CN106920949B - Silicon-carbon negative electrode material and preparation method thereof - Google Patents
Silicon-carbon negative electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the field of energy storage research, and particularly relates to a silicon-carbon anode material which comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conducting network with a porous structure and primary nano particles filled in the porous structure of the main electric conducting network; strong chemical bonds and force action exist among the dominant network structures; the chemical bond tightly locks the nano-sized primary particles in the pore structure of the main conducting network. Thereby ensuring that the silicon-carbon negative electrode material has excellent electrochemical performance.
Description
Technical Field
The invention belongs to the technical field of energy storage materials, and particularly relates to a silicon-carbon negative electrode material and a preparation method thereof.
Background
Since the birth of the lithium ion battery, the lithium ion battery brings revolutionary changes to the field of energy storage due to the advantages of large specific energy, high working voltage, small self-discharge rate, small volume, light weight and the like, and is widely applied to various portable electronic devices and electric automobiles. However, with the improvement of living standard of people, higher user experience puts higher requirements on the lithium ion battery: lighter weight, longer service life, etc.; in order to solve the above problems, it is necessary to find a new electrode material having more excellent properties.
The current commercialized lithium ion battery cathode material is mainly graphite, but the theoretical capacity of the lithium ion battery cathode material is only 372mAh g-1The urgent needs of users cannot be met; therefore, the development of a negative electrode material having a higher specific capacity is imminent. Silicon materials have been attracting attention as negative electrode materials for lithium ion batteries. The theoretical capacity is 4200mAh g-1Is more than 10 times of the capacity of the commercialized graphite,and has the advantages of low lithium intercalation potential, low atomic weight, high energy density, low price, environmental friendliness and the like, so that the lithium-doped lithium iron oxide material is one of the optimal choices for.
However, the silicon material has poor conductivity and is easy to cause structural damage and mechanical crushing due to large volume expansion in the charging and discharging processes, so that the cycle performance of the silicon material is quickly attenuated, and the wider application of the silicon material is limited. In order to solve the problems, the prior art mainly comprises the steps of nano-crystallizing silicon particles, adding a conductive material with excellent conductive performance into the silicon-based material particles and the like, and is used for improving the conductive performance of the integral particles of the silicon-based material and simultaneously solving the problems of mechanical crushing of the silicon-based material in the charging and discharging processes of the material.
However, silicon-based particles with nano structures are extremely easy to agglomerate and have high dispersion difficulty; the common conductive agent materials are generally small in size (nanometer), large in specific surface area and high in dispersion difficulty; meanwhile, in the charging and discharging process, the huge volume change of the silicon-based particles generates huge impact on the structural stability of the silicon-carbon cathode particles. However, in order to maximize the conductive effect of the conductive agent and to prepare a silicon-based secondary particle material with better performance, it is necessary to ensure uniform dispersion of the nano silicon-based particles and the conductive agent and the stability of the structure of the silicon-carbon material. Meanwhile, the bonding force between the silicon-based material with the nano structure and the conductive agent is weak, and the silicon-based material and the conductive agent are easily disconnected in the volume expansion process, so that the electrochemical performance of the silicon-carbon material is influenced.
In view of the above, there is a need for a silicon-carbon negative electrode material and a preparation method thereof, which can uniformly disperse two materials (nano silicon-based particles and conductive agent) with high dispersion difficulty, and ensure that the two materials are tightly connected together (i.e., the silicon-carbon material has stable structure), so as to prepare a silicon-carbon negative electrode material with excellent performance.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the provided silicon-carbon anode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conducting network with a porous structure and nano primary particles filled in the pore structure of the main electric conducting network; strong chemical bonds and force action exist among the dominant network structures; the chemical bond tightly locks the nano-sized primary particles in the pore structure of the main conducting network. Thereby ensuring that the silicon-carbon negative electrode material has excellent electrochemical performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a silicon-carbon anode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main conducting network with a porous structure and nano primary particles filled in the pore structure of the main conducting network; strong chemical bonds and force action exist among the dominant network structures; the chemical bond tightly locks the nano-sized primary particles in the pore structure of the main conducting network. The shell structure is a coating layer commonly used for cathode materials and is mainly obtained by coating and carbonizing materials such as asphalt and the like, so that the invention is not explained in detail.
As an improvement of the silicon-carbon anode material, the bond types providing the strong bonding force are hydrogen bonds or/and chemical bonds; the mass of the oxygen-containing functional groups forming the hydrogen bonds or/and the chemical bonds accounts for 1-40% of the mass of the whole main electric network structure.
As an improvement of the silicon-carbon negative electrode material, the main electric conducting network has flexibility, and the inside of the main electric conducting network contains functional groups; the hydrogen bonds or/and chemical bonds result from the reaction of oxygen-containing functional groups within the main conducting network.
As an improvement of the silicon-carbon negative electrode material, the main conducting network structure is at least one of an open graphene structure, an open expanded graphite structure and a vermicular graphene structure; the primary particles comprise nano silicon-based negative electrode particles; an auxiliary electric conduction network can be distributed between the main electric conduction network and the primary particles and tightly connects the main electric conduction network and the nano primary particles together.
As an improvement of the silicon-carbon negative electrode material, the nano silicon-based negative electrode particles are nano silicon particles or/and nano silicon oxidation; the primary particles may further include non-nano silicon-based anode particles; the non-nano silicon-based negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, pyrolytic resin carbon, lithium carbonate, a tin-based negative electrode material, transition metal nitride, a tin-based alloy, a germanium-based alloy, an aluminum-based alloy, an antimony-based alloy and a magnesium-based alloy; the auxiliary conducting network is obtained by carbonizing a high polymer material; the high molecular material is obtained by in-situ polymerization of a high molecular polymer monomer; the auxiliary conducting network can also comprise at least one of conductive carbon black, super conductive carbon, Ketjen black, carbon nano tubes, graphene and acetylene black;
the invention also discloses a preparation method of the silicon-carbon cathode material, which is characterized by mainly comprising the following steps of:
step 1, precursor preparation: uniformly dispersing the primary particles in a solvent to obtain a precursor;
step 2, preparing a modified main power guide network structure: placing the main conducting network structure with the porous structure in an oxidation environment, and grafting a functional group to obtain a modified main conducting network structure;
step 3, filling: filling the precursor prepared in the step 1 into a modified main power transmission network structure;
step 4, closing the opening: placing the porous main electric network structure in a reducing atmosphere to promote functional groups grafted on the main electric network structure to react to generate strong bonding force, and sealing or partially sealing the pore structure in the porous main electric network structure;
and 5, coating and carbonizing the product obtained in the step 4 to obtain the finished silicon-carbon cathode material.
As an improvement of the preparation method of the silicon-carbon anode material, the surface of the primary particles in the step 1 is modified to be functionalized primary particles, and the functional groups are carboxyl or/and hydroxyl; the grafted functional group in the step 2 comprises at least one of carboxyl, hydroxyl, epoxy, carbonyl, nitro and amino; and 4, adding a reducing agent or/and performing direct hydrothermal reduction on the reducing environment.
As an improvement of the preparation method of the silicon-carbon negative electrode material, polymer monomers can be added in the step 1, namely, the primary particles and the polymer monomers are mixed and kneaded to obtain a precursor in which the polymer monomers are uniformly dispersed on the surfaces of the primary particles; in this case, it is necessary to perform a polymerization reaction after step 3, in which the product of step 3 is placed in an environment where an initiator is present to promote polymerization of the polymer monomer dispersed on the surface of the primary particles, thereby obtaining a high molecular polymer.
As an improvement of the preparation method of the silicon-carbon anode material, the nano primary particles in the step 1 comprise nano silicon-based particles; the nano primary particles can also comprise non-nano silicon-based negative electrode particles; during kneading reaction, high molecular polymer, carbon source component, conductive agent component and solvent component can be added; in step 1, the kneading process is as follows: kneading the nano primary particles, the silane coupling agent, the polymer monomer and the solvent 1 to obtain a mixture 1; kneading the conductive agent component, the surfactant and the solvent 2 to obtain a mixture 2; and then blending the mixture 1 and the mixture 2, and uniformly dispersing to obtain precursor slurry.
As an improvement of the preparation method of the silicon-carbon anode material, the filling process in the step 3 is as follows:
pretreating the porous main conducting network structure material, wherein the pretreatment comprises surface activation or/and surfactant addition;
before filling, placing the porous main conducting network structure material in a vacuum environment, vacuumizing, removing air in a pore structure, vacating a space for filling a precursor, and then placing the porous main conducting network structure material in precursor slurry to start filling;
in the filling process, pressure is applied to extrude the precursor into the hole; the temperature is increased, and the viscosity of the precursor is reduced; and (5) adding mechanical disturbance and opening the hole opening.
As an improvement of the preparation method of the silicon-carbon negative electrode material, in the step 1, the polymer monomer comprises acrylates, methacrylates, styrene, acrylonitrile, methacrylonitrile, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, trimethylolpropane trimethacrylate, methyl methacrylate, N-dimethylacrylamide, N-acryloyl morpholine, methyl acrylate, ethyl acrylate, butyl acrylate, hexyl N-acrylate, cyclohexyl 2-acrylate, dodecyl acrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, neopentyl glycol diacrylate, 1, 6-hexanediol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, ethylene glycol diacrylate, propylene glycol diacrylate, ethylene, At least one of ethoxylated pentaerythritol tetraacrylate, propoxylated pentaerythritol acrylate, bis-trihydroxypropane tetraacrylate, pentaerythritol triacrylate, trimethylolpropane trimethacrylate, propoxylated glycerol triacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate; and 4, at least one of initiator cumene hydroperoxide, tert-butyl hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, dibenzoyl peroxide, lauroyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate.
As an improvement of the preparation method of the silicon-carbon anode material, the nano primary particles in the step 1 comprise nano silicon-based particles; the nano primary particles can also comprise non-nano silicon-based negative electrode particles, and the non-nano silicon-based negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, pyrolytic resin carbon, lithium carbonate, a tin-based negative electrode material, transition metal nitride, a tin-based alloy, a germanium-based alloy, an aluminum-based alloy, an antimony-based alloy and a magnesium-based alloy; during the kneading reaction, a high molecular polymer, a carbon source component, a conductive agent component or/and a solvent component can be added, wherein the high molecular polymer comprises at least one of polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC) and polyacrylonitrile, the carbon source component comprises glucose, sucrose, soluble starch, cyclodextrin, furfural, sucrose, glucose, corn starch, tapioca starch, wheat starch, cellulose, polyvinyl alcohol, polyethylene glycol, polyethylene wax, phenolic resin, vinyl pyrrolidone, epoxy resin, polyvinyl chloride, polyalditol, furan resin, urea-formaldehyde resin, polymethyl methacrylate, polyvinylidene fluoride or polyacrylonitrile, petroleum coke, oil-based needle coke and coal-based needle coke, and the conductive agent component comprises at least one of conductive carbon black, conductive carbon, conductive agent component or/and solvent component, At least one of super conductive carbon, Ketjen black, carbon nanotubes, graphene and acetylene black, and at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran.
As an improvement of the preparation method of the silicon-carbon cathode material, the preparation process of the main power conducting network structure in the step 2 comprises the following steps: preparing an open graphene structure, an open expanded graphite structure and a vermicular graphene structure: the preparation method comprises the following steps of taking crystalline flake graphite or microcrystalline graphite (vermicular graphene can be prepared, graphene lamella are connected together tightly, developed gap structures are distributed among the lamellae, and primary particles can be conveniently filled, meanwhile, the particle size of the microcrystalline graphene is small, the particle size of the prepared vermicular graphene is about 10 mu m and is matched with the diameter of a final finished silicon carbon cathode particle), controlling the degree of oxidation intercalation (mainly moderate in degree of oxidation, too low in degree of oxidation and incapable of forming a porous structure), completely stripping the graphite lamellae in the reduction process, and incapable of forming a connected porous structure), and then carrying out heat treatment and expansion to obtain the porous structure with the openings between the lamellae connected together and the same graphite; then, functional groups are grafted in an oxidizing environment to obtain the modified main conducting network structure
As an improvement of the preparation method of the silicon-carbon negative electrode material, the silane coupling agent is at least one of alkyl silane coupling agent, amino silane coupling agent, alkenyl silane coupling agent, epoxy alkyl silane coupling agent and alkyl acryloxy silane coupling agent; the solvent 1 is at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran. The surfactant is at least one of a wetting agent, a dispersing agent, a penetrating agent, a solubilizer, a cosolvent and a latent solvent; the solvent 2 is at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran.
The invention has the advantages that:
1. the modified main electric conduction network structure and the modified primary particles have similar functional groups, so that a precursor formed by the primary particles can enter the pore structure of the main electric conduction network more conveniently; the full filling of the pore structure is realized, and the specific gravity of the primary particles in the silicon-carbon composite material is improved;
2. the strong bonding acting force between the inner sheet layers of the main power grid structure can effectively seal primary particles in the main power grid structure, and the primary particles can not be separated from the main power grid structure in the charging and discharging process; meanwhile, the stability of the structure of the main power network structure can be ensured due to the strong bonding force, so that the main power network structure can not collapse in the circulating process;
3. the auxiliary conducting network structure tightly connects the main conducting network structure with the primary particles, so that all the primary particles can be effectively and tightly connected with the main conducting network structure in the reciprocating expansion and contraction process of the charge and discharge volume to form an electronic channel; thereby ensuring that the electrochemical performance of each primary particle can be fully exerted in the circulating process;
4. in the preparation process, the polymer monomer with low viscosity and the primary nano-particles are kneaded and dispersed, so that the uniform dispersion of the primary nano-particles can be ensured, and the polymer monomer is uniformly distributed on the surfaces of the primary nano-particles;
5. the precursor with lower viscosity (because the viscosity of the polymer monomer is low) is easier to fill into the pore structure of the main conducting network, and the pores of the porous structure of the main conducting network are all filled with the primary nanoparticles.
Detailed Description
The present invention and its advantageous effects will be described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.
Comparative example, a silicon carbon secondary particulate material having a particle diameter of 10 μm was prepared;
step 1, mixing: elemental silicon with the particle size of 100nm, polymethyl methacrylate, conductive carbon black, tetraethoxysilane, polyvinylpyrrolidone and NMP (solid content is 0.5%) are mixed and stirred for 10 hours to obtain slurry, wherein the mass ratio of the elemental silicon to the polymethyl methacrylate to the conductive carbon black to the tetraethoxysilane to the polyvinylpyrrolidone is 90:4:4.9:1: 0.1.
Step 2, preparing secondary particles: adjusting the spray drying condition to prepare the silicon-carbon secondary particles with the particle diameter of 10 mu m; and then coating and carbonizing to obtain the finished product of the silicon-carbon cathode material.
Example 1 is different from the comparative example in that the present example includes the following steps:
step 1, precursor preparation: mixing simple substance silicon with the particle size of 100nm, methyl methacrylate, tetraethoxysilane (the mass ratio of the simple substance silicon to the methyl methacrylate to the tetraethoxysilane is 95:4:1) and NMP, kneading the mixture (the solid content is 10 percent), wherein the revolution is 30 revolutions per minute, and the rotation is 300 revolutions per minute; kneading for 4h to obtain a precursor with uniformly dispersed simple substance silicon, methyl methacrylate and tetraethoxysilane;
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 1% of functional groups for later use;
step 3, filling: vacuumizing the modified vermicular graphene obtained in the step 2, then placing the modified vermicular graphene in the precursor obtained in the step 1, applying pressure to the precursor, simultaneously performing ultrasonic oscillation to enable the precursor to be filled into the pore structure of the vermicular graphene, and separating to obtain the modified vermicular graphene filled with the precursor;
step 4, polymerization reaction: dissolving tert-butyl peroxybenzoate in NMP to obtain a solution, spraying the solution on the surface of the modified vermicular graphene filled with the precursor obtained in the step (3), and heating to promote the polymerization of methyl methacrylate dispersed on the surface of the simple substance silicon particles, so that the simple substance silicon particles and the modified vermicular graphene sheet layer are tightly bonded together;
step 5, closing the opening: carrying out solvothermal reaction on the product obtained in the step (4), promoting functional groups grafted on vermicular graphene sheet layers (between adjacent sheet layers) to react, generating new chemical bonds, and sealing the openings of the vermicular graphene sheet layers;
and 6, coating and carbonizing the product obtained in the step 5 (and carbonizing the coating layer and the polymer at the same time) to obtain the finished silicon-carbon cathode material.
Embodiment 2 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 5% of functional groups for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 3 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 15% of functional groups for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 4 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 20% of functional groups for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 5 differs from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 25% of functional groups for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 6 differs from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 40% of functional groups for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 7 is different from embodiment 1 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing modified simple substance silicon (surface hydroxylation) with the particle size of 100nm and NMP (solid content is 10%) and kneading, wherein the revolution is 30 revolutions per minute, and the rotation is 300 revolutions per minute; kneading for 4h to obtain precursor slurry with uniformly dispersed nano simple substance silicon;
step 2, preparing a main conducting network structure of the modified vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide, and performing heat treatment to obtain vermicular graphene; putting the vermicular graphene into a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the vermicular graphene to obtain modified vermicular graphene grafted with 20% of functional groups for later use;
step 3, filling: vacuumizing the modified vermicular graphene obtained in the step 2, then placing the modified vermicular graphene in the precursor obtained in the step 1, applying pressure to the precursor, simultaneously performing ultrasonic oscillation to enable the precursor to be filled into a vermicular graphene pore structure, and separating to obtain the modified vermicular graphene filled with the precursor;
step 4, closing the opening: carrying out solvothermal reaction on the product obtained in the step (3) to promote functional groups grafted on the vermicular graphene sheet layers (between adjacent sheet layers) to react to generate new chemical bonds, and sealing the openings of the vermicular graphene sheet layers;
and 5, coating and carbonizing the product obtained in the step 4 (and carbonizing the coating layer and the polymer at the same time) to obtain the finished silicon-carbon cathode material.
The rest is the same as the embodiment 1, and the description is omitted.
Embodiment 8 differs from embodiment 1 in that this embodiment includes the following steps:
step 1, kneading: mixing 100 nm-sized silica + artificial graphite (silica: artificial graphite in a mass ratio of 1: 9), methyl methacrylate, methyl vinyldimethoxysilane (methyl methacrylate: methylvinyldimethoxysilane: 90:4:1) and ethanol (with a solid content of 10%), kneading the mixture, revolving the mixture at 5 revolutions per minute and rotating the mixture at 10 revolutions per minute; kneading for 8h to obtain a mixture 1; mixing methyl vinyl dimethoxysilane, graphene, polyoxyethylene alkylphenol ether (mass ratio of methyl vinyl dimethoxysilane to graphene: polyoxyethylene alkylphenol ether is 5:4.9:0.1) and ethanol, kneading (solid content is 4%), revolving for 5 revolutions/min, and rotating for 10 revolutions/min; kneading for 8h to obtain a mixture 2; mixing the mixture 1 and the mixture 2 (the mass ratio is (silicon monoxide + artificial graphite): graphene is 90:4.9), kneading continuously, revolving for 5 revolutions/min, and rotating for 10 revolutions/min; kneading for 6h to obtain a precursor in which the polymer monomer is uniformly coated on the surface of the primary particles (silicon monoxide and artificial graphite), the polymer monomer and the graphene are uniformly dispersed, and the graphene and the primary particles are uniformly dispersed;
step 2, preparing the main conducting network structure of the modified expanded graphite: flake graphite is selected as a raw material, then concentrated sulfuric acid and potassium permanganate are added for oxidation intercalation to obtain graphite oxide, and then heat treatment is carried out to obtain expanded graphite; placing the expanded graphite in a mixture of concentrated sulfuric acid, potassium permanganate and sodium nitrate to modify the expanded graphite to obtain a modified expanded graphite main power grid structure grafted with 20% of functional groups for later use;
step 3, filling: vacuumizing the main conductive network structure of the modified expanded graphite obtained in the step (2), then placing the vacuumized main conductive network structure of the modified expanded graphite in the precursor obtained in the step (1), applying pressure to the precursor, simultaneously performing ultrasonic oscillation to enable the precursor to be filled into the main conductive network structure of the modified expanded graphite, and separating to obtain the main conductive network structure of the modified expanded graphite filled with the precursor;
step 4, polymerization reaction: dissolving tert-butyl peroxybenzoate in NMP to obtain a solution, spraying the solution on the surface of the modified expanded graphite filled with the precursor obtained in the step (3), and heating to promote the polymerization of methyl methacrylate dispersed on the surface of the primary particles, so that the primary particles and the modified expanded graphite sheet are tightly bonded together;
step 5, closing the opening: adding a reducing agent into the product obtained in the step (4) to promote functional groups grafted on the modified expanded graphite sheet layers (between the adjacent sheet layers) to react to generate new chemical bonds, and sealing the openings of the modified expanded graphite sheet layers;
the rest is the same as the embodiment 1, and the description is omitted.
Assembling the battery: stirring the silicon-carbon negative electrode material prepared in comparative example, example 1 to example 10 with a conductive agent, a binder and a solvent to obtain electrode slurry, and then coating the electrode slurry on a current collector to form a negative electrode; assembling the negative electrode, the positive electrode (lithium cobaltate is used as an active substance) and the isolating membrane to obtain a bare cell, and then bagging to perform top side sealing, drying, liquid injection, standing, formation, shaping and degassing to obtain a finished battery.
And (3) testing the material performance:
and (3) gram capacity test: the gram capacity test of the battery cores prepared from the silicon-carbon materials of the examples and the comparative examples is carried out in an environment at 25 ℃ according to the following flow: standing for 3 min; charging to 4.2V by a constant current of 0.2C and charging to 0.05C by a constant voltage of 4.2V; standing for 3 min; discharging to 3.0V at constant current of 0.2C to obtain discharge capacity D1; standing for 3 min; discharging to 3.85V at constant current of 0.2C; and (3) standing for 3min, then completing the capacity test, and dividing the weight of the silicon-carbon material in the negative electrode plate by D1 to obtain the gram capacity of the negative electrode, wherein the obtained result is shown in Table 1.
And (3) rate performance test: the rate performance of the battery cells prepared from the silicon-carbon materials of the examples and the comparative examples is tested in an environment at 25 ℃ according to the following procedures: standing for 3 min; charging to 4.2V by a constant current of 0.2C and charging to 0.05C by a constant voltage of 4.2V; standing for 3 min; discharging to 3.0V at constant current of 0.2C to obtain discharge capacity D1; standing for 3 min; charging to 4.2V by a constant current of 0.2C and charging to 0.05C by a constant voltage of 4.2V; standing for 3 min; discharging the 2C to 3.0V at constant current to obtain discharge capacity D21; standing for 3 min; rate performance testing was then completed and the cell rate performance was D2/D1 x 100% with the results shown in table 1.
And (3) cycle test, namely, performing cycle test on the battery cells prepared from the silicon-carbon materials of the examples and the comparative examples in an environment at 25 ℃ according to the following flow: standing for 3 min; charging to 4.2V by a constant current of 0.2C and charging to 0.05C by a constant voltage of 4.2V; standing for 3 min; discharging to 3.0V at constant current of 0.2C to obtain discharge capacity D1; standing for 3min, charging to 4.2V at constant current of 0.2C and charging to 0.05C at constant voltage of 4.2V; standing for 3 min; discharging to 3.0V at constant current of 0.2C to obtain discharge capacity Di; standing for 3min "and repeating 299 times to obtain D300, then completing the cycle test, and calculating the capacity retention rate to be D300/D1 × 100%, and obtaining the results shown in Table 1.
TABLE 1 electrochemical performance of assembled cells made of silicon carbon negative electrode materials prepared in different comparative examples and examples
From table 1, the silicon-carbon negative electrode material with excellent performance can be prepared, and the battery cell assembled by taking the silicon-carbon negative electrode material as the negative electrode active material has excellent electrochemical performance. Specifically, comparing the comparative example with examples 1 to 6, it can be seen that, with the increase of the oxygen-containing functional group on the modified main conducting network structure sheet layer, the material capacity is firstly kept unchanged and then sharply decayed, the cycle performance is firstly gradually improved and then kept unchanged, and the rate performance is firstly kept unchanged and then sharply decayed; the reason for this is that when the oxygen-containing functional group is too small, the closed-end reaction occurs only in a very small amount, and thus the effective main electric network structure stabilization effect cannot be achieved; when the oxygen-containing functional groups are too many and a closed reaction occurs, more openings of the porous structure are closed until the openings are blocked, so that the transmission of ions is influenced; resulting in a decay of the dynamic properties of the material. The present invention has general applicability as can be seen from the various embodiments.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (7)
1. A silicon-carbon anode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conducting network with a porous structure and nano primary particles filled in the pore structure of the main electric conducting network; stronger bonding force action exists between the main power supply networks; and tightly locking the nano-sized primary particles in the pore structure of the main conducting network by the bonding force;
the category of bonds providing strong bonding forces are hydrogen bonds or/and chemical bonds;
the preparation method mainly comprises the following steps:
step 1, precursor preparation: uniformly dispersing the primary particles in a solvent to obtain a precursor;
step 2, preparing a modified main power guide network structure: placing the main conducting network structure with the porous structure in an oxidation environment, and grafting a functional group to obtain a modified main conducting network structure;
step 3, filling: filling the precursor prepared in the step 1 into a modified main power transmission network structure;
step 4, closing the opening: placing the porous main electric network structure in a reducing atmosphere to promote functional groups grafted on the main electric network structure to react to generate strong bonding force, and sealing or partially sealing the pore structure in the porous main electric network structure;
step 5, coating and carbonizing the product obtained in the step 4 to obtain a finished product of the silicon-carbon cathode material;
modifying the surface of the primary particles in the step 1 to form functionalized primary particles, wherein the functional groups are carboxyl or/and hydroxyl;
the main electric conducting network is at least one of an open graphene structure, an open expanded graphite structure and a vermicular graphene structure;
the grafted functional group in the step 2 comprises at least one of carboxyl, hydroxyl, epoxy, carbonyl and nitro; and 4, adding a reducing agent or/and performing direct hydrothermal reduction on the reducing environment.
2. The silicon-carbon negative electrode material as claimed in claim 1, wherein the mass of the oxygen-containing functional group constituting the hydrogen bond or/and the chemical bond is 1 to 40% of the mass of the entire main electric network.
3. The silicon-carbon negative electrode material as claimed in claim 1, wherein the main conductive network has flexibility, and the main conductive network contains functional groups inside; the hydrogen bonds or/and chemical bonds result from the reaction of oxygen-containing functional groups within the main conducting network.
4. The silicon-carbon anode material of claim 1, wherein the nano primary particles comprise nano silicon-based anode particles; and an auxiliary electric conduction network is also distributed between the main electric conduction network and the primary particles and tightly connects the main electric conduction network and the nano primary particles together.
5. The silicon-carbon anode material as claimed in claim 4, wherein the nano silicon-based anode particles are nano silicon particles or/and nano silicon oxide particles; the primary particles further comprise non-nano silicon-based negative electrode particles; the non-nano silicon-based negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, pyrolytic resin carbon, lithium carbonate, a tin-based negative electrode material, transition metal nitride, a germanium-based alloy, an aluminum-based alloy, an antimony-based alloy and a magnesium-based alloy; the auxiliary conducting network is obtained by carbonizing a high polymer material; the high polymer material is obtained by in-situ polymerization of a high polymer monomer; the auxiliary conducting network further comprises at least one of conductive carbon black, super conductive carbon, Ketjen black, carbon nanotubes, graphene and acetylene black.
6. The silicon-carbon negative electrode material as claimed in claim 1, wherein a polymer monomer is further added in the step 1, i.e. the primary particles and the polymer monomer are mixed and kneaded to obtain a precursor in which the polymer monomer is uniformly dispersed on the surface of the nano primary particles; in this case, it is necessary to perform a polymerization reaction after step 3, in which the product of step 3 is placed in an environment where an initiator is present to promote polymerization of the polymer monomer dispersed on the surface of the primary particles, thereby obtaining a high molecular polymer.
7. The silicon-carbon negative electrode material as claimed in claim 1, wherein the filling process in step 3 is:
pretreating the porous main conducting network structure material, wherein the pretreatment comprises surface activation or/and surfactant addition;
before filling, placing the porous main conducting network structure material in a vacuum environment for vacuumizing, discharging air in a hole structure to make space for filling a precursor, and then placing the porous main conducting network structure material in precursor slurry for starting filling;
in the filling process, pressure is applied to extrude the precursor into the hole; the temperature is increased, and the viscosity of the precursor is reduced; and (5) adding mechanical disturbance and opening the hole opening.
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