CN111916745A - Silicon negative electrode material, preparation method thereof and electrochemical cell - Google Patents
Silicon negative electrode material, preparation method thereof and electrochemical cell Download PDFInfo
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Abstract
The invention discloses a silicon negative electrode material which is a secondary composite particle, wherein the secondary composite particle comprises a silicon particle, a conductive agent and a thermosetting high polymer, and the thermosetting high polymer is at least arranged on the outer layer of the secondary composite particle. The invention discloses a preparation method of a silicon cathode material. The invention also discloses an electrochemical cell.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a silicon negative electrode material, a preparation method thereof and an electrochemical battery.
Background
The current commercialized negative electrode material is mainly graphite, and the defects of low theoretical specific capacity, poor high-rate charge and discharge performance and the like of the graphite can not completely meet the development requirement of the lithium ion battery, and the development of the high-energy power lithium ion battery urgently needs to find a novel high-capacity negative electrode with high capacity, long service life, safety and reliability to replace a graphite carbon negative electrode.
The silicon negative electrode material has higher theoretical specific capacity and low lithium-releasing and-inserting potential, and is a high-capacity negative electrode material with great development prospect. The main problem that currently limits the application of silicon negative electrodes is that silicon changes in volume during the charging and discharging processes of batteries, thereby causing the performance of the batteries to be reduced.
Disclosure of Invention
Based on this, there is a need for a novel silicon anode material, a method for preparing the same, and an electrochemical cell.
The silicon negative electrode material is a secondary composite particle, the secondary composite particle comprises a silicon particle, a conductive agent and a thermosetting high polymer, and the thermosetting high polymer is at least arranged on the outer layer of the secondary composite particle.
In one embodiment, the silicon negative electrode material is of a core-shell structure, the thermosetting high polymer is uniformly and continuously arranged on a shell layer of the core-shell structure, and the silicon particles are in a core of the core-shell structure.
In one embodiment, the shell layer of the core-shell structure is denser than the core.
In one embodiment, the thermosetting polymer material is selected from one or more of cross-linked polymers of sodium carboxymethyl cellulose and polyacrylic acid, epoxy resin, phenolic resin, polyurethane, polyamide, and polyimide.
In one embodiment, the conductive agent is selected from one or more of activated carbon, graphene, carbon nanotubes, ketjen black, Super P, acetylene black, and graphite.
In one embodiment, the mass ratio of the silicon particles, the conductive agent and the thermosetting high polymer is (30-50): (1-20): (4-10).
In one embodiment, the secondary composite particles have a particle size of 5 μm to 100 μm.
A preparation method of the silicon negative electrode material comprises the following steps:
mixing the silicon particles, the conductive agent and a thermosetting high molecular polymer monomer in a solvent to form a dispersion liquid;
and carrying out spray drying on the dispersion liquid to form silicon anode material precursor particles.
In one embodiment, the temperature of the spray drying is 50 ℃ to 400 ℃.
An electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, said negative electrode comprising said silicon negative electrode material. And
and heating the silicon negative electrode material precursor particles to enable the thermosetting high polymer monomer to be crosslinked and polymerized into the thermosetting high polymer.
In the silicon cathode material, the thermosetting high molecular polymer directly forms secondary composite particles with the primary particles of silicon particles and the conductive agent without carbonization, and the size of the silicon particles is limited by utilizing the strength and toughness of the thermosetting high molecular polymer, so that the secondary composite particles are prevented from cracking due to the size change of the silicon particles, the shape and the structure of the secondary composite particles have better stability and integrity in the charge-discharge cycle process, and an electrochemical battery has better electrochemical performance.
Drawings
Fig. 1 is a schematic flow chart of a method for preparing a silicon negative electrode material according to an embodiment of the invention;
fig. 2A and 2B are scanning electron micrographs of silicon negative electrode material products according to example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the silicon negative electrode material, the preparation method thereof and the electrochemical cell of the present invention are further described in detail by the following embodiments with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a silicon negative electrode material which is a secondary composite particle, wherein the secondary composite particle comprises a silicon particle, a conductive agent and a thermosetting high polymer, and the thermosetting high polymer is at least arranged on the outer layer of the secondary composite particle.
In the traditional silicon cathode material, a carbon source is mostly pyrolyzed to form a carbon simple substance, and the carbon simple substance is compounded with silicon to form a silicon-carbon composite material, but the inventor finds that carbon obtained after high-temperature pyrolysis has larger brittleness, silicon is subjected to volume change in the charging and discharging process of a battery to easily cause the silicon-carbon composite particles to break, and the external expression is that the charging and discharging cycle performance of the battery is reduced along with the increase of cycle times. In the silicon negative electrode material provided by the embodiment of the invention, the thermosetting high molecular polymer directly forms secondary composite particles with the primary particles of silicon and the conductive agent without carbonization, and the size of the silicon particles is limited by utilizing the strength and toughness of the thermosetting high molecular polymer, so that the secondary composite particles are prevented from cracking due to the size change of the silicon particles, the shape and the structure of the secondary composite particles have better stability and integrity in the charge-discharge cycle process, and the electrochemical battery has better electrochemical performance.
The thermosetting high molecular polymer is a three-dimensional cross-linked network and has the property of insolubility and infusibility. The thermosetting high molecular polymer can be formed by heating and crosslinking polymerization of monomers of the thermosetting high molecular polymer, once the thermosetting high molecular polymer is processed and crosslinked to be formed, the thermosetting high molecular polymer cannot be processed again, the shape of the thermosetting high molecular polymer is not changed, and the thermosetting high molecular polymer has better strength and toughness, can keep the inherent shape and structure in the charging and discharging process of an electrochemical battery, and plays a role in supporting the secondary composite particles. In one embodiment, the thermosetting high molecular polymer may be selected from thermosetting resins. In some embodiments, the thermosetting resin may be selected from one or more of a cross-linked polymer of sodium carboxymethylcellulose (CMC) and polyacrylic acid (PAA), an epoxy, a phenolic, a polyurethane, a polyamide, and a polyimide.
In one embodiment, the silicon particles, the conductive agent, and the thermosetting high molecular polymer may be uniformly mixed. The thermosetting high molecular polymer is arranged on the outer layer and the inner part of the secondary composite particles and distributed between the silicon particles and the conductive agent. The thermosetting high molecular polymer forms a firm mesh support in the secondary composite particles, the silicon particles and the conductive agent are dispersed in gaps of the mesh support, and the mesh support supports and maintains the structures of the silicon particles and the conductive agent, so that the negative electrode of the electrochemical cell keeps stable in the process of ion extraction. And the thermosetting high molecular polymer is uniformly distributed in the secondary composite particles, so that the overall uniformity of the secondary composite particles is kept, and the conductive stability of the electrochemical cell is kept.
In another embodiment, the silicon negative electrode material is a core-shell structure, and the core-shell structure may include a shell layer and a core. The shell layer of the core-shell structure comprises the thermosetting high molecular polymer, the thermosetting high molecular polymer can be uniformly and continuously arranged on the shell layer, and the silicon particles can be coated on the core of the core-shell structure. The conductive agent can be uniformly mixed with the thermosetting high molecular polymer and the silicon particles, namely, distributed in the whole secondary composite particles. In one embodiment, the core also includes a quantity of the thermosetting high molecular polymer mixed with the silicon particles and the conductive agent.
In one embodiment, the shell layer of the core-shell structure has a greater compactness than the core, and the core has a certain porosity. The secondary composite particles can be manufactured by spray drying, and in the spray drying process, the surface layers of the secondary composite particles can be dried and skinned firstly, so that the secondary composite particles are shaped from the outside, and the pores formed in the subsequent drying process in the inside are reserved to form a structure with a compact shell layer and a loose core. The compact shell layer can protect the silicon particles from reacting with electrolyte after lithiation (or sodium treatment and magnesium treatment), and the loose core can provide buffer for volume expansion of the silicon particles and further protect the secondary composite particles from cracking, so that the secondary composite particles have good electrochemical performance.
In one embodiment, the conductive agent may be selected from conductive agents commonly used in lithium ion batteries, including but not limited to one or more of activated carbon, graphene, carbon nanotubes, ketjen black, Super P, acetylene black, and graphite.
In one embodiment, the mass ratio of the silicon particles, the conductive agent, and the thermosetting polymer may be (30-50): (1-20): (4-10). The mass of the silicon particles may account for 30% to 50% of the total mass of the secondary composite particles, the mass of the conductive agent may account for 1% to 20% of the total mass of the secondary composite particles, and the mass of the thermosetting high molecular polymer may account for 4% to 10% of the total mass of the secondary composite particles. Preferably, the mass of the solid high molecular polymer may be 5% to 7% of the total mass of the secondary composite particles.
In one embodiment, the secondary composite particles may have a particle size of 5 μm to 100 μm. Preferably, the secondary composite particles may have a particle size of 6 to 20 μm. The silicon particles may have a particle size of 10nm to 500 nm. The silicon particles may be particulate elemental silicon.
Referring to fig. 1, an embodiment of the present invention further provides a method for preparing the silicon negative electrode material, including:
s10, mixing the silicon particles, the conductive agent and the thermosetting high molecular polymer monomer in a solvent to form a dispersion liquid;
and S20, spray drying the dispersion liquid to form silicon anode material precursor particles.
In the embodiment of the invention, the silicon anode material precursor particles are formed in a spray drying mode, and the thermosetting high molecular polymer monomers in the silicon anode material precursor particles are crosslinked through further heating to form the thermosetting high molecular polymer with a three-dimensional network structure.
The step S10 may further include the step of mixing other additive auxiliaries, such as a curing agent, in the dispersion. The type of the curing agent is matched with the type of the thermosetting high molecular polymer monomer. In one embodiment, the thermosetting high molecular polymer monomer is an epoxy resin monomer, and the curing agent may be at least one selected from aliphatic amines, alicyclic amines, aromatic amines, polyamides, acid anhydrides, resins, and tertiary amines.
The solvent may include a volatile organic solvent that does not chemically react with the thermosetting high molecular polymer monomer. The volatile organic solvent may be selected from, but not limited to, one or more of N-methylpyrrolidone (NMP), methanol, ethanol, ethylene glycol, propanol, isopropanol, acetonitrile, acetone, diethyl ether, N Dimethylformamide (DMF), N dimethylacetamide (DMAc), and Tetrahydrofuran (THF). The mass ratio of the silicon particles, the conductive agent and the thermosetting high polymer monomer can be (30-50): (1-20): (4-10) according to the proportion of each corresponding component in the silicon negative electrode material.
In step S20, when the silicon anode material precursor particles are prepared by spray drying, a dispersion liquid formed by mixing the silicon particles, the conductive agent and the thermosetting high molecular polymer monomer is atomized into fine droplets by an atomizer, and the droplets are in sufficient contact with the injected hot air, so that the solvent is rapidly vaporized, and the spherical or spheroidal silicon anode material precursor particles are collected. By adjusting the proportion of the silicon particles, the conductive agent and the thermosetting high polymer monomer, the silicon anode material precursor particles with a core-shell structure or the uniform mixture of the silicon particles, the conductive agent and the thermosetting high polymer monomer can be obtained. By increasing the solvent volatilization speed in spray drying, a core-shell structure with loose cores and compact shells can be formed.
In one embodiment, the temperature of the spray drying may be 50 to 250 ℃. The temperature of the spray drying may be adjusted according to the kinds of the thermosetting high molecular polymer monomer and the solvent.
Preferably, between the steps S10 and S20, the method further includes: and a step of ball-milling the dispersion to reduce the particle size of the silicon particles by ball-milling. The ball milling temperature may be normal temperature. The particle size of the silicon particles after ball milling may be 10nm to 500 nm.
When the spray drying temperature is too low, step S30 may be further included: and heating the silicon negative electrode material precursor particles to enable the thermosetting high polymer monomer to be crosslinked and polymerized into the thermosetting high polymer. In step S30, under the heating condition, the thermosetting high molecular polymer monomer in the outer layer and the inner part of the silicon negative electrode material precursor particle is crosslinked to form a thermosetting high molecular polymer having a three-dimensional network structure. The temperature of the heat crosslinking is adjusted according to the type of the thermosetting high molecular polymer. In an embodiment, the thermosetting high molecular polymer is polyimide, and the temperature for heating and crosslinking the polyimide may be 200 ℃ to 400 ℃. It can be understood that the heating process does not pyrolyze or carbonize the polymer to form carbon simple substance, so that the heating temperature needs to be controlled not to be too high, and the polymer monomer is crosslinked and polymerized to obtain the thermosetting crosslinked polymer with certain strength and toughness.
The embodiment of the invention also provides an electrochemical battery, which comprises a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises the silicon negative electrode material.
In an embodiment, the negative electrode may further include a negative electrode current collector, the silicon negative electrode material and a volatile organic solvent are prepared into a slurry, the slurry is coated on the surface of the negative electrode current collector, and the negative electrode is obtained after drying in vacuum, protective gas or inert gas.
The volatile organic solvent may be selected from solvents that are not capable of dissolving the silicon negative electrode material, do not chemically react with the silicon negative electrode material, and can be completely removed at a relatively low temperature, such as low molecular weight volatile organic solvents, and may be selected from one or more of but not limited to N-methylpyrrolidone (NMP), methanol, ethanol, ethylene glycol, propanol, isopropanol, acetonitrile, acetone, diethyl ether, N Dimethylformamide (DMF), N dimethylacetamide (DMAc), and Tetrahydrofuran (THF).
The positive electrode can comprise a positive electrode material and a positive electrode current collector, the positive electrode material and a volatile organic solvent are prepared into slurry, the slurry is coated on the surface of the positive electrode current collector, and the positive electrode is obtained after drying in vacuum, protective gas or inert gas.
Preferably, the electrochemical cell may be a lithium ion cell, a sodium ion cell or a magnesium ion cell. The positive electrode material may include a positive electrode active material, a conductive agent, and a binder.
In one example, the electrochemical cell is a lithium ion cell, and the positive active material and the electrolyte both contain lithium ions. The positive electrode active material may be at least one of lithium transition metal oxides such as layered-structured lithium transition metal oxides, spinel-structured lithium transition metal oxides, and olivine-structured lithium transition metal oxides, for example, olivine-type lithium iron phosphate, layered-structured lithium cobaltate, layered-structured lithium manganate, spinel-type lithium manganate, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide.
In another embodiment, the electrochemical cell is a sodium ion cell, and the positive active material and the electrolyte both contain sodium ions. The positive active material may be a layered transition metal oxide of sodium (e.g., Na)xCoO2) Tunnel structure oxides (e.g. Na)0.44MnO2) Polyanionic compounds (Na)3V2(PO4)3) And simple compounds (e.g. Na)2S).
The conductive agents in the anode and the silicon cathode materials can be respectively the same or different.
The positive electrode current collector and the negative electrode current collector are used for respectively carrying the positive electrode material and the silicon negative electrode material and conducting current, and the shape of the positive electrode current collector and the negative electrode current collector can be foil or net. The material of the positive electrode current collector may be selected from aluminum, titanium, stainless steel, carbon cloth, or carbon paper. The material of the negative electrode current collector may be selected from copper, nickel, stainless steel, carbon cloth, or carbon paper.
In one embodiment, the electrochemical cell may further include a separator disposed between the positive electrode and the negative electrode, and the electrolyte is an electrolyte solution, and infiltrates the separator, the positive electrode, and the negative electrode. In another embodiment, the electrolyte of the electrochemical cell is a solid electrolyte membrane or a gel electrolyte membrane, instead of a separator, disposed between the cathode and the anode.
The separator may be a conventional lithium battery separator capable of blocking electrons and passing metal ions, such as lithium ions. The separator may be any one of an organic polymer separator and an inorganic separator, and may be selected from, for example, but not limited to, any one of a polyethylene porous membrane, a polypropylene porous membrane, a polyethylene-polypropylene double-layer porous membrane, a polypropylene-polyethylene-polypropylene triple-layer porous membrane, a glass fiber porous membrane, a nonwoven fabric porous membrane, an electrospun porous membrane, a PVDF-HFP porous membrane, and a polyacrylonitrile porous membrane. Examples of the nonwoven fabric separator include polyimide nanofiber nonwoven fabrics, polyethylene terephthalate (PET) nanofiber nonwoven fabrics, cellulose nanofiber nonwoven fabrics, aramid nanofiber nonwoven fabrics, nylon nanofiber nonwoven fabrics, and polyvinylidene fluoride (PVDF) nanofiber nonwoven fabrics. Examples of the electrospun porous membrane include a polyimide electrospun membrane, a polyethylene terephthalate electrospun membrane, and a polyvinylidene fluoride electrospun membrane.
The electrolyte is a non-aqueous electrolyte and comprises a solvent and an electrolyte dissolved in the solvent, wherein the solvent can be selected from one or more of cyclic carbonate, chain carbonate, cyclic ether, chain ether, nitrile and amide, such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methylethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, diethyl ether, acetonitrile, propionitrile, anisole, butyrate, glutaronitrile, adiponitrile, gamma-butyrolactone, gamma-valerolactone, tetrahydrofuran, 1, 2-dimethoxyethane and one or more of acetonitrile and dimethylformamide.
When the electrochemical cell is a lithium ion cell, the electrolyte is a lithium salt, which may be selected from, but not limited to, lithium chloride (LiCl), lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium methanesulfonate (LiCH)3SO3) Lithium trifluoromethanesulfonate (LiCF)3SO3) Lithium hexafluoroarsenate (LiAsF)6) Lithium perchlorate (LiClO)4) And lithium bis (oxalato) borate (LiBOB).
When the electrochemical cell is a sodium ion cell, the electrolyte is a sodium salt selected from sodium hexafluorophosphate (NaPF)6) Sodium perchlorate (NaClO)4) Sodium bistrifluoromethylsulfonimide (NaTFSI), preferably sodium perchlorate (NaClO)4)。
The electrochemical cell may further include a sealed housing in which the positive electrode, the negative electrode, the separator, and the electrolyte are disposed.
Example 1
The silicon particles, KS-6 and polyimide monomers were mixed in an ethanol solution to form a dispersion. In the dispersion, the mass fraction of the silicon particles was 40%, the mass fraction of the conductive agent was 10%, the mass fraction of the polyimide monomer was 5%, and the balance was an ethanol solvent.
Ball-milling the dispersion at normal temperature until the particle size of the silicon particles is below 500 nm.
And carrying out spray drying on the dispersion liquid after ball milling at the temperature of 100-120 ℃ to form silicon anode material precursor particles.
Heating and crosslinking the silicon cathode material precursor particles at 280-320 ℃, and crosslinking the thermosetting high-molecular polymer monomer into the thermosetting high-molecular polymer. The secondary composite particles of the silicon negative electrode material are obtained, and the electron micrographs of the secondary composite particles are shown in fig. 2A and fig. 2B.
And adding the obtained secondary composite particles into an N-methylpyrrolidone (NMP) solvent, stirring for 4 hours, coating on a copper foil, and drying in vacuum at the temperature of 120 ℃ for 10 hours to obtain the negative electrode.
And assembling the prepared negative electrode into a lithium ion battery.
Please refer to table 1, the electrochemical performance of the lithium ion battery was tested by using a blue charge/discharge instrument at a voltage range of 0.005-4.3V.
Example 2
Silicon particles, C45, sodium carboxymethylcellulose (CMC) and polyacrylic acid (PAA) were mixed in an aqueous solution to form a dispersion. In the dispersion, the mass fraction of the silicon particles was 30%, the mass fraction of the conductive agent was 10%, the mass fractions of CMC and PAA were both 5%, and the balance was an aqueous solvent.
Mixing silicon particles and a small amount of red phosphorus powder, and ball-milling at normal temperature until the particle size of the silicon particles is below 500 nm.
And carrying out spray drying on the dispersion liquid after ball milling at the temperature of between 100 and 130 ℃ to form silicon anode material precursor particles.
And heating the silicon negative electrode material precursor particles at 140-170 ℃, and crosslinking the CMC and the PAA to obtain the silicon negative electrode material secondary composite particles.
The obtained secondary composite particles are mixed with a conductive agent (such as conductive graphite) commonly used for lithium batteries, a binder (such as PVDF) and a pulping solvent (such as N-methyl pyrrolidone, NMP) for pulping, and vacuum-dried at the temperature of 120 ℃ for 10 hours to prepare a negative electrode.
And assembling the prepared negative electrode into a lithium ion battery.
Please refer to table 1, the electrochemical performance of the lithium ion battery was tested by using a blue charge/discharge instrument at a voltage range of 0.005-4.3V.
Example 3
Example 3 is substantially the same as example 1 except that the mass fraction of the polyimide monomer in the dispersion is 2% and the mass fraction of the silicon particles is 37%.
Example 4
Example 4 is substantially the same as example 1 except that the mass fraction of the polyimide monomer in the dispersion is 20% and the mass fraction of the silicon particles is 25%.
Comparative example 1
Providing the silicon anode material secondary composite particles obtained in the embodiment 1, and sintering the silicon anode material secondary composite particles in a nitrogen atmosphere to obtain the silicon-carbon composite microspheres. The sintering condition is that the temperature is increased from room temperature to 500-1000 ℃, the sintering temperature is kept for 20-30 h, and the temperature is cooled to room temperature.
Table 1 electrochemical performance of silicon-based anode materials prepared in different examples
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. The silicon negative electrode material is characterized in that the silicon negative electrode material is secondary composite particles, the secondary composite particles comprise silicon particles, a conductive agent and a thermosetting high polymer, and the thermosetting high polymer is at least arranged on the outer layer of the secondary composite particles.
2. The silicon negative electrode material as claimed in claim 1, wherein the silicon negative electrode material is of a core-shell structure, the thermosetting high molecular polymer is uniformly and continuously arranged on a shell layer of the core-shell structure, and the silicon particles are in a core of the core-shell structure.
3. The silicon anode material according to claim 2, wherein the shell layer of the core-shell structure has a denseness greater than that of the core.
4. The silicon negative electrode material of claim 1, wherein the thermosetting polymer material is selected from one or more of cross-linked polymers of sodium carboxymethylcellulose and polyacrylic acid, epoxy resin, phenolic resin, polyurethane, polyamide, and polyimide.
5. The silicon negative electrode material as claimed in claim 1, wherein the conductive agent is selected from one or more of activated carbon, graphene, carbon nanotubes, ketjen black, Super P, acetylene black, and graphite.
6. The silicon negative electrode material as claimed in claim 1, wherein the mass ratio of the silicon particles, the conductive agent and the thermosetting polymer is (30-50): (1-20): (4-10).
7. The silicon negative electrode material according to claim 1, wherein the secondary composite particles have a particle diameter of 5 to 100 μm.
8. A method for preparing the silicon anode material according to any one of claims 1 to 7, comprising:
mixing the silicon particles, the conductive agent and a thermosetting high molecular polymer monomer in a solvent to form a dispersion liquid;
and carrying out spray drying on the dispersion liquid to form silicon anode material precursor particles.
9. The method for preparing the silicon negative electrode material as claimed in claim 8, wherein the temperature of the spray drying is 50 ℃ to 400 ℃.
10. An electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, the negative electrode comprising the silicon negative electrode material according to any one of claims 1 to 7.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112768674A (en) * | 2021-02-09 | 2021-05-07 | 中国科学院成都有机化学有限公司 | Silicon-based composite negative electrode material and preparation method thereof, and negative electrode and preparation method thereof |
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