A pole piece, a method for preparing the pole piece, a battery cell and a secondary battery

Abstract

The present invention discloses a pole piece, a method for preparing the pole piece, a battery cell and a secondary battery. The pole piece is provided with embossing, and the depth of the embossing and the thickness of the pole piece satisfy the following relationship: X=0.2273*Z-21.81; wherein X is the depth of the embossing and Z is the thickness of the pole piece. The present invention prepares embossing on the pole piece and reasonably matches the relationship between the depth X of the embossing and the thickness Z of the pole piece, so that when designing the pole piece, as long as the depth X of the embossing and the thickness Z of the pole piece satisfy the specific relationship X=0.2273*Z-21.81, deformation and wrinkling of the pole piece in the battery cell made of the pole piece can be avoided, thereby improving the safety performance and cycle performance of the battery cell.

Description

Technical Field

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

[0002] In recent years, under the general environment of sustainable development, energy strategies are facing major changes. New energy vehicles have become an industry that society and the country focus on, and lithium-ion batteries, as an important component of new energy vehicles, have also been placed with high hopes by the industry.

[0003] During the charging process of the battery, the thickness of the electrode will rebound, causing the stress inside the battery to continue to increase and be unable to be released, eventually leading to deformation of the battery cell and wrinkling of the electrode. Especially in the later stages of the cycle, the deformation of the battery cell and the wrinkling of the electrode will become more and more serious, and may even break, affecting the battery's cycle performance.

[0004] In order to solve the problem of cell deformation and electrode wrinkling, the conventional practice is to prepare embossing on the positive electrode to provide space for the subsequent thickness rebound of the electrode, thereby avoiding cell deformation and electrode wrinkling. However, the current problem is that the depth of the embossing prepared on all positive electrode sheets is the same. For positive electrode sheets of different thicknesses, the improvement effect of this uniform depth of embossing is not the same, resulting in cell deformation and electrode wrinkling even if some positive electrode sheets have been embossed due to inconsistent embossing depth.

[0005] Therefore, it is necessary to study a technology that can determine the required embossing depth for positive electrode sheets of different thicknesses.

[0006] The above information is presented as background information only to assist with understanding the present disclosure and no determination or admission is made as to whether any of the above may be used as prior art with respect to the present disclosure. Summary of the invention

[0007] The present invention provides a pole piece, a method for preparing the pole piece, a battery cell and a secondary battery, so as to solve the problem in the prior art that after the pole piece is made into a battery cell, the battery cell is deformed and the pole piece is wrinkled during the charging process.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a pole piece, on which embossing is prepared, and the depth of the embossing and the thickness of the pole piece satisfy the following relationship:

[0010] X = 0.2273 * Z - 21.81;

[0011] Wherein, X is the depth of embossing and Z is the thickness of the electrode.

[0012] Furthermore, in the pole piece, the embossing is prepared at a position on the pole piece corresponding to a large surface of the battery cell.

[0013] Further, in the pole piece, the embossing includes a plurality of first embossings;

[0014] A plurality of the first embossments are convexly arranged in one direction.

[0015] Further, in the pole piece, the embossing includes a plurality of first embossings and a plurality of second embossings;

[0016] A plurality of the first embossments are convexly arranged in one direction;

[0017] A plurality of the second embossments are protruded toward another direction opposite to the first embossments.

[0018] In a second aspect, the present invention provides a method for preparing a pole piece, which is used to prepare the pole piece as described in the first aspect above, and the method comprises:

[0019] Get the thickness of the pole piece;

[0020] The depth of the embossing to be prepared on the pole piece is determined by calculation according to the thickness of the pole piece and the following relationship: X=0.2273*Z-21.81; wherein X is the depth of the embossing and Z is the thickness of the pole piece;

[0021] The embossing is produced on the pole piece to a determined depth.

[0022] Furthermore, in the method for preparing the pole piece, the method further comprises:

[0023] The calculation results are rounded off.

[0024] Furthermore, in the method for preparing the pole piece, the step of preparing the embossing of a certain depth on the pole piece comprises:

[0025] The embossing is made on the pole piece in one direction or two opposite directions with a certain depth. In a third aspect, the present invention provides a battery cell, comprising a negative pole piece, a separator and a positive pole piece stacked and wound in sequence, wherein the positive pole piece is the pole piece described in the first aspect.

[0026] Furthermore, in the battery cell, the misalignment amount of the tabs of the battery cell, the number of windings, and the depth of the embossing prepared on the positive electrode sheet satisfy the following relationship:

[0027] L = 3.14*X*Y*(Y-1) / 1000;

[0028] Among them, L is the misalignment of the tab, X is the depth of embossing, and Y is the number of winding turns.

[0029] In a fourth aspect, the present invention provides a secondary battery, comprising a battery cell and a shell for accommodating the battery cell, wherein the battery cell is the battery cell as claimed in claim 5.

[0030] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0031] The present invention provides a pole piece, a method for preparing a pole piece, a battery cell and a secondary battery. By preparing embossing on the pole piece and reasonably matching the relationship between the depth X of the embossing and the thickness Z of the pole piece, when designing the pole piece, as long as the depth X of the embossing and the thickness Z of the pole piece satisfy the specific relationship X=0.2273*Z-21.81, deformation and wrinkling of the battery cell made of the pole piece can be avoided, thereby improving the safety performance and cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a schematic diagram of the structure of a pole piece provided in the first embodiment of the present invention;

[0034] Figure 2 is another structural schematic diagram of a pole piece provided by the first embodiment of the present invention;

[0035] Figure 3 This is a disassembly diagram of a battery cell with a pole piece having a thickness of 184 μm in the first embodiment of the present invention;

[0036] Figure 4 This is a disassembly diagram of a battery cell with a pole piece having a thickness of 162 μm in the first embodiment of the present invention;

[0037] Figure 5 It is a schematic flow chart of a method for preparing a pole piece provided in the second embodiment of the present invention.

[0038] Reference numerals:

[0039] Pole piece 1, embossing 2;

[0040] The first embossing 21 and the second embossing 22 . DETAILED DESCRIPTION

[0041] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In the description of the present invention, it is to be understood that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally disposed component. When a component is considered to be "disposed on" another component, it may be directly disposed on the other component or there may be a centrally disposed component.

[0043] In addition, terms such as "long", "short", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention. They do not indicate or imply that the device or component referred to must have this specific direction or operate with a specific direction structure, and should not be understood as a limitation of the present invention.

[0044] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0045] Embodiment 1

[0046] In view of the defects of the above-mentioned existing pole piece technology, the applicant, based on many years of rich practical experience and professional knowledge in the design and manufacture of such products, and in conjunction with the application of theory, actively conducts research and innovation, hoping to create a technology that can solve the defects in the existing technology and make the pole piece more practical. After continuous research and design, and repeated trial production and improvement, the present invention with real practical value was finally created.

[0047] Please refer to Figure 1 , Embodiment 1 of the present invention provides a pole piece, wherein the pole piece 1 is provided with an embossing 2, and the depth of the embossing 2 and the thickness of the pole piece 1 satisfy the following relationship:

[0048] X = 0.2273 * Z - 21.81;

[0049] Wherein, X is the depth of the embossing 2 , and Z is the thickness of the electrode 1 .

[0050] It should be noted that, in the above relationship, the unit of the depth of the embossing 2 is μm, and the unit of the thickness of the pole piece 1 is μm.

[0051] As for how to design a pole piece with the ability to improve winding core deformation and pole piece wrinkling, the applicant found after research that it is not just a simple preparation of embossing 2 on pole piece 1, but a reasonable matching of the relationship between the depth X of embossing 2 and the thickness Z of pole piece 1, because the depth X of embossing 2 and the thickness Z of pole piece 1 influence and restrict each other. When the relationship between them satisfies the relationship: X=O.2273*Z-21.81, a pole piece with the ability to improve winding core deformation and pole piece wrinkling can be finally designed.

[0052] In other words, for pole pieces 1 of different thicknesses Z, as long as the depth X of the embossing 2 prepared accordingly satisfies the relationship X=0.2273*Z-21.81, the battery cell (i.e., winding core) formed by winding the pole piece will basically not deform the battery cell during charging, and the pole piece will basically not wrinkle. Compared with the prior art method of preparing embossing of uniform depth for pole pieces of different thicknesses, this embodiment can ensure that it can effectively improve the effect of pole pieces of different thicknesses, and compared with the method of conducting a large number of tests during the preparation process, this embodiment can achieve the purpose of saving manpower and material resources and being fast and effective.

[0053] If embossing 2 (i.e., convex point) is prepared on the negative electrode sheet, the negative electrode sheet is easy to lose powder before winding. Therefore, before winding, it is generally recommended to prepare embossing 2 on the positive electrode sheet, and the corresponding current collector can be selected from engraved aluminum foil or plain aluminum foil.

[0054] In this embodiment, the embossing 2 is prepared on the pole piece 1 at a position corresponding to the large surface of the battery cell.

[0055] It should be noted that after the core is hot-pressed, the embossing 2 on the electrode 1 corresponding to the large surface of the battery cell will be flattened, and then the area of ​​the embossing 2 will be completely transferred to the corner, thereby improving the deformation of the core and the wrinkling of the electrode.

[0056] As mentioned above, preparing the embossing 2 is actually preparing convex points. In general, the design of the embossing 2 is only convex on one side, but there are also special designs, that is, the embossing 2 is convex on both opposite sides. In view of these two situations, this embodiment further refines the embossing 2, namely:

[0057] In one embodiment, please refer again to Figure 1 , the embossing 2 includes a plurality of first embossings 21;

[0058] A plurality of the first embossments 21 are convexly arranged in one direction.

[0059] It should be noted that, at this time, the depth X of the embossing 2 is equal to the depth of the first embossing 21 .

[0060] In another embodiment, please refer to Figure 2 , the embossing 2 includes a plurality of first embossings 21 and a plurality of second embossings 22;

[0061] A plurality of the first embossments 21 are convexly arranged in one direction;

[0062] A plurality of the second embossments 22 are protruded in another direction opposite to the first embossments.

[0063] It should be noted that, at this time, the depth X of the embossing 2 is equal to the sum of the depth of the first embossing 21 and the depth of the second embossing 22 .

[0064] In order to verify the feasibility of the pole piece design provided in this embodiment, this embodiment first uses the pole piece 1 that satisfies the relationship to prepare a wound structure battery cell, and then conducts a comparative verification experiment, as follows:

[0065] (1) Preparation of positive electrode sheet: The positive electrode formula is NCM: CNT: SP: PVDF mass ratio = 93-98%: 0-1%: 0-1%: 0-2%, mixed and stirred in a mixing tank, and coated on a carved aluminum foil or a plain aluminum foil, and cold pressed. The electrode sheet with a surface density of 300-330 mg / 1540.25 mm2 and a thickness of 184 microns is recorded as P1; the electrode sheet with a surface density of 250-300 mg / 1540.25 mm2 and a thickness of 1 The 62μm pole piece is denoted as P2, the P1 pole piece is prepared with embossing depths of 0, 10, 15, and 20μm respectively (wherein the embossing depth of 20μm is determined by calculation using a relationship), and are denoted as P1-0, P1-10, P1-15, and P1-20 respectively; the P2 pole piece is prepared with embossing depths of 0, 10, and 15μm respectively (wherein the embossing depth of 15μm is determined by calculation using a relationship), and are denoted as P2-0, P2-10, and P2-15 respectively.

[0066] (2) Preparation of negative electrode sheet: The negative electrode material is a carbon-based material, and the negative electrode formula is C:SP:CMC:SBR=95-97%:0-1%:0-1.5%:0-1.5%; it is mixed and stirred in a mixing tank, coated on a foil, and cold pressed, which is recorded as electrode sheet N.

[0067] (3) Preparing battery cells: using a positive electrode sheet and a negative electrode sheet N, winding or stacking the positive and negative electrode sheets and the separator, baking and injecting liquid to form and separate the capacity. The prepared battery cells are respectively denoted as P1-0@N, P1-10@N, P1-15@N, P1-20@N, P2-0@N, P2-10@N, and P2-15@N; and fully charging these battery cells, then disassembling them and performing cycle tests.

[0068] The following Table 1 is a summary of the performance of battery cells formed by electrodes with different embossing depths.

[0069] Table 1: Performance summary of cells formed by electrodes with different embossing depths

[0070] Battery Cell Deformation of battery cells Pole wrinkle condition Cycle number @80% capacity retention P1-0@N Severe deformation Severe wrinkling 2823 P1-10@N Small deformation Slightly wrinkled 3023 P1-15@N Small deformation Slightly wrinkled 3146 P1-20@N No deformation No wrinkles 3325 P2-0@N Severe deformation Severe wrinkling 3124 P2-10@N Small deformation Slightly wrinkled 3386 P2-15@N No deformation No wrinkles 3642

[0071] It can be seen from Table 1 that for electrodes of different thicknesses, when the appropriate embossing depth is calculated using the relationship X=O.2273*Z-21.81, the prepared embossing can ensure that the battery cell is not deformed and the electrode is not wrinkled, thereby ensuring excellent battery cycle performance.

[0072] The specific experimental effect diagram is as follows Figure 3-4 As shown, Figure 3 This is a disassembly diagram of a battery cell with a pole piece with a thickness of 184μm. Figure 4 This is a disassembly diagram of a battery cell with a pole piece that is 162μm thick.

[0073] Although the terms such as pole piece, embossing, current collector, and battery cell are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0074] An embodiment of the present invention provides a pole piece, which prepares embossing on the pole piece and reasonably matches the relationship between the depth X of the embossing and the thickness Z of the pole piece. When designing the pole piece, as long as the depth X of the embossing and the thickness Z of the pole piece satisfy the specific relationship X=0.2273*Z-21.81, deformation and wrinkling of the battery cell made of the pole piece can be avoided, thereby improving the safety performance and cycle performance of the battery cell.

[0075] Embodiment 2

[0076] Please refer to Figure 5 , Figure 5 This is a schematic flow chart of a method for preparing a pole piece provided in the second embodiment of the present invention. The method is applicable to the scenario of preparing embossing on pole pieces of different thicknesses to solve the problem of battery cell deformation and pole piece wrinkling. The method specifically comprises the following steps:

[0077] S101, obtaining the thickness of the electrode.

[0078] S102. Determine the depth of the embossing required to be prepared on the electrode piece by calculation according to the thickness of the electrode piece and the following relationship: X=0.2273*Z-21.81; wherein X is the depth of the embossing, and Z is the thickness of the electrode piece.

[0079] S103, preparing the embossing with a determined depth on the pole piece.

[0080] It should be noted that this embodiment calculates and determines the corresponding embossing depth required for pole pieces of different thicknesses, so that the embossing depth finally prepared thereon is the most appropriate, ensuring that the anti-deformation and anti-wrinkle improvement effect of the embossing is also the best.

[0081] In this embodiment, step S103 can be further refined into the following steps:

[0082] The embossing is made on the pole piece in one direction or in two opposite directions with a determined depth.

[0083] It should be noted that, when embossing is performed in one direction, the embossing depth X is the depth of embossing in one direction; when embossing is performed in two opposite directions, the embossing depth X is the sum of the embossing depths in the two opposite directions.

[0084] In this embodiment, after step S102, the method further includes:

[0085] The calculation results are rounded off.

[0086] It should be noted that the purpose of rounding the calculation result in this embodiment is to reduce the precision loss caused by the intermediate process of calculation.

[0087] A method for preparing a pole piece provided in an embodiment of the present invention first substitutes the thickness of the pole piece into the relationship X=0.2273*Z-21.81 to calculate and determine the depth of embossing required for the pole piece, and then prepares the embossing of the determined depth on the pole piece, so that the depth of embossing required for pole pieces of different thicknesses can be calculated quickly and accurately, thereby avoiding deformation of the battery cell and wrinkling of the pole piece, thereby ensuring the cycle performance of the battery.

[0088] Embodiment 3

[0089] An embodiment of the present invention provides a battery cell, comprising a negative electrode plate, a separator and a positive electrode plate stacked in sequence, wherein the positive electrode plate is the plate as described in the first embodiment above.

[0090] The battery cell is formed by winding the positive electrode sheet, the separator and the negative electrode sheet.

[0091] It should be noted that this embodiment only improves the positive electrode plate, thereby improving the problems of battery cell deformation and electrode plate wrinkling, while the negative electrode plate and diaphragm are still consistent with conventional technology. In view of the fact that these designs have been implemented in many existing technologies and are not the focus of this design, they will not be elaborated in depth here.

[0092] In this embodiment, the misalignment amount of the tabs of the battery cell, the number of windings, and the depth of the embossing prepared on the positive electrode sheet satisfy the following relationship:

[0093] L = 3.14*X*Y*(Y-1) / 1000;

[0094] Among them, L is the misalignment of the tab, X is the depth of embossing, and Y is the number of winding turns.

[0095] It should be noted that in the above relationship, the unit of the amount of misalignment of the pole tab is mm, and the unit of the depth of the embossing is μm. As mentioned above, after the core is hot-pressed, the embossing will be flattened, and then the embossing area will be completely transferred to the corners to improve the deformation of the core and the wrinkling of the pole piece. Therefore, in order to avoid the misalignment of the pole tabs caused by the transfer of the embossing area, this embodiment further designs the pole tabs of the battery cell to have a misalignment, and the amount of misalignment L of the pole tab needs to satisfy the relationship L = 3.14*X*Y*(Y-1) / 1000 with the number of winding turns Y of the battery cell and the depth X of the embossing prepared on the positive pole piece.

[0096] For example, if the number of winding turns Y of the battery cell is 34 and the embossing depth X is 10 μm, then calculation shows that the tab misalignment of the battery cell needs to be designed to be 35.23 mm.

[0097] An embodiment of the present invention provides a battery cell, which prepares embossing on a positive electrode sheet and reasonably matches the relationship between the embossing depth X and the thickness Z of the sheet, so that when designing the positive electrode sheet, as long as the embossing depth X and the thickness Z of the sheet satisfy the specific relationship X=0.2273*Z-21.81, deformation of the battery cell made of the positive electrode sheet and wrinkling of the sheet can be avoided, thereby improving the safety performance and cycle performance of the battery cell.

[0098] Embodiment 4

[0099] An embodiment of the present invention provides a secondary battery, comprising a battery cell and a shell for accommodating the battery cell, wherein the battery cell is the battery cell as described in the third embodiment above.

[0100] It should be noted that the secondary battery should also include necessary component designs such as electrolyte and top cover. The specific function of these component designs is to ensure the normal operation of various functions of the secondary battery. In view of the fact that these component designs have been implemented in many existing technologies and are not the focus of this design, they will not be elaborated in depth here.

[0101] In addition, the secondary battery in this embodiment can be used in electronic devices such as electronic devices, electric vehicles or power storage systems, but is not limited to it. Among them, the electronic device can be, for example, various computers, mobile phones, display screens and other equipment that use secondary batteries as driving power sources. Electric vehicles can be, for example, electric cars, electric tricycles, electric bicycles, etc. that use secondary batteries as driving power sources. The power storage system can be, for example, a power storage system that uses secondary batteries as power storage sources.

[0102] In these electronic devices, the secondary battery can be electrically connected to the electrical components to provide electrical energy to the electrical components. Since the fast charging capability of the secondary battery provided in this application is relatively excellent, it is conducive to the use of electronic devices in application scenarios such as outdoor energy storage, short-term backup power and mobile energy storage, thereby making the application scenarios of electronic devices more extensive.

[0103] A secondary battery provided by an embodiment of the present invention prepares embossing on a positive electrode sheet and reasonably matches the relationship between the depth X of the embossing and the thickness Z of the sheet, so that when designing the positive electrode sheet, as long as the depth X of the embossing and the thickness Z of the sheet satisfy the specific relationship X=0.2273*Z-21.81, deformation of the battery cell made of the positive electrode sheet and wrinkling of the sheet can be avoided, thereby improving the safety performance and cycle performance of the battery cell.

[0104] In summary, after reading this detailed disclosure, it will be apparent to those skilled in the art that the aforementioned detailed disclosure may be presented only by way of example and may not be restrictive. Although not explicitly stated herein, it will be appreciated by those skilled in the art that this application is intended to encompass various reasonable changes, improvements and modifications to the embodiments. These changes, improvements and modifications are intended to be proposed by this application and are within the spirit and scope of the exemplary embodiments of this application.

[0105] In addition, certain terms in this application have been used to describe embodiments of the present application. For example, "one embodiment", "embodiment" and / or "some embodiments" mean that a particular feature, structure or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. Therefore, it can be emphasized and should be understood that two or more references to "embodiment" or "one embodiment" or "alternative embodiment" in various parts of this specification do not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics may be appropriately combined in one or more embodiments of the present application.

[0106] It should be understood that in the foregoing description of the embodiments of the present application, in order to help understand a feature and for the purpose of simplifying the present application, the present application combines various features in a single embodiment, drawing or its description. However, this does not mean that the combination of these features is necessary. When reading the present application, it is entirely possible for a person skilled in the art to extract some of the features and understand them as separate embodiments. In other words, the embodiments in the present application can also be understood as the integration of multiple secondary embodiments. This is also true when the content of each secondary embodiment is less than all the features of a single aforementioned disclosed embodiment.

[0107] Each patent, patent application, patent application publication, and other materials, such as articles, books, specifications, publications, documents, articles, etc., cited herein may be incorporated herein by reference in its entirety for all purposes, except for any prosecution document history related thereto, any equivalent that may be inconsistent or conflicting with this document, or any equivalent prosecution document history that may have a limiting effect on the broadest scope of the claims now or later associated with this document. For example, if there is any inconsistency or conflict between the description, definition, and / or use of a term associated with any of the incorporated materials and the term, description, definition, and / or use associated with this document, the term in this document shall control.

[0108] Finally, it should be understood that the embodiments of the application disclosed herein are explanations of the principles of the embodiments of the present application. Other modified embodiments are also within the scope of the present application. Therefore, the embodiments disclosed in the present application are merely examples and not limitations. Those skilled in the art can adopt alternative configurations according to the embodiments in the present application to implement the application in the present application. Therefore, the embodiments of the present application are not limited to the embodiments accurately described in the application.

Claims

1. A battery cell, characterized in that: The invention comprises a negative electrode sheet, a separator and a positive electrode sheet which are sequentially stacked and wound, wherein the positive electrode sheet is provided with embossing and a tab, and the misalignment amount of the tab, the number of windings of the positive electrode sheet and the depth of the embossing satisfy the following relationship: L=3.14*X*Y*(Y-1) / 1000; Among them, L is the misalignment of the tab, in mm, X is the depth of embossing, in μm, and Y is the number of windings of the positive electrode sheet.

2. The battery cell according to claim 1, characterized in that: The depth of the embossing and the thickness of the positive electrode sheet satisfy the following relationship: X=0.2273*Z-21.81; Wherein, X is the depth of embossing, in μm, and Z is the thickness of the positive electrode sheet, in μm.

3. The battery cell according to claim 1, characterized in that: The embossing is prepared at a position on the positive electrode sheet corresponding to the large surface of the battery cell.

4. The battery cell according to claim 1, 2 or 3, characterized in that: The embossing includes a plurality of first embossings; A plurality of the first embossments are convexly arranged in one direction.

5. The battery cell according to claim 1, 2 or 3, characterized in that: The embossing includes a plurality of first embossings and a plurality of second embossings; A plurality of the first embossments are convexly arranged in one direction; A plurality of the second embossments are protruded toward another direction opposite to the first embossments.

6. A method for preparing a pole piece, used for preparing a positive pole piece in a battery cell as claimed in any one of claims 1 to 5, characterized in that: The method comprises: Get the thickness of the positive electrode sheet; The depth of the embossing to be prepared on the positive electrode sheet is determined by calculating according to the thickness of the positive electrode sheet and the following relationship: X=0.2273*Z-21.81; wherein X is the depth of the embossing and Z is the thickness of the positive electrode sheet; The embossing with a determined depth is prepared on the positive electrode sheet.

7. The method for preparing a pole piece according to claim 6, characterized in that: The method further comprises: The calculation results are rounded off.

8. The method for preparing a pole piece according to claim 6, characterized in that: The step of preparing the embossing of a certain depth on the positive electrode sheet comprises: The embossing with a determined depth is prepared on the positive electrode sheet in one direction or two opposite directions.

9. A secondary battery, comprising a battery cell and a shell for accommodating the battery cell, characterized in that: The battery cell is the battery cell according to any one of claims 1 to 5.

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