CN112310344A - Positive plate and lithium ion battery containing same - Google Patents
Positive plate and lithium ion battery containing same Download PDFInfo
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- CN112310344A CN112310344A CN202011207903.9A CN202011207903A CN112310344A CN 112310344 A CN112310344 A CN 112310344A CN 202011207903 A CN202011207903 A CN 202011207903A CN 112310344 A CN112310344 A CN 112310344A
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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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
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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
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a positive plate and a lithium ion battery containing the same. The positive plate comprises a current collector and a coating positioned in a current collector coating area; the coating comprises a first coating region and a second coating region; the first coating area is positioned on the surface of the current collector coating area, and the contact surface of the first coating area and the current collector coating area completely covers the current collector coating area; the second coating area is positioned above the first coating area and comprises an area E and an area E ', the area E and the area E ' are respectively positioned at the long side of the first coating area, and the area E ' are independent from each other or at least have an intersection point; the first coating zone and the second coating zone both contain an active material. The invention fully solves the problem of lithium precipitation in the edge area of the negative electrode, improves the endurance capacity of the lithium ion battery, solves the problems of cyclic expansion and battery core deformation, and reduces the safety risk.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a positive plate and a lithium ion battery containing the same.
Background
With the rapid development of lithium ion battery technology, the application of lithium ion batteries in portable mobile electronic devices such as notebook computers and smart phones is more and more extensive, but with the rapid pace of life of people, the energy density and the charging speed of the current lithium ion batteries still cannot meet the requirements of various consumer electronic products on the lithium ion batteries. Therefore, increasing the charging speed of the lithium ion battery while increasing the energy density of the lithium ion battery becomes a key point of research in the lithium ion battery industry today. However, when the battery cell is disassembled at present, the lithium precipitation condition (edge lithium precipitation) of the edge area of the lithium ion battery negative plate is more serious than that of the negative plate body area, and the edge lithium precipitation phenomenon is more obvious when the charging rate is larger, so that the bottom and the top of the battery cell bulge in the long-term circulation process, and the deformation of a cover of the battery cell causes a safety problem.
Disclosure of Invention
The invention provides a positive plate and a lithium ion battery containing the same, which can solve the safety problems that the bottom and the top of a battery cell bulge in the long-term circulation process and the deformation of a pot cover of the battery cell are caused by lithium separation in the edge area of a negative electrode plate. The positive plate provided by the invention can reduce the dynamic capability of the edge region of the positive plate of the lithium ion battery under the condition of not reducing the energy density of the battery by mainly adjusting the dynamic performance of active substances in the edge region (namely the second coating region) and the body region (namely the first coating region) of the positive plate of the lithium ion battery, effectively improve the problem that the edge of the negative plate of the lithium ion battery separates out lithium to form lithium dendrite, thereby generating potential safety hazard, prolong the cycle life of the lithium ion battery on the premise of not reducing the energy density, and improve the problems of cycle expansion and safety.
The invention adopts the following technical scheme:
a positive plate comprises a current collector and a coating positioned in a current collector coating area; the coating comprises a first coating region and a second coating region;
wherein the first coating area is positioned on the surface of the current collector coating area, and the contact surface of the first coating area and the current collector coating area completely covers the current collector coating area;
the second coating area is positioned above the first coating area and comprises an area E and an area E ', the area E and the area E ' are respectively positioned at the long sides of the first coating area, and the area E ' are independent from each other or at least have an intersection point;
the first coating zone and the second coating zone both contain an active material.
According to an embodiment of the present invention, the current collector further comprises a blank area for welding a tab.
According to an embodiment of the invention, the interfaces of said zones E and E' with the first coating zone have at least one bevel. According to the invention, the inclined plane refers to a plane that is not parallel to the surface of the current collector or to the outer surface of the coating zone. The bevel may reduce the dynamic capability of the edge region of the positive pole piece.
According to an embodiment of the present invention, the slope may be a smooth and/or non-smooth (e.g., curved or stepped) slope. As another example, the bevel may have a clear boundary with the first coated region, or may also be interpenetrating with the first coated region.
According to an embodiment of the present invention, the regions E and E' may be symmetrically or asymmetrically disposed at the long side of the first coating region, preferably symmetrically disposed.
According to an embodiment of the invention, the sum of the maximum widths of said zones E and E' is less than or equal to the maximum width of the first coating zone. Wherein the maximum width of the first coating area is equal to the width of the current collector coating area or the positive plate. When the maximum width of the first coating area is equal to the width of the positive electrode sheet, meaning that the current collector coating area width is equal to the width of the positive electrode sheet, no blank current collector exists in the extension of the current collector coating area width.
According to an embodiment of the invention, the length of said zones E and E' is equal to the length of the first coating zone.
For example, the shape of the regions E and E' may be triangular, and the shape of the first coating region may be triangular, trapezoidal, pentagonal, or hexagonal, in cross section along the wide side of the first coating region.
For example, the region E and the region E' may intersect at a point, line or plane.
Preferably, the horizontal cathetus of the triangular area E is located between the edge of the first coating zone (or positive plate) and the midline of the first coating zone (or positive plate). Preferably, the horizontal cathetus of the triangular region E' is located between the other edge of the first coating zone (or positive electrode sheet) and the midline of the first coating zone (or positive electrode sheet). Wherein said edge means the area extending 0-15mm, for example 5-10mm, from the long side of the positive electrode tab towards the median line of the positive electrode tab. Wherein, the central line means the central line equidistant from the two long sides of the positive plate.
The current collector is preferably a regularly shaped current collector, for example rectangular in shape, based on the general understanding of the person skilled in the art.
According to an embodiment of the present invention, the maximum thickness of the regions E and E '(i.e. the vertical legs of the triangular regions E and E') may be less than or equal to the maximum thickness of the first coating zone.
According to an embodiment of the present invention, the first coating region, the region E and the region E' enclose a rectangular region or an approximately rectangular region having a flat or approximately flat surface along a cross section of a wide side of the first coating region.
According to an embodiment of the present invention, the active material of the first coating region is denoted as a first positive electrode active material, and the active material of the second coating region is denoted as a second positive electrode active material.
According to an embodiment of the present invention, the first positive electrode active material and the second positive electrode active material are the same or different, preferably different. For example, each may be selected from one, two or more of the following: lithium cobaltate, ternary materials, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate and lithium manganese-containing base materials. Illustratively, the first positive electrode active material is lithium cobaltate, and the second positive electrode active material is a ternary material; or the first positive electrode active material is lithium cobaltate, the second positive electrode active material is a mixture of the lithium cobaltate and the ternary material, and the mixture of the lithium cobaltate and the ternary material in a mass ratio of 1: 1 is preferred.
According to one embodiment of the present invention, the median particle diameter D of the first positive electrode active material50Smaller than the median particle diameter D of the second positive electrode active material50. Preferably, the median particle diameter D of the first positive electrode active material50The value range of (D) is more than or equal to 13 mu m50Less than or equal to 19 μm, for example 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm; preferably, the median particle diameter D of the second positive electrode active material50The value range of (D) is not less than 17 mu m50Less than or equal to 23 μm, for example 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm;
and the median particle diameter D of the first positive electrode active material50Smaller than the median particle diameter D of the second positive electrode active material50。
Illustratively, the first positive electrode active material is D5017 μm lithium cobaltate, and the second positive electrode active material is D50Lithium cobaltate 20 μm; or, the first positive electrode active material is D5017 μm lithium cobaltate, and the second positive electrode active material is D5023 μm lithium cobaltate; or, the first positive electrode active material is D5013 μm lithium cobaltate, and the second positive electrode active material D5020 μm lithium cobaltate.
For example, the particle size distribution of the second active material may include: d is more than 8 mu m10＜13μm，17μm≤D50≤23μm，28μm＜D90Less than 40 μm; for example, the first active material particle size distribution may include: d is more than 4 mu m10＜8μm，13μm≤D50≤19μm，26μm＜D90＜35μm。
According to yet another embodiment of the present invention, the first coated region and the second coated region further contain a conductive agent. Preferably, the amount of conductive agent in the second coating region is less than the amount of conductive agent in the first coating region to impair the kinetic properties of the second coating region. For example, the conductive agent may be the same or different in the two coated regions; for example, the conductive agent may be selected from one, two or more of the following: conductive carbon black, carbon fibers, ketjen black, acetylene black, carbon nanotubes, and graphene. For example, the mass ratio of the conductive agent to the positive electrode active material in the same coating region is (0.1-5) to 100, preferably (0.5-3) to 100.
According to still another embodiment of the present invention, the second positive electrode active material may be a positive electrode material of single crystal grains, and the first positive electrode active material may be a positive electrode material of polycrystalline grains. Wherein the polycrystalline particles refer to secondary particles in which hundreds to thousands of primary nanoparticles are closely combined, and the single crystalline particles refer to secondary particles in which several to several tens of primary microparticles are stacked. Since the polycrystalline particles are composed of nano-particles and the single crystalline particles are composed of micro-particles, the polycrystalline particles have a shorter lithium ion bulk diffusion path and thus have less resistance and better kinetic properties than the single crystalline particles, and the positive electrode single crystalline or polycrystalline active materials include, but are not limited to, the above-mentioned positive electrode active materials. For example, the positive electrode active material has the selection as described above, for example, lithium cobaltate; illustratively, the first positive electrode active material is a lithium cobaltate polycrystal, and the second positive electrode active material is a lithium cobaltate single crystal. In summary, it is desirable to ensure that the dynamic properties of the first coating layer are better than the dynamic properties of the second coating layer.
According to an embodiment of the invention, the first and second coating zones further comprise the same or different binders. For example, the binder is selected from one, two or more of the following: polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and lithium Polyacrylate (PAALi).
According to the embodiment of the present invention, the length of the positive electrode sheet is not particularly limited, and is preferably 800mm to 1700mm, and more preferably 882 mm to 1000 mm.
According to an embodiment of the invention, the maximum thickness of the regions E and/or E' is between 50 μm and 180 μm, preferably between 50 μm and 105 μm.
According to the embodiment of the present invention, the width of the positive electrode sheet may be determined according to the width of the battery cell, and may be 10mm to 150mm, and preferably 50mm to 100 mm.
According to an embodiment of the invention, the current collector is an aluminum foil.
According to an exemplary aspect of the present invention, the positive electrode sheet includes a current collector, and a coating layer located at a current collector coating region; the coating comprises a first coating region and a second coating region;
wherein the first coating area is positioned on the surface of the current collector coating area, and the contact surface of the first coating area and the current collector coating area completely covers the current collector coating area;
the second coating area is positioned above the first coating area and comprises an area E and an area E ', the area E and the area E ' are respectively positioned at the long sides of the first coating area, and the area E ' are independent of each other;
the interfaces of the regions E and E' and the first coating region have at least one inclined surface;
the sum of the maximum widths of the regions E and E' is less than or equal to the maximum width of the first coating zone, which is equal to the width of the current collector coating zone;
the maximum thickness of the regions E and E' is less than or equal to the maximum thickness of the first coated region;
the first coating area and the second coating area both contain active substances, the active substances in the first coating area are marked as first active substances, and the active substances in the second coating area are marked as second active substances;
median particle diameter D of the first active substance50Smaller than the median particle diameter D of the second active substance50；
And/or the first active substance has a kinetic property superior to the second active substance;
and/or the first active material is polycrystalline, and the second active material is single crystal;
and/or the first coating area and the second coating area also contain a conductive agent, and the content of the conductive agent in the first coating area is larger than that in the second coating area.
The invention also provides a preparation method of the positive plate, which comprises the following steps: coating the first active material slurry on the first coating area, coating the second active material slurry on the second coating area, and drying to obtain the positive plate;
the first coated region, the second coated region, the first active substance and the second active substance have the meaning as described above.
According to an embodiment of the present invention, the first active material slurry contains a first active material, a conductive agent, and a binder. Wherein the mass ratio of the first active material, the conductive agent and the binder is in a known ratio in the art. Preferably, the solid content of the first active material slurry is 70 to 75%. Preferably, the first active material slurry is prepared by a method known in the art.
According to an embodiment of the present invention, the second active material slurry contains a second active material, a conductive agent, and a binder. Wherein the mass ratio of the second active material, the conductive agent and the binder is in a known ratio in the art. Preferably, the solids content of the second active substance slurry is 70 to 75%. Preferably, the second active material slurry is prepared by methods known in the art.
The conductive agent and binder have the meanings as described above.
According to an embodiment of the present invention, the first active material slurry and the second active material slurry further contain a first solvent. For example, the first solvent is NMP.
The positive electrode in the invention refers to an electrode which obtains electrons and generates reduction reaction; in some cases (such as in an electrolytic cell), it is also referred to as the "cathode".
The invention also provides application of the positive plate in an electrochemical device.
The invention also provides an electrochemical device which contains the positive plate. Preferably, the electrochemical device is an electrochemical cell, preferably a lithium ion cell.
The invention also provides a preparation method of the lithium ion battery, which comprises the following steps: and assembling the positive plate, the negative plate, the diaphragm and the electrolyte to form the lithium ion battery.
According to the embodiment of the invention, the negative plate is prepared by coating the negative slurry on a current collector and drying.
According to an embodiment of the present invention, the negative electrode slurry contains a negative electrode active material, a conductive agent, and a binder. Wherein the anode active material may be selected from one, two or more of the following materials: lithium titanate, a carbon material, and a mixture of the carbon material and silicon; wherein the carbon material is selected from one, two or more of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon and organic polymer compound carbon; an example is artificial graphite. Wherein the conductive agent and the binder may be selected from the group consisting of those described above.
According to an embodiment of the present invention, the negative electrode slurry contains a second solvent, for example, the second solvent is water.
According to an embodiment of the present invention, the solid content of the anode slurry is 40 to 45%.
According to an embodiment of the present invention, the electrolyte may be selected from electrolytes known in the art to be suitable for use in lithium ion batteries.
According to an embodiment of the invention, the assembly may be an assembly method known in the art.
The invention has the beneficial effects that:
the inventor finds that lithium is easy to be separated from the edge area of the negative pole piece, and the edge lithium separation phenomenon is more obvious when the charging rate is larger, so that bottom and top bulges can occur to the battery cell in the long-term circulation process, and the deformation of the pot cover of the battery cell causes safety problems. The root cause of lithium analysis at the edge of the negative pole piece of the lithium ion battery is that the edge of the positive pole piece is in full contact with electrolyte, the concentration polarization of the edge area is smaller compared with that of a positive pole body (the middle area of the pole piece), the positive pole lithium ions are extracted and migrated more quickly in the charging process, the current density and the lithium ion density of the edge area are the maximum, the potential of the edge area of the negative pole is lower, more lithium is inserted into the negative pole area corresponding to the edge of the positive pole piece in the same time, and finally lithium analysis in the area is caused. The solution to the problem of edge lithium deposition from the mechanical point of view requires the coating of the positive electrode active material in the edge region (i.e., the second coating region) of the positive electrode sheet with a kinetic property inferior to that of the bulk region (i.e., the first coating region) of the positive electrode sheet.
The positive plate with the novel structure can solve the problems:
1. the positive active materials with different dynamic properties or the slurry containing the positive active materials with different dynamic properties are coated in different areas, so that the function of each area can be fully exerted, the problem of lithium precipitation in the edge area of the negative electrode is fully solved, the endurance of the lithium ion battery is improved, the problems of cyclic expansion and battery core deformation are solved, and the safety risk is reduced.
2. The lithium ion battery containing the positive plate realizes the effect of taking the energy density and the quick charging capability into consideration to a certain extent.
Drawings
Fig. 1 is a front view of a positive electrode sheet.
Fig. 2 is a plan view (a) and a sectional view (b) of a positive electrode sheet.
Fig. 3 is a positive electrode sheet of a conventional structure.
Reference numerals: 1-second coated area, 2-first coated area, 3-blank area, E-area E, E '-area E'.
Detailed Description
The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.
[ Positive plate ]
The positive electrode sheet constructed as shown in fig. 1, includes a current collector, and a coating layer located at a current collector coating region (i.e., section bc in fig. 1); the coating comprises a first coating zone 2 and a second coating zone 1;
the first coating area 2 is positioned on the surface of the current collector coating area, and the contact surface of the first coating area 2 and the current collector coating area completely covers the current collector coating area;
the second coating region 1 is positioned above the first coating region 2 and includes a region E and a region E', which are respectively positioned at the long sides of the first coating region 2, and are independent from each other;
both the first coating zone 2 and the second coating zone 1 contain active substances.
The current collector further comprises a blank area 3, i.e. section ab in fig. 1, the blank area 3 being used for welding a tab.
The regions E and E' are symmetrically arranged on the long sides of the first coating region 2. The length of the regions E and E' is equal to the length of the first coating zone 2. The maximum width of the first coating region 2 is equal to the width of the current collector coating region or the positive electrode tab.
As shown in fig. 2 (a) and (b), the coating direction of the slurry of the positive electrode sheet is parallel to the long side of the current collector, and on the section of the coated region of the current collector perpendicular to the coating direction, i.e., the cross section along the wide side of the first coated region, the shapes of the region E and the region E' are triangles (structures (1) - (4) shown in fig. 2 (b)), the shape of the first coated region 2 is triangle (structure (2) shown in fig. 2 (b)), trapezoid (structure (4) shown in fig. 2 (b)), pentagon (structure (1) shown in fig. 2 (b)), and hexagon (structure (3) shown in fig. 2 (b)).
The horizontal cathetus of the triangular area E is located between the edge of the first coating zone (or positive plate) and the midline of the first coating zone (or positive plate), and the horizontal cathetus of the triangular area E' is located between the other edge of the first coating zone (or positive plate) and the midline of the first coating zone (or positive plate). I.e., point M and point M' are free to move between 5mm from the pole piece edge to the midline position. Wherein, the edge means the area which extends 0-15mm from the long edge of the positive plate to the central line of the positive plate; as shown in fig. 1, the width indicated by the section de is the edge area, but the position of the active material coating with poorer dynamic performance of the pole piece structure in the invention is not limited to the edge area in the invention. Wherein, the median line means the symmetry axis with the two long sides of the positive electrode tab. The width of the pole piece is determined by the cell model, such as model 466483, the width of the positive pole piece is 76mm, wherein the line position is 39mm, namely the M point and the M' point of the triangular area can freely move between 5mm and 38mm away from the edge of the pole piece.
The interfaces of the regions E and E ' with the first coating zone 2 have at least one bevel, i.e. at least a bevel formed by the hypotenuses of the triangle (i.e. MN, M ' N '). The bevel is a smooth and/or non-smooth (e.g., curved or stepped) bevel. As another example, the bevel may have a clear boundary with the first coated region, or may be interpenetrating with the first coated region.
The maximum thickness of regions E and E '(i.e. the vertical legs of triangular regions E and E') is less than (structures (1) and (3) as shown in fig. 2 (b)) or equal to (structures (2) and (4) as shown in fig. 2 (b)) the maximum thickness of the first coated region. Namely, the N points and the N' points of the triangular area can freely move in the thickness direction of the pole piece paste coating; if the coating thickness of the pole piece is 150 μm, the moving position of the point N and the point N' in the triangular area is more than 0 and not more than 150 μm, and when the moving position is equal to 150 μm, the thickness of the second coating area is equal to the maximum thickness of the first coating area.
The first coating region 2, the region E and the region E' enclose a rectangular or approximately rectangular region with a flat or approximately flat surface along the cross section of the wide side of the first coating region.
The active material in the first coating region 2 is referred to as a first positive electrode active material, the active material in the second coating region 1 is referred to as a second positive electrode active material, and the median particle diameter D of the first positive electrode active material50Smaller than the median particle diameter D of the second positive electrode active material50. The first coating region coats the region of the electrode active material having a smaller particle size more facilitates the movement of lithium ions inside the electrode material and thus exhibits better ion diffusion kinetics. The region of the second coating layer coated with the electrode active material having a large particle size is not conducive to the release of lithium ions from the inside of the material during charging, and thus, the negative electrode can be effectively prevented from failing to completely receive the lithium ions in a short time, which may lead to the occurrence ofPart of the lithium ions "bin" the problem of precipitating lithium at the edge of the negative electrode to form lithium dendrites.
The first active substance and the second active substance are the same or different, preferably different. For example, each may be selected from one, two or more of the following: lithium cobaltate, ternary materials, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate and lithium manganese-containing base materials.
The first and second coated regions also contain a conductive agent, preferably in a lesser amount than in the first coated region, to impair the dynamic properties of the second coated region. For example, the conductive agent may be the same or different in the two coated regions; for example, the conductive agent may be selected from one, two or more of the following: conductive carbon black, carbon fibers, ketjen black, acetylene black, carbon nanotubes, and graphene.
The cathode material in the second coating region may be a cathode material of single crystal grains, and the cathode material of the first coating region may be a cathode material of polycrystalline grains. The polycrystalline particles have a shorter lithium ion bulk diffusion path and thus have less resistance and better kinetic properties than the single crystal particles to ensure that the kinetic properties of the first coating layer are better than the kinetic properties of the second coating layer.
The first and second coating regions may also contain the same or different binders. For example, the binder is selected from one, two or more of the following: polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and lithium Polyacrylate (PAALi).
In the following examples, the dynamic performance of the positive electrode sheet is improved mainly by adjusting the particle size of the positive electrode active material, the kind of the positive electrode active material, and the content of the conductive agent in the positive electrode sheet. The following examples mainly take the sectional structure (4) shown in fig. 2 (b) as an example to prepare the positive electrode sheet and the lithium ion battery thereof, but it should be noted that the positive electrode sheet structure of the present invention can achieve at least the same effect as the structure (4) by being applied to the other three sectional structures shown in fig. 2 (b).
Examples 1 to 11 and comparative examples 1 to 5
In the following examples and comparative examples, the negative electrode sheet was prepared by a method known in the art, and the details of the preparation process are described below.
The chemical formula of the ternary material used in the following examples and comparative examples is: LiNi0.5Co0.2Mn0.3O2(NCM523)。
Both 1 wt% and 3 wt% of the carbon-coated lithium cobaltate used in the following examples and comparative examples were obtained after being purchased commercially.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Example 1
The preparation method of the positive plate comprises the following steps:
(1) preparation of the slurry
Positive electrode slurry:
preparing a first active material slurry: adding a first positive active substance, conductive carbon black and a binder polyvinylidene fluoride (PVDF) into a stirring tank according to the mass ratio of 97.2: 1.5: 1.3, adding NMP according to a known batching process to prepare a first positive active substance slurry, and sieving the first positive active substance slurry by a 200-mesh sieve to prepare a first positive active substance slurry, wherein the solid content of the slurry is 70-75%;
preparing a second active material slurry: adding a second positive active substance, conductive carbon black and a binder polyvinylidene fluoride (PVDF) into a stirring tank according to the mass ratio of 97.2: 1.5: 1.3, adding NMP according to a known batching process to prepare a second positive active substance slurry, and sieving the second positive active substance slurry by a 200-mesh sieve to prepare a second positive active substance slurry, wherein the solid content of the slurry is 70-75%;
(2) coating of positive electrode by regions
Coating was performed using a coater, and a first active material slurry was coated in the first coating region and a second active material slurry was coated in the second coating region, to prepare a positive electrode sheet having a structure (4) shown in fig. 2 (b). It is to be noted that the structure (4) is schematically illustrated and not to strict scale, and the dimensions of the various coating zones are subject to the following description: the length of the pole piece is 969MM, the maximum thickness of the first coated area is 85 μm, and the maximum width of the coating MM' is 76 MM; the areas E and E' in the second coating area are completely symmetrical, the maximum thickness is 85 μm, and the width (namely the width of a horizontal right-angle surface) is 30 mm; and drying the prepared positive plate at the temperature of 120 ℃ to obtain the positive plate.
Preparing a lithium ion battery:
(3) coating of negative electrode
The method comprises the steps of taking artificial graphite as a negative electrode active material, adding the artificial graphite, conductive carbon black and binder sodium carboxymethyl cellulose into a stirring tank according to the mass ratio of 97: 1.5, adding a deionized water solvent, fully stirring according to a known batching process, and screening by a 200-mesh screen to prepare negative electrode slurry, wherein the solid content of the negative electrode slurry is 40-45%.
And coating the negative electrode slurry on the copper foil by using a coating machine according to a known coating mode, and drying at the temperature of 80 ℃ to obtain the negative electrode sheet.
(4) Assembling the battery cell:
coiling the positive plate, the negative plate and the diaphragm together to form a coil core, packaging the coil core by using an aluminum plastic film, baking the coil core to remove moisture, and injecting electrolyte, wherein the preparation process of the electrolyte is as follows: propylene Carbonate (PC), Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a weight ratio of about 1: 0.5: 1, and LiPF is added6Mixing uniformly, wherein LiPF6The concentration of (A) is about 1mol/L, and the electrolyte is obtained by uniformly mixing. And (4) forming by adopting a hot pressing formation process to obtain the battery cell.
Examples 2 to 11
Examples 2-11 differ from example 1 in that: different positive electrode active materials (examples 2 to 6), active materials with different particle sizes (examples 7 to 9), and conductive agents with different contents (examples 10 to 11) were used.
Comparative examples 1 to 5
The positive electrode sheets of comparative examples 1 to 2 were coated with a known lithium ion battery positive electrode single layer, as shown in fig. 3. Positive electrode sheet preparation of comparative examples 3 to 5 reference was made to example 1 except that the positive electrode active materials of the first and second coating regions were different.
The positive plates prepared in the examples and the comparative examples are compacted identically, a soft package battery cell with the model number of 426484 is assembled, 0.2C/0.2C charging and discharging is carried out at 25 ℃ to test the energy density of the soft package battery cell, 1.5C charging/0.7C discharging is carried out on each manufactured soft package battery cell at 25 ℃, the battery is disassembled at different cycle times to confirm the lithium precipitation condition of the edge of the negative electrode plate of the battery, the disassembly result and the energy density, the layered coating condition of the positive electrode plate and the lithium precipitation condition of the edge of the negative electrode plate in the cycle process, and specific reference is made to table 1.
Those skilled in the art will appreciate that the technical effects equivalent to the embodiments can be obtained by replacing the conductive agent, the adhesive, the electrolyte used in the embodiments with other conductive agents, adhesives and electrolytes which are conventional in the art, or by combining any of the three embodiments.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The positive plate is characterized by comprising a current collector and a coating positioned in a current collector coating area; the coating comprises a first coating region and a second coating region;
wherein the first coating area is positioned on the surface of the current collector coating area, and the contact surface of the first coating area and the current collector coating area completely covers the current collector coating area;
the second coating area is positioned above the first coating area and comprises an area E and an area E ', the area E and the area E ' are respectively positioned at the long sides of the first coating area, and the area E ' are independent from each other or at least have an intersection point;
the first coating zone and the second coating zone both contain an active material.
2. The positive electrode sheet according to claim 1, wherein the current collector further comprises a blank area for welding a tab.
Preferably, the interfaces of the regions E and E' with the first coating zone have at least one bevel.
Preferably, the bevel is a smooth and/or non-smooth bevel. Preferably, the bevel has a clear boundary with the first coating zone or is interpenetrating with the first coating zone.
Preferably, said zones E and E' are arranged symmetrically or asymmetrically, preferably symmetrically, on the long sides of the first coated zone.
Preferably, the sum of the maximum widths of said zones E and E' is less than or equal to the maximum width of the first coating zone; the maximum width of the first coating area is equal to the width of the current collector coating area or the positive plate.
Preferably, the length of the regions E and E' is equal to the length of the first coating zone.
Preferably, the shape of the regions E and E' is triangular and the shape of the first coating region is triangular, trapezoidal, pentagonal or hexagonal in cross section along the wide side of the first coating region.
Preferably, the regions E and E' intersect at a point, line or plane.
3. The positive electrode sheet according to claim 2, wherein the horizontal cathetus of the triangular area E is located between the edge of the first coating zone or positive electrode sheet and the midline of the first coating zone or positive electrode sheet. Preferably, the horizontal cathetus of the triangular area E' is located between the other edge of the first coating zone or positive electrode sheet and the midline of the first coating zone or positive electrode sheet. Wherein, the edge means that the edge extends 0-15mm from the long side of the positive plate to the central line of the positive plate. Wherein, the central line means the central line equidistant from the two long sides of the positive plate.
Preferably, the maximum thickness of the regions E and E '(i.e. the vertical legs of the triangular regions E and E') is less than or equal to the maximum thickness of the first coated region.
Preferably, the first coating region, the region E and the region E' enclose a rectangular or approximately rectangular region with a flat or approximately flat surface along the cross section of the wide side of the first coating region.
4. The positive electrode sheet according to any one of claims 1 to 3, wherein the active material in the first coating region is referred to as a first positive electrode active material, and the active material in the second coating region is referred to as a second positive electrode active material;
preferably, the median particle diameter D of the first positive electrode active material50Smaller than the median particle diameter D of the second positive electrode active material50(ii) a Preferably, the median particle diameter D of the first positive electrode active material50The value range of (D) is more than 13 mu m50Less than 19 μm, median particle diameter D of the second positive electrode active material50The value range of (1) is more than 17 mu m and less than D50< 23 μm, and the median particle diameter D of the first positive electrode active material50Smaller than the median particle diameter D of the second positive electrode active material50。
And/or, preferably, the first positive electrode active material and the second positive electrode active material are the same or different, preferably different, and preferably the first positive electrode active material has a kinetic performance superior to the second positive electrode active material. Preferably one, two or more selected from the following: lithium cobaltate, ternary materials, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate and lithium manganese-containing base materials.
And/or, preferably, the second positive electrode active material is a positive electrode material of single crystal particles, and the first positive electrode active material is a positive electrode material of polycrystalline particles.
5. The positive electrode sheet according to any one of claims 1 to 4, wherein the first coating region and the second coating region further contain a conductive agent.
Preferably, the content of the conductive agent in the second coating region is less than the content of the conductive agent in the first coating region.
Preferably, the conductive agent is the same or different in both coating zones; preferably, the conductive agent is selected from one, two or more of the following: conductive carbon black, carbon fibers, ketjen black, acetylene black, carbon nanotubes, and graphene.
Preferably, the first coating region and the second coating region further contain the same or different binders. Preferably, the binder is selected from one, two or more of the following: polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and lithium Polyacrylate (PAALi).
6. The positive electrode sheet according to any one of claims 1 to 5, wherein the length of the positive electrode sheet is 800mm to 1700mm, preferably 882 mm to 1000 mm.
Preferably, the maximum thickness of the region E and/or the region E' is 50 μm to 180 μm, preferably 50 μm to 105 μm.
Preferably, the width of the positive electrode sheet is 10mm to 150mm, preferably 50mm to 100 mm.
Preferably, the current collector is an aluminum foil.
7. The method for producing the positive electrode sheet according to any one of claims 1 to 6, characterized by comprising the steps of: and coating the first active material slurry on the first coating area, coating the second active material slurry on the second coating area, and drying to obtain the positive plate.
8. Use of the positive electrode sheet according to any one of claims 1 to 6 in an electrochemical device.
9. An electrochemical device comprising the positive electrode sheet according to any one of claims 1 to 6. Preferably, the electrochemical device is an electrochemical cell, preferably a lithium ion cell.
10. The preparation method of the lithium ion battery comprises the following steps: assembling the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte according to any one of claims 1 to 6 to form a lithium ion battery.
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