CN112635745A - Composite material, preparation method thereof, lithium battery cathode and lithium battery - Google Patents

Composite material, preparation method thereof, lithium battery cathode and lithium battery Download PDF

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Publication number
CN112635745A
CN112635745A CN201910952520.5A CN201910952520A CN112635745A CN 112635745 A CN112635745 A CN 112635745A CN 201910952520 A CN201910952520 A CN 201910952520A CN 112635745 A CN112635745 A CN 112635745A
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composite material
silicon
source
lithium battery
solvent
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CN112635745B (en
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张丝雨
孙赛
张同宝
高焕新
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China Petroleum and Chemical Corp
Sinopec Shanghai Research Institute of Petrochemical Technology
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China Petroleum and Chemical Corp
Sinopec Shanghai Research Institute of Petrochemical Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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

Abstract

The invention relates to the field of lithium batteries, in particular to a composite material and a preparation method thereof, a lithium battery cathode and a lithium battery. The composite material comprises active main body silicon and a carbon layer coated on the surface of the active main body silicon; wherein the active host silicon contains a P (O) -O-Si structure. The preparation method of the composite material comprises the following steps: contacting a silicon source and a phosphorus source in the presence of a solvent to obtain a first component; after mixing the first component and a carbon source, carrying out solvent removal treatment on the obtained mixture to obtain a precursor; and carrying out heat treatment on the precursor under an inert atmosphere to obtain the composite material. The preparation method can ensure that the organic carbon source is uniformly coated on the surface of the active component, is beneficial to improving the electrical property of the composite material, and further improves the electrical properties of the lithium battery cathode and the lithium battery prepared by using the composite material.

Description

Composite material, preparation method thereof, lithium battery cathode and lithium battery
Technical Field
The invention relates to the field of lithium batteries, in particular to a composite material and a preparation method thereof, a lithium battery cathode and a lithium battery.
Background
In recent years, clean and efficient new energy technology is receiving much attention due to the increasing problems of environmental pollution and resource shortage. Nowadays, lithium ion batteries are widely applied to various fields such as electronic products and electric automobiles. With the development of technology, the market demands for energy density and cycle performance of lithium ion batteries are higher and higher. The current commercialized lithium ion battery cathode material is mainly a carbon material, the theoretical specific capacity of the lithium ion battery cathode material is only 372mAh/g, and the theoretical specific capacity is far lower than the demand of people on high-energy-density lithium batteries. In the existing research, silicon becomes one of the research hotspots of the non-carbon negative electrode material at present by virtue of the theoretical specific capacity of the silicon as high as 4200 mAh/g. However, the silicon material has large volume expansion in the charging and discharging process, which causes material pulverization failure, and causes the problems of performance attenuation, battery short circuit and the like of the battery. In order to solve the problem of volume expansion of silicon, the performance of silicon is generally improved by means of nanocrystallization, compounding, coating, and the like. The silicon surface is coated by a common method for preparing the silicon-carbon composite material, and the volume expansion of silicon particles can be effectively relieved.
CN106257716A discloses a preparation method of a silicon-carbon negative electrode material, which specifically comprises placing nano silicon and graphite micropowder in a ball mill, ball-milling in an organic solvent environment for uniform dispersion, vacuum drying, placing the mixture and pitch in a conical mixer for coarse mixing, placing the mixed powder after coarse mixing in a mechanical fusion machine for mechanical fusion, finally performing heat treatment under the protection of inert gas, and cooling to obtain the silicon-carbon composite negative electrode material. The first charge-discharge efficiency and the cycle performance of the silicon-carbon cathode material coated by the asphalt are improved.
CN109599551A discloses a doped multilayer core-shell silicon-based composite material, wherein a silicon oxide compound, a carbon source and a precursor containing a doped element are subjected to multiple crushing, screening and mixing and then subjected to heat treatment, and finally, the element-doped multilayer core-shell silicon-carbon cathode material is obtained.
However, the powder material obtained by the above methods of ball milling, mechanical crushing and mixing has a problem that the coating layer is thick on the surface, and it is difficult to completely coat the surface of silicon with carbon.
CN103633295A discloses a preparation method of a silicon-carbon composite material, and specifically, silica powder, silica fume and an organic carbon source are fully mixed by a wet ball milling method to obtain slurry, then graphite and a conductive agent are added, and a spray drying method is adopted to obtain spheroidal particles. And (3) carrying out asphalt coating treatment on the spheroidal particles in an inert atmosphere, and carbonizing to obtain the silicon-carbon composite material. The amorphous carbon coated outside the silicon-carbon composite material can effectively avoid direct contact between internal particles and electrolyte, and improves the first coulombic efficiency and the circulation stability of the material. However, the spray drying method is expensive and not suitable for industrial production.
Therefore, the coating mode of the silicon-carbon material needs to be further improved to realize uniform and compact coating with controllable thickness on the surface of the nano silicon powder to improve the electrochemical performance of the silicon-carbon material and improve the stability of the silicon-carbon material, and meanwhile, the coating mode needs to be simple to operate and meets the requirement of industrial production.
Disclosure of Invention
The invention aims to solve the problems of thicker coating layer, incomplete coating, complex operation and high cost in the coating technology of the existing silicon-carbon material, and provides a composite material and a preparation method thereof, a lithium battery cathode and a lithium battery.
In order to achieve the above object, an aspect of the present invention provides a composite material including active host silicon and a carbon layer coated on a surface of the active host silicon; wherein the active host silicon contains a P (O) -O-Si structure.
In a second aspect the present invention provides a method of making a composite material, the method comprising:
(1) contacting a silicon source and a phosphorus source in the presence of a solvent to obtain a first component;
(2) after mixing the first component and a carbon source, carrying out solvent removal treatment on the obtained mixture to obtain a precursor;
(3) and carrying out heat treatment on the precursor under an inert atmosphere to obtain the composite material.
A third aspect of the invention provides a composite material made according to the method as described above.
A fourth aspect of the invention provides a negative electrode for a lithium battery, comprising a negative active material, a binder, and a conductive agent, the negative active material being the composite material as described above.
A fifth aspect of the invention provides a lithium battery comprising a negative electrode for a lithium battery as described above, a positive electrode material containing lithium, a separator, and an electrolyte.
In the composite material, the active main body silicon is externally provided with a compact inert nano protective layer, namely a carbon layer, so that electrode material pulverization caused by a volume effect in the charging and discharging processes of the active main body silicon is avoided, the corrosion of electrolyte to a lithium battery cathode is inhibited, the uncontrollable growth of an SEI film is inhibited, and the cycling stability of the material is improved.
The active main body silicon of the composite material provided by the invention contains phosphorus element, and is connected with active substance Si through a P (O) -O-Si structure, so that on one hand, the problem that a silicon source is difficult to disperse in a solution can be solved, on the other hand, the silicon source and an inert nano protective layer on the surface are connected together through a phosphorus-containing buffer layer, the silicon surface of the active main body can be uniformly coated, and the improvement of the cycle stability of a lithium battery cathode is facilitated.
The preparation method can ensure that the organic carbon source is uniformly coated on the surface of the active component, a thin and uniform inert interface can be formed on the surface of the active material after carbonization, and the thickness of the coating layer can be regulated and controlled by controlling the addition amount. In addition, other components, such as lithium, vanadium, boron, aluminum and the like, are added into the organic carbon source, and the doping of the mixed elements can be realized.
The lithium battery cathode and the lithium battery prepared from the composite material have better performances, and taking example 1 as an example, the specific capacity of the lithium battery prepared from the composite material applied to the cathode reaches 3000 mAh.g-1The first coulombic efficiency is 86.9%, and the capacity retention rate after 50 cycles is more than 95%.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is an SEM photograph of the composite material of example 1.
Fig. 2 is a transmission electron microscope image of the composite material of example 1, in which a is a carbon layer and B is active host silicon.
FIG. 3 is an X-ray photoelectron spectrum of C1s of the composite material of example 1.
FIG. 4 is an X-ray photoelectron spectrum of P2P of the composite material of example 1.
FIG. 5 is an X-ray photoelectron spectrum of Si2p of the composite material of example 1.
Fig. 6 is a first charge and discharge curve of the composite material of example 1.
FIG. 7 is a graph of the cycling stability of the composite material of example 1.
Fig. 8 is a first charge and discharge curve of the negative electrode of the lithium battery in comparative example 1.
Fig. 9 is a cycle stability curve of the negative electrode of the lithium battery in comparative example 1.
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a composite material, wherein the composite material comprises active main body silicon and a carbon layer coated on the surface of the active main body silicon; wherein the active host silicon contains a P (O) -O-Si structure.
In the present invention, the shape of the composite material is not particularly limited, and in a preferred embodiment of the present invention, an SEM photograph of the resulting composite material is shown in fig. 1.
In a preferred embodiment of the present invention, as shown in fig. 2, the composite material comprises active bulk silicon and a carbon layer coated on the surface of the active bulk silicon, forming a silicon-carbon composite material with a coated structure.
In the present invention, the particle size of the active host silicon may be selected within a wide range, and preferably, the particle size of the active host silicon is in the range of 50 to 300 nm. Under the preferred conditions, the electrical properties of the composite material can be further improved.
In the present invention, the method of measuring the particle size is dynamic light scattering.
In the invention, the carbon layer forms a compact inert nano protective film to coat the surface of the active main body silicon, so that electrode material pulverization caused by volume effect of the active main body silicon in the charging and discharging process is avoided, corrosion of electrolyte to a lithium battery cathode is inhibited, uncontrollable growth of an SEI film is inhibited, and the cycling stability of the material is improved.
In the present invention, the thickness of the carbon layer may be selected from a wide range, and may be adjusted as necessary. However, in a preferred case, the maximum thickness of the carbon layer is not more than 50nm, and the minimum thickness of the carbon layer is not less than 0.5nm, such as 0.5nm, 1nm, 2nm, 4nm, 6nm, 8nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, and any range between any two values, and more preferably, the thickness of the carbon layer is 1 to 20 nm. In a preferred embodiment of the present invention, as shown in fig. 2, the carbon layer a of the composite material has a thickness in the range of 2 to 4nm and is coated on the surface of the active bulk silicon B more uniformly. Under the preferable conditions, the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
Preferably, the difference between the maximum thickness and the minimum thickness of the carbon layer is 1-10nm, more preferably 1-5 nm. The smaller the difference between the maximum thickness and the minimum thickness of the carbon layer, the more uniform the coating of the carbon layer, in which case the electrical properties of the composite material can be further improved, and its specific capacity and cycling stability are improved.
In the present invention, the thickness of the carbon layer may be measured by scanning the composite material using a transmission electron microscope and measuring the thickness of the carbon layer in the resultant pattern.
In a preferred embodiment of the present invention, as shown in fig. 3 to 5, in the composite material, a p (O) -O-C structure and a p (O) -O-Si structure are present, which illustrates that the phosphorus element is present in a form of being indirectly connected to the Si element or the C element at least partially through a chemical bond, indicating that the silicon source and the carbon layer on the surface are connected together through the phosphorus-containing buffer layer, specifically, the connection is realized through the p (O) -O-C structure and the p (O) -O-Si structure, so that the silicon surface of the active main body is uniformly coated, which is beneficial to improving the cycle stability of the negative electrode of the lithium battery.
In the present invention, the weight ratio of the Si element, the C element, and the P element in the composite material can be selected in a wide range. Preferably, the weight ratio of the Si element, the C element and the P element in the composite material is 100: (5-30): (10-40); under the preferable conditions, the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
In the present invention, preferably, the specific capacity of the composite material at 0.1C rate is 2100-3000 mAh/g.
In the present invention, preferably, the specific capacity of the composite material at 0.2C rate is 1800 and 2700 mAh/g.
In the present invention, the "specific capacity" is the "specific mass capacity", specifically, the energy that can be released by a unit mass of the battery, and the unit is mAh/g.
In the present invention, preferably, the first coulombic efficiency of the composite material reaches 83-86.9% at a 0.1C rate.
In the present invention, coulombic efficiency (also called discharge efficiency) refers to the ratio of the discharge capacity of the battery to the charge capacity in the same cycle process, i.e. the percentage of the discharge capacity to the charge capacity. For the positive electrode material, the lithium insertion capacity/lithium removal capacity, namely the discharge capacity/charge capacity; for a negative electrode of a lithium battery, it is a lithium removal capacity/lithium insertion capacity, i.e., a discharge capacity/charge capacity. The term "first coulombic efficiency" refers to the percentage of discharge capacity to charge capacity during the first charge-discharge process.
In the present invention, the capacity retention of the composite material after 50 cycles at 0.1C rate is preferably 90% or more, more preferably 95% or more.
In the invention, other components, such as lithium, vanadium, boron, aluminum and the like, can be added into the carbon layer to realize the doping of the mixed elements.
In a second aspect the present invention provides a method of making a composite material, the method comprising:
(1) contacting a silicon source and a phosphorus source in the presence of a solvent to obtain a first component;
(2) after mixing the first component and a carbon source, carrying out solvent removal treatment on the obtained mixture to obtain a precursor;
(3) and carrying out heat treatment on the precursor under an inert atmosphere to obtain the composite material.
The inventors of the present invention found in research that, although a composite material can be produced by directly mixing a silicon source, a phosphorus source and a carbon source, the composite material has poor coating effect of a carbon layer, and the carbon layer has non-uniform thickness and incomplete coating, thereby affecting the electrical properties of a negative electrode of a lithium battery and the lithium battery. By adopting the method, the silicon source and the phosphorus source are contacted in the presence of the solvent to react, and then are mixed with the carbon source to form the structure of the active component silicon-phosphorus buffer layer-carbon layer from inside to outside in sequence, and finally the composite material with good electrical property, uniform coating and integrity is obtained. In addition, the phosphorus source is added, so that the dispersibility of the silicon source is improved, and the contribution to the improvement of the performance of the composite material is also made.
In the present invention, the silicon source is preferably present in the form of elemental silicon and/or silicon oxide. The silicon oxide refers to a molecular formula of SiOxWherein 0 < x < 2.
The source of the silicon source is not particularly limited, and the content of the active ingredient is not less than 95%, and the silicon source can be obtained commercially.
The particle size of the silicon source may be selected from a wide range, and preferably, the particle size of the active host silicon is in a range of 50-300nm, such as 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, and any range therebetween.
In the present invention, the kind of the phosphorus source may not be particularly limited as long as it is soluble in a solvent and provides the P element. Preferably, the source of phosphorus is selected from phytic acid and/or phosphoric acid, more preferably phytic acid (i.e. inositol hexaphosphate).
In the present invention, the amount of the phosphorous source may be selected from a wide range, and preferably, the amount of the phosphorous source is 15 to 100 parts by weight, for example, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100 parts by weight and any range between any two values, and more preferably 15 to 70 parts by weight, relative to 100 parts by weight of the silicon source. Under the optimal condition, the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
In the present invention, the environment in which the silicon source and the phosphorus source are contacted is preferably acidic, i.e., pH < 7.
In the present invention, the order of adding the phosphorus source and the silicon source is not particularly limited, and for example, the phosphorus source and the silicon source may be added simultaneously to the solvent, or the phosphorus source and the silicon source may be added to the solvent first, or the silicon source and the phosphorus source may be added to the solvent first. Preferably, the phosphorus source is added to the solvent to dissolve the phosphorus source, and then the silicon source is added.
In the present invention, the carbon source is for providing a carbon layer coated on the silicon surface of the active host, and thus the type of the carbon source is not particularly limited, and it is sufficient that the carbon source can provide C element and can be dissolved in a solvent. The carbon source may be the same as or different from the phosphorus source, and preferably, the carbon source is different from the phosphorus source.
In the present invention, the carbon source is preferably hard carbon, i.e., a carbon source that is difficult to be graphitized; more preferably at least one selected from the group consisting of modified asphalt, polyacrylonitrile, cellulose derivatives, polymethyl methacrylate, polyamide, polyimide, phytic acid, pyrrole, thiophene, saccharides, polyacrylic acid, and polyvinyl alcohol.
The type of the modified asphalt is not particularly limited as long as it is soluble in a solvent, and examples thereof include rubber and thermoplastic elastomer modified asphalt, plastic and synthetic resin modified asphalt, and/or blend type high molecular polymer modified asphalt.
Wherein the molecular formula of the polyacrylonitrile is (C)3H3N) N, wherein the size of N is not particularly limited, and the weight average molecular weight of the polyacrylonitrile may be in the range of 850000-150000. The polyacrylonitrile may be of a kind not particularly limited as long as it is soluble in a solvent, and may be, for example, a homo-polyacrylonitrile and/or a co-polyacrylonitrile. The polyacrylonitrile may be obtained commercially, for example, as a poly (ethylene-co-propylene) polymer available from carbofuran, Mw 150000Acrylonitrile.
The cellulose derivative may be any conventional cellulose derivative, such as one or more of methyl cellulose, ethyl cellulose, carboxymethyl cellulose, cellulose acetate, and hydroxypropylmethyl cellulose. The cellulose derivative is commercially available, and may be, for example, carboxymethyl cellulose (viscosity 800cP · s) available from carbofuran corporation.
Of these, polymethyl methacrylate, polyamide, polyimide, polyacrylic acid, and polyvinyl alcohol are commercially available products as long as they are soluble in a solvent, and are not described one by one.
The saccharide may be various saccharides, and may be one or more of monosaccharide, disaccharide and polysaccharide, for example. The monosaccharide can be glucose, the disaccharide can be sucrose, and the polysaccharide can be starch and the like.
In the present invention, the amount of the carbon source may be selected from a wide range, and preferably, the amount of the carbon source is 5 to 50 parts by weight, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 parts by weight and any range between any two values, and more preferably 10 to 30 parts by weight, based on 100 parts by weight of the silicon source. Under the optimal condition, the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
In the present invention, the solvent may be an organic solvent, and preferably, the organic solvent is an amide-based solvent and/or N-methylpyrrolidone. Wherein the amide-based solvent may be at least one of N, N-Dimethylformamide (DMF), N-dimethylacetamide (MDA), N-Dimethylpropionamide (DMP), N-Diethylformamide (DEF), N-Diethylacetamide (DEA), and N, N-Diethylacrylamide (DEP).
In the present invention, the amount of the solvent to be used may be selected from a wide range as long as the phosphorus source and the carbon source can be dissolved. Preferably, the solvent is used in an amount of 100-1000 parts by weight, for example, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 parts by weight and any range between any two values, and more preferably 150-300 parts by weight, relative to 100 parts by weight of the silicon source.
In the invention, the composite material is prepared by the combination of the preferred silicon source, the preferred phosphorus source, the preferred carbon source and the preferred solvent according to the preferred proportion, so that the carbon layer can be more uniformly coated on the surface of the active main body silicon, the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
In the step (1), the time and temperature of the contact are not particularly limited as long as the silicon source is sufficiently dispersed in the solvent and sufficiently reacted with the phosphorus source. Preferably, the contact time is 1 to 6h, preferably 2 to 4 h. The temperature of the contact may be 20 to 50 deg.C, preferably 25 to 35 deg.C.
The method of contacting may not be particularly limited, and the silicon source and the phosphorus source may be contacted in the presence of a solvent by at least one of stirring, ultrasonic treatment, shaking, and the like. It will be appreciated that the contact time may be reduced by a combination of methods.
In the present invention, in the step (2), before mixing the first component and the carbon source, it is further preferable to include dissolving the carbon source in the solvent. Preferably, the solvent for dissolving the carbon source in the step (2) is used in an amount of 10 to 100 parts by weight, more preferably 20 to 50 parts by weight, relative to 100 parts by weight of the silicon source.
Wherein, the solvent in step (1) and step (2) may be the same or different, and is preferably the same solvent.
Wherein the time and temperature of the dissolution are not particularly limited as long as the carbon source can be dissolved in the solvent. Preferably, the dissolution time is 1-6 h. The temperature of the dissolution may be 20-50 ℃.
The method of dissolution may not be particularly limited, and the dissolution process of the carbon source in the solvent may be accelerated by at least one of stirring, ultrasonic treatment, shaking, and the like. It will be appreciated that the dissolution time may be shortened by a combination of methods.
In the step (2), the method for mixing the first component with the carbon source may not be particularly limited as long as the carbon source can be sufficiently mixed with the first component. In a preferred embodiment of the present invention, a solvent in which a carbon source is dissolved is slowly added to the first component, followed by mixing. The slow degree means that the addition rate of the first component is 0.5 to 2g/min relative to 10g of the solvent dissolving the carbon source. Under the preferable condition, the carbon layer can be coated on the surface of the active main body silicon more uniformly, so that the electrical performance of the composite material can be further improved, and the specific capacity and the cycling stability of the composite material are improved.
In the step (2), the time and temperature of the mixing are not particularly limited as long as the carbon source can be dissolved in the solvent. The mixing time is 2-8 h; the mixing temperature is 20-80 deg.C.
Wherein the method of mixing may not be particularly limited, and the process of mixing the first component and the carbon source may be accelerated by at least one of stirring, sonication, shaking, and the like. It will be appreciated that the mixing time may be reduced by a combination of methods.
It should be understood that during the contacting, dissolving and mixing, the material should be treated with at least one of agitation, sonication or shaking to ensure the dispersion of the material.
In the step (2), the resultant mixture is subjected to a solvent removal treatment, and the method of removing the solvent may not be particularly limited as long as the solvent in the mixture can be removed. Preferably, the method for removing the solvent comprises the steps of sequentially carrying out solid-liquid separation and drying treatment on the mixture.
The solid-liquid separation method is not particularly limited, and for example, the solid-liquid separation may be performed by centrifugation or filtration. In a preferred embodiment of the invention, the mixture is centrifuged for 5-40min at 6000-15000rpm in a centrifuge.
Herein, the drying method may not be particularly limited, and may be, for example, at least one of drying, lyophilization, spray drying, and/or vacuum drying. In a preferred embodiment of the invention, the mixture after solid-liquid separation is dried to constant weight at 60-120 ℃.
In the step (3), the precursor is subjected to heat treatment in an inert atmosphere, and the heat treatment method is preferably: heating the precursor to 500-1000 ℃ at a heating rate of 3-10 ℃/min, and keeping the temperature at 500-1000 ℃ for 10min-10 h.
Wherein the heat treatment may be performed in a tube furnace.
In the present invention, the inert atmosphere is a gas that does not participate in the reaction of the present invention, and for example, the inert atmosphere is provided by one or more of nitrogen and a gas of group zero in the periodic table of elements, preferably nitrogen, helium or argon.
In the present invention, the flow rate of the inert atmosphere can be selected from a wide range as long as the precursor can be protected by the inert atmosphere. Preferably, the flow rate of the inert atmosphere is 40-80mL/min per g of the precursor.
Under the preferable operation conditions, the carbon layer can be coated on the surface of the active host silicon more uniformly, so that the electrical properties of the composite material can be further improved, for example, the specific capacity and the cycling stability of the composite material are improved.
In the present invention, the composite material after the heat treatment may be subjected to cooling and pulverization treatment in this order. The method of pulverization is not particularly limited, and for example, a method of hand milling, ball milling, ultrafine pulverizer pulverization, or the like may be used.
A third aspect of the invention provides a composite material made according to the method as described above.
Based on the above composite material, a fourth aspect of the invention provides a negative electrode for a lithium battery, the negative electrode for a lithium battery comprising a negative electrode active material, a binder, and a conductive agent, the negative electrode active material being the composite material as described above.
In the present invention, the kind and content of the binder can be selected from a wide range, and the binder can be one or more of the binders known to those skilled in the art, such as fluorine-containing resin and polyolefin compound, such as polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Styrene Butadiene Rubber (SBR), and preferably, the binder is a mixture of cellulose derivative and rubber latex, such as a mixture of cellulose derivative and Styrene Butadiene Rubber (SBR). The amounts of the cellulose derivative and styrene-butadiene rubber are well known to those skilled in the art.
In the present invention, the kind and content of the conductive agent may be selected from a wide range, and the conductive agent may be a negative electrode conductive agent conventional in the art, such as one or more of ketjen black carbon, acetylene black, furnace black, carbon fiber VGCF, conductive carbon black, and conductive graphite.
In the present invention, the amounts of the negative electrode active material, the binder, and the conductive agent may be selected from a wide range, and preferably, the binder is used in an amount of 1 to 10 parts by weight and the conductive agent is used in an amount of 1 to 19 parts by weight, relative to 1 part by weight of the negative electrode active material.
The current collector forming the negative electrode in the present invention is not particularly limited, and may be a negative electrode current collector conventionally used in lithium ion batteries, such as a stamped metal, a metal foil, a net metal or a foamed metal, and preferably a copper foil is used as the negative electrode current collector.
The lithium ion battery negative electrode provided by the invention can be prepared by various methods in the prior art, for example, a slurry containing a negative electrode active material, a conductive agent and optionally a binder and a solvent is coated and/or filled on a current collector, dried, and pressed or not pressed, wherein the slurry containing the negative electrode active material, the conductive agent, the binder and the solvent can be obtained by uniformly mixing dry powders of the negative electrode active material and the conductive agent and then uniformly mixing the dry powders with the binder, the solvent or a binder solution formed by the binder and the solvent; the slurry can also be obtained by first uniformly mixing the negative electrode active material, the binder and the solvent, and then uniformly mixing the mixture with the conductive agent.
Among them, the solvent is preferably N-methylpyrrolidone (NMP). The solvent may be used in an amount that provides the paste with viscosity and fluidity and that can be applied to the current collector. The methods and conditions for drying and compression molding are well known to those skilled in the art.
A fifth aspect of the invention provides a lithium battery comprising a negative electrode for a lithium battery as described above, a positive electrode material containing lithium, a separator, and an electrolyte.
The main invention point of the invention is to improve the silicon-carbon composite material in the negative electrode of the lithium battery, therefore, the preparation of other components in the negative electrode of the lithium battery and the negative electrode of the lithium battery, the positive electrode material and the preparation thereof, and the lithium battery and the preparation thereof are not particularly limited, and the components and the preparation methods known by the technicians in the field can be adopted.
The separator and the nonaqueous electrolytic solution forming the lithium ion battery of the present invention may be those conventionally used in the art.
Wherein the separator is provided between the positive electrode and the negative electrode, has an electrical insulating property and a liquid retaining property, and allows the electrode core to be housed in a battery case together with the nonaqueous electrolytic solution. The separator may be selected from various separators used in lithium ion batteries, such as high molecular polymer microporous films, including polypropylene microporous films and multilayer composite microporous films of polypropylene and polyethylene. The location, nature and kind of the diaphragm are well known to those skilled in the art.
The nonaqueous electrolytic solution is a mixed solution of an electrolytic lithium salt and a nonaqueous solvent, and is not particularly limited, and a nonaqueous electrolytic solution that is conventional in the art can be used. For example, the electrolyte lithium salt is selected from lithium hexafluorophosphate (LiPF)6) One or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium halide, lithium chloroaluminate and lithium fluoro alkyl sulfonate. The organic solvent is a mixed solution of chain acid ester and cyclic acid ester, wherein the chain acid ester can be at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Methyl Propyl Carbonate (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds, and the cyclic acid ester can be Ethylene Carbonate (EC), Propylene Carbonate (PC), Vinylene Carbonate (VC), gamma-butyrolactone (gamma-BL), sulfolaneLactone and at least one of other cyclic organic esters containing fluorine, sulfur or unsaturated bonds. When the amount of the electrolyte to be injected is generally 1.5 to 4.9g/A, the concentration of the electrolyte is generally 0.5 to 2.9 mol/L.
Further, according to the present invention, other steps are known to those skilled in the art, except that the negative electrode is prepared according to the method provided by the present invention. Generally, a battery is obtained by forming a positive electrode, a negative electrode, and a separator into one core, and sealing the obtained core and an electrolyte solution in a battery case.
In the specific embodiment of the present invention, a half cell (the composite material pole piece in the present invention versus the Li piece) is generally fabricated for ease of detection. In a half-cell, the Li sheet generally functions as the negative electrode, while the study subject generally functions as the positive electrode in a half-cell. The shape of the battery according to the embodiment of the present invention is not particularly limited, and may be various shapes such as button shape, coin shape, cylindrical shape, and the like. For button cells, it can be prepared by sandwiching a separator between a sheet-like positive electrode and a negative electrode.
The present invention will be described in detail below by way of examples.
In the following examples, the high-purity silicon powder is a commercial product with the trademark of S130844 by Aladdin company;
the silicon oxide powder is a commercial product with a product number of 041710 of Bailingwei company;
the phytic acid is a commercial product with the brand number of P0409 of the carbofuran company;
the modified asphalt is a commercial product with the brand number GB/8175 of super-union new material science and technology Limited;
polyacrylonitrile is a commercial product with a molecular weight of 150000 from carbofuran;
the polypropylene microporous membrane is commercially available as Celgard 2400.
Example 1
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
(1) 100g of high-purity silicon powder is added into 280g N 'N-dimethylformamide/phytic acid mixed solution (230g N' N-dimethylformamide and 25g of phytic acid), and stirred for 4 hours at the temperature of 30 ℃ to obtain slurry A.
(2) Taking 10g of modified asphalt, adding 25g N' N-dimethylformamide, and obtaining slurry B after ultrasonic dissolution.
(3) Slowly adding the slurry A into the slurry B at the temperature of 30 ℃, stirring while adding, then carrying out ultrasonic treatment for 30min, stirring for 4h, centrifuging for 15min at the temperature of 8000r/min, removing supernatant, and drying in an oven at the temperature of 60 ℃ to obtain a precursor.
(4) And (3) placing the precursor in a tube furnace, heating to 800 ℃ at the speed of 5 ℃/min under the nitrogen atmosphere (the nitrogen flow rate is 60mL/min), keeping for 10min, then cooling to room temperature, and crushing to obtain the composite material.
The resulting composite was analyzed, wherein:
fig. 1 is an SEM photograph of the composite material.
FIG. 2 is a transmission electron microscope image of the composite material. As can be seen, the silicon surface is uniformly coated with a protective film of about 2-4 nm.
FIG. 3 is an X-ray photoelectron spectrum of C1s of the composite material, from which the presence of a C-O-P functional group can be confirmed.
FIG. 4 is an X-ray photoelectron spectrum of P2P of the composite material. In this diagram, both P (O) -O-C functional groups and P (O) -O-Si functional groups are present.
FIG. 5 is an X-ray photoelectron spectrum of Si2P of the composite material, from which the presence of Si-O-P functional groups can be confirmed.
The three spectrogram results jointly show that the nano high-purity silicon powder is connected with the inert nano film protective layer on the surface through phytic acid (a phosphorus-containing buffer layer).
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the composite material is used as a positive electrode, a metal lithium sheet is used as a negative electrode, 1mol/L LiPF6 solution is used as electrolyte, a polypropylene microporous membrane is used as a diaphragm, and the CR2016 button cell is assembled to represent the electrical performance of the composite material, and a Wuhan blue battery test system (CT2001B) is adopted. And (3) testing conditions are as follows: the voltage range is 0.005V-3V, and the current range is 0.05A-2A. 10 coin cells were assembled per sample and cell performance was tested at the same voltage and current.
Fig. 6 is a first charge and discharge curve of the negative electrode of the lithium battery, and fig. 7 is a cycle stability curve of the negative electrode of the lithium battery. As can be seen from the figure, the specific capacity of the composite material reaches 3000 mAh.g under the constant current discharge rate of 0.1C-1The first coulombic efficiency was 86.9%, and the specific results are listed in table 2.
Example 2
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
(1) 100g of silicon oxide powder was added to 245g N-methylpyrrolidone/phytic acid mixed solution (230g of N-methylpyrrolidone and 15g of phytic acid), and stirred at 20 ℃ for 6 hours to obtain slurry A.
(2) Taking 15g of polyacrylonitrile, adding 25g N-methyl pyrrolidone, and dissolving by ultrasonic to obtain slurry B.
(3) Slowly adding the slurry A into the slurry B at the temperature of 20 ℃, stirring while adding, carrying out ultrasonic treatment for 30min, then stirring for 6h, centrifuging for 15min at the temperature of 8000r/min, removing supernatant, and drying in an oven at the temperature of 60 ℃ to obtain a precursor.
(4) And (3) placing the precursor in a tube furnace, heating to 500 ℃ at the speed of 3 ℃/min in a nitrogen atmosphere (the nitrogen flow rate is 60mL/min), keeping for 10h, then cooling to room temperature, and crushing to obtain the composite material.
The resulting composite was analyzed, wherein:
the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 3
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
(1) 100g of high-purity silicon powder is added into 300g N 'N-dimethylacetamide/phytic acid mixed solution (230g of N' N-dimethylacetamide and 70g of phytic acid), and stirred for 1h at the temperature of 50 ℃ to obtain slurry A.
(2) 30g of hydroxypropyl cellulose is taken, 50g N' N-dimethylacetamide is added, and after ultrasonic dissolution, slurry B is obtained.
(3) Slowly adding the slurry A into the slurry B at 50 ℃, stirring while adding, carrying out ultrasonic treatment for 30min, then stirring for 1h, centrifuging for 15min at 8000r/min, removing supernatant, and drying in a 60 ℃ oven to obtain a precursor.
(4) And (3) placing the precursor in a tube furnace, heating to 1000 ℃ at the speed of 10 ℃/min under the nitrogen atmosphere (the nitrogen flow rate is 60mL/min), keeping for 10min, then cooling to room temperature, and crushing to obtain the composite material.
The resulting composite was analyzed, wherein:
the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 4
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
example 4-1: the procedure of example 1 was followed, except that 100g of the high-purity silicon powder in the step (1) was added to a 330g N 'N-dimethylformamide/phytic acid mixed solution (230g of N' N-dimethylformamide and 100g of phytic acid), and stirred at 30 ℃ for 4 hours to obtain slurry A. In step (2), 10g of modified asphalt was added to 25g N' N-dimethylformamide.
Example 4-2: the procedure of example 1 was followed, except that 100g of the high-purity silicon powder in the step (1) was added to 255g N 'N-dimethylformamide/phytic acid mixed solution (230g of N' N-dimethylformamide and 25g of phytic acid), and stirred at 30 ℃ for 4 hours to obtain slurry A. In step (2), 40g of the modified asphalt was added to 25g N' N-dimethylformamide.
The resulting composite was analyzed, wherein:
the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 5
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
the procedure of example 1 was followed except that an equal amount of silicon powder having a particle size of 500nm was used in place of the high-purity silicon powder.
The resulting composite was analyzed, wherein: the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 6
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
the procedure of example 1 was followed except that an equal amount of phosphoric acid was used instead of phytic acid.
The resulting composite was analyzed, wherein: the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 7
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
the procedure of example 1 was followed except that an equal amount of chopped carbon fibers was used in place of the modified pitch.
The resulting composite was analyzed, wherein: the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 8
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
the procedure is as in example 1, except that the operating conditions are different, in particular:
(1) 100g of high-purity silicon powder is added into 175g N 'N-dimethylformamide/phytic acid mixed solution (255g of N' N-dimethylformamide and 25g of phytic acid), and stirred for 4 hours at the temperature of 30 ℃ to obtain slurry A.
(2) 10g of modified asphalt is slowly added into the slurry A under the stirring condition. And (3) carrying out ultrasonic treatment for 30min, stirring for 4h, centrifuging for 15min at 8000r/min, removing supernatant, and drying in a 60 ℃ oven to obtain a precursor.
(3) The precursor is placed in a tube furnace at N2Heating to 800 ℃ at the speed of 5 ℃/min in the atmosphere, keeping for 10min, then cooling to room temperature, and crushing to obtain the composite material.
The resulting composite was analyzed, wherein: the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Example 9
This example is to illustrate the preparation and evaluation of the composite material and the preparation and evaluation of the lithium battery according to the present invention
1. Preparation method and evaluation of composite material:
the procedure was as in example 1, except that the stirring time in step (1) was 1 hour and the temperature was 30 ℃.
The resulting composite was analyzed, wherein: the SEM photograph, X-ray photoelectron spectrum of C1s, X-ray photoelectron spectrum of P2P and X-ray photoelectron spectrum of Si2P thereof were substantially identical to those of the composite material obtained in example 1 and are not listed one by one.
Determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Comparative example 1
Comparative example for illustrating the preparation and evaluation of a reference composite and the preparation and evaluation of a lithium cell
1. Preparation method and evaluation of composite material:
the procedure is as in example 1, except that, in step (1), the same amount of modified asphalt is added instead of phytic acid.
Wherein the SEM photograph thereof was substantially identical to that of the composite material obtained in example 1;
the X-ray photoelectron spectra of C1s, P2P and Si2P show no presence of P (O) -O-Si functional groups;
determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the composite material is used as a negative electrode, a metal lithium sheet is used as a positive electrode, 1mol/L LiPF6 solution is used as electrolyte, a polypropylene microporous membrane is used as a diaphragm, and the composite material is assembled into a CR2016 button battery to represent the electrical property of the composite material.
Fig. 8 is a first charge-discharge curve of a reference negative electrode for a lithium battery, and fig. 9 is a cycle stability curve of the reference negative electrode for the lithium battery. Specific results are listed in table 2.
Comparative example 2
Comparative example for illustrating the preparation and evaluation of a reference composite and the preparation and evaluation of a lithium cell
1. Preparation method and evaluation of composite material:
the procedure of example 1 was followed, except that 100g of silica fume and 10g of modified asphalt were added to 280g N 'N-dimethylformamide/phytic acid mixed solution (255g of N' N-dimethylformamide and 25g of phytic acid), respectively, stirred for 5 hours after the ultrasonic treatment, centrifuged at 8000r/min for 15 minutes, removed of the supernatant, dried in an oven at 60 ℃ to obtain a precursor, and heat-treated according to the procedure (4) of example 1.
Wherein the SEM photograph thereof was substantially identical to that of the composite material obtained in example 1;
the X-ray photoelectron spectra of C1s, P2P and Si2P show the presence of P (O) -O-Si functional groups;
determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
Comparative example 3
Comparative example for illustrating the preparation and evaluation of a reference composite and the preparation and evaluation of a lithium cell
1. Preparation method and evaluation of composite material:
the procedure of example 1 was followed except that the silicon powder, phytic acid and modified asphalt were mixed by ball milling. The ball milling speed is 500rpm, and the time is 4h, so that the precursor is obtained. And the subsequent operations were carried out in the same manner as in example 1.
Wherein, SEM photo shows that the carbon layer is not completely coated and is not uniform;
the X-ray photoelectron spectra of C1s, P2P and Si2P show no presence of P (O) -O-Si functional groups;
determining the particle size of active host silicon in the composite material according to a dynamic light scattering method; the elemental composition of the composite was determined by inductively coupled plasma emission spectroscopy, the specific results are shown in table 1.
2. Preparation method and evaluation of lithium battery:
the electrical performance of the composite material is characterized by being assembled into a CR2016 button cell by taking the composite material as a negative electrode, a metal lithium sheet as a positive electrode, 1mol/L LiPF6 solution as electrolyte and a polypropylene microporous membrane as a diaphragm, and specific results are listed in Table 2.
TABLE 1
Numbering Maximum thickness of carbon layer/nm Minimum thickness/nm of carbon layer The weight ratio of Si element, C element and P element
Example 1 4 2 100:7:10
Example 2 5 2 100:4:15
Example 3 10 6 100:20:30
Example 4-1 8 3 100:28:10
Example 4 to 2 13 7 100:7:40
Example 5 5.5 2 100:7:10
Example 6 4.5 2 100:7:10
Example 7 3 1.5 100:14:10
Example 8 7 1 100:7:10
Example 9 6 1 100:7:10
Comparative example 1 2 1 100:10:0
Comparative example 2 7 1.5 100:7:10
Comparative example 3 20 0 100:7:10
TABLE 2
Figure BDA0002226224090000251
Figure BDA0002226224090000261
Note: the specific capacity, the primary coulombic efficiency and the capacity retention rate are the specific capacity, the primary coulombic efficiency and the capacity of the composite material under the constant current discharge rate of 0.1C; wherein the capacity retention rate refers to the capacity retention rate after 50 cycles.
As can be seen from the results in tables 1 and 2, the composite material prepared by the method of the present invention has a p (O) -O-Si structural fragment, which can achieve uniform coating of a carbon layer on the silicon surface of the active host, and the lithium battery prepared by using the composite material has better electrical properties, such as higher specific capacity, first coulombic efficiency, and capacity retention rate.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (12)

1. A composite material, comprising active host silicon and a carbon layer coated on a surface of the active host silicon; wherein the active host silicon contains a P (O) -O-Si structure.
2. The composite of claim 1, wherein the carbon layer has a maximum thickness of no greater than 50nm and a minimum thickness of no less than 0.5 nm;
preferably, the difference between the maximum thickness and the minimum thickness of the carbon layer is 1-10 nm.
3. The composite material according to claim 1, wherein the weight ratio of the Si element, the P element and the C element in the composite material is 100: (5-30): (10-40);
preferably, the specific capacity of the composite material measured at a constant current discharge rate of 0.1C is 2100-3000 mAh/g.
4. A method of making a composite material, the method comprising:
(1) contacting a silicon source and a phosphorus source in the presence of a solvent to obtain a first component;
(2) after mixing the first component and a carbon source, carrying out solvent removal treatment on the obtained mixture to obtain a precursor;
(3) and carrying out heat treatment on the precursor under an inert atmosphere to obtain the composite material.
5. The method according to claim 4, wherein the silicon source is present in the form of elemental silicon and/or silicon oxide, preferably the particle size of the silicon source is 50-300 nm;
preferably, the phosphorus source is selected from phytic acid and/or phosphoric acid;
preferably, the carbon source is selected from at least one of modified pitch, polyacrylonitrile, cellulose derivatives, polymethyl methacrylate, polyamide, polyimide, phytic acid, pyrrole, thiophene, saccharides, polyacrylic acid, and polyvinyl alcohol;
preferably, the solvent is an amide solvent and/or N-methylpyrrolidone.
6. The method according to claim 4 or 5, wherein the phosphorus source is used in an amount of 15 to 100 parts by weight and the carbon source is used in an amount of 5 to 50 parts by weight, relative to 100 parts by weight of the silicon source; and/or
The amount of the solvent used in step (1) is 100-1000 parts by weight relative to 100 parts by weight of the silicon source.
7. The method according to claim 4, wherein in step (1), the contact time is 1-6 h; the contact temperature is 20-50 ℃;
in the step (2), the mixing time is 1-6 h; the mixing temperature is 20-50 deg.C.
8. The method of claim 4, wherein step (2), prior to mixing the first component and the carbon source, further comprises dissolving the carbon source in a solvent;
preferably, the solvent is used in the step (2) in an amount of 10 to 100 parts by weight, relative to 100 parts by weight of the silicon source;
preferably, in the step (2), the method for removing the solvent comprises the steps of sequentially carrying out solid-liquid separation and drying treatment on the mixture.
9. The method of claim 4, wherein in step (3), the heat treatment is performed by: heating the precursor to 500-1000 ℃ at the heating rate of 3-10 ℃/min, and keeping the temperature at 500-1000 ℃ for 10min-10 h;
the flow rate of the inert atmosphere is 40-80mL/min per g of the precursor.
10. A composite material made according to the method of any one of claims 4 to 9.
11. A negative electrode for a lithium battery comprising a negative active material, a binder and a conductive agent, wherein the negative active material is the composite material according to any one of claims 1 to 3 and 10.
12. A lithium battery comprising the negative electrode for a lithium battery according to claim 11, a positive electrode material containing lithium, a separator, and an electrolyte.
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