Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrode assembly of a winding structure, the electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm, the diaphragm comprises a base film and a coating coated on at least one surface of the base film, and the base film comprises plane areas and corner areas which are continuously and alternately arranged along the winding direction of the diaphragm; the coatings comprise a first coating and a second coating, the first coating is arranged in the plane area of the base membrane, the second coating is arranged in the corner area of the base membrane, the liquid retention rate of the first coating is VA, the liquid retention rate of the second coating is VB, and the VB is greater than VA, the characteristics are met by regulating and controlling the secondary battery, the liquid retention rate of the corner area of the secondary battery diaphragm is relatively high, and the secondary battery diaphragm has a good application prospect. The gap between the corner area of the secondary battery diaphragm and the pole piece is reduced, purple spots or black spots of the negative pole piece are reduced, and the problem of lithium precipitation in the corner area of the secondary battery in a full charge state is well relieved, so that the cycle performance and the safety performance of the secondary battery are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] As the rate performance of lithium-ion batteries improves, the amount of gas generated during the formation of square soft-pack lithium-ion batteries with wound structure increases during high-rate fast charging cycles. Large gaps are prone to appear at the corners, and there are also problems such as poor electrolyte wetting and poor contact between the separator and the electrode at the corners, which can lead to lithium plating. This increases the risk of lithium-ion batteries experiencing capacity drops and short circuits during cycling.

[0003] At present, a single-thickness separator is usually used or the tension between the electrode and the separator is increased during the winding process to reduce the gap between the electrode. However, a single-thickness separator cannot eliminate the gap between the separator and the electrode. Increasing the tension between the electrode and the separator has a limited range of increase, and excessive tension can easily lead to problems such as separator wrinkling and electrode breakage. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device, wherein the swelling rate of the corner area of ​​the secondary battery separator is large, which reduces the gap between the corner area of ​​the secondary battery separator and the electrode, improves the wetting of the electrode at the corner, reduces the generation of purple or black spots on the negative electrode, and better alleviates the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] This application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator. The separator includes a base film and a coating applied to at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The coating includes a first coating and a second coating. The first coating is disposed in the planar region of the base film, and the second coating is disposed in the corner region of the base film. The liquid retention rate of the first coating is V. A The liquid retention rate of the second coating is V B V B >V A Due to the liquid retention rate V of the second coating B The liquid retention rate V is greater than that of the first coating. AThe second coating has a stronger electrolyte retention capacity than the first coating, with a larger electrolyte retention capacity at the corner of the separator. The corner area retains more electrolyte during the secondary battery formation process. On the one hand, this increases the thickness of the second coating at the corner, better filling the gaps created by gas generation in the corner area during the electrode assembly formation process. This ensures good contact between the electrode and the separator, thereby reducing the risk of lithium plating and the possibility of secondary battery expansion due to gas generation, thus improving the safety performance of the secondary battery. On the other hand, the larger electrolyte retention capacity of the second coating at the corner area is beneficial to improving the electrolyte replenishment capacity of the secondary battery during cycling, improving the situation of poor electrolyte wetting of the electrode assembly during cycling. This reduces the formation of purple or black spots on the electrode and also reduces the risk of lithium plating, thus improving the cycle performance of the secondary battery. Therefore, when the separator in the electrode assembly meets the above characteristics, a second coating with a high liquid retention rate is set in advance in the corner area to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, thereby reducing the generation of purple or black spots on the negative electrode and effectively alleviating the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thus improving the cycle performance and safety performance of the secondary battery.

[0007] In one or more embodiments of this application, 5% ≤ V A ≤20%, 110%≤V B ≤200%. By adjusting V A and V B When the values ​​are within the aforementioned range, the first and second coatings have suitable electrolyte retention rates. Specifically, when the electrolyte retention rates of the first and second coatings are respectively within the aforementioned ranges, the electrolyte retention rate of the second coating is greater than that of the first coating, resulting in greater electrolyte retention at the corner area of ​​the separator. This means the corner area retains more electrolyte during the secondary battery formation process, which is beneficial for improving the electrolyte replenishment capacity at the corner area of ​​the secondary battery and mitigating poor electrolyte wetting during electrode assembly cycling, thereby reducing the formation of purple or black spots on the electrodes. Correspondingly, the thickness of the second coating after absorbing electrolyte is greater than that of the first coating, which is beneficial for better filling the voids generated in the corner area during electrode assembly formation due to gas production, ensuring good contact between the electrodes and the separator. This helps alleviate the problem of lithium plating at the corner area of ​​the secondary battery under full charge conditions, thereby improving the cycle performance and safety performance of the secondary battery.

[0008] In one or more embodiments of this application, the first coating comprises a first material, which includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, or polyimide. Based on the mass of the first coating, the mass percentage of the first material is M1, where 15% ≤ M1 ≤ 45%. The second coating comprises a second material, which includes at least one of polystyrene, polystyrene-propylene, polyvinyl alcohol, polyamide, polyurethane, or ethyl cellulose. Based on the mass of the second coating, the mass percentage of the second material is M2, where 55% ≤ M2 ≤ 85%. By adjusting the secondary battery to meet the above characteristics, selecting suitable first and second materials with appropriate mass percentages for the first and second coatings helps to achieve suitable liquid retention rates, better fills the voids in the corner area of ​​the electrode, and simultaneously reduces the risk of excessive expansion and the appearance of new voids at the electrode connection end due to excessive liquid retention. Specifically, the second material has a stronger liquid retention capacity than the first material, the second coating has a higher liquid retention rate than the first coating, and the swelling rate of the corner area of ​​the secondary battery separator is larger, which reduces the gap between the corner area of ​​the secondary battery separator and the electrode, improves the wetting of the electrode at the corner, reduces the generation of purple or black spots on the negative electrode, and better alleviates the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0009] In one or more embodiments of this application, the average thickness of the negative electrode sheet is D. M μm, the average thickness of the positive electrode is D N μm, the average thickness of the first coating is D A μm, the average thickness of the second coating is D B μm, D B >D A , 0 < (D B -D A ) / (D M +D N ≤0.13. During the formation of the secondary battery, due to the low liquid retention rate V of the second coating... B The liquid retention rate V is greater than that of the first coating. AThe second coating has a stronger electrolyte retention capacity than the first coating, with a greater electrolyte retention at the corner of the separator. The corner area retains more electrolyte during the secondary battery formation process, therefore its thickness is greater than that of the planar area. By adjusting the secondary battery to meet the above characteristics, the ratio of the average thickness difference between the second and first coatings to the sum of the negative and positive electrode thicknesses is within the aforementioned range. This results in a suitable thickness for the second coating, effectively reducing the risk of excessive thickness at the electrode corners affecting packaging quality and improving the safety performance of the secondary battery. Simultaneously, the suitable thickness of the second coating helps to better fill the gaps between the separator corners and the electrodes, improving electrode wetting at the corners, reducing the formation of purple or black spots on the negative electrode, and effectively mitigating lithium plating at the corners under full charge conditions, thereby improving the cycle performance and safety performance of the secondary battery.

[0010] In one or more embodiments of this application, 60≤D M ≤270. By adjusting the thickness of the negative electrode sheet within the above range, the negative electrode sheet has a suitable thickness, which is beneficial for the negative electrode sheet to have suitable charge transport performance and suitable internal resistance. This reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode sheet. At the same time, the secondary battery has a suitable volumetric energy density, which is beneficial for improving the process stability during the production of the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0011] In one or more embodiments of this application, 90≤D N ≤400. By adjusting the thickness of the positive electrode sheet within the above range, the positive electrode sheet has a suitable thickness, which is beneficial for the positive electrode sheet to have a suitable internal resistance and a suitable energy density. This reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the positive electrode sheet, thereby improving the cycle performance of the secondary battery.

[0012] In one or more embodiments of this application, 5≤D A ≤35. By adjusting the average thickness of the first coating within the above range, the first coating has a suitable thickness after the secondary battery is formed, which is beneficial to the good adhesion between the separator and the electrode, thereby improving the cycle performance and safety performance of the secondary battery.

[0013] In one or more embodiments of this application, correspondingly, 5≤D B ≤122.5. By adjusting the average density of the second coating within the above range, the second coating after secondary battery formation has a suitable thickness, which is beneficial for better filling the gap between the secondary battery separator corner area and the electrode, improving the wetting of the electrode at the corner, and at the same time, reducing the risk of excessive thickness of the second coating causing the electrode assembly corner area to be too thick, affecting the packaging quality, thereby improving the cycle performance and safety performance of the secondary battery.

[0014] In one or more embodiments of this application, the electrode assembly includes N turns, 9≤N≤100. In any turn of the electrode assembly, the width of the negative electrode sheet formed by winding along the width direction of the electrode assembly is W1 mm, the width of the planar region of the base film is W2 mm, and the thickness of the negative electrode sheet formed by winding along the thickness direction of the electrode assembly is D1 mm, where W2<W1-D1. After the secondary battery is formed, the difference between the width and thickness of the negative electrode sheet in any ring of electrode assembly can be considered as the width of the negative electrode sheet relative to the planar area of ​​the base film in that ring. By adjusting the secondary battery to meet the above characteristics, the planar area of ​​the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode sheet. That is, the width of the planar area in the base film ring is smaller than the width of the corresponding area of ​​the negative electrode sheet. Thus, the corner area of ​​the base film has a suitable width, which is beneficial to better cover the area on the negative electrode sheet corresponding to the corner area of ​​the base film, improve the wetting of the negative electrode sheet at the corner, better fill the gap between the corner area of ​​the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, and thus improve the cycle performance of the secondary battery.

[0015] In one or more embodiments of this application, 3≤D1≤300. By adjusting the thickness of any single turn of the negative electrode assembly within the scope of this application, on the one hand, the negative electrode has a suitable thickness, which is beneficial for the negative electrode to have suitable charge transport performance and suitable internal resistance, and better reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode, while also better mitigating the problem of decarburization and powder shedding during the manufacturing process caused by excessive thickness of the negative electrode; on the other hand, it is beneficial for the wound electrode assembly to have a suitable thickness, which better reduces the risk of packaging performance being affected by excessive thickness of a single turn of the negative electrode after winding, thereby improving the cycle performance of the secondary battery.

[0016] In one or more embodiments of this application, starting from the beginning of the separator winding, the second coating is only disposed in the corner region of the base film from the N / 3th turn to the Nth turn along the winding direction of the separator. Specifically, as the number of turns of the electrode assembly increases, the thickness of the electrode assembly increases, and the corner region also increases accordingly. Correspondingly, the possibility of voids being generated due to gas production during the secondary battery formation process is also greater. By disposing of the second coating in the corner region of the base film from the N / 3th turn to the Nth turn, the corner region can be better matched, and the voids between the corner region of the secondary battery separator and the electrode can be better filled, reducing the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0017] In one or more embodiments of this application, in any ring of electrode assembly, along the width direction of the electrode assembly, the width of any corner region of the base film is W3 mm, where W3 > D1 / 2. After the secondary battery is formed, in any ring of electrode assembly, the width of the corner region of the base film is greater than half the thickness of the negative electrode sheet of that ring. By adjusting the width of the corner region to meet the above characteristics, the corner region has a suitable width. Specifically, the width of the corner region is greater than the width of the corresponding area of ​​the negative electrode sheet, which is beneficial to better cover the area on the negative electrode sheet corresponding to the corner region of the base film, improve the wetting of the negative electrode sheet at the corner, better fill the gap between the corner region of the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0018] In one or more embodiments of this application, the widths of any two planar regions of the base membrane are equal. By adjusting the secondary battery to meet the above characteristics, the equal widths of any two planar regions on the base membrane are beneficial for optimizing production steps and improving the manufacturability of the separator.

[0019] In one or more embodiments of this application, a coating is disposed on one surface of the base film along the thickness direction of the separator, with the coated base film surface facing the negative electrode. During secondary battery cycling, lithium plating typically occurs on the surface of the negative electrode. By adjusting the secondary battery to meet the above-mentioned characteristics, the second coating corresponds to the negative electrode, which helps to better cover the area on the negative electrode corresponding to the corner region of the base film, improves the wetting of the negative electrode at the corner, better fills the gap between the corner region of the secondary battery separator and the electrode, reduces the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0020] A second aspect of this application provides an electronic device that includes the secondary battery found in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance.

[0021] The beneficial effects of this application are:

[0022] This application provides a secondary battery and an electronic device. The secondary battery includes a wound electrode assembly, which includes a positive electrode, a negative electrode, and a separator. The separator includes a base film and a coating applied to at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The coating includes a first coating and a second coating. The first coating is disposed in the planar region of the base film, and the second coating is disposed in the corner region of the base film. The liquid retention rate of the first coating is V. A The liquid retention rate of the second coating is V B V B >V ABy adjusting the secondary battery to meet the above characteristics, the liquid retention rate of the secondary battery separator corner area is relatively large, which reduces the gap between the secondary battery separator corner area and the electrode, reduces the generation of purple or black spots on the negative electrode, and effectively alleviates the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0023] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in some embodiments of this application;

[0026] Figure 2 This is a schematic diagram of the winding structure of a one-loop electrode assembly in some embodiments of this application;

[0027] In the figure, electrode assembly 001; positive electrode 10; positive current collector 11; positive electrode material layer 12; negative electrode 20; negative current collector 21; negative electrode material layer 22; separator 30; base film 31; first coating 32; second coating 33; planar region 301; corner region 302. Detailed Implementation

[0028] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0029] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0030] This application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator. The separator includes a base film and a coating applied to at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The coating includes a first coating and a second coating. The first coating is disposed in the planar region of the base film, and the second coating is disposed in the corner region of the base film. The liquid retention rate of the first coating is V.A The liquid retention rate of the second coating is V B V B >V A .

[0031] The winding direction of the electrode assembly is defined as the W direction. For example, as shown... Figure 1 As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a positive current collector 11 and a positive electrode material layer 12 disposed on two surfaces of the positive current collector 11. The negative electrode 20 includes a negative current collector 21 and a negative electrode material layer 22 disposed on two surfaces of the negative current collector 21. The separator 30 includes a base film 31 and a first coating 32 disposed on two surfaces of the planar region 301 and a second coating 33 disposed on two surfaces of the corner region 302 on the base film 31.

[0032] With the widespread adoption of wound lithium-ion batteries, improving their cycle performance and safety has become increasingly important. Due to their unique structure, wound batteries contain planar areas and corner areas formed during winding. During the formation of the secondary battery, as gas production increases, the voids in these corner areas also increase. On one hand, increased voids in the corner areas can lead to poorer contact between the electrodes and the separator, increasing the risk of lithium plating. On the other hand, excessive residual reactant gases in the corner areas can result in poor electrolyte wetting of the electrode components during secondary battery cycling, leading to purple or black spots. Further lithium plating can occur under full charge conditions as cycling continues. This increases the probability of reduced cycle capacity, lithium plating, purple spots on the electrodes, and short circuits. This application provides a secondary battery including a wound electrode assembly. The separator of the electrode assembly is designed such that, along the winding direction of the separator, continuously alternating planar regions and corner regions are pre-planned on a base film. A first coating is formed in the planar regions of the base film, and a second coating is formed in the corner regions. The liquid retention rate of the first coating is V. A The liquid retention rate of the second coating is V B V B >V A Due to the liquid retention rate V of the second coating B The liquid retention rate V is greater than that of the first coating. AThe second coating has a stronger electrolyte retention capacity than the first coating, with a larger electrolyte retention capacity at the corner of the separator. The corner area retains more electrolyte during the secondary battery formation process. On the one hand, this increases the thickness of the second coating at the corner, better filling the gaps created by gas generation in the corner area during the electrode assembly formation process. This ensures good contact between the electrode and the separator, thereby reducing the risk of lithium plating and the possibility of secondary battery expansion due to gas generation, thus improving the safety performance of the secondary battery. On the other hand, the larger electrolyte retention capacity of the second coating at the corner area is beneficial to improving the electrolyte replenishment capacity of the secondary battery during cycling, improving the situation of poor electrolyte wetting of the electrode assembly during cycling. This reduces the formation of purple or black spots on the electrode and also reduces the risk of lithium plating, thus improving the cycle performance of the secondary battery. Therefore, when the separator in the electrode assembly meets the above characteristics, a second coating with a high liquid retention rate is set in advance in the corner area to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, thereby reducing the generation of purple or black spots on the negative electrode and effectively alleviating the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thus improving the cycle performance and safety performance of the secondary battery.

[0033] In one or more embodiments of this application, 5% ≤ V A ≤20%. For example, V A The value can be 5%, 6%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values, V A The value range can be 5% to 20%, 6% to 18%, 7% to 16%, 9% to 14%, 10% to 12%, and all of these ranges and subranges. 110% ≤ V B ≤200%. For example, V B The value can be 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, or a range consisting of any two of the above values. B The value range can be 110% to 200%, 120% to 190%, 130% to 170%, 140% to 160%, and all of these ranges and sub-ranges. This can be achieved by adjusting V. A and V BWhen the values ​​are within the aforementioned range, the first and second coatings have suitable electrolyte retention rates. Specifically, when the electrolyte retention rates of the first and second coatings are respectively within the aforementioned ranges, the electrolyte retention rate of the second coating is greater than that of the first coating, resulting in greater electrolyte retention at the corner area of ​​the separator. This means the corner area retains more electrolyte during the secondary battery formation process, which is beneficial for improving the electrolyte replenishment capacity at the corner area of ​​the secondary battery and mitigating poor electrolyte wetting during electrode assembly cycling, thereby reducing the formation of purple or black spots on the electrodes. Correspondingly, the thickness of the second coating after absorbing electrolyte is greater than that of the first coating, which is beneficial for better filling the voids generated in the corner area during electrode assembly formation due to gas production, ensuring good contact between the electrodes and the separator. This helps alleviate the problem of lithium plating at the corner area of ​​the secondary battery under full charge conditions, thereby improving the cycle performance and safety performance of the secondary battery.

[0034] In one or more embodiments of this application, the first coating comprises a first material, which includes at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, or polyimide. Based on the mass of the first coating, the mass percentage content of the first material is M1, where 15% ≤ M1 ≤ 45%. For example, the value of M1 can be 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, or a range consisting of any two of the above values. The range of M1 can be 15% to 45%, 17.5% to 42.5%, 20% to 40%, 22.5% to 37.5%, 25% to 35%, and all ranges and sub-ranges thereof. The second coating comprises a second material, which includes at least one selected from polystyrene, polystyrene-propylene, polyvinyl alcohol, polyamide, polyurethane, or ethyl cellulose. Based on the mass of the second coating, the mass percentage content of the second material is M2, where 55% ≤ M2 ≤ 85%. For example, the value of M2 can be 55%, 57.5%, 60%, 62.5%, 65%, 67.5%, 70%, 72.5%, 75%, 77.5%, 80%, 82.5%, 85%, or any range of two of the above values. The value range of M2 can be 55% to 85%, 57.5% to 82.5%, 60% to 80%, 62.5% to 77.5%, 65% to 75%, and all ranges and sub-ranges thereof. By adjusting the secondary battery to meet the above characteristics, the first coating and the second coating are made of suitable first and second materials with suitable mass percentages, which helps to make the first coating and the second coating have suitable liquid retention rates, better fill the gaps in the corner area of ​​the electrode, and at the same time, better reduce the risk of new gaps appearing at the electrode connection end due to excessive expansion caused by excessive liquid retention. Specifically, the second material has a stronger liquid retention capacity than the first material, the second coating has a higher liquid retention rate than the first coating, and the swelling rate of the corner area of ​​the secondary battery separator is larger, which reduces the gap between the corner area of ​​the secondary battery separator and the electrode, improves the wetting of the electrode at the corner, reduces the generation of purple or black spots on the negative electrode, and better alleviates the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0035] In one or more embodiments of this application, the first coating further includes inorganic fillers and additives. The inorganic fillers include at least one of alumina, silicon dioxide, or zirconium oxide; the additives include at least one of triphenyl phosphate, carbon nanotubes, or graphene. Based on the mass of the first coating, the mass percentage of inorganic fillers can be 45% to 84%, and the mass percentage of additives can be 1% to 10%.

[0036] In one or more embodiments of this application, the second coating further includes inorganic fillers and additives. The inorganic fillers include at least one of alumina, silicon dioxide, or zirconium oxide; the additives include at least one of triphenyl phosphate, carbon nanotubes, or graphene. Based on the mass of the second coating, the mass percentage of inorganic fillers can be from 5% to 44%, and the mass percentage of additives can be from 1% to 10%.

[0037] In one or more embodiments of this application, the average thickness of the negative electrode sheet is D. M μm, the average thickness of the positive electrode is D N μm, the average thickness of the first coating is D A μm, the average thickness of the second coating is D B μm, D B >D A , 0 < (D B -D A ) / (D M +D N ) ≤ 0.13. For example, (D B -D A ) / (D M +D N The value of ) can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, or a range consisting of any two of the above values. (D) B -D A ) / (D M +D N The value range of ) can be 0.01 to 0.13, 0.02 to 0.12, 0.03 to 0.11, 0.04 to 0.1, and all ranges and subranges thereof. Specifically, such as Figure 1 As shown, the thickness of the positive electrode 10 is D. N The thickness of the negative electrode sheet 20 is D. M The average thickness of the single-layer first coating 32 disposed on the planar area 301 is D. A The average thickness of the single-layer second coating 33 disposed on the corner area 302 is D. B During the formation of a secondary battery, due to the low liquid retention rate (V) of the second coating... B The liquid retention rate V is greater than that of the first coating. AThe second coating has a stronger electrolyte retention capacity than the first coating, with a greater electrolyte retention at the corner of the separator. The corner area retains more electrolyte during the secondary battery formation process, therefore its thickness is greater than that of the planar area. By adjusting the secondary battery to meet the above characteristics, the ratio of the average thickness difference between the second and first coatings to the sum of the negative and positive electrode thicknesses is within the aforementioned range. This results in a suitable thickness for the second coating, effectively reducing the risk of excessive thickness at the electrode corners affecting packaging quality and improving the safety performance of the secondary battery. Simultaneously, the suitable thickness of the second coating helps to better fill the gaps between the separator corners and the electrodes, improving electrode wetting at the corners, reducing the formation of purple or black spots on the negative electrode, and effectively mitigating lithium plating at the corners under full charge conditions, thereby improving the cycle performance and safety performance of the secondary battery.

[0038] In one or more embodiments of this application, 60≤D M ≤270. For example, D M The value can be 60, 70, 100, 130, 150, 170, 200, 210, 230, 250, 270, or a range consisting of any two of the above values. M The value range can be 60 to 270, 70 to 250, 100 to 230, 130 to 210, 150 to 200, and all of these ranges and sub-ranges. By adjusting the thickness of the negative electrode sheet within the above ranges, the negative electrode sheet has a suitable thickness, which is beneficial for achieving suitable charge transport performance and suitable internal resistance. This reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode sheet. At the same time, the secondary battery has a suitable volumetric energy density, which is beneficial for improving the process stability during the production of the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0039] In one or more embodiments of this application, 90≤D N ≤400. For example, D N The value can be 90, 95, 100, 110, 130, 150, 200, 250, 300, 350, 400, or a range consisting of any two of the above values. N The value range can be 90 to 400, 95 to 350, 100 to 300, 110 to 250, 130 to 200, and all of these ranges and sub-ranges. By adjusting the thickness of the positive electrode within the above ranges, the positive electrode can have a suitable thickness, which is beneficial for achieving appropriate internal resistance and energy density. This reduces the risk of excessive thickness of the positive electrode affecting lithium-ion transport efficiency, thereby improving the cycle performance of the secondary battery.

[0040] In one or more embodiments of this application, 5≤DA ≤35. For example, D A The value can be 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, or 35, which is a range consisting of any two of the above values. A The value range can be 5 to 35, 7 to 33, 9 to 31, 11 to 29, 13 to 27, and all of these ranges and sub-ranges. By adjusting the average thickness of the first coating within the above range, the first coating has a suitable thickness after the secondary battery is formed, which is beneficial for good adhesion between the separator and the electrode, thereby improving the cycle performance and safety performance of the secondary battery.

[0041] In one or more embodiments of this application, correspondingly, 5 < D B ≤122.5. For example, D B The value can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 122.5, or a range consisting of any two of the above values. B The value range can be 5 to 122.5, 10 to 120, 20 to 110, 30 to 100, 40 to 90, and all of these ranges and sub-ranges. By adjusting the average density of the second coating within the above range, the second coating after secondary battery formation has a suitable thickness, which is beneficial for better filling the gaps between the secondary battery separator corner area and the electrode, improving the wetting of the electrode at the corner, and at the same time, reducing the risk of excessive thickness of the second coating leading to excessive thickness of the electrode assembly corner area affecting the encapsulation quality, thereby improving the cycle performance and safety performance of the secondary battery.

[0042] In one or more embodiments of this application, the electrode assembly includes N turns, where 9 ≤ N ≤ 100. For example, the value of N can be 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range consisting of any two of the above values. The range of N can be 9 to 100, 10 to 90, 20 to 80, 30 to 79, 40 to 60, and all such ranges and sub-ranges. In any turn of the electrode assembly, along the width direction of the electrode assembly, the width of the negative electrode sheet formed by winding is W1 mm, the width of the planar region of the base film is W2 mm, and along the thickness direction of the electrode assembly, the thickness of the negative electrode sheet formed by winding is D1 mm, where W2 < W1 - D1. Specifically, as... Figure 2As shown, along the thickness direction Z, the thickness of the wound negative electrode 20 is D1, and along the width direction Y, the width of the wound negative electrode 20 is W1. The width of the planar region 301 on the base film 31 is W2, and the width of the corner region 302 is W3. After the secondary battery is formed, in any ring of electrode assembly, the difference between the width and thickness of the negative electrode can be considered as the width of the negative electrode relative to the planar region of the base film in that ring. By adjusting the secondary battery to meet the above characteristics, the planar region of the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode. That is, the width of the planar region in that ring of base film is smaller than the width of the corresponding area of ​​the negative electrode. Thus, the corner region of the base film has a suitable width, which is beneficial for better covering the area of ​​the negative electrode corresponding to the corner region of the base film, improving the wetting of the negative electrode at the corner, better filling the gap between the corner region of the secondary battery separator and the electrode, reducing the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0043] In this application, along the thickness direction of the wound electrode assembly, the electrode assembly is formed by stacking and winding a separator, a negative electrode sheet, a separator, and a positive electrode sheet sequentially from the winding center outwards. Therefore, an electrode assembly with N turns is prepared by winding the aforementioned stacked separator, negative electrode sheet, separator, and positive electrode sheet N times. The separator referred to in the following embodiments and tests is the separator near the winding center along the thickness direction of the electrode assembly.

[0044] In one or more embodiments of this application, 3 ≤ D1 ≤ 300. For example, the value of D1 can be 3, 5, 10, 30, 50, 70, 90, 100, 150, 200, 250, 300 or a range consisting of any two of the above values. The value range of D1 can be 3 to 300, 5 to 250, 10 to 200, 30 to 150, 50 to 100, 70 to 90, and all such ranges and subranges. Within the scope of this application, by adjusting the thickness of the negative electrode sheet of any single turn of the electrode assembly, on the one hand, the negative electrode sheet has a suitable thickness, which is beneficial for the negative electrode sheet to have suitable charge transport performance and suitable internal resistance, and better reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode sheet, while also better mitigating the problem of decarburization and powder shedding during the process caused by excessive thickness of the negative electrode sheet; on the other hand, it is beneficial for the wound electrode assembly to have a suitable thickness, which better reduces the risk of packaging performance being affected by excessive thickness of a single turn of the negative electrode sheet after winding, thereby improving the cycle performance of the secondary battery.

[0045] In one or more embodiments of this application, 5 ≤ W1 ≤ 150. For example, the value of W1 can be 5, 10, 20, 30, 40, 60, 80, 100, 120, 140, 150, or a range consisting of any two of the above values. The value range of W1 can be 5 to 150, 10 to 140, 20 to 120, 30 to 100, 40 to 80, and all such ranges and sub-ranges. By adjusting the value of W1 within the above range, the negative electrode sheet in any loop electrode assembly has a suitable width, which is beneficial for the negative electrode sheet to have suitable charge transport performance and suitable internal resistance, while also ensuring the fabrication feasibility of the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0046] In one or more embodiments of this application, 3.5 ≤ W2 ≤ 145. For example, the value of W2 can be 3.5, 5, 10, 30, 50, 70, 90, 100, 110, 130, 140, 145, or a range consisting of any two of the above values. The value range of W2 can be 3.5 to 145, 5 to 140, 10 to 130, 30 to 110, 50 to 100, and all such ranges and sub-ranges. By adjusting the value of W2 within the above range, the base film plane region in any ring electrode assembly has a suitable width, which is beneficial for synergistic effect with the corner region. This ensures that the width of the corner region covers the corresponding area on the negative electrode sheet, improves the wetting of the negative electrode sheet at the corner, better fills the gap between the corner region of the secondary battery separator and the electrode sheet, reduces the generation of purple or black spots on the negative electrode sheet, and thus improves the cycle performance of the secondary battery.

[0047] In one or more embodiments of this application, starting from the beginning of the separator winding, the second coating is only disposed in the corner region of the base film from the N / 3th turn to the Nth turn along the winding direction of the separator. Specifically, as the number of turns of the electrode assembly increases, the thickness of the electrode assembly increases, and the corner region also increases accordingly. Correspondingly, the possibility of voids being generated due to gas production during the secondary battery formation process is also greater. By disposing of the second coating in the corner region of the base film from the N / 3th turn to the Nth turn, the corner region can be better matched, and the voids between the corner region of the secondary battery separator and the electrode can be better filled, reducing the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0048] In one or more embodiments of this application, in any ring of electrode assembly, along the width direction of the electrode assembly, the width of any corner region of the base film is W3 mm, where W3 > D1 / 2. After the secondary battery is formed, in any ring of electrode assembly, the width of the corner region of the base film is greater than half the thickness of the negative electrode sheet of that ring. By adjusting the width of the corner region to meet the above characteristics, the corner region has a suitable width. Specifically, the width of the corner region is greater than the width of the corresponding area of ​​the negative electrode sheet, which is beneficial to better cover the area on the negative electrode sheet corresponding to the corner region of the base film, improve the wetting of the negative electrode sheet at the corner, better fill the gap between the corner region of the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0049] In one or more embodiments of this application, the widths of any two planar regions of the base membrane are equal. By adjusting the secondary battery to meet the above characteristics, the equal widths of any two planar regions on the base membrane are beneficial for optimizing production steps and improving the manufacturability of the separator.

[0050] In one or more embodiments of this application, a coating is disposed on one surface of the base film along the thickness direction of the separator, with the coated base film surface facing the negative electrode. During secondary battery cycling, lithium plating typically occurs on the surface of the negative electrode. By adjusting the secondary battery to meet the above-mentioned characteristics, the second coating corresponds to the negative electrode, which helps to better cover the area on the negative electrode corresponding to the corner region of the base film, improves the wetting of the negative electrode at the corner, better fills the gap between the corner region of the secondary battery separator and the electrode, reduces the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0051] In this application, the liquid retention rate of the first coating can be controlled by adjusting the mass percentage of the first material. For example, under the same conditions, as M1 increases, V... A Increase; M1 decreases, V A Decrease.

[0052] In this application, the liquid retention rate of the second coating can be controlled by adjusting the mass percentage of the second material. For example, under the same conditions, as M2 increases, V... B Increase; M2 decreases, V B Decrease.

[0053] In this application, the average thickness D of the positive electrode sheet can be controlled by adjusting the coating weight or compaction density of the positive electrode material layer. N The value of D. For example, under the same conditions, as the coating weight of the positive electrode material layer increases, D N Increase; the coating weight of the positive electrode material layer decreases, D N Decrease; increase the compaction density of the positive electrode material layer, D NDecrease; the compaction density of the positive electrode material layer decreases, D N Increase.

[0054] In this application, the average thickness D of the negative electrode sheet can be controlled by adjusting the coating weight or compaction density of the negative electrode material layer. M The value of D. For example, under the same conditions, as the coating weight of the negative electrode material layer increases, D M Increase; the coating weight of the negative electrode material layer decreases, D M Decrease; increase the compaction density of the negative electrode material layer, D M Decrease; the compaction density of the negative electrode material layer decreases, D M Increase.

[0055] In this application, the average thickness D of the first coating in the diaphragm planar region can be adjusted by regulating the liquid retention rate of the first coating. A The value of V. For example, all other things being equal, V A Increase, D A Increase; V A Decrease, D A Decrease.

[0056] In this application, the average thickness D of the second coating in the diaphragm corner region can be controlled by adjusting the liquid retention rate of the second coating. B The value of V. For example, all other things being equal, V B Increase, D B Increase; V B Decrease, D B Decrease.

[0057] In this application, the value of D1 can be adjusted by regulating the average thickness of the first coating in the plane region of the positive electrode, the negative electrode, and the separator, or by adjusting the winding gap in the electrode assembly. For example, under the same conditions, D N As D increases, D1 increases; D N As D decreases, D1 decreases; D M As D increases, D1 increases; D M As D decreases, D1 decreases; D A As D increases, D1 increases; D A Decrease, D1 decreases; increase winding gap, D1 increases; decrease winding gap, D1 decreases.

[0058] In this application, the size of the winding gap in the electrode assembly can be adjusted by regulating the winding tension of the diaphragm and the electrode sheet. For example, under the same conditions, increasing the winding tension reduces the gap in the electrode assembly, while decreasing the winding tension increases the gap in the electrode assembly.

[0059] In this application, the width W1 of any ring of the negative electrode in the electrode assembly can be adjusted by regulating the average thickness of the second coating at the corner of the positive electrode, negative electrode, and separator. For example, under the same conditions, D N As D increases, W1 increases; N As D decreases, W1 decreases; M As D increases, W1 increases; M As D decreases, W1 decreases; B As D increases, W1 increases; B As W1 decreases, W1 decreases.

[0060] In this application, the width W2 of any turn of the plane region of the electrode assembly can be adjusted by controlling the number of winding turns. For example, under the same conditions, as N increases, W2 increases; as N decreases, W2 decreases.

[0061] In this application, the width W3 of any corner region of the electrode assembly can be adjusted by regulating the average thickness of the second coating at the corner of the positive electrode, negative electrode, and separator. For example, under the same conditions, D N Increase, W3 increases; D N Decrease, W3 decreases; D M Increase, W3 increases; D M Decrease, W3 decreases; D B Increase, W3 increases; D B As W3 decreases, W3 decreases.

[0062] In this application, the diaphragm can be prepared by the following method: (1) Mix the first material, inorganic filler and additive in proportion and add solvent, stir evenly to obtain the first coating slurry; mix the second material, inorganic filler and additive in proportion and add solvent, stir evenly to obtain the second coating slurry. (2) Take the base film, and alternately set the planar area and corner area along the winding direction of the base film. Apply the first coating slurry to one surface of the planar area of ​​the base film, apply the second coating slurry to the same surface of the corner area of ​​the base film, and dry to obtain a diaphragm with the first coating and the second coating on one side; (3) Repeat the above steps on the other surface of the planar area and the corner area of ​​the base film to obtain a finished diaphragm with the first coating and the second coating on both sides.

[0063] In this application, "a material layer disposed on at least one surface of the current collector" means that the material layer can be disposed on one surface of the current collector along its own thickness direction, or on two surfaces of the current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0064] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0065] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0066] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. The conductive agent may include at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, or graphene. The conductive carbon black may be at least one of acetylene black, Super P, or Ketjen black. The carbon nanotubes may be at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The carbon fibers may be at least one of vapor-grown carbon fibers (VGCF) or carbon nanofibers. This application does not impose any particular restrictions on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0067] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0068] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0069] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0070] The negative electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0071] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0072] This application does not impose any particular limitation on the type of base membrane, as long as it can achieve the purpose of this application. For example, the base membrane can be a nonwoven fabric or composite membrane with a porous structure, and the material of the base membrane can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be used.

[0073] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0074] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application also does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0075] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0076] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0077] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0078] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0079] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking a separator, a negative electrode sheet, a separator, and a positive electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0080] A second aspect of this application provides an electronic device that includes the secondary battery found in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance.

[0081] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In one or more embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0082] Example

[0083] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0084] Test methods and equipment:

[0085] Electrode assembly sampling:

[0086] At 25°C, the lithium-ion battery was charged to 3.6V at a constant current of 0.3C, then charged to the cutoff current of 0.05C at a constant voltage of 3.6V. After standing for 15 minutes, it was discharged to 2.0V at a constant current of 0.3C. The discharged lithium-ion battery was then disassembled under an argon atmosphere, the electrode assembly was removed, and the electrode assembly was soaked in dimethyl carbonate solvent (DMC) for 2 hours and dried at 60°C for 1 hour to obtain the electrode assembly.

[0087] W1, W2, W3, D A D B D N D M test

[0088] After disassembling the electrode assembly from turn N to turn N-1, the N-2 core sample is prepared. Along the thickness direction of the electrode assembly, a scanning electron microscope (SEM) is used to photograph the assembly, allowing for the measurement of the thickness of each part of the diaphragm. Areas with a thickness difference ≤1μm are designated as planar regions, and areas >1μm are designated as corner regions. Then, along the width direction of the electrode assembly, the sample width is directly measured using vernier calipers to obtain W1. The width of the planar regions is measured to obtain W2, and the width of the corner regions is measured to obtain W3.

[0089] Unwind the electrode assembly along the winding direction and disassemble it to obtain the positive electrode plate, negative electrode plate, and separator. Use a high-precision micrometer to measure the thickness of the positive electrode plate, negative electrode plate, and separator in the planar and corner areas. Take five thickness values ​​at different locations and average them to obtain D. A D B D N D M Numerical value.

[0090] Liquid retention rate of the first coating and liquid retention rate of the second coating were tested.

[0091] The finished lithium-ion battery was disassembled to obtain the separator. Areas of 1540.25 mm² were taken from both the planar and corner regions of the separator. 2 Five samples of each were immersed in DMC solvent for 6 hours. After immersion, the samples were removed, and the residual solvent on the surface was wiped off with lint-free paper. The samples were then weighed to obtain the sample weight M. A The samples were then placed in a vacuum oven at 120°C and vacuum dried for 12 hours. After drying, the samples were weighed to obtain the weight M of the dried samples. B The liquid retention rate V of the first coating is obtained by calculating the average value of 5 samples in each group. A Liquid retention rate V of the second coating B Liquid retention rate = (M) A -M B ) / M B .

[0092] Purple spot test

[0093] After placing the lithium-ion battery in a 45℃ environment for 60 minutes, charge it to 3.6V at a constant current of 1C, then charge it to the cutoff current of 0.05C at a constant voltage of 3.6V, let it stand for 5 minutes, and then discharge it to 2.5V at a constant current of 1C, and let it stand for 5 minutes. This process is considered one cycle. Repeat the above cycle with the lithium-ion battery. After the 100th cycle, disassemble the lithium-ion battery to obtain the positive and negative electrode sheets. Soak the positive and negative electrode sheets in dimethyl carbonate solvent for 2 hours and dry them at 60℃ for 1 hour to obtain the positive and negative electrode sheets. Use a scanning electron microscope (SEM) to photograph the positive and negative electrode sheets and observe whether purple spots appear on the surface of the electrode sheets.

[0094] Lithium plating test

[0095] After placing the lithium-ion battery in a 15°C environment for 60 minutes, charge it to 3.6V at a constant current of 1C, then charge it to 0.05C at a constant voltage of 3.6V until the cutoff current is reached. Let it rest for 5 minutes, then discharge it to 2.5V at a constant current of 1C and let it rest for 5 minutes. This process is considered one cycle. Repeat the above cycle for the lithium-ion battery. After the 10th cycle, disassemble the lithium-ion battery to obtain the negative electrode. Observe the lithium deposition state on the surface of the negative electrode material layer. The non-lithium-deposited area on the surface of the negative electrode material layer is golden yellow, and the lithium-deposited area is grayish white. Measure the lithium deposition area on the surface of the negative electrode material layer in the planar area and the corner area. For each example and comparative example, the lithium deposition state of the negative electrode material layer surface in 10 groups of lithium-ion batteries is statistically analyzed, and the average value is calculated to obtain the percentage of lithium deposition area to evaluate the lithium deposition state of the negative electrode material layer.

[0096] The criteria for judging the lithium plating state on the surface of the negative electrode material layer are as follows: lithium plating area less than or equal to 1% is no lithium plating, lithium plating area greater than 1% and less than or equal to 3% is slight lithium plating, lithium plating area greater than 3% and less than or equal to 5% is moderate lithium plating, and lithium plating area greater than 5% is severe lithium plating.

[0097] Cyclic capacity retention test:

[0098] At 45℃, the lithium-ion battery was charged at a constant current of 0.5C to 3.6V, then charged at a constant voltage of 3.6V to 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 1C to 2.5V, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle, and the discharge capacity of each cycle was recorded. The lithium-ion battery was subjected to 1000 cycles under the above conditions, and the discharge capacity was measured after each cycle. Cycle capacity retention (%) = (Capacity after 1000 discharge cycles / First discharge cycle capacity) × 100%.

[0099] Example 1

[0100] <Preparation of the positive electrode>

[0101] Lithium iron phosphate (LiFePO4, Dv50=12μm), the positive electrode active material, polyvinylidene fluoride (PVDF), the positive electrode binder, and Super P, were added to N-methylpyrrolidone (NMP) at a solid mass ratio of 95:2.5:2.5 and mixed evenly under vacuum stirring to obtain a positive electrode material slurry with a solid content of 60wt%. The positive electrode material slurry was then uniformly coated onto one surface of a 13μm thick aluminum foil for the positive electrode current collector and dried at 80℃ for 1 hour to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The single-sided coating weight of the positive electrode material layer was 300mg / 1540.25mm. 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After cold pressing, cutting, and welding of tabs, a positive electrode sheet with a size of 7600mm×64mm is obtained. The thickness of the single-sided positive electrode material layer is 118.5μm, and the thickness of the prepared positive electrode sheet is 250μm.

[0102] <Preparation of Negative Electrode Sheets>

[0103] Artificial graphite (negative electrode active material), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 120°C for 1 hour to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 230 mg / 1540.25 mm. 2 The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with dimensions of 7842mm×67mm for later use. The thickness of the single-sided negative electrode material layer is 72μm, and the thickness of the prepared negative electrode sheet is 150μm.

[0104] <Preparation of the diaphragm>

[0105] The first material, polystyrene, the inorganic filler, alumina, and the additive, triphenyl phosphate, are mixed in a mass ratio of 30:67:3. Deionized water is added as a solvent, and the mixture is stirred under vacuum until homogeneous to obtain the first coating slurry.

[0106] The second material, polyvinylidene fluoride, inorganic filler, alumina, and additive triphenyl phosphate are mixed in a mass ratio of 70:27:3, and deionized water is added as solvent. After vacuum stirring, the second coating slurry is obtained.

[0107] A 5μm thick polyethylene base membrane was used as the base membrane for the diaphragm. Planar regions and corner regions were alternately formed on the base membrane along its width. The width of each planar region was 91mm, and the width of each corner region was 9mm. A first coating slurry was applied to the planar regions at a weight of 70mg / 5000mm². 2 The first coating slurry applied to the corner area has a coating weight of 85 mg / 5000 mm. 2 After drying, a diaphragm is obtained.

[0108] <Preparation of Electrolyte>

[0109] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, the electrolyte salt LiPF6 was added to the organic solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the electrolyte salt comprised 12.5% ​​by mass, with the remainder being the organic solvent.

[0110] <Preparation of Lithium-ion Batteries>

[0111] The prepared positive electrode, separator, and negative electrode are stacked in the order of separator, negative electrode, separator, and positive electrode, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound with 100 turns. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 3.6V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0112] Examples 2 to 9

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1. Specifically, when the mass percentage of the first material in the first coating changes, the mass percentage of the additive in the first coating remains unchanged, while the mass percentage of the inorganic filler alumina changes accordingly; when the mass percentage of the second material in the second coating changes, the mass percentage of the additive in the second coating remains unchanged, while the mass percentage of the inorganic filler alumina changes accordingly.

[0114] Examples 10 to 12

[0115] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0116] Example 13

[0117] Except for adjusting the number of winding turns to 9 in <Preparation of Lithium-ion Battery>, adjusting the size of the positive electrode to 1080mm×64mm in <Preparation of Positive Electrode>, and adjusting the size of the negative electrode to 1290mm×67mm in <Preparation of Negative Electrode>, the rest is the same as in Example 1.

[0118] Example 14

[0119] Except for adjusting the number of winding turns to 100 in <Preparation of Lithium-ion Battery>, adjusting the size of the positive electrode to 12600mm×64mm in <Preparation of Positive Electrode>, and adjusting the size of the negative electrode to 12842mm×67mm in <Preparation of Negative Electrode>, the rest is the same as in Example 1.

[0120] Example 15

[0121] Except for adjusting the coating weight of the single-sided positive electrode material layer to 105 mg / 1540.25 mm in the <Preparation of Positive Electrode Sheet> section. 2 In the preparation of the negative electrode sheet, the coating weight of the negative electrode sheet was adjusted to 80.5 mg / 1540.25 mm. 2 Except for the above, the rest is the same as in Example 1.

[0122] Example 16

[0123] Except for adjusting the coating weight of the single-sided positive electrode material layer to 540 mg / 1540.25 mm in the <Preparation of Positive Electrode Sheet> section. 2 In the preparation of the negative electrode sheet, the coating weight of the negative electrode sheet was adjusted to 414 mg / 1540.25 mm. 2 Except for the above, the rest is the same as in Example 1.

[0124] Example 17

[0125] In addition to adjusting the coating weight of the single-sided positive electrode material layer to 600 mg / 1540.25 mm in the <Preparation of Positive Electrode Sheet> section, 2 In the preparation of the negative electrode sheet, the coating weight of the negative electrode sheet was adjusted to 460 mg / 1540.25 mm. 2 Except for the above, the rest is the same as in Example 1.

[0126] Examples 18 to 19

[0127] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0128] Example 20

[0129] Except for adjusting the alternating arrangement of the first and second coatings in the first 20 turns of the electrode assembly in the <Preparation of the Separator> section to only the second coating, the rest is the same as in Example 1.

[0130] Example 21

[0131] Except that in the <Preparation of the Separator>, the first coating and the second coating are alternately applied only on the side of the separator facing the negative electrode, and only the second coating is applied on the other side, the rest is the same as in Example 1.

[0132] Comparative Example 1

[0133] Except for the use of a 5 μm thick porous polyethylene film (provided by Celgard) as the separator in the <Separator Preparation> section, the rest is the same as in Example 1.

[0134] Comparative Example 2

[0135] Except for applying a second coating to the planar area and a first coating to the corner area in the <Preparation of the diaphragm>, the rest is the same as in Example 1.

[0136] Table 1

[0137] Note: In Table 1, " / " indicates that the corresponding preparation parameter or substance does not exist; M1 represents the mass percentage of the first material; M2 represents the mass percentage of the second material; V A V represents the liquid retention rate of the first coating. B Indicates the liquid retention rate of the second coating; D A D represents the average thickness of the first coating; B W1 represents the average thickness of the second coating; W2 represents the width of the planar area; W3 represents the width of the corner area; D N D represents the average thickness of the positive electrode sheet. M D1 represents the average thickness of the negative electrode sheet; W1 represents the thickness of the negative electrode sheet in the 57th turn of the electrode assembly; N represents the number of turns of the electrode assembly.

[0138] As can be seen from Examples 1 to 21 and Comparative Examples 1 to 2, by setting a first coating and a second coating that meet the characteristics of this application on the separator and adjusting the liquid retention rate of the first coating and the second coating within the range of this application, the lithium-ion battery has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the embodiments of this application are good. Comparative Example 1 uses a conventional separator, and the secondary battery showed purple spots during cycling, obvious lithium plating in the later stage of cycling, and a poor cycle capacity retention rate; in Comparative Example 2, the liquid retention rate of the first coating is greater than that of the second coating, the liquid retention capacity of the separator corner area is poor, and it cannot fill the gaps in the corner area well. The secondary battery showed purple spots during cycling, severe lithium plating in the later stage of cycling, and a poor cycle capacity retention rate. This indicates that embodiments that do not meet the requirements of this application have poor cycle performance and safety performance, while embodiments of this application, while reducing the possibility of purple spots, have a lower lithium plating rate and a higher cycle capacity retention rate. This shows that embodiments that meet the features of this application can reduce the formation of purple or black spots on the electrode, improve the liquid replenishment capacity during the cycle of the secondary battery, thereby enhancing the safety performance and improving the cycle performance of the secondary battery.

[0139] As can be seen from Examples 1 to 5, the mass percentage of the first material affects the cycle performance and safety performance of the secondary battery. When the value of M1 is adjusted within the range of this application, the first coating can have a suitable liquid retention rate, thereby improving the liquid replenishment capacity during the cycle of the secondary battery. While reducing the formation of purple or black spots on the electrode, it also has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial to enhancing the safety performance and improving the cycle performance of the secondary battery.

[0140] As can be seen from Examples 1, 6 to 9, the mass percentage of the second material affects the cycle performance and safety performance of the secondary battery. When the value of M2 is adjusted within the range of this application, the second coating can have a suitable liquid retention rate, and the second coating in the corner area of ​​the separator can better fill the gaps in the corner area, thereby improving the liquid replenishment capacity during the cycle of the secondary battery. While reducing the formation of purple or black spots on the electrode, it also has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial to enhancing the safety performance and improving the cycle performance of the secondary battery.

[0141] As can be seen from Examples 1 to 9 and Examples 15 to 17, the thickness of each part of the electrode assembly affects the cycle performance and safety performance of the secondary battery. Adjusting the thickness of each part of the electrode assembly within the scope of this application is beneficial to enhancing the safety performance and improving the cycle performance of the secondary battery. Specifically, as can be seen from Examples 1 to 9, when the average thickness of the second coating is greater than the average thickness of the first coating, the second coating located in the corner area can better fill the gaps in the corner area, and the secondary battery has a lower lithium plating rate and a higher cycle capacity retention rate while reducing the formation of purple or black spots on the electrode. As can be seen from Examples 1 and Examples 15 to 17, when the average thickness of the negative electrode and the positive electrode is adjusted within the scope of this application, the electrodes of the secondary battery have suitable kinetic performance and suitable internal resistance, which is beneficial to improving the cycle performance of the secondary battery. As can be seen from Examples 1 to 9 and Examples 15 to 17, when the thickness of each part (D...) is adjusted... B -D A ) / (D M +D N When the value of the material is within the range of this application, each part has a suitable thickness, enabling them to work synergistically and effectively fill the gaps in the corner area. This results in the secondary battery exhibiting a lower lithium plating rate and a higher cycle capacity retention rate while reducing the formation of purple or black spots on the electrodes. Therefore, the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of secondary batteries.

[0142] As can be seen from Examples 1, 13, and 14, the number of turns of the electrode assembly affects the cycle performance and safety performance of the secondary battery. When the number of turns of the electrode assembly is adjusted within the range of this application, the secondary battery has a suitable energy density. Specifically, when the number of turns of the electrode assembly is small, the energy density of the secondary battery is low, and the cycle capacity retention rate is low; when the number of turns of the electrode assembly is large, the capacity loss during cycling is high, and the cycle capacity retention rate is low. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0143] As can be seen from Examples 1 and 18, the width and thickness of the negative electrode sheet and the width of the planar region in any loop electrode assembly affect the cycle performance and safety performance of the secondary battery. When the above values ​​are adjusted to satisfy W2 < W1 - D1, the planar region of the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode sheet. Thus, the corner region of the base film has a suitable width, which is beneficial for better covering the area on the negative electrode sheet corresponding to the corner region of the base film, improving the wetting of the negative electrode sheet at the corner, reducing the formation of purple or black spots on the electrode sheet, and having a lower lithium plating rate and a higher cycle capacity retention rate. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0144] As can be seen from Examples 1 and 19, the width of the corner region and the thickness of the negative electrode sheet in any ring of electrode assembly affect the cycle performance and safety performance of the secondary battery. When the above values ​​are adjusted to satisfy W3 > D1 / 2, the width of the base film corner region is greater than half the thickness of the negative electrode sheet of that ring. This is beneficial for better coverage of the area on the negative electrode sheet corresponding to the base film corner region, improving the wetting of the negative electrode sheet at the corner. While reducing the formation of purple or black spots on the electrode sheet, it also has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0145] As can be seen from Examples 1 and 20, the number of winding turns of the separator coating affects the cycle performance and safety performance of the secondary battery. Along the winding direction of the separator, the thickness of the electrode assembly increases, and the corner area also increases accordingly. This increases the likelihood of voids being generated during the secondary battery formation process due to gas production. When the second coating is only applied to the corner area of ​​the base film from the N / 3rd to the Nth turn, it can better match the corner area and better fill the voids between the secondary battery separator corner area and the electrode. This reduces the formation of purple or black spots on the negative electrode while exhibiting a lower lithium plating rate and a higher cycle capacity retention rate. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0146] As can be seen from Examples 1 and 21, the location of the separator coating affects the cycle performance and safety performance of the secondary battery. When the separator coating is only disposed on one surface of the base film along the thickness direction of the separator, and the coated base film surface faces the negative electrode, during the cycle of the secondary battery, the second coating corresponds to the negative electrode, which is beneficial for better covering the area on the negative electrode corresponding to the corner area of ​​the base film, improving the wetting of the negative electrode at the corner, and better filling the gap between the corner area of ​​the secondary battery separator and the electrode. While reducing the formation of purple or black spots on the negative electrode, it has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0147] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0148] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator, the separator including a base film and a coating coated on at least one surface of the base film, the base film including continuously alternating planar regions and corner regions along the winding direction of the separator; the coating including a first coating and a second coating, the first coating being disposed in the planar regions of the base film, the second coating being disposed in the corner regions of the base film, the first coating having a liquid retention rate of V. A The liquid retention rate of the second coating is V B V B >V A .

2. The secondary battery according to claim 1, wherein, 5%≤V A ≤20%,110%≤V B ≤200%。 3. The secondary battery according to claim 1, wherein, The first coating comprises a first material, which includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, or polyimide. Based on the mass of the first coating, the mass percentage of the first material is M1, where 15% ≤ M1 ≤ 45%. The second coating comprises a second material, which includes at least one of polystyrene, polystyrene-propylene, polyvinyl alcohol, polyamide, polyurethane, or ethyl cellulose. Based on the mass of the second coating, the mass percentage of the second material is M2, where 55% ≤ M2 ≤ 85%.

4. The secondary battery according to claim 1, wherein, The average thickness of the negative electrode sheet is D. M μm, the average thickness of the positive electrode sheet is D N μm, the average thickness of the first coating is D A μm, the average thickness of the second coating is D B μm, D B >D A , 0 < (D B -D A ) / (D M +D N ≤0.

13.

5. The secondary battery according to claim 4, wherein, The secondary battery satisfies at least one of the following characteristics: （1）60≤D M ≤270； （2）90≤D N ≤400； （3）5≤D A ≤35。 6. The secondary battery according to claim 1, wherein, The electrode assembly comprises N turns, where 9 ≤ N ≤ 100; in any turn of the electrode assembly, the width of the negative electrode sheet formed by winding along the width direction of the electrode assembly is W1 mm, the width of the planar region of the base film is W2 mm, and the thickness of the negative electrode sheet formed by winding along the thickness direction of the electrode assembly is D1 mm, where W2 < W1 - D1.

7. The secondary battery according to claim 6, wherein, 3≤D1≤300。 8. The secondary battery according to claim 6, wherein, Starting from the beginning of the winding of the diaphragm, along the winding direction of the diaphragm, the second coating is only applied to the corner area of ​​the base film from the N / 3th turn to the Nth turn.

9. The secondary battery according to claim 6, wherein, In any of the electrode assemblies, along the width direction of the electrode assembly, the width of any corner region of the base film is W3 mm, where W3 > D1 / 2.

10. The secondary battery according to claim 6, wherein, The widths of any two planar regions of the base film are equal.

11. The secondary battery according to claim 1, wherein, Along the thickness direction of the separator, the coating is disposed on one surface of the base film, and the surface of the base film with the coating is facing the negative electrode.

12. An electronic device comprising a secondary battery as described in any one of claims 1 to 11.

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