CN112635712A - Negative plate and lithium ion battery - Google Patents
Negative plate and lithium ion battery Download PDFInfo
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- CN112635712A CN112635712A CN202011503490.9A CN202011503490A CN112635712A CN 112635712 A CN112635712 A CN 112635712A CN 202011503490 A CN202011503490 A CN 202011503490A CN 112635712 A CN112635712 A CN 112635712A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a negative plate and a lithium ion battery. The invention provides a negative plate, which comprises a negative current collector and a first negative active layer arranged on the negative current collector, wherein the first negative active layer comprises a negative active substance, and the negative active substance is composed of a composite silicon material and a carbon material; the composite silicon material comprises a plurality of substrate particles and a conductive material dispersed among the substrate particles, the substrate particles are silicon materials with graphite particles adhered to the surfaces, the conductive material is graphene and/or conductive carbon tubes, in addition, a second negative electrode active layer can be further arranged on the surface, away from a negative electrode current collector, of the first negative electrode active layer, the second negative electrode active layer comprises a negative electrode active substance, and the negative electrode active substance is composed of a carbon material. The cathode plate provided by the invention can effectively prolong the cycle life and improve the safety of the lithium ion battery.
Description
Technical Field
The invention relates to a negative plate and a lithium ion battery, and relates to the technical field of lithium ion batteries.
Background
In recent years, consumer portable electronic products have seen explosive growth in sales. The lithium ion battery is used as a core component of consumer portable electronic products, and in order to solve the problem of 'endurance and charging anxiety' of the products, the high energy density also becomes the development direction of the lithium ion battery.
The specific capacity of the carbon material is basically and fully exerted as the most mature anode material at present, the theoretical specific capacity of the silicon material as a novel anode material is up to 4200mAh/g, and on the basis of the existing chemical system and materials, the silicon material and the carbon material are mixed to be used as an anode active substance, so that the energy density is ideally improved.
However, the silicon material is easy to expand in the charging and discharging processes, so that the negative active materials are structurally collapsed and granular differentiated in the circulating process, and the electronic conductivity between the negative active materials and a negative current collector is lost; in addition, due to the difference between the conductivity and the lithium storage capacity of the silicon material and the graphite material, in the charging process, the potentials and the polarization degrees of the silicon material and the carbon material are different, so that the potential of the silicon material is high, the graphite potential near doped silicon is the lowest, the concentration distribution of lithium ions in the negative plate is uneven, and the problem of lithium precipitation is easily caused, and the precipitated lithium ions not only influence the cycle life of the lithium ion battery, but also cause hidden troubles to the use safety of the lithium ion battery.
Disclosure of Invention
The invention provides a negative plate which is used for relieving the problems of silicon material expansion and negative plate lithium separation and improving the cycle life and safety of a lithium ion battery.
The invention provides a negative plate, which comprises a negative current collector and a first negative active layer arranged on the negative current collector, wherein the first negative active layer comprises a negative active substance, and the negative active substance is composed of a composite silicon material and a carbon material;
the composite silicon material comprises a plurality of base particles and a conductive material dispersed among the base particles, wherein the base particles are silicon materials with graphite particles adhered to the surfaces, and the conductive material is graphene and/or conductive carbon tubes.
The invention provides a negative plate, which comprises a negative current collector and a negative active layer arranged on the negative current collector according to the conventional structure of the current negative plate, wherein figure 1 is a schematic structural diagram of the negative plate provided by an embodiment of the invention, as shown in figure 1, the negative plate comprises the negative current collector 1 and a first negative active layer 2 arranged on the negative current collector 1, the first negative active layer 2 comprises a negative active substance, and for the negative active substance formed by a silicon material and a carbon material, the silicon material is mainly improved to obtain a composite silicon material, so as to solve the problems of short cycle life and safety of a lithium ion battery caused by the silicon material, specifically, the composite silicon material comprises a plurality of matrix particles and a conductive material dispersed among the matrix particles, wherein the matrix particles are the silicon material with graphite particles adhered on the surface, it can be understood that the silicon material and the graphite particles are both granular solid materials, the graphite particles are adhered to the surface of the silicon material and wrap the silicon material inside, and in the charging process, the graphite particles adhered to the surface of the silicon material can provide a buffer channel for lithium ions for the silicon material, so that the potential and polarization difference between the silicon material and the carbon material are reduced, and the problem of lithium precipitation of a negative electrode plate is solved; the conductive material is dispersed in gaps among the matrix particles, the conductive material can improve the conductivity of the silicon material, and a conductive network formed by the conductive material can restrict the expansion of the silicon material, so that the cycle life of the lithium ion battery is prolonged, wherein the conductive material can be selected from graphene and/or conductive carbon tubes; therefore, the composite silicon material provided by the invention can improve the cycle life and the safety of the lithium ion battery, and correspondingly, the negative plate comprising the composite silicon material can also improve the cycle life and the safety of the lithium ion battery.
In order to further alleviate the problem of lithium precipitation of the negative electrode sheet, with reference to the structure of the composite silicon material, a second negative electrode active layer may be disposed on the surface of the first negative electrode active layer away from the current collector, where the second negative electrode active layer includes a negative electrode active material, and the negative electrode active material is composed of a carbon material.
Fig. 2 is a schematic structural diagram of a negative electrode sheet according to still another embodiment of the present invention, and as shown in fig. 2, the negative electrode sheet includes a negative electrode collector 1, and a first negative electrode active layer 2 and a second negative electrode active layer 3 sequentially stacked on a surface of the negative electrode collector 1, wherein a negative electrode active material in the second negative electrode active layer 3 is composed of a carbon material and does not include a silicon material. It is understood that when the second anode active layer is provided, the thickness of the first anode active layer may be appropriately reduced, for example, the total thickness of the first anode active layer and the second anode active layer is 100-135 μm, wherein the thickness of the first anode active layer is 40-75 μm and the thickness of the second anode active layer is 60-90 μm. According to the invention, the second negative electrode active layer only comprising the carbon material is arranged on the surface of the first negative electrode active layer, and lithium ions pass through the second negative electrode active layer and then enter the first negative electrode active layer in the quick charging process, so that the potential difference of the surface of the first negative electrode active layer is further reduced, the problem of lithium precipitation is relieved, and the cycle life and the safety of the lithium ion battery are further improved.
Further, the negative electrode active material in the first negative electrode active layer is composed of 75-99% of carbon material and 1-25% of the composite silicon material by mass percentage, further, the negative electrode active material in the first negative electrode active layer is composed of 85-97% of carbon material and 3-15% of the composite silicon material by mass percentage, in the actual preparation process, the composite silicon material and the carbon material can be mixed to be used as the negative electrode active material, and in order to enable the two to be mixed more uniformly, the two can be mixed and then ground.
The following mainly describes the composite silicon material in detail:
the inventor of the present application finds that, as the content of the conductive material in the composite silicon material increases, the performance of the lithium ion battery may be improved, but when the content of the conductive material is too high, the conductive material may adversely affect the transmission of lithium ions, which may result in the reduction of the energy density and the cycle life of the lithium ion battery, and therefore, the mass of the conductive material is 3.5 to 20% of the mass of the composite silicon material, further, the mass of the conductive material is 3.5 to 18% of the mass of the composite silicon material, and further, the mass of the conductive material is 3.5 to 15% of the mass of the composite silicon material.
In order to further reduce the difference between the composite silicon material and the carbon material and relieve the problem of lithium precipitation of the negative plate, D of the composite silicon material can be used50With carbon materials D50Kept close, specifically, according to the particle size distribution range of conventional carbon materials, i.e., 5 μm. ltoreq.D10≤8μm，12μm≤D50≤18μm，23μm≤D90Less than or equal to 29 mu m, and controlling the D of the composite silicon material50Is 12-18 μm.
In order to ensure that the conductive material can be uniformly dispersed among the matrix particles, the matrix particles can be dispersed in conductive slurry comprising graphene and conductive carbon tubes, and the composite silicon material can be obtained after uniform mixing and solvent removal, specifically, the composite silicon material is obtained by a preparation method comprising the following steps:
adhering graphite particles to the surface of a silicon material to obtain the matrix particles;
dispersing the conductive material in a solvent to obtain conductive slurry;
and dispersing the matrix particles in the conductive slurry to uniformly disperse the graphene and the conductive carbon tubes among the matrix particles to obtain the composite silicon material.
The preparation method of the composite silicon material is explained in detail as follows:
step 1, adhering graphite particles to the surface of a silicon material to obtain matrix particles;
first, in order to uniformly adhere graphite particles to the surface of the silicon material, the silicon material and the graphite particles may be selected in a suitable particle size range, specifically, the particle size of the silicon material is 4 to 9 μm, and the particles of the graphite particles areA diameter of 3-7 μm, and D of the silicon material50Greater than D of the graphite particles50。
The silicon material and the graphite particles are conventional materials in the field and can be obtained commercially, and if the particle size of the silicon material and the graphite particles is slightly larger, the silicon material and the graphite particles can be ground and sieved;
secondly, in order to improve the bonding force between the graphite particles and the silicon material, the graphite particles can be adhered to the surface of the silicon material by using an adhesive, and the method specifically comprises the following steps:
putting the silicon material into a reaction kettle, adding a surfactant, then increasing the temperature to 270-580 ℃, atomizing the asphalt and spraying the asphalt into the reaction kettle to obtain the silicon material with the surface coated with the asphalt;
adding the graphite particles, and increasing the temperature to 750-1080 ℃ to obtain a silicon material with the graphite particles adhered on the surface;
and carbonizing the silicon material with the graphite particles adhered on the surface at 850-1600 ℃ for 3-7h to obtain the matrix particles.
In the embodiment, asphalt can be used as a binder, a silicon material is firstly put into a reaction kettle, and a surfactant is added, wherein the surfactant can be PVP, and the mass of the surfactant is 1% of that of the silicon material; then, the temperature is increased to 270-580 ℃, and then the asphalt is atomized and sprayed into the reaction kettle, so that the asphalt is uniformly coated on the surface of the silicon material, and the silicon material coated with the asphalt is obtained, wherein in order to improve the atomization effect of the asphalt, liquid asphalt with stronger fluidity can be used, the mass ratio of the liquid asphalt to the silicon material is (95-85): 5-15), further, the mass ratio of the liquid asphalt to the silicon material is 90:10, and the stirring state is kept in the whole process, so that the asphalt is uniformly coated on the surface of the silicon material;
secondly, adding graphite particles, raising the temperature to 750-1080 ℃, and keeping the temperature for 8-17h to ensure that the graphite particles are uniformly adhered to the surfaces of the silicon material particles, wherein specifically, the mass ratio of the silicon material coated with the asphalt on the surfaces to the graphite particles is (10-50): (50-90), further, the mass ratio of the silicon material coated with the asphalt on the surface to the graphite particles is (20-40): 60-80); and after the preparation is finished, cooling the reaction product to prepare the silicon material with the graphite particles adhered on the surface. In addition, if the particle size of the prepared particles is too large, the particles can be filtered by using a 800-1100-mesh screen;
and finally, carbonizing the prepared silicon material with the graphite particles adhered to the surface for 3-7h at 850-1600 ℃ to obtain the matrix particles.
specifically, the mass ratio of the graphene to the conductive carbon tubes is 1: (1.25-9); further, the mass ratio of the graphene to the conductive carbon tubes is 1: 4;
the solvent can be absolute ethyl alcohol, the total mass of the graphene and the conductive carbon tubes is 3-10% of the mass of the conductive slurry, and further the total mass of the graphene and the conductive carbon tubes is 5% of the mass of the conductive slurry.
And 3, dispersing the matrix particles in the conductive slurry to uniformly disperse the graphene and the conductive carbon tubes among the matrix particles to obtain the composite silicon material:
dispersing the base particles prepared in the step 1 in the conductive slurry prepared in the step 2, specifically, the mass of the base particles is 43-85% of the mass of the conductive slurry, further, the mass of the base particles is 55-80% of the mass of the conductive slurry, stirring in a water bath at 60 ℃ until all the solvent anhydrous ethanol is evaporated to obtain solid particles, and primarily grinding, drying, ball-milling and filtering the solid particles to obtain the composite silicon material.
In conclusion, the composite silicon material provided by the invention can be mixed with a conventional carbon material to be used as a negative electrode active material, so that the problem of lithium precipitation of the silicon material can be further alleviated on the basis of improving the energy density of the lithium ion battery, and the cycle life and the safety of the lithium ion battery can be improved.
The carbon material is a carbon material commonly used in the art, and for example, the carbon material may be one or more of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, and organic polymer carbon (i.e., a product obtained by carbonizing an organic polymer).
The silicon material is one of silicon simple substance, silicon oxide, silicon carbide, silicon nitride and silicon monoxide.
In the specific preparation process, 75-99% of carbon material and 1-25% of composite silicon material can be mixed according to the mass percentage to be used as the negative active material, wherein in order to fully mix the carbon material and the composite silicon material, the carbon material and the composite silicon material can be mixed and subjected to ball milling to obtain the negative active material.
On the basis of preparing the negative active material, the conductive agent, the binder and the thickening agent are added into solvent deionized water according to the mass percentage to prepare a first negative active layer slurry, and the solid content of the first negative active layer slurry is 40-45%.
The length, width and thickness of the negative electrode sheet are not further limited in the present invention, and those skilled in the art can set the length, width and thickness according to actual requirements, for example, the length of the negative electrode sheet can be 800-.
The invention provides a lithium ion battery, which comprises any one of the negative electrode sheets.
On the basis of the negative plate provided by the invention, a person skilled in the art can prepare the lithium ion battery by combining the positive plate, the diaphragm and the electrolyte according to a conventional technical means, wherein the positive plate comprises a positive current collector and a positive active layer, the positive active layer comprises a positive active substance, a conductive agent and a binder, in the specific preparation process, the positive active substance, the conductive agent and the binder can be mixed with a solvent NMP according to a certain mass ratio to prepare positive active layer slurry, the solid content of the positive active layer slurry is 70-75%, then the positive active layer is coated on the surface of the positive current collector, and the positive plate is obtained after drying;
the conductive agent and the binder used in the positive electrode active layer and the negative electrode active layer may be performed according to conventional technical means, for example, the conductive agent is one or more of conductive carbon black, carbon fiber, ketjen black, acetylene black, carbon nanotube and graphene, and the binder is one or more of polyvinylidene fluoride, styrene-butadiene latex, polyacrylic acid, polytetrafluoroethylene and polyethylene oxide; the thickening agent is sodium carboxymethyl cellulose;
the cathode plate and the diaphragm provided by the invention are combined and packaged in a winding or laminating mode, and electrolyte is injected to obtain the lithium ion battery.
The implementation of the invention has at least the following advantages:
1. the invention provides a composite silicon material, wherein in the charging process, a graphite material adhered to the surface of the silicon material can provide a buffer channel of lithium ions for the silicon material, and the potential and polarization difference between the silicon material and the carbon material is reduced, so that the problem of lithium precipitation of a negative plate is solved; the conductive material comprises graphene and conductive carbon tubes, the graphene and the conductive carbon tubes are dispersed in gaps among matrix particles, the graphene can form effective point-surface contact with the matrix particles, and the conductive carbon tubes can form effective point-line-surface contact with the matrix particles and the graphene, so that the conductivity of the silicon material is improved, in addition, the conductive carbon tubes can prevent the graphene from agglomerating, the conductive effect of the graphene is improved, meanwhile, a conductive network formed by the conductive carbon tubes can restrict the expansion of the silicon material, and the cycle life of the lithium ion battery is prolonged; therefore, the composite silicon material provided by the invention can improve the cycle life and the safety of the lithium ion battery, and correspondingly, the negative plate comprising the composite silicon material can also improve the cycle life and the safety of the lithium ion battery.
2. According to the invention, the second negative electrode active layer only comprising the carbon material is arranged on the surface of the first negative electrode active layer, and lithium ions pass through the second negative electrode active layer and then enter the first negative electrode active layer in the quick charging process, so that the potential difference of the surface of the first negative electrode active layer is further reduced, the problem of lithium precipitation is relieved, and the cycle life and the safety of the lithium ion battery are further improved.
Drawings
Fig. 1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a negative electrode sheet according to yet another embodiment of the present invention.
Description of reference numerals:
1-negative current collector, 2-first negative active layer, 3-second negative active layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The silica used in the examples below was obtained from the group of New Material Bobei, Inc.; the graphite particles were obtained from Jiangxi purple light envelope science and technology, and the graphene and the conductive carbon tube were obtained from Jiangsu Tiannai science and technology, Inc.
Example 1
The embodiment provides a composite silicon material, which comprises base particles and a conductive material, wherein the base particles are silicon monoxide with graphite particles adhered to the surfaces, and the conductive material is graphene and a conductive carbon tube; composite silicon material D50The thickness is 13 μm, and the mass of the graphene and the conductive carbon tube is 6.67% of that of the composite silicon material.
The preparation method of the composite silicon material provided by the embodiment comprises the following steps:
1. will D50Putting 7 mu m of silica into a reaction kettle, adding 1% of PVP, increasing the temperature to 310 ℃ at the same time under the stirring speed of 45rmp, and then atomizing and spraying liquid asphalt to the surface of the silica to ensure that the liquid asphalt is uniformly coated on the surface of the silica, wherein the mass ratio of the liquid asphalt to the silica is 90: 10;
2. d was added at a stirring rate of 100rmp504 μm graphite particles, silica and graphite coated with asphalt solutionThe mass ratio of the particles is 40: 60, adding a solvent to the mixture; keeping the temperature at 900 ℃ for 10h to ensure that graphite particles are uniformly adhered to the surfaces of the silicon oxide particles, performing ball milling and 800-mesh 1100-mesh screen filtering on the cooled product to obtain silicon oxide with graphite particles adhered to the surfaces, and then putting the silicon oxide with graphite particles adhered to the surfaces in a tubular furnace to be carbonized at 1200 ℃ for 6 h to obtain matrix particles;
3. mixing the components in a mass ratio of 1: 4, dispersing the graphene and the conductive carbon tubes in absolute ethyl alcohol to obtain conductive slurry, wherein the total mass of the graphene and the conductive carbon tubes is 8% of the mass of the conductive slurry;
4. putting 70 parts by mass of matrix particles into 100 parts by mass of conductive slurry, stirring in a water bath at 60 ℃ until the absolute ethyl alcohol is evaporated to obtain solid particles, then carrying out primary grinding by using an agate mortar, drying at 120 ℃, ball-milling, filtering by using a 800-mesh 1100-mesh screen to obtain D50A composite silicon material with a particle size of 13 μm.
Example 2
The composite silicon material provided by the present embodiment can refer to embodiment 1, and the difference is that:
the mass of the graphene and the conductive carbon tube is 3.6% of that of the composite silicon material.
The preparation method of the composite silicon material provided in this embodiment specifically refers to embodiment 1, and the difference is that:
the total mass of the graphene and the conductive carbon tubes is 3% of the mass of the conductive slurry, and 80 parts by mass of the matrix particles are placed in 100 parts by mass of the conductive slurry to obtain the composite silicon material.
Example 3
The composite silicon material provided by the present embodiment can refer to embodiment 1, and the difference is that:
the mass of the graphene and the conductive carbon tube is 14.29 percent of that of the composite silicon material.
The preparation method of the composite silicon material provided in this embodiment specifically refers to embodiment 1, and the difference is that:
the total mass of the graphene and the conductive carbon tubes is 10% of the mass of the conductive slurry, and 60 parts by mass of the matrix particles are placed in 100 parts by mass of the conductive slurry to obtain the composite silicon material.
Example 4
The composite silicon material provided by the present embodiment can refer to embodiment 1, and the difference is that:
the mass of the graphene and the conductive carbon tube is 1.41 percent of that of the composite silicon material.
The preparation method of the composite silicon material provided in this embodiment specifically refers to embodiment 1, and the difference is that:
the total mass of the graphene and the conductive carbon tubes is 1% of the mass of the conductive slurry.
Example 5
The composite silicon material provided by the present embodiment can refer to embodiment 1, and the difference is that:
the mass of the graphene and the conductive carbon tubes is 22.22% of that of the composite silicon material.
The preparation method of the composite silicon material provided in this embodiment specifically refers to embodiment 1, and the difference is that:
the total mass of the graphene and the conductive carbon tubes is 20% of the mass of the conductive slurry.
Example 6
This embodiment provides a negative pole piece, including negative pole current collector copper foil and range upon range of the first negative pole active layer and the second negative pole active layer that set up on the copper foil surface in proper order, wherein:
the first negative electrode active layer comprises 96.9 parts by mass of a negative electrode active material, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethyl cellulose, and the negative electrode active material comprises 97 parts by mass of graphite and 3 parts by mass of the composite silicon material provided in example 1;
the second negative active layer includes 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex, and 1.3 parts by mass of sodium carboxymethylcellulose.
The preparation method of the negative electrode plate provided by the embodiment comprises the following steps:
1. mixing 97 parts by mass of graphite and 3 parts by mass of the composite silicon material provided in example 1, and performing ball milling for 2-5min to obtain a negative electrode active material, and dissolving 96.9 parts by mass of the negative electrode active material, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex, and 1.3 parts by mass of sodium carboxymethylcellulose in deionized water to prepare a first negative electrode active layer slurry, wherein the solid content is 45.3%;
2. dissolving 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethylcellulose in deionized water to prepare second negative electrode active layer slurry, wherein the solid content is 45.3%;
3. coating the first negative electrode active layer slurry on the surface of a negative electrode current collector copper foil to obtain a first negative electrode active layer, coating the second negative electrode active layer slurry on the surface of the first negative electrode active layer to obtain a second negative electrode active layer, and finally drying to obtain a negative plate; the length of the negative plate is 883 +/-2 mm, the width of the negative plate is 79mm +/-0.5 mm, the thickness of the first negative active layer is 50 mu m, and the thickness of the second negative active layer is 50 mu m.
Example 7
The negative electrode sheet provided in this example can be referred to example 6 except that the negative electrode active material in the first negative electrode active layer includes 95 parts by mass of graphite and 5 parts by mass of a silicon composite material.
Example 8
The negative electrode sheet provided in this example can be referred to example 6 except that the negative electrode active material in the first negative electrode active layer includes 92 parts by mass of graphite and 8 parts by mass of a silicon composite material.
Example 9
The negative electrode sheet provided in this example can be referred to example 6 except that the negative electrode active material in the first negative electrode active layer includes 90 parts by mass of graphite and 10 parts by mass of a silicon composite material.
Example 10
The negative electrode sheet provided in this example was referred to example 6 except that the thickness of the first negative electrode active layer was 40 μm and the thickness of the second negative electrode active layer was 60 μm.
Example 11
The negative electrode sheet provided in this example was referred to example 6 except that the thickness of the first negative electrode active layer was 60 μm and the thickness of the second negative electrode active layer was 40 μm.
Example 12
The negative electrode sheet provided in this example can be referred to example 6 except that 97 parts by mass of graphite and 3 parts by mass of the silicon composite material provided in example 2 were included in the negative electrode active material in the first negative electrode active layer.
Example 13
The negative electrode sheet provided in this example can be referred to example 6 except that 97 parts by mass of graphite and 3 parts by mass of the silicon composite material provided in example 3 were included in the negative electrode active material in the first negative electrode active layer.
Example 14
The negative electrode sheet provided in this example can be referred to example 6 except that 97 parts by mass of graphite and 3 parts by mass of the silicon composite material provided in example 4 were included in the negative electrode active material in the first negative electrode active layer.
Example 15
The negative electrode sheet provided in this example can be referred to example 6 except that 97 parts by mass of graphite and 3 parts by mass of the silicon composite material provided in example 5 were included in the negative electrode active material in the first negative electrode active layer.
Comparative example 1
The negative plate provided by the comparative example comprises a negative current collector copper foil and a negative active layer arranged on the surface of the copper foil, wherein the negative active layer comprises 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethyl cellulose.
The thickness of the negative electrode active layer was 100 μm.
Comparative example 2
The negative electrode sheet provided by this comparative example can be referred to example 6 except that the negative electrode active material in the first negative electrode active layer includes 97 parts by mass of graphite and 3 parts by mass of silica.
Comparative example 3
The negative pole piece that this comparative example provided includes negative pole mass flow body copper foil and range upon range of the first negative pole active layer and the second negative pole active layer of setting in proper order on the copper foil surface, wherein:
the first negative active layer comprises 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethylcellulose;
the second negative electrode active layer includes 96.9 parts by mass of a negative electrode active material, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex, and 1.3 parts by mass of sodium carboxymethylcellulose, and the negative electrode active material includes 95 parts by mass of graphite and 5 parts by mass of silica.
Comparative example 4
The negative electrode sheet provided by this comparative example can be referred to comparative example 3, except that the negative electrode active material in the second negative electrode active layer includes 95 parts by mass of graphite and 5 parts by mass of the silicon composite material prepared in example 1.
The lithium ion batteries were prepared by matching the negative electrode sheets provided in examples 6 to 15 and comparative examples 1 to 4 with the positive electrode sheets, the separators and the electrolyte, and the energy density, the safety performance and the cycle life of the lithium ion batteries were tested, and the test results are shown in table 1:
the preparation method of the positive plate comprises the following steps: dissolving 97.2 parts by mass of lithium cobaltate, 1.5 parts by mass of conductive carbon black and 1.3 parts by mass of polyvinylidene fluoride in NMP, uniformly mixing, filtering by using a 200-mesh screen to obtain positive active layer slurry, uniformly coating the positive active layer slurry on the surface of an aluminum foil, and drying at 120 ℃ to obtain a positive plate;
winding the negative plate, the positive plate and the diaphragm prepared in the steps to obtain a winding core, packaging the winding core by using an aluminum plastic film, baking the winding core to remove moisture, injecting an electrolyte (mixing Propylene Carbonate (PC), Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the weight ratio of 1:1:0.5: 1), and then adding LiPF6Obtaining an electrolyte solution in which LiPF6The concentration of the lithium ion battery is 1mol/L), and the lithium ion battery is obtained by adopting a hot pressing formation process.
The energy density testing method comprises the following steps: carrying out 0.2C/0.2C charge and discharge on the lithium ion battery at 25 ℃ to test the discharge energy of the lithium ion battery, and further testing to obtain the length, height and thickness of the lithium ion battery; calculating the energy density of the lithium ion battery according to the energy density, namely the discharge energy/length/height/thickness;
the safety performance testing method comprises the following steps: carrying out 1.0C step charging/0.7C discharging on the lithium ion battery at 25 ℃, disassembling the lithium ion battery under different cycle times, observing the lithium separation condition on the surface of the negative plate, and dividing the lithium ion battery into five grades according to the lithium separation condition of the lithium ion battery, wherein 0 represents no lithium separation phenomenon, 5 represents serious lithium separation phenomenon, and the 0-5 represents gradual serious lithium separation phenomenon;
the method for testing the capacity retention rate comprises the following steps: the lithium ion battery was subjected to 1.0 charge/0.7 discharge cycles at 25 ℃ and tested for initial capacity Q1And testing the capacity of the lithium ion battery after the cycle of 700T according to 2.0C/0.7C to obtain the capacity Q2Capacity retention (%) ═ Q2/Q1*100％；
The method for testing the expansion rate comprises the following steps: the lithium ion battery is charged at 1.0/discharged at 0.7 at 25 ℃, and the thickness P of the lithium ion battery is tested1And testing the thickness P of the lithium ion battery after 700T of circulation2The percent of cyclic expansion (P) (%)2-P1)/P1*100％。
Table 1 test results for lithium ion batteries provided in examples 6-15 and comparative examples 1-4
According to the data provided in table 1, it can be known that the problem of lithium separation can be alleviated to a certain extent by the negative electrode sheet provided in the present application, and on the basis of improving the energy density, the cycle life and safety of lithium ions are further improved, and according to the data provided in examples 12 to 15, the content of the conductive material in the composite silicon material has a large influence on the performance of the lithium ion battery, and when the content of the conductive material is high, the transmission of lithium ions is easily hindered, which is not favorable for the exertion of capacity, so that the energy density of the lithium ion battery is reduced, the cycle life is quickly attenuated, the negative electrode sheet is easily deteriorated and expanded, and the problem of lithium separation also easily occurs in the negative electrode sheet, and particularly when the content of the conductive material is greater than 20%, the performance of the lithium ion battery; when the content of the conductive material is low, the formed conductive network is not complete enough, and the function of the composite silicon material is not obvious.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The negative plate is characterized by comprising a negative current collector and a first negative active layer arranged on the negative current collector, wherein the first negative active layer comprises a negative active substance, and the negative active substance is composed of a composite silicon material and a carbon material;
the composite silicon material comprises a plurality of base particles and a conductive material dispersed among the base particles, wherein the base particles are silicon materials with graphite particles adhered to the surfaces, and the conductive material is graphene and/or conductive carbon tubes.
2. The negative electrode sheet according to claim 1, wherein a second negative electrode active layer is further provided on a surface of the first negative electrode active layer remote from the negative electrode current collector, and the second negative electrode active layer includes a negative electrode active material composed of a carbon material.
3. The negative electrode sheet according to claim 1 or 2, wherein the mass of the conductive material is 3.5-20% of the mass of the composite silicon material.
4. Negative electrode sheet according to any one of claims 1 to 3, wherein D is the silicon composite material50Is 12-18 μm.
5. Negative electrode sheet according to any of claims 1 to 4, characterized in that the silicon composite material is obtained by a preparation method comprising the following processes:
adhering graphite particles to the surface of a silicon material to obtain the matrix particles;
dispersing the conductive material in a solvent to obtain conductive slurry;
and dispersing the substrate particles in the conductive slurry to uniformly disperse the conductive material among the substrate particles to obtain the composite silicon material.
6. Negative electrode sheet according to claim 1, characterized in that D of the silicon material504-9 μm, D of the graphite particles50Is 3-7 μm, and D of the silicon material50Greater than D of the graphite particles50。
7. The negative electrode sheet according to claim 5, wherein the adhering of the graphite particles to the surface of the silicon material to obtain the matrix particles specifically comprises:
putting the silicon material into a reaction kettle, adding a surfactant, then increasing the temperature to 270-580 ℃, atomizing the asphalt and spraying the asphalt into the reaction kettle to obtain the silicon material with the surface coated with the asphalt;
adding the graphite particles, and increasing the temperature to 750-1080 ℃ to obtain a silicon material with the graphite particles adhered on the surface;
and carbonizing the silicon material with the graphite particles adhered on the surface at 850-1600 ℃ for 3-7h to obtain the matrix particles.
8. The negative electrode sheet according to claim 7, wherein the mass ratio of the silicon material coated with the asphalt on the surface to the graphite particles is (10-50): (50-90).
9. The negative electrode sheet according to claim 1, wherein the negative electrode active material is composed of 75 to 99% by mass of a carbon material and 1 to 25% by mass of the silicon composite material.
10. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1 to 9.
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