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 material layer and the insulating layer are located on at least one surface of the positive current collector; the positive electrode current collector comprises a main body part and an epitaxial part, the positive electrode material layer comprises a first positive electrode material layer and a second positive electrode material layer, and the insulating layer comprises a first insulating layer and a second insulating layer; the positive electrode material layer and the first insulating layer are arranged on the main body part; along the thickness direction, the first insulating layer is positioned between the second positive electrode material layer and the positive electrode current collector; the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer; the epitaxial part comprises a connecting region and a tab region, and the second insulating layer is arranged in the connecting region; the compaction density of the first positive electrode material layer is PD1 g / cm < 3 >, the compaction density of the second positive electrode material layer is PD2 g / cm < 3 >, 2 < = PD1 < = 4.3, and 1 < = PD2 / PD1 < = 1.1. By adopting the positive pole piece, the safety performance of the secondary battery can be improved, and the energy density of the secondary battery is considered.

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] Secondary batteries, such as lithium-ion batteries, are widely used in fields such as smartphones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. With the widespread application of lithium-ion batteries in the above-mentioned fields, the market has increasingly higher requirements for the safety performance of lithium-ion batteries. However, for lithium-ion batteries, there is a high risk of short circuit between the positive electrode current collector and the negative electrode plate, especially in the tab area, which makes the safety performance of lithium-ion batteries poor. In order to improve safety performance, an insulating layer is usually coated on the edge of the positive electrode material layer after coating the positive electrode material layer. However, the insulating layer is usually redundant and an additional insulating layer is formed on the upper surface of the positive electrode material layer, which affects the movement path of the active material ions on the upper surface of the positive electrode material layer, thereby reducing the energy density of the secondary battery. In addition, after the insulating layer is cold-pressed during the preparation of the positive electrode plate, there is a risk of wrinkles and ruptures at the junction of the positive electrode current collector and the insulating layer, which affects the safety performance. Therefore, the market urgently needs a lithium-ion battery with good safety performance and energy density. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode sheet, a secondary battery, and an electronic device to improve the safety performance of the secondary battery while taking into account the energy density of the secondary battery. The specific technical solution is as follows:

[0004] The first aspect of the present application provides a positive electrode sheet, which includes a positive electrode current collector, a positive electrode material layer, and an insulating layer, wherein the positive electrode material layer and the insulating layer are located on at least one surface of the positive electrode current collector; the positive electrode current collector includes a main body and an extension portion, the direction from the main body to the extension portion is a first direction, the positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer sequentially connected along the first direction, and the insulating layer includes a first insulating layer and a second insulating layer sequentially connected along the first direction; the positive electrode material layer and the first insulating layer are arranged in the main body; along the thickness direction of the positive electrode sheet, the first insulating layer is located between the second positive electrode material layer and the positive electrode current collector; the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer; the extension portion includes a connection area and a tab area sequentially arranged along the first direction, and the second insulating layer is arranged in the connection area; the compaction density of the first positive electrode material layer is PD1 g / cm 3 The compaction density of the second cathode material layer is PD2 g / cm 3, 2≤PD1≤4.3, 1≤PD2 / PD1≤1.1. By adopting a positive electrode plate having the structure and composition of the present application, the root of the positive electrode tab can be insulated and protected, the risk of short circuit between the positive electrode current collector and the negative electrode plate can be reduced, and the problem of edge thinning of the positive electrode material layer can be improved. At the same time, PD1 and PD2 / PD1 are regulated within the scope of the present application so that the compaction density of the first positive electrode material layer and the second positive electrode material layer is within an appropriate range, which is beneficial to improving the wrinkling and rupture of the positive electrode current collector after cold pressing during the preparation of the positive electrode plate, and reducing the risk of local excessive thickness of the positive electrode plate, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0005] In some embodiments, the first positive electrode material layer includes a first positive electrode active material, and the second positive electrode material layer includes a second positive electrode active material; the first positive electrode active material and the second positive electrode active material each independently include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, or lithium manganese oxide. By employing the aforementioned first and second positive electrode active materials, the present application enables a secondary battery to have both good safety performance and high energy density.

[0006] In some embodiments, the positive electrode sheet satisfies at least one of the following characteristics: (1) the first positive electrode active material includes lithium cobalt oxide, 3.8≤PD1≤4.3; (2) the first positive electrode active material includes lithium nickel cobalt manganese oxide, 3.2≤PD1≤3.5; (3) the first positive electrode active material includes lithium iron phosphate, 2.3≤PD1≤2.7; (4) the first positive electrode active material includes lithium manganese oxide, 2.0≤PD1≤2.6. The present application adopts the above-mentioned first positive electrode active material and adjusts PD1 within the above-mentioned range, so that the first positive electrode material layer has a more appropriate thickness, further reduces the risk of local excessive thickness of the positive electrode sheet, improves the wrinkling and cracking of the positive electrode collector after cold pressing during the preparation of the positive electrode sheet, and improves the edge thinning of the positive electrode material layer, so that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0007] In some embodiments, the thickness of the first positive electrode material layer is H1 μm, the thickness of the second positive electrode material layer is H2 μm, 25 ≤ H2 < H1 ≤ 100, preferably 25 ≤ H2 < H1 ≤ 70. By regulating H1 and H2 within the above ranges, the first positive electrode material layer, the second positive electrode material layer, and the first insulating layer can all have appropriate thicknesses, which is beneficial for insulating and protecting the base of the positive electrode tab, reducing the risk of short circuit between the positive electrode current collector and the negative electrode electrode sheet, and at the same time improving the wrinkling and cracking of the positive electrode current collector after cold pressing during the preparation of the positive electrode electrode sheet, as well as the thinning of the edge of the positive electrode material layer, thereby providing the secondary battery with better safety performance and higher energy density.

[0008] In some embodiments, along the first direction, the first insulating layer has a size of h mm, and the second insulating layer has a size of imm, with 0 < h ≤ 3, 1 ≤ i ≤ 5, and preferably 0 < h ≤ 1, 1 ≤ i ≤ 3. Regulating h and i within the above ranges can further enhance insulation protection at the base of the positive electrode tab and reduce the risk of short circuits between the positive electrode current collector and the negative electrode tab, thereby further improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0009] In some embodiments, 0 < h / (h+i) ≤ 0.3. Adjusting h / (h+i) within the above range can further enhance insulation protection at the base of the positive electrode tab, reduce the risk of short circuit between the positive electrode current collector and the negative electrode tab, and improve the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0010] In some embodiments, the thickness of the first insulating layer is e μm, and the thickness of the second insulating layer is g μm, where 1 ≤ e < g ≤ 30. The present application regulates e and g within the above ranges to ensure that the first and second insulating layers have appropriate thicknesses, thereby further strengthening the insulation protection of the base of the positive electrode tab and further reducing the risk of short circuit between the positive electrode current collector and the negative electrode tab, thereby further improving the safety performance of the secondary battery while also taking into account the energy density of the secondary battery.

[0011] In some embodiments, a thickness mutation region exists at the junction of the first insulating layer and the second insulating layer, and the maximum thickness of the thickness mutation region is fμm, 1≤f≤20, 2≤e+f≤g. In the present application, the thickness mutation region exists at the junction of the first insulating layer and the second insulating layer. Controlling f, e+f, and g within the above ranges can reduce the risk of local excessive thickness of the positive electrode sheet, while also helping to strengthen the insulation protection of the base of the positive electrode tab and reduce the risk of short circuit between the positive electrode collector and the negative electrode sheet, thereby ensuring that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0012] In some embodiments, the first insulating layer is disposed at intervals or continuously along a second direction perpendicular to both the first direction and the thickness direction. In the present application, regulating the spacing of the first insulating layer can increase the positive electrode active material of the positive electrode sheet, which is beneficial to improving the energy density of the secondary battery, so that the secondary battery has both good safety performance and high energy density. Regulating the continuous arrangement of the first insulating layer can increase the impedance of the edge area of the positive electrode material layer, improve the problem of lithium deposition at the edge of the negative electrode sheet, further improve the safety performance of the secondary battery, and at the same time take into account the energy density of the secondary battery.

[0013] In some embodiments, along the second direction, the positive electrode sheet has a size of L0 mm, the first insulating layer has a size of L1 mm, and the second insulating layer has a size of L2 mm. The positive electrode sheet satisfies one of the following characteristics: (1) the first insulating layer is arranged at intervals, L2≤L1, 1≤L1≤50, 0.5≤L2≤20, and 0.025≤L1 / L0≤0.25; (2) the first insulating layer is arranged continuously, L2<L1, 0.9≤L1 / L0≤1, and 0.5≤L2≤20. By regulating the interval arrangement or continuous arrangement of the first insulating layer and regulating L1, L2, and L1 / L0 within the above ranges, the secondary battery can have both good safety performance and high energy density.

[0014] In some embodiments, the positive electrode sheet may or may not include a third positive electrode material layer. When the positive electrode sheet includes the third positive electrode material layer, the third positive electrode material layer is located on the surface of the second insulating layer away from the positive electrode current collector along the thickness direction of the positive electrode sheet. The thickness of the third positive electrode material layer is C1 μm, 0 < C1 ≤ 70, preferably 0 < C1 ≤ 50. The present application utilizes a positive electrode sheet including the third positive electrode material layer, and regulates C1 within the above range to reduce the risk of burrs on the positive electrode current collector contacting and puncturing the separator, thereby improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0015] In some embodiments, the positive electrode plate does not include the third positive electrode material layer. The present application uses a positive electrode plate that does not include the third positive electrode material layer, which can enable the secondary battery to maintain good safety performance and high energy density.

[0016] In some embodiments, along the second direction, the dimension of the third positive electrode material layer is C2 mm, 0.5 ≤ C2 ≤ 20, and C2 / L2 ≤ 1. Along the first direction, the dimension of the third positive electrode material layer is C3 mm, 1 ≤ C3 ≤ 5. Regulating C2, C2 / L2, and C3 within the above ranges helps reduce the risk of burrs on the positive electrode current collector contacting and puncturing the separator, thereby improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0017] In some embodiments, the second positive electrode material layer has a thickness of H2 μm, the first insulating layer has a thickness of e μm, and the second insulating layer has a thickness of g μm, where C1 + g < H2 + e. The positive electrode sheet employing the above structure is beneficial for improving the safety performance of the secondary battery while also taking into account the energy density of the secondary battery.

[0018] In some embodiments, the positive electrode material layer and the insulating layer are located on both surfaces of the positive electrode current collector. Along a first direction, the second insulating layer includes a first edge and a second edge facing each other, with the first edge distal to the tab region and the second edge proximal to the tab region. The distance between the orthographic projections of the first edges on the two surfaces onto the positive electrode current collector is s mm, where 0≤s≤1; and the distance between the orthographic projections of the second edges on the two surfaces onto the positive electrode current collector is t mm, where 0≤t≤2. By regulating s and t within the above ranges, the problem of locally excessive thickness of the positive electrode tab can be alleviated, insulation protection at the base of the positive electrode tab can be enhanced, and the risk of short circuit between the positive electrode current collector and the negative electrode tab can be reduced, thereby improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0019] In some embodiments, the first insulating layer includes a first binder and a first material, the second insulating layer includes a second binder and a second material, and the positive electrode sheet satisfies at least one of the following characteristics: (1) based on the mass of the first insulating layer, the mass percentage A1% of the first binder is 5% to 20%; (2) based on the mass of the first insulating layer, the mass percentage B1% of the first material is 80% to 95%; (3) based on the mass of the second insulating layer, the mass percentage A2% of the second binder is 5% to 20%; (4) based on the mass of the second insulating layer, the mass percentage B2% of the second material is 80% to 95%; (5) the first binder and the second binder each independently include at least one of polyvinylidene fluoride, polyurethane, polyacrylic acid, polyethylene glycol, polyvinyl alcohol, or polyacrylonitrile; (6) the first material and the second material each independently include at least one of boehmite, silica material, polymethyl methacrylate, or aluminum oxide. The present application improves the safety performance of the secondary battery by using the first binder, the second binder, the first material, and the second material within the above-mentioned content and / or type ranges.

[0020] In some embodiments, the thickness of the positive electrode current collector is H0 μm, 8 ≤ H0 ≤ 20. Using a positive electrode current collector with H0 within the above range can alleviate the problem of wrinkling of the positive electrode current collector during the cold pressing process and reduce the risk of positive electrode tab fracture, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0021] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet provided in the first aspect of the present application. The secondary battery provided in the second aspect of the present application has good safety performance and high energy density.

[0022] A third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application.

[0023] The present application provides a positive electrode sheet, a secondary battery and an electronic device, wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode material layer and an insulating layer, wherein the positive electrode material layer and the insulating layer are located on at least one surface of the positive electrode current collector; the positive electrode current collector comprises a main body and an extension portion, wherein the direction from the main body to the extension portion is a first direction, the positive electrode material layer comprises a first positive electrode material layer and a second positive electrode material layer sequentially connected along the first direction, and the insulating layer comprises a first insulating layer and a second insulating layer sequentially connected along the first direction; the positive electrode material layer and the first insulating layer are arranged in the main body; along the thickness direction of the positive electrode sheet, the first insulating layer is located between the second positive electrode material layer and the positive electrode current collector; the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer; the extension portion comprises a connection area and a tab area sequentially arranged along the first direction, and the second insulating layer is arranged in the connection area; the compaction density of the first positive electrode material layer is PD1 g / cm 3 The compaction density of the second cathode material layer is PD2 g / cm 3 , 2≤PD1≤4.3, 1≤PD2 / PD1≤1.1. By adopting a positive electrode sheet having the structure and composition of the present application, the base of the positive electrode tab can be insulated and protected, reducing the risk of short circuit between the positive electrode collector and the negative electrode sheet. At the same time, PD1 and PD2 / PD1 are regulated within the scope of the present application so that the compaction density of the first positive electrode material layer and the second positive electrode material layer is within an appropriate range, which is beneficial to improving the wrinkling and rupture of the positive electrode collector and the edge thinning of the positive electrode material layer after cold pressing during the preparation of the positive electrode sheet, reducing the risk of local excessive thickness of the positive electrode sheet, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0024] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0026] Figure 1 A cross-sectional view of a positive electrode sheet along the X direction in the prior art;

[0027] Figure 2 A cross-sectional view of a positive electrode sheet along the XZ direction in one embodiment of the present application;

[0028] Figure 3 This is a cross-sectional view of the insulating layer of the positive electrode sheet along the XZ direction in one embodiment of the present application;

[0029] Figure 4 This is a cross-sectional view of the insulating layer of the positive electrode sheet along the XZ direction in another embodiment of the present application;

[0030] Figure 5 This is a cross-sectional view of the insulating layer of the positive electrode sheet along the XZ direction in another embodiment of the present application;

[0031] Figure 6 This is a schematic structural diagram of a positive electrode sheet in one embodiment of the present application;

[0032] Figure 7 This is a schematic structural diagram of a positive electrode sheet in another embodiment of the present application;

[0033] Figure 8 This is a schematic structural diagram of a positive electrode sheet in another embodiment of the present application;

[0034] Figure 9 This is a schematic structural diagram of a positive electrode sheet in another embodiment of the present application;

[0035] Figure 10 This is a cross-sectional view of a positive electrode sheet along the XZ direction in another embodiment of the present application;

[0036] Figure 11 This is an electron microscope photograph of the extension portion of the positive electrode sheet in one embodiment of the present application;

[0037] Figure 12 This is an electron microscope photograph of the extension portion of the positive electrode sheet in another embodiment of the present application;

[0038] Figure 13 This is a cross-sectional view of a positive electrode sheet along the XZ direction in another embodiment of the present application;

[0039] Figure markings: positive electrode sheet 10, positive electrode material layer 110, first positive electrode material layer 111, second positive electrode material layer 112, third positive electrode material layer 113, insulating layer 120, first insulating layer 121, second insulating layer 122, thickness mutation region 123, first edge 1221, second edge 1222, positive electrode current collector 130, main body 100, extension portion 200, connection area 210, tab area 220, straight area 310, corner area 320, thinning area 400, X direction: first direction, Z direction: thickness direction, Y direction: second direction perpendicular to both the first direction and the thickness direction. DETAILED DESCRIPTION

[0040] 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 this application. Obviously, the embodiments described 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 this application are within the scope of protection of this application.

[0041] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0042] At present, in secondary batteries, the tab is usually the epitaxial area of the current collector. Each tab is the current output point of the single-layer electrode sheet where it is located, and plays the role of a conductor. Because the risk of short circuit between the positive current collector and the negative electrode sheet is high, in order to improve safety performance and reduce the probability of short circuit in the tab area, Figure 1 As shown, during the secondary battery manufacturing process, the positive electrode sheet is typically coated using a "zebra coating" process. A positive electrode material layer 110 is formed on the surface of the positive electrode current collector 130, and an insulating layer 120 is applied to the edges of the positive electrode material layer 110. In the traditional zebra coating process, due to surface tension in the positive electrode material layer 110 slurry during coating, the thickness of the resulting positive electrode material layer 110 is less than that in the center of the positive electrode material layer 110. This results in a thinned region 400 at the edge of the positive electrode material layer 110. Furthermore, due to process limitations, redundant coating of the insulating layer 120 often results in an additional insulating layer being formed on the upper surface of the positive electrode material layer 110. The insulating layer 120 on the positive electrode sheet occupies a certain amount of space, increasing the thickness of the secondary battery and, in turn, reducing its energy density. Furthermore, coating the insulating layer 120 at the edges of the positive electrode material layer 110 can easily cause wrinkling and breakage of the positive electrode current collector 130 during the cold pressing process. Traditional zebra coating inevitably leads to thinning in the tab area. After the secondary battery is manufactured, a gap exists between the positive electrode and the separator, which can easily cause adhesion loss, gradually deteriorating the secondary battery's cycling interface and affecting its safety performance. Furthermore, the presence of thinned area 400 reduces the amount of positive electrode active material in this area, which also reduces the secondary battery's energy density.

[0043] The present application provides a positive electrode plate. By designing the structure of the positive electrode material layer and the insulating layer and regulating the compaction density of the positive electrode material layer, the root of the positive electrode tab can be insulated, thereby reducing the risk of short circuit between the positive electrode collector and the negative electrode plate, and reducing the risk of local excessive thickness of the positive electrode plate. At the same time, the problems of wrinkling and rupture of the positive electrode collector after cold pressing and thinning of the edge of the positive electrode material layer during the preparation of the positive electrode plate are improved, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0044] The first aspect of the present application provides a positive electrode sheet, which includes a positive electrode current collector, a positive electrode material layer, and an insulating layer, wherein the positive electrode material layer and the insulating layer are located on at least one surface of the positive electrode current collector; the positive electrode current collector includes a main body and an extension portion, the direction from the main body to the extension portion is a first direction, the positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer sequentially connected along the first direction, and the insulating layer includes a first insulating layer and a second insulating layer sequentially connected along the first direction; the positive electrode material layer and the first insulating layer are arranged in the main body; along the thickness direction of the positive electrode sheet, the first insulating layer is located between the second positive electrode material layer and the positive electrode current collector; the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer; the extension portion includes a connection area and a tab area sequentially arranged along the first direction, and the second insulating layer is arranged in the connection area; the compaction density of the first positive electrode material layer is PD1 g / cm 3 The compaction density of the second cathode material layer is PD2 g / cm 3 , 2≤PD1≤4.3, 1≤PD2 / PD1≤1.1. For example, PD1 g / cm 3 Can be 2g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 、3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 、3.9g / cm 3 , 4g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3Or a range consisting of any two values therebetween. PD2 / PD1 can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, or a range consisting of any two values therebetween. The above-mentioned “the positive electrode material layer and the insulating layer are located on at least one surface of the positive electrode current collector” means that the positive electrode material layer and the insulating layer can be arranged on one surface of the positive electrode current collector along its own thickness direction, or can be arranged on both surfaces of the positive electrode current collector along its own thickness direction. In this application, “the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer” means that the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer, but there may be a thickness error of ±5%, that is, the upper surfaces of the first positive electrode material layer and the second positive electrode material layer are at the same height. The positive electrode sheet meets the above characteristics, which is conducive to increasing the volume proportion of the positive electrode active material in the secondary battery, so that the secondary battery has a higher energy density.

[0045] Specifically, if Figure 2 As shown, the positive electrode sheet 10 includes a positive electrode current collector 130, a positive electrode material layer 110, and an insulating layer 120. The positive electrode material layer 110 and the insulating layer 120 are located on one surface of the positive electrode current collector 130; the positive electrode current collector 130 includes a main body 100 and an extension portion 200. The direction from the main body 100 to the extension portion 200 is a first direction, i.e., an X direction. The positive electrode material layer 110 includes a first positive electrode material layer 111 and a second positive electrode material layer 112 sequentially connected along the X direction. The insulating layer 120 includes a first insulating layer 112 sequentially connected along the X direction. layer 121 and a second insulating layer 122; the positive electrode material layer 110 and the first insulating layer 121 are arranged in the main body 100; along the thickness direction of the positive electrode sheet 10, that is, the Z direction, the first insulating layer 121 is located between the second positive electrode material layer 112 and the positive electrode current collector 130; the thickness of the first positive electrode material layer 111 is equal to the total thickness of the second positive electrode material layer 112 and the first insulating layer 121; the extension portion 200 includes a connection area 210 and a tab area 220 arranged in sequence along the X direction, and the second insulating layer 122 is arranged in the connection area 210.

[0046] When PD1 is too large, for example, greater than 4.3 g / cm 3 During the cold pressing process, the positive electrode current collector may be damaged due to excessive pressure, which increases the risk of brittle fracture of the positive electrode current collector and reduces the safety performance of the secondary battery. 3, which can easily make the secondary battery too thick and affect the energy density of the secondary battery. When PD2 / PD1 is too large, for example, greater than 1.1, the risk of damage and breakage of the positive electrode collector will increase, and the safety performance of the secondary battery will be reduced. By adopting a positive electrode plate with the structure and composition of the present application, the root of the positive electrode tab can be insulated and protected, reducing the risk of short circuit between the positive electrode collector and the negative electrode plate. At the same time, PD1 and PD2 / PD1 are regulated within the scope of the present application so that the compaction density of the first positive electrode material layer and the second positive electrode material layer is within a suitable range, which is beneficial to improve the wrinkle and rupture of the positive electrode collector after cold pressing during the preparation of the positive electrode plate, and the problem of thinning the edge of the positive electrode material layer, and reduce the risk of local excessive thickness of the positive electrode plate, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0047] In some embodiments, 2≤PD2≤4.3. For example, PD2 g / cm 3 Can be 2g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 、3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 、3.9g / cm 3 , 4g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 or a range consisting of any two values therebetween. By regulating PD2 within the above range, the second positive electrode material layer can have an appropriate thickness, which helps reduce the risk of localized excessive thickness of the positive electrode sheet. This can also improve the wrinkling and cracking of the positive electrode current collector and the edge thinning of the positive electrode material layer after cold pressing during the preparation of the positive electrode sheet, thereby ensuring that the secondary battery has better safety performance and higher energy density.

[0048] In some embodiments, a method for preparing a positive electrode sheet includes the following steps: preparing an insulating layer slurry and a positive electrode material layer slurry; prescribing a main body region and an extension region on at least one surface of a positive electrode current collector, wherein the main body region is prescribing a first positive electrode material layer region and a first insulating layer region; and prescribing a second insulating layer region and a tab region on the extension region; applying adhesive tape to the first positive electrode material layer region and the tab region, coating the insulating layer slurry on the first and second insulating layer regions, and drying; peeling off the adhesive tape from the first positive electrode material layer region, coating the positive electrode material layer slurry on the main body region and the second insulating layer region, and drying; using adhesive tape to peel off the dried positive electrode material layer in the second insulating layer region, and peeling off the adhesive tape in the tab region; then cold pressing the main body, cutting corresponding positions in the tab region and the second insulating layer region to obtain a positive electrode tab, thereby obtaining a positive electrode sheet comprising a positive electrode collector, and a positive electrode material layer and an insulating layer on at least one surface of the positive electrode collector. In some embodiments, the pressure of the cold pressing is 30-120 tons (t). For example, the pressure of the cold pressing treatment can be 30t, 35t, 40t, 45t, 50t, 55t, 60t, 65t, 70t, 75t, 80t, 85t, 90t, 95t, 100t, 105t, 110t, 115t, 120t or a range consisting of any two values therebetween.

[0049] In the present application, the compaction density PD1 of the first positive electrode material layer can be controlled by regulating the amount of positive electrode material layer slurry applied in the first positive electrode material layer region and the pressure of the cold press treatment. Specifically, increasing the amount of positive electrode material layer slurry applied in the first positive electrode material layer region will increase PD1; increasing the pressure of the cold press treatment will also increase PD1. In the present application, the compaction density PD2 of the second positive electrode material layer can be controlled by regulating the amount of positive electrode material layer slurry applied in the second positive electrode material layer region and the pressure of the cold press treatment. Specifically, increasing the amount of positive electrode material layer slurry applied in the second positive electrode material layer region will increase PD2; increasing the pressure of the cold press treatment will also increase PD2. By adopting the positive electrode plate prepared by the preparation method of the present application, the root of the positive electrode tab can be protected by insulation treatment, thereby reducing the risk of short circuit between the positive electrode collector and the negative electrode plate, and reducing the risk of wrinkling, rupture and breakage of the positive electrode collector after cold pressing during the preparation of the positive electrode plate, thereby improving the safety performance of the secondary battery; at the same time, the edge of the positive electrode material layer can be free of "thinning area", the tab area can achieve zero thinning, reducing the risk of excessive thickness of the positive electrode plate, and thus helping to improve the energy density of the secondary battery.

[0050] In some embodiments, the first positive electrode material layer includes a first positive electrode active material, and the second positive electrode material layer includes a second positive electrode active material. The first positive electrode active material and the second positive electrode active material each independently include at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium iron phosphate, or lithium manganese oxide. By employing the aforementioned first and second positive electrode active materials, the present application enables a secondary battery to have both good safety performance and high energy density.

[0051] In some embodiments, the first cathode active material comprises lithium cobalt oxide, and 3.8≤PD1≤4.3. For example, PD1 g / cm 3 Can be 3.8g / cm 3 、3.85g / cm 3 、3.9g / cm 3 、3.95g / cm 3 , 4g / cm 3 , 4.05g / cm 3 , 4.1g / cm 3 , 4.15g / cm 3 , 4.2g / cm 3 , 4.25g / cm 3 , 4.3g / cm 3 Or a range consisting of any two values therebetween. The present application uses the above-mentioned first positive electrode active material and regulates PD1 within the above-mentioned range, which can make the first positive electrode material layer have a more appropriate thickness, further reducing the risk of local excessive thickness of the positive electrode sheet, and improving the wrinkling and cracking of the positive electrode current collector after cold pressing during the preparation of the positive electrode sheet, as well as the edge thinning of the positive electrode material layer, so that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0052] In some embodiments, the first cathode active material includes lithium nickel cobalt manganese oxide, 3.2≤PD1≤3.5. For example, PD1g / cm 3 Can be 3.2g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 、3.5g / cm 3Or a range consisting of any two values therebetween. The present application uses the above-mentioned first positive electrode active material and regulates PD1 within the above-mentioned range, which can make the first positive electrode material layer have a more appropriate thickness, further reducing the risk of local excessive thickness of the positive electrode sheet, and improving the wrinkling and cracking of the positive electrode current collector after cold pressing during the preparation of the positive electrode sheet, as well as the edge thinning of the positive electrode material layer, so that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0053] In some embodiments, the first cathode active material includes lithium iron phosphate, 2.3≤PD1≤2.7. For example, PD1g / cm 3 Can be 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 Or a range consisting of any two values therebetween. The present application uses the above-mentioned first positive electrode active material and regulates PD1 within the above-mentioned range, which can make the first positive electrode material layer have a more appropriate thickness, further reducing the risk of local excessive thickness of the positive electrode sheet, and improving the wrinkling and cracking of the positive electrode current collector after cold pressing during the preparation of the positive electrode sheet, as well as the edge thinning of the positive electrode material layer, so that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0054] In some embodiments, the first cathode active material comprises lithium manganate, 2.0≤PD1≤2.6. For example, PD1 g / cm 3 Can be 2g / cm 3 , 2.05g / cm 3 , 2.1g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 , 2.25g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3Or a range consisting of any two values therebetween. The present application uses the above-mentioned first positive electrode active material and regulates PD1 within the above-mentioned range, which can make the first positive electrode material layer have a more appropriate thickness, further reducing the risk of local excessive thickness of the positive electrode sheet, and improving the wrinkling and cracking of the positive electrode current collector after cold pressing during the preparation of the positive electrode sheet, as well as the edge thinning of the positive electrode material layer, thereby further improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0055] In some embodiments, the thickness of the first positive electrode material layer is H1 μm, the thickness of the second positive electrode material layer is H2 μm, 25≤H2

[0056] ​In some embodiments, along the first direction, the first insulating layer has a size of h mm, and the second insulating layer has a size of imm, where 0<h≤3, 1≤i≤5, and preferably 0<h≤1, 1≤i≤3. For example, h mm can be 0.01 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.3 mm, 1.5 mm, 1.6 mm, 1.8 mm, 2 mm, 2.2 mm, 2.3 mm, 2.5 mm, 2.6 mm, 2.8 mm, 3 mm, or a range consisting of any two values therebetween. 1 mm can be 1 mm, 1.2 mm, 1.3 mm, 1.5 mm, 1.6 mm, 1.8 mm, 2 mm, 2.2 mm, 2.3 mm, 2.5 mm, 2.6 mm, 2.8 mm, 3 mm, 3.2 mm, 3.3 mm, 3.5 mm, 3.6 mm, 3.8 mm, 4 mm, 4.2 mm, 4.3 mm, 4.5 mm, 4.6 mm, 4.8 mm, 5 mm, or a range consisting of any two values therebetween. For example, Figure 2 As shown, along the X direction, the first insulating layer 121 has a size of h mm, and the second insulating layer 122 has a size of imm. In some embodiments, 0 < h ≤ 3, 1 ≤ i ≤ 5, preferably 0 < h ≤ 1, 1 ≤ i ≤ 3. Regulating h and i within the above ranges can further enhance insulation protection at the base of the positive electrode tab and reduce the risk of short circuits between the positive current collector and the negative electrode tab, thereby further improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0057] In some embodiments, 0 < h / (h+i) ≤ 0.3. For example, h / (h+i) can be 0.01, 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.17, 0.18, 0.2, 0.22, 0.23, 0.25, 0.26, 0.27, 0.28, 0.3, or a range consisting of any two values therebetween. By regulating h / (h+i) within the above range, the insulation protection of the base of the positive electrode tab can be further enhanced, the risk of short circuit between the positive electrode current collector and the negative electrode sheet can be reduced, and the secondary battery can have better safety performance while taking into account the energy density of the secondary battery.

[0058] In some embodiments, the thickness of the first insulating layer is e μm, and the thickness of the second insulating layer is g μm, where 1 ≤ e < g ≤ 30. For example, e μm can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 29.5 μm, 29.9 μm, 29.99 μm, or a range consisting of any two values therebetween. gμm can be 1.01μm, 1.1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 13μm, 15μm, 16μm, 18μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 29.5μm, 30μm, or a range consisting of any two values therebetween. For example, Figure 2 As shown, along the Z direction, the thickness of the first insulating layer 121 is eμm, and the thickness of the second insulating layer 122 is gμm. In some embodiments, 1≤e<g≤30. The present application regulates e and g within the above ranges so that the first insulating layer and the second insulating layer have appropriate thicknesses, which is conducive to further strengthening the insulation protection of the base of the positive electrode tab and further reducing the risk of short circuit between the positive electrode current collector and the negative electrode sheet, thereby further improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0059] In the present application, the thickness of the first positive electrode material layer H1 μm is equal to the total thickness H2+e μm of the second positive electrode material layer and the first insulating layer, and there may be a thickness error of ±5%, that is, H1 / (H2+e)=(100±5)%.

[0060] In some embodiments, there is a thickness mutation region at the junction of the first insulating layer and the second insulating layer, and the maximum thickness of the thickness mutation region is fμm, 1≤f≤20, 2≤e+f≤g. For example, fμm can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 13μm, 15μm, 16μm, 18μm, 20μm or a range consisting of any two values therebetween. In the present application, after cold pressing treatment, since the first insulating layer and the second insulating layer are subjected to different forces during the cold pressing process, and the movement states of the equipment and the positive electrode sheet during the preparation process are not completely consistent, a thickness mutation region formed by the insulating layer material can be formed at the junction of the first insulating layer and the second insulating layer. For example, as Figure 3 、 Figure 4 or Figure 5 As shown, there is a thickness mutation region 123 at the junction of the first insulating layer 121 and the second insulating layer 122. Along the Z direction, the maximum thickness of the thickness mutation region 123 is fμm. In some embodiments, 1≤f≤20, 2≤e+f≤g. In the present application, there is a thickness mutation region at the junction of the first insulating layer and the second insulating layer. Controlling f, e+f, and g within the above range can reduce the risk of local excessive thickness of the positive electrode sheet, while helping to strengthen the insulation protection of the root of the positive electrode ear and reduce the risk of short circuit between the positive electrode collector and the negative electrode sheet, so that the secondary battery has better safety performance while taking into account the energy density of the secondary battery.

[0061] In some embodiments, the first insulating layer is disposed at intervals or continuously along a second direction perpendicular to both the first direction and the thickness direction. In the present application, regulating the spacing of the first insulating layer can increase the positive electrode active material of the positive electrode sheet, which is beneficial to improving the energy density of the secondary battery, so that the secondary battery has both good safety performance and high energy density. Regulating the continuous arrangement of the first insulating layer can increase the impedance of the edge area of the positive electrode material layer, improve the problem of lithium deposition at the edge of the negative electrode sheet, further improve the safety performance of the secondary battery, and at the same time take into account the energy density of the secondary battery.

[0062] In some embodiments, along the second direction, the positive electrode tab has a size of L0 mm, the first insulating layer has a size of L1 mm, the second insulating layer has a size of L2 mm, the first insulating layers are arranged at intervals (non-continuously), L2 ≤ L1, 1 ≤ L1 ≤ 50, 0.5 ≤ L2 ≤ 20, and 0.025 ≤ L1 / L0 ≤ 0.25. For example, L1 mm can be 1 mm, 2 mm, 3 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 13 mm, 15 mm, 16 mm, 18 mm, 20 mm, 22 mm, 23 mm, 25 mm, 26 mm, 28 mm, 30 mm, 32 mm, 33 mm, 35 mm, 37 mm, 38 mm, 40 mm, 42 mm, 43 mm, 45 mm, 47 mm, 48 mm, 50 mm, or a range consisting of any two values therebetween. L2mm can be 0.5mm, 1mm, 2mm, 3mm, 5mm, 6mm, 8mm, 10mm, 12mm, 13mm, 15mm, 16mm, 18mm, 20mm or a range consisting of any two values therebetween. L1 / L0 can be 0.025, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.12, 0.13, 0.15, 0.17, 0.18, 0.2, 0.22, 0.23, 0.25 or a range consisting of any two values therebetween. For example, the positive electrode sheet is a positive electrode sheet of a secondary battery with a laminated structure, such as Figure 6As shown, along the Y direction, the size of the positive electrode sheet 10 is L0 mm, the size of the first insulating layer 121 is L1 mm, the size of the second insulating layer 122 is L2 mm, and the first insulating layer 121 is discontinuous. In some embodiments, L2≤L1, 1≤L1≤50, 0.5≤L2≤20, 0.025≤L1 / L0≤0.25. For another example, the positive electrode sheet is a positive electrode sheet of a secondary battery with a wound structure, such as Figure 7 As shown, the positive electrode sheet 10 includes a straight region 310 and a corner region 320. Each straight region 310 is a structural unit of a single-layer positive electrode sheet 10. Along the Y direction, the straight region 310 has a size of L0 mm, the first insulating layer 121 has a size of L1 mm, and the second insulating layer 122 has a size of L2 mm. The first insulating layers 121 are arranged at intervals. In some embodiments, L2 ≤ L1, 1 ≤ L1 ≤ 50, 0.5 ≤ L2 ≤ 20, and 0.025 ≤ L1 / L0 ≤ 0.25. By regulating the spacing of the first insulating layers and adjusting L1, L2, and L1 / L0 within the above ranges, the amount of positive active material in the positive electrode sheet can be further increased, thereby improving the energy density of the secondary battery. At the same time, the base of the tab can be better insulated and protected, thereby improving the safety performance of the secondary battery, resulting in a secondary battery with both better safety performance and higher energy density.

[0063] In some embodiments, along the second direction, the size of the positive electrode sheet is L0 mm, the size of the first insulating layer is L1 mm, the size of the second insulating layer is L2 mm, the first insulating layer is continuously arranged, L2<L1, 0.9≤L1 / L0≤1, 0.5≤L2≤20. For example, L1 / L0 can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two values therebetween. L2 mm can be 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 13 mm, 15 mm, 16 mm, 18 mm, 20 mm or a range consisting of any two values therebetween. For example, the positive electrode sheet is a positive electrode sheet of a secondary battery with a laminated structure, such as Figure 8 As shown, along the Y direction, the positive electrode sheet 10 has a size of L0 mm, the first insulating layer 121 has a size of L1 mm, the second insulating layer 122 has a size of L2 mm, and the first insulating layer 121 is continuously provided. In some embodiments, L2 < L1, 0.9 ≤ L1 / L0 ≤ 1, 0.5 ≤ L2 ≤ 20. For example, the positive electrode sheet is a positive electrode sheet of a secondary battery with a wound structure, such as Figure 9As shown, the positive electrode sheet 10 includes a straight area 310 and a corner area 320. Each straight area 310 is a structural unit of a single-layer positive electrode sheet 10. Along the Y direction, the straight area 310 has a size of L0 mm, the first insulating layer 121 has a size of L1 mm, and the second insulating layer 122 has a size of L2 mm. The first insulating layer 121 is continuously provided. In some embodiments, L2 < L1, 0.9 ≤ L1 / L0 ≤ 1, 0.5 ≤ L2 ≤ 20. By regulating the continuous provision of the first insulating layer and regulating L1 / L0 and L2 within the above ranges, the impedance of the edge area of the positive electrode material layer can be further increased, the problem of lithium deposition at the edge of the negative electrode sheet can be improved, and the base of the tab can be better insulated and protected, thereby further improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0064] This application does not impose any particular restrictions on the size L0 of the positive electrode sheet, as long as the objectives of this application can be achieved. In some embodiments, 5 ≤ L0 ≤ 200. In this application, when the positive electrode sheet is a positive electrode sheet of a secondary battery with a laminated structure, the positive electrode sheet size refers to the size of each positive electrode sheet; when the positive electrode sheet is a positive electrode sheet of a secondary battery with a wound structure, the positive electrode sheet size refers to the size of each flat area of the positive electrode sheet.

[0065] In some embodiments, the positive electrode plate may or may not include a third positive electrode material layer. In some embodiments, the positive electrode plate includes the third positive electrode material layer, and along the thickness direction of the positive electrode plate, the third positive electrode material layer is located on the surface of the second insulating layer away from the positive electrode current collector; the thickness of the third positive electrode material layer is C1 μm, 0<C1≤70, preferably 0<C1≤50. For example, C1μm can be 0.01μm, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 26μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 45μm, 48μm, 50μm, 52μm, 55μm, 58μm, 60μm, 62μm, 65μm, 68μm, 70μm, or a range consisting of any two values therebetween. Figure 10 As shown, the positive electrode sheet 10 includes a third positive electrode material layer 113. Along the Z direction, the third positive electrode material layer 113 is located on the surface of the second insulating layer 122 away from the positive electrode current collector 130; the thickness of the third positive electrode material layer 113 is C1 μm. In some embodiments, 0<C1≤70, preferably 0<C1≤50. For example, an electron microscope photograph of the outer portion of the positive electrode sheet is shown as follows: Figure 11As shown, the positive electrode plate includes a third positive electrode material layer. The dark portion on the right side of the figure shows the third positive electrode material layer located on the surface of the second insulating layer, and the light portion on the left side is the positive electrode current collector. This application uses a positive electrode plate including a third positive electrode material layer and regulates C1 within the above range to enhance protection of the base of the positive electrode tab, reduce the risk of burrs of the positive electrode current collector contacting and puncturing the diaphragm, and improve the safety performance of the secondary battery while also taking into account the energy density of the secondary battery.

[0066] In some embodiments, the positive electrode sheet does not include a third positive electrode material layer. For example, an electron microscope photograph of the outer portion of the positive electrode sheet is as follows: Figure 12 As shown in the figure, the dark part on the left shows the positive electrode current collector, and the light part on the right shows the second insulating layer. The present application uses a positive electrode sheet that does not include a third positive electrode material layer, which can maintain good safety performance and high energy density of the secondary battery.

[0067] In some embodiments, along the second direction, the size of the third positive electrode material layer is C2 mm, 0.5 ≤ C2 ≤ 20, and C2 / L2 ≤ 1. Along the first direction, the size of the third positive electrode material layer is C3 mm, 1 ≤ C3 ≤ 5. For example, C2 mm can be 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 13 mm, 15 mm, 16 mm, 18 mm, 20 mm, or a range consisting of any two values therebetween. C2 / L2 can be 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two values therebetween. C3 mm can be 1mm, 1.2mm, 1.3mm, 1.5mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.3mm, 2.5mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.3mm, 3.5mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.3mm, 4.5mm, 4.6mm, 4.8mm, 5mm, or a range consisting of any two values therebetween. Regulating C2, C2 / L2, and C3 within the above ranges helps reduce the risk of burrs on the positive current collector contacting the separator and puncturing the separator, thereby improving the safety performance of the secondary battery while taking into account the energy density of the secondary battery.

[0068] In some embodiments, the second positive electrode material layer has a thickness of H2 μm, the first insulating layer has a thickness of e μm, and the second insulating layer has a thickness of g μm, where C1 + g < H2 + e. The positive electrode sheet employing the above structure is beneficial for improving the safety performance of the secondary battery while also taking into account the energy density of the secondary battery.

[0069] In some embodiments, the third positive electrode material layer includes a third positive electrode active material, which includes at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium iron phosphate, or lithium manganese oxide. By using such a third positive electrode active material, the secondary battery can have both good safety performance and high energy density.

[0070] In some embodiments, the positive electrode material layer and the insulating layer are located on both surfaces of the positive electrode current collector. Along a first direction, the second insulating layer includes a first edge and a second edge facing each other, the first edge being away from the tab region and the second edge being closer to the tab region. The distance between the orthographic projections of the first edges on the two surfaces on the positive electrode current collector is s mm, where 0≤s≤1; and the distance between the orthographic projections of the second edges on the two surfaces on the positive electrode current collector is t mm, where 0≤t≤2. For example, s mm can be 0 mm, 0.01 mm, 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or a range consisting of any two values therebetween. t mm can be 0 mm, 0.01 mm, 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.2 mm, 1.3 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 2 mm, or a range consisting of any two values therebetween. For example, Figure 13 As shown, the positive electrode material layer 110 and the insulating layer 120 are located on both surfaces of the positive electrode current collector 130. Along the X direction, the second insulating layer 122 includes a first edge 1221 and a second edge 1222, with the second edge 1222 being closer to the tab region 220 than the first edge 1221. The distance between the orthographic projections of the first edge 1221 on the two surfaces onto the positive electrode current collector 130 is s mm, and the distance between the orthographic projections of the second edge 1222 on the two surfaces onto the positive electrode current collector 130 is t mm. In some embodiments, 0 ≤ s ≤ 1; 0 ≤ t ≤ 2. By regulating s and t within the above ranges, the problem of locally excessive thickness of the positive electrode tab can be alleviated, insulation protection at the base of the positive electrode tab can be enhanced, and the risk of short circuit between the positive electrode current collector and the negative electrode tab can be reduced, thereby improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0071] In some embodiments, the compacted density of the first insulating layer is PD3 g / cm 3 The compaction density of the second insulating layer is PD4 g / cm 3, 1<PD3 / PD4≤2. For example, PD3 / PD4 can be 1.01, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, or a range consisting of any two values therebetween. Adjusting PD3 / PD4 within the above range helps strengthen the protective effect of the insulating layer on the base of the positive electrode tab while reducing the risk of damage and brittle fracture of the positive electrode current collector due to high pressure during the cold pressing process, thereby improving the safety performance of the secondary battery while also taking into account the energy density of the secondary battery.

[0072] In some embodiments, 1.5≤PD3≤2.7, 1<PD4≤1.8. For example, PD3 g / cm 3 Can be 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 2g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 Or a range consisting of any two values. PD4 g / cm 3 Can be 1.01g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or a range consisting of any two values therebetween. By regulating PD3 and PD4 within the above range, the first and second insulating layers have appropriate compaction densities, further enhancing the protective effect of the insulating layers on the base of the positive electrode tabs. This also reduces the risk of damage and brittle fracture of the positive electrode current collector due to high pressure during the cold pressing process, thereby further improving the safety performance of the secondary battery while also ensuring the energy density of the secondary battery.

[0073] In some embodiments, the first insulating layer includes a first binder, and based on the mass of the first insulating layer, the mass percentage A1% of the first binder is 5% to 20%. For example, A1% can be 5%, 6%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18%, 20%, or a range consisting of any two values therebetween. By regulating A1 within the above range, the first insulating layer has suitable adhesion, which can reduce the risk of brittle fracture of the positive electrode sheet after cold pressing, and at the same time reduce the risk of the first insulating layer falling off due to insufficient adhesion, thereby reducing the risk of short circuit between the positive current collector and the negative electrode sheet, thereby improving the safety performance of the secondary battery.

[0074] In some embodiments, the first insulating layer includes a first material, and the mass percentage B1% of the first material is 80% to 95% based on the mass of the first insulating layer. For example, B1% can be 80%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, or a range consisting of any two values therebetween. Adjusting B1 within the above range helps improve the safety performance of the secondary battery.

[0075] In some embodiments, the second insulating layer includes a second binder, and based on the mass of the second insulating layer, the mass percentage A2% of the second binder is 5% to 20%. For example, A2% can be 5%, 6%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18%, 20%, or a range consisting of any two values therebetween. By regulating A2 within the above range, the second insulating layer has suitable adhesion, which can reduce the risk of brittle fracture of the positive electrode sheet after cold pressing, and at the same time reduce the risk of the second insulating layer falling off due to insufficient adhesion, thereby reducing the risk of short circuit between the positive current collector and the negative electrode sheet, thereby improving the safety performance of the secondary battery.

[0076] In some embodiments, the second insulating layer includes a second material, and the mass percentage B2% of the second material is 80% to 95% based on the mass of the second insulating layer. For example, B2% can be 80%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, or a range consisting of any two values therebetween. Adjusting B2 within the above range helps improve the safety performance of the secondary battery.

[0077] In some embodiments, the first binder includes at least one of polyvinylidene fluoride, polyurethane, polyacrylic acid, polyethylene glycol (PEG), polyvinyl alcohol (PVA), or polyacrylonitrile. Using these first binders improves the adhesion of the first insulating layer, reduces the risk of short circuits between the positive current collector and the negative electrode, and thus improves the safety of the secondary battery.

[0078] In some embodiments, the second binder includes at least one of polyvinylidene fluoride, polyurethane, polyacrylic acid, polyethylene glycol, polyvinyl alcohol or polyacrylonitrile. By using the second binder of the above types, it is beneficial to improve the adhesion of the second insulating layer, reduce the risk of short circuit between the positive current collector and the negative electrode sheet, and thus improve the safety performance of the secondary battery.

[0079] In some embodiments, the first material includes at least one of boehmite, silicon oxide material (SiOx(0 < x ≤ 2)), polymethyl methacrylate (PMMA) or alumina. By using the first material of the above types, it is beneficial to improve the safety performance of the secondary battery.

[0080] In some embodiments, the second material includes at least one of boehmite, silicon oxide material (SiOx(0 < x ≤ 2)), polymethyl methacrylate or alumina. By using the second material of the above types, it is beneficial to improve the safety performance of the secondary battery.

[0081] In some embodiments, the thickness of the positive current collector is H0 μm, where 8 ≤ H0 ≤ 20. For example, H0 μm can be 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm or any range composed of any two values therebetween. By using the positive current collector with H0 within the above range, the problem of wrinkling of the positive current collector during cold pressing can be alleviated, and the risk of breakage of the positive electrode tab can be reduced. Thus, the safety performance of the secondary battery can be improved while taking into account the energy density of the secondary battery.

[0082] This application does not particularly limit the material of the positive current collector as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector), etc.

[0083] In the present application, the first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer each independently further include a conductive agent and a binder. The present application has no particular restrictions on the types of the conductive agent and the binder, 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 powder 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 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, 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 binder in any of the first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer. Those skilled in the art can select the mass ratio according to actual needs, as long as the purpose of the present application can be achieved. For example, in any of the first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80 to 98): (1 to 10): (1 to 10).

[0084] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet provided in the first aspect of the present application. The secondary battery provided in the second aspect of the present application has good safety performance and high energy density.

[0085] In the present application, the secondary battery also includes a negative electrode plate, which 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 is not particularly limited, as long as the purpose of this application can be achieved.

[0086] The present application has no particular restrictions 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 can 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.

[0087] 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 alloys.

[0088] In some embodiments, the negative electrode material layer may further include a conductive agent and a binder. This application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of this application. For example, they can be at least one of the above-mentioned conductive agents and binders. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as they can achieve the purpose of this application.

[0089] In some embodiments, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent and the binder may be at least one of the above-mentioned conductive agents and the above-mentioned binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickener 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.

[0090] 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.

[0091] 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.

[0092] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0093] In the present application, the secondary battery also includes a separator. The present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0094] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven 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 non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0095] Optionally, a surface treatment layer is provided 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.

[0096] In some embodiments, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to the inorganic particles. For example, the inorganic particles can 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 application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments, 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, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0097] In the present application, the thickness of the separator is not particularly limited 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.

[0098] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0099] The present application does not specifically limit the lithium salt, as long as the objectives 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 does not specifically limit the content of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.

[0100] 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.

[0101] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).Above-mentioned cyclic carbonate can include but not limited to at least one in 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, decanoic acid lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 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, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0102] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. 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 it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0103] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited 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 sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound 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 sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with 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, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0104] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0105] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD 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, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0106] Example

[0107] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0108] Test methods and equipment:

[0109] Energy density test:

[0110] Place the lithium-ion battery in a constant temperature box at 25°C ± 2°C and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery at a constant current of 0.5C to a voltage of 4.5V, then charge it at a constant voltage of 4.5V to a current of 0.05C, and discharge it at a constant current of 0.2C to a voltage of 3.0V. Record the discharge energy. Energy density (Wh / L) = discharge capacity (Wh) / lithium-ion battery volume (L). The dimensional parameters of the lithium-ion battery are measured using a micrometer. Each value is measured 3 times, and the average value is taken as the final result.

[0111] Drop performance test:

[0112] The lithium-ion battery was placed in a 25°C environment and charged at a constant current of 0.5C to a voltage of 4.5V. Then, it was charged at a constant voltage of 4.5V to a cutoff current of 0.05C and left to stand for 5 minutes to reach a fully charged state. The lithium-ion battery was placed in a fixed fixture, and the appearance was inspected and photographed before and after the test. The battery was dropped from a height of 1.8m onto the floor, and dropped once along the head and tail, and once at each of the four corners. A total of 7 rounds of testing were performed, with 6 drops per round. The drop order was: head, tail, right corner of the head, right corner of the tail, left corner of the head, and left corner of the tail (angle: 45±15 degrees).

[0113] The voltage and internal resistance of the lithium-ion battery were measured before and 24 hours after the drop test. The criteria for passing the drop test were: no fire, no explosion, no smoke, no leakage, and a voltage drop of <50mV. The voltage drop was measured by placing a universal voltmeter at the tab of the lithium-ion battery and reading the voltage values before and 24 hours after the drop test. Voltage drop = voltage value before the drop test - voltage value after the drop test. Twenty lithium-ion batteries were tested for each embodiment or comparative example, and the number of batteries that passed was recorded. The drop test pass rate (%) = number of batteries that passed / total number of batteries tested × 100%. For example, 90% means that 18 of 20 lithium-ion batteries passed the drop test.

[0114] Compaction density test:

[0115] The lithium-ion battery was discharged to 3V at a constant current of 0.2C and then disassembled. The positive electrode sheet was taken out and soaked in dimethyl carbonate (DMC) for 30 minutes. Then, it was dried in a fume hood for 4 hours and the dried positive electrode sheet was taken out. Five 5cm×5cm positive electrode sheets were cut from the area coated with the first positive electrode material layer. The thickness of the positive electrode sheet was measured with a micrometer and the average value was recorded as d1. The mass of the positive electrode sheet was weighed with a balance and the average value was recorded as m1. The first positive electrode material layer coated on both sides was scraped off with a scraper to obtain the positive electrode current collector. The thickness of the positive electrode current collector was measured with a micrometer and the average value was recorded as d0. The mass of the positive electrode current collector was weighed with a balance and the average value was recorded as m0. The compacted density of the first positive electrode material layer was calculated according to the following formula: PD1 g / cm 3=(m1-m0) / [5cm×5cm×(d1-d0)].

[0116] Cut 5 positive electrode sheets of 1 cm × 0.01 cm in size from the area coated with the second positive electrode material layer, measure the thickness of the positive electrode sheets with a micrometer, and take the average value, which is recorded as d1 ’ , weigh the mass of the positive electrode by a balance, take the average value, and record it as m1 ’ Use a scraper to scrape off the second positive electrode material layer coated on both sides, and measure the thickness of the positive electrode sheet after scraping off the second positive electrode material layer by a micrometer, and take the average value, recorded as d0 ’ , use a balance to weigh the mass of the positive electrode sheet after scraping off the second positive electrode material layer, take the average value, and record it as m0 ’ Calculate the compaction density of the second positive electrode material layer according to the following formula: PD2g / cm 3 =(m1 ’ -m0 ’ ) / [1cm×0.01cm×(d1 ’ -d0 ’ )].

[0117] Size Measurements:

[0118] H1, H2, e, g, f, and C1 measurements: Disassemble the lithium-ion battery, remove the positive electrode, and wipe away any residual electrolyte. Ion polish (CP) the thickness of the positive electrode to obtain a cross-section. Observe and measure H1, H2, e, g, f, and C1 under a VHX5000 microscope. Each dimension is measured at 10 points, and the average value is used as the final result.

[0119] h, i, C3, s, t, L0, L1, L2, C2 measurement: Use a micrometer to measure 10 points and take the average value as the final result.

[0120] Tests for A1, B1, A2, and B2:

[0121] After the lithium-ion battery is discharged to 3V at a constant current of 0.2C, the positive electrode sheet sample is disassembled and cleaned with dimethyl carbonate (DMC) and then dried at 60°C. The second positive electrode material layer, or the second positive electrode material layer and the third positive electrode material layer are peeled off to expose the first insulating layer and the second insulating layer. The powder of the first insulating layer and the second insulating layer is scraped off, and the mass of the first insulating layer powder sample is recorded as M 11 g, the mass of the second insulating layer powder sample is recorded as M 21 g. Heat the first insulating layer powder sample and the second insulating layer powder sample to 800℃ and keep them for 1 hour, and weigh the mass of the remaining powder. The mass of the remaining powder of the first insulating layer is recorded as M. 12 g, and the remaining powder mass of the second insulating layer is recorded as M22 The mass percentage of the first binder A1%, the mass percentage of the first material B1%, the mass percentage of the second binder A2%, and the mass percentage of the second material B2% are calculated by the following formula: A1(%) = (M 11 -M 12 ) / M 11 ×100%, B1(%)=M 12 / M 11 × 100%, A2(%)=(M 21 -M 22 ) / M 21 ×100%, B1(%)=M 22 / M 21 For each example or comparative example, 10 lithium-ion batteries were disassembled to obtain positive electrode sheets. A1%, B1%, A2%, and B2% of the positive electrode sheets of each lithium-ion battery were tested, and the average value was taken as the final result.

[0122] Example 1-1

[0123] <Preparation of positive electrode sheet>

[0124] Preparation of the insulating layer slurry: The ceramic material boehmite and the insulating layer binder polyvinylidene fluoride were mixed uniformly in a deionized water solvent at a mass ratio of 90:10 to obtain an insulating layer slurry with a solid content of 35 wt%.

[0125] Preparation of the positive electrode material slurry: Conductive carbon black (a conductive agent) and polyvinylidene fluoride (a binder) are mixed, and N-methylpyrrolidone (NMP) is added as a solvent to produce a conductive paste with a solid content of 7 wt%. Lithium cobalt oxide (a positive electrode active material) is added and stirred in a vacuum until a positive electrode material slurry with a solid content of 75 wt% is obtained. The mass ratio of the positive electrode active material, conductive agent, and binder is 97:1:2.

[0126] A positive electrode current collector aluminum foil with a thickness of 8μm (H0μm) was selected. A main body region and an extension region were preset on one surface of the positive electrode current collector. The main body region was preset with a first positive electrode material layer region and a first insulating layer region; the extension region was preset with a second insulating layer region and a tab region. Adhesive tape was applied to the first positive electrode material layer region and the tab region, and an insulating layer slurry was applied to the first and second insulating layer regions, followed by drying at 85°C. The adhesive tape in the first positive electrode material layer region was peeled off, and the positive electrode material layer slurry was applied to the main body region and the second insulating layer region, followed by drying at 85°C. The above steps were then repeated on the other surface of the aluminum foil. The dried positive electrode material layer in the second insulating layer region was peeled off with adhesive tape, and the adhesive tape in the tab region was peeled off. The main body was then 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 tab is obtained by cutting the corresponding positions of the tab area and the second insulating layer area, and then vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 74mm×84mm, including a first positive electrode material layer, a second positive electrode material layer and a first insulating layer located in the main body, and a second insulating layer, a third positive electrode material layer and a tab area located in the extension part; along the thickness direction of the positive electrode sheet, the first insulating layer is located between the second positive electrode material layer and the positive electrode current collector, and the third positive electrode material layer is located on the surface of the second insulating layer away from the positive electrode current collector; wherein, along the thickness direction of the positive electrode sheet, the thickness H1 of the first positive electrode material layer is 50μm, the thickness H2 of the second positive electrode material layer is 40μm, the thickness e of the first insulating layer is 10μm, the thickness g of the second insulating layer is 20μm, and the thickness at the junction of the first insulating layer and the second insulating layer is 10μm. The maximum thickness f of the mutation region is 5 μm, and the thickness C1 of the third positive electrode material layer is 10 μm. Along the first direction from the main body to the extension, the first insulating layer dimension h is 1.0 mm, the second insulating layer dimension i is 3.0 mm, and the third positive electrode material layer dimension C3 is 3.0 mm. The distance s between the orthographic projections of the first edges of the second insulating layer on both surfaces of the positive electrode current collector, away from the tab region, on the positive electrode current collector is 0 mm, and the distance t between the orthographic projections of the second edges of the second insulating layer on both surfaces of the positive electrode current collector, near the tab region, on the positive electrode current collector is 0 mm. Along the second direction, which is perpendicular to both the first direction and the thickness direction, the positive electrode tab dimension L0 is 84 mm. The first insulating layer is continuously provided, dimension L1 is 84 mm, the second insulating layer dimension L2 is 10 mm, and the third positive electrode material layer dimension C2 is 8 mm. Specific parameters are shown in Tables 1 to 3.

[0127] <Preparation of negative electrode sheet>

[0128] The negative electrode active material artificial graphite, the binder styrene-butadiene rubber and the thickener sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:2, deionized water was added as a solvent, and the mixture was stirred evenly to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was 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 negative electrode material layer. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After cold pressing, cutting and welding the tabs, vacuum drying was performed at 120°C for 12h to obtain a negative electrode sheet with a specification of 78mm×88mm for use. The thickness of the single-sided negative electrode material layer was 40μm, and the compaction density of the negative electrode material layer was 1.7g / cm 3 .

[0129] <Preparation of Electrolyte>

[0130] Under a dry argon atmosphere with a water content of less than 10 ppm, ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 to form a non-aqueous solvent. LiPF6, a lithium salt, was then added to the non-aqueous solvent and mixed thoroughly to form an electrolyte. The molar concentration of LiPF6 was 1.15 mol / L, with the remainder being the non-aqueous solvent.

[0131] <Preparation of Separator>

[0132] A porous polyethylene film with a thickness of 7 μm (supplied by Celgard) was used.

[0133] <Preparation of lithium-ion batteries>

[0134] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as an insulator. The four corners of the stack are then secured with tape to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film outer packaging foil and dehydrated at 80°C. The prepared electrolyte is then injected and vacuum packaged, allowed to stand, formed, shaped, and tested for capacity to obtain a soft-pack lithium-ion battery. The formation temperature is 80°C, and the formation stand time is 2 hours.

[0135] Example 1-2 to Example 1-18

[0136] Except for adjusting the corresponding preparation parameters according to Table 1 in <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1-1, wherein the compaction density of the first positive electrode material layer and the second positive electrode material layer is as shown in Table 1 by adjusting the coating amount of the positive electrode material layer, the coating amount of the insulating layer and the pressure of the cold pressing treatment.

[0137] Example 2-1 to Example 2-19

[0138] Except that in <Preparation of Positive Electrode Plate>, the parameter dimensions of the positive electrode plate are as shown in Table 2 by adjusting the preset area position, the coating amount of the positive electrode material layer, the coating amount of the insulating layer and the pressure of the cold pressing treatment, the rest are the same as Example 1-1.

[0139] Example 3-1 to Example 3-10

[0140] Except that in <Preparation of Positive Electrode Plate>, the parameter dimensions of the positive electrode plate are as shown in Table 3 by adjusting the preset area position, the coating amount of the positive electrode material layer, the coating amount of the insulating layer and the pressure of the cold pressing treatment, the rest are the same as Example 1-1.

[0141] Example 4-1 to Example 4-7

[0142] The same procedures as in Example 1-1 were used except that in the "Preparation of Positive Electrode Sheet," the predetermined area position, the coating amount of the positive electrode material layer, the coating amount of the insulating layer, and the cold pressing pressure were adjusted to achieve the parameters and dimensions of the positive electrode sheet as shown in Table 4. When the positive electrode sheet dimension L0 changes, the dimension of the negative electrode sheet also changes accordingly, and the negative electrode sheet is 4 mm larger in both length and width than the positive electrode sheet.

[0143] Example 5-1 to Example 5-4

[0144] Except for adjusting the corresponding preparation parameters according to Table 5 in <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0145] Comparative Example 1

[0146] Except that the positive electrode sheet was prepared according to the following <Preparation of Positive Electrode Sheet>, the rest was the same as Example 1-1.

[0147] <Preparation of positive electrode sheet>

[0148] Preparation of the insulating layer slurry: The ceramic material boehmite and the insulating layer binder polyvinylidene fluoride were mixed uniformly in a deionized water solvent at a mass ratio of 90:10 to obtain an insulating layer slurry with a solid content of 35 wt%.

[0149] Preparation of the positive electrode material slurry: Conductive carbon black (a conductive agent) and polyvinylidene fluoride (PVDF) (a positive electrode binder) are mixed and N-methylpyrrolidone (NMP) is added as a solvent to produce a conductive paste with a solid content of 7 wt%. Lithium cobalt oxide (a positive electrode active material) is added and stirred in a vacuum until a positive electrode material slurry with a solid content of 75 wt% is obtained. The mass ratio of the positive electrode active material, conductive agent, and binder is 97:1:2.

[0150] A positive electrode current collector aluminum foil with a thickness H0 μm of 8 μm is selected, and a main body region and an extension region are preset on one surface of the positive electrode current collector. The main body region is preset with a first positive electrode material layer region and a first insulating layer region.

[0151] Adhesive tape is applied to the first positive electrode material layer region and the epitaxial region, and insulating layer slurry is applied to the first insulating layer region, followed by drying at 85°C.

[0152] Peel off the adhesive tape from the first positive electrode material layer area, apply the positive electrode material layer slurry to the main body area, and dry at 85°C. Repeat the above steps on the other surface of the aluminum foil. Peel off the adhesive tape from the extension area. Then, cold press the main body at a pressure of 90t to obtain the positive electrode sheet. Cut the positive electrode sheet to a fixed size, and obtain the positive electrode tab by cutting the corresponding position of the extension part. Then vacuum dry at 85°C for 4 hours to obtain a positive electrode sheet with a size of 74mm×84mm for use. The specific parameters are shown in Table 1.

[0153] Comparative Examples 2 to 7

[0154] Except for adjusting the corresponding preparation parameters according to Table 1 in <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1-1, wherein the compaction density of the first positive electrode material layer and the second positive electrode material layer is as shown in Table 1 by adjusting the coating amount of the positive electrode material layer, the coating amount of the insulating layer and the pressure of the cold pressing treatment.

[0155] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 5.

[0156]

[0157]

[0158]

[0159] It can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 7 that the present application is provided with a first insulating layer and a second insulating layer, and the value of the compaction density PD1 of the first positive electrode material layer and the ratio PD2 / PD1 of the compaction density of the second positive electrode material layer to the compaction density of the first positive electrode material layer are regulated within the scope of the present application, which can enable the lithium-ion battery to have a higher energy density and a higher drop test pass rate, indicating that the lithium-ion battery of the present application has high energy density and good safety performance.

[0160] The values of h, i, h / (h+i), C3, s, t, H1, H2, e, g, f, and C1 generally affect the energy density and safety performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-1 to 2-19, lithium-ion batteries using values of h, i, h / (h+i), C3, s, t, H1, H2, e, g, f, and C1 within the ranges of this application have higher energy density and higher drop test pass rates, indicating that the lithium-ion batteries have higher energy density and better safety performance.

[0161] The values of L1, L2, L1 / L0, C2, and C2 / L2 generally affect the energy density and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-10, and 4-1 to 4-7, lithium-ion batteries using values of L1, L2, L1 / L0, C2, and C2 / L2 within the ranges of this application have higher energy density and higher drop test pass rates, indicating that lithium-ion batteries have higher energy density and better safety performance.

[0162] The values of A1, B1, A2, and B2 generally affect the energy density and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 5-1, and 5-4, lithium-ion batteries using values of A1, B1, A2, and B2 within the ranges of this application have higher energy density and higher drop test pass rates, indicating that lithium-ion batteries have higher energy density and better safety performance.

[0163] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0164] The terms "one of," "one of," "a kind of," or other similar terms used to connect elements refer to any one of the listed elements. For example, "one of A or B" refers to only A or only B; as another example, "one of A, B, and C" refers to only A, only B, or only C. The terms "at least one of," "at least one of," "at least one of," or other similar terms used to connect elements refer to any combination of the listed elements. For example, "at least one of A or B" refers to only A, only B, or A and B. As another example, "at least one of A, B, or C" refers to only A, only B, only C, only A and B, only A and C, only B and C, or A, B, and C.

[0165] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

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 material layer and the insulating layer are located on at least one surface of the positive electrode current collector; The positive electrode current collector includes a main body and an extension portion, wherein a direction from the main body to the extension portion is a first direction; the positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer sequentially connected along the first direction; and the insulating layer includes a first insulating layer and a second insulating layer sequentially connected along the first direction; the positive electrode material layer and the first insulating layer are disposed on the main body; along the thickness direction of the positive electrode sheet, the first insulating layer is located between the second positive electrode material layer and the positive electrode current collector; the thickness of the first positive electrode material layer is equal to the total thickness of the second positive electrode material layer and the first insulating layer; The extension portion includes a connection area and a tab area sequentially arranged along a first direction, and the second insulating layer is arranged in the connection area; The compaction density of the first positive electrode material layer is PD1g / cm 3 The compaction density of the second positive electrode material layer is PD2g / cm 3 , 2≤PD1≤4.3, 1≤PD2 / PD1≤1.

1.

2. The positive electrode sheet according to claim 1, wherein: The first positive electrode material layer includes a first positive electrode active material, and the second positive electrode material layer includes a second positive electrode active material; the first positive electrode active material and the second positive electrode active material each independently include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate or lithium manganese oxide.

3. The positive electrode sheet according to claim 2, wherein: The positive electrode sheet satisfies at least one of the following characteristics: (1) The first positive electrode active material includes lithium cobalt oxide, 3.8≤PD1≤4.3; (2) The first positive electrode active material includes lithium nickel cobalt manganese oxide, 3.2≤PD1≤3.5; (3) The first positive electrode active material includes lithium iron phosphate, 2.3≤PD1≤2.7; (4) The first positive electrode active material includes lithium manganate, 2.0≤PD1≤2.

6.

4. The positive electrode sheet according to claim 1, wherein: The thickness of the first positive electrode material layer is H1 μm, the thickness of the second positive electrode material layer is H2 μm, and 25≤H2<H1≤100.

5. The positive electrode sheet according to claim 1, wherein: 25≤H2<H1≤70.

6. The positive electrode sheet according to claim 1, wherein: Along the first direction, a size of the first insulating layer is h mm, a size of the second insulating layer is i mm, 0<h≤3, 1≤i≤5.

7. The positive electrode sheet according to claim 6, wherein: 0<h≤1, 1≤i≤3.

8. The positive electrode sheet according to claim 6, wherein: 0<h / (h+i)≤0.

3.

9. The positive electrode sheet according to claim 1, wherein: The thickness of the first insulating layer is e μm, the thickness of the second insulating layer is g μm, and 1≤e<g≤30.

10. The positive electrode sheet according to claim 9, wherein: A thickness mutation region exists at the junction of the first insulating layer and the second insulating layer, and the maximum thickness of the thickness mutation region is f μm, 1≤f≤20, 2≤e+f≤g.

11. The positive electrode sheet according to claim 1, wherein: The first insulating layers are arranged at intervals or continuously along a second direction perpendicular to both the first direction and the thickness direction.

12. The positive electrode sheet according to claim 11, wherein: Along the second direction, the size of the positive electrode sheet is L0 mm, the size of the first insulating layer is L1 mm, the size of the second insulating layer is L2 mm, and the positive electrode sheet meets one of the following characteristics: (1) The first insulating layer is set at an interval of L2≤L1, 1≤L1≤50, 0.5≤L2≤20, 0.025≤L1 / L0≤0.25; (2) The first insulating layer is continuously provided, L2<L1, 0.9≤L1 / L0≤1, 0.5≤L2≤20.

13. The positive electrode sheet according to claim 12, wherein: The positive electrode plate includes a third positive electrode material layer. Along the thickness direction of the positive electrode plate, the third positive electrode material layer is located on the surface of the second insulating layer away from the positive electrode current collector; the thickness of the third positive electrode material layer is C1μm, 0<C1≤70.

14. The positive electrode sheet according to claim 13, wherein: 0＜C1≤50。 15. The positive electrode sheet according to claim 13, wherein: Along the second direction, the size of the third positive electrode material layer is C2 mm, 0.5≤C2≤20, C2 / L2≤1; Along the first direction, the size of the third positive electrode material layer is C3 mm, 1≤C3≤5.

16. The positive electrode sheet according to claim 13, wherein: The thickness of the second positive electrode material layer is H2 μm, the thickness of the first insulating layer is e μm, and the thickness of the second insulating layer is g μm, where C1+g<H2+e.

17. The positive electrode sheet according to claim 1, wherein: The positive electrode material layer and the insulating layer are located on two surfaces of the positive electrode current collector. Along the first direction, the second insulating layer includes a first edge and a second edge opposite to each other, the first edge is away from the tab region, and the second edge is close to the tab region; The distance between the orthographic projections of the first edges on the two surfaces on the positive electrode current collector is s mm, 0≤s≤1; The distance between the orthographic projections of the second edges on the two surfaces onto the positive electrode current collector is t mm, and 0≤t≤2.

18. The positive electrode sheet according to any one of claims 1 to 17, wherein: The first insulating layer includes a first binder and a first material, the second insulating layer includes a second binder and a second material, and the positive electrode sheet meets at least one of the following characteristics: (1) Based on the mass of the first insulating layer, the mass percentage A1% of the first binder is 5% to 20%; (2) Based on the mass of the first insulating layer, the mass percentage B1% of the first material is 80% to 95%; (3) Based on the mass of the second insulating layer, the mass percentage A2% of the second binder is 5% to 20%; (4) Based on the mass of the second insulating layer, the mass percentage B2% of the second material is 80% to 95%; (5) The first binder and the second binder each independently include at least one of polyvinylidene fluoride, polyurethane, polyacrylic acid, polyethylene glycol, polyvinyl alcohol or polyacrylonitrile; (6) The first material and the second material each independently include at least one of boehmite, a silica material, polymethyl methacrylate, or alumina. 19 . A secondary battery comprising the positive electrode sheet according to claim 1 . 20 . An electronic device comprising the secondary battery according to claim 19 .

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