CN113140697B - Positive plate, lithium ion battery and preparation method of positive plate - Google Patents
Positive plate, lithium ion battery and preparation method of positive plate Download PDFInfo
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- CN113140697B CN113140697B CN202110436483.XA CN202110436483A CN113140697B CN 113140697 B CN113140697 B CN 113140697B CN 202110436483 A CN202110436483 A CN 202110436483A CN 113140697 B CN113140697 B CN 113140697B
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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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- 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 application discloses a positive plate, a lithium ion battery and a preparation method of the positive plate, and relates to the technical field of lithium ion batteries. The positive electrode sheet includes: a current collector, and a conductive coating and an active coating applied to the current collector; wherein the active coating comprises a first sub-active coating and a second sub-active coating, the thickness of the first sub-active coating is less than the thickness of the second sub-active coating; the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector; n tabs are arranged on the first edge of the current collector, N is a positive integer, and the N tabs extend out of the conductive coating along the first direction of the current collector. Therefore, the thickness of the positive plate is more uniform and can be better contacted with the diaphragm, so that the transmission performance of lithium ions in the battery core is ensured, the occurrence of lithium precipitation is effectively reduced, and the effect of improving the safety of the battery is achieved.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a positive plate, a lithium ion battery and a preparation method of the positive plate.
Background
With the rapid development of lithium ion battery technology, in order to enable a lithium ion battery to have rapid charging capability and high-rate charging capability, a multi-lug winding battery core is widely applied to the lithium ion battery. The positive plate used by the existing multi-lug winding battery core generally causes the active coating at the edge of the pole piece to have a thinning part, and the top of the multi-lug winding battery core is stressed unevenly, so that the lithium precipitation condition occurs, and the safety of the battery is lower.
Disclosure of Invention
The embodiment of the invention provides a positive plate, a lithium ion battery and a preparation method of the positive plate, which are used for solving the problem of low safety of the battery caused by uneven top stress of the conventional multi-lug winding battery core.
In a first aspect, an embodiment of the present invention provides a positive electrode sheet, including: a current collector, and a conductive coating and an active coating applied to the current collector;
wherein the active coating comprises a first sub-active coating and a second sub-active coating, the thickness of the first sub-active coating is less than the thickness of the second sub-active coating;
the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector;
n tabs are arranged on the first edge of the current collector, N is a positive integer, and the N tabs extend out of the conductive coating along the first direction of the current collector.
Optionally, the thickness of the conductive coating is less than or equal to the difference between the thickness of the second sub-active coating and the thickness of the first sub-active coating.
Optionally, the width of the conductive coating is less than or equal to the width of the first sub-active coating.
Optionally, the thickness of the conductive coating is less than or equal to 5 microns; and/or the width of the conductive coating is less than or equal to 5 millimeters.
Optionally, the conductive coating includes a conductive agent and a binder;
wherein the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes and carbon fibers;
the binder comprises at least one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene butadiene rubber and polyacrylate.
Optionally, the active coating comprises an active agent, the conductive agent, and the binder;
wherein the active agent comprises at least one of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material and lithium titanate.
Optionally, the median particle diameter of the conductive agent is in the range of 0.05 to 50 microns.
In a second aspect, an embodiment of the present invention provides a lithium ion battery, including the positive electrode sheet according to the first aspect.
In a third aspect, an embodiment of the present invention provides a method for preparing a positive electrode sheet, where the method includes:
coating a conductive coating on a current collector through gravure coating equipment, wherein N lugs are arranged on the first edge of the current collector, N is a positive integer, and the N lugs extend out of the conductive coating along the first direction of the current collector;
applying a first sub-active coating on the conductive coating by a zebra coating apparatus and a second sub-active coating on the current collector; wherein the thickness of the first sub-active coating is less than the thickness of the second sub-active coating; the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector;
and drying, rolling, slitting and die cutting the coated current collector to obtain the positive plate.
In an embodiment of the present invention, the positive electrode sheet includes: a current collector, and a conductive coating and an active coating applied to the current collector; wherein the active coating comprises a first sub-active coating and a second sub-active coating, the thickness of the first sub-active coating is less than the thickness of the second sub-active coating; the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector; n tabs are arranged on the first edge of the current collector, N is a positive integer, and the N tabs extend out of the conductive coating along the first direction of the current collector. Therefore, the conductive coating can be arranged between the current collector and the first sub-active coating, the thickness difference between the first sub-active coating and the second sub-active coating is made up through the thickness of the conductive coating, so that the thickness of the positive plate is more uniform and can be better contacted with the diaphragm, the transmission performance of lithium ions in the battery core is ensured, the occurrence of lithium precipitation is effectively reduced, and the effect of improving the safety of the battery is achieved.
Drawings
FIG. 1 is a top view of a positive plate provided by an embodiment of the present invention;
FIG. 2 is a cross-sectional view along the AA' direction of a positive plate according to an embodiment of the present invention;
fig. 3 is a schematic view of a prior art coated current collector;
fig. 4 is a schematic structural diagram of a coated current collector according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. 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 terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged, as appropriate, such that embodiments of the present invention may be implemented in sequences other than those illustrated or described herein, and that the objects identified by "first," "second," etc. are generally of a type, and are not limited to the number of objects, such as the first object may be one or more. Furthermore, in the description and claims, "and/or" means at least one of the connected objects, and the character "/", generally means that the associated object is an "or" relationship.
The positive plate, the battery cell, the lithium ion battery and the preparation method of the positive plate provided by the embodiment of the invention are described in detail through specific embodiments and application scenes thereof by combining the accompanying drawings.
Referring to fig. 1 and 2, fig. 1 is a top view of a positive plate provided by an embodiment of the present invention, and fig. 2 is a cross-sectional view of the positive plate along the AA' direction provided by the embodiment of the present invention. As shown in fig. 1 and 2, the positive electrode sheet includes: current collector 100, conductive coating 200 and active coating 300 applied to current collector 100;
wherein the active coating 300 comprises a first sub-active coating 301 and a second sub-active coating 302, the thickness of the first sub-active coating 301 being less than the thickness of the second sub-active coating 302;
the conductive coating 200 is positioned between the current collector 100 and the first sub-active coating 301 and is disposed at a first edge of the current collector 100;
n tabs are disposed at the first edge of the current collector 100, N is a positive integer, and N tabs 101 extend out of the conductive coating 200 along the first direction of the current collector 100.
Specifically, the first sub-active coating 301 and the second sub-active coating 302 have the same composition, and the two are different in thickness, wherein the thickness of the first sub-active coating 301 is smaller than the thickness of the second sub-active coating 302. When the active coating 300 is directly coated on the current collector 100 by using the zebra coating method, the thickness of the middle position (i.e. the second sub-active coating 302) of the active coating 300 is greater than the thickness of the edge position (i.e. the first sub-active coating 301) due to the limitation of the shape of the zebra coating die head, and thus the coated current collector 100 is also thick in the middle and thin on both sides, as shown in fig. 3. Thus, after roll slitting along the symmetrical center line BB' of the current collector 100 shown in fig. 3, a positive electrode sheet is obtained. The thickness of the positive plate on the side close to the lug 101 is small, the thickness of the positive plate on the side far away from the lug 101 is large, and the thickness in the whole width direction is uneven, so that the contact difference between the positive plate and the diaphragm can be caused, the top interface of the battery core manufactured by adopting the positive plate is poor in adhesion, the lithium precipitation is easy to occur, and the safety of the battery is low.
The N tabs 101 may be provided on the first edge of the current collector 100, and the number of the N tabs 101 may be one or more, which is not particularly limited in the present invention. When the positive electrode sheet is used to manufacture a wound battery, the first direction may be the width direction of the current collector 100; when the positive electrode sheet is used to manufacture a laminated battery, the first direction may be the width direction or the length direction of the current collector 100.
The battery made of the positive plate not only has quick charging capability and high-rate charging capability, but also can reduce the lithium precipitation condition and improve the safety of the battery. Specifically, the plurality of tabs 101 may be disposed at the first edge of the current collector 100 at equal intervals, or may be disposed at the first edge of the current collector 100 at unequal intervals, which is not particularly limited in the present invention.
In this embodiment, the conductive coating 200 may be coated on the current collector 100 by gravure coating before the active coating 300 is coated on the current collector 100 by zebra coating. The conductive coating 200 is made of a conductive material, and has the characteristics of good conductivity and capability of improving the adhesion between the current collector 100 and the active coating 300. The area of application of the conductive coating 200 on the current collector 100 is the same as the area of coverage of the first sub-active coating 301 on the current collector 100. In this way, the resulting coated current collector 100 is shown in fig. 4. After roll slitting along the symmetrical center line of the current collector 100, the positive electrode sheet shown in fig. 2 can be obtained. Because the conductive coating 200 is coated between the first sub-active coating 301 and the current collector 100, the thickness difference between the first sub-active coating 301 and the second sub-active coating 302 is reduced through the conductive coating 200, so that the thickness of the positive plate is more uniform, the positive plate can be better contacted with the diaphragm, the transmission performance of lithium ions in the battery core is ensured, the occurrence of lithium precipitation is effectively reduced, and the effect of improving the safety of the battery is achieved.
Further, the thickness of the conductive coating 200 is less than or equal to the difference between the thickness of the second sub-active coating 302 and the thickness of the first sub-active coating 301.
In one embodiment, since the conductive coating 200 is used to reduce the difference in thickness between the first sub-active coating 301 and the second sub-active coating 302 by using the thickness of the conductive coating 200 itself, the thickness of the conductive coating 200 needs to be less than or equal to the difference in thickness between the second sub-active coating 302 and the first sub-active coating 301 when the conductive coating 200 is applied. This can avoid an excessive thickness of the conductive coating 200, resulting in a sum of the thicknesses of the conductive coating 200 and the first sub-active coating 301 being greater than the second sub-active coating 302. Preferably, the thickness of the conductive coating 200 may be set to be the difference between the thickness of the second sub-active coating 302 and the thickness of the first sub-active coating 301. In this way, the upper surface of the first sub-active coating 301 can be made to lie on the same plane as the upper surface of the second sub-active coating 302, in full contact with the separator.
Further, the width of the conductive coating 200 is less than or equal to the width of the first sub-active coating 301.
In one embodiment, since the conductive coating 200 functions to reduce the thickness difference between the first sub-active coating 301 and the second sub-active coating 302 by using the thickness of the conductive coating 200 itself, the width of the conductive coating 200 needs to be less than or equal to the width of the first sub-active coating 301 when the conductive coating 200 is applied. This can avoid bringing a new thickness difference to the positive electrode sheet when the width of the conductive coating 200 is greater than the width of the first sub-active coating 301. Preferably, the width of the conductive coating 200 may be set to be equal to the width of the first sub-active coating 301, so that the entire upper surface of the first sub-active coating 301 can be positioned on the same plane as the upper surface of the second sub-active coating 302, i.e., the entire thickness of the positive electrode sheet is uniform, so that the positive electrode sheet is sufficiently contacted with the separator.
Further, the thickness of the conductive coating 200 is less than or equal to 5 microns; and/or the width of the conductive coating 200 is less than or equal to 5 millimeters.
In one embodiment, the difference in thickness between the first sub-active coating 301 and the second sub-active coating 302 is typically in the range of 5 microns and the width of the first sub-active coating 301 is typically in the range of 5 millimeters when the active coating 300 is applied using a zebra coating method due to the limitations of the shape of the zebra coating die. For example, in practical applications, the thickness of the first sub-active coating 301 is typically 85 microns and the width is 5 millimeters, and the thickness of the second sub-active coating 302 is typically 90 microns, the width being selected according to practical needs. Thus, in the present embodiment, the thickness of the conductive coating 200 may be set to be less than or equal to 5 micrometers, and the width of the conductive coating 200 may be set to be less than or equal to 5 millimeters, so that the conductive coating 200 can compensate for the thickness of the first sub-active coating 301.
Further, the resistance of the conductive coating 200 is less than the resistance of the first sub-active coating 301; and/or the resistance of the conductive coating 200 is less than the resistance of the second sub-active coating 302. This may allow conductive coating 200 to be more conductive than first sub-active coating 301 and/or conductive coating 200 to be more conductive than second sub-active coating 302, thereby facilitating the transfer of lithium ions between current collector 100 and active coating 300.
Further, the conductive coating 200 includes a conductive agent and a binder;
wherein the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes and carbon fibers;
the binder comprises at least one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene butadiene rubber and polyacrylate.
Specifically, the conductive agent of the conductive coating 200 may be one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, and carbon fibers. For example, the conductive agent of the conductive coating 200 may be obtained by mixing ketjen black and carbon nanotubes according to a certain mass percentage, or may be obtained by mixing carbon fibers and conductive carbon black according to a certain mass percentage, or may be conductive carbon black, acetylene black, ketjen black, carbon nanotubes or carbon fibers alone, as the conductive agent of the conductive coating 200, which is not particularly limited in the present invention.
The binder of the conductive coating 200 may be one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene butadiene rubber, and polyacrylate. For example, the binder of the conductive coating 200 may be obtained by mixing styrene-butadiene rubber and polyacrylate according to a certain mass percentage, or may be obtained by mixing polyvinylidene fluoride and polyacrylonitrile according to a certain mass percentage, or may be obtained by independently using polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber or polyacrylate as the binder of the conductive coating 200, which is not particularly limited in the present invention.
In one embodiment, the ratio of the conductive agent and the binder of the conductive coating 200 may be 9:1 to 7:3, the conductive agent and the binder within the range can make the adhesion of the conductive coating 200 and the current collector 100 tight, while ensuring the conductive performance of the conductive coating 200. Thus, the conductive coating 200 has the characteristics of good conductivity and capability of improving the adhesion between the current collector 100 and the active coating 300, so that the conductive coating 200 is coated between the current collector 100 and the active coating 300, not only can the transmission of lithium ions be effectively ensured, but also the adhesion of the top interface of the battery cell can be improved.
Further, the active coating 300 includes an active agent, a conductive agent, and a binder;
wherein the active agent comprises at least one of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material and lithium titanate.
In one embodiment, the active agent in the active coating 300 may be one or more of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, and lithium titanate. For example, the active agent in the active coating 300 may be obtained by mixing lithium cobalt oxide and lithium iron phosphate according to a certain mass percentage, or may be obtained by mixing a nickel cobalt manganese ternary material and lithium titanate according to a certain mass percentage, or may be obtained by independently using lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material or lithium titanate as the active agent in the active coating 300, which is not particularly limited in the present invention.
The conductive agent in the active coating 300 has the same material selection range as the conductive agent in the conductive coating 200, and the binder in the active coating 300 has the same material selection range as the binder in the conductive coating 200. Specifically, the material of the conductive agent in the active coating 300 and the material of the conductive agent in the conductive coating 200 may be the same or different; the binder in the active coating 300 may be the same as or different from the binder in the conductive coating 200.
Specifically, in the active coating 300, the mass percentage of the active agent may be 80% to 99%, the mass percentage of the conductive agent may be 0.3% to 10%, and the mass percentage of the binder may be 0.7% to 10%. The particle size distribution of the active agent may satisfy: 3 μm < D10<6 μm,8 μm < D50<15 μm,20 μm < D90<30 μm, wherein D10 represents a particle size with a cumulative distribution of particles of 10%, i.e. a particle volume content of less than this particle size is 10% of the total particles; d50 represents a particle diameter at which the cumulative distribution of particles is 50%, i.e., a particle volume content of less than this particle diameter is 50% of the total particles, also called median diameter or median diameter; d90 represents a particle diameter at which the cumulative distribution of particles is 90%, i.e., the volume content of particles smaller than this particle diameter is 90% of the total particles. The adoption of the active coating 300 is beneficial to improving the energy density, the quick charge cycle life, the lithium precipitation probability and other performances of the battery.
Alternatively, the median particle diameter of the conductive agent may range from 0.05 to 50 microns.
The conductive agent can be one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotubes and carbon fibers. When the conductive agent is selected, the median particle diameter of the conductive agent may be satisfied in the range of 0.05 to 50 μm. Therefore, the conductive coating can be ensured to have larger conductivity, and the speed of lithium ion extraction can be ensured, so that the overall performance of the battery is improved.
In addition, the invention also provides a lithium ion battery, which comprises the positive plate.
It should be noted that, the specific embodiment of the lithium ion battery is the same as the positive electrode sheet, and will not be described herein.
In addition, the invention also provides a preparation method of the positive plate, which comprises the following steps:
coating a conductive coating on a current collector through gravure coating equipment, wherein N lugs are arranged on the first edge of the current collector, N is a positive integer, and the N lugs extend out of the conductive coating along the first direction of the current collector;
coating a first sub-active coating on the conductive coating by a zebra coating device, and coating a second sub-active coating on the current collector, wherein the thickness of the first sub-active coating is smaller than that of the second sub-active coating; the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector;
and drying, rolling, slitting and die cutting the coated current collector to obtain the positive plate.
Specifically, the width and thickness of the conductive coating may be set according to practical situations. For example, when the difference in thickness of the first sub-active coating layer and the second sub-active coating layer in the active coating layer coated by the zebra coating method is 5 micrometers and the width of the first sub-active coating layer is 5 millimeters, the thickness of the conductive coating layer may be set to be 5 micrometers and the width to be 5 millimeters. Through the conductive coating, the thickness of the first sub-active coating can be compensated, so that the thickness of the coated current collector is uniform.
After the coated current collector is obtained, the coated current collector can be dried, rolled, cut and die-cut in sequence to obtain the positive plate. Wherein, the drying is mainly to dry the conductive coating and the active coating. Roll slitting is mainly to divide the coated current collector into slices of a certain length and width, such as dividing the current collector into two halves along the symmetrical center line of the current collector, and then dividing the divided halves into a certain length. The die cutting is mainly to die-cut the electrode lug from the edge of one side of the current collector, which is close to the conductive coating.
In this embodiment, the conductive coating may be coated on the current collector by a gravure coating method, and then the first sub-active coating may be coated on the conductive coating and the second sub-active coating may be coated on the current collector by a zebra coating device. Like this, can reduce the thickness difference of first sub-active coating and second sub-active coating for the thickness of positive plate is more even, can contact with the diaphragm better, guarantees the transmission performance of lithium ion in the electric core, effectively reduces the emergence of lithium evolution condition, reaches the effect that improves the security of battery.
The advantageous effects of the present invention are further illustrated below with reference to examples.
The preparation method of the negative plate used in the invention comprises the following steps:
the negative electrode active agent artificial graphite (d50=10μm), conductive carbon black as a conductive agent, styrene-butadiene rubber as a binder and carboxymethyl cellulose are mixed according to the proportion of 97.0wt%, 0.5wt%, 1.2wt% and 1.3wt%, respectively, and then deionized water is added for dispersion to prepare the active coating with proper solid content. The active coating is coated on a current collector through zebra coating equipment, and then the negative plate is obtained through drying, rolling slitting and die cutting. Wherein the maximum thickness of the active coating layer of the negative electrode sheet was 105. Mu.m.
The negative electrode sheets of examples 1 to 7 and comparative examples 1 to 7 were each produced using the above-described component ratios and the above-described production methods, and the positive electrode sheets of examples 1 to 7 and comparative examples 1 to 7 were each produced using different component ratios and production methods, specifically as follows:
example 1:
the positive electrode active material lithium cobaltate (d50=10μm), conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.8wt%, 1.0wt% and 1.2wt%, respectively, and then adjusted to an active coating of the positive electrode sheet with N-methylpyrrolidone. Firstly, the mass percentage is 2:1 and the carbon nano tube are uniformly mixed to obtain the conductive coating. Firstly, coating a conductive coating on the surface of an aluminum foil current collector with the thickness of 10 mu m (the coating width is 5mm, and the coating thickness is 5 mu m) through gravure coating equipment; then, the active coating is coated on the current collector and the conductive coating by using zebra coating equipment; and then drying, rolling, slitting and die cutting to obtain the positive plate. Wherein the thickness of the conductive coating is 5 μm, the sum of the thicknesses of the conductive coating and the first sub-active coating is 90 μm, and the thickness of the second sub-active coating is 90 μm.
Example 2:
example 2 was prepared in the same manner as in example 1, except that the particle size d50=12 μm of lithium cobaltate was selected.
Example 3:
example 3 was prepared in the same manner as in example 1, except that the particle size d50=14 μm of lithium cobaltate was selected.
Example 4:
example 4 was prepared in the same manner as in example 1, except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.5wt%, 1.3wt% and 1.2wt%, respectively.
Example 5:
example 5 was prepared in the same manner as in example 1, except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.4wt%, 1.4wt% and 1.2wt%, respectively.
Example 6:
example 6 was prepared in the same manner as in example 1, except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.3wt%, 1.5wt% and 1.2wt%, respectively.
Example 7:
example 7 was prepared in the same manner as in example 1, except that the positive electrode active material was lithium iron phosphate (d50=10μm), the conductive agent was conductive carbon fiber, and the adhesive was styrene-butadiene rubber, respectively, in a proportion of 97.8wt%, 1.0wt% and 1.2 wt%.
Comparative example 1:
the positive electrode active material lithium cobaltate (d50=10μm), conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.8wt%, 1.0wt% and 1.2wt%, respectively, and then adjusted to an active coating of the positive electrode sheet with N-methylpyrrolidone. Coating the active coating on the current collector and the conductive coating by using a zebra coating device; and then drying, rolling, slitting and die cutting to obtain the positive plate. Wherein the thickness of the second sub-active coating is 90 μm. Comparative example 1 is different from example 1 in that the positive electrode sheet has no precoated carbon layer, i.e., the active coating layer of the positive electrode sheet in comparative example 1 has an edge-thinned region, whereas example 1 gives a positive electrode sheet having a uniform thickness, and other conditions remain uniform.
Comparative example 2:
comparative example 2 was prepared in the same manner as comparative example 1, except that the particle size d50=12 μm of lithium cobaltate was selected.
Comparative example 3:
comparative example 3 was prepared in the same manner as comparative example 1, except that the particle size d50=14 μm of lithium cobaltate was selected.
Comparative example 4:
comparative example 4 was prepared in the same manner as comparative example 1 except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.5wt%, 1.3wt% and 1.2wt%, respectively.
Comparative example 5:
comparative example 5 was prepared in the same manner as comparative example 1 except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.4wt%, 1.4wt% and 1.2wt%, respectively.
Comparative example 6:
comparative example 6 was prepared in the same manner as comparative example 1 except that lithium cobaltate (d50=10μm) as a positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.3wt%, 1.5wt% and 1.2wt%, respectively.
Comparative example 7:
comparative example 7 was prepared in the same manner as comparative example 1 except that the positive electrode active material was lithium iron phosphate (d50=10μm), the conductive agent was conductive carbon fiber, and the adhesive was styrene-butadiene rubber based, respectively, in a proportion of 97.8wt%, 1.0wt% and 1.2 wt%.
The positive electrode sheet, the negative electrode sheet and the separator prepared in examples 1 to 7 and comparative examples 1 to 7 were wound into a roll core by a winding machine, and then were packaged with an aluminum plastic film to prepare a battery cell, and then were subjected to the steps of liquid injection, aging, formation, secondary packaging and the like, and finally the electrochemical performance of the battery was tested.
The batteries of examples 1 to 7 and comparative examples 1 to 7 prepared as described above were respectively subjected to the following performance tests, which were conducted as follows:
(1) Quick charge cycle life test:
the batteries of examples 1 to 7 and comparative examples 1 to 7 were constant-current charged to 4.35V at 25 ℃, then constant-voltage charged to 2C at 4.35V, then constant-current charged to 4.45V at 2C, the off-current was 0.025C, then constant-current discharged at 0.7C, and the off-voltage was 3.0V, which is a charge-discharge cycle. The charge-discharge cycle process was repeated until the capacity retention rate of the battery was less than 80% or the cycle number reached 1000 times.
(2) Lithium precipitation condition test:
the batteries of examples 1 to 7 and comparative examples 1 to 7 were constant-current charged to 4.35V at 25 ℃, then constant-voltage charged to 2C at 4.35V, then constant-current charged to 4.45V at 2C, the off-current was 0.025C, then constant-current discharged at 0.7C, and the off-voltage was 3.0V, which is a charge-discharge cycle. And repeating the charge-discharge cycle process for 20 times, fully charging the battery after the charge-discharge cycle process is finished, disassembling the battery core in the environment of a drying room, and observing the lithium precipitation condition of the surface of the negative electrode. The lithium precipitation degree is classified into three grades of no lithium precipitation, slight lithium precipitation and serious lithium precipitation. The slight lithium precipitation indicates that the lithium precipitation area on the surface of the positive plate is less than 1/10 of the total surface of the positive plate, and the serious lithium precipitation indicates that the lithium precipitation area on the surface of the positive plate exceeds 1/3 of the total surface of the positive plate.
According to the above test methods, test results of the batteries of examples 1 to 7 and comparative examples 1 to 7 were obtained as shown in table 1.
| Battery class | Energy density Wh/L | Quick charge cycle life | Lithium evolution condition |
| Example 1 | 620 | Satisfy 1000T | Lithium is not separated out |
| Example 2 | 619 | Satisfy 1000T | Lithium is not separated out |
| Example 3 | 618 | 902T | Slight top lithium evolution |
| Example 4 | 620 | Satisfy 1000T | Lithium is not separated out |
| Example 5 | 622 | 934T | Slight top lithium evolution |
| Example 6 | 623 | 892T | Slight top lithium evolution |
| Example 7 | 620 | Satisfy 1000T | Lithium is not separated out |
| Comparative example 1 | 621 | 781T | Severe top lithium evolution |
| Comparative example 2 | 620 | 757T | Severe top lithium evolution |
| Comparative example 3 | 619 | 739T | Severe top lithium evolution |
| Comparative example 4 | 622 | 758T | Severe top lithium evolution |
| Comparative example 5 | 624 | 750T | Severe top lithium evolution |
| Comparative example 6 | 625 | 735T | Severe top lithium evolution |
| Comparative example 7 | 621 | 780T | Severe top lithium evolution |
List one
As can be seen from the comparison between the embodiment 1 and the comparative example 1, since the positive electrode sheet of the battery of the embodiment 1 is coated with the conductive coating, the thickness of the first sub-active coating is compensated by the conductive coating, and the thickness of the obtained positive electrode sheet is relatively uniform, so that the cycle performance of the battery cell under quick charge can be remarkably improved, the capacity retention rate after 1000T can be satisfied to be higher than 80%, and the lithium precipitation does not occur during the 20T cycle disassembly. And the energy densities of the batteries of example 1 and comparative example 1 were almost comparable, and it can be considered that the energy densities of the batteries were not lost. The positive electrode sheet of the battery of comparative example 1 was not coated with the conductive coating, resulting in uneven thickness of the positive electrode sheet of the battery of comparative example 1, poor adhesion of the top interface of the battery cell during formation, severe lithium precipitation at the top of the battery cell, and severe capacity fade (781T post cycle retention rate lower than 80%).
Similarly, the difference between the comparative examples 2 and 2, the comparative examples 3 and 3, the examples 4 and 4, the examples 5 and 5, the examples 6 and 6, and the examples 7 and 7 is whether the positive electrode sheet of the battery is coated with the conductive coating, and as can be seen from the table, the battery in the examples has a higher fast charge cycle life than the battery in the corresponding comparative examples, and the lithium precipitation of the battery in the examples is superior to that of the battery in the comparative examples. The results show that the battery in the comparative example has a non-uniform thickness of the positive electrode sheet obtained by zebra coating because the current collector is not coated with the conductive coating, and the interface at the top of the battery cell is not well bonded during formation, so that serious lithium precipitation occurs at the top.
As is clear from the comparison between example 2 and example 1, the particle diameter D50 of lithium cobaltate in example 2 is larger than the particle diameter D50 of lithium cobaltate in example 1, and the lithium ion extraction rate in example 2 is not as high as that in example 1, but still satisfies the cycle life of 1000T, and no lithium precipitation occurs.
As is clear from the comparison between example 3 and example 2, the particle diameter D50 of lithium cobaltate in example 3 is larger than the particle diameter D50 of lithium cobaltate in example 2, and the lithium ion extraction rate in example 3 is not as high as that in example 2, and the cycle life of 902T is satisfied, and slight lithium precipitation occurs at the top. This also demonstrates that the particle size of lithium cobaltate affects the cycle life of the battery and lithium evolution.
As is clear from the comparison of example 4 with example 1, the content of lithium cobaltate in example 4 in the active coating layer was lower than that in example 1, and the cycle life of 1000T was satisfied at this time, and no lithium precipitation occurred.
As can be seen from a comparison of example 5 with example 4, the content of lithium cobaltate in example 5 in the active coating layer was lower than that in example 4, and the cycle life of 934T was satisfied, and slight lithium precipitation occurred at the top.
As can be seen from a comparison of example 6 and example 5, the content of lithium cobaltate in the active coating layer in example 6 was lower than that in example 5, and the cycle life of 892T was satisfied, and slight lithium precipitation occurred at the top. This also demonstrates that the amount of active agent can have an effect on the battery's fast charge cycle life.
As is evident from comparison of example 7 with example 1, the active material, the conductive agent and the binder in the active coating layer have different compositions, and the lithium deposition condition of the battery has a small difference.
The comparison between the comparative examples is the same as the comparison between the above examples, and serious lithium precipitation occurs in each comparative example, which indicates that the uneven thickness of the positive electrode sheet can indeed cause poor adhesion of the interface at the top of the battery cell, causing serious lithium precipitation at the top and serious capacity fade. According to the invention, the conductive coating is coated on the current collector, so that the problem of uneven thickness of the positive plate can be solved, and the problems of quick charge cycle life and lithium precipitation of the battery can be improved.
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, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A positive electrode sheet, the positive electrode sheet comprising: a current collector, and a conductive coating and an active coating applied to the current collector;
wherein in the width direction, the active coating comprises a first sub-active coating and a second sub-active coating, the thickness of the first sub-active coating is smaller than the thickness of the second sub-active coating;
the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector;
n lugs are arranged at the first edge of the current collector, N is a positive integer, and the N lugs extend out of the conductive coating along the width direction of the current collector;
the width of the conductive coating is less than or equal to the width of the first sub-active coating;
the resistance of the conductive coating is less than the resistance of the first sub-active coating; and/or the resistance of the conductive coating is less than the resistance of the second sub-active coating.
2. The positive electrode sheet of claim 1, wherein the thickness of the conductive coating is less than or equal to the difference between the thickness of the second sub-active coating and the thickness of the first sub-active coating.
3. The positive electrode sheet of claim 1, wherein the conductive coating has a thickness of less than or equal to 5 microns; and/or the width of the conductive coating is less than or equal to 5 millimeters.
4. The positive electrode sheet according to claim 1, wherein the conductive coating layer includes a conductive agent and a binder;
wherein the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes and carbon fibers;
the binder comprises at least one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene butadiene rubber and polyacrylate.
5. The positive electrode sheet according to claim 4, wherein the active coating layer includes an active agent, the conductive agent, and the binder;
wherein the active agent comprises at least one of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material and lithium titanate.
6. The positive electrode sheet according to claim 4, wherein the conductive agent has a median particle diameter ranging from 0.05 to 50 μm.
7. A lithium ion battery comprising the positive electrode sheet according to any one of claims 1 to 5.
8. A method for producing the positive electrode sheet according to any one of claims 1 to 5, characterized in that the method comprises:
coating a conductive coating on a current collector through gravure coating equipment, wherein N lugs are arranged on the first edge of the current collector, N is a positive integer, and the N lugs extend out of the conductive coating along the width direction of the current collector;
applying a first sub-active coating on the conductive coating by a zebra coating device and applying a second sub-active coating on the current collector, wherein the thickness of the first sub-active coating is less than the thickness of the second sub-active coating; the conductive coating is positioned between the current collector and the first sub-active coating and is arranged at the first edge of the current collector;
and drying, rolling, slitting and die cutting the coated current collector to obtain the positive plate.
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| CN111952541A (en) * | 2020-09-14 | 2020-11-17 | 珠海冠宇电池股份有限公司 | Positive plate, preparation method and battery |
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| CN112563455A (en) * | 2020-12-25 | 2021-03-26 | 东莞维科电池有限公司 | Preparation method of pole piece, pole piece and lithium ion battery |
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| CN111952541A (en) * | 2020-09-14 | 2020-11-17 | 珠海冠宇电池股份有限公司 | Positive plate, preparation method and battery |
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