A pole piece and a battery

Abstract

The present invention relates to the field of battery technology, and more particularly to a pole piece and a battery including the pole piece. The pole piece includes a current collector, an active material layer located on one or both sides of the current collector, and a primer layer disposed between the current collector and the active material layer. The primer layer has a patterned structure that divides the primer layer into a continuous coating area and a plurality of dispersed exposed foil areas. The active material layer fills the exposed foil areas and covers the surface of the coating areas. The pole piece of the present invention has excellent adhesion between the active material layer and the current collector and has a high energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a pole piece and a battery comprising the pole piece. Background Art

[0002] Batteries are currently widely used in consumer electronics, electric vehicles, energy storage, and other fields. Batteries are composed of pole pieces and separators as core components. Pole pieces are typically formed by coating active materials on a current collector. However, the adhesion between the active material layer and the current collector is typically low.

[0003] Therefore, it is very important to find a way to enhance the adhesion of the active material layer to the current collector while maintaining performance. Summary of the Invention

[0004] The present invention aims to overcome the above problems in the prior art and provide a pole piece and a battery including the pole piece. The active material layer in the pole piece of the present invention has good adhesion to the current collector and has a high energy density.

[0005] A first aspect of the present invention provides a pole piece, comprising a current collector, an active material layer located on one side or both sides of the current collector, and a primer layer arranged between the current collector and the active material layer, wherein the primer layer has a pattern structure, which divides the primer layer into a continuous coating area and a plurality of scattered exposed foil areas; the active material layer fills the exposed foil area and covers the surface of the coating area.

[0006] A second aspect of the present invention provides a battery, wherein the negative electrode sheet and / or the positive electrode sheet of the battery are the electrode sheets described in the first aspect of the present invention.

[0007] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0008] (1) The active material layer of the electrode of the present invention has good adhesion to the current collector;

[0009] (2) The battery of the present invention has a higher energy density.

[0010] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Shown is a top view of a primer according to an embodiment of the present invention.

[0012] Figure 2 The present invention is shown Figure 1 Side view of the primer shown in .

[0013] Figure 3Shown is a side view of a pole piece according to an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0015] A specific embodiment of the pole piece is as follows Figure 1 、 Figure 2 and Figure 3 shown. Figure 1 A top view of a primer is provided for an example. Figure 2 for Figure 1 Side view of the primer shown in Figure 3 The figure shows a side view of a pole piece provided in an example. Figure 1 、 Figure 2 and Figure 3 As shown, the pole piece 05 includes: a current collector 00; the surface of the current collector 00 is coated with a primer layer 01, wherein the primer layer 01 has a pattern structure, and the pattern structure divides the primer layer 01 into a continuous coating area and a plurality of scattered exposed foil areas 02; the surface of the primer layer 01 is covered with an active material layer, and the active material layer fills the exposed foil area 02 and covers the surface of the coating area, and the active material layer includes granular active substances 03 and conductive agents 04.

[0016] In order to increase the adhesion between the current collector and the active material layer, a primer layer can be applied to the current collector, and the adhesive content of the primer layer is higher than the adhesive content of the active material layer. Therefore, the adhesion between the active material layer and the current collector is stronger, thereby enhancing the adhesion between the active material layer and the current collector. However, the inventors of the present invention have found that the primer layer in this method will affect the energy density of the battery. Therefore, the inventors of the present invention propose a method of providing an exposed foil area on the primer layer, so that most of the exposed foil area can be embedded in the active material particles, thereby effectively facilitating the space of the primer layer, and can improve the adhesion between the active material and the current collector while also taking into account the energy density.

[0017] The exposed foil area 02 is the area where the primer layer does not cover the current collector 00 (exposing the current collector so as to be in contact with the active material).

[0018] In the present invention, by filling the exposed foil area 02 with the active material layer and covering the surface of the coating area, the active material layer and the current collector 00 are in direct contact, which enables the battery electrode to achieve a higher energy density without changing the bonding force compared to the solution with a primer layer.

[0019] The primer layer and the active material layer may be located on one side of the current collector 00 or on both sides of the current collector 00 .

[0020] According to a specific embodiment, the primer layer 01 may first cover the current collector 00 , and then the active material layer may be covered on the primer layer 01 to form the electrode of the present invention.

[0021] In one embodiment, the area of the basecoat 01 not covering the current collector is the exposed foil area. There are multiple exposed foil areas (preferably as evenly as possible) dispersed throughout the basecoat, and the remaining areas are the coated areas. When the coverage of the coated areas of the basecoat 01 on the current collector 00 is within a certain range, it can ensure a certain degree of adhesion to the electrode 05 while also enabling the battery to have a high energy density.

[0022] According to a specific embodiment, the coverage of the coating area of the primer layer 01 on the current collector 00 is 30-80% (eg, 30%, 40%, 50%, 60%, 70%, 80% and a range consisting of any two points).

[0023] Preferably, the coverage of the coating area of the primer layer 01 on the current collector 00 is 50-70%.

[0024] According to a specific embodiment, the exposed foil areas 02 are each independently circular, square, strip, polygonal, patterned, irregular, or any other shape.

[0025] The minimum distance of the exposed foil area 02 is represented by d, which refers to the distance between the two closest points in the exposed foil area where the primer coating is not applied. For example, when the exposed foil area is circular, d is the diameter; when the exposed foil area is irregular, d is the shortest distance between any two points; when the exposed foil area is strip-shaped (such as Figure 1 As shown), the shortest distance is (as shown Figure 2 The distance in the width direction shown).

[0026] The parameter "dn" is set for the exposed foil area to represent the d value of more than n% of the exposed foil area, for example, d80 < the d value of 80% of the exposed foil area and > the d value of 20% of the exposed foil area.

[0027] In one example, d80 of the exposed foil area is 30 μm-500 μm (e.g., 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm).

[0028] In one example, d80 of the exposed foil area is 30 μm-200 μm.

[0029] The active material in the active material layer is in granular form, such as Figure 3 As shown in the figure 03, the parameter "Dm" is set for the active material. Dm refers to the particle size that represents the mth percentile of the cumulative volume, starting from the smallest particle size in the volume-based particle size distribution. D90 refers to the particle size that represents the 90th percentile of the cumulative volume, starting from the smallest particle size in the volume-based particle size distribution. For example, if D90 = 30 μm, then the volume of particles ≤ 30 μm accounts for 90% of the total volume.

[0030] In one embodiment, the D90 of the active substance is 15 μm-50 μm.

[0031] According to a specific embodiment, the d80 of the exposed foil area is greater than the D90 of the active material. Most of the active material particles 03 meeting the above size conditions can be embedded in most of the exposed foil area 02 and can have good contact with the current collector 00.

[0032] The term "dn of the exposed foil area is greater than Dm of the active material" encompasses various possible size relationships that can achieve this condition, and is not limited to the numbers n and m themselves. For example, "d80 of the exposed foil area is greater than D90 of the active material" requires that at least 90% of the active material can be embedded in 80% of the exposed foil area. This includes the case where "all active material can be embedded in at least 80% of the exposed foil area." It also includes the case where "at least 90% of the active material can be embedded in all exposed foil areas" (for example, when all pores in the exposed foil area have the same diameter), and so on.

[0033] The method for forming the exposed foil area is not particularly limited. In one embodiment, the exposed foil area is formed by coating the basecoat slurry on the current collector by gravure printing. In another embodiment, the exposed foil area is formed by laser drilling in the basecoat where the foil is not exposed.

[0034] According to a specific embodiment, the primer layer includes a first adhesive, a first conductive agent and a first thickener, wherein based on the total weight of the primer layer 01, the content of the first adhesive is 20-40 weight % (for example, 20%, 25%, 30%, 35%, 40%), the content of the first conductive agent is 30-60 weight % (for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%), the composition and content of the primer layer are the composition and content in the coating area, and the content of the first thickener is 20-40 weight % (for example, 20%, 25%, 30%, 35%, 40%).

[0035] According to a specific embodiment, the active material layer includes an active substance, a second adhesive, a second conductive agent and a second thickener, wherein based on the total weight of the active material layer, the content of the active substance is 94-98 weight % (for example, 94%, 95%, 96%, 97%, 98%), the content of the second adhesive is 1-2.5 weight % (for example, 1%, 1.5%, 2%, 2.5%), the content of the second conductive agent is 0.5-1.5 weight % (for example, 0.5%, 1%, 1.5%), and the content of the second thickener is 0.5-2 weight % (for example, 0.5%, 1%, 1.5%, 2%).

[0036] In one example, the first thickener and the second thickener may be the same or different, and each independently selected from one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, and polyvinyl pyrrolidone.

[0037] According to a specific embodiment, the first adhesive and the second adhesive may be the same or different, and are each independently selected from adhesives containing carboxyl groups and / or ester groups.

[0038] In one example, the first adhesive and the second adhesive are independently selected from one or more of polyacrylates, acrylic acid-modified styrene-butadiene rubbers, and acrylic acid-modified vinylidene fluoride.

[0039] According to a specific embodiment, the thickness of the primer layer is 0.2 μm-2 μm (e.g., 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm).

[0040] According to a specific embodiment, the thickness of the primer layer is 0.4 μm-0.8 μm.

[0041] According to a specific embodiment, the thickness of the active material layer is 30 μm-70 μm (the thickness of a single side of the current collector).

[0042] In one embodiment, the first and second conductive agents are one or more of carbon black, carbon nanotubes, graphene, metal conductive powder, carbon fiber, acetylene black, and Ketjen black. For example, the second conductive agent in the active material layer can be a mixture of graphene and carbon black at a certain mass percentage, or a mixture of carbon black and metal conductive powder at a certain mass percentage, or carbon black, graphene, or metal conductive powder can be used alone as the conductive agent in the active material layer. This invention is not particularly limited.

[0043] In one embodiment, the average particle size of the first conductive agent and the second conductive agent is independently 10 μm. 2 / g~1000m 2 / g.

[0044] The undercoat layer of the present invention can be applied to either a positive electrode sheet or a negative electrode sheet.

[0045] When the undercoat layer of the present invention is used for a negative electrode sheet:

[0046] The primer layer 01 uses an adhesive containing a carboxyl group or an ester group to generate a chemical bond with the copper foil to enhance the bonding strength.

[0047] In one embodiment, the active material is a negative electrode active material.

[0048] In one embodiment, the negative electrode active material includes one or more of hard carbon, artificial graphite, natural graphite, silicon oxide, a silicon-carbon compound, and lithium titanate. For example, the negative electrode active material in the active material layer may be a mixture of artificial graphite and natural graphite at a certain mass percentage, or a mixture of artificial graphite and silicon oxide at a certain mass percentage, or artificial graphite, natural graphite, or silicon oxide may be used alone as the conductive agent in the active material layer, and the present invention is not particularly limited thereto.

[0049] When the primer layer of the present invention is used for a positive electrode sheet:

[0050] In one embodiment, the active material is a positive electrode active material.

[0051] The positive electrode current collector may be an aluminum foil commonly used in the art.

[0052] The positive electrode active material is selected from one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, and lithium titanate. For example, the positive electrode active material in the active material layer may be obtained by mixing lithium cobalt oxide and lithium manganese oxide in a certain mass percentage, or by mixing lithium cobalt oxide and lithium nickel oxide in a certain mass percentage, or by using lithium cobalt oxide, lithium manganese oxide, or lithium nickel oxide alone as the conductive agent in the active material layer, which is not specifically limited in the present invention.

[0053] A second aspect of the present invention provides a battery, wherein the negative electrode sheet and / or the positive electrode sheet of the battery are the electrode sheets described in the second aspect of the present invention.

[0054] The selection of other components (such as a separator, an electrolyte, etc.) in the battery of the present invention and the assembly of the battery can be carried out according to conventional methods in the art and will not be described in detail here.

[0055] Compared with the conventional method with a primer layer, the active material layer and the current collector of the pole piece of the present invention maintain good adhesion between the active material layer and the current collector, while being able to reduce the thickness and significantly improve the energy density.

[0056] The terms "first", "second", etc. in the present invention are used to distinguish similar objects, and are not used to describe a specific order or sequence.

[0057] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0058] The following examples only apply the primer layer to the negative electrode. This configuration is merely one embodiment and should not be construed as limiting the present invention. It is understood that significant effects can also be achieved when applied to the positive electrode.

[0059] Example 1

[0060] (1) Preparing a negative electrode undercoat slurry: 30 wt% of acrylic acid-modified styrene-butadiene rubber, 20 wt% of carbon black, 20 wt% of carbon nanotubes, and 30 wt% of sodium carboxymethyl cellulose were mixed, deionized water was added, and the solid content of the slurry was adjusted to 30 wt%, and the mixture was stirred to prepare a negative electrode undercoat slurry;

[0061] (2) Preparing a negative electrode active material layer slurry: 96 wt% of artificial graphite (active material, D90 is 28 μm), 1 wt% of carbon black, 1.5 wt% of acrylic acid-modified styrene-butadiene rubber, and 1.5 wt% of sodium carboxymethyl cellulose were mixed, deionized water was added, and the solid content of the slurry was adjusted to 40 wt%. The mixture was stirred to prepare a negative electrode active material layer slurry;

[0062] (3) Preparation of negative electrode sheet: The negative electrode undercoat slurry was coated on copper foil and dried to obtain an undercoat layer. The undercoat layer was then laser-drilled to obtain an exposed foil area (so that the exposed foil area was circular, with d80 as shown in Table 1). The negative electrode slurry from step 3 was coated on the undercoat sheet by extrusion coating; the negative electrode sheet was rolled, cut, and welded to the tabs, and protective tape was applied to obtain the negative electrode sheet. The thickness of the undercoat layer was measured to be 0.8 μm, the thickness of the active material layer was 50 μm, and the coverage of the undercoat layer was shown in Table 1.

[0063] (4) Preparation of positive electrode sheets: 96 wt% lithium cobalt oxide, 1 wt% carbon black, 1 wt% carbon nanotubes, and 2 wt% PVDF were mixed, a certain amount of NMP was added, and the solid content of the slurry was adjusted to 70 wt%. The positive electrode slurry was prepared by stirring; the positive electrode slurry was coated on the positive electrode current collector and dried to obtain a positive electrode sheet; the positive electrode sheet was obtained by rolling, cutting, welding the tabs, and applying protective tape.

[0064] (5) Place the separator between the positive and negative electrodes and wind or stack them, assemble the battery, and obtain a qualified battery product.

[0065] Example 2 group

[0066] This group of examples is used to illustrate the effect of changing the coverage of the primer layer.

[0067] The process was carried out in accordance with Example 1, except that different laser drilling conditions were used to change the coverage of the primer layer (keeping the size distribution and d80 of the exposed foil area unchanged), as shown in Table 1.

[0068] Example 3 group

[0069] This group of embodiments is used to illustrate the effect of changing the exposed foil area d80.

[0070] The process was carried out in accordance with Example 1, except that different gravure plates were used for coating to change the d80 of the exposed foil area (keeping the coverage of the primer layer unchanged), as shown in Table 1.

[0071] Comparative Example 1

[0072] No exposed foil area is provided on the primer layer, and the primer layer is entirely covered with the primer slurry; other steps are carried out according to Example 1.

[0073] Comparative Example 2

[0074] The process was carried out in accordance with Example 1, except that step (1) was omitted, that is, no primer layer was provided, and the negative electrode active material was directly coated on the negative electrode current collector.

[0075] Test Case

[0076] (1) Energy density test

[0077] The test method includes: charging the batteries obtained in the embodiment and the comparative example at a current of 0.5C to the cut-off voltage, and charging at a constant voltage to a cut-off voltage of 0.02C; after standing for 10 minutes, the battery is discharged at a current of 0.2C to 3.0V; the discharge energy is the energy of the battery, and the energy density is calculated as energy / (battery length*width*height), in units of Wh / L, and the results are recorded in Table 1.

[0078] (2) Negative electrode peel strength test

[0079] The test method includes: cutting the negative electrode sheets obtained in the embodiment and the comparative example into small pieces with a length of 240 mm and a width of 30 mm, and using NITTO No. 5000NS tape was cut into small pieces with a length of 200 mm and a width of 24 mm. One side of the tape piece was adhered to a steel plate (260 mm * 50 mm), and the negative electrode sheet was adhered to the other side of the tape piece, ensuring that the negative electrode sheet completely covered the tape piece. A handheld roller (diameter 95 mm, width 45 mm, weight 2 kg) was used to roll back and forth three times to adhere the negative electrode sheet and the tape piece together. The tape was then tested using a tensile testing machine (tensile testing machine model Dongguan Kejian KJ-1065 series) (180-degree peel). The testing equipment automatically recorded the tensile force value as the peel displacement changed, and a curve of the tensile force value versus peel displacement was plotted, with the peel displacement as the abscissa and the tensile force as the ordinate. The tensile force value at which the curve flattens and the peel displacement is greater than 5 mm is the peel force. This peel force represents the peel strength in N / m. The results are recorded in Table 1.

[0080] Table 1

[0081]

[0082]

[0083] As can be seen from Table 1, the data of the embodiment proves that the method of setting the exposed foil area on the bottom coating layer allows most of the exposed foil area to be embedded with active material particles, which can make the active material layer have good adhesion with the current collector and the battery also has a higher energy density.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pole piece, characterized in that: The present invention comprises a current collector, an active material layer located on one side or both sides of the current collector, and an undercoat layer disposed between the current collector and the active material layer, wherein the undercoat layer has a pattern structure that divides the undercoat layer into a continuous coating area and a plurality of dispersed foil-exposed areas; the active material layer fills the foil-exposed area and covers the surface of the coating area; The coverage of the coating area of the primer layer on the current collector is 50-70%; The minimum distance of the exposed foil area is d, and the minimum distance of more than 80% by number of the exposed foil areas is d80, and d80 is greater than D90 of the active material in the active material layer; The D90 of the active substance is 15 μm-50 μm; The d80 of the exposed foil area is 30 μm-200 μm; The thickness of the primer layer is 0.2 μm-2 μm.

2. The pole piece according to claim 1, wherein: The exposed foil areas are each independently circular, square, strip, polygonal, patterned or irregular in shape.

3. The pole piece according to claim 1, wherein: The primer layer includes a first adhesive, a first conductive agent and a first thickener, wherein based on the total weight of the primer layer, the content of the first adhesive is 20-40 weight %, the content of the first conductive agent is 30-60 weight %, and the content of the first thickener is 20-40 weight %.

4. The pole piece according to claim 1, wherein: The active material layer includes an active material, a second adhesive, a second conductive agent and a second thickener, wherein, based on the total weight of the active material layer, the content of the active material is 94-98 weight %, the content of the second adhesive is 1-2.5 weight %, the content of the second conductive agent is 0.5-1.5 weight %, and the content of the second thickener is 0.5-2 weight %.

5. The pole piece according to claim 3, wherein: The first adhesive is selected from adhesives containing carboxyl groups and / or ester groups.

6. The pole piece according to claim 4, wherein: The second adhesive is selected from adhesives containing carboxyl groups and / or ester groups.

7. The pole piece according to claim 1, wherein: The thickness of the active material layer is 30 μm-70 μm.

8. A battery, characterized in that: The negative electrode sheet and / or the positive electrode sheet of the battery is the electrode sheet according to any one of claims 1 to 7.

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