Patterned positive electrode sheet for winding type square can, method for manufacturing the same, winding type square can, and secondary battery

Abstract

The application relates to the technical field of secondary batteries, in particular to a patterned positive pole piece of a winding type square shell battery cell and a preparation method of the winding type square shell battery cell, a winding type square shell battery cell and a secondary battery. The positive pole piece is provided with a patterned surface on a semicircle of an R angle of the winding type square shell battery cell and on a large surface of the winding type square shell battery cell. In the length direction of the positive pole piece, the width D2 of the patterned surface formed by the positive pole piece on the large surface of the winding type square shell battery cell is 3-50 mm. The positive pole piece provided by the application is provided with the patterned surface on the semicircle of the R angle of the winding type square shell battery cell and on the large surface of the winding type square shell battery cell, and the width D2 of the patterned surface formed by the positive pole piece on the large surface of the winding type square shell battery cell is 3-50 mm, so that the cycle life of a lithium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a patterned positive electrode sheet of a wound square can battery cell, a preparation method thereof, a wound square can battery cell and a secondary battery. BACKGROUND

[0002] In order to improve the consistency of the thickness of the positive electrode sheet and increase the expansion space of the battery cell, a patterned roller (P roller) is used to roll the positive electrode sheet during winding, the rolling pattern is increased to increase the expansion space of the battery cell and improve the performance of the battery cell.

[0003] In the prior art, the rolling of the P roller on the positive electrode sheet is usually uniform and full coverage. Although this method is simple, it increases the expansion space of the entire battery cell, but the stress concentration degree of each part of the wound core is actually different, especially the R angle part. The battery cell obtained by the rolling method of the prior art will still preferentially start to fail at the R angle part during long-term use, resulting in a short cycle life of the lithium ion battery.

[0004] Therefore, how to improve the cycle life of the wound square can lithium ion battery is a technical problem to be solved in the art. SUMMARY

[0005] In view of the above problems in the prior art, the present application provides a patterned positive electrode sheet of a wound square can battery cell, a preparation method thereof, a wound square can battery cell and a secondary battery. The positive electrode sheet has a patterned surface on the semicircle of the R angle of the wound square can battery cell and on the large surface of the wound square can battery cell. The width D2 of the patterned surface formed on the large surface of the wound square can battery cell is 3-50 mm, which can improve the cycle life of the lithium ion battery.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a patterned positive electrode sheet of a wound square can battery cell. The positive electrode sheet has a patterned surface on the semicircle of the R angle of the wound square can battery cell and on the large surface of the wound square can battery cell. In the length direction of the positive electrode sheet, the width D2 of the patterned surface formed on the large surface of the wound square can battery cell is 3-50 mm.

[0008] The positive electrode sheet provided by the present application has a patterned surface on the semicircle of the R angle of the wound square can battery cell and on the large surface of the wound square can battery cell. The width D2 of the patterned surface formed on the large surface of the wound square can battery cell is 3-50 mm, which can improve the cycle life of the lithium ion battery.

[0009] Further, the width D3 of the pattern surface formed by the positive electrode tab in the length direction of the positive electrode tab is the same for different turns.

[0010] Further, the width D2 of the pattern surface formed by the positive electrode tab in the length direction of the positive electrode tab is the same for different turns.

[0011] Further, the center positions of the R corners of different layers of the wound square shell battery are in the same plane.

[0012] Further, the wound square shell battery comprises the patterned positive electrode tab, the negative electrode tab and the separator, the distance from the center position of the R corner of the wound square shell battery to the top end position of the R corner half circle is D1, D1=(a+b+c+d)*X*π / 2, wherein a is the thickness of the positive electrode tab, b is the thickness of the negative electrode tab, c is the thickness of the separator, d is the air gap value, and X is the number of turns.

[0013] Further, the d is 0-20 μm and not 0.

[0014] Further, the width D3 of the pattern surface formed by the positive electrode tab in the length direction of the positive electrode tab is the same for different turns.

[0015] Further, the ratio of the D3 of different turns to the D1 is equal.

[0016] Further, the positive electrode tab further comprises a full-coverage pattern surface, which fully covers the one side of the positive electrode tab on which the pattern surface is formed in the R corner half circle and the large surface of the wound square shell battery.

[0017] Further, the shape of the pattern includes but is not limited to at least one of a round hole, a triangle and a square.

[0018] Further, the shape of the pattern is a concave uniformly distributed round hole, the diameter of the round hole is 1-5 mm, and the depth is 1-15 μm.

[0019] In the second aspect, the application provides a preparation method of the patterned positive electrode tab of the wound square shell battery according to the first aspect, which comprises the following steps:

[0020] In the winding of the positive electrode tab body, the positive electrode tab body is subjected to embossing treatment on the R corner half circle and the large surface of the wound square shell battery, so that the pattern surface is formed on the positive electrode tab body.

[0021] Further, after the embossing treatment, an additional embossing treatment is performed on the entire patterned positive electrode tab to form the full-coverage patterned surface;

[0022] And / or, the positive electrode tab body is embossed using a P roller;

[0023] And / or, the positive electrode tab body includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector, wherein the active material of the positive electrode active material layer includes at least one of lithium iron phosphate, ternary material, lithium cobaltate, and lithium nickelate.

[0024] In a third aspect, the present application provides a wound square can cell, which includes the patterned positive electrode tab of the first aspect or is prepared by the preparation method of the second aspect.

[0025] In a fourth aspect, the present application provides a secondary battery, which includes the wound square can cell of the third aspect.

[0026] Compared with the prior art, the present application has at least one of the following advantages:

[0027] (1) The positive electrode tab provided by the present application has a patterned surface formed on the semicircle of the R angle of the wound square can cell and on the large surface of the wound square can cell, and the width D2 of the patterned surface formed by the positive electrode tab on the large surface of the wound square can cell is 3-50 mm, which can improve the cycle life of the lithium ion battery.

[0028] (2) The positive electrode tab provided by the present application can improve the problem of local stress being too high at the top of the R angle of the wound square can cell, and reduce the risk of cell swelling and deformation.

[0029] (3) The positive electrode tab provided by the present application can improve the performance of the produced battery, leave more space for the position that is easily stressed, avoid the electrolyte from being squeezed out during the cycle process, and improve the consistency and cycle performance of the battery, etc.

[0030] (4) Combined with the conventional P roller process, the range of expandable space is increased, which can take into account different tension and expansion force requirements. BRIEF DESCRIPTION OF DRAWINGS

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the patterned positive electrode sheet of the wound square-shell battery cell provided by the present invention in its unfolded state.

[0033] Figure 2 A schematic diagram of the patterned positive electrode sheet of the wound square-shell battery cell provided by the present invention in the wound state;

[0034] Figure 3 The capacity decay trend of lithium-ion batteries prepared by wound square-shell cells provided for embodiments and comparative examples of the present invention at 1C. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0036] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0037] Firstly, such as Figure 1 and Figure 2 As shown, the present invention provides a patterned positive electrode sheet for a wound square-shell battery cell. The positive electrode sheet has a patterned surface formed on the semicircle of the R-corner of the wound square-shell battery cell and on the large surface of the wound square-shell battery cell. In the length direction of the positive electrode sheet, the width D2 of the patterned surface formed by the positive electrode sheet on the large surface of the wound square-shell battery cell is 3 to 50 mm, for example, it can be 3 mm, 10 mm, 20 mm, 30 mm, 40 mm or 50 mm.

[0038] Here, the surface with the largest area of ​​the wound square-shell battery cell is defined as the large surface of the battery cell.

[0039] The positive electrode sheet provided by the present invention forms a patterned surface on the semicircle of the R-corner of the wound square battery cell and on the large surface of the wound square battery cell. The width D2 of the patterned surface formed by the positive electrode sheet on the large surface of the wound square battery cell is 3 to 50 mm. This can improve the problem of excessive local stress at the top of the R-corner of the wound battery cell, reduce the risk of cell expansion and deformation, and thus improve the cycle life of the lithium-ion battery.

[0040] In the above-mentioned patterned positive electrode of the wound square battery cell, as an optional embodiment, the width D3 of the patterned surface formed by different turns of the positive electrode on the semicircle of the R-corner of the wound square battery cell is the same in the length direction of the positive electrode.

[0041] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the width D2 of the patterned surface formed by different turns of the positive electrode sheet on the large surface of the wound square-shell battery cell is the same in the length direction of the positive electrode sheet.

[0042] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the center positions of the R-angles of different layers of the wound square-shell battery cell are on the same plane.

[0043] In the above-mentioned patterned positive electrode of the wound square-shell battery cell, as an optional embodiment, the wound square-shell battery cell includes the patterned positive electrode, negative electrode, and separator. The distance from the center of the R-angle of the wound square-shell battery cell to the top of the semicircle of the R-angle is D1, where D1 = (a + b + c + d) * X * π / 2, where a is the thickness of the positive electrode, b is the thickness of the negative electrode, c is the thickness of the separator, d is the air gap value, and X is the number of turns.

[0044] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the d is 0 to 20 μm and is not 0, for example, it can be 1 μm, 3 μm, 5 μm, 10 μm, 15 μm or 20 μm.

[0045] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the width of the patterned surface formed by the positive electrode sheet on the semicircle of the R-angle of the wound square-shell battery cell in the length direction of the positive electrode sheet is D3, wherein D3 satisfies: 0≤D3≤D1 in the first to third turns; 0<D3≤D1 when the number of turns is not less than 4 turns, that is, 0≤D3≤D1 in the first three turns (including the third turn), and 0<D3≤D1 from the fourth turn onwards.

[0046] In the above-mentioned patterned positive electrode of the wound square-shell battery cell, as an optional implementation, the ratio of D3 to D1 in different turns is equal.

[0047] In the aforementioned patterned positive electrode sheet of the wound prismatic battery cell, as an optional embodiment, a fully covered patterned surface is also formed on the positive electrode sheet. This fully covered patterned surface completely covers the semicircle of the radius (R-angle) of the wound prismatic battery cell and the side of the large surface of the wound prismatic battery cell where the patterned surface is formed. This is equivalent to forming the pattern using a P-roller at key local locations, and then performing another P-roller pressing on the entire electrode sheet, ensuring greater expansion space at the radius (R-angle). This embodiment of the invention provides sufficient expansion space for the entire wound core and also solves the problem of localized stress.

[0048] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the shape of the pattern includes, but is not limited to, at least one of round hole shape, triangle shape, and square shape.

[0049] In the above-mentioned patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, the pattern is a concave and uniformly distributed circular hole shape, the diameter of the circular hole is 1-5mm (for example, it can be 1mm, 2mm, 3mm, 4mm, 5mm), and the depth is 1-15μm (for example, it can be 1μm, 3μm, 5μm, 7μm, 11μm, 13μm or 15μm).

[0050] In a second aspect, the present invention provides a method for preparing a patterned positive electrode sheet of a wound prismatic battery cell as described in the first aspect, the method comprising the following steps:

[0051] When winding the positive electrode body, the positive electrode body on the semicircle of the R-corner and the large surface of the wound square-shell battery cell is embossed to form a patterned surface on the positive electrode body.

[0052] In the above-mentioned method for preparing the patterned positive electrode sheet of the wound square-shell battery cell, as an optional embodiment, after the embossing process, the entire patterned positive electrode sheet is subjected to an additional embossing process to form the full-coverage patterned surface.

[0053] In the above-mentioned method for preparing the positive electrode sheet, as an optional implementation, a P-roller is used to emboss the positive electrode sheet body.

[0054] In the above-mentioned method for preparing the positive electrode sheet, as an optional embodiment, the positive electrode sheet body includes a positive current collector and a positive active material layer, wherein the positive active material layer is coated on the surface of the positive current collector.

[0055] In the above-mentioned method for preparing the positive electrode sheet, as an optional embodiment, the active material of the positive electrode active material layer includes at least one of lithium iron phosphate, ternary materials, lithium cobalt oxide, and lithium nickel oxide.

[0056] Here, the preparation method of the positive electrode body is a conventional preparation method, specifically: the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and the positive electrode body is obtained after baking, cold pressing and cutting.

[0057] Thirdly, the present invention provides a wound square-shell battery cell, the wound square-shell battery cell comprising the patterned positive electrode sheet described in the first aspect, or the patterned positive electrode sheet prepared by the preparation method described in the second aspect.

[0058] In the above-mentioned wound square-shell battery cell, as an optional embodiment, the wound square-shell battery cell further includes a negative electrode sheet and a separator, and the wound square-shell battery cell is made by winding the positive electrode sheet, the negative electrode sheet and the separator.

[0059] In the above-mentioned wound square-shell battery cell, as an optional embodiment, the R-angle centers of different layers of the wound square-shell battery cell are located on the same plane.

[0060] In the above-mentioned wound square-shell battery cell, as an optional embodiment, the distance from the center position of the R-corner of the wound square-shell battery cell to the top position of the semicircle of the R-corner is D1, where D1 = (a + b + c + d) * X * π / 2, where a is the thickness of the positive electrode, b is the thickness of the negative electrode, c is the thickness of the separator, d is the air gap value, and X is the number of turns of winding.

[0061] In the above-mentioned wound square-shell battery cell, as an optional embodiment, the d is 0 to 20 μm, for example, it can be 1 μm, 3 μm, 5 μm, 10 μm, 15 μm or 20 μm.

[0062] Fourthly, the present invention provides a secondary battery, the secondary battery comprising the wound prismatic cell described in the third aspect.

[0063] Specifically, the battery can be a lithium-ion battery.

[0064] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0065] The active material of the positive electrode is lithium iron phosphate, the active material of the negative electrode is graphite, and the separator is 9μm PE + 2μm PVDF + 2μm Al2O3.

[0066] The distance from the center of the R-corner of the wound square-shell battery cell to the top of the semicircular R-corner is D1, where D1 = (a + b + c + d) * X * π / 2, where a is the thickness of the positive electrode, b is the thickness of the negative electrode, c is the thickness of the separator, d is the air gap value, and X is the number of turns of winding, and d is 0 to 20 μm and not 0.

[0067] Example 1

[0068] This embodiment provides a wound square-shell battery cell, which includes a patterned positive electrode, a negative electrode, and a separator. The patterned positive electrode has a patterned surface formed on the semicircle of the radius (R-angle) of the wound square-shell battery cell and on the large surface of the wound square-shell battery cell. The wound square-shell battery cell has two large surfaces. The pattern is a circular pit with a diameter of 2 mm and a depth of 8 μm. In the length direction of the patterned positive electrode, the width of the patterned surface formed by the positive electrode on the large surface of the wound square-shell battery cell is D2, and the width of the patterned surface formed by the positive electrode on the semicircle of the radius (R-angle) of the wound square-shell battery cell is D3. D3 is 5 mm for different loops (especially when the inner loop D1 area is less than 5 mm, D3 = D1), and D2 is 30 mm for different loops. The patterned positive electrode sheet is wound around the central axis 30 times, for a total of 60 layers. The width of the wound square-shell battery cell (generally referring to the maximum width in the industry, including the R-angle, i.e., the center distance between the two R-angles) is 210mm. The thickness of the wound square-shell battery cell is 20mm. The R-angle centers of different layers are on the same plane.

[0069] The method for preparing a wound prismatic battery cell provided in this embodiment includes the following steps: preparing the wound prismatic battery cell by winding a negative electrode sheet, the patterned positive electrode sheet, and a separator, wherein the method for preparing the patterned positive electrode sheet includes: when winding the positive electrode sheet body, according to... Figure 1 Method (shaded area is P-roller pressing area): P-roller is used to emboss the positive electrode body on the semicircle of the R-corner of the wound square-shell battery cell and on the large surface of the battery cell, so that a patterned surface is formed on the positive electrode body. The pressure of P-roller is 0.3 MPa. The positive electrode body includes aluminum foil and a positive active material layer, and the positive active material layer is coated on the surface of the aluminum foil.

[0070] Example 2

[0071] The wound square-shell battery cell provided in this embodiment is basically the same as that in embodiment 1. The difference is that a fully covered patterned surface is also formed on the patterned positive electrode sheet. The fully covered patterned surface fully covers the positive electrode sheet on the semicircle of the R-corner of the wound square-shell battery cell and the side of the large surface of the wound square-shell battery cell where the patterned surface is formed.

[0072] The preparation method of the wound square-shell battery cell provided in this embodiment is basically the same as that in Embodiment 1. The difference is that, in the preparation process of the patterned positive electrode sheet, after the positive electrode sheet body on the semicircle of the R corner of the wound square-shell battery cell and the large surface of the battery cell is embossed by a P roller, the patterned positive electrode sheet is subjected to an additional P roller pressing to form the full-coverage patterned surface. The P roller is designed with a pressure of 0.3 MPa, and the diameter of the circular pit formed by the rolling is 2 mm and the depth is 8 μm.

[0073] Example 3

[0074] The wound square-shell battery cell provided in this embodiment is basically the same as that in Embodiment 1, except that the ratio of D3 to D1 in different turns is 1:3.

[0075] The wound square-shell battery cell provided in this embodiment is prepared according to the preparation method of the wound square-shell battery cell provided in Example 1.

[0076] Example 4

[0077] The wound square-shell battery cell provided in this embodiment is basically the same as that in embodiment 1, except that the ratio of D3 to D1 in different turns is 1:1.

[0078] The wound square-shell battery cell provided in this embodiment is prepared according to the preparation method of the wound square-shell battery cell provided in Example 1.

[0079] Example 5

[0080] The wound square-shell battery cell provided in this embodiment is basically the same as that in Embodiment 1, except that D2 is 10mm.

[0081] The wound square-shell battery cell provided in this embodiment is prepared according to the preparation method of the wound square-shell battery cell provided in Example 1.

[0082] Example 6

[0083] The wound square-shell battery cell provided in this embodiment is basically the same as that in Embodiment 1, except that D2 is 50mm.

[0084] The wound square-shell battery cell provided in this embodiment is prepared according to the preparation method of the wound square-shell battery cell provided in Example 1.

[0085] Comparative Example 1

[0086] This comparative example provides a method for preparing a wound square-shell battery cell. The method includes the following steps: preparing the wound square-shell battery cell by winding a negative electrode sheet, a patterned positive electrode sheet, and a separator. The method for preparing the patterned positive electrode sheet includes: during the winding of the positive electrode sheet body, using a P-roller to emboss the entire positive electrode sheet body according to industry conventions, forming a patterned surface on the positive electrode sheet body. The pressure of the P-roller is 0.3 MPa. The positive electrode sheet body includes an aluminum foil and a positive active material layer. The positive active material layer is coated on the surface of the aluminum foil. The pattern is a circular pit with a diameter of 2 mm and a depth of 8 μm. The patterned positive electrode sheet is wound around the central axis 30 times, for a total of 60 layers. The width of the wound square-shell battery cell is 210 mm, and the thickness of the wound square-shell battery cell is 20 mm. The center positions of the R-corners of different layers are on the same plane.

[0087] Comparative Example 2

[0088] The wound square-shell battery cell provided in this embodiment is basically the same as that in Embodiment 1, except that D2 is 80mm.

[0089] The wound square-shell battery cell provided in this embodiment is prepared according to the preparation method of the wound square-shell battery cell provided in Example 1.

[0090] Performance testing

[0091] The wound prismatic cells provided in the examples and comparative examples were assembled into lithium-ion batteries using conventional methods. The cycle performance of these lithium-ion batteries was then tested, and the testing process is as follows:

[0092] 1) The temperature was maintained at 45℃ for 5 hours to reach thermal equilibrium;

[0093] 2) Charge to 3.65V using 1C constant current and constant voltage, with a cutoff current of 0.05C (1C = 1 times the rated capacity current);

[0094] 3) Let stand for 60 minutes;

[0095] 4) Discharge at a constant current of 1C to 2.5V;

[0096] 5) Let stand for 60 minutes; 6) Repeat steps 2)-5) until the capacity retention rate is less than 80% at 1C.

[0097] A capacity decay trend graph is plotted based on the relationship between the number of cycles and the 1C capacity retention rate, such as... Figure 3 As shown.

[0098] Depend on Figure 3 At least the following points can be observed:

[0099] (1) The comparison results of the above embodiments and Comparative Example 1 show that the present invention can significantly improve the lithium plating and cycle drop caused by excessive expansion and stress at the local position of the R corner in the later stage of the cycle, and has a significant effect on improving the cycle life and safety performance of the wound square shell battery cell.

[0100] (2) Comparing Example 1 and Comparative Examples 1-2, it can be seen that if D2 is too large, it cannot improve the lithium plating and cycle drop caused by excessive expansion and stress at the local position of R corner in the later stage of the cycle.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A patterned positive electrode sheet for a wound square-shell battery cell, characterized in that, The positive electrode sheet has a patterned surface formed on the semicircle of the R-corner of the wound square battery cell and on the large surface of the wound square battery cell. In the length direction of the positive electrode sheet, the width D2 of the patterned surface formed by the positive electrode sheet on the large surface of the wound square battery cell is 3~50mm. Along the length of the positive electrode sheet, the width D3 of the patterned surface formed by different turns of the positive electrode sheet on the semicircle of the R-corner of the wound square-shell battery cell is the same. Along the length of the positive electrode sheet, the width D2 of the patterned surface formed by different turns of the positive electrode sheet on the large surface of the wound square-shell battery cell is the same.

2. The patterned positive electrode sheet of the wound square-shell battery cell according to claim 1, characterized in that, Along the length of the positive electrode plate, The center positions of the radius (R-angle) of different layers of the wound square-shell battery cell are on the same plane.

3. The patterned positive electrode sheet of the wound square-shell battery cell according to claim 1, characterized in that, The wound square-shell battery cell includes the patterned positive electrode, negative electrode, and separator. The distance from the center of the R-corner of the wound square-shell battery cell to the top of the semicircle of the R-corner is D1, where D1 = (a + b + c + d) × X × π / 2, where a is the thickness of the positive electrode, b is the thickness of the negative electrode, c is the thickness of the separator, d is the air gap value, and X is the number of turns.

4. The patterned positive electrode sheet of the wound square-shell battery cell according to claim 3, characterized in that, The value of d is 0~20μm and is not 0; And / or, in the length direction of the positive electrode sheet, the width of the patterned surface formed by the positive electrode sheet on the semicircle of the R-corner of the wound square-shell battery cell is D3, wherein D3 satisfies: 0 < D3 < D1.

5. The patterned positive electrode sheet of the wound square-shell battery cell according to claim 1, characterized in that, The shape of the pattern includes at least one of round holes, triangles, and squares; And / or, the pattern is a concave, uniformly distributed circular hole, the diameter of which is 1-5 mm and the depth is 1-15 μm.

6. A method for preparing the patterned positive electrode sheet of a wound prismatic battery cell as described in any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: When winding the positive electrode body, the positive electrode body on the semicircle of the R-corner and the large surface of the wound square-shell battery cell is embossed to form a patterned surface on the positive electrode body.

7. The method for preparing the patterned positive electrode sheet of the wound square-shell battery cell according to claim 6, characterized in that, The positive electrode sheet body is embossed using a P-roller; And / or, the positive electrode body includes a positive current collector and a positive active material layer, wherein the positive active material layer is coated on the surface of the positive current collector, and the active material of the positive active material layer includes at least one of lithium iron phosphate, ternary materials, lithium cobalt oxide, and lithium nickel oxide.

8. A wound square-shell battery cell, characterized in that, The wound square-shell battery cell includes the patterned positive electrode sheet according to any one of claims 1 to 5, or the patterned positive electrode sheet prepared by the preparation method according to claim 6 or 7.

9. A secondary battery, the secondary battery comprising the wound prismatic cell of claim 8.

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