CN113140697A - 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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- CN113140697A CN113140697A CN202110436483.XA CN202110436483A CN113140697A CN 113140697 A CN113140697 A CN 113140697A CN 202110436483 A CN202110436483 A CN 202110436483A CN 113140697 A CN113140697 A CN 113140697A
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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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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: the current collector, and a conductive coating and an active coating coated on the current collector; wherein the active coating comprises a first sub active coating and a second sub active coating, and 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; the first edge of mass flow body sets up a N utmost point ear, and N is the positive integer, just a N utmost point ear is followed the first direction of mass flow body extends to outside the conductive coating. Therefore, the thickness of the positive plate is more uniform, and the positive plate can be better contacted with the diaphragm, so that the transmission performance of lithium ions in the battery cell is ensured, the occurrence of the lithium precipitation condition 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 a rapid charging capability and a high-rate charging capability, a multi-tab winding battery cell is widely applied to the lithium ion battery. The positive plate used by the existing multi-tab winding battery cell generally can cause an active coating at the edge of the plate to have a thinned part, and can cause the top of the multi-tab winding battery cell to be stressed unevenly, so that the lithium precipitation condition is caused, 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, aiming at solving the problem that the battery safety is lower due to uneven stress on the top of the conventional multi-tab winding battery core.
In a first aspect, an embodiment of the present invention provides a positive electrode plate, where the positive electrode plate includes: the current collector, and a conductive coating and an active coating coated on the current collector;
wherein the active coating comprises a first sub active coating and a second sub active coating, and 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;
the first edge of mass flow body sets up a N utmost point ear, and N is the positive integer, just a N utmost point ear is followed the first direction of mass flow body extends to outside the conductive coating.
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 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.
Optionally, the conductive coating comprises 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;
the active agent comprises at least one of lithium cobaltate, lithium iron phosphate, a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material and lithium titanate.
Optionally, the median particle size of the conductive agent ranges from 0.05 to 50 microns.
In a second aspect, embodiments of the present invention provide a lithium ion battery, where the lithium ion battery includes 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 plate, where the method includes:
coating a conductive coating on a current collector by gravure coating equipment, wherein N tabs are arranged on a first edge of the current collector, N is a positive integer, and the N tabs extend out of the conductive coating along a 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 layer is less than the thickness of the second sub-active coating layer; 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: the current collector, and a conductive coating and an active coating coated on the current collector; wherein the active coating comprises a first sub active coating and a second sub active coating, and 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; the first edge of mass flow body sets up a N utmost point ear, and N is the positive integer, just a N utmost point ear is followed the first direction of mass flow body extends to outside the conductive coating. Like this, can set up conductive coating between mass flow body and first sub active coating, compensate the thickness difference between first sub active coating and the sub active coating of second through conductive coating's thickness for the thickness of positive plate is more even, can contact with the diaphragm better, thereby guarantees lithium ion's transmission performance in the electric core, effectively reduces the emergence of the lithium condition of analyzing, reaches the effect that improves the battery security.
Drawings
Fig. 1 is a plan view of a positive electrode sheet according to an embodiment of the present invention;
fig. 2 is a cross-sectional view of a positive electrode tab along the AA' direction according to an embodiment of the present invention;
fig. 3 is a schematic structural view of a coated current collector in the prior art;
fig. 4 is a schematic structural diagram of a coated current collector provided in an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terms first, second and the like in the description and in the claims of the present invention are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It will be appreciated that the data so used may be interchanged under appropriate circumstances such that embodiments of the invention may be practiced other than those illustrated or described herein, and that the objects identified as "first," "second," etc. are generally a class of objects and do not limit the number of objects, e.g., a first object may be one or more. In addition, "and/or" in the specification and claims means at least one of connected objects, a character "/" generally means that a preceding and succeeding related objects are in an "or" relationship.
The positive electrode sheet, the battery cell, the lithium ion battery and the method for manufacturing the positive electrode sheet according to the embodiments of the present invention are described in detail below with reference to the accompanying drawings.
Referring to fig. 1 and 2, fig. 1 is a plan view of a positive electrode tab according to an embodiment of the present invention, and fig. 2 is a cross-sectional view of the positive electrode tab according to an embodiment of the present invention, taken along direction AA'. As shown in fig. 1 and 2, the positive electrode sheet includes: a current collector 100, and a conductive coating 200 and an active coating 300 coated on the current collector 100;
wherein, the active coating layer 300 comprises a first sub active coating layer 301 and a second sub active coating layer 302, the thickness of the first sub active coating layer 301 is smaller than that of the second sub active coating layer 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;
the first edge of the current collector 100 is provided with N tabs, where N is a positive integer, and the N tabs 101 extend to the outside of the conductive coating 200 along the first direction of the current collector 100.
Specifically, the first sub active coating layer 301 and the second sub active coating layer 302 have the same composition, and are different from each other in terms of the thickness thereof, wherein the thickness of the first sub active coating layer 301 is smaller than that of the second sub active coating layer 302. When the active coating 300 is directly coated on the current collector 100 by the zebra coating method, due to the limitation of the shape of the zebra coating die, 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), 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 tab 101 is small, the thickness of the positive plate on the side far away from the tab 101 is large, and the thickness of the positive plate in the whole width direction is uneven, so that the contact between the positive plate and the diaphragm is poor, the top interface bonding of the battery cell made of the positive plate is poor, the lithium precipitation condition is easy to occur, and the safety of the battery is low.
It should be noted that N tabs 101 are provided at the first edge of the current collector 100, and the number of the N tabs 101 may be one or multiple, and the present invention is not limited in particular. When the positive electrode sheet is used to manufacture a wound battery, the first direction may be a width direction of the current collector 100; when the positive electrode sheet is used to manufacture a laminated battery, the first direction may be a width direction or a 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, and the present invention is not particularly limited.
In this embodiment, the conductive coating 200 may be coated on the current collector 100 by a gravure coating method before the active coating 300 is coated on the current collector 100 by a zebra coating method. The conductive coating 200 is made of a conductive material, and has a good conductivity, and can improve the adhesion between the current collector 100 and the active coating 300. The coated area of the conductive coating 200 on the current collector 100 is the same as the covered area of the first sub-active coating 301 on the current collector 100. In this manner, the resulting coated current collector 100 is shown in fig. 4. And rolling and cutting along the symmetrical center line of the current collector 100 to obtain the positive plate shown in fig. 2. Because the conductive coating 200 coats between first sub active coating 301 and the mass flow body 100, the thickness that has reduced first sub active coating 301 and second sub active coating 302 through conductive coating 200 is poor 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 the lithium condition of educing, thereby reaches the effect that improves the security of battery.
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 an 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 thickness of the conductive coating 200 needs to be 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 when the conductive coating 200 is applied. This can avoid the conductive coating 200 having an excessive thickness, resulting in the sum of the thicknesses of the conductive coating 200 and the first sub-active coating 301 being greater than that of 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 layer 301 can be positioned on the same plane as the upper surface of the second sub active coating layer 302, and can be sufficiently in contact with the separator.
Further, the width of the conductive coating layer 200 is less than or equal to the width of the first sub-active coating layer 301.
In an 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 prevent a new thickness difference from being brought to the positive electrode tab when the width of the conductive coating layer 200 is greater than that of the first sub-active coating layer 301. Preferably, the width of the conductive coating layer 200 may be set to be equal to the width of the first sub-active coating layer 301, so that the entire upper surface of the first sub-active coating layer 301 can be positioned on the same plane as the upper surface of the second sub-active coating layer 302, i.e., the entire thickness of the positive electrode tab is uniform, so that the positive electrode tab is sufficiently in contact with the separator.
Further, the conductive coating 200 has a thickness 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, due to the limitations of the zebra coating die shape, when the active coating 300 is applied by zebra coating, the difference between the thicknesses of the first sub-active coating 301 and the second sub-active coating 302 is generally in the range of 5 μm, and the width of the first sub-active coating 301 is generally in the range of 5 mm. For example, in practical applications, the thickness of the first sub-active coating 301 is typically 85 micrometers and the width is 5 millimeters, and the thickness of the second sub-active coating 302 is typically 90 micrometers, and the width is selected according to practical requirements. 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 also 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 layer 200 is smaller than that of the first sub-active coating layer 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 the conductive coating 200 to have a conductivity greater than that of the first sub active coating 301 and/or the conductive coating 200 to have a conductivity greater than that of the second sub active coating 302, thereby facilitating the transfer of lithium ions between the current collector 100 and the 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 in a certain mass percentage, or may be obtained by mixing carbon fibers and conductive carbon black in a certain mass percentage, or may be obtained by separately using conductive carbon black, acetylene black, ketjen black, carbon nanotubes, or carbon fibers as the conductive agent of the conductive coating 200, and the present invention is not particularly limited.
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 separately 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 in the range can tightly bond the conductive coating 200 and the current collector 100, and simultaneously can ensure the conductivity of the conductive coating 200. Thus, the conductive coating 200 has the characteristics of good conductivity and improved 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, the transmission of lithium ions can be effectively ensured, and 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;
the activator comprises at least one of lithium cobaltate, lithium iron phosphate, a nickel-cobalt-manganese ternary material, a 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 cobaltate 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 separately using lithium cobaltate, lithium iron phosphate, a nickel-cobalt-manganese ternary material, a 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 and the conductive agent in the conductive coating 200 are selected in the same range, and the binder in the active coating 300 and the binder in the conductive coating 200 are selected in the same range. Specifically, the material of the conductive agent in the active coating layer 300 and the material of the conductive agent in the conductive coating layer 200 may be the same or different; the binder in the active coating layer 300 and the binder in the conductive coating layer 200 may be the same or different.
Specifically, in the active coating layer 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 can 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 particle distribution of 10%, i.e. the volume content of particles smaller than this particle size is 10% of the total particles; d50 denotes the particle size with a cumulative particle distribution of 50%, i.e. the volume fraction of particles smaller than this accounts for 50% of the total particles, also called median or median particle size; d90 denotes the particle size with a cumulative particle distribution of 90%, i.e. the volume fraction of particles smaller than this accounts for 90% of the total particles. By adopting the active coating 300, the energy density of the battery can be improved, the quick charge cycle life can be prolonged, and the lithium precipitation probability can be reduced.
Optionally, the median particle size of the conductive agent ranges 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 higher conductivity, and the lithium ion extraction speed can be ensured, so that the overall performance of the battery is improved.
In addition, the invention also provides a lithium ion battery, and the lithium ion battery comprises the positive plate.
It should be noted that the specific embodiment of the lithium ion battery is the same as the positive plate, and is not described herein again.
In addition, the invention also provides a preparation method of the positive plate, which comprises the following steps:
coating the conductive coating on a current collector by gravure coating equipment, wherein 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;
coating a first sub-active coating on the conductive coating through 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 arranged at the first edge of the current collector;
and drying, rolling, slitting and die cutting are carried out on the coated current collector to obtain the positive plate.
In particular, the width and thickness of the conductive coating may be set according to the actual situation. For example, when the difference between the thicknesses of the first sub-active coating layer and the second sub-active coating layer in the active coating layer applied by the zebra coating method is 5 micrometers, and the width of the first sub-active coating layer is 5mm, the conductive coating layer may be set to have a thickness of 5 micrometers and a width of 5 mm. 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 coated conductive coating and the active coating. The rolling and cutting mainly comprises the steps of cutting the coated current collector into slices with certain length and width, for example, cutting the current collector into two halves along the symmetrical center line of the current collector, and then cutting the halved current collector into certain length. The die cutting is mainly to die cut the tab from one side edge of the current collector close to the conductive coating.
In this embodiment, the conductive coating may be coated on the current collector by using a gravure coating method, and then the first sub active coating is coated on the conductive coating by using a zebra coating apparatus, and the second sub active coating is coated on the current collector. Like this, can reduce the thickness difference of first sub active coating and the sub active coating of second for the thickness of positive plate is more even, can contact with the diaphragm better, guarantees lithium ion's in the electric core transmission performance, effectively reduces the emergence of the lithium condition of analyzing, reaches the effect that improves the security of battery.
The following examples are provided to further illustrate the advantageous effects of the present invention.
The preparation method of the negative plate used in the invention comprises the following steps:
mixing artificial graphite (D50 ═ 10 mu m) as a negative electrode active agent, conductive carbon black as a conductive agent, styrene-butadiene rubber as a binder and carboxymethyl cellulose according to the proportion of 97.0 wt%, 0.5 wt%, 1.2 wt% and 1.3 wt%, then adding deionized water, and dispersing to prepare an active coating with proper solid content. And coating the active coating on a current collector by using zebra coating equipment, and then drying, rolling, slitting and die cutting to obtain the negative plate. Wherein the maximum thickness of the active coating of the negative plate is 105 μm.
The negative electrode sheets of examples 1 to 7 and comparative examples 1 to 7 were prepared according to the above composition ratios and the above preparation methods, and the positive electrode sheets of examples 1 to 7 and comparative examples 1 to 7 were prepared according to different composition ratios and preparation methods, respectively, as follows:
example 1:
the positive electrode active material lithium cobaltate (D50 ═ 10 μm), conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.8 wt%, 1.0 wt%, and 1.2 wt%, respectively, and then adjusted to the active coating layer of the positive electrode sheet with N-methylpyrrolidone. Firstly, the mass percentage is 2: 1, uniformly mixing the Ketjen black and the carbon nano tube 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 by a gravure coating device (the coating width is 5mm, and the coating thickness is 5 mu m); then coating the active coating on the current collector and the conductive coating by using zebra coating equipment; and then drying, rolling, slitting and die cutting are carried out 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 example 1 except that the particle size D50 of the lithium cobaltate was 12 μm.
Example 3:
example 3 was prepared in the same manner as example 1 except that the particle size D50 of the lithium cobaltate was 14 μm.
Example 4:
example 4 was prepared in the same manner as in example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.5 wt%, 1.3 wt%, and 1.2 wt%, respectively.
Example 5:
example 5 was prepared in the same manner as in example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.4 wt%, 1.4 wt%, and 1.2 wt%, respectively.
Example 6:
example 6 was prepared in the same manner as in example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.3 wt%, 1.5 wt%, and 1.2 wt%, respectively.
Example 7:
example 7 was prepared in the same manner as in example 1, except that lithium iron phosphate (D50 ═ 10 μm) was used as the positive electrode active material, conductive carbon fibers were used as the conductive agent, and styrene butadiene rubbers were used as the binder, and the mixture was mixed in proportions of 97.8 wt%, 1.0 wt%, and 1.2 wt%, respectively.
Comparative example 1:
the positive electrode active material lithium cobaltate (D50 ═ 10 μm), conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in proportions of 97.8 wt%, 1.0 wt%, and 1.2 wt%, respectively, and then adjusted to the active coating layer of the positive electrode sheet with N-methylpyrrolidone. Coating the active coating on the current collector and the conductive coating by using zebra coating equipment; and then drying, rolling, slitting and die cutting are carried out to obtain the positive plate. Wherein the thickness of the second sub-active coating layer is 90 μm. Comparative example 1 is different from example 1 in that the positive electrode sheet has no precoated carbon layer, that is, the active coating layer of the positive electrode sheet in comparative example 1 has edge-thinned regions, whereas example 1 gives a positive electrode sheet having a uniform thickness, and in addition, other conditions are kept the same.
Comparative example 2:
comparative example 2 was prepared in the same manner as in comparative example 1 except that the particle size D50 of the lithium cobaltate was 12 μm.
Comparative example 3:
comparative example 3 was prepared in the same manner as in comparative example 1 except that the particle size D50 of the lithium cobaltate was 14 μm.
Comparative example 4:
comparative example 4 was prepared in the same manner as in comparative example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.5 wt%, 1.3 wt%, and 1.2 wt%, respectively.
Comparative example 5:
comparative example 5 was prepared in the same manner as in comparative example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.4 wt%, 1.4 wt%, and 1.2 wt%, respectively.
Comparative example 6:
comparative example 6 was prepared in the same manner as in comparative example 1 except that the positive electrode active material lithium cobaltate (D50 ═ 10 μm), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in proportions of 97.3 wt%, 1.5 wt%, and 1.2 wt%, respectively.
Comparative example 7:
comparative example 7 was prepared in the same manner as in comparative example 1, except that lithium iron phosphate (D50 ═ 10 μm) was used as the positive electrode active material, conductive carbon fiber was used as the conductive agent, and styrene butadiene rubber was used as the binder, and they were mixed in proportions of 97.8 wt%, 1.0 wt%, and 1.2 wt%, respectively.
And (3) making the positive plate, the negative plate and the diaphragm respectively prepared in the examples 1 to 7 and the comparative examples 1 to 7 into a winding core by using a winding machine, packaging the winding core by using an aluminum plastic film to prepare a battery core, then carrying out the working procedures of liquid injection, aging, formation, secondary packaging and the like, and finally testing the electrochemical performance of the battery.
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, the procedures of which were:
(1) and (3) testing the quick charge cycle life:
the batteries of examples 1 to 7 and comparative examples 1 to 7 were subjected to constant current charging at a rate of 3C to 4.35V at 25C, then to constant voltage charging at 4.35V to 2C, then to constant current charging at a rate of 2C to 4.45V with a cutoff current of 0.025C, and then to constant current discharging at a rate of 0.7C with a cutoff voltage of 3.0V, which is a charge-discharge cycle. The charge-discharge cycle process is repeated until the capacity retention rate of the battery is lower than 80% or the cycle frequency reaches 1000 times.
(2) Lithium separation condition test:
the batteries of examples 1 to 7 and comparative examples 1 to 7 were subjected to constant current charging at a rate of 3C to 4.35V at 25C, then to constant voltage charging at 4.35V to 2C, then to constant current charging at a rate of 2C to 4.45V with a cutoff current of 0.025C, and then to constant current discharging at a rate of 0.7C with a cutoff voltage of 3.0V, which is a charge-discharge cycle. The charge-discharge cycle was repeated 20 times, after which the battery was fully charged, the cell was disassembled in the environment of the drying room, and the lithium deposition on the surface of the negative electrode was observed. The lithium separation degree is divided into three grades of no lithium separation, slight lithium separation and serious lithium separation. Slight lithium deposition means that the lithium deposition area on the surface of the positive electrode sheet is below 1/10 of the entire surface of the positive electrode sheet, and severe lithium deposition means that the lithium deposition area on the surface of the positive electrode sheet exceeds 1/3 of the entire surface of the positive electrode sheet.
Test results for the cells of examples 1 to 7 and comparative examples 1 to 7 were obtained according to the above test manner, as shown in table 1.
| Battery class | Energy density Wh/L | Fast charge cycle life | Case of lithium evolution |
| Example 1 | 620 | Satisfy 1000T | Does not separate out lithium |
| Example 2 | 619 | Satisfy 1000T | Does not separate out lithium |
| Example 3 | 618 | 902T | Slight top precipitation of lithium |
| Example 4 | 620 | Satisfy 1000T | Does not separate out lithium |
| Example 5 | 622 | 934T | Slight top precipitation of lithium |
| Example 6 | 623 | 892T | Slight top precipitation of lithium |
| Example 7 | 620 | Satisfy 1000T | Does not separate out lithium |
| Comparative example 1 | 621 | 781T | Top heavy lithium evolution |
| Comparative example 2 | 620 | 757T | Top heavy lithium evolution |
| Comparative example 3 | 619 | 739T | Top heavy lithium evolution |
| Comparative example 4 | 622 | 758T | Top heavy lithium evolution |
| Comparative example 5 | 624 | 750T | Top heavy lithium evolution |
| Comparative example 6 | 625 | 735T | Top heavy lithium evolution |
| Comparative example 7 | 621 | 780T | Top heavy lithium evolution |
Watch 1
As can be seen from comparison between the embodiment 1 and the comparative example 1, since the conductive coating is coated on the positive plate of the battery in the embodiment 1, and the thickness of the first sub-active coating is compensated by the conductive coating, the thickness of the obtained positive plate is uniform, so that the cycle performance under the quick charge of the battery cell can be remarkably improved, the capacity retention rate is higher than 80% after 1000T, and no lithium precipitation occurs during 20T cycle disassembly. And the energy densities of the batteries of example 1 and comparative example 1 were almost different, it can be considered that the energy density of the battery was not lost. The positive plate of the battery of the comparative example 1 is not coated with the conductive coating, so that the thickness of the positive plate of the battery of the comparative example 1 is uneven, the interface adhesion of the top of the battery cell is not good during formation, the lithium precipitation on the top of the battery cell is serious, and the capacity attenuation is serious (the cycle retention rate is lower than 80% after 781T).
Similarly, it can be seen from table one that the batteries in the examples have faster charge cycle life than the corresponding batteries in the comparative examples and have better lithium deposition than the batteries in the comparative examples, as compared with example 2 and comparative example 2, example 3 and comparative example 3, example 4 and comparative example 4, example 5 and comparative example 5, example 6 and comparative example 6, and example 7 and comparative example 7. The results show that the positive plate obtained by zebra coating of the battery in the comparative example has uneven thickness because the conductive coating is not coated on the current collector, and the interface at the top of the battery core is not well adhered during formation, so that the top of the battery is seriously separated from lithium.
As is clear from 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 rate of lithium ion extraction in example 2 is not as high as that in example 1, but the cycle life of 1000T is satisfied, and no lithium deposition occurs.
As is clear from 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 rate of lithium ion extraction in example 3 is inferior to that in example 2, and at this time, the cycle life of 902T is satisfied, and slight lithium deposition occurs at the top. This also indicates that the particle size of lithium cobaltate affects the cycle life of the battery and the lithium deposition.
As can be seen from comparison of example 4 with example 1, the content of lithium cobaltate in the active coating layer in example 4 was lower than that in example 1, and at this time, the cycle life of 1000T was satisfied, and no lithium deposition occurred.
As can be seen by comparing example 5 with example 4, the content of lithium cobaltate in the active coating layer in example 5 is lower than that in example 4, and the cycle life of 934T is satisfied, and slight lithium precipitation occurs at the top.
As can be seen by comparing example 6 with example 5, the content of lithium cobaltate in the active coating layer in example 6 is lower than that in example 5, and 892T of cycle life is satisfied, and slight lithium precipitation occurs at the top. This also indicates that the amount of active agent present will have an effect on the fast charge cycle life of the battery.
Comparing example 7 with example 1, it can be seen that the lithium deposition of the battery is slightly different due to the different components of the active material, the conductive agent and the binder in the active coating layer.
The comparison between each pair of proportions is the same as that of the embodiments, and each pair of proportions has severe lithium precipitation, which indicates that the uneven thickness of the positive plate can cause poor adhesion of the interface at the top of the battery cell, resulting in severe lithium precipitation at the top and severe capacity attenuation. 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 short charge cycle life and lithium precipitation of the battery are 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, 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. A positive electrode sheet, comprising: the current collector, and a conductive coating and an active coating coated on the current collector;
wherein the active coating comprises a first sub active coating and a second sub active coating, and 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;
the first edge of mass flow body sets up a N utmost point ear, and N is the positive integer, just a N utmost point ear is followed the first direction of mass flow body extends to outside the conductive coating.
2. The positive electrode sheet according to claim 1, wherein the thickness of the conductive coating layer is less than or equal to the difference between the thickness of the second sub-active coating layer and the thickness of the first sub-active coating layer.
3. The positive electrode sheet according to claim 2, wherein the width of the conductive coating layer is less than or equal to the width of the first sub-active coating layer.
4. The positive electrode sheet according to claim 3, wherein the conductive coating layer has a thickness of 5 μm or less; and/or the width of the conductive coating is less than or equal to 5 millimeters.
5. The positive electrode sheet according to claim 1, wherein the electrical resistance of the conductive coating layer is smaller than the electrical resistance of the first sub-active coating layer; and/or the resistance of the conductive coating is less than the resistance of the second sub-active coating.
6. The positive electrode sheet according to claim 1, wherein the conductive coating layer comprises 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.
7. The positive electrode sheet according to claim 6, wherein the active coating layer comprises an active agent, the conductive agent, and the binder;
the active agent comprises at least one of lithium cobaltate, lithium iron phosphate, a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material and lithium titanate.
8. The positive electrode sheet according to claim 6, wherein the median particle diameter of the conductive agent is in a range of 0.05 to 50 μm.
9. A lithium ion battery, characterized in that it comprises a positive electrode sheet according to any one of claims 1 to 7.
10. A method for producing a positive electrode sheet according to any one of claims 1 to 7, comprising:
coating a conductive coating on a current collector by gravure coating equipment, wherein N tabs are arranged on a first edge of the current collector, N is a positive integer, and the N tabs extend out of the conductive coating along a first direction of the current collector;
coating a first sub-active coating on the conductive coating and coating a second sub-active coating on the current collector by using a zebra coating device, wherein the thickness of the first sub-active coating is less 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.
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| WO2024021025A1 (en) * | 2022-07-29 | 2024-02-01 | 宁德时代新能源科技股份有限公司 | Electrode sheet, electrode assembly, battery cell, battery, and electric device |
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