CN111668472A - Silicon-based composite negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Silicon-based composite negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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- CN111668472A CN111668472A CN202010600361.5A CN202010600361A CN111668472A CN 111668472 A CN111668472 A CN 111668472A CN 202010600361 A CN202010600361 A CN 202010600361A CN 111668472 A CN111668472 A CN 111668472A
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- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 109
- 239000010703 silicon Substances 0.000 title claims abstract description 109
- 239000007773 negative electrode material Substances 0.000 title claims abstract description 62
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 20
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 20
- 238000002360 preparation method Methods 0.000 title abstract description 14
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- QFBDCSDDHUBEGG-UHFFFAOYSA-N 1,2-dibutylnaphthalene;sodium Chemical compound [Na].C1=CC=CC2=C(CCCC)C(CCCC)=CC=C21 QFBDCSDDHUBEGG-UHFFFAOYSA-N 0.000 description 1
- QMWFSAOKXWLOGH-UHFFFAOYSA-N 1,2-dimethylnaphthalene;sodium Chemical compound [Na].C1=CC=CC2=C(C)C(C)=CC=C21 QMWFSAOKXWLOGH-UHFFFAOYSA-N 0.000 description 1
- WZGREKNBSLUCPW-UHFFFAOYSA-N 1-butylnaphthalene;sodium Chemical compound [Na].C1=CC=C2C(CCCC)=CC=CC2=C1 WZGREKNBSLUCPW-UHFFFAOYSA-N 0.000 description 1
- NNIYOCKBODDMIU-UHFFFAOYSA-N 1-methylnaphthalene;sodium Chemical compound [Na].C1=CC=C2C(C)=CC=CC2=C1 NNIYOCKBODDMIU-UHFFFAOYSA-N 0.000 description 1
- CDMGNVWZXRKJNS-UHFFFAOYSA-N 2-benzylphenol Chemical compound OC1=CC=CC=C1CC1=CC=CC=C1 CDMGNVWZXRKJNS-UHFFFAOYSA-N 0.000 description 1
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- 239000002253 acid Substances 0.000 description 1
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- 238000005275 alloying Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
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- MWOBKFYERIDQSZ-UHFFFAOYSA-N benzene;sodium Chemical compound [Na].C1=CC=CC=C1 MWOBKFYERIDQSZ-UHFFFAOYSA-N 0.000 description 1
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- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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Abstract
The invention provides a silicon-based composite negative electrode material, a preparation method thereof and a lithium ion battery. The negative electrode material comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, and the outer shell comprises a carbon coating layer and a polymer-carbon nano material composite material. The preparation method comprises the following steps: mixing graphite, an emulsifier and a first solvent to obtain an emulsified graphite emulsion; mixing the emulsified graphite emulsion with nano-silicon and granulating to obtain a first composite material; carbon coating is carried out on the first composite material to obtain a second composite material; and mixing a second composite material, a carbon nano material, a polymer monomer and a doping agent in a second solvent, adding an oxidant for reaction, and carrying out solid-liquid separation to obtain the silicon-based composite negative electrode material. The silicon-based composite negative electrode material provided by the invention has higher reversible capacity and first coulombic efficiency, and has lower volume expansion, excellent cycle performance and rate capability.
Description
Technical Field
The invention belongs to the technical field of energy storage materials, relates to a negative electrode material, a preparation method thereof and a lithium ion battery, and particularly relates to a silicon-based composite negative electrode material, a preparation method thereof and a lithium ion battery.
Background
The energy crisis and environmental problems of the current society are increasingly prominent, and the storage of novel clean energy and energy has become a hotspot of research of people. Under the background, the lithium ion battery basically occupies the market of portable consumer electronic products due to the characteristics of high energy density, high power density, long service life, environmental friendliness and the like, and has wide application prospects in the fields of electric automobiles, large-scale energy storage equipment, distributed mobile power supplies and the like. However, with the increase in demand, especially in the field of electric vehicles, which have been vigorously developed in recent years, the improvement in driving range has made the development of high energy density batteries urgent. The energy density of the battery is improved, and more problems are involved, if high-capacity anode and cathode materials with excellent performance need to be developed.
In the aspect of negative electrode materials, the theoretical capacity of the graphite negative electrode material which is most widely applied at present is 372mA · h/g, the actual measured capacity of the commercialized high-end graphite material reaches 365mA · h/g, and the technology is mature. The silicon material as the negative electrode material has high theoretical specific capacity (4200mAh/g), and the silicon has low voltage platform in the lithium intercalation and lithium deintercalation reaction, does not precipitate lithium on the surface, has good safety and is generally concerned and researched by the material field. However, silicon also has significant disadvantages, namely low silicon conductivity; in addition, the volume expansion change is huge in the silicon circulation process, pulverization is easy to occur, the active substances and the current collector lose electric contact and even further fall off from the current collector, and the circulation performance is seriously attenuated finally; in addition, the swelling causes the formed SEI film to be broken, exposes a new interface, and continues to form a new SEI film, resulting in an increasingly thick SEI film on the outer layer of the silicon particles after cycling, and eventually blocking the intercalation of lithium ions.
In order to solve the problem of silicon volume expansion, silicon is mainly modified, including silicon nanocrystallization, alloying, porosification, doping, cladding and the like. The carbon coating is conventionally formed by a solid phase method, a liquid phase method, an impregnation method. Although the side reaction of silicon and electrolyte can be reduced to a certain extent, and the volume expansion is inhibited, the problems that the carbon coating layer covers silicon unevenly and the bonding force between materials is poor exist, so that the long cycle performance of the composite material is poor, the expansion is too large, and the like.
Such as a preparation method of a silicon-carbon composite negative electrode material taking silica sol as a silicon source. The method comprises the following specific preparation steps: through silica sol pretreatment, SiO2Preparing the intercalation expanded graphite by taking SiO2The lithium battery negative electrode material comprises artificial graphite, natural graphite or hard carbon, the proportion of the artificial graphite, the natural graphite or the hard carbon is selected according to the requirements of different material capacities, and the adding quality is required to ensure that the theoretical silicon content is below 20%. Stirring and mixing the two, and reducing SiO in the mixture by using a magnesiothermic method2Reducing, and then carrying out acid washing, water washing, drying and crushing to obtain the silicon-carbon composite negative electrode material. Although the silicon-carbon composite negative electrode material is obtained by the scheme, the specific capacity of the composite negative electrode material obtained by the scheme is poor, and the cycle performance is to be improved.
Therefore, how to improve the first effect and the conductivity of the silicon-based composite material, effectively relieve the volume expansion of silicon, ensure the cycling stability of the silicon cathode, and obtain the silicon cathode material with high specific capacity, high multiplying power and long cycle life is a technical hotspot to be solved urgently in the field of the current lithium batteries.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a silicon-based composite negative electrode material, a preparation method thereof and a lithium ion battery. The silicon-based composite negative electrode material provided by the invention has higher reversible capacity and first coulombic efficiency, has lower volume expansion and excellent cycle performance and rate capability, is particularly suitable for a quick-charging lithium ion battery, and the preparation method has a simple process and is easy for large-scale production.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a silicon-based composite anode material, which comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, and the outer shell comprises a carbon coating layer and a polymer-carbon nano material composite material.
In the silicon-based composite negative electrode material provided by the invention, the hydrophilic emulsified graphite is selected to uniformly disperse the nano-silicon in the emulsified graphite network, and when the nano-silicon is fixed between the graphite after carbon coating, the electrical contact between the nano-silicon and the graphite is strengthened, and the volume expansion of the nano-silicon is favorably inhibited; in addition, under the synergistic action of the shell conductive polymer and the conductive carbon nano material, the conductivity of the composite material can be obviously improved, the impedance of the material is reduced, the quick charge performance of the material is improved, and the cycle life of the material is prolonged.
In the invention, the hydrophilic emulsified graphite is selected to be tightly combined with the nano-silicon by interface acting force on the basis of not forming a new chemical bond, so that the nano-silicon is uniformly dispersed in the emulsified graphite network, the electrical contact between the nano-silicon and the graphite is strengthened, and the volume expansion of the nano-silicon is favorably inhibited.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
As a preferable technical scheme, the emulsified graphite is prepared by emulsifying graphite with an emulsifier.
Preferably, the graphite comprises natural graphite and/or artificial graphite.
Preferably, the graphite has a median particle diameter of 1.0 μm to 8.0. mu.m, such as 1.0. mu.m, 2.0. mu.m, 3.0. mu.m, 4.0. mu.m, 5.0. mu.m, 6.0. mu.m, 7.0. mu.m, 8.0. mu.m, or the like, preferably 2.0. mu.m to 5.0. mu.m.
Preferably, the nano-silicon has a median particle diameter of 5.0 μm to 200.0nm, such as 5.0nm, 10.0nm, 20.0nm, 30.0nm, 40.0nm, 50.0nm, 60.0nm, 70.0nm, 80.0nm, 90.0nm, 100.0nm, 120.0nm, 130.0nm, 140.0nm, 150.0nm, 160.0nm, 170.0nm, 180.0nm, 190.0nm or 200.0nm, etc., preferably 10.0 to 100.0nm, and more preferably 20.0 μm to 80.0 nm.
Preferably, the median particle size of the inner core is from 1 μm to 8 μm, such as 1 μm, 2 μm, 4 μm, 6 μm or 8 μm and the like, preferably from 2 μm to 5 μm.
In a preferred embodiment of the present invention, the polymer-carbon nanomaterial composite includes at least one of carbon nanotubes, carbon fibers, and carbon nanoballs.
Preferably, the carbon fibers are acrylonitrile carbon fibers and/or pitch carbon fibers.
Preferably, the carbon fibers have a length of 10 μm to 50 μm, such as 10 μm, 20 μm, 30 μm, 40 μm or 50 μm, etc.
Preferably, the carbon nanoball is a fullerene-based carbon nanoball.
Preferably, the fullerene-based carbon nanoball includes at least one of C60, C70 and a non-completely graphitized nanocarbon sphere.
Preferably, the carbon nanoball has a diameter of 50nm to 1 μm, such as 50nm, 100nm, 500nm, or 1 μm, etc.
Preferably, in the polymer-carbon nanomaterial composite, the carbon nanomaterial has a hydrophilic group.
Preferably, the hydrophilic group includes at least one of a carboxylic acid group, a sulfonic acid group, a phosphoric acid amino group, a quaternary ammonium group, an ether group, a hydroxyl group, a carboxylic acid group, and a block polyether group.
Preferably, the carbon nanotubes have a diameter of 2nm to 20nm, such as 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm or 20nm, etc., preferably 2 to 10 nm.
Preferably, the carbon nanotubes have a length of 1 μm to 30 μm, such as 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm, and preferably 5 μm to 15 μm.
Preferably, the carbon nanotubes are single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
In the polymer-carbon nanomaterial composite material, the polymer is a conductive polymer.
Preferably, the conductive polymer includes at least one of polypyrrole, polyaniline, polythiophene, poly-p-phenylene, and poly-p-phenylene sulfide.
Preferably, in the housing, the carbon coating layer is an amorphous carbon layer.
Preferably, the outer shell comprises an inner layer on the surface of the inner core and an outer layer on the surface of the inner layer, the inner layer comprises a carbon coating layer, and the outer layer comprises a polymer-carbon nano-material composite material.
In the invention, when the polymer in the polymer-carbon nano material composite material is polypyrrole and the carbon nano material is a carbon nano tube, the polypyrrole is easy to polymerize into a film, so that the conductivity and the surface stability of the material can be improved. The coated carbon nano tube can enhance the structural stability of the carbon nano tube, and the molecular chain of the polymer can isolate the carbon nano tube, thereby improving the dispersibility of the carbon nano tube and enhancing the interaction of the carbon nano tube and the composite material. On the contrary, because p electrons of carbon atoms on the carbon nano tube form a large-range delocalized pi bond, the conjugation effect is obvious, so that polypyrrole forms a larger conjugation system, the mobility of polarons on a polypyrrole conjugation chain is favorably improved, and the conductivity of the polypyrrole is increased; in addition, carbon atoms in the carbon nano tubes adopt SP2Hybridization to make it have very high strength and toughnessThe defects of mechanical property of the polypyrrole are compensated. Namely, under the synergistic effect of polypyrrole and carbon nanotubes, the conductivity of the composite material can be obviously improved, the impedance of the material is reduced, the quick-filling performance of the material is improved, and the cycle life of the material is prolonged.
Preferably, the inner layer has a thickness of 1 μm to 5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, etc., preferably 2 μm to 4 μm.
Preferably, the outer layer has a thickness of 10nm to 200nm, such as 10nm, 50nm, 100nm, 150nm or 200nm, etc., preferably 50nm to 100 nm.
Preferably, the mass percentage of the nano silicon is 20-50%, such as 20%, 30%, 40% or 50%, and preferably 30-40%, based on 100% of the mass of the silicon-based composite anode material.
Preferably, the mass percentage of the emulsified graphite is 15-35%, such as 15%, 20%, 25%, 30% or 35%, and preferably 20-30%, based on 100% of the mass of the silicon-based composite anode material.
Preferably, the mass percentage of the carbon coating layer is 15% to 35%, such as 15%, 20%, 25%, 30% or 35%, and preferably 20% to 30%, based on 100% of the mass of the silicon-based composite anode material.
Preferably, the mass percentage of the carbon nano material is 1-5%, such as 1%, 2%, 3%, 4% or 5%, and preferably 1-2%, based on 100% of the mass of the silicon-based composite anode material.
Preferably, the mass percentage of the polymer is 1-5%, such as 1%, 2%, 3%, 4% or 5%, and preferably 1-3%, based on 100% of the mass of the silicon-based composite anode material.
In a second aspect, the present invention provides a method for preparing the silicon-based composite anode material according to the first aspect, the method comprising the following steps:
mixing graphite, an emulsifier and a first solvent to obtain an emulsified graphite emulsion;
mixing the emulsified graphite emulsion with nano-silicon and granulating to obtain a first composite material;
carrying out carbon coating on the first composite material to obtain a second composite material;
and mixing the second composite material, the carbon nano material, the polymer monomer and the doping agent in a second solvent, adding an oxidant for reaction, and carrying out solid-liquid separation to obtain the silicon-based composite negative electrode material.
In the preparation method provided by the invention, the first composite material is a silicon/emulsified graphite composite material, and the second composite material is a carbon-coated silicon/emulsified graphite composite material.
In the present invention, the dopant serves to oxidize or reduce the polymer, thereby improving the electrical conductivity of the polymer.
The preparation method provided by the invention is simple in process and easy for large-scale production.
The oxidizing agent is preferably added slowly to the dispersion.
In a preferred embodiment of the present invention, the emulsifier is a nonionic emulsifier and/or an anionic emulsifier.
Preferably, the ionic emulsifier is an ether nonionic emulsifier and/or an ester nonionic emulsifier.
Preferably, the ether nonionic emulsifier comprises any one or a combination of at least two of alkylphenol polyoxyethylene ether, benzyl phenol polyoxyethylene ether, phenethylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, phenethylphenol polyoxyethylene ether polyoxypropylene ether or fatty amine polyoxyethylene ether.
Preferably, the ester-type nonionic emulsifier includes any one of or a combination of at least two of polyoxyethylene fatty acid ester, polyoxyethylene castor oil ester, polyol fatty acid ester, or polyoxyethylene ester.
Preferably, the anionic emulsifier is a sulfonic acid-based emulsifier and/or a sulfuric acid-based emulsifier.
Preferably, the anionic emulsifier comprises any one or a combination of at least two of dialkyl benzene sodium sulfonate, alkyl aryl sodium sulfonate, dodecyl benzene sodium sulfonate, butyl naphthalene sodium sulfonate, dibutyl naphthalene sodium sulfonate, diisopropyl naphthalene sodium sulfonate, monomethyl naphthalene sodium sulfonate, dimethyl naphthalene sodium sulfonate, alkyl alkenyl sodium sulfonate, hydroxyalkyl sodium sulfonate, alkyl succinate sodium sulfonate, alkyl polyoxyethylene ether succinate sulfonate, alkylphenol polyoxyethylene ether succinate sulfonate, alkyl diphenyl ether sulfonate, naphthalene sulfonic acid formaldehyde condensate or sodium dodecyl sulfate.
Preferably, the first solvent comprises water and/or an organic solvent.
Preferably, the step of mixing the graphite, the emulsifier and the solvent is an operation of adding a co-emulsifier.
Preferably, the co-emulsifier comprises at least one of n-butanol, ethylene glycol, ethanol, propylene glycol, glycerol, and polyglycerol ester.
Preferably, the method of mixing in the step of mixing graphite, an emulsifier and a solvent is accelerated stirring.
Preferably, the method of mixing in the step of mixing and granulating the emulsion of graphite with nano-silicon is ultrasonic dispersion.
Preferably, the granulation method is spray drying granulation.
As a preferred embodiment of the present invention, the carbon coating method includes: pyrolysis and/or chemical vapor deposition;
preferably, the pyrolysis process comprises: mixing the first composite material and an organic carbon source, and then carrying out coating treatment under protective gas.
Preferably, the organic carbon source comprises any one of a polymer, a saccharide, an organic acid, or pitch, or a combination of at least two thereof.
Preferably, the organic carbon source comprises any one of polyvinyl butyral, sucrose, glucose, maltose, citric acid, pitch, furfural resin, epoxy resin, or phenolic resin, or a combination of at least two thereof.
Preferably, the organic carbon source is in the form of a powder with a median particle size of 0.5 μm to 5 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, and the like.
Preferably, the first composite material and the organic carbon source are mixed in a VC mixer at a mixing speed of 500.0rpm to 3000.0rpm, such as 500.0rpm, 1000.0rpm, 1500.0rpm, 2000.0rpm, 2500.0rpm, 3000.0rpm, or the like, for a mixing time of 0.5h or more, such as 0.5h, 1h, 1.5h, 2h, or the like.
Preferably, the protective gas comprises any one of nitrogen, helium, neon, argon or hydrogen or a combination of at least two thereof.
Preferably, the temperature of the coating treatment under a protective gas is 550 ℃ to 1200 ℃, such as 550 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, or 1200 ℃.
Preferably, the temperature rise rate of the coating treatment under the protective gas is 1 ℃/min to 20 ℃/min, such as 1 ℃/min, 5 ℃/min, 10 ℃/min, 15 ℃/min or 20 ℃/min and the like.
Preferably, the time for the coating treatment under the protective gas is 0.5h to 8h, such as 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h or 8 h.
Preferably, the chemical vapor deposition method includes: and mixing the first composite material with a gas-phase organic carbon source, and performing coating treatment under a rotating condition.
Preferably, the gas phase organic carbon source is at least one of methane, ethylene, acetylene, benzene, toluene, xylene, styrene, phenol, ethane, propane, and acetone.
Preferably, the speed of rotation is 0.2rpm to 10rpm, such as 0.2rpm, 0.5rpm, 1rpm, 2rpm, 5rpm, 8rpm, 10rpm, or the like.
Preferably, the temperature of the coating treatment is 600 ℃ to 1200 ℃, such as 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃ or the like, preferably 700 ℃ to 1000 ℃.
Preferably, the time of the coating treatment is 1h to 8h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h or 8h, and the like.
Preferably, the median particle diameter of the second composite material is from 1.0 μm to 10.0 μm, such as 1.0 μm, 2.0 μm, 5.0 μm, 8.0 μm, or 10.0 μm, and the like.
Preferably, after the carbon coating, the method further comprises: the resulting product is cooled, crushed and sieved.
As a preferred embodiment of the present invention, the carbon nanomaterial includes at least one of a carbon nanotube, a carbon fiber, and a carbon nanoball.
Preferably, the polymer monomer includes at least one of pyrrole monomer, aniline monomer, thiophene monomer, p-phenylene monomer and p-phenylene sulfide monomer.
Preferably, the dopant includes at least one of p-toluenesulfonic acid, sodium dodecylbenzenesulfonate, camphorsulfonic acid, hydrochloric acid, and sodium dodecylsulfonate.
Preferably, the second solvent comprises water and/or an organic solvent.
Preferably, the mixing in the step of mixing the second composite material, the carbon nanomaterial, the polymer monomer, and the dopant in the second solvent is ultrasonic dispersion.
Preferably, the oxidant comprises at least one of ammonium persulfate, ferric trichloride, ferric perchlorate and hydrogen peroxide.
Preferably, the temperature of the reaction in the step of adding an oxidizing agent to carry out the reaction is 0 ℃ to 5 ℃, for example, 0 ℃, 1 ℃, 2 ℃, 3 ℃, 4 ℃ or 5 ℃, etc.
Preferably, the reaction is carried out for a time of 18h to 24h, such as 18h, 20h, 22h or 24h, etc.
Preferably, the solid-liquid separation is centrifugal separation.
Preferably, the method further comprises the steps of washing the solid obtained by the solid-liquid separation with ethanol, washing with water and drying.
As a preferred technical scheme of the invention, the method comprises the following steps:
stirring and mixing graphite, an emulsifier, an auxiliary emulsifier and water at an accelerated speed to obtain an emulsified graphite emulsion;
carrying out ultrasonic dispersion and spray drying granulation on the emulsified graphite emulsion and nano-silicon to obtain a first composite material;
mixing the first composite material and the organic carbon source in a VC mixer, wherein the mixing speed is 500.0-3000.0 rpm, the mixing time is more than 0.5h, then heating to 550-1200 ℃ at the heating rate of 1-20 ℃/min under protective gas for reaction for 0.5-8 h, and cooling, crushing and screening the obtained product to obtain a second composite material with the median particle size of 1.0-10.0 mu m;
or introducing a gas phase carbon source into the first composite material, and depositing for 1h-8h at the rotation speed of 0.2-10 rpm and the temperature of 700-1000 ℃ to obtain a second composite material with the median particle size of 1.0-10.0 μm;
and ultrasonically dispersing the second composite material, the carbon nano tube, the pyrrole monomer and the dopant in water, adding an oxidant to react at 0-5 ℃, centrifugally separating to obtain a solid, and washing the obtained solid with ethanol, washing with water and drying to obtain the silicon-based composite negative electrode material.
In a third aspect, the present invention provides a lithium ion battery comprising the silicon-based composite anode material according to the first aspect.
Preferably, the lithium ion battery is a fast-charging lithium ion battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) in the silicon-based composite negative electrode material provided by the invention, the hydrophilic emulsified graphite can enable the nano-silicon to be uniformly dispersed in the emulsified graphite network, and when the nano-silicon is fixed between the graphite after carbon coating, the electrical contact between the nano-silicon and the graphite is strengthened, and the volume expansion of the nano-silicon is favorably inhibited; in addition, the carbon nano material (such as the carbon nano tube) is coated by the polymer (such as polypyrrole) in the shell, the structural stability of the carbon nano material is maintained, and the carbon nano material enables the polymer to form a larger conjugated system, so that the mobility of electrons on a conjugated chain of the polymer is improved, namely, under the synergistic effect of the polymer and the carbon nano material, the conductivity of the composite material can be obviously improved, the impedance of the material is reduced, the quick charging performance of the material is improved, and the cycle life of the material is prolonged. Therefore, the material has lower volume expansion, higher first coulombic efficiency, excellent rate capability and excellent cycling stability when being used as the lithium ion battery cathode material.
The first reversible capacity of the silicon-based composite negative electrode material provided by the invention is more than 900mAh/g and can reach 1035mAh/g to the maximum, the first coulombic efficiency is more than 85 percent and can reach more than 90 percent to the maximum, the retention rate of the 100-time circulating capacity is more than 91.5 percent and can reach more than 95.6 percent to the maximum, the constant-current charging capacity ratio of 0.5C can reach more than 80 percent, and the silicon-based composite negative electrode material has excellent rate capability.
(2) The preparation method provided by the invention is simple in process and easy for large-scale production.
Drawings
Fig. 1 is an SEM image of a silicon-based composite anode material provided in example 1 of the present invention.
Fig. 2 is a diffraction pattern of a crystal structure of the silicon-based composite anode material provided in embodiment 1 of the present invention.
Fig. 3 is a first charge-discharge curve diagram of the silicon-based composite anode material prepared in example 1 of the present invention.
Fig. 4 is a cycle curve of a lithium ion battery assembled by using the silicon-based composite anode material provided in example 1 of the present invention.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
The following are typical but non-limiting examples of the invention:
example 1
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 37.5g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 60g of silicon particles with the median particle size of 50nm into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 5 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 3 mu m) into a VC mixer according to the mass ratio of 1:0.8, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving the temperature for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 8.0 mu m.
(3) And (3) adding 3g of the second composite material in the step (2), the carbon nano tube with the diameter of 5nm and the length of 10 microns, 4mL of pyrrole monomer and 0.5g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 1mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 2 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon nanotube composite material. The median particle size of the natural graphite is 3 μm, and the median particle size of the nano silicon is 50 nm; the carbon nano tube has a diameter of 5nm and a length of 10 μm, and has a sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 5 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon nano tube is 2%, and the mass percentage of the polypyrrole is 3%.
Fig. 1 is an SEM image of the silicon-based composite anode material provided in this example, and it can be seen from the SEM image that the particle size of the anode material provided in example 1 is about 8 μm.
Fig. 2 is a diffraction diagram of a crystal structure of the silicon-based composite anode material provided in this embodiment, and it can be seen from the diagram that a silicon peak and a graphite peak are obvious, and a broad peak with lower intensity is seen at 25 °, which proves that polypyrrole, which is a conductive layer in the intermediate layer, has a certain crystallinity.
Example 2
In this example, the kind of raw materials and the operating conditions were the same as those of example 1 except that the graphite used in step (1) was an artificial graphite having a median particle diameter of 3 μm.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon nanotube composite material. The median particle size of the artificial graphite is 3 μm, and the median particle size of the nano-silicon is 50 nm; the carbon nanotubes have a diameter of 5nm and a length of 10 μm. The carbon nano tube has sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 5 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon nano tube is 2%, and the mass percentage of the polypyrrole is 3%.
Example 3
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 37.5g of natural graphite with the median particle size of 2 mu m, 5g of fatty acid polyoxyethylene ester and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 60g of silicon particles with the median particle size of 20nm into the liquid, performing ultrasonic treatment for 10min, and performing spray drying to obtain a first composite material with the median particle size of 3.5 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 0.5 mu m) into a VC mixer according to the mass ratio of 1:0.8, mixing at the rotating speed of 500rpm/min for 1.5h, then placing the mixture into a high-temperature furnace, introducing argon gas, heating to 550 ℃ at the speed of 1.0 ℃/min, preserving heat for 8h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 6.0 mu m.
(3) And (3) adding 3g of C60 with the median particle size of 100nm, 4mL of pyrrole monomer and 0.4g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 1.5mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 0 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite anode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-C60 composite material. The median particle size of the graphite is 2 μm, and the median particle size of the nano silicon is 20 nm; the median particle size of C60 was 100 nm. C60 has sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 4 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the C60 is 2%, and the mass percentage of the polypyrrole is 3%.
Example 4
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 45g of natural graphite with the median particle size of 5 microns, 6g of sodium diisopropyl naphthalene sulfonate and 25mL of ethanol into 200mL of water, accelerating stirring, then adding 67.5g of silicon particles with the median particle size of 80nm into the liquid, performing ultrasonic treatment for 10min, and performing spray drying to obtain a first composite material with the median particle size of 7 microns;
(2) adding the first composite material and phenolic resin (the median particle size is 5 microns) into a VC mixer according to the mass ratio of 1:0.8, mixing at the rotating speed of 2000rpm/min for 3h, then placing the mixture into a high-temperature furnace, introducing argon gas, heating to 1000 ℃ at the speed of 20 ℃/min, preserving heat for 0.5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 10.0 mu m.
(3) And (3) adding the second composite material obtained in the step (2), 4g of carbon fiber with the length of 30 microns, 5mL of pyrrole monomer and 0.6g of sodium dodecyl sulfate into 100mL of water for ultrasonic dispersion, slowly adding 10mL of ferric perchlorate solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 5 ℃ for 18 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and a shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the shell consists of an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon fiber composite material. The median particle size of the graphite is 5 μm, and the median particle size of the nano silicon is 80 nm; the length of the carbon fibers was 30 μm. The carbon fiber has sulfonic acid groups.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 6 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 120 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 35%, the mass percentage of the emulsified graphite is 30%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon fiber is 2%, and the mass percentage of the polypyrrole is 3%.
Example 5
The operation of the steps of the present invention other than the step (2) was the same as in example 1. In the operation of step (2) of this example, a gas phase carbon source, methane, was introduced into a reactor containing the composite material of step (2), the reactor was rotated at 5rpm, and deposition was carried out at 850 ℃ for 6 hours to obtain a second composite material having a median particle size of 5 μm.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 6 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon nano tube is 2%, and the mass percentage of the polypyrrole is 3%.
Examples 6,
The operation of the steps of the present invention other than the step (2) was the same as in example 1. In the operation of step (2) of this example, a gaseous carbon source, ethylene, was introduced into a reactor containing the composite material of step (2), the reactor was rotated at 0.2rpm and deposited at 700 ℃ for 6 hours to obtain a second composite material having a median particle size of 5 μm.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 6 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon nano tube is 2%, and the mass percentage of the polypyrrole is 3%.
Example 7
The operation of the steps of the present invention other than the step (2) was the same as in example 1. In the operation of step (2) of this example, a gas phase carbon source, methane, was introduced into a reactor containing the composite material of step (2), the rotation speed of the reactor was 10rpm, and the deposition was performed at 1000 ℃ for 6 hours to obtain a second composite material having a median particle size of 5 μm.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 6 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 40%, the mass percentage of the emulsified graphite is 25%, the mass percentage of the amorphous carbon layer is 30%, the mass percentage of the carbon nano tube is 2%, and the mass percentage of the polypyrrole is 3%.
Example 8
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 30g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 75g of silicon particles with the median particle size of 50nm into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 5 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 3 mu m) into a VC mixer according to the mass ratio of 1.75:1, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving the temperature for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 8.0 mu m.
(3) And (3) adding 7.5g of the second composite material in the step (2), a carbon nano tube with the diameter of 5nm and the length of 10 microns, 6mL of pyrrole monomer and 1.5g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 1mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 2 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon nanotube composite material. The median particle size of the natural graphite is 3 μm, and the median particle size of the nano silicon is 50 nm; the carbon nano tube has a diameter of 5nm and a length of 10 μm, and has a sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 5 μm, the thickness of the inner layer in the shell is 1.5 μm, and the thickness of the outer layer is 100 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 50%, the mass percentage of the emulsified graphite is 20%, the mass percentage of the amorphous carbon layer is 20%, the mass percentage of the carbon nano tube is 5%, and the mass percentage of the polypyrrole is 5%.
Example 9
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 52.5g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 30g of silicon particles with the median particle size of 50nm into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 6 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 3 mu m) into a VC mixer according to the mass ratio of 1:1.27, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving the temperature for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 9.0 mu m.
(3) And (3) adding 7.5g of the second composite material in the step (2), a carbon nano tube with the diameter of 5nm and the length of 10 microns, 6mL of pyrrole monomer and 1.5g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 1mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 2 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon nanotube composite material. The median particle size of the natural graphite is 3 μm, and the median particle size of the nano silicon is 50 nm; the carbon nano tube has a diameter of 5nm and a length of 10 μm, and has a sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 6 μm, the thickness of the inner layer in the shell is 2.5 μm, and the thickness of the outer layer is 125 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 20%, the mass percentage of the emulsified graphite is 35%, the mass percentage of the amorphous carbon layer is 35%, the mass percentage of the carbon nano tube is 5%, and the mass percentage of the polypyrrole is 5%.
Example 10
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 45g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 64.5g of silicon particles with the median particle size of 50nm into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 7 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 3 mu m) into a VC mixer according to the mass ratio of 1.46:1, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving the temperature for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 9.0 mu m.
(3) And (3) adding 1.5g of the second composite material in the step (2), the carbon nano tube with the diameter of 5nm and the length of 10 microns, 1mL of pyrrole monomer and 0.15g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 1mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 2 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
The silicon-based composite negative electrode material provided by the embodiment comprises an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, the outer shell comprises an inner layer positioned on the surface of the inner core and an outer layer positioned on the surface of the inner layer, the inner layer is an amorphous carbon layer, and the outer layer is a polypyrrole-carbon nanotube composite material. The median particle size of the natural graphite is 3 μm, and the median particle size of the nano silicon is 50 nm; the carbon nano tube has a diameter of 5nm and a length of 10 μm, and has a sulfonic acid group.
The median particle size of the core of the silicon-based composite negative electrode material provided by the embodiment is 7 μm, the thickness of the inner layer in the shell is 1.0 μm, and the thickness of the outer layer is 50 nm. By taking the mass of the silicon-based composite negative electrode material as 100%, the mass percentage of the nano silicon is 43%, the mass percentage of the emulsified graphite is 30%, the mass percentage of the amorphous carbon layer is 25%, the mass percentage of the carbon nano tube is 1%, and the mass percentage of the polypyrrole is 1%.
Comparative example 1
(1) Respectively adding 37.5g of natural graphite with the median particle size of 3 mu m, 60g of silicon particles with the median particle size of 50nm and 75g of epoxy resin into a VC mixer, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving heat for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain the silicon-based composite material with the median particle size of 8.0 mu m.
(2) And adding 3g of carbon nano tube with the diameter of 5nm and the length of 10 mu m, 4mL of pyrrole monomer and 0.5g of p-toluenesulfonic acid into 100mL of water for ultrasonic dispersion, slowly adding 10mL of ferric trichloride solution with the concentration of 1moL/L into the dispersion, stirring and reacting at 0-5 ℃ for 24 hours, centrifugally separating the obtained product, washing with ethanol and water, and drying to obtain the silicon-based composite negative electrode material.
This comparative example did not emulsify graphite compared to example 1.
Comparative example 2
(1) Adding 37.5g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 60g of 50nm silicon particles, 3g of carbon nano tubes with the diameter of 5nm and the length of 10 mu m into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 5 mu m;
(2) the first composite material and the epoxy resin are respectively added into a VC mixer according to the mass ratio of 1:1.5, the mixture is mixed for 1h at the rotating speed of 3000rpm/min, then the mixture is placed into a high-temperature furnace, nitrogen gas is introduced, the temperature is raised to 1100 ℃ at the speed of 2.0 ℃/min, the temperature is kept for 5h, and the mixture is naturally cooled to the room temperature. And crushing and screening the high-temperature product to obtain the silicon-based composite material with the median particle size of 8.0 mu m.
This comparative example does not coat the silicon-based composite with an outer layer of polypyrrole-carbon nanotube composite relative to example 1.
Comparative example 3
In this example, a silicon-based composite anode material was prepared as follows:
(1) adding 37.5g of natural graphite with the median particle size of 3 mu m, 4g of sodium dodecyl benzene sulfonate and 20mL of ethanol into 200mL of water, accelerating stirring, then adding 60g of silicon particles with the median particle size of 50nm into the liquid, and performing ultrasonic treatment for 10min and then performing spray drying to obtain a first composite material with the median particle size of 5 mu m;
(2) respectively adding the first composite material and epoxy resin (the median particle size is 3 mu m) into a VC mixer according to the mass ratio of 1:0.8, 3g of carbon nano tubes with the diameter of 5nm and the length of 10 mu m and 4.5g of pre-prepared polypyrrole, mixing at the rotating speed of 3000rpm/min for 1h, then placing the mixture into a high-temperature furnace, introducing nitrogen gas, heating to 1100 ℃ at the speed of 2.0 ℃/min, preserving heat for 5h, and naturally cooling to room temperature. And crushing and screening the high-temperature product to obtain a second composite material with the median particle size of 8.0 mu m.
This comparative example has a single-layer structure of the outer shell, compared to example 1.
Testing
(1) Apparent morphology: observing the surface appearance and the particle size of a sample by adopting a scanning electron microscope of Hitachi S4800;
(2) the material structure is as follows: testing the structure of the material by adopting an X-ray diffractometer;
(3) and (3) conductivity test: the Powder conductivity of the material was tested using a Powder resistance Measurement System (Loresta) with a 4kN loading.
The silicon-based composite negative electrode materials prepared in the embodiments and the comparative proportions are prepared into negative electrode plates and batteries, and the method comprises the following steps:
negative pole piece: dissolving and mixing a negative electrode material (88-94), a conductive agent (1-4), a binder (1-4) and a solvent (1-4), coating the mixture on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate;
a battery: and assembling the prepared negative pole piece, positive pole piece, electrolyte, diaphragm and shell into the lithium ion battery by adopting a conventional production process.
And (3) carrying out performance test on the prepared negative pole piece and the battery, wherein the method comprises the following steps:
(4) capacitance to hold-off and first coulombic efficiency: and (3) carrying out button cell test on the prepared negative pole piece, wherein the button cell assembling method comprises the following steps: dissolving a negative electrode material, a conductive agent and a binder in a solvent according to the mass percentage of 94:1:5, mixing, controlling the solid content to be 50%, coating the mixture on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate; the electrode used was a lithium metal plate and 1.2mol/L LiPF6And the button cell of the model LIR2016 is assembled by adopting/EC + DMC + EMC (v/v is 1:1:1) electrolyte and Celgard 2400 diaphragm.
The charge and discharge test is carried out on a LAND battery test system of Wuhan Jinnuo electronic Co., Ltd, constant current charge and discharge are carried out at 0.1C under the normal temperature condition, and the charge and discharge voltage is limited to 0.005-1.5V;
(5) cycle performance: the charge and discharge test of the button cell is carried out on a LAND cell test system of Wuhanjinnuo electronic Limited company, and the constant current charge and discharge are carried out at 0.1C under the normal temperature condition, and the charge and discharge voltage is limited to 0.005-1.5V.
(6) Rate capability: the charge and discharge test of the button cell is carried out on a LAND cell test system of Wuhanjinnuo electronic Limited company, and the capacity ratio of the button cell under the constant current charging condition of 0.5C and the constant current charging condition of 0.1C is tested under the normal temperature condition.
Wherein, fig. 3 is a first charge-discharge curve diagram of the composite negative electrode material prepared in example 1, from which it can be observed that the reversible capacity of the material is 1014.6mAh/g, and the first coulomb efficiency of the material is 90.1%, that is, the silicon-based composite negative electrode material prepared by the present invention has a higher capacity and a higher first coulomb efficiency.
Fig. 4 is a cycle curve of a lithium ion battery assembled by using the silicon-based composite anode material provided in example 1, and it can be seen from the graph that the cycle retention rate of the anode material provided by the present invention after 100 cycles is high, and is 95.6% or more.
The test results of examples 1-10 and comparative examples 1-3 are shown in Table 1 below:
TABLE 1
The test results of the embodiment show that the silicon-based composite negative electrode material provided by the invention has good cycle stability, high first reversible capacity and first coulombic efficiency, wherein the first reversible capacity is more than 900mAh/g and can reach 1035mAh/g at most, the first coulombic efficiency is more than 85 percent and can reach more than 90 percent at most, the cycle capacity retention rate of 100 times is more than 91.5 percent and can reach more than 96.4 percent at most, and the constant current charge capacity ratio of 0.5C can reach more than 80 percent.
As can be seen from the comparison between example 1 and comparative examples 1-2, the silicon-based composite anode material obtained by the present invention has better performance, and presumably the reason is that: compared with the conventional graphite, the emulsified graphite is selected to be hydrophilic, so that nano-silicon with the same hydrophilicity can be uniformly dispersed in an emulsified graphite network, the electric contact between the nano-silicon and the graphite is strengthened, and the volume expansion of the nano-tube in the charging and discharging processes is inhibited; in addition, under the synergistic effect of the shell conductive material polypyrrole and the conductive material carbon nano tube, the conductivity of the composite material can be obviously improved, the impedance of the material is reduced, the quick charging performance of the material is improved, and the cycle life of the material is prolonged.
Comparative example 3 since the structure of polypyrrole was destroyed during the high temperature coating process and the amorphous carbon separated the carbon nanotube and the polypyrrole, the synergistic effect of the two could not be exerted, the conductivity was greatly reduced, and the performance of the composite material was deteriorated.
The applicant states that the present invention is illustrated by the above examples to the silicon-based composite anode material and the preparation method thereof, but the present invention is not limited to the above process steps, i.e. it does not mean that the present invention must rely on the above process steps to be implemented. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.
Claims (10)
1. The silicon-based composite anode material is characterized by comprising an inner core and an outer shell positioned on the surface of the inner core, wherein the inner core comprises emulsified graphite and nano silicon, and the outer shell comprises a carbon coating layer and a polymer-carbon nano material composite material.
2. The silicon-based composite anode material as claimed in claim 1, wherein the emulsified graphite is prepared by emulsifying graphite with an emulsifier;
preferably, the graphite comprises natural graphite and/or artificial graphite;
preferably, the graphite has a median particle diameter of from 1.0 μm to 8.0 μm, preferably from 2.0 μm to 5.0 μm;
preferably, the median particle diameter of the nano silicon is 5.0nm to 200.0nm, preferably 10.0nm to 100.0nm, and further preferably 20.0nm to 80.0 nm;
preferably, the median particle size of the inner core is from 1 μm to 8 μm, preferably from 2 μm to 5 μm.
3. The silicon-based composite anode material according to claim 1 or 2, wherein in the polymer-carbon nanomaterial composite, the carbon nanomaterial comprises at least one of carbon nanotubes, carbon fibers and carbon nanospheres;
preferably, the diameter of the carbon nanotube is 2nm-20nm, preferably 2nm-10 nm;
preferably, the length of the carbon nanotube is 1 μm to 30 μm, preferably 5 μm to 15 μm;
preferably, the carbon nanotubes are single-walled carbon nanotubes and/or multi-walled carbon nanotubes;
preferably, the carbon fibers are acrylonitrile carbon fibers and/or pitch carbon fibers;
preferably, the carbon fibers have a length of 10 μm to 50 μm;
preferably, the carbon nanospheres are fullerene-based carbon nanospheres;
preferably, the fullerene-based carbon nanosphere comprises at least one of C60, C70 and incompletely graphitized nanocarbon spheres;
preferably, the carbon nanoball has a diameter of 50nm to 1 μm;
preferably, in the polymer-carbon nanomaterial composite, the carbon nanomaterial has a hydrophilic group;
preferably, the hydrophilic group includes at least one of a carboxylic acid group, a sulfonic acid group, a phosphoric acid amino group, a quaternary ammonium group, an ether group, a hydroxyl group, a carboxylate group, and a block polyether group.
4. The silicon-based composite anode material according to any one of claims 1 to 3, wherein in the polymer-carbon nanomaterial composite, the polymer is a conductive polymer;
preferably, the conductive polymer includes at least one of polypyrrole, polyaniline, polythiophene, poly-p-phenylene and poly-p-phenylene sulfide;
preferably, in the housing, the carbon coating layer is an amorphous carbon layer;
preferably, the outer shell comprises an inner layer located on the surface of the inner core and an outer layer located on the surface of the inner layer, wherein the inner layer comprises a carbon coating layer, and the outer layer comprises a polymer-carbon nano material composite material;
preferably, the thickness of the inner layer is 1 μm to 5 μm, preferably 2 μm to 4 μm;
preferably, the thickness of the outer layer is 10nm to 200nm, preferably 50nm to 100 nm;
preferably, the mass percentage of the nano silicon is 20-50%, preferably 30-40%, based on 100% of the mass of the silicon-based composite anode material;
preferably, the mass percentage of the emulsified graphite is 15-35%, and preferably 20-30%, based on 100% of the mass of the silicon-based composite anode material;
preferably, the mass percentage of the carbon coating layer is 15-35%, preferably 20-30%, based on 100% of the mass of the silicon-based composite anode material;
preferably, the mass percentage of the carbon nano material is 1-5%, preferably 1-2%, based on 100% of the mass of the silicon-based composite anode material;
preferably, the mass percentage of the polymer is 1-5%, preferably 1-3%, based on 100% of the mass of the silicon-based composite anode material.
5. A method for preparing a silicon-based composite anode material according to any one of claims 1 to 4, characterized in that the method comprises the following steps:
mixing graphite, an emulsifier and a first solvent to obtain an emulsified graphite emulsion;
mixing the emulsified graphite emulsion with nano-silicon and granulating to obtain a first composite material;
carrying out carbon coating on the first composite material to obtain a second composite material;
and mixing the second composite material, the carbon nano material, the polymer monomer and the doping agent in a second solvent, adding an oxidant for reaction, and carrying out solid-liquid separation to obtain the silicon-based composite negative electrode material.
6. The method according to claim 5, wherein the emulsifier is a nonionic emulsifier and/or an anionic emulsifier;
preferably, the ionic emulsifier is at least one of an ether nonionic emulsifier and an ester nonionic emulsifier;
preferably, the ether nonionic emulsifier comprises at least one of alkylphenol polyoxyethylene, benzyl phenol polyoxyethylene, phenethyl phenol polyoxyethylene, fatty alcohol polyoxyethylene, phenethyl phenol polyoxyethylene, polyoxypropylene ether and fatty amine polyoxyethylene;
preferably, the ester-type nonionic emulsifier comprises at least one of polyoxyethylene fatty acid ester, polyoxyethylene castor oil ester, polyol fatty acid ester and polyoxyethylene ester;
preferably, the anionic emulsifier is at least one of a sulfonic acid emulsifier and a sulfuric acid emulsifier;
preferably, the anionic emulsifier comprises at least one of dialkyl benzene sulfonic acid sodium salt, alkyl aryl sulfonic acid sodium salt, dodecyl benzene sulfonic acid sodium salt, butyl naphthalene sulfonic acid sodium salt, dibutyl naphthalene sulfonic acid sodium salt, diisopropyl naphthalene sulfonic acid sodium salt, monomethyl naphthalene sulfonic acid sodium salt, dimethyl naphthalene sulfonic acid sodium salt, alkyl alkenyl sulfonic acid sodium salt, hydroxyl alkyl sulfonic acid sodium salt, alkyl succinic acid ester sodium salt, alkyl polyoxyethylene ether succinic acid ester sulfonate, alkylphenol polyoxyethylene ether succinic acid ester sulfonate, alkyl diphenyl ether sulfonate, naphthalene sulfonic acid formaldehyde condensate and lauryl sodium sulfate;
preferably, the first solvent comprises water and/or an organic solvent;
preferably, the step of mixing the graphite, the emulsifier and the solvent is an operation of adding a co-emulsifier;
preferably, the co-emulsifier comprises at least one of n-butanol, ethylene glycol, ethanol, propylene glycol, glycerol, and polyglycerol ester;
preferably, the method of the mixing in the step of mixing graphite, an emulsifier and a solvent is accelerated stirring;
preferably, the mixing method in the step of mixing and granulating the emulsified graphite emulsion with nano-silicon is ultrasonic dispersion;
preferably, the granulation method is spray drying granulation.
7. The method of claim 5 or 6, wherein the carbon coating method comprises: pyrolysis and/or chemical vapor deposition;
preferably, the pyrolysis process comprises: mixing the first composite material with an organic carbon source, and then carrying out coating treatment under protective gas;
preferably, the organic carbon source comprises at least one of a polymer, a saccharide, an organic acid, and pitch;
preferably, the organic carbon source comprises at least one of polyvinyl butyral, sucrose, glucose, maltose, citric acid, pitch, furfural resin, epoxy resin, and phenolic resin;
preferably, the organic carbon source is in the form of powder, wherein the median particle size is 0.5-5 μm;
preferably, the first composite material and the organic carbon source are mixed in a VC mixer, the mixing speed is 500.0rpm-3000.0rpm, and the mixing time is more than 0.5 h;
preferably, the protective gas comprises at least one of nitrogen, helium, neon, argon, and hydrogen;
preferably, the temperature of the coating treatment under the protective gas is 550-1200 ℃;
preferably, the heating rate of the coating treatment under the protective gas is 1-20 ℃/min;
preferably, the time for coating treatment under the protective gas is 0.5h-8 h;
preferably, the chemical vapor deposition method includes: mixing the first composite material with a gas-phase organic carbon source, and performing coating treatment under a rotating condition;
preferably, the gas phase organic carbon source is at least one of methane, ethylene, acetylene, benzene, toluene, xylene, styrene, phenol, ethane, propane and acetone;
preferably, the speed of rotation is 0.2rpm to 10 rpm;
preferably, the temperature of the coating treatment is 600-1200 ℃, preferably 700-1000 ℃;
preferably, the time of the coating treatment is 1h-8 h;
preferably, the median particle diameter of the second composite material is from 1.0 μm to 10.0 μm;
preferably, after the carbon coating, the method further comprises the steps of cooling, crushing and screening the obtained product.
8. The method of any one of claims 5 to 7, wherein the carbon nanomaterial comprises at least one of carbon nanotubes, carbon fibers, and carbon nanoballs;
preferably, the polymer monomer comprises at least one of pyrrole monomer, aniline monomer, thiophene monomer, p-phenylene monomer and p-phenylene sulfide monomer;
preferably, the dopant includes at least one of p-toluenesulfonic acid, sodium dodecylbenzenesulfonate, camphorsulfonic acid, hydrochloric acid and sodium dodecylsulfonate;
preferably, the second solvent comprises water and/or an organic solvent;
preferably, the mixing in the step of mixing the second composite material, the carbon nanomaterial, the polymer monomer, and the dopant in the second solvent is ultrasonic dispersion;
preferably, the oxidant comprises at least one of ammonium persulfate, ferric trichloride, ferric perchlorate and hydrogen peroxide;
preferably, the temperature of the reaction in the step of adding the oxidant for reaction is 0 ℃ to 5 ℃;
preferably, the reaction is carried out for 18-24 h;
preferably, the solid-liquid separation is centrifugal separation;
preferably, the method further comprises the steps of washing the solid obtained by the solid-liquid separation with ethanol, washing with water and drying.
9. The method for preparing according to any one of claims 5 to 8, characterized in that it comprises the steps of:
stirring and mixing graphite, an emulsifier, an auxiliary emulsifier and water at an accelerated speed to obtain an emulsified graphite emulsion;
carrying out ultrasonic dispersion and spray drying granulation on the emulsified graphite emulsion and nano-silicon to obtain a first composite material;
mixing the first composite material and the organic carbon source in a VC mixer, wherein the mixing speed is 500.0-3000.0 rpm, the mixing time is more than 0.5h, then heating to 550-1200 ℃ at the heating rate of 1-20 ℃/min under protective gas for reaction for 0.5-8 h, and cooling, crushing and screening the obtained product to obtain a second composite material with the median particle size of 1.0-10.0 mu m;
or introducing a gas phase carbon source into the first composite material, and depositing for 1h-8h at the rotation speed of 0.2-10 rpm and the temperature of 700-1000 ℃ to obtain a second composite material with the median particle size of 1.0-10.0 μm;
and ultrasonically dispersing the second composite material, the carbon nano tube, the pyrrole monomer and the dopant in water, adding an oxidant to react at 0-5 ℃, centrifugally separating to obtain a solid, and washing the obtained solid with ethanol, washing with water and drying to obtain the silicon-based composite negative electrode material.
10. A lithium ion battery, characterized in that the lithium ion battery comprises the silicon-based composite anode material according to any one of claims 1 to 4;
preferably, the lithium ion battery is a fast-charging lithium ion battery.
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