CN113675365A - Negative plate and lithium ion battery - Google Patents

Negative plate and lithium ion battery Download PDF

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Publication number
CN113675365A
CN113675365A CN202111019058.7A CN202111019058A CN113675365A CN 113675365 A CN113675365 A CN 113675365A CN 202111019058 A CN202111019058 A CN 202111019058A CN 113675365 A CN113675365 A CN 113675365A
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negative electrode
electrode material
coating
coating layer
carbon
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CN113675365B (en
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张保海
彭冲
李俊义
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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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
    • 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
    • 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
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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, wherein the negative plate comprises: a current collector; the first coating is coated on the surface of the current collector and comprises a first negative electrode material; a second coating is coated on the surface of the first coating, and the second coating comprises a second negative electrode material; wherein the particle size range of the first anode material is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm. The cathode plate provided by the invention can achieve the aim of taking high dynamics and high compaction into consideration on the surface of the cathode plate. Meanwhile, the fusion degree of the junction between layers is high, the transition is mild, the interlayer bonding is favorably improved, the distribution of current density at the interlayer interface in the charge and discharge process is favorably realized, and the problem of expansion failure of the pole piece in the long-cycle process is further improved.

Description

Negative plate and lithium ion battery
Technical Field
The invention relates to the technical field of batteries, in particular to a negative plate and a lithium ion battery.
Background
With the coming of the 5G era and the rapid development of the lithium ion battery technology, people put higher demands on the energy density and the rapid charging capability of the lithium ion battery, the rapid charging lithium battery is also the development trend of the consumer lithium ion battery, and meanwhile, with the increase of the power consumption of the 5G universal equipment, the cruising capability of the lithium ion battery is also the development trend of the consumer lithium ion battery. The method for improving the energy density of the lithium ion battery at the present stage is to increase the compaction of a negative electrode by using graphite with large particle size and high compaction, and increase the voltage of a positive electrode by using high-voltage lithium cobaltate, but the rapid charging capability of the lithium ion battery is reduced. The improvement of the rapid charging capability necessitates the use of graphite with a small particle size and a high surface carbon coating with superior dynamic properties, while reducing the negative electrode compaction, which leads to a reduction in the energy density of the lithium ion battery. How to balance the energy density and the quick charging capability of the lithium ion battery becomes a problem which prevents the wide application of the lithium ion battery and needs to be solved urgently.
Disclosure of Invention
In view of the above, the invention provides a negative plate and a lithium ion battery, and the invention realizes the purpose of taking high dynamics and high compaction into account by respectively coating negative materials with different particle sizes on the bottom layer close to a current collector and the surface layer far away from the current collector, thereby achieving the effect of improving the high energy density and the quick charge capacity of the lithium ion battery.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a negative electrode sheet, comprising:
a current collector;
a first coating coated on a surface of at least one side of the current collector, the first coating comprising a first negative electrode material;
a second coating layer coated on the surface of the first coating layer, wherein the second coating layer comprises a second negative electrode material;
wherein the particle size range of the first anode material is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm.
Further, the first negative electrode material is any one or a combination of more than two of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon and lithium titanate; the second negative electrode material is any one or a combination of more than two of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon and lithium titanate.
Further, the particle size of the first anode material in the first coating layer satisfies the following relationship:
5 μm < D50-D10<11 μm; and/or
10 μm < D90-D50<15 μm; and/or
18μm<D90-D10<22μm。
Further, the particle size of the second anode material in the second coating layer satisfies the following relationship:
6 μm < D50-D10<10 μm; and/or
8 μm < D90-D50<14 μm; and/or
15μm<D90-D10<20μm。
Further, the particle diameters of the first anode material and the second anode material satisfy the following relationship:
the D10 of the first negative electrode material is 1-5 mu m larger than the D10 of the second negative electrode material; and/or
The D50 of the first negative electrode material is 2-8 mu m larger than the D50 of the second negative electrode material; and/or
The D90 of the first negative electrode material is larger than the D90 of the second negative electrode material by 3-10 μm.
Further, the particle diameters of the first anode material and the second anode material satisfy the following relationship:
the D50 of the first negative electrode material is 3-11 μm larger than the D10 of the second negative electrode material; and/or
The D90 of the first negative electrode material is 12-24 mu m larger than the D10 of the second negative electrode material; and/or
The D90 of the first negative electrode material is 9-18 mu m larger than the D50 of the second negative electrode material; and/or
The D50 of the second negative electrode material is 2-8 μm larger than the D10 of the first negative electrode material; and/or
The D90 of the second negative electrode material is 8-15 mu m larger than the D10 of the first negative electrode material; and/or
The second negative electrode material D90 is 5 to 11 μm larger than the first negative electrode material D50.
Further, the surfaces of the first negative electrode material and the second negative electrode material are both provided with carbon coating layers.
Further, the carbon in the carbon coating layer comprises at least one of soft carbon, hard carbon, organic carbon and graphitized asphalt.
Further, the coating amount of the carbon coating layer of the first negative electrode material is 1-4 wt.%, the carbon coating amount of the carbon coating layer of the second negative electrode material is 3-8 wt.%, and the carbon coating amount of the second negative electrode material is greater than that of the first negative electrode material.
In a second aspect, the invention provides a lithium ion battery comprising the negative electrode sheet as described above.
Further, the lithium ion battery also comprises a positive plate, and the positive plate comprises a current collector; a first coating coated on a surface of at least one side of the current collector, the first coating including lithium cobaltate; a second coating layer coated on a surface of the first coating layer, the second coating layer including lithium cobaltate; wherein the lithium cobaltate in the first coating layer and the lithium cobaltate in the second coating layer are both lithium cobaltates doped with metal elements; the D50 of the lithium cobaltate in the first coating layer is less than the D50 of the lithium cobaltate in the second coating layer; the particle size distribution of the lithium cobaltate in the first coating comprises a first interval and a second interval, the particle size of the lithium cobaltate in the first interval is smaller than that in the second interval, and the doping amount of a metal element of the lithium cobaltate in the first interval is smaller than that in the second interval; the particle size distribution of the lithium cobaltate in the second coating comprises a third interval and a fourth interval, the particle size of the lithium cobaltate in the third interval is smaller than that in the fourth interval, and the doping amount of a metal element of the lithium cobaltate in the third interval is smaller than that in the fourth interval.
Further, in the positive electrode sheet, the particle size range of lithium cobaltate in the first coating layer is: 3 μm < D10<6 μm, 11 μm < D50<16 μm, 19 μm < D90<25 μm; the particle size range of lithium cobaltate in the second coating is as follows: 6 μm < D10<10 μm, 15 μm < D50<19 μm, 26 μm < D90<32 μm.
Further, in the positive plate, the doped metal element includes Al doping, wherein the Al doping amount in the lithium cobaltate in the first coating is as follows: the Al doping amount of the lithium cobaltate with the particle size of less than D10 is 2000 ppm-3500 ppm, the Al doping amount of the lithium cobaltate with the particle size of D10-D50 is 4000 ppm-5500 ppm, and the Al doping amount of the lithium cobaltate with the particle size of D50-D90 is 6000 ppm-7500 ppm; the doping amount of Al in the lithium cobaltate in the second coating is as follows: the Al doping amount of the lithium cobaltate with the particle size of less than D10 is 3500 ppm-5000 ppm, the Al doping amount of the lithium cobaltate with the particle size of D10-D50 is 5500 ppm-6500 ppm, and the Al doping amount of the lithium cobaltate with the particle size of D50-D90 is 7000 ppm-9000 ppm.
The technical scheme of the invention has the following beneficial effects:
the invention provides a negative plate, which comprises: a current collector; a first coating coated on a surface of at least one side of the current collector, the first coating comprising a first negative electrode material; a second coating layer coated on the surface of the first coating layer, wherein the second coating layer comprises a second negative electrode material; wherein the particle size range of the first anode material is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm. The invention coats the large-particle-size high-compaction anode material (namely, a first coating) at the side close to the current collector and coats the small-particle-size high-dynamics anode material (namely, a second coating) at the side far away from the current collector. The negative electrode material in the first coating has large particle size and can improve the compaction of the pole piece, thereby improving the energy density, and the negative electrode material in the second coating has small particle size, good dynamic performance, low compaction, high porosity, high liquid retention and fast ion transmission. Therefore, the purpose of realizing both high dynamics and high compaction of the pole piece surface can be realized. Meanwhile, the particle sizes of the first negative electrode material and the second negative electrode material are set to meet the relation, so that the fusion degree of the coatings of the two layers of negative electrode materials at the junction of the layers is high, the transition is mild, the interlayer bonding is favorably improved, the distribution of current density at the interface between the layers in the charge-discharge process is favorably realized, and the problem of expansion failure of the pole piece in the long-cycle process is solved.
Drawings
Fig. 1 is a schematic structural view of a negative electrode sheet.
Reference numerals:
a first coating layer L1; second coating L2.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention in conjunction with the following examples, but it will be understood that the description is intended to illustrate the features and advantages of the invention further, and not to limit the invention.
In a first aspect, the present invention provides a negative electrode sheet, comprising: a current collector; a first coating coated on a surface of at least one side of the current collector, the first coating comprising a first negative electrode material; a second coating layer coated on the surface of the first coating layer, wherein the second coating layer comprises a second negative electrode material; wherein the particle size range of the first anode material is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm.
Specifically, in order to solve the problem that the high energy density and the quick charge capacity of the traditional lithium ion battery are difficult to be considered, the invention provides the negative plate with the double-layer structure. The invention provides a negative plate which comprises the following components: the negative electrode material with large particle size and high compaction (namely, a first coating) is coated on the side close to the current collector, and the negative electrode material with small particle size and high kinetics (namely, a second coating) is coated on the side far away from the current collector. The negative electrode material in the first coating has large particle size and can improve the compaction of the pole piece, thereby improving the energy density, and the negative electrode material in the second coating has small particle size, good dynamic performance, low compaction, high porosity, high liquid retention and fast ion transmission.
Meanwhile, it is noted that the particle size difference of the negative electrode materials in the first coating and the second coating cannot be too great, the great particle size difference can cause an obvious interface between an upper layer and a lower layer, the two layers cannot be well fused, the physical bonding and the chemical bonding at the transition position between the layers are poor, the bonding at the interface of the upper layer and the lower layer is poor, the separation of the upper layer and the lower layer is easy to occur in the long circulation process, and the expansion of the pole piece is excessively thick and the circulation failure is caused. After experimental verification, the particle size of the negative electrode material in the first coating and the second coating is specifically limited, wherein the particle size range of the first negative electrode material in the first coating is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material in the second coating is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm. The particle size of the negative electrode materials in the first coating and the second coating is set to meet the relation, so that the fusion degree of the coatings of the two layers of negative electrode materials at the junction of the layers is high, the transition is mild, the interlayer bonding is favorably improved, the distribution of current density at the interface between the layers in the charge-discharge process is favorably realized, and the problem of expansion failure of the pole piece in the long-cycle process is further improved.
In some embodiments of the present invention, the first negative electrode material is any one or a combination of two or more of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon, and lithium titanate; the second negative electrode material is any one or a combination of more than two of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon and lithium titanate. The first negative electrode material and the second negative electrode material may be the same or different, for example, the first negative electrode material may be artificial graphite, and the second negative electrode material may also be artificial graphite, lithium titanate, or a combination of artificial graphite and lithium titanate.
In some embodiments of the invention, the particle size of the first anode material in the first coating satisfies the following relationship: 5 μm < D50-D10<11 μm; and/or 10 μm < D90-D50<15 μm; and/or 18 μm < D90-D10<22 μm. In addition to the above-defined D10, D50 and D90 of the first anode material in the first coating layer, it is preferable that there is also a proper size relationship among D10, D50 and D90 of the first anode material in the first coating layer, i.e. the particle sizes of the first anode material in the first coating layer should also be uniformly distributed, and the particle sizes of the anode materials in the same coating layer should not be too different.
In some embodiments of the invention, the particle size of the second anode material in the second coating satisfies the following relationship: 6 μm < D50-D10<10 μm; and/or 8 μm < D90-D50<14 μm; and/or 15 μm < D90-D10<20 μm. The same principle as defining the particle size distribution of the first anode material in the first coating, there is preferably also a suitable size relationship between D10, D50 and D90 of the second pole material in the second layer of the invention.
In some embodiments of the present invention, the particle size of the first anode material and the second anode material satisfies the following relationship: the D10 of the first negative electrode material is 1-5 mu m larger than the D10 of the second negative electrode material; and/or the D50 of the first negative electrode material is 2-8 μm larger than the D50 of the second negative electrode material; and/or the D90 of the first negative electrode material is larger than the D90 of the second negative electrode material by 3-10 mu m.
In some embodiments of the present invention, the particle size of the first anode material and the second anode material satisfies the following relationship: the D50 of the first negative electrode material is 3-11 μm larger than the D10 of the second negative electrode material; and/or the D90 of the first negative electrode material is 12-24 μm larger than the D10 of the second negative electrode material; and/or the D90 of the first negative electrode material is 9-18 μm larger than the D50 of the second negative electrode material; and/or the D50 of the second negative electrode material is 2-8 μm larger than the D10 of the first negative electrode material; and/or the D90 of the second negative electrode material is 8-15 μm larger than the D10 of the first negative electrode material; and/or the D90 of the second negative electrode material is 5-11 μm larger than the D50 of the first negative electrode material.
Preferably, the invention also defines the particle size relationship between the first negative electrode material and the second negative electrode material, so as to ensure that the particle size of the first negative electrode material is larger than that of the second negative electrode material, and simultaneously, the particle size difference between the first negative electrode material and the second negative electrode material is not too great, so that the fusion degree of the first coating and the second coating at the junction between the layers is high, and the transition is relatively mild, thereby ensuring the interlayer bonding effect and avoiding the problem that the pole piece of the lithium ion battery made of the negative pole piece expands and fails in the long-cycle process.
In some embodiments of the invention, the invention further defines the thickness relationship of the first coating and the second coating: thickness ratio of the first coating layer to the second coating layer 3: 7-7: 3, preferably 4: 6-6: 4, more preferably 5: 5.
in some embodiments of the invention, the first negative electrode material and the second negative electrode material have carbon coatings on their surfaces.
In some embodiments of the present invention, the carbon in the carbon coating layer comprises at least one of soft carbon, hard carbon, organic carbon, graphitized pitch.
In some embodiments of the present invention, the coating amount of the carbon coating layer of the first negative electrode material is 1 to 4 wt.%, the carbon coating amount of the carbon coating layer of the second negative electrode material is 3 to 8 wt.%, and the carbon coating amount of the second negative electrode material is greater than the carbon coating amount of the first negative electrode material.
In the invention, before the first negative electrode material and the second negative electrode material are prepared into the negative electrode plate, carbon coating is further performed, and carbon in the carbon coating comprises soft carbon, hard carbon, organic carbon, graphitized asphalt and the like. And mixing the carbon-coated raw material with the first negative electrode material or the second negative electrode material in proportion, and calcining at high temperature to realize carbon coating of the first negative electrode material or the second negative electrode material.
In a second aspect, the invention provides a lithium ion battery comprising the negative electrode sheet as described above.
In some embodiments of the present invention, the lithium ion battery further comprises a positive plate, the positive plate comprising a current collector; a first coating coated on a surface of at least one side of the current collector, the first coating including lithium cobaltate; a second coating layer coated on a surface of the first coating layer, the second coating layer including lithium cobaltate; wherein the lithium cobaltate in the first coating layer and the lithium cobaltate in the second coating layer are both lithium cobaltates doped with metal elements; the D50 of the lithium cobaltate in the first coating layer is less than the D50 of the lithium cobaltate in the second coating layer; the particle size distribution of the lithium cobaltate in the first coating comprises a first interval and a second interval, the particle size of the lithium cobaltate in the first interval is smaller than that in the second interval, and the doping amount of a metal element of the lithium cobaltate in the first interval is smaller than that in the second interval; the particle size distribution of the lithium cobaltate in the second coating comprises a third interval and a fourth interval, the particle size of the lithium cobaltate in the third interval is smaller than that in the fourth interval, and the doping amount of a metal element of the lithium cobaltate in the third interval is smaller than that in the fourth interval.
In some embodiments of the present invention, in the positive electrode sheet, the particle size range of lithium cobaltate in the first coating layer is: 3 μm < D10<6 μm, 11 μm < D50<16 μm, 19 μm < D90<25 μm; the particle size range of lithium cobaltate in the second coating is as follows: 6 μm < D10<10 μm, 15 μm < D50<19 μm, 26 μm < D90<32 μm.
In some embodiments of the present invention, in the positive electrode sheet, the doped metal element includes Al doping, wherein an Al doping amount in the lithium cobaltate in the first coating layer is: the Al doping amount of the lithium cobaltate with the particle size of less than D10 is 2000 ppm-3500 ppm, the Al doping amount of the lithium cobaltate with the particle size of D10-D50 is 4000 ppm-5500 ppm, and the Al doping amount of the lithium cobaltate with the particle size of D50-D90 is 6000 ppm-7500 ppm; the doping amount of Al in the lithium cobaltate in the second coating is as follows: the Al doping amount of the lithium cobaltate with the particle size of less than D10 is 3500 ppm-5000 ppm, the Al doping amount of the lithium cobaltate with the particle size of D10-D50 is 5500 ppm-6500 ppm, and the Al doping amount of the lithium cobaltate with the particle size of D50-D90 is 7000 ppm-9000 ppm.
The negative electrode material in the first coating of the negative electrode plate has large particle size, can improve the compaction of the negative electrode plate, thereby improving the energy density, and the negative electrode material in the second coating has small particle size, good dynamic performance, low compaction, high porosity, high liquid retention and fast ion transmission. Therefore, the lithium ion battery comprising the negative plate can achieve the effect of improving the high energy density and the quick charging capacity of the lithium ion battery.
The invention is further illustrated by the following specific examples.
Example 1
Preparation of first coating (L1) slurry: taking artificial graphite as a negative active material (L1 negative material), wherein the particle size distribution of the artificial graphite is shown in Table 1, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black into a stirring tank according to the mass ratio of 96.9:1.5:1.3:13, adding a deionized water solvent, fully stirring according to the batching process of the prior art, and filtering through a 150-mesh screen to obtain a first coating (L1) slurry with the solid content of 40-45%;
preparation of a second coating (L2) slurry: taking artificial graphite as a negative active material (L2 negative material), wherein the particle size distribution of the artificial graphite is shown in Table 1, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black into a stirring tank according to the mass ratio of 96.9:1.5:1.3:13, adding a deionized water solvent, fully stirring according to the batching process of the prior art, filtering through a 150-mesh screen, and preparing second coating (L2) slurry with the negative solid content of 40-45%;
coating a negative electrode, and preparing a sheet: coating the negative electrode slurry on a copper foil current collector by using a double-layer coating machine, coating an L1 layer on the current collector, coating an L2 layer on an L1 layer, wherein the thickness ratio of the L1 layer to the L2 layer is 1:1, forming a double-layer structure, and drying at the temperature of 100 ℃ to prepare an initial negative electrode piece; and cutting the initial pole piece according to actual requirements to prepare the negative pole piece.
Preparing positive electrode slurry: lithium cobaltate is used as a positive electrode active material, then the positive electrode active material, a conductive agent and polyvinylidene fluoride are added into a stirring tank according to the mass ratio of 97.2:1.5:1.3, NMP solvent is added, the materials are fully stirred according to the batching process in the prior art, and the mixture is sieved by a 200-mesh sieve to prepare positive electrode slurry, wherein the solid content of the positive electrode slurry is 70-75%;
coating the positive electrode and preparing a sheet:
coating the positive electrode slurry on an aluminum foil current collector by using a coating machine, and drying at the temperature of 120 ℃ to prepare an initial positive electrode piece; and cutting the initial pole piece according to actual requirements to prepare the positive pole piece.
Assembling the battery cell:
and winding the positive plate, the negative plate and the diaphragm together to form a winding core, packaging by using an aluminum plastic film, baking to remove moisture, injecting electrolyte, and forming by adopting a hot-pressing formation process to obtain the battery core.
Example 2
Preparing carbon-coated artificial graphite: mixing the artificial graphite particles with the asphalt micropowder, carrying out thermal dynamic kneading, then carbonizing at 800-1500 ℃, coating, and then crushing and screening to obtain the carbon-coated artificial graphite particles. Wherein, the pitch micro powder adopted by the artificial graphite particles in the L1 layer is 8% when the artificial graphite particles are coated by carbon, and the coating amount of the actually obtained carbon-coated artificial graphite is 2%. Wherein the content of pitch micropowder adopted in the artificial graphite particles in the L2 layer during carbon coating is 13%, and the coating amount of the actually obtained carbon-coated artificial graphite is 5%.
Preparing cathode slurry by using the two artificial graphites with different carbon coating amounts as cathode materials, wherein the particle size distribution of the artificial graphites is shown in table 1, and the preparation method of the cathode slurry is the same as that of the cathode slurry prepared in the example 1;
and (3) preparing a negative plate: same as example 1;
coating the positive plate, and preparing the plate: same as example 1;
assembling the battery cell: same as in example 1.
Examples 3 to 6
Preparing anode slurry: selecting artificial graphite particles according to the particle size distribution in the examples 3-6 in the table 1, and preparing first coating (L1) slurry and second coating (L2) slurry by the same steps as the example 1;
coating the negative plate, and preparing the plate: same as example 1;
preparing a positive plate: same as example 1;
assembling the battery cell: same as in example 1.
Example 7
Selecting natural graphite particles according to the particle size distribution in example 7 in table 1, and preparing a first coating (L1) slurry and a second coating (L2) slurry by the same steps as in example 1;
coating the negative plate, and preparing the plate: same as example 1;
preparing a positive plate: same as example 1;
assembling the battery cell: same as in example 1.
Comparative example 1
Preparing anode slurry: taking artificial graphite as a negative electrode active material, wherein the particle size distribution of the artificial graphite is shown in table 1, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black, the styrene butadiene rubber and the sodium carboxymethyl cellulose into a stirring tank according to the mass ratio of 96.9:1.5:1.3:13, adding a deionized water solvent, fully stirring according to the batching process of the prior art, and filtering through a 150-mesh screen to prepare a negative electrode slurry with the solid content of 40-45%;
coating the negative plate, and preparing the plate: coating the negative electrode slurry on a copper foil current collector by using a coating machine, and drying at the temperature of 100 ℃ to prepare an initial negative electrode piece; cutting the initial pole piece according to actual requirements to prepare a negative pole piece;
preparing a positive plate: same as example 1;
assembling the battery cell: same as in example 1.
Comparative example 2
Preparing anode slurry: taking artificial graphite as a negative electrode active material, wherein the particle size distribution of the artificial graphite is shown in table 1, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black, the styrene butadiene rubber and the sodium carboxymethyl cellulose into a stirring tank according to the mass ratio of 96.9:1.5:1.3:13, adding a deionized water solvent, fully stirring according to the batching process of the prior art, and filtering through a 150-mesh screen to prepare a negative electrode slurry with the solid content of 40-45%;
coating the negative plate, and preparing the plate: coating the negative electrode slurry on a copper foil current collector by using a coating machine, and drying at the temperature of 100 ℃ to prepare an initial negative electrode piece; cutting the initial pole piece according to actual requirements to prepare a negative pole piece;
preparing a positive plate: same as example 1;
assembling the battery cell: same as in example 1.
Comparative example 3
Preparing anode slurry: taking natural graphite as a negative electrode active material, wherein the particle size distribution of the natural graphite is shown in table 1, taking conductive carbon black as a conductive agent, styrene butadiene rubber as a binder and sodium carboxymethyl cellulose as a thickening agent, adding the conductive carbon black, styrene butadiene rubber and sodium carboxymethyl cellulose into a stirring tank according to the mass ratio of 96.9:1.5:1.3:13, adding a deionized water solvent, fully stirring according to the batching process of the prior art, and filtering through a 150-mesh screen to prepare a negative electrode slurry with the solid content of 40-45%;
coating the negative plate, and preparing the plate: coating the negative electrode slurry on a copper foil current collector by using a coating machine, and drying at the temperature of 100 ℃ to prepare an initial negative electrode piece; cutting the initial pole piece according to actual requirements to prepare a negative pole piece;
preparing a positive plate: same as example 1;
assembling the battery cell: same as in example 1.
And (3) testing:
the lithium ion batteries prepared in examples 1-8 and comparative examples 1-2 were tested for 3C charge/0.7C cycle at 25 ℃, using the following specific test methods: using a blue test apparatus, a test cycle was performed 1000 times at 25 ℃ using 3C charging to the upper limit voltage, and then 0.7V discharging to 3.0V. The cycle life and energy density are shown in table 2. The results in table 2 show that the negative electrode sheet and the lithium ion battery thereof prepared by the invention can effectively solve the problem of high energy density and quick charging capability, and meanwhile, the invention is beneficial to limiting the particle sizes of the upper layer and the lower layer, and the particle sizes of the upper layer and the lower layer are not too greatly different, so that the fusion degree of two layers of graphite at the junction of the layers is high, the transition is mild, the physical bonding and the chemical bonding at the transition between the layers are good, and the problem of expansion failure of the electrode sheet in the long-circulating process of improving the interlayer bonding is favorably solved.
TABLE 1 particle size distribution of negative electrode active materials in examples 1 to 8 and comparative examples 1 to 2
Figure BDA0003241093280000121
TABLE 2 test results of the lithium ion batteries of examples 1 to 8 and comparative examples 1 to 2
ED Capacity retention rate Expansion of
800T％ 800T％
Example 1 734 81.95％ 9.75％
Example 2 733 83.27％ 9.58％
Example 3 731 82.93％ 8.78％
Example 4 736 80.77％ 10.29％
Example 5 737 81.18％ 9.35％
Example 6 730 84.35％ 9.03％
Example 7 714 71.68％ 10.95％
Comparative example 1 730 74.75％ 14.04％
Comparative example 2 719 83.66％ 10.88％
Comparative example 3 709 63.77％ 12.35％
Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (10)

1. A negative electrode sheet, comprising:
a current collector;
a first coating coated on a surface of at least one side of the current collector, the first coating comprising a first negative electrode material;
a second coating layer coated on the surface of the first coating layer, wherein the second coating layer comprises a second negative electrode material;
wherein the particle size range of the first anode material is as follows: 6 μm < D10<10 μm, 13 μm < D50<17 μm, 23 μm < D90<28 μm; the particle size range of the second anode material is as follows: 4 μm < D10<7 μm, 9 μm < D50<14 μm, 19 μm < D90<25 μm.
2. The negative electrode sheet according to claim 1, wherein the first negative electrode material is any one or a combination of two or more of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon, and lithium titanate; the second negative electrode material is any one or a combination of more than two of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, organic polymer compound carbon and lithium titanate.
3. The negative electrode sheet according to claim 1, wherein the particle size of the first negative electrode material in the first coating layer satisfies the following relationship:
5 μm < D50-D10<11 μm; and/or
10 μm < D90-D50<15 μm; and/or
18μm<D90-D10<22μm。
4. The negative electrode sheet according to claim 1, wherein the particle size of the second negative electrode material in the second coating layer satisfies the following relationship:
6 μm < D50-D10<10 μm; and/or
8 μm < D90-D50<14 μm; and/or
15μm<D90-D10<20μm。
5. The negative electrode sheet according to claim 1, wherein the particle diameters of the first negative electrode material and the second negative electrode material satisfy the following relationship:
the D10 of the first negative electrode material is 1-5 mu m larger than the D10 of the second negative electrode material; and/or
The D50 of the first negative electrode material is 2-8 mu m larger than the D50 of the second negative electrode material; and/or
The D90 of the first negative electrode material is larger than the D90 of the second negative electrode material by 3-10 μm.
6. The negative electrode sheet according to claim 1, wherein the particle diameters of the first negative electrode material and the second negative electrode material satisfy the following relationship:
the D50 of the first negative electrode material is 3-11 μm larger than the D10 of the second negative electrode material; and/or
The D90 of the first negative electrode material is 12-24 mu m larger than the D10 of the second negative electrode material; and/or
The D90 of the first negative electrode material is 9-18 mu m larger than the D50 of the second negative electrode material; and/or
The D50 of the second negative electrode material is 2-8 μm larger than the D10 of the first negative electrode material; and/or
The D90 of the second negative electrode material is 8-15 mu m larger than the D10 of the first negative electrode material; and/or
The second negative electrode material D90 is 5 to 11 μm larger than the first negative electrode material D50.
7. The negative electrode sheet according to any one of claims 1 to 6, wherein the first negative electrode material and the second negative electrode material each have a carbon coating layer on the surface thereof;
the carbon in the carbon coating layer comprises at least one of soft carbon, hard carbon, organic carbon and graphitized asphalt.
8. The negative electrode sheet according to claim 7, wherein the coating amount of the carbon coating layer of the first negative electrode material is 1 to 4 wt.%, the coating amount of the carbon coating layer of the second negative electrode material is 3 to 8 wt.%, and the coating amount of the carbon coating layer of the second negative electrode material is greater than the coating amount of the carbon coating layer of the first negative electrode material.
9. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1 to 8.
10. The lithium ion battery of claim 9, further comprising a positive plate, the positive plate comprising a current collector; a first coating coated on a surface of at least one side of the current collector, the first coating including lithium cobaltate; a second coating layer coated on a surface of the first coating layer, the second coating layer including lithium cobaltate; wherein the lithium cobaltate in the first coating layer and the lithium cobaltate in the second coating layer are both lithium cobaltates doped with metal elements;
the D50 of the lithium cobaltate in the first coating layer is less than the D50 of the lithium cobaltate in the second coating layer;
the particle size distribution of the lithium cobaltate in the first coating comprises a first interval and a second interval, the particle size of the lithium cobaltate in the first interval is smaller than that in the second interval, and the doping amount of a metal element of the lithium cobaltate in the first interval is smaller than that in the second interval;
the particle size distribution of the lithium cobaltate in the second coating comprises a third interval and a fourth interval, the particle size of the lithium cobaltate in the third interval is smaller than that in the fourth interval, and the doping amount of a metal element of the lithium cobaltate in the third interval is smaller than that in the fourth interval.
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