CN115472804A - Silicon composite negative electrode material and preparation method and application thereof - Google Patents

Silicon composite negative electrode material and preparation method and application thereof Download PDF

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CN115472804A
CN115472804A CN202211284724.4A CN202211284724A CN115472804A CN 115472804 A CN115472804 A CN 115472804A CN 202211284724 A CN202211284724 A CN 202211284724A CN 115472804 A CN115472804 A CN 115472804A
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silicon
negative electrode
binder
carbon
silicon composite
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李华
熊杰
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Shanghai Lanjun 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
    • H01M4/362—Composites
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of 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
    • H01M4/38—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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a silicon composite anode material and a preparation method and application thereof. The silicon composite negative electrode material comprises carbon nanotubes, a binder and silicon nanoparticles, the carbon nanotubes and the binder are mutually staggered to form a spider-web-like structure, and the silicon nanoparticles are wrapped at the nodes of the web of the spider-web-like structure. The invention provides a silicon composite negative electrode material with a special structure, wherein a spider-web-like structure formed by carbon nano tubes and a binder has high strength, elasticity and flexibility, the intrinsic conductivity of the carbon tubes is high, a good conductive network can be formed in an electrode, and the interlaced net-like structures cannot easily slide in the silicon expansion and contraction process to cause the conductive network to be damaged, so that the volume expansion of a silicon material is effectively inhibited, and the energy density, the conductivity and the cycling stability of the silicon material are improved.

Description

Silicon composite negative electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a silicon composite negative electrode material, and a preparation method and application thereof.
Background
In order to solve the problem of mileage anxiety of electric vehicle users, the energy density of the battery must be increased, and there are various ways to increase the energy density of the battery, such as optimizing the structure of the battery, increasing the energy density of active materials, and reducing the proportion of inactive materials. For the negative electrode material, the capacity of the graphite negative electrode widely used by the current commercial lithium battery is about 360mAh/g, which is very close to the theoretical specific capacity (372 mAh/g), so that the breakthrough on the graphite negative electrode is difficult to obtain, people turn the attention to the silicon material, and the lithium battery has the problem that the silicon material forms Li at high temperature 22 Si 5 The corresponding specific capacity is 4200mAh/g, and Li is formed at room temperature 15 Si 4 The corresponding specific capacity is 3579mAh/g, and the lithium removal potential of silicon is lower, so that the silicon serving as a negative electrode can reduce the material consumption and improve the energy density of the battery, and the silicon is the next important development direction of a negative electrode material of a power battery.
However, the silicon material has poor conductivity and is Li + The embedding and the stripping have serious volume effect, the volume expansion rate is as high as 400 percent, the material pulverization is caused to be more even separated from a current collector, and the rapid cycle attenuation and serious water jump are caused. In addition, the expansion during charge and discharge causes the active material to continuously repair the SEI film, and the consumption of active Li also causes poor cycle. In order to solve the above problems, research has been mainly focused on the size-nanosized silicon, and specific structures such as core-shell, porous, and the like. Nanocrystallization can slow down volume expansion, but the specific surface of the nanocrystallized silicon is large, the coulombic efficiency of the battery is low, and the nanocrystallization has the possibility of being reunited into large particles along with circulation. The synthesis process of the special core-shell and porous structure is complex and high in cost.
CN111933919A discloses a nano silicon powder, a silicon-based negative electrode, a lithium ion battery containing the silicon-based negative electrode and a manufacturing method thereof. The cycle performance of the silicon-based negative electrode is equivalent to that of a graphite negative electrode, the first discharge efficiency is more than 89%, and the discharge capacity is equivalent to that of a graphite negative electrode>3000mAh/g. The invention utilizes the in-situ reaction of nano metal oxide, nano silicon particles and a lithium source on the surfaces of the nano silicon particles at high temperature to generate the lithium ion conductor Li 2 SiO 3 And a conductive nanometal. The low melting point tin also binds the nano-silicon particles. Organic titanium source and/or zirconium sourcePyrolysis to produce TiO 2 And/or ZrO 2 And side reactions between the nano-silicon and the electrolyte are reduced. Cracking an organic aluminum source, and reacting the organic aluminum source with a lithium source to generate a lithium ion conductor LiAlO 2 . The organic carbon source is cracked into conductive carbon. This document describes nanoparticles of silicon, which have a large specific surface area, low coulombic efficiency and the possibility of re-aggregation into large particles with cycling, although the nanocrystallization can slow down the volume expansion.
CN111755677A is a core-shell structure porous silicon negative electrode material for lithium ion batteries and a preparation method thereof; the porous silicon negative electrode material is of a core-shell structure, the inner core comprises nano porous silicon, graphite and amorphous carbon, and the shell is made of amorphous carbon; the negative electrode material comprises 30-70 wt% of nano porous silicon, 20-45 wt% of graphite and 10-40 wt% of amorphous carbon; the micro-porous silicon raw material contains 1-10 wt% of oxygen, and the oxygen content in the nano-porous silicon obtained by wet grinding is 12-35 wt%. The synthesis process of the porous special structure is complex and has high cost.
Therefore, it is an urgent technical problem to fully utilize the high capacity advantage of the silicon negative electrode material, and simultaneously reduce the volume expansion of the silicon negative electrode material and improve the conductivity of the silicon negative electrode material.
Disclosure of Invention
The invention aims to provide a silicon composite negative electrode material and a preparation method and application thereof. The invention provides a silicon composite negative electrode material with a special structure, wherein a spider-web-like structure formed by carbon nano tubes and a binder has high strength, elasticity and flexibility, the intrinsic conductivity of the carbon tubes is high, a good conductive network can be formed in an electrode, and the interlaced net-like structures cannot easily slide in the silicon expansion and contraction process to cause the conductive network to be damaged, so that the volume expansion of a silicon material is effectively inhibited, and the conductivity of the silicon material is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a silicon composite anode material, which includes carbon nanotubes, a binder and silicon nanoparticles, wherein the carbon nanotubes and the binder are interlaced with each other to form a spider-web-like structure, and the silicon nanoparticles are wrapped at nodes of the web of the spider-web-like structure.
The invention provides a silicon composite negative electrode material with a special structure, wherein a spider-web-like structure formed by carbon nano tubes and a binder has high strength, elasticity and flexibility, the intrinsic conductivity of the carbon tubes is high, a good conductive network can be formed in an electrode, and the interlaced net-like structures cannot easily slide in the silicon expansion and contraction process to cause the conductive network to be damaged, so that the volume expansion of a silicon material is effectively inhibited, and the conductivity of the silicon material is improved.
Preferably, the carbon nanotubes have a tube diameter of 10 to 100nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or the like.
Preferably, the carbon nanotubes have a length of 10 to 100 μm, such as 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 95 μm, 100 μm, or the like.
In the invention, the carbon tube is easy to fold and wind due to the overlong length of the carbon nano tube, and the stability of the spider web structure is influenced due to the overlong length of the carbon nano tube.
Preferably, the silicon nanoparticles have an average particle size of 10 to 100nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or the like.
Preferably, the binder comprises any one of carboxymethyl cellulose, polymethyl methacrylate, polyacrylic acid, sodium alginate, polyurethane, polyimide or polyacrylamide or a combination of at least two of them.
Preferably, the mass ratio of the silicon nanoparticles to the carbon nanotubes is (4-8) 1, such as 4.
In the invention, too small mass ratio of the silicon nanoparticles to the carbon nanotubes, i.e. too few silicon nanoparticles, is not favorable for improving the energy density of the battery, while too large mass ratio, i.e. too many silicon nanoparticles, affects the inhibition effect on silicon expansion.
Preferably, the mass ratio of the binder to the carbon nanotubes is (0.5-5): 1, 2.
In the invention, the excessive mass ratio of the binder to the carbon nano tubes influences the performance of silicon capacity, thereby influencing the battery performance of the cathode material, and the excessive mass ratio of the binder to the carbon nano tubes influences the unstable structure of the cathode material after silicon expands in the circulation process.
In a second aspect, the present invention provides a method for preparing a silicon composite anode material as described in the first aspect, the method comprising the steps of:
(1) In the environment of an external magnetic field, depositing a metal catalyst and a carbon source in a chemical vapor deposition mode to obtain a carbon nano tube;
(2) After the carbon nano tube in the step (1) is obtained, introducing a gas-phase silicon source, and carrying out chemical vapor deposition to obtain a precursor, wherein silicon nano particles are deposited on the carbon nano tube in the precursor;
(3) And (3) mixing and crosslinking the binder solution and the precursor in the step (2) to obtain the silicon composite negative electrode material.
According to the preparation method provided by the invention, in the step (1), the divergent carbon nano tube arrangement extending outwards from the center is obtained under the action of an external magnetic field, the nano silicon is deposited on the carbon nano tubes in situ by a chemical vapor deposition method, the uniform deposition of the nano silicon can be realized by the chemical vapor deposition method, and the staggered spider web-like structure is obtained by mixing and crosslinking the binder and the precursor in the step (3), and the nano silicon is in a coated state at the junction.
In the invention, if the external magnetic field is not added in the step (1), the appearance of the spider-web-like structure in the invention cannot be obtained, and the carbon nano tubes and the silicon particles cannot be uniformly distributed.
Preferably, the magnetic field strength of the externally applied magnetic field in step (1) is 0.5-5T, such as 0.5T, 1T, 1.5T, 2T, 2.5T, 3T, 3.5T, 4T, 4.5T or 5T.
In the invention, the external magnetic field intensity is too large, which leads to the dense net structure, thus being not beneficial to the exertion of silicon capacity, while the magnetic field intensity is too small, which leads to the loose net structure, the unstable structure of the material, and the influence on the exertion of the performance of the cathode material.
Preferably, the metal catalyst of step (1) comprises ferrocene.
Preferably, the carbon source of step (1) comprises xylene.
Preferably, the step (1) of chemical vapor deposition comprises:
in the environment of an external magnetic field, mixing a metal catalyst with a carbon source to obtain a catalyst precursor solution, feeding the catalyst precursor solution into a reaction chamber by using carrier gas, and performing chemical vapor deposition on the surface of a substrate to obtain the carbon nano tube.
Preferably, the carrier gas includes a mixed gas of hydrogen and argon.
Preferably, the temperature of the chemical vapor deposition is 400 to 1000 ℃, such as 400 ℃,500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, or 1000 ℃ and the like.
Preferably, the fumed silica source of step (2) comprises silane.
Preferably, in the step (2), the carrier gas is introduced while the silicon source in the gas phase is introduced.
Preferably, the temperature of the chemical vapor deposition in the step (2) is 300 to 800 ℃, such as 300 ℃, 400 ℃,500 ℃, 600 ℃, 700 ℃ or 800 ℃ and the like.
Preferably, a cross-linking agent solution is further included in the hybrid cross-linking process in the step (3).
Preferably, the crosslinking agent comprises epichlorohydrin.
In the invention, epichlorohydrin is selected as a cross-linking agent, which is more favorable for increasing the hydrogen bond function between silicon and the binder.
Preferably, the mass fraction of the binder in the binder solution of step (3) is 0.5-2.5%, such as 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, etc.
Preferably, the binder solution further comprises a dispersant.
Preferably, the mass ratio of the binder to the dispersant is (1-3) 1, for example 1.
Preferably, the hybrid crosslinking process of step (3) comprises:
and (3) coating a binder solution on the surface of the precursor in the step (2), and then mixing with a cross-linking agent solution for cross-linking.
Preferably, the mixed and crosslinked material in the step (3) is soaked in water and dried.
As a preferred technical scheme, the preparation method comprises the following steps:
(1) Mixing a metal catalyst with a carbon source in an external magnetic field environment with the magnetic field intensity of 0.55T to obtain a catalyst precursor solution, introducing the catalyst precursor solution into a reaction chamber by using a mixed gas of hydrogen and argon, and performing chemical vapor deposition on the surface of a substrate at the temperature of 400-1000 ℃ to obtain a carbon nano tube;
(2) After the carbon nano tube in the step (1) is obtained, introducing a gas-phase silicon source, and performing chemical vapor deposition at the temperature of 300-800 ℃ to obtain a precursor, wherein silicon nano particles are deposited on the carbon nano tube in the precursor;
(3) And (3) coating a binder solution with the mass fraction of 0.5-2.5% on the surface of the precursor in the step (2), then mixing with a cross-linking agent solution for cross-linking, soaking the mixed and cross-linked substance in water, and drying to obtain the silicon composite negative electrode material.
In a third aspect, the present invention provides a negative electrode plate, including the silicon composite negative electrode material according to the first aspect and a binder.
In the invention, when the negative electrode material of the first aspect is selected as the negative electrode pole piece, no additional conductive agent is needed, the carbon nano tube is used as a conductive network while forming the spider-web-like structure support, and the carbon nano tube has high conductivity.
In a fourth aspect, the present invention provides a method for preparing the negative electrode plate according to the third aspect, wherein the method for preparing the negative electrode plate comprises:
and mixing the silicon composite negative electrode material with a binder by a dry method, and coating the mixture on the surface of a negative electrode current collector to obtain the negative electrode piece.
According to the invention, the negative pole piece can be prepared by a solvent-free method, a solvent is not required, organic matter pollution is avoided, and meanwhile, the compaction density of the electrode is improved, so that the negative pole piece is more beneficial to exerting the capacity of the negative pole and improving the energy density of the battery.
In a fifth aspect, the present invention further provides a lithium ion battery, where the lithium ion battery includes the silicon composite negative electrode material according to the first aspect or the negative electrode sheet according to the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention provides a silicon composite negative electrode material with a special structure, wherein a spider-web-like structure formed by carbon nano tubes and a binder has high strength, elasticity and flexibility, the intrinsic conductivity of the carbon tubes is high, a good conductive network can be formed in an electrode, and the interlaced net-like structures cannot easily slide in the silicon expansion and contraction process to cause the conductive network to be damaged, so that the volume expansion of a silicon material is effectively inhibited, and the conductivity and the cycle stability of the silicon material are improved.
(2) According to the preparation method provided by the invention, the divergent carbon nanotube arrangement extending from the center to the outside is obtained in the step (1) under the action of an external magnetic field, the nano-silicon is deposited on the carbon nanotubes in situ by a chemical vapor deposition method, the uniform deposition of the nano-silicon can be realized by the chemical vapor deposition method, and the staggered spider-like web structure is obtained by mixing and crosslinking the binder and the precursor in the step (3), and the nano-silicon is in a coated state at the junction. When the battery adopts the cathode material provided by the invention, the energy density can reach over 330Wh/kg, the capacity can be attenuated to be below 80 percent after the battery is circulated for at least 1300 circles at 25 ℃, and the capacity can be attenuated to be below 80 percent after the battery is circulated for at least 1000 circles at 45 ℃.
Drawings
FIG. 1 is a schematic structural diagram of the framework of Si/CNT provided in example 1.
Fig. 2 is a schematic structural diagram of a silicon composite anode material provided in example 1.
Fig. 3 is an SEM image of the carbon nanotubes provided in example 1.
Detailed Description
The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present embodiment provides a silicon composite negative electrode material, which includes carbon nanotubes (with a tube diameter of 100nm and a length of 100 μm), carboxymethyl cellulose (CMC), and silicon nanoparticles (with an average particle size of 70 nm), where the carbon nanotubes and the carboxymethyl cellulose are interlaced with each other to form a spider-web-like structure (as shown in fig. 2), and the silicon nanoparticles are wrapped at nodes of a web of the spider-web-like structure; wherein, the mass ratio of the silicon nano-particles to the carbon nano-tubes is 5.
The preparation method of the silicon composite negative electrode material comprises the following steps:
(1) Dissolving 0.1g ferrocene (sublimation point 190 deg.C) in 10ml xylene (boiling point 140 deg.C), ultrasonic oscillating for 15min to obtain catalyst precursor solution, and mixing 1cm ferrocene 2 Putting the cleaned iron-nickel alloy substrate into a quartz tube, slowly adjusting a vacuum pump after sealing two ends of the furnace, vacuumizing the quartz tube, wherein the vacuum degree is less than-0.098 MPa, then introducing ultra-high-purity argon with the flow rate of 100sccm to expel air in the quartz tube, continuously injecting a catalyst precursor solution into a reaction chamber at the liquid flow rate of 0.11ml/min, preheating the temperature in the reaction chamber to 200 ℃, rapidly volatilizing the injected ferrocene solution, introducing 100sccm ultra-high-purity argon and 10% pure hydrogen into the reaction chamber, reacting at 770 ℃ for a period of time (the reaction process is carried out in an external magnetic field environment with the magnetic field intensity of 3T), introducing argon to cool, and obtaining a divergent carbon nanotube structure (as shown in figure 3);
(2) Then the temperature of the quartz tube is raised to 500 ℃, and SiH with the flow rate of 20sccm is introduced 4 And 680sccm of argon, silicon deposited on the carbon nanotubesForming a framework of Si/CNT (shown in figure 1) on the rice tube to obtain a precursor,
(3) After a framework of Si/CNT is formed, epoxy Chloropropane (ECH) is used as a cross-linking agent, a CMC solution with the mass fraction of 1% (the solvent in the solution is water, a PVP dispersing agent is also added, the mass ratio of the dispersing agent to the CMC is 1 and 2) undergoes a self-crosslinking reaction at 60 ℃, and a spiral sticky line is formed on the framework, specifically: uniformly coating a CMC solution with the mass fraction of 1% on a Si/CNT skeleton, immersing the Si/CNT skeleton into an ECH/ethanol solution with the mass fraction of 2% for crosslinking for a period of time, taking out the CMC solution, immersing the CMC solution in deionized water for 24 hours, and drying the CMC solution to obtain the silicon composite negative electrode material with the spider web structure.
Example 2
The embodiment provides a silicon composite negative electrode material, which comprises carbon nanotubes (with a pipe diameter of 80nm and a length of 45 μm), carboxymethyl cellulose (CMC) and silicon nanoparticles (with an average particle size of 50 nm), wherein the carbon nanotubes and the carboxymethyl cellulose are interlaced with each other to form a spider-web-like structure, and the silicon nanoparticles are wrapped at nodes of a web of the spider-web-like structure; wherein, the mass ratio of the silicon nano-particles to the carbon nano-tubes is 4.
The preparation method of the silicon composite negative electrode material comprises the following steps:
(1) Dissolving 0.1g ferrocene (sublimation point 190 deg.C) in 10ml xylene (boiling point 140 deg.C), ultrasonic oscillating for 15min to obtain catalyst precursor solution, mixing 1cm ferrocene 2 Putting the cleaned iron-nickel alloy substrate into a quartz tube, sealing two ends of the furnace, slowly adjusting a vacuum air pump, vacuumizing the quartz tube to a vacuum degree within-0.098 MPa, introducing ultra-high-purity argon with the flow of 100sccm to expel air in the quartz tube, continuously injecting a catalyst precursor solution into a reaction chamber at the liquid flow of 0.11ml/min, preheating the reaction chamber at 200 ℃, rapidly volatilizing the injected ferrocene solution, introducing 100sccm ultra-high-purity argon and 10% pure hydrogen into the reaction chamber, reacting at 500 ℃ for a period of time (the reaction process is carried out in an external magnetic field environment with the magnetic field strength of 0.5T), introducing argon for cooling to obtain the divergent carbon nano-tubePipe structure
(2) Then the temperature of the quartz tube is raised to 300 ℃, and SiH with the flow rate of 20sccm is introduced 4 And 680sccm of argon gas, depositing silicon on the carbon nano tube to form a framework of Si/CNT and obtain a precursor,
(3) After a framework of Si/CNT is formed, taking Epichlorohydrin (ECH) as a cross-linking agent, and a CMC solution with the mass fraction of 2.5% (the solvent in the solution is water, and PVP dispersant is also added, the mass ratio of the dispersant to the CMC is 1: uniformly coating a CMC solution with the mass fraction of 2.5% on a Si/CNT skeleton, immersing the Si/CNT skeleton into an ECH/ethanol solution with the mass fraction of 2% for crosslinking for a period of time, taking out the CMC solution, immersing the CMC solution in deionized water for 24 hours, and drying the CMC solution to obtain the silicon composite negative electrode material with the spider web structure.
Example 3
The embodiment provides a silicon composite anode material, which comprises carbon nanotubes (with a pipe diameter of 30nm and a length of 10 μm), polymethyl methacrylate (PMMA) and silicon nanoparticles (with an average particle size of 10 nm), wherein the carbon nanotubes and the PMMA are interlaced with each other to form a spider-web-like structure, and the silicon nanoparticles are wrapped at junctions of the web of the spider-web-like structure; wherein the mass ratio of the silicon nano-particles to the carbon nano-tubes is 8.
The preparation method of the silicon composite negative electrode material comprises the following steps:
(1) Dissolving 0.1g ferrocene (sublimation point 190 deg.C) in 10ml xylene (boiling point 140 deg.C), ultrasonic oscillating for 15min to obtain catalyst precursor solution, mixing 1cm ferrocene 2 Putting the cleaned iron-nickel alloy substrate into a quartz tube, sealing two ends of the furnace, slowly adjusting a vacuum air pump, vacuumizing the quartz tube to a vacuum degree within-0.098 MPa, introducing ultra-high-purity argon with the flow of 200sccm to expel air in the quartz tube, continuously injecting a catalyst precursor solution into a reaction chamber at the liquid flow of 0.2ml/min, preheating the temperature in the reaction chamber to 200 ℃, rapidly volatilizing the injected ferrocene solution, and passing the ultra-high-purity argon with the flow of 150sccm and 10% pure hydrogenIntroducing gas into the reaction chamber, reacting at 1000 deg.C for a period of time (the reaction process is carried out in an external magnetic field environment with a magnetic field intensity of 5T), introducing argon gas for cooling to obtain divergent carbon nanotube structure
(2) Then the temperature of the quartz tube is raised to 800 ℃, siH with the flow rate of 25sccm is introduced 4 And argon gas of 700sccm, silicon is deposited on the carbon nano tube to form a framework of Si/CNT, a precursor is obtained,
(3) After a framework of Si/CNT is formed, epoxy Chloropropane (ECH) is used as a cross-linking agent, a PMMA solution with the mass fraction of 0.5% (the solvent in the solution is water, PVP dispersing agent is also added, the mass ratio of the dispersing agent to CMC is 1) undergoes a self-crosslinking reaction at 60 ℃, and a spiral sticky line is formed on the framework, and the method specifically comprises the following steps: uniformly coating a PMMA solution with the mass fraction of 0.5% on a Si/CNT framework, immersing the Si/CNT framework in an ECH/ethanol solution with the mass fraction of 2% for crosslinking for a period of time, taking out the solution, immersing the solution in deionized water for 24 hours, and drying the solution to obtain the silicon composite negative electrode material with the spider web structure.
Example 4
The present example is different from example 1 in that the length of the carbon nanotube in the present example is 110 μm, and the reaction is stopped after the reaction time in the preparation method reaches the length.
The remaining preparation methods and parameters were in accordance with example 1.
Example 5
The difference between this example and example 1 is that the average particle size of the silicon nanoparticles in this example is 110nm.
The remaining preparation methods and parameters were in accordance with example 1.
Example 6
The difference between the present embodiment and embodiment 1 is that the mass ratio of the silicon nanoparticles to the carbon nanotubes in the present embodiment is 3.
The remaining preparation methods and parameters were in accordance with example 1.
Example 7
The difference between this example and example 1 is that the mass ratio of the silicon nanoparticles to the carbon nanotubes in this example is 9.
The remaining preparation methods and parameters were in accordance with example 1.
Example 8
The difference between the present example and example 1 is that the mass ratio of carboxymethyl cellulose to carbon nanotubes in the present example is 0.3.
The remaining preparation methods and parameters were in accordance with example 1.
Example 9
The difference between this example and example 1 is that the mass ratio of carboxymethyl cellulose to carbon nanotubes in this example is 6.
The remaining preparation methods and parameters were in accordance with example 1.
Example 10
The difference between this embodiment and embodiment 1 is that the magnetic field intensity of the externally applied magnetic field in step (1) of this embodiment is 0.2T.
The remaining preparation methods and parameters were in accordance with example 1.
Example 11
The difference between this embodiment and embodiment 1 is that the magnetic field intensity of the externally applied magnetic field in step (1) of this embodiment is 6T.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 1
The difference between the comparative example and the example 1 is that the silicon composite negative electrode material provided by the comparative example is that silicon nano-silicon particles are loaded on carbon nanotubes, the carbon nanotubes and carboxymethyl cellulose are not arranged in a staggered manner, and the step (3) is not performed in the preparation method.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 2
The comparative example is different from example 1 in that no external magnetic field is applied in step (1) of the comparative example.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 3
The comparative example differs from example 1 in that it is a pure silicon negative electrode.
Mixing the silicon composite negative electrode materials provided in the embodiments 1-11 and the comparative examples 1-2 with polyvinylidene fluoride, preparing a negative electrode plate by a dry method, assembling the negative electrode plate with an NCM811 positive electrode plate to obtain a battery cell, and carrying out formation and capacity grading to obtain the battery.
And mixing the pure silicon negative electrode, polyvinylidene fluoride, conductive carbon black and NMP provided by the comparative example 3 to obtain negative electrode slurry, coating the negative electrode slurry on the surface of copper foil, drying and rolling to obtain a negative electrode plate, assembling the negative electrode plate and an NCM811 positive electrode plate to obtain a battery cell, and carrying out formation and grading to obtain the battery.
Cutting the negative electrode sheets obtained in examples 1 to 11 and the negative electrode sheets obtained in comparative examples 1 to 3 into long sheets with the length of 51mm and the length of 90 mm; the electrode sheet containing the NCM811 positive electrode material in an amount of 97.6% was cut into a PE separator having a length of 49mm, a length of 85mm, and a width of 94 mm. And assembling the battery on a laminating machine according to a layer of diaphragm, a layer of negative plate, a layer of diaphragm, a layer of positive plate, a layer of diaphragm and a layer of negative plate, wherein the number of the positive plate layers is set to be 22, the number of the negative plate layers is set to be 23, and the number of the diaphragm layers is set to be 46. And packaging the assembled soft package battery by using a 230X 133mm aluminum plastic film, baking to reach the moisture content of below 200ppm, injecting an electrolyte for silicon, standing at high temperature for 24 hours, forming according to a small current, and performing 0.33C capacity grading to obtain the battery. The provided battery is subjected to electrochemical performance test under the following test conditions: the test voltage is 4.2-2.5V, and the charge-discharge circulation is respectively carried out at the test environment temperature of 25 ℃ and 45 ℃ at the charge-discharge rate of 1C/1C until the capacity retention rate is 80%. The results are shown in Table 1.
TABLE 1
Figure BDA0003892932390000141
Need to explain: the energy density in table 1 is the rounded numerical result, and the rounded data result has a slight influence on the final battery performance, but has a limited degree and does not influence the final data results of other performances.
As can be seen from the data results of examples 1 and 4, the carbon nanotubes are too long, and are liable to wrap around, which is not favorable for the performance of the battery.
As is clear from the results of examples 1 and 5, the average particle size of the silicon nanoparticles is too large, which makes it difficult to deposit silicon particles on the carbon tubes, and thus makes it difficult to control the silicon expansion during the cycle, resulting in a decrease in cycle performance.
From the data of example 1 and examples 6 and 7, it can be seen that too small a mass ratio of silicon nanoparticles to carbon nanotubes affects the energy density of the battery, and too large a mass ratio of silicon nanoparticles to carbon nanotubes causes the silicon cyclic expansion to be difficult to control.
From the data results of example 1 and examples 8 and 9, it is understood that if the mass ratio of carboxymethyl cellulose to carbon nanotubes is too small, the spider structure is not stable and the battery cycle is affected, and if the mass ratio is too large, the improvement of the energy density of the battery is not facilitated.
From the data results of example 1 and examples 10 and 11, it is understood that the magnetic field intensity of the applied magnetic field is too small, so that the network structure is relatively loose, and the magnetic field intensity is too large, so that the network structure is too dense, which affects the battery performance.
As can be seen from the data results of example 1 and comparative example 1, the silicon composite anode material provided by the present invention, which does not contain a binder, cannot form a stable spider-web structure, and thus cannot achieve suppression of silicon cycle expansion, ensure a stable structure, and cause poor battery cycle.
From the data results of example 1 and comparative example 2, it can be seen that a carbon tube and silicon composite network structure with uniform distribution can not be obtained without applying an external magnetic field during the preparation of the carbon nanotubes, thereby affecting the cycle performance of the battery.
From the data results of the embodiment 1 and the comparative example 3, it can be known that, compared with the conventional pure silicon anode material, the silicon composite anode material provided by the invention has higher energy density and greatly improved cycle stability.
In conclusion, the spider-web-like structure formed by the carbon nano tubes and the binder provided by the invention has high strength, elasticity and flexibility, and the silicon nano particles coated on the junctions cannot easily slide in the silicon expansion and contraction process to cause the damage of a conductive network, so that the volume expansion of a silicon material is effectively inhibited. When the battery adopts the cathode material provided by the invention, the energy density can reach over 330Wh/kg, the capacity can be attenuated to be below 80 percent after the battery is circulated for at least 1300 circles at 25 ℃, and the capacity can be attenuated to be below 80 percent after the battery is circulated for at least 1000 circles at 45 ℃.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. The silicon composite negative electrode material is characterized by comprising carbon nanotubes, a binder and silicon nanoparticles, wherein the carbon nanotubes and the binder are mutually staggered to form a spider-web-like structure, and the silicon nanoparticles are wrapped at nodes of a web of the spider-web-like structure.
2. The silicon composite anode material as claimed in claim 1, wherein the carbon nanotubes have a tube diameter of 10 to 100nm;
preferably, the length of the carbon nanotube is 10 to 100 μm;
preferably, the silicon nanoparticles have an average particle diameter of 10 to 100nm;
preferably, the binder comprises any one or a combination of at least two of carboxymethyl cellulose, polymethyl methacrylate, polyacrylic acid, sodium alginate, polyurethane, polyimide or polyacrylamide;
preferably, the mass ratio of the silicon nano particles to the carbon nano tubes is (4-8): 1;
preferably, the mass ratio of the binder to the carbon nanotubes is (0.5-5): 1.
3. A method for preparing a silicon composite anode material according to claim 1 or 2, characterized in that the method comprises the steps of:
(1) In the environment of an external magnetic field, depositing a metal catalyst and a carbon source in a chemical vapor deposition mode to obtain a carbon nano tube;
(2) After the carbon nano tube in the step (1) is obtained, introducing a gas-phase silicon source, and performing chemical vapor deposition to obtain a precursor, wherein silicon nano particles are deposited on the carbon nano tube in the precursor;
(3) And (3) mixing and crosslinking the binder solution and the precursor in the step (2) to obtain the silicon composite negative electrode material.
4. The preparation method of the silicon composite anode material according to claim 3, wherein the magnetic field intensity of the external magnetic field in the step (1) is 0.5-5T;
preferably, the metal catalyst of step (1) comprises ferrocene;
preferably, the carbon source of step (1) comprises xylene;
preferably, the step (1) of chemical vapor deposition comprises:
mixing a metal catalyst with a carbon source in an environment with an external magnetic field to obtain a catalyst precursor solution, introducing the catalyst precursor solution into a reaction chamber by using carrier gas, and performing chemical vapor deposition on the surface of a substrate to obtain a carbon nano tube;
preferably, the carrier gas comprises a mixed gas of hydrogen and argon;
preferably, the temperature of the chemical vapor deposition is 400 to 1000 ℃.
5. The method for preparing a silicon composite anode material according to claim 3 or 4, wherein the fumed silicon source of step (2) comprises silane;
preferably, in the step (2), the carrier gas is introduced while the gas-phase silicon source is introduced;
preferably, the temperature of the chemical vapor deposition in the step (2) is 300-800 ℃.
6. The method for preparing the silicon composite anode material according to any one of claims 3 to 5, wherein the mixing and crosslinking process of the step (3) further comprises a crosslinking agent solution;
preferably, the crosslinking agent comprises epichlorohydrin;
preferably, the mass fraction of the binder in the binder solution in the step (3) is 0.5-2.5%;
preferably, the binder solution further comprises a dispersant;
preferably, the mass ratio of the binder to the dispersant is (1-3) to 1;
preferably, the hybrid crosslinking process of step (3) comprises:
coating a binder solution on the surface of the precursor in the step (2), and then mixing the precursor with a cross-linking agent solution for cross-linking;
preferably, the mixed and crosslinked material in the step (3) is soaked in water and dried.
7. The method for preparing a silicon composite anode material according to any one of claims 3 to 6, characterized by comprising the steps of:
(1) Mixing a metal catalyst with a carbon source in an external magnetic field environment with the magnetic field intensity of 0.55T to obtain a catalyst precursor solution, introducing the catalyst precursor solution into a reaction chamber by using a mixed gas of hydrogen and argon, and performing chemical vapor deposition on the surface of a substrate at the temperature of 400-1000 ℃ to obtain a carbon nano tube;
(2) After the carbon nano tube in the step (1) is obtained, introducing a gas-phase silicon source, and performing chemical vapor deposition at the temperature of 300-800 ℃ to obtain a precursor, wherein silicon nano particles are deposited on the carbon nano tube in the precursor;
(3) And (3) coating a binder solution with the mass fraction of 0.5-2.5% on the surface of the precursor in the step (2), then mixing with a cross-linking agent solution for cross-linking, soaking the mixed and cross-linked substance in water, and drying to obtain the silicon composite negative electrode material.
8. A negative electrode tab, characterized in that it comprises the silicon composite negative electrode material of claim 1 or 2 and a binder.
9. The preparation method of the negative electrode plate of claim 8, which comprises the following steps:
and mixing the silicon composite negative electrode material with a binder by a dry method, and coating the mixture on the surface of a negative current collector to obtain the negative electrode piece.
10. A lithium ion battery, characterized in that the lithium ion battery comprises the silicon composite negative electrode material of claim 1 or 2 or the negative electrode tab of claim 8.
CN202211284724.4A 2022-10-17 2022-10-17 Silicon composite negative electrode material and preparation method and application thereof Pending CN115472804A (en)

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