Positive electrode sheet, secondary battery, and electronic device

Abstract

A positive electrode sheet, a secondary battery, and an electronic device. The positive electrode sheet comprises a positive electrode film, the positive electrode film comprising: a positive electrode active material, a conductive agent, a binder and a dispersing additive, wherein the dispersing additive comprises at least one of an aluminate coupling agent and a titanate coupling agent, and the surface coverage a% of the positive electrode active material satisfies: 50≤a≤75. In the positive electrode sheet, by adding the dispersing additive to the positive electrode film, the conductive agent and the binder can be better dispersed on the surface of the positive electrode active material, thereby improving the surface coverage of the positive electrode active material, and reducing active sites on the surface of the positive electrode active material to reduce the decomposition of an electrolyte solution and side reactions and thus to improve the cycle performance of a secondary battery. Moreover, by controlling the surface coverage of the positive electrode active material within a suitable range, the deterioration of the dynamic performance of the secondary battery can be reduced.

Description

Positive electrode sheet, secondary battery and electronic device Technical Field

[0001] The present application relates to the field of battery technology, and more particularly, 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 digital electronics, energy storage, drones, power tools, electric vehicles, and other products due to their high energy density, long cycle life, high safety, and fast charging capabilities. However, the increasing use of secondary batteries has led to higher demands for their cycle life. Active sites on the surface of the positive electrode active material in the positive electrode sheet can decompose the electrolyte in contact, resulting in reduced cycle performance.

[0003] Therefore, it is necessary to reduce the decomposition and side reactions of the electrolyte during the cycle to improve the cycle performance of the secondary battery.

[0004] Summary of the Invention

[0005] The present application provides a positive electrode plate, a secondary battery and an electronic device. The positive electrode active material in the positive electrode plate has a high surface coverage, which can effectively improve the cycle performance of the secondary battery.

[0006] In a first aspect, the present application provides a positive electrode plate, comprising a positive electrode film layer, wherein the positive electrode film layer comprises: a positive electrode active material, a conductive agent, a binder and a dispersing additive, wherein the dispersing additive comprises at least one of an aluminate coupling agent and a titanate coupling agent, and the surface coverage a% of the positive electrode active material satisfies: 50≤a≤75.

[0007] According to the present application, by adding dispersing additives to the positive electrode film layer, the conductive agent and the binder can be better dispersed on the surface of the positive electrode active material, thereby improving the surface coverage of the positive electrode active material, reducing the active sites on the surface of the positive electrode active material, reducing the decomposition and side reactions of the electrolyte, and improving the cycle performance of the secondary battery. At the same time, the surface coverage of the positive electrode active material is controlled within an appropriate range, which can reduce the deterioration of the kinetic performance of the secondary battery.

[0008] In some embodiments, 60≤a≤70.

[0009] In some embodiments, the cohesive force FN / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material satisfy: F≥0.8a; optionally, F≥1.0a.

[0010] In some embodiments, the cohesive force FN / m of the positive electrode film layer satisfies: 40≤F≤100; optionally, 60≤F≤80.

[0011] In some embodiments, the sum of the mass percentages b% of the conductive agent and the binder in the positive electrode film layer and the mass percentage c% of the dispersing additive in the positive electrode film layer satisfy: c≥0.05b; optionally, c≥0.1b.

[0012] In some embodiments, 2≤b≤5, optionally, 2.5≤b≤4; and / or 0.1≤c≤1.

[0013] In some embodiments, the positive electrode film layer satisfies at least one of the following conditions: 1) the average particle size d1 μm of the conductive agent satisfies: 1≤d1≤10, optionally, 1≤d1≤5; 2) the density of the conductive agent is ρg / cm 3 Satisfies: 0.5≤ρ≤5; 3) The weight average molecular weight Mw of the binder satisfies: 10000≤Mw≤50000; optionally, 20000≤Mw≤30000; 4) The specific surface area BET m of the positive electrode active material 2 / g satisfies: 0.05≤BET≤0.8; 5) the average particle size d1μm of the conductive agent, the density ρg / cm 3 and the specific surface area BET m of the positive electrode active material 2 / g satisfies: BET≤1 / (ρ×d1).

[0014] In some embodiments, the positive electrode film layer satisfies at least one of the following conditions: 1) the mass percentage of the conductive agent in the positive electrode film layer is 0.5% to 2.5%; 2) the mass percentage of the binder in the positive electrode film layer is 1.0% to 3.0%; 3) the mass percentage of the dispersing additive in the positive electrode film layer is 0.1% to 1.0%; 4) the mass percentage of the positive electrode active material in the positive electrode film layer is 95.0% to 97.8%.

[0015] In some embodiments, the aluminate coupling agent includes [Al(OR)3] n , wherein R is an alkyl group or an allyl group having 3 to 15 carbon atoms, and n is a positive integer.

[0016] In some embodiments, the aluminate coupling agent includes at least one of monoisopropyl aluminate and isopropyl dioleoyl aluminate, and the titanate coupling agent includes at least one of di(octyl pyrophosphate)hydroxyacetic acid titanate and di(dioctyl phosphate)ethylene glycol titanate.

[0017] In some embodiments, the positive electrode film layer satisfies at least one of the following conditions: 1) the conductive agent includes at least one of conductive carbon black, Ketjen black, carbon nanotubes and conductive graphite; 2) the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin; 3) the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate and lithium nickel cobalt manganese oxide.

[0018] In some embodiments, the thickness of the positive electrode film layer is 20 to 100 μm.

[0019] In a second aspect, the present application provides a secondary battery comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte according to any embodiment of the first aspect.

[0020] In a third aspect, the present application provides an electronic device, comprising: a secondary battery according to any embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0022] FIG1 is a SEM image of the surface of the positive electrode film layer in backscattering mode in Example 1.

[0023] FIG2 is an SEM image of the surface of the positive electrode film layer in comparative example 1 under backscattering mode. DETAILED DESCRIPTION

[0024] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first" and "second" in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary-secondary relationship.

[0026] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0027] The term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects are in an "or" relationship.

[0028] The term "plurality" used in this application refers to two or more (including two).

[0029] As described in the background art, during the charge and discharge process of a secondary battery, active sites on the surface of the positive electrode active material in the positive electrode sheet may cause electrolyte decomposition and side reactions, which may seriously affect the cycle performance of the secondary battery.

[0030] In response to the above problems, related technologies include adding positive electrode protection additives to the electrolyte. The positive electrode protection additives can form a protective layer on the surface of the positive electrode active material, thereby reducing the contact between the positive electrode active material and the electrolyte, and further reducing the decomposition and side reactions of the electrolyte. However, the problem is that the addition of positive electrode protection additives may affect the kinetic performance of the secondary battery; in addition, related technologies also include coating the surface of the positive electrode active material to reduce the decomposition and side reactions of the electrolyte, but the problem is that it will also deteriorate the kinetic performance of the secondary battery, and the gram capacity of the positive electrode active material cannot be effectively exerted, and the energy density is reduced.

[0031] Based on this, the present application provides a positive electrode sheet, a secondary battery, and an electronic device. By adding a dispersing additive to the positive electrode film layer of the positive electrode sheet, the dispersion of the components in the positive electrode film layer is improved, and the surface coverage of the positive electrode active material is increased, thereby reducing electrolyte decomposition and side reactions, and improving the cycle performance of the secondary battery. The specific embodiments of the present application are described in detail below.

[0032] Positive electrode

[0033] In the first aspect, the present application provides a positive electrode plate, including a positive electrode film layer, the positive electrode film layer including: a positive electrode active material, a conductive agent, a binder and a dispersing additive, wherein the dispersing additive includes at least one of an aluminate coupling agent and a titanate coupling agent, and the surface coverage a% of the positive electrode active material satisfies: 50≤a≤75.

[0034] According to the present application, by adding dispersing additives to the positive electrode film layer, the conductive agent and the binder can be better dispersed on the surface of the positive electrode active material, thereby improving the surface coverage of the positive electrode active material, reducing the active sites on the surface of the positive electrode active material, reducing the decomposition and side reactions of the electrolyte, and improving the cycle performance of the secondary battery. At the same time, the surface coverage of the positive electrode active material is controlled within an appropriate range, which can reduce the deterioration of the kinetic performance of the secondary battery.

[0035] Specifically, the dispersing additive includes at least one of an aluminate coupling agent and a titanate coupling agent. On the one hand, the above-mentioned dispersing additive can improve the dispersion of the binder, the conductive agent and the positive electrode active material, so that the components in the positive electrode film layer are more evenly dispersed. Therefore, when the content of the positive electrode active material in the positive electrode film layer is certain, the more evenly dispersed binder and the conductive agent have a higher coverage rate on the surface of the positive electrode active material, thereby reducing the exposure of active sites on the surface of the positive electrode active material and reducing electrolyte decomposition and side reactions; on the other hand, the above-mentioned dispersing additive can further improve the bonding between the binder and the conductive agent and the positive electrode active material through coupling, so that during the cycle of the secondary battery, the distribution structure of the binder in the positive electrode film layer is not easy to change, and will not affect the conductive path formed by the conductive agent, and the binder on the surface of the positive electrode active material is not easy to fall off, reducing the exposure of new active sites due to the falling off of the binder during the cycle, thereby further improving the cycle performance of the secondary battery. In addition, aluminate coupling agents and titanate coupling agents have good stability in secondary batteries and are not easily decomposed during the charge and discharge process, so they are not easily invalidated during the use of secondary batteries, thereby ensuring that the above-mentioned dispersing additives can stably play the above-mentioned role and improve the cycle performance of secondary batteries.

[0036] In addition, it is also necessary to control the coverage of the surface of the positive electrode active material within an appropriate range. This is because although the use of dispersing additives to reduce the exposure of active sites on the surface of the positive electrode active material can reduce electrolyte decomposition and side reactions, if the coverage is too high, it may affect the deintercalation of active ions by the positive electrode active material, thereby affecting the kinetic performance of the secondary battery. Therefore, the coverage of the surface of the positive electrode active material is required. When the surface coverage a% of the positive electrode active material satisfies: 50≤a≤75, the positive electrode sheet can effectively improve the cycle performance and kinetic performance of the secondary battery. For example, a can be 50, 52, 55, 57, 60, 62, 65, 67, 70, 72, 75, or within the range of any of the above values. Further, when the surface coverage a% of the positive electrode active material satisfies: 60≤a≤70, the positive electrode sheet can more effectively balance the cycle performance and kinetic performance of the secondary battery.

[0037] The surface coverage of the positive electrode active material can be tested according to the following method:

[0038] 1) Remove the electrode coated with the positive electrode active material layer from the finished battery cell at a temperature of (25±3)°C. Wipe away any residual electrolyte on the electrode surface with a dust-free paper.

[0039] 2) Observe the disassembled electrode piece using a scanning electron microscope (SEM) in backscatter mode, wherein the SEM voltage is set to 10.0 kV, the working distance of the center of the field of view is maintained at 10 mm, and the magnification is set to 1000 times;

[0040] 3) The SEM image was processed and the area ratio with a grayscale value ≤ 100 was calculated and recorded as the surface coverage of the positive electrode active material.

[0041] It should also be noted that the surface coverage of the positive electrode active material is related to multiple factors, including but not limited to the types and contents of the components in the positive electrode film layer, the preparation method of the positive electrode sheet, etc. The surface coverage of the positive electrode active material can be adjusted by controlling relevant parameters. For example, the surface coverage of the positive electrode active material can be adjusted by changing the binder content and the specific surface area of ​​the positive electrode active material.

[0042] In some embodiments, the cohesive force FN / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material satisfy: F≥0.8a; alternatively, F≥1.0a.

[0043] In some of the above embodiments, the higher the surface coverage of the positive electrode active material, the greater the cohesion required for the positive electrode film layer. The higher cohesion can effectively reduce the peeling of the binder and conductive agent on the surface of the positive electrode active material, reduce the exposure of the active sites on the surface of the positive electrode active material during the cycle, and also improve the stability of the conductive path in the positive electrode film layer, thereby further improving the cycle performance and kinetic performance of the secondary battery. When the cohesion FN / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material meet the following conditions: F ≥ 0.8a, the positive electrode sheet obtained at this time can further improve the cycle performance and kinetic performance of the secondary battery. For example, F can be 0.8a, 0.85a, 0.9a, 0.95a, 1.0a, 1.05a, 1.1a, 1.2a, 1.3a, or within the range of any of the above values. Furthermore, when the cohesive force FN / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material satisfy: F≥1.0a, the secondary battery including the positive electrode sheet has better cycle performance and kinetic performance.

[0044] In some embodiments, the cohesive force FN / m of the positive electrode film layer satisfies: 40≤F≤100; optionally, 60≤F≤80.

[0045] In some of the above embodiments, the cohesive force of the positive electrode film layer can be between 40N / m and 100N / m. In this case, the positive electrode film layer is more stable during the battery cycle, the binder and conductive agent on the surface of the positive electrode active material are not easily peeled off, and a high surface coverage can be maintained, thereby further reducing the decomposition and side reactions of the electrolyte; in addition, appropriate cohesive force is also conducive to reducing the processing difficulty of the positive electrode sheet. For example, F can be 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or within the range of any of the above values. Furthermore, in the case of 60≤F≤80, the secondary battery including the positive electrode sheet has better cycle performance and kinetic performance, and the positive electrode sheet is easier to prepare.

[0046] It is also understood that the cohesive force of the positive electrode film is also related to factors such as the types and contents of the components in the positive electrode film, the preparation method of the positive electrode sheet, etc., and the cohesive force of the positive electrode film can be adjusted by controlling relevant parameters. For example, the cohesive force of the positive electrode film can be adjusted by changing the binder content, the binder weight-average molecular weight, the content of the dispersing additive, etc.

[0047] It should be noted that the cohesion of the positive electrode film layer has a meaning well known in the art and can be tested according to methods and instruments known in the art. For example, the cohesion of the positive electrode film layer can be tested using a high-speed rail tensile test machine commonly used in the lithium battery industry and the 90° angle method. Specifically, the portion of the electrode sheet coated with the active layer in the finished battery is formed into a strip. A portion of the electrode sheet is adhered to a steel plate along the length direction from one end of the electrode sheet using double-sided tape. The steel plate is then fixed to the corresponding position of the high-speed rail tensile test machine, and the electrode sheet not adhered to the steel plate is pulled up. The electrode sheet is placed in a chuck through a connector or directly clamped. When the clamp tension is greater than 0 kgf and less than 0.02 kgf, the high-speed rail tensile test machine test can be started. The final average value of the measured tension is recorded as the cohesion of the film layer.

[0048] In some embodiments, the sum of the mass percentages b% of the conductive agent and the binder in the positive electrode film layer and the mass percentage c% of the dispersing additive in the positive electrode film layer satisfy: c≥0.05b; optionally, c≥0.1b.

[0049] In some of the above embodiments, the dispersing additive is conducive to promoting the dispersion of the conductive agent and the binder, thereby increasing the surface coverage of the positive electrode active material, and at the same time improving the bonding performance of the binder with the conductive agent and the positive electrode active material. When c≥0.05b is satisfied, the conductive agent and the binder in the positive electrode film layer are more easily evenly dispersed on the surface of the positive electrode active material, while forming a stable conductive path, improving the cohesion of the positive electrode film layer, so that the secondary battery including the positive electrode sheet has better cycle performance and kinetic performance. For example, c can be 0.05b, 0.06b, 0.07b, 0.08b, 0.09b, 0.1b, 0.11b, 0.12b, 0.13b, 0.14b, 0.15b, 0.2b, or within the range of any of the above values. Further, when c≥0.1b, the secondary battery including the positive electrode sheet has better cycle performance and kinetic performance.

[0050] In some embodiments, 2≤b≤5.

[0051] In some of the above embodiments, the combined weight percentage of the conductive agent and binder in the positive electrode film layer can be 2% to 5%. In this case, the surface coverage of the positive electrode active material and the cohesive strength of the positive electrode film layer are high, which is beneficial for improving the cycling performance and kinetic performance of the secondary battery. For example, b can be 2, 2.5, 3, 3.5, 4, 4.5, 5, or any of the above values. Furthermore, b can be 2.5 to 4.

[0052] In some embodiments, the average particle size d1 μm of the conductive agent satisfies the following conditions: 1 ≤ d1 ≤ 10, and optionally, 1 ≤ d1 ≤ 5. In this case, the conductive agent, under the action of the dispersing additive, is more easily dispersed on the surface of the positive electrode active material, thereby increasing the surface coverage of the positive electrode active material and forming a more complete conductive pathway, thereby further improving the cycling performance and kinetic performance of the secondary battery. For example, d1 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any of the above values. Furthermore, 1 ≤ d1 ≤ 5.

[0053] The average particle size of the conductive agent has a well-known meaning in the art and can be measured using methods and instruments known in the art. For example, GB / T 19077-2016 describes the following steps: 1 g of sample is weighed and mixed evenly with 20 mL of deionized water and a trace amount of dispersant. The mixture is then ultrasonicated for 5 minutes, and then poured into a sample injection system, a Hydro 2000SM, for testing. The testing equipment used is a Malvern Mastersizer 3000. During the test, particle size is measured by measuring the intensity of scattered light as a laser beam passes through the dispersed particle sample. This data is then used to analyze and calculate the particle size distribution, which forms the scattering spectrum. The particles used in the test have a refractive index of 1.8. Each sample is tested three times, and the particle size is ultimately averaged over the three tests, with Dv50 being the average particle size.

[0054] In some embodiments, the density of the conductive agent is pg / cm 3 Satisfies: 0.5 ≤ ρ ≤ 5. This allows for better processability of the conductive agent and, with the help of dispersing additives, easier uniform dispersion within the positive electrode film, forming a complete conductive pathway and further improving the cycling and kinetic performance of the secondary battery. For example, ρ can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any of these values.

[0055] The density of a conductive agent has a well-known meaning in the art and can be measured using methods and instruments known in the art. For example, it can be measured using the inclusion method. A container of known volume (e.g., a 10 ml graduated cylinder) is filled with the conductive agent and the mass of the conductive agent is measured. The density of the conductive agent is obtained by dividing the mass of the conductive agent by the volume.

[0056] In some embodiments, the weight average molecular weight Mw of the binder satisfies: 10,000 ≤ Mw ≤ 50,000; alternatively, 20,000 ≤ Mw ≤ 30,000. In this case, the binder is more easily dispersed evenly in the positive electrode film layer under the action of the dispersing additive, and the binder has good bonding properties, which can more effectively improve the surface coverage of the positive electrode active material. It is also beneficial to improve the cohesion of the positive electrode film layer, thereby further improving the cycle performance and dynamic performance of the secondary battery. For example, the weight average molecular weight Mw of the binder can be 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, or within the range of any of the above values. Further, 20,000 ≤ Mw ≤ 30,000.

[0057] In some embodiments, the weight average molecular weight of the binder has a meaning well known in the art and can be detected according to methods and instruments known in the art. As an example, the weight average molecular weight Mw of the binder is determined by gel permeation chromatography (GPC).

[0058] In some embodiments, the specific surface area BET m 2 / g satisfies: 0.05≤BET≤0.8. In this case, the positive electrode active material is more easily dispersed in the positive electrode film layer, the surface coverage of the positive electrode active material is easier to control, and the positive electrode active material also has good active ion deintercalation performance, which is conducive to further improving the cycle performance and kinetic performance of the secondary battery. For example, BET can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any of the above values.

[0059] The specific surface area of ​​the positive electrode active material has a meaning well known in the art and can be detected according to methods and instruments known in the art. As an example, it can be detected with reference to GB / T 19587-2017, specifically: weigh 1 to 8 g of the sample (the sample weight should be at least 1 / 3 of the volume of the sphere) and place it in a 1 / 2-inch long tube with a bulb (the diameter of the spherical part is 12 mm), pre-treated at 200°C for 2 hours, and then placed in a test equipment TriStar3030 (Machinery, USA) for testing. The adsorption gas used is N2 (purity: 99.999%), the test conditions are carried out at 77K, and the specific surface area is measured by the BET calculation method.

[0060] In some embodiments, the average particle size d of the conductive agent is 1 μm, the density of the conductive agent is ρg / cm 3 and the specific surface area of ​​the positive electrode active material BET m 2 / g satisfies: BET ≤ 1 / (ρ × d1). In this case, the conductive agent is more easily and evenly dispersed on the surface of the positive electrode active material, improving the surface coverage of the positive electrode active material while better forming a complete conductive path between the positive electrode active materials. At the same time, under the action of the binder and dispersing additive, the positive electrode active material is less likely to expose new active sites during the secondary cycle, and the conductive path is also less likely to be destroyed, thereby further improving the cycle performance and kinetic performance of the secondary battery.

[0061] In some embodiments, the conductive agent has a mass percentage of 0.5% to 2.5% in the positive electrode film layer, which provides a more complete conductive path in the positive electrode sheet and can further improve the cycle performance and kinetic performance of the secondary battery.

[0062] In some embodiments, the binder content in the positive electrode film is 1.0% to 3.0% by weight, which can enhance the cohesion of the positive electrode film and stabilize the bonding between the components, thereby further improving the cycle performance and dynamic performance of the secondary battery.

[0063] In some embodiments, the mass percentage of the dispersing additive in the positive electrode film layer is 0.1% to 1.0%. In this case, the dispersing additive can better promote the dispersion of the components in the film layer, while also improving the adhesion between the binder and the conductive agent and the positive electrode active material, without affecting the electrical performance of the secondary battery, and can further improve the cycle performance and kinetic performance of the secondary battery.

[0064] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode film layer is 95.0% to 97.8%, which is beneficial to further improve the energy density of the secondary battery.

[0065] In some embodiments, the aluminate coupling agent includes [Al(OR)3] n , wherein R is an alkyl group or an allyl group having 3 to 15 carbon atoms, and n is a positive integer.

[0066] In some embodiments, the aluminate coupling agent includes at least one of monoisopropyl aluminate and isopropyl dioleoyl aluminate, and the titanate coupling agent includes at least one of di(octyl pyrophosphate) glycolate titanate and di(dioctyl phosphate) ethylene glycol titanate. It is understood that aluminate coupling agents and titanate coupling agents include but are not limited to those described above, and those skilled in the art can select other known aluminate coupling agents and titanate coupling agents as needed.

[0067] In some embodiments, the conductive agent includes at least one of conductive carbon black, Ketjen black, carbon nanotubes, and conductive graphite. It is understood that the conductive agent includes but is not limited to the above-mentioned ones, and those skilled in the art can select other known conductive agents as needed.

[0068] In some embodiments, the binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. It is understood that the binder includes but is not limited to the aforementioned ones, and those skilled in the art can select other known binders as needed.

[0069] In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt manganese oxide. It is understood that the positive electrode active materials include but are not limited to the aforementioned ones, and those skilled in the art can select other known positive electrode active materials as needed.

[0070] In some embodiments, the thickness of the positive electrode film layer is 20 to 100 μm.

[0071] In some of the above embodiments, since dispersing additives are added to the positive electrode film layer, the components in the positive electrode film layer can be uniformly dispersed, and the cohesion of the positive electrode film layer can be effectively improved. Therefore, the thickness of the positive electrode film layer can be appropriately increased to further improve the energy density of the secondary battery.

[0072] The thickness of the positive electrode film layer has a well-known meaning in the art and can be measured using methods and instruments known in the art. As an example, it can be measured by the following method:

[0073] 1) In an environment of (25±3)℃, remove the electrode coated with the positive electrode film from the finished battery cell. Use dust-free paper to wipe off the residual electrolyte on the surface of the electrode;

[0074] 2) The electrode sheet coated with the positive electrode film is cut under plasma to obtain its cross section;

[0075] 3) Observe the cross section of the electrode obtained in 2) under SEM and test the thickness of the single-sided positive electrode film layer. The adjacent test points are spaced 2mm to 3mm apart. At least 15 different points are tested. The average of all test points is recorded as the thickness of the positive electrode film layer.

[0076] In some embodiments, the positive electrode sheet includes a positive electrode current collector. As an example, the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0077] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone), and stirred to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0079] In some embodiments, the specific stirring conditions may be stirring at 1200-2000 r / h for 100-400 minutes. It is understood that the conditions for preparing the positive electrode slurry will also affect the surface coverage of the positive electrode active material. Those skilled in the art can control the surface coverage of the positive electrode active material by adjusting the specific stirring conditions. Generally speaking, the faster the stirring speed and the longer the stirring time, the higher the surface coverage of the positive electrode active material.

[0080] secondary batteries

[0081] In a second aspect, the present application provides a secondary battery comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte according to any embodiment of the first aspect.

[0082] According to the present application, the positive electrode sheet of the secondary battery is the positive electrode sheet according to any embodiment of the first aspect. The embodiments of the first aspect have been described and illustrated in detail above and will not be repeated here. It is understood that the secondary battery of the present application can achieve the beneficial effects of the first aspect of the present application.

[0083]

Positive electrode

[0084] The selection is made according to any one of the embodiments of the first aspect.

[0085]

Negative electrode

[0086] The material, composition and manufacturing method of the negative electrode sheet used in the secondary battery of the present application may include any technology known in the prior art.

[0087] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector. The present application does not limit the negative electrode current collector, and it is selected according to the current collector provided in the first aspect. As an example, the current collector is a copper foil.

[0088] The specific type of the negative electrode active material is not specifically limited and can be selected according to requirements. For example, the negative electrode active material can be one or several of carbonaceous materials, metal compounds that can be alloyed with lithium, metal oxides that can be doped and undoped with lithium, and composites including metal compounds and carbonaceous materials. As an example, the carbonaceous materials can include one or several of artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; the metal compounds that can be alloyed with lithium can include one or several of silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy, or Al alloy; the metal oxides that can be doped and undoped with lithium can include one or several of SiOv (0 < v < 2), SnO2, vanadium oxides, and lithium vanadium oxides; the composites including metal compounds and carbonaceous materials can include Si-C composites and / or Sn-C composites. These negative electrode active materials can be used alone or in combination of two or more.

[0089] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0090] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may include at least one of conductive carbon black, acetylene black, discrete carbon nanotubes, carbon fibers, Ketjen black, and graphene.

[0091] In some embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0092] However, the present application is not limited to the above materials, and the negative electrode plate of the present application can also use other well-known materials that can be used as negative electrode active materials, conductive agents, binders, and thickeners.

[0093] The negative electrode sheet in this application can be prepared according to conventional methods in the art. For example, the negative electrode active material, conductive agent, binder, and thickener are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, dried, and cold pressed to obtain a negative electrode film layer, thereby obtaining the negative electrode sheet.

[0094]

Isolation film

[0095] The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0096] In some embodiments, the material of the isolation membrane can be selected from one or more of, but not limited to, fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Alternatively, the isolation membrane can include polyethylene and / or polypropylene. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the isolation membrane can also be provided with a ceramic coating or a metal oxide coating.

[0097]

Electrolyte

[0098] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The electrolyte that can be used in the secondary electrolyte of this application can be an electrolyte known in the prior art.

[0099] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives. The types of the organic solvent, the lithium salt, and the additives are not particularly limited and may be selected according to needs.

[0100] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte salt may include a lithium salt. As an example, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDODFP (lithium difluorooxalatophosphate), and LiOTFP (lithium tetrafluorooxalatophosphate). The above lithium salts may be used alone or in combination.

[0101] In some embodiments, the secondary battery is a sodium ion battery, and the electrolyte salt may include a sodium salt. As an example, the sodium salt may be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0102] In some embodiments, as an example, the organic solvent includes but is not limited to ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The above organic solvents can be used alone or in combination. Alternatively, two or more organic solvents are used in combination.

[0103] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0104] As an example, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0105] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the electrolyte salt can be first added to the organic solvent, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0106] electronic devices

[0107] A third aspect of the present application provides an electronic device comprising the secondary battery according to the second aspect of the present application.

[0108] The electronic device of the present application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, 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, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0109] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0110] Cyclic performance test:

[0111] 45°C Cycle Retention Test: At (45±3)°C, charge the battery at 0.5C to 4.5V, then charge at 4.5V constant voltage to 0.025C. Then, discharge the battery at 0.5C to a cutoff voltage of 3.0V. Repeat the charge and discharge cycle 500 times. The 45°C cycle retention rate is calculated by dividing the 500th discharge capacity by the first discharge capacity.

[0112] Rate performance test:

[0113] Take a lithium-ion battery and place it at a test temperature of 25°C for 5 minutes. Then, charge it at a constant current of 0.7C to 4.5V. Then, charge it at a constant voltage of 4.5V to 0.05C. After 5 minutes of rest, discharge it at a constant current of 0.2C to 3.0V. Record the 0.2C discharge capacity. After 5 minutes of rest, repeat the above charging process. Then, discharge it at a constant current of 2C. Record the 2C discharge capacity. Rate performance = 2C discharge capacity / 0.2C discharge capacity × 100%.

[0114] Example 1

[0115] Preparation of positive electrode sheet: Lithium cobalt oxide (BET is 0.15m 2 / g), dispersing additive monoisopropyl aluminate, conductive agent conductive carbon (d1 is 2.5μm, ρ is 2g / m 3 ) and binder PVDF (Mw 30,000) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 97.1:0.5:0.9:1.5, and stirred at 1500 rpm for 180 minutes to form a uniform positive electrode slurry. The positive electrode slurry was then coated onto aluminum foil and dried at 90°C. The above steps were then repeated on the other surface of the positive electrode sheet to produce a double-sided positive electrode sheet coated with a positive electrode active material layer. After cold pressing, cutting, and slitting, a positive electrode sheet measuring 74 mm x 867 mm was obtained, which was then welded to the tabs for later use. The thickness of the positive electrode active material layer was 50 μm.

[0116] Negative electrode sheet preparation: Graphite, conductive agent carbon black, SBR, and thickener CMC are dispersed in deionized water at a mass ratio of 97:1:1.5:0.5 to form a uniform negative electrode slurry. This slurry is then coated onto copper foil and dried at 120°C to produce a negative electrode sheet coated on one side with the negative electrode active material layer. The above steps are repeated on the other side of the copper foil. After cold pressing, cutting, and slitting, the negative electrode sheet is coated on both sides with the negative electrode active material layer. The negative electrode sheet is cut into 78mm x 875mm dimensions and the tabs are welded before use.

[0117] Preparation of electrolyte: Ethylene carbonate, propylene carbonate and dimethyl carbonate are mixed evenly in a mass ratio of 10:10:80, and then lithium salt LiPF6 is dissolved in the above mixed solution to obtain an electrolyte with a mass percentage of LiPF6 of 12.5%.

[0118] Preparation of isolation membrane: A 7 μm thick polyethylene (PE) isolation membrane substrate was coated with a 3 μm ceramic coating.

[0119] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is placed between the positive and negative electrode sheets to act as an isolation, and then wind them to obtain a bare cell; after welding the tabs, place the bare cell in the outer packaging foil aluminum-plastic film, inject the prepared electrolyte into the dried bare cell, and after vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft-pack lithium-ion battery is obtained.

[0120] Examples 2 to 12, Comparative Examples 1 to 3

[0121] The preparation method is substantially the same as that of Example 1, with the only difference being some parameters in the positive electrode film layer. For specific differences, see Table 1.

[0122] Performance Testing

[0123] The lithium-ion batteries obtained in Examples 1 to 12 and Comparative Examples 1 to 3 were subjected to cycle performance and rate performance tests, and the cohesive force F of the positive electrode film layer in the positive electrode sheet and the surface coverage a% of the positive electrode active material were tested. The results are shown in Table 1.

[0124] According to Table 1, the cycle capacity retention rate of the batteries in each embodiment at 45°C is better than that of each comparative example, indicating that the surface coverage of the positive electrode active material can be effectively adjusted to an appropriate range by adding a dispersing additive to improve the cycle performance of the battery.

[0125] In Comparative Example 1, no dispersing additive was added, the surface coverage of the positive electrode active material was low, and the electrolyte was easily decomposed during the charge and discharge process, resulting in reduced cycle performance. Figures 1 and 2 show the SEM images of the positive electrode film surface in backscattering mode in Example 1 and Comparative Example 1, respectively. It can be seen that under the action of the dispersing additive, the dispersion of the components in the positive electrode film layer is more uniform, and the surface coverage of the positive electrode active material is higher, which is beneficial to improving the cycle performance and kinetic performance of the battery.

[0126] In Comparative Example 2, the surface coverage of the positive electrode active material is too high, which will affect the deintercalation and extraction of active ions by the positive electrode active material, thereby affecting the cycle performance and kinetic performance of the battery.

[0127] In Comparative Example 3, although the surface coverage of the positive electrode active material can be improved by adding a silane coupling agent as a dispersant, it is unstable during the charge and discharge process and easily decomposes and fails during the cycle process, resulting in the exposure of new active sites, and the structural stability of the positive electrode film layer deteriorates, resulting in reduced cycle performance and kinetic performance.

[0128] According to Examples 1 to 10, by adding different types of dispersing additives to the positive electrode film layer and adjusting the types and contents of each component, the surface coverage of the positive electrode active material can be controlled within an appropriate range, which can effectively improve the cycle performance and kinetic performance of the battery.

[0129] According to Examples 1, 11, and 12, the cohesive force of the positive electrode film layer has a certain influence on the cycle performance and kinetic performance of the battery. When F≥0.8a, the battery has good cycle performance and kinetic performance. When F≥a, the cycle performance and kinetic performance of the battery are even better.

[0130] Examples 13 to 15

[0131] The preparation method is substantially the same as that of Example 1, with the only difference being some parameters in the positive electrode film layer. For specific differences, see Table 2.

[0132] Performance Testing

[0133] The lithium-ion batteries obtained in Examples 13 to 15 were subjected to cycle performance and rate performance tests, and the surface coverage (a%) of the positive electrode active material in the positive electrode sheet was tested. The results are shown in Table 2.

[0134] According to Examples 1 and 13, the parameters of the positive electrode active material and the conductive agent have a certain influence on the cycle performance and kinetic performance of the battery. When BET≤1 / (ρ×d1), the cycle performance and kinetic performance of the battery are better.

[0135] According to Examples 1, 14, and 15, the mass percentages of the dispersing additives, conductive agents, and binders have a certain influence on the cycle performance and kinetic performance of the battery. When c ≥ 0.05b, the battery has better cycle performance and kinetic performance. When c ≥ 0.1b, the battery has better cycle performance and kinetic performance.

[0136] Examples 16 to 18

[0137] The preparation method is substantially the same as that of Example 5, with the only difference being the stirring speed and time during the preparation of the positive electrode slurry. For specific differences, see Table 3.

[0138] Performance Testing

[0139] The lithium-ion batteries obtained in Examples 16 to 18 were subjected to cycle performance and rate performance tests, and the surface coverage (a%) of the positive electrode active material in the positive electrode sheet was tested. The results are shown in Table 3.

[0140] Table 3

[0141] According to Table 3, by controlling the specific process of preparing the positive electrode slurry, the surface coverage of the positive electrode active material can be adjusted, thereby affecting the cycle performance and kinetic performance of the battery. At the same time, it can be seen that when the surface coverage of the positive electrode active material is 60% to 70%, the battery has better cycle performance and performance.

[0142] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode sheet, comprising a positive electrode film layer, and the positive electrode film layer includes: A positive electrode active material, a conductive agent, a binder, and a dispersion additive, wherein the dispersion additive includes at least one of an aluminate coupling agent and a titanate coupling agent, and the surface coverage a% of the positive electrode active material satisfies: 50 ≤ a ≤ 75.

2. The positive electrode sheet according to claim 1, wherein, 60≤a≤70。 3. The positive electrode sheet according to claim 1, wherein, The cohesive force F N / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material satisfy: F ≥ 0.8a.

4. The positive electrode sheet according to claim 3, wherein, The cohesive force F N / m of the positive electrode film layer and the surface coverage a% of the positive electrode active material satisfy: F ≥ 1.0a.

5. The positive electrode sheet according to claim 3, wherein, The cohesive force F N / m of the positive electrode film layer satisfies: 40 ≤ F ≤ 100.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein, The sum b% of the mass percentages of the conductive agent and the binder in the positive electrode film layer and the mass percentage c% of the dispersion additive in the positive electrode film layer satisfy: c ≥ 0.05b.

7. The positive electrode tab according to claim 6, wherein 2 ≤ b ≤ 5; and / or 0.1≤c≤1。 8. The positive electrode sheet according to any one of claims 1 to 5, wherein, The positive electrode film layer satisfies at least one of the following conditions: 1) The average particle size d1 μm of the conductive agent satisfies: 1 ≤ d1 ≤ 10; 2) The density ρ of the conductive agent is g / cm 3 satisfies: 0.5 ≤ ρ ≤ 5; 3) The weight average molecular weight Mw of the binder satisfies: 10000 ≤ Mw ≤ 50000; 4) The specific surface area BET m of the positive electrode active material 2 / g satisfies: 0.05 ≤ BET ≤ 0.8; 5) The average particle size d1 μm of the conductive agent, the density ρ g / cm of the conductive agent 3 and the specific surface area BET m of the positive electrode active material 2 / g satisfy: BET ≤ 1 / (ρ × d1).

9. The positive electrode sheet according to any one of claims 1 to 5, wherein, The positive electrode film layer satisfies at least one of the following conditions: 1) The mass percentage of the conductive agent in the positive electrode film layer is 0.5% to 2.5%; 2) The mass percentage of the binder in the positive electrode film layer is 1.0% to 3.0%; 3) The mass percentage of the dispersion additive in the positive electrode film layer is 0.1% to 1.0%; 4) The mass percentage of the positive electrode active material in the positive electrode film layer is 95.0% to 97.8%.

10. The positive electrode tab according to any one of claims 1 to 5, wherein The aluminate coupling agent includes [Al(OR)3] n , where R is an alkyl or allyl group with 3 to 15 carbon atoms, and n is a positive integer.

11. The positive electrode tab according to any one of claims 1 to 5, wherein The aluminate coupling agent includes at least one of monoisopropyl aluminate and isopropyl dioleoyl aluminate; The titanate coupling agent includes at least one of bis(octyl pyrophosphate) glycolate titanate and bis(dioctyl phosphate) ethylene glycol titanate.

12. The positive electrode sheet according to any one of claims 1 to 5, wherein, The positive electrode film layer satisfies at least one of the following conditions: 1) The conductive agent includes at least one of conductive carbon black, Ketjen black, carbon nanotubes, and conductive graphite; 2) The binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin; 3) The positive electrode active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, and lithium nickel cobalt manganate.

13. A secondary battery, comprising: A positive electrode tab, a negative electrode tab, a separator, and an electrolyte according to any one of claims 1 to 12.

14. An electronic device, comprising: The secondary battery according to claim 13.

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