A positive electrode sheet, a secondary battery, and an electronic device

Abstract

The application provides a positive electrode sheet, a secondary battery and an electronic device. The positive electrode sheet comprises a positive current collector and a positive material layer. The positive current collector comprises opposite first and second edges along the width direction of the positive electrode sheet. The positive material layer comprises an edge region and a main body region in sequence from the first edge to the second edge. The width of the edge region is W1 mm, the thickness of the edge region is T1 μm, the width of the main body region is W2 mm, the thickness of the main body region is T2 μm, W1 / W2≤8%, 90%≤T1 / T2≤100%, 18≤T1≤300, and 20≤T2≤300. The positive material layer comprises an organosilicon and polyether modified ester polymer. The positive electrode sheet satisfies the above characteristics, and can improve the processing problems of edge shrinkage or edge drumming of the positive electrode sheet in the coating process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to a positive electrode sheet, a secondary battery and an electronic device. BACKGROUND

[0002] At present, when the positive electrode sheet of the lithium ion battery is prepared, the edge shrinkage or edge bulging of the positive electrode sheet will occur after coating. The edge shrinkage of the positive electrode sheet will affect the measurement of the size parameters of the positive electrode sheet, cause the yield rate to decrease, and also cause the positive electrode sheet and the negative electrode sheet to be misaligned, thereby causing the lithium ion battery to have safety problems. The edge bulging of the positive electrode sheet will cause the appearance of the positive electrode sheet to be abnormal, and will cause the lithium ion battery to be too thick. In addition, the edge bulging will cause the positive electrode sheet to be over-pressed during cold pressing, thereby causing the ion conductivity of the over-pressed part to be greatly reduced, the kinetic performance of the over-pressed part of the positive electrode sheet to be poor, and the risk of lithium precipitation to increase. In addition, the edge bulging will also cause the ratio of the local negative electrode capacity to the positive electrode capacity (NP ratio) to decrease, and when the NP ratio is less than 1, the lithium ion battery will cause lithium precipitation.

[0003] Therefore, it is urgent to provide a positive electrode sheet which can improve the processing problems of the edge shrinkage or edge bulging of the positive electrode sheet during coating. SUMMARY

[0004] The present application aims to provide a positive electrode sheet, a secondary battery and an electronic device to improve the processing problems of the edge shrinkage or edge bulging of the positive electrode sheet during coating. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. Along the width direction of the positive electrode sheet, the positive electrode current collector comprises opposite first and second edges. From the first edge to the second edge, the positive electrode material layer comprises an edge region and a main body region in sequence. The width of the edge region is W1 mm, the thickness of the edge region is T1 μm, the width of the main body region is W2 mm, the thickness of the main body region is T2 μm, W1 / W2≤8%, 90%≤T1 / T2≤100%, 18≤T1≤300, and 20≤T2≤300. The positive electrode material layer comprises an organosilicon and polyether modified ester polymer. When the positive electrode material layer comprises the edge region and the main body region, the ratio of the width of the edge region to the width of the main body region, the thickness of the edge region, the thickness of the main body region, and the ratio of the thickness of the edge region to the thickness of the main body region are within the scope of the present application, and the positive electrode material layer comprises the above-mentioned substances, which can improve the wettability between the positive electrode slurry and the positive electrode current collector, reduce the contact angle between the positive electrode slurry and the positive electrode current collector, and thereby improve the processing problems of the edge shrinkage or edge bulging of the positive electrode sheet during coating.

[0006] In an embodiment of the present application, the organosilicon includes at least one of trisiloxane, polydimethylsiloxane, polyoxyethylene ether trisiloxane, or vinyl trimethoxysilane. In an embodiment of the present application, the polyether includes at least one of monoallyl polyether, propylene glycol polyether, methallyl alcohol polyoxyethylene ether, or lauryl alcohol polyether. In an embodiment of the present application, the polymer body in the ester-based polymer includes at least one of polybutyl acrylate, polymethyl acrylate, polycarbonate, polyvinyl acetate, or polyarylate.

[0007] In an embodiment of the present application, the mass percentage of the ester-based polymer is w1%, 0.05≤w1≤1, based on the mass of the positive electrode material layer. By adjusting the mass percentage of the ester-based polymer within the range of the present application, the ester-based polymer has a suitable mass percentage, which can effectively improve the wettability between the positive electrode slurry and the positive electrode current collector, effectively reduce the contact angle between the positive electrode slurry and the positive electrode current collector, effectively improve the processing problem of edge shrinkage or edge curling of the positive electrode sheet during the coating process, and also enable the mass percentage of the positive electrode active material to be relatively high, thereby enabling the secondary battery to have a high energy density.

[0008] In an embodiment of the present application, the positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methyl pyrrolidone (NMP) to obtain a positive electrode slurry with a solid content of 60% to 80%, the surface tension of the positive electrode slurry is γN / m, the surface tension of the positive electrode current collector is D dyn / cm, and the angle of the edge region is θ, 0≤D-γ×cosθ≤15. The positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, and the positive electrode material layer powder is dissolved in N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 60% to 80%. The surface tension of the positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge region satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, which facilitates the wetting and spreading of the positive electrode slurry on the positive electrode current collector, the wettability between the positive electrode slurry and the positive electrode current collector is good, the contact angle between the positive electrode slurry and the positive electrode current collector is small, and the processing problem of edge shrinkage or edge curling of the positive electrode sheet during the coating process is effectively improved.

[0009] In an embodiment of the present application, the positive electrode sheet satisfies at least one of the following characteristics: (1) 26≤D≤39; (2) 30≤γ≤45; (3) 5°≤θ≤75°.

[0010] The positive electrode sheet satisfies the above characteristics, which can improve the processing problem of edge shrinkage or edge curling of the positive electrode sheet during the coating process.

[0011] In an embodiment of the present application, the mass percentage of the organic silicon is 10% to 25% and the mass percentage of the polyether is 20% to 30% based on the mass of the ester polymer. By adjusting the mass percentage of the organic silicon and the mass percentage of the polyether within the range of the present application, the ester polymer can have a suitable content of the NMP-phobic group and the NMP-philic group, which is more stable in the arrangement at the interface between the solvent NMP and the air, can further improve the wetting performance between the positive electrode slurry and the positive electrode current collector, further reduce the contact angle between the positive electrode slurry and the positive electrode current collector, and thus further improve the processing problem of edge shrinkage or edge curling of the positive electrode sheet during the coating process.

[0012] In an embodiment of the present application, the weight average molecular weight Mw of the ester polymer is 10,000 to 200,000. By adjusting the weight average molecular weight of the ester polymer within the range of the present application, the chain segment of the ester polymer can be stretched into NMP, which is beneficial to the dispersion of the ester polymer itself and the auxiliary dispersion of the positive electrode slurry, can further improve the wetting performance between the positive electrode slurry and the positive electrode current collector, further reduce the contact angle between the positive electrode slurry and the positive electrode current collector, and thus further improve the processing problem of edge shrinkage or edge curling of the positive electrode sheet during the coating process.

[0013] In an embodiment of the present application, the positive electrode material layer satisfies at least one of the following characteristics: (1) the coating weight of the positive electrode material layer is CW, 100 mg / 1540.25 mm 2 ≤ CW≤ 500 mg / 1540.25 mm 2 ; (2) the compaction density of the positive electrode material layer is PD g / cc, 2.0≤ PD≤ 4.0.

[0014] In an embodiment of the present application, the edge curling value of the positive electrode sheet is G μm, G / T2≤ 5%. When the value of G / T2 is within the above range, the ratio of the edge curling value of the positive electrode sheet to the thickness of the main body area is relatively small, which can reduce the belt breakage of the positive electrode sheet during the coating process and the cold pressing process, improve the processing performance of the positive electrode sheet, and also reduce the overpressure at the edge of the positive electrode sheet during the cold pressing process, so that the positive electrode sheet also has good ion conductivity at the edge, thereby improving the kinetic performance of the secondary battery and reducing the lithium precipitation of the secondary battery.

[0015] The second aspect of the present application provides a secondary battery comprising the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by the present application has good safety performance and kinetic performance.

[0016] The third aspect of the present application provides an electronic device comprising the secondary battery according to any one of the foregoing embodiments. Therefore, the electronic device provided by the present application has good use performance.

[0017] Advantages of the present application:

[0018] The present application provides a positive electrode sheet, a secondary battery and an electronic device. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The positive electrode current collector comprises opposite first and second edges in the width direction of the positive electrode sheet. The positive electrode material layer comprises an edge region and a main body region in sequence from the first edge to the second edge. The width of the edge region is W1 mm, the thickness of the edge region is T1 μm, the width of the main body region is W2 mm, the thickness of the main body region is T2 μm, W1 / W2≤8%, 90%≤T1 / T2≤100%, 18≤T1≤300, and 20≤T2≤300. The positive electrode material layer comprises an organosilicon and polyether modified ester polymer. The positive electrode sheet satisfies the above characteristics, and can improve the processing problems of edge shrinkage or edge bulging of the positive electrode sheet in the coating process.

[0019] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0021] Figure 1 Structure schematic diagram of the width direction and length direction of the positive electrode sheet of an embodiment of the present application;

[0022] Figure 2 Structure schematic diagram of the edge region of the positive electrode material layer of an embodiment of the present application;

[0023] Figure 3 Structure schematic diagram of the width direction and thickness direction of the positive electrode sheet of an embodiment of the present application;

[0024] Figure 4 Appearance diagram of the edge region of the positive electrode sheet of embodiments 1-12 of the present application;

[0025] Figure 5 Appearance diagram of the edge region of the positive electrode sheet of embodiments 1-11 of the present application;

[0026] Figure 6Figure 1 is an appearance diagram of an edge region of a positive electrode tab according to an embodiment of the present application.

[0027] Figure 7 Figure 1 is an appearance diagram of an edge region of a positive electrode tab according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. All other embodiments obtained by a person skilled in the art based on the present application belong to the scope of protection of the present application.

[0029] It should be noted that in the specific embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

[0030] The present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The positive electrode current collector comprises opposite first and second edges in the width direction of the positive electrode tab. The positive electrode material layer comprises, in sequence from the first edge to the second edge, an edge region and a main body region. For the convenience of understanding, a three-dimensional rectangular coordinate system is established with the width direction of the positive electrode tab as the Y direction, the length direction of the positive electrode tab as the X direction, and the thickness direction of the positive electrode tab as the Z direction. It can be understood that the size of the edge region in the Y direction is the width of the edge region, and the size of the edge region in the Z direction is the thickness of the edge region; the size of the main body region in the Y direction is the width of the main body region, and the size of the main body region in the Z direction is the thickness of the main body region. As shown in Figure 1, the edge region and the main body region are arranged in sequence from the first edge to the second edge. Figure 1As shown, the positive electrode tab 10 includes a positive electrode current collector 100 and a positive electrode material layer 200 disposed on one surface of the positive electrode current collector 100. The positive electrode current collector 100 includes opposite first and second edges 110 and 120 along the width direction of the positive electrode tab 10, i.e., the Y direction. The positive electrode material layer 200 includes, in sequence from the first edge 110 to the second edge 120, an edge region 210 and a main body region 220. The edge region has a width of W1 mm and a thickness of T1 μm, and the main body region has a width of W2 mm and a thickness of T2 μm. W1 / W2≤8%, and exemplarily, the value of W1 / W2 can be 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or a range between any two of the above values. 90%≤T1 / T2≤100%, and exemplarily, the value of T1 / T2 can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a range between any two of the above values. 18≤T1≤300, and exemplarily, the value of T1 can be 18, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, or a range between any two of the above values. 20≤T2≤300, and exemplarily, the value of T2 can be 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, or a range between any two of the above values. In the present application, the width of the edge region is W1 mm, and W1≤22; and the width of the main body region is W2 mm, and 40≤W2≤310. The above "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be disposed on both surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire region of the positive electrode current collector, or can be a partial region of the positive electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0031] The positive electrode material layer includes an ester polymer modified by organosilicon and polyether. The inventors have found that when the positive electrode material layer includes an edge region and a main body region, the ratio of the width of the edge region to the width of the main body region, the thickness of the edge region, the thickness of the main body region, and the ratio of the thickness of the edge region to the thickness of the main body region are within the scope of the present application, and the ester polymer modified by organosilicon and polyether is added during the preparation of the positive electrode slurry, because the ester polymer modified by organosilicon and polyether includes NMP-repellent groups and NMP-attractive groups, the NMP-repellent groups being hydroxyl groups, carboxyl groups, and polyether polar groups, and the NMP-attractive groups being organosilicon and carbon-oxygen organic segments, the ester polymer can be arranged at the interface between the solvent NMP and air, the wettability between the positive electrode slurry and the positive electrode current collector is improved, the contact angle between the positive electrode slurry and the positive electrode current collector is reduced, and thus the processing problem of edge shrinkage or edge drumming of the positive electrode sheet during the coating process is improved. In the present application, the "ester polymer" refers to the "ester polymer modified by organosilicon and polyether".

[0032] In an embodiment of the present application, the organosilicon includes at least one of trisiloxane, polydimethylsiloxane, polyoxyethylene ether trisiloxane, or vinyltrimethoxysilane. In an embodiment of the present application, the polyether includes at least one of monoallyl polyether, propylene glycol polyether, methallyl alcohol polyoxyethylene ether, or lauryl alcohol polyether. In an embodiment of the present application, the polymer body in the ester polymer includes at least one of polybutyl acrylate, polymethyl acrylate, polycarbonate, polyvinyl acetate, or polyarylate. In the present application, the above-mentioned "trisiloxane" can refer to octamethyltrisiloxane, the chemical formula of which is C8H 24 O2Si3, which is not modified. The above-mentioned "polyoxyethylene ether trisiloxane" refers to a polyether-modified trisiloxane. The chemical formula of the above-mentioned "monoallyl polyether" can be CH2=CHCH2O(CH2CH2O) n H, 10 < n < 100. The chemical formula of the above-mentioned "propylene glycol polyether" can be H2C=CHCH2O(C2H4O)a(C3H6O)bH, 5 < a < 50, 5 < b < 50. The above-mentioned "lauryl alcohol polyether" can refer to sodium lauryl alcohol polyether sulfate.

[0033] In one embodiment of the present application, the mass percentage of the ester-based polymer is w1%, 0.05≤w1≤1, based on the mass of the positive electrode material layer. Illustratively, the value of w1may be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range defined by any two of the above values. By adjusting the mass percentage of the ester-based polymer within the range of the present application, the ester-based polymer has a suitable mass percentage, which can effectively improve the wettability between the positive electrode slurry and the positive electrode current collector, effectively reduce the contact angle between the positive electrode slurry and the positive electrode current collector, effectively improve the processing problems of edge shrinkage or edge curling of the positive electrode sheet during the coating process, and also enable the mass percentage of the positive electrode active material to be relatively high, thereby enabling the secondary battery to have a high energy density.

[0034] In one embodiment of the present application, the positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 60% to 80%, the surface tension of the positive electrode slurry is γN / m, the surface tension of the positive electrode current collector is D dyn / cm, and the angle of the edge region is θ, 0≤D-γ×cosθ≤15. Illustratively, the value of D-γ×cosθmay be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range defined by any two of the above values. In order to facilitate understanding of the angle of the edge region, Figure 2 A schematic diagram of the local structure of the edge region of the positive electrode material layer is shown. As shown in Figure 2 The angle θ of the edge region refers to the angle between the contact interface of the positive electrode current collector 100 and the edge region 210 and the contact interface of the edge region 210 and the air. The positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, and the positive electrode material layer powder is dissolved in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 60% to 80%. The surface tension of the positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge region satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, facilitating the wetting and spreading of the positive electrode slurry on the positive electrode current collector, the wettability between the positive electrode slurry and the positive electrode current collector is good, the contact angle between the positive electrode slurry and the positive electrode current collector is small, and the processing problems of edge shrinkage or edge curling of the positive electrode sheet during the coating process are effectively improved.

[0035] In one embodiment of this application, the positive electrode material layer includes a positive electrode active material, which includes lithium iron phosphate. The positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder. The positive electrode material layer powder is dissolved in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 60% to 70%. The surface tension of the positive electrode slurry is γN / m; the surface tension of the positive electrode current collector is D dyn / cm, and the angle of the edge region is θ, where 0 ≤ D - γ × cosθ ≤ 15. Exemplarily, the value of D - γ × cosθ can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two of the above values. The positive electrode active material in the positive electrode material layer includes lithium iron phosphate, and the positive electrode slurry is prepared according to the above method. The surface tension of the prepared positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge region satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, which facilitates the wetting and spreading of the positive electrode slurry on the positive electrode current collector. The wetting performance between the positive electrode slurry and the positive electrode current collector is good, and the contact angle between the positive electrode slurry and the positive electrode current collector is small, which effectively improves the processing problems of edge shrinkage or edge bulging that occur during the coating process of the positive electrode sheet.

[0036] In one embodiment of this application, the positive electrode material layer includes a positive electrode active material, which includes a nickel-cobalt-manganese ternary material, and the nickel-cobalt-manganese ternary material includes LiNi 0.9 Co 0.05 Mn 0.05 O2(Ni90), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn1 / 3The positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 68% to 78%, the surface tension of the positive electrode slurry is γ N / m; the surface tension of the positive electrode current collector is D dyn / cm, the angle of the edge area is θ, and 0≤D-γ×cosθ≤15. Exemplarily, the value of D-γ×cosθ can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range formed by any two of the above values. The positive electrode active material in the positive electrode material layer includes a nickel-cobalt-manganese ternary material, and the positive electrode slurry is prepared according to the above method, the surface tension of the prepared positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge area satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, the wetting and spreading of the positive electrode slurry on the positive electrode current collector are facilitated, the wetting performance between the positive electrode slurry and the positive electrode current collector is better, and the contact angle between the positive electrode slurry and the positive electrode current collector is smaller, thereby effectively improving the processing problems of edge shrinkage or edge drumming of the positive electrode plate in the coating process.

[0037] In an embodiment of the present application, the positive electrode material layer includes a positive electrode active material, the positive electrode active material includes lithium manganate, the positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 65% to 75%, the surface tension of the positive electrode slurry is γ N / m; the surface tension of the positive electrode current collector is D dyn / cm, the angle of the edge area is θ, and 0≤D-γ×cosθ≤15. Exemplarily, the value of D-γ×cosθ can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range formed by any two of the above values. The positive electrode active material in the positive electrode material layer includes lithium manganate, and the positive electrode slurry is prepared according to the above method, the surface tension of the prepared positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge area satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, the wetting and spreading of the positive electrode slurry on the positive electrode current collector are facilitated, the wetting performance between the positive electrode slurry and the positive electrode current collector is better, and the contact angle between the positive electrode slurry and the positive electrode current collector is smaller, thereby effectively improving the processing problems of edge shrinkage or edge drumming of the positive electrode plate in the coating process.

[0038] In an embodiment of the present application, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material comprises lithium cobaltate, the positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 70% to 80%, the surface tension of the positive electrode slurry is γ N / m; the surface tension of the positive electrode current collector is D dyn / cm, the angle of the edge area is θ, and 0≤D-γ×cosθ≤15. Exemplarily, the value of D-γ×cosθ can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range formed by any two of the above values. The positive electrode active material in the positive electrode material layer comprises lithium cobaltate, and the positive electrode slurry is prepared by the above method. The surface tension of the prepared positive electrode slurry, the surface tension of the positive electrode current collector, and the angle of the edge area satisfy the above relationship, so that the surface tension of the positive electrode slurry matches the surface tension of the positive electrode current collector, facilitating the wetting and spreading of the positive electrode slurry on the positive electrode current collector, the wetting performance between the positive electrode slurry and the positive electrode current collector is good, the contact angle between the positive electrode slurry and the positive electrode current collector is small, and the processing problems of edge shrinkage or edge drumming of the positive electrode plate during the coating process are effectively improved.

[0039] In an embodiment of the present application, 26≤D≤39, preferably 29≤D≤33. Exemplarily, the value of D can be 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or a range formed by any two of the above values. By adjusting the value of D within the range of the present application, the positive electrode current collector has a suitable surface tension. On the one hand, the positive electrode current collector has less residual oil. When the positive electrode active material is lithium iron phosphate, the water-based gravure coating method has good coverage effect for coating the conductive slurry on the surface of the positive electrode current collector, which can improve the adhesion between the positive electrode material layer and the positive electrode current collector. When the positive electrode active material is a nickel-cobalt-manganese ternary material, lithium manganate or lithium cobaltate, the shrinkage of the positive electrode plate can be reduced, the possibility of misalignment between the positive electrode plate and the negative electrode plate can be reduced, and the safety performance of the secondary battery can be further improved. On the other hand, the surface treatment steps of the positive electrode current collector can be reduced, such as reducing the corona or water washing steps, thereby reducing the production cost of the secondary battery. In addition, the wetting performance between the positive electrode slurry and the positive electrode current collector can be effectively improved, the contact angle between the positive electrode slurry and the positive electrode current collector can be effectively reduced, and the processing problems of edge shrinkage or edge drumming of the positive electrode plate during the coating process can be effectively improved.

[0040] In an embodiment of the present application, 30≤γ≤45. Illustratively, the value of γ can be 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 or a range between any two of the aforementioned values. The mass percentage of the ester-based polymer affects the surface tension of the positive electrode slurry. When the surface tension of the positive electrode slurry is within the aforementioned range, the wettability between the positive electrode slurry and the positive electrode current collector is better, and the contact angle between the positive electrode slurry and the positive electrode current collector is smaller, effectively improving the processing problem of edge shrinkage or edge bulging of the positive electrode plate during the coating process.

[0041] In an embodiment of the present application, 5°≤θ≤75°. Illustratively, θ can be 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75° or a range between any two of the aforementioned angles. The positive electrode material layer comprises an organosilicon and a polyether-modified ester-based polymer, and the wettability between the positive electrode slurry and the positive electrode current collector is better during the coating process. When the angle of the edge region is within the aforementioned range, the processing problem of edge shrinkage or edge bulging of the positive electrode plate during the coating process is effectively improved.

[0042] In an embodiment of the present application, the mass percentage of the organosilicon is 10% to 25% based on the mass of the ester-based polymer. Illustratively, the mass percentage of the organosilicon can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or a range between any two of the aforementioned values. The mass percentage of the polyether is 20% to 30%. Illustratively, the mass percentage of the polyether can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30% or a range between any two of the aforementioned values. By adjusting the mass percentage of the organosilicon and the mass percentage of the polyether within the range of the present application, the ester-based polymer has a suitable content of NMP-repellent groups and NMP-philic groups, which are more stable in the arrangement at the interface between the solvent NMP and the air, further improving the wettability between the positive electrode slurry and the positive electrode current collector, further reducing the contact angle between the positive electrode slurry and the positive electrode current collector, and thus further improving the processing problem of edge shrinkage or edge bulging of the positive electrode plate during the coating process.

[0043] In an embodiment of the present application, the weight average molecular weight Mw of the ester polymer is 10000 to 200000. Illustratively, the value of Mw can be 10000, 20000, 40000, 60000, 80000, 100000, 120000, 140000, 160000, 180000, 200000 or a range between any two of the above values. By adjusting the weight average molecular weight of the ester polymer within the range of the present application, the chain segments of the ester polymer can be stretched into NMP, which is beneficial to the dispersion of the ester polymer itself and the auxiliary dispersion of the positive electrode slurry, can further improve the wetting performance between the positive electrode slurry and the positive electrode current collector, further reduce the contact angle between the positive electrode slurry and the positive electrode current collector, and thus further improve the processing problems of edge shrinkage or edge drumming of the positive electrode sheet during the coating process.

[0044] In an embodiment of the present application, the coating weight of the positive material layer is CW, 100 mg / 1540.25 mm 2 ≤ CW≤ 500 mg / 1540.25 mm 2 . Illustratively, CW can be 100 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 200 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 350 mg / 1540.25 mm 2 , 400 mg / 1540.25 mm 2 , 450 mg / 1540.25 mm 2 , 500 mg / 1540.25 mm 2 or a range between any two of the above values. By adjusting the coating weight of the positive material layer within the range of the present application, the cracking of the positive material layer during the processing process can be reduced; the lithium ion can have a suitable transmission distance and the positive electrode sheet can be well infiltrated, so that the secondary battery has good cycle performance and rate performance; at the same time, the equipment capacity can be met, so that the positive electrode sheet has a high rate during the coating process.

[0045] In one embodiment of this application, the compaction density of the positive electrode material layer is PD g / cc, where 2.0 ≤ PD ≤ 4.0. Exemplarily, the value of PD can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or a range of any two of the above values. By adjusting the compaction density of the positive electrode material layer within the scope of this application, on the one hand, when lithium iron phosphate is used as the positive electrode active material, the embrittlement and powder shedding of the positive electrode material layer can be reduced; when nickel-cobalt-manganese ternary materials, lithium manganese oxide, or lithium cobalt oxide are used as the positive electrode active material, the integrity of the positive electrode active material particles can be better maintained, the occurrence of side reactions can be reduced, and the cycle performance of the secondary battery can be improved; on the other hand, it can also ensure that the positive electrode active material particles and the conductive agent have a suitable contact area, resulting in low contact resistance and improved rate performance and cycle performance of the secondary battery.

[0046] In one embodiment of this application, the edge value of the positive electrode sheet is Gμm, and G / T2 ≤ 5%, preferably, G / T2 ≤ 3%. Exemplarily, the value of G / T2 can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of the above values. To facilitate understanding of the edge value of the positive electrode sheet, Figure 3 A schematic diagram of the positive electrode sheet's structure in the width and thickness directions is shown. (See attached diagram.) Figure 3 As shown, along the Z direction, the distance between the highest point of the edge region 210 and the highest point of the main body region 220 is the edge value G of the positive electrode sheet. When the value of G / T2 is within the above range, the ratio of the edge value of the positive electrode sheet to the thickness of the main body region is relatively small. This can reduce strip breakage during the coating and cold pressing processes, improve the processing performance of the positive electrode sheet, and also reduce overvoltage at the edge of the positive electrode sheet during cold pressing, giving the edge of the positive electrode sheet better ionic conductivity, thereby improving the kinetic performance of the secondary battery and reducing lithium plating.

[0047] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (e.g., aluminum-carbon composite current collector). This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode current collector may be 8 μm to 20 μm.

[0048] The positive electrode material layer of the present application further includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material of the present application is not particularly limited as long as the object of the present application can be achieved, for example, the positive electrode active material can include, but is not limited to, at least one of lithium iron phosphate, nickel-cobalt-manganese ternary material, lithium manganate, lithium cobaltate, lithium nickel-cobalt-aluminate, lithium manganese iron phosphate, or lithium titanate. The binder of the present application is not particularly limited as long as the object of the present application can be achieved, for example, the binder can include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, sodium carboxymethyl cellulose, polyimide, polyamide-imide, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, or potassium carboxymethyl cellulose. The conductive agent of the present application is not particularly limited as long as the object of the present application can be achieved, for example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer. The above-mentioned conductive carbon black can include, but is not limited to, acetylene black and / or ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fibers, and in particular, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The mass percentage content of the positive electrode active material, the binder, and the conductive agent in the positive electrode material layer of the present application is not particularly limited, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode active material is w2%, the mass percentage content of the binder is w3%, and the mass percentage content of the conductive agent is w4%, 90≤w2≤98.95, 0.5≤w3≤5, and 0.5≤w4≤5.

[0049] The preparation method of the organic silicon and polyether modified ester polymer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the organic silicon and polyether modified ester polymer includes but is not limited to the following steps: placing polyether, polymer main body and catalyst in a reaction kettle, reacting at 180-240°C for 6-8h, and after post-treatment such as filtration and distillation, obtaining reaction product A, placing reaction product A, organic silicon and catalyst in a reaction kettle, and reacting at 75-95°C for 2-6h to obtain the organic silicon and polyether modified ester polymer. The catalyst is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the catalyst can include but is not limited to organic acid catalyst or titanium tetrachloride, and the above-mentioned organic acid catalyst can include but is not limited to benzene sulfonic acid, p-toluene sulfonic acid or phosphoric acid. In the present application, commercially available organic silicon and polyether modified ester polymers can also be used, which are not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0050] The preparation method of the positive electrode sheet is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode sheet includes but is not limited to the following steps: uniformly mixing the positive electrode active material, the conductive agent, the binder and the organic silicon and polyether modified ester polymer, adding a solvent to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on one surface of the positive electrode current collector, dried to obtain a positive electrode sheet with a single-side coated positive electrode material layer, and then the above steps are repeated on the other surface of the positive electrode current collector to obtain a positive electrode sheet with a double-side coated positive electrode material layer.

[0051] In the present application, the positive electrode slurry prepared by the method of "separating the positive electrode material layer from the positive electrode current collector to obtain a positive electrode material layer powder, dissolving the positive electrode material layer powder in N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 60-80%" has the same surface tension test results as the positive electrode slurry obtained in the process of preparing the positive electrode sheet.

[0052] The regulation method of the mass percentage content of the ester polymer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass percentage content of the ester polymer can be regulated by regulating the mass percentage content of the added ester polymer.

[0053] The regulation method of the surface tension of the positive electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, commercially available positive electrode current collectors with different surface tensions can be selected, and the surface tension of the positive electrode current collector can be tested by combining the test method of "surface tension test of positive electrode current collector" in the present application, and the positive electrode current collector with the desired surface tension can be selected.

[0054] The application does not have special restrictions on the regulation method of the surface tension of the positive electrode slurry, as long as the purpose of the application can be achieved. For example, the surface tension of the positive electrode slurry can be regulated by regulating the mass percentage of the ester polymer. Illustratively, when the mass percentage of the ester polymer is within a certain range, increasing the mass percentage of the ester polymer reduces the surface tension of the positive electrode slurry; reducing the mass percentage of the ester polymer increases the surface tension of the positive electrode slurry.

[0055] The application does not have special restrictions on the regulation method of the mass percentage of the organic silicon, as long as the purpose of the application can be achieved. For example, when the total mass of the reactants is constant, the mass percentage of the organic silicon can be regulated by regulating the amount of organic silicon added.

[0056] The application does not have special restrictions on the regulation method of the mass percentage of the polyether, as long as the purpose of the application can be achieved. For example, when the total mass of the reactants is constant, the mass percentage of the polyether can be regulated by regulating the amount of polyether added.

[0057] The application does not have special restrictions on the regulation method of the weight average molecular weight of the ester polymer, as long as the purpose of the application can be achieved. For example, commercially available ester polymers with different weight average molecular weights can be selected, and the weight average molecular weight of the ester polymer can be tested by combining the test method of "test of weight average molecular weight of ester polymer" in the application, and the ester polymer with the desired weight average molecular weight can be selected.

[0058] In the application, the coating weight of the positive electrode material layer can be regulated by means known to those skilled in the art, for example, when the positive electrode slurry is coated on the surface of the positive electrode current collector, the coating weight of the positive electrode material layer can be increased by increasing the coating amount of the positive electrode slurry on the basis of a certain solid content of the positive electrode slurry. The application does not have special restrictions, as long as the purpose of the application can be achieved.

[0059] In the application, the compaction density of the positive electrode material layer can be regulated by means known to those skilled in the art, for example, the compaction density of the positive electrode material layer can be regulated by regulating the cold pressing pressure of the cold pressing process. Illustratively, when other conditions are constant, increasing the cold pressing pressure increases the compaction density of the positive electrode material layer; reducing the cold pressing pressure reduces the compaction density of the positive electrode material layer.

[0060] The second aspect of the application provides a secondary battery comprising the positive electrode tab in any of the preceding embodiments. Therefore, the secondary battery provided by the application has good safety performance and kinetic performance.

[0061] In the present application, the secondary battery further includes a negative electrode tab including a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector in the thickness direction thereof, or can be provided on both surfaces of the negative electrode current collector in the thickness direction thereof. It should be noted that the "surface" herein can be the entire region of the negative electrode current collector, or can be a partial region of the negative electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved. The present application is not particularly limited to the negative electrode current collector as long as the object of the present application can be achieved, and for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector (for example, a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, or the like).

[0062] The negative electrode material layer of the present application includes a negative electrode active material. The present application is not particularly limited to the negative electrode active material as long as the object of the present application can be achieved, and for example, the negative electrode active material can include at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O 12 12 with a spinel structure, Li-Al alloy, or metallic lithium. The negative electrode material layer of the present application further includes a binder and a conductive agent. The present application is not particularly limited to the binder and the conductive agent in the negative electrode material layer as long as the object of the present application can be achieved, and for example, the binder in the negative electrode material layer can be at least one of the above-mentioned binders, and the conductive agent in the negative electrode material layer can be at least one of the above-mentioned conductive agents. The mass ratio of the negative electrode active material, the binder, and the conductive agent in the negative electrode material layer is not particularly limited in the present application, and can be selected by a person skilled in the art as needed as long as the object of the present application can be achieved.

[0063] The thickness of the negative electrode current collector is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the thickness of the negative electrode current collector is 4 μm to 12 μm. The thickness of the negative electrode material layer is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the thickness of the single-sided negative electrode material layer is 30 μm to 250 μm.

[0064] In the present application, the secondary battery further includes an electrolyte. The electrolyte includes a lithium salt. The kind of the lithium salt is not particularly limited in the present application, and a lithium salt known in the art can be used, and exemplarily, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis-trifluoromethanesulfonimide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluoro(oxalato)borate (LiBF2(C2O4), LiDFOB). The mass percentage content of the lithium salt in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved. The electrolyte includes a non-aqueous organic solvent. The non-aqueous organic solvent is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous organic solvent can include at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents. The above-mentioned carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The above-mentioned chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The above-mentioned cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The above-mentioned fluorinated carbonate compound can include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The above-mentioned ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphoric acid ester.The mass percentage content of the non-aqueous organic solvent in the electrolyte is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0065] In the present application, the secondary battery further includes a separator. The separator is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. The present application does not have a particular limitation on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0066] In the present application, the separator can include a base film and a surface treatment layer. The base film can be a non-woven fabric or a composite film with a porous structure, and the material of the base film can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base film, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing polymer and inorganic matter. For example, the inorganic layer includes inorganic particles and a separator binder, and the present application does not have a particular limitation on the inorganic particles, which can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application does not have a particular limitation on the separator binder, which can be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0067] The secondary battery of the present application further includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the art, which are not limited in the present application. The packaging bag is not particularly limited in the present application, and can be a packaging bag known in the art, as long as the purpose of the present application can be achieved. For example, an aluminum-plastic film packaging bag can be used.

[0068] The secondary battery of the present application is not particularly limited, and can include any device that undergoes an electrochemical reaction. In one embodiment of the present application, the secondary battery can include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.

[0069] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, or the like as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, then fixing the four corners of the entire stack structure with tape to obtain an electrode assembly of a stack structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, a current overprotection element, a guide plate, or the like can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging. The packaging bag is a packaging bag known in the art, and the present application does not limit it.

[0070] The third aspect of the present application provides an electronic device comprising the secondary battery of any of the preceding embodiments. Therefore, the electronic device provided by the present application has good use performance.

[0071] The present application does not particularly limit the type of electronic device, which can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, and the like.

[0072] Embodiments

[0073] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0074] Test methods and equipment:

[0075] Surface tension test of positive electrode current collector:

[0076] Draw lines on the surface of the positive current collector along the tape and its vertical direction with different dyne pens (manufacturer: ACCU), and the straight line does not shrink within 3s to reach this dyne value. Test three times with the same dyne pen, and if the straight line does not shrink within 3s each time, the dyne value is the surface tension of the positive current collector. For the positive current collector in the lithium ion battery, the positive current collector at the tab position is relatively flat, and the lithium ion battery can be disassembled, the welded tab is torn open, and the positive current collector at the tab position is taken for testing.

[0077] Surface tension test of positive electrode slurry:

[0078] Disassemble the lithium ion battery, take out the positive electrode sheet, wash the electrolyte on the positive electrode sheet with DMC solution, dry the positive electrode sheet, and then scrape off the positive electrode material layer powder with a small knife. The surface scanning of the positive electrode material layer powder is carried out by using a scanning electron microscope energy dispersive spectrometer, and the type of the positive electrode active material is obtained according to the obtained element types. According to the solid content given above (if the positive electrode active material is lithium iron phosphate, the solid content of the positive electrode slurry is 60% to 70%; if the positive electrode active material is nickel-cobalt-manganese ternary material, the solid content of the positive electrode slurry is 68% to 78%; if the positive electrode active material is lithium manganate, the solid content of the positive electrode slurry is 65% to 75%; if the positive electrode active material is lithium cobaltate, the solid content of the positive electrode slurry is 70% to 80%), the positive electrode material layer powder is uniformly dispersed into NMP to obtain a positive electrode slurry, and the surface tension of the positive electrode slurry is tested by using a contact angle measuring instrument (model: JC2000CS). Clean the sample injector, rinse it with the positive electrode slurry to be tested for 3 times, then suck the positive electrode slurry, drop the sample on the contact angle measuring instrument for testing, adopt the pendant drop method, select the pre-dropping photo for "image analysis", and obtain the surface tension of the positive electrode slurry. Each group of positive electrode slurry samples is tested 5 times, and the average value is taken.

[0079] Edge zone angle test:

[0080] Disassemble the lithium ion battery, take out the positive electrode sheet, and dry the positive electrode sheet. Then cut 5 cm from the first edge of the positive current collector along the Y direction with a slitting knife to obtain an edge zone slitting surface sample, and test the angle of the edge zone by using a charge-coupled device (CCD) detector. First, focus, twist the fine adjustment nut, adjust the image to be clear, and then take a photo, and then use the "angle measurement tool" to measure the angle of the edge zone. As shown in Figure 2 , the angle θ of the edge zone refers to the angle between the contact interface of the positive current collector and the edge zone and the contact interface of the edge zone and the air.

[0081] Mass percentage content of organosilicon and mass percentage content of polyether test:

[0082] The lithium ion battery is disassembled, the positive electrode sheet is taken out, the electrolyte on the positive electrode sheet is washed away using a DMC solution, the positive electrode sheet is dried, then the positive electrode material layer powder is scraped off using a small knife, the positive electrode active material and the conductive agent are removed through centrifugation, and then distillation is performed to obtain the ester polymer sample. The infrared spectroscopy is used to utilize the absorption peaks (the organic silicon characteristic peaks and the wave number ranges: the carbon hydrogen bond stretching vibration peak is 2000cm -1 to 2200cm -1 , the carbon silicon bond stretching vibration peak is 1000cm -1 to 1300cm -1 ; the polyether characteristic peaks and the wave number ranges: C-O is 800cm -1 to 1000cm -1 , O-H is 3200cm -1 to 3600cm -1 , and C=O is 1850cm -1 to 1600cm -1 ) generated by the ester polymer sample when absorbing infrared light at a specific wavelength, combined with a standard curve and a concentration calculation formula (the standard curve can be obtained through the Lambert Beer law, and the concentration can be obtained according to the standard curve and Y (concentration) = aX (absorbance) + b; wherein a and b can be obtained from the standard curve), to obtain the mass percentage content of the organic silicon and the mass percentage content of the polyether. The test wave number range of the infrared spectroscopy is 4000cm -1 to 400cm -1 .

[0083] Test of the weight average molecular weight of the ester polymer:

[0084] The lithium ion battery is disassembled, the positive electrode sheet is taken out, the electrolyte on the positive electrode sheet is washed away using a DMC solution, the positive electrode sheet is dried, then the positive electrode material layer powder is scraped off using a small knife, the positive electrode active material and the conductive agent are removed through centrifugation, and then distillation is performed to obtain the ester polymer. The gel chromatograph is used to test the weight average molecular weight of the ester polymer. 0.01g of the ester polymer is dissolved in 5mL of a solvent (N-methyl pyrrolidone) to obtain a solution, the solution is completely dissolved, the impurities in the solution are filtered out using a filter head, and then the gel chromatograph (model PL-GPC220) is used to test the weight average molecular weight of the ester polymer.

[0085] Test of the coating weight of the positive electrode material layer:

[0086] The lithium ion battery is disassembled, the positive electrode sheet is taken out, the positive electrode sheet is cleaned using DMC, and then the positive electrode sheet is dried. The area including the double-sided positive electrode material layer on the positive electrode sheet is selected, 10 pieces of the area with an area of 1540.25mm 2small discs, weigh, take the average value M; then remove the positive electrode material layer on 10 small discs, weigh, take the average value m. The coating weight CW of the positive electrode material layer = (M-m) / (2*1540.25).

[0087] The compaction density of the positive electrode material layer is tested as follows:

[0088] The lithium ion battery is disassembled, and the positive electrode sheet is taken out. After the positive electrode sheet is cleaned with DMC, the positive electrode sheet is dried. The area of the positive electrode sheet including the double-sided positive electrode material layer is selected, and 10 small discs with an area of 1540.25 mm 2 are cut by a disc cutter. The thickness of the small discs is measured by a micrometer, and the average value H is taken. Then the positive electrode material layer on 10 small discs is removed, weighed, and the average value m is taken. Then the thickness of the positive electrode current collector is measured by a micrometer, and the average value h is taken. The compaction density PD of the positive electrode material layer = (M-m) / [1540.25*(H-h)].

[0089] The drum edge value of the positive electrode sheet is tested as follows:

[0090] The lithium ion battery is disassembled, and the positive electrode sheet is taken out. After the positive electrode sheet is cleaned with DMC, the positive electrode sheet is dried. Then, along the Y direction, a 5 cm cut is made from the first edge of the positive electrode current collector by a cutting knife to obtain an edge area cut surface sample. The drum edge value of the positive electrode sheet is tested by a charge-coupled device (CCD) detector. First, focus, twist the fine adjustment nut, adjust the image to be clear, and then take a photo. Then, using the "parallel line measurement tool", the drum edge value of the positive electrode sheet is measured. As shown in Figure 3 , along the Z direction, the distance between the highest point of the edge area and the highest point of the main body area is the drum edge value G of the positive electrode sheet.

[0091] Example 1-1

[0092] Preparation of the positive electrode sheet

[0093] The positive electrode active material nickel-cobalt-manganese ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2), the conductive agent acetylene black, the binder polyvinylidene fluoride (PVDF), and the organosilicon and polyether modified ester polymer are mixed in a weight ratio of 90:4.5:4.5:1, NMP is added as a solvent, and a slurry with a solid content of 68wt% is prepared. After uniform vacuum stirring, a positive electrode slurry is obtained. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 120°C to obtain a single-sided coated positive electrode material layer positive electrode sheet; wherein the coating weight CW of the positive electrode material layer is 485 mg / 1540.25 mm 2Then the above steps are repeated on the other surface of the aluminum foil, i.e. a positive electrode tab with a double-side coated positive electrode material layer is obtained. After cold pressing, cutting and welding of the tab, the positive electrode tab is dried in vacuum at 85°C for 4h, and a positive electrode tab with a positive electrode material layer of 84mm x 867mm is obtained. The compacted density PD of the positive electrode material layer after cold pressing is 2.1g / cc.

[0094] wherein the organosilicon in the organosilicon and polyether modified ester polymer is trisiloxane, the polyether is lauryl alcohol polyether, and the polymer main body is polymethyl acrylate; the mass percentage of organosilicon is 15% and the mass percentage of polyether is 25% based on the mass of the ester polymer; the weight average molecular weight Mw of the ester polymer is 100000.

[0095] The structure of the prepared positive electrode tab is shown in Figure 1 The positive electrode material layer comprises an edge region and a main body region from the first edge to the second edge, the width W1 of the edge region is 4mm, and the width W2 of the main body region is 80mm; the thickness T1 of the edge region is 140μm, the thickness T2 of the main body region is 150μm, W1 / W2 is 5%, and T1 / T2 is 93%.

[0096] <Preparation of negative electrode tab>

[0097] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 95:2:2:1, deionized water is added, and the mixture is stirred uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry with a solid content of 75wt%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and is dried at 120°C to obtain a negative electrode tab with a single-side coated negative electrode material layer. The above steps are repeated on the other surface of the copper foil, i.e. a negative electrode tab with a double-side coated negative electrode material layer is obtained. After drying in vacuum at 120°C for 1h, the negative electrode tab is subjected to cold pressing, cutting, and slitting, and a negative electrode tab with a negative electrode active material layer of 88mm x 875mm is obtained.

[0098] <Preparation of electrolyte>

[0099] In an argon atmosphere glove box with a water content of less than 10ppm, non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1, and then lithium salt lithium hexafluorophosphate (LiPF6) is added and mixed uniformly to obtain an electrolyte. The mass percentage of lithium salt LiPF6 is 12.5% based on the mass of the electrolyte.

[0100] <Separator>

[0101] A porous polyethylene film (thickness: 7 μm, supplied by Celgard) was used as a separator.

[0102] Preparation of a lithium ion battery

[0103] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to function as a separator, and wound to obtain an electrode assembly. After welding the tabs, the electrode assembly was placed in an aluminum laminate packaging bag, dried, and then injected with an electrolyte solution. The lithium ion battery was obtained by performing processes such as vacuum packaging, standing, formation, degassing, and edge cutting.

[0104] Examples 1-2 to 1-20

[0105] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0106] Example 2-1

[0107] Except for adjusting the coating width so that the width of the edge region and the width of the main body region were as shown in Table 2, adjusting the surface tension of the positive electrode current collector to 32 dyn / cm, and adjusting the relevant preparation parameters according to Table 2, the rest was the same as Example 1-1.

[0108] Examples 2-2 to 2-4

[0109] Except for adjusting the coating weight so that the thickness of the edge region and the thickness of the main body region were as shown in Table 2, the rest was the same as Example 2-1.

[0110] Examples 2-5 to 2-7

[0111] Except for adjusting the relevant preparation parameters according to Table 2, the rest was the same as Example 2-1.

[0112] Example 3-1

[0113] Except for adjusting the relevant preparation parameters according to Table 3, the rest was the same as Example 1-1.

[0114] Examples 3-2 to 3-5

[0115] Except for adjusting the amount of addition of the organosilicon so that the mass percentage content of the organosilicon was as shown in Table 3, the rest was the same as Example 3-1.

[0116] Examples 3-6 to 3-9

[0117] Except for adjusting the amount of addition of the polyether so that the mass percentage content of the polyether was as shown in Table 3, the rest was the same as Example 3-1.

[0118] Example 3-10 to Example 3-13

[0119] The rest was the same as Example 3-1 except that the relevant preparation parameters were adjusted according to Table 3.

[0120] Example 3-14 to Example 3-15

[0121] The rest was the same as Example 3-1 except that the coating weight of the positive electrode material layer was adjusted by adjusting the coating amount of the positive electrode slurry, as shown in Table 3.

[0122] Example 3-16 to Example 3-17

[0123] The rest was the same as Example 3-1 except that the compaction density of the positive electrode material layer was adjusted by adjusting the cold-pressing pressure of the cold-pressing process, as shown in Table 3.

[0124] Comparative Example 1

[0125] The rest was the same as Example 1-1 except that the relevant preparation parameters were adjusted according to Table 1.

[0126] Comparative Example 2

[0127] The rest was the same as Example 2-1 except that the organic silicon and polyether modified ester polymer was not added in the preparation of the positive electrode tab, but polyvinylpyrrolidone (PVP) was added.

[0128] The preparation parameters and tab performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0129] Table 1

[0130]

[0131] Note: In Table 1, the degree of positive electrode tab edge shrinkage or edge curling from small to large is in turn: slight < general < moderate < severe, wherein "slight" means that the degree of positive electrode tab edge shrinkage or edge curling is relatively light, and the processing performance is good; "severe" means that the degree of positive electrode tab edge shrinkage or edge curling is relatively heavy, and the processing performance is poor, and the same applies to other examples.

[0132] Table 2

[0133]

[0134] As can be seen from Examples 1-1 to 1-20, Examples 2-1 to 2-7, and Comparative Examples 1 to 2, the positive electrode material layer includes an edge region and a main body region, the ratio of the width of the edge region to the width of the main body region, the thickness of the edge region, the thickness of the main body region, and the ratio of the thickness of the edge region to the thickness of the main body region are within the scope of the present application, the positive electrode material layer includes an ester polymer modified by organic silicon and polyether, and the organic silicon and polyether in the present application are selected, the angle of the edge region of the positive electrode tab is smaller, the value of G / T2 is smaller, and the value of D-γ×cosθ is smaller, the edge shrinkage or edge curling of the positive electrode tab is relatively slight, and the processing problem of the edge shrinkage or edge curling of the positive electrode tab in the coating process can be effectively improved. In Comparative Example 1, the positive electrode material layer does not include an ester polymer modified by organic silicon and polyether, the angle of the edge region of the positive electrode tab is larger, the value of G / T2 is larger, and the value of D-γ×cosθ is larger, and the processing problem of the edge shrinkage or edge curling of the positive electrode tab in the coating process is more serious. As can be seen from Comparative Example 2 and Example 2-1, the positive electrode material layer of Comparative Example 2 includes PVP, the angle of the edge region of the positive electrode tab is larger, the value of G / T2 is larger, and the value of D-γ×cosθ is larger, which indicates that adding an ester polymer modified by organic silicon and polyether to the positive electrode material layer can more effectively improve the processing problem of the edge shrinkage or edge curling of the positive electrode tab in the coating process.

[0135] The mass percentage content of the ester polymer can affect the degree of edge shrinkage or edge curling of the positive electrode tab in the coating process. As can be seen from Examples 1-1 to 1-13 and Examples 1-18 to 1-20, by adjusting the mass percentage content of the ester polymer within the scope of the present application, the angle of the edge region of the positive electrode tab is smaller, the value of G / T2 is smaller, and the value of D-γ×cosθ is smaller, the edge shrinkage or edge curling of the positive electrode tab is relatively slight, and the processing problem of the edge shrinkage or edge curling of the positive electrode tab in the coating process can be effectively improved. The mass percentage content of the ester polymer in Example 1-19 is low, and the effect of improving the edge shrinkage or edge curling of the positive electrode tab in the coating process is poor. The addition amount of the ester polymer and the improvement effect show an exponential distribution, the addition amount of the ester polymer is small in the early stage, the improvement effect is obviously improved as the addition amount increases, and the growth rate of the improvement effect decreases when the addition amount continues to increase. The mass percentage content of the ester polymer in Example 1-20 is high, and the effect of improving the edge shrinkage or edge curling of the positive electrode tab in the coating process is good, but the improvement effect is not great compared with Examples 1-1 to 1-13 and Example 1-18; moreover, the mass percentage content of the ester polymer is too high, which can affect the energy density of the lithium ion battery.

[0136] The surface tension of the positive electrode current collector can affect the degree of edge contraction or edge curling of the positive electrode tab during the coating process. As can be seen from Examples 1-11, Examples 1-14 to 1-17, by adjusting the surface tension of the positive electrode current collector within the scope of the present application, the angle of the edge region of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, the degree of edge contraction or edge curling of the positive electrode tab is relatively lighter, and the processing problem of edge contraction or edge curling of the positive electrode tab during the coating process can be effectively improved.

[0137] The mass percentage content of the ester polymer can affect the surface tension of the positive electrode slurry. As can be seen from Examples 1-1 to 1-13, Examples 1-18 to 1-20, the mass percentage content of the ester polymer is within the scope of the present application, and thus the surface tension of the positive electrode slurry is within the scope of the present application, the angle of the edge region of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, the degree of edge contraction or edge curling of the positive electrode tab is relatively lighter, and the processing problem of edge contraction or edge curling of the positive electrode tab during the coating process can be effectively improved.

[0138] By Figure 4 and Figure 7 It can be seen that, compared with Comparative Example 1, the degree of edge contraction of the positive electrode tab of Example 1-12 during the coating process is slight.

[0139] By Figure 5 and Figure 7 It can be seen that, compared with Comparative Example 1, the degree of edge contraction of the positive electrode tab of Example 1-11 during the coating process is slight.

[0140] By Figure 6 and Figure 7 It can be seen that, compared with Comparative Example 1, the degree of edge contraction of the positive electrode tab of Example 1-13 during the coating process is slight.

[0141] By Figure 7 and Figure 4 , Figure 5 , Figure 6 It can be seen that, compared with Example 1-12, Example 1-11, and Example 1-13, the degree of edge contraction of the positive electrode tab of Comparative Example 1 during the coating process is severe.

[0142] Table 3

[0143]

[0144] Note: In Table 3, the "positive electrode tab edge shrinkage or edge curl degree" in Examples 3-5 is "moderate (edge shrinkage)", which means that the positive electrode tab edge shrinkage degree is moderate and the positive electrode tab edge curl degree is slight, and the same applies to other examples.

[0145] The mass percentage of silicone and the mass percentage of polyether affect the dispersibility of the ester polymer, thereby affecting the edge shrinkage or edge curl degree of the positive electrode tab during coating. As can be seen from Examples 3-1 to 3-9, by adjusting the mass percentage of silicone and the mass percentage of polyether within the scope of the present application, the edge zone angle of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, and the edge shrinkage or edge curl degree of the positive electrode tab is relatively slight, which can effectively improve the processing problem of edge shrinkage or edge curl of the positive electrode tab during coating.

[0146] The weight average molecular weight of the ester polymer affects the edge shrinkage or edge curl degree of the positive electrode tab during coating. As can be seen from Examples 3-1, 3-10 to 3-13, by adjusting the weight average molecular weight of the ester polymer within the scope of the present application, the edge zone angle of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, and the edge shrinkage or edge curl degree of the positive electrode tab is relatively slight, which can effectively improve the processing problem of edge shrinkage or edge curl of the positive electrode tab during coating.

[0147] The coating weight of the positive electrode material layer affects the processing performance of the positive electrode tab, the cycle performance and the rate performance of the lithium ion battery. As can be seen from Examples 3-1, 3-14 and 3-15, by adjusting the coating weight of the positive electrode material layer within the scope of the present application, the edge zone angle of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, and the edge shrinkage or edge curl degree of the positive electrode tab is relatively slight.

[0148] The compaction density of the positive electrode material layer affects the processing performance of the positive electrode tab, the cycle performance and the rate performance of the lithium ion battery. As can be seen from Examples 3-1, 3-16 and 3-17, by adjusting the compaction density of the positive electrode material layer within the scope of the present application, the edge zone angle of the positive electrode tab is smaller, the value of G / T2 is smaller, the value of D-γ×cosθ is smaller, and the edge shrinkage or edge curl degree of the positive electrode tab is relatively slight.

[0149] It is to be noted that, in the present document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0150] Various embodiments are described herein with reference to particular applications with a specific configuration and contents for convenience. It is to be understood that the application is not limited to those embodiments but cover any technical equivalents in principle as far as they are within the scope of a patent protection. The same or similar parts or features between the embodiments are designated by the same reference numerals, and a repeated explanation of these parts or features is omitted.

[0151] The above description is merely illustrative of the application and is not to be taken in a limiting sense. It is contemplated that departures from the specific design choices disclosed can still come within the scope of the application.

Claims

1. A positive electrode tab, comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode current collector comprising opposite first and second edges along a width direction of the positive electrode tab, the positive electrode material layer comprising, in order from the first edge to the second edge, an edge region and a main body region, the edge region having a width of W1 mm, the edge region having a thickness of T1 pm, the main body region having a width of W2 mm, the main body region having a thickness of T2 pm, W1 / W2≤8%, 90%≤T1 / T2≤100%, 18≤T1≤300, 20≤T2≤300; the positive electrode material layer comprising an organosilicon and a polyether-modified ester polymer.

2. The cathode sheet of claim 1, wherein, The positive electrode tab satisfies at least one of the following characteristics: (1) the organosilicon comprises at least one of trisiloxane, polydimethylsiloxane, polyoxyethylene ether trisiloxane, or vinyltrimethoxysilane; (2) the polyether comprises at least one of monoallyl polyether, propylene glycol polyether, methylallyl alcohol polyoxyethylene ether, or lauryl alcohol polyether; (3) the polymer main body in the ester polymer comprises at least one of polybutyl acrylate, polymethyl acrylate, polycarbonate, polyvinyl acetate, or polyarylate; (4) the mass percentage content of the ester polymer is w1%, 0.05≤w1≤1, based on the mass of the positive electrode material layer.

3. The cathode sheet of claim 1, wherein, The positive electrode material layer is separated from the positive electrode current collector to obtain a positive electrode material layer powder, the positive electrode material layer powder is dissolved in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 60% to 80%, the surface tension of the positive electrode slurry is g N / m; the surface tension of the positive electrode current collector is D dyn / cm, the angle of the edge region is Q, 0≤D-g×cosQ≤15. 4.The positive electrode tab according to claim 3, satisfying at least one of the following characteristics: (1)26≤D≤39； (2) 30≤g≤45; (3) 5°≤Q≤75°.

5. The cathode sheet of Claim 1, wherein, The mass percentage content of the organosilicon is 10% to 25%, and the mass percentage content of the polyether is 20% to 30%, based on the mass of the ester polymer.

6. The cathode sheet of Claim 1, wherein, The weight average molecular weight Mw of the ester polymer is 10000 to 200000.

7. The cathode sheet of Claim 1, wherein, The positive electrode material layer satisfies at least one of the following characteristics: (1) a coating weight of the positive electrode material layer is CW, 100 mg / 1540.25 mm 2 ≤ CW≤ 500 mg / 1540.25 mm 2 ; (2) a compacted density of the positive electrode material layer is PD g / cc, 2.0≤ PD≤ 4.

0.

8. The cathode sheet of Claim 1, wherein, The drum edge value of the positive electrode tab is G pm, G / T2≤5%. 9.A secondary battery comprising the positive electrode tab according to any one of claims 1 to 8. 10.An electronic device comprising the secondary battery according to claim 9.

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