Winding type positive plate and secondary battery

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a coiled positive plate and a secondary battery, the coiled positive plate comprises a positive current collector, a safety coating and a positive active material layer, the length of the safety coating is less than or equal to that of the positive current collector, and the length of the safety coating is less than or equal to that of the positive active material layer. The length of the positive active material layer is smaller than or equal to that of the safety coating, and the bonding force of the safety coating is larger than that of the positive active material layer. According to the invention, the safety coating is arranged between the positive current collector and the positive active material layer, and the bonding force of the safety coating is relatively large, so that the positive current collector and the safety coating are firmly bonded, and the positive current collector is prevented from being in contact with the negative active material layer when the battery cell is subjected to a mechanical abuse safety test, so that the mechanical abuse safety of the battery cell is improved; and meanwhile, the safety coating increases the diaphragm resistance of the positive pole piece, reduces the short-circuit current in the mechanical abuse safety test process, and improves the safety performance of the battery cell.

Description

[0001] This application is a divisional application of patent application filed on August 25, 2022, with application number 202211026486.7 and invention title "A wound positive electrode sheet and a secondary battery". Technical Field

[0002] This invention belongs to the field of secondary battery technology, and particularly relates to a wound positive electrode and a secondary battery. Background Technology

[0003] Lithium-ion batteries are widely used in power fields such as electric vehicles and consumer fields such as mobile phones, watches, tablets, and laptops because of their advantages such as high specific energy, strong range, long cycle life, wide operating range, short charging time, and ability to discharge at high current.

[0004] As lithium-ion batteries gradually develop towards fast charging and high energy density, the safety issues associated with battery cells have become a major concern. Mechanical abuse safety tests for lithium-ion batteries, such as needle penetration, unilateral compression, and foreign object compression, are a focus of attention.

[0005] Lithium-ion batteries can experience four types of short circuits during tests such as nail penetration, unilateral extrusion, and foreign object extrusion: "positive electrode active material and negative electrode active material", "positive electrode active material and negative electrode current collector", "positive electrode current collector and negative electrode active material", and "positive electrode current collector and negative electrode current collector". Among these four short circuit types, the short circuit between the "positive electrode current collector and negative electrode active material" is the most likely to cause thermal runaway.

[0006] Existing separators and electrolytes have limited ability to improve cell safety, primarily focusing on thermal abuse safety improvements such as thermal shock. They offer little effect on mechanical abuse safety improvements such as needle penetration, 45° needle penetration, and foreign object compression. Therefore, a technical solution to address these issues is urgently needed. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a wound positive electrode sheet with a safety coating between the positive current collector and the positive active material layer. The safety coating has a strong adhesive force, ensuring a firm bond between the positive current collector and the safety coating. This prevents the positive current collector from contacting the negative active material layer during mechanical abuse safety testing, thus improving the mechanical abuse safety of the battery cell. At the same time, the safety coating increases the film resistance of the positive electrode sheet, reducing the short-circuit current during mechanical abuse safety testing and enhancing the safety performance of the battery cell.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A wound positive electrode sheet includes a positive current collector, a safety coating disposed on at least one side of the positive current collector, and a positive active material layer disposed on the side of the safety coating away from the positive current collector. The length of the safety coating is less than or equal to the length of the positive current collector, the length of the positive active material layer is less than or equal to the length of the safety coating, and the adhesive force of the safety coating is greater than the adhesive force of the positive active material layer.

[0010] Preferably, the thickness of the safety coating is less than the thickness of the positive electrode active material layer.

[0011] Preferably, the safety coating comprises the following raw materials in parts by weight: 80-97 parts of inorganic filler, 1-10 parts of first conductive agent, and 2-10 parts of first binder.

[0012] Preferably, the inorganic filler includes one or more of alumina, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, and yttrium oxide.

[0013] Preferably, the first conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the first binder is one or more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate.

[0014] Preferably, the positive electrode active material layer comprises the following raw materials in parts by weight: 90-98 parts of positive electrode active material, 1-6 parts of second conductive agent, and 1-4 parts of second binder.

[0015] Preferably, the positive electrode active material includes one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide.

[0016] Preferably, the first conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the first binder is one or more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate.

[0017] Preferably, the resistance value of the safety coating is 0.2 to 4 Ω.

[0018] Another objective of this invention is to provide a secondary battery that can pass mechanical abuse safety tests such as needle penetration, one-sided compression, and foreign object compression, thus exhibiting good safety performance, in order to address the shortcomings of the prior art.

[0019] To achieve the above objectives, the present invention adopts the following technical solution:

[0020] A secondary battery includes a separator, a negative electrode, an electrolyte, and a housing. The separator separates the positive electrode and the negative electrode, and the housing encapsulates the positive electrode, the separator, the negative electrode, and the electrolyte. The positive electrode is a wound positive electrode as described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a safety coating between the positive current collector and the positive active material layer. The safety coating has a large adhesive force, which makes the positive current collector and the safety coating firmly bonded. This reduces the contact between the positive current collector and the negative active material layer during mechanical abuse safety testing, thereby improving the mechanical abuse safety of the battery cell. At the same time, the safety coating increases the film resistance of the positive electrode sheet, reduces the short-circuit current during mechanical abuse safety testing, and improves the safety performance of the battery cell. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 1 of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 2 of the present invention.

[0024] Figure 3 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 3 of the present invention.

[0025] Figure 4 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 4 of the present invention.

[0026] Figure 5 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 5 of the present invention.

[0027] Figure 6 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 6 of the present invention.

[0028] Figure 7 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 7 of the present invention.

[0029] Figure 8 This is a schematic diagram of the structure of the wound positive electrode sheet of Embodiment 8 of the present invention.

[0030] Among them: 1. Positive current collector; 2. Safety coating; 3. Positive active material layer. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0032] A wound positive electrode sheet includes a positive electrode current collector 1, a safety coating 2 disposed on at least one side of the positive electrode current collector 1, and a positive electrode active material layer 3 disposed on the side of the safety coating 2 away from the positive electrode current collector 1. The length of the safety coating 2 is less than or equal to the length of the positive electrode current collector 1, the length of the positive electrode active material layer 3 is less than or equal to the length of the safety coating 2, and the adhesive force of the safety coating 2 is greater than the adhesive force of the positive electrode active material layer 3. Preferably, the length of the long film surface of the positive electrode active material layer 3 is less than the length of the safety coating 2 on the other side.

[0033] This invention increases the film resistance of the positive electrode by providing a safety coating 2 between the positive current collector 1 and the positive active material layer 3, thereby reducing the short-circuit current of the battery cell during mechanical abuse safety testing. Furthermore, the safety coating 2 has good adhesion, preventing it from detaching during mechanical abuse safety testing and avoiding direct contact between the current collector and the negative active material layer; thus improving the mechanical abuse safety performance of the battery cell.

[0034] In some embodiments, the thickness of the safety coating 2 is less than the thickness of the positive electrode active material layer 3. The safety coating 2 has a thinner thickness, which can cover the surface of the positive electrode current collector 1, reducing the risk of short circuit when the negative electrode directly contacts the positive electrode current collector 1 during mechanical abuse testing, thereby increasing the mechanical abuse safety of the cell, while not occupying too much volume and having little impact on energy density.

[0035] In some embodiments, the safety coating 2 comprises the following raw materials in parts by weight: 80-97 parts of inorganic filler, 1-10 parts of first conductive agent, and 2-10 parts of first binder. The presence of inorganic filler in the safety coating 2 increases its resistance, improves the pass rate of mechanical abuse tests, and the presence of a significant amount of first binder gives the safety coating 2 greater adhesion, ensuring a firm bond between the positive current collector 1 and the positive active material layer 3, resulting in good mechanical properties of the electrode. Preferably, the safety coating 2 comprises the following raw materials in parts by weight: 80-90 parts of inorganic filler, 3-10 parts of first conductive agent, and 5-8 parts of first binder; 82-90 parts of inorganic filler, 4-10 parts of first conductive agent, and 5-7 parts of first binder; specifically, 82 parts of inorganic filler, 6 parts of first conductive agent, and 8 parts of first binder; 85 parts of inorganic filler, 7 parts of first conductive agent, and 9 parts of first binder; and 87 parts of inorganic filler, 8 parts of first conductive agent, and 7 parts of first binder.

[0036] In some embodiments, the inorganic filler includes one or more of alumina, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, and yttrium oxide. Inorganic fillers have poor electrical conductivity; their addition to the safety coating 2 imparts a certain resistance, thereby increasing the resistance value during a short circuit, reducing the short-circuit current, and improving safety performance. Furthermore, inorganic fillers are heat-resistant materials, which can increase the heat resistance of the safety coating 2, thereby improving safety performance. Preferably, the inorganic filler is boehmite.

[0037] In some embodiments, the first conductive agent is one or a combination of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the first binder is one or a combination of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate. The first binder can bond the inorganic filler and the first conductive agent together to form the safety coating 2, and the first binder can also bond to the positive electrode current collector 1 and the second binder in the positive electrode active coating, thereby improving the overall strength of the electrode sheet. The first conductive agent can improve the conductivity of the safety coating 2, which is beneficial for ion insertion / extraction and electron conduction.

[0038] In some embodiments, the positive electrode active material layer 3 comprises the following raw materials in parts by weight: 90-98 parts of positive electrode active material, 1-6 parts of second conductive agent, and 1-4 parts of second binder. Compared with the safety coating 2, the positive electrode active material layer 3 uses positive electrode active material instead of inorganic filler, thereby increasing capacity. Moreover, the amount of second binder in the positive electrode active material layer 3 is smaller, which helps to improve ion intercalation and deintercalation, thereby improving chemical performance.

[0039] In some embodiments, the positive electrode active material includes one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide. The presence of lithium in the positive electrode active material can improve capacity.

[0040] In some embodiments, the first conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the first binder is one or more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate.

[0041] In some embodiments, the resistance value of the safety coating 2 is 0.2 to 4 Ω.

[0042] A secondary battery that can pass mechanical abuse safety tests such as needle penetration, one-sided compression, and foreign object compression, has good safety performance.

[0043] A secondary battery includes a positive electrode, a separator, a negative electrode, an electrolyte, and a housing. The separator separates the positive electrode and the negative electrode, and the housing encapsulates the positive electrode, the separator, the negative electrode, and the electrolyte. The positive electrode is a wound positive electrode as described above.

[0044] The positive electrode sheet includes a positive current collector 1 and a positive active coating disposed on at least one surface of the positive current collector 1. The positive current collector 1 is typically a structure or component that collects current. The positive current collector 1 can be any material suitable for use as a positive current collector 1 in a lithium-ion battery. For example, the positive current collector 1 can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0045] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which may be one or more of the following: graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion batteries, for example, it may be, but is not limited to, metal foil, and more specifically, copper foil. The negative electrode active material layer also includes a binder and a conductive agent, wherein the binder is polyvinylidene fluoride.

[0046] The separator can be any material suitable for lithium-ion battery separators in the art, such as, but not limited to, one or more combinations of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0047] The shell is made of either aluminum-plastic film or stainless steel.

[0048] Example 1

[0049] (1) Boehmite, conductive carbon, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 92:5:3. The viscosity of the slurry after mixing was 1550 mPa·s. The slurry was then uniformly coated onto both sides of the positive electrode current collector 1 using a gravure coating to obtain a safety coating 2. At this time, the coating length of the safety coating 2 on both sides was equal to the length of the electrode sheet. Figure 1The current collector thickness is 9 μm, and the coating surface density is 14 mg / 1540.25 mm. 2 At this point, the diaphragm resistance was measured to be 0.8Ω and the Mohs hardness to be 7.

[0050] (2) Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride binder are mixed evenly at a mass ratio of 96:2.5:1.5 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The slurry is coated onto the aluminum foil of the positive electrode current collector 1 with the safety coating 2. The coating length of the positive electrode active material layer 3 on both sides is less than that of the safety coating 2. Figure 1 This process produces a wound positive electrode sheet. On the shorter side of the wound positive electrode sheet, the length of the positive active material layer 3 is less than the length of the safety coating 2. On the longer side of the wound positive electrode sheet, the length of the positive active material layer 3 is less than the length of the safety coating 2. The lengths of the safety coating 2 on both sides are equal to the length of the positive current collector 1. At this point, the film resistance of the positive electrode sheet is 2.0Ω. The positive electrode sheet is then cold-pressed; subsequently, it is trimmed, cut, and slit. After slitting, it is dried at 110℃ under vacuum for 4 hours, and then the tabs are welded to produce a lithium-ion battery positive electrode sheet.

[0051] (3) Preparation of lithium-ion batteries:

[0052] The positive electrode, separator, and negative electrode are wound together to form a battery cell. The separator is located between the positive and negative electrode. The positive electrode is led out by spot welding with aluminum tabs, and the negative electrode is led out by spot welding with nickel tabs. Then the battery cell is placed in an aluminum-plastic packaging bag, electrolyte is injected, and after processes such as encapsulation, formation, and capacity testing, a lithium-ion battery is manufactured.

[0053] Example 2

[0054] The difference from Example 1 is that: the length of the positive electrode active material layer 3 on the short film side of the wound positive electrode sheet is less than the length of the safety coating 2, the length of the positive electrode active material layer 3 on the long film side of the wound positive electrode sheet is equal to the length of the safety coating 2, and the lengths of the safety coatings 2 on both sides are equal to the lengths of the positive electrode current collector 1. Figure 2 .

[0055] The rest is the same as in Example 1.

[0056] Example 3

[0057] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is equal to the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is equal to the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode current collector 1. Figure 3 .

[0058] The rest is the same as in Example 1.

[0059] Example 4

[0060] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is equal to the length of the safety coating 2, the length of the safety coating 2 is less than the length of the positive electrode current collector 1, and the lengths of the safety coating 2 on both sides are equal. Figure 4 .

[0061] The rest is the same as in Example 1.

[0062] Example 5

[0063] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, the length of the safety coating 2 is equal to the length of the positive electrode current collector 1, and the length of the positive electrode active material layer 3 in the long film surface is equal to the length of the safety coating 2 in the short film surface. Figure 5 .

[0064] The rest is the same as in Example 1.

[0065] Example 6

[0066] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode current collector 1, and the lengths of the safety coating 2 on both sides are equal. Figure 6 .

[0067] The rest is the same as in Example 1.

[0068] Example 7

[0069] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode current collector 1, and the length of the safety coating 2 on the short film surface is less than the length of the safety coating 2 on the other side. Figure 7 .

[0070] The rest is the same as in Example 1.

[0071] Example 8

[0072] The difference from Example 1 is that: in the short film surface of the wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode active material layer 3; in the long film surface of the paper-wound positive electrode sheet, the length of the positive electrode active material layer 3 is less than the length of the safety coating 2, and the length of the safety coating 2 is less than the length of the positive electrode current collector 1, and the length of the safety coating 2 on the short film surface is greater than the length of the safety coating 2 on the other side. Figure 8 .

[0073] The rest is the same as in Example 1.

[0074] Example 9

[0075] The difference from Example 1 is that the safety coating 2 comprises the following raw materials in parts by weight: 90 parts of inorganic filler, 5 parts of first conductive agent, and 5 parts of first binder.

[0076] The rest is the same as in Example 1.

[0077] Example 10

[0078] The difference from Example 1 is that the safety coating 2 comprises the following raw materials in parts by weight: 88 parts of inorganic filler, 8 parts of first conductive agent, and 4 parts of first binder.

[0079] The rest is the same as in Example 1.

[0080] Example 11

[0081] The difference from Example 1 is that the safety coating 2 comprises the following raw materials in parts by weight: 85 parts of inorganic filler, 9 parts of first conductive agent, and 6 parts of first binder.

[0082] The rest is the same as in Example 1.

[0083] Example 12

[0084] The difference from Example 1 is that the safety coating 2 comprises the following raw materials in parts by weight: 83 parts of inorganic filler, 9 parts of first conductive agent, and 8 parts of first binder.

[0085] The rest is the same as in Example 1.

[0086] Example 13

[0087] The difference from Example 1 is that the positive electrode active material layer 3 includes the following raw materials in parts by weight: 95 parts of positive electrode active material, 3 parts of second conductive agent, and 2 parts of second binder.

[0088] The rest is the same as in Example 1.

[0089] Example 14

[0090] The difference from Example 1 is that the positive electrode active material layer 3 includes the following raw materials in parts by weight: 96 parts of positive electrode active material, 3 parts of second conductive agent, and 1 part of second binder.

[0091] The rest is the same as in Example 1.

[0092] Example 15

[0093] The difference from Example 1 is that the positive electrode active material layer 3 includes the following raw materials in parts by weight: 98 parts of positive electrode active material, 1 part of second conductive agent, and 1 part of second binder.

[0094] The rest is the same as in Example 1.

[0095] Example 16

[0096] The difference from Example 1 is that the positive electrode active material layer 3 includes the following raw materials in parts by weight: 92 parts of positive electrode active material, 5 parts of second conductive agent, and 3 parts of second binder.

[0097] The rest is the same as in Example 1.

[0098] Example 17

[0099] The difference from Example 1 is that the positive electrode active material layer 3 includes the following raw materials in parts by weight: 90 parts of positive electrode active material, 6 parts of second conductive agent, and 4 parts of second binder.

[0100] The rest is the same as in Example 1.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that the wound positive electrode does not have a safety coating 2.

[0103] The rest is the same as in Example 1, and will not be repeated here.

[0104] The positive electrode sheets and secondary batteries prepared in Examples 1-17 and Comparative Example 1 were subjected to foreign object extrusion, needle penetration and 45° needle penetration tests. The test results are recorded in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As shown in Table 1 above, the wound positive electrode sheet of the present invention has better mechanical abuse performance and good safety performance compared with the positive electrode sheet of the prior art. The pass rates of the needle penetration test, 45° needle penetration test and foreign object extrusion test are all above 90%. A comparison of Example 1 and Comparative Example 1 shows that the safety coating can significantly improve the foreign object extrusion test of the electrode sheet. Therefore, the safety coating 2 has a certain mechanical strength, which can improve the impact resistance of the electrode sheet and prevent the punctured positive electrode active coating from directly contacting the positive electrode current collector 1 during the foreign object extrusion test. At the same time, the safety coating 2 has strong adhesion, which can firmly bond the positive electrode active material layer 3 to the positive electrode current collector 1, preventing the coating from falling off during the foreign object extrusion test and improving mechanical abuse performance.

[0109] Comparing Examples 1 and 9-12, it is found that when the safety coating 2 includes the following parts by weight of raw materials: 92 parts of inorganic filler, 5 parts of first conductive agent, and 5 parts of first binder, the prepared secondary battery has better mechanical abuse performance and better safety.

[0110] Comparing Examples 1 and 13-17, it can be seen that when the positive electrode active material layer 3 is provided with the following raw materials in parts by weight: 98 parts of positive electrode active material, 1 part of second conductive agent, and 1 part of second binder, the prepared secondary battery has better mechanical abuse performance and better safety.

[0111] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A wound positive electrode sheet, characterized in that, It includes a positive current collector, a safety coating disposed on at least one side of the positive current collector, and a positive active material layer disposed on the side of the safety coating away from the positive current collector. The length of the safety coating is less than or equal to the length of the positive current collector, the length of the positive active material layer is less than or equal to the length of the safety coating, the adhesive force of the safety coating is greater than the adhesive force of the positive active material layer, and the resistance value of the safety coating is 0.2 to 4 Ω. The safety coating comprises the following raw materials in parts by weight: 80-97 parts boehmite, 1-10 parts first conductive agent, and 2-10 parts first binder.

2. The wound positive electrode sheet according to claim 1, characterized in that, The thickness of the safety coating is less than the thickness of the positive electrode active material layer.

3. The wound positive electrode sheet according to claim 1, characterized in that, The first conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the first binder is one or more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate.

4. The wound positive electrode sheet according to claim 1, characterized in that, The positive electrode active material layer comprises the following raw materials in parts by weight: 90-98 parts of positive electrode active material, 1-6 parts of second conductive agent, and 1-4 parts of second binder.

5. The wound positive electrode sheet according to claim 4, characterized in that, The positive electrode active material includes one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide.

6. The wound positive electrode sheet according to claim 4, characterized in that, The second conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers; the second binder is one or more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acrylate.

7. A secondary battery, characterized in that, The device includes a positive electrode, a separator, a negative electrode, an electrolyte, and a housing. The separator is used to separate the positive electrode and the negative electrode, and the housing is used to encapsulate the positive electrode, the separator, the negative electrode, and the electrolyte. The positive electrode is a wound positive electrode as described in any one of claims 1-6.

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