WO2021217323A1 - 一种负极复合材料及其应用 - Google Patents

一种负极复合材料及其应用 Download PDF

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WO2021217323A1
WO2021217323A1 PCT/CN2020/087168 CN2020087168W WO2021217323A1 WO 2021217323 A1 WO2021217323 A1 WO 2021217323A1 CN 2020087168 W CN2020087168 W CN 2020087168W WO 2021217323 A1 WO2021217323 A1 WO 2021217323A1
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composite material
negative electrode
electrode composite
5ppm
ppm
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PCT/CN2020/087168
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English (en)
French (fr)
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易婷
陈志焕
崔航
谢远森
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宁德新能源科技有限公司
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Priority to JP2022562542A priority Critical patent/JP7480340B2/ja
Priority to PCT/CN2020/087168 priority patent/WO2021217323A1/zh
Publication of WO2021217323A1 publication Critical patent/WO2021217323A1/zh
Priority to US17/974,775 priority patent/US20230062442A1/en

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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
    • 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
    • H01M4/13—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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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
    • 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 technical field of lithium-ion batteries, in particular to a negative electrode composite material and its application.
  • Lithium-ion batteries have the characteristics of large specific energy, high working voltage, low self-discharge rate, small size, light weight, etc., and have a wide range of applications in the field of consumer electronics. With the rapid development of electric vehicles and portable electronic equipment, people have higher and higher requirements for the energy density, safety, and cycle performance of lithium-ion batteries. Among them, silicon material has a high theoretical gram capacity (4200mAh/g), and its application in lithium-ion batteries has broad prospects. With the insertion and extraction of lithium ions, silicon-based materials will change in volume by 120% to 300%, causing silicon-based materials to pulverize and separate from the current collector. These problems will reduce the cycle performance of lithium-ion batteries and hinder silicon-based materials. Further applications of anode materials.
  • the main methods to solve the large volume change during the cycle of silicon-based materials include designing porous silicon-based materials and reducing the size of silicon-based materials.
  • the expansion problem can be improved to a certain extent, but as the cycle progresses, side reactions occur and uncontrollable SEI (Solid Electrolyte Interphase) )
  • SEI Solid Electrolyte Interphase
  • the purpose of this application is to provide a silicon-based negative electrode composite material and its application, so as to at least improve the cycle stability of the lithium ion battery and reduce the volume expansion of the lithium ion battery.
  • the first aspect of the present application provides a negative electrode composite material, which includes a Si-MC composite material and graphene present on the surface thereof, wherein M includes at least one of boron, nitrogen or oxygen, and the Si-MC composite material is tested by solid-state nuclear magnetic resonance.
  • the chemical shifts of silicon in MC composite materials include -5ppm ⁇ 5ppm, -35ppm ⁇ 5ppm, -75ppm ⁇ 5ppm, -110ppm ⁇ 5ppm, and the half-width K at -5ppm ⁇ 5ppm satisfies: 7ppm ⁇ K ⁇ 28ppm.
  • the mass of the graphene accounts for 1% to 20% of the mass of the negative electrode composite material.
  • the Dv50 of the Si-M-C composite material is 3.0 ⁇ m to 8.0 ⁇ m.
  • the Dv50 of the negative electrode composite material is 6.0 ⁇ m to 15.0 ⁇ m.
  • the Raman test of the negative electrode composite material satisfies a peak intensity ratio of 0 ⁇ I 1350 /I 1580 ⁇ 1.
  • the specific surface area of the negative electrode composite material is 0.5 m 2 /g to 8 m 2 /g.
  • the electrical conductivity of the negative electrode composite material is 2.0 S/cm to 30 S/cm.
  • the second aspect of the present application provides a negative electrode sheet, which includes a mixture layer containing the negative electrode composite material provided in the first aspect of the present application.
  • the resistance of the mixture layer is 0.02 ⁇ to 0.1 ⁇ .
  • the third aspect of the present application provides an electrochemical device, including the negative pole piece provided in the second aspect of the present application.
  • the fourth aspect of the present application provides an electronic device, including the electrochemical device provided in the third aspect of the present application.
  • the Si-MC composite material has a lower expansion rate, and graphene exists on the surface of the Si-MC composite material, which improves the conductivity of the negative electrode composite material.
  • the device has good cycle performance.
  • Dv50 means the particle size at which the cumulative distribution of particles is 50%; that is, the volume content of particles smaller than this size accounts for 50% of all particles.
  • the particle size is measured with a laser particle size analyzer.
  • FIG. 1 is a solid-state nuclear magnetic resonance spectrum chart of the Si-M-C composite material of Example 7.
  • Figure 2 is the capacity decay curve of Example 7 and Comparative Example 1.
  • the first aspect of the present application provides a negative electrode composite material, which includes a Si-MC composite material and graphene present on the surface thereof, wherein M includes at least one of boron, nitrogen or oxygen, and the Si-MC composite material is tested by solid-state nuclear magnetic resonance.
  • the chemical shifts of silicon in MC composite materials include -5ppm ⁇ 5ppm, -35ppm ⁇ 5ppm, -75ppm ⁇ 5ppm, -110ppm ⁇ 5ppm, and the half-width K at -5ppm ⁇ 5ppm satisfies: 7ppm ⁇ K ⁇ 28ppm.
  • the inventor of the present application unexpectedly discovered in the research that the Si-MC composite material of the present application, compared with some existing composite materials such as carbon, silicon and oxygen, uses solid-state nuclear magnetic resonance to test the chemical shift of the silicon element, which contains -5ppm ⁇ 5ppm. More unexpectedly, the inventor found that when the half-width K at -5ppm ⁇ 5ppm satisfies: 7ppm ⁇ K ⁇ 28ppm; the Si-MC composite material has a lower expansion rate.
  • Si-MC composite material and graphene present on its surface in this application can be understood as the presence of graphene on part of the surface of the Si-MC composite material, or the presence of graphene on the entire surface. There is no specific restriction.
  • the mass of the graphene accounts for 1% to 20% of the mass of the negative electrode composite material.
  • the inventor also discovered in research that the presence of graphene can increase the conductivity of the negative electrode composite material and improve its electrical performance; however, as the graphene content increases, the first efficiency of the full battery decreases and the expansion increases. Not limited to any theory, this may be because, on the one hand, the presence of graphene increases the specific surface area of the negative electrode composite material, resulting in a larger contact area with the electrolyte, forming more solid electrolyte interfaces (SEI), and producing more solid electrolyte interfaces (SEI). Many by-products; on the other hand, the increase in conductivity causes the depth of lithium insertion to increase, so the cycle expansion increases.
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • SEI solid electrolyte interfaces
  • the Dv50 of the Si-M-C composite material is 3.0 ⁇ m to 8.0 ⁇ m.
  • the Dv50 of the negative electrode composite material is 6.0 ⁇ m to 15.0 ⁇ m.
  • the inventor found that when the particle size of the negative electrode composite material is too small, its specific surface area is large, the contact area with the electrolyte is large, the lithium source is consumed more, and the first time efficiency is low; It will cause the negative electrode to locally expand too much, which will eventually affect the cycle stability.
  • the Raman test of the negative electrode composite material satisfies a peak intensity ratio of 0 ⁇ I 1350 /I 1580 ⁇ 1.
  • I 1350 represents the defects of carbon in the material.
  • the specific surface area of the negative electrode composite material is 0.5 m 2 /g to 8 m 2 /g.
  • the electrical conductivity of the negative electrode composite material is 2.0 S/cm to 30 S/cm.
  • the negative electrode composite material of the present application can be prepared by the following methods:
  • step 2) The product obtained in step 1) is cracked at a high temperature at 900°C to 1500°C under the protection of an inert gas to obtain a Si-M-C composite material;
  • the carbon source can be selected from at least one of glucose or sucrose;
  • the organic solvent can be selected from organic solvents commonly used in the art, and this application is not limited herein, for example, it can be selected from xylene, acetone, and cyclohexyl alcohol.
  • the organosilicon may be selected from one or more of polysiloxane, polysilazane, polycarborane methylsiloxane, and polysilazaborazane.
  • the heating and stirring in step 1) is a common technical means in the field, and its purpose is to remove the organic solvent therein. For example, it can be stirred at 60°C to 100°C, which is not limited in this application.
  • the drying in step 1) is a common technical means in the art. For example, it can be dried in a drying oven at 60°C to 100°C for 20 to 30 hours, and the application is not limited herein.
  • the inert gas in step 2) can be selected from nitrogen or argon, which is a protective gas commonly used in the art, and is not limited in this application.
  • step 2) high-temperature cracking is performed at 900°C to 1500°C.
  • the reaction conditions may be: heating up to 500°C at 1°C/min, holding for 30 minutes, and then heating up to 900°C to 1500°C at 3°C/min, Keep it for 3h.
  • the inventor unexpectedly discovered in the research that the high temperature pyrolysis reaction temperature affects the performance of the Si-MC composite material.
  • the temperature is less than 900°C, I 1350 /I 1580 >1, and the Si-MC composite material has many surface defects, which leads to the deterioration of the first-time coulombic efficiency and cycle performance of the whole battery, and the increase of cycle expansion.
  • step 4 before spray drying and granulation, deionized water can be added to the mixed slurry to adjust the viscosity and solid content of the mixed slurry.
  • the application does not limit the spray drying and granulation equipment, as long as the purpose of the application can be achieved.
  • the small spray drying equipment QM-1500-A of Shanghai Oumeng or the super large spray drying equipment of Wuxi Fu can be used.
  • the second aspect of the present application provides a negative electrode sheet, which includes a mixture layer containing the negative electrode composite material provided in the first aspect of the present application.
  • the negative pole piece may further include a current collector, and the mixture layer may be coated on one or both surfaces of the current collector.
  • the current collector is not particularly limited, and any current collector known to those skilled in the art can be used. Specifically, for example, a current collector formed of at least one of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, and the like can be used. Among them, as the negative electrode current collector, copper foil or copper alloy foil is particularly preferred. The above-mentioned materials may be used singly or in combination of two or more in any ratio.
  • the mixture layer further includes graphite, and the graphite may be selected from one or more of natural graphite, artificial graphite, mesophase carbon microspheres, etc., in some embodiments of the present application ,
  • the mixture of the negative electrode composite material of the present application and graphite is used as the negative electrode active material.
  • the mixture layer may further include an adhesive.
  • the adhesive is not particularly limited, and can be any adhesive or combination known to those skilled in the art.
  • binders may be used alone or in combination of two or more in any ratio.
  • the mixture layer may further include a conductive agent.
  • the conductive agent is not particularly limited, and may be any conductive agent known to those skilled in the art or a combination thereof.
  • at least one of a zero-dimensional conductive agent, a one-dimensional conductive agent, and a two-dimensional conductive agent may be used.
  • the conductive agent may include at least one of carbon black, conductive graphite, carbon fiber, carbon nanotube, VGCF (Vapour Grown Carbon Fiber) or graphene.
  • the amount of the conductive agent is not particularly limited, and can be selected according to common knowledge in the art.
  • the above-mentioned conductive agent may be used alone or in combination of two or more in any ratio.
  • the resistance of the mixture layer is 0.02 ⁇ to 0.1 ⁇ .
  • the third aspect of the present application provides an electrochemical device, including the negative pole piece provided in the second aspect of the present application.
  • the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.
  • a typical electrochemical device is a lithium ion battery, which is a secondary battery.
  • Electrochemical devices, such as lithium-ion batteries, generally include a negative pole piece, a positive pole piece, a separator, and an electrolyte.
  • the electrochemical device may be a lithium ion battery provided in the present application.
  • the negative pole piece of the electrochemical device adopts the negative pole piece provided in this application; and other components, including the positive pole piece, separator, electrolyte, etc., are not particularly limited.
  • the positive electrode material contained in the positive pole piece may include, but is not limited to, lithium cobaltate, lithium manganate, lithium iron phosphate, and the like.
  • the material of the diaphragm may include, but is not limited to, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof.
  • the electrolyte generally includes organic solvents, lithium salts and additives.
  • Organic solvents may include, but are not limited to, carbon ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate , At least one of ethyl propionate.
  • the lithium salt may include at least one of an organic lithium salt or an inorganic lithium salt; for example, the lithium salt may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), and double trifluorophosphate (LiPF6).
  • Lithium fluoromethanesulfonimide LiN(CF 3 SO 2 ) 2 LiTFSI
  • Lithium bisoxalate borate LiB(C 2 At least one of O 4 ) 2 LiBOB
  • lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) LiDFOB
  • a secondary battery can be manufactured by the following process: overlap the positive electrode and the negative electrode via spacers, and place them in the battery container after winding, folding and other operations as needed, and inject the electrolyte into the battery container and seal it.
  • the negative electrode used is The above-mentioned negative pole piece provided in this application.
  • an overcurrent prevention element, a guide plate, etc. can also be placed in the battery container as needed, so as to prevent the internal pressure of the battery from rising and overcharging and discharging.
  • the fourth aspect of the present application provides an electronic device, including the electrochemical device provided in the third aspect of the present application.
  • the 29 Si solid-state nuclear magnetic resonance spectrum test was performed on the AVANCE III 400 WB wide-cavity solid-state nuclear magnetic resonance instrument.
  • the rotation rate of 8kHz corresponds to 29 Si.
  • the solid-state nuclear magnetic resonance spectrum of the Si-MC composite material of Example 7 is shown in FIG. 1.
  • excitation light source is 532nm, scanning the wave number range of 0cm -1 ⁇ 4000cm -1, a test sample an area of 100 ⁇ m ⁇ 100 ⁇ m, worth to a final I 1350 / I 1580 value by counting 100 I 1350 / I 1580 .
  • the adsorption amount of the sample monolayer is calculated based on the Brownauer-Ett-Taylor adsorption theory and its formula (BET formula), thereby calculating The specific surface area of the solid.
  • the four-probe method is used to test the resistance of the negative electrode mixture layer.
  • the instrument used in the four-probe method is a precision DC voltage and current source (type SB118).
  • Four copper plates of 1.5cm long x 1cm wide x 2mm thick are fixed on a line at equal distances. , The distance between the two copper plates in the middle is L (1-2cm), and the base material for fixing the copper plates is an insulating material.
  • press the lower ends of the four copper plates on the mixture layer of the tested negative electrode (the pressure is 3000Kg), and hold for 60s.
  • the copper plates at both ends are connected with a DC current I.
  • the voltage V is measured on the two copper plates in the middle, and I is read three times. Take the average values of I and V, Ia and Va, respectively.
  • the value of Va/Ia is the resistance of the mixture layer at the test site. Take 12 points to test each pole piece, and take the average value.
  • the scanning electron microscope characterization was recorded by PhilipsXL-30 field emission scanning electron microscope, and the detection was performed under the conditions of 10kV and 10mA.
  • the negative electrode composite material obtained in each example or comparative example, conductive carbon black, and binder PAA were mixed with deionized water at a mass ratio of 80:10:10 to form a slurry with a solid content of 30%, and the mass was taken as M
  • the slurry is coated on copper foil, dried in a vacuum drying oven at 85°C for 12 hours, and then cut into a disc with a diameter of 1.4cm using a punching machine in a dry environment.
  • the metal lithium sheet is used as the pair in the glove box.
  • Electrode, isolation membrane choose ceglard composite membrane, add electrolyte to assemble button cell.
  • Use LAND series battery test system to charge and discharge the battery to test its charge and discharge performance.
  • the first efficiency test of the whole battery During the first charge and discharge of the whole battery, charge to 4.45V at a constant current of 0.5C, then charge to 0.025C at a constant voltage of 4.45V, (the obtained capacity is C0), after standing for 5 minutes, discharge at 0.5C To 3.0V (to get the discharge capacity D0).
  • the first efficiency of the whole battery D0/C0.
  • the test temperature is 45°C, and it is charged to 4.45V at a constant current of 0.5C, charged to 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes.
  • the capacity obtained in this step is the initial capacity, and the 0.5C charge/0.5C discharge is carried out for the cycle test, and the capacity at each step is used as the ratio of the initial capacity to obtain the capacity attenuation curve; among them, the capacity attenuation of Example 7 and Comparative Example 1
  • the curve is shown in Figure 2; the capacity retention rates of each example and comparative example after 400 cycles are shown in Table 1 and Table 2.
  • the negative electrode composite material prepared in each example and comparative example was mixed with graphite in a certain ratio to obtain a negative electrode active material powder with a designed mixing capacity of 500mAh/g.
  • the negative electrode active material powder, conductive agent acetylene black, and PAA were mixed in a weight ratio of 95 :1.2:3.8
  • After fully stirring and mixing in a deionized water solvent system coat it on the two surfaces of a copper foil current collector with a thickness of 10 ⁇ m, the coating thickness is 100 ⁇ m; the pole pieces are dried and cold pressed, double-sided
  • the compaction density is 1.8 g/cm 3 , and the negative pole piece is obtained.
  • the active material LiCoO 2 , conductive carbon black, and binder polyvinylidene fluoride (PVDF) are formulated into a slurry with a solid content of 0.75 in an N-methylpyrrolidone solvent system at a weight ratio of 96.7:1.7:1.6. Stir well.
  • the slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 ⁇ m, and the coating thickness was 115 ⁇ m, dried at 90° C., and cold pressed to obtain a positive pole piece.
  • a PE porous polymer film with a thickness of 15 ⁇ m is used as the separator.
  • the positive pole piece, the isolation film, and the negative pole piece are stacked in order, so that the isolation film is in the middle of the cathode and anode for isolation, and the electrode assembly is obtained by winding.
  • the mixed slurry is transferred to the centrifugal turntable nozzle of the spray drying granulator, and the centrifugal speed is 2000 rpm to form tiny droplets.
  • the spray drying granulator has an inlet temperature of 260°C and an outlet temperature of 105°C.
  • the powder is cooled and collected to obtain a negative electrode composite material with graphene on the surface, and the graphene content is 1%.
  • the dosage of glucose was adjusted to 20 g, and the rest was the same as in Example 7.
  • the amount of polydimethylsiloxane was adjusted to 10 g, and the rest was the same as in Example 16.
  • the Si-O-C composite material prepared in Example 7 is not compounded and granulated with graphene, but is directly used as a negative electrode composite material for the preparation of a negative electrode sheet, and the rest is the same as in Example 7.
  • the mixed slurry is transferred to the centrifugal turntable nozzle of the spray drying granulator, and the centrifugal speed is 2000 rpm to form tiny droplets.
  • the spray drying granulator has an inlet temperature of 260°C and an outlet temperature of 105°C.
  • the powder is cooled and collected to obtain a negative electrode composite material without graphene on the surface.
  • the negative electrode composite material and graphite in a certain ratio to obtain the negative electrode active material powder with a designed mixing capacity of 500mAh/g.
  • the negative electrode active material powder, the conductive agent acetylene black, and PAA are mixed in deionized water at a weight ratio of 95:1.2:3.8 Stir in the solvent system for 30 minutes and add the graphene slurry so that the mass of the graphene accounts for 5% of the total mass of the negative active material powder, conductive agent acetylene black, and PAA; add deionized water and stir until it is kneaded, and the thickness is coated
  • the two surfaces of the 10 ⁇ m copper foil current collector are coated with a thickness of 100 ⁇ m; the pole pieces are dried and then cold pressed, with a double-sided compaction density of 1.8 g/cm 3 , to obtain a negative pole piece.
  • Comparing each example with Comparative Example 1 shows that the negative electrode composite material with graphene on the surface has significantly improved conductivity, reduced resistance of the electrode mixture layer, and significantly improved full battery cycle performance.
  • the swelling rate of the battery increases with the The increase gradually increases; the inventor found that when the half-width of the shift peak at -5ppm ⁇ 5ppm of silicon in the solid nuclear magnetic test is between 7ppm-28ppm, the battery can have a higher cycle capacity retention rate and coulombic efficiency, and Low expansion rate.
  • the reaction temperature of high-temperature cracking affects the half-width of the shift peak at -5 ppm ⁇ 5 ppm, which is not limited to any theory.
  • the processing temperature has a greater effect on the degree of crystallization of the material. The higher the temperature, the higher the degree of crystallization of the material.
  • the half-width of the shift peak at -5ppm ⁇ 5ppm of 29 Si is smaller; relatively, the lower the temperature, the lower the degree of crystallization of the material.
  • the half-width of the displacement peak at -5ppm ⁇ 5ppm is reduced; in addition, the treatment temperature of Examples 1, 2, and 3 are all 900°C, and the obtained Si-MC composite solid nuclear magnetic field is -5ppm ⁇ 5ppm. same.
  • I 1350 represents the defect of carbon in the material, when the temperature ⁇ At 900°C, I 1350 /I 1580 >1, Si-MC composite material has many surface defects, which is not limited to any theory. There are many surface defects of the material, and the obstacles to free electron flow increase, the resistance is high, the conductivity of the material becomes poor, and the full battery The first time the coulombic efficiency and cycle performance deteriorate, the reaction by-products will increase, and the cycle expansion will increase.
  • the particle size of the negative electrode composite material is between 6 ⁇ m and 15 ⁇ m.
  • Example 7 shows that, compared to directly adding graphene to the slurry of the negative electrode active material, the negative electrode composite material obtained by the composite granulation of graphene and Si-MC composite material makes the negative electrode sheet smaller.
  • the film resistance, cycle performance and expansion performance of the film are also better. It is not limited to any theory. This may be because the direct addition of graphene to the slurry cannot guarantee the uniformity of the dispersion, and it cannot make better contact with the Si-MC composite. , It is difficult to improve its conductivity, resulting in accelerated cycle attenuation and increased expansion.

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Abstract

一种负极复合材料，包括Si-M-C复合材料和在其表面存在的石墨烯，其中M包括硼、氮或氧中的至少一种，固体核磁共振测试所述Si-M-C复合材料中硅元素的化学位移包括-5ppm±5ppm、-35ppm±5ppm、-75ppm±5ppm、-110ppm±5ppm，且-5ppm±5ppm处的半峰宽K满足：7ppm＜K＜28ppm。采用该负极复合材料，及应用其的负极极片、电化学装置具有良好的循环性能。

Description

一种负极复合材料及其应用 技术领域
本申请涉及锂离子电池技术领域，具体涉及一种负极复合材料及其应用。
背景技术
锂离子电池具有比能量大、工作电压高、自放电率低、体积小、重量轻等特点，在消费电子领域具有广泛的应用。随着电动汽车和可移动电子设备的高速发展，人们对锂离子电池的能量密度、安全性、循环性能等相关要求越来越高。其中，硅材料具有高的理论克容量(4200mAh/g)，在锂离子电池中的应用有着广阔的前景。硅基材料随着锂离子的嵌入和脱出，会发生120％至300％的体积变化，导致硅基材料粉化并与集流体脱离，这些问题会降低锂离子电池的循环性能，阻碍了硅基负极材料的进一步应用。
解决硅基材料循环过程中体积变化大的主要方法有设计多孔硅基材料、降低硅基材料的尺寸等。对于设计多孔硅基材料和降低硅基材料的尺寸的手段，能够在一定程度上可以改善膨胀问题，但随着循环的进行，副反应的发生以及不可控的SEI(Solid electrolyte interphase，固体电解质界面)膜的生长进一步限制了硅基负极材料的循环稳定性。
因此，亟需一种能够进一步提高锂离子电池循环稳定性和降低锂离子电池体积膨胀的硅基负极材料。
发明内容
本申请的目的是提供一种硅基的负极复合材料及其应用，以至少提高锂离子电池的循环稳定性、降低锂离子电池的体积膨胀。
本申请第一方面提供了一种负极复合材料，包括Si-M-C复合材料和在其表面存在的石墨烯，其中M包括硼、氮或氧中的至少一种，固体核磁共振测试所述Si-M-C复合材料中硅元素的化学位移包括-5ppm±5ppm、-35ppm±5ppm、-75ppm±5ppm、-110ppm±5ppm，且-5ppm±5ppm处的半峰宽K满足：7ppm＜K＜28ppm。
在本申请第一方面的一些实施方式中，所述石墨烯的质量占负极复合材 料质量的1％至20％。
在本申请第一方面的一些实施方式中，所述Si-M-C复合材料的Dv50为3.0μm至8.0μm。
在本申请第一方面的一些实施方式中，所述负极复合材料的Dv50为6.0μm至15.0μm。
在本申请第一方面的一些实施方式中，所述负极复合材料拉曼测试满足峰强度比0＜I 1350/I 1580＜1。
在本申请第一方面的一些实施方式中，所述负极复合材料的比表面积为0.5m 2/g至8m 2/g。
在本申请第一方面的一些实施方式中，所述负极复合材料的电导率为2.0S/cm至30S/cm。
本申请第二方面提供了一种负极极片，包括合剂层，所述合剂层包含本申请第一方面所提供的负极复合材料。
在本申请第二方面的一些实施方式中，所述合剂层的电阻为0.02Ω至0.1Ω。
本申请第三方面提供了一种电化学装置，包括本申请第二方面所提供的负极极片。
本申请第四方面提供了一种电子装置，包括本申请第三方面所提供的电化学装置。
本申请所提供的负极复合材料，其中Si-M-C复合材料具有较低的膨胀率，Si-M-C复合材料表面存在石墨烯，提高了负极复合材料的导电性，应用其的负极极片、电化学装置具有良好的循环性能。
本文中，术语“Dv50”表示颗粒累积分布为50％的粒径；即小于此粒径的颗粒体积含量占全部颗粒的50％。所述粒径用激光粒度仪进行测定。
附图说明
为了更清楚地说明本申请实施例和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中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，还可以根据这些附图获得其他的附图。
图1是实施例7的Si-M-C复合材料的固体核磁共振谱图。
图2是实施例7和对比例1的容量衰减曲线。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请第一方面提供了一种负极复合材料，包括Si-M-C复合材料和在其表面存在的石墨烯，其中M包括硼、氮或氧中的至少一种，固体核磁共振测试所述Si-M-C复合材料中硅元素的化学位移包括-5ppm±5ppm、-35ppm±5ppm、-75ppm±5ppm、-110ppm±5ppm，且-5ppm±5ppm处的半峰宽K满足：7ppm＜K＜28ppm。
本申请的发明人在研究中意外地发现，本申请的Si-M-C复合材料，与现有的一些碳硅氧等的复合材料相比，采用固体核磁共振测试硅元素的化学位移，其包含了-5ppm±5ppm，更出人意料的是，发明人发现当-5ppm±5ppm处的半峰宽K满足：7ppm＜K＜28ppm时；所述Si-M-C复合材料具有更低的膨胀率。
此外，本申请中“Si-M-C复合材料和在其表面存在的石墨烯”，可以理解为Si-M-C复合材料的一部分表面上存在石墨烯，也可能在全部表面上存在石墨烯，本申请对此不作具体限制。
在本申请第一方面的一些实施方式中，所述石墨烯的质量占负极复合材料质量的1％至20％。
发明人在研究中还发现，石墨烯的存在可以增加负极复合材料的导电性，改善其电性能；然而随着石墨烯含量升高，全电池的首次效率降低，膨胀增加。不限于任何理论，这可能是由于，一方面石墨烯的存在增加了负极复合材料的比表面积，导致与电解液接触面积更大，形成了更多的固体电解质界面(SEI)，而产生了更多的副产物；另一方面，导电性提升造成嵌锂深度增加，因此循环膨胀增加。发明人发现，当石墨烯的含量占负极复合材料质量的1％至20％时，负极复合材料能够保持高的循环性能和低膨胀率。
在本申请第一方面的一些实施方式中，所述Si-M-C复合材料的Dv50为3.0μm至8.0μm。
在本申请第一方面的一些实施方式中，所述负极复合材料的Dv50为6.0μm至15.0μm。
不限于任何理论，发明人发现，当负极复合材料粒径过小，其比表面积大，与电解液接触面积大，消耗锂源更多，首次效率低；当粒径过大，在循环过程中会导致负极局部膨胀过大，最终影响循环稳定性。
在本申请第一方面的一些实施方式中，所述负极复合材料拉曼测试满足峰强度比0＜I 1350/I 1580＜1。
其中，I 1350表示材料中碳的缺陷，I 1350/I 1580值越大，说明Si-M-C复合材料表面缺陷越多，自由电子流动的阻碍因素增加，材料电阻高，导电性差。
在本申请第一方面的一些实施方式中，所述负极复合材料的比表面积为0.5m 2/g至8m 2/g。
在本申请第一方面的一些实施方式中，所述负极复合材料的电导率为2.0S/cm至30S/cm。
本申请的负极复合材料可以通过以下方法制备：
1)将碳源溶解于有机溶剂中，待完全溶解后将有机硅加入其中，搅拌3到5小时，使碳源溶液与有机硅充分混合，随后加热搅拌去除有机溶剂，干燥；其中，碳源与有机溶剂的质量体积比为0.01g/ml至0.1g/ml，优选为0.05g/ml；所述碳源与所述有机硅的质量比为1:(2～0.5)；
2)将步骤1)中得到的产物在惰性气体的保护下，在900℃至1500℃高温裂解得到Si-M-C复合材料；
3)将Si-M-C复合材料与石墨烯浆料混合搅拌得到混合浆料；其中，Si-M-C复合材料与石墨烯的质量比为(4～99)：1；
4)将混合浆料喷雾干燥造粒。
其中，步骤1)中，碳源可以选自葡萄糖或蔗糖的至少一种；有机溶剂可 以选自本领域常用的有机溶剂，本申请在此不做限制，例如可以选自二甲苯、丙酮、环己烷或三乙胺中的至少一种；有机硅可以选自聚硅氧烷、聚硅氮烷、聚碳硼烷甲基硅氧烷、聚硅硼氮烷中的一种或多种。
步骤1)中的加热搅拌为本领域常用技术手段，其目的为去除其中的有机溶剂，例如可以在60℃至100℃下搅拌，本申请在此不做限定。
步骤1)中的干燥为本领域常用技术手段，例如可以在干燥箱中，60℃至100℃下干燥20至30小时，本申请在此不做限定。
步骤2)中的惰性气体可以选自氮气或者氩气，此为本领域常用的保护气体，本申请在此不做限定。
步骤2)中，在900℃至1500℃下高温裂解，具体地，反应条件可以为：以1℃/min升温至500℃，保温30min，再以3℃/min升温至900℃至1500℃，保持3h。
发明人在研究中意外地发现，高温裂解反应温度影响Si-M-C复合材料的性能。当温度＜900℃时，I 1350/I 1580＞1，Si-M-C复合材料表面缺陷多，导致全电池首次库伦效率、循环性变差，循环膨胀增加。
步骤4)中，在喷雾干燥造粒之前，还可以向混浆料中加入去离子水，以调节混合浆料的黏度及固含量。
本申请对喷雾干燥造粒的设备没有限定，只要能实现本申请的目的即可，例如可以采用上海欧蒙的小型喷雾干燥设备QM-1500-A或者无锡富超大型喷雾干燥设备。
本申请第二方面提供了一种负极极片，包括合剂层，所述合剂层包含本申请第一方面所提供的负极复合材料。
在本申请第二方面的一些实施方式中，所述负极极片还可以包括集流体，合剂层可以涂布于集流体的一个或两个表面上，本领域技术人员可根据实际需要具体选择，本申请在此不做限制。
所述集流体没有特别限制，可以采用本领域技术人员公知的任何集流体。具体而言，例如，可以使用由铁、铜、铝、镍、不锈钢、钛、钽、金、铂等 中的至少一种所形成的集流体。其中，作为负极集流体，特别优选铜箔或铜合金箔。上述材料可以单独使用一种，也可以将两种以上以任意比例组合使用。
在本申请的一些实施方式中，合剂层中还包含石墨，所述石墨可以选自天然石墨、人造石墨、中间相碳微球等中的一种或多种，在本申请的一些实施方式中，采用本申请的负极复合材料和石墨的混合物作为负极活性材料。
在本申请的一些实施方式中，合剂层中还可以包含粘合剂。粘合剂没有特别限制，可以是本领域技术人员公知的任何粘合剂或其组合，例如可以使用聚丙烯酸酯、聚酰亚胺、聚酰胺、聚酰胺酰亚胺、聚偏氟乙烯、丁苯橡胶、海藻酸钠、聚乙烯醇、聚四氟乙烯、聚丙烯腈、羧甲基纤维素钠、羧甲基纤维素钾、羟甲基纤维素钠、羟甲基纤维素钾等的至少一种。这些粘合剂可以单独使用一种，也可以将两种以上以任意比例组合使用。
在本申请的一些实施方式中，合剂层还可以包含导电剂。导电剂没有特别限制，可以是本领域技术人员公知的任何导电剂或其组合，例如，可以采用零维导电剂、一维导电剂及二维导电剂中的至少一种。优选地，导电剂可以包括炭黑、导电石墨、碳纤维、碳纳米管、VGCF(气相法生长碳纤维)或石墨烯中的至少一种。导电剂的用量没有特别限制，可以根据本领域公知常识进行选择。上述导电剂可以单独使用一种，也可以将两种以上以任意比例组合使用。
在本申请第二方面的一些实施方式中，所述合剂层的电阻为0.02Ω至0.1Ω。
本申请第三方面提供了一种电化学装置，包括本申请第二方面所提供的负极极片。
本申请的电化学装置包括但不限于：所有种类的一次电池、二次电池、燃料电池、太阳能电池或电容。一种典型的电化学装置就是锂离子电池，其是一种二次电池。电化学装置，例如锂离子电池一般包含有负极极片、正极极片、隔膜及电解液。
进一步，电化学装置可以是本申请提供的锂离子电池。
本申请提供的电化学装置，其负极极片采用本申请提供的负极极片；而其它的组成部分，包括正极极片、隔膜及电解液等，没有特别的限制。示例性地，正极极片所包含的正极材料可以包括但不限于钴酸锂、锰酸锂、磷酸铁锂等。隔膜的材质可以包括但不限于玻璃纤维、聚酯、聚乙烯、聚丙烯、聚四氟乙烯或其组合。电解液一般包括有机溶剂、锂盐和添加剂。有机溶剂可以包括但不限于碳碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯、丙酸乙酯中的至少一种。锂盐可以包括有机锂盐或无机锂盐中的至少一种；例如，锂盐可以包括六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF 4)、二氟磷酸锂(LiPO 2F 2)、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)、二氟草酸硼酸锂LiBF 2(C 2O 4)(LiDFOB)中的至少一种。
电化学装置的制备过程为本领域技术人员所熟识的，本申请没有特别的限制。例如二次电池可以通过以下过程制造：将正极和负极经由间隔件重叠，并根据需要将其卷绕、折叠等操作后放入电池容器，将电解液注入电池容器并封口，其中所用的负极为本申请提供的上述负极极片。此外，也可以根据需要将防过电流元件、导板等置于电池容器中，从而防止电池内部的压力上升、过充放电。
本申请第四方面提供了一种电子装置，包括本申请第三方面所提供的电化学装置。
以下，基于实施例对本申请进行具体地说明，但本申请并不限于这些实施例。
固体核磁：
29Si固体核磁共振光谱测试在仪器AVANCE III 400 WB宽腔固体核磁共振仪上进行，旋转速率8kHz对应 29Si。实施例7的Si-M-C复合材料的固体核磁共振谱图如图1所示。
拉曼测试：
采用Jobin Yvon LabRAM HR光谱仪，激发光源为532nm，扫描波数范围为0cm -1～4000cm -1，测试样品面积为100μm×100μm，通过统计100个I 1350/I 1580值得到最终I 1350/I 1580值。
粒度测试：
50ml洁净烧杯中加入约0.02g各样品粉末，加入约20ml去离子水，再滴加几滴1％的表面活性剂，使粉末完全分散于水中，120W超声清洗机中超声5分钟，利用MasterSizer 2000测试粒度分布。
复合材料比表面积测试：
在恒温低温下，测定不同相对压力时的气体在固体表面的吸附量后，基于布朗诺尔-埃特-泰勒吸附理论及其公式(BET公式)求得试样单分子层吸附量，从而计算出固体的比表面积。
复合材料粉末电导率测试：
取5g负极复合材料粉末样品，用电子压力机恒压至5000kg±2kg，维持15-25s，将样品置于电阻率测试仪(苏州晶格电子ST-2255A)电极间，样品高度h(cm)，两端电压U，电流I，电阻R(KΩ)；粉末压片后的面积S＝3.14cm 2，根据公式δ＝h/(S*R)/1000计算得到粉末电子电导率，单位为S/cm。
负极膜片电阻测试：
采用四探针法测试负极合剂层电阻，四探针法测试所用仪器为精密直流电压电流源(SB118型)，四只长1.5cm×宽1cm×厚2mm的铜板被等距固定在一条线上，中间两块铜板的间距为L(1-2cm)，固定铜板的基材为绝缘材料。测试时将四只铜板下端面压在所测负极的合剂层上(压力为3000Kg)，维持时间60s，两端铜板接通直流电流I，在中间两只铜板测取电压V，读取三次I和V值，分别取I和V的平均值Ia和Va，Va/Ia的值即为测试处的合剂层电阻。每张极片取12个点测试，取平均值。
SEM测试：
扫描电镜表征由PhilipsXL-30型场发射扫描电子显微镜记录，在10kV，10mA条件下进行检测。
负极复合材料比容量检测：
将各实施例或对比例中得到的负极复合材料与导电炭黑、粘结剂PAA按照质量比80：10：10加去离子水经过搅成固含量为30％的浆料，取质量为M的浆料涂布于铜箔上，85℃经过12小时真空干燥箱烘干后，利用在干燥环境中用冲压机切成直径为1.4cm的圆片，在手套箱中以金属锂片作为对电极，隔离膜选择ceglard复合膜，加入电解液组装成扣式电池。运用蓝电(LAND)系列电池测试系统对电池进行充放电测试，测试其充放电性能，其中得到容量为C(mAh)，则负极复合材料的克容量＝C/(M×30％×80％)。
全电池性能测试：
全电池首次效率测试：全电池首次充放电过程中，以0.5C恒流充电到4.45V，再4.45V恒压充电到0.025C，(得到的容量为C0)，静置5min后，0.5C放电到3.0V(得到放电容量D0)。全电池首次效率＝D0/C0。
循环测试：
测试温度为45℃，以0.5C恒流充电到4.45V，恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步得到的容量为初始容量，进行0.5C充电/0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量衰减曲线；其中，实施例7和对比例1的容量衰减曲线如图2所示；各实施例和对比例循环400次后的容量保持率如表1和表2所示。
锂离子电池的满充膨胀率测试：
用螺旋千分尺测试初始半充时锂离子电池的厚度。45℃下，充放电循环至400次时，锂离子电池于满充状态下，再用螺旋千分尺测试此时锂离子电池的厚度，与初始半充时锂离子电池的厚度对比，即可得此时满充锂离子电池的膨胀率。
全电池制备：
负极极片制备：
将各实施例和对比例制备的负极复合材料与石墨按一定比例混合，得到 设计混合克容量为500mAh/g的负极活性材料粉末，将负极活性材料粉末、导电剂乙炔黑、PAA按照重量比95：1.2：3.8在去离子水溶剂体系中充分搅拌混合均匀后，涂覆于厚度为10μm的铜箔集流体的两个表面上，涂布厚度100μm；将极片烘干后冷压，双面压实密度为1.8g/cm 3，得到负极极片。
正极极片制备：
将活性物质LiCoO 2、导电炭黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96.7：1.7：1.6在N-甲基吡咯烷酮溶剂体系中，调配成为固含量为0.75的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为12μm正极集流体铝箔的一个表面上，涂布厚度为115μm，90℃条件下烘干，冷压，得到正极极片。
全电池组装：
以厚度为15μm的PE多孔聚合薄膜作为隔离膜。将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于阴阳极中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装中，注入配好的电解液(EC:DMC:DEC＝1:1:1vol％，10wt％FEC，1mol/L LiPF 6)并封装，经过化成，脱气，切边等工艺流程得到全电池。
负极复合材料制备
实施例1
将10g葡萄糖完全溶解在200mL二甲苯溶剂中，将20g聚二甲基硅氧烷(单体为C 2H 6OSi)加入其中，搅拌4h，使葡萄糖溶液与聚二甲基硅氧烷充分混合，随后80℃搅拌加热去除溶剂，80℃烘箱干燥24h，得到的产物在管式炉中高温裂解，以N 2为保护气氛，900℃下高温裂解，升温程序：1℃/min升温至500℃，保温30min，进一步以3℃/min升温至900℃保持3h，得到Si-O-C复合材料；
将10g Si-O-C复合材料与1.01g固含量为10％的石墨烯浆料加入到MSK-SFM-10真空搅拌器中搅拌，公转速度10～40rpm，搅拌180分钟后，加入100mL去离子水，公转转速为10～40rpm，自转转速为1000～1500rpm，继续搅拌120min得到混合浆料；
将混合浆料转移到喷雾干燥造粒机的离心转盘喷头，离心转速为2000rpm，形成微小雾滴。喷雾干燥造粒机进口温度260℃，出口温度为105℃，冷却收集粉末，得到表面存在石墨烯的负极复合材料，石墨烯含量为1％。
实施例2
除了将聚二甲基硅氧烷替换为聚六甲基环三硅氮烷(单体为C 6H 21N 3Si 3)，其他与实施例1相同，制备获得包含Si-N-C复合材料的负极复合材料。
实施例3
除了将聚二甲基硅氧烷替换为聚碳硼烷甲基硅氧烷(单体为C 10H 34B 10Si 4)，其他与实施例1相同，制备获得包含Si-B-C复合材料的负极复合材料。
实施例4
除了高温裂解温度为1100℃，其余与实施例1相同。
实施例5
除了高温裂解温度为1300℃，其余与实施例1相同。
实施例6
除了高温裂解温度为1500℃，其余与实施例1相同。
实施例7
除了石墨烯浆料的质量为5.26g，得到石墨烯含量为5％的负极复合材料，其余与实施例4相同。
实施例8
除了石墨烯浆料的质量为11.11g，得到石墨烯含量为10％的负极复合材料，其余与实施例4相同。
实施例9
除了石墨烯浆料的质量为17.65g，得到石墨烯含量为15％的负极复合材料，其余与实施例4相同。
实施例10
除了石墨烯浆料的质量为25g，得到石墨烯含量为20％的负极复合材料，其余与实施例4相同。
实施例11
除了喷雾干燥造粒的离心转速为6000rpm，其余与实施例7相同。
实施例12
除了喷雾干燥造粒的离心转速为5000rpm，其余与实施例7相同。
实施例13
除了喷雾干燥造粒的离心转速为3000rpm，其余与实施例7相同。
实施例14
除了喷雾干燥造粒的离心转速为500rpm，其余与实施例7相同。
实施例15
除了喷雾干燥造粒的离心转速为200rpm，其余与实施例7相同。
实施例16
将葡萄糖的用量调整为20g，其余与实施例7相同。
实施例17
将聚二甲基硅氧烷的用量调整为10g，其余与实施例16相同。
实施例18
将10g聚二甲基硅氧烷与10g聚碳硼烷甲基硅氧烷加入葡萄糖的二甲苯溶液中，其余与实施例7相同，得到包含Si-B-O-C复合材料的负极复合材料。
对比例1
将实施例7制备的Si-O-C复合材料不与石墨烯复合造粒，直接作为负极复合材料用于负极极片制备，其余与实施例7相同。
对比例2
除了高温裂解温度为600℃，其余与实施例1相同。
对比例3
除了高温裂解温度为1800℃，其余与实施例1相同。
对比例4
除了石墨烯浆料的质量为42.86g，得到石墨烯含量为30％的负极复合材料，其余与实施例4相同。
对比例5
将实施例4制备的Si-O-C复合材料10g加入100mL去离子水中，以公转转速为10～40rpm，自转转速为1000～1500rpm，继续搅拌120min得到混合浆料；
将混合浆料转移到喷雾干燥造粒机的离心转盘喷头，离心转速为2000rpm，形成微小雾滴。喷雾干燥造粒机进口温度260℃，出口温度为105℃，冷却收集粉末，得到表面不存在石墨烯的负极复合材料。
将负极复合材料与石墨按一定比例混合，得到设计混合克容量为500mAh/g的负极活性材料粉末，将负极活性材料粉末、导电剂乙炔黑、PAA按照重量比95：1.2：3.8在去离子水溶剂体系中搅拌30分钟，加入石墨烯浆料，使得石墨烯的质量占负极活性材料粉末、导电剂乙炔黑、PAA总质量的5％；加入去离子水搅拌至捏合状态，涂覆于厚度为10μm的铜箔集流体的两个表面上，涂布厚度100μm；将极片烘干后冷压，双面压实密度为1.8g/cm 3，得到负极极片。
各实施例的参数及测试结果见表1；各对比例的参数及测试结果见表2。
Figure PCTCN2020087168-appb-000001
Figure PCTCN2020087168-appb-000002
各实施例与对比例1相比较说明，表面存在石墨烯的负极复合材料，导电性明显提升，极片合剂层电阻降低，全电池循环性能明显改善。
从实施例1、2、3中可以看出，采用不同的有机硅烷，获得组成不同的Si-M-C复合材料，均能够获得高的容量保持率和低的膨胀率；同时，发明人还发现，有机硅单体分子量越大，制备得到的Si-M-C复合材料粒径越大，不限于任何理论，发明人认为，粒径增加后，比表面积减小，化成过程中与电解液的接触面积更小，消耗的锂更少，所以全电池首次库伦效率提高。
实施例1、4、5、6与对比例2、3对比可以看出，固体核磁测试中硅元素-5ppm±5ppm处位移峰的半峰宽在7ppm-28ppm之间时，半峰宽越小，全电池的首次库伦效率越高，循环容量保持率越高；另外，电池的膨胀率随着半峰宽的增加逐渐降低，半峰宽达到20ppm之后，电池的膨胀率随着半峰宽的增加逐渐增加；发明人发现，当固体核磁测试中硅元素-5ppm±5ppm处位移峰的半峰宽在在7ppm-28ppm之间时，电池可以具有较高的循环容量保持率和库伦效率，以及较低的膨胀率。
另外，通过实施例1、4、5、6还可以看出，高温裂解的反应温度影响-5ppm±5ppm处的位移峰的半峰宽，不限于任何理论，处理温度对材料晶化程度影响较大，温度越高，材料晶化程度越高，在固体核磁测试中 29Si的-5ppm±5ppm处的位移峰的半峰宽越小；相对地，温度越低，材料晶化程度越低，-5ppm±5ppm处的位移峰的半峰宽减越大；另外，实施例1、2、3的处理温度均为900℃，所得的Si-M-C复合材料固体核磁-5ppm±5ppm处半峰宽相同。
此外，相同石墨烯含量下，Si-M-C复合材料高温裂解的温度越高，得到的负极复合材料拉曼测试的I 1350/I 1580值越小，I 1350表示材料中碳的缺陷，当温度＜900℃时，I 1350/I 1580＞1，Si-M-C复合材料表面缺陷多，不限于任何理论，材料表面缺陷多，自由电子流动的阻碍因素增加，电阻高，材料导电性变差，全电池首次库伦效率及循环性能变差，反应副产物也会增加，循环膨胀增加。
实施例7-10与对比例4相比较可以看出，随着石墨烯含量的升高，电池的循环膨胀增加，不限于任何理论，这可能是由于导电性提升使嵌锂深度增 加造成的，另外石墨烯比表面积大，会导致与电解液接触面积更大，副产物增多，循环膨胀增加；因此石墨烯的量应控制在1％～20％。
通过实施例11-15可以看出，负极复合材料的粒径越大，全电池首次库伦效率越高，不限于任何理论，这可能是由于小的粒径造成材料比表面积增大，与电解液接触面积大，消耗锂源更多造成的；同时可以看出，在一定范围内，负极复合材料粒径越大，容量保持率越高，膨胀率越低；然而当粒径大于15μm时，全电池的容量保持率下降，膨胀增加，不限于任何理论，可能是由于粒径过大在循环过程中会导致负极局部膨胀过大，最终影响循环稳定性；因此在本申请的一些优选的实施方式中，负极复合材料的粒径在6μm-15μm。
实施例7与对比例5对比说明，相比于直接将石墨烯添加到负极活性材料的浆料中，石墨烯与Si-M-C复合材料复合造粒得到的负极复合材料使负极极片具有更小的膜片电阻，循环性能与膨胀性能也更好，不限于任何理论，这可能是因为石墨烯直接加到浆料中无法保证分散的均匀性，并且不能与Si-M-C复合材料更好的接触，难以改善其导电性，导致循环衰减加速以及膨胀增大。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (11)

  1. 一种负极复合材料，其包括Si-M-C复合材料和在其表面存在的石墨烯，其中M包括硼、氮或氧中的至少一种，固体核磁共振测试所述Si-M-C复合材料中硅元素的化学位移包括-5ppm±5ppm、-35ppm±5ppm、-75ppm±5ppm、-110ppm±5ppm，且-5ppm±5ppm处的半峰宽K满足：7ppm＜K＜28ppm。
  2. 根据权利要求1所述的负极复合材料，其中，所述石墨烯的质量占负极复合材料质量的1％～20％。
  3. 根据权利要求1所述的负极复合材料，其中，所述Si-M-C复合材料的Dv50为3.0μm至8.0μm。
  4. 根据权利要求1所述的负极复合材料，其中，所述负极复合材料的Dv50为6.0μm至15.0μm。
  5. 根据权利要求1所述的负极复合材料，其中，所述负极复合材料拉曼测试满足峰强度比0＜I 1350/I 1580＜1。
  6. 根据权利要求1所述的负极复合材料，其中，所述负极复合材料的比表面积为0.5m 2/g至8m 2/g。
  7. 根据权利要求1所述的负极复合材料，其中，所述负极复合材料的电导率为2.0S/cm至30S/cm。
  8. 一种负极极片，包括合剂层，所述合剂层包含权利要求1-7中任一项所述的负极复合材料。
  9. 根据权利要求8所述的负极极片，其中，所述合剂层的电阻为0.02Ω至0.1Ω。
  10. 一种电化学装置，包括权利要求8或9所述的负极极片。
  11. 一种电子装置，包括权利要求10所述的电化学装置。
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