CN114914444A - Silicon-carbon negative electrode plate, preparation method thereof and lithium ion battery - Google Patents

Silicon-carbon negative electrode plate, preparation method thereof and lithium ion battery Download PDF

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CN114914444A
CN114914444A CN202110184727.XA CN202110184727A CN114914444A CN 114914444 A CN114914444 A CN 114914444A CN 202110184727 A CN202110184727 A CN 202110184727A CN 114914444 A CN114914444 A CN 114914444A
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silicon
conductive agent
binder
mixed solution
particles
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涂志强
林伟国
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Sinopec Research Institute of Petroleum Processing
China Petroleum and Chemical Corp
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Sinopec Research Institute of Petroleum Processing
China Petroleum and Chemical Corp
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
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Abstract

The invention provides a silicon-carbon negative pole piece, a preparation method thereof and a lithium ion battery, wherein the preparation method comprises the following steps: dispersing a first conductive agent in a dispersant solution to obtain a first mixed solution; mixing the active particles, a first binder and a second conductive agent to obtain first particles; placing the first particles and the second binder in the first mixed solution to obtain a second mixed solution; coating the second mixed solution and graphite on a current collector after mixing to obtain a silicon-carbon negative pole piece; the first conductive agent is a linear conductive agent and/or a planar conductive agent, and the second conductive agent is a linear conductive agent. The preparation method provided by the invention has the advantages that the long-period cycling stability of the obtained silicon-carbon negative pole piece is obviously improved, the structure of the silicon-carbon negative pole piece is stable, the service life of the silicon-carbon negative pole piece is long, the silicon-carbon negative pole piece is applied to a lithium ion battery, the battery performance can be effectively improved, and the preparation method has a good application prospect.

Description

Silicon-carbon negative electrode plate, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a silicon-carbon negative electrode plate, a preparation method thereof and a lithium ion battery.
Background
The lithium ion battery is a recyclable energy storage device, also called as a lithium ion secondary battery, and mainly comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte system. Such batteries are characterized by high energy density, no memory effect and low self-discharge compared to other primary batteries. The current commercialized negative electrode material is graphite, and the theoretical specific capacity is 372mAh g -1 The demand for high energy density batteries has not been satisfied, and therefore, development of a high-capacity anode active material is urgently required.
Silicon has high theoretical specific capacity (4200mA h g) -1 ) The characteristics of low working voltage and the like cause extensive research of people, the silicon-based lithium ion battery has abundant reserves in the earth crust, low cost and environmental friendliness, is one of the most potential next-generation lithium ion battery cathode materials, but silicon generates huge volume expansion in the charge and discharge processes to seriously influence the cycle performance and the service life of the battery. The surface modification of the silicon particles is often carried out by various means, and then the silicon particles are mixed with graphite to obtain the silicon-carbon composite particles, so that the expansion of the silicon-carbon composite particles can be effectively relieved. However, in the cycle process, the stability of the pole piece is related to active materials, and the preparation process of the pole piece is also particularly important, otherwise the expansion and cycle performance of the silicon-carbon negative electrode are influenced.
CN209104267U adopts graphite buffer layer and graphite alkene protective layer in order to promote pole piece stability, and the graphite buffer layer can absorb and release silicon among the silicon carbon material in the produced stress of volume expansion in the charge-discharge process, prevents pulverization and the drop of silicon carbon active layer to graphite itself is as lithium ion battery negative pole material. CN102891290B also uses graphene to alleviate the expansion of silicon-based particles. However, graphene is not easily dispersed, and conductivity is again reduced after modification.
CN107275572A discloses a novel negative electrode plate, the surface of the negative electrode current collector is coated with a layer of negative electrode ceramic layer, the negative electrode ceramic is at least one of magnesium oxide, zirconium oxide, titanium dioxide, iridium oxide and aluminum oxide, the thickness is 3 μm-5 μm, the ceramic diaphragm adopted by the novel negative electrode plate and the negative electrode plate coated with the ceramic layer both have high temperature resistance, and the safety and the thermal stability of the lithium ion battery can be improved. However, the addition of the oxide may cause a decrease in the conductive performance of the current collector.
CN107768595A adopts the method of ion sputtering, vacuum evaporation, chemical growth or physical coating to generate the film state solid electrolyte layer on the surface of the electrode slice containing the negative active material, to obtain the negative electrode slice of the lithium ion battery, the negative electrode slice of the lithium ion battery has stable structure and long service life, wide and stable electrochemical window, the lithium ion battery containing the negative electrode slice of the lithium ion battery has the advantages of long storage and cycle life, unaffected basic electrochemical performance and the like. However, the technology has high operation difficulty, and the thickness of the solid electrolyte layer is not easy to control.
It is noted that the information disclosed in the foregoing background section is only for enhancement of background understanding of the invention and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.
Disclosure of Invention
The invention mainly aims to overcome at least one defect in the prior art, and provides a silicon-carbon negative electrode plate, a preparation method thereof and a lithium ion battery, so as to solve the problems of low stability, poor cycle performance, short service life and the like of the conventional silicon-carbon negative electrode plate.
In order to achieve the purpose, the invention adopts the following technical scheme:
the first aspect of the invention provides a preparation method of a silicon-carbon negative pole piece, which comprises the following steps: dispersing a first conductive agent in a dispersant solution to obtain a first mixed solution; mixing the active particles, a first binder and a second conductive agent to obtain first particles; placing the first particles and the second binder in the first mixed solution to obtain a second mixed solution; coating the second mixed solution and graphite on a current collector after mixing to obtain a silicon-carbon negative pole piece; the first conductive agent is a linear conductive agent and/or a planar conductive agent, and the second conductive agent is a linear conductive agent.
According to an embodiment of the present invention, the first conductive agent is selected from one or more of carbon nanotubes, carbon nanofibers, and graphene, and the second conductive agent is selected from one or more of carbon nanotubes, super-p, acetylene black, ketjen black, and carbon nanofibers.
According to one embodiment of the present invention, the first conductive agent is a water-soluble conductive agent, and the dispersant solution is a water-soluble polymer solution.
According to one embodiment of the present invention, the water-soluble polymer solution contains 1% to 10%, preferably 1% to 6%, by mass of the water-soluble polymer; the water soluble polymer is selected from one or more of sodium carboxymethylcellulose, hydroxyethyl cellulose, modified starch, sodium alginate, citric acid, polyacrylic acid, polyacrylamide, polyvinylpyrrolidone and polyvinyl alcohol.
According to an embodiment of the present invention, the first conductive agent accounts for 0.01% to 0.1%, preferably 0.02% to 0.06%, by mass of the first mixed solution; the dispersant solution accounts for 99.90-99.99% of the first mixed solution by mass, and preferably 99.94-99.98%.
According to one embodiment of the present invention, the first conductive agent is dispersed in the dispersant solution using a homogenizer or a shearer; when the shearing machine is adopted, the rotating speed of the shearing machine is 1000 rpm-2000 rpm, preferably 1500 rpm-1800 rpm, and the shearing time is 1 h-8 h, preferably 2h-4 h.
According to one embodiment of the invention, the active particles are a mixture of spheroidal graphite and silicon-based particles selected from the group consisting of nano-silicon and/or nano-silica SiO x Wherein 0 is<x<2; the mass ratio of the spherical graphite to the silicon-based particles is 1-4: 1, and preferably 1-2: 1.
According to one embodiment of the invention, the silicon-based particles are carbon-coated silicon-based particles, wherein the thickness of the carbon coating is between 2nm and 10 nm.
According to one embodiment of the present invention, the nano-silicon has a particle size of 20nm to 500nm, preferably 50nm to 150 nm; the nano silicon is pure nano silicon and/or surface oxidized nano silicon, the oxygen content of the surface oxidized nano silicon is less than 5%, the oxidation thickness is 1 nm-20 nm, and the preferred oxidation thickness is 1 nm-10 nm; nano silicon oxide SiO x Has a particle diameter of 10nm to 200nm, preferably 10nm to 100nm, wherein, preferably, 0.3<x<1.6。
According to one embodiment of the present invention, the first binder is a binder powder, and the binder powder is a hydrophilic polymer and/or an amphiphilic polymer; wherein the hydrophilic polymer is selected from one or more of sodium carboxymethylcellulose, hydroxyethyl cellulose, sodium alginate and polyacrylic acid; the amphiphilic polymer is formed by copolymerizing a hydrophilic section and a hydrophobic section, the hydrophilic section is selected from one or more of polyethylene glycol, polyvinyl alcohol, polyvinyl ether, polyvinylpyrrolidone, polyacrylic acid and polystyrene sulfonate, and the hydrophobic section is selected from one or more of polypropylene oxide, polymethyl methacrylate, polymethyl acrylate, polystyrene and polysiloxane.
According to an embodiment of the present invention, further comprising: mixing the active particles with a first binder to obtain active particles coated by the first binder; mixing the active particles wrapped by the first binder with a second conductive agent to obtain first particles; wherein the mass ratio of the first binder to the active particles is (15-2): 85-98, preferably (10-3): 90-97); the mass ratio of the second conductive agent to the active particles coated by the first binder is (1-20): 99-80, preferably (5-20): 80-95).
According to one embodiment of the present invention, the mixing of the first binder and the active particles, and/or the mixing of the second conductive agent and the active particles coated with the first binder is performed using a planetary ball mill or a powder mixer at a rotation speed of 100rpm to 500rpm for 1h to 12h, preferably 1h to 6 h.
According to one embodiment of the present invention, the second binder is a water-soluble binder emulsion, the water-soluble binder emulsion comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, polymethacrylic acid, sodium alginate and polytetrafluoroethylene, and the solid content of the water-soluble binder emulsion is 1 wt% to 60 wt%.
According to an embodiment of the present invention, further comprising: dispersing the first particles in the first mixed solution to obtain a third mixed solution; adding a second binder into the third mixed solution, and stirring to obtain a second mixed solution; wherein, the adding amount of the second binder accounts for 1-8% of the third mixed solution by mass, and preferably 1-4%.
According to one embodiment of the present invention, the first particles are dispersed in the first mixed solution by using a vacuum mixer at a rotation speed of 200rpm to 1000rpm for 2h to 12h, preferably 350rpm to 600rpm for 3h to 6 h; and adding the second binder into the third mixed solution by a vacuum stirrer for stirring at the rotating speed of 200-900 rpm for 1-10 h, preferably at 200-500 rpm for 1-3 h.
According to an embodiment of the present invention, the method further comprises adding graphite to the third mixed solution while stirring after adding the second binder; the mass ratio of the added amount of the graphite to the first particles is 0.5-4: 1, preferably 1-2: 1.
According to one embodiment of the present invention, the graphite is spherical graphite selected from one or more of spherical natural graphite, spherical artificial graphite and spherical carbon microspheres, and the spherical graphite has a tap density of 0.8g cm -3 ～1.1g cm -3 The median particle diameter is 10-25 μm.
The second aspect of the invention provides a silicon-carbon negative electrode plate which is prepared by the method.
The third aspect of the invention provides a lithium ion battery, which comprises a positive electrode and a negative electrode, wherein the negative electrode adopts the silicon-carbon negative electrode piece.
According to the technical scheme, the invention has the beneficial effects that:
according to the method for preparing the silicon-carbon negative pole piece, a specific process is adopted, and a specific binder and a specific conductive agent are selected, so that on one hand, the conductivity of a dispersing agent solution is enhanced, and the dried dispersing agent solution plays a role of a conductive network in the pole piece; on the other hand, the mode that the active particles are directly contacted with the conductive agent is changed, the surface cohesiveness of the active particles is improved by adding the binding powder and the like, the dispersion of the conductive agent on the surfaces of the particles is promoted, the dispersion of the conductive agent is further promoted, and the conductive resistance of the contact between the particles is reduced. The preparation method provided by the invention has the advantages that the long-period cycling stability of the obtained silicon-carbon negative pole piece is obviously improved, the structure of the silicon-carbon negative pole piece is stable, the service life of the silicon-carbon negative pole piece is long, the silicon-carbon negative pole piece is applied to a lithium ion battery, the battery performance can be effectively improved, and the preparation method has a good application prospect.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
Fig. 1 is a flow chart of a preparation process of a silicon-carbon negative electrode sheet according to an embodiment of the invention;
FIG. 2 is a scanning electron micrograph of the silicon carbon negative electrode sheet of example 1;
FIG. 3 is a scanning electron micrograph of graphene used in example 3;
FIG. 4 is a graph of cycle performance of lithium ion batteries prepared from the silicon-carbon negative electrode sheets of example 1 and comparative example 1;
fig. 5 is a graph of cycle performance of lithium ion batteries prepared from the silicon-carbon negative electrode sheets of example 2 and comparative example 2.
Detailed Description
The following presents various embodiments or examples in order to enable those skilled in the art to practice the invention with reference to the description herein. These are, of course, merely examples and are not intended to limit the invention. The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, combinations of values between the endpoints of each of the ranges, between the endpoints of each of the ranges and individual values, and between individual values can result in one or more new numerical ranges, and such numerical ranges should be considered as being specifically disclosed herein.
Fig. 1 is a flow chart of a preparation process of a silicon-carbon negative electrode sheet according to an embodiment of the present invention, and as shown in fig. 1, the present invention provides a preparation method of a silicon-carbon negative electrode sheet, including: dispersing a first conductive agent in a dispersant solution to obtain a first mixed solution; mixing the active particles, a first binder and a second conductive agent to obtain first particles; placing the first particles and the second binder in the first mixed solution to obtain a second mixed solution; coating the second mixed solution and graphite on a current collector after mixing to obtain a silicon-carbon negative pole piece; the first conductive agent is a linear conductive agent and/or a planar conductive agent, and the second conductive agent is a linear conductive agent.
According to the invention, the performance of the electrode material is improved by adopting a silicon-carbon compounding mode at present, however, the inventor of the invention finds that the stability of the pole piece is particularly important in the preparation process of the pole piece except that the stability of the pole piece is related to an active material in the circulation process, and otherwise, the expansion, the circulation performance and the like of the silicon-carbon negative electrode can be influenced. Therefore, the invention provides a novel preparation method of a silicon-carbon negative pole piece, which changes the mode that the traditional dispersant solution does not contain a conductive agent, and enhances the conductivity of the negative pole piece by adding the specific conductive agent, a binding agent and the like into the dispersant solution according to a specific sequence, and the negative pole piece plays a role of a conductive network after being dried; in addition, the invention changes the mode that the active particles are directly contacted with the conductive agent, and the bonding powder is added to improve the surface cohesiveness of the active particles, promote the dispersion of the conductive agent on the surfaces of the particles, further promote the dispersion of the conductive agent and reduce the conductive resistance of the contact between the particles. By adopting a specific process and selecting a specific conductive agent and a specific binder, the long-period cycling stability of the obtained silicon-carbon negative pole piece is obviously improved, and the silicon-carbon negative pole piece can effectively improve the performance of a battery when being applied to a lithium ion battery and has a good application prospect.
The following describes a method for preparing a silicon-carbon negative electrode sheet according to an embodiment of the present invention with reference to fig. 1.
First, a first conductive agent is dispersed in a dispersant solution to obtain a first mixed solution.
Specifically, the first conductive agent is a linear conductive agent and/or a planar conductive agent, wherein the linear conductive agent is preferably a carbon nanotube, a carbon nanofiber, or the like, or a combination thereof, and the planar conductive agent is preferably graphene. The dispersant solution is a water-soluble polymer solution, wherein the water-soluble polymer is one or more selected from sodium carboxymethylcellulose, hydroxyethyl cellulose, starch, sodium alginate, citric acid, polyacrylic acid, polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol and the like, and the solvent is pure water, and the mass fraction of the solvent is 1% to 10%, for example, 1%, 2%, 3%, 4%, 6%, 8%, 10% and the like, preferably 1% to 6%. By selecting the linear conductive agent and/or the planar conductive agent as the first conductive agent, a conductive network can be formed in the dispersant solution, thereby enhancing the conductivity of the dispersant solution.
Preferably, the carbon nanotube is a metal multi-wall carbon nanotube, the diameter of the tube bundle is 10 nm-100 nm, and the length of the tube bundle is 1 μm-50 μm. The graphene is preferably few-layer graphene, the thickness of a sheet layer is 3 to 10 layers, and the size of the sheet layer is 1 to 30 micrometers. In order to increase the conductivity of the dispersant solution, a linear conductive agent and a planar conductive agent can be mixed for use, and the first conductive agent can be a hydrophilic modified first conductive agent, namely a water-soluble conductive agent, so that the hydrophilicity is stronger, and the dispersibility of the first conductive agent in the solution is enhanced.
In some embodiments, the first conductive agent may be dispersed in the dispersant solution by using a homogenizer or a shearing machine to achieve uniform dispersion of the conductive agent. For example, when a shear is used, the rotation speed is 1000rpm to 2000rpm, and the time is 1h to 8h, preferably 1500rpm to 1800rpm, 2h to 4 h.
In some embodiments, the first conductive agent accounts for 0.01% to 0.1% by mass of the first mixed solution, for example, 0.01%, 0.02%, 0.05%, 0.06%, 0.08%, 0.1%, etc., preferably 0.02% to 0.06%; the dispersant solution accounts for 99.90-99.99% of the first mixed solution by mass, and preferably 99.94-99.98%.
Next, the active particles, the first binder, and the second conductive agent are mixed to obtain first particles. Of course, the first particles may be prepared first and then the first mixed solution may be prepared, and the present invention is not limited to the above preparation sequence.
Specifically, the active particles are a mixture of spherical graphite and silicon-based particles, the spherical graphite can be spherical natural graphite, spherical artificial graphite, etc., and the tap density of the spherical graphite is 0.8g cm -3 ～1.1g cm -3 The median particle diameter is 10-25 μm. The silicon-based particles are selected from nano silicon and/or nano silicon oxide SiO x Wherein 0 is<x<2, preferably 0.3<x<1.6. The mass ratio of the spherical graphite to the silicon-based particles is 1-4: 1, and preferably, the spherical graphite and the silicon-based particles are mixed according to the proportion of 1: 1. The grain diameter of the nano silicon is 20 nm-500 nm, preferably 50 nm-150 nm; the nano silicon is pure nano silicon and/or surface oxidized nano silicon, the oxygen content of the surface oxidized nano silicon is less than 5%, the oxidation thickness is 1 nm-20 nm, and the preferred oxidation thickness is 1 nm-10 nm; nano silicon oxide SiO x The particle diameter of (A) is 10 to 200nm, preferably 10 to 100 nm.
In some embodiments, the aforementioned silicon-based particles are preferably carbon-coated silicon-based particles, wherein the carbon coating has a thickness of 2nm to 10 nm. The carbon coating method can be vapor deposition, thermal cracking, etc.
The first binder is bonding powder, and the bonding powder is hydrophilic polymer and/or amphiphilic polymer; wherein the hydrophilic polymer is selected from one or more of sodium carboxymethylcellulose, hydroxyethyl cellulose, sodium alginate and polyacrylic acid; the amphiphilic polymer is formed by copolymerizing a hydrophilic section and a hydrophobic section, wherein the hydrophilic section is selected from one or more of polyethylene glycol, polyvinyl alcohol, polyvinyl ether, polyvinylpyrrolidone, polyacrylic acid and polystyrene sulfonate, and the hydrophobic section is selected from one or more of polypropylene oxide, polymethyl methacrylate, polymethyl acrylate, polystyrene and polysiloxane.
The second conductive agent is a linear conductive agent, and is preferably one or more of carbon nanotubes, super-p, acetylene black, ketjen black, and carbon nanofibers. The second conductive agent and the bonding powder are mixed with the active particles, so that the mode that the active particles are directly contacted with the conductive agent can be changed, the bonding powder is utilized to improve the surface cohesiveness of the active particles, promote the dispersion of the second conductive agent on the surfaces of the particles and further promote the dispersion of the second conductive agent, meanwhile, the second conductive agent is a linear conductive agent, a fibrous conductive network can be formed, the conductive resistance of the contact between the particles can be reduced, and the expansion of silicon particles can be reduced.
In some embodiments, further comprising: mixing the active particles with a first binder to obtain active particles coated by the first binder; mixing the active particles wrapped by the first binder with a second conductive agent to obtain first particles; wherein the mass ratio of the first binder to the active particles is (15-2) to (85-98), preferably (10-3) to (90-97); the mass ratio of the second conductive agent to the active particles coated by the first binder is (1-20): 99-80, preferably (5-20): 80-95).
Preferably, the mixing of the first binder and the active particles and the mixing of the second conductive agent and the active particles coated with the first binder may be performed using a planetary ball mill or a powder mixer at a rotation speed of 100rpm to 500rpm for 1h to 12h, preferably 1h to 6 h. Preferably a planetary ball mill, with a rotation speed of 200rpm to 350rpm for 1h to 6 h.
Further, the obtained first particles and the second binder are placed in the prepared first mixed solution to obtain a second mixed solution.
Specifically, the second binder is a water-soluble binder emulsion, i.e., in a water-soluble emulsion state, the water-soluble binder emulsion includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polymethacrylic acid, sodium alginate and polytetrafluoroethylene, preferably polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber emulsion or a combination thereof, and the solid content of the water-soluble binder emulsion is 1 wt% to 60 wt%, for example, 1 wt%, 5 wt%, 10 wt%, 20 wt%, 25 wt%, 40 wt%, or the like.
In some embodiments, further comprising: dispersing the first particles in the first mixed solution to obtain a third mixed solution; adding a second binder into the third mixed solution, and stirring to obtain a second mixed solution; the solid content of the second binder is 1% to 8% of the third mixed solution, for example, 1%, 3%, 4%, 5%, 6%, 8%, etc., preferably 1% to 4%.
Preferably, the first particles are dispersed in the first mixed solution, and a vacuum stirrer may be used, at a rotation speed of 200rpm to 1000rpm, for example, 200rpm, 300rpm, 500rpm, 600rpm, etc., for a mixing time of 2h to 12h, preferably 350rpm to 600rpm, for a time of 3h to 6 h. Preferably, after the second binder is added to the third mixed solution, a vacuum mixer is also used, the rotation speed is 200rpm to 900rpm, for example, 200rpm, 300rpm, 500rpm, 600rpm, etc., and the mixing time is 1h to 10h, preferably 200h to 500rpm, for 1h to 3 h.
And finally, mixing the prepared second mixed solution with graphite and then coating the mixture on a current collector to obtain the silicon-carbon negative pole piece.
Preferably, after the second binder is added to the third mixed solution, graphite is added and mixed during the stirring process, for example, when the mixing time is half; the mass ratio of the added amount of the graphite to the first particles is 0.5-4: 1, preferably 1-2: 1.
The graphite is preferably spherical graphite, the spherical graphite is selected from one or more of spherical natural graphite, spherical artificial graphite and spherical carbon microspheres, and the tap density of the spherical graphite is 0.8g cm -3 ～1.1g cm -3 The median particle diameter is 10-25 μm. Preferably, the graphite used here is the same graphite as that used in the active particles, although a different graphite may be used, and the present invention is not limited thereto.
In conclusion, the invention provides a novel method for preparing a silicon-carbon negative pole piece, which adopts a specific process and a selected specific binder and conductive agent, so that on one hand, the conductivity of a dispersant solution is enhanced, and the dispersant solution can play a role of a conductive network in the pole piece after being dried; on the other hand, the mode that the active particles are directly contacted with the conductive agent is changed, the surface cohesiveness of the active particles is improved by adding the binding powder and the like, the dispersion of the conductive agent on the surfaces of the particles is promoted, the dispersion of the conductive agent is further promoted, and the conductive resistance of the contact between the particles is reduced. The preparation method provided by the invention can obviously improve the long-period cycling stability of the obtained silicon-carbon negative pole piece, can effectively improve the battery performance when being applied to a lithium ion battery, and has a good application prospect.
The invention will be further illustrated by the following examples, but is not to be construed as being limited thereto. Unless otherwise specified, the reagents, materials and the like used in the present invention are commercially available.
In the following examples, all the dispersion solutions used were carboxymethylcellulose sodium (CMC) hydrosol with a mass percentage of 1.5 wt%, and the second binder used was SBR emulsion, which was a ZOEN BM-451B type emulsion with a mass percentage of 40 wt%, diluted 4 times for use. The active particles are lower fine particles obtained by screening through a standard sieve with 325 meshes.
The morphology of the active particle material and the morphology of the various silicon-carbon composite materials prepared in the examples were observed by a scanning electron microscope (Hitachi SU8010, 3 kV).
Example 1
(1) 0.02g of Carbon Nano Tube (CNT) is dispersed in 99.98g of CMC (carboxymethyl cellulose) glue solution by a paddle stirrer to obtain a first mixed solution, wherein the CMC hydrosol is colorless clear colloid and has the mass fraction of 1.5 wt%.
(2) Mixing nano silicon with the particle size of about 100nm with asphalt according to the mass ratio of 10:1, and then carrying out thermal cracking carbonization for 3h at 600 ℃ in the argon atmosphere to obtain the carbon-coated nano silicon.
(3) Spherical artificial graphite (fibrate-resiqui series) and the carbon-coated nano-silicon prepared in (2) were mixed in a ratio of 1:1 to form 20g of active particles, mixed and coated with CMC as a binder powder in a ratio of 95:5, and the coated particles were mixed with super-p in a ratio of 85:15 to obtain 24.7g of first particles.
(4) 24.7g of the first granules were dispersed in 100g of the first mixed solution using a vacuum stirrer at 500rpm for 4 hours.
(5) And (3) adding 5g of SBR emulsion (with the solid content of 40%) into the solution obtained in the step (4) and stirring to obtain a second mixed solution, wherein the solid content of the SBR emulsion accounts for 2% of the second mixed solution by mass, and mixing the second mixed solution with 72.5g of spherical graphite.
(6) And (3) coating the slurry obtained in the step (5) on a current collector, wherein the current collector is a carbon-sprayed copper current collector, after the slurry is coated on the current collector, the pole piece is firstly dried in a drying oven for about 10 minutes, and after the drying is finished, the pole piece is dried in a vacuum oven at 90 ℃ for 10 hours. And after finishing, rolling to obtain the silicon-carbon negative pole piece.
Fig. 2 is a scanning electron microscope image of the silicon-carbon negative electrode plate of example 1, and it can be seen from fig. 2 that most of the silicon-carbon particles are tens of microns, and the nano-silicon is relatively uniformly distributed around the graphite.
Example 2
The silicon-carbon negative electrode plate is prepared by the method and the raw materials of the embodiment 1, except that the carbon-coated nano silicon oxide is adopted in the step (2), wherein the nano silicon oxide SiO is 2 Has a particle diameter of about 80 nm.
Example 3
The method and the raw materials in example 1 are adopted to prepare the silicon-carbon negative electrode piece, except that graphene is adopted to replace carbon nanotubes in the step (1), fig. 3 is a scanning electron microscope image of the graphene used in example 3, and as shown in fig. 3, the graphene has a thickness of about 4 layers and a size of about 10 micrometers.
Example 4
The method and the raw materials of example 1 are used to prepare a silicon-carbon negative electrode piece, except that in step (4), 4.0g of SBR emulsion (with a solid content of 40%) and 6.7g of PAA emulsion (with a solid content of 6%) are added to the solution obtained in step (3) and stirred to obtain a second mixed solution, wherein the total solid content of the SBR emulsion and the PAA emulsion accounts for 2% by mass of the second mixed solution.
Comparative example 1
A silicon-carbon negative electrode sheet was prepared according to the method of example 1, except that the CNT was changed to super-p in the step (1).
Comparative example 2
A silicon-carbon negative electrode piece was prepared according to the method of example 2, except that the bonding powder CMC was changed to starch in step (3).
Comparative example 3
The silicon-carbon negative electrode piece is prepared according to the method in the embodiment 1, except that the super-b in the step (3) is changed into graphene.
Comparative example 4
Carbon-coated nano-silicon was prepared according to the method of example 1, and then 20g of carbon-coated nano-silicon, 0.02g of carbon nanotubes, 72.5g of spherical graphite, and 3.5g of super-p were mixed together into 99.98g of CMC sol, wherein the CMC sol was a colorless clear colloid with a mass fraction of 1.5 wt%.
Test example
The silicon-carbon negative electrode pieces of the above examples and comparative examples were assembled into a lithium ion battery, specifically: the prepared electrode plate is used as a positive electrode, a metal lithium plate is used as a negative electrode, a Celgard 2400 type diaphragm is selected, and 1 mol.L -1 LiPF 6 (volume ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate: 1: 1) was added with 5% fluoroethylene carbonate, assembled into a button half cell in a glove box, and the cell was subjected to charge and discharge test using a blue light system. The parameters are set as follows: the current density is 0.1C for the first turn, 0.2C for the subsequent turn, and the voltage interval is 0.005-1.5V. The specific test results are shown in table 1 below:
TABLE 1
Figure BDA0002942608630000111
Fig. 4 is a cycle performance diagram of lithium ion batteries prepared from the silicon-carbon negative electrode plates of example 1 and comparative example 1, fig. 5 is a cycle performance diagram of lithium ion batteries prepared from the silicon-carbon negative electrode plates of example 2 and comparative example 2, and by combining fig. 4, fig. 5 and table 1 above, it can be seen that the CNT or super-p linear conductive agent can improve the cycle stability of the electrode plates better than the graphene planar conductive agent, and in addition, the CMC has a carboxymethyl group, which can improve the stability of the electrode plates better than starch. In addition, the stability of the pole piece can be improved by adding the conductive agent and the binder step by step compared with the method of adding all materials at one time.
It should be noted by those skilled in the art that the described embodiments of the present invention are merely exemplary and that various other substitutions, alterations, and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the above-described embodiments, but is only limited by the claims.

Claims (19)

1. A preparation method of a silicon-carbon negative pole piece is characterized by comprising the following steps:
dispersing a first conductive agent in a dispersant solution to obtain a first mixed solution;
mixing the active particles, a first binder and a second conductive agent to obtain first particles;
placing the first particles and a second binder into the first mixed solution to obtain a second mixed solution; and
coating the second mixed solution and graphite on a current collector after mixing to obtain the silicon-carbon negative pole piece;
the first conductive agent is a linear conductive agent and/or a planar conductive agent, and the second conductive agent is a linear conductive agent.
2. The production method according to claim 1, wherein the first conductive agent is one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphene, and the second conductive agent is one or more selected from the group consisting of carbon nanotubes, super-p, acetylene black, ketjen black, and carbon nanofibers.
3. The production method according to claim 1, wherein the first conductive agent is a water-soluble conductive agent, and the dispersant solution is a water-soluble polymer solution.
4. The method according to claim 3, wherein the water-soluble polymer solution contains 1 to 10% by mass, preferably 1 to 6% by mass of a water-soluble polymer; the water-soluble polymer is selected from one or more of sodium carboxymethylcellulose, hydroxyethyl cellulose, starch, sodium alginate, citric acid, polyacrylic acid, polyacrylamide, polyvinylpyrrolidone and polyvinyl alcohol.
5. The preparation method according to claim 1, wherein the first conductive agent accounts for 0.01 to 0.1 percent of the first mixed solution by mass, preferably 0.02 to 0.06 percent of the first mixed solution by mass; the dispersant solution accounts for 99.90-99.99% of the first mixed solution by mass, and preferably 99.94-99.98%.
6. The production method according to claim 1, characterized in that the first conductive agent is dispersed in the dispersant solution using a homogenizer or a shear; when the shearing machine is adopted, the rotating speed of the shearing machine is 1000 rpm-2000 rpm, preferably 1500 rpm-1800 rpm, and the shearing time is 1 h-8 h, preferably 2h-4 h.
7. The method according to claim 1, wherein the active particles are a mixture of spheroidal graphite and silicon-based particles selected from nano-silicon and/or nano-silica SiO x Wherein 0 is<x<2; the mass ratio of the spherical graphite to the silicon-based particles is 1-4: 1, and preferably 1-2: 1.
8. The method according to claim 7, wherein the silicon-based particles are carbon-coated silicon-based particles, and wherein the thickness of the carbon coating is 2nm to 10 nm.
9. The method according to claim 7, wherein the nano silicon has a particle size of 20nm to 500nm, preferably 50nm to 150 nm; the nano silicon is pure nano silicon and/or surface oxidized nano silicon, the oxygen content of the surface oxidized nano silicon is less than 5%, the oxidation thickness is 1 nm-20 nm, and 1 nm-10 nm is preferred; the nano silicon oxide SiO x Has a particle diameter of 10nm to 200nm, preferably 10nm to 100nm, wherein, preferably, 0.3<x<1.6。
10. The method according to claim 1, wherein the first binder is a binder powder, and the binder powder is a hydrophilic polymer and/or an amphiphilic polymer; wherein the hydrophilic polymer is selected from one or more of sodium carboxymethylcellulose, hydroxyethyl cellulose, sodium alginate and polyacrylic acid; the amphiphilic polymer is formed by copolymerizing a hydrophilic section and a hydrophobic section, the hydrophilic section is selected from one or more of polyethylene glycol, polyvinyl alcohol, polyvinyl ether, polyvinylpyrrolidone, polyacrylic acid and polystyrene sulfonate, and the hydrophobic section is selected from one or more of polypropylene oxide, polymethyl methacrylate, polymethyl acrylate, polystyrene and polysiloxane.
11. The method of claim 1, further comprising: mixing the active particles with the first binder to obtain first binder-coated active particles; mixing the active particles wrapped by the first binder with the second conductive agent to obtain the first particles; wherein the mass ratio of the first binder to the active particles is (15-2): 85-98, preferably (10-3): 90-97); the mass ratio of the second conductive agent to the active particles wrapped by the first binder is (1-20): 99-80, preferably (5-20): 80-95).
12. The method of claim 11, wherein the mixing of the first binder and the active particles, and/or the mixing of the second conductive agent and the active particles coated with the first binder is performed using a planetary ball mill or a powder mixer at a rotation speed of 100rpm to 500rpm for 1h to 12h, preferably 1h to 6 h.
13. The preparation method of claim 1, wherein the second binder is a water-soluble binder emulsion, the water-soluble binder emulsion comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polymethacrylic acid, sodium alginate and polytetrafluoroethylene, and the solid content of the water-soluble binder emulsion is 1-60 wt%.
14. The method of claim 1, further comprising: dispersing the first particles in the first mixed solution to obtain a third mixed solution; adding the second binder into the third mixed solution, and stirring to obtain a second mixed solution; wherein the solid content of the second binder is 1-8% of the third mixed solution, preferably 1-4%.
15. The method according to claim 14, wherein the first granules are dispersed in the first mixed solution by a vacuum mixer at a speed of 200rpm to 1000rpm for 2h to 12h, preferably 350rpm to 600rpm, for 3h to 6 h; and adding the second binder into the third mixed solution by using a vacuum stirrer, and stirring at the rotating speed of 200-900 rpm for 1-10 h, preferably 200-500 rpm for 1-3 h.
16. The method according to claim 14, further comprising adding the graphite during stirring after adding the second binder to the third mixed solution; the mass ratio of the added amount of the graphite to the first particles is 0.5-4: 1, and preferably 1-2: 1.
17. The method according to claim 1, wherein the graphite is spheroidal graphite selected from one or more of spheroidal natural graphite, spheroidal artificial graphite, and spheroidal carbon microspheres, and the spheroidal graphite has a tap density of 0.8g cm -3 ～1.1g cm -3 The median particle diameter is 10-25 μm.
18. A silicon-carbon negative electrode plate prepared by the method of any one of claims 1 to 17.
19. A lithium ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode adopts the silicon-carbon negative electrode plate of claim 18.
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