Positive electrode sheet, method for manufacturing the same, electrode assembly, and battery

Abstract

The application provides a positive electrode sheet, a preparation method thereof, an electrode assembly and a battery, and belongs to the technical field of batteries. The positive electrode sheet comprises a positive electrode current collector, and a plurality of positive electrode flat regions and positive electrode to-be-bent regions are sequentially arranged along the length direction of the positive electrode current collector. The positive electrode current collector is attached with a positive electrode active material layer on at least one side, wherein the capacity of the positive electrode active material contained in each square meter of the positive electrode flat region is greater than the capacity of the positive electrode active material contained in each square meter of the positive electrode to-be-bent region. The preparation method adopts double-layer coating on at least one side of the positive electrode current collector to form the positive electrode active material layer. The double-layer coating is combined with intermittent coating and continuous coating. The blank area formed by the intermittent coating covers the positive electrode to-be-bent region. Further, the electrode assembly and the battery are obtained. Through intermittent coating and continuous coating, defects or low-capacity main materials are constructed in the to-be-bent region of the positive electrode sheet, the capacity of the to-be-bent region of the positive electrode sheet is reduced, and then the lithium precipitation in the bent region of the wound battery cell is relieved, and the safety and service life of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular, to a positive electrode tab, a preparation method thereof, an electrode assembly and a battery. BACKGROUND

[0002] In a winding type electrode assembly, the bending degree is different inside and outside the bending area, the N / P of the inner bending area of the positive electrode tab covering the outer bending area of the negative electrode tab is reduced to a certain extent, and lithium precipitation is prone to occur. Once lithium precipitation occurs, not only the service life of the battery is reduced, but also the lithium dendrites pierce the separator, causing internal short circuit of the battery and safety risks.

[0003] For example, the patent application file with the Chinese patent application number 201220156974.5 and the application publication date of April 24, 2013 discloses a square lithium ion battery with winding structure. The lithium ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte, the positive electrode includes a positive electrode current collector and a positive electrode material layer coated on the positive electrode current collector, the ratio of the thickness of the positive electrode material layer in the corner area to the thickness of the positive electrode material layer in the body area of the positive electrode is less than or equal to 90%, and the length of the corner area in the winding direction is 0.5-4 cell thicknesses. Compared with the prior art, the battery optimizes the winding type square lithium ion battery with electrode structure, the thickness of the electrode material layer coated in the corner area of the electrode is lower than that in the body area, so as to reduce the stress caused by electrode expansion during charging and discharging and cycling of the battery, reduce the deformation rate of the battery, reduce the apparent thickness of the battery during cycling, improve the energy density of the battery, and improve the performance of the battery. However, during winding, the difference in thickness of the corner area will cause inconsistent winding tension at the corner, poor adhesion of the separator and the electrode tab, large local resistance difference during charging and discharging, and high risk of lithium precipitation.

[0004] The patent application with international publication number WO 2022 / 188009 Al and international publication date September 15, 2022 discloses a wound electrode assembly, a battery monomer, a battery and an electric device. The electrode assembly includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a first positive electrode winding end and a positive electrode winding middle section; the negative electrode sheet includes a first part and a second part; the active material layer of the negative electrode sheet exceeds the active material layer of the positive electrode sheet, and the difference between the maximum width of the negative electrode active material layer of the first part and the minimum width of the positive electrode active material layer of the first positive electrode winding end is greater than the difference between the maximum width of the negative electrode active material layer of the second part and the minimum width of the positive electrode active material layer of the positive electrode winding middle section. The electrode assembly can reduce the risk of lithium precipitation caused by the fact that the size of the part of the negative electrode active material layer of the negative electrode sheet exceeding the positive electrode active material layer of the positive electrode sheet along the winding axis direction does not meet the design requirements. However, the redundancy space given from the electrode sheet structure to solve the problem of lithium precipitation causes a certain degree of waste to the limited battery space, resulting in a large capacity loss, which cannot meet the increasingly high energy density demand of lithium batteries.

[0005] Therefore, it is urgent to seek a positive electrode sheet and its preparation method, an electrode assembly and a battery, which can reduce the risk of lithium precipitation without changing the original space of the battery. SUMMARY

[0006] 1. Problem to be solved

[0007] In view of the deficiencies of the prior art in reducing the risk of lithium precipitation, the present application provides a positive electrode sheet, which can improve the problem of easy lithium precipitation caused by the folding of the positive electrode sheet in the winding type battery core bending area.

[0008] The present application also provides a preparation method of the positive electrode sheet to obtain the positive electrode sheet of the present application.

[0009] Meanwhile, the present application also provides an electrode assembly and a battery,

[0010] 2. Technical solution

[0011] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0012] The positive electrode sheet comprises a positive electrode current collector, and the positive electrode current collector is sequentially provided with a plurality of positive electrode flat areas and positive electrode bending areas along the length direction. At least one side of the positive electrode current collector is attached with a positive electrode active material layer, wherein the capacity of the positive electrode active material contained in each square meter of the positive electrode flat area is greater than the capacity of the positive electrode active material contained in each square meter of the positive electrode bending area.

[0013] Further, two layers of positive electrode active material layers are attached on the positive electrode flat area, and one layer of positive electrode active material layer is attached on the positive electrode bending area.

[0014] Further, the capacity C of the positive electrode active material contained in the positive electrode bending area per square meter a1 mAh and the capacity C of the positive electrode active material contained in the positive electrode flat area per square meter a2 mAh are in a ratio K, that is, C a1 / C a2 =K, wherein 0

[0015] The preparation method of the positive electrode sheet, the double-layer coating is adopted on at least one side of the positive electrode current collector to form the positive electrode active material layer, the double-layer coating is combined with intermittent coating and continuous coating, and the blank area formed by the intermittent coating covers the positive electrode bending area. The positive electrode active material layer comprises a bottom layer and a surface layer, and the intermittent coating and the continuous coating are combined as follows: the bottom layer formed by the continuous coating and the surface layer formed by the intermittent coating, or the bottom layer formed by the intermittent coating and the surface layer formed by the continuous coating.

[0016] By combining the intermittent coating and the continuous coating, the defects or the low-capacity main material are constructed in the bending area of the positive electrode sheet, so as to reduce the capacity of the bending area of the positive electrode sheet:

[0017] The defect is that the positive electrode active material of the bottom layer is coated by the continuous coating, the positive electrode active material of the surface layer is coated by the intermittent coating, and the bending area is the intermittent blank area.

[0018] The low-capacity main material is that the positive electrode active material of the bottom layer is coated by the intermittent coating, and the positive electrode active material of the surface layer is coated by the continuous coating.

[0019] Further, the length of the blank area formed by the intermittent coating is greater than or equal to the length of the positive electrode bending area, wherein the length of the blank area formed by the intermittent coating is L a mm, and in the wound electrode assembly, La≥ the maximum length Ln of the negative electrode bending area.

[0020] Further, the positive electrode active material slurries of the intermittent coating and the continuous coating are the same or different.

[0021] The electrode assembly is a wound electrode assembly, and comprises at least one bending area. The bending area of the electrode assembly corresponds to the positive electrode sheet, the negative electrode sheet and the separator in sequence to form a wound structure, wherein the positive electrode bending area is bent.

[0022] Further, in the wound structure of the electrode assembly, the length of the positive electrode bending area formed by the positive electrode bending area is greater than or equal to the maximum length of the negative electrode bending area.

[0023] Further, in the turning of the wound structure, the capacity of the positive electrode sheet is C a mAh, the capacity of the negative electrode sheet is C c mAh, and C c *K / (Ca The preset N / P value is greater than or equal to 1.

[0024] Further, the diaphragm is a polypropylene porous membrane.

[0025] A battery comprising the electrode assembly.

[0026] 3. Beneficial effects

[0027] Compared with the prior art, the beneficial effects of the present application are:

[0028] The positive electrode tab of the present application makes up for the deficiency of N / P at the bending corner of the electrode assembly, avoids the defect of uneven thickness at the corner leading to uneven winding tension, effectively alleviates the risk of lithium precipitation at the corner of the electrode assembly roll core; at the same time, the present application solves the problem of lithium precipitation with small capacity loss on the basis of ensuring the original internal space of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Figure 1 is a structural schematic diagram of the electrode assembly of the present application;

[0030] Figure 2 Figure 2 is a partial enlarged view of the A area in Figure 1; Figure 1

[0031] Figure 3 Figure 3 is a partial schematic diagram of the application of the bottom continuous coating and surface intermittent coating positive electrode tab of the present application to the electrode assembly;

[0032] Figure 4 Figure 4 is an expanded schematic diagram of the positive electrode tab in Figure 3; Figure 3

[0033] Figure 5 Figure 5 is a partial schematic diagram of the application of the bottom intermittent coating and surface continuous coating positive electrode tab of the present application to the electrode assembly in one case;

[0034] Figure 6 Figure 6 is an expanded schematic diagram of the positive electrode tab in Figure 5; Figure 5

[0035] Figure 7 is a partial schematic diagram of the application of the bottom intermittent coating and surface continuous coating positive electrode tab of the present application to the electrode assembly in another case; Figure 7

[0036] Figure 8 is an expanded schematic diagram of the positive electrode tab in Figure 7; Figure 8 Figure 7 Figure 9 is a partial schematic diagram of the application of the bottom intermittent coating and surface continuous coating positive electrode tab of the present application to the electrode assembly in another case;

[0037] Figure 10 is an expanded schematic diagram of the positive electrode tab in Figure 9;

[0038] ​​​1. Positive electrode sheet; 11. Positive electrode current collector; 111. Positive electrode flat area; 112. Positive electrode to be bent area; 12. Positive electrode active material layer; 121. bottom layer; 122. surface layer; 2. Negative electrode sheet; 3. Separator. DETAILED DESCRIPTION

[0039] In the detailed description, the preparation of the materials is as follows:

[0040] I. Preparation of positive electrode sheet 1 material:

[0041] (1) Preparation of first positive electrode active material slurry:

[0042] 95-98% by weight of ternary positive electrode material (NCM), 0.5-1.5% by weight of carbon nanotube slurry (CNTs), 0.5-1.5% by weight of conductive carbon black (SP), 0.6-1.2% by weight of polyvinylidene fluoride (PVDF), and an appropriate amount of nitrogen-methyl pyrrolidone, the sum of the weight of each substance is 100%. Use a high-speed blender to stir and disperse, so that it forms a uniform first positive electrode active material slurry.

[0043] (2) Preparation of first positive electrode active material slurry: The second positive electrode active material is different from the first positive electrode active material in at least one of the conductive agent, the binder, the main material, or the ratio of the materials.

[0044] In the detailed description, the first positive electrode active material is a 5-series NCM material, and the second positive electrode active material is a 6-series or 7-series NCM material. The ratio of the second positive electrode active material NCM, CNTs, SP, and PVDF is 97:1.2:0.5:1.3, while the ratio of the first positive electrode active material NCM, CNTs, SP, and PVDF is 96.2:1.5:0.5:1.8.

[0045] In different embodiments, one or both of the first positive electrode active material and the second positive electrode active material are used, and a twice or double-layer coating method is used: intermittent for the bottom layer, the intermittent width of the bottom layer is the length of the outermost electrode sheet bending area, and continuous for the surface layer. The slurry is coated onto the aluminum foil current collector, and after drying, the positive electrode density is pressed to 3.4 g / cm 3 The specific capacity of the positive electrode corner area 122 and the positive electrode flat area 121 is shown in Table 1; the electrode sheet is cut to the appropriate size to obtain the positive electrode sheet 1.

[0046] II. Preparation of negative electrode sheet 2 material:

[0047] 95-96 parts by weight of natural graphite powder, 1-2 parts by weight of conductive carbon black (SP), 1.5-2.5 parts by weight of butadiene-styrene rubber (emulsion, solid content about 50%, 1.5-2.5% is the weight ratio of dry substance), 1-2 parts by weight of sodium carboxymethyl cellulose, and an appropriate amount of water, the sum of the parts by weight of each substance being 100%. A high-speed mixer is used to stir and disperse, so that a uniform negative electrode slurry is formed. The slurry is coated onto a copper foil current collector, the solvent is dried, and after drying the electrode is compacted, and after compaction the density of the coating is about 1.6 g / cm 3 ; the electrode is cut to the appropriate size to obtain a negative electrode 2.

[0048] III. Preparation of electrolyte: lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent with a weight ratio of ethylene carbonate: diethyl carbonate: methyl ethyl carbonate = 1:1:1, so that the lithium salt concentration is 1 mole per liter, and vinylene carbonate is added as an additive, the weight of the vinylene carbonate in the electrolyte is 3%, to obtain the electrolyte.

[0049] IV. Preparation of separator 3: a polypropylene porous membrane is selected.

[0050] V. Preparation of lithium ion secondary battery: the positive electrode, the separator, and the negative electrode are wound to form an electrode assembly, with the separator between the positive electrode and the negative electrode. The obtained electrode assembly is placed in a battery case, electrolyte is injected into the battery case, and after infiltration and formation, the battery is sealed to complete the preparation of the battery.

[0051] The application will be further described below in conjunction with specific examples.

[0052] Example 1

[0053] In the specific embodiment, the positive electrode 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12 formed by a first positive electrode active material slurry, and the positive electrode current collector 11 has a positive electrode flat area 111 and a positive electrode to-be-bent area 112 distributed along the length direction in sequence: the positive electrode flat area 111 has two layers of positive electrode active material layers 12 attached, which are a bottom layer 121 and a surface layer 122; and the positive electrode to-be-bent area 112 has only one layer of positive electrode active material layer 12 attached, i.e., the bottom layer 121, as shown in Figure 3 and Figure 4 .

[0054] The preparation method of the positive electrode of this embodiment includes: using double-layer coating on at least one side of the positive electrode current collector 11, wherein the bottom layer 121 is coated by continuous coating, and the surface layer 122 is coated by intermittent coating; the positive electrode flat area 111 contains a bottom layer continuous coating coating area and a surface layer intermittent coating coating area; and the positive electrode to-be-bent area 112 is an intermittent coating blank area, which contains only a bottom layer continuous coating coating area. The positive electrode to-be-bent area 112 contains a positive electrode active material capacity of C a1The positive electrode flat region 111 contains a positive electrode active material capacity of C per square meter. a2 C a1 / C a2 =K, 0 < K ≤ 0.98.

[0055] The electrode assembly in this embodiment, such as Figure 1 and Figure 2 As shown, the number of folds in the wound negative electrode is n, and the length of the intermittently coated blank area is L. a mm, La ≥ maximum length of negative electrode bending region L n The electrode assembly has an inward fold of the same area, with the effective positive electrode inward fold covering the negative electrode outward fold. The positive electrode capacity is C. a mAh, negative electrode capacity is C c mAh, C c *K / (C a *Preset N / P value)≥1. Wherein, the flat region of the positive electrode corresponds to the flat region of the negative electrode sheet, the capacity of the positive active material in the positive electrode flat region 111 is C1 mAh, and the capacity of the negative active material on the side opposite the positive electrode flat region 111 is C2 mAh; preset N / P value = C2 / C1.

[0056] Example 2

[0057] The same coating method as in Example 1 was used, except that, as Figure 3 As shown and Figure 4 The bottom layer 121 is continuously coated with the first positive electrode active material slurry, and the surface layer 122 is intermittently coated with the second positive electrode active material slurry. The second active material is different from the first positive electrode active material in at least one of the materials or ratios such as conductive agent, binder, and positive electrode main material. The second positive electrode active material has a higher capacity to reduce the thickness difference between the bending area and the straight area.

[0058] The active material mass ratio of the first positive electrode active material slurry is w t1 The percentage is 95-98%, and the specific capacity is C'mAh / g; the active material mass ratio of the second positive electrode slurry is w t2 The percentage is 95-98%, and the specific capacity is C" mAh / g. The positive electrode active material, with the same area of ​​the straight region and the region to be bent, is taken from the inner fold. ρ1*w t1 %*C' / (ρ1*w t1 %*C'+ρ2*w t2 %*C”)=K.

[0059] Example 3

[0060] like Figure 5 and Figure 6As shown, a first positive electrode active material is applied to the positive electrode current collector in an intermittent coating manner to form a bottom layer 121. The straight positive electrode region 111 is the intermittent coating region, and the positive electrode region to be bent 112 is the intermittent coating blank region. A second positive electrode active material slurry is applied to the surface of the bottom layer 121 in a continuous coating manner to form a surface layer 122.

[0061] The surface area density of the coating on the bottom layer 121 of the straight region of the positive electrode is ρ3, and the surface area density of the coating on the top layer 122 is ρ4; the surface area density of the coating on the region to be bent in the positive electrode is ρ5. Take positive electrode active materials of the same area in the straight region and the region to be bent:

[0062] ρ5*w t2 %*C” / (ρ3*w t1 %*C'+ρ4*w t2 %*C”)=K.

[0063] Example 4

[0064] like Figure 7 and Figure 8 As shown, a second positive electrode active material slurry is applied to the positive electrode current collector 11 in an intermittent coating manner to form a bottom layer 121. The straight positive electrode region 111 is an intermittent blank region, and the positive electrode region to be bent 112 is an intermittent coating region. A first positive electrode active material slurry is applied continuously to form a surface layer 122, that is, the first positive electrode active material slurry is applied to the surface of the bottom layer second positive electrode active material and the intermittent coating blank region.

[0065] The surface area density of the coating in the straight region 111 of the positive electrode is ρ6; the surface area density of the bottom coating in the region to be bent 112 of the positive electrode is ρ7, and the surface area density of the top coating is ρ8; positive electrode active materials of the same area in the straight region and the region to be bent are taken as follows:

[0066] (ρ8*w t1 %*C'+ρ7*w t2 %*C”) / (ρ6*w t1 %*C')=K.

[0067] Through the above four embodiments, the capacity of the lithium-ion battery positive electrode sheet of this application exhibits a regionally differentiated distribution, resulting in a certain degree of reduction in the capacity within the bending area of ​​the positive electrode sheet, thus reducing lithium deposition in the bending area. The specific implementation methods of the above four embodiments are described in detail below:

[0068] The first aspect of the present application provides a lithium ion battery positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer sequentially stacked on the positive electrode current collector by continuous coating and intermittent coating. The positive electrode active material layer contains positive electrode active material, conductive agent and binder; wherein the content of positive electrode active material is 95-98wt%, the content of conductive agent is 1-2wt%, and the content of binder is 1-2wt%. By using the combination of continuous coating and intermittent coating, the capacity of the positive electrode active material in the positive electrode inner fold covering the negative electrode outer fold at the to-be-bent area is reduced, the N / P in this area is reduced, and the lithium precipitation problem in this area is effectively alleviated.

[0069] In Example 1, the first positive electrode active material slurry is continuously coated on the positive electrode current collector 11 to form a bottom layer 121, and the first positive electrode active material slurry is coated on the surface of the first positive electrode active material in the bottom layer 121 to form a surface layer 122. The intermittent coating area is a flat area, and the intermittent blank area is a to-be-bent area.

[0070] Wherein, the number of winding negative electrode folds is n, the length of the intermittent coating blank area is La mm, and La≥the maximum length Ln of the negative electrode to-be-bent area. Wherein, the number of winding negative electrode folds is increased by 1 for each time the negative electrode sheet passes through the bending area. For example, if the negative electrode sheet winds around the winding needle for 5 times, the number of winding negative electrode folds is 10.

[0071] Preferably, the active material content of the first positive electrode active material slurry is w t1 %, the surface density of the bottom layer continuous coating area is p1, and the surface density of the surface layer intermittent coating area is p2; p1 / (p1+p2)=K, 0

[0072] Preferably, in the effective positive electrode inner fold covering the negative electrode outer fold area of the to-be-bent area, the positive electrode capacity is C a mAh, the negative electrode capacity is C c mAh, and C c *K / (C a *the preset N / P value)≥1. Wherein, the flat area 111 of the negative electrode sheet corresponds to the first positive electrode active material flat area 121, the capacity of the first positive electrode active material flat area is C1 mAh, and the capacity of the negative electrode active material on the side opposite to the first positive electrode active material flat area is C2 mAh; the preset N / P value=C2 / C1.

[0073] The embodiment 2 uses the same coating method as the embodiment 1, and the only difference is that the first positive electrode active material is continuously coated in the bottom layer, and the second positive electrode active material is intermittently coated in the surface layer, wherein the second active material and the first positive electrode active material are different in at least one of the conductive agent, the binder, the positive electrode main material, or the material or ratio.

[0074] The active material mass ratio w of the first positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g. t1 The active material mass ratio w of the second positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g. t2 The active material mass ratio w of the second positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g. t1 The active material mass ratio w of the second positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g. t1 The active material mass ratio w of the second positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g. t2 The active material mass ratio w of the second positive electrode active material slurry is 95-98%, and the gram capacity is C'mAh / g.

[0075] In the embodiment 3, the first positive electrode active material 126 is intermittently coated on the positive electrode current collector in the bottom layer, the flat area is the intermittent coating area, the to-be-bent area is the intermittent coating blank area, and the second positive electrode active material 127 is continuously coated on the surface of the bottom layer.

[0076] The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w t2 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w t1 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w t2 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w

[0077] In the embodiment 4, the second positive electrode active material 126 is intermittently coated on the positive electrode current collector in the bottom layer, the flat area is the intermittent blank area, the to-be-bent area is the intermittent coating area, and the first positive electrode active material 127 is continuously coated on the surface of the second positive electrode active material in the bottom layer and the intermittent coating blank area.

[0078] Preferably, the coating surface density of the flat area is ρ6, the coating surface density of the bottom layer in the to-be-bent area is ρ7, and the coating surface density of the surface layer is ρ8. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and (ρ8*w t1 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w t2 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w t1 The coating surface density of the flat area in the bottom layer is ρ3, the coating surface density of the surface layer is ρ4, and the coating surface density of the to-be-bent area is ρ5. The same area of the flat area and the to-be-bent area of the positive electrode active material is taken, and ρ5*w

[0079] The batteries obtained in the embodiments 1-4 are subjected to battery cycle test, and the method is as follows:

[0080] The battery was constrained by two steel plates with a constraint force of about 100 kgf, charged to 4.3 V at 25 DEG C with a 1C rate constant current and constant voltage, the cutoff current was 0.05C, and then rested for 1 h, and then discharged to 2.8 V with a 1C constant current, and then rested for 1 h; the cycle was repeated for 100 times, the battery was disassembled, and the lithium precipitation at the corner of the negative electrode sheet was tested, as shown in Table 1:

[0081] Table 1 Performance test of the battery of Examples 1-4

[0082]

[0083] The examples described in the present application are merely to describe the preferred embodiments of the present application, and do not limit the concept and scope of the present application. Without departing from the design idea of the present application, various modifications and improvements of the technical solutions of the present application made by the engineering and technical personnel in the field shall fall within the protection scope of the present application.

Claims

1. An electrode assembly, characterized in that: Includes positive electrode plate, negative electrode plate (2) and separator (3): The positive electrode sheet includes a positive current collector (11), and the positive current collector (11) has several positive straight regions (111) and positive bending regions (112) distributed sequentially along its length. The positive current collector (11) has a positive active material layer (12) attached to at least one side. The positive active material per square meter of the positive straight region (111) is greater than the positive active material per square meter of the positive bending region (112). The ratio of the positive active material per square meter of the positive bending region (112) to the positive active material per square meter of the positive straight region (111) is K, where 0.90≤K≤0.

98. Method for preparing positive electrode sheet: A positive active material layer (12) is formed on at least one side of the positive current collector (11) by double coating. The double coating adopts a combination of intermittent coating and continuous coating. The blank area formed by intermittent coating covers the positive electrode bending area (112). The double coating is first applied to the positive current collector by intermittent coating, and then a surface layer is formed on the surface of the bottom layer by continuous coating. A positive electrode sheet, together with a negative electrode sheet (2) and a separator (3), forms a wound electrode assembly, wherein the positive electrode bending area (112) is bent; at the bend of the wound structure, the capacity of the positive electrode sheet is C. a mAh, the capacity of the negative electrode is C c mAh, C c *K / (C a *Preset N / P value) ≥ 1.

2. The electrode assembly according to claim 1, characterized in that: The length of the blank area formed by intermittent coating is greater than or equal to the length of the positive electrode bending area (112).

3. An electrode assembly according to claim 1, characterized in that: The capacity of the positive electrode active material slurry used in intermittent coating and continuous coating may be the same or different.

4. An electrode assembly according to any one of claims 1 to 3, characterized in that: The diaphragm (3) is a polypropylene porous membrane.

5. A battery, characterized in that: It includes the electrode assembly as described in claim 4.

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