Diaphragm and secondary battery

Abstract

The utility model belongs to the technical field of secondary batteries, and mainly relates to a diaphragm which is suitable for a winding type electrode assembly, and the winding type electrode assembly is provided with a corner area in a bent state. The diaphragm comprises: a base film, in a flattened state, the base film comprises a straight section and a to-be-bent section which are sequentially and alternately connected along a predetermined direction, and the to-be-bent section corresponds to a corner area; comprising a plurality of polymer layers which are arranged at intervals in the length direction of the base film; at least one polymer layer is arranged corresponding to the to-be-bent section; according to the application, the diaphragm areas corresponding to the corner areas and the straight areas of the winding type electrode assembly are subjected to differential coating design, so that the diaphragm can provide different effects in different areas, and the working stability of the diaphragm is guaranteed while the thickness of the battery is reduced. In addition, the utility model also comprises a secondary battery, and the battery adopts the design comprising the diaphragm, so that the stability is improved.

Description

Technical Field

[0001] This utility model belongs to the field of secondary battery technology, and mainly relates to a separator and a secondary battery. Background Technology

[0002] In modern electronic devices, batteries are a crucial energy supply component, and their performance directly determines the operational stability and lifespan of the device. The separator, one of the four main materials in lithium-ion batteries, primarily functions to provide ion transport channels and prevent direct contact between the positive and negative electrodes. Currently, most lithium-ion batteries employ a wound structure, which is susceptible to significant pressure at the corners. Especially in the later stages of cycling, when the anode and cathode expand, they further compress the corner areas, potentially causing the ion transport path to break, forming the so-called "black spot lithium plating" phenomenon, thus impairing the battery's cycle performance.

[0003] In existing technologies, materials with specific compression ratios are typically used to coat the separator surface to alleviate pressure in corner areas during battery winding and ensure stable separator operation. However, a common practice in current technologies is to directly coat these materials onto the separator, which leads to a large accumulation of material in areas not involved in battery winding, resulting in a significant increase in battery thickness and adversely affecting battery performance.

[0004] Therefore, it is urgent to improve existing separators and secondary batteries to address the shortcomings of the aforementioned technologies. Utility Model Content

[0005] One of the objectives of this invention is to overcome the shortcomings of the prior art by providing a method that coats polymer material only in the corresponding area at the corner of the battery to alleviate the pressure on the separator during the winding process, thus solving the technical problem that existing separators cannot ensure stable operation while reducing battery thickness.

[0006] To achieve the above technical objectives, this application adopts the following technical solution:

[0007] A diaphragm is suitable for a wound electrode assembly having a corner region in a bent state; wherein the diaphragm includes: a base film, which, in a flattened state, includes a straight section and a section to be bent that are sequentially and alternately connected along a predetermined direction, the section to be bent corresponding to the corner region; and a plurality of polymer layers, which are spaced apart along the length direction of the base film; at least one polymer layer is disposed corresponding to the section to be bent.

[0008] The above technical solution has produced the following technical effects:

[0009] By coating the polymer layer only on the base film of the separator in the corner area of ​​the wound electrode, this application effectively reduces material loss during the separator coating process. Simultaneously, since the straight sections of the base film corresponding to the non-corner areas of the wound electrode are not coated with the polymer layer, it further helps to control the thickness of the wound electrode, allowing for a reduction in the thickness of most areas of the wound electrode. Furthermore, the polymer layer of this application also contains polymer particles, further improving the compressibility coefficient of the polymer layer, effectively mitigating the risk of separator damage due to compression during electrode assembly winding, and ensuring the working stability of the separator.

[0010] As a further improvement to the diaphragm of this utility model, the section to be bent is coated with a polymer layer on both sides in the thickness direction.

[0011] As a further improvement to the diaphragm of this utility model, at least one straight section has an adhesive layer coated on at least one surface in its thickness direction.

[0012] As a further improvement to the diaphragm of this invention, an adhesive layer is coated on the side of the polymer layer away from the base membrane.

[0013] As a further improvement to the diaphragm of this utility model, the polymer layer comprises an emulsion of polymer particles; the adhesive layer comprises a ceramic material.

[0014] As a further improvement to the diaphragm of this utility model, the thickness of the polymer layer first increases and then decreases along the length direction of the base membrane, with the thickness of the polymer layer corresponding to the center of the section to be bent being the largest.

[0015] As a further improvement to the diaphragm of this utility model, the thickness of the polymer layer is D1, and D1 satisfies: 0.5 micrometers ≤ D1 ≤ 10 micrometers.

[0016] As a further improvement to the diaphragm of this utility model, the wound electrode assembly includes an electrode sheet with a wound structure, the electrode sheet being in contact with the diaphragm; the length of the polymer layer corresponding to the section to be bent is L1, the diaphragm has a concave area and a convex area in the section to be bent, and the arc length of the electrode sheet corresponding to the section to be bent adjacent to the convex area is L2, wherein L1 and L2 satisfy: L2≥L1≥0.8L2.

[0017] As a further improvement to the diaphragm of this utility model, the thickness of the base film is D2, where D2 satisfies: 3 micrometers ≤ D2 ≤ 10 micrometers, and the width of the base film is consistent with the width of the polymer layer and the adhesive layer; and / or,

[0018] The thickness of the adhesive layer is D3, which satisfies 3 micrometers ≤ D3 ≤ 10 micrometers.

[0019] As a second technical objective of this utility model, in order to overcome the defects of the prior art, a secondary battery with higher working stability is provided.

[0020] To achieve the above technical objectives, this application adopts the following technical solution:

[0021] A secondary battery comprising any of the separators shown above.

[0022] The above technical solution has produced the following technical effects:

[0023] Thanks to the separator provided by this invention, by coating the corner area of ​​the electrode assembly with a polymer layer with a high compressibility coefficient, the separator in that specific area can more effectively adapt to deformation when the battery is subjected to pressure. This innovative improvement effectively avoids the occurrence of "black spot lithium plating," thereby improving the cycle stability of the battery and extending its service life. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the present invention and constitute a part of this invention, illustrate exemplary embodiments of the present invention and are used to explain the present invention, but do not constitute an undue limitation of the present invention. In the drawings:

[0025] Figure 1 This is a schematic diagram of the diaphragm structure in Embodiment 1 of this utility model;

[0026] Figure 2 This is a schematic diagram of the electrode assembly structure in Embodiment 1 of this utility model;

[0027] Figure 3 for Figure 2 Enlarged view of A in the middle;

[0028] Figure 4 This is a schematic diagram of the structure of the electrode and diaphragm in Embodiment 2 of this utility model.

[0029] in:

[0030] 1-Base film;

[0031] 11-Straight section;

[0032] 12 - The section to be bent;

[0033] 2-Wound electrode assembly;

[0034] 21-Corner area;

[0035] 22-Electrode;

[0036] 3-Polymer layer;

[0037] 4-Adhesive layer. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application.

[0039] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0040] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

[0041] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0042] Implementation Method 1

[0043] like Figure 1 As shown, in order to address the technical shortcomings of existing technologies that cannot ensure stable operation of the separator while reducing battery thickness, this application improves the coating distribution of the separator.

[0044] The wound electrode assembly 2 of this application has a bend in the corner region 21. Common winding methods for the wound electrode assembly 2 include Z-winding and J-winding, which typically involve winding the positive and negative electrode sheets 22 and the separator outwards layer by layer. Regardless of the winding method, during the winding and bending process of the electrode sheets 22 and the separator, the corner region 21 of the battery becomes a stress concentration point due to the force exerted. Consequently, the bending force borne by the electrode sheets 22 and the separator in this area is much greater than that in the non-corner region (i.e., the straight area of ​​the wound electrode assembly 2).

[0045] It is worth noting that during the battery charge-discharge cycle, the electrode 22 and the separator in the corner region 21 will undergo expansion and contraction, which further exacerbates the accumulation of stress and increases the stress load at the corner. In particular, the negative electrode of the battery will expand in volume during the cycle due to the insertion and extraction of lithium ions, which makes the separator more susceptible to damage and deformation, and may even lead to lithium plating (i.e., lithium metal deposits at the corner, affecting battery performance and safety).

[0046] Therefore, this application coats a corresponding polymer layer 3 between the diaphragm and the electrode 22 in the corner region 21 of the wound electrode assembly 2. During winding, the polymer layer 3 forms a buffer zone between itself and the electrode 22. When the electrode 22 in the corner region 21 is compressed, the coating disperses stress through compression. Simultaneously, the polymer layer 3, through its gaps and compressibility, ensures a more uniform stress distribution at the corner, preventing diaphragm damage due to localized stress concentration. This structural design ensures that the corner region 21 maintains its structural integrity even under extreme cycling conditions.

[0047] However, the inventors discovered that if the thickness direction of the base film 1 in the diaphragm (i.e., as shown in the figure) Figure 1 The presence of polymer layers 3 (including corner regions 21 and non-corner regions) coated on both sides (one side along the Y direction and the other side opposite to the Y direction) increases the material thickness between the separator and the electrode 22, which is detrimental to the battery's charge-discharge cycle performance. Furthermore, because polymer layers 3 are also coated on the non-corner regions, they exert additional compressive force on the separator in the corner region 21, causing secondary damage to the separator. Therefore, this application optimizes the length of the polymer layers 3 coated on both sides of the base film 1 in the separator's thickness direction to avoid secondary damage to the separator.

[0048] It should be noted that in this application, when the specific structure of the diaphragm is described separately without associating the diaphragm with the electrode assembly, the diaphragm should be regarded as being in a flattened state.

[0049] The base film 1 and the polymer layer 3 coated on both sides of the base film 1 in the thickness direction. The base film 1, in a flattened state, includes a straight section 11 and a bending section 12 connected alternately in a predetermined direction (X direction in this embodiment). The bending section 12 corresponds to the corner area 21. The straight section 11 is not coated with the polymer layer 3, but is coated with other materials that are conducive to the adhesion of the electrode 22 to the separator.

[0050] Furthermore, considering that the wound electrode assembly 2 prepared in this application is a wound electrode assembly 2, the diaphragm needs to be bent multiple times to adapt to the winding situation of the wound electrode assembly 2. Therefore, this application provides multiple straight sections 11 and multiple bending sections 12 in the base film 1, wherein the number of polymer layers 3 also increases with the number of bending sections 12.

[0051] Specifically, polymer layer 3 is an emulsion containing multiple polymer particles, wherein there are height differences and a certain spacing between the polymer particles, thereby alleviating the extrusion pressure on the separator and electrode 22 during winding. It is worth noting that the gaps formed between the multiple polymer particles can also store more electrolyte. At the corner region 21, sufficient electrolyte storage also helps to ensure uniform lithium ion transport in the local area, preventing lithium ion deposition (lithium plating) due to insufficient electrolyte.

[0052] In the specific implementation process, at least one polymer layer 3 is correspondingly set with the section to be bent 12. When the actual production of the wound electrode assembly 2 requires a high thickness, this application can coat only the corresponding position of the section to be bent 12 on the side of the base film 1 near the core, thereby minimizing the impact on the thickness of the wound electrode assembly 2 and also protecting the separator. When the actual production of the wound electrode assembly 2 requires a high degree of separator working stability, the polymer layer 3 can be evenly coated on both sides of the section to be bent 12 in the thickness direction of the corner area 21 of the wound electrode assembly 2, further realizing the control of separator working stability and battery thickness.

[0053] In specific implementation, the adhesive layer 4 is an oil-based coating layer, including PVDF and / or ceramic materials, where PVDF is polyvinylidene fluoride. Specifically, considering the thickness requirements of the wound electrode assembly 2, this application coats the adhesive layer 4 only on one side of the base film 1 in the thickness direction to achieve adhesion between the separator and the electrode 22, while reducing the impact on the battery thickness, further contributing to maintaining the stability of the wound electrode assembly 2 during battery charging and discharging. The number of adhesive layers 4 is less than or equal to the number of straight sections 11 of the base film 1. When the number is equal, each straight section 11 is coated with the adhesive layer 4 to ensure good adhesion between the electrode 22 and the separator, without significantly increasing the total thickness of the battery.

[0054] In practical implementation, the separator of this application can be used in conjunction with various types of positive and negative electrode materials, such as lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (NCM), and lithium iron phosphate (LFP). Specifically, by optimizing the coating distribution of the separator, this application not only improves the cycle stability of the wound electrode assembly 2, but also adapts to different winding forms of the wound electrode assembly 2.

[0055] Furthermore, an adhesive layer 4 is coated on the side of the polymer layer 3 away from the base membrane 1. This adhesive layer 4, applied over the polymer layer 3, significantly improves the adhesion between the electrode 22 and the separator at the corner region 21, preventing separation of the electrode 22 from the separator during cycling due to displacement or stress. This superior adhesion further ensures the stability of ion transport.

[0056] Implementation Method 2

[0057] like Figure 1-4 As shown, unlike Embodiment 1, this embodiment further optimizes the diaphragm to enhance its effect on relieving pressure in the corner region 21. Specifically, the thickness of the polymer layer 3 increases and then decreases along the length direction of the base film (i.e., the X direction); the thickness of the polymer layer 3 is greatest at the center of the section to be bent 12.

[0058] In practical implementation, the thickness of the diaphragm can be designed to vary with a gradient or a smooth curve. Regardless of the method used, the core principle is to match the diaphragm thickness with the bending angle of the corner region 21. This ensures that the thickness of the polymer layer 3 corresponding to the position with the maximum corner angle in the wound electrode assembly 2 is also the thickest in the bending section 12 of the base film 1. This design enhances the structural stability of the corner region 21 while maintaining the ion conduction efficiency of the straight region unaffected.

[0059] Furthermore, the thickness of polymer layer 3 is D1, where D1 satisfies the following condition: 0.5 μm ≤ D1 ≤ 10 μm. Specifically, in practical applications, D1 can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm, etc. Within the above range, polymer layer 3 can provide sufficient elastic space to alleviate compression at corners without significantly increasing the battery thickness.

[0060] Furthermore, the wound electrode assembly 2 includes a wound electrode sheet 22 in contact with the diaphragm. The length of the polymer layer 3 corresponding to the bending section 12 is L1. The diaphragm has a recessed area and a raised area in the bending section 12. The arc length of the electrode sheet 22 corresponding to the bending section 12 adjacent to the raised area is L2, where L1 and L2 satisfy: L2≥L1≥0.8L2. The length of the polymer layer 3 is designed to match or be less than the arc length of the corner area 21 of the wound electrode assembly 2 because the arc length of the electrode sheet 22 corresponding to the bending section 12 adjacent to the raised area changes with the number of bends of the wound electrode assembly 2. In addition, even if the arc length of the electrode sheet 22 corresponding to the bending section 12 is greater than the length of the polymer layer 3, it can still be ensured that the entire corner area 21 is effectively covered and protected, avoiding stress concentration due to insufficient coverage.

[0061] As a further improvement to the separator of this utility model, the thickness of the base film 1 is D2, where D2 satisfies 3 μm ≤ D2 ≤ 10 μm. In specific implementations, D2 can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or 10 μm, etc. Simultaneously, the selection of the thickness of the base film 1 needs to comprehensively consider the mechanical strength, permeability, and compatibility with the electrolyte of the separator. A thinner base film 1 is beneficial for improving the energy density of the battery, but too thin a film may lead to insufficient mechanical strength, affecting the cycle stability of the battery. Specifically, the thickness of the base film 1 is selected between 3 μm and 10 μm to balance the mechanical strength and ion transport performance of the separator. A thinner base film 1 is beneficial for reducing the overall thickness of the battery and increasing energy density, but too thin a film may reduce its mechanical strength, affecting the cycle stability of the battery. Therefore, selecting a suitable thickness range can ensure the reliability of the separator during winding and use while guaranteeing battery performance.

[0062] Specifically, the length direction (Y direction), thickness direction (X direction), and width direction of the base film 1 are perpendicular to each other. The width of the base film 1 matches the width of the polymer layer 3 and the adhesive layer 4 to ensure a tight fit between the components during battery assembly, preventing misalignment or loosening. The length of the base film 1 is customized according to the battery specifications and design requirements to meet the needs of different application scenarios. In actual production, the length of the base film 1 can be any value, such as 100 mm, 200 mm, 300 mm, or even longer, to accommodate the manufacturing of batteries of different sizes.

[0063] Furthermore, the thickness of the adhesive layer 4 is D3, which satisfies the condition: 3 micrometers ≤ D3 ≤ 10 micrometers. In specific implementations, D3 can be 3 micrometers, 4 micrometers, 5 micrometers, 6 micrometers, 7 micrometers, 8 micrometers, 9 micrometers, or 10 micrometers. The selection of the thickness of the adhesive layer 4 requires comprehensive consideration of its adhesive strength and its impact on the overall battery thickness. A thinner adhesive layer 4 helps reduce its contribution to the battery thickness, but if it is too thin, it may lead to insufficient adhesive strength, affecting the stability of the wound electrode assembly 2. Therefore, selecting a suitable thickness range can ensure adhesive strength while minimizing the increase in the overall battery thickness.

[0064] Other aspects that are the same as in Implementation Method 1 will not be described again in this implementation method.

[0065] Implementation Method 3

[0066] Unlike embodiments 1-2, this application designs a secondary battery comprising the separator described in any of embodiments 1-2, wherein the secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive and negative electrodes are in contact with the separator. Specifically, the positive electrode material of the secondary battery can be lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate (LFP), etc., while the negative electrode material can be graphite, silicon-based materials, or other negative electrode active materials. The electrolyte can be an organic solvent containing lithium salts, such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), etc.

[0067] Furthermore, in the manufacturing process of the secondary battery, the positive electrode material, negative electrode material, and separator are first wound or stacked in a predetermined order, and then the wound or stacked electrode assembly 2 is placed into the battery casing. Next, electrolyte is injected and the casing is sealed. Finally, formation and aging treatments are performed to ensure that the battery performance meets the design requirements.

[0068] Secondly, the secondary battery of this embodiment exhibits excellent cycle stability, thanks to the design of the polymer layer 3 in the corner region 21 of the separator. Since the thickness of the polymer layer 3 in the corner region 21 matches the bending angle (in the preferred embodiment), stress concentration is effectively alleviated during charging and discharging, thereby reducing separation between the electrode 22 and the separator. Furthermore, the design of the adhesive layer 4 ensures good adhesion between the electrode 22 and the separator, further improving the cycle stability of the battery.

[0069] In practical applications, the secondary battery of this embodiment exhibits high energy density and long service life. Due to the optimized thickness of the separator and adhesive layer 4, the overall thickness of the battery is effectively controlled, thereby improving the battery's energy density. Simultaneously, because the structural stability of the corner region 21 is enhanced, the battery maintains good performance during long-term cycle use, extending its service life.

[0070] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A diaphragm suitable for a wound electrode assembly (2) having a bend-shaped corner region (21), characterized in that, The diaphragm includes: The base film (1), in a flattened state, includes a straight section (11) and a section to be bent (12) that are alternately connected in a predetermined direction, and the section to be bent (12) corresponds to the corner area (21); It includes multiple polymer layers (3), which are spaced apart along the length of the base film (1); At least one of the polymer layers (3) is disposed corresponding to the segment to be bent (12).

2. The diaphragm according to claim 1, characterized in that, The section to be bent (12) is coated with the polymer layer (3) on both sides in its thickness direction.

3. The diaphragm according to claim 1, characterized in that, At least one of the straight segments (11) has an adhesive layer (4) coated on at least one surface in its thickness direction.

4. The diaphragm according to claim 3, characterized in that, The polymer layer (3) is coated with an adhesive layer (4) on the side away from the base film (1).

5. The diaphragm according to claim 3, characterized in that, The polymer layer (3) comprises an emulsion of polymer particles; the adhesive layer (4) comprises a ceramic material.

6. The diaphragm according to claim 1, characterized in that, Along the length of the base film (1), the thickness of the polymer layer (3) first increases and then decreases, with the thickness of the polymer layer (3) being the greatest at the center of the section to be bent (12).

7. The diaphragm according to claim 1, characterized in that, The thickness of the polymer layer (3) is D1, and D1 satisfies: 0.5 micrometers ≤ D1 ≤ 10 micrometers.

8. The diaphragm according to claim 1, characterized in that: The wound electrode assembly (2) includes an electrode sheet (22) with a wound structure, the electrode sheet (22) being in contact with the diaphragm; the length of the section to be bent (12) corresponding to the polymer layer (3) is L1, the diaphragm has a recessed area and a raised area in the section to be bent (12), and the arc length of the electrode sheet (22) corresponding to the section to be bent (12) adjacent to the raised area is L2, wherein L1 and L2 satisfy: L2≥L1≥0.8L2.

9. The diaphragm according to claim 3, characterized in that, The thickness of the base film (1) is D2, where D2 satisfies 3 μm ≤ D2 ≤ 10 μm, and the width of the base film (1) is consistent with the width of the polymer layer (3) and the adhesive layer (4); and / or, The thickness of the adhesive layer (4) is D3, and D3 satisfies: 3 micrometers ≤ D3 ≤ 10 micrometers.

10. A secondary battery, characterized in that, Includes the diaphragm as described in any one of claims 1-9.

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