A positive electrode sheet, a method for manufacturing the same, and a lithium ion battery

Abstract

The application provides a positive electrode sheet, a preparation method thereof and a lithium ion battery. The positive electrode sheet comprises a foil and an active material layer arranged on at least one side surface of the foil. A first thinning area is arranged inward along one side long edge of the active material layer. A second thinning area is arranged inward along the other side long edge of the active material layer. The area of the first thinning area is greater than or equal to the area of the second thinning area. The active material layer in the first thinning area is a first thinning layer. The active material layer in the second thinning area is a second thinning layer. The thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer. An electrode lug groove is arranged in the first thinning layer, and the surface of the foil is exposed in the electrode lug groove. The positive electrode sheet has high mechanical strength and low risk of lithium precipitation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a positive electrode sheet, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the continuous improvement of living standards, the demand for lithium ion batteries is increasing, and therefore it is urgent to improve the performance of lithium ion batteries to meet the demand.

[0003] CN112582583A discloses a preparation method of a fast-charging lithium ion battery electrode sheet, which comprises the following operations: coating a slurry with an active material on both surfaces of a current collector to obtain an electrode sheet with symmetrically arranged first and second active material layers; rolling both surfaces of the electrode sheet; and cleaning the excess first active material layer to obtain a fast-charging lithium ion battery electrode sheet with double-sided coating areas and a single-sided coating area. The method controls the thickness of the active material layer to make the electrode sheet suitable for fast charging.

[0004] In addition to the above method, the charging speed can also be improved by using a tab centering structure, but there are still problems with this structure. When cutting the entire electrode sheet, there is no way to cut exactly to the edge of the tab slot due to tolerances, so a small amount of active material will be left on one side edge of the tab slot. When the tab slot is connected to the tab, the thickness increases, affecting the performance. The active material on the edge can be punched out to form a notch to avoid the increase in thickness when the tab slot is connected to the tab, but this will reduce the mechanical strength of the electrode sheet. In addition, the tab slot of the positive electrode sheet has a high current density, which makes it prone to lithium precipitation, which is not conducive to the operation of the battery.

[0005] Therefore, it is urgent to solve the problems of low mechanical strength of the positive electrode sheet and lithium precipitation. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a positive electrode sheet, a preparation method thereof and a lithium ion battery. The positive electrode sheet of the present application adopts a tab centering structure, and when the tab slot is connected to the tab, there is no thickness superposition, which can improve the flatness of the battery cell. Moreover, the electrode sheet of the present application has no notch, which can improve the mechanical strength of the electrode sheet. In addition, the thinning layer around the tab slot can reduce the risk of lithium precipitation caused by the large current density at the tab site and reduce lithium precipitation.

[0007] To achieve this purpose, the following technical solutions are adopted in the present application:

[0008] In a first aspect, the present application provides a positive electrode sheet, which comprises a foil and an active material layer arranged on at least one side surface of the foil, a first thinning area is arranged inward along one long side of the active material layer, a second thinning area is opened inward along the other long side of the active material layer, and the area of the first thinning area is greater than or equal to the area of the second thinning area.

[0009] The active material layer in the first thinning area is a first thinning layer, and the active material layer in the second thinning area is a second thinning layer, and the thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer.

[0010] An inner portion of the first thinning layer is provided with a tab slot, and a surface of the foil is exposed by the tab slot.

[0011] The application provides a positive electrode tab with a tab centering structure, a first thinning area is provided on the surface of the tab, and a tab slot is provided in the inner portion of the first thinning area. The tab slot can be directly connected to the tab, without thickness superposition, and the flatness of the battery cell can be improved. In addition, the tab of the application has no notch, and the mechanical strength of the tab can be improved. Furthermore, the thinning layer around the tab slot can reduce the risk of lithium precipitation caused by large current density at the tab site and reduce lithium precipitation.

[0012] It should be noted that the CB value refers to the ratio of the positive facing negative electrode capacity to the positive electrode capacity.

[0013] As a preferred technical solution of the application, the thickness of the first thinning layer is H1, and the median particle size of the active material in the first thinning layer is D 50 , H1≥D 50 .

[0014] Preferably, the thickness of the second thinning layer is equal to the thickness of the first thinning layer.

[0015] As a preferred technical solution of the application, the depth of the first thinning area into the active material layer is 4-100 mm, for example, it can be 4 mm, 5 mm, 7 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm, etc.

[0016] Preferably, the depth of the second thinning area into the active material layer is 2-100 mm, for example, it can be 2 mm, 3 mm, 4 mm, 5 mm, 7 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm, etc.

[0017] Preferably, the depth of the first thinning area into the active material layer is greater than the depth of the second thinning area into the active material layer.

[0018] In the application, the depth of the first thinning area into the active material layer refers to the side length of the first thinning area in the width direction of the positive electrode tab, and the depth of the second thinning area into the active material layer refers to the side length of the second thinning area in the width direction of the tab.

[0019] As a preferred technical solution of the present application, the lug slot is connected with a lug.

[0020] Preferably, the difference between the width of the first thinning area and the width of the lug is 8-40 mm, for example, it can be 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm or 40 mm, etc.

[0021] Preferably, the difference between the width of the second thinning area and the width of the lug is 8-40 mm, for example, it can be 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm or 40 mm, etc.

[0022] Preferably, the width of the first thinning area is the same as the width of the second thinning area.

[0023] Preferably, the first thinning area and the second thinning area are coaxially arranged.

[0024] As a preferred technical solution of the present application, the surface of the lug slot connected with the lug is pasted with adhesive tape.

[0025] Preferably, the adhesive tape completely covers the lug slot and partially covers the first thinning area.

[0026] In the present application, the edge of the adhesive tape does not exceed the first thinning area, which can improve the flatness of the battery cell and increase the CB value of the local edge of the adhesive tape, reduce the risk of lithium precipitation, and reduce lithium precipitation. The first thinning area is not completely covered because of the existence of errors, and it is difficult for the adhesive tape to exactly cover the first thinning area.

[0027] As a preferred technical solution of the present application, the distance between the long side of the adhesive tape and the long side of the first thinning area is 2-5 mm, for example, it can be 2 mm, 3 mm, 4 mm or 5 mm, etc.

[0028] Preferably, the distance between the long side of the adhesive tape and the long side of the lug slot is 2-5 mm, for example, it can be 2 mm, 3 mm, 4 mm or 5 mm, etc.

[0029] Preferably, the distance between the short side of the adhesive tape and the short side of the first thinning area is 2-5 mm, for example, it can be 2 mm, 3 mm, 4 mm or 5 mm, etc.

[0030] Preferably, the distance between the short side of the adhesive tape and the short side of the lug slot is 2-5 mm, for example, it can be 2 mm, 3 mm, 4 mm or 5 mm, etc.

[0031] In a second aspect, the present application provides a preparation method of the positive electrode tab of the first aspect, which comprises:

[0032] Providing a pole piece mother plate, forming at least two thin layer regions on the surface of the pole piece mother plate through a first cleaning step, the thin layer regions are arranged at intervals along a first direction, and forming grooves on the surface of each thin layer region through a second cleaning step;

[0033] Slitting the pole piece mother plate along a slitting line, the slitting line is located between the edge of the thin layer region and the edge of the groove, the slitting line is parallel to the width direction of the thin layer region, the included angle between the slitting line and the first direction is 10-90° (for example, it can be 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° or 90°, etc.), and the slitting step is obtained. The positive pole piece.

[0034] The preparation method of the positive pole piece provided by the application does not need to perform the punching operation after slitting, and is suitable for industrial production.

[0035] In the application, after slitting, each thin layer region forms an independent first thin layer region and a second thin layer region, the area of the first thin layer region is greater than or equal to the area of the second thin layer region, and the first thin layer region and the second thin layer region between the two adjacent slitting lines correspond to the first thinning region and the second thinning region respectively.

[0036] It should be noted that after slitting each thin layer region along the slitting line, the length of the first thin layer region corresponds to the depth of the first thinning region into the active material layer.

[0037] Preferably, the lug groove and the lug are connected by welding, the length of the welding is C1, the slitting mechanism tolerance is ±X, the depth of the first thinning region into the active material layer is L1, and (2X+C1+4) mm≤L1≤(2X+C1+40) mm.

[0038] Preferably, the depth of the second thinning region into the active material layer is L2, and L2≥2X.

[0039] As a preferred technical solution of the application, in the direction perpendicular to the slitting line, the center interval of the adjacent two thin layer regions is the same as the interval of the adjacent two slitting lines.

[0040] As a preferred technical solution of the application, the first cleaning step and the second cleaning step independently include laser cleaning and / or rubbing coating.

[0041] Preferably, the slitting step includes any one or a combination of at least two of laser cutting, die cutting or cutting.

[0042] In a third aspect, the application provides a lithium ion battery, the lithium ion battery comprising the positive pole piece of the first aspect.

[0043] The numerical ranges recited herein are inclusive of the endpoints and of any range that would be formed in omission of the endpoints. To the extent that any numerical ranges are set forth herein, those ranges include any and all sub-ranges of the same numerical limits, unless expressly indicated otherwise. To the extent that any numerical ranges are set forth herein, it is contemplated that any such ranges include any and all sub-ranges between the stated range limits (i.e., each range of fractions of the difference between the upper and lower range limits). To the extent that any numerical ranges are set forth herein, it is contemplated that any such ranges include any and all sub-ranges of the same numerical limits, unless expressly indicated otherwise.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] The present application provides a positive electrode tab with a tab centering structure, the surface of the tab is provided with a first thinning area, and an tab slot is formed in the inside of the first thinning area, which can be directly connected with the tab without thickness superposition, thereby improving the flatness of the battery cell; and the tab of the present application has no notch, which can improve the mechanical strength of the tab; in addition, the thinning layer around the tab slot can reduce the risk of lithium precipitation caused by large current density at the tab site and reduce lithium precipitation. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 A structure schematic diagram of the positive electrode tab provided for the present application embodiment 1 is provided;

[0047] Figure 2 A cutting schematic diagram of the tab mother plate provided by the present application embodiment 1 is provided;

[0048] Figure 3 A structure schematic diagram of the positive electrode tab provided for the present application comparative example 1 is provided;

[0049] Figure 4 A cutting schematic diagram of the tab mother plate provided by the present application comparative example 1 is provided;

[0050] 1- first thinning area; 2- second thinning area; 3- tab slot; 4- adhesive paper; 5- notch. DETAILED DESCRIPTION

[0051] It should be understood that, in the description of the present application, the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise stated.

[0052] It should be noted that in the description of the present application, unless otherwise explicitly specified and limited, the terms "arranged", "connected", "linked" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0053] The technical solutions of the present application are further illustrated by specific embodiments.

[0054] Embodiment 1

[0055] The present embodiment provides a positive electrode sheet, as shown in the structure of Figure 1 The aluminum foil and the active material layer arranged on both sides of the aluminum foil, wherein the active material is lithium cobaltate, the median particle size of lithium cobaltate is 15 μm, a first thinning area 1 is arranged inward along one side of the active material layer, a second thinning area 2 is arranged inward along the other side of the active material layer, the area of the first thinning area 1 is greater than or equal to the area of the second thinning area 2, and the first thinning area 1 and the second thinning area 2 are coaxially arranged; the active material layer in the first thinning area 1 is a first thinning layer, the active material layer in the second thinning area 2 is a second thinning layer, and the thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer; an ear slot 3 is arranged in the first thinning layer, and the ear slot 3 exposes the surface of the foil;

[0056] The single-sided density of the positive electrode sheet is 180 g / m 2 , the A-side coating film length is 1118 mm, the B-side length is 996 mm, the electrode sheet width is 76 mm, the ear welding length is 5 mm, the ear width is 3 mm, and the cutting tolerance is 1 mm. The thickness of the first thinning layer is 50 μm; the thickness of the second thinning layer is 50 μm; the depth of the first thinning area 1 into the active material layer is 12 mm; the depth of the second thinning area 2 into the active material layer is 2 mm; the width of the first thinning area 1 is 12 mm; and the width of the second thinning area 2 is 12 mm.

[0057] The surface of the ear slot 3 connected with the ear is pasted with adhesive tape 4, the adhesive tape 4 completely covers the ear slot 3 and partially covers the first thinning area 1; the distance between the long side of the adhesive tape 4 and the long side of the first thinning area 1 is 2 mm; the distance between the long side of the adhesive tape 4 and the long side of the ear slot 3 is 2 mm; the distance between the short side of the adhesive tape 4 and the short side of the first thinning area 1 is 2 mm; and the distance between the short side of the adhesive tape 4 and the short side of the ear slot 3 is 2 mm.

[0058] The embodiment also provides a preparation method of the positive electrode tab, which comprises the following steps: providing a tab blank, forming three thin layer areas on the surface of the tab blank by laser cleaning, the thin layer areas being coaxially and vertically spaced apart along a first direction, and forming grooves on the surface of each thin layer area by laser cleaning. Figure 2

[0059] slitting each thin layer area along a slitting line, the slitting line being located between the short side of the thin layer area and the short side of the groove, the slitting line being parallel to the short side of the thin layer area, the included angle between the slitting line and the first direction being 90°, the interval between the centers of two adjacent thin layer areas in the direction perpendicular to the slitting line being the same as the interval between two adjacent slitting lines, and obtaining the positive electrode tab after slitting.

[0060] The groove on the positive electrode tab is the tab slot 3, the tab is connected to the tab slot 3 by welding, and the adhesive tape 4 is attached to the surface thereof.

[0061] Embodiment 2

[0062] The embodiment provides a positive electrode tab, which comprises an aluminum foil and an active material layer arranged on the surface of the aluminum foil, wherein the active material is lithium cobaltate, the median particle size of the lithium cobaltate is 15 μm, a first thinning area is arranged inward along one long side of the active material layer, a second thinning area is arranged inward along the other long side of the active material layer, the area of the first thinning area is greater than or equal to the area of the second thinning area, and the first thinning area and the second thinning area are coaxially arranged; the active material layer in the first thinning area is a first thinning layer, the active material layer in the second thinning area is a second thinning layer, the thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer, and a tab slot is arranged in the first thinning layer, and the surface of the foil material is exposed in the tab slot.

[0063] The single-sided density of the positive electrode tab is 180 g / m 2 , the length of the A-side coating film is 1118 mm, the length of the B-side is 996 mm, the width of the tab is 76 mm, the welding length of the tab is 5 mm, the width of the tab is 3 mm, the cutting tolerance is 1 mm, the thickness of the first thinning layer is 30 μm, the thickness of the second thinning layer is 30 μm, the depth of the first thinning area into the active material layer is 25 mm, the depth of the second thinning area into the active material layer is 5 mm, the width of the first thinning area is 20 mm, and the width of the second thinning area is 20 mm.

[0064] ​The surface of the tab slot connected with the tab is pasted with adhesive paper, the adhesive paper completely covers the tab slot and partially covers the first thinning area; the distance between the long side of the adhesive paper and the long side of the first thinning area is 3 mm; the distance between the long side of the adhesive paper and the long side of the tab slot is 3 mm; the distance between the short side of the adhesive paper and the short side of the first thinning area is 3 mm; and the distance between the short side of the adhesive paper and the short side of the tab slot is 3 mm.

[0065] The embodiment also provides a preparation method of the positive electrode tab, which comprises the following steps: providing a tab mother plate, forming three thin layer areas on the surface of the tab mother plate by means of laser cleaning, the thin layer areas being coaxially and vertically spaced apart along a first direction, and forming a groove on the surface of each thin layer area by means of laser cleaning.

[0066] Each thin layer area is slitted along a slitting line, the slitting line being located between the short side of the thin layer area and the short side of the groove, the slitting line being parallel to the short side of the thin layer area, the included angle between the slitting line and the first direction being 90°, the interval between the centers of two adjacent thin layer areas in the direction perpendicular to the slitting line being the same as the interval between two adjacent slitting lines, and the positive electrode tab being obtained after slitting.

[0067] The groove on the positive electrode tab is a tab slot, a tab is connected to the tab slot by welding, and adhesive paper is pasted on the surface thereof.

[0068] Embodiment 3

[0069] The embodiment provides a positive electrode tab, which comprises an aluminum foil and an active material layer arranged on the surfaces of the aluminum foil on both sides, wherein the active material is lithium cobaltate, the median particle size of the lithium cobaltate is 15 μm, a first thinning area is arranged inward along one long side of the active material layer, a second thinning area is arranged inward along the other long side of the active material layer, the area of the first thinning area is greater than or equal to the area of the second thinning area, and the first thinning area and the second thinning area are coaxially arranged; the active material layer in the first thinning area is a first thinning layer, the active material layer in the second thinning area is a second thinning layer, the thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer; a tab slot is arranged in the first thinning layer, and the surface of the foil material is exposed from the tab slot.

[0070] The single-sided density of the positive electrode tab is 180 g / m 2, the length of the A surface coating film is 1118 mm, the length of the B surface is 996 mm, the width of the pole piece is 76 mm, the length of the pole lug welding is 5 mm, the width of the pole lug is 3 mm, the cutting tolerance is 1 mm, the thickness of the first thinning layer is 20 pm; the thickness of the second thinning layer is 20 pm; the depth of the first thinning area into the active material layer is 40 mm; the depth of the second thinning area into the active material layer is 10 mm; the width of the first thinning area is 30 mm; the width of the second thinning area is 30 mm;

[0071] The surface of the pole lug groove connected with the pole lug is pasted with adhesive tape, the adhesive tape completely covers the pole lug groove and partially covers the first thinning area; the distance between the long side of the adhesive tape and the long side of the first thinning area is 5 mm; the distance between the long side of the adhesive tape and the long side of the pole lug groove is 5 mm; the distance between the short side of the adhesive tape and the short side of the first thinning area is 5 mm; the distance between the short side of the adhesive tape and the short side of the pole lug groove is 5 mm.

[0072] The embodiment also provides a preparation method of the positive electrode pole piece, the method comprising: providing a pole piece mother plate, forming three thin layer areas on the surface of the pole piece mother plate by means of laser cleaning, the thin layer areas being coaxially and vertically spaced apart along a first direction, and then forming a groove on the surface of each thin layer area by means of laser cleaning;

[0073] Each thin layer area is slitted along a slitting line, the slitting line being located between the short side of the thin layer area and the short side of the groove, the slitting line being parallel to the short side of the thin layer area, the included angle between the slitting line and the first direction being 90°, the interval between the centers of adjacent two thin layer areas in the direction perpendicular to the slitting line being the same as the interval between adjacent two slitting lines, and after slitting, a positive electrode pole piece is obtained;

[0074] The groove on the positive electrode pole piece is a pole lug groove, a pole lug is connected to the pole lug groove by welding, and adhesive tape is pasted on the surface thereof.

[0075] Comparative Example 1

[0076] The comparative example provides a positive electrode pole piece, as shown in Figure 3 The difference between the comparative example and Example 1 is that there is no first thinning area 1 and second thinning area 2, and there is a notch 5 at the edge of the pole lug groove 3, and the rest of the parameters are the same as those of Example 1.

[0077] The comparative example also provides a preparation method of the positive electrode pole piece, the method comprising: providing a pole piece mother plate, forming three cleaning grooves on the surface of the pole piece mother plate by means of laser cleaning, the cleaning grooves being vertically spaced apart, and the cleaning grooves being coaxially arranged, as shown in Figure 4 .

[0078] The mother plate of the pole piece is slitting along a slitting line parallel to the width direction of the cleaning tank, and the included angle between the slitting line and the first direction is 90°, and the distance between the slitting line and the edge of the cleaning tank is 2mm. After slitting, the surface of the pole piece has only one groove, which is the tab slot 3.

[0079] The active substance remaining at the edge of the tab slot 3 is punched to form a notch 5 penetrating the positive pole piece along the thickness direction of the positive pole piece, and the positive pole piece is obtained.

[0080] The tab is connected to the tab slot by welding, and the surface is covered with adhesive tape 4.

[0081] Performance test

[0082] (1) Pole piece mechanical strength test

[0083] The pole pieces of Examples 1-3 and Comparative Example 1 were subjected to mechanical strength test. First, the length and width of the pole piece sample overlap surface were measured, respectively recorded as b and d, accurate to 0.05mm; then the sample was loaded into the upper and lower clamps, loaded at a speed of 5±1mm, and the maximum load p of the sample shear failure was recorded. Tensile strength σ = p / (b*d).

[0084] (2) Positive electrode lithium precipitation test

[0085] The positive pole pieces provided by Examples 1-3 and Comparative Example 1 were respectively assembled into lithium ion batteries with a negative pole piece, the negative pole piece comprising a copper foil with a thickness of 8μm, a negative active material layer with a single-sided density of 99.8g / m 2 , A side coating film length of 1130mm, B side coating film length of 1017mm, and a pole piece width of 77.5mm, which is a conventional structure. The mass ratio of artificial graphite (first efficiency 91%), polyvinylidene fluoride and conductive carbon black in the negative active material layer is 96:2:2. The separator is a 9μm polyethylene-based film coated with 1μm adhesive on both sides, and the electrolyte is a 1mol / L LiPF6 / EC+DMC+EMC electrolyte (EC is ethylene carbonate, EMC is methyl ethyl carbonate, DMC is dimethyl carbonate, and the volume ratio of EC, DMC and EMC is 1:1:1).

[0086] The assembled battery was subjected to 6C / 1C charge and discharge at a temperature of 10℃, and after 20 weeks, the full battery was disassembled and the negative pole piece lithium precipitation was observed.

[0087] The test results of Examples 1-3 and Comparative Example 1 are shown in Table 1.

[0088] Table 1

[0089] Mechanical strength (Mpa) Lithium precipitation Example 1 19.4 No lithium precipitation Example 2 19.6 No lithium precipitation Example 3 19.3 No lithium precipitation Comparative Example 1 16.8 Lithium precipitation

[0090] Analysis:

[0091] As can be seen from the results of Examples 1-3 and Comparative Example 1, the positive electrode tab provided by the present application has high mechanical strength and can effectively reduce the risk of lithium precipitation at the tab position and reduce lithium precipitation. The positive electrode tab in Comparative Example 1 cannot achieve the above effects. Further, the structure of the positive electrode tab provided by the present application itself can reduce lithium precipitation, and on this basis, the material system, rate window and temperature window of the battery design can be widened.

[0092] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A positive electrode sheet, characterized by, The positive electrode sheet comprises a foil and an active material layer arranged on at least one side surface of the foil, a first thinning area is arranged inward along one side long edge of the active material layer, a second thinning area is arranged inward along the other side long edge of the active material layer, and the area of the first thinning area is greater than or equal to the area of the second thinning area. The active material layer in the first thinning area is a first thinning layer, the active material layer in the second thinning area is a second thinning layer, and the thicknesses of the first thinning layer and the second thinning layer are both less than the thickness of the active material layer. An inner portion of the first thinning layer is provided with a tab slot, and a surface of the tab slot exposes a surface of the foil; and the tab slot is connected with a tab. A surface of the tab slot connected with the tab is pasted with adhesive paper, and the adhesive paper completely covers the tab slot and partially covers the first thinning area. The positive electrode sheet is prepared by the following method, which comprises the following steps: A sheet mother plate is provided, at least two thin layer areas are formed on a surface of the sheet mother plate by a first cleaning step, the thin layer areas are arranged at intervals along a first direction, and grooves are formed on surfaces of the thin layer areas by a second cleaning step; A slitting step is performed on the sheet mother plate along a slitting line, the slitting line is located between edges of the thin layer areas and edges of the grooves, the slitting line is parallel to a width direction of the thin layer areas, an included angle between the slitting line and the first direction is 10-90°, and the positive electrode sheet is obtained after the slitting step; The tab slot and the tab are connected by welding, a length of the welding is C1, a slitting mechanism tolerance is ±X, a depth of the first thinning area into the active material layer is L1, (2X+C1+4) mm≤L1≤(2X+C1+40) mm, and a depth of the second thinning area into the active material layer is L2, L2≥2X.

2. The cathode electrode of claim 1, wherein, The first thinned layer has a thickness H1, and the active substance in the first thinned layer has a median particle size D 50 H1≥D 50 .

3. The cathode electrode of claim 1, wherein The thickness of the second thinning layer is equal to the thickness of the first thinning layer.

4. The cathode electrode of claim 1, wherein The depth of the first thinning area into the active material layer is 4-100 mm.

5. The cathode sheet of claim 1, wherein, The depth of the second thinning area into the active material layer is 2-100 mm.

6. The cathode sheet of claim 1, wherein, The depth of the first thinning area into the active material layer is greater than the depth of the second thinning area into the active material layer.

7. The cathode sheet of claim 1, wherein, A difference between the width of the first thinning area and the width of the tab is 8-40 mm.

8. The cathode sheet of claim 1, wherein, A difference between the width of the second thinning area and the width of the tab is 8-40 mm.

9. The cathode electrode of claim 1, wherein, The width of the first thinning area is the same as the width of the second thinning area.

10. The cathode electrode of claim 1, wherein, The first thinning area and the second thinning area are coaxially arranged.

11. The cathode electrode of claim 1, wherein, A distance between a long edge of the adhesive paper and a long edge of the first thinning area is 2-5 mm.

12. The cathode sheet of claim 1, wherein, A distance between a long edge of the adhesive paper and a long edge of the tab slot is 2-5 mm.

13. The cathode sheet of claim 1, wherein, A distance between a short edge of the adhesive paper and a short edge of the first thinning area is 2-5 mm.

14. The cathode sheet of claim 1, wherein, A distance between a short edge of the adhesive paper and a short edge of the tab slot is 2-5 mm.

15. A method of making the positive electrode sheet of any one of claims 1-14, characterized by, The preparation method comprises: A sheet mother plate is provided, at least two thin layer areas are formed on a surface of the sheet mother plate by a first cleaning step, the thin layer areas are arranged at intervals along a first direction, and grooves are formed on surfaces of the thin layer areas by a second cleaning step; slitting the jelly-roll along a slitting line, the slitting line being located between the edge of the thin layer region and the edge of the groove, the slitting line being parallel to the width direction of the thin layer region, the slitting line having an angle of 10-90° with the first direction, and obtaining the positive electrode after the slitting step.

16. The method of claim 15, wherein, In a direction perpendicular to the slitting line, the center distance between two adjacent thin layer regions is the same as the distance between two adjacent slitting lines.

17. The preparation method according to claim 15, characterized in that, The first cleaning step and the second cleaning step independently comprise laser cleaning and / or wiping.

18. The method of claim 15, wherein, The slitting step comprises any one or a combination of at least two of laser cutting, die cutting, and cutting.

19. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode of any one of claims 1-14.

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