Positive electrode sheet and battery comprising same

Abstract

A positive electrode sheet and a secondary battery comprising same. The positive electrode sheet comprises a current collector (1), at least one surface of the current collector (1) is provided with a positive electrode active material layer (2) and an insulating layer (4), and the insulating layer (4) is located at at least one end of the positive electrode active material layer (2). The positive electrode sheet further comprises a safety primer layer (3), the safety primer layer (3) is arranged between the current collector (1) and the positive electrode active material layer (2), and at least one side of the safety primer layer (3) is connected to the insulating layer (4). The positive electrode sheet satisfies the following relational expression: formula (I), wherein ρ1 is the sheet resistivity of the insulating layer (4), ρ1≥60 kΩ•cm, ρ2 is the sheet resistivity of the positive electrode active material layer (2), ρ2≤500 Ω•cm, and d1 and d2 are respectively the thickness of the insulating layer (4) and the thickness of the current collector (1), with the unit of μm.

Description

Positive electrode sheet and battery thereof

[0001] This application is based on the Chinese invention with application number: 202410255328.1 filed on March 6, 2024, and entitled “A positive electrode sheet and its battery”, and claims its priority. Technical Field

[0002] The present invention belongs to the technical field of secondary batteries, and in particular relates to a positive electrode sheet and a secondary battery thereof. Background Art

[0003] Lithium-ion batteries are gradually being used more and more widely in production and life, such as in electronic products such as mobile phones and laptops, as well as in transportation fields such as new energy vehicles. These applications have put forward higher requirements on the safety performance of lithium-ion batteries.

[0004] Currently, the main safety performance test for lithium-ion batteries is the needle penetration test. When a lithium-ion battery is subjected to a needle penetration test, a metal needle punctures the lithium-ion battery, causing a short circuit, generating a large amount of heat, accompanied by reactions such as gas production and material decomposition, leading to thermal runaway such as smoke, fire, and explosion. There are several main forms of short circuits within the battery: first, a short circuit between the positive and negative current collectors; second, a short circuit between the positive current collector and the negative active material; third, a short circuit between the positive active material and the negative current collector; and fourth, a short circuit between the positive and negative electrode sheets. Among these, the short circuit caused by the contact between the positive current collector and the negative active material is the most dangerous.

[0005] Current lithium-ion batteries typically use aluminum foil as the positive electrode current collector, and a coating containing the positive electrode active material is applied to the aluminum foil to form the positive electrode sheet. When lithium-ion batteries with this structure are subjected to a needle penetration test, especially if the positive electrode current collector aluminum foil comes into contact with the negative electrode active material, a reaction will immediately react and generate a large amount of heat, making the battery prone to thermal runaway and reducing battery safety performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that when a battery using aluminum foil as a positive electrode current collector is subjected to a needle penetration test, the positive electrode current collector aluminum foil contacts the negative electrode active material, and the battery is prone to thermal runaway. The present application provides a positive electrode sheet and a secondary battery thereof.

[0007] To solve the above technical problems, the present application provides a positive electrode sheet, comprising a current collector, wherein at least one surface of the current collector is provided with a positive electrode active material layer and an insulating layer, and the insulating layer is located at at least one end of the positive electrode active material layer; the positive electrode sheet further comprises a safety primer layer, wherein the safety primer layer is provided between the current collector and the positive electrode active material layer, and at least one side of the safety primer layer is connected to the insulating layer;

[0008] The positive electrode sheet satisfies the following relationship:

[0009] And ρ1 ≥ 60 kΩ·cm, ρ2 ≤ 500 Ω·cm;

[0010] Where ρ1 is the sheet resistivity of the insulating layer, in kΩ·cm;

[0011] ρ2 is the resistivity of the positive electrode active material layer, in Ω·cm;

[0012] d1 is the thickness of the insulating layer, in μm;

[0013] d2 is the thickness of the current collector, in μm.

[0014] Preferably, the positive electrode sheet satisfies the following relationship:

[0015] Preferably, the film resistivity ρ1 of the insulating layer is in the range of 600 to 1000 kΩ·cm.

[0016] Preferably, the resistivity ρ2 of the positive electrode active material layer is in the range of 250 to 500 Ω·cm.

[0017] Preferably, the thickness d1 of the insulating layer ranges from 8 to 16 μm.

[0018] Preferably, the positive electrode sheet further includes a safety primer layer, which is disposed between the current collector and the positive electrode active material layer, and at least one side of the safety primer layer is connected to the insulating layer.

[0019] Preferably, the distance between the end of the positive electrode active material layer close to the insulating layer and the insulating layer is greater than 0.

[0020] Preferably, the insulating layer includes additives and adhesives,

[0021] The additives include one or more of magnesium oxide, boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate, and calcium sulfate.

[0022] Preferably, in the insulating layer, the mass ratio of the additive to the binder is (10-98):(2-90).

[0023] Preferably, the safety primer layer comprises a positive electrode active material, a conductive agent, a binder, a thickener and an additive; the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder; in the safety primer layer, the mass ratio of the positive electrode active material, the conductive agent, the binder, the thickener and the additive is (20-98): (0.1-10): (2-20): (0-20): (5-80);

[0024] In the positive electrode active material layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95-98.5): (0.1-5): (1.5-5).

[0025] In a second aspect, the present application provides a secondary battery comprising a negative electrode sheet, a separator and the positive electrode sheet described above.

[0026] According to the positive electrode sheet provided by the present application, when the film resistivity and thickness of the insulating layer, the film resistivity of the positive electrode active material layer, and the thickness of the current collector satisfy the relationship The high insulating layer sheet resistivity ρ1 reduces the current generated during needle puncture, thereby reducing the heat generated. The insulating layer also prevents short circuits between the positive electrode current collector and the negative electrode active material, effectively avoiding short circuits between the aluminum foil and the negative electrode active material during needle puncture, reducing the risk of battery runaway and improving the battery needle puncture pass rate. The safety primer layer has a greater resistivity than the active material layer, increasing the internal resistance of the battery to a certain extent and also preventing contact between the positive electrode current collector and the negative electrode active material layer. Connecting the safety primer layer to the insulating layer can further prevent contact between the positive electrode current collector and the negative electrode active material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic diagram of a positive electrode structure provided in one embodiment of the present application.

[0028] Among them, 1. current collector; 2. positive electrode active material layer; 3. safety primer layer; 4. insulating layer. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] As shown in FIG1 , the present application provides a positive electrode sheet, comprising a current collector 1, wherein at least one surface of the current collector 1 is provided with a positive electrode active material layer 2 and an insulating layer 4, and the insulating layer 4 is located on at least one side of the positive electrode active material layer 2; the positive electrode sheet further comprises a safety primer layer 3, wherein the safety primer layer 3 is provided between the current collector 1 and the positive electrode active material layer 2, and at least one side of the safety primer layer 3 is connected to the insulating layer 4;

[0031] The positive electrode sheet satisfies the following relationship:

[0032] And ρ1>60kΩ·cm, ρ2≤500Ω·cm;

[0033] Wherein, ρ1 is the sheet resistivity of the insulating layer 4, in kΩ·cm;

[0034] ρ2 is the resistivity of the positive electrode active material layer 2, in Ω·cm;

[0035] d1 is the thickness of the insulating layer 4, in μm;

[0036] d2 is the thickness of the current collector 1, in μm.

[0037] Specifically, at least one surface of the current collector 1 is provided with a positive electrode active material layer 2, that is, a positive electrode active material layer 2 is provided on one surface or both surfaces of the current collector 1; at least one surface of the current collector 1 is provided with an insulating layer 4, that is, an insulating layer 4 is provided on one surface or both surfaces of the current collector 1. As shown in Figure 1, an insulating layer 4 and a positive electrode active material layer 2 are provided on both the upper and lower sides of the current collector 1. The insulating layer 4 is located at at least one end of the positive electrode active material layer 2; that is, the insulating layer 4 is provided at one end of the positive electrode active material layer 2, or the insulating layer 4 is provided at both ends of the positive electrode active material layer 2, or the insulating layer 4 is provided on all four sides of the positive electrode active material layer 2.

[0038] The inventors have found through extensive research that the film resistivity and thickness of the insulating layer 4 have a certain impact on the safety performance of the battery. When the film resistivity and thickness of the insulating layer 4, the film resistivity of the positive electrode active material layer 2, and the thickness of the current collector 1 satisfy the relationship The high sheet resistivity ρ1 of the insulating layer 4 reduces the current generated during needle puncture, thereby reducing the heat generated. The insulating layer 4 also prevents short circuits between the positive electrode current collector 1 and the negative electrode active material, effectively avoiding short circuits between the aluminum foil and the negative electrode active material during needle puncture, reducing the risk of battery runaway and improving the battery needle puncture pass rate. The resistivity of the safety primer layer 3 is greater than that of the active material layer, increasing the internal resistance of the battery to a certain extent and also preventing contact between the positive electrode current collector 1 and the negative electrode active material layer. Connecting the safety primer layer 3 to the insulating layer 4 can further prevent contact between the positive electrode current collector 1 and the negative electrode active material layer.

[0039] The film resistivity of the positive electrode active material layer 2 directly affects the battery impedance. Controlling the film resistivity of the positive electrode active material layer 2 within the range of ≤500Ω·cm can ensure that the positive electrode sheet has a low film resistivity while not affecting the electrical performance of the battery.

[0040] In some preferred embodiments, the positive electrode sheet satisfies the following relationship:

[0041] Specifically, the positive electrode sheet meets the above range, and the insulating layer 4 can effectively prevent the short circuit between the positive electrode current collector 1 and the negative electrode active material, effectively avoid the short circuit between the aluminum foil and the negative electrode active material during needle puncture, reduce the risk of battery runaway, and improve the battery needle puncture pass rate.

[0042] In some embodiments, the sheet resistivity ρ1 of the insulating layer 4 ranges from 600 to 1000 kΩ·cm.

[0043] Specifically, the diaphragm resistivity ρ1 of the insulating layer 4 is in the range of 600 to 1000 kΩ·cm. The high diaphragm resistivity of the insulating layer 4 effectively reduces the current generated during acupuncture, effectively reduces the heat generated, reduces the risk of battery runaway, and improves the battery acupuncture pass rate.

[0044] The sheet resistivity ρ1 of the insulating layer 4 may be 600 kΩ·cm, 650 kΩ·cm, 700 kΩ·cm, 750 kΩ·cm, 800 kΩ·cm, 850 kΩ·cm, 900 kΩ·cm, 950 kΩ·cm or 1000 kΩ·cm, as long as ρ1 satisfies the range of 600 to 1000 kΩ·cm.

[0045] In some embodiments, the sheet resistivity ρ2 of the positive electrode active material layer 2 is in the range of 250 to 500 Ω·cm.

[0046] Specifically, the film resistivity ρ2 of the positive electrode active material layer 2 is in the range of 250 to 500 Ω·cm, which ensures that the battery has a low internal resistance while also having a high capacity without affecting the electrical performance of the battery.

[0047] The sheet resistivity ρ2 of the positive electrode active material layer 2 may be 250Ω·cm, 300Ω·cm, 350Ω·cm, 400Ω·cm, 450Ω·cm or 500Ω·cm, as long as ρ2 is within the range of 250 to 500Ω·cm.

[0048] In some embodiments, the thickness d1 of the insulating layer 4 ranges from 8 μm to 16 μm.

[0049] Specifically, the thickness d1 of the insulating layer 4 is in the range of 8 to 16 μm. The insulating layer 4 prevents short circuit between the positive electrode current collector 1 and the negative electrode active material, effectively avoids short circuit between the aluminum foil and the negative electrode active material during needle puncture, and reduces the risk of battery runaway.

[0050] The thickness d1 of the insulating layer 4 may be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, as long as the thickness d1 of the insulating layer 4 is within the range of 8 to 16 μm.

[0051] In some embodiments, the thickness d of the current collector 1 ranges from 8 to 9 μm.

[0052] In some embodiments, a distance between one end of the positive electrode active material layer 2 close to the insulating layer 4 and the insulating layer 4 is greater than 0.

[0053] Specifically, the insulating layer 4 is non-conductive, and the distance between the end of the positive electrode active material layer 2 close to the insulating layer 4 and the insulating layer 4 is limited to be greater than 0, that is, the insulating layer 4 is not connected to the active material layer, does not affect the insertion and extraction of lithium ions in the positive electrode active material layer 2, and does not affect the electrical performance of the battery.

[0054] In some embodiments, the insulating layer 4 includes additives and binders, and the additives include one or more of magnesium oxide, boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate, and calcium sulfate.

[0055] In some embodiments, the safety primer layer 3 includes a positive electrode active material, a conductive agent, a binder, a thickener, and an additive; the positive electrode active material layer 2 includes a positive electrode active material, a conductive agent, and a binder;

[0056] Specifically, the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyurethane, epoxy resin, styrene-butadiene rubber, polymethyl cellulose, polymethyl cellulose sodium, hydroxypropyl methyl cellulose, and polypropylene alcohol.

[0057] The conductive agent includes one or more of hard carbon, soft carbon, acetylene black, carbon nanotubes, graphene, conductive carbon black, conductive graphite, and mesophase carbon microbeads.

[0058] The positive electrode active material includes one or more of lithium iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide.

[0059] Thickeners include sodium carboxymethylcellulose.

[0060] The insulating layer 4 is prepared by mixing an additive, a binder, and a solvent to obtain a mixed solution, and then coating the mixed solution on the surface of the positive electrode current collector 1 and drying it.

[0061] Solvents included NMP.

[0062] The safety primer layer 3 is prepared by mixing the positive electrode active material, the conductive agent, the binder, the thickener, the additive and the solvent to obtain a safety primer slurry, and then coating the safety primer slurry on the surface of the positive electrode current collector 1 and drying it.

[0063] The positive electrode active material layer 2 is prepared by mixing and stirring the positive electrode active material, the conductive agent, the binder and the solvent to obtain a positive electrode active material slurry, and then coating the positive electrode active material slurry on the side of the safety primer layer 3 facing away from the positive electrode current collector 1 and drying it; or coating the positive electrode active material slurry on the surface of the positive electrode current collector 1 and drying it.

[0064] In some embodiments, in the insulating layer 4 , the mass ratio of the additive to the binder is (10-98):(2-90).

[0065] Specifically, the binder plays a bonding role, which can better mix the additive particles and facilitate coating on the surface of the current collector.

[0066] In some embodiments, in the safety primer layer 3, the mass ratio of the positive electrode active material, the conductive agent, the binder, the thickener and the additive is (20-98): (0.1-10): (2-20): (0-20): (5-80).

[0067] Specifically, the safety primer layer may contain additives including one or more of magnesium oxide, boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate, and calcium sulfate. These additives are non-conductive and can increase the safety primer layer's internal resistance, thereby preventing contact between the positive electrode current collector 1 and the negative electrode active material layer.

[0068] In some embodiments, in the positive electrode active material layer 2 , the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95-98.5): (0.1-5): (1.5-5).

[0069] In a second aspect, the present application provides a secondary battery comprising a negative electrode sheet, a separator and the positive electrode sheet described above.

[0070] The battery provided in the present application adopts the above-mentioned positive electrode sheet, which can effectively avoid the short circuit between the aluminum foil and the negative electrode active material during needle puncture, thereby reducing the risk of battery loss of control.

[0071] The positive electrode current collector 1 is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector 1 includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector 1 is selected from aluminum foil.

[0072] The present invention is further described below with reference to the following examples.

[0073] The positive electrode sheet and the secondary battery disclosed in the present invention are specifically described, including the following steps:

[0074] Example 1

[0075] Preparation of positive electrode:

[0076] 1) Lithium iron phosphate and conductive agent SP 、 Conductive agents CNT, PVDF, CMC, and boehmite are uniformly mixed in a mass ratio of 70:0.6:0.6:3.3:0.5:25, and dispersed in N-methyl-2-pyrrolidone to obtain a safety primer slurry. The safety primer slurry is coated on both sides of an aluminum foil and dried to obtain a safety primer layer 3.

[0077] 2) Boehmite and polyvinylidene fluoride were uniformly mixed in a mass ratio of 75:25 and dispersed in N-methyl-2-pyrrolidone to obtain a mixed solution. The mixed solution was coated on the surface of aluminum foil and dried to obtain an insulating layer 4. Insulating layer 4 was formed on both sides of safety primer layer 3. The sheet resistivity ρ1 and thickness d1 of insulating layer 4 are shown in Table 1.

[0078] 3) Lithium cobalt oxide, conductive agent SP, conductive agent CNT, and polyvinylidene fluoride were uniformly mixed in a mass ratio of 97:0.6:0.6:1.8 and dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode active material slurry. The positive electrode active material slurry was evenly coated on the surface of the safety primer layer 3 facing away from the aluminum foil, and dried to obtain a positive electrode active material layer 2. The distance between the end of the positive electrode active material layer 2 closest to the insulating layer 4 and the insulating layer 4 was greater than 0. The sheet resistivity ρ2 of the positive electrode active material layer 2 is shown in Table 1.

[0079] The thickness d2 of the aluminum foil used as the positive electrode current collector 1 was 8 μm.

[0080] Preparation of negative electrode sheet: Graphite, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose were mixed in a mass ratio of 97.2:0.3:0.7:1.8, dispersed in deionized water to obtain negative electrode slurry, and the negative electrode slurry was coated on both sides of copper foil and dried.

[0081] Battery assembly: Assemble the positive electrode, negative electrode, and separator, inject the electrolyte with commercially available solution, and then obtain the battery after aging and formation steps.

[0082] Examples 2-14 and Comparative Examples 1-7, 10-11

[0083] Examples 2-14 and Comparative Examples 1-7, 10-11 differ from Example 1 in that the mass ratio of boehmite to polyvinylidene fluoride in insulating layer 4 was varied to obtain different sheet resistivities (specific values ​​for ρ1 are shown in Table 1); the thickness of insulating layer 4 was also varied (specific values ​​for d1 are shown in Table 1). Positive electrode active material layer 2 was prepared by varying the mass ratio of lithium cobalt oxide, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride to obtain positive electrode active material layers 2 with different sheet resistivities (specific values ​​for ρ2 are shown in Table 1).

[0084] Comparative Example 8

[0085] In the positive electrode sheet preparation method in Comparative Example 8, no insulating layer 4 is prepared, and the rest is the same as in Example 1.

[0086] Comparative Example 9

[0087] Most of the steps of Comparative Example 9 are the same as those of Example 1, except that the positive electrode sheet in Comparative Example 9 has no undercoat layer.

[0088] Electrode resistivity test method:

[0089] The electrode was cut into a 6cm×10cm rectangle and placed flatly in a fixture. The fixture was placed in an IEST BER1300 electrode resistance meter and tested under a pressure of 25MPa.

[0090] Insulation layer 4 thickness test method:

[0091] Place a Mitutoyo digital micrometer on a stable workbench and press the zero button to ensure measurement accuracy. Place the electrode to be measured in a fixture to ensure accurate measurement. Turn the knob on the right side of the digital micrometer to lightly touch the electrode to automatically read the measurement. The thickness of the insulation layer 4 is measured. The thickness results of the insulation layer 4 obtained in the Examples and Comparative Examples are shown in Table 1.

[0092] Table 1 Parameters of positive electrode sheets of various embodiments and comparative examples

[0093] Battery puncture test:

[0094] Using a BE9002CY battery penetration tester, a fully charged battery was placed in the instrument. A 3mm diameter steel needle was inserted into the geometric center of the cell at a rate of 15mm / min until it penetrated the entire battery. The needle remained in the battery for 30 seconds before being removed. The batteries obtained in the Examples and Comparative Examples were subjected to the battery penetration test. The test results are reported in Table 2.

[0095] Table 2

[0096] As can be seen from Tables 1 and 2, the comparison between Comparative Examples 1-7, Comparative Examples 10 and 11 and Examples 1-14 shows that if the positive electrode sheet satisfies the relationship And ρ1≥60kΩ·cm, ρ2≤500Ω·cm, the battery has a high needle puncture pass rate; it is speculated that the high resistivity ρ1 of the insulating layer 4 will reduce the current generated during needle puncture, thereby reducing the heat generated. At the same time, the insulating layer 4 will also prevent the short circuit between the positive electrode collector 1 and the negative electrode active material, effectively avoiding the short circuit between the aluminum foil and the negative electrode active material during needle puncture, reducing the risk of battery runaway, and improving the battery needle puncture pass rate. When the positive electrode sheet satisfies the relationship The battery has a higher puncture rate.

[0097] Compared with Comparative Examples 8-9, in Example 1, the positive electrode sheet in Comparative Example 8 has no insulating layer 4, and the positive electrode sheet in Comparative Example 9 has no safety primer layer 3. The puncture pass rate of the battery is 0, indicating that the insulating layer 4 and the safety primer layer 3 are indispensable. The insulating layer 4 and the safety primer layer 3 work together to prevent the short circuit between the positive electrode collector 1 and the negative electrode active material, effectively avoid the short circuit between the aluminum foil and the negative electrode active material during puncture, reduce the risk of battery loss of control, and improve the puncture pass rate of the battery.

[0098] Compared with Examples 1-14, when the membrane resistivity ρ2 of the positive electrode active material layer 2 is in the range of 600 to 1000 kΩ·cm, or the membrane resistivity ρ1 of the insulating layer 4 is in the range of 250 to 500 Ω·cm, or the thickness d1 of the insulating layer 4 is in the range of 8 to 16 μm, the battery has a higher needle puncture pass rate.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a current collector, at least one surface of which is provided with a positive electrode active material layer and an insulating layer, and the insulating layer is located at at least one end of the positive electrode active material layer; the positive electrode sheet further comprises a safety primer layer, the safety primer layer is provided between the current collector and the positive electrode active material layer, and at least one side of the safety primer layer is connected to the insulating layer; The positive electrode sheet satisfies the following relationship: And ρ1 ≥ 60 kΩ·cm, ρ2 ≤ 500 Ω·cm; Where ρ1 is the sheet resistivity of the insulating layer, in kΩ·cm; ρ2 is the resistivity of the positive electrode active material layer, in Ω·cm; d1 is the thickness of the insulating layer, in μm; d2 is the thickness of the current collector, in μm.

2. The positive electrode sheet according to claim 1, characterized in that The positive electrode sheet satisfies the following relationship:

3. The positive electrode sheet according to claim 1, characterized in that The sheet resistivity ρ1 of the insulating layer ranges from 600 to 1000 kΩ·cm.

4. The positive electrode sheet according to claim 1, characterized in that The resistivity ρ2 of the positive electrode active material layer is in the range of 250 to 500 Ω·cm.

5. The positive electrode sheet according to claim 1, characterized in that: The thickness d1 of the insulating layer ranges from 8 to 16 μm.

6. The positive electrode sheet according to claim 1, characterized in that: A distance between one end of the positive electrode active material layer close to the insulating layer and the insulating layer is greater than 0.

7. The positive electrode sheet according to claim 1, characterized in that: The insulating layer includes additives and a binder, The additives include one or more of magnesium oxide, boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate, and calcium sulfate.

8. The positive electrode sheet according to claim 7, characterized in that: In the insulating layer, the mass ratio of the additive to the binder is (10-98):(2-90).

9. The positive electrode sheet according to claim 7, characterized in that: The safety primer layer includes a positive electrode active material, a conductive agent, a binder, a thickener and an additive; in the safety primer layer, the mass ratio of the positive electrode active material, the conductive agent, the binder, the thickener and the additive is (20-98): (0.1-10): (2-20): (0-20): (5-80).

10. The positive electrode sheet according to claim 7, characterized in that: The positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder; In the positive electrode active material layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95-98.5): (0.1-5): (1.5-5).

11. A secondary battery, characterized in that: The invention comprises a negative electrode sheet, a separator and the positive electrode sheet according to any one of claims 1 to 10.

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