CN115084461A - Composite material, preparation method and application thereof, lithium ion battery negative electrode piece and lithium ion battery - Google Patents

Composite material, preparation method and application thereof, lithium ion battery negative electrode piece and lithium ion battery Download PDF

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CN115084461A
CN115084461A CN202210558063.3A CN202210558063A CN115084461A CN 115084461 A CN115084461 A CN 115084461A CN 202210558063 A CN202210558063 A CN 202210558063A CN 115084461 A CN115084461 A CN 115084461A
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composite material
silicon
lithium ion
ion battery
tin
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CN115084461B (en
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许家齐
李丹荣
李文俊
俞会根
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Beijing WeLion New Energy Technology Co ltd
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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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/387—Tin or alloys based on tin
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • 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

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  • General Chemical & Material Sciences (AREA)
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  • Materials Engineering (AREA)
  • Composite Materials (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a composite material, a preparation method and application thereof, a lithium ion battery negative electrode plate and a lithium ion battery. The composite material comprises a substrate, and a metal doped layer and a carbon coating layer which are sequentially wrapped on the surface of the substrate; wherein the substrate is silicon-tin alloy, and the chemical composition of the metal doped layer is MgSiO 3 The carbon coating layer is composed of continuous carbon particles. The composite material provided by the invention has the characteristics of low thickness expansion coefficient and high specific capacity, and simultaneously, the composite material has the advantages of low thickness expansion coefficient and high specific capacityThe composite material is used in the lithium ion battery, can effectively improve the first coulombic efficiency and the structural stability of the lithium ion battery, and reduces the electrochemical expansion of the battery.

Description

Composite material, preparation method and application thereof, lithium ion battery negative electrode piece and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a composite material, a preparation method and application thereof, a lithium ion battery negative electrode plate and a lithium ion battery.
Background
With the rapid development of consumer electronics, electric vehicles and electrochemical energy storage industries, the technology of lithium ion batteries is also continuously updated and iterated, high specific energy lithium ion batteries are gradually becoming trend, and in order to further improve the energy density of lithium ion batteries, redesign is needed based on a battery material system.
The negative electrode material is used as an important component of the lithium ion battery, the specific capacity and the cycle life of the lithium ion battery are influenced, and the current general graphite negative electrode material cannot meet the requirement of high specific energy density due to the limit of the limit capacity of the material (the theoretical specific capacity is 372 mAh/g). Under the background, the silicon negative electrode is widely concerned due to the ultrahigh specific capacity (the theoretical specific capacity is 4200mAh/g), and a great deal of research on the silicon negative electrode is carried out at home and abroad, so that the silicon negative electrode is a negative electrode material which is most probably popularized and applied to electric automobiles at present and further promotes the development of the electric automobile industry.
CN111164803A discloses a silicon-based negative electrode material for secondary battery, comprising: the core comprises a core, a first shell and a second shell, wherein the core is made of Si particles and silicon oxide SiO x1 X1 is more than 0 and less than 2; the first shell layer comprises the general formula MySiO z Compound (e.g., MgSiO) 3 ) And an elemental C material, M is selected from at least one of Li, Na, Mg, Al, Fe and Ca; the second shell layer comprises a carbon film layer.
CN112310355A discloses a negative active material, which comprises a core structure and a polymer modified coating layer coated on at least a part of the outer surface of the core structure, wherein the core structure comprises a silicon-based material and/or a tin-based material.
CN110556529A discloses a negative electrode composite material with a multilayer core-shell structure, which has a multilayer core-shell structure, wherein the core of the negative electrode composite material is silica particles, the middle layer is a metal-doped silica composite material, the outermost layer is a carbon coating layer formed by continuous carbon particles or carbon films, and the metal-doped silica composite material is a composite material formed by metal-doped element oxides and/or composite oxides and silica.
According to the method, the nano silicon carbon and the silicon oxide material are used as silicon-based materials, and the high specific capacity characteristic of silicon is not really exerted due to low specific capacity and low first efficiency; in addition, the nano silicon carbon is not used in a large scale due to higher cost and the problems of carbon coating, slurry dispersion and the like in practical application; the silicon protoxide material is developed and produced in mass due to good cycle performance, but the first coulombic efficiency is low, so that the first coulombic efficiency of the material needs to be further improved by a pre-lithium or pre-magnesium mode.
Disclosure of Invention
The invention aims to overcome the defects that the silicon-based material in the prior art has low specific capacity and high volume expansion in the process of lithium extraction of a battery; and the problems of low coulombic efficiency, poor structural stability, high electrochemical expansion and the like of the lithium ion battery containing the silicon-based material for the first time, and provides a composite material, a preparation method and application thereof, a lithium ion battery cathode pole piece and a lithium ion battery.
In order to achieve the above object, a first aspect of the present invention provides a composite material, which includes a substrate, and a metal doped layer and a carbon coating layer sequentially wrapped on a surface of the substrate; wherein the substrate is silicon-tin alloy, and the chemical composition of the metal doped layer is MgSiO 3 The carbon coating layer is composed of continuous carbon particles.
In a second aspect, the present invention provides a method for preparing a composite material, the method comprising: carrying out vacuum sintering on the simple substance silicon and the simple substance tin to obtain a silicon-tin alloy; the silicon-tin alloy is taken as a matrix to carry out surface oxidation reaction and shallow magnesium reaction in sequence so as to form a chemical composition MgSiO on the surface of the matrix 3 Doping the metal layer to obtain an intermediate product; and carrying out carbon coating on the intermediate product to form a carbon coating layer consisting of continuous carbon particles on the surface of the metal doped layer, thereby obtaining the composite material.
The invention provides a composite material prepared by the method provided by the first aspect, or an application of the composite material prepared by the method provided by the second aspect in lithium ion batteries, electric automobiles, electric tools or electrochemical energy storage.
The invention provides a lithium ion battery negative pole piece, which contains the composite material provided by the first aspect or the composite material prepared by the method provided by the second aspect.
The fifth aspect of the invention provides a lithium ion battery, which comprises the lithium ion battery negative electrode plate provided by the fourth aspect.
Compared with the prior art, the invention has the following advantages:
(1) according to the composite material with the multilayer core-shell structure, the silicon-tin alloy is used as the matrix, and the metal doping layer and the carbon coating layer are sequentially wrapped, so that the problem of high volume expansion of the composite material in the lithium release process of a battery can be effectively solved, the composite material has the characteristics of low thickness expansion coefficient and high specific capacity, and particularly, the content and physical parameters of each component in the composite material are limited, so that the performance of the composite material is improved;
(2) the preparation method of the composite material provided by the invention has the characteristics of simple method, environmental friendliness and low cost, and is easy for industrial production design; meanwhile, the method solves the problem of commercial application of the existing silicon-based material due to carbon coating, slurry dispersion and the like;
(3) the composite material provided by the invention has wide application prospect in the fields of lithium ion batteries, electric automobiles, electrical tools, electrochemical energy storage and the like;
(4) when the composite material provided by the invention is used in a lithium ion battery, the first coulombic efficiency and the structural stability of the lithium ion battery can be effectively improved, and the electrochemical expansion of the battery is reduced.
Drawings
FIG. 1 is a schematic illustration of the preparation of a composite material provided by the present invention;
FIG. 2 is a graph showing the first charge and discharge curves of button cells made of the composite materials provided in examples 1-2 and comparative example 1 under the conditions of 0.05C rate of current and 0.005-1.5V voltage interval;
fig. 3 is a graph of cycling curves for button cells made from the composite materials provided in examples 1-2.
Detailed Description
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, which comprises a substrate, a metal doped layer and a carbon coating layer, wherein the metal doped layer and the carbon coating layer are sequentially wrapped on the surface of the substrate; wherein the substrate is silicon-tin alloy, and the chemical composition of the metal doped layer is MgSiO 3 The carbon coating layer is composed of continuous carbon particles.
The inventor of the invention researches and finds that: the carbon coating layer is used as a first buffer layer of the composite material, so that a relatively flexible structure protection can be provided for the whole structure, and the whole material particle can be ensured to have good electronic conductivity and ionic conductivity; the metal doped layer is used as a second buffer layer of the composite material, so that a rigid structure protection can be provided for the matrix, and the rapid transmission of lithium ions can be ensured. Meanwhile, the silicon-tin alloy is used as the silicon-based material, so that the problem that the initial coulomb efficiency of the material is low due to the fact that the existing silicon-based material needs to be improved in a lithium or magnesium pre-preparation mode on the premise that the high specific capacity of the silicon-based material is ensured is solved, the composite material provided by the invention has low volume expansion and high specific capacity, the initial coulomb efficiency and the structural stability of a lithium ion battery containing the composite material are effectively improved, and the electrochemical expansion of the battery is reduced.
In the invention, the composite material has a multilayer core-shell structure without special description, wherein the core is silicon-tin alloy, and the middle layer has a chemical composition of MgSiO 3 The outermost layer of the metal doped layer is a carbon bag consisting of continuous carbon particlesAnd (7) coating.
In some embodiments of the present invention, preferably, the matrix is present in an amount of 85 to 98 wt%, preferably 92 to 97 wt%; the content of the metal doped layer is 1-10 wt%, preferably 2-5 wt%; the content of the carbon coating layer is 1 to 5 wt%, preferably 1 to 3 wt%. In the invention, the contents of the matrix and the metal doped layer in the composite material influence the specific capacity exertion of the material, and the content of the carbon coating layer influences the first coulombic efficiency of the material.
In some embodiments of the invention, it is preferred that the average particle diameter D50 of the matrix is 1 μm to 10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm, 8 μm, 10 μm, and any value in the range of any two values, preferably 3 μm to 7 μm. In the invention, when the thickness of the metal doping and the thickness of the carbon cladding are in a certain condition, the smaller the average particle size D50 of the matrix is, the better the cycle performance of the composite material is.
In some embodiments of the present invention, the metal doped layer preferably has a thickness of 1 to 50nm, for example, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 40nm, 50nm, and any value in the range of any two values, preferably 5 to 25 nm. In the invention, when the thickness of the metal doped layer is larger, the volume expansion of the material in the circulation process can be protected more, and the circulation performance of the composite material is effectively improved.
In some embodiments of the invention, preferably the carbon coating has a thickness of 2-30nm, for example 2nm, 5nm, 10nm, 15nm, 20nm, 30nm, and any value in the range of any two values, preferably 5-15 nm. In the invention, the optimal conditions are adopted, so that the first coulombic efficiency of the composite material is improved.
In the invention, the average particle diameter D50 parameter is measured by a laser particle sizer method without special description; the thickness parameter was measured using transmission electron microscopy.
In some embodiments of the present invention, preferably, the weight ratio of tin to silicon in the silicon-tin alloy is 1: 1-5, e.g., 1:1, 1:2, 1:3, 1:5, and any value in the range of any two values, preferably 1: 2-4. The preferable weight ratio is more favorable for improving the capacity of the composite material.
According to the invention, the specific capacity of the composite material is preferably more than or equal to 2800mAh/g, and preferably 3000-3500 mAh/g.
According to the invention, the composite material preferably has a thickness coefficient of expansion of 150% or less, preferably 90-120%.
The specific capacity refers to the capacity obtained by a unit mass or unit volume battery and is respectively called as the mass specific capacity or the volume specific capacity, and in the invention, under the condition of no special condition, the specific capacity parameter represents the first charge mass specific capacity parameter, wherein the mass specific capacity parameter is measured by adopting a lithium ion button battery test system method; the thickness expansion coefficient refers to the thickness expansion coefficient of a negative electrode plate made of the composite material in a full lithium intercalation (100% DOD) state compared with a non-lithium intercalation (0% DOD) state.
In a second aspect, the present invention provides a method for preparing a composite material, the method comprising: carrying out vacuum sintering on the simple substance silicon and the simple substance tin to obtain a silicon-tin alloy; the silicon-tin alloy is used as a matrix to carry out surface oxidation reaction and shallow magnesium reaction in sequence so as to form a chemical composition MgSiO on the surface of the matrix 3 Doping the metal layer to obtain an intermediate product; and carrying out carbon coating on the intermediate product to form a carbon coating layer consisting of continuous carbon particles on the surface of the metal doped layer.
According to the preparation method of the composite material, as shown in fig. 1, elemental silicon and elemental tin are sintered in vacuum to obtain a silicon-tin alloy; then, the silicon-tin alloy is subjected to surface layer oxidation reaction to form SiO on the surface of the silicon-tin alloy 2 To obtain silicon-tin-containing alloy and SiO 2 The surface oxidation reaction product of (1); carrying out shallow magnesium reaction on the surface oxidation reaction product and a magnesium forming agent to form a chemical composition MgSiO on the surface of the silicon-tin alloy 3 Obtaining an intermediate product containing the silicon-tin alloy and the metal doped layer; finally, the intermediate product is coated with carbon so as to form continuous carbon particles on the surface of the metal doped layerAnd (4) coating the carbon coating layer formed by the particles to obtain the composite material with a multilayer core-shell structure.
In some embodiments of the present invention, preferably, the method comprises the steps of:
(1) carrying out vacuum sintering on the simple substance silicon and the simple substance tin until the simple substance tin completely reacts, and cooling to obtain the silicon-tin alloy;
(2) performing the surface oxidation reaction by using the silicon-tin alloy as the substrate in an oxygen-containing gas atmosphere to generate SiO on the surface of the substrate 2 To obtain a surface oxidation reaction product;
(3) mixing the surface oxidation reaction product and a magnesium reagent in an inert gas atmosphere, and carrying out the shallow magnesium reaction to form the metal doping layer on the surface of the substrate, so as to obtain an intermediate product;
(4) and carrying out carbon coating on the intermediate product and a carbon source to form a carbon coating layer on the surface of the metal doped layer, so as to obtain the composite material.
In some embodiments of the present invention, preferably, in step (1), the weight ratio of the elemental tin to the elemental silicon is 1: 1-5, e.g., 1:1, 1:2, 1:3, 1:5, and any value in the range of any two values, preferably 1: 2-4.
In some embodiments of the present invention, it is preferable that the average particle diameter D50 of the elemental silicon is 0.1 to 10 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, and any value in the range of any two values, preferably 0.5 to 7 μm; the maximum particle diameter Dmax is < 20 μm, preferably 12-15 μm.
In some embodiments of the present invention, it is preferable that the elemental silicon has a silicon content of 98 wt% or more, preferably 99 to 99.5 wt%.
In some embodiments of the present invention, it is preferred that the elemental tin has a tin content of 98 wt.% or more, preferably 99 to 99.5 wt.%. In the present invention, the elemental tin includes, but is not limited to, tin ingot, tin powder, and tin foil.
In the invention, the vacuum sintering aims to react the simple substance silicon and the simple substance tin to generate the silicon-tin alloy. Preferably, the temperature of the vacuum sintering is 800-.
In the present invention, the vacuum sintering is performed in a medium frequency furnace having two material chambers. Namely, placing simple substance silicon and simple substance tin in an intermediate frequency furnace with A, B raw material chambers respectively, sintering in vacuum to 800-2000 ℃, stopping heating after the simple substance tin completely reacts, cooling to room temperature, and obtaining the silicon-tin alloy in a precipitation zone of the intermediate frequency furnace.
In the present invention, the surface layer oxidation reaction is intended to oxidize the silicon of the silicon-tin alloy surface layer to silicon dioxide.
In the present invention, the surface oxidation reaction product includes a substrate and SiO coated on the surface of the substrate 2 。
In some embodiments of the invention, it is preferred that the oxygen content of the oxygen-containing gas is ≧ 20% by volume, preferably 50-80% by volume. In the present invention, the oxygen-containing gas includes, but is not limited to, air, oxygen, and the like.
In some embodiments of the present invention, preferably, the conditions of the surface oxidation reaction include: the temperature is 500-1000 ℃, and the optimal temperature is 600-800 ℃; the time is 0.1-5h, preferably 0.5-2 h.
In some embodiments of the present invention, it is preferred that SiO in the surface oxidation reaction product is based on the total weight of the surface oxidation reaction product 2 The content is 1 to 15 wt%, preferably 5 to 10 wt%.
In some embodiments of the present invention, it is preferred that the substrate is pulverized to an average particle diameter D50 of 1 to 10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, and any value in the range of any two numerical values, preferably 3 to 7 μm, before the surface layer oxidation reaction is performed.
In the present invention, the superficial layer magnesium reaction is intended to oxidize the surface layer productSiO 2 2 Conversion to MgSiO 3 Thereby improving the ionic conductivity of the composite material.
In the invention, the intermediate product comprises a substrate and MgSiO coated on the substrate 3 The metal doped layer of (a).
In some embodiments of the present invention, it is preferred that the weight ratio of the surface oxidation reaction product to the magnesium reagent is 98-85: 2-15, preferably 95-90: 5-10. The SiO layer is fully formed by adopting the optimized weight ratio 2 Conversion to MgSiO 3 And further improve the relevant performance parameters of the composite material.
In some embodiments of the present invention, preferably, the magnesium-forming agent is selected from at least one of elemental magnesium, magnesium nitride and magnesium oxide.
In some embodiments of the present invention, preferably, the mixing conditions include: the rotation speed is 100-1000rpm, preferably 300-800 rpm; the time is 0.1 to 5 hours, preferably 0.5 to 1 hour.
In some embodiments of the present invention, preferably, the conditions of the shallow magnesium reaction include: the temperature is 500-900 ℃, and preferably 600-800 ℃; the time is 0.5-10h, preferably 1-5 h.
In some embodiments of the present invention, preferably, in the step (4), the weight ratio of the intermediate product to the carbon source is 100: 1-8, e.g., 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:8, and any value in the range of any two values, preferably 100: 2-5. The optimal weight ratio is adopted, the surface layers of the particles are fully and uniformly coated, and the related performance parameters of the composite material are improved.
In some embodiments of the present invention, preferably, the carbon source is selected from a high polymer, preferably at least one selected from polyacrylonitrile, polyethylene glycol, polymethyl acrylate, polyvinyl acetate, epoxy resin, and polyurethane; further preferably, the average molecular weight of the polymer is 3000-10000 g/mol.
In some embodiments of the present invention, preferably, the carbon-coated conditions include: the temperature is 500-1000 ℃, and the optimal temperature is 600-900 ℃; the time is 0.1-10h, preferably 0.5-5 h.
The invention provides a composite material prepared by the method provided by the first aspect, or an application of the composite material prepared by the method provided by the second aspect in lithium ion batteries, electric automobiles, electric tools or electrochemical energy storage.
The composite material provided by the invention has high specific capacity and low thickness expansion coefficient; when the lithium ion battery is used for the lithium ion battery, the first coulombic efficiency and the structural stability of the lithium ion battery can be effectively improved, and the electrochemical expansion of the battery is reduced.
The invention provides a lithium ion battery negative pole piece, which contains the composite material provided by the first aspect or the composite material prepared by the method provided by the second aspect.
The fifth aspect of the invention provides a lithium ion battery, which comprises the lithium ion battery negative electrode plate provided by the fourth aspect.
According to a particularly preferred embodiment of the invention, the composite material comprises a substrate, and a metal doped layer and a carbon coating layer which are sequentially wrapped on the surface of the substrate; wherein the substrate is silicon-tin alloy, and the chemical composition of the metal doped layer is MgSiO 3 The carbon coating layer is composed of continuous carbon particles;
wherein the matrix is present in an amount of 92 to 97 wt%, based on the total weight of the composite; the content of the metal doped layer is 2-5 wt%; the content of the carbon coating layer is 1-3 wt%;
wherein the average particle diameter D50 of the matrix is 3-7 μm; the thickness of the metal doped layer is 5-25 nm; the thickness of the carbon coating layer is 5-15 nm;
wherein the weight ratio of tin to silicon in the silicon-tin alloy is 1: 2-4.
The present invention will be described in detail below by way of examples.
Example 1
(1) Placing elemental tin (tin ingot with the purity of 98 wt%) and elemental silicon (silicon powder with the average particle size D50 of 5 mu m, the maximum particle size Dmax of less than 20 mu m and the purity of 99 wt%) in an intermediate frequency furnace with A, B raw material chambers according to the weight ratio of 1:1, carrying out vacuum sintering at 1300 ℃, cooling to room temperature of 25 ℃, and crushing to obtain a silicon-tin alloy with the average particle size D50 of 5 mu m;
(2) performing surface oxidation reaction (at 800 deg.C for 1 hr) in air atmosphere with the above silicon-tin alloy as matrix to generate SiO on the surface of the matrix 2 To obtain a surface oxidation reaction product;
wherein SiO is present in the reaction mixture based on the total weight of the surface oxidation reaction products 2 The content is 8 wt%;
(3) mixing the surface oxidation reaction product and a magnesium agent (magnesium powder) according to a weight ratio of 90:10 in a nitrogen atmosphere (the rotating speed is 300rpm, the time is 1h), and performing shallow magnesium reaction (the temperature is 800 ℃, the time is 0.5h) to form MgSiO with a chemical composition on the surface of a substrate 3 Doping the metal layer to obtain an intermediate product;
(4) the intermediate product and a carbon source (epoxy resin having an average molecular weight of 3000 g/mol) were carbon-coated at a weight ratio of 100:4 (temperature 900 ℃ C., time 0.5h) to form a carbon coating layer composed of continuous carbon particles on the surface of the metal-doped layer, and a composite material S1 was obtained.
Wherein the content of the matrix is 90 wt%, the content of the metal doped layer is 8 wt%, and the content of the carbon coating layer is 2 wt%, based on the total weight of the composite material S1.
Example 2
(1) Placing elemental tin (tin ingot with the purity of 98 wt%) and elemental silicon (silicon powder with the average particle size D50 of 2 mu m, the maximum particle size Dmax of less than 20 mu m and the purity of 99 wt%) in an intermediate frequency furnace with A, B raw material chambers according to the weight ratio of 1:1, carrying out vacuum sintering at 1500 ℃, cooling to room temperature of 25 ℃, and crushing to obtain a silicon-tin alloy with the average particle size D50 of 3 mu m;
(2) performing surface oxidation reaction (at 700 deg.C for 1 hr) in air atmosphere with the above silicon-tin alloy as matrix to generate SiO on the surface of the matrix 2 To obtain a surface oxidation reaction product;
wherein SiO is present in the reaction mixture based on the total weight of the surface oxidation reaction products 2 The content is 5 wt%;
(3) mixing the surface oxidation reaction product and a magnesium reagent (magnesium powder) according to a weight ratio of 90:10 in a nitrogen atmosphere (the rotating speed is 500rpm, the time is 0.5h), and performing shallow magnesium reaction (the temperature is 600 ℃, the time is 5h) to form a chemical composition MgSiO on the surface of the substrate 3 Doping the metal layer to obtain an intermediate product;
(4) the intermediate product and a carbon source (epoxy resin having an average molecular weight of 5000 g/mol) were carbon-coated at a weight ratio of 100:5 (temperature of 800 ℃ C., time of 2 hours) to form a carbon coating layer composed of continuous carbon particles on the surface of the metal-doped layer, thereby obtaining a composite material S2.
Wherein the content of the matrix is 93 wt%, the content of the metal doped layer is 4 wt%, and the content of the carbon coating layer is 3 wt%, based on the total weight of the composite material S2.
Example 3
(1) Placing elemental tin (tin ingot with the purity of 98 wt%) and elemental silicon (silicon powder with the average particle size D50 of 7 mu m, the maximum particle size Dmax of less than 20 mu m and the purity of 99 wt%) in an intermediate frequency furnace with A, B raw material chambers according to the weight ratio of 1:2, sintering at 1700 ℃ in vacuum until the elemental tin completely reacts, cooling to the room temperature of 25 ℃, and crushing to obtain a silicon-tin alloy with the average particle size D50 of 7 mu m;
(2) performing surface oxidation reaction (at 600 deg.C for 2 hr) in air atmosphere with the above silicon-tin alloy as matrix to generate SiO on the surface of the matrix 2 To obtain a surface oxidation reaction product;
wherein SiO is present in the reaction mixture based on the total weight of the surface oxidation reaction products 2 The content is 7 wt%;
(3) mixing the surface oxidation reaction product and a magnesium reagent (magnesium powder) according to a weight ratio of 90:10 in a nitrogen atmosphere (the rotating speed is 800rpm, the time is 0.5h), and performing shallow magnesium reaction (the temperature is 700 ℃ and the time is 2h) to form MgSiO with a chemical composition on the surface of a substrate 3 Doping the metal layer to obtain an intermediate product;
(4) the intermediate product and a carbon source (average molecular weight 10000g/mol, epoxy resin) were carbon-coated at a weight ratio of 100:2 (temperature 600 ℃ C., time 5h) to form a carbon coating layer composed of continuous carbon particles on the surface of the metal doped layer, to obtain a composite material S3.
Wherein the content of the matrix is 94 wt%, the content of the metal doped layer is 5 wt%, and the content of the carbon coating layer is 1 wt% based on the total weight of the composite material S3.
Example 4
(1) Placing elemental tin (tin ingot with the purity of 98 wt%) and elemental silicon (silicon powder with the average particle size D50 of 5 mu m, the maximum particle size Dmax of less than 20 mu m and the purity of 99 wt%) in an intermediate frequency furnace with A, B raw material chambers according to the weight ratio of 1:2, carrying out vacuum sintering at 1500 ℃, cooling to room temperature of 25 ℃, and crushing to obtain a silicon-tin alloy with the average particle size D50 of 3 mu m;
(2) performing surface oxidation reaction (at 700 deg.C for 1 hr) in air atmosphere with the silicon-tin alloy as matrix to generate SiO on the surface of the matrix 2 To obtain a surface oxidation reaction product;
wherein SiO is present in the reaction mixture based on the total weight of the surface oxidation reaction products 2 The content is 2 wt%;
(3) mixing the surface oxidation reaction product and a magnesium reagent (magnesium powder) according to a weight ratio of 90:10 in a nitrogen atmosphere (the rotating speed is 300rpm, the time is 0.5h), and performing shallow magnesium reaction (the temperature is 800 ℃, the time is 2h) to form MgSiO with a chemical composition on the surface of a substrate 3 Doping the metal layer to obtain an intermediate product;
(4) the intermediate product and a carbon source (average molecular weight 10000g/mol, epoxy resin) were carbon-coated at a weight ratio of 100:5 (temperature 900 ℃ C., time 3h) to form a carbon coating layer composed of continuous carbon particles on the surface of the metal doped layer, to obtain a composite material S4.
Wherein the content of the matrix is 95 wt%, the content of the metal doped layer is 2 wt%, and the content of the carbon coating layer is 3 wt%, based on the total weight of the composite material S4.
Example 5
According to the method of example 2, except that the weight ratio of elemental tin to elemental silicon was changed to 1:5 in step (1), the same conditions were applied to obtain composite material S5.
Wherein the content of the matrix is 92 wt%, the content of the metal doped layer is 6 wt%, and the content of the carbon coating layer is 2 wt%, based on the total weight of the composite material S5.
Example 6
Following the procedure of example 2, except that the temperature for vacuum sintering was changed to 800 ℃ in step (1), the same conditions were applied to obtain composite material S6.
Wherein the content of the matrix is 91 wt%, the content of the metal doped layer is 4 wt%, and the content of the carbon coating layer is 5 wt%, based on the total weight of the composite material S6.
Example 7
According to the method of example 2, except that in the step (2), the conditions for the surface layer oxidation reaction were changed to 500 ℃ for 5 hours, and the other conditions were the same, composite material S7 was obtained.
Wherein the content of the matrix is 93 wt%, the content of the metal doped layer is 2 wt%, and the content of the carbon coating layer is 5 wt%, based on the total weight of the composite material S7.
Example 8
A composite material S8 was obtained in the same manner as in example 2 except that in step (3), the weight ratio of the surface oxidation reaction product to the magnesium compound (magnesium powder) was changed to 98: 2.
Wherein the content of the matrix is 94 wt%, the content of the metal doped layer is 2 wt%, and the content of the carbon coating layer is 4 wt%, based on the total weight of the composite material S8.
Example 9
According to the method of example 2, except that the conditions for the shallow magnesium reaction were changed to 900 ℃ for 0.5 hour in the step (3), the other conditions were the same, to obtain composite material S9.
Wherein the content of the matrix is 95 wt%, the content of the metal doped layer is 1 wt%, and the content of the carbon coating layer is 4 wt%, based on the total weight of the composite material S9.
Example 10
According to the method of example 2, except that, in the step (4), the weight ratio of the above intermediate product to the carbon source was changed to 100:1, and the other conditions were the same, composite material S10 was obtained.
Wherein the content of the matrix is 90.5 wt%, the content of the metal doped layer is 8.5 wt%, and the content of the carbon coating layer is 1 wt%, based on the total weight of the composite material S10.
Comparative example 1
A single silicon powder (5 μm in average particle size D50) was used as material DS 1.
Comparative example 2
Following the procedure of example 2, except that the substrate was replaced with nano silicon carbon, the same conditions were followed to obtain composite DS 2.
Wherein, based on the total weight of the composite material DS2, the content of the matrix is 95 wt%, the content of the metal doped layer is 3 wt%, and the content of the carbon coating layer is 2 wt%.
Comparative example 3
A composite material DS3 was obtained following the procedure of example 2, except that the substrate was replaced with silica, and the conditions were otherwise the same.
Wherein, based on the total weight of the composite material DS3, the content of the matrix is 95 wt%, the content of the metal doped layer is 3 wt%, and the content of the carbon coating layer is 2 wt%.
Test example
The composite materials (S1-S10 and DS1-DS3) obtained in examples 1-10 and comparative examples 1-3 were subjected to electrochemical performance tests.
Preparing a button cell: respectively mixing the composite materials (S1-S10 and DS1-DS3) with superconducting carbon black (SP), single-walled carbon nanotube (SWCNT), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) according to the weight ratio of 90:1.45:0.05:2:6.5, uniformly mixing, coating on copper foil, and drying at 70 ℃ for 12 hours to obtain a negative pole piece; with lithium metal, Celgard2400 as separator, containing 1mol/L LiPF 6 The solvent was EC/DMC (volume ratio 1:1) and 10% FEC additive was used as electrolyte, and the 2032 type was assembled in an argon atmosphere glove boxButton cells, button cells P1-P10 and DP1-DP3 were obtained.
And (3) testing conditions are as follows: the button cells P1-P10 and DP1-DP3 are subjected to first charge and discharge tests respectively under the conditions that the current is 0.05C multiplying power (1C is 3850mA/g) and the voltage interval is 0.005-1.5V, and the test results are listed in Table 1; the button cells P1-P10 and DP1-DP3 were subjected to charge and discharge tests after 20 cycles at 0.1C/0.1C, respectively, and the test results are shown in Table 1.
Wherein, the first charge and discharge curve of the button cell prepared by the composite material provided by the examples 1-2 and the comparative example 1 under the conditions of 0.05C multiplying power and 0.005-1.5V voltage interval is shown in figure 2. As shown in fig. 2, the button cell P1 prepared in example 1 had a specific first discharge capacity of 3261.18mAh/g, a specific first charge capacity of 2953.25mAh/g, and a first coulombic efficiency of 90.56%; the button cell P2 prepared in the embodiment 2 has the specific discharge capacity of 3796.89mAh/g, the specific charge capacity of 3491.1mAh/g and the coulombic efficiency of 91.95%; the button cell DP1 prepared from comparative example 1 had a first discharge specific capacity of 3181.9mAh/g, a first charge specific capacity of 824mAh/g, and a first coulombic efficiency of only 25.90%.
Wherein the cycling curves of button cells made from the composites provided in examples 1-2 are shown in figure 3. As can be seen from fig. 3, under the charge and discharge conditions of 0.1C/0.1C, after 20 cycles, the button cell P1 prepared in example 1 has a specific discharge capacity of 2839.59mAh/g, a specific charge capacity of 2814.03mAh/g, and a coulombic efficiency of 99.1%; the button cell P2 prepared in embodiment 2 has a specific discharge capacity of 3348.71mAh/g, a specific charge capacity of 3320.92mAh/g and a coulomb efficiency of 99.17%. Namely, the lithium ion battery prepared from the composite material provided by the invention has excellent cycle performance and coulombic efficiency.
TABLE 1
Figure BDA0003655562240000161
As can be seen from the data in Table 1, the composite materials provided in examples 1-10 of the present invention have high specific capacity and low thickness expansion coefficient, compared to comparative examples 1-3; when the lithium ion battery is used for the lithium ion battery, the first coulombic efficiency and the structural stability are higher.
As can be seen from comparison between example 2 and example 5, by limiting the weight ratio of elemental tin to elemental silicon in step (1) within a preferred protection range, the obtained composite material has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
As can be seen from comparison between example 2 and example 6, by limiting the temperature of vacuum sintering in step (1) within a preferred protection range, the obtained composite material has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
As can be seen from comparison between example 2 and example 7, by limiting the conditions of the surface layer oxidation reaction in step (2) within the preferable protection range, the obtained composite material has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
It can be known from comparing example 2 and example 8 that the composite material obtained by limiting the weight ratio of the surface layer oxidation reaction product and the magnesium forming agent in the step (3) within the preferable protection range has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
As can be seen from comparison between example 2 and example 9, by limiting the conditions of the shallow layer magnesium reaction in step (3) within the preferable protection range, the obtained composite material has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
As can be seen from comparison between example 2 and example 10, by limiting the weight ratio of the intermediate product and the carbon source in step (4) within the preferable protection range, the obtained composite material has high specific capacity and low thickness expansion coefficient, and the prepared lithium ion battery has high first coulombic efficiency and structural stability.
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 (14)

1. The composite material is characterized by comprising a matrix, and a metal doped layer and a carbon coating layer which are sequentially wrapped on the surface of the matrix; wherein the substrate is silicon-tin alloy, and the chemical composition of the metal doped layer is MgSiO 3 The carbon coating layer is composed of continuous carbon particles.
2. The composite material according to claim 1, wherein the matrix is present in an amount of 85-98 wt%, preferably 92-97 wt%, based on the total weight of the composite material; the content of the metal doped layer is 1-10 wt%, preferably 2-5 wt%; the content of the carbon coating layer is 1 to 5 wt%, preferably 1 to 3 wt%.
3. Composite according to claim 1 or 2, wherein the average particle size D50 of the matrix is 1-10 μ ι η, preferably 3-7 μ ι η;
preferably, the thickness of the metal doped layer is 1-50nm, preferably 5-25 nm;
preferably, the thickness of the carbon coating layer is 2 to 30nm, preferably 5 to 15 nm.
4. The composite material according to any one of claims 1-3, wherein the weight ratio of tin to silicon in the silicon-tin alloy is 1: 1-5, preferably 1: 2-4.
5. The composite material according to any one of claims 1 to 4, wherein the specific capacity of the composite material is not less than 2800mAh/g, preferably 3000-3500 mAh/g;
preferably, the thickness expansion coefficient of the composite material is less than or equal to 150 percent, and preferably 90 to 120 percent.
6. A method of making a composite material, the method comprising: carrying out vacuum sintering on the simple substance silicon and the simple substance tin to obtain a silicon-tin alloy; the silicon-tin alloy is used as a matrix to carry out surface oxidation reaction and shallow magnesium reaction in sequence so as to form a chemical composition MgSiO on the surface of the matrix 3 Doping the metal layer to obtain an intermediate product; and carrying out carbon coating on the intermediate product to form a carbon coating layer consisting of continuous carbon particles on the surface of the metal doped layer, thereby obtaining the composite material.
7. The method of claim 6, wherein the method comprises the steps of:
(1) carrying out vacuum sintering on the simple substance silicon and the simple substance tin until the simple substance tin completely reacts, and cooling to obtain the silicon-tin alloy;
(2) performing the surface oxidation reaction on the silicon-tin alloy as the substrate in an oxygen-containing gas atmosphere to generate SiO on the surface of the substrate 2 To obtain a surface oxidation reaction product;
(3) mixing the surface oxidation reaction product and a magnesium reagent in an inert gas atmosphere, and carrying out the shallow magnesium reaction to form the metal doping layer on the surface of the substrate, so as to obtain an intermediate product;
(4) and carrying out carbon coating on the intermediate product and a carbon source to form a carbon coating layer on the surface of the metal doping layer, thereby obtaining the composite material.
8. The method of claim 7, wherein in step (1), the weight ratio of elemental tin to elemental silicon is 1: 1-5, preferably 1: 2-4;
preferably, the average particle diameter D50 of the simple substance silicon is 0.1-10 μm, preferably 0.5-7 μm; the maximum particle size Dmax is less than 20 mu m, and is preferably 12 to 15 mu m;
preferably, the content of silicon in the simple substance silicon is more than or equal to 98 wt%, and preferably 99-99.5 wt%;
preferably, the content of tin in the simple substance tin is more than or equal to 98 wt%, and preferably 99-99.5 wt%;
preferably, the temperature of the vacuum sintering is 800-2000 ℃, preferably 1000-1700 ℃.
9. The method according to claim 7 or 8, wherein in the step (2), the conditions of the surface oxidation reaction comprise: the temperature is 500-1000 ℃, and the optimal temperature is 600-800 ℃; the time is 0.1 to 5 hours, preferably 0.5 to 2 hours;
preferably, SiO in the surface oxidation reaction product is present in the form of a solid oxide, based on the total weight of the surface oxidation reaction product 2 The content is 1-15 wt%.
10. The method according to any one of claims 7 to 9, wherein in step (3), the weight ratio of the surface oxidation reaction product to the magnesium-forming agent is 98 to 85: 2-15, preferably 95-90: 5-10;
preferably, the magnesium oxidant is selected from at least one of elemental magnesium, magnesium nitride and magnesium oxide;
preferably, the mixing conditions include: the rotation speed is 100-; the time is 0.1-5h, preferably 0.5-1 h;
preferably, the conditions of the superficial layer magnesium reaction include: the temperature is 500-900 ℃, and preferably 600-800 ℃; the time is 0.5-10h, preferably 1-5 h.
11. The method according to any one of claims 7 to 10, wherein in step (4), the weight ratio of the intermediate product to the carbon source is 100: 1-8, preferably 100: 2-5;
preferably, the carbon source is selected from high polymers, preferably at least one selected from polyacrylonitrile, polyethylene glycol, polymethyl acrylate, polyvinyl acetate, epoxy resin and polyurethane; the average molecular weight of the high polymer is 3000-10000g/mol,
preferably, the carbon-coated conditions include: the temperature is 500-1000 ℃, and the preferred temperature is 600-900 ℃; the time is 0.1-10h, preferably 0.5-5 h.
12. Use of a composite material according to any one of claims 1 to 5, or a composite material obtained by a method according to any one of claims 6 to 11, in a lithium ion battery, an electric vehicle, an electrical tool or an electrochemical energy storage, preferably in a lithium ion battery.
13. A lithium ion battery negative pole piece is characterized in that the negative pole piece contains the composite material of any one of claims 1 to 5 or the composite material prepared by the method of any one of claims 6 to 11.
14. A lithium ion battery comprising the negative electrode sheet of claim 13.
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