Positive pole piece, secondary battery and electronic device

Abstract

The invention provides a positive pole piece, a secondary battery and an electronic device. The positive pole piece comprises a positive current collector, a positive material layer and an insulating layer, and the positive current collector comprises an empty foil region and a coating region; the positive electrode material layer and the insulating layer are arranged on at least one surface of the coating area, the insulating layer and the positive electrode material layer are connected in the length direction of the positive electrode current collector, and the insulating layer is closer to the empty foil area than the positive electrode material layer; the insulating layer comprises a binder and a ceramic material, the binder comprises at least one of polyurethane, polyacrylic acid or polyacrylonitrile, and based on the mass of the insulating layer, the mass percentage W1 of the binder is 70%-90%. The positive pole piece provided by the invention has good production process yield, and the obtained secondary battery has good safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a positive electrode sheet, a secondary battery and an electronic device. Background Art

[0002] With the rapid development of secondary batteries in portable electronic devices, electric vehicles and other application fields, people's demand for fast-charging secondary batteries continues to increase. Multi-pole secondary batteries use a multi-pole design to add more electrode contact points in the positive or negative electrode of the secondary battery, shorten the transmission path of electrons during charging, reduce the internal resistance of the secondary battery, reduce energy loss, and improve the efficiency of power conversion, thereby achieving fast charging. However, during the use of secondary batteries with multi-pole structures, after the positive electrode ear breaks, the exposed positive current collector fracture is easy to contact the negative electrode plate and cause a short circuit, making the secondary battery ineffective.

[0003] At present, the short circuit problem is mainly solved by coating an insulating layer on the empty foil area corresponding to the positive electrode ear that may contact the negative electrode plate, that is, the edge of the positive electrode material layer. However, during the cold pressing process of manufacturing the positive electrode plate, there is usually a large stress concentration at the junction between the edge of the positive electrode material layer and the conventional insulating layer, which can easily cause wrinkles or fractures near the above-mentioned junction, thereby reducing the production process efficiency of the positive electrode plate and the safety performance of the resulting secondary battery. Summary of the invention

[0004] The purpose of the present application is to provide a positive electrode plate, a secondary battery and an electronic device to improve the production process efficiency of the positive electrode plate and the safety performance of the secondary battery.

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

[0006] The first aspect of the present application provides a positive electrode sheet, which includes a positive electrode collector, a positive electrode material layer, and an insulating layer, wherein the positive electrode collector includes a hollow foil area and a coating area; the positive electrode material layer and the insulating layer are arranged on at least one surface of the coating area, and the insulating layer and the positive electrode material layer are connected and arranged along the length direction of the positive electrode collector, and the insulating layer is closer to the hollow foil area than the positive electrode material layer; the insulating layer includes a binder and a ceramic material, and the binder includes at least one of polyurethane, polyacrylic acid or polyacrylonitrile, and based on the mass of the insulating layer, the mass percentage content W1 of the binder is 70% to 90%. In some embodiments of the present application, the mass percentage content W1 of the binder is 70% to 85%. By regulating W1 within the above range, the phenomenon of wrinkling and breaking of the edge of the positive electrode material layer during the cold pressing process can be alleviated, the flexibility and processing stability of the insulating layer can be improved, and the risk of the insulating layer falling off can be reduced, which is conducive to improving the production process excellence rate of the positive electrode sheet and improving the safety performance of the secondary battery obtained.

[0007] In some embodiments of the present application, the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 1 μm. In some embodiments of the present application, the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 0.8 μm. When the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is within the above range, it is beneficial to improve the energy density of the secondary battery. At the same time, the above-mentioned insulating layer is also beneficial to improve the cycle stability and safety performance of the secondary battery.

[0008] In some embodiments of the present application, the maximum thickness of the insulating layer is d μm and the width is b mm, wherein 10≤d≤40 and 1.5≤b≤3.5. In some embodiments of the present application, 10≤d≤25; and / or, 2.0≤b≤3.0. By controlling the maximum thickness d and width b of the insulating layer within the above range, not only can the probability of positive electrode tab breakage be reduced and the safety performance of the secondary battery be improved, but also the energy density of the secondary battery can be taken into consideration.

[0009] In some embodiments of the present application, along the direction from the positive electrode material layer to the insulating layer, the positive electrode material layer includes a first edge and a second edge relative to each other, the first edge is close to the insulating layer, the edge of the insulating layer close to the positive electrode material layer is the third edge, the third edge coincides with the first edge, or the third edge is located between the first edge and the second edge, and the distance between the third edge and the first edge is s mm, 0≤s≤0.5. In some embodiments of the present application, 0≤s≤0.3. By regulating the distance s between the third edge and the first edge within the above range, the safety performance of the secondary battery can be improved, while also facilitating the consideration of the energy density of the secondary battery.

[0010] In some embodiments of the present application, the positive electrode material layer and the insulating layer are arranged on the two surfaces of the coating area, and the distance between the third edges of the insulating layer on both sides of the positive electrode current collector along the direction from the positive electrode material layer to the insulating layer is Δs mm, 0≤Δs≤0.3. In some embodiments of the present application, 0≤Δs≤0.1. By regulating the distance Δs between the third edges of the insulating layer on both sides of the positive electrode current collector within the above range, it is not only beneficial to improve the safety performance and production process excellence of the secondary battery, but also beneficial to take into account the energy density of the secondary battery.

[0011] In some embodiments of the present application, the positive electrode material layer and the insulating layer are arranged on two surfaces of the coating area. In some embodiments of the present application, the difference in the maximum thickness of the insulating layer on both sides of the positive electrode current collector is Δdμm, 0≤Δd≤15. In some embodiments of the present application, 0≤Δd≤10. In some embodiments of the present application, 0≤Δd≤5. By regulating the value of Δd within the above range, the uniformity of the insulating layer coating on both sides of the positive electrode current collector is better, which is not only conducive to improving the insulation performance between the positive electrode tab and the negative electrode tab, but also conducive to reducing the risk of fracture of the positive electrode tab and improving the safety performance of the secondary battery.

[0012] In some embodiments of the present application, the difference in width of the insulating layer on both sides of the positive electrode current collector is Δb mm, 0≤Δb≤0.3. In some embodiments of the present application, 0≤Δb≤0.1. By regulating Δb within the above range, it is helpful to reduce the occurrence of wrinkling and curling of the first edge of the positive electrode material layer, thereby reducing the risk of positive electrode tab fracture, improving the safety performance and production process excellence of the secondary battery, and also helping to take into account the energy density of the secondary battery.

[0013] In some embodiments of the present application, the secondary battery meets at least one of the following characteristics: (1) the ceramic material includes at least one of boehmite or alumina; (2) based on the mass of the insulating layer, the mass percentage W2 of the ceramic material is 10% to 30%; (3) the thickness of the positive electrode current collector is hμm, 8≤h≤10. The secondary battery meets at least one of the above characteristics, and the obtained secondary battery has a higher energy density, which is also conducive to improving the production process excellence rate of the secondary battery and the number of batteries that pass the drop test, thereby improving the safety performance of the secondary battery.

[0014] A second aspect of the present application provides a secondary battery, which includes the positive electrode sheet in any of the aforementioned embodiments.

[0015] A third aspect of the present application provides an electronic device, which includes the positive electrode sheet in any of the aforementioned embodiments or the secondary battery in any of the aforementioned embodiments.

[0016] Beneficial effects of this application:

[0017] The present application provides a positive electrode sheet, a secondary battery and an electronic device, wherein the positive electrode sheet includes a positive electrode current collector, a positive electrode material layer and an insulating layer, wherein the positive electrode current collector includes an empty foil area and a coating area; the positive electrode material layer and the insulating layer are arranged on at least one surface of the coating area, the insulating layer and the positive electrode material layer are connected in sequence, and the insulating layer is closer to the empty foil area than the positive electrode material layer; the insulating layer includes a binder and a ceramic material, the binder includes at least one of polyurethane, polyacrylic acid or polyacrylonitrile, and based on the mass of the insulating layer, the mass percentage content W1 of the binder is 70% to 90%. By controlling the mass percentage content W1 of the binder within the above range, the stress concentration problem between the edge of the positive electrode material layer and the insulating layer during the cold pressing process can be improved, the phenomenon of wrinkling and breaking of the edge of the positive electrode material layer can be alleviated, the risk of the insulating layer falling off can be reduced, the production process excellence rate of the positive electrode sheet can be improved, and the safety performance of the secondary battery can be improved.

[0018] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0020] Figure 1 A schematic diagram of the cross-sectional structure of a positive electrode sheet along the thickness direction according to an embodiment of the present application;

[0021] Figure 2 A schematic diagram of a cross-sectional structure of a positive electrode sheet along the thickness direction according to another embodiment of the present application;

[0022] Figure 3 This is a schematic diagram of the cross-sectional structure of a positive electrode sheet along the thickness direction according to another embodiment of the present application;

[0023] Figure 4 This is a schematic diagram of the cross-sectional structure of a positive electrode sheet along the thickness direction according to another embodiment of the present application;

[0024] Figure 5 A schematic diagram of the structure of a lithium-ion battery according to an embodiment of the present application;

[0025] Figure 6a This is a photo of the positive electrode sheet obtained after coating the insulating layer and cold pressing in Example 1;

[0026] Figure 6b This is a photo of the positive electrode sheet obtained after coating the insulating layer and cold pressing in Comparative Example 4. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0028] It should be noted that in the specific implementation manner of the present application, the present application is explained by taking a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0029] Multi-electrode secondary batteries are technical improvements made to meet people's demand for fast charging. They have a wide range of applications, such as secondary batteries with winding structures or secondary batteries with laminated structures. Especially for secondary batteries with laminated structures, the multi-electrode structure is almost a necessary technology. The pole ear is usually the extension of the current collector, which acts as a conductor. Each pole ear is the current output point of the positive electrode plate or negative electrode plate where it is located. The positive pole ear of the secondary battery is obtained by stacking multiple positive pole ears and then welding them together, and the negative pole ear of the secondary battery is obtained by stacking multiple negative pole ears and then welding them together. The parallel effect is achieved, so that the secondary battery can be charged and discharged at a high rate, such as 5C, 10C or even higher rates, to meet the needs of fast charging. However, in multi-electrode secondary batteries, after the positive pole ear breaks, the exposed positive current collector fracture is easy to contact the negative electrode plate and cause a short circuit. Therefore, it is necessary to coat an insulating layer in the area corresponding to the positive pole ear in the positive electrode plate to reduce the risk of short circuit and improve the safety performance of the secondary battery.

[0030] The positive electrode plate is usually prepared by the "zebra coating" process. Due to the surface tension of the positive electrode material layer slurry during the coating process, the thickness of the edge area of ​​the obtained positive electrode material layer is less than the thickness of the central area of ​​the positive electrode material layer, that is, a "thinning zone" inevitably appears at the edge of the positive electrode material layer. After being assembled into an electrode assembly, due to the existence of the "thinning zone", a gap will appear between the edge of the positive electrode material layer and the diaphragm, resulting in the gradual deterioration of the circulation interface of the obtained secondary battery and affecting the overall safety performance of the secondary battery. When the positive electrode plate of the secondary battery of the present application adopts the design of a "zero thinning" positive electrode material layer, that is, there is almost no "thinning zone" at the edge of the positive electrode material layer, during the cold pressing process of the secondary battery manufacturing, there is usually a greater stress concentration between the edge of the "zero thinning" positive electrode material layer and the traditional insulating layer, and the two are difficult to match, which leads to wrinkles near the edge of the positive electrode material layer, or even fracture, reducing the production process excellence rate of the positive electrode plate, and it is easy to cause the positive electrode ear to break or the insulating layer to fall off due to falling during use, and the safety performance of the secondary battery is reduced.

[0031] The solution of the present application can be used in the design of positive electrode material layers with or without thinning areas, which can improve the production process excellence of positive electrode plates and promote the improvement of the production process excellence and safety performance of secondary batteries.

[0032] Based on the above problems, the present application provides a secondary battery and an electronic device, which can improve the stress concentration problem of the positive electrode material layer and the insulating layer during the cold pressing process, alleviate the wrinkling and fracture of the edge of the positive electrode material layer, and reduce the risk of the insulating layer falling off, thereby improving the production process excellence of the positive electrode sheet and promoting the improvement of the production process excellence and safety performance of the secondary battery.

[0033] The present application provides a positive electrode plate, a secondary battery and an electronic device. The positive electrode plate includes a positive current collector, a positive electrode material layer and an insulating layer. The positive current collector includes a hollow foil area and a coating area. The hollow foil area of ​​the present application refers to an area where both sides of the current collector do not contain a positive electrode material layer and an insulating layer. The positive electrode material layer and the insulating layer are arranged on at least one surface of the coating area. The insulating layer and the positive electrode material layer are connected and arranged along the length direction of the positive current collector. The above-mentioned "length direction" refers to the length direction of the positive current collector. Figure 5 the direction indicated by the rightmost arrow, or Figure 1 In the direction from the positive electrode material layer 20 to the insulating layer 30, the insulating layer 30 is closer to the empty foil area 012 than the positive electrode material layer 20. Figure 1 As shown, the positive electrode material layer 20 and the insulating layer 30 are disposed on one surface of the coating area 011. Figure 3As shown, the positive electrode material layer 20 and the insulating layer 30 are arranged on the two surfaces of the coating area 011. The insulating layer includes an insulating layer binder and a ceramic material, and the insulating layer binder includes at least one of polyurethane, polyacrylic acid or polyacrylonitrile. Based on the mass of the insulating layer, the mass percentage W1 of the insulating layer binder is 70% to 90%. In some embodiments of the present application, the mass percentage W1 of the binder is 70% to 85%. Among them, W1 can be 70%, 72%, 75%, 78%, 80%, 83%, 85%, 87%, 90% or a range composed of any two values ​​therein. When W1 is too small, for example, less than 70%, the obtained insulating layer is not flexible enough. During the cold pressing process, a certain stress concentration will still appear at the junction of the edge of the positive electrode material layer and the insulating layer, which is easy to cause wrinkles or fractures at the edge of the positive electrode material layer, thereby affecting the safety performance and production process excellence of the secondary battery. When W1 is too large, for example, greater than 90%, not only will the insulation performance of the insulating layer be reduced, and the secondary battery obtained will be prone to short circuit during the drop test, but it will also cause the heat resistance of the insulating layer to deteriorate, and it will be easy to shrink during the subsequent laser die-cutting process of the ear, which will reduce the safety performance of the secondary battery. Therefore, by regulating W1 within the scope of this application, the obtained insulating layer has suitable flexibility while having good insulation performance, so that during the cold pressing process of the positive electrode sheet, it is beneficial to disperse the stress between the positive electrode material layer and the insulating layer, alleviate the wrinkles and fractures in the empty foil area of ​​the positive electrode sheet, improve the production process excellence rate of the positive electrode sheet, and reduce the risk of the insulating layer falling off, thereby increasing the number of secondary batteries that pass the drop test and improving the safety performance of the secondary battery.

[0034] Therefore, by regulating W1 within the above range, the stress concentration problem between the positive electrode material layer and the insulating layer during the cold pressing process can be improved, the wrinkling and fracture of the edge of the positive electrode material layer can be alleviated, and the risk of the insulating layer falling off can be reduced, which is beneficial to improving the production process efficiency of the positive electrode sheet and obtaining a secondary battery with higher safety performance.

[0035] The present application has no particular restrictions on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet may include but is not limited to the following steps:

[0036] Prepare a positive electrode material layer slurry, then place the positive electrode material layer slurry on at least one surface of the positive electrode current collector, and after drying, place an insulating layer on the edge of the positive electrode material layer close to the empty foil area and then cold press to obtain a positive electrode sheet. There is a thinning area in the positive electrode material layer. The present application has no particular restrictions on the pressure of the cold pressing treatment, as long as the purpose of the present application can be achieved. For example, the pressure of the cold pressing treatment can be 30t to 120t.

[0037] In some embodiments of the present application, the difference ΔT between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 1 μm. In some embodiments of the present application, the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 0.8 μm. For example, the difference between the maximum thickness and the minimum thickness of the positive electrode material layer can be 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm or a range consisting of any two of these values. When the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is within the above range, it means that there is almost no "thinning zone" at the edge of the positive electrode material layer, which can improve the energy density of the secondary battery. At the same time, the above-mentioned insulating layer is also beneficial to improve the cycle stability and safety performance of the secondary battery. Generally, the outer contour of the cross section of the positive electrode material layer without a "thinning zone" along its own thickness direction is close to a rectangle. Along the direction from the insulating layer to the positive electrode material layer, the positive electrode material layer includes a first edge and a second edge relative to each other, the first edge is close to the insulating layer, and the difference between the maximum thickness and the minimum thickness refers to the difference between the maximum thickness and the minimum thickness of the positive electrode material layer in the area within 8 mm extending from the first edge to the above direction.

[0038] The present application has no particular restrictions on the method for preparing the positive electrode sheet having almost no "thinning area" at the edge of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet may include but is not limited to the following steps:

[0039] Prepare the positive electrode material layer slurry, stick the adhesive tape on the area of ​​the positive electrode current collector corresponding to the empty foil area and the insulating layer, and then set the positive electrode material layer slurry in the area corresponding to the positive electrode material layer. Since the positive electrode material layer slurry has fluidity and the thickness of the adhesive tape is relatively small, the positive electrode material layer slurry will cover at least part of the adhesive tape. After the positive electrode material layer slurry is coated, it is dried, and then the adhesive tape is peeled off. The obtained positive electrode material layer basically does not have a "thinning area". Then, at the edge of the positive electrode material layer near the empty foil area where the adhesive tape is peeled off, that is, the first edge, an insulating layer is set and then cold pressing is performed to obtain a positive electrode sheet. The present application does not have any special restrictions on the pressure of the cold pressing treatment, as long as the purpose of the present application can be achieved. For example, the pressure of the cold pressing treatment can be 30t to 120t.

[0040] In the present application, when setting the positive electrode material layer slurry, the size of the adhesive tape covering the positive electrode material layer slurry can be changed by changing the starting position of setting the positive electrode material layer slurry. Generally, the larger the size of the adhesive tape covering the positive electrode material layer slurry, the smaller the ΔT of the positive electrode material layer obtained after peeling off the adhesive tape and cold pressing, and vice versa. The above-mentioned "size of the adhesive tape covering the positive electrode material layer slurry" refers to the size of the adhesive tape covering the positive electrode material layer slurry along the direction from the insulating layer to the positive electrode material layer.

[0041] In some embodiments of the present application, the adhesive force of the adhesive tape is 0.5 N / m to 5 N / m. The present application has no particular restrictions on the thickness of the adhesive tape, as long as the purpose of the present application can be achieved. For example, the thickness of the adhesive tape is 5 μm to 20 μm. The present application has no particular restrictions on the type of the adhesive tape, as long as the purpose of the present application can be achieved.

[0042] The positive electrode sheet obtained by the above method is first provided with adhesive tape in the area corresponding to the empty foil area and the insulating layer, and then the adhesive tape and the positive electrode material layer on its surface are removed, and the obtained positive electrode material layer may not have a "thinning area", which can optimize the contact interface between the positive electrode material layer and the diaphragm, improve the cycle performance of the secondary battery, and also take into account the energy density. In addition, during the cold pressing process, compared with the current conventional insulating layer, the insulating layer of the present application has suitable flexibility, which is conducive to relieving the stress between the first edge of the positive electrode material layer and the insulating layer, reducing the generation of wrinkles on the first edge of the positive electrode sheet, and matching the "zero thinning" positive electrode material layer, thereby reducing the risk of positive electrode ear fracture, improving the production process excellence rate of the positive electrode sheet, and then improving the safety performance of the secondary battery and taking into account the energy density. In addition, the insulating layer of the present application has good adhesion with the positive electrode current collector, and the secondary battery is not easy to fall off during the drop test, which is conducive to improving the safety performance of the secondary battery.

[0043] In some embodiments of the present application, Figure 1 As shown, along the direction from the positive electrode material layer 20 to the insulating layer 30, that is, Figure 1 In the direction indicated by the arrow, the positive electrode material layer 20 includes a first edge 21 and a second edge 22 opposite to each other, the first edge 21 is close to the insulating layer 30, and the edge of the insulating layer 30 close to the positive electrode material layer 20 is a third edge 31, and the third edge 31 coincides with the first edge 21. In some embodiments of the present application, as Figure 2As shown, the third edge 31 is between the first edge 21 and the second edge 22, and the distance between the third edge 31 and the first edge 21 is s mm. In some embodiments of the present application, 0≤s≤0.5. In some embodiments of the present application, 0≤s≤0.3. For example, the value of s can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or a range consisting of any two values ​​therebetween. Among them, the third edge coincides with the first edge, that is, s=0; the third edge is located between the first edge and the second edge, that is, 0<s≤0.5. In the present application, when setting the insulating layer, the insulating layer slurry is first set on the positive electrode current collector empty foil at a certain distance from the first edge of the positive electrode material layer. Since the insulating layer slurry is in a flowable state and has surface tension, the insulating layer slurry will spread and level in the direction of the positive electrode material layer until the third edge of the insulating layer coincides with the first edge of the positive electrode material layer, that is, s=0; or, the insulating layer slurry spreads along the first edge of the positive electrode material layer to the surface of the positive electrode material layer under the action of siphon, and penetrates into the positive electrode material layer under the action of gravity to form a new composite material layer, and the composite material layer is part of the insulating layer, so that the third edge of the insulating layer is located between the first edge and the second edge, that is, 0<s≤0.5. The surface of the above-mentioned composite material layer will present a color close to that of the insulating layer, and can be clearly observed and tested by a scanning electron microscope (SEM). Therefore, under the condition of controlling the amount of the insulating layer to be constant, the regulation of s can be achieved by controlling the distance between the position where the insulating layer slurry is initially set and the first edge. By adjusting the distance s between the third edge and the first edge within the above range, it is beneficial to improve the production process efficiency of the positive electrode plate, while reducing the risk of lithium plating of the secondary battery, thereby improving the safety performance of the secondary battery, and it is also beneficial to take into account the energy density of the secondary battery.

[0044] In some embodiments of the present application, Figure 3 As shown, the positive electrode sheet 01 includes a positive electrode current collector 10 and a positive electrode material layer 20 and an insulating layer 30 respectively arranged on the two surfaces of the positive electrode current collector 10, the positive electrode material layer 20 includes a first positive electrode material layer 201 arranged on one surface of the positive electrode current collector and a second positive electrode material layer 202 arranged on the other surface of the positive electrode current collector, the insulating layer 30 includes a first insulating layer 301 arranged on one surface of the positive electrode current collector and a second insulating layer 302 arranged on the other surface of the positive electrode current collector, the first positive electrode material layer 201 and the first insulating layer 301 are located on the same side of the positive electrode current collector 10, and the second positive electrode material layer 202 and the second insulating layer 302 are located on the same side of the positive electrode current collector 10. Along the direction from the first positive electrode material layer 201 to the first insulating layer 301, that is, Figure 3In the direction indicated by the middle arrow, the distance between the third edge 31 of the first insulating layer 301 and the first edge 21 of the first positive electrode material layer 201 is s1, and the distance between the third edge 31 of the second insulating layer 302 and the first edge 21 of the second positive electrode material layer 202 is s2. In some embodiments of the present application, the difference between the distances s1 and s2 is Δs mm, 0≤Δs≤0.3. In some embodiments of the present application, 0≤Δs≤0.1, for example, Δs can be 0, 0.02, 0.05, 0.07, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3 or a range consisting of any two values ​​therebetween. By adjusting the distance Δs between the third edges of the insulating layer on both sides of the positive electrode current collector within the above range, it is not only helpful to alleviate the stress concentration between the first edge of the positive electrode material layer and the insulating layer, reduce the generation of wrinkles, thereby reducing the risk of positive electrode ear fracture, and improve the production process of positive electrode sheets. At the same time, it is not easy to produce lithium deposition and black spots during the secondary battery cycle, which is beneficial to improve the cycle stability and safety performance of the secondary battery. In addition, it is also beneficial to take into account the energy density of the secondary battery.

[0045] In some embodiments of the present application, the maximum thickness of the insulating layer is d μm, d is 10 to 40, and in some embodiments of the present application, d is 10 to 25. For example, the value of d can be 10, 15, 18, 20, 22, 25, 27, 30, 33, 35, 38, 40 or a range consisting of any two values ​​therebetween. Figure 1 and Figure 2 As shown, due to the surface tension of the insulating layer slurry during the coating process, the thickness of the insulating layer 30 obtained is not uniform. Therefore, the outer contour of the insulating layer 30 is usually irregular. Figure 1 In the direction indicated by the middle arrow, the area from 21aμm away from the first edge to the surface intersection of the insulating layer 30 and the positive electrode current collector 10 is used as the area for evaluating the thickness parameters of the insulating layer 30. The above a=0.2, and the maximum thickness of the insulating layer 30 in this area is d. The maximum thickness d of the insulating layer is regulated by regulating the coating amount of the insulating layer slurry. By controlling the maximum thickness d of the insulating layer within the above range, the stress concentration between the first edge of the positive electrode material layer and the insulating layer of the positive electrode sheet during the cold pressing process can be alleviated, and the wrinkles in the area corresponding to the positive electrode ear in the positive electrode sheet can be reduced, thereby reducing the probability of the positive electrode ear breaking, improving the production process excellence rate of the positive electrode sheet, and improving the safety performance of the secondary battery.

[0046] In some embodiments of the present application, along the direction from the positive electrode material layer 20 to the insulating layer 30, the distance between the third edge 31 and the fourth edge 32 of the insulating layer 30 is the width b of the insulating layer 30, in mm, 1.5≤b≤3.5. In some embodiments of the present application, 2.0≤b≤3.0. For example, 1.5, 1.7, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5 or a range consisting of any two values ​​therebetween. Along the length direction of the positive electrode current collector, when the sum of the sizes of the positive electrode material layer and the insulating layer is constant, the size of b will affect the size of the positive electrode material layer, and thus affect the energy density of the secondary battery, and also affect the number of secondary batteries that pass the drop test. Therefore, by controlling the width b of the insulating layer within the above range, not only can the stress concentration between the first edge of the positive electrode material layer and the insulating layer of the positive electrode sheet during the cold pressing process be alleviated, the wrinkles in the area corresponding to the positive electrode ear in the positive electrode sheet can be reduced, thereby reducing the probability of the positive electrode ear breaking, improving the production process efficiency of the positive electrode sheet, and improving the safety performance of the secondary battery, but it is also beneficial to take into account the energy density of the secondary battery.

[0047] In some embodiments of the present application, Figure 3 and Figure 4 As shown, the positive electrode sheet 01 includes a positive electrode collector 10 and a positive electrode material layer 20 and an insulating layer 30 respectively arranged on the two surfaces of the positive electrode collector 10, the positive electrode material layer 20 includes a first positive electrode material layer 201 arranged on one surface of the positive electrode collector and a second positive electrode material layer 202 arranged on the other surface of the positive electrode collector, and the insulating layer 30 includes a first insulating layer 301 arranged on one surface of the positive electrode collector and a second insulating layer 302 arranged on the other surface of the positive electrode collector, the first positive electrode material layer 201 and the first insulating layer 301 are located on the same side of the positive electrode collector 10, and the second positive electrode material layer 202 and the second insulating layer 302 are located on the same side of the positive electrode collector 10. The maximum thickness of the first insulating layer 301 is d1, and the maximum thickness of the second insulating layer 302 is d2. The absolute value of the difference between d1 and d2 is Δd, in μm. In some embodiments of the present application, Δd is 0 to 15. In some embodiments of the present application, Δd is 0 to 10. In some embodiments of the present application, Δd is 0 to 5. For example, Δd can be 0, 2.5, 5, 7.5, 10, 12.5, 15, or a range consisting of any two values ​​therebetween. By regulating the value of Δd within the scope of the present application, the uniformity of the insulating layer coating on both sides of the positive electrode current collector is better, which is not only conducive to improving the insulation performance between the positive electrode tab and the negative electrode sheet, but also conducive to improving the stress concentration between the first edge of the positive electrode material layer and the insulating layer, reducing the generation of wrinkles, thereby reducing the risk of fracture of the positive electrode tab, and improving the safety performance and production process excellence of the secondary battery.

[0048] In some embodiments of the present application, Figure 3 and Figure 4 As shown, the positive electrode sheet 01 includes a positive electrode current collector 10 and a positive electrode material layer 20 and an insulating layer 30 respectively arranged on the two surfaces of the positive electrode current collector 10, the insulating layer 30 includes a first insulating layer 301 arranged on one surface of the positive electrode current collector and a second insulating layer 302 arranged on the other surface of the positive electrode current collector, the width of the first insulating layer 301 is b1, the width of the second insulating layer 302 is b2, and the absolute value of the difference between b1 and b2 is Δb mm. In some embodiments of the present application, 0≤Δb≤0.3. In some embodiments of the present application, 0≤Δb≤0.1. For example, Δb can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3 or a range consisting of any two values ​​therebetween. By regulating Δb within the above range, it is helpful to alleviate the stress concentration between the first edge of the positive electrode material layer and the insulating layer during the cold pressing process, reduce the occurrence of wrinkles and curling at the first edge of the positive electrode material layer, thereby reducing the risk of positive electrode tab breakage, improving the production process efficiency of the positive electrode sheet, and the obtained secondary battery has good safety performance. In addition, Δb within the above range is also conducive to the better transmission of active ions of the secondary battery, such as lithium ions, between the positive electrode sheet and the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0049] In some embodiments of the present application, the secondary battery meets at least one of the following characteristics: (1) the ceramic material includes at least one of boehmite or alumina; (2) based on the mass of the insulating layer, the mass percentage W2 of the ceramic material is 10% to 30%; (3) the thickness of the positive electrode collector is hμm, 8≤h≤10. The secondary battery meets at least one of the above characteristics, and the obtained secondary battery has a higher energy density, and can also alleviate the problem of wrinkles and fractures of the positive electrode sheet during the cold pressing process, reduce the risk of tab fracture, thereby improving the production process excellence rate of the secondary battery and the number of pass in the drop test, thereby improving the safety performance of the secondary battery.

[0050] In some embodiments of the present application, the ceramic material includes at least one of boehmite or alumina. The ceramic material not only has good insulation performance at room temperature, but also exhibits good insulation performance at high temperature. Therefore, even when thermal runaway occurs in the secondary battery, it is still beneficial for the positive electrode tab and the negative electrode sheet to maintain good insulation performance, thereby improving the safety performance of the secondary battery.

[0051] In some embodiments of the present application, based on the mass of the insulating layer, the mass percentage content W2 of the ceramic material is 10% to 30%. For example, W2 can be 10%, 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30% or a range consisting of any two values ​​therebetween. In the insulating layer, the mass percentage content of the ceramic material is within the above range, which can control the insulation resistance of the insulating layer within the required range, improve the reliability of the insulating layer, and thus improve the safety performance of the secondary battery.

[0052] In order to alleviate the problem of wrinkles and fractures in the positive electrode current collector corresponding to the positive electrode tab area caused by stress concentration between the first edge of the positive electrode material layer and the insulating layer during the manufacturing process of the secondary battery, a positive electrode current collector with a larger thickness is usually used, for example, more than 12μm, but the use of such a thicker positive electrode current collector will significantly reduce the energy density of the secondary battery. In some embodiments of the present application, the thickness of the positive electrode current collector is hμm, 8≤h≤10, for example, h can be 8, 9, 10 or a range consisting of any two values ​​therebetween. By selecting a positive electrode current collector within the above range and providing the above-mentioned flexible insulating layer, the problem of wrinkles caused by stress concentration between the edge of the positive electrode material layer and the insulating layer in the positive electrode sheet can be alleviated, the risk of positive electrode tab fracture can be reduced, and the production process efficiency and safety performance of the secondary battery can be improved, and it is also beneficial to take into account the energy density of the secondary battery.

[0053] In the present application, the technical features in the above embodiments can be combined arbitrarily as long as the purpose of the present application can be achieved.

[0054] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0055] In the present application, positive electrode current collectors of different thicknesses can be purchased and measured with a micrometer to select a positive electrode current collector of the desired thickness.

[0056] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as 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 iron manganese phosphate or lithium titanate.

[0057] The positive electrode material layer may also include a conductive agent and a positive electrode binder. The present application has no particular restrictions on the types of conductive agents and positive electrode binders, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0058] The present application has no particular limitation on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0059] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a positive electrode binder. The present application has no particular restrictions on the conductive agent and the positive electrode binder in the conductive layer, for example, it can be at least one of the above conductive agent and the above positive electrode binder.

[0060] In the present application, the secondary battery also includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0061] The present application has no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector may be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0062] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 Or at least one of Li-Al alloy.

[0063] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a negative electrode binder. The present application does not particularly limit the types of the conductive agent and the negative electrode binder, as long as the purpose of the present application can be achieved. For example, it may be at least one of the above conductive agent and the above positive electrode binder. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the negative electrode material layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0064] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode material layer is 30 μm to 120 μm. The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0065] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular restrictions on the composition of the conductive layer, which may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a negative electrode binder. The present application has no particular restrictions on the conductive agent and the negative electrode binder in the conductive layer, which may be, for example, at least one of the above conductive agent and the above negative electrode binder.

[0066] In the present application, the secondary battery also includes a diaphragm. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) films), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a nonwoven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0067] In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0068] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0069] In some embodiments of the present application, the inorganic layer includes inorganic particles and a separator binder. The present application has no particular restrictions on inorganic particles, for example, inorganic particles may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the separator binder, for example, the separator binder may be at least one of the above-mentioned positive electrode binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0070] In the present application, there is no particular limitation on the thickness of the separator, as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0071] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0072] The present application has no particular restrictions on lithium salts, as long as the purpose of the present application can be achieved. 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(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of lithium salts in the electrolyte, as long as the purpose of the present application can be achieved.

[0073] The present application has no particular limitation on the non-aqueous solvent as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0074] The carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). The cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is 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, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is 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. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restrictions on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0075] The secondary battery also includes a shell for accommodating a positive electrode plate, a separator, a negative electrode plate and an electrolyte, as well as other components known in the field of secondary batteries, and this application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as the purpose of this application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and this application does not limit the type of metal. A metal hard shell known in the art can be used, as long as the purpose of this application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0076] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular limitation in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly of a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0077] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet in any of the above embodiments. Therefore, the secondary battery of the present application has good safety performance and takes energy density into consideration.

[0078] The present application does not particularly limit the type of secondary battery, and any secondary battery known in the prior art can be used. In some embodiments of the present application, the secondary battery can include but is not limited to lithium ion batteries, sodium ion batteries, nickel hydrogen batteries, lithium polymer batteries, lithium sulfur batteries, sodium sulfur batteries, and lithium metal sulfide batteries.

[0079] The third aspect of the present application provides an electronic device, which includes a positive electrode sheet in any of the aforementioned embodiments or a secondary battery in any of the aforementioned embodiments. Thus, the electronic device provided by the present application has good performance. The present application does not particularly limit the type of electronic device, and it can be used for any electronic device known in the prior art. In some embodiments of the present application, the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0080] Example

[0081] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0082] Test methods and equipment:

[0083] Drop performance test:

[0084] The lithium-ion battery to be tested was placed in an environment of 25°C, charged at a constant current of 0.5C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a cut-off current of 0.05C, and left to stand for 5 minutes to be fully charged;

[0085] Place the lithium-ion battery in a fixed fixture, inspect its appearance and take photos before and after the test;

[0086] On a metal drop floor, drop from a height of 1.8m along the head and tail once, and drop once at the four corners, for a total of 7 rounds of testing, 6 times per round, the drop order is: head->tail->right corner of the head->right corner of the tail->left corner of the head->left corner of the tail (angle: 45±15 degrees).

[0087] The voltage and internal resistance of the lithium-ion battery were measured after the drop test and 24 hours after the test. The criteria for passing the drop test were: no fire, no explosion, no smoke, no leakage, and a voltage drop of <50mV. Ten lithium-ion batteries were tested for each embodiment or comparative example, and the number of batteries that passed was recorded, which was recorded as: the number of batteries that passed / the number of batteries tested, such as 9 / 10, which means that 9 lithium-ion batteries passed the test out of the 10 lithium-ion batteries tested.

[0088] Energy density test:

[0089] (1) Test of discharge capacity: At an ambient temperature of 25°C, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.5V, then charge at a constant voltage of 4.5V to a cut-off current of 0.05C, let stand for 5 minutes, then discharge at a constant current of 0.2C to a voltage of 3.0V, let stand for 5 minutes, and record the discharge capacity at this time as C, in Wh.

[0090] (2) Lithium-ion battery size test: Figure 5 , along the extension direction of the positive pole ear 70, i.e., the direction of the arrow in the figure, the lithium-ion battery 02 includes a fifth edge 401 and a sixth edge 601 opposite to each other, the edge of the positive pole ear 70 is set as the fifth edge 401, the area within 3 mm extending from the fifth edge 401 in the opposite direction of the extension direction of the positive pole ear 70 is the head area 40, the area within 3 mm extending from the sixth edge 601 in the extension direction of the positive pole ear 70 is the tail area 60, and the remaining area between the head area 40 and the tail area 60 is the middle area 50. The distance between the fifth edge 401 and the sixth edge 601 is the length L of the lithium-ion battery 02, the length of the fifth edge 401 is the width M of the lithium-ion battery 02, and the size of the lithium-ion battery 02 in the lamination direction is its thickness D. The length L and width M of the lithium-ion battery are respectively scanned and measured using a laser measuring instrument. Use a micrometer to measure the thickness Da of the head area 40, the thickness Db of the middle area 50, and the thickness Dc of the tail area 60 respectively; the thickness of each area is measured 3 times, and the average value of the 3 tests is taken as the thickness of the corresponding area. The thickness D of the lithium-ion battery is calculated by the following formula: D = 1 / 3 × (Da + Db + Dc). Among them, the units of D, L, and M are dm.

[0091] (3) Calculation of lithium-ion battery energy density X: X = C / (D × L × M);

[0092] The energy density X0 of comparative example 4 is recorded as the lowest grade standard, X0 = 712.2Wh / L, and each increase of 0.5% is a gradient of energy density. The energy density of the obtained lithium-ion battery is ranked from low to high as follows: high>upper middle>middle>lower middle>low. Among them, energy density greater than X0 and less than or equal to 1.005X0 is recorded as "lower middle", energy density greater than 1.005X0 and less than or equal to 1.010X0 is recorded as "middle", energy density greater than 1.010X0 and less than or equal to 1.015X0 is recorded as "upper middle", and energy density greater than 1.015X0 is recorded as "high".

[0093] Size Measurements:

[0094] The difference between the maximum thickness and the minimum thickness of the positive electrode material layer: Use a micrometer to measure, measure 10 points and take the difference between the maximum and minimum values ​​as the final result.

[0095] d, b, s: The cross section of the positive electrode piece along the thickness direction is ion polished and the cross section of the electrode piece is observed and measured under a VHX5000 microscope at a magnification of 500. The above dimensions are measured at 10 points and the average value is taken as the final result.

[0096] Δd, Δb, Δs: Measure d1, d2, b1, b2, s1, s2 of the two surfaces respectively, and calculate Δd, Δb, Δs. Δd=|d1-d2|, Δb=|b1-b2|, Δs=|s1-s2|.

[0097] h: Use a micrometer to measure and take the average value of 10 points as the final result.

[0098] Example 1-1

[0099] <Preparation of Insulating Layer>

[0100] The insulating layer binder polyacrylic acid and the ceramic material boehmite were mixed uniformly in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:2 to obtain an insulating layer slurry with a solid content of 10 wt %.

[0101] <Preparation of positive electrode sheet>

[0102] Conductive carbon black and positive electrode binder polyvinylidene fluoride are mixed, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a conductive glue with a solid content of 7wt%; the positive electrode active material is added to the conductive glue, and after vacuum stirring, a positive electrode material layer slurry with a solid content of 75wt% is obtained. Among them, the mass ratio of the positive electrode active material, the conductive agent and the positive electrode binder is 97:1:2, and the positive electrode active material is lithium cobalt oxide.

[0103] Select a positive electrode current collector aluminum foil with a thickness h of 9μm. On one surface of the positive electrode current collector, stick a 10μm thick adhesive tape to the area of ​​the positive electrode current collector corresponding to the empty foil area and the insulating layer. Then set the positive electrode material layer slurry in the area corresponding to the positive electrode material layer. Along the direction from the insulating layer to the positive electrode material layer, the size of the positive electrode material layer slurry covering the adhesive tape is 8mm. Bake at 105°C for 15min, peel off the adhesive tape, and obtain a positive electrode pole piece with a single-sided coating of a 75μm thick positive electrode material layer. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode pole piece with a double-sided coating of a "zero thinning" positive electrode material layer. Then apply the insulating layer slurry on the first edge of the positive electrode material layer on both surfaces of the aluminum foil and dry them. The coating amount of the insulating layer is 48mg / 1540.25mm 2, and then cold pressing treatment is carried out, and the pressure of cold pressing treatment is 90t, that is, the positive electrode sheet is obtained. The positive electrode sheet is cut into a fixed size, and the positive electrode ear is obtained by cutting from the corresponding position of the empty foil area, and then vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 58mm×65mm for standby use. The thickness of the single-sided positive electrode material layer is 46μm, and the difference ΔT between the maximum thickness and the minimum thickness of the positive electrode material layer is 1μm. Specific parameters are shown in Tables 1 to 3. The thickness of the above-mentioned single-sided positive electrode material layer refers to the area of ​​the positive electrode material layer except the edge area. The edge area is the area where the first edge extends 10mm from the insulating layer to the positive electrode material layer, and the area where the second edge extends 10mm from the positive electrode material layer to the insulating layer. The following embodiments and comparative examples are understood in the same way.

[0104] <Preparation of negative electrode sheet>

[0105] The negative electrode material artificial graphite, the negative electrode binder styrene butadiene rubber and the negative electrode binder sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:2, deionized water is added as a solvent, and the negative electrode slurry with a solid content of 45wt% is obtained after being stirred evenly. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of a 100μm thick negative electrode material layer. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of a negative electrode material layer. After cold pressing, cutting, and cutting from the corresponding position of the empty foil area to obtain a negative electrode ear, vacuum drying at 120°C for 12h, a negative electrode sheet with a specification of 60mm×67mm is obtained for standby use.

[0106] <Preparation of Electrolyte>

[0107] In an environment with a water content of less than 10 ppm, ethylene carbonate, propylene carbonate, and diethyl carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then an electrolyte salt LiPF6 is added to the organic solvent and mixed evenly to obtain an electrolyte solution. The molar concentration of the electrolyte salt is 1.15 mol / L based on the total mass of the electrolyte solution.

[0108] <Preparation of Separator>

[0109] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used.

[0110] <Preparation of lithium-ion batteries>

[0111] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then the four corners of the entire stacked structure are fixed with tape to obtain the electrode assembly of the stacked structure, and then the multiple positive electrode tabs of the multiple positive electrode sheets are integrated and welded to obtain the positive electrode tab of the lithium-ion battery, and the multiple negative electrode tabs of the multiple negative electrode sheets are integrated and welded to obtain the negative electrode tab of the lithium-ion battery; the electrode assembly is placed in an aluminum-plastic film outer packaging foil, and the moisture is removed at 80°C, and the prepared electrolyte is injected, and the soft-pack lithium-ion battery is obtained after vacuum packaging, standing, forming, shaping, capacity testing and other processes. Among them, the formation temperature is 80°C and the formation standing time is 2h.

[0112] Example 1-2 to Example 1-12

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. Among them, in Examples 1-8 to 1-11 and Comparative Examples 1 to 3, after the positive electrode current collector is pasted with adhesive tape, the starting coating position of the positive electrode material layer slurry is changed, so that the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is as shown in Table 1.

[0114] Examples 1-13

[0115] Except for preparing the positive electrode sheet according to the following steps, the rest is the same as Example 1:

[0116] <Preparation of positive electrode sheet>

[0117] The positive electrode material layer slurry is the same as that of Example 1-1.

[0118] Select a positive electrode current collector aluminum foil with a thickness of 9μm, set the positive electrode material layer slurry on one surface of the positive electrode current collector, and dry it at 105℃ for 15min to obtain a positive electrode sheet with a single-sided positive electrode material layer of 75μm thickness. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a "thinning area" with a double-sided positive electrode material layer, and then apply the insulating layer slurry on the first edge of the positive electrode material layer on both sides of the positive electrode current collector. The coating amount of the insulating layer is 48mg / 1540.25mm 2 . Then it is dried and cold pressed at a pressure of 90t to obtain a positive electrode sheet. The positive electrode sheet is cut into a fixed size, and the positive electrode ear is cut from the corresponding position of the empty foil area, and then vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 58mm×65mm for standby use. The specific parameters are shown in Table 1. The thickness of the single-sided positive electrode material layer is 46μm.

[0119] Example 2-1 to Example 2-18

[0120] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1. Among them, in Example 2-7 to Example 2-12, along the direction from the insulating layer to the positive electrode material layer, the sum of the sizes of the positive electrode material layer and the insulating layer is constant, and when b1 and b2 increase or decrease compared with Example 1-1, the size of the positive electrode material layer decreases or increases accordingly.

[0121] Example 3-1 to Example 3-11

[0122] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-1. Among them, in Example 3-9 to Example 3-11, along the direction from the insulating layer to the positive electrode material layer, the sum of the sizes of the positive electrode material layer and the insulating layer is constant, and when b2 decreases compared with Example 1-1, the size of the positive electrode material layer increases accordingly.

[0123] Comparative Examples 1 to 3, Comparative Example 5

[0124] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0125] Comparative Example 4

[0126] Except for preparing the positive electrode sheet according to the following steps, the rest is the same as Example 1-1:

[0127] <Preparation of positive electrode sheet>

[0128] The positive electrode material layer slurry is the same as that of Example 1-1.

[0129] Select a positive electrode current collector aluminum foil with a thickness of 9μm, set the positive electrode material layer slurry on one surface of the positive electrode current collector, and dry it at 105℃ for 15min to obtain a positive electrode sheet with a single-sided positive electrode material layer of 75μm thickness. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a "thinning area" with a double-sided positive electrode material layer, and then apply the insulating layer slurry on the first edge of the positive electrode material layer on both sides of the positive electrode current collector. The coating amount of the insulating layer is 48mg / 1540.25mm 2 . Then dry it and then cold press it with a pressure of 90t to obtain the positive electrode sheet. Cut the positive electrode sheet into a fixed size, cut the positive electrode ear from the corresponding position of the empty foil area, and then vacuum dry it at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 58mm×65mm for standby use. The specific parameters are shown in Table 1. The thickness of the single-sided positive electrode material layer is 46μm, and the thickness of the above-mentioned single-sided positive electrode material layer refers to the thickness of the positive electrode material layer from 10mm from the first edge to the second edge area. The preparation parameters and performance tests of each embodiment and comparative example are shown in Tables 1 to 3.

[0130] Table 1

[0131]

[0132]

[0133] In Table 1, it can be seen from Examples 1-1 to 1-12 and Comparative Examples 1 to 3 that the positive electrode sheets in the embodiments use the insulating layer of the present application, and the obtained lithium-ion batteries pass more in the drop test, that is, the safety performance is higher. However, the number of lithium-ion batteries obtained in Comparative Examples 1 to 3 that pass the drop test is relatively small. Among them, the insulating layer binder content in Comparative Example 1 is low and the flexibility is insufficient, which will not only affect the number of lithium-ion batteries that pass the drop test, but also affect the production process excellence rate of the positive electrode sheets, and then affect the production process excellence rate of the secondary battery. In Comparative Example 2, the insulating layer binder content is too high. During the laser die-cutting process of the positive electrode sheets, the insulating layer will shrink or even fall off, and the obtained lithium-ion batteries will pass fewer in the drop test. In Comparative Example 3, the binder is polyvinylidene fluoride, and the flexibility of the insulating layer is insufficient, which affects the excellence rate of the production process, and the obtained lithium-ion batteries pass fewer in the drop test. It can be seen from Examples 1-13 and Comparative Example 4 that when a positive electrode sheet with a thinned area is used, the lithium-ion batteries within the scope of the present application have more pass numbers in the drop test. However, Comparative Example 4 uses a conventional insulating layer, and the flexibility of the insulating layer is poor. There is stress concentration during the cold pressing process of the positive electrode sheet preparation, which affects the number of lithium-ion batteries that pass the drop test, that is, affects its safety performance. This shows that the insulating layer within the scope of the present application has a lower risk of falling off, has good heat resistance, and also has suitable flexibility. The stress between the positive electrode material layer and the insulating layer is relieved during the cold pressing process, and the resulting lithium-ion battery has higher safety performance and production process excellence.

[0134] The difference between the maximum thickness and the minimum thickness of the positive electrode material layer usually affects the energy density and safety performance of the secondary battery. From Example 1-1, Example 1-8 to Example 1-11, Example 1-13, and Comparative Example 4, it can be seen that when the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is within the scope of this application, the number of lithium-ion batteries obtained that pass the drop test is large, and a higher energy density is taken into account. This shows that when the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is within the scope of this application, the lithium-ion battery obtained has higher safety performance and higher energy density.

[0135] Table 2

[0136]

[0137]

[0138] The maximum thickness d of the insulating layer usually affects the safety performance and production process excellence of the lithium-ion battery, while the width b usually affects the energy density, production process excellence and safety performance of the lithium-ion battery. In Table 2, it can be seen from Examples 1-1, 2-1 to 2-6 that in the present application, d is less than or equal to the thickness of the positive electrode material layer, so the change of d has little effect on the volume energy density of the secondary battery. When d is too large, such as Example 2-6, the risk of breaking the belt is prone to occur during mass production, which affects the production process excellence of the positive electrode sheet. When the maximum thickness d1 and d2 of the insulating layer on both sides of the positive current collector are within the scope of this application, the number of lithium-ion batteries that pass the drop test is more. Along the length of the positive current collector, the sum of the dimensions of the positive electrode material layer and the insulating layer is constant, so the change of b will affect the change in the dimension of the positive electrode material layer, and then affect the energy density of the secondary battery. It can be seen from Examples 1-1, 2-7 to 2-12 that when the width b of the insulating layer is within the scope of this application, the number of lithium-ion batteries that pass the drop test is more and has a higher energy density. This shows that the maximum thickness d of the insulating layer and the width b of the insulating layer within the scope of this application can alleviate the wrinkling phenomenon of the positive electrode plate during the cold pressing process, thereby improving the safety performance and production process efficiency of the lithium-ion battery while taking into account the energy density.

[0139] The distance s between the third edge and the first edge will affect the energy density, safety performance and production process excellence of the lithium-ion battery. In Table 2, it can be seen from Example 1-1, Example 2-13 to Example 2-18 that when s is within the scope of the present application, the obtained lithium-ion battery has a higher energy density, and a larger number of batteries pass the drop test. When the value of s is too large, such as Example 2-18, although it is beneficial to improve the safety performance of the lithium-ion battery, it will affect the transmission of lithium ions between the positive electrode sheet and the negative electrode sheet, thereby affecting the electrochemical properties of the lithium-ion battery. It can be explained that the wrinkling phenomenon of the positive electrode sheet within the scope of the present application is alleviated during the cold pressing process, which is beneficial to improve the production process excellence of the positive electrode sheet, and then promote the obtained lithium-ion battery to have higher safety performance and production process excellence. At the same time, a suitable s is beneficial to improving the kinetic performance of the lithium-ion battery, and then helps to reduce the occurrence of lithium precipitation on the surface of the positive electrode sheet.

[0140] Table 3

[0141]

[0142] The difference Δd in the maximum thickness of the insulating layer on both sides of the positive current collector usually affects the production process quality rate and safety performance of the lithium-ion battery. In Table 3, it can be seen from Examples 3-5 to 3-8 that when the difference Δd in the maximum thickness of the insulating layer on both sides of the positive current collector is within the scope of this application, the number of lithium-ion batteries obtained that pass the drop test is greater. When Δd is too large, such as in Example 3-8, during the cold pressing process, there is a large stress concentration between the insulating layer on both sides of the positive current collector and the positive electrode material layer, which affects the production process quality rate of the positive electrode sheet. This shows that by regulating Δd within the scope of this application, it is beneficial to reduce the risk of fracture of the positive electrode tab, and the obtained lithium-ion battery has better production process quality rate and safety performance.

[0143] The difference Δb in the width of the insulating layer on both sides of the positive electrode current collector will affect the production process optimization rate, energy density and safety performance of the lithium-ion battery during processing. In Table 3, it can be seen from Example 1-1, Example 3-9 to Example 3-11 that when Δb is within the scope of this application, the number of lithium-ion batteries obtained that pass the drop test is relatively large. This shows that Δb is within the scope of this application, which is beneficial to alleviate the stress concentration between the first edge of the positive electrode material layer and the insulating layer during the cold pressing process of the positive electrode sheet, and thus is beneficial for the lithium-ion battery to have a better production process optimization rate, higher energy density and safety performance.

[0144] The distance Δs between the third edges of the insulating layer on both sides of the positive electrode current collector usually affects the energy density, production process excellence and safety performance of the lithium-ion battery. In Table 3, it can be seen from Example 1-1, Example 3-1 to Example 3-4 that when the positive electrode material layer and the insulating layer are arranged on the two surfaces of the coating area, and the distance Δs between the third edges of the insulating layer on both sides of the positive electrode current collector is within the scope of this application, the obtained lithium-ion battery has both a higher energy density and the number of passes in the drop test. It can be seen that within the scope of this application, the curling and wrinkling of the positive electrode pole piece is alleviated, and the obtained lithium-ion battery has a higher production process excellence and safety performance. In addition, Δs is within the scope of this application, and the obtained lithium-ion battery not only has a higher energy density, but also has better kinetic performance, and the risk of lithium deposition on the positive electrode pole piece is smaller. As in Example 3-4, Δs is too large, and the obtained lithium-ion battery has poor kinetic performance. The positive electrode pole piece removed after cycling has slight lithium deposition and black spots.

[0145] In addition, the embodiments in Tables 1 to 3 above showed no wrinkles during the cold pressing process, while the positive electrode sheets in Comparative Examples 1, 3 to 5 showed severe wrinkles during the cold pressing process. Figure 6a and Figure 6b As shown, the areas with different colors from right to left are the empty foil area, the area where the insulating layer is set, and the area where the positive electrode material layer is set. Figure 6bThe photo of the positive electrode sheet obtained after coating the insulating layer and cold pressing in Comparative Example 4. Due to the insufficient flexibility of the insulating layer, obvious wrinkles appeared at the edge of the positive electrode material layer after cold pressing. The photo of the positive electrode sheet obtained after coating the insulating layer and cold pressing in Example 1-1 is as follows Figure 6a Due to the use of the insulating layer with good flexibility of the present application, no obvious wrinkles appear at the junction of the empty foil area and the insulating layer after cold pressing, indicating that the stress concentration problem between the positive electrode material layer and the insulating layer during the cold pressing process has been improved. Therefore, the wrinkles and fractures of the positive electrode sheet that meets the requirements of the present application during the processing process have been improved, and the production process quality and safety performance of the obtained lithium-ion battery have been improved.

[0146] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

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

[0148] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A positive electrode sheet, comprising a positive electrode current collector, a positive electrode material layer, and an insulating layer, wherein the positive electrode current collector comprises a hollow foil area and a coating area; the positive electrode material layer and the insulating layer are arranged on at least one surface of the coating area, the insulating layer and the positive electrode material layer are connected and arranged along the length direction of the positive electrode current collector, and along the direction, the insulating layer is closer to the hollow foil area than the positive electrode material layer; The insulating layer includes a binder and a ceramic material, the binder includes at least one of polyurethane, polyacrylic acid or polyacrylonitrile, and based on the mass of the insulating layer, the mass percentage W1 of the binder is 70% to 90%.

2. The positive electrode sheet according to claim 1, wherein: The mass percentage W1 of the binder is 70% to 85%, and / or the difference between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 1 μm.

3. The positive electrode sheet according to claim 1, wherein: The maximum thickness of the insulating layer is d μm and the width is b mm, wherein 10≤d≤40 and 1.5≤b≤3.

5.

4. The positive electrode sheet according to claim 3, wherein: 10≤d≤25; and / or, 2.0≤b≤3.

0.

5. The positive electrode sheet according to claim 1, wherein: Along the direction from the positive electrode material layer to the insulating layer, the positive electrode material layer includes a first edge and a second edge relative to each other, the first edge is close to the insulating layer, the edge of the insulating layer close to the positive electrode material layer is a third edge, and the distance between the third edge and the first edge is smm, 0≤s≤0.

5.

6. The positive electrode sheet according to claim 5, wherein: 0≤s≤0.3。 7. The positive electrode sheet according to claim 5, wherein: The positive electrode material layer and the insulating layer are arranged on two surfaces of the coating area, and along the direction from the positive electrode material layer to the insulating layer, the distance between the third edges of the insulating layer on both sides of the positive electrode current collector is Δs mm, 0≤Δs≤0.

3.

8. The positive electrode sheet according to claim 7, wherein: 0≤Δs≤0.

1.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The positive electrode material layer and the insulating layer are disposed on both surfaces of the coating region.

10. The positive electrode sheet according to claim 9, wherein: The maximum thickness difference between the insulating layers on both sides of the positive electrode current collector is Δd μm, 0≤Δd≤15.

11. The positive electrode sheet according to claim 10, wherein: 0≤Δd≤10.

12. The positive electrode sheet according to claim 10, wherein: 0≤Δd≤5.

13. The positive electrode sheet according to claim 9, wherein: The difference in width between the insulating layers on both sides of the positive electrode current collector is Δb mm, 0≤Δb≤0.

3.

14. The positive electrode sheet according to claim 13, wherein: 0≤Δb≤0.

1.

15. The positive electrode sheet according to any one of claims 1 to 14, which satisfies at least one of the following characteristics: (1) The ceramic material includes at least one of boehmite or alumina; (2) Based on the mass of the insulating layer, the mass percentage W2 of the ceramic material is 10% to 30%; (3) The thickness of the positive electrode current collector is h μm, 8≤h≤10.

16. The positive electrode sheet according to claim 1, wherein: The difference between the maximum thickness and the minimum thickness of the positive electrode material layer is less than or equal to 0.8 μm. 17 . A secondary battery comprising the positive electrode sheet according to claim 1 . 18 . An electronic device comprising the positive electrode sheet according to claim 1 , or the secondary battery according to claim 17 .

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