WO2021189211A1 - 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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WO2021189211A1
WO2021189211A1 PCT/CN2020/080745 CN2020080745W WO2021189211A1 WO 2021189211 A1 WO2021189211 A1 WO 2021189211A1 CN 2020080745 W CN2020080745 W CN 2020080745W WO 2021189211 A1 WO2021189211 A1 WO 2021189211A1
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silicon
negative electrode
composite material
graphene
electrode composite
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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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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to CN202080095939.4A priority Critical patent/CN115088100B/zh
Priority to PCT/CN2020/080745 priority patent/WO2021189211A1/zh
Publication of WO2021189211A1 publication Critical patent/WO2021189211A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • 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.
  • Silicon material has a high theoretical gram capacity (4200mAh/g), and its application in lithium-ion batteries has broad prospects.
  • a volume change of 120% to 300% will occur, causing the silicon-based material to be powdered and separated from the current collector, resulting in poor conductivity of the negative electrode. Reduce the cycle performance of lithium-ion batteries.
  • the purpose of this application is to provide a negative electrode composite material to at least improve the problem of large volume changes and poor conductivity of silicon-based negative electrode materials.
  • the first aspect of the present application provides a negative electrode composite material, including silicon-based materials, graphene, and graphite, wherein the graphene accounts for 1% to 20% of the mass of the negative electrode composite material; the silicon-based material accounts for graphite and silicon 10-100% of the total mass of the base material;
  • the Dv50 of the silicon-based material is 3.0-10 ⁇ m; the Dv50 of the graphite is 8.0-20 ⁇ m; the Dv50 of the negative electrode composite material is 9.5-40 ⁇ m.
  • the number of graphene layers is 3-10 layers.
  • the graphite includes at least one of natural graphite, artificial graphite, or mesocarbon microspheres.
  • the silicon-based material includes at least one of silicon, silicon oxide, or silicon carbon material.
  • carbon is present on at least a part of the surface of the silicon-based material.
  • the electrical conductivity of the negative electrode composite material is 2.0-30 S/cm.
  • the second aspect of the present application provides a negative electrode sheet, which includes a current collector and a mixture layer coated on the current collector, and the mixture layer comprises the negative electrode composite material provided in the first aspect of the present application.
  • the third aspect of the present application provides a battery, including the negative pole piece provided in the second aspect of the present application.
  • the expansion rate of the battery is 6.5-10%.
  • the fourth aspect of the present application provides an electronic device, including the battery provided in the third aspect of the present application.
  • the silicon-based material is composited with graphene and graphite, wherein graphite can relieve the expansion of the silicon-based material, and graphene can increase the conductivity of the composite material;
  • the multilayer structure and slip characteristics of graphene can release the expansion stress of the silicon-based material in the process of deintercalating lithium, thereby eliminating the pulverization of silicon-based particles caused by expansion, and improving the cycle performance of the negative electrode material.
  • the negative pole piece and battery provided by this application have 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 an SEM photograph of the negative electrode composite material prepared in Example 3 of the application.
  • Figure 2 shows the capacity decay curves of Example 5, Example 16, Example 19 and Comparative Example 4.
  • the first aspect of the present application provides a negative electrode composite material, including silicon-based materials, graphene, and graphite, wherein the graphene accounts for 1% to 20% of the mass of the negative electrode composite material; the silicon-based material accounts for graphite and silicon 10-100% of the total mass of the base material;
  • the Dv50 of the silicon-based material is 3.0-10 ⁇ m; the Dv50 of the graphite is 8.0-20 ⁇ m; the Dv50 of the negative electrode composite particles is 9.5-40 ⁇ m, and the specific surface area BET is 1.0-15 m 2 /g.
  • High-energy density batteries require a negative electrode material with a gram capacity of> 500mAh/g.
  • the inventor found in the research that when the negative electrode composite material contains more than 10% of the total mass of graphite and silicon-based materials, it can meet high-energy requirements. Density requirements.
  • the inventor also discovered in the research that it is not limited to any theory.
  • the content of graphene in the negative electrode composite material of the present application is greater than 20%, there is too much graphene around silicon and graphite, which affects the insertion and extraction of lithium ions, thereby As a result, the rate performance of the full battery deteriorates; when the content of graphene is less than 1%, it cannot play the role of alleviating the expansion of the negative electrode composite material.
  • the particle size of the silicon-based material, graphite and the negative electrode composite material has an important impact on the performance of the battery; not limited to any theory, the inventor found in the research that the silicon-based material Dv50 ⁇ 3 ⁇ m, the composite The material Dv50 ⁇ 9.5 ⁇ m, the material has a large specific surface area and a large contact area with the electrolyte, so the irreversible lithium loss is greater and the cycle capacity retention rate is reduced.
  • graphite Dv50>20 ⁇ m, composite material Dv50>40 ⁇ m it will cause local expansion of the battery during cycling. Excessive expansion will result in poor electrical contact between the materials in the pole pieces and accelerate the decrease in battery capacity; in some of the preferred applications of this application
  • the number of graphene layers is 3-10 layers.
  • the number of graphene layers is too large, such as more than 10 layers, or the number of layers is too small, such as single-layer graphene.
  • the conductivity of the composite material is significantly reduced. It is not limited to any theory. The inventor believes that this may be because there are more exposed end faces when the number of graphene layers is too large. Defects will increase, resulting in a decrease in conductivity; while single-layer graphene is prone to wrinkles, resulting in increased resistance and decreased conductivity.
  • the negative electrode material intercalates lithium and expands to make the graphene slippery. Too much shift causes the graphene to fail to recover, thereby increasing the expansion and accelerating the cycle capacity attenuation.
  • the graphite includes at least one of natural graphite, artificial graphite, or mesocarbon microspheres.
  • the silicon-based material includes at least one of silicon, silicon oxide, or silicon carbon material.
  • carbon is present on at least a part of the surface of the silicon-based material. It can be understood that at least part of the surface of the silicon-based material is coated with carbon, which may be partially coated or completely coated.
  • Carbon coating can increase the conductivity of silicon-based materials and improve their electrical properties.
  • Carbon-coated silicon-based materials such as carbon-coated silicon oxide, are materials known in the art; they can be prepared according to the prior art or obtained through commercial channels.
  • the electrical conductivity of the negative electrode composite material is 2.0-30 S/cm.
  • the preparation method of the negative electrode composite material provided in this application is not particularly limited, for example, it can be prepared by the following method:
  • the spray-drying granulation method does not contain a binder in the resulting negative electrode composite material, which is beneficial to improve the rate performance of the battery.
  • the inlet temperature of the spray drying granulator is 240-280°C, preferably 260°C; the outlet temperature is 100-110°C, preferably 105°C.
  • baking the granulated material in an inert atmosphere can effectively remove impurities such as moisture and organic matter in the material; the baking temperature of the negative electrode material has a greater impact on the cycle expansion and capacity retention of the battery.
  • too high a processing temperature such as higher than 900°C, will cause material to agglomerate, resulting in a significant increase in Dv50, resulting in poorer contact between small particles after cyclic expansion, resulting in accelerated cycle capacity attenuation, and increased battery expansion .
  • the treatment temperature is too low, such as lower than 600°C, the residual dispersant in the graphene preparation process will not be completely decomposed, the composite material has more surface active groups, and more solid electrolyte interfaces (SEI) are generated, and the cyclic expansion increases. , The capacity maintenance rate is reduced.
  • SEI solid electrolyte interfaces
  • the firing conditions are: the firing temperature is 600-900°C, the holding time is 1-5 hours, preferably 2 hours; during firing, the heating rate can be selected from 3-8°C/min, preferably 5°C/min. min.
  • the second aspect of the present application provides a negative electrode sheet, which includes a current collector and a mixture layer coated on the current collector, and the mixture layer includes the negative electrode composite material provided in the first aspect of the present application.
  • the mixture layer can be coated on one or both surfaces of the current collector, and those skilled in the art can make specific selections according to actual needs, and the application is not limited herein.
  • 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 iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or 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 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.
  • These 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 third aspect of the present application provides a battery, including the negative pole piece provided in the second aspect of the present application.
  • the expansion rate of the battery is 6.5-10%.
  • the battery in this application includes but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.
  • a typical battery is a lithium ion battery, which is a secondary battery.
  • the battery such as a lithium ion battery, generally includes a negative pole piece, a positive pole piece, a separator, and an electrolyte.
  • the negative pole piece of this application 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 application also provides an electronic device, which includes the battery provided in the application.
  • 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 test temperature is 25°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 a 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, Examples 5, 16, 19 and comparative examples
  • the capacity decay curve of 4 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 test temperature is 25°C, and it is charged to 4.45V at a constant current of 0.5C, and charged to 0.025C at a constant voltage. After standing for 5 minutes, it is discharged to 3.0V at 0.2C.
  • the capacity obtained in this step is the initial capacity, charge at 0.5C, discharge at 2C, and the ratio of the 2C discharge capacity to the 0.2C discharge capacity is the rate 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 capacity obtained before is C0), after standing for 5 minutes, 0.5C Discharge to 3.0V (obtain discharge capacity D0).
  • the first efficiency of the whole battery D0/C0.
  • the first reversible capacity test of a half-cell The negative pole pieces obtained in each example and comparative example were cut into discs with a diameter of 1.4cm with a punching machine in a dry environment. The metal lithium sheet was used as the counter electrode, and the isolation membrane was selected as ceglard composite. Membrane, adding electrolyte to assemble button cell. The LAND series battery test system was used to detect the first reversible capacity of the half-cell, and the results are shown in Table 1 and Table 2.
  • the prepared negative electrode mixture layer material was coated on both surfaces of a copper foil current collector with a thickness of 10 ⁇ m, and the coating thickness was 100 ⁇ m; the pole pieces were dried and cold pressed, and the double-sided compaction density was 1.8 g/cm 3 .
  • 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 a N-methylpyrrolidone solvent system at a weight ratio of 96.7:1.7:1.6, and Stir well.
  • the slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 ⁇ m, 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 bare cell is obtained by winding.
  • Place the bare cell in the outer package, inject the prepared electrolyte (EC:DMC:DEC 1:1:1vol%, 10wt% FEC, 1mol/L LiPF 6 ) and package, after forming, degassing, cutting
  • the full battery is obtained by waiting for the technological process.
  • the pellets in 3) are calcined in an inert atmosphere (Ar), the heating rate is controlled at 5°C/min, and the temperature is kept at 750°C for 2h.
  • the powder is passed through a 400-mesh sieve to obtain the desired negative electrode composite material.
  • Example 1 The graphene in Example 1 was replaced with graphene with 7, 5, and 3 layers, and the rest were the same as Example 1.
  • SEM scanning electron micrograph
  • Example 3 Adjusts the amount of graphene slurry in Example 3 to 5.26 kg, 11.11 kg, 17.65 kg, and 25 kg, so that the content of graphene is 5%, 10%, 15%, and 20%, respectively, and the rest are the same as in Example 3.
  • Example 5 The silicon-based material in Example 5 is replaced with silicon (Si), and the rest is the same as in Example 5.
  • Example 5 The silicon-based material in Example 5 is replaced with silicon carbon material (SiC), and the rest is the same as in Example 5.
  • SiC silicon carbon material
  • Example 5 The firing temperature in Example 5 was adjusted to 600°C and 900°C, respectively, and the rest were the same as in Example 5.
  • Example 5 2 kg of silicon oxide powder was mixed with 8 kg of graphite so that the content of the silicon-based material was 20%, and the rest were the same as in Example 5.
  • Example 5 5 kg of silicon oxide powder and 5 kg of graphite were mixed so that the content of the silicon-based material was 50%, and the rest were the same as in Example 5.
  • Example 5 8 kg of silicon oxide powder was mixed with 2 kg of graphite so that the content of the silicon-based material was 80%, and the rest were the same as in Example 5.
  • Example 5 10 kg of silicon oxide was directly used to make the content of the silicon-based material 100%, and the rest were the same as in Example 5.
  • the particle size (Dv50) of the silicon oxide in Example 5 is adjusted to 3.5 ⁇ m and 8 ⁇ m, respectively, and the rest is the same as in Example 5.
  • the particle size (Dv50) of graphite in Example 5 was adjusted to 15 ⁇ m and 20 ⁇ m, and the rest was the same as in Example 5.
  • Example 5 The graphene in Example 5 was replaced with graphene having a 15-layer structure and a single-layer structure, and the rest were the same as in Example 5.
  • the dosage of the graphene slurry in Example 5 is adjusted to 33.3 kg, so that the content of graphene is 25%, and the rest are the same as in Example 5.
  • Example 5 5 kg of deionized water was directly used instead of the graphene slurry, and the rest were the same as in Example 5 (that is, without graphene).
  • Example 5 The firing temperature in Example 5 was adjusted to 500° C. and 1000° C., and the rest were the same as in Example 5.
  • Example 5 10 kg of graphite was directly used, that is, no silicon-based material was used, and the rest were the same as in Example 5.
  • Example 5 0.5 kg of silicon oxide powder was mixed with 9.5 kg of graphite so that the content of the silicon-based material was 5%, and the rest were the same as in Example 5.
  • the particle size (Dv50) of the silicon oxide in Example 5 was adjusted to 1.5 ⁇ m, and the rest were the same as in Example 5.
  • Example 5 The particle size (Dv50) of graphite in Example 5 was adjusted to 25 ⁇ m, and the rest were the same as in Example 5.
  • the parameters and performance test results of the negative electrode composite material in each embodiment are shown in Table 1; the parameters and performance test results of the negative electrode composite material in each comparative example are shown in Table 2.
  • Comparing Example 5 with Comparative Examples 1 and 2 it can be seen that when the number of graphene layers exceeds 10 or is a single layer, the conductivity is significantly reduced. It is not limited to any theory. The inventor believes that because the number of graphene layers is too large, the exposed More end faces will increase the number of defects, which will lead to a decrease in conductivity; single-layer graphene is prone to wrinkles, which leads to an increase in resistance and a decrease in conductivity.
  • graphene has a sliding effect, can relieve the expansion stress, and can return to the original state after cyclic expansion.
  • Comparative Example 2 it can be seen from Comparative Example 2 that when the number of layers is less than 3 layers, the negative electrode material lithium intercalation will cause graphene to expand. Too much slip causes the graphene to be unable to recover, thereby increasing the expansion and accelerating the attenuation of the cycle capacity.
  • the inventor also found that when the graphene content is less than 5%, the first reversible capacity of the composite material increases significantly as the conductivity increases, but when the content exceeds 5%, as the conductivity increases, the composite material’s gram On the contrary, the capacity drops, not limited to any theory, this may be caused by the increase in graphene content leading to a decrease in the overall content of high-capacity silicon-based materials. On the other hand, as the content of graphene increases, the efficiency of the whole battery decreases for the first time. It is not limited to any theory. The inventor believes that this may be due to the increase in the content of graphene. Larger, more SEI film is generated, resulting in lower efficiency for the first time.
  • Examples 5, 17, 18 and Comparative Example 9 shows that when the silicon-based material Dv50 ⁇ 3 ⁇ m, the composite material particle size Dv50 ⁇ 9.5 ⁇ m, the material specific surface area is larger, the contact area with the electrolyte is larger, and the irreversible lithium loss is greater. The cycle capacity retention rate is reduced. Comparing Examples 5, 19, and 20 with Comparative Example 10, it can be seen that when the graphite Dv50>20 ⁇ m, the composite material Dv50>40 ⁇ m, will cause the local expansion of the battery during the cycle, and the excessive expansion will lead to the gap between the materials in the pole piece. The electrical contact becomes worse, and the battery capacity declines faster; comprehensive data considerations are preferably 8 ⁇ m ⁇ graphite Dv50+silicon Dv50 ⁇ 15um.

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Abstract

一种负极复合材料，包括硅基材料、石墨烯和石墨，其中，所述石墨烯占负极复合材料质量的1％～20％；所述硅基材料占石墨与硅基材料总质量的10～100％；所述硅基材料的Dv50为3.0-10μm；所述石墨的Dv50为8.0-20μm；所述负极复合材料的Dv50为9.5-40μm。采用本申请所提供的负极复合材料，其中石墨能够缓解硅基材料的膨胀，石墨烯能够增加复合材料的导电性；进一步地，石墨烯的多层结构和滑移特性可释放硅基材料在脱嵌锂过程中的膨胀应力，从而消除膨胀导致的硅基颗粒的粉化，提高了负极材料的循环性能。

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
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。但硅材料在充放电循环过程中，随着锂离子的嵌入和脱出，会发生120％～300％的体积变化，导致硅基材料粉化并与集流体脱离，从而导致负极导电性变差，降低锂离子电池的循环性能。
发明内容
本申请的目的是提供一种负极复合材料，以至少改善硅基负极材料体积变化大，导电性差的问题。
本申请第一方面提供了一种负极复合材料，包括硅基材料、石墨烯和石墨，其中，所述石墨烯占负极复合材料质量的1％～20％；所述硅基材料占石墨与硅基材料总质量的10～100％；
所述硅基材料的Dv50为3.0-10μm；所述石墨的Dv50为8.0-20μm；所述负极复合材料的Dv50为9.5-40μm。
在本申请第一方面的一些实施方式中，石墨烯的层数为3-10层。
在本申请第一方面的一些实施方式中，所述石墨包括天然石墨、人造石墨或中间相碳微球中的至少一种。
在本申请第一方面的一些实施方式中，所述硅基材料包括硅、硅氧化物或硅碳材料中的至少一种。
在本申请第一方面的一些实施方式中，所述硅基材料的至少一部分表面存在碳。
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2.0～30S/cm。
本申请第二方面提供了一种负极极片，包括集流体和涂布在集流体上的 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。
本申请第三方面提供了一种电池，包括本申请第二方面所提供的负极极片。
在本申请第三方面的一些实施方式中，所述电池的膨胀率为6.5-10％。
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池。
使用本申请所提供的负极复合材料，将硅基材料与石墨烯、石墨复合，其中石墨能够缓解硅基材料的膨胀，石墨烯能够增加复合材料的导电性；
进一步地，石墨烯的多层结构和滑移特性可释放硅基材料在脱嵌锂过程中的膨胀应力，从而消除膨胀导致的硅基颗粒的粉化，提高了负极材料的循环性能。
此外，本申请提供的负极极片、电池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发明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发明的一些实施例，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为本申请实施例3制备的负极复合材料的SEM照片。
图2为实施例5、实施例16、实施例19与对比例4容量衰减曲线。
具体实施方式
为使本发明的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本发明进一步详细说明。显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，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，都属于本发明保护的范围。
本申请第一方面提供了一种负极复合材料，包括硅基材料、石墨烯和石 墨，其中，所述石墨烯占负极复合材料质量的1％～20％；所述硅基材料占石墨与硅基材料总质量的10～100％；
所述硅基材料的Dv50为3.0-10μm；所述石墨的Dv50为8.0-20μm；所述负极复合材料颗粒的Dv50为9.5-40μm，比表面积BET为1.0～15m 2/g。
高能量密度电池要求负极材料克容量＞500mAh/g，发明人在研究中发现，当所述负极复合材料中，硅基材料占石墨与硅基材料总质量的10％以上，才能够满足高能量密度要求。
发明人在研究中还发现，不限于任何理论，当本申请的负极复合材料中，石墨烯的含量大于20％，硅与石墨周围的石墨烯太多，则影响锂离子的嵌入和脱出，从而导致全电池倍率性能变差；当石墨烯的含量低于1％，不能起到缓解负极复合材料膨胀的作用。
负极复合材料中，硅基材料、石墨以及负极复合材料颗粒的粒径，对电池的性能均有着重要的影响；不限于任何理论，发明人在研究中发现，硅基材料Dv50＜3μm时，复合材料Dv50＜9.5μm，材料比表面积大，与电解液接触面积大，因此不可逆锂损失更多，循环容量保持率降低。当石墨Dv50＞20μm时，复合材料Dv50＞40μm，会造成电池循过程中局部膨胀大，膨胀过大会导致极片中材料之间的电接触变差，电池容量下降加速；在本申请的一些优选的实施方式中，8μm＜石墨Dv50+硅基材料Dv50＜15um。
在本申请第一方面的一些实施方式中，石墨烯的层数为3-10层。
发明人在研究中发现，石墨烯的加入能够明显提高复合材料的导电性，然而当石墨烯的层数过多，如多于10层，或者层数过少，如采用单层石墨烯时，与采用10层以下3层以上的多层石墨烯相比，复合材料的导电性明显下降，不限于任何理论，发明人认为，这可能是因为石墨烯层数过多时，暴露的端面更多，缺陷会增多，从而导致导电性降低；而单层石墨烯容易产生褶皱，导致电阻增加，从而导电性也降低。发明人在研究中发现，石墨烯具有滑移作用，可缓解膨胀应力，在循环膨胀后可恢复到原始状态，但当石墨烯的层数＜3层时，负极材料嵌锂膨胀使石墨烯滑移过多，导致石墨烯无法恢复，从而膨胀增加，循环容量衰减加速。
在本申请第一方面的一些实施方式中，所述石墨包括天然石墨、人造石 墨或中间相碳微球中的至少一种。
在本申请第一方面的一些实施方式中，所述硅基材料包括硅、硅氧化物或硅碳材料中的至少一种。
在本申请第一方面的一些实施方式中，所述硅基材料的至少一部分表面存在碳。可以理解为，所述硅基材料的至少部分表面被碳包覆，既可以是部分包覆，也可以是全部包覆。
碳包覆可以提高硅基材料的导电性，改善其电性能。碳包覆的硅基材料，例如碳包覆的硅氧化物为本领域已知的材料；可以根据现有技术来制备或者通过商业途径获得。
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2.0～30S/cm。
本申请所提供的负极复合材料的制备方法没有特别限制，例如可以通过以下方法制备：
1)将粉末状的硅基材料与石墨混合搅拌；
2)将石墨烯浆料加入到硅基材料与石墨的混合物中，继续搅拌；
3)加水，将浆料固含量调节到30％～60％，继续搅拌得到混合浆料；
4)将混合浆料转移到喷雾干燥造粒机进行造粒；
5)造粒后的材料在惰性气氛中进行焙烧，得到所述负极活性材料。
发明人在研究中发现，采用喷雾干燥造粒的方法，生成的负极复合材料中不含有粘结剂，有利于提高电池的倍率性能。
其中，喷雾干燥造粒机进口温度240-280℃，优选为260℃；出口温度100-110℃，优选为105℃。
发明人在研究中还发现，造粒后的材料在惰性气氛中进行焙烧可以有效去除材料中的水分及有机物等杂质；负极材料的焙烧温度对电池循环膨胀和容量保持具有较大的影响，不限于任何理论地，处理温度过高，例如高于900℃，会导致材料团聚，从而Dv50明显增大，循环膨胀后造成小颗粒之间接触变差，造成循环容量衰减加速，以及电池膨胀增大。当处理温度过低，例如低于600℃时，会导致石墨烯制备过程中残留的分散剂分解不完全，复合材料表面活性基团多，生成的固体电解质界面(SEI)更多，循环膨胀增加， 容量维持率降低。
在本申请一些实施方式中，焙烧条件为：焙烧温度为600～900℃，保温时间1-5小时，优选2小时；焙烧时，升温速率可选择3-8℃/min，优选为5℃/min。
本申请第二方面提供了一种负极极片，包括集流体和涂布在集流体上的合剂层，所述合剂层包含本申请第一方面所提供的负极复合材料。
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。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。
本申请第三方面提供了一种电池，包括本申请第二方面所提供的负极极片。
在本申请第三方面的一些实施方式中，所述电池的膨胀率为6.5-10％。
本申请的电池包括但不限于：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。一种典型的电池就是锂离子电池，其是一种二次电 池。所述电池，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。
本申请提供的电池，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
电池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。
本申请还提供了一种电子设备，其包含本申请提供的电池。
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。
复合材料粒度测试：
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。
全电池性能测试：
循环测试：
测试温度为25℃，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5、16、19以及对比例4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。
倍率性能：
测试温度为25℃，以0.5C恒流充电到4.45V，恒压充电到0.025C，静置5分钟后以0.2C放电到3.0V。以此步得到的容量为初始容量，进行0.5C充电，2C放电，2C放电容量与0.2C放电容量比值为倍率性能。
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。25℃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，(此前得到的容量为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。
半电池首次可逆容量测试：将各实施例和对比例中得到的负极极片在干燥环境中用冲压机切成直径为1.4cm的圆片，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 池测试系统检测半电池首次可逆容量，结果如表1和表2所示。
半电池首次效率测试：以锂片为对电极，组装成纽扣电池，0.05C放电至5mV,再以0.05mA放电至5mv，静置1小时后，用0.01mA放电5mv，(此前得到嵌锂容量C 0)，静置5min，0.05C充电到2.0V(得到脱锂容量D 0)，半电池首次效率＝D 0/C 0。
全电池制备：
负极合剂层材料制备：
1)在MSK-SFM-10真空搅拌器中，分别将各实施例和对比例中制备的负极复合材料2.8kg和35g导电炭黑加入到搅拌器中搅拌40min公转速度10～30rpm；
2)将95g聚偏氟乙烯加入到1)中搅拌的混合物中，搅拌60min分散均匀，再加入去离子水搅拌120min分散均匀，得到粘度为2000mPa.S，固含量为35％的混合浆料；复合材料、导电剂、粘结剂质量比为：95.6:1.2:3.2；
3)将2)中得到的混合浆料用170目双层筛网过滤，即得到负极合剂层材料。
负极极片制备：
将制备的负极合剂层材料涂布于厚度为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。
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，并卷绕得到裸电芯。将裸电芯置于外包装中，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
1、将1kg硅氧化物(Dv50为5μm)粉末与9kg石墨(Dv50为8um)加入到水中，在MSK-SFM-10真空搅拌器中搅拌180min，公转速度10～40rpm，混合均匀(硅基材料含量10wt％)。
2、将2.04kg，固含量10％的石墨烯(10层结构)水基浆料加入到搅拌器中，搅拌120min分散均匀。加入5kg的去离子水，继续搅拌120min得到混合浆料，公转转速为40rpm，自转转速为1500rpm，固体中的石墨烯含量为2％。
3、将2)中的浆料转移到喷雾干燥造粒机的离心转盘喷头，离心转速为5000rpm，形成微小雾滴。喷雾干燥造粒机进口温度260℃，出口温度为105℃，冷却收集造粒料。
4、将3)中的造粒料在惰性气氛(Ar)中进行焙烧，升温速率控制在5℃/min，在750℃保持2h。将粉末过400目筛，得到所需负极复合材料。
实施例2-4
将实施例1中的石墨烯，分别替换为具有7层、5层、3层结构的石墨烯，其余均与实施例1相同；其中实施例3所制备的负极复合材料的扫描电镜照片(SEM照片)如图1所示。
实施例5-8
调整实施例3中石墨烯浆料的用量为5.26kg、11.11kg、17.65kg、25kg，使石墨烯的含量分别为5％、10％、15％、20％，其余均与实施例3相同。
实施例9
将实施例5中的硅基材料替换为硅(Si)，其余与实施例5相同。
实施例10
将实施例5中的硅基材料替换为硅碳材料(SiC)，其余与实施例5相同。
实施例11、12
将实施例5中焙烧温度分别调整为600℃和900℃，其余与实施例5均相 同。
实施例13
将实施例5中，将2kg硅氧化物粉末与8kg石墨混合，使硅基材料的含量为20％，其余与实施例5均相同。
实施例14
将实施例5中，将5kg硅氧化物粉末与5kg石墨混合，使硅基材料的含量为50％，其余与实施例5均相同。
实施例15
将实施例5中，将8kg硅氧化物粉末与2kg石墨混合，使硅基材料的含量为80％，其余与实施例5均相同。
实施例16
将实施例5中，直接采用10kg硅氧化物，使硅基材料的含量为100％，其余与实施例5均相同。
实施例17、18
调整实施例5中硅氧化物的粒径(Dv50)分别为3.5μm、8μm，其余与实施例5相同。
实施例19、20
调整实施例5中石墨的粒径(Dv50)分别为15μm、20μm，其余与实施例5相同。
对比例1、2
将实施例5中的石墨烯，分别替换为具有15层结构和单层结构的石墨烯，其余均与实施例5相同。
对比例3
调整实施例5中石墨烯浆料的用量为33.3kg，使石墨烯的含量分别为25％，其余均与实施例5相同。
对比例4
实施例5中，直接采用5kg去离子水代替石墨烯浆料，其余均与实施例5相同(即不含石墨烯)。
对比例5、6
将实施例5中焙烧温度分别调整为500℃和1000℃，其余与实施例5均相同。
对比例7
实施例5中，直接采用10kg石墨，即不含硅基材料，其余与实施例5均相同。
对比例8
将实施例5中，将0.5kg硅氧化物粉末与9.5kg石墨混合，使硅基材料的含量为5％，其余与实施例5均相同。
对比例9
调整实施例5中硅氧化物的粒径(Dv50)为1.5μm，其余均与实施例5相同。
对比例10
调整实施例5中石墨的粒径(Dv50)为25μm，其余均与实施例5相同。
各实施例中负极复合材料的参数及性能测试结果见表1；各对比例中负极复合材料的参数及性能测试结果见表2。
表1
Figure PCTCN2020080745-appb-000001
Figure PCTCN2020080745-appb-000002
表2
Figure PCTCN2020080745-appb-000003
实施例1-12与对比例4对比可见，相同硅含量条件下，混合石墨烯造粒，可明显改善负极材料的导电性，全电池倍率得到明显提升。
通过实施例1、2、3、4相比较，在石墨烯层数满足10-3层时，随着石墨烯层数减少，粉末电导率增加；而随着导电性增加，锂离子更容易在负极材料中脱出和嵌入，所以首次可逆容量增加。随着石墨烯层数的增加，材料比表面积也增加，颗粒更容易团聚，因此复合材料的粒径随之增加；另外，比表面积增加会导致电解液与活性物质接触面更大，生成更多的SEI膜，全电池循环膨胀增加，容量衰减加速，容量保持率下降更明显。
实施例5与对比例1，2对比可见，石墨烯层数超过10层或为单层时，导电性明显降低，不限于任何理论地，发明人认为，因为石墨烯层数过多时，暴露的端面更多，缺陷会增多，从而导致导电性降低；单层石墨烯容易产生褶皱，导致电阻增加，从而导电性也降低。
另外，石墨烯具有滑移作用，可缓解膨胀应力，在循环膨胀后可恢复到原始状态，但从对比例2中可以看出，层数＜3层时，负极材料嵌锂膨胀会导致石墨烯滑移过多，导致石墨烯无法恢复，从而膨胀增加，循环容量衰减加速。
通过实施例3、5、6、7、8与对比例3的比较可以看出，石墨烯含量增加也可明显提升材料导电性，同时，电池倍率性能也随石墨烯含量的增加而提高；但是当石墨烯含量＞20％(对比例3)时，电率性能反而降低，不限于任何理论，发明人认为，石墨烯含量过高可能会导致硅和石墨周围的石墨烯太多，影响锂离子的嵌入和脱出，所以全电池倍率性能变差。
此外，发明人还发现，石墨烯含量＜5％时，随着导电性的增加，复合材料的首次可逆容量明显提升，但当含量超过5％时，随着导电性的增加，复合材料的克容量反而下降，不限于任何理论地，这可能是石墨烯含量的增多导致高容量的硅基材料总体含量下降造成的。另一方面，随着石墨烯含量增加，全电池首次效率降低，不限于任何理论地，发明人认为，这可能是由于石墨烯含量的增加使复合材料比表面积明显增加，与电解液接触面积更大，生成 更多的SEI膜，从而导致首次效率更低。
实施例5、11、12与对比例5、6比较可以看出，当焙烧温度高于900℃时，复合材料易发生聚集，因此复合材料的粒径增大；不限于任何理论地，发明人认为，粒径增加，导致循环膨胀后造成小颗粒之间接触变差，循环容量衰减加速，以及电池膨胀增加；而当焙烧温度低于600℃时，会导致石墨烯浆料中的分散剂分解不完全，表面活性基团多，生成的SEI更多，循环膨胀增加，容量维持率降低。
实施例5、13、14、15、16与对比例7、8对比说明，硅基活性物质含量越高，材料的克容量越高。但是随着容量的增加电池循环过程中的膨胀增大，当硅基含量超过20％时，膨胀增加明显。硅含量＜10％时，无法满足高能量密度的需求(高能量密度需求阳极克容量＞500mAh/g)
实施例5、17、18与对比例9对比说明，硅基材料Dv50＜3μm时，复合材料粒径Dv50＜9.5μm，材料比表面积大，与电解液接触面积更大，不可逆锂损失更多，循环容量保持率降低。实施例5、19、20与对比例10相比可以看出，当石墨Dv50＞20μm时，复合材料Dv50＞40μm，会造成电池循过程中局部膨胀大，膨胀过大会导致极片中材料之间的电接触变差，电池容量下降加速；综合数据考虑优选8μm＜石墨Dv50+硅Dv50＜15um。
以上所述仅为本发明的较佳实施例，并不用以限制本发明，凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明保护的范围之内。

Claims (10)

  1. 一种负极复合材料，包括硅基材料、石墨烯和石墨，其中，
    所述石墨烯占负极复合材料质量的1％～20％；所述硅基材料占石墨与硅基材料总质量的10～100％；
    所述硅基材料的Dv50为3.0-10μm；所述石墨的Dv50为8.0-20μm；所述负极复合材料的Dv50为9.5-40μm。
  2. 根据权利要求1所述的负极复合材料，其中，石墨烯的层数为3-10层。
  3. 根据权利要求1所述的负极复合材料，其中，所述石墨包括天然石墨、人造石墨或中间相碳微球中的至少一种。
  4. 根据权利要求1所述的负极复合材料，其中，所述硅基材料包括硅、硅氧化物或硅碳材料中的至少一种。
  5. 根据权利要求1-4中任一项所述的负极复合材料，其中，所述硅基材料的至少一部分表面存在碳。
  6. 根据权利要求1-4中任一项所述的负极复合材料，其中，所述负极复合材料的电导率为2.0～30S/cm。
  7. 一种负极极片，包括集流体和涂布在集流体上的合剂层，所述合剂层包含权利要求1-6中任一项所述的负极复合材料。
  8. 一种电池，包括权利要求7所述的负极极片。
  9. 根据权利要求8所述的电池，其中，所述电池的膨胀率为6.5-10％。
  10. 一种电子装置，包括权利要求8或9所述的电池。
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