Positive electrode sheet, secondary battery, and electric device

Abstract

A positive electrode sheet, a secondary battery, and an electric device. The positive electrode sheet comprises a current collector and a positive electrode film layer located on at least one side of the current collector; the positive electrode film layer comprises a first area and a second area; the particle size distribution index of an active material in the first area is smaller than the particle size distribution index of an active material in the second area, wherein the particle size distribution index is the ratio of the standard deviation of the particle size of an active material to the average particle size thereof, the first area is an area where the positive electrode film layer extends vertically from the surface on the side close to the current collector to the positive electrode film layer within a distance h1, the second area is an area where the positive electrode film layer extends vertically from the surface on the side close to the current collector to the positive electrode film layer with a distance from h1 to H, and H is the thickness of the positive electrode film layer, and h1 is less than H.

Description

Positive electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202310875559.8 filed on July 17, 2023, entitled “Positive Electrode Sheet, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] In recent years, as secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, the market's performance requirements for secondary batteries have become increasingly higher.

[0005] Improving the energy density of secondary batteries has become a major market priority. However, this increase in energy density often leads to safety issues. Therefore, how to increase battery energy density while maintaining battery safety has become a pressing technical challenge.

[0006] Summary of the Invention

[0007] In view of the problems existing in the background technology, the present application provides a positive electrode plate, which aims to increase the volume energy density of the battery while increasing the flexibility of the plate, reducing the possibility of brittle fracture of the plate, and simultaneously improving the safety performance of the battery.

[0008] A first aspect of the present application provides a positive electrode plate, comprising a current collector and a positive electrode film layer located on at least one side of the current collector, the positive electrode film layer comprising a first region and a second region, the particle size distribution index of the active material in the first region being smaller than the particle size distribution index of the active material in the second region, wherein the particle size distribution index refers to the ratio of the standard deviation of the active material particle size to the average particle size, the first region refers to a region where the positive electrode film layer extends from a surface close to the current collector toward the positive electrode film layer for a distance of less than h1, and the second region refers to a region where the positive electrode film layer extends vertically from a surface close to the current collector toward the positive electrode film layer for a distance of from h1 to H, wherein H is the thickness of the positive electrode film layer, and h1 is less than H. Optionally, the difference between the particle size distribution index of the active material in the second region and the particle size distribution index of the active material in the first region is 0.08-0.80, and can optionally be 0.20-0.70.

[0009] The uniform distribution of active materials in the first region can achieve good slippage between active materials, significantly improving the flexibility of the positive electrode sheet after cold pressing. At the same time, the size grading of active materials in the second region is conducive to improving the compaction density of the positive electrode sheet, so that the positive electrode sheet maintains good flexibility while achieving a high compaction density, thereby maintaining the safety performance of the battery while improving the battery energy density.

[0010] In any embodiment, the particle size distribution index of the active material in the first region is 0.05 to 0.52.

[0011] The particle size distribution index of the active material in the first region is 0.05-0.52, indicating that the particle size of the active material in the first region is uniform, so that the electrode has good flexibility while having a high compaction density.

[0012] In any embodiment, the particle size distribution index of the active material in the second region is 0.60 to 0.82, and optionally 0.65 to 0.78.

[0013] The particle size distribution index of the active material in the second region is 0.60-0.82, indicating that the particle size dispersion of the active material in the second region is large and has a size gradation relationship, which is conducive to achieving tight filling to increase the compaction density and enhance the volume energy density of the battery.

[0014] In any embodiment, the average particle size of the active material in the first region is 150 nm to 2000 nm, optionally 300 nm to 2000 nm.

[0015] The particle size of the active material in the first region is moderate, with fewer large single crystal particles at the micron level, which causes less damage to the substrate. It can take into account both the battery capacity and the flexibility of the electrode, and achieve simultaneous optimization of the battery volume energy density and safety performance.

[0016] In any embodiment, in the second region, based on the total amount of active materials, the percentage of active materials having a particle size of 50 nm to 200 nm is 10% to 50%, optionally 10% to 25%.

[0017] The presence of small-particle active materials helps to achieve close packing of the second region, thereby improving the compaction density and energy density. In addition, the small particle size can reduce the diffusion distance of active ions and improve the power performance and low-temperature performance of the battery.

[0018] In any embodiment, in the second region, the cross-sectional area percentage of the active material having a particle size of not less than 1500 nm is 5%-25%, optionally 10%-25%, based on the total cross-sectional area of ​​the active material.

[0019] The above arrangement enables the active materials in the second region to produce size gradations and achieve close stacking, which is beneficial to improving the ultimate compaction density and volume energy density of the battery.

[0020] In any embodiment, the specific surface area of ​​the active material in the first region is 4-14 m 2 / g, optional 6-12m 2 / g.

[0021] There are fewer active materials with extremely small particle sizes in the first region, and the specific surface area of ​​the active materials is lower, which helps to reduce the amount of binder used, thereby increasing the active material loading, increasing the battery volume energy density, while improving the flexibility of the electrode and enhancing the safety performance of the battery.

[0022] In any embodiment, the mass percentage of the binder in the first region is lower than the mass percentage of the binder in the second region, the mass percentage of the binder in the first region is the ratio of the mass of the binder in the first region to the mass of the positive electrode film layer in the first region, and the mass percentage of the binder in the second region is the ratio of the mass of the binder in the second region to the mass of the positive electrode film layer in the second region.

[0023] The binder in the positive electrode active material layer is mostly crystalline or semi-crystalline, with a high elastic modulus. This high binder content makes the positive electrode film less susceptible to displacement or deformation under external forces. Consequently, when the electrode is bent, the binder is prone to intergranular cracks, which can cause brittle fracture of the positive electrode film. Reducing the binder mass percentage in the first region can further improve the electrode's flexibility.

[0024] In any embodiment, the mass percentage of the binder in the first region is 0.5%-2.5%, and optionally 1.5%-2%.

[0025] In any embodiment, the ratio of h1 to H satisfies 1:10 to 5:10, and can be optionally 2:10-4:10.

[0026] When the thickness ratio of the first region to the positive electrode film layer is within the above range, the energy density and safety of the battery can be improved simultaneously.

[0027] In any embodiment, the surface density of the positive electrode film layer is 350 mg / 1540.25 cm 2 -500mg / 1540.25cm 2 .

[0028] The positive electrode plate provided in this application is particularly suitable for thick electrode plate design.

[0029] In any embodiment, the active material in the first region and / or the second region comprises a polyanionic compound.

[0030] The positive electrode plate provided in the present application can effectively solve the problem of low compaction density of polyanion compounds while ensuring the flexibility of the plate, thereby effectively improving the volume energy density of the battery.

[0031] In any embodiment, the positive electrode film layer is prepared by one-time coating using a double-sided double-cavity coater.

[0032] The double-sided double-cavity coater's one-time coating preparation helps improve efficiency and increase production capacity.

[0033] A second aspect of the present application provides a secondary battery, comprising the positive electrode sheet of the first aspect.

[0034] The secondary battery provided in this application has both excellent volume energy density and safety performance.

[0035] A third aspect of the present application provides an electrical device comprising the secondary battery of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic diagram of a positive electrode sheet according to an embodiment of the present application;

[0037] FIG2 is a scanning electron microscope image of the positive electrode film layer of Example 1 of the present application;

[0038] FIG3 is a particle size diagram obtained by processing a scanning electron microscope image of a cross section of a polar fragment using Avizo 3D software according to an embodiment of the present application; (A) is a particle size diagram of the second region, and (B) is a particle size diagram of the first region.

[0039] FIG4 is a scanning electron microscope image of the first region in FIG2 ;

[0040] FIG5 is a scanning electron microscope image of the second region in FIG2 ;

[0041] FIG6 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0042] FIG7 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG6 ;

[0043] FIG8 is a schematic diagram of an electrical device according to an embodiment of the present application.

[0044] Reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate; 6 positive electrode sheet; 61 current collector; 62 positive electrode film layer; 621 first region; 622 second region. DETAILED DESCRIPTION

[0045] Below, the embodiments of the positive electrode sheet, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0046] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0049] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0051] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0052] Increasing the compaction density of electrode sheets is one of the most effective ways to increase battery energy density. However, this increased density can make the electrode sheets brittle, making them more susceptible to fracture during processing or recycling. Broken electrode sheets can easily puncture the separator, allowing direct contact between the positive and negative electrode sheets, resulting in a short circuit and potentially causing battery safety issues.

[0053] [Positive electrode]

[0054] Based on this, as shown in Figure 1, the present application provides a positive electrode plate 6, including a current collector 61 and a positive electrode film layer 62 located on at least one side of the current collector, the positive electrode film layer 62 including a first region 621 and a second region 622, the particle size distribution index of the active material in the first region 621 is smaller than the particle size distribution index of the active material in the second region 622, wherein the particle size distribution index refers to the ratio of the standard deviation of the active material particle size to the average particle size, the first region 621 refers to the region where the positive electrode film layer 62 extends vertically from the surface close to the current collector 61 to the positive electrode film layer 62 for a distance of less than h1, and the second region 622 refers to the region where the positive electrode film layer 62 extends vertically from the surface close to the current collector 61 to the positive electrode film layer 62 for a distance of h1 to H, wherein H is the thickness of the positive electrode film layer 62, h1 is less than H, optionally, the difference between the particle size distribution index of the active material in the second region and the particle size distribution index of the active material in the first region is 0.08-0.80, and can be optionally 0.20-0.70.

[0055] The structure of the positive electrode plate 6 can be characterized by any method known in the art. As an example, an argon ion beam is used to cut the plate perpendicular to its large surface, exposing a cross-section. The cross-section is then photographed using a scanning electron microscope, and the particle size of the active material in each layer is statistically analyzed. The scanning electron microscope image is shown in Figure 2.

[0056] The particle size of the positive electrode active material can be characterized using any method known in the art. As an example, the particle size of the positive electrode active material is calculated using the area equivalent circle diameter statistical method. As shown in Figure 3, a cross-sectional scanning electron micrograph of a positive electrode sheet is used to separate particles and count the area of ​​each particle using Avizo 3D software. The equivalent circle diameter is calculated based on the area of ​​each particle counted by the software, thereby obtaining the particle size value of each particle.

[0057] The particle size distribution index (PDI) has a well-known meaning in the art and can be measured using methods and instruments known in the art. The PDI is an important parameter for measuring particle size uniformity. The lower the PDI, the smaller the particle size deviation and the more uniform the particle size.

[0058] The particle size distribution index (PDI) is the standard deviation of the particle size divided by the average particle size.

[0059] Where σ is the standard deviation of particle size, x i is the particle size value, is the average particle size, n is the total number of particles counted, and the average particle size is the total particle size value divided by the total number of particles counted.

[0060] As an example, the positive electrode current collector 61 has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer 62 is provided on either or both of the two opposite surfaces of the positive electrode current collector 61 .

[0061] In some embodiments, the positive electrode current collector 61 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.).

[0062] In some embodiments, the thickness of the positive electrode current collector 61 is 10 μm-20 μm.

[0063] A positive electrode current collector 61 of a certain thickness can reduce the possibility of breakage of the positive electrode sheet and improve the safety performance of the battery.

[0064] As can be seen from Figures 3-5, the particle size distribution index of the active material in the first region 621 is smaller than the particle size distribution index of the active material in the second region 622, indicating that the particle size distribution of the active material in the first region 621 is more uniform than that in the second region 622. The uniform distribution of the active material in the first region 621 enables good slippage between the active materials, significantly improving the flexibility of the positive electrode sheet 6 after cold pressing. At the same time, the size gradation of the active material in the second region 621 helps to increase the compaction density of the positive electrode sheet 6, allowing the positive electrode sheet 6 to achieve a high compaction density while maintaining good flexibility, thereby improving the battery's energy density while maintaining battery safety.

[0065] In some embodiments, the difference between the particle size distribution index of the active material in the second region and the particle size distribution index of the active material in the first region is 0.08, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, or any value therebetween.

[0066] Controlling the difference in particle size distribution index within the above range can effectively increase the ultimate compaction density of the electrode, improve the flexibility of the electrode, and optimize the battery energy density.

[0067] In some embodiments, the particle size distribution index of the active material in the first region is 0.05 to 0.52.

[0068] In some embodiments, the particle size distribution index of the active material in the first region can be selected to be 0.52, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.1, 0.05, or any value therebetween.

[0069] The particle size distribution index of the active material in the first region is 0.05-0.52, indicating that the particle size of the active material in the first region is uniform, so that the electrode has good flexibility while having a high compaction density.

[0070] In some embodiments, the particle size distribution index of the active material in the second region is 0.60 to 0.82, and optionally 0.65 to 0.78.

[0071] In some embodiments, the particle size distribution index of the active material in the second region can be selected from 0.60, 0.62, 0.64, 0.65, 0.68, 0.70, 0.73, 0.76, 0.78, 0.82, or any value therebetween.

[0072] The particle size distribution index of the active material in the second region is 0.60-0.82, indicating that the particle size dispersion of the active material in the second region is large and has a size gradation relationship, which is conducive to achieving tight filling to increase the compaction density and enhance the volume energy density of the battery.

[0073] In some embodiments, the average particle size of the active material in the first region is 150 nm to 2000 nm, optionally 300 nm to 2000 nm.

[0074] In some embodiments, the average particle size of the active material in the first region can be selected to be 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm or any value therebetween.

[0075] The particle size of the active material in the first region is moderate, with fewer large single crystal particles at the micron level, which causes less damage to the substrate. It can take into account both the battery capacity and the flexibility of the electrode, and achieve simultaneous optimization of the battery volume energy density and safety performance.

[0076] In some embodiments, in the second region, based on the total amount of active materials, the percentage of active materials having a particle size of 50 nm-200 nm is 10% to 50%, optionally 10% to 25%.

[0077] In some embodiments, in the second region, based on the total amount of active materials, the percentage of active materials with a particle size of 50 nm-200 nm can be selected as 10%, 16%, 20%, 25%, 30%, 40%, 50% or any value therebetween.

[0078] The amount of active material with a particle size between 50 nm and 200 nm can be determined by any method known in the art. For example, the amount of active material with a particle size between 50 nm and 200 nm in a cross-sectional scanning electron micrograph can be calculated by dividing the amount of active material with a particle size between 50 nm and 200 nm by the total amount of active material determined.

[0079] The presence of small-particle active materials helps to achieve close packing of the second region, thereby improving the compaction density and energy density. In addition, the small particle size can reduce the diffusion distance of active ions and improve the power performance and low-temperature performance of the battery.

[0080] In some embodiments, in the second region, based on the total cross-sectional area of ​​the active material, the cross-sectional area percentage of the active material having a particle size of not less than 1500 nm is 5%-25%, optionally 10%-25%.

[0081] In some embodiments, in the second region, based on the total cross-sectional area of ​​the active material, the cross-sectional area percentage of the active material with a particle size of not less than 1500 nm can be selected as 5%, 10%, 15%, 19%, 20%, 25% or any value therebetween.

[0082] The cross-sectional area percentage of active material with a particle size of 1500 nm or greater can be determined by any method known in the art. For example, it can be calculated by dividing the cross-sectional area of ​​active material with a particle size of 1500 nm or greater in a cross-sectional scanning electron micrograph by the total area of ​​active material measured. The cross-sectional area of ​​the active material can be determined by statistically analyzing scanning electron micrographs of electrode cross sections using Avizo 3D software.

[0083] The above arrangement enables the active materials in the second region to produce size gradations and achieve close stacking, which is beneficial to improving the ultimate compaction density and volume energy density of the battery.

[0084] In some embodiments, the specific surface area of ​​the active material in the first region is 4-14 m 2 / g, optional 6-12m 2 / g.

[0085] In some embodiments, the specific surface area of ​​the active material in the first region may be 4 m 2 / g、6m 2 / g、8m 2 / g、10m 2 / g、12m 2 / g、14m 2 / g or any value therebetween.

[0086] There are fewer active materials with extremely small particle sizes in the first region, and the specific surface area of ​​the active materials is lower, which helps to reduce the amount of binder used, thereby increasing the active material loading, increasing the battery volume energy density, while improving the flexibility of the electrode and enhancing the safety performance of the battery.

[0087] In some embodiments, the mass percentage of the binder in the first region is lower than the mass percentage of the binder in the second region, the mass percentage of the binder in the first region is the ratio of the mass of the binder in the first region to the mass of the positive electrode film layer in the first region, and the mass percentage of the binder in the second region is the ratio of the mass of the binder in the second region to the mass of the positive electrode film layer in the second region.

[0088] In some embodiments, the binder includes a fluoropolymer, and the fluoropolymer includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0089] The binder in the positive electrode film is mostly crystalline or semi-crystalline, with a high elastic modulus, making it difficult to deform under external forces. Therefore, when a positive electrode sheet with a high binder content is bent, the positive electrode film is difficult to displace or deform under external forces. The binder is prone to intergranular cracks, which can cause brittle fracture in the active material layer. Reducing the binder mass percentage in the first region can further improve the flexibility of the electrode sheet.

[0090] In some embodiments, the mass percentage of the binder in the first region is 0.5%-2.5%, optionally 1.5%-2%.

[0091] In some embodiments, the mass percentage of the binder in the first region may be 0.5%, 1%, 1.5%, 2%, 2.5%, or any value therebetween.

[0092] In some embodiments, the ratio of h1 to H is 1:10 to 5:10, and can be optionally 2:10-4:10.

[0093] In some embodiments, the ratio of h1 to H can be 1:10, 2:10, 3:10, 4:10, 5:10, or any value therebetween.

[0094] When the ratio of the thickness h1 of the first region to the thickness H of the positive electrode film layer is within the above range, the energy density and safety of the battery can be improved simultaneously.

[0095] In some embodiments, the surface density of the positive electrode film layer is 350 mg / 1540.25 cm 2 -500mg / 1540.25cm 2 .

[0096] The positive electrode provided in this application is particularly suitable for thick electrode designs. The double-layer design of the electrode improves the problems of unstable cavity pressure, large weight fluctuations, and poor electrode uniformity during single-layer electrode coating, effectively improving the electrode quality.

[0097] Moreover, thick pole pieces are more prone to cracking than ordinary pole pieces. The cracking phenomenon refers to the compression of the inner film layer during hot pressing and shaping after the battery cell is wound and formed. The positive electrode active material on the inner film layer is squeezed and deformed in the restrained space, generating an extrusion force on the current collector and the outer film layer, causing the current collector or the outer film layer to be broken due to insufficient tension resistance, thereby generating cracks or pinholes, causing the pole piece to become light-transmitting. Due to the high extrusion force on the inner film layer of thick pole pieces, cracking is more common in thick pole pieces. The uniform distribution of active material in the first region can effectively disperse the extrusion force generated by the inner film layer, thereby reducing the probability of cracking.

[0098] In some embodiments, the active material in the first region and / or the second region comprises a polyanionic compound.

[0099] The general formula of polyanionic compounds is as follows: Ne x M y (A z O k ) m Z w

[0100] Among them, Ne includes at least one of Na and Li, M includes at least one of Fe, Mn, Ni, Co, Ti, V, Cr, V, Ca, Mg, and Al, A includes at least one of Si, S, and P, and Z includes at least one of F and OH, wherein 0.98≤x≤10, 0.94≤y≤10, 0.94≤z≤10, 2≤k≤10, 0.5≤m≤10, and 0<w≤10.

[0101] In some embodiments, the polyanionic compound is a complex salt containing an alkali metal whose crystal framework is constructed by a series of tetrahedral and polyhedral anionic units, and is mainly divided into olivine structure, NASICON structure, triclinic structure and mixed polyanionic compound materials.

[0102] In some embodiments, the polyanionic compound includes lithium iron phosphate, sodium iron phosphate, or sodium vanadium phosphate.

[0103] Polyanionic compounds have a stable structure, excellent safety performance, high thermal stability, and are readily available from inexpensive raw materials. Furthermore, during charge and discharge, the materials experience minimal volume change and structural rearrangement, resulting in a high operating voltage and excellent stability. However, the electronic conductivity of bulk polyanionic compounds is low, and carbon coating and particle nanocrystallization are generally required to improve both electrical and ionic conductivity. However, carbon-coated and nanocrystallized polyanionic compounds are difficult to process and compact tightly, making it difficult to effectively increase the electrode density and the battery's volumetric energy density.

[0104] The positive electrode plate provided in the present application can effectively solve the problem of low compaction density of polyanion compounds while ensuring the flexibility of the plate, thereby effectively improving the volume energy density of the battery.

[0105] In some embodiments, the positive electrode film layer is prepared by one-time coating using a double-sided double-cavity coater.

[0106] The double-sided double-cavity coater's one-time coating preparation helps improve efficiency and increase production capacity.

[0107] In some embodiments, the positive electrode film layer is prepared by multiple coating processes.

[0108] [Negative electrode]

[0109] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0110] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0113] In some embodiments, the negative electrode film layer may further 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).

[0114] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0117] [Electrolytes]

[0118] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0119] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0120] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0121] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0122] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0123] [Isolation film]

[0124] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0125] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0126] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0127] A second aspect of the present application provides a secondary battery, comprising a negative electrode sheet according to any embodiment, and / or a negative electrode sheet prepared by a preparation method according to any embodiment.

[0128] In some embodiments, the secondary battery includes an electrolyte, and the silicon interface layer is located between the electrolyte and the metal layer.

[0129] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0130] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0131] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG6 shows a secondary battery 5 with a square structure as an example.

[0132] In some embodiments, referring to Figure 7, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0133] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0134] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0135] Figure 8 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0136] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0137] Example

[0138] 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.

[0139] 1. Preparation method

[0140] Example 1

[0141] 1) Preparation of the first positive electrode slurry

[0142] 96.5 wt% of the first positive electrode active material, lithium iron phosphate (Dv50 of 800 nm, Dv10 of 150 nm, and Dv90 of 1800 nm), 1.0 wt% of a conductive agent (conductive carbon black), 2.0 wt% of a binder (polyvinylidene fluoride), and 0.5 wt% of a dispersant (polyvinyl pyrrolidone) were mixed, and then N-methylpyrrolidone was added and stirred to disperse and adjust the slurry viscosity to 8000-12000 mPa·s to prepare a first positive electrode slurry. Where Dv50 is the particle size corresponding to the 50% cumulative volume distribution percentage of the sample; Dv10 is the particle size corresponding to the 10% cumulative volume particle size distribution percentage of the sample; and Dv90 is the particle size corresponding to the 50% cumulative volume particle size distribution percentage of the sample.

[0143] 2) Preparation of the second positive electrode slurry

[0144] 96.5 wt% of the second positive electrode active material lithium iron phosphate (Dv50 is 1200 nm, Dv10 is 200 nm, Dv90 is 3500 nm), 1.0 wt% of the conductive agent (conductive carbon black), 2.0 wt% of the binder (polyvinylidene fluoride), and 0.5 wt% of the dispersant polyvinyl pyrrolidone were mixed, and then N-methylpyrrolidone was added and stirred and dispersed, and the slurry viscosity was adjusted to 8000-12000 mPa·s to prepare the second positive electrode slurry.

[0145] 3) Preparation of positive electrode sheet

[0146] The first positive electrode slurry and the second positive electrode slurry were coated with a double-sided double-cavity coating device at a rate of 100 mg / 1540.25 cm 2 、300mg / 1540.25cm 2 The coating weight (referring to the weight of dry material in the slurry) is coated on the aluminum foil at one time, wherein the first positive electrode slurry is coated on the lower layer close to the aluminum foil, which is the first active material layer, located in the first area of ​​the electrode; the second positive electrode slurry is coated on the upper layer, which is the second active material layer, located in the second area of ​​the electrode; after the double-sided coating is completed, the positive electrode sheet is prepared by drying, cold pressing, slitting, and the thickness of the aluminum foil is 15μm.

[0147] 4) Preparation of negative electrode sheet

[0148] 95 wt% of the negative electrode active material (artificial graphite), 1.0 wt% of the conductive agent (conductive carbon black), 2.0 wt% of the binder (styrene-butadiene rubber (SBR)) and 2.0 wt% of the thickener (sodium carboxymethyl cellulose (CMC)) were mixed, deionized water was added and stirred, and the mixture was dispersed to form a negative electrode slurry.

[0149] Then the negative electrode slurry is coated on the Cu foil. After both sides are completed, it is dried, cold pressed, cut and sliced ​​to prepare the negative electrode sheet.

[0150] 5) Battery Preparation

[0151] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to form a bare cell. The bare cell is then placed in an outer package, injected with the prepared electrolyte, and packaged, injected, formed, and vented. This completes the lithium-ion battery.

[0152] The preparation method of Examples 2-21 is similar to that of Example 1, but the particle size of each layer material, the binder content or the coating quality are changed to adjust the relevant parameters. The specific parameters are shown in Table 1.

[0153] The preparation method of Example 14 is basically the same as that of Example 1, except that the mass content of the positive electrode active material is 97 wt %, the mass content of the binder is 1.5%, and the proportion of the small-particle positive electrode active material is reduced to reduce the specific surface area of ​​the positive electrode active material;

[0154] The preparation method of Example 15 is basically the same as that of Example 1, except that the mass content of the positive electrode active material is 96.7wt%, the mass content of the binder is 1.8%, and the proportion of small-particle positive electrode active material is reduced to reduce the specific surface area of ​​the positive electrode active material.

[0155] The preparation method of Comparative Example 1 is substantially the same as that of Example 1, except that the components of the first active material layer and the second active material layer in Comparative Example 1 are the same as those of the first active material layer.

[0156] The preparation method of Comparative Example 2 is substantially the same as that of Example 1, except that the components of the first active material layer and the second active material layer in Comparative Example 2 are the same as the components of the second active material layer.

[0157] The preparation method of Comparative Example 3 is substantially the same as that of Example 1, except that the components of the first active material layer and the second active material layer in Comparative Example 3 are the same as those of the second active material layer and the first active material layer in Example 1, respectively.

[0158] 2. Test Method

[0159] 1) Average particle size and particle size distribution test method

[0160] The electrode was cut open perpendicularly to its large surface using an argon ion beam to expose the cross section, which was then photographed using a scanning electron microscope. The particle size of the active material was statistically analyzed using the length diameter statistical method, as shown in Figure 3.

[0161] The average particle size is the total particle size value divided by the total number of particles;

[0162] The particle size distribution index (PDI) is the standard deviation of the particle size divided by the average particle size.

[0163] Where σ is the standard deviation of particle size, x i is the particle size value, is the average particle size, and n is the total number of particles counted.

[0164] Since particles with a size of 0 < r ≤ 50 nm are prone to adhesion, there are large errors in statistics and it is difficult to clearly identify them individually. Therefore, during the particle size statistics process, particles with a size of 0 < r ≤ 50 nm are not included in the statistical range.

[0165] The amount content of active materials with a particle size of 50nm-200nm is calculated by dividing the amount of active materials with a particle size of 50nm-200nm in the cross section by the amount of the total active materials.

[0166] The cross-sectional area percentage of the active material having a particle size of not less than 1500 nm is calculated by dividing the cross-sectional area of ​​the active material having a particle size of not less than 1500 nm in the end surface by the cross-sectional area of ​​the total active material.

[0167] The cross-sectional area of ​​the active material was obtained by statistical analysis of the obtained electrode cross-sectional scanning electron microscopy images using Avizo 3D software.

[0168] 2) Specific surface area test method

[0169] The specific surface area was tested by gas adsorption method according to the GB / T19587-2017 test standard, as follows: the positive electrode active material was taken as a sample, the sample tube was immersed in liquid nitrogen at -196°C, and the adsorption amount of nitrogen on the solid surface at different pressures was measured at a relative pressure of 0.05-0.30. The monolayer adsorption amount of the sample was obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area of ​​the material.

[0170] 3) Ultimate compaction density test method

[0171] The double-sided coated electrode is cold-pressed by a roller press to test the elongation of the electrode after cold pressing, and the flexibility of the electrode after cold pressing is also evaluated.

[0172] By increasing the pressure of the roller press, pole pieces with different compaction densities will be obtained. As the pressure increases, the compaction density of the pole piece increases, the elongation of the pole piece increases, and the flexibility of the pole piece decreases. A pole piece with too high an elongation can easily cause the pole piece to warp, while a pole piece with too low flexibility can easily lead to brittle fracture. Therefore, the smaller of the compaction density corresponding to the pole piece elongation of 6‰ or the number of times the pole piece is folded three times is defined as the limit compaction density.

[0173] The compacted density is calculated by dividing the mass of the single-sided positive electrode film layer by the volume of the positive electrode film layer.

[0174] The test method for elongation is as follows:

[0175] Lay the electrode flat on a horizontal table and cut it into sections, with each electrode about 100 cm long; remove the copper foil at the edge of the electrode substrate, and be careful to keep the cut edge of the electrode parallel to the MD direction of the electrode (perpendicular to the direction of the cold pressing roller), ensuring that the electrode part is completely covered by the coating, and use a steel ruler to measure the length between the marking points at the same position of the length and width at the head and tail of the electrode, estimate it to 0.1mm, and record the length before cold pressing; after cold pressing by the cold press, record the length between the corresponding marking points after cold pressing, and use (length after cold pressing - length before cold pressing) / length before cold pressing as the elongation of the electrode.

[0176] The test method for the number of flexible folds is shown below.

[0177] 4) Compacted density is 2.5g / cm 3 The number of times the pole piece can be folded

[0178] The compacted density is 2.5 g / cm 3 The positive electrode sheet is cut into 20×100mm 2 Fold the test specimen in the forward direction, flatten it with a 2kg roller, unfold it and check against the light to see if there is any light transmittance. If there is no light transmittance, fold it in the reverse direction, flatten it with a 2kg roller, and check against the light again. Repeat this process until there is light transmittance. Record the number of folds. Repeat the test three times and take the average value as the reference data for the flexibility of the electrode.

[0179] 5) Battery volume energy density test method

[0180] The battery at the ultimate compaction density was left at rest at 25°C for 2 hours to ensure that the battery temperature was 25°C. After charging the battery at 0.33C at 25°C to the charge cut-off voltage, constant voltage charging was continued at the charge cut-off voltage until the current reached 0.05C and the charge was cut off (where C0 represents the rated capacity of the battery). After the battery was left at rest at 25°C for 1 hour, it was discharged at 0.33C at 25°C to the discharge cut-off voltage, and the total discharge energy of the battery was recorded as E0;

[0181] Measure the battery volume as V0;

[0182] Battery volume energy density = battery discharge energy E0 / battery volume M0.

[0183] 3. Analysis of test results of various embodiments and comparative examples

[0184] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Tables 1 to 4 below.

[0185] Table 1

[0186] Table 2

[0187] The positive electrode sheets in Examples 1-21 all include a current collector and a positive electrode film layer located on at least one side of the current collector. The positive electrode film layer includes a first region and a second region. The particle size distribution index of the active material in the first region is smaller than the particle size distribution index of the active material in the second region. The particle size distribution index refers to the ratio of the standard deviation of the active material particle size to the average particle size. The first region refers to a region of the positive electrode film layer extending perpendicularly from the surface of the current collector toward the positive electrode film layer for a distance of h1 or less. The second region refers to a region of the positive electrode film layer extending perpendicularly from the surface of the current collector toward the positive electrode film layer for a distance of h1 to H, where H is the thickness of the positive electrode film layer, and h1 is less than H. As can be seen from Figures 2-5, the positive electrode film layer includes a first region and a second region. The particle size of the active material in the first region is more uniform, while the deviation of the active material particle size in the second region is larger.

[0188] From the comparison of Examples 1-21 and Comparative Example 3, it can be seen that when the particle size distribution index of the active material in the first region is smaller than that of the active material in the second region and is 0.20-0.70, the flexibility of the electrode can be improved, the ultimate compaction density that can be achieved by the electrode can be improved, and the volume energy density of the battery can be increased.

[0189] Table 3

[0190] From the comparison between Examples 1-21 and Comparative Example 2, it can be seen that the positive electrode sheet with the above characteristics can improve the flexibility of the electrode sheet and increase the ultimate compaction density that can be achieved by the electrode sheet compared with the positive electrode sheet with a single component.

[0191] From the comparison between Examples 1-3, 20-21 and Comparative Examples 2 and 3, it can be seen that when the particle size distribution index of the active material in the first region is 0.05-0.52, the flexibility and ultimate compaction density of the electrode sheet increase significantly.

[0192] Table 4

[0193] From the comparison between Examples 1-21 and Comparative Example 1, it can be seen that the positive electrode sheet with the above characteristics can increase the ultimate compaction density that can be achieved by the electrode sheet compared to the positive electrode sheet with a single component, and improve the volume energy density of the battery cell.

[0194] From the comparison between Examples 1-3, 20-21 and Comparative Examples 1 and 3, it can be seen that when the particle size distribution index of the active material in the first region is 0.05-0.52, the ultimate compaction density of the electrode and the volume energy density of the battery increase significantly.

[0195] It can be seen from Examples 1 and 4-7 that when the average particle size of the active material in the first region is 150 nm-2000 nm, the battery has excellent flexibility, high ultimate compaction density and volume energy density.

[0196] From the comparison between Examples 5-7 and Example 4, it can be seen that when the average particle size of the active material in the first region is 300 nm-2000 nm, the flexibility, ultimate compaction density and volume energy density of the battery are simultaneously improved.

[0197] As shown in Examples 8-10, in the second region, when the percentage of active material with a particle size of 50 nm to 200 nm is 10% to 50% based on the total amount of active material, the battery has excellent flexibility, high ultimate compaction density, and high volumetric energy density. In the second region, when the percentage of active material with a particle size of 50 nm to 200 nm is 10% to 25% based on the total amount of active material, the battery's flexibility, ultimate compaction density, and volumetric energy density are even more significantly improved.

[0198] As shown in Examples 1 and 11-13, in the second region, when the cross-sectional area percentage of active material having a particle size of 1500 nm or greater, based on the total cross-sectional area of ​​the active material, is 5%-25%, the battery exhibits excellent flexibility, high ultimate compaction density, and high volumetric energy density. In the second region, when the cross-sectional area percentage of active material having a particle size of 1500 nm or greater, based on the total cross-sectional area of ​​the active material, is 10%-25%, the battery's flexibility, ultimate compaction density, and volumetric energy density are even more significantly improved.

[0199] It can be seen from Examples 1 and 14-15 that the specific surface area of ​​the active material in the first region is low, so that the amount of binder used in the first region can be reduced compared to the amount of binder used in the second region, thereby improving the flexibility and ultimate compaction density of the electrode and increasing the volume energy density of the battery.

[0200] As shown in Examples 1 and 16-19, when the ratio of the thickness of the first region to the thickness of the positive electrode film is 1:10 to 5:10, the battery exhibits excellent flexibility, high ultimate compaction density, and high volumetric energy density. When the ratio of the thickness of the first region h1 to the thickness of the positive electrode film is 2:10-4:10, the battery's flexibility, ultimate compaction density, and volumetric energy density are even more significantly improved.

[0201] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that: It includes a current collector and a positive electrode film layer located on at least one side of the current collector, the positive electrode film layer includes a first region and a second region, the particle size distribution index of the active material in the first region is smaller than the particle size distribution index of the active material in the second region, wherein the particle size distribution index refers to the ratio of the standard deviation of the active material particle size to the average particle size, the first region refers to the region where the positive electrode film layer extends vertically from the surface close to the current collector to the positive electrode film layer within a distance of h1, and the second region refers to the region where the positive electrode film layer extends vertically from the surface close to the current collector to the positive electrode film layer for a distance of h1 to H, wherein H is the thickness of the positive electrode film layer, and h1 is less than H. Optionally, the difference between the particle size distribution index of the active material in the second region and the particle size distribution index of the active material in the first region is 0.08-0.80, and can be optionally 0.20-0.

70.

2. The positive electrode sheet according to claim 1, characterized in that: The particle size distribution index of the active material in the first region is 0.05 to 0.

52.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The particle size distribution index of the active material in the second region is 0.60 to 0.82, and can be optionally 0.65 to 0.

78.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The average particle size of the active material in the first region is 150 nm-2000 nm, and can be optionally 300 nm-2000 nm.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: In the second region, based on the total amount of active materials, the percentage of active materials with a particle size of 50 nm-200 nm is 10% to 50%, and can be optionally 10%-25%.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: In the second region, based on the total cross-sectional area of ​​the active material, the cross-sectional area percentage of the active material having a particle size of not less than 1500 nm is 5%-25%, and optionally 10%-25%.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The specific surface area of ​​the active material in the first region is 4-14 m 2 / g, optional 6-12m 2 / g.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The mass percentage of the binder in the first region is lower than the mass percentage of the binder in the second region. The mass percentage of the binder in the first region is the ratio of the mass of the binder in the first region to the mass of the positive electrode film layer in the first region. The mass percentage of the binder in the second region is the ratio of the mass of the binder in the second region to the mass of the positive electrode film layer in the second region.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The mass percentage of the binder in the first region is 0.5%-2.5%, and can be optionally 1.5%-2%.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The ratio of h1 to H is 1:10 to 5:10, and can be optionally 2:10-4:

10.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The surface density of the positive electrode film layer is 350 mg / 1540.25 cm 2 -500mg / 1540.25cm 2 .

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The active material in the first region and / or the second region includes a polyanionic compound.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode film layer is prepared by one-time coating using a double-sided double-cavity coating machine.

14. A secondary battery, characterized in that: A positive electrode sheet comprising any one of claims 1 to 13.

15. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 14.

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