Pole piece structure, battery cell and secondary battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a pole piece structure, a battery cell and a secondary battery. The pole piece structure comprises a current collector, an active material layer and a filling layer, the current collector is provided with at least one empty foil area and at least one coating area; the active material layer is connected to the coating area; the active material layer is provided with the thinning area; the thinning area is communicated with the empty foil area; the filling layer is connected to the empty foil area; and the projection of the filling layer towards the current collector is at least partially overlapped with the thinning region. According to the invention, the unevenness of the pole piece can be reduced, the use safety and stability are improved, and the cycle use life of the pole piece is prolonged.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in various fields such as 3C, energy storage and new energy vehicles due to their advantages such as high specific energy and long cycle life. Among them, stacked structure batteries have great advantages in energy density and fast charging, and are one of the main development trends of the lithium battery industry in the future.

[0003] Because the zebra coating method used in the production process of the battery pole piece causes the edge thickness of the pole piece to be relatively thin due to edge thinning and stress problems on both sides of the pressing roller, the flatness of the battery cell is uneven, and the pole piece head cannot be completely fitted, which leads to lithium deposition on the head of the subsequent finished battery cell, reducing the safety and stability of use; and greatly affecting the battery cell performance and shortening the battery cell cycle life. Summary of the invention

[0004] The purpose of the present invention is to provide a pole piece structure, a battery cell and a secondary battery to address the deficiencies of the prior art, which can solve the technical problems of low safety and stability in the use of the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A pole piece structure comprises a current collector, an active material layer and a filling layer; the current collector is provided with at least one empty foil area and at least one coating area; the active material layer is connected to the coating area; and the active material layer is provided with the thinning area; the thinning area is connected to the empty foil area; the filling layer is connected to the empty foil area; and the projection of the filling layer toward the current collector is at least partially overlapped with the thinning area.

[0007] Preferably, the filling layer is NMP solvent or water solvent.

[0008] Preferably, the number of the empty foil areas is at least two; the number of the coating areas is at least two; and the empty foil areas and the coating areas are arranged alternately;

[0009] On two of the thinned areas in two adjacent coating areas, projections of the filling layer toward the current collector are at least partially overlapped with the corresponding two thinned areas.

[0010] Preferably, the active material layer further comprises a main body region; and the thinned region is arranged at left and right side ends of the main body region.

[0011] Preferably, the relationship between the length W1 of the thinning area, the spraying length W3 of the filling layer, and the sum W2 of the lengths of two adjacent thinning areas and the empty foil areas satisfies: W1≤W3≤W2.

[0012] Preferably, the relationship between the width L1 of the filling layer and the width L2 of the current collector satisfies: L2≤L1.

[0013] Preferably, the relationship between the coating weight CW1 of the active material layer and the spraying weight CW2 of the filling layer satisfies: CW2≤0.5%*CW1.

[0014] The present invention also discloses a battery cell, comprising a first pole piece, an isolation membrane and a second pole piece stacked in sequence; and the polarity of the second pole piece is opposite to the polarity of the first pole piece; the second pole piece and / or the first pole piece is the pole piece structure described above.

[0015] Preferably, the relationship between the thickness T of the entire battery cell, the thickness Ta of the first pole piece, the thickness Tc of the second pole piece, the length W3 of a single filling layer and the thickness Ts of the isolation film satisfies: (2Ta+5Ts+2Tc)*π / 2≤W3<T*π / 2;

[0016] And / or, the relationship between the number of layers of the battery core being N, the number of layers between the two tabs that are farthest apart being M, and the number of filling layers being N0, satisfies: M+2≤N0<N-1.

[0017] The invention also discloses a secondary battery, comprising the battery core.

[0018] The beneficial effect of the present invention is that the technical solution can quickly and effectively increase the thickness of the thinned area by spraying a filling layer on the empty foil area and at least part of the thinned area, thereby helping to reduce the unevenness of the electrode; and further can reduce the gap at this position during molding, reduce or avoid lithium plating of the battery cell, and improve the safety and stability of use, thereby extending its cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The following will refer to the attached Figures 1 to 5 To describe the features, advantages and technical effects of exemplary embodiments of the present invention.

[0020] Figure 1 A schematic structural diagram of a pole piece structure according to an embodiment of the present invention;

[0021] Figure 2 A top view of a pole piece structure according to an embodiment of the present invention;

[0022] Figure 3A schematic structural diagram of a pole piece structure according to an embodiment of the present invention;

[0023] Figure 4 A schematic structural diagram of a pole piece structure according to an embodiment of the present invention;

[0024] Figure 5 FIG. 4 is a schematic diagram of a battery cell according to an embodiment of the present invention.

[0025] In the figure: 1-current collector; 11-empty foil area; 12-coating area; 2-active material layer; 21-thinning area; 22-main area; 3-filling layer; 100-first pole piece; 200-second pole piece; 300-isolating film. DETAILED DESCRIPTION

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0027] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0028] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and multiple situations exist alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0030] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0031] The following is combined with Figure 1 to Figure 5 The present invention is further described in detail, but is not intended to limit the present invention.

[0032] like Figure 1 and 2 As shown, in one embodiment of the present invention, the electrode structure includes a current collector 1, an active material layer 2 and a filling layer 3; at least one empty foil area 11 and at least one coating area 12 are provided on the current collector 1; the active material layer 2 is connected to the coating area 12; and a thinning area 21 is provided on the active material layer 2; the thinning area 21 is connected to the empty foil area 11; the filling layer 3 is connected to the empty foil area 11; and the projection of the filling layer 3 toward the current collector 1 is at least partially overlapped with the thinning area 21.

[0033] The technical solution of the present invention can quickly and effectively increase the thickness of the thinned area by spraying a filling layer on the empty foil area and at least part of the thinned area, thereby helping to reduce the unevenness of the electrode; further, it can reduce the gap at this position during molding, reduce or avoid lithium plating of the battery cell, and improve the safety and stability of use, thereby extending its cycle life.

[0034] Specifically, in some embodiments, the filling layer 3 may be an NMP (N-methylpyrrolidone) solvent or an aqueous solvent. Among them, in some embodiments, when the pole piece structure is an anode piece, the filling layer 3 may be an NMP (N-methylpyrrolidone) solvent or an aqueous solvent. When the pole piece structure is a cathode piece, the filling layer 3 is an NMP (N-methylpyrrolidone) solvent. That is to say, during the spraying and thickening process of the anode piece, since the NMP (N-methylpyrrolidone) solvent or the aqueous solvent can be dissolved in the anode active material layer, therefore, when the NMP (N-methylpyrrolidone) solvent or the aqueous solvent is sprayed, it will dissolve in the active material layer, so that the active material layer in the spraying area will expand, thereby increasing the thickness. During the spraying and thickening process of the cathode piece, since the NMP (N-methylpyrrolidone) solvent can be dissolved in the cathode active material layer, therefore, when the NMP (N-methylpyrrolidone) solvent is sprayed, it will dissolve in the active material layer, so that the active material layer in the spraying area will expand, thereby increasing the thickness. Furthermore, when the pole piece structure is used for a laminated battery cell, it is necessary to cut from the edge of the empty foil area 11, leaving the coating area 12; the increased thickness of the filling layer 3 just makes up for the thickness difference of the edge thinning area. When the pole piece structure is used for a wound battery cell, the thickness of the corner position can be increased to reduce the gap at the corner; reduce or avoid the lithium deposition phenomenon of the battery cell, and improve the safety and stability of use, and extend its cycle life.

[0035] Specifically, in some embodiments, Figure 1 and 2 As shown, the number of the empty foil areas 11 is at least two; the number of the coating areas 12 is at least two; and the empty foil areas 11 and the coating areas 12 are arranged alternately; on the two thinning areas 21 in two adjacent coating areas 12, the projection of the filling layer 3 toward the current collector 1 is at least partially overlapped with the corresponding two thinning areas 21. This structure can cover the two thinning areas 21 by spraying a large range at one time, thereby improving the spraying efficiency and ensuring the spraying effect.

[0036] Specifically, in some embodiments, Figure 2 As shown, the active material layer 2 also includes a main body region 22; and the thinning regions 21 are arranged at the left and right ends of the main body region 22. That is, due to the zebra coating method used in the production process of the pole piece, and due to the edge thinning combined with the stress problem on both sides of the pressing roller, the pole piece forms a main body region 22 that is thicker in the middle and thinning regions 21 that are thinner on both sides.

[0037] Specifically, in some embodiments, Figure 1 and 3As shown, the thickness d3 of the thinning area 21 satisfies: 1um≤d3≤2um; and the relationship between the thickness d3 of the thinning area 21, the thickness d1 of the main area 22 and the thickness d2 of the filling layer 3 satisfies: d3<d2≤d1. In other words, when spraying NMP solvent to the thinning area 21 and the empty foil area 11, a sufficient amount is required to ensure that the material area at the edge of the thinning area 21 can contact the filling layer 3; thereby achieving the increased thickness just to make up for the thickness difference of the edge thinning area.

[0038] Specifically, in some embodiments, Figure 2 , 3 As shown in , 4, the relationship between the length W1 of each thinning area 21, the spraying length W3 of each filling layer 3, and the sum W2 of the lengths of two adjacent thinning areas 21 and the empty foil area 11 satisfies: W1≤W3≤W2. In other words, the spraying coverage of the filling layer 3 is controlled to be within the thinning area 21 and the empty foil area 11; avoid spraying the main area 22 in the normal area, which may cause the thickness of the active material layer 2 in the main area 22 to be too large, thereby effectively controlling the overall flatness and uniformity. However, the length W3 of the sprayed filling layer 3 is too small to spray to the material area at the edge of the thinning area 21, which will still affect the degree of fit of the battery head. If the length W3 of the sprayed filling layer 3 is too large, it may be sprayed to the normal area of ​​the pole piece, resulting in an increase in the overall thickness of the pole piece and affecting the thickness of the battery cell.

[0039] Specifically, in some embodiments, Figure 4 As shown, the relationship between the width L1 of the filling layer 3 and the width L2 of the current collector 1 satisfies: L2≤L1. This structure can ensure the full coverage of the fusion filling and further guarantee the appropriate thickening operation of the thinned area.

[0040] Specifically, in some embodiments, the relationship between the coating weight CW1 of the active material layer 2 and the spraying weight CW2 of the filling layer 3 satisfies: CW2≤0.5%*CW1. By limiting the spraying weight CW2 of the filling layer 3 to below 0.5%*coating surface density CW1, the complete fusion with the active material layer can be guaranteed and the increase in its thickness can be controlled. If the spraying amount is too high, the solvent cannot be completely volatilized, affecting the subsequent battery performance, and due to its fluidity, it may affect other normal areas, causing the overall thickness of the pole piece to be too large, affecting the size of the battery cell.

[0041] Example 1

[0042] At least one group of filling layers 3 whose material is a water solvent are sprayed on the thinned area 21 and the empty foil area 11 of the anode sheet; wherein the relationship between the length W1 of each thinned area 21, the sprayed length W3 of each filling layer 3 and the sum W2 of the lengths of two adjacent thinned areas 21 and the empty foil area 11 satisfies W1≤W3≤W2; and the relationship between the coating weight CW1 of the active material layer 2 and the sprayed weight CW2 of the filling layer 3 satisfies: CW2≤0.5%*CW1;

[0043] At least one group of filling layer 3 with NMP solvent as the material is sprayed on the thinned area 21 and the empty foil area 11 of the anode sheet; wherein the relationship between the length W1 of each thinned area 21, the sprayed length W3 of each filling layer 3 and the sum W2 of the lengths of two adjacent thinned areas 21 and the empty foil area 11 satisfies W1≤W3≤W2; and the relationship between the coating weight CW1 of the active material layer 2 and the sprayed weight CW2 of the filling layer 3 satisfies: CW2≤0.5%*CW1;

[0044] Assembling the anode sheet and the cathode sheet to form a bare cell structure;

[0045] Detect and determine the degree of lithium plating and thickness level of bare batteries.

[0046] Example 2

[0047] The difference between Example 2 and Example 1 is that the thinned area 21 and the empty foil area 11 of the anode sheet are not subjected to at least one group of spraying treatment of the filling layer 3 whose material is a water solvent.

[0048] Example 3

[0049] The difference between Example 3 and Example 1 is that the thinned area 21 and the empty foil area 11 of the anode sheet are not subjected to at least one group of spraying treatment of the filling layer 3 whose material is NMP solvent.

[0050] Comparative Example 1

[0051] The difference between Comparative Example 1 and Example 1 is that the filling layer 3 is not sprayed in the thinned area 21 and the empty foil area 11 of the anode sheet; and the filling layer 3 is not sprayed in the thinned area 21 and the empty foil area 11 of the cathode sheet.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 2 and Example 1 is that the relationship between the length W1 of each thinning area 21, the spraying length W3 of each filling layer 3 and the sum W2 of the lengths of two adjacent thinning areas 21 and the empty foil area 11 satisfies W3<W1.

[0054] Comparative Example 3

[0055] The difference between Comparative Example 3 and Example 1 is that the relationship between the length W1 of each thinning area 21, the spraying length W3 of each filling layer 3 and the sum W2 of the lengths of two adjacent thinning areas 21 and the empty foil area 11 satisfies W2<W3.

[0056] Table 1

[0057]

[0058]

[0059] It can be seen from the above table that: 1) the thickness levels of the battery cells in Examples 1, 2 and 3 are comparable, but the experimental group in Example 1 has better flatness; at the same time, the circulation interface is the best in the experimental group in Example 1, and is comparable to that in Example 2 and 3. This may be because the compaction is reduced after the anode head is thickened, the charging capacity is increased, and at the same time, the flatness is improved after the cathode head is thickened.

[0060] 2) The thickness level and flatness of the battery cells in the experimental group of Example 1 are the best; and the interface of the experimental group of Example 1 is the best after 400 cycles under the same system.

[0061] The present invention also provides a battery cell, such as Figure 5 As shown, the battery cell includes a first pole piece 100, an isolation membrane 300, and a second pole piece 200 which are stacked in sequence; and the polarity of the second pole piece 200 is opposite to that of the first pole piece 100; the second pole piece 200 and / or the first pole piece 100 is a pole piece structure; the specific structure of the pole piece structure refers to the above-mentioned embodiment. Since the present battery cell adopts all the technical solutions of all the above-mentioned embodiments, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be described one by one here. Preferably, one of the second pole piece 200 and the first pole piece 100 is a pole piece structure; most preferably, the second pole piece 200 and the first pole piece 100 are both pole piece structures. Among them, as Figure 5 As shown, the second pole piece 200 is a positive pole piece (cathode piece); the first pole piece 100 is a negative pole piece (anode piece).

[0062] Specifically, in some embodiments, Figure 4 and 5 As shown, the relationship between the overall thickness T of the battery cell, the thickness Ta of the first pole piece 100, the thickness Tc of the second pole piece 200, the length W3 of the single filling layer 3 and the thickness Ts of the isolation film 300 satisfies: (2Ta+5Ts+2Tc)*π / 2≤W3<T*π / 2. This structure can ensure the structural stability of the battery cell during winding, and can also ensure the suitability of the thickness of the thinning area 21, avoiding uneven thickness of the pole piece surface affecting the flatness of the battery cell.

[0063] Specifically, in some embodiments, Figure 4 and 5 As shown, the relationship between the width L1 of a single filling layer 3 and the width Wa of the first pole piece 100 satisfies: L1 ≥ Wa. This structure can ensure the full coverage of the fusion filling and further guarantee the appropriate thickening operation of the thinned area.

[0064] Specifically, in some embodiments, the relationship between the number of battery core layers N, the number of layers between the two tabs that are farthest apart M, and the number of filling layers 3 N0 satisfies: M+2≤N0<N-1. This structure can effectively limit the filling layer 3 to each folded corner; thereby only increasing the thickness of the pole piece at the corner, reducing the gap at the corner, and thus improving the corner lithium deposition.

[0065] Further, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is coated on the surface of the positive electrode current collector; the positive electrode current collector includes a positive electrode coating area and a positive electrode ear connected to the positive electrode coating area, the positive electrode coating area is coated with a positive electrode active material layer, and the positive electrode ear is not coated with the positive electrode active material layer. The material of the positive electrode current collector can be aluminum, and the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganate, etc. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is coated on the surface of the negative electrode current collector; the negative electrode current collector includes a negative electrode coating area and a negative electrode ear connected to the negative electrode coating area, the negative electrode coating area is coated with a negative electrode active material layer, and the negative electrode ear is not coated with a negative electrode active material layer. The material of the negative electrode current collector can be copper, and the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material can be carbon or silicon, etc. The material of the isolation film 300 can be PP (polypropylene) or PE (polyethylene).

[0066] The present invention further provides a secondary battery, which includes a battery cell. The specific structure of the battery cell refers to the above embodiments. Since the secondary battery adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0067] Among them, secondary battery (Rechargeable battery) is also called rechargeable battery or storage battery, which refers to a battery that can be used to activate the active material by charging after the battery is discharged. A new battery can be built by using the reversibility of chemical reactions, that is, after a chemical reaction is converted into electrical energy, the chemical system can be repaired by electrical energy, and then converted into electrical energy by chemical reaction again, so it is called a secondary battery (rechargeable battery). The main rechargeable batteries on the market are nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead storage) batteries, lithium-ion batteries, polymer lithium-ion batteries, etc. The most common secondary battery is the lead storage battery, which is composed of two groups of grid-shaped plates arranged alternately, the positive plate is covered with PbO2, the negative plate is covered with Pb, and the electrolyte is H2SO4 solution.

[0068] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0069] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A pole piece structure, characterized in that: It includes a current collector, an active material layer and a filling layer; at least one empty foil area and at least one coating area are provided on the current collector; the active material layer is connected to the coating area; and the thinning area is provided on the active material layer; the thinning area is connected to the empty foil area; the filling layer is connected to the empty foil area; and the projection of the filling layer toward the current collector is at least partially overlapped with the thinning area.

2. The pole piece structure according to claim 1, characterized in that: The filling layer is NMP solvent or water solvent.

3. The pole piece structure according to claim 1 or 2, characterized in that: The number of the empty foil areas is at least two; the number of the coating areas is at least two; and the empty foil areas and the coating areas are arranged alternately; On two of the thinned areas in two adjacent coating areas, projections of the filling layer toward the current collector are at least partially overlapped with the corresponding two thinned areas.

4. The pole piece structure according to claim 2, characterized in that: The active material layer further includes a main body region; the thinning region is arranged at left and right side ends of the main body region.

5. The pole piece structure according to claim 1, characterized in that: The relationship between the length W1 of the thinning area, the spraying length W3 of the filling layer and the sum W2 of the lengths of two adjacent thinning areas and the empty foil areas satisfies: W1≤W3≤W2.

6. The pole piece structure according to claim 5, characterized in that: The relationship between the width L1 of the filling layer and the width L2 of the current collector satisfies: L2≤L1.

7. The pole piece structure according to claim 1 or 5, characterized in that: The relationship between the coating weight CW1 of the active material layer and the spraying weight CW2 of the filling layer satisfies: CW2≤0.5%*CW1.

8. A battery cell, characterized in that: It comprises a first pole piece, an isolation membrane and a second pole piece which are stacked in sequence; and the polarity of the second pole piece is opposite to the polarity of the first pole piece; the second pole piece and / or the first pole piece is the pole piece structure as described in any one of claims 1 to 7 above.

9. The battery cell according to claim 8, characterized in that: The relationship between the thickness T of the entire battery cell, the thickness Ta of the first pole piece, the thickness Tc of the second pole piece, the length W3 of a single filling layer and the thickness Ts of the isolation film satisfies: (2Ta+5Ts+2Tc)*π / 2≤W3<T*π / 2; And / or, the relationship between the number of layers of the battery core being N, the number of layers between the two tabs that are farthest apart being M, and the number of filling layers being N0, satisfies: M+2≤N0<N-1.

10. A secondary battery, characterized in that: A battery cell comprising the battery cell described in any one of claims 8 to 9.

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