Positive electrode sheet of a wound structure battery and application thereof

Abstract

The application provides a positive electrode sheet of a winding structure battery and an application thereof. The positive electrode sheet comprises a substrate and a coating layer, the coating layer comprises an A-surface coating layer and a B-surface coating layer, the A-surface coating layer is arranged in an outer circle in the winding structure, and the B-surface coating layer is arranged in an inner circle in the winding structure; the A-surface coating layer comprises an A-surface first coating layer and an A-surface second coating layer connected with the substrate in sequence, the B-surface coating layer comprises a B-surface first coating layer and a B-surface second coating layer connected with the substrate in sequence, and the B-surface second coating layer is an intermittent coating layer. The second coating layer is an intermittent coating layer, the load of the positive electrode in the inner circle at the bending position is reduced, the NP ratio is improved, and the risk of lithium precipitation is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and specifically to a positive electrode sheet of a wound-structured battery and its application. Background Technology

[0002] Winded batteries boast high production efficiency and low overall manufacturing costs, representing the mainstream development direction in battery manufacturing technology. The NP ratio (NP-to-NP ratio) is the remaining capacity of the negative electrode compared to the positive electrode under the same conditions and in the same stage. The NP-to-NP ratio corresponds to the initial charging stage, and the NP-to-NP ratio corresponds to the discharge stage. A fundamental problem with wound batteries is the inconsistent curvature of the inner and outer electrode rings (smaller inner ring, larger outer ring), resulting in inconsistent NP-to-NP ratios. Improper design can easily lead to lithium plating. Currently, the industry uses an interference fit NP design for cylindrical wound batteries to ensure a sufficient NP-to-NP ratio for both inner and outer rings. However, this method can cause an excessively high NP-to-NP ratio on one side, reducing battery performance. Another method is to use a coating method on both the positive and negative sides, but this method is only suitable for cylindrical batteries.

[0003] For wound prismatic or pouch batteries, the cells are flattened after winding, resulting in a core with both planar and curved structures. Currently, there is no good method in the industry to handle the NP ratio at the curved structure. Using the NP ratio of the inner negative electrode ring to the outer positive electrode ring as the cell design NP ratio will result in insufficient NP at the inner positive electrode ring to the outer negative electrode ring. This makes the cell prone to lithium plating at the curved outer negative electrode ring, affecting the cell's cycle life and safety. Therefore, it is necessary to improve the NP ratio at this point.

[0004] CN205211872U discloses a lithium-ion battery and its wound cell structure. In this structure, no polar coating is present in the areas corresponding to the negative electrode and the positive electrode tab, or in the areas where the positive and negative electrode tabs are aligned. This reduces the thickness of the areas containing the positive and negative electrode tabs in the wound cell structure, and decreases the thickness difference at different locations, resulting in a more uniform overall thickness and thus improving the energy density and overall battery energy. However, an increase in energy density does not necessarily mean an increase in the NP ratio, and the reduction in the thickness difference in the wound cell structure can decrease the NP ratio at bends.

[0005] CN114039025A discloses a lithium-ion battery electrode preparation process and gravure printing equipment. After drying, a negative electrode paste layer is printed or sprayed on the thinned area of ​​the negative electrode, which can fill the thickness difference between the positive and negative electrode thinning areas, increase the areal density of the thinned area of ​​the negative electrode, thereby improving the NP ratio of the thinned area and improving the problem of lithium plating during cycling caused by thinning. However, in wound structure batteries, gravure printing is performed on the curved part, making it difficult to control the printing thickness of the battery and increasing the cost.

[0006] Therefore, how to prepare a cell structure that improves the NP ratio at the curved surface of the cell, thereby enhancing the cycle life and safety of the cell, is an important research direction in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a positive electrode sheet for a wound structure battery and its application.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] One objective of this invention is to provide a positive electrode sheet for a wound structure battery, the positive electrode sheet comprising a substrate and a coating, the coating comprising an A-side coating and a B-side coating, the A-side coating being disposed on the outer ring of the wound structure, and the B-side coating being disposed on the inner ring of the wound structure.

[0010] The A-side coating includes a first A-side coating and a second A-side coating that are sequentially connected to the substrate, and the B-side coating includes a first B-side coating and a second B-side coating that are sequentially connected to the substrate, wherein the second B-side coating is an intermittent coating.

[0011] This invention reduces the load on the inner positive electrode at the bend by using an intermittent second coating, thereby increasing the NP ratio and reducing the risk of lithium plating.

[0012] As a preferred embodiment of the present invention, the first coating on surface A is a continuous coating.

[0013] Preferably, the second coating on surface A is a continuous coating.

[0014] Preferably, the first coating on surface B is a continuous coating.

[0015] As a preferred embodiment of the present invention, the second coating on side B is not applied to the curved surface of the core.

[0016] As a preferred technical solution of the present invention, the surface density of the coating on side A is 100%, and the surface density of the first coating on side A is 80-99.5%. The surface density can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 99.5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 95-99%.

[0017] Preferably, the areal density of the first coating on side A is equal to the areal density of the first coating on side B.

[0018] Preferably, the areal density of the coating on side A is 100%, and the areal density of the second coating on side A is 0.5% to 20%. The areal density can be 0.5%, 1%, 2%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1% to 5%.

[0019] Preferably, the areal density of the second coating on side A is equal to the areal density of the second coating on side B.

[0020] As a preferred technical solution of the present invention, the active material of the coating includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium iron phosphate, or lithium cobalt oxide. Typical but non-limiting examples of such combinations include: a combination of lithium nickel cobalt manganese oxide and lithium iron phosphate, a combination of lithium iron phosphate and lithium cobalt oxide, or a combination of lithium nickel cobalt manganese oxide and lithium cobalt oxide, etc.

[0021] Preferably, the conductive agent of the coating includes any one or a combination of at least two of carbon nanotubes, conductive carbon black, or graphite conductive agents, wherein typical but non-limiting examples of the combination include: a combination of carbon nanotubes and conductive carbon black, a combination of conductive carbon black and graphite conductive agents, or a combination of carbon nanotubes and graphite conductive agents, etc.

[0022] Preferably, the binder of the coating comprises polyvinylidene fluoride and / or polyimide.

[0023] As a preferred technical solution of the present invention, with the dry material of the coating as 100%, the active substance of the coating accounts for 90-98% of the dry material of the coating by mass fraction. The mass fraction can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 98%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 95-97%.

[0024] Preferably, with the dry material of the coating as 100%, the conductive agent of the coating accounts for 0.1% to 10% of the dry material of the coating by mass fraction. The mass fraction can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.5% to 5%.

[0025] Preferably, with the dry material of the coating as 100%, the binder of the coating accounts for 0.1% to 5% of the dry material of the coating by mass fraction. The mass fraction can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1% to 2%.

[0026] As a preferred technical solution of the present invention, the solid content of the second coating on surface A is 5-10% higher than that of the first coating on surface A. The fraction can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the viscosity of the slurry for the first coating layer on surface A is greater than the viscosity of the slurry for the second coating layer on surface A.

[0028] As a preferred technical solution of the present invention, the slurry solid content of the second coating on side B is 5-10% higher than that of the slurry solid content of the first coating on side B. The fraction can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the viscosity of the slurry for the first coating layer on side B is greater than the viscosity of the slurry for the second coating layer on side B.

[0030] As a preferred embodiment of the present invention, when the active material of the coating is lithium iron phosphate, the solid content of the slurry is 50-65%, and the viscosity of the slurry is 5000-20000 mPa·s. The solid content can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, or 65%, etc., and the viscosity of the slurry can be 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 12000 mPa·s, 14000 mPa·s, 16000 mPa·s, 18000 mPa·s, or 20000 mPa·s, etc., but is not limited to the listed values; other unlisted values ​​within the above ranges are also applicable.

[0031] Preferably, when the active material of the coating is a ternary cathode material or lithium cobalt oxide, the solid content of the slurry is 70-80%, and the viscosity of the slurry is 2000-8000 mPa·s. The solid content can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, etc., and the viscosity can be 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s, 6000 mPa·s, 6500 mPa·s, 7000 mPa·s, 7500 mPa·s, or 8000 mPa·s, etc., but is not limited to the listed values; other unlisted values ​​within the above ranges are also applicable.

[0032] The second objective of this invention is to provide an application of the positive electrode sheet of the wound structure battery as described in the first objective, wherein the positive electrode sheet is applied in the field of lithium-ion batteries.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The wound battery prepared by this invention has excellent high-temperature cycling performance, and its capacity retention rate can reach more than 86% after 450 cycles at 60°C. Attached Figure Description

[0035] Figure 1 This is a structural diagram of the positive electrode sheet in Embodiments 1-6 of the present invention.

[0036] Figure 2 This is a diagram of the battery cell winding formed by embodiments 1-6 of the present invention.

[0037] Figure 3 These are the cyclic curves from Embodiment 1 and Comparative Example 1 of the present invention.

[0038] In the figure: 1-substrate; 2-first coating on side A; 3-second coating on side B; 4-first coating on side B; 5-second coating on side B; 6-gap between second coatings on side B; 7-outer ring positive electrode; 8-inner ring negative electrode. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1

[0041] This embodiment provides a method for preparing a wound-structured positive electrode sheet for a battery. The structure of the positive electrode sheet is as follows: Figure 1 As shown:

[0042] Preparation of the first coating slurry, wherein the first coating slurry includes a first coating slurry for side A and a first coating slurry for side B:

[0043] The first coating slurry was prepared according to the formula of lithium nickel cobalt manganese oxide: conductive carbon black: polyvinylidene fluoride = 97.3:1.5:1.2.

[0044] First, the conductive adhesive solution is prepared by pre-dissolving polyvinylidene fluoride into a 6% adhesive solution, and then adding conductive carbon black in two equal portions, each time rotating at 25 rpm and dispersing at 3000 rpm for 60 minutes, to obtain the conductive adhesive solution.

[0045] After the conductive adhesive solution was prepared, lithium nickel cobalt manganese oxide (NCO) was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 min. Then, N-methylpyrrolidone was added to adjust the solid content to 72% and the viscosity to 4000 mPa·s, thus obtaining the first coating slurry.

[0046] Preparation of the second coating slurry, wherein the second coating slurry includes a second coating slurry for side A and a second coating slurry for side B:

[0047] The second coating slurry was prepared according to the formula of lithium nickel cobalt manganese oxide: conductive carbon black: polyvinylidene fluoride = 97.3:1.5:1.2.

[0048] First, the conductive adhesive solution was prepared by pre-dissolving polyvinylidene fluoride into a 6% adhesive solution. Then, conductive carbon black and 0.1% of the dispersing agent vinylpyrrolidone were added in two equal portions. Each time, the mixture was rotated at 25 rpm and dispersed at 3000 rpm for 60 minutes to obtain the conductive adhesive solution.

[0049] After the conductive adhesive solution was prepared, lithium nickel cobalt manganese oxide (NCO) was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 min. Then, N-methylpyrrolidone was added to adjust the solid content to 77% and the viscosity to 4000 mPa·s, thus obtaining the second coating slurry.

[0050] Using a double-layer extrusion coating machine, a first coating 2 and a second coating 3 on side A are coated on substrate 1. The areal density of the first coating 2 on side A accounts for 95% of the total areal density of the coating, and the areal density of the second coating 3 on side A accounts for 5% of the total areal density. The areal density of the first coating 4 on side B accounts for 95% of the total areal density of the coating, and the areal density of the second coating 5 on side B accounts for 5% of the total areal density of the coating. Side A is coated continuously, while the second coating 5 on side B is coated intermittently, creating gaps 6 in the second coating on side B on the electrode sheet. The coating structure of the positive electrode sheet is as follows. Figure 1 As shown.

[0051] Example 2

[0052] This embodiment provides a method for preparing a wound-structured positive electrode sheet for a battery. The structure of the positive electrode sheet is as follows: Figure 1 As shown:

[0053] Preparation of the first coating slurry, wherein the first coating slurry includes a first coating slurry for side A and a first coating slurry for side B:

[0054] The first coating slurry was prepared according to the formula of lithium nickel cobalt manganese oxide: conductive carbon black: polyvinylidene fluoride = 97.3:1.5:1.2.

[0055] First, the conductive adhesive solution is prepared by pre-dissolving polyvinylidene fluoride into a 6% adhesive solution, and then adding conductive carbon black in two equal portions, each time rotating at 25 rpm and dispersing at 3000 rpm for 60 minutes, to obtain the conductive adhesive solution.

[0056] After the conductive adhesive solution was prepared, lithium nickel cobalt manganese oxide (NCO) was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 min. Then, N-methylpyrrolidone was added to adjust the solid content to 70% and the viscosity to 2000 mPa·s, thus obtaining the first coating slurry.

[0057] Preparation of the second coating slurry, wherein the second coating slurry includes a second coating slurry for side A and a second coating slurry for side B:

[0058] The second coating slurry was prepared according to the formula of lithium nickel cobalt manganese oxide: conductive carbon black: polyvinylidene fluoride = 97.3:1.5:1.2.

[0059] First, the conductive adhesive solution was prepared by pre-dissolving polyvinylidene fluoride into a 6% adhesive solution. Then, conductive carbon black and 0.1% polystyrene acrylate dispersant were added in two equal portions. Each time, the mixture was rotated at 25 rpm and dispersed at 3000 rpm for 60 minutes to obtain the conductive adhesive solution.

[0060] After the conductive adhesive solution was prepared, lithium nickel cobalt manganese oxide (NCO) was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 min. Then, N-methylpyrrolidone was added to adjust the solid content to 80% and the viscosity to 5000 mPa·s, thus obtaining the second coating slurry.

[0061] Using a double-layer extrusion coating machine, a first coating 2 and a second coating 3 on side A are coated on substrate 1. The areal density of the first coating 2 on side A accounts for 80% of the total areal density of the coating, and the areal density of the second coating 3 on side A accounts for 20% of the total areal density. Similarly, the areal density of the first coating 4 on side B accounts for 80% of the total areal density of the coating, and the areal density of the second coating 5 on side B accounts for 20% of the total areal density. Side A is coated continuously, while the second coating 5 on side B is coated intermittently, creating gaps 6 in the second coating on side B on the electrode sheet. The coating structure of the positive electrode sheet is as follows: Figure 1 As shown.

[0062] Example 3

[0063] This embodiment provides a method for preparing a wound-structured positive electrode sheet for a battery. The structure of the positive electrode sheet is as follows: Figure 1 As shown:

[0064] Preparation of the first coating slurry, wherein the first coating slurry includes a first coating slurry for side A and a first coating slurry for side B:

[0065] The first coating slurry was prepared according to the formula of lithium iron phosphate: carbon nanotubes: polyimide = 97.3:1.5:1.2.

[0066] First, the conductive adhesive solution was prepared by pre-dissolving polyimide into a 6% adhesive solution, and then adding carbon nanotubes in two equal portions. Each time, the nanotubes were rotated at 25 rpm and dispersed at 3000 rpm for 60 minutes to obtain the conductive adhesive solution.

[0067] After the conductive adhesive solution was prepared, lithium iron phosphate, the main material, was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 minutes. Then, N-methylpyrrolidone was added to adjust the solid content to 65% and the viscosity to 18000 mPa·s, thus obtaining the first coating slurry.

[0068] Preparation of the second coating slurry, wherein the second coating slurry includes a second coating slurry for side A and a second coating slurry for side B:

[0069] The second coating slurry was prepared according to the formula of lithium iron phosphate: carbon nanotubes: polyimide = 97.3:1.5:1.2.

[0070] First, the conductive adhesive solution was prepared by pre-dissolving PI to a 6% solution. Carbon nanotubes and 0.1% of dispersant nitrile rubber were added in two equal portions. Each time, the solution was rotated at 25 rpm and dispersed at 3000 rpm for 60 minutes to obtain the conductive adhesive solution.

[0071] After the conductive adhesive solution was prepared, lithium iron phosphate, the main material, was added to the conductive adhesive solution in two batches, each time at 25 rpm and 3000 rpm for 90 minutes. Then, N-methylpyrrolidone was added to adjust the solid content to 75% and the viscosity to 20000 mPa·s, thus obtaining the second coating slurry.

[0072] Using a double-layer extrusion coating machine, a first coating 2 and a second coating 3 on side A are coated on substrate 1. The areal density of the first coating 2 on side A accounts for 99.5% of the total areal density of the coating, and the areal density of the second coating 3 on side A accounts for 0.5% of the total areal density of the coating. Similarly, the areal density of the first coating 4 on side B accounts for 99.5% of the total areal density of the coating, and the areal density of the second coating 5 on side B accounts for 0.5% of the total areal density of the coating. Side A is coated continuously, while the second coating 5 on side B is coated intermittently, creating gaps 6 in the second coating on side B on the electrode sheet. The coating structure of the positive electrode sheet is as follows: Figure 1 As shown.

[0073] Example 4

[0074] In this embodiment, all other conditions are the same as in Example 1, except that the areal density of the first coating 2 on side A accounts for 95% of the total areal density, the areal density of the second coating 3 on side A accounts for 5% of the total areal density, the areal density of the first coating 4 on side B accounts for 95% of the total areal density, and the areal density of the second coating 5 on side B accounts for 5% of the total areal density, are replaced with the areal density of the first coating 2 on side A accounting for 78% of the total areal density, the areal density of the second coating 3 on side A accounting for 22% of the total areal density, the areal density of the first coating 4 on side B accounting for 78% of the total areal density, and the areal density of the second coating 5 on side B accounting for 22% of the total areal density.

[0075] Example 5

[0076] In this embodiment, the only difference is that N-methylpyrrolidone was added to adjust the solid content to 77% during the preparation of the second coating slurry, which was replaced by adding N-methylpyrrolidone to adjust the solid content to 75%. All other conditions are the same as in Example 1.

[0077] Example 6

[0078] In this embodiment, all conditions are the same as in Example 1, except that the solid content in the first coating slurry is replaced with 65% instead of 72%.

[0079] Comparative Example 1

[0080] In this comparative example, except that the second coating 5 on side B is applied intermittently and the gap 6 between the second coating 5 on side B on the electrode sheet is replaced by a fully continuous coating on side B, all other conditions are the same as in Example 1.

[0081] Comparative Example 2

[0082] The conditions in this comparative example are the same as in Example 3, except that the second coating 5 on side B is applied intermittently and the gap 6 between the second coatings on side B on the electrode sheet is replaced by a fully continuous coating on side B.

[0083] The positive electrode sheets in Examples 1-6 and Comparative Examples 1-2 are rolled into small soft-pack batteries with side B facing inward, forming a curved structure. The curved structure includes: an outer positive electrode sheet 7, a first coating layer 4 on side B, and a second coating layer 5 on side B. The second coating layer 5 is not applied at the curved surface of the core, but is applied normally at the flat surface of the core. An inner negative electrode sheet 8 is coated on the first coating layer 4 and the second coating layer 5 on side B. (See cell winding diagram below.) Figure 2 (As shown).

[0084] The negative electrode sheet is prepared by homogenization, coating, rolling, and laser cutting according to the formula of graphite: conductive carbon black: sodium carboxymethyl cellulose: styrene-butadiene rubber = 96.3:1.0:1.2:1.5.

[0085] After formation, the small pouch battery was subjected to a high-temperature cycle test at 60°C. The test results are shown in Table 1. The cycle test diagrams for Example 1 and Comparative Example 1 are shown below. Figure 3 As shown.

[0086] The formula for calculating the NP ratio is: Negative electrode active material specific capacity × Negative electrode surface density × Negative electrode active material content ratio ÷ (Positive electrode active material specific capacity × Positive electrode surface density × Positive electrode active material content ratio).

[0087] Table 1

[0088] Example 1 86.9 1.05 Example 2 87.2 1.07 Example 3 90.2 1.08 Example 4 84.2 1.12 Example 5 86.1 1.06 Example 6 86.2 1.06 Comparative Example 1 84.5 1.08 Comparative Example 2 88.7 1.09

[0089] As can be seen from the table above, the positive electrode manufactured by this invention has a reasonable control over the overall NP ratio of the electrode, which effectively improves the cycle performance.

[0090] Meanwhile, Example 4 shows that if the areal density of the second coating is too high, the NP ratio will increase, the negative electrode film will consume more active ions, and the cycle performance will decrease. Example 5 shows that the solid content of the second coating is 3% higher than that of the first coating but less than 5%. Example 6 shows that the solid content of the second coating is 12% higher than that of the first coating but more than 10%, which decreases the cycle performance of the battery and increases the NP ratio. Therefore, the battery has the best cycle performance when the solid content of the second coating is 5-10% higher than that of the first coating. Comparative Examples 1-2 show that the cycle performance of the battery decreases after replacing intermittent coating with continuous coating.

[0091] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode sheet for a wound-structure battery, characterized in that, The positive electrode sheet includes a substrate and a coating. The coating includes an A-side coating and a B-side coating. The A-side coating is disposed on the outer ring of the winding structure, and the B-side coating is disposed on the inner ring of the winding structure. The A-side coating includes a first A-side coating and a second A-side coating that are sequentially connected to the substrate. The B-side coating includes a first B-side coating and a second B-side coating that are sequentially connected to the substrate. The second B-side coating is an intermittent coating, and the second B-side coating is not applied at the curved surface of the core. The first coating on surface A is a continuous coating; the second coating on surface A is a continuous coating; the first coating on surface B is a continuous coating; With the surface density of the coating on side A being 100%, the surface density of the first coating on side A is 80~99.5%; the surface density of the first coating on side A is equal to the surface density of the first coating on side B; With the surface density of the coating on side A being 100%, the surface density of the second coating on side A being 0.5~20%; the surface density of the second coating on side A and the surface density of the second coating on side B are equal.

2. The positive electrode sheet according to claim 1, characterized in that, With the surface density of the coating on side A being 100%, the surface density of the first coating on side A is 95-99%.

3. The positive electrode sheet according to claim 1, characterized in that, With the surface density of the A-side coating being 100%, the surface density of the second coating on the A-side is 1~5%.

4. The positive electrode sheet according to claim 1, characterized in that, The active material of the coating includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium iron phosphate, or lithium cobalt oxide.

5. The positive electrode sheet according to claim 1, characterized in that, The conductive agent of the coating includes any one or a combination of at least two of carbon nanotubes, conductive carbon black, or graphite conductive agents.

6. The positive electrode sheet according to claim 1, characterized in that, The adhesive for the coating includes polyvinylidene fluoride and / or polyimide.

7. The positive electrode sheet according to claim 1, characterized in that, With the dry material of the coating as 100% by mass, the active substance of the coating accounts for 90-98% of the mass fraction of the dry material of the coating.

8. The positive electrode sheet according to claim 7, characterized in that, With the dry material of the coating as 100% by mass, the active substance of the coating accounts for 95-97% of the mass fraction of the dry material of the coating.

9. The positive electrode sheet according to claim 1, characterized in that, With the dry material of the coating as 100% by mass, the conductive agent in the coating accounts for 0.1 to 10% of the dry material of the coating by mass fraction.

10. The positive electrode sheet according to claim 9, characterized in that, With the dry material of the coating as 100% by mass, the conductive agent in the coating accounts for 0.5 to 5% of the dry material of the coating by mass fraction.

11. The positive electrode sheet according to claim 1, characterized in that, With the dry material of the coating as 100% by mass, the binder of the coating accounts for 0.1-5% of the dry material of the coating by mass fraction.

12. The positive electrode sheet according to claim 11, characterized in that, With the dry material of the coating as 100% by mass, the binder of the coating accounts for 1 to 2% of the dry material of the coating by mass fraction.

13. The positive electrode sheet according to claim 1, characterized in that, The solid content of the second coating on surface A is 5-10% higher than that of the first coating on surface A.

14. The positive electrode sheet according to claim 1, characterized in that, The viscosity of the slurry for the first coating layer on surface A is greater than the viscosity of the slurry for the second coating layer on surface A.

15. The positive electrode sheet according to claim 1, characterized in that, The solid content of the slurry in the second coating layer on side B is 5-10% higher than that in the first coating layer on side B.

16. The positive electrode sheet according to claim 1, characterized in that, The viscosity of the slurry for the first coating layer on side B is greater than the viscosity of the slurry for the second coating layer on side B.

17. The positive electrode sheet according to claim 1, characterized in that, When the active material of the coating is lithium iron phosphate, the solid content of the slurry is 50-65% and the viscosity of the slurry is 5000-20000 mPa·s.

18. The positive electrode sheet according to claim 1, characterized in that, When the active material of the coating is a ternary cathode material or lithium cobalt oxide, the solid content of the slurry is 70-80%, and the viscosity of the slurry is 2000-8000 mPa·s.

19. An application of the positive electrode sheet of a wound structure battery as described in any one of claims 1-18, characterized in that, The positive electrode sheet is used in the field of lithium-ion batteries.

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