CN111540889B - Silicon negative electrode material coated by double-layer coating layer and preparation method and application thereof - Google Patents

Silicon negative electrode material coated by double-layer coating layer and preparation method and application thereof Download PDF

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CN111540889B
CN111540889B CN202010383197.7A CN202010383197A CN111540889B CN 111540889 B CN111540889 B CN 111540889B CN 202010383197 A CN202010383197 A CN 202010383197A CN 111540889 B CN111540889 B CN 111540889B
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layer
silicon
coating
transition metal
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CN111540889A (en
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袁号
李素丽
赵伟
李俊义
徐延铭
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Zhuhai Cosmx Battery 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
    • H01M4/362—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
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • 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
    • 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 provides a silicon anode material coated by a double-layer coating layer and a preparation method and application thereof; according to the invention, a double-shell silicon-coated material is formed by coating a double-layer material on a silicon powder substrate, the first layer of coating is a transition metal sulfide, the second layer of coating is a carbon layer, and the proportion of the particle size of the silicon nanoparticles to the thickness of the double-layer coating is controlled by controlling the molar ratio of the silicon nanoparticles to a transition metal precursor and the mass ratio of the silicon nanoparticles to the carbon precursor, so that the advantages of better energy density, longer cycle life, inhibition of volume expansion of a pole piece and better safety are realized. The double-layer coating layer is too thin and easily causes the expansion of the pole piece to be large, the safety performance is poor, the energy density is low due to the fact that the double-layer coating layer is too thick, meanwhile, the multi-sulfur ion shuttling easily causes the cycle attenuation to be fast, the multi-sulfur ion shuttling is reduced through the coating carbon layer, and the conductivity of the material is improved.

Description

Silicon negative electrode material coated by double-layer coating layer and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to a silicon negative electrode material coated by a double-layer coating layer, a preparation method of the silicon negative electrode material and application of the silicon negative electrode material in a lithium ion battery.
Background
The lithium ion battery is widely applied to the fields of electronic equipment, electric appliances, electric automobiles and the like as an efficient, light and portable energy storage device. At present, graphite (370mAh g) with lower specific capacity is mostly adopted in commercial lithium ion batteries-1) Silicon (Li) with higher theoretical specific capacity as negative active material15Si4，3590mAh g-1) The lithium ion battery cathode material is very suitable for preparing a high-performance lithium ion battery.
However, silicon as an anode material expands greatly in volume (about 400%) during charge and discharge cycles, which severely limits the amount of silicon anode material used. The root of the volume expansion of the silicon negative electrode material lies in that a new SEI layer is continuously formed on the silicon material in the charging and discharging processes, an old SEI layer is continuously broken, and the silicon material is seriously pulverized, so that the silicon negative electrode material is greatly expanded in volume, and the silicon material is separated from a current collector due to expansion, and further capacity attenuation is caused. In addition, the silicon material has poor conductivity, so that the charging and discharging efficiency of the silicon material is low.
At present, silicon materials are often subjected to doping coating, element doping and nanocrystallization, but the modification means have limited volume inhibition capability, and the capacity of the silicon materials is not greatly improved.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a double-layer coating-layer coated silicon negative electrode material, and a preparation method and application thereof.
The inventor of the present application found that the ratio of the silicon nanoparticles to the thickness of the coating layer affects cycle life, energy density, expansion rate of the electrode sheet, and battery safety. If the coating layer is too thin, the cycle life is poor, the expansion rate of the pole piece is high, and the safety is poor; if the clad layer is too thick, significant reduction in energy density is likely to result. By regulating and controlling the ratio of the particle size of the silicon nano particles to the thickness of the coating layer, the silicon anode material with excellent comprehensive performance can be obtained.
The silicon negative electrode material provided by the invention is characterized in that by means of a double-coating layer structure of transition metal sulfide and carbon, the optimal ratio of the particle size of the silicon nano particles to the thickness of a coating layer is regulated and controlled by controlling the particle size of the silicon nano particles, the thickness of the transition metal sulfide layer and the thickness of a carbon layer, so that the prepared silicon nano particles coated by the double-coating layer have good cycle life, higher energy density and obvious inhibition of the expansion rate of a pole piece.
In the invention, the ratio of the particle size of the silicon nanoparticle to the thickness of the coating layer comprises the ratio of the particle size of the silicon nanoparticle to the thickness of the transition metal sulfide coating layer, the ratio of the particle size of the silicon nanoparticle to the thickness of the carbon coating layer, and the ratio of the particle size of the silicon nanoparticle to the thickness of the total coating layer.
The purpose of the invention is realized by the following scheme:
a silicon material coated by double-layer coating layers is characterized in that a first coating layer is close to the silicon material in the double-layer coating layers, and a second coating layer is far away from the silicon material in the double-layer coating layers;
the first coating layer is a transition metal sulfide layer, the second coating layer is a carbon layer, and the silicon material is silicon nanoparticles;
the particle size of the silicon nanoparticles is 50-100nm, and the ratio of the particle size of the silicon nanoparticles to the thickness of the first coating layer is 20:1-5: 1; the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 20:1-5: 1; and the ratio of the particle size of the silicon nano-particles to the thickness of the double-layer coating is 10:1-5: 2.
According to the invention, the particle size of the silicon nanoparticles is between 50 and 100nm, the ratio of the particle size of the silicon nanoparticles to the thickness of the first coating layer is 15:1 to 10:1, such as 15:1, 14:1, 13:1, 12:1, 11:1 or 10: 1; the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 10:1-5:1, such as 10:1, 9:1, 8:1, 7:1, 6:1, or 5: 1; and the ratio of the particle size of the silicon nanoparticles to the thickness of the double-layer coating is 10:1-3:1, such as 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1 or 3: 1.
According to the invention, the first coating layer is a transition metal sulfide layer, in particular FeS2Layer, MoS2Layer, VS2Layer, CoS2Layer, WS2A layer,TiS2Layer, NiS2Layer or Ni3S2Layers, and the like.
According to the invention, the transition metal sulfide layer is of a nanosheet structure, the size of the single nanosheet layer is 1-100nm, and the thickness of the single nanosheet layer is 0.1-10 nm.
According to the invention, the second cladding layer is a carbon layer.
According to the present invention, the carbon in the carbon layer may be at least one of crystalline carbon, graphitized carbon, and the like.
According to the invention, the silicon material coated by the double-layer coating layer is used as a silicon negative electrode material.
The invention provides a preparation method of the silicon material coated by the double-layer coating layer, which comprises the following steps:
step (S1): placing a silicon material in a transition metal precursor solution for hydrothermal reaction, and coating a transition metal sulfide layer on the surface of the silicon material to be used as a first coating layer; wherein the silicon material is silicon nanoparticles, and the particle size of the silicon nanoparticles is 50-100 nm; the molar ratio of the silicon nanoparticles to the transition metal precursor is 200:1-10: 1;
step (S2): placing the silicon material coated with the transition metal sulfide in a carbon precursor solution for reaction, and coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to be used as a second coating layer; the mass ratio of the silicon nanoparticles to the carbon precursor is 10:1-1: 5; alternatively, the first and second electrodes may be,
placing the silicon material coated with the transition metal sulfide in a vapor deposition furnace, performing vapor deposition, coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to serve as a second coating layer, wherein the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 20:1-5: 1; the ratio of the particle size of the silicon nano-particles to the thickness of the double-layer coating is 10:1-5: 2.
According to the present invention, in the step (S1), the temperature of the hydrothermal reaction is 120-200 ℃, and the time of the hydrothermal reaction is 6-12 h.
According to the present invention, in the step (S1), the transition metal precursor solution includes a transition metal source, a sulfur source, and a solvent.
According to the present invention, in the step (S1), the transition metal is selected from at least one of Fe, Mo, V, Co, W, Ti, Ni, and the like.
According to the present invention, in the step (S1), the transition metal source is selected from soluble salts of the above-mentioned transition metals, for example, at least one selected from nitrates, acetates, sulfates, chlorates, chlorides, ammonium salts, and the like of the above-mentioned transition metals, and further, for example, at least one selected from iron nitrate, cobalt nitrate, ammonium molybdate, sodium vanadate, ammonium metavanadate, nickel nitrate, sodium tungstate, sodium titanate, and the like.
According to the present invention, in the step (S1), the sulfur source is at least one selected from thiourea, sodium thiosulfate, thioacetamide and the like.
According to the present invention, in the step (S1), the solvent is selected from deionized water.
According to the present invention, in step (S1), the concentration of the transition metal in the transition metal precursor solution is 1 to 100mg/mL, for example, 1mg/mL, 2mg/mL, 5mg/mL, 8mg/mL, 10mg/mL, 15mg/mL, 20mg/mL, 25mg/mL, 30mg/mL, 35mg/mL, 40mg/mL, 45mg/mL, 50mg/mL, 55mg/mL, 60mg/mL, 65mg/mL, 70mg/mL, 75mg/mL, 80mg/mL, 85mg/mL, 90mg/mL, 95mg/mL, 100 mg/mL. The thickness of the first coating layer can be controlled by adjusting the molar ratio of the silicon nanoparticles to the transition metal precursor, so that the ratio of the particle size of the silicon nanoparticles to the thickness of the first coating layer satisfies 20:1-5: 1. The molar ratio of the silicon nanoparticles to the transition metal precursor is, for example, 200:1, 190:1, 180:1, 170:1, 160:1, 150:1, 140:1, 130:1, 120:1, 110:1, 100:1, 90:1, 80:1, 70:1, 60:1, 50:1, 40:1, 30:1, 20:1, 10: 1; the method for adjusting the molar ratio of the silicon nanoparticles to the transition metal precursor is, for example, adjusting the concentration of the transition metal precursor in the transition metal precursor solution.
According to the present invention, in step (S1), the concentration of the sulfur source in the transition metal precursor solution is 1 to 100mg/mL, for example, 1mg/mL, 2mg/mL, 5mg/mL, 8mg/mL, 10mg/mL, 15mg/mL, 20mg/mL, 25mg/mL, 30mg/mL, 35mg/mL, 40mg/mL, 45mg/mL, 50mg/mL, 55mg/mL, 60mg/mL, 65mg/mL, 70mg/mL, 75mg/mL, 80mg/mL, 85mg/mL, 90mg/mL, 95mg/mL, 100 mg/mL.
According to the present invention, in the step (S1), the transition metal precursor solution has a sulfur source and a transition metal precursor at a mass ratio of 1-5:1-20, for example, 5:1, 4:1, 3:1, 2:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:76, 1:17, 1:18, 1:19, 1: 20.
According to the present invention, the step (S2) specifically includes the steps of:
placing the silicon material coated with the transition metal sulfide in a carbon precursor solution for reaction, calcining at high temperature, and coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to be used as a second coating layer; the mass ratio of the silicon nanoparticles to the carbon precursor is 10:1-1: 5. Controlling the thickness of the second coating layer by adjusting the mass ratio of the silicon nanoparticles to the carbon precursor to be 10:1-1:5, so that the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 20:1-5: 1; and the ratio of the particle size of the silicon nano-particles to the thickness of the double-layer coating is 10:1-5: 2.
According to the present invention, in the step (S2), the temperature and time of the reaction may be adjusted according to the type of the carbon precursor so that the carbon precursor is coated on the surface of the silicon material coated with the transition metal sulfide layer.
According to the present invention, in the step (S2), the temperature of the high temperature calcination is 500-1000 ℃, and the time of the high temperature calcination is 1-5h, and the high temperature calcination is performed under an inert atmosphere, such as at least one of argon, helium, and neon.
According to the present invention, in the step (S2), the carbon precursor solution includes a carbon precursor and a solvent.
According to the present invention, in the step (S2), the carbon precursor is at least one carbon-containing precursor selected from dopamine hydrochloride, carbon nanotubes, graphene oxide, graphite, glucose, and the like, or is a simple substance of carbon.
According to the present invention, in the step (S2), the solvent is selected from deionized water.
According to the present invention, the carbon precursor concentration in the carbon precursor solution is 1-100mg/mL, for example, 1mg/mL, 2mg/mL, 5mg/mL, 8mg/mL, 10mg/mL, 15mg/mL, 20mg/mL, 25mg/mL, 30mg/mL, 35mg/mL, 40mg/mL, 45mg/mL, 50mg/mL, 55mg/mL, 60mg/mL, 65mg/mL, 70mg/mL, 75mg/mL, 80mg/mL, 85mg/mL, 90mg/mL, 95mg/mL, 100 mg/mL.
According to the present invention, the step (S2) specifically includes the steps of:
placing the silicon material coated with the transition metal sulfide in a vapor deposition furnace, performing vapor deposition, coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to serve as a second coating layer, wherein the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 10:1-5: 1; the ratio of the particle size of the silicon nano-particles to the thickness of the double-layer coating layer is 10:1-5: 2; wherein the time of the vapor deposition is 1-5 h; the temperature of the vapor deposition is 800-1200 ℃, and the gas flow of the vapor deposition is 50-200cm3And/min. By adjusting the time and the air flow of vapor deposition, the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 20:1-5: 1; the ratio of the particle size of the silicon nano-particles to the thickness of the double-layer coating is 10:1-5: 2.
According to the invention, the precursor of vapor deposition is a mixed gas of methane and hydrogen, or a mixed gas of acetylene and hydrogen.
The invention also provides a negative plate which comprises the silicon material coated by the double-layer coating layer.
According to the invention, the negative plate comprises a negative current collector and a negative active material layer coated on one side or two sides of the negative current collector, wherein the negative active material layer comprises a negative active material, and the negative active material is selected from the silicon material coated by the double-layer coating layer.
According to the present invention, the anode active material layer further includes at least one of a binder, a conductive agent, a dispersant, and a thickener.
According to the invention, in the negative electrode active material layer, the mass percentage of each component is as follows:
60-99.6 wt% of negative electrode active material, 0.1-10 wt% of binder, 0.1-10 wt% of dispersant, 0.1-10 wt% of conductive agent and 0.1-10 wt% of thickening agent.
Preferably, in the negative electrode active material layer, the mass percentages of the components are:
68-98.3 wt% of negative electrode active material, 0.5-8 wt% of binder, 0.5-8 wt% of dispersant, 0.5-8 wt% of conductive agent and 0.2-8 wt% of thickening agent.
Still preferably, in the negative electrode active material layer, the mass percentages of the components are:
80-98.3 wt% of negative electrode active material, 0.5-5 wt% of binder, 0.5-5 wt% of dispersant, 0.5-5 wt% of conductive agent and 0.2-5 wt% of thickening agent.
According to the invention, the binder is selected from at least one of high molecular polymers such as polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Polyethyleneimine (PEI), Polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC-Na), phenolic resin or epoxy resin.
According to the present invention, the dispersant is selected from at least one of Polypropylene (PVA), cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), etc., and more preferably at least one of cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, and ethanol.
According to the invention, the conductive agent is selected from at least one of the conductive agents commonly used in industry, such as Carbon Nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microbeads (MCMB), graphene, Ketjen black, Super P, acetylene black, conductive carbon black or hard carbon.
According to the invention, the thickener is selected from sodium carboxymethylcellulose.
According to the present invention, the thickness of the anode active material layer is 20 to 150 μm.
The invention also provides a lithium ion battery which comprises the negative plate.
According to the invention, the lithium ion battery has the expansion rate of 10-40% when the lithium ion battery is cycled for 500 times under the conditions of charging and discharging at 25 ℃ and 0.5C/0.5C.
According to the invention, the cycle number of the lithium ion battery, which is used for the capacity fading to 80% of the initial capacity, is more than 500 times under the charging and discharging conditions of 25 ℃ and 0.5C/0.5C.
The invention has the beneficial effects that:
the invention provides a silicon anode material coated by a double-layer coating layer and a preparation method and application thereof; according to the invention, a double-shell silicon-coated material is formed by coating a double-layer material on a silicon powder substrate, the first layer of coating is a transition metal sulfide, and the proportion of the particle size of the silicon nanoparticles to the thickness of the coating is controlled by controlling the molar ratio of the silicon nanoparticles to the transition metal precursor, so that the advantages of better energy density, longer cycle life, inhibition of volume expansion of a pole piece and better safety are realized. Too thin transition metal sulfide coating easily causes the pole piece to expand greatly, causes the security performance poor, and too thick transition metal sulfide leads to energy density lower, and polysulfide ion shuttles back and forth simultaneously and easily causes cyclic attenuation faster. Meanwhile, the coated carbon layer is thin, so that the volume expansion of the silicon pole piece and the shuttle of polysulfide ions cannot be well inhibited, and the first effect is low and the energy density is reduced due to the fact that the coated layer is too thick, so that the thickness of the double-layer coated layer is optimal through concentration adjustment. Thereby preparing the double-layer cladding silicon negative electrode material with high energy density, long cycle life, obvious inhibition of the volume expansion of the silicon pole piece and high safety.
Drawings
Fig. 1 is a schematic structural diagram of a silicon negative electrode material coated with a double-layer coating layer according to the present invention.
Fig. 2 is a transmission electron micrograph of the double clad silicon anode material of example 3.
Fig. 3 is a scanning electron microscope image of the negative plate of example 3 before cycling.
FIG. 4 is a scanning electron microscope photograph of the negative plate of example 3 after 300 cycles.
Fig. 5 is a scanning electron microscope image of the negative electrode sheet of comparative example 3 after 300 cycles.
Fig. 6 is a scanning electron microscope image of the negative electrode sheet of comparative example 10 after 300 cycles.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Example 1
2g of nano silicon powder with the particle size of 50-100nm is put into a reaction kettle containing 40mL of mixed solution of ammonium molybdate (with the concentration of 5mg/mL) and thiourea (with the concentration of 20mg/mL) and reacted for 24 hours at 180 ℃, and MoS uniformly growing on the surface of the nano silicon can be obtained2Layer, washed and dried, will grow with MoS2Adding the nano silicon material of the layer into a glucose solution with the concentration of 10mg/mL for reaction for 12h at 180 ℃, cleaning the silicon material by deionized water, and placing the silicon material in an argon tube type furnace at 800 ℃ for high-temperature annealing for 2h to prepare the silicon material coated by the double-layer coating layer.
Example 2
2g of nano silicon powder with the particle size of 50-100nm is put into a reaction kettle containing 40mL of mixed solution of cobalt nitrate hexahydrate (5.8mg/mL) and sodium thiosulfate pentahydrate (10mg/mL) and reacts for 10 hours at 180 ℃, and then CoS uniformly growing on the surface of the nano silicon can be obtained2Layer, washed and dried, will grow CoS2Adding the nano silicon material into 5mg/mL dopamine hydrochloride solution, stirring at room temperature for reaction for 24h, washing with deionized water, and annealing at 1000 deg.C in neon tube furnace for 1h to obtain double-layerSilicon material coated by the coating layer.
Example 3
2g of nano silicon powder with the particle size of 50-100nm is put into a reaction kettle containing 40mL of mixed solution containing ferric nitrate (8mg/mL) and thiourea (8mg/mL) and reacts for 12 hours at 200 ℃, and then FeS uniformly growing on the surface of the nano silicon can be obtained2Layer, washed and dried, will grow FeS2Adding the nano silicon material of the layer into 5mg/mL graphene oxide solution, stirring and reacting for 24h at room temperature, cleaning with deionized water, and placing in an argon tube type furnace at 800 ℃ for high-temperature annealing for 5h to prepare the silicon material coated with the double-layer coating layer.
Examples 4 to 5 and comparative examples 1 to 4
In addition to example 3, the concentration of the transition metal precursor solution was adjusted to 2 times and 1/2 times the concentration of the transition metal precursor solution in example 3, and the conditions were not changed, and examples 4 to 5 were respectively prepared.
In addition to example 3, the concentrations of the transition metal precursor solutions were adjusted to 8 times, 4 times, 1/4 times, and 1/8 times the concentrations of the transition metal precursor solutions in example 3, and the remaining conditions were not changed, respectively, to obtain comparative examples 1 to 4.
Examples 6 to 7 and comparative examples 5 to 8
In example 3, the concentrations of the carbon precursor solutions were adjusted to 2 times and 1/2 times the concentrations of the carbon precursor solutions in example 3, and the conditions were not changed, respectively, to obtain examples 6 to 7.
On the basis of example 3, the concentrations of the carbon precursor solutions were adjusted to 8 times, 4 times, 1/4 times, and 1/8 times the concentrations of the carbon precursor solutions in example 3, and the remaining conditions were unchanged, and they were respectively used as comparative examples 5 to 8.
Examples 8 to 9 and comparative examples 9 to 12
In addition to example 3, the concentrations of the transition metal precursor solution and the carbon precursor solution were adjusted to 2 times and 1/2 times the concentrations in example 3, and the conditions were not changed, respectively, to obtain examples 8 to 9.
The concentrations of the transition metal precursor solutions and the carbon precursor solutions were adjusted to 8 times, 4 times, 1/4 times, and 1/8 times the concentrations in example 3, respectively, as comparative examples 9 to 12, respectively, without changing the other conditions.
The two-layer clad silicon materials prepared in the examples and comparative examples were tested as follows:
(1) transmission electron microscope test:
and dispersing the prepared silicon material coated by the double-layer coating layer in an ethanol solution, performing ultrasonic treatment on the silicon material by 100W power ultrasonic wave for 30min, further sucking 1mL of the solution after ultrasonic treatment, dropwise adding the solution onto a special copper net for a projection electron microscope, performing hot light irradiation for 10min for drying, putting a sample into a sample stage of the projection electron microscope after drying, vacuumizing, emitting high pressure, and observing the thickness of the coating layer by using a transmission electron microscope. Table 1 shows the ratio of the thickness of the silicon nanoparticles to the thickness of the coating layer in the present invention, and fig. 2 shows a transmission electron microscope of the silicon anode material coated with the double coating layer in example 3 of the present invention.
TABLE 1
Figure BDA0002482988840000101
(2) Energy density and cycle number testing
Adding the silicon material coated by the double-layer coating layer, the adhesive polyacrylic acid and the conductive agent carbon nano tube in a mass ratio of 80:10:10 into a proper amount of deionized water, uniformly stirring to form slurry, and further coating the slurry on the copper foil; and (3) rolling and matching the lithium cobaltate positive plate, the liquid electrolyte and the diaphragm after drying to prepare a button battery, and testing the energy density of the button battery.
The prepared coin cell was charged and discharged at 25 ℃ at 0.5C/0.5C, and the number of cycles when the capacity had decayed to 80% of the initial capacity was recorded, and the test results are shown in Table 2.
(3) Expansion ratio test
And (3) disassembling the battery cell after circulating for 500 circles, measuring the thickness of the pole piece after the negative pole piece is discharged by using a micrometer so as to calculate the expansion rate of the negative pole piece, wherein the test result is shown in table 2.
TABLE 2
Energy Density (Wh/kg) Number of cycles Expansion ratio of negative electrode sheet
Example 1 285 856 23.2％
Example 2 292 961 18.2％
Example 3 271 823 20.3％
Comparative example 1 227 572 16.2％
Comparative example 2 239 612 17.3％
Example 4 244 653 19.3％
Example 5 272 771 38.1％
Comparative example 3 268 379 54.1％
Comparative example 4 252 205 89.2％
Comparative example 5 231 721 18.5％
Comparative example 6 248 619 17.3％
Example 6 251 721 19.7％
Example 7 264 626 28.0％
Comparative example 7 269 378 73.8％
Comparative example 8 258 208 118.4％
Comparative example 9 211 682 14.2％
Comparative example 10 222 723 16.3％
Example 8 242 784 19.3％
Example 9 269 612 36.2％
Comparative example 11 258 538 85.8％
Comparative example 12 252 389 139.6％
(4) Safety test
After the lithium ion batteries obtained in the above examples and comparative examples are fully charged (the charge cut-off voltage is 4.45V), 4 safety tests of needling, heating, external short circuit and overcharge of the batteries are tested, the test method refers to the GB/T31485-2015 standard, 10 batteries are tested in parallel in each group, and the pass rate is calculated. The test results are shown in table 3.
TABLE 3
Needle penetration Rate (%) Heating passage (%) Overcharge pass rate (%) External short circuit passage (%)
Example 1 100 100 100 100
Example 2 100 100 100 100
Example 3 100 100 100 100
Comparative example 1 100 100 100 100
Comparative example 2 100 100 100 100
Example 4 100 100 100 100
Example 5 100 100 100 100
Comparative example 3 80 100 90 80
Comparative example 4 80 90 90 80
Comparative example 5 100 100 100 100
Comparative example 6 100 100 100 100
Example 6 100 100 100 100
Example 7 100 100 100 100
Comparative example 7 90 90 100 90
Comparative example 8 80 90 90 90
Comparative example 9 100 100 100 100
Comparative example 10 100 100 100 100
Example 8 100 100 100 100
Example 9 100 100 100 100
Comparative example 11 80 90 90 90
Comparative example 12 70 80 80 70
(5) And (3) testing by a scanning electron microscope:
and (3) sticking the prepared negative plate to a scanning electron microscope sample stage, putting the sample into the scanning electron microscope sample stage, vacuumizing, emitting high voltage, and observing the appearance of the negative plate by an electron microscope.
Fig. 3-6 are scanning electron microscopes of the negative plate of the present invention. As can be seen from fig. 3-4, the negative electrode sheet of example 3 is relatively flat before circulation, has no cracks and no protruding particles, and after the negative electrode sheet of example 3 is circulated for 300 cycles, the negative electrode sheet has uneven surface, but no cracks and smaller pulverization degree due to the growth of the SEI film. As can be seen from fig. 5, after the negative electrode sheet of comparative example 3 was cycled for 300 cycles, the negative electrode sheet was more severely pulverized and the particle size was more significant. As can be seen from fig. 5, when the coating layer was thick (comparative example 10), the negative electrode sheet was hardened into a block, and significant voids appeared. It follows that an appropriate coating thickness is critical for the pole piece cycle.
From examples 1 to 9, it can be seen that when the particle size of the silicon nanoparticle and the coating layer are 10:1 to 5:2, and the particle size of the silicon nanoparticle, the thickness of the first coating layer and the thickness of the second coating layer are both 20:1 to 5:1, the double-layer coating silicon material prepared by the invention has good energy density and cycle life, and can effectively inhibit the expansion rate of the pole piece. It can be seen from comparative examples 1 to 12 that the higher the ratio of the particle size of the silicon nanoparticle to the thickness of the coating layer, the poorer the safety of the prepared battery is, mainly because the thinner the coating layer is, the more easily the silicon nanoparticle is exposed in the electrolyte, causing the continuous volume expansion, thereby causing the poor safety, and meanwhile, the thicker the coating layer is, the lower the energy density is, so the double-layer coated silicon nanoparticle prepared by the present invention has good structural stability and excellent electrochemical performance.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A silicon material coated by double-layer coating layers is provided, wherein the double-layer coating layer close to the silicon material is a first coating layer, and the double-layer coating layer far away from the silicon material is a second coating layer;
the first coating layer is a transition metal sulfide layer, the second coating layer is a carbon layer, and the silicon material is silicon nanoparticles;
the particle size of the silicon nanoparticles is 50-100nm, and the ratio of the particle size of the silicon nanoparticles to the thickness of the first coating layer is 15:1-10: 1; the ratio of the particle size of the silicon nanoparticles to the thickness of the second coating layer is 10:1-5: 1; the ratio of the particle size of the silicon nano particles to the thickness of the double-layer coating layer is 10:1-3: 1;
wherein the transition metal sulfide layer is FeS2Layer, MoS2Layer, VS2Layer, CoS2Layer, WS2Layer, TiS2Layer, NiS2Layer or Ni3S2And (3) a layer.
2. The silicon material of claim 1, wherein the transition metal sulfide layer is a nanosheet structure, the size of the monolithic nanosheet being 1-100nm, and the thickness of the monolithic nanosheet being 0.1-10 nm.
3. A method of preparing a double clad silicon material as claimed in any one of claims 1-2, said method comprising the steps of:
step (S1): placing a silicon material in a transition metal precursor solution for hydrothermal reaction, and coating a transition metal sulfide layer on the surface of the silicon material to be used as a first coating layer; wherein the silicon material is silicon nanoparticles, and the particle size of the silicon nanoparticles is 50-100 nm; the molar ratio of the silicon nanoparticles to the transition metal precursor is 200:1-10: 1; the transition metal precursor solution comprises a transition metal source, a sulfur source and a solvent; the temperature of the hydrothermal reaction is 120-200 ℃;
step (S2): placing the silicon material coated with the transition metal sulfide in a carbon precursor solution for reaction, and coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to be used as a second coating layer; the mass ratio of the silicon nanoparticles to the carbon precursor is 10:1-1: 5; alternatively, the first and second electrodes may be,
putting the silicon material coated with the transition metal sulfide in a vapor deposition furnace, performing vapor deposition, and coating a carbon layer on the surface of the silicon material coated with the transition metal sulfide layer to be used as a second coating layer;
the carbon precursor solution comprises a carbon precursor and a solvent, wherein the carbon precursor is selected from at least one of dopamine hydrochloride, carbon nano tubes, graphene oxide, graphite and glucose or is a simple carbon substance;
the temperature of the vapor deposition is 800-1200 ℃, and the gas flow of the vapor deposition is 50-200cm3/min；
Wherein, in the step (S1), the transition metal is at least one selected from Fe, Mo, V, Co, W, Ti, and Ni; the sulfur source is at least one selected from thiourea, sodium thiosulfate and thioacetamide; the solvent is selected from deionized water.
4. A lithium ion battery comprising a negative electrode sheet comprising the double-layer coating-coated silicon material according to any one of claims 1 to 2.
5. The lithium ion battery of claim 4, wherein the lithium ion battery has a negative plate expansion rate of 10-40% when cycled 500 times at 25 ℃ and with 0.5C/0.5C charging and discharging.
6. The lithium ion battery according to claim 4 or 5, wherein the number of cycles in which the capacity decays to 80% of the initial capacity is 500 or more at 25 ℃ and at 0.5C/0.5C charging and discharging.
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