CN115275097A - Negative pole piece and preparation method and application thereof - Google Patents
Negative pole piece and preparation method and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 68
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 64
- 239000010439 graphite Substances 0.000 claims abstract description 64
- 229910021384 soft carbon Inorganic materials 0.000 claims abstract description 27
- 229910021385 hard carbon Inorganic materials 0.000 claims abstract description 23
- 239000013543 active substance Substances 0.000 claims abstract description 19
- 239000000203 mixture Substances 0.000 claims abstract description 17
- 239000002002 slurry Substances 0.000 claims description 42
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 37
- 229910001416 lithium ion Inorganic materials 0.000 claims description 37
- 239000011248 coating agent Substances 0.000 claims description 22
- 238000000576 coating method Methods 0.000 claims description 22
- 238000003825 pressing Methods 0.000 claims description 17
- 238000005056 compaction Methods 0.000 claims description 16
- 239000002245 particle Substances 0.000 claims description 15
- 229920003048 styrene butadiene rubber Polymers 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 12
- 239000006258 conductive agent Substances 0.000 claims description 11
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 10
- 239000002904 solvent Substances 0.000 claims description 10
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 8
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 claims description 8
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 7
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 7
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 claims description 6
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 5
- 239000007787 solid Substances 0.000 claims description 5
- 239000008367 deionised water Substances 0.000 claims description 4
- 229910021641 deionized water Inorganic materials 0.000 claims description 4
- 239000002086 nanomaterial Substances 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 239000003921 oil Substances 0.000 claims description 3
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 claims description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 2
- 239000002041 carbon nanotube Substances 0.000 claims description 2
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 2
- 229910021389 graphene Inorganic materials 0.000 claims description 2
- 229920003123 carboxymethyl cellulose sodium Polymers 0.000 claims 2
- 229940063834 carboxymethylcellulose sodium Drugs 0.000 claims 2
- 238000007600 charging Methods 0.000 abstract description 15
- 239000011149 active material Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 13
- 239000002131 composite material Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 230000005012 migration Effects 0.000 description 7
- 238000013508 migration Methods 0.000 description 7
- 230000010287 polarization Effects 0.000 description 7
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 5
- 238000010521 absorption reaction Methods 0.000 description 5
- 239000007788 liquid Substances 0.000 description 5
- 229910052744 lithium Inorganic materials 0.000 description 5
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 4
- 239000002174 Styrene-butadiene Substances 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 4
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 4
- 238000009830 intercalation Methods 0.000 description 4
- 230000002687 intercalation Effects 0.000 description 4
- 230000007774 longterm Effects 0.000 description 4
- 239000007790 solid phase Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- RXBBZJPEEIUBJG-UHFFFAOYSA-N [O].[Si].[Li] Chemical compound [O].[Si].[Li] RXBBZJPEEIUBJG-UHFFFAOYSA-N 0.000 description 3
- 229910003481 amorphous carbon Inorganic materials 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007773 negative electrode material Substances 0.000 description 3
- 229920006184 cellulose methylcellulose Polymers 0.000 description 2
- 238000010277 constant-current charging Methods 0.000 description 2
- 230000001351 cycling effect Effects 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 241001391944 Commicarpus scandens Species 0.000 description 1
- 102000004310 Ion Channels Human genes 0.000 description 1
- 239000006183 anode active material Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 239000012752 auxiliary agent Substances 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000375 suspending agent Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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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
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- 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
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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
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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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
-
- 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
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- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a negative pole piece and a preparation method and application thereof, wherein the negative pole piece comprises a negative pole current collector, a second active substance layer and a first active substance layer arranged between the negative pole current collector and the second active substance layer, the active substance of the first active substance layer comprises a mixture of first graphite and soft carbon and/or hard carbon, and the active substance of the second active substance layer comprises second graphite and Li x Si y O z The negative pole piece is double-layerThe structure has good wettability, and simultaneously meets the requirements of high energy density and quick charging.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a negative pole piece and a preparation method and application thereof.
Background
The lithium ion battery has high energy density, high working voltage, environmental friendliness and strong manufacturability, and is widely applied to the fields of mobile phones, notebook computers, electric automobiles and energy storage at present. With the increasing market of power batteries, in order to pursue higher endurance and higher charging speed, greater challenges are provided for the energy density and rate capability of lithium ion batteries.
The method for improving the energy density and the rate performance of the lithium ion battery in the market at present mainly depends on battery materials and electrode design, for example, gram capacity and compaction density of positive and negative electrode materials are improved to improve the energy density of a battery core, but the method has large technical barrier and is difficult to industrialize, and the supported charging rate can be gradually reduced along with the improvement of gram capacity of the negative electrode material, so that the energy density and the quick charging performance can not be considered; if a high-surface-density electrode process is adopted, the wettability of the pole piece is greatly influenced, meanwhile, the migration distance of lithium ions is increased, the migration channel is reduced, and the charging multiplying power is greatly reduced.
CN113380983A discloses a high compaction negative pole piece, a preparation method thereof and a lithium ion battery containing the pole piece, wherein the high compaction negative pole piece comprises a negative pole coating and a negative pole current collector; the negative electrode coating comprises a negative electrode active material, an additive, a conductive agent, a suspending agent and a binder, wherein the additive is a high compaction additive.
CN113299918A discloses a negative electrode plate and a lithium ion battery comprising the same, wherein a dispersing auxiliary agent is directly added into the negative electrode plate, so that the operation is convenient, the impregnation of electrolyte is improved, and the multiplying power charge and discharge performance of the battery can be improved.
According to the scheme, the additive is added to improve the compaction density and wettability of the negative pole piece, and the rate performance and the energy density of the pole piece are affected, so that the application of the pole piece in practice is limited.
Disclosure of Invention
The invention aims to provide a negative pole piece and a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a negative electrode plate, including a negative electrode current collector, a second active material layer, and a first active material layer disposed between the negative electrode current collector and the second active material layer, wherein the active material of the first active material layer includes first graphite and soft carbon and/or ∑ ∑ nOr a mixture of hard carbons, the active material of the second active material layer including second graphite and Li x Si y O z Wherein x is 1 to 4 (1, 2, 3, 4, etc.), y is 0.1 to 2 (e.g., 0.1, 0.5, 1, 1.5, 2, etc.), and z is 3 to 5 (3, 3.5, 4, 4.5, 5, etc.).
The negative pole piece adopts a double-layer structure design, the first active substance layer is an inner layer, the layer is made of a mixture of small-particle-size graphite and soft carbon or hard carbon, when lithium ions are embedded, the small-particle-size graphite has a shorter migration distance, the solid-phase diffusion impedance of the lithium ions can be effectively reduced, the anode polarization is reduced, meanwhile, the mixed soft carbon and hard carbon are amorphous carbon, more lithium ion embedding channels are formed, the interface impedance is effectively reduced when the lithium ions are embedded, the effect of reducing the anode polarization can be achieved, the multiplying power performance is improved, the second active substance layer is an outer layer, the layer is made of a mixed material of large graphite and lithium silicon oxygen composite oxide, and the Li is an Li/Si/O composite oxide composite material x Si y O z To prelithiate SiO, a potential difference between the anode and cathode occurs during long-term cycling as lithium ions are consumed, at which point Li x Si y O z Can gradually release lithium ions to replenish lost lithium ions, improve the long-term cycle life of the battery and provide higher energy density.
Preferably, the median particle diameter D50 of the first graphite is from 5 to 15 μm, for example: 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, or the like.
Preferably, the median particle diameter D50 of the soft and/or hard carbon is from 6 to 10 μm, for example: 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or the like.
Preferably, the mass ratio of the first graphite to the soft carbon and/or the hard carbon is (70-87) to (13-30), such as: 70, 75, 20, 82.
The inner layer of the negative pole piece adopts the mixture of small-particle-size graphite and soft carbon or hard carbon, so that the conductivity between the negative pole piece and a current collector is improved, the lithium ion embedding distance is shortened, the lithium ion embedding speed is increased, and the internal resistance of a battery cell is reduced.
Preferably, the median particle diameter D50 of the second graphite is from 15 to 25 μm, for example: 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, or the like.
Preferably, the Li x Si y O z Is a nano material.
Preferably, the second graphite and Li x Si y O z The mass ratio of (87-95) to (5-13), for example: 87: 13. 88.
The outer layer of the negative pole piece adopts graphite with large particle size and Li x Si y O z The nanometer materials are mixed, the graphite with large particle size improves the compaction density of the pole piece, meanwhile, the graphite with outer layer still has higher porosity after cold pressing, and the lithium ions can be ensured to smoothly enter the pole piece, li x Si y O z The nano material improves the energy density of the cell by pre-lithiating SiO.
In a second aspect, the present invention provides a method for preparing the negative electrode plate according to the first aspect, wherein the preparation method comprises the following steps:
(1) Mixing first graphite, soft carbon and/or hard carbon, a conductive agent and a binder with a first solvent to obtain first slurry, and mixing second graphite and Li x Si y O z Mixing the conductive agent, the binder and a second solvent to obtain a second slurry;
(2) And coating the first slurry on the surface of a negative current collector, coating the second slurry on the surface of the first slurry, and performing cold pressing treatment to obtain the negative pole piece.
Preferably, the conductive agent in step (1) comprises any one or a combination of at least two of conductive carbon black, carbon nanotubes or graphene.
Preferably, the binder comprises sodium carboxymethyl cellulose and/or styrene butadiene rubber, preferably sodium carboxymethyl cellulose and styrene butadiene rubber.
Preferably, the first solvent comprises deionized water.
Preferably, the oil-based solvent includes any one of or a combination of at least two of dimethylsulfoxide, N-dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.
Preferably, the mass ratio of the mixture of the first graphite and the soft carbon and/or the hard carbon, the conductive agent, the sodium carboxymethyl cellulose, and the styrene-butadiene rubber is (94-97): 1.0-2.0: (1.2-1.8): 1.5-2.5), for example: 94:1.8:1.7:2.5, 95.
Preferably, the second graphite and Li x Si y O z The mass ratio of the mixture of (1) and (96) to the conductive agent of sodium carboxymethyl cellulose to the styrene-butadiene rubber is (0.5-1.7) to (1.0-3.2) to (1.2-2.8), for example: 94:1.8:1.7:2.5, 95.
Preferably, the solid content of the first slurry in the step (1) is 55 to 60%, for example: 55%, 56%, 57%, 58%, 59%, 60%, etc.
Preferably, the viscosity of the first slurry is 3000 to 5500 mPa-s, for example: 3000 mPas, 3500 mPas, 4000 mPas, 4500 mPas or 5500 mPas, etc.
Preferably, the solids content of the second slurry is from 51 to 55%, for example: 51%, 52%, 53%, 54%, 55%, or the like.
Preferably, the viscosity of the first slurry is 3000 to 5500 mPa-s, for example: 3000 mPas, 3500 mPas, 4000 mPas, 4500 mPas or 5500 mPas, etc.
Preferably, the coating thickness of the first slurry, the coating thickness of the second slurry and the compacted density of the cold pressing treatment in the step (2) satisfy the relation that c = (0.047 b-0.021 a)/3, c is 1.50-1.68 g/cm 3 For example: 1.50g/cm 3 、1.52g/cm 3 、1.55g/cm 3 、1.6g/cm 3 Or 1.68g/cm 3 And the like, wherein the coating thickness of the first slurry is a mu m, the coating thickness of the second slurry is b mu m, and the compaction density of the cold pressing treatment is c g/cm 3 。
The inner layer slurry is a combination of small-particle-size graphite and soft carbon or hard carbon, when lithium ions are embedded, the small-particle-size graphite has a shorter migration distance, the solid-phase diffusion impedance of the lithium ions can be effectively reduced, the anode polarization is reduced, meanwhile, the mixed soft carbon and hard carbon are amorphous carbon, more lithium ion embedding channels are formed, the interface impedance is effectively reduced when the lithium ions are embedded, and the effect of reducing the anode polarization can be achieved as wellThe particle size of the slurry particles is small, and meanwhile, the quick filling performance needs to be ensured, so that the compacted density is small; the outer layer slurry is large-particle-size graphite and Li X Si y O z In the industrial production of the mixture, the cold pressing speed can often reach 40-80m/min, the outer layer and the inner layer of the pole piece are stressed unevenly, so that the pressure on graphite on the outer layer of the pole piece is often larger, the outer layer adopts graphite with large particle size, the graphite with large particle size has higher compaction density, better pore channels can be ensured after cold pressing, and the electrolyte infiltration and lithium ion channels are ensured.
In a third aspect, the present invention provides a lithium ion battery, including the negative electrode tab according to the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The negative pole piece adopts a double-layer structure design, the first layer is an inner layer which is made of a mixture of small-particle-size graphite and soft carbon or hard carbon and improves the rate capability, and the second layer is an outer layer which is made of a mixture of large graphite and lithium silicon oxygen composite oxide and provides higher energy density.
(2) The porosity of the negative pole piece can reach more than 40 percent, the negative pole piece shows good liquid absorption rate and pole piece wettability, the 1C discharge capacity at 25 ℃ after the battery is prepared can reach more than 2489mAh, the 3C charging constant current ratio can reach more than 96.9 percent, and the DCR can reach less than 13.4m omega.
Drawings
Fig. 1 is a schematic view of the structure of the negative electrode sheet described in example 1, (1) -a current collector, (2) -a first active material layer, (3) -a second active material layer.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The proportions in the examples of the present invention and comparative examples are mass ratios unless otherwise specified.
Example 1
The embodiment provides a negative pole piece, which is prepared by the following method:
(1) A first graphite with a D50 of 10 μm and a soft carbon mixture with a D50 of 8 μm, conductive carbon black, sodium carboxymethylcellulose (hereinafter abbreviated as CMC) and styrene butadiene rubber (hereinafter abbreviated as SBR) were mixed with deionized water according to a ratio of 95.1.8 to homogenize with stirring, so as to obtain a first slurry with a solid content of 58% and a viscosity of 4500mPa · s, wherein the mass ratio of the first graphite to the soft carbon is 80 2 Si 1 O 3 The mixture, conductive carbon black, CMC, and SBR were mixed with dimethyl sulfoxide at a ratio of 95.8 2 Si 1 O 3 The mass ratio of (1) to (2) is 90;
(2) Coating a first slurry on the surface of a negative current collector, coating a second slurry on the surface of the first slurry, and performing cold pressing treatment to obtain the negative pole piece, wherein the coating thickness of the first slurry is a =60 μm, the coating thickness of the second slurry is b =130 μm, and the compaction density of the cold pressing treatment is 1.62g/cm 3 。
The structure schematic diagram of the negative electrode plate is shown in fig. 1, wherein (1) is a current collector, (2) is a first active material layer, and (3) is a second active material layer.
Example 2
The embodiment provides a negative pole piece, which is prepared by the following method:
(1) Mixing a first graphite with a D50 of 12 microns and a hard carbon mixture with a D50 of 8.5 microns, conductive carbon black, sodium carboxymethyl cellulose (hereinafter referred to as CMC) and styrene butadiene rubber (hereinafter referred to as SBR) with deionized water according to a ratio of 95.1 2 Si 1 O 3 The mixture, conductive carbon black, CMC, and SBR were mixed with dimethylformamide at a ratio of 95.8 2 Si 1 O 3 The mass ratio of (A) to (B) is 90;
(2) Coating a first slurry on the surface of a negative electrode current collector, coating a second slurry on the surface of the first slurry, and performing cold pressing treatment to obtain the negative electrode plate, wherein the coating thickness a =50 μm of the first slurry, the coating thickness b =120 μm of the second slurry, and the compaction density of the cold pressing treatment is 1.53g/cm 3 。
Example 3
This example is different from example 1 only in that the mass ratio of the first graphite to the soft carbon is 95.
Example 4
This example differs from example 1 only in that the second graphite and Li 2 Si 1 O 3 The mass ratio of (2) was 98, and the other conditions and parameters were exactly the same as those in example 1.
Example 5
This example differs from example 1 only in that the second graphite and Li 2 Si 1 O 3 The mass ratio of (b) was 80.
Example 6
This example differs from example 1 only in that the cold-pressing treatment had a compacted density of 1.72g/cm 3 Other conditions and parameters were exactly the same as those in example 1.
Example 7
This example differs from example 1 only in that the cold-pressing treatment had a compacted density of 1.45g/cm 3 Other conditions and parameters were exactly the same as those in example 1.
Comparative example 1
This comparative example is different from example 1 only in that the soft carbon is not added to the inner layer, and other conditions and parameters are exactly the same as example 1.
Comparative example 2
This comparative example differs from example 1 only in that the outer layer does not contain Li 2 Si 1 O 3 Other conditions and parameters were exactly the same as those in example 1.
Comparative example 3
This comparative example is different from example 1 only in that only the inner layer is provided, and other conditions and parameters are exactly the same as those of example 1.
Comparative example 4
This comparative example differs from example 1 only in that only the outer layer is provided, and the other conditions and parameters are exactly the same as those of example 1.
And (3) performance testing:
the negative electrode pole pieces obtained in examples 1 to 7 and comparative examples 1 to 4 were tested for porosity, and the liquid absorption rate and the pole piece wettability were characterized by the pole piece porosity. And assembling the negative pole piece with the LFP positive pole piece, the diaphragm and the electrolyte respectively to form the lithium iron phosphate battery. Method for testing 1C discharge capacity at 25 ℃: charging to 3.65V at 25 deg.C with 1C current and constant current, discharging to 2.5V with 1C current and constant current, and recording discharge capacity C 0 Namely the discharge capacity at 25 ℃ and 1C; method for testing constant current ratio of 25 ℃ 3C charging: discharging to 2.5V at constant current with 1C current at 25 deg.C, charging to 3.65V at constant current and constant voltage with 3C current, and recording constant current charging capacity as C 1 Recording constant current and constant voltage charging capacity as C 2 And the 3C charging constant current ratio is as follows: c 1 /C 2 *100 percent; DCR test method: discharging to 2.5V with 1C current constant current at 25 deg.C, charging to 50% SOC with 1C current constant current, charging for 10 s with 1C current constant current, and recording the end point position as V 0 Then constant current discharge is carried out for 10 seconds, and the tail end voltage is recorded as V 1 The current is recorded as I, DCR is: (V0-V1)/I, the test results are shown in Table 1:
TABLE 1
As can be seen from Table 1, the porosity of the negative electrode plate of the invention can reach more than 40%, and the negative electrode plate shows good liquid absorption rate and electrode plate wettability, and the discharge capacity at 25 ℃ and 1C of the battery manufactured by the negative electrode plate can reach more than 2489mAh, the 3C charging constant current ratio can reach more than 96.9%, and the DCR can reach less than 13.4m omega.
Compared with the embodiment 1 and the embodiments 2 to 3, in the first active material layer of the negative electrode plate, the quality ratio of the first graphite to the soft carbon and/or the hard carbon affects the performance of the first graphite, and the quality ratio of the first graphite to the soft carbon and/or the hard carbon is controlled to be (70-87): 13-30, so that the negative electrode plate has good performance, if the first graphite is excessively large, the soft carbon and/or the hard carbon is excessively small, a lithium ion intercalation channel is reduced, a solid phase migration speed is reduced, anode polarization is increased, internal resistance of a battery cell is increased, a lithium intercalation speed is reduced, and the battery cell charging rate performance is poor, and if the first graphite is excessively small, a lithium storage position of the anode is reduced, an NP ratio of the battery cell is reduced, lithium precipitation is easy to occur, and the battery cell capacity is attenuated, and a safety accident is caused when the battery cell is serious.
As can be seen from comparison between example 1 and examples 4 to 5, in the second active material layer of the negative electrode sheet of the present invention, the second graphite was in contact with Li x Si y O z The first graphite and Li have a mass ratio of (A) to (B) which affects the properties of the graphite x Si y O z The mass ratio of the second graphite to the anode is controlled to be (87-95) to (5-13), the prepared anode plate has good performance, if the ratio of the second graphite to the anode plate is too large, li x Si y O z The proportion of the second graphite is too small, the capacity of the battery cell is reduced, lithium loss in the circulation process cannot be supplemented in time, the circulation life of the battery cell is reduced, and if the proportion of the second graphite is too small, li is added x Si y O z The proportion of the positive electrode is too large, the compaction of the positive electrode is reduced, the pressure on the second active material layer of the positive electrode is larger during cold pressing, the porosity of the pole piece is reduced, the liquid absorption performance of the pole piece is deteriorated, and lithium precipitation of the battery core is easily caused.
As can be seen from comparison between example 1 and examples 6 to 7, the cold-pressed compacted density of the negative electrode sheet of the present invention affects the performance thereof, and the cold-pressed compacted density c and the coating thickness a of the first slurry and the coating thickness b of the second slurry need to satisfy the relation c = (0.047 b-0.021 a)/3, and c is 1.50-1.68 g/cm 3 If the compaction density is too low, the contact of the anode active substance is not tight, the conductivity is poor, and meanwhile, the lithium ion migration distance is long during charging, and the rate performance is poor; if the compaction density is too large, the anode active material layer is over-pressurized, the pores among particles are reduced, the liquid absorption of the pole piece is deteriorated, and when lithium ions are embedded, the channels are reduced, the multiplying power performance of the battery cell is influenced, and the compaction is too largeAnd graphite particles are easy to break, and because graphite is broken, the active point position is increased, side reaction between the active point position and electrolyte is aggravated, and different degrees of battery core circulation, multiplying power, service life and the like are reduced.
Compared with the comparative example 1, the negative pole piece disclosed by the invention has the advantages that the inner layer is formed by mixing the small-particle-size graphite with the soft carbon or the hard carbon, so that the conductivity between the negative pole piece and the current collector is improved, the lithium ion intercalation distance is shortened, the lithium ion intercalation speed is increased, and the internal resistance of a battery cell is reduced.
Compared with the comparative example 2, the negative pole piece of the invention adopts large-particle-size graphite and Li as the outer layer X Si y O z The nanometer materials are mixed, the graphite with large particle size improves the compaction density of the pole piece, and simultaneously ensures that the outer layer of graphite still has higher porosity after cold pressing, thereby ensuring that lithium ions smoothly enter the inside of the pole piece, and Li X Si y O z The nano material improves the energy density of the battery cell by pre-lithiating SiO.
Compared with the comparative examples 3 to 4, the negative pole piece adopts a double-layer structure design, the first active substance layer is an inner layer, the material of the inner layer is small-particle-size graphite and soft carbon or hard carbon mixture, when lithium ions are embedded, the small-particle-size graphite has shorter migration distance, the solid-phase diffusion impedance of the lithium ions can be effectively reduced, the anode polarization is reduced, meanwhile, the mixed soft carbon and hard carbon are amorphous carbon, more lithium ion embedding channels are formed, the interface impedance when the lithium ions are embedded can be effectively reduced, the effect of reducing the anode polarization can be achieved, the rate capability is improved, the second active substance layer is an outer layer, the material of the outer layer is large graphite and lithium silicon oxygen composite oxide mixed material, and the Li is a Li/silicon oxygen composite oxide composite material x Si y O z To prelithiate SiO, a potential difference between the anode and cathode occurs during long-term cycling as lithium ions are consumed, at which point Li x Si y O z Can gradually release lithium ions to replenish lost lithium ions, improve the long-term cycle life of the battery and provide higher energy density.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention disclosed herein fall within the scope and disclosure of the present invention.
Claims (10)
1. The negative pole piece is characterized by comprising a negative pole current collector, a second active substance layer and a first active substance layer arranged between the negative pole current collector and the second active substance layer, wherein the active substance of the first active substance layer comprises a mixture of first graphite and soft carbon and/or hard carbon, and the active substance of the second active substance layer comprises second graphite and Li x Si y O z Wherein x is 1 to 4, y is 0.1 to 2, and z is 3 to 5.
2. The negative electrode sheet according to claim 1, wherein the median particle diameter D50 of the first graphite is 5 to 15 μm;
preferably, the median particle diameter D50 of the soft carbon and/or the hard carbon is 6 to 10 μm.
3. The negative electrode sheet according to claim 1 or 2, wherein the mass ratio of the first graphite to the soft carbon and/or the hard carbon is (70-87) to (13-30).
4. The negative electrode tab of any one of claims 1-3, wherein the median particle diameter D50 of the second graphite is 15 to 25 μm;
preferably, the Li x Si y O z Is a nano material.
5. The negative electrode tab of any one of claims 1-4, wherein the second graphite and Li x Si y O z The mass ratio of (87-95) to (5-13).
6. The preparation method of the negative pole piece according to any one of claims 1 to 5, characterized by comprising the following steps:
(1) Mixing first graphite, soft carbon and/or hard carbon, a conductive agent and a binder with a first solvent to obtain first slurry, and mixing second graphite and Li x Si y O z Mixing the conductive agent, the binder and a second solvent to obtain a second slurry;
(2) And coating the first slurry on the surface of a negative current collector, coating the second slurry on the surface of the first slurry, and performing cold pressing treatment to obtain the negative pole piece.
7. The method according to claim 6, wherein the conductive agent of step (1) comprises any one of or a combination of at least two of conductive carbon black, carbon nanotubes, or graphene;
preferably, the binder comprises sodium carboxymethyl cellulose and/or styrene butadiene rubber, preferably sodium carboxymethyl cellulose and styrene butadiene rubber;
preferably, the first solvent comprises deionized water;
preferably, the second solvent comprises an oil-based solvent;
preferably, the oil-based solvent comprises any one of or a combination of at least two of dimethyl sulfoxide, N-dimethylformamide, dimethylacetamide or N-methylpyrrolidone;
preferably, the mass ratio of the mixture of the first graphite and the soft carbon and/or the hard carbon to the conductive agent to the carboxymethylcellulose sodium to the styrene butadiene rubber is (94-97) to (1.0-2.0) to (1.2-1.8) to (1.5-2.5);
preferably, the second graphite and Li x Si y O z The mass ratio of the mixture of the conductive agent, the carboxymethyl cellulose sodium and the styrene butadiene rubber is (94-96), (0.5-1.7), (1.0-3.2) and (1.2-2.8).
8. The method according to claim 6 or 7, wherein the solid content of the first slurry in the step (1) is 55 to 60%;
preferably, the viscosity of the first slurry is 3000 to 5500mPa · s;
preferably, the solid content of the second slurry is 51-55%;
preferably, the viscosity of the second slurry is 3000 to 5500mPa · s.
9. The method according to any one of claims 6 to 8, wherein the thickness of the first slurry applied, the thickness of the second slurry applied and the compacted density of the cold pressing treatment in step (2) satisfy the relationship of c = (0.047 b-0.021 a)/3, and c is 1.50 to 1.68g/cm 3 Wherein the coating thickness of the first slurry is a mu m, the coating thickness of the second slurry is b mu m, and the compaction density of the cold pressing treatment is c g/cm 3 。
10. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1 to 5.
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