CN117293267A - Negative plate and application thereof - Google Patents
Negative plate and application thereof Download PDFInfo
- Publication number
- CN117293267A CN117293267A CN202311393295.9A CN202311393295A CN117293267A CN 117293267 A CN117293267 A CN 117293267A CN 202311393295 A CN202311393295 A CN 202311393295A CN 117293267 A CN117293267 A CN 117293267A
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- China
- Prior art keywords
- negative electrode
- active layer
- electrode active
- graphite material
- current collector
- Prior art date
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- 239000007770 graphite material Substances 0.000 claims abstract description 125
- 239000011159 matrix material Substances 0.000 claims abstract description 84
- 238000005087 graphitization Methods 0.000 claims abstract description 49
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 88
- 229910001416 lithium ion Inorganic materials 0.000 claims description 88
- 239000011230 binding agent Substances 0.000 claims description 38
- 239000000843 powder Substances 0.000 claims description 35
- 238000011049 filling Methods 0.000 claims description 30
- 229920000642 polymer Polymers 0.000 claims description 28
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- 238000005056 compaction Methods 0.000 claims description 26
- 229910052751 metal Inorganic materials 0.000 claims description 19
- 239000002184 metal Substances 0.000 claims description 19
- 229910021383 artificial graphite Inorganic materials 0.000 claims description 16
- 229910021382 natural graphite Inorganic materials 0.000 claims description 6
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- 238000002156 mixing Methods 0.000 description 48
- 230000000052 comparative effect Effects 0.000 description 34
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 30
- 229910052744 lithium Inorganic materials 0.000 description 30
- 238000012360 testing method Methods 0.000 description 30
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- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
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- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
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- FKRCODPIKNYEAC-UHFFFAOYSA-N ethyl propionate Chemical compound CCOC(=O)CC FKRCODPIKNYEAC-UHFFFAOYSA-N 0.000 description 2
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- 238000001878 scanning electron micrograph Methods 0.000 description 2
- ZPFAVCIQZKRBGF-UHFFFAOYSA-N 1,3,2-dioxathiolane 2,2-dioxide Chemical compound O=S1(=O)OCCO1 ZPFAVCIQZKRBGF-UHFFFAOYSA-N 0.000 description 1
- FSSPGSAQUIYDCN-UHFFFAOYSA-N 1,3-Propane sultone Chemical compound O=S1(=O)CCCO1 FSSPGSAQUIYDCN-UHFFFAOYSA-N 0.000 description 1
- HNAGHMKIPMKKBB-UHFFFAOYSA-N 1-benzylpyrrolidine-3-carboxamide Chemical compound C1C(C(=O)N)CCN1CC1=CC=CC=C1 HNAGHMKIPMKKBB-UHFFFAOYSA-N 0.000 description 1
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- FALRKNHUBBKYCC-UHFFFAOYSA-N 2-(chloromethyl)pyridine-3-carbonitrile Chemical compound ClCC1=NC=CC=C1C#N FALRKNHUBBKYCC-UHFFFAOYSA-N 0.000 description 1
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- 229910000881 Cu alloy Inorganic materials 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
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- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
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- 229910021393 carbon nanotube Inorganic materials 0.000 description 1
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- NHZZUJIRMHDTKR-UHFFFAOYSA-N carbonic acid;toluene Chemical compound OC(O)=O.CC1=CC=CC=C1 NHZZUJIRMHDTKR-UHFFFAOYSA-N 0.000 description 1
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- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- ROORDVPLFPIABK-UHFFFAOYSA-N diphenyl carbonate Chemical compound C=1C=CC=CC=1OC(=O)OC1=CC=CC=C1 ROORDVPLFPIABK-UHFFFAOYSA-N 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
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- CYEDOLFRAIXARV-UHFFFAOYSA-N ethyl propyl carbonate Chemical compound CCCOC(=O)OCC CYEDOLFRAIXARV-UHFFFAOYSA-N 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 229910021389 graphene Inorganic materials 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000009830 intercalation Methods 0.000 description 1
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- KQNPFQTWMSNSAP-UHFFFAOYSA-N isobutyric acid Chemical compound CC(C)C(O)=O KQNPFQTWMSNSAP-UHFFFAOYSA-N 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- 238000001755 magnetron sputter deposition Methods 0.000 description 1
- KKQAVHGECIBFRQ-UHFFFAOYSA-N methyl propyl carbonate Chemical compound CCCOC(=O)OC KKQAVHGECIBFRQ-UHFFFAOYSA-N 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
- UUIQMZJEGPQKFD-UHFFFAOYSA-N n-butyric acid methyl ester Natural products CCCC(=O)OC UUIQMZJEGPQKFD-UHFFFAOYSA-N 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000006259 organic additive Substances 0.000 description 1
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Classifications
-
- 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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- 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
-
- 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
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/72—Grids
- H01M4/74—Meshes or woven material; Expanded metal
-
- 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 application thereof, wherein the negative plate comprises a current collector with a reticular structure, a negative active layer matrix and a surface negative active layer; the negative electrode active layer matrix is at least partially filled in the interior of the network structure; the surface negative electrode active layer is arranged on the outer surface of the negative electrode active layer matrix and/or the outer surface of the current collector; the negative electrode active layer matrix comprises a first graphite material, the surface negative electrode active layer comprises a second graphite material, and the graphitization degree of the second graphite material is smaller than that of the first graphite material; the graphitization degree of the first graphite material is not less than 90%, and/or the graphitization degree of the second graphite material is not less than 90%. The negative plate has higher energy density and can also obviously improve the quick charge performance of the battery.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and relates to a negative plate, in particular to a negative plate and application thereof.
Background
Lithium ion batteries are widely used in the fields of power batteries, energy storage and 3C digital codes due to the advantages of high operating voltage, wide operating temperature, long cycle life and environmental friendliness. At present, with the continuous development of fast-charge digital products, lithium ion batteries are required to have excellent fast-charge performance and improved energy density.
The energy density of the lithium ion battery can be generally improved by methods such as improving the capacity of the anode active material, improving the compaction density of the anode sheet, reducing the content of inactive substances in the anode active layer, increasing the surface density of the anode sheet or reducing the thickness of the separator and the current collector, but if the quick charge performance of the lithium ion battery is considered, some of the methods have limitations. For example, increasing the areal and compacted density of the negative electrode sheet is the most effective means of increasing the energy density, but can result in reduced porosity of the negative electrode active layer, affecting the fast charge performance of the lithium ion battery. Therefore, there is a need to develop a lithium ion battery that combines excellent fast charge performance with high energy density.
Disclosure of Invention
In view of the above-mentioned drawbacks, the present invention provides a negative electrode sheet that can significantly improve the fast charge performance of a battery while having a higher energy density.
The invention provides a lithium ion battery, which comprises the negative plate. The lithium ion battery has excellent quick charge performance and higher energy density.
The invention provides a negative plate, which comprises a current collector with a net-shaped structure, a negative active layer matrix and a surface negative active layer; the negative electrode active layer matrix is at least partially filled inside the network structure; the surface negative electrode active layer is arranged on the outer surface of the negative electrode active layer matrix and/or the outer surface of the current collector;
The negative electrode active layer matrix comprises a first graphite material, and the surface negative electrode active layer comprises a second graphite material, wherein the graphitization degree of the second graphite material is smaller than that of the first graphite material;
the graphitization degree of the first graphite material is not less than 90%, and/or the graphitization degree of the second graphite material is not less than 90%.
Further, the negative electrode tab according to claim 1, the negative electrode active layer matrix including a first negative electrode active layer matrix filled inside the mesh structure and a second negative electrode active layer matrix covering at least a part of a surface of the current collector.
Further, the graphitization degree of the first graphite material is 93-95%;
the graphitization degree of the second graphite material is 90-92%;
the first graphite material comprises at least one of artificial graphite and natural graphite;
the second graphite material comprises at least one of artificial graphite and natural graphite.
Further, the first graphite material has a capacity of not less than 348mAh/g and/or a powder compacted density of not less than 1.75g/cm 3 ；
The second graphite material has a capacity of not less than 335mAh/g and/or a powder compacted density of not less than 1.65/cm 3 。
Further, the first graphite material has a capacity of not less than 358mAh/g and/or a powder compacted density of not less than 1.95g/cm 3 ；
And/or; the second graphite material has a powder compaction density of not less than 1.85g/cm 3 。
Further, the Dv50 of the first graphite material is greater than the Dv50 of the second graphite material.
The Dv50 of the first graphite material is 10-20 mu m;
the Dv50 of the second graphite material is 5-15 mu m.
Further, the current collector comprises a 3D reticular framework formed by polymer spinning and a metal layer, wherein the metal layer is coated on the outer surface of the polymer spinning;
the diameter of the polymer spinning is 3-8 mu m; and/or the thickness of the metal monolayer is 1-3 μm.
Further, the thickness of the current collector is 40 to 100 μm, and/or the opening ratio of the current collector is 45 to 55%, and/or the breaking elongation of the current collector is not less than 1%.
Further, the surface negative electrode active layer and the negative electrode active layer substrate further comprise a binder;
The mass percentage of the binder contained in the surface negative electrode active layer is greater than the mass percentage of the binder contained in the negative electrode active layer matrix;
the mass percentage of the binder in the surface negative electrode active layer is 1-1.5wt%; and/or the mass percentage of the binder in the negative electrode active layer matrix is not higher than 0.5wt%.
The invention also provides a lithium ion battery, which comprises the negative plate.
The negative electrode sheet comprises a current collector with a net structure, a negative electrode active layer matrix and a surface negative electrode active layer, wherein the negative electrode active layer matrix is at least partially filled in the net structure, and the surface negative electrode active layer is arranged on the outer surface of the negative electrode active layer matrix and/or the outer surface of the current collector. The structure of the current collector and the negative electrode active layer in the negative electrode plate is changed, and the graphitization degree of the first graphite material in the negative electrode active layer matrix is larger than that of the second graphite material in the surface negative electrode active layer, wherein the graphitization degree of the first graphite material is not lower than 90%, and/or the graphitization degree of the second graphite material is not lower than 90%, so that the higher energy density can be realized, the porosity of the surface negative electrode active layer can be increased, the porosity of the surface negative electrode active layer in the finally formed negative electrode plate and the porosity of the negative electrode active layer matrix tend to be consistent, and lithium ions in the electrolyte can easily enter the negative electrode active layer of the negative electrode plate to react in the charging process, and excellent quick charging performance is further realized.
Drawings
FIG. 1 is a schematic view of a negative electrode sheet of the present invention in one embodiment;
FIG. 2 is a schematic view of a negative electrode sheet of the present invention in one embodiment;
FIG. 3 is a schematic view of a negative electrode sheet according to another embodiment of the present invention;
fig. 4 is an SEM image of the current collector of the negative electrode sheet of example 1 of the present invention;
fig. 5 is a graph showing the expansion rate test of lithium ion batteries of examples 1 to 4 and comparative examples 1 to 3 according to the present invention.
Reference numerals illustrate:
1-a second graphite material;
2-a surface negative electrode active layer;
3-a first graphite material;
4-a negative active layer matrix;
5-current collector;
6-mesh structure;
7-a first negative active layer matrix;
8-a second negative active layer matrix.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The first aspect of the present invention provides a negative electrode sheet comprising a current collector 5 having a mesh structure, a negative electrode active layer substrate 4, and a surface negative electrode active layer 2; the negative electrode active layer matrix 4 is at least partially filled inside the mesh structure 6; the surface negative electrode active layer 2 is provided on the outer surface of the negative electrode active layer substrate 4 and/or the outer surface of the current collector 5;
the negative electrode active layer matrix 4 comprises a first graphite material 3, the surface negative electrode active layer 2 comprises a second graphite material 1, and the graphitization degree of the second graphite material 1 is smaller than that of the first graphite material 3;
the graphitization degree of the first graphite material is not less than 90%, and/or the graphitization degree of the second graphite material is not less than 90%.
It is understood that, for the current collector 5, the region defined by the outer periphery thereof has two outer surfaces disposed opposite to each other in the thickness direction and having the largest area. In one embodiment, the negative electrode active layer matrix 4 is entirely filled inside the mesh structure 6, and the surface negative electrode active layers 2 are covered on both outer surfaces of the current collector 5, as shown in fig. 1.
The first graphite material 3 and the second graphite material 1 of the present invention may be obtained by using commercially available products known to those skilled in the art or products prepared by a conventional preparation method, preferably, by subjecting the graphite materials to heat treatment, and in particular, different graphitization degrees may be achieved using different kinds of graphite material raw materials or different heat treatment temperatures.
The negative electrode sheet comprises a negative electrode active layer substrate 4 and a surface negative electrode active layer 2, wherein the graphitization degree of a first graphite material 3 contained in the negative electrode active layer substrate 4 is larger than that of a second graphite material 1 contained in the surface negative electrode active layer 2, and the higher the graphitization degree is, the softer the graphite material is. Therefore, according to the invention, at least part of the negative electrode active layer matrix 4 is filled in the current collector 5, the surface negative electrode active layer 2 is arranged on the outer surface of the negative electrode active layer matrix 4, and/or the outer surface of the current collector 5, the first graphite material 3 with softer material at the bottom layer is easy to compact in the rolling or pressing process of the negative electrode plate, the porosity of the negative electrode active layer matrix 4 is reduced, the second graphite material 1 with harder material at the surface layer is not easy to compact, and the porosity of the surface negative electrode active layer 2 is improved, so that the porosities of the surface negative electrode active layer 2 and the negative electrode active layer matrix 4 in the negative electrode plate tend to be consistent after rolling or pressing. In the charging process, lithium ions in the electrolyte can easily enter the cathode active layer from the surface cathode active layer 2, and timely combine with electrons to generate lithium intercalation reaction, so that the quick charge performance of the battery is improved. Meanwhile, the higher the graphitization degree is, the higher the capacity is, the graphitization degree of the first graphite material 3 is not lower than 90%, and/or the graphitization degree of the second graphite material 1 is not lower than 90%, so that the negative electrode plate has higher capacity, and the energy density of the battery can be effectively improved.
In addition, the current collector 5 in the negative plate is of a net structure, and the bearing capacity of the negative active material in the negative plate is increased on the premise of not changing the thickness of the negative plate, so that the energy density of the battery can be improved, and the weight of the battery can be reduced; meanwhile, the negative electrode active layer matrix 4 is firmly networked in the network structure of the current collector 5, the contact area between the negative electrode active matrix 4 and the current collector 5 is increased, higher peeling strength can be realized by using a lower-dosage non-negative electrode active material, the expansion of a battery caused by falling of the negative electrode active layer is avoided, the cycle performance of the battery is improved, the impedance of a negative electrode sheet is effectively reduced, and the quick charge performance of the battery is further improved; meanwhile, because the special structure of the negative plate can enable lithium ions to enter the negative active layer more easily, lithium ions are not easy to accumulate on the surface of the negative plate during charging, and therefore the problem of lithium precipitation of the negative electrode of the battery can be solved.
In addition to the anode active layer substrates 4 shown in fig. 1 each being filled in the mesh structure 6, a part of the anode active layer substrates 4 may be disposed on the outer surface of the current collector. That is, the anode active layer includes a portion filled inside the mesh structure 6, and also includes a portion provided outside the mesh structure.
Specifically, the anode active layer substrate 4 includes a first anode active layer substrate 7 and a second anode active layer substrate 8, the first anode active layer substrate 7 is filled inside the mesh structure 6, and the second anode active layer substrate 8 covers at least part of the surface of the current collector 5.
In one embodiment, the first anode active layer substrate 7 is filled inside the mesh structure 6, the second anode active layer substrate 8 is covered on both outer surfaces of the current collector 5, and the surface anode active layer 2 is covered on the surface of the second anode active layer substrate 8, as shown in fig. 2.
In another embodiment, the first anode active layer substrate 7 is filled inside the mesh structure 6, the second anode active layer substrate 8 covers part of the outer surface of the current collector 5, and the surface anode active layer 2 covers the surface of the second anode active layer substrate 4 and the outer surface of the current collector 5, as shown in fig. 3.
When the second negative electrode active layer substrate 8 covers at least part of the surface of the current collector 5, the content of the first graphite material 3 in the negative electrode sheet can be increased, thereby further increasing the battery energy density.
In one embodiment, the graphitization degree of the first graphite material 3 is 93 to 95%; the graphitization degree of the second graphite material 1 is 90-92%; the first graphite material comprises at least one of artificial graphite and natural graphite; the second graphite material includes at least one of artificial graphite and natural graphite. In this range, the first graphite material 3 and the second graphite material 1 have better capacities, so that the energy density of the battery is further improved, and meanwhile, the first graphite material 3 and the second graphite material 1 have proper hardness differences, so that the surface negative electrode active layer 2 and the negative electrode active layer matrix 4 form better porosities, and the quick charge performance of the battery is improved. When the two types of substances are respectively a mixture of a plurality of specific substances, the proportion of each specific substance is not excessively limited.
In one embodiment, the first graphite material 3 has a capacity of not less than 348mAh/g. In this range, the lithium ion battery including the negative electrode sheet has a higher energy density.
In one embodiment, the first graphite material 3 has a powder compaction density of not less than 1.75g/cm 3 . When the powder compaction density of the first graphite material 3 is in the above range, the energy density of the lithium ion battery can be further improved, and meanwhile, the lithium ion battery can also have a better porosity, so that the migration of lithium ions in the anode active layer is not hindered, and the quick charge performance of the battery is further improved.
In one embodiment, the capacity of the second graphite material 1 is not less than 335mAh/g. In this range, the energy density of the lithium ion battery including the negative electrode sheet can be further improved.
In one embodiment, the second graphite material 1 has a powder compaction density of not less than 1.65g/cm 3 . When the powder compacted density of the second graphite material 1 is in the above rangeThe surface negative electrode active layer 2 has higher porosity, reduces the resistance of lithium ions to be inserted into the negative electrode, ensures that the lithium ions can be quickly inserted into the negative electrode under high-rate charging, and further improves the quick charging performance of the battery.
In one embodiment, the first graphite material 3 has a capacity of not less than 358mAh/g. In this range, the energy density of the lithium ion battery can be further improved.
In one embodiment, the first graphite material 3 has a powder compaction density of not less than 1.95g/cm 3 . In this range, the lithium ion battery including the negative electrode sheet can be made to have a higher energy density without adversely affecting the quick-charge performance of the battery.
In one embodiment, the second graphite material 1 has a powder compaction density of not less than 1.85g/cm 3 . In this range, the energy density of the battery can be further improved on the premise of ensuring that the surface anode active layer 2 has a higher porosity.
In a specific embodiment, the Dv50 of the first graphite material 3 is greater than the Dv50 of the second graphite material 1; the Dv50 of the first graphite material is 10-20 μm and/or the Dv50 of the second graphite material is 5-15 μm. Wherein Dv50 represents the particle size of 50% of the volume accumulation degree. Since the large-particle-diameter first graphite material 3 has a higher capacity and the small-particle-diameter second graphite material 1 can further provide more electrolyte channels, lithium ions are more easily intercalated, and thus when the Dv50 of the first graphite material 3 is greater than that of the second graphite material 1, the energy density and the fast charge performance of the battery can be further improved. When the Dv50 of the first graphite material 3 and/or the second graphite material 1 is in the above range, the first graphite material 3 has not only a higher capacity but also a shorter lithium ion diffusion path, so that it has a better charging capacity; the particle size of the second graphite material 1 is not too small, so that side reactions are reduced, the consumption of lithium ions in the process of forming an SEI film in the first charge and discharge process is reduced, irreversible capacity loss is reduced, and the cycle performance of the battery is improved.
In one embodiment, the current collector 5 comprises a 3D mesh-like skeleton formed by polymer spinning and a metal layer coated on the outer surface of the polymer spinning.
Specifically, polymer spinning in the invention refers to fiber filaments with the diameter of micron, which are generated by high molecular polymers through an electrostatic spinning technology, and form a 3D reticular framework through winding, stacking and other modes. Further, the high molecular polymer comprises at least one of aromatic polyamide, polyimide, polyethylene and polypropylene.
The metal layer in the present invention means that the layer containing the metal composition includes metallic copper or copper alloy.
The metal layer of the present invention is coated on the outer surface of the polymer spinning, and preferably, the polymer spinning is completely coated. The invention is not limited to the coating method of the metal layer, and only the outer surface of the polymer spinning is required to be completely coated. For example, a layer of metallic copper can be coated on the surface of the polymer spinning by a physical vapor deposition process (magnetron sputtering), and then the coating is thickened by electroplating.
The polymer spinning has certain elasticity, and can correspondingly deform along with the expansion and contraction of the first graphite material 3 in the circulation process, so that the current collector 5 and the negative electrode active layer matrix 4 are kept in a good contact state, the negative electrode plate has a good conductive network, and the multiplying power performance of the negative electrode plate is further improved; the outer metal layer serves as an electron channel of the current collector, and makes the current collector 5 exhibit high conductivity, thereby improving electrochemical performance of the battery. In addition, due to the smaller mass of the polymer spinning, the weight reduction of the battery and the further improvement of the energy density can be realized.
In one embodiment, the polymer spinning has a diameter of 3 to 8 μm. In this range, the polymer spinning mechanical strength is high, and breakage is not easy to occur due to expansion deformation of the first graphite material 3 in the circulation process, and the opening ratio is also high, so that the current collector 5 can bear more negative electrode active substances, and the energy density and the circulation performance of the battery are further effectively improved. Specifically, the aperture ratio of the current collector 5 in the present invention is defined by the formula 1:
opening ratio = (a-B)/a 100% formula 1
Wherein A is the apparent volume of the current collector 5, namely the volume of the area surrounded by the outer layer boundary of the current collector 5; b is the volume of the 3D mesh skeleton and metal layer in the current collector 5.
In one embodiment, the metal layer has a thickness of 1 to 3 μm. In this range, the current collector 5 has better flexibility, is not easy to generate current collector stripping phenomenon or polymer spinning fracture due to expansion of graphite materials in the circulation process, improves the battery circulation performance, and can also enable the current collector 5 to have larger opening ratio, so that the current collector can bear more negative electrode active materials, improve the battery energy density, and meanwhile, the current collector 5 also has better conductivity, can promote electron transfer and improve the battery multiplying power performance.
In one embodiment, the thickness of the current collector 5 is 40 to 100 μm. When the thickness of the current collector 5 is less than 40 μm, the processing difficulty is high, breakage during rolling is easy, and the negative electrode sheet including the current collector 5 is low in toughness, breakage during cycling is easy, resulting in degradation of battery cycle performance. In this range, the size of the available space in the current collector 5 can be increased, carrying more negative electrode active material, thereby further increasing the energy density of the battery; meanwhile, when the thickness of the current collector 5 is in the above range, the negative electrode sheet manufactured by the current collector 5 can have stronger toughness and is not easy to break, so that the cycle performance of the lithium ion battery is improved.
The thickness of the current collector 5 in the present invention is measured by measuring the original thickness of the current collector 5 directly prepared by spinning the polymer coated with the metal layer, and the current collector 5 is not subjected to any treatment such as pressing or rolling.
In one embodiment, the opening ratio of the current collector 5 is 45 to 55%. In this range, the current collector 5 can bear more negative electrode active materials, so that the lithium receiving capacity of the negative electrode is remarkably improved, the lithium conducting performance of the battery is effectively improved, and the energy density of the battery is further improved. Specifically, the aperture ratio of the current collector may be made within the above range by changing the diameter of the polymer spinning, and/or the thickness of the metal layer, and/or the solid matter coverage volume in the current collector.
In one embodiment, the breaking elongation of current collector 5 is not less than 1%. In this range, the current collector 5 has high mechanical strength, and can prevent the negative current collector from being damaged or broken when the battery is abused such as needled or extruded, thereby remarkably improving the safety performance of the battery. Meanwhile, corresponding deformation can be generated along with expansion and contraction of the first graphite material 3 in the circulation process, so that the current collector 5 is always in contact with the negative electrode active layer matrix 4, and the current collector has a sufficient conductive network, reduces the internal resistance of the battery and improves the rate capability of the battery. Specifically, the implementation scheme of the breaking elongation of the current collector 5 includes: the opening ratio of the current collector 5 is further limited under the condition that the opening ratio of the current collector 5 is 45% -55%, so that the breaking extensibility of the current collector 5 is in the range; the diameter of the polymer spinning is further limited in the case where the diameter of the polymer spinning is 3 to 8 μm so that the fracture elongation of the negative electrode current collector is achieved to reach the above range.
In one embodiment, the surface negative electrode active layer and the negative electrode active layer matrix further comprise a binder; the mass percentage of the binder included in the surface negative electrode active layer is greater than the mass percentage of the binder included in the negative electrode active layer matrix; the mass percentage of the binder in the surface negative electrode active layer is 1-1.5wt%; and/or the mass percentage of the binder in the negative electrode active layer matrix is not higher than 0.5wt%. When the mass percentage of the binder in the surface anode active layer is in the above range, the surface anode active layer 2 can form higher bonding strength with the current collector 5 and/or the anode active layer matrix 4, so that the anode active layer is not easy to fall off, and the cycle performance of the battery is improved. When the mass percentage of the binder in the negative electrode active layer matrix is in the above range, the current collector has a network structure, so that the amount of the binder in the negative electrode active layer matrix can be reduced, and under the condition of less binder amount, the negative electrode active layer matrix 4 and the current collector 5 can have larger peel strength, thereby effectively improving the energy density of the battery, reducing the internal resistance, improving the multiplying power performance and prolonging the cycle life of the battery.
Further, the binder includes at least one of styrene-butadiene latex, styrene-acrylic latex, polyacrylate copolymer, polymethacrylate, polyvinyl alcohol, polyurethane, polyacrylamide, acrylic acid, and acrylonitrile copolymer.
In one embodiment, the negative electrode active layer 2 is surface-coated, and/or the negative electrode active layer matrix 4 further comprises a dispersant; preferably, the dispersant is contained in the surface anode active layer 2 and/or the anode active layer matrix 4 in an amount of 0.5 to 1wt%. When the dispersant is in the above range, the first graphite material 3 in the anode active layer matrix 4 and/or the second graphite material 1 in the surface anode active layer 2 can be stably dispersed.
Further, the dispersant may be at least one selected from a cellulose dispersant, a polyacrylic dispersant, a polyacrylate dispersant, and a polyacrylamide dispersant.
In one embodiment, the negative electrode active layer 2 is surface-coated, and/or the negative electrode active layer substrate 4 further comprises a conductive agent; preferably, the mass percentage of the conductive agent in the surface anode active layer 2 and/or the anode active layer matrix 4 is 0.05 to 1wt%. In this range, a sufficient conductive network may be formed in the surface anode active layer 2 and/or the anode active layer matrix 4, effectively increasing the rate of movement of electrons and lithium ions in the electrode material, thereby increasing the charge-discharge efficiency of the electrode.
Further, the conductive agent may include at least one of carbon black, carbon nanotubes, graphite, graphene.
The present invention is not limited to the preparation method of the negative electrode sheet, for example, the negative electrode sheet is prepared by a method comprising the following processes:
mixing and stirring the first graphite material 3, a conductive agent, a dispersing agent and a binder to obtain a negative electrode active layer matrix slurry; mixing and stirring the second graphite material 1, a conductive agent, a dispersing agent and a binder to obtain surface negative electrode active layer slurry; and filling the negative electrode active layer matrix slurry in a current collector, or filling and covering at least part of the outer surface of the current collector, drying, coating the surface negative electrode active layer slurry on the outer surface of the current collector, and/or drying, rolling, slitting and tab welding the outer surface of the negative electrode active layer matrix to obtain the negative electrode plate.
The stirring mode is not particularly limited in the present invention, and illustratively, a star stirrer, a ball mill, or a conventional stirring means may be selected.
The negative electrode plate prepared by the preparation method has a special double-layer structure, and can be applied to a lithium ion battery to remarkably improve the energy density and the quick charge performance of the battery.
The second aspect of the invention provides a lithium ion battery comprising the negative electrode sheet, the positive electrode sheet, electrolyte and a separation membrane of any one of the above. Because the negative plate has a special double-layer structure, namely the surface negative electrode active layer 2 and the negative electrode active layer matrix 4, the graphitization degree of the first graphite material 3 included in the negative electrode active layer matrix 4 is larger than that of the second graphite material 1 included in the surface negative electrode active layer 2, and the graphitization degree of the first graphite material 3 and the graphitization degree of the second graphite material 1 are both larger than 90%, the high energy density can be realized, the porosity of the surface negative electrode active layer 2 can be increased, the porosity of the surface negative electrode active layer 2 and the porosity of the negative electrode active layer matrix 4 in the finally formed negative plate tend to be consistent, and the quick charge performance of the battery is further improved.
The lithium ion battery of the present invention may be manufactured by a conventional method known to those skilled in the art to which the present invention pertains.
The composition of the electrolyte is not particularly limited, and for example, may include lithium salts, organic solvents, and additives, wherein the lithium salts may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium bisoxalato borate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium difluorophosphate, lithium perchlorate, and lithium hexafluoroarsenate; the organic solvent is at least one selected from dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, ethyl propionate, ethyl acetate, methyl acetate, dimethyl acetate, methyl butyrate, ethyl butyrate, and n-propyl acetate; the additive can be at least one selected from ethylene carbonate, fluoroethylene carbonate, 1, 3-propane sultone, ethylene sulfate, diphenyl carbonate, toluene carbonate, acrylonitrile, succinic anhydride, succinonitrile and adiponitrile. When the three types of compounds are respectively a mixture of a plurality of specific compounds, the proportion of each specific compound is not excessively limited in the invention.
The invention does not limit the positive plate in particular, for example, the positive plate comprises a positive current collector and positive active materials distributed on the surface of the positive current collector, wherein the positive current collector can be any one of an aluminum current collector, a nickel current collector and a stainless steel current collector; the positive electrode active material may be selected from any one of lithium cobaltate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.
The separator is not particularly limited in the present invention, and may include any material commonly used in lithium batteries, as long as the negative electrode is separated from the positive electrode and a transmission path is provided for lithium ions. For example, at least one selected from the group consisting of glass fiber microporous membrane, polyester microporous membrane, polyethylene microporous membrane, polypropylene microporous membrane, polytetrafluoroethylene microporous membrane, and ceramic-coated separator.
Hereinafter, a lithium ion battery including the negative electrode sheet of the present invention will be described in detail by way of specific examples.
Example 1
(1) Preparing a negative electrode sheet: graphitization degree of 92%, capacity of 352mAh/g, powder compaction density of 1.87g/cm 3 Placing artificial graphite with the Dv50 of 10 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentage of 97wt%, 0.5wt%, 1wt% and 1.5wt% and uniformly mixing to obtain surface negative electrode active layer slurry;
Graphitization degree of 95%, capacity of 360mAh/g, and powder compaction density of 1.94g/cm 3 Placing artificial graphite with the Dv50 of 15 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentages of 98wt%, 0.5wt%, 1wt% and 0.5wt% and uniformly mixing to obtain matrix slurry of a negative electrode active layer;
taking 50 μm thick aromatic polyamide fiberA current collector having a network structure with a dimension of 4 μm, a thickness of a metallic copper layer of 1.8 μm, an aperture ratio of 52.1% and an elongation at break of 2.4%, and a negative electrode active layer substrate slurry having a surface density of 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 2
(1) Preparing a negative electrode sheet: graphitization degree of 91%, capacity of 348mAh/g, powder compaction density of 1.86g/cm 3 Placing artificial graphite with the Dv50 of 10 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentage of 97wt%, 0.5wt%, 1wt% and 1.5wt% and uniformly mixing to obtain surface negative electrode active layer slurry;
graphitization degree of 95%, capacity of 360mAh/g, and powder compaction density of 1.94g/cm 3 The artificial graphite with the Dv50 of 15 mu m, the conductive agent carbon black, the dispersant carboxymethyl cellulose and the adhesive styrene-butadiene rubber are placed in a batching tank according to the weight percentage of 98.2wt%, 0.5wt%, 1wt% and 0.3wt%Uniformly mixing to obtain a negative electrode active layer matrix slurry;
a current collector having a network structure and having a thickness of 50 μm, a diameter of an aromatic polyamide fiber of 4 μm, a thickness of a metallic copper layer of 1.8 μm, an opening ratio of 52% and an elongation at break of 1.8% was taken, and a negative electrode active layer substrate slurry was prepared at a surface density of 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of single-walled carbon nanotubes and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain anode active layer slurry, coating the slurry on two opposite surfaces of an aluminum foil with the thickness of 10 mu m, drying, rolling, slitting and welding lugs to obtain the anode sheet of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 3
(1) Preparing a negative electrode sheet: graphitization degree of 90%, capacity of 345mAh/g and powder compaction density of 1.85g/cm 3 Placing artificial graphite with the Dv50 of 10 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentage of 97wt%, 0.5wt%, 1wt% and 1.5wt% and uniformly mixing to obtain surface negative electrode active layer slurry;
graphitization degree of 94%, capacity of 358mAh/g and compaction density of 1.92g/cm 3 Artificial graphite with Dv50 of 14 μm, conductive agent carbon black and branchPowder carboxymethyl cellulose and binder styrene-butadiene rubber are placed in a material mixing tank according to the weight percentages of 98.2wt%, 0.5wt%, 1wt% and 0.3wt% and are evenly mixed to obtain negative electrode active layer matrix slurry;
a current collector having a mesh structure with a thickness of 60 μm, a diameter of an aromatic polyamide fiber of 4 μm, a thickness of a metallic copper layer of 1.8 μm, an opening ratio of 52.5% and an elongation at break of 2.5% was taken, and a negative electrode active layer base slurry was prepared at a surface density of 4mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 4
(1) Preparing a negative electrode sheet: graphitization degree of 90%, capacity of 345mAh/g and powder compaction density of 1.85g/cm 3 Placing artificial graphite with the Dv50 of 10 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentage of 97wt%, 0.5wt%, 1wt% and 1.5wt% and uniformly mixing to obtain surface negative electrode active layer slurry;
Graphitizing94% strength, 358mAh/g capacity, 1.92g/cm powder compaction density 3 Placing artificial graphite with the Dv50 of 14 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentages of 98.2wt%, 0.5wt%, 1wt% and 0.3wt% and uniformly mixing to obtain matrix slurry of a negative electrode active layer;
a current collector having a mesh structure with a thickness of 70 μm, a diameter of an aromatic polyamide fiber of 4 μm, a thickness of a metallic copper layer of 1.8 μm, an opening ratio of 70.3% and an elongation at break of 0.8% was taken, and a negative electrode active layer base slurry was prepared at a surface density of 3mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 5
(1) Preparing a negative electrode sheet: placing a graphite material with the graphitization degree of 92%, the capacity of 352mAh/g, the powder compaction density of 1.87g/cm < 3 >, and the Dv50 of 10 mu m, conductive agent carbon black, dispersant CMC, and binder SBR in a mixing tank according to weight percentage of 97%, 0.5%, 1% and 1.5% and uniformly mixing to obtain surface negative electrode active layer slurry;
placing graphite material with graphitization degree of 95%, capacity of 360mAh/g, powder compaction of 1.94g/cm < 3 >, dv50 of 15 mu m, conductive agent carbon black, dispersant CMC and binder SBR in a mixing tank according to weight percentage of 98wt%, 0.5wt%, 1wt% and 0.5wt% and uniformly mixing to obtain negative electrode active layer matrix sizing agent;
collecting current collector with 50 μm thick, 5.6 μm polymer spinning diameter, 1 μm metal layer thickness, 52.1% opening ratio and 2.8% fracture expansion ratio, and mixing the negative electrode active layer matrix slurry with surface density of 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the PE diaphragm into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic film after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 6
(1) Preparing a negative electrode sheet: graphitization degree is 92%, capacity is 352mAh/g, and powder compaction density is 1.87g/cm 3 The graphite material with the Dv50 of 10 mu m, the conductive agent carbon black, the dispersant carboxymethyl cellulose and the adhesive styrene-butadiene rubber are placed in a mixing tank for uniform mixing according to the weight percentage of 97 percent, 0.5 percent, 1 percent and 1.5 percentCombining to obtain surface negative electrode active layer slurry;
compacting powder with graphitization degree of 92.5%, capacity of 353mAh/g and powder of 1.9g/cm 3 Placing a graphite material with the Dv50 of 15 mu m, carbon black serving as a conductive agent, carboxymethyl cellulose serving as a dispersing agent and styrene-butadiene rubber serving as a binder in a mixing tank according to the weight percentage of 98wt%, 0.5wt%, 1wt% and 0.5wt% and uniformly mixing to obtain a matrix slurry of a negative electrode active layer;
collecting current collector with 50 μm thick, polymer spinning diameter 4 μm thick, metal layer thickness 1.8 μm thick, opening ratio 52.1% and fracture expansion ratio 2.4%, and mixing the matrix slurry of negative electrode active layer with surface density 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 7
(1) Preparing a negative electrode sheet: graphitization degree is 90%, capacity is 320mAh/g, powder compaction density is 1.76g/cm 3 Graphite material with Dv50 of 6 mu m, conductive agent carbon black, dispersant CMC and binder SBR according to weight percentage of 97Placing the materials in a mixing tank for uniformly mixing, wherein the weight percent is 0.5 weight percent, the weight percent is 1 weight percent and the weight percent is 1.5 weight percent, so as to obtain surface negative electrode active layer slurry;
placing graphite material with graphitization degree of 95%, capacity of 360mAh/g, powder compaction of 1.94g/cm < 3 >, dv50 of 15 mu m, conductive agent carbon black, dispersant CMC and binder SBR in a mixing tank according to weight percentage of 98wt%, 0.5wt%, 1wt% and 0.5wt% and uniformly mixing to obtain negative electrode active layer matrix sizing agent;
Collecting current collector with 50 μm thick, polymer spinning diameter 4 μm thick, metal layer thickness 1.8 μm thick, opening ratio 52.1% and fracture expansion ratio 2.4%, and mixing the matrix slurry of negative electrode active layer with surface density 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the PE diaphragm into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic film after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 8
(1) Preparing a negative electrode sheet: graphitization degree is 92%, capacity is 352mAh/g, and powder compaction density is 1.87g/cm 3 Artificial graphite with Dv50 of 18 mu m, conductive agent carbon black, dispersant carboxymethyl cellulose and binder styrene butadiene rubber according to weight percentage97wt%, 0.5wt%, 1wt% and 1.5wt% are placed in a material mixing tank and evenly mixed to obtain surface negative electrode active layer slurry;
compacting powder with graphitization degree of 95%, capacity of 360mAh/g and powder density of 1.94g/cm 3 Placing 98wt%, 0.5wt%, 1wt% and 0.5wt% of artificial graphite with Dv50 of 15 mu m, carbon black as a conductive agent, carboxymethyl cellulose as a dispersing agent and styrene-butadiene rubber as a binder into a mixing tank, and uniformly mixing to obtain a matrix slurry of the negative electrode active layer;
a current collector having a network structure and having a thickness of 50 μm, a diameter of an aromatic polyamide fiber of 4 μm, a thickness of a metallic copper layer of 1.8 μm, an opening ratio of 52.1% and a fracture elongation of 2.4% was taken, and a negative electrode active layer substrate slurry was prepared to have a surface density of 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body filled and covered with a negative electrode active layer matrix;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the polyethylene microporous membrane into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic membrane after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Example 9
(1) Preparing a negative electrode sheet: placing a graphite material with the graphitization degree of 92%, the capacity of 352mAh/g, the powder compaction density of 1.87g/cm < 3 >, and the Dv50 of 10 mu m, conductive agent carbon black, dispersant CMC, and binder SBR in a mixing tank according to weight percentage of 97%, 0.5%, 1% and 1.5% and uniformly mixing to obtain surface negative electrode active layer slurry;
Placing graphite material with graphitization degree of 95%, capacity of 360mAh/g, powder compaction of 1.94g/cm < 3 >, dv50 of 15 mu m, conductive agent carbon black, dispersant CMC and binder SBR in a mixing tank according to weight percentage of 98wt%, 0.5wt%, 1wt% and 0.5wt% and uniformly mixing to obtain negative electrode active layer matrix sizing agent;
collecting current collector with 50 μm thick, polymer spinning diameter of 2 μm, metal layer thickness of 1.8 μm, aperture ratio of 58.7% and fracture expansion ratio of 1.3%, and mixing the matrix slurry of negative electrode active layer with the surface density of 5mg/cm 2 Filling and covering the current collector, and performing vacuum drying to obtain a netlike filling body;
the surface negative electrode active layer slurry is prepared according to the surface density of 5mg/cm 2 Covering on the surface of the netlike filling body, vacuum drying, and compacting according to a density of 1.8g/cm 2 Rolling, slitting and tab welding are carried out to obtain the negative plate of the embodiment;
(2) Preparing a positive plate: adding 97wt% of lithium cobaltate, 1.5wt% of conductive carbon black and 1.5wt% of polyvinylidene fluoride into N, N-dimethylformamide, mixing and stirring uniformly to obtain positive electrode active layer slurry, coating the slurry on two opposite surfaces of aluminum foil with the thickness of 10 mu m, drying, rolling, cutting and welding lugs to obtain the positive electrode plate of the embodiment;
(3) And assembling the positive plate, the negative plate and the PE diaphragm into a lithium ion battery, packaging the lithium ion battery by using an aluminum plastic film after short circuit test is qualified, baking the lithium ion battery in an oven to remove water until the water content reaches the water content standard required by liquid injection, injecting electrolyte, aging for 36 hours, and completing primary charging by using a hot-press formation process to obtain the lithium ion battery of the embodiment.
Comparative example 1
The lithium ion battery of this comparative example was prepared in substantially the same manner as in example 1, except that the current collector of the negative electrode sheet was different, and the current collector of this comparative example replaced the current collector having a mesh structure with a conventional copper foil current collector having a thickness of 6 μm.
Comparative example 2
The lithium ion battery preparation method in this comparative example was basically identical to that of example 1, except that the graphitization degree, capacity, powder compaction density Dv50 of the first graphite material in this comparative example were the same as those of the second graphite material, and the others were kept unchanged.
Comparative example 3
The lithium ion battery preparation method in this comparative example was basically identical to that of example 1, except that the graphitization degree, capacity, and powder compaction density Dv50 of the second graphite material in this comparative example were the same as those of the first graphite material, and the others were kept unchanged.
Comparative example 4
The lithium ion battery preparation method in this comparative example was basically identical to that of example 1, except that the positions of the original surface anode active layer and the anode active layer matrix were changed, i.e., the original surface anode active layer slurry was filled and covered on the current collector, and the original anode active layer matrix was covered on the surface of the mesh-like filler, and the others were kept unchanged.
Test examples
1. The graphite materials, current collectors and negative electrode sheets in the above examples and comparative examples were subjected to physical and chemical property characterization, and characterization results are shown in tables 1 to 3. Table 1 shows the physicochemical property characterization results of the second graphite material in the above examples and comparative examples; table 2 shows the physical and chemical properties of the first graphite material and the negative electrode active layer matrix slurry formulations in the above examples and comparative examples; table 3 shows the results of the characterization of the conditioning properties of the current collectors and the negative electrode sheets in the above examples and comparative examples.
2. SEM test was performed on the current collector having the mesh structure in example 1 described above, and the test results are shown in fig. 4.
Fig. 4 is an SEM image of the current collector of example 1, and as can be seen from fig. 4, the spinning in the current collector is randomly arranged, and a large number of voids exist, so that more negative electrode active material can be carried.
3. The lithium ion batteries prepared in the above examples and comparative examples were subjected to a capacity retention test, a battery cycle expansion test, a negative electrode sheet resistance test, a rate discharge test, a lithium precipitation test, and a pole piece peel strength test:
(1) Capacity retention test
The lithium ion batteries prepared in the above examples and comparative examples were charged to a full charge state at 25C using a rate of 2C, and discharged to 3.0V at a rate of 0.7C, which was recorded as one cycle number. Recording initial capacity Q 0 Capacity at recording cycle up to 300 weeks is Q 1 The capacity retention after normal temperature cycle was calculated by equation 2:
capacity retention (%) = (Q) 1 /Q 0 ) X 100% of 2
The test results are shown in Table 4.
(2) Cell cycle expansion rate test
The lithium ion batteries prepared in the above examples and comparative examples were charged to a full charge state at 25C using a rate of 2C, and discharged to 3.0V at a rate of 0.7C, which was recorded as one cycle number. Cell thickness L when not cycled 0 The cell thickness at the time of recording cycle to 300 weeks was L 1 The battery cycle expansion rate after normal temperature cycle is calculated by the formula 3:
battery cycle expansion ratio (%) = (L) 1 －L 0 )/L 0 X 100% 3
The test results are shown in table 4 and fig. 5.
Fig. 5 is a graph showing the cycle expansion ratios of the lithium ion batteries of examples 1 to 4 and comparative examples 1 to 3, and it is understood from fig. 5 that the battery expansion ratios of comparative examples 1 to 3 are higher than those of examples 1 to 4, and that the battery expansion ratios of comparative examples 1 to 3 are increased more rapidly after 100 cycles, and the battery expansion ratios of examples 1 to 4 are flatter, so that the negative electrode sheet prepared according to the present invention can reduce the battery expansion ratio to some extent.
(3) Negative plate resistance test
The negative electrode sheets in the above examples and comparative examples were subjected to resistance test at 25℃under a pressure of 0.3MPa using a diaphragm resistance meter.
The test results are shown in Table 4.
(4) Multiplying power charging test
The lithium ion batteries prepared in the above examples and comparative examples were discharged to a lower limit voltage using 0.2C at 25C, allowed to stand for 10min, and then charged to an upper limit voltage at 2C rate, with a cut-off current of 0.025C. Recording the constant current charging capacity as C 0 The constant voltage charge capacity was noted as C 1 The rate of rate discharge of the battery at normal temperature was calculated by equation 4:
rate of discharge (%) =c 0 /(C 0 +C 1 ) 4. The method is to
The test results are shown in Table 4.
(5) Lithium evolution test
The lithium ion batteries prepared in the above examples and comparative examples were discharged to a lower limit voltage at 25C using 0.2C, left stand for 10min, the batteries were charged to a full charge state using 2C rate and discharged to 3.0V using 0.7C rate, recorded as one cycle number, the batteries were disassembled in a glove box after 30 cycles to observe whether metallic lithium was precipitated on the surface of the negative electrode sheet.
The test results are shown in Table 4.
(6) Pole piece peel strength test
Fixing the negative electrode plates of the embodiment and the comparative example on a steel plate with the same width by using double-sided adhesive tape, fixing the steel plate on a tensile machine, clamping one non-adhered end of the negative electrode plate on the steel plate, setting the running speed of the tensile machine to be 50mm/min, and measuring the tension change of the negative electrode plate in the tensile displacement to obtain an average tension value F, wherein the width of the negative electrode plate is W, W=24 mm, and calculating the peel strength of the negative electrode plate by using a formula 5;
Peel strength (N/m) =f/W type 5
The test results are shown in Table 4.
TABLE 1
TABLE 2
TABLE 3 Table 3
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TABLE 4 Table 4
As can be seen from table 1:
(1) The lithium ion batteries of examples 1-9 have higher capacity retention rate and rate discharge rate and lower cyclic expansion rate than the lithium ion batteries of comparative examples 1-4, the capacity retention rate can reach 97.05% at the highest, the rate discharge rate is 85.72% at the highest, and the cyclic expansion rate is 5.86% at the lowest; meanwhile, the negative electrode sheets of the examples 1-9 also have higher peeling strength and lower resistance, the peeling strength is at most 24.8N/m, and the resistance is at least 2.45mΩ; moreover, the lithium ion batteries of examples 1 to 9 did not show a lithium precipitation phenomenon after cycling, whereas comparative examples 1 to 4 showed a slight or severe lithium precipitation phenomenon.
(2) In addition, the negative electrode sheet in comparative example 1 showed slight lithium precipitation compared to the negative electrode sheet in example 1, because the conventional current collector is used in comparative example 1, and compared to the net-shaped current collector in the negative electrode sheet of the present invention, the negative electrode sheet having higher compacted density and more compact structure is more easily formed during rolling, migration of lithium ions is hindered to some extent, and lithium ions are accumulated on the surface of the negative electrode sheet during high-rate charging, thereby causing slight lithium precipitation; the comparative example 2 also showed slight lithium precipitation compared with example 1, because the graphite materials in the negative electrode active layer in comparative example 2 are all second graphite materials with harder materials and have no double-layer structure, and the porosity of the surface layer of the negative electrode active layer is lower in the rolling process, so that lithium ions are not easy to combine with electrons in time to react, and slight lithium precipitation occurs; the serious lithium precipitation phenomenon occurs in comparative examples 3 and 4, because the surface layers of the negative electrode active layers in comparative examples 3 and 4 are both made of the first graphite material with a softer material, and the porosity of the surface layers is further reduced during the rolling process, so that the difficulty of lithium ions entering the negative electrode active layers from the surface layers is increased, and the serious lithium precipitation phenomenon occurs.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (10)
1. The negative electrode plate is characterized by comprising a current collector with a net-shaped structure, a negative electrode active layer matrix and a surface negative electrode active layer; the negative electrode active layer matrix is at least partially filled inside the network structure; the surface negative electrode active layer is arranged on the outer surface of the negative electrode active layer matrix and/or the outer surface of the current collector;
the negative electrode active layer matrix comprises a first graphite material, and the surface negative electrode active layer comprises a second graphite material, wherein the graphitization degree of the second graphite material is smaller than that of the first graphite material;
the graphitization degree of the first graphite material is not less than 90%, and/or the graphitization degree of the second graphite material is not less than 90%.
2. The negative electrode tab of claim 1, wherein the negative electrode active layer matrix comprises a first negative electrode active layer matrix and a second negative electrode active layer matrix, the first negative electrode active layer matrix filling the interior of the mesh structure, the second negative electrode active layer matrix covering at least a portion of the surface of the current collector.
3. The negative electrode sheet according to claim 1 or 2, wherein the graphitization degree of the first graphite material is 93 to 95%;
the graphitization degree of the second graphite material is 90-92%;
the first graphite material comprises at least one of artificial graphite and natural graphite;
the second graphite material comprises at least one of artificial graphite and natural graphite.
4. A negative electrode sheet according to any one of claims 1 to 3, wherein the first graphite material has a capacity of not less than 348mAh/g and/or a powder compacted density of not less than 1.75g/cm 3 ；
The second graphite material has a capacity of not less than 335mAh/g and/or a powder compacted density of not less than 1.65g/cm 3 。
5. The negative electrode sheet according to any one of claims 1 to 4, wherein the first graphite material has a capacity of not less than 358mAh/g and/or a powder compacted density of not less than 1.95g/cm 3 ；
And/or; the second graphite material has a powder compaction density of not less than 1.85g/cm 3 。
6. The negative electrode sheet of any one of claims 1-5, wherein the Dv50 of the first graphite material is greater than the Dv50 of the second graphite material;
the Dv50 of the first graphite material is 10-20 μm and/or the Dv50 of the second graphite material is 5-15 μm.
7. The negative electrode sheet of any one of claims 1-6, wherein the current collector comprises a 3D mesh-like skeleton formed by polymer spinning and a metal layer coated on an outer surface of the polymer spinning;
the diameter of the polymer spinning is 3-8 mu m; and/or the thickness of the metal layer is 1-3 mu m.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein the current collector has a thickness of 40 to 100 μm and/or an opening ratio of 45 to 55% and/or an elongation at break of not less than 1%.
9. The negative electrode sheet according to any one of claims 1 to 8, wherein the surface negative electrode active layer and the negative electrode active layer base further comprise a binder;
the mass percentage of the binder contained in the surface negative electrode active layer is greater than the mass percentage of the binder contained in the negative electrode active layer matrix;
The mass percentage of the binder in the surface negative electrode active layer is 1-1.5wt%; and/or the mass percentage of the binder in the negative electrode active layer matrix is not higher than 0.5wt%.
10. A lithium ion comprising the negative electrode sheet according to any one of claims 1 to 9.
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