能。
本申请的第二方面提供一种制备复合石墨材料的方法，包括以下步骤：
(1)将包括可环化的聚合物的溶液与石墨混合，得到浆料，其中所述石墨与所述可环化的聚合物的质量比为30:1～400:1；
(2)干燥所述浆料，得到粉末；
(3)在300～400℃的温度下对所述粉末进行热处理，得到所述复合石墨材料；
其中，所述复合石墨材料包括核材料和包覆在所述核材料表面至少一部分的包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，其中，当将所述复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。
本申请的第三方面提供一种二次电池，包括负极极片，所述负极极片包括负极活性材料，所述负极活性材料包括本申请第一方面所描述的复合石墨材料。
本申请的第四方面提供一种装置，所述装置包括本申请的第三方面所提供的二次电池。
采用本申请的具有环状结构片段的包覆层的复合石墨材料不仅改善了负极活性材料的克容量，而且降低了包含该复合石墨材料的负极极片的膨胀率；进一步地，在制成电池时还可以提高电池的动力学性能和/或循环性能。在本申请的第二方面的方法中，通过严格控制包覆层中聚合物的环化、炭化的程度，获得了具有上述优异性能的复合石墨材料。这是本领域技术人员无法预料到的。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是说明聚丙烯腈环化、部分炭化的示意性反应式。
图2是本申请实施例2与对比例1的复合石墨材料的拉曼谱图。
图3是本申请实施例2与对比例1的复合石墨材料的TG图。
图4是具有环状结构片段的聚合物材料的红外谱图。
图5是本申请实施例提供的一种二次电池的示意图。
图6是本申请实施例提供的一种电池模块的示意图。
图7是本申请实施例提供的一种电池包的示意图。
图8是图7的电池包的分解图。
图9是本申请实施例提供的一种装置的示意图。
图10a-10b是本申请实施例提供的复合石墨材料的SEM(scanning electron microscope，扫描电镜)图片。
图11是本申请实施例提供的一种复合石墨材料的结构示意图。
其中，附图标记说明如下：
1、电池包；
2、上箱体；
3、下箱体；
4、电池模块；
5、二次电池；
10、核材料；
20、包覆层。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
在组合物被描述为包括或包括特定组分的情况下，预计该组合物中并不排 除本发明未涉及的可选组分，并且预计该组合物可由所涉及的组分构成或组成，或者在方法被描述为包括或包括特定工艺步骤的情况下，预计该方法中并不排除本发明未涉及的可选工艺步骤，并且预计该方法可由所涉及的工艺步骤构成或组成。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包括在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包括本数，“一种或几种”中“几种”的含义是两种或两种以上。
术语“优选的”和“优选地”是指在某些情况下可提供某些益处的本发明实施方案。然而，在相同或其他情况下，其他实施方案也可能是优选的。另外，一个或多个优选的实施方案的叙述不意味着其他实施方案是不可用的，并且不旨在将其他实施方案排除在本发明范围外。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施方式提供了指导。这些实施方式可以以各种组合形式使用，并且组合后的实施方式应被认为是本文中公开的具体的实施方式或实例。在各个实例中，列举仅作为代表性组，不应解释为穷举。
包覆石墨材料
本申请的第一方面提供一种复合石墨材料，包括核材料和包覆在所述核材料表面至少一部分的包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，并且当将复合石墨材料在惰性非氧化性气体气氛中从 40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。
在一些优选的实施方式中，当将复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，复合石墨材料的失重率为0.1％-0.4％；更优选为0.1％-0.3％。发明人研究发现，当将所述复合石墨材料的失重率控制在所给范围内时，复合石墨材料具有更高的克容量的同时，电池也具有更优的循环性能和抗膨胀性能。如果复合石墨材料失重率小于0.1％，则包覆层在石墨核材料表面的包覆完整度大幅降低，从而使得一方面包覆层本身起到的提升材料克容量的效果降低；另一方面包覆层与粘结剂之间的作用减弱，使得极片粘结力和内聚力偏低，循环过程中极片的膨胀率变大。所述复合石墨材料失重率大于0.55％，会导致材料在循环过程中过多的消耗活性离子，使电芯的循环性能变差；同时活性离子消耗越多，复合材料表面副反应层越厚，也会导致极片膨胀变大。
在一些实施方式中，所述惰性非氧化性气体可以选自氮气、二氧化碳、氨气、氦气、氩气中的一种或几种。在一些优选的实施方式中，可以采用氮气作为惰性非氧化性气体。
在本申请的基础上，本领域技术人员能够合理地确定失重过程中的加热速率。例如，失重过程的加热速率可以为10℃/min或更低，优选地5℃/min或更低的速率。在一个示例性实施方式中，失重率是在惰性非氧化性气体(例如，氮气)气氛中以10℃/min的速率从40℃至800℃过程中测定的。
在本申请的复合石墨材料中，核材料表面至少一部分被包覆层包覆。在一些优选的实施方式中，复合石墨材料包括核材料和包覆在所述核材料表面至少80％的包覆层。更优选地，复合石墨材料包括核材料和包覆在所述核材料表面至少90％的包覆层。在一些优选的实施方式中，复合石墨材料包括核材料和包覆在所述核材料表面的包覆层。
在一些实施方式中，包覆层中包括具有氮杂环结构片段的包覆材料，且至少部分氮杂环结构上具有碳氮双键。这样，石墨材料的亲水性得到较大改善，在水系阳极浆料搅拌过程中，复合石墨在浆料中分散更稳定，与粘结剂的接触更均匀，极片的粘结力和内聚力因此提升，从而可以改善电池的循环膨胀性能。
具有上述结构片段的包覆层本身可以参与活性离子脱嵌，且提供更多的活性离子脱嵌通道，为石墨材料提供除核以外的额外容量，从而提高其克容量。这是本领域技术人员所预料不到的，因为一般来说，在石墨材料表面涂布其他 包覆层(如无定形碳包覆层、常规聚合物包覆层)会导致材料有效活性物质的减少，从而降低材料的克容量。而且，考虑到随着石墨材料的克容量靠近理论值时进一步提高克容量的难度，本申请的包覆改性对石墨材料的克容量的提升表现出更重要的意义和技术进步。
另外，由于具有上述结构片段的包覆层提供了更多适于活性离子脱嵌的通道，提高了材料的活性离子传输效率。并且，该包覆层还具有良好的电子传导性。因此，该石墨材料具有较好的动力学特性，使采用其的电池的动力学性能和循环性能得到提高。
氮杂环结构片段可以是稠环或非稠环。在一些优选的实施例中，氮杂环结构片段包括氮杂稠环结构片段，所述氮杂稠环结构片段中至少部分的氮杂环上具有碳氮双键。
在一些实施例中，氮杂环上还具有碳碳双键。该包覆层的导电性得到进一步改善。
在一些实施例中，氮杂环为五元环或六元环。这样，包覆层具有较高的弹性和韧性，能更好地适应核反复脱/嵌锂的膨胀和收缩，隔绝材料表面与电解液的接触，减少材料由于电解液侵蚀造成的容量损失，从而能提高电池的循环性能。
在一些实施例中，氮杂环结构片段可以包括含吡啶环、咪唑环、喹啉环、嘧啶环中的一种或几种。优选地，氮杂环结构片段包括式1～式3中的一种或几种氮杂稠环结构片段。优选地，氮杂环结构片段包括式1～式3中的至少两种的组合。更优选地，氮杂环结构片段包括式1～式3中的三种的组合。
Figure PCTCN2019122743-appb-000001
Figure PCTCN2019122743-appb-000002
在一些实施方式中，复合石墨材料的核材料可以选自人造石墨及天然石墨中的一种或几种。
在一些优选的实施方式中，当核材料选自人造石墨时，复合石墨材料还满足下述参数中的一个或几个时，可以进一步改善材料的性能。
在一些实施方式中，复合石墨材料的D峰强度I D与G峰强度I G的比值I D/I G为0.4～1.0。D峰和G峰是石墨材料的拉曼(Raman)特征峰。D峰和G峰的强度可以使用激光拉曼光谱测得，例如采用LabRAM HR Evolution型拉曼光谱仪。在通过拉曼光谱仪测得的拉曼光谱图中，D峰是在1300cm -1～1400cm -1的位置，G峰是在1550cm -1至1620cm -1的位置。
在一些实施方式中，复合石墨材料的I D/I G为0.4～1.0。例如，复合石墨材料的I D/I G可以为0.4～0.95，0.45～0.9，0.5～0.8。当本申请的复合石墨材料的I D/I G在所给范围内时，可以进一步提高材料表面的稳定性，进而能进一步降低负极极片在电池循环过程中的体积膨胀。优选地，复合石墨材料的I D/I G为0.5～0.8。
在一些实施方式中，当复合石墨材料在压实密度(PD)为1.6g/cm 3～1.7g/cm 3的极片中时，在极片中复合石墨材料的取向指数OI值≤15，优选为8～12。
当复合石墨材料在特定压实密度的极片中时OI值在所给范围内，复合石墨材料具有较高的各向同性度，由此在电池循环过程中复合石墨材料在极片中的膨胀被分散到各个方向，从而能进一步降低极片在循环过程的膨胀。
在本申请中，定义复合石墨材料的取向指数OI值＝C 004/C 110。其中，所述复合石墨材料在X射线衍射分析中，归属于(004)晶面的衍射峰的峰面积为C 004，归属于(110)晶面的衍射峰的峰面积为C 110。
X射线衍射分析可以参考标准JISK 0131-1996，使用X射线衍射仪(例如 Bruker D8 Discover型X射线衍射仪)进行测试。X射线衍射分析可以参考标准JISK 0131-1996，使用X射线衍射仪(例如Bruker D8 Discover型X射线衍射仪)进行测试。在X射线衍射分析测试中可以采用铜靶作为阳极靶，使用厚度为0.02mm的Ni滤波片过滤CuK β，以CuK α射线为辐射源，射线波长
Figure PCTCN2019122743-appb-000003
(取K α1和K α2的加权平均值)，扫描2θ角范围为20°～80°，扫描速率为4°/min。
用于测试上述复合石墨材料的取向指数OI的极片的示例性制备方法如下：
将本申请的复合石墨材料与粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)、导电剂导电炭黑(Super P)按照质量比96.2:1.8:1.2:0.8分散于溶剂去离子水中，混合均匀制备成浆料；将浆料均匀涂覆在铜箔集流体上，涂覆的面密度可以为10mg/cm 2～11mg/cm 2(例如10.5mg/cm 2)，极片烘干后使用冷压机冷压，冷压后的压实密度为1.6g/cm 3～1.7g/cm 3(例如1.65g/cm 3)。将制备好的极片置于X射线衍射仪中，通过X射线衍射分析法得到极片中复合石墨材料的(004)晶面衍射峰的峰面积C 004以及(110)晶面衍射峰的峰面积C 110，复合石墨材料的取向指数OI值＝C 004/C 110。
在一些实施方式中，复合石墨材料的Dv50为15μm～20μm，优选为15μm～18μm。
复合石墨材料的D v50适于使其具有较高的活性离子和电子传输性能的同时，还能减少电解液在负极的副反应。具有适当体积平均粒径D v50的复合石墨材料还有利于提升自身的粉体压实密度。
在一些实施方式中，复合石墨材料的体积平均粒径D v10≥6μm。例如，复合石墨材料的D v10可以为6μm以上，6.5μm以上，7μm以上，7.5μm以上。采用该人造石墨，活性比表面积较小，能使二次电池中的副反应能得到进一步减少。进一步地，人造石墨的D v10可以为11μm以下，10.5μm以下，10μm以下，9.5μm以下，9μm以下。优选地，6.5μm≤D v10≤10.5μm。
在一些实施方式中，复合石墨材料的Dn10为1.0μm～3.0μm，优选为1.2～2.0μm，更优选为1.3μm～1.8μm。例如，复合石墨材料的Dn10可以为约1.3μm、1.4μm、1.5μm、1.6μm、1.7μm或1.8μm。
复合石墨材料的D n10适当，则其与电解液之间的副反应较少。且该复合石墨材料制备的负极极片中，复合石墨材料与粘结剂等添加剂之间能均匀分散，极片整体粘结力较高。因此，电池的循环性能和抗膨胀性能得到进一步降低。 尤其是，复合石墨材料的D n10适当，还能使其自身具有较高的克容量。
在本申请中，所述复合石墨材料的D n10、D v10、D v50可以参照标准GB/T 19077.1-2016，使用激光粒度分析仪(如Malvern Master Size 3000)测定。
其中，D n10、D v10、D v50的物理定义如下：
D n10：材料累计数量分布百分数达到10％时所对应的粒径；
D v10：材料累计体积分布百分数达到10％时所对应的粒径；
D v50：材料累计体积分布百分数达到50％时所对应的粒径。
在一些实施方式中，复合石墨材料的比表面积(SSA)为0.5m 2/g～1.3m 2/g，优选为0.6m 2/g～1.0m 2/g。
复合石墨材料具有适当的比表面积，能减少电解液在其表面的副反应，降低产气量，从而能降低二次电池在循环过程中的体积膨胀。同时，该复合石墨材料能具有较高的电化学反应活性，从而使二次电池具有较高的动力学性能，这有利于满足装置的功率需求。此外，适当的比表面积还能使复合石墨材料与粘结剂之间具有较强的结合力，由此能提高极片的内聚力和粘结力，从而进一步降低极片的循环膨胀。
比表面积可以采用本领域已知的方法测试。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
在一些实施方式中，复合石墨材料在5吨的压力下测得的压实密度为1.80g/cm 3～2.10g/cm 3，优选地1.93g/cm 3～2.05g/cm 3。通过采用上述实施方式的压实密度，能使复合石墨材料自身具有较高的克容量。采用该复合石墨材料的负极极片也具有较高的压实密度，使得电池具有较高的能量密度。
粉体压实密度可以采用本领域已知的方法测试。例如可参照GB/T 24533-2009，使用电子压力试验机(如UTM7305)测试：将一定量的粉末放于压实专用模具上，设置不同压力，在设备上可以读出不同压力下粉末的厚度，计算可得不同压力下的压实密度。
在一些实施方式中，复合石墨材料的振实密度为0.8g/cm 3～1.15g/cm 3，优选地0.9g/cm 3～1.05g/cm 3。通过采用上述实施方式的振实密度的复合石墨材料，负极极片可以具有合适的孔隙率，保证极片具有较好的电解液浸润性能，以便 使电池具有较高的循环性能。此外，复合石墨材料的振实密度有利于使其获得较高的克容量。采用该复合石墨材料的负极极片的压实密度也较高，从而能提升电池的能量密度。
复合石墨材料的振实密度可以采用本领域已知的方法测试。例如可参照标准GB/T 5162-2006，使用粉体振实密度测试仪(如丹东百特BT-301)测试。
在一些实施方式中，复合石墨材料的硫含量小于0.02wt％。包覆层中存在硫可能影响上述结构片段的稳定性，使得难以控制包覆层中聚合物的环化和炭化程度。硫含量可以通过元素分析方法来测定。
本申请的复合石墨材料可以通过本申请第二方面的方法来制备。因此，本申请也记载了通过本申请第二方面的方法获得的复合石墨材料。
制备复合石墨材料的方法
本申请的第二方面提供一种制备复合石墨材料的方法，其特征在于，包括以下步骤：
(1)将包括可环化的聚合物的溶液与石墨核材料混合，得到浆料，其中所述石墨核材料与所述可环化的聚合物的质量比为30:1～400:1；
(2)干燥所述浆料，得到粉末；
(3)在300～400℃的温度下对所述粉末进行热处理，得到所述复合石墨材料。
所述复合石墨材料包括核材料和包覆在所述核材料表面至少一部分的包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料。当将复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。
包覆层可以具有上文中所讨论的结构。图4示出了聚合物材料经过上述干燥和热处理后获得的红外谱图。在图4中可以明显观察到环状结构片段中碳氮双键和碳碳双键的吸收峰。
在一些优选的实施方式中，包覆层包括具有
Figure PCTCN2019122743-appb-000004
环状结构片段的包覆材料。包覆层的具体示例包括具有下式中的一种或多种结构片段的包覆材料：
Figure PCTCN2019122743-appb-000005
优选地，包覆层具有至少两种上述结构片段。更优选地，包覆层具有至少两种上述结构片段。甚至更优选地，包覆层具有上述结构片段的组合。
步骤(1)中的石墨核材料可以通过商购获得。
可以通过调节聚合物的添加量来控制复合石墨中包覆层的含量。通过调节热处理步骤的温度和时间，来控制聚合物的环化和炭化的程度。通过大量实验，本申请的发明人研究发现了较优选的原料的量、热处理步骤的温度和时间。调节包覆层的含量在一定的范围的优点如前文所讨论，在此不作赘述。
在一些优选的实施方式中，石墨与可环化的聚合物的质量比m G:m P为40:1～200:1，更优选50:1～150:1。例如，石墨与可环化的聚合物的质量比m G:m P可以为70:1～120:1，更优选地80:1～110:1。在一些示例性实施方式中，石墨与可环化的聚合物的质量比m G:m P为100:1。
在一些优选的实施方式中，在步骤(1)中，可环化的聚合物包括聚丙烯腈(PAN)或其共聚物。优选地，可环化的聚合物包括聚丙烯腈或丙烯腈与烯烃类的共聚物。更优选地，可环化的聚合物包括聚丙烯腈或丙烯腈与丙烯酸类、丙烯酰胺类、衣康酸单体的共聚物。例如，可环化的聚合物包括聚丙烯腈或者丙烯腈与衣康酸(IA)、醋酸乙烯酯(Vac)、丙烯酸(AA)、丙烯酸甲酯(MA)和丙烯酰胺(AM)中的一种或几种的共聚物。尤其优选地，可环化的聚合物是或包括聚丙烯腈。
在一些实施方式中，可环化的聚合物的数均分子量为50000～150000Da，优选地80000～120000Da。
在一些实施方式中，在步骤(1)中，所述包括可环化的聚合物的溶液可以包括水、N-二甲基甲酰胺、N,N-二甲基乙酰胺、N-甲基吡咯烷酮和二甲基亚砜中的一种或几种。更优选地，所述包括可环化的聚合物的溶液可以是或者包括N-二甲基甲酰胺。
步骤(1)中的所述包括可环化的聚合物的溶液可以通过本领域中已知的方 法获得。例如，可以通过将可环化的聚合物溶解于溶剂中并搅拌至溶解，来获得包括可环化的聚合物的溶液。
可以采用本领域中已知的方法来使包含可环化的聚合物的浆料干燥。例如，干燥的方式包括但不限于喷雾干燥、闪蒸、旋转蒸发、冷冻干燥等。在一些实施方式中，在步骤(2)中，采用喷雾干燥。干燥的温度可以根据溶液或浆料所使用的溶剂来调整。优选地，在步骤(2)中，干燥是在180～210℃下进行的喷雾干燥。更优选地，干燥是在190℃～205℃下进行的喷雾干燥。
在一些实施方式中，步骤(3)中，热处理在惰性非氧化性气体中进行。惰性非氧化性气体的示例包括但不限于氮气、二氧化碳、氨气和惰性气体(例如，氦气、氩气)，以及它们的组合。在一些优选的实施方式中，可以采用氮气作为惰性非氧化性气体。
在一些实施方式中，步骤(3)中，所述热处理是在350℃～400℃的温度下进行的。在可环化的聚合物(尤其聚丙烯腈)的热处理过程中，热处理的温度对聚合物的环化和炭化具有关键的影响。经大量研究发现，在200℃或更低的温度下进行热处理时，聚合物包覆层还未热裂解，仍处于聚合物状态，聚合物本身无克容量，因而包覆后的材料克容量降低。温度从300℃升到400℃，随着温度的升高，包覆层开始分解，材料的克容量增加，抗膨胀性能也达到最大限度的改善。随着温度进一步增加，例如在500℃或更高的温度下进行热处理时，聚合物分解后的包覆层本身的无序度降低，其无法改善极片的循环膨胀问题。因此，可以通过严格控制热处理的温度来调节聚合物环化和炭化程度。通过控制上述优选的热处理的温度，能够较好地控制可环化的聚合物(尤其聚丙烯腈)发生部分炭化，同时保持上文所讨论的环状结构片段。
在一些实施方式中，步骤(3)中，所述热处理的时间为3～6小时；优选地，所述热处理的时间为3.5～5小时。通过采用上述优选的热处理的时间，能够控制可环化的聚合物(尤其聚丙烯腈)的炭化过程，使得包覆层具有上文所讨论的环状结构片段。
在热处理过程中，可环化的聚合物(尤其聚丙烯腈)逐渐脱氢、并环化，形成环状结构，并释放NH 3、HCN等小分子。C≡N键逐渐消失，形成环状结构片段。图1中示出了聚丙烯腈环化、部分炭化的示意性反应式。一般来说，可以认为聚丙烯腈在220℃以下主要发生分子内环化(如图1(a)所示)，并在约 300℃下发生分子间环化(如图1(b)所示)。
当热处理温度达到约350℃、甚至达到400℃时，环状结构片段开始发生部分炭化，形成具有碳氮双键和碳碳双键的环状结构片段，或者具有
Figure PCTCN2019122743-appb-000006
的环状结构片段。而且，随着炭化的进行，形成具有下式中的一种或多种结构片段的包覆材料：
Figure PCTCN2019122743-appb-000007
Figure PCTCN2019122743-appb-000008
值得注意的是，炭化过程还影响复合石墨材料在惰性非氧化性气体气氛中从40℃至800℃过程中的失重率。如果炭化程度过高，使得大部分的环状结构片段分解，则获得的复合石墨材料的失重率显著降低。例如，当炭化过程在1000℃进行4小时，则获得的复合石墨材料在从40℃至800℃过程中的失重率极小，表明包覆层中的绝大部分(甚至几乎全部)可环化的聚合物转化成无定形碳，使得克容量降低并且电池的抗膨胀性能降低。如果炭化程度过低，使得可环化的聚合物(尤其聚丙烯腈)仍大量保持环状结构，而未发生足够的炭化分解，则获得的复合石墨材料在从40℃至800℃过程中的失重率升高，而且获得的复合石墨材料对电池的性能改善非常有限，例如电池的动力学性能不足，最大充电倍率降低或者出现轻微析锂。
在一些优选的实施方式中，步骤(1)中的石墨核材料也可以通过如下步骤制备获得：
S10、将生焦原料进行破碎，并分级处理。
S20、将步骤S10所得产物进行整形。
S30、对步骤S20所得产物进行造粒，其中，所述造粒过程加入的粘结剂用量不超过生焦原料总重量的5％。
S40、对步骤S30所得产物在2800℃～3200℃的温度下进行石墨化处理，得到所述石墨。
在上述制备方法中，所述石墨是人造石墨。
在上述制备方法中，在步骤S10，所述生焦原料可以选自生石油焦和生沥青焦中的一种或几种，优选地包括生石油焦。
优选地，所述生焦原料为非针状焦。所述非针状焦可以选自非针状生石油焦和非针状生沥青焦中的一种或几种。优选地，所述非针状焦包括非针状生石油焦。
在一些实施例中，在步骤S10，优选地，生焦原料的挥发分含量为6％～12％(重量百分含量)；优选地，生焦原料的挥发分含量为7％～10％。
生焦原料的挥发分含量适当，能使其在步骤S20的造粒过程中具有较高的自粘接性，提高石墨中一次颗粒之间的粘接强度，使人造石墨具有较高的结构强度及较高的克容量。
在一些实施例中，生焦原料的硫含量可以为2％以下，1.5％以下，1％以下，0.5％以下。生焦原料具有较低的硫含量，能防止后续工艺过程中较多的硫组分逸出而造成的石墨材料的比表面积增大。优选地，生焦原料的硫含量≤1％。
在一些实施例中，在步骤S20中还包括在整形之后去除细粉。通过去细粉处理以调控整形后前驱体的D n10在适当范围内，以便使所得人造石墨的D n10在所需范围内。
经大量研究发现，通过步骤S20中的整形后去细粉处理，有利于进一步提升人造石墨的克容量。
在步骤S30，优选地，所述造粒过程在不加入粘结剂的条件下进行。当粘结剂的用量控制在所给范围内时，可以进一步提升石墨的克容量；尤其是，在不存在粘结剂的条件下，利用生焦的自粘接性对其进行造粒，能提升人造石墨颗粒整体的结构强度。当所述人造石墨做为本申请石墨材料的核时，石墨材料的相应特性也因此得到改善。优选地，当生焦原料的挥发分含量在7％以上时，所述步骤S30可以在不加入粘结剂的条件下对步骤S20所得颗粒产物进行造粒。但生焦原料的挥发分含量不宜过高，否则会显著降低石墨的克容量以及影响其在后续使用过程中的加工性能。
进一步地，通过调控上述工艺条件还能使造粒所得产物的体积平均粒径D v50在所需范围内，或者使造粒所得产物的D v10、D v50和D v90均在所需范围内。
通过调控步骤S10和/或S30的粒径分布，能使最终的复合石墨材料的D v50、D v10在所需范围内。通过调控石墨的粒径分布在适当范围内，还有利于其获得适当的振实密度和粉体压实密度。
在一些优选的实施例中，步骤S40进行石墨化处理的温度为2900℃～3100℃。
二次电池
本申请的第三方面提供一种二次电池，包括负极极片，所述负极极片包括负极活性材料，其特征在于，所述负极活性材料包括本申请第一方面所述的复合石墨材料。
在一些实施方式中，所述负极极片包括负极集流体以及设置在负极集流体至少一个表面上且包括负极活性材料的负极膜片，所述负极活性材料包括本申请第一方面所述的复合石墨材料。
由于采用了本申请第一方面的复合石墨材料，本申请的二次电池具有较高的能量密度、优异的抗膨胀性能，进而使电池同时兼具较高的能量密度和较好的循环性能。
在一些实施方式中，负极集流体具有在其自身厚度方向相对的两个表面，负极膜片层合设置在负极集流体相对的两个表面的其中任意一者或两者上。负极集流体可以采用具有良好导电性及机械强度的材质。在一些实施方式中，负极集流体采用铜箔。
在一些实施方式中，负极膜片还可选的包括可用于二次电池负极的其他负极活性材料。其他负极活性材料可以是其他石墨材料、中间相微碳球(简写为MCMB)、硬碳及软碳中的一种或几种。
在一些实施方式中，负极膜片还包括粘结剂。作为示例，粘结剂可以选自聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚乙烯醇(PVA)、丁苯橡胶(SBR)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种或几种。
在一些实施方式中，负极膜片还可选地包括增稠剂。作为示例，增稠剂可以是羧甲基纤维素钠(CMC-Na)。
在一些实施方式中，负极膜片还可选地包括导电剂。作为示例，用于负极膜片的导电剂可以选自石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或几种。
二次电池还可以包括正极极片。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。在一些实施方式中，正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性材料的正极膜片。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜片层合设置在正极集流体相对的两个表面的其中任意一者或两者上。正极集流体可以采用具有良好导电性及机械强度的材质。在一些实施方式中，正极集流体可以采用为铝箔。
正极极片可以包括正极活性材料。本申请对正极活性材料的具体种类不做具体限制，可以采用本领域已知的能够用于二次电池正极的材料，本领域技术人员可以根据实际需求进行选择。
在一些实施方式中，正极活性材料可以选自锂过渡金属氧化物及其改性化合物中的一种或几种。改性化合物可以是对锂过渡金属氧化物进行掺杂改性和/或包覆改性。例如，锂过渡金属氧化物可选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及橄榄石结构的含锂磷酸盐中的一种或几种。优选地，所述正极活性材料包括锂镍钴锰氧化物、锂镍钴铝氧化物中的一种或几种。
作为示例，二次电池的正极活性材料可选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4(LFP)和LiMnPO 4中的一种或几种。
在一些实施方式中，正极膜片中还可选地包括粘结剂。对粘结剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极膜片的粘结剂可以包括聚偏氟乙烯(PVDF)和聚四氟乙烯(PTFE)中的一种或几种。
在一些实施方式中，正极膜片中还可选地包括导电剂。对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正 极膜片的导电剂可以包括石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或几种。
所述二次电池还包括电解质。电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以选自固态电解质及液态电解质(即电解液)中的至少一种。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可以选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的一种或几种。
在一些实施方式中，溶剂可以选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或几种。
在一些实施方式中，所述电解液中还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
采用电解液的二次电池、以及一些采用固态电解质的二次电池中，还包括隔离膜。隔离膜设置在正极极片和负极极片之间起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可以选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种或几种。隔离膜可以是单层薄膜，也可以是多层复合薄膜。隔离膜为多层复合薄膜时，各层的材料可以相同或不同。
本申请的一些实施方式还提供一种二次电池的制备方法，其中包括采用本申请任意一种或几种复合石墨材料制备负极极片的步骤。
在一些实施方式中，采用本申请的复合石墨材料制备负极极片的步骤可以包括：将包括本申请第一方面的复合石墨材料的负极活性材料与粘结剂、以及可选的增稠剂和导电剂分散于溶剂中，溶剂可以是去离子水，形成均匀的负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，得到负极极片。
二次电池的制备方法还可以包括制备正极极片的步骤。在一些实施方式中，可以将正极活性材料、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮，简称NMP)中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
二次电池的制备方法还包括将负极极片、正极极片和电解质组装形成二次电池的步骤。在一些实施方式中，可以将正极极片、隔离膜、负极极片按顺序卷绕或叠片，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯；将电芯置于外包装中，注入电解液并封口，得到本申请的二次电池。
在一些实施方式中，所述二次电池可以是锂离子二次电池。
在一些实施方式中，二次电池可以包括外包装和封装在外包装内的电芯。所述二次电池中电芯的数量可以为一个或几个，可以根据需求进行调节。
在一些实施例中，二次电池的外包装可以是软包(例如袋式，其材质可以是塑料，如聚丙烯PP、聚对苯二甲酸丁二醇酯PBT、聚丁二酸丁二醇酯PBS等中的一种或几种)，也可以是硬壳(例如铝壳等)。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图5是作为一个示例的方形结构的二次电池5。
在一些实施例中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可以根据电池模块的应用和容量进行调节。
图6示出了作为一个示例的电池模块4。参照图6，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的壳体，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图7和图8示出了作为一个示例的电池包1。参照图7和图8，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
装置
本申请的第四方面提供一种装置。该装置包括本申请第三方面的二次电池。所述二次电池可以用作装置的电源或储能装置。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图9是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
本申请下述实施例中使用的核材料可通过商购获得，也可以按照如下制备 方法获得：
(1)人造石墨A的制备：使用非针状生石油焦作为原料(挥发份约为9.5％，硫含量约为0.5％)，破碎后进行分级处理；对破碎后所得颗粒产物进行整形；将整形后所得颗粒产物加入造粒机的反应釜中，在不加入粘结剂的条件下对生石油焦原料进行造粒处理；然后在约3000℃的温度下进行石墨化处理，得到人造石墨A。
(2)人造石墨B的制备：使用针状熟石油焦作为原料，破碎后进行分级处理；以沥青为粘结剂进行造粒，沥青的用量占原料总重量的8％；然后在约2900℃的温度下进行石墨化处理，得到人造石墨B。
实施例1
复合石墨材料的制备
1)提供包括可环化的聚合物的溶液：将聚丙烯腈溶于溶剂N-二甲基甲酰胺中，搅拌至聚合物全部溶解；
2)将人造石墨A加入步骤1所得聚合物溶液中，搅拌混合均匀，得到混合浆料；
3)将步骤2所得混合浆料采用蠕动泵转移至喷雾干燥设备中，在氮气气氛中进行干燥处理，得到干燥粉料，其中蠕动泵转速为20rpm，并且喷雾干燥温度范围为190℃；
4)将步骤3所得干燥粉料在氮气气氛中进行热处理，热处理的温度为400℃，热处理的时间为4h，得到复合石墨材料。
负极极片的制备
将上述制备的复合石墨材料、导电剂Super P、粘结剂丁苯橡胶(SBR)、增稠剂CMC-Na按96.2:0.8:1.8:1.2的质量比在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料；将负极浆料涂覆于负极集流体铜箔的表面上，经干燥、冷压后，得到负极极片。所述负极极片的压实密度为1.65g/cm 3，面密度为10.7mg/cm 2。
正极极片的制备
将正极活性材料LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、导电剂Super-P、粘接剂聚偏氟乙烯(PVDF)按重量比96:2:2溶于溶剂N-甲基吡咯烷酮(NMP)中混 合均匀制成正极浆料，之后将正极浆料均匀涂布在集流体铝箔上，经干燥、冷压后，得到正极极片。
电解液的制备
将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中得到电解液，其中LiPF 6的浓度为1mol/L。
隔离膜
采用聚乙烯(PE)薄膜。
二次电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，经卷绕后得到电芯，将电芯装入外包装中，加入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。
实施例2-11和对比例1-8
在实施例2-11和对比例1-8中，采用与实施例1类似的制备方法，不同之处详见表1中。
测试部分
(1)热失重(TG)
采用STA449F3型号的同步热分析仪测定各实施例及对比例中的负极活性材料。其中，气氛采用氮气，测试温度区间为40℃～800℃，升温速率10℃/min。记录在不同温度下测得的材料质量相对于初始材料质量的质量百分比。
(3)克容量
将制备的复合石墨材料、导电剂Super P、粘结剂(PVDF)按91.6:1.8:6.6的质量比与溶剂NMP(N-甲基吡咯烷酮)混合均匀，制成浆料将制备好的浆料涂覆于铜箔集流体上，于烘箱中干燥后备用；以金属锂片为对电极；采用聚乙烯(PE)薄膜做为隔离膜；将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中得到电解液，其中LiPF 6的浓度为1mol/L；在氩气保护的手套箱中将上述各部分组装成CR2430型扣式电池。
将所得扣式电池静置12小时后，以0.05C的电流进行恒流放电至0.005V，静置10分钟，以50μA的电流再进行恒流放电至0.005V，静置10分钟，以10μA的电流再进行恒流放电至0.005V；然后以0.1C的电流进行恒流充电至2V，记录充电容量。充电容量与复合石墨材料质量的比值即为所制备人造石墨的克容量。
可以使用蓝电电池测试系统LAND CT2001A对上述扣式电池进行测试，计算得到所述复合石墨材料的克容量。
(4)循环性能
在25℃下，将锂离子二次电池以1C的倍率恒流充电至4.3V，再恒压充电至电流小于等于0.05C，再以1C的倍率恒流放电至2.8V，此为一个充放电循环，此次的放电容量即为第1次循环的放电容量。将锂离子二次电池按照上述方法进行1400次充放电循环，记录第1400次循环的放电容量，计算锂离子二次电池1C/1C循环1400次后的容量保持率。
锂离子二次电池1C/1C循环1400次后的容量保持率(％)＝第1400次循环的放电容量/第1次循环的放电容量×100％。
(5)负极极片的膨胀率测试
将负极极片冷压后的厚度记为H 0。将冷压后的负极极片与正极极片、隔离膜、电解液制成二次电池。在25℃下，将二次电池在新威充放电机进行100％DOD(100％放电深度，也就是满充后再满放)的1C/1C循环。一次满充满放循环记为一圈，当循环至1400圈时，循环停止。然后将二次电池充电至100％SOC(State of Charge，荷电状态)，拆解二次电池并测试对应负极极片的厚度，记为H 1。则负极极片的循环膨胀率为：(H 1/H 0－1)×100％。
(6)动力学性能
在25℃下，将实施例和对比例制备得到的电池以x C满充、以1C满放重复10次后，再将电池以x C满充，然后拆解出负极极片，并观察负极极片表面析锂情况。如果负极表面未析锂，则将充电倍率x C以0.1C为梯度递增再次进行测试，直至负极表面析锂，停止测试，此时的充电倍率(x-0.1)C即为电池的最大充电倍率。
按照前文所述的测试方法对复合石墨材料的其他参数进行测试。
Figure PCTCN2019122743-appb-000009
将对比例1与实施例1-5进行比较以及将对比例2与实施例11进行比较，可以看出，通过在石墨表面包覆具有特定结构的包覆材料，可以同时显著改善克容量和抗膨胀性能。将对比例3-4与实施例1-5进行比较，可以看出，在相同的热处理条件下，通过控制石墨与可环化的聚合物的质量比，调节复合石墨材料的失重率，可以获得更高的克容量和优异的抗膨胀性能。在对比例4中，包覆过多时，包覆层对活性锂消耗过多，活性锂损失较多，循环变差。
将对比例7与实施例4进行比较，可以看出，与未进行炭化的聚合物包覆石墨材料相比，部分炭化的复合石墨材料能够显著改善克容量，并且显著改善电池的循环性能和抗膨胀性能。将对比例5与实施例4进行比较，可以看出，热处理温度达到1000℃时，炭化程度过高，包覆层中所期望的环状结构片段逐渐受到破坏，克容量降低，而且膨胀率明显升高。
将对比例1、8与实施例4进行比较，可以看出，与常规的包覆材料相比，采用聚丙烯腈作为可环化的聚合物时，克容量显著升高，而且抗膨胀性能得到有效改善。
除了上文所讨论的包覆材料和炭化程度对电池性能的影响外，发明人还惊奇地发现，当核材料采用人造石墨A时，明显降低了电池中极片的膨胀率，改善了电池的循环性能。这可以从实施例4与实施例11的比较中得到证实。
如图2所示，实施例2的复合石墨的D峰强度I D与G峰强度I G的比值I D/I G为0.82，在0.4～1.0范围内。对比例1的D峰强度I D与G峰强度I G的比值I D/I G为0.21，不在0.4～1.0范围内。其中，D峰是在1300cm -1～1400cm -1的位置，G峰是在1550cm -1至1620cm -1的位置。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (16)

  1. 一种复合石墨材料，包括核材料和包覆在所述核材料表面至少一部分的包覆层，其特征在于，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，其中，当将所述复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。
  2. 权利要求1所述的复合石墨材料，其特征在于，当将所述复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％-0.4％，优选为0.1％-0.3％。
  3. 权利要求1或2所述的复合石墨材料，其特征在于，所述环状结构片段具有碳氮双键和碳碳双键。
  4. 权利要求1-3中任一项所述的复合石墨材料，其特征在于，所述环状结构片段包括式1～式3中的一种或几种：
    Figure PCTCN2019122743-appb-100001
  5. 权利要求1-4任一项所述的复合石墨材料，其特征在于，所述核材料为人造石墨。
  6. 权利要求5所述的复合石墨材料，其特征在于，所述复合石墨材料的D 峰强度I D与G峰强度I G的比值I D/I G为0.4～1.0，优选0.5～0.8。
  7. 权利要求5-6中任一项所述的复合石墨材料，其特征在于，所述复合石墨材料满足：当所述复合石墨材料在压实密度为1.6g/cm 3～1.7g/cm 3的极片中时，所述复合石墨材料的(004)晶面的峰面积C 004与(110)晶面的峰面积C 110之比C 004/C 110≤15，优选为8≤C 004/C 110≤12。
  8. 权利要求5-7中任一项所述的复合石墨材料，其特征在于，所述复合石墨材料还满足以下(1)–(6)中的一种或几种：
    (1)所述复合石墨材料的Dv50为15μm～20μm，优选地15μm～18μm；
    (2)所述复合石墨材料的Dv10≥6μm，优选为6.5μm≤D v10≤10.5μm；
    (3)所述复合石墨材料的Dn10为1.0μm～3.0μm，优选地1.2μm～2.0μm；
    (4)所述复合石墨材料的比表面积为0.5m 2/g～1.2m 2/g，优选地0.6m 2/g～1.0m 2/g；
    (5)在5吨的压力下测得的压实密度为1.80g/cm 3～2.10g/cm 3，优选地1.93g/cm 3～2.05g/cm 3；以及
    (6)所述复合石墨材料的振实密度为0.8g/cm 3～1.15g/cm 3，优选地0.9g/cm 3～1.05g/cm 3。
  9. 权利要求1-8中任一项所述的复合石墨材料，其特征在于，所述复合石墨材料的硫含量小于0.02wt％。
  10. 一种制备复合石墨材料的方法，其特征在于，包括以下步骤：
    (1)将包括可环化的聚合物的溶液与石墨核材料混合，得到浆料，其中所述石墨核材料与所述可环化的聚合物的质量比为30:1～400:1；
    (2)干燥所述浆料，得到粉末；
    (3)在300～400℃的温度下对所述粉末进行热处理，得到所述复合石墨材料；
    其中所述复合石墨材料包括核材料和包覆在所述核材料表面至少一部分的 包覆层，所述核材料包括石墨，所述包覆层包括具有环状结构片段的包覆材料，其中，当将所述复合石墨材料在惰性非氧化性气体气氛中从40℃升温至800℃时，所述复合石墨材料的失重率为0.1％～0.55％。
  11. 权利要求10所述的方法，其特征在于，所述石墨核材料与所述可环化的聚合物的质量比m G:m P为40:1～200:1，优选为50:1～150:1。
  12. 权利要求10-11中任一项所述的方法，其特征在于，所述可环化的聚合物包括聚丙烯腈或其共聚物中的一种或几种；优选地，所述可环化的聚合物包括聚丙烯腈。
  13. 权利要求10-12中任一项所述的方法，其特征在于，所述可环化的聚合物的数均分子量为50000～150000Da，优选地80000～120000Da。
  14. 权利要求10所述的方法，其特征在于，步骤(3)中，在350～400℃的温度下对所述粉末进行热处理；和/或，
    所述热处理的时间为3～6小时，优选为3.5～5小时。
  15. 一种二次电池，包括负极极片，所述负极极片包括负极活性材料，其特征在于，所述负极活性材料包括权利要求1-9中任一项所述的复合石墨材料。
  16. 一种装置，其特征在于，所述装置包括权利要求15所述的二次电池。
PCT/CN2019/122743 2019-12-03 2019-12-03 复合石墨材料及其制备方法、二次电池和装置 WO2021108996A1 (zh)

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