CN111916745A - Silicon negative electrode material, preparation method thereof and electrochemical cell - Google Patents

Abstract

The invention discloses a silicon negative electrode material. The silicon negative electrode material is secondary composite particles. The secondary composite particles include silicon particles, a conductive agent and a thermosetting polymer. The thermosetting polymer is arranged at least in the outer layer of the secondary composite particles. The invention discloses a preparation method of a silicon negative electrode material. The invention also discloses an electrochemical cell.

Description

Silicon anode material and preparation method thereof, and electrochemical cell

technical field

The invention relates to the technical field of batteries, in particular to a silicon negative electrode material and a preparation method thereof, and an electrochemical battery.

Background technique

At present, the commercialized negative electrode material is mainly graphite, which has the disadvantages of low theoretical specific capacity and poor high-rate charge-discharge performance. It is impossible to fully meet the needs of the development of lithium-ion batteries. A new type of high-capacity negative electrode with high capacity, long life, safe and reliable to replace the graphite-like carbon negative electrode.

Silicon anode material has high theoretical specific capacity and low lithium-deintercalation potential, and is a very promising high-capacity anode material. The main problem that currently restricts the application of silicon anodes is that the volume of silicon will change during the charging and discharging process of the battery, which will lead to the decline of the battery performance.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a new type of silicon anode material and its preparation method, as well as an electrochemical cell.

A silicon negative electrode material, the silicon negative electrode material is secondary composite particles, the secondary composite particles include silicon particles, a conductive agent and a thermosetting high molecular polymer, and the thermosetting high molecular polymer is arranged at least on the secondary composite particles. The outer layer of the composite particle.

In one embodiment, the silicon negative electrode material is a core-shell structure, the thermosetting polymer is uniformly and continuously arranged in the shell layer of the core-shell structure, and the silicon particles are in the core of the core-shell structure .

In one embodiment, the density of the shell layer of the core-shell structure is greater than the density of the core.

In one embodiment, the thermosetting polymer material is selected from a cross-linked polymer of sodium carboxymethyl cellulose and polyacrylic acid, epoxy resin, phenolic resin, polyurethane, polyamide and polyimide or more.

In one embodiment, the conductive agent is selected from one or more of activated carbon, graphene, carbon nanotubes, Ketjen black, SuperP, acetylene black and graphite.

In one embodiment, the mass ratio of the silicon particles, the conductive agent and the thermosetting polymer is (30-50):(1-20):(4-10).

In one embodiment, the particle size of the secondary composite particles is 5 μm˜100 μm.

A preparation method of the described silicon anode material, comprising:

mixing the silicon particles, the conductive agent and the thermosetting polymer monomer in a solvent to form a dispersion;

The dispersion liquid is spray-dried to form silicon anode material precursor particles.

In one embodiment, the temperature of the spray drying is 50°C to 400°C.

An electrochemical cell includes a positive electrode, a negative electrode and an electrolyte, and the negative electrode includes the silicon negative electrode material. as well as

The silicon anode material precursor particles are heated to cross-link and polymerize the thermosetting polymer monomer into the thermosetting polymer.

In the silicon negative electrode material of the present invention, the thermosetting macromolecular polymer directly forms secondary composite particles with the primary particles of silicon particles and the conductive agent without carbonization. Strength and toughness, while limiting the volume of silicon particles, avoiding the rupture of the secondary composite particles caused by the volume change of the silicon particles, so that the shape and structure of the secondary composite particles have better stability during the charge-discharge cycle. properties and integrity, so that the electrochemical cell has better electrochemical performance.

Description of drawings

1 is a schematic flowchart of a method for preparing a silicon negative electrode material according to an embodiment of the present invention;

FIG. 2A and FIG. 2B are scanning electron microscope photographs of the silicon anode material product in Example 1 of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the following examples and the accompanying drawings will further describe the silicon negative electrode material and the preparation method thereof, as well as the electrochemical cell of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

An embodiment of the present invention provides a silicon negative electrode material, the silicon negative electrode material is secondary composite particles, and the secondary composite particles include silicon particles, a conductive agent and a thermosetting polymer, and the thermosetting polymer is at least set in the outer layer of the secondary composite particles.

In traditional silicon anode materials, carbon source is pyrolyzed to form carbon element, which is compounded with silicon to form silicon-carbon composite material. The volume change of the medium silicon easily leads to the rupture of the silicon-carbon composite particles, and the external manifestation is that the charge-discharge cycle performance of the battery decreases with the increase of the number of cycles. In the silicon negative electrode material according to the embodiment of the present invention, the thermosetting high molecular polymer directly forms secondary composite particles with the primary silicon particles and the conductive agent without carbonization. Strength and toughness, while limiting the volume of silicon particles, avoiding the rupture of the secondary composite particles caused by the volume change of the silicon particles, so that the shape and structure of the secondary composite particles have better stability during the charge-discharge cycle. properties and integrity, so that the electrochemical cell has better electrochemical performance.

The thermosetting macromolecular polymer is a three-dimensional cross-linked network with insoluble and infusible properties. The thermosetting macromolecular polymer can be obtained by cross-linking and polymerizing the monomers of the thermosetting macromolecular polymer. Once the thermosetting macromolecular polymer is processed and cross-linked, it cannot be processed again, the shape will not change, and it has Good strength and toughness can maintain the inherent shape and structure during the charging and discharging process of the electrochemical cell, and play the role of supporting the secondary composite particles. In one embodiment, the thermosetting polymer can be selected from thermosetting resins. In some embodiments, the thermosetting resin may be selected from cross-linked polymers of sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA), epoxy resins, phenolic resins, polyurethanes, polyamides, and polyimides one or more of.

In one embodiment, the silicon particles, the conductive agent and the thermosetting polymer may be uniformly mixed. The thermosetting macromolecular polymer is arranged on the outer layer and inside of the secondary composite particles, and is distributed between the silicon particles and the conductive agent. The thermosetting macromolecular polymer forms a firm mesh scaffold in the secondary composite particles, the silicon particles and the conductive agent are dispersed in the gaps of the mesh scaffold, and the mesh scaffold supports and maintains The structures of the silicon particles and the conductive agent keep the structure of the negative electrode of the electrochemical cell stable during the process of deintercalating ions. In addition, the thermosetting macromolecular polymer is uniformly distributed in the secondary composite particles, so that the secondary composite particles maintain overall uniformity, which is beneficial to maintain the electrical conductivity stability of the electrochemical cell.

In another embodiment, the silicon anode 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 includes the thermosetting macromolecular polymer, the thermosetting macromolecular polymer can be uniformly and continuously arranged in the shell layer, and the silicon particles can cover the core of the core-shell structure. The conductive agent can be uniformly mixed with the thermosetting polymer and the silicon particles, that is, distributed throughout the secondary composite particles. In one embodiment, the core also includes a certain amount of the thermosetting polymer, which is mixed with the silicon particles and the conductive agent.

In one embodiment, the density of the shell layer of the core-shell structure is greater than the density of the core, and the core has certain pores. The secondary composite particles can be produced by spray drying. In the process of spray drying, the surface layer of the secondary composite particles can be dried and "skinned" first, so that the secondary composite particles can be shaped from the outside, and the interior is subsequently dried. The pores formed during the process are retained, forming a structure with a dense shell and a loose core. The dense shell layer can protect the silicon particles from reacting with the electrolyte after lithiation (or sodiumization or magnesiumization), and the crisp core can provide buffers for the volume expansion of the silicon particles, further protecting the secondary composite particles from occurring fracture, so that the secondary composite particles have good electrochemical performance.

In one embodiment, the conductive agent can be selected from the conductive agents commonly used in lithium-ion batteries, including but not limited to one of activated carbon, graphene, carbon nanotubes, Ketjen black, Super P, acetylene black and graphite. or more.

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 thermosetting properties are high. The mass of the molecular polymer may account for 4% to 10% of the total mass of the secondary composite particles. Preferably, the mass of the solid macromolecular polymer may account for 5% to 7% of the total mass of the secondary composite particles.

In one embodiment, the particle size of the secondary composite particles may be 5 μm˜100 μm. Preferably, the particle size of the secondary composite particles may be 6 μm˜20 μm. The particle size of the silicon particles may be 10 nm˜500 nm. The silicon particles may be granular elemental silicon.

Referring to FIG. 1, an embodiment of the present invention also provides a method for preparing the silicon anode material, including:

S10, mixing the silicon particles, the conductive agent and the thermosetting polymer monomer in a solvent to form a dispersion;

S20, spray-drying the dispersion to form silicon anode material precursor particles.

In the embodiment of the present invention, the silicon anode material precursor particles are formed by spray drying, and the thermosetting macromolecular polymer monomer in the silicon anode material precursor particles is cross-linked by further heating and cross-linking to form a three-dimensional network structure. molecular polymers.

The step S10 may further include the step of mixing other additives, such as a curing agent, into the dispersion. The type of the curing agent is matched with the type of the thermosetting polymer monomer. In one embodiment, the thermosetting polymer monomer is an epoxy resin monomer, and the curing agent can be selected from aliphatic amines, alicyclic amines, aromatic amines, polyamides, acid anhydrides, resins and tertiary amines at least one of.

The solvent may include a volatile organic solvent that does not chemically react with the thermosetting polymer monomer. The volatile organic solvent can be selected from but not limited to N-methylpyrrolidone (NMP), methanol, ethanol, ethylene glycol, propanol, isopropanol, acetonitrile, acetone, ether, N,N dimethylformamide One or more of (DMF), N,N dimethylacetamide (DMAc) and tetrahydrofuran (THF). The mass ratio of the silicon particles, the conductive agent, and the thermosetting polymer monomer may be (30-50): (1-20): (4-10), according to each of the silicon negative electrode materials. The proportions of the corresponding components are determined.

In step S20, when the silicon anode material precursor particles are prepared by spray drying, the dispersion liquid formed by mixing the silicon particles, the conductive agent and the thermosetting polymer monomer is misted by an atomizer The droplets are formed into fine droplets, and the droplets are fully contacted with the injected hot air, so that the solvent is rapidly vaporized, thereby collecting spherical or quasi-spherical silicon anode material precursor particles. By adjusting the proportions of the silicon particles, the conductive agent and the thermosetting polymer monomer, the three can be uniformly mixed, or the silicon anode material precursor particles with a core-shell structure can be obtained. By increasing the solvent evaporation rate in spray drying, a core-shell structure with loose core and dense shell can be formed.

In one embodiment, the temperature of the spray drying may be 50-250°C. The temperature of the spray drying can be adjusted according to the type of the thermosetting polymer monomer and the solvent.

Preferably, between the steps S10 and S20, the method further includes: a step of ball-milling the dispersion, and reducing the particle size of the silicon particles by ball-milling. The ball milling temperature can be normal temperature. The particle size of the silicon particles after ball milling may be 10 nm˜500 nm.

When the spray drying temperature is too low, step S30 may also be included: heating the silicon anode material precursor particles to cross-link and polymerize the thermosetting polymer monomer into the thermosetting polymer. In step S30, under the heating condition, the outer layer of the silicon anode material precursor particles and the thermosetting polymer monomer inside are cross-linked to form a thermosetting polymer having a three-dimensional network structure. The temperature of the thermal crosslinking is adjusted according to the type of the thermosetting polymer. In one embodiment, the thermosetting polymer is polyimide, and the temperature of the polyimide for crosslinking by heating may be 200°C to 400°C. It can be understood that the heating process does not cause the polymer to be pyrolyzed or carbonized to form a carbon element, so it is necessary to control the heating temperature so as not to be too high, so that the polymer monomer can be cross-linked and polymerized to obtain a thermosetting cross-linked polymer with certain strength and toughness.

An embodiment of the present invention further provides an electrochemical cell, including a positive electrode, a negative electrode and an electrolyte, and the negative electrode includes the silicon negative electrode material.

In one embodiment, the negative electrode may further include a negative electrode current collector, and the silicon negative electrode material and a volatile organic solvent are prepared into a slurry, which is coated on the surface of the negative electrode current collector, and is obtained after drying in vacuum, protective gas or inert gas. negative electrode.

The volatile organic solvent can be selected from solvents that cannot dissolve the silicon negative electrode material, do not chemically react with the silicon negative electrode material, and can be completely removed at a lower temperature, such as low molecular weight volatile organic solvents, which can be selected. From but not limited to N-methylpyrrolidone (NMP), methanol, ethanol, ethylene glycol, propanol, isopropanol, acetonitrile, acetone, ether, N,N dimethylformamide (DMF), N,N diethyl ether One or more of methylacetamide (DMAc) and tetrahydrofuran (THF).

The positive electrode may include a positive electrode material and a positive electrode current collector, the positive electrode material and a volatile organic solvent are prepared into a slurry, coated on the surface of the positive electrode current collector, and dried in vacuum, protective gas or inert gas to obtain the positive electrode.

Preferably, the electrochemical battery may be a lithium-ion battery, a sodium-ion battery or a magnesium-ion battery. 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 both the positive electrode active material and the electrolyte contain lithium ions. The positive electrode active material may be a lithium transition metal oxide, such as at least one of a layered lithium transition metal oxide, a spinel-type lithium transition metal oxide, and an olivine-type lithium transition metal oxide. Species, for example, olivine-type lithium iron phosphate, layered-structure lithium cobaltate, layered-structure 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 battery, and both the positive electrode active material and the electrolyte contain sodium ions. The positive electrode active material can be a layered transition metal oxide of sodium (such as Na _x CoO ₂ ), a tunnel structure oxide (such as Na _0.44 MnO ₂ ), a polyanionic compound (Na ₃ V ₂ (PO ₄ ) ₃ ) and at least one of simple _compounds such as Na2S.

The conductive agents in the positive electrode material and the silicon negative electrode material may be the same or different, respectively.

The positive electrode current collector and the negative electrode current collector are used to respectively support the positive electrode material and the silicon negative electrode material, and conduct current, and can be in the shape of a foil or a mesh. The material of the positive electrode current collector can be selected from aluminum, titanium, stainless steel, carbon cloth or carbon paper. The material of the negative electrode current collector can 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 that 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, which is arranged between the positive electrode and the negative electrode instead of the separator.

The separator may be a conventional lithium battery separator capable of isolating electrons and allowing metal ions, such as lithium ions, to pass through. The separator can be any one of an organic polymer separator or an inorganic separator, for example, it can be selected from but not limited to polyethylene porous membrane, polypropylene porous membrane, polyethylene-polypropylene double-layer porous membrane, polypropylene-polyethylene porous membrane - Any one of polypropylene three-layer porous membrane, glass fiber porous membrane, non-woven porous membrane, electrospun porous membrane, PVDF-HFP porous membrane and polyacrylonitrile porous membrane. The non-woven separator can be listed as polyimide nanofiber nonwoven, polyethylene terephthalate (PET) nanofiber nonwoven, cellulose nanofiber nonwoven, aramid nanofiber nonwoven cloth, nylon nanofiber nonwoven and polyvinylidene fluoride (PVDF) nanofiber nonwoven. The electrospun porous membrane can be exemplified by polyimide electrospun membrane, polyethylene terephthalate electrospun membrane, and polyvinylidene fluoride electrospun membrane.

The electrolyte is a non-aqueous electrolyte, including a solvent and an electrolyte dissolved in the solvent, the solvent can be selected from but not limited to cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, nitriles One or more of amides and amides, such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, propyl acetate, propionic acid Methyl ester, ethyl propionate, diethyl ether, acetonitrile, propionitrile, anisole, butyrate, glutaronitrile, adiponitrile, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, 1,2- One or more of dimethoxyethane, acetonitrile and dimethylformamide.

When the electrochemical cell is a lithium ion battery, the electrolyte is a lithium salt, which can be selected from, but not limited to, lithium chloride (LiCl), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), methanesulfonic acid One of lithium (LiCH ₃ SO ₃ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ) and lithium bis-oxalate borate (LiBOB) one or more.

When the electrochemical cell is a sodium-ion battery, the electrolyte is a sodium salt, which can be selected from sodium hexafluorophosphate (NaPF ₆ ), sodium perchlorate (NaClO ₄ ), sodium bis-trifluoromethylsulfophthalimide One or more of (NaTFSI), preferably sodium perchlorate (NaClO ₄ ).

The electrochemical cell may further include a sealed casing in which the positive electrode, the negative electrode, the separator and the electrolyte are disposed.

Example 1

The silicon particles, KS-6 and polyimide monomer were mixed in an ethanol solution to form a dispersion. In the dispersion liquid, the mass fraction of silicon particles is 40%, the mass fraction of conductive agent is 10%, the mass fraction of polyimide monomer is 5%, and the rest is ethanol solvent.

The dispersion was ball-milled at room temperature until the particle size of the silicon particles was 500 nm or less.

The ball-milled dispersion is spray-dried at 100° C. to 120° C. to form silicon anode material precursor particles.

The silicon negative electrode material precursor particles are heated and cross-linked at 280° C. to 320° C., and the thermosetting macromolecular polymer monomer is cross-linked to form a thermosetting macromolecular polymer. The secondary composite particles of the silicon negative electrode material are obtained, and the electron microscope photos of the secondary composite particles are shown in FIG. 2A and FIG. 2B .

The obtained secondary composite particles were added to N-methylpyrrolidone (NMP) solvent, stirred for 4 hours, coated on copper foil, and vacuum-dried at 120° C. for 10 hours to obtain a negative electrode.

The prepared negative electrode was assembled into a lithium ion battery.

Please refer to Table 1 to test the electrochemical performance of lithium-ion batteries in the voltage range of 0.005 to 4.3V using a blue-electric charge-discharge instrument.

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 liquid, the mass fraction of silicon particles is 30%, the mass fraction of conductive agent is 10%, the mass fraction of CMC and PAA is 5%, and the rest is water solvent.

Mix silicon particles with a small amount of red phosphorus powder, and ball-mill at room temperature until the particle size of silicon particles is below 500 nm.

The ball-milled dispersion is spray-dried at 100° C. to 130° C. to form silicon anode material precursor particles.

The silicon anode material precursor particles are heated at 140° C. to 170° C., and the CMC and the PAA are cross-linked to obtain the silicon anode material secondary composite particles.

The obtained secondary composite particles are mixed with a commonly used conductive agent for lithium batteries (such as conductive graphite), a binder (such as PVDF) and a slurry solvent (such as N-methylpyrrolidone, NMP), and the slurry is vacuumed at a temperature of 120 ° C. The negative electrode was prepared after drying for 10 hours.

The prepared negative electrode was assembled into a lithium ion battery.

Please refer to Table 1 to test the electrochemical performance of lithium-ion batteries in the voltage range of 0.005 to 4.3V using a blue-electric charge-discharge instrument.

Example 3

Example 3 is basically the same as Example 1, except that the mass fraction of polyimide monomer in the dispersion liquid is 2%, and the mass fraction of silicon particles is 37%.

Example 4

Example 4 is basically the same as Example 1, except that the mass fraction of polyimide monomer in the dispersion liquid is 20%, and the mass fraction of silicon particles is 25%.

Comparative Example 1

The silicon negative electrode material secondary composite particles obtained in Example 1 are provided, and the silicon negative electrode material secondary composite particles are sintered in a nitrogen atmosphere to obtain the silicon carbon composite microspheres. The sintering condition is to increase from room temperature to a sintering temperature of 500°C to 1000°C, maintain the sintering temperature for 20h to 30h, and cool to room temperature.

Table 1 Electrochemical properties of silicon-based anode materials prepared in different examples

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that, for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. a silicon negative electrode material, is characterized in that, described silicon negative electrode material is secondary composite particle, and described secondary composite particle comprises silicon particle, conductive agent and thermosetting macromolecular polymer, and described thermosetting macromolecular polymer at least provided on the outer layer of the secondary composite particles. 2 . The silicon negative electrode material according to claim 1 , wherein the silicon negative electrode material has a core-shell structure, the thermosetting high molecular polymer is uniformly and continuously arranged in the shell layer of the core-shell structure, and the silicon The particles are within the core of the core-shell structure. 3 . The silicon negative electrode material according to claim 2 , wherein the density of the shell layer of the core-shell structure is greater than the density of the core. 4 . 4. The silicon negative electrode material according to claim 1, wherein the thermosetting polymer material is selected from the group consisting of cross-linked polymer of sodium carboxymethyl cellulose and polyacrylic acid, epoxy resin, phenolic resin, polyurethane, polyacrylic acid One or more of amide and polyimide. 5. silicon negative electrode material according to claim 1, is characterized in that, described conductive agent is selected from one or more in activated carbon, graphene, carbon nanotube, Ketjen black, Super P, acetylene black and graphite . 6 . The silicon negative electrode material according to claim 1 , wherein the mass ratio of the silicon particles, the conductive agent and the thermosetting polymer is (30-50): (1-20): 6 . (4 to 10). 7 . The silicon negative electrode material according to claim 1 , wherein the particle size of the secondary composite particles is 5 μm˜100 μm. 8 . 8. A preparation method of the silicon negative electrode material according to any one of claims 1-7, comprising: mixing the silicon particles, the conductive agent and the thermosetting polymer monomer in a solvent to form a dispersion; The dispersion liquid is spray-dried to form silicon anode material precursor particles. 9 . The method for preparing a silicon negative electrode material according to claim 8 , wherein the temperature of the spray drying is 50° C.˜400° C. 10 . 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 1-7.

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