CN113066962B - Silicon-containing negative plate and high-energy-density battery - Google Patents

Silicon-containing negative plate and high-energy-density battery Download PDF

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CN113066962B
CN113066962B CN202110314048.XA CN202110314048A CN113066962B CN 113066962 B CN113066962 B CN 113066962B CN 202110314048 A CN202110314048 A CN 202110314048A CN 113066962 B CN113066962 B CN 113066962B
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coating
silicon
negative electrode
based material
graphite
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CN113066962A (en
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蒋亚北
田爽
刘兆平
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Ningbo Institute of Material Technology and Engineering of CAS
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Ningbo Institute of Material Technology and Engineering of CAS
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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
    • 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
    • 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 silicon-containing negative plate, which comprises a current collector, a first coating coated on the surface of the current collector, a second coating applied to the surface of the first coating, a third coating applied to the surface of the second coating; the first coating, the second coating and the third coating respectively comprise a silicon-containing active substance, a conductive agent and a binder, the silicon-containing active substance is a mixture of a silicon-based material and graphite, and the mass of the silicon-based material in the second coating is larger than that of the silicon-based material in the first coating and that of the silicon-based material in the third coating. The present application further provides a high energy density battery. Due to the arrangement of the silicon-containing negative plate coating, the coating is not easy to fall off from the current collector in the charging process, the surface structure of the electrode is complete, the side reaction of an electrode interface and electrolyte is effectively reduced, and the battery has higher energy density and excellent cycle performance.

Description

Silicon-containing negative plate and high-energy-density battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a silicon-containing negative plate and a high-energy-density battery.
Background
In recent years, in order to meet the demand for rapid development of new energy automobiles, smart grids and the like, development of lithium ion batteries with high energy density, high safety and long cycle life becomes a research hotspot in the current energy storage field. The improvement of the energy density of the battery mainly depends on the development of key electrode materials, such as the improvement of the capacity of positive and negative electrode materials and the improvement of the specific capacity of negative electrode materials, and the improvement of the energy density of the battery is more remarkable. The silicon material has higher theoretical specific capacity (more than 4000 mAh/g), is far higher (about 10 times) than graphite which is close to the limit capacity, has low lithium voltage, and is expected to become the first choice of a high-energy density battery.
At present, the main reasons for restricting the large-scale application of silicon materials are that the silicon can generate huge volume expansion in the charging and discharging processes, so that electrode materials are pulverized, the surface is cracked, and the electric contact between an active substance and a current collector is lost in the circulating process, thereby causing the rapid capacity attenuation. And the addition amount of silicon in the lithium battery cathode is very low, and the capacity of the silicon-containing cathode used by the current high-energy-density power battery in the industry is only 400-450 mAh/g. Therefore, the high-capacity silicon-containing negative electrode has great significance for lithium ion batteries.
Disclosure of Invention
The invention aims to solve the technical problem of providing a silicon-containing negative plate so as to solve the problems of large negative electrode volume expansion, coating falling off and poor cycle life of a battery in the charging and discharging processes and ensure that the energy density of the battery is high and the cycle life of the battery is excellent.
The application provides a silicon-containing negative plate, it include the mass flow body and in order superpose in first coating, second coating and the third coating on the mass flow body surface, wherein contain most silica-based material in the second coating, and lie in between first coating and the third coating, do not directly contact with the mass flow body, also can not expose in the electrode surface, only expand at the intermediate level in charge-discharge process, the pole piece can not come off from the mass flow body, the surface also is difficult for the fracture to fall the powder and electrolyte and takes place the side reaction to can guarantee excellent cycle performance. Furthermore, the silicon content in the first coating layer in contact with the current collector is minimum, the volume change of the battery is minimum in the charging and discharging process, the active substance is not easy to separate from the current collector, and the problem that the active substance falls off can be remarkably improved. Therefore, the silicon-based material with a high proportion can be used for the silicon-containing negative plate provided by the application, so that the negative electrode is ensured to have high capacity, the expansion of the silicon negative plate is reduced, the active substance is prevented from falling off from the current collector, and the energy density of the battery is improved.
Drawings
Fig. 1 is a schematic structural diagram of a silicon-containing negative electrode sheet provided by the present invention;
fig. 2 shows that the lithium ion batteries prepared in the examples and comparative examples have 100 cycles of disassembly of the negative electrode sheet in a full-charge state.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In view of the problems that the silicon material generates volume expansion and is easy to fall off in the charging and discharging processes of the battery so as to reduce the silicon content and finally influence the battery capacity, the application provides the silicon-containing negative plate, and the silicon-containing negative plate is provided with the three-layer coating, and the silicon-based material content in the second coating is the highest, so that the problems of large negative plate volume expansion, coating falling and poor cycle life of the battery in the charging and discharging processes are solved, and the obtained battery is high in energy density and excellent in cycle life. Specifically, fig. 1 is a schematic structural diagram of the silicon-containing negative electrode plate provided by the present invention, where the silicon-containing negative electrode plate includes a current collector A0, a first coating T1 coated on the current collector A0, a second coating T2 coated on the surface of the first coating T1, and a third coating T3 coated on the surface of the second coating T2. More specifically, the embodiment of the invention discloses a silicon-containing negative plate, which comprises a current collector, a first coating applied to the surface of the current collector, a second coating applied to the surface of the first coating, and a third coating applied to the surface of the second coating;
the first coating, the second coating and the third coating respectively comprise a silicon-containing active substance, a conductive agent and a binder, the silicon-containing active substance is a mixture of a silicon-based material and graphite, and the mass of the silicon-based material in the second coating is larger than that of the silicon-based material in the first coating and that of the silicon-based material in the third coating.
More specifically, the mass of the silicon-based material in the second coating layer is greater than the mass of the silicon-based material in the third coating layer.
The mass ratio of the silicon-based material to the graphite in the first coating is (1-10): (90-99), the coating only contains a very small amount of silicon-based materials, so that the expansion of the first coating in contact with the current collector is greatly reduced in the lithium embedding process, and the active substance is well connected with the current collector and is not easy to fall off. In a specific embodiment, the mass ratio of the silicon-based material to the graphite is (1.5-6.5): (93.5 to 98.5), more specifically, the mass ratio of the silicon-based material to the graphite is 1.9.
The mass ratio of the silicon-based material to the graphite in the second coating is (10-50): (25-90), the second coating is positioned in the middle of the negative plate coating and can allow a certain degree of expansion without damaging the electrode structure, and the large amount of silicon-based materials in the second coating can provide more negative electrode capacity, thereby providing the energy density of the battery. In a specific embodiment, the mass ratio of the silicon-based material to the graphite is (25-45): (25-75), more specifically, the mass ratio of said silicon-based material to said graphite is 28.5
The mass ratio of the silicon-based material to the graphite material in the third coating is (5-35): (65-95), the third coating is positioned on the surface of the negative plate coating, and a small amount of silicon-based material can provide a certain capacity and simultaneously can not cause surface cracking of the negative plate due to excessive expansion, generate side reaction with electrolyte, and have large interface resistance to influence the performance of the battery. In a specific embodiment, the mass ratio of the silicon-based material to the graphite is (9-30): (70-93), more specifically, the mass ratio of the silicon-based material to the graphite is 9.5:85.5, 11.4:83.6 or 12.8:82.2.
in the present application, the silicon-based material, the graphite, the conductive agent and the binder in the first coating layer, the second coating layer and the third coating layer may be selected to be the same, may be selected to be different, and are not particularly limited; specifically, the silicon-based material is specifically selected from one or more of nano silicon particles, silicon-oxygen-carbon composite materials, silicon alloy materials and nano silicon/silicon dioxide composites; the graphite is selected from one or two of natural graphite and artificial graphite; the conductive agent is selected from one or more of carbon black, carbon nano tubes and graphene; the binder is selected from one or more of sodium carboxymethylcellulose, styrene butadiene rubber, polyacrylic acid, polyacrylonitrile and sodium alginate. The current collector is selected from current collectors well known to those skilled in the art, and in particular embodiments, the current collector is selected from copper foil having a thickness of 4 to 15 μm. In the application, the total coating formed by the first coating, the second coating and the third coating comprises 5-50%, 50-90%, 1-5% and 1-5% of silicon-based material, graphite, conductive agent and binder respectively by weight.
The application also provides a high-energy density battery, which comprises a positive electrode and a negative electrode, wherein the negative electrode is the silicon-containing negative plate in the scheme. In the present application, the set value of N/P of the positive electrode and the negative electrode is 1.02 to 1.2.
For further understanding of the present invention, the following examples are provided to describe the silicon-containing negative electrode sheet and the high energy density battery in detail, and the scope of the present invention is not limited by the following examples.
Example 1
Manufacturing a positive plate:
the mass ratio of the positive electrode is as follows: nickel cobalt manganese ternary material 811: conductive carbon black: polyvinylidene fluoride =96.5: 2; dissolving polyvinylidene fluoride in N-methyl pyrrolidone solvent to prepare 7% glue solution, then adding conductive carbon black, adding nickel-cobalt-manganese ternary material 811 after complete dispersion until the pulp is uniformly mixed and dispersed, adding N-methyl pyrrolidone to adjust the viscosity to 5000-8000 cp, then uniformly coating the mixed pulp on an aluminum foil with the thickness of 12 mu m, wherein the coating double-sided density is 40mg/cm 2 And rolling and slitting to obtain the positive plate.
And (3) manufacturing a negative plate:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =1.9:93.1:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =28.5:66.5:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 3: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =9.5:85.5:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
to correspond toThe cathode active material weight required by the corresponding cathode is calculated when the capacity of the cathode is excessive by 8%, and the surface density of each coating is set, so that the sum of the silicon-oxygen-carbon composite material and the graphite material in the three coatings is ensured to be the actually required total weight. Setting the double-sided surface density of the first coating layer to be 6.0mg/cm 2 The density of the double-sided surface of the second coating is 4.6mg/cm 2 The density of the double-sided surface of the third coating is 6.0mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil by using an extrusion coating machine in sequence, coating a second coating on the first coating, and coating a third coating on the second coating;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Example 2
The positive electrode sheet was produced in the same manner as in example 1.
And (3) manufacturing a negative plate:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =4.75:91.25:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =42.75:52.25:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 3: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =11.4:83.6:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
and calculating the weight of the negative active material required by the corresponding negative electrode by using the corresponding positive electrode capacity excess of 8%, and setting the surface density of each coating to ensure that the sum of the silicon-oxygen-carbon composite material and the graphite material in the three coatings is the actually required total weight. Setting the double-sided surface density of the first coating layer to be 3.4mg/cm 2 The density of the double-sided surface of the second coating is 6.0mg/cm 2 The density of the double-sided surface of the third coating is 3.4mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil by using an extrusion coating machine in sequence, coating a second coating on the first coating, and coating a third coating on the second coating;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Example 3
The positive electrode sheet was produced in the same manner as in example 1.
And (3) manufacturing a negative plate:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =4.75:91.25:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =57:38:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 3: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =12.8:82.2:1.5:1.5:2; dissolving sodium carboxymethyl cellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
and calculating the weight of the negative active material required by the corresponding negative electrode by using the corresponding positive electrode capacity excess of 8%, and setting the surface density of each coating to ensure that the sum of the silicon-oxygen-carbon composite material and the graphite material in the three coatings is the actually required total weight. Setting the double-sided surface density of the first coating layer to be 2.0mg/cm 2 The density of the double-sided surface of the second coating is 6.0mg/cm 2 The density of the double-sided surface of the third coating is 2.4mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil by using an extrusion coating machine in sequence, coating a second coating on the first coating, and coating a third coating on the second coating;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 1
The positive electrode sheet was produced in the same manner as in example 1.
The weights of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e., the capacity provided by the negative electrode sheet, were exactly the same as in example 1, with the following differences:
the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =11.7:83.3:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
the mixed slurry was then uniformly coated on a copper foil having a thickness of 6 μm at a coating surface density of 16.6mg/cm as calculated corresponding to an excess of 8% in the capacity of the positive electrode 2 The total density of the coated negative electrode is the same as that of the negative electrode coated in the embodiment 1, and a negative electrode sheet is obtained by rolling and slitting;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 2
The positive electrode sheet was produced in the same manner as in example 1.
The weight of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e. the capacity provided by the negative electrode sheet, was exactly the same as in example 1, with the following differences:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =1.9:93.1:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =18.1:76.9:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
and calculating the weight of the negative active material required by the corresponding negative electrode by using the corresponding positive electrode capacity excess of 8%, and setting the surface density of each coating to ensure that the sum of the silicon-oxygen-carbon composite material and the graphite material in the two coatings is the actually required total weight. Setting the double-sided surface density of the first coating layer to be 6.0mg/cm 2 The density of the double-sided surface of the second coating is 10.6mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil and a second coating on the first coating in sequence by using an extrusion coating machine;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 3
The positive electrode sheet was produced in the same manner as in example 1.
The weight of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e. the capacity provided by the negative electrode sheet, was exactly the same as in example 2, with the following differences:
the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =24.7:70.3:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
the mixed slurry was then uniformly coated on a copper foil having a thickness of 6 μm at a coating surface density of 12.8mg/cm calculated as excess of 8% in terms of capacity of the positive electrode 2 The total density of the coated negative electrode is the same as that of the negative electrode coated in the embodiment 2, and the negative electrode sheet is obtained by rolling and slitting;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 4
The positive electrode sheet was produced in the same manner as in example 1.
The weights of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e., the capacity provided by the negative electrode sheet, were exactly the same as in example 2, with the following differences:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =4.75:91.25:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =31.3:63.7:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
and calculating the weight of the negative active material required by the corresponding negative electrode by using the corresponding positive electrode capacity excess of 8%, and setting the surface density of each coating to ensure that the sum of the silicon-oxygen-carbon composite material and the graphite material in the two coatings is the actually required total weight. Setting the double-sided surface density of the first coating layer to be 3.4mg/cm 2 The density of the double-sided surface of the second coating is 9.4mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil and a second coating on the first coating in sequence by using an extrusion coating machine;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminum-plastic shell, injecting electrolyte, forming, aging, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 5
The positive electrode sheet was produced in the same manner as in example 1.
The weight of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e. the capacity provided by the negative electrode sheet, was exactly the same as in example 3, with the following differences:
the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =36.6:58.4:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
the mixed slurry was then uniformly coated on a copper foil having a thickness of 6 μm at a coating surface density of 10.4mg/cm calculated as an excess of 8% in terms of capacity of the positive electrode 2 The total density of the coated negative electrode is the same as that of the negative electrode coated in the embodiment 3, and a negative electrode sheet is obtained by rolling and slitting;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
Comparative example 6
The positive electrode sheet was produced in the same manner as in example 1.
The weight of the silicon-oxygen-carbon composite material and graphite material used for the negative electrode, i.e. the capacity provided by the negative electrode sheet, was exactly the same as in example 3, with the following differences:
negative electrode slurry 1: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =4.75:91.25:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
negative electrode slurry 2: the mass ratio of the negative electrode is as follows: silicon-oxygen-carbon composite material: artificial graphite: conductive carbon black: sodium carboxymethylcellulose, styrene butadiene rubber =44.2:50.8:1.5:1.5:2; dissolving sodium carboxymethylcellulose as a thickening agent in deionized water to prepare a 2.5% glue solution, then adding conductive carbon black, adding the silicon-oxygen-carbon composite material and the artificial graphite in batches after complete dispersion, adding a binder styrene-butadiene rubber emulsion after uniform mixing, and adding water to adjust the viscosity to 2000-4000 cp;
and calculating the weight of the negative active material required by the corresponding negative electrode by using the corresponding positive electrode capacity excess of 8%, and setting the surface density of each coating to ensure that the sum of the silicon-oxygen-carbon composite material and the graphite material in the three coatings is the actually required total weight. Setting the double-sided surface density of the first coating layer to be 2mg/cm 2 The density of the double-sided surface of the second coating is 8.4mg/cm 2 And rolling and slitting to obtain the negative plate. Coating a first coating on a 6um copper foil and a second coating on the first coating in sequence by using an extrusion coating machine;
baking positive and negative plates, die cutting, laminating, welding electrode lugs, packaging with aluminium-plastic shell, injecting electrolyte, ageing, exhausting air and sealing.
And respectively detecting various indexes of internal resistance, capacity, energy density and cycle performance of the aged battery.
The performance test results of the lithium ion batteries prepared in the embodiments 1 to 3 and the comparative examples 1 to 6 of the invention are as follows:
taking each of the example and comparative batteries, charging to 50% SOC at 0.33C at normal temperature, discharging for 10s at 1C, and calculating the direct current internal resistance of the battery at 50% SOC; charging to full charge at normal temperature by 0.33C current, and respectively testing 0.33C discharge capacity and discharge energy of each group of batteries, wherein the constant-voltage cut-off current is 0.033C, and calculating the energy density of the batteries; testing the cycle performance of each group of batteries according to the 1C charging and discharging test flow; fully charging and disassembling the battery which circulates for 100 circles, and observing the state of the negative plate; the test results are shown in table 1 below:
TABLE 1 comparison of Performance tests of examples 1 to 3 with comparative examples 1 to 6
Figure BDA0002990400390000111
Figure BDA0002990400390000121
As can be seen from table 1, the lithium ion battery provided by the invention has small direct current internal resistance of the battery while ensuring higher energy density, and the difference is particularly obvious on a high-capacity negative electrode; specifically, when the negative electrode capacity is 500mAh/g, the performance difference is not large, because the low silicon content and the unobvious expansion have small influence on the performance, but when the negative electrode capacity is improved and the silicon content is increased, namely the negative electrode capacity reaches 650mAh/g and 800mAh/g, the method provided by the invention can obviously improve the performance of the battery. As can be seen from figure 2, the fully charged negative plate can not fall off from the current collector, the interface is free from cracking and pulverization, the side reaction with the electrolyte is greatly reduced, the cycle life of the battery is excellent, and the performance improvement is remarkable.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (7)

1. The silicon-containing negative plate comprises a current collector, a first coating applied to the surface of the current collector, a second coating applied to the surface of the first coating, and a third coating applied to the surface of the second coating;
the first coating, the second coating and the third coating respectively comprise a silicon-containing active substance, a conductive agent and a binder, the silicon-containing active substance is a mixture of a silicon-based material and graphite, and the mass of the silicon-based material in the second coating is larger than that of the silicon-based material in the first coating and that of the silicon-based material in the third coating;
the mass of the silicon-based material in the second coating layer is more than that of the silicon-based material in the third coating layer is more than that of the silicon-based material in the first coating layer;
the mass ratio of the silicon-based material to the graphite in the first coating is (1.5-6.5): (93.5-98.5), wherein the mass ratio of the silicon-based material to the graphite in the second coating is (25-45): (25-75), wherein the mass ratio of the silicon-based material to the graphite in the third coating is (9-30): (70 to 93).
2. The silicon-containing negative electrode plate according to claim 1, wherein the total mass of the silicon-based materials in the coating formed by the first coating, the second coating and the third coating is 5-50 wt% of the total coating mass, the total mass of the graphite is 50-90 wt% of the total coating mass, the total mass of the conductive agent is 1-5 wt% of the total coating mass, and the total mass of the binder is 1-5 wt% of the total coating mass.
3. The silicon-containing negative electrode sheet according to claim 1, wherein the areal density of the first coating layer, the second coating layer and the third coating layer is (1-6): (1-6): (1-6).
4. The silicon-containing negative electrode plate according to claim 1, wherein the silicon-based material is selected from one or more of nano silicon particles, silicon-oxygen-carbon composite materials, silicon alloy materials and nano silicon/silicon dioxide composites; the graphite is selected from one or two of natural graphite and artificial graphite.
5. The silicon-containing negative electrode sheet according to claim 1, wherein the conductive agent is one or more selected from carbon black, carbon nanotubes and graphene; the binder is selected from one or more of sodium carboxymethylcellulose, styrene butadiene rubber, polyacrylic acid, polyacrylonitrile and sodium alginate.
6. The silicon-containing negative electrode sheet according to claim 1, wherein the current collector is a copper foil and has a thickness of 4 to 15 μm.
7. A high energy density battery comprising a positive electrode and a negative electrode, wherein the negative electrode is the silicon-containing negative electrode sheet according to any one of claims 1 to 6.
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