Battery cell, battery apparatus, and electric apparatus

Abstract

The present application discloses a battery cell, a battery apparatus, and an electric apparatus. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet comprises a positive electrode composite current collector, a first positive electrode active layer, and a second positive electrode active layer, wherein the first positive electrode active layer is arranged on at least one side of the positive electrode composite current collector, the first positive electrode active layer is a water-soluble film layer, the second positive electrode active layer is arranged on the side of the first positive electrode active layer facing away from the positive electrode composite current collector, and the second positive electrode active layer is an oil-soluble film layer. By means of the described arrangement, the first positive electrode active layer can cover burrs, and can also cover a reverse curl of a metal layer generated after nail penetration of the positive electrode composite current collector, while the probability of the first positive electrode active layer being corroded by the second positive electrode active layer to form bottom voids is reduced, thereby improving the safety performance of the battery cell.

Description

Battery cells, battery packs, electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510127446.9, filed on January 27, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to battery cells, battery devices, and electrical devices. Background Technology

[0004] Lithium-ion batteries are widely used in consumer electronics, energy storage, and power applications due to their advantages such as high output voltage, high energy density, high power density, long cycle life, and good environmental friendliness. With continuous technological advancements, lithium-ion batteries will continue to play a vital role and drive innovation in energy storage technologies. For lithium-ion batteries, safety performance is a key factor influencing their development.

[0005] Lithium-ion batteries consist of a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the current collector. Currently, metal foil current collectors or composite current collectors are commonly used for the positive electrode. When using a composite current collector, the metal layer of the composite current collector is relatively thin during battery cell insertion, resulting in smaller burrs. However, it is prone to reverse curling, posing a certain risk of battery short circuit. Summary of the Invention

[0006] This application provides a battery cell, a battery device, and an electrical device to improve the safety performance of the battery cell.

[0007] To solve the above-mentioned technical problems, the first aspect of this application provides a battery cell, which includes a positive electrode, a negative electrode and an electrolyte; the positive electrode includes a positive electrode composite current collector, a first positive electrode active layer and a second positive electrode active layer, the first positive electrode active layer is disposed on at least one side of the positive electrode composite current collector 231, the first positive electrode active layer is a water-soluble film layer, and the second positive electrode active layer is disposed on the side of the first positive electrode active layer away from the positive electrode composite current collector, the second positive electrode active layer is an oil-soluble film layer.

[0008] By setting the first positive electrode active layer as a water-soluble film layer and the second positive electrode active layer as an oil-soluble film layer, the properties of the second positive electrode active layer are different from those of the first positive electrode active layer. When the second positive electrode active layer is coated on the side of the first positive electrode active layer away from the positive electrode composite current collector to form the second positive electrode active layer, the solvent in the slurry of the second positive electrode active layer has no dissolving effect on the first positive electrode active layer, reducing the probability of the first positive electrode active layer forming bottom voids. This maintains the good coverage of the metal burrs and reverse curling of the metal layer generated after the first positive electrode active layer is needled by the positive electrode composite current collector, making it difficult for the metal burrs or reverse curling of the metal layer to penetrate the separator and contact the negative electrode sheet. This greatly reduces the probability of the metal layer of the positive electrode composite current collector contacting the negative electrode sheet, thus improving the safety performance of the battery cell.

[0009] In one embodiment, the first positive electrode active layer includes a water-soluble binder; the second positive electrode active layer includes an oil-soluble binder.

[0010] By setting the first positive electrode active layer to include a water-soluble binder, which has good water solubility, the first positive electrode active layer maintains good water solubility. By setting the second positive electrode active material to include an oil-soluble binder, which has good solubility or dispersion in oily solvents, the second positive electrode active material maintains good solubility or dispersion in oily solvents. By setting the first positive electrode active layer as a water-soluble film layer and the second positive electrode active layer as an oil-soluble film layer, the safety performance of the battery cell is improved, and the wrinkling problem of the positive electrode composite current collector caused by drying during the coating process of forming the first and second positive electrode active layers is also improved.

[0011] In one embodiment, the water-soluble binder accounts for a greater mass percentage in the first positive electrode active layer than the oil-soluble binder accounts for in the second positive electrode active layer.

[0012] By setting the mass ratio of water-soluble binder in the first positive electrode active layer to be greater than that of oil-soluble binder in the second positive electrode active layer, the water-soluble binder in the first positive electrode active layer has a relatively large proportion. The larger binder in the first positive electrode active layer can better cover burrs and prevent the metal layer from curling in the opposite direction, which greatly reduces the probability of the metal layer of the positive electrode composite current collector coming into contact with the negative electrode sheet, thus improving the safety performance of the battery cell.

[0013] In one embodiment, the water-soluble binder accounts for 3.9%-19% of the mass of the first positive electrode active layer; and / or, the oil-soluble binder accounts for 1.5%-5% of the mass of the second positive electrode active layer.

[0014] By setting the mass ratio of water-soluble binder and / or oil-soluble binder as described above, the mass ratio of water-soluble binder in the first positive electrode active layer is greater than that of oil-soluble binder in the second positive electrode active layer. The relatively large proportion of water-soluble binder in the first positive electrode active layer can better cover burrs and prevent the metal layer from curling in the opposite direction, which is beneficial to improving the safety performance of the battery cell.

[0015] In one embodiment, the water-soluble binder includes one or more of polyacrylic acid (PAA) and its derivatives, polyvinyl alcohol and its derivatives; and / or, the oil-soluble binder includes one or more of polyvinylidene fluoride (PVDF) and its derivatives, polyimide and its derivatives.

[0016] By selecting one or more of polyacrylic acid and its derivatives, and polyvinyl alcohol and its derivatives as water-soluble binders, not only can the water-soluble properties of the binders be maintained, but they also have lower thermal shrinkage stress. This helps reduce the thermal shrinkage stress generated during the drying process of the slurry forming the first positive electrode active layer, thus reducing the impact of the thermal shrinkage stress generated during the drying process of the first positive electrode active layer on the positive electrode composite current collector, and effectively improving the coating wrinkling problem. Similarly, by selecting one or more of polyvinylidene fluoride and its derivatives, and polyimide and its derivatives as oil-soluble binders, not only can the oil-soluble properties of the binders be maintained, but they also have lower thermal shrinkage stress. This helps reduce the thermal shrinkage stress generated during the drying process of the slurry forming the second positive electrode active layer, thus reducing the impact of the thermal shrinkage stress generated during the drying process of the second positive electrode active layer on the positive electrode composite current collector, and effectively improving the coating wrinkling problem.

[0017] In one embodiment, the first positive electrode active layer includes a first dispersant, which includes one or more of polyacrylamide (PAM) and its derivatives, carboxymethyl cellulose (CMC) and its derivatives; and / or, the second positive electrode active layer includes a second dispersant, which includes one or more of polyacrylamide (PAM) and its derivatives, polyvinylpyrrolidone (PVP) and its derivatives.

[0018] By selecting one or more of polyacrylamide (PAM) and its derivatives, and carboxymethyl cellulose (CMC) and its derivatives as the first dispersant, the dispersibility of water-based binders is improved, reducing the phenomenon of local agglomeration of the material. Simultaneously, the shorter molecular chain length of the first dispersant results in more suitable cross-linking between molecules, leading to lower thermal shrinkage stress. The first dispersant can reduce the surface tension of the slurry, mitigating the impact of thermal shrinkage stress generated during the drying process of the first positive electrode active layer on the positive electrode composite current collector, effectively improving the coating wrinkling problem. Similarly, by selecting one or more of polyacrylamide (PAM) and its derivatives, and polyvinylpyrrolidone (PVP) and its derivatives as the second dispersant, the dispersibility of oil-based binders is improved, reducing the phenomenon of local agglomeration of the material. Furthermore, the shorter molecular chain length of the second dispersant results in more suitable cross-linking between molecules, leading to lower thermal shrinkage stress. This reduces the impact of thermal shrinkage stress generated during the drying process of the second positive electrode active layer on the positive electrode composite current collector, effectively improving the coating wrinkling problem.

[0019] In one embodiment, the thickness of the first positive electrode active layer is less than the thickness of the second positive electrode active layer.

[0020] By setting the thickness of the first positive electrode active layer to be smaller than that of the second positive electrode active layer, the relatively smaller thickness of the first positive electrode active layer, which is closer to the positive electrode composite current collector, results in a smaller amount of solvent evaporation per cycle. This makes the first positive electrode active layer easier to dry, reducing the impact of drying on the positive electrode composite current collector and improving coating wrinkling. Furthermore, the first positive electrode active layer primarily functions to cover burrs and prevent the metal layer from curling in the opposite direction, while the second positive electrode active layer mainly provides capacity to the battery cell. Setting the thickness of the second positive electrode active layer to be thicker is beneficial for the battery cell to have a higher energy density.

[0021] In one embodiment, the thickness of the first positive electrode active layer is 5 micrometers to 30 micrometers; and / or, the thickness of the second positive electrode active layer is 50 micrometers to 150 micrometers.

[0022] By setting the thickness of the first positive electrode active layer and / or the second positive electrode active layer as described above, the thickness of the first positive electrode active layer, which is closer to the positive electrode composite current collector, is relatively smaller. This results in a smaller amount of solvent evaporation per cycle, making the first positive electrode active layer easier to dry. This reduces the impact on the positive electrode composite current collector during the drying process and improves the coating wrinkling phenomenon. Furthermore, by setting the thickness of the first positive electrode active layer and / or the second positive electrode active layer as described above, the battery cell achieves a higher energy density.

[0023] In one embodiment, the first positive electrode active layer includes a first active material, and the second positive electrode active layer includes a second active material, wherein the particle size of the first active material is smaller than the particle size of the second active material.

[0024] Because the thickness of the first positive electrode active layer is less than that of the second positive electrode active layer, the first positive electrode active layer is relatively thinner, while the second positive electrode active layer is relatively thicker. For the relatively thinner first positive electrode active layer, the particle size of the selected first active material is smaller, maintaining the uniformity of the first active material's coverage of the positive electrode composite current collector surface, which is beneficial for improving the performance of the battery cell. For the relatively thicker second positive electrode active layer, the particle size of the selected second active material is larger, reducing the amount of solvent evaporation during the drying process, making the second positive electrode active layer easier to dry, reducing the impact of drying on the positive electrode composite current collector, and improving coating wrinkling; using a second active material with a larger particle size can reduce the surface tension during slurry evaporation, reducing the probability of positive electrode sheet cracking.

[0025] In one embodiment, the first active material comprises lithium iron phosphate, and the particle size Dv50 of the first active material is 0.5 micrometers to 1.1 micrometers; and / or, the second active material comprises lithium iron phosphate, and the particle size Dv50 of the second active material is 1.5 micrometers to 3 micrometers.

[0026] By setting the particle size of the first active material and / or the second active material as described above, the particle size of the first active material in the thinner first positive electrode active layer is relatively small, maintaining the uniformity of the first active material's coverage of the positive electrode composite current collector surface; the particle size of the second active material in the thicker second positive electrode active layer is relatively large, reducing the amount of solvent evaporation during the drying process, making the second positive electrode active layer easier to dry, and improving coating wrinkling.

[0027] In one embodiment, the mass percentage of the first active material in the first positive electrode active layer is less than the mass percentage of the second active material in the second positive electrode active layer.

[0028] By setting the mass ratio of the first active material in the first positive electrode active layer and / or the mass ratio of the second active material in the second positive electrode active layer as described above, the relatively thick second positive electrode active layer contains a relatively large amount of second active material, which is beneficial for the battery cell to have a higher energy density and improve the performance of the battery cell.

[0029] In one embodiment, the first active material accounts for 70%-90% of the mass of the first positive electrode active layer; and / or, the second active material accounts for 90%-97% of the mass of the second positive electrode active layer.

[0030] By setting the mass ratio of the first active material in the first positive electrode active layer and / or the mass ratio of the second active material in the second positive electrode active layer as described above, the mass ratio of the first active material in the first positive electrode active layer is less than the mass ratio of the second active material in the second positive electrode active layer. The relatively thick second positive electrode active layer contains a relatively large amount of second active material, which is beneficial for the battery cell to have a higher energy density and improve the performance of the battery cell.

[0031] In one embodiment, the first active material is the same as the second active material.

[0032] By setting the first active material and the second active material to be the same, the same active material has similar electrochemical characteristics and reaction kinetics. The interface between the first positive electrode active layer and the second positive electrode active layer is relatively stable, maintaining a good electrochemical environment inside the positive electrode sheet and maintaining the stability of the battery cell performance.

[0033] In one embodiment, the first positive electrode active layer includes a first conductive material, and the second positive electrode active layer includes a second conductive material, wherein the mass percentage of the first conductive material in the first positive electrode active layer is greater than the mass percentage of the second conductive material in the second positive electrode active layer.

[0034] By setting the mass ratio of the first conductive material in the first positive electrode active layer and / or the mass ratio of the second conductive material in the second positive electrode active layer as described above, the first positive electrode active layer, which is closer to the positive electrode composite current collector, contains a relatively large amount of the first conductive material. This allows for the construction of a denser and more efficient electron conduction network, forming a good conductive channel between the active material and the positive electrode composite current collector, reducing the internal resistance of electron transport, improving the conductivity of the positive electrode sheet, and ultimately enhancing the performance of the battery cell.

[0035] In one embodiment, the first conductive material accounts for 5%-20% of the mass of the first positive electrode active layer; and / or, the second conductive material accounts for 1%-10% of the mass of the second positive electrode active layer.

[0036] By setting the mass ratio of the first conductive material in the first positive electrode active layer and / or the mass ratio of the second conductive material in the second positive electrode active layer as described above, the first positive electrode active layer, which is closer to the positive electrode composite current collector, contains a relatively large amount of the first conductive material. This allows for the construction of a denser and more efficient electron conduction network, forming a good conductive channel between the active material and the positive electrode composite current collector, reducing the internal resistance of electron transport, improving the conductivity of the positive electrode sheet, and ultimately enhancing the performance of the battery cell.

[0037] In one embodiment, the positive electrode composite current collector includes a support layer and a conductive layer located on at least one side of the support layer.

[0038] The support layer provides the basic support structure, ensuring that the positive electrode composite current collector maintains a stable shape during battery charging and discharging. The conductive layer has good conductivity, enabling it to efficiently collect and transport electrons generated inside the battery.

[0039] In one embodiment, the support layer includes at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene; the conductive layer includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0040] By designing the support layer using the aforementioned materials, the support layer possesses good flexibility and a certain degree of strength. This allows the positive electrode composite current collector to withstand a certain degree of tensile, bending, and compressive forces during battery manufacturing and use, making it less prone to breakage or damage and contributing to the stability of the battery. Furthermore, by designing the conductive layer to include the aforementioned materials, the positive electrode current collector exhibits excellent conductivity, enabling rapid and smooth electron transport within the battery.

[0041] A second aspect of this application provides a battery device comprising a battery cell as described in any of the foregoing embodiments. The battery device has at least the same advantages as the described battery cell.

[0042] A third aspect of this application provides an electrical device comprising a battery cell or a battery device as described above. The electrical device has at least the same advantages as the battery cell or battery device described above.

[0043] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 is a schematic diagram of the pin insertion of the positive electrode composite current collector;

[0046] Figure 2 is an exploded structural diagram of a battery cell provided in an embodiment of this application;

[0047] Figure 3 is a schematic diagram of the structure of the positive electrode sheet provided in an embodiment of this application;

[0048] Figure 4 is a schematic diagram of the needle-punched structure of the positive electrode sheet shown in Figure 3;

[0049] Figure 5 is a SEM diagram showing the dissolution of the underlying layer in the related technology;

[0050] Figure 6 is a well-preserved SEM image of the bottom layer of the first positive electrode active layer and the second positive electrode active layer provided in the embodiments of this application;

[0051] Figure 7 is a SEM image of the dispersion state of the slurry in the related technology;

[0052] Figure 8 is a SEM image of the dispersion state of the slurry under the action of PAM in the embodiment of this application.

[0053] Figure 9 is a SEM image of the first positive electrode active layer and the second positive electrode active layer provided in the embodiment of this application;

[0054] Figure 10 is another SEM image of the first positive electrode active layer and the second positive electrode active layer provided in the embodiments of this application;

[0055] Figure 11 is a schematic diagram of the battery device provided in an embodiment of this application;

[0056] Figure 12 is a structural schematic diagram of the vehicle provided in an embodiment of this application.

[0057] Label Explanation:

[0058] Battery device 100, housing 10, first part 11, second part 12, battery cell 20, end cap 21, electrode terminal 21a, housing 22, cell assembly 23, tab 23a, positive electrode composite current collector 231, first positive electrode active layer 232, second positive electrode active layer 233, controller 200, motor 300, vehicle 1000. Embodiments of the present invention

[0059] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0061] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

[0062] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0063] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0064] Quantities, ratios, and other numerical values ​​are presented in range format in this document. It should be understood that this range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0065] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or in parallel, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) may be performed simultaneously in parallel. For example, the method may also 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 steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0066] To ensure the safety of individual battery cells, a nail penetration test is typically performed. Currently, metal foil current collectors or positive electrode composite current collectors are commonly used. When using metal foil current collectors, large burrs are easily generated during nail penetration, causing internal short circuits and potentially leading to thermal runaway. When using positive electrode composite current collectors, the polymer substrate in the middle of the current collector softens upon heating during nail penetration, which helps to block the penetration gap, forming an open circuit and preventing full-scale thermal runaway. This significantly reduces the short-circuit current and effectively reduces safety issues such as fires and explosions caused by short circuits. Therefore, positive electrode composite current collectors offer better safety performance for individual battery cells compared to metal foil current collectors.

[0067] When inserting a battery cell through a stud, the metal layer of the positive electrode composite current collector is relatively thin, resulting in smaller burrs. However, the burrs are prone to curling in the opposite direction, posing a certain risk of short circuit (see Figure 1, which is a schematic diagram of inserting the positive electrode composite current collector through a stud).

[0068] In view of this, embodiments of this application provide a battery cell, a battery device, and an electrical device to improve the safety performance of the battery cell.

[0069] Please refer to Figure 2, which is an exploded structural diagram of a battery cell provided in an embodiment of this application.

[0070] The battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0071] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. In any case, the shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that end cap 21 is less prone to deformation under pressure and impact, enabling battery cell 20 to have higher structural strength and improved stability.

[0072] The end cap 21 may be provided with functional components such as electrode terminals 21a. The electrode terminals 21a can be used to electrically connect with the cell assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 may also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold.

[0073] The end cap 21 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special restrictions on this.

[0074] In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0075] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0076] The cell assembly 23 is the component in the battery cell 20 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 includes a positive electrode, a negative electrode, and an electrolyte. The positive and negative electrode sheets are wound or stacked to form the cell assembly 23. The portions of the positive and negative electrode sheets containing active material constitute the main body of the cell assembly 23, while the portions of the positive and negative electrode sheets without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery device 100, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals 21a to form a current circuit.

[0077] In one embodiment, the electrolyte may be one of a solid electrolyte, a semi-solid electrolyte, or a liquid electrolyte (i.e., an electrolyte solution).

[0078] In one embodiment, the electrolyte is a liquid electrolyte, and the cell assembly 23 further includes a separator located between the positive electrode and the negative electrode.

[0079] Please refer to Figures 3 and 4. Figure 3 is a schematic diagram of the structure of the positive electrode sheet provided in the embodiment of this application, and Figure 4 is a schematic diagram of the needle-punched structure of the positive electrode sheet shown in Figure 3.

[0080] In this embodiment of the application, the positive electrode sheet includes a positive electrode composite current collector 231, a first positive electrode active layer 232 and a second positive electrode active layer 233. The first positive electrode active layer 232 is disposed on at least one side of the positive electrode composite current collector 231 and is a water-soluble film layer. The second positive electrode active layer 233 is disposed on the side of the first positive electrode active layer 232 away from the positive electrode composite current collector 231 and is an oil-soluble film layer.

[0081] The positive electrode composite current collector 231 is composed of two or more different materials combined through a specific process, integrating the advantages of multiple materials and possessing excellent electron collection capabilities. Exemplarily, the positive electrode composite current collector 231 includes a support layer and a conductive layer located on at least one side of the support layer. The support layer provides a basic support structure, ensuring that the positive electrode composite current collector maintains a stable shape during battery charging and discharging. The conductive layer has good conductivity, enabling efficient collection and transfer of electrons generated inside the battery. By incorporating the positive electrode composite current collector 231 into the positive electrode sheet, the metal layer used in the positive electrode composite current collector 231 is thinner than that of a metal foil current collector, which helps to reduce the size of metal burrs generated after needle punching.

[0082] A water-soluble membrane refers to a membrane material that exhibits good solubility or dispersibility in water. It is formed by dispersing the material of the first positive electrode active layer 232 in water to form an aqueous slurry and coating it. Water-soluble membranes have a strong affinity for water; this affinity is not only reflected in the material's ability to dissolve or disperse in water, but also in its ability to maintain its structure and performance in the electrolyte, ensuring smooth ion transport.

[0083] An oil-soluble membrane refers to a membrane material that exhibits good solubility or dispersibility in an oily solution. It is formed by dispersing the material of the second positive electrode active layer 233 in an oily solution to create an oily slurry, which is then coated onto the membrane. The oil-soluble membrane maintains its structure and properties in the electrolyte, ensuring smooth ion transport.

[0084] The first positive electrode active layer 232 disposed on at least one side of the positive electrode composite current collector 231 can cover the metal burrs generated after the positive electrode composite current collector 231 is needled, and can also cover the reverse curling of the metal layer generated after the positive electrode composite current collector 231 is needled.

[0085] By setting the first positive electrode active layer 232 as a water-soluble film layer and the second positive electrode active layer 233 as an oil-soluble film layer, the properties of the second positive electrode active layer 233 are different from those of the first positive electrode active layer 232. When the second positive electrode active layer 233 is coated on the side of the first positive electrode active layer 232 away from the positive electrode composite current collector 231 to form the second positive electrode active layer 233, the solvent in the slurry of the second positive electrode active layer has no dissolving effect on the first positive electrode active layer. This greatly reduces the probability that the first positive electrode active layer 232 will be corroded by the second positive electrode active layer 233 to form bottom voids. It also maintains the good coverage of the metal burrs and reverse curling of the metal layer generated after the first positive electrode active layer 232 is punctured by the positive electrode composite current collector 231. This makes it difficult for the metal burrs or reverse curling of the metal layer to penetrate the separator and contact the negative electrode sheet. This greatly reduces the probability that the metal layer of the positive electrode composite current collector 231 will contact the negative electrode sheet, thus improving the safety performance of the battery cell.

[0086] Please refer to Figures 5 and 6. Figure 5 is a SEM diagram showing the dissolution of the bottom layer in related technologies, and Figure 6 is a SEM diagram showing the good bottom layer of the first positive electrode active layer and the second positive electrode active layer provided in the embodiments of this application.

[0087] As shown in Figure 5, in related technologies, two active layers are formed on the surface of the current collector. Both active layers are oil-soluble films. Scanning electron microscopy (SEM) revealed that the surface of the active layer closer to the current collector exhibits dissolution. As shown in Figure 6, the positive electrode composite current collector 231 provided in this application embodiment has a first positive electrode active layer 232 and a second positive electrode active layer 233 sequentially disposed on one side. The first positive electrode active layer 232 is a water-soluble film, and the second positive electrode active layer 233 is an oil-soluble film. The properties of the first positive electrode active layer 232 and the second positive electrode active layer 233 are different. The first positive electrode active layer 232 does not exhibit dissolution, maintaining good coverage of the metal burrs and reverse curling of the metal layer generated after the positive electrode composite current collector 231 is punctured, which is beneficial to improving the safety performance of the battery cell.

[0088] In addition, for positive electrode sheets of the same thickness, the active layer on one side of the positive electrode composite current collector 231 is divided into a first positive electrode active layer 232 and a second positive electrode active layer 233, which reduces the thickness of a single drying process, reduces the amount of solvent evaporation per drying process, and improves the wrinkling problem of the positive electrode composite current collector 231 caused by drying during the coating process of forming the first positive electrode active layer 232 and the second positive electrode active layer 233.

[0089] The test method for the second positive electrode active layer 233 being an oil-soluble film layer is as follows: after coating and drying, the positive electrode sheet is immersed in N-methylpyrrolidone solution (NMP). It is found that there are obvious corrosion holes on the surface of the electrode sheet, indicating that there is dissolution behavior, which shows that the second positive electrode active layer 233 on the surface of the positive electrode sheet is an oil-soluble film layer.

[0090] The test method for determining whether the first positive electrode active layer 232 is a water-soluble film layer is as follows: The electrode sheet coated only with the first active slurry is immersed in an NMP solution. If there are no obvious surface corrosion pores and the dissolution phenomenon is not obvious, it indicates that the first positive electrode active layer 232 is a water-soluble film layer. The first active slurry is dried to form the first positive electrode active layer 232. Alternatively, the coated and dried positive electrode sheet is immersed in an N-methylpyrrolidone solution (NMP) for a long time. If obvious corrosion pores are found on the electrode surface, indicating dissolution behavior, the immersion time is further extended until the depth of the corrosion pores basically stops increasing. The cross-sectional state of the positive electrode sheet after immersion in NMP is observed. If the first positive electrode active layer 232 in the inner layer of the positive electrode sheet has no obvious corrosion pores, it indicates that the first positive electrode active layer 232 is a water-soluble film layer.

[0091] The test method for the current collector of the positive electrode sheet as the positive electrode composite current collector 231 is as follows: obtain the cross-section of the positive electrode sheet, and observe that there is a difference in the contrast between the intermediate layer and the surface layer of the composite current collector 231.

[0092] In one embodiment, a first positive electrode active layer 232 is disposed on the surface of the positive electrode composite current collector 231, and a second positive electrode active layer 233 is disposed on the surface of the first positive electrode active layer 232 away from the surface of the positive electrode composite current collector 231.

[0093] In one embodiment, a first positive electrode active layer 232 and a second positive electrode active layer 233 are respectively stacked on two opposing surfaces of the positive electrode composite current collector 231.

[0094] In one embodiment, the first positive electrode active layer 232 includes a water-soluble binder; the second positive electrode active layer 233 includes an oil-soluble binder.

[0095] Water-soluble binders refer to binders that exhibit good solubility or dispersibility in water. Oil-soluble binders refer to binders that exhibit good solubility or dispersibility in oily solutions (e.g., NMP, N-methylpyrrolidone).

[0096] By providing a water-soluble binder for the first positive electrode active layer 232, which has good water solubility, the first positive electrode active layer 232 maintains good water solubility. By providing an oil-soluble binder for the second positive electrode active material, which has good solubility or dispersion properties in oily solvents, the second positive electrode active material maintains good solubility or dispersion properties in oily solvents. By providing a water-soluble film layer for the first positive electrode active layer 232 and an oil-soluble film layer for the second positive electrode active layer 233, the safety performance of the battery cell is improved. At the same time, the wrinkling problem of the positive electrode composite current collector 231 caused by drying during the coating process of forming the first positive electrode active layer 232 and the second positive electrode active layer 233 is improved.

[0097] In one embodiment, the water-soluble binder has a greater mass percentage in the first positive electrode active layer 232 than the oil-soluble binder has in the second positive electrode active layer 233.

[0098] The mass percentage of the water-soluble binder in the first positive electrode active layer 232 refers to the ratio of the mass of the water-soluble binder to the total mass of the first positive electrode active layer 232 among all the substances constituting the first positive electrode active layer 232. The mass percentage of the oil-soluble binder in the second positive electrode active layer 233 refers to the ratio of the mass of the oil-soluble binder to the total mass of the second positive electrode active layer 233 among all the substances constituting the second positive electrode active layer 233.

[0099] By setting the mass ratio of water-soluble binder in the first positive electrode active layer 232 to be greater than that of oil-soluble binder in the second positive electrode active layer 233, the water-soluble binder in the first positive electrode active layer 232 has a relatively large proportion. The larger binder in the first positive electrode active layer 232 can better cover burrs and prevent the metal layer from curling in the opposite direction, which greatly reduces the probability of the metal layer of the positive electrode composite current collector 231 coming into contact with the negative electrode sheet, thus improving the safety performance of the battery cell.

[0100] In one embodiment, the water-soluble binder accounts for 3.9%-19% of the mass of the first positive electrode active layer 232; and / or, the oil-soluble binder accounts for 1.5%-5% of the mass of the second positive electrode active layer 233.

[0101] By setting the mass ratio of water-soluble binder and / or oil-soluble binder as described above, the mass ratio of water-soluble binder in the first positive electrode active layer 232 is greater than that of oil-soluble binder in the second positive electrode active layer 233. The relatively large proportion of water-soluble binder in the first positive electrode active layer 232 can better cover burrs and prevent the reverse curling of the metal layer, which is beneficial to improving the safety performance of the battery cell.

[0102] The water-soluble binder in the first positive electrode active layer 232 can have a mass percentage of 3.9%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 11.2%, 12%, 12.5%, 13%, 13.9%, 14%, 15%, 16%, 17%, 18%, 19%, etc., or a range consisting of any two of the above values, such as 12%-14%, 13%-15%, etc. The oil-soluble binder in the second positive electrode active layer 233 can have a mass percentage of 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.4%, 2.6%, 3%, 4%, 5%, etc., or a range consisting of any two of the above values, such as 1.5%-2%, 1.5%-3%, etc.

[0103] In one embodiment, the water-soluble binder includes one or more of polyacrylic acid (PAA) and its derivatives, polyvinyl alcohol (PVA) and its derivatives; and / or, the oil-soluble binder includes one or more of polyvinylidene fluoride (PVDF) and its derivatives, polyimide (PI) and its derivatives.

[0104] By selecting one or more of polyacrylic acid and its derivatives, polyvinyl alcohol and its derivatives as water-soluble binders, not only can the water-soluble properties of the binders be maintained, but they also have lower thermal shrinkage stress. This helps to reduce the thermal shrinkage stress generated during the drying process of the slurry forming the first positive electrode active layer 232, thereby reducing the impact of the thermal shrinkage stress generated during the drying process of the first positive electrode active layer 232 on the positive electrode composite current collector 231 and effectively improving the coating wrinkling problem.

[0105] By selecting one or more of polyvinylidene fluoride and its derivatives, and polyimide and its derivatives as oil-soluble binders, not only can the oil-soluble properties of the binders be maintained, but they also have lower thermal shrinkage stress. This helps to reduce the thermal shrinkage stress generated during the drying process of the slurry forming the second positive electrode active layer 233, thereby reducing the impact of the thermal shrinkage stress generated during the drying process of the second positive electrode active layer 233 on the positive electrode composite current collector 231 and effectively improving the coating wrinkling problem.

[0106] In addition, using one or more of polyacrylic acid and its derivatives, polyvinyl alcohol and its derivatives as water-soluble binders can maintain good adhesion between the first positive electrode active layer 232 and the positive electrode composite current collector 231; using one or more of polyvinylidene fluoride and its derivatives, polyimide and its derivatives as oil-soluble binders can maintain good adhesion between the second positive electrode active layer 233 and the first positive electrode active layer 232, which is beneficial to improving the performance of the battery cell.

[0107] In one embodiment, the first positive electrode active layer 232 includes a first dispersant, which includes one or more of polyacrylamide (PAM) and its derivatives, carboxymethyl cellulose (CMC) and its derivatives; and / or, the second positive electrode active layer 233 includes a second dispersant, which includes one or more of polyacrylamide (PAM) and its derivatives, polyvinylpyrrolidone (PVP) and its derivatives.

[0108] By selecting one or more of polyacrylamide (PAM) and its derivatives, carboxymethyl cellulose (CMC) and its derivatives as the first dispersant, the dispersibility of the water-based binder is better, reducing the phenomenon of local agglomeration of the material. At the same time, the molecular chain length of the first dispersant is relatively short, the cross-linking between molecules is more suitable, and it has lower thermal shrinkage stress. The first dispersant can reduce the surface tension of the slurry and reduce the impact of the thermal shrinkage stress generated during the drying process of the first positive electrode active layer 232 on the positive electrode composite current collector 231, effectively improving the coating wrinkling problem.

[0109] By selecting one or more of polyacrylamide (PAM) and its derivatives, polyvinylpyrrolidone (PVP) and its derivatives as the second dispersant, the dispersibility of oily binders is better, reducing the phenomenon of local agglomeration of materials. At the same time, the molecular chain length of the second dispersant is shorter, the cross-linking between molecules is more suitable, and it has lower thermal shrinkage stress, reducing the impact of thermal shrinkage stress generated during the drying process of the second positive electrode active layer 233 on the positive electrode composite current collector 231, and effectively improving the coating wrinkling problem.

[0110] Please refer to Figures 7 and 8. Figure 7 is a SEM image of the dispersion state of slurry in related technologies, and Figure 8 is a SEM image of the dispersion state of slurry under the action of PAM in the embodiments of this application.

[0111] As shown in Figure 7, without the addition of dispersant PAM, the agglomeration between slurry particles is quite severe, resulting in significant agglomeration of PVDF in the slurry. As shown in Figure 8, with the addition of PAM, the dispersion between slurry particles is more uniform, and the dispersion of PVDF in the slurry is also more uniform. It can be understood that by introducing the dispersant PAM, the dispersion of PVDF is promoted, maintaining a more uniform slurry dispersion, reducing the occurrence of localized PVDF agglomeration, and thus reducing the probability of sudden increases in localized thermal shrinkage stress caused by localized PVDF agglomeration. Furthermore, PAM has low swelling, and the cross-linked network formed by its molecules can limit the shrinkage of PVDF, reducing slurry swelling and improving coating wrinkling.

[0112] In one embodiment, the first dispersant has a mass percentage of 0.1%-2% in the first positive electrode active layer 232; and / or, the second dispersant has a mass percentage of 0.1%-2% in the second positive electrode active layer 233.

[0113] The mass percentage of the first dispersant in the first positive electrode active layer 232 refers to the ratio of the mass of the first dispersant to the total mass of the first positive electrode active layer 232 among all substances constituting the first positive electrode active layer 232. The mass percentage of the second dispersant in the second positive electrode active layer 233 refers to the ratio of the mass of the second dispersant to the total mass of the second positive electrode active layer 233 among all substances constituting the second positive electrode active layer 233.

[0114] By setting the mass ratio of the first dispersant in the first positive electrode active layer 232 as described above, a good dispersion effect can be achieved for the water-based binder. At the same time, the surface tension of the slurry can be reduced, and the impact of the thermal shrinkage stress generated during the drying process of the first positive electrode active layer 232 on the positive electrode composite current collector 231 can be reduced. By setting the mass ratio of the second dispersant in the second positive electrode active layer 233 as described above, a good dispersion effect can be achieved for the oil-based binder. At the same time, the surface tension of the slurry can be reduced, and the impact of the thermal shrinkage stress generated during the drying process of the second positive electrode active layer 233 on the positive electrode composite current collector 231 can be reduced, effectively improving the coating wrinkling problem.

[0115] The mass percentage of the first dispersant in the first positive electrode active layer 232 can be 0.1%, 0.5%, 0.9%, 1%, 1.2%, 1.4%, 1.5%, 1.9%, 2%, etc., or it can be a range of any two of the above values, such as 0.5%-1.4%, 0.9%-1.9%, etc. The mass percentage of the second dispersant in the second positive electrode active layer 233 can be 0.1%, 0.5%, 0.8%, 0.9%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.9%, 2%, etc., or it can be a range of any two of the above values, such as 0.5%-1.3%, 0.8%-1.9%, etc.

[0116] In one embodiment, the thickness of the first positive electrode active layer 232 is less than the thickness of the second positive electrode active layer 233.

[0117] As shown in Figure 9, Figure 9 is a SEM image of the first positive electrode active layer and the second positive electrode active layer provided in the embodiment of this application; it can be seen from Figure 9 that the thickness of the first positive electrode active layer 232 is less than the thickness of the second positive electrode active layer 233.

[0118] The thickness of the first positive electrode active layer 232 refers to the average vertical distance between the surface of the first positive electrode active layer 232 near the positive electrode composite current collector 231 and the surface of the first positive electrode active layer 232 away from the positive electrode composite current collector 231. The thickness of the second positive electrode active layer 233 refers to the average vertical distance between the surface of the second positive electrode active layer 233 near the first positive electrode active layer 232 and the surface of the second positive electrode active layer 233 away from the first positive electrode active layer 232.

[0119] By setting the thickness of the first positive electrode active layer 232 to be less than the thickness of the second positive electrode active layer 233, the thickness of the first positive electrode active layer 232, which is closer to the positive electrode composite current collector 231, is relatively smaller. This results in a smaller amount of solvent evaporation per cycle, making the first positive electrode active layer 232 easier to dry, reducing the impact of drying on the positive electrode composite current collector 231, and improving the coating wrinkling phenomenon. Furthermore, the first positive electrode active layer 232 mainly serves to cover burrs and prevent the metal layer from curling in the opposite direction, while the second positive electrode active layer 233 mainly provides capacity to the battery cell. By setting the thickness of the second positive electrode active layer 233 to be thicker, it is beneficial for the battery cell to have a higher energy density.

[0120] The method for testing the thickness of the first positive electrode active layer 232 and the second positive electrode active layer 233 is as follows: after obtaining the cross-section of the positive electrode sheet, the thickness is measured by a micrometer.

[0121] In one embodiment, the thickness of the first positive electrode active layer 232 is 5 micrometers to 30 micrometers; and / or, the thickness of the second positive electrode active layer 233 is 50 micrometers to 150 micrometers.

[0122] By setting the thickness of the first positive electrode active layer 232 and / or the second positive electrode active layer 233 as described above, the thickness of the first positive electrode active layer 232, which is closer to the positive electrode composite current collector 231, is relatively small. This results in a smaller amount of solvent evaporation per cycle, making the first positive electrode active layer 232 easier to dry. This reduces the impact on the positive electrode composite current collector 231 during the drying process and improves coating wrinkling. Furthermore, by setting the thickness of the first positive electrode active layer 232 and / or the second positive electrode active layer 233 as described above, the battery cell achieves a higher energy density.

[0123] The thickness of the first positive electrode active layer 232 can be 5 micrometers, 7 micrometers, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, etc., or it can be a range of any two of the above values, such as 5 micrometers-15 micrometers, 20 micrometers-30 micrometers, etc. The thickness of the second positive electrode active layer 233 can be 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 110 micrometers, 120 micrometers, 130 micrometers, 140 micrometers, 150 micrometers, etc., or it can be a range of any two of the above values, such as 50 micrometers-80 micrometers, 60 micrometers-130 micrometers, etc.

[0124] In one embodiment, the first positive electrode active layer 232 includes a first active material, and the second positive electrode active layer 233 includes a second active material, wherein the particle size of the first active material is smaller than the particle size of the second active material.

[0125] As shown in Figure 10, Figure 10 is another SEM image of the first positive electrode active layer and the second positive electrode active layer provided in the embodiment of this application; it can be seen from Figure 10 that the particle size of the first active material of the first positive electrode active layer 232 is relatively small, and the particle size of the second active material of the second positive electrode active layer 233 is relatively large.

[0126] Since the thickness of the first positive electrode active layer 232 is less than the thickness of the second positive electrode active layer 233, the first positive electrode active layer 232 is relatively thinner, while the second positive electrode active layer 233 is relatively thicker. For the relatively thinner first positive electrode active layer 232, the particle size of the selected first active material is smaller, maintaining the uniformity of the first active material's coverage of the positive electrode composite current collector 231, which is beneficial for improving the performance of the battery cell. For the relatively thicker second positive electrode active layer 233, the particle size of the selected second active material is larger, reducing the amount of solvent evaporation during the drying process, making the second positive electrode active layer 233 easier to dry, reducing the impact of drying on the positive electrode composite current collector 231, and improving coating wrinkling; using a second active material with a larger particle size can reduce the surface tension during slurry evaporation, reducing the probability of positive electrode sheet cracking.

[0127] In one embodiment, the first active material comprises lithium iron phosphate, and the particle size Dv50 of the first active material is 0.5 micrometers to 1.1 micrometers; and / or, the second active material comprises lithium iron phosphate, and the particle size Dv50 of the second active material is 1.5 micrometers to 3 micrometers.

[0128] Particle size Dv50 refers to the particle size value that, when arranged in ascending order of particle size, represents the cumulative percentage of 50% in a particle group.

[0129] By setting the particle size of the first active material and / or the second active material as described above, the particle size of the first active material in the thinner first positive electrode active layer 232 is relatively small, maintaining the uniformity of the first active material's coverage of the positive electrode composite current collector 231 surface; the particle size of the second active material in the thicker second positive electrode active layer 233 is relatively large, reducing the amount of solvent evaporation during the drying process, making the second positive electrode active layer 233 easier to dry, and improving coating wrinkling.

[0130] The particle size Dv50 of the first active material can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, etc., or it can be a range of any two of the above values, such as 0.7 μm-1.0 μm or 0.8 μm-1.1 μm. The particle size Dv50 of the second active material can be 1.5 μm, 1.7 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 2.9 μm, 3.0 μm, etc., or it can be a range of any two of the above values, such as 1.5 μm-2.0 μm or 1.7 μm-2.4 μm.

[0131] In one embodiment, the mass percentage of the first active material in the first positive electrode active layer 232 is less than the mass percentage of the second active material in the second positive electrode active layer 233.

[0132] The mass percentage of the first active material in the first positive electrode active layer 232 refers to the ratio of the mass of the first active material to the total mass of the first positive electrode active layer 232 among all substances constituting the first positive electrode active layer 232. The mass percentage of the second active material in the second positive electrode active layer 233 refers to the ratio of the mass of the second active material to the total mass of the second positive electrode active layer 233 among all substances constituting the second positive electrode active layer 233.

[0133] By setting the mass ratio of the first active material in the first positive electrode active layer 232 and / or the mass ratio of the second active material in the second positive electrode active layer 233 as described above, the relatively thick second positive electrode active layer 233 contains a relatively large amount of second active material, which is beneficial for the battery cell to have a higher energy density and improve the performance of the battery cell.

[0134] In one embodiment, the first active material accounts for 70%-90% of the mass of the first positive electrode active layer 232; and / or, the second active material accounts for 90%-97% of the mass of the second positive electrode active layer 233.

[0135] By setting the mass ratio of the first active material in the first positive electrode active layer 232 and / or the mass ratio of the second active material in the second positive electrode active layer 233 as described above, the mass ratio of the first active material in the first positive electrode active layer 232 is less than the mass ratio of the second active material in the second positive electrode active layer 233. The relatively thick second positive electrode active layer 233 contains a relatively large amount of second active material, which is beneficial for the battery cell to have a higher energy density and improve the performance of the battery cell.

[0136] The mass percentage of the first active material in the first positive electrode active layer 232 can be 70%, 75%, 80%, 85%, 90%, etc., or a range consisting of any two of the above values, for example, 70%-85% or 80%-90%. The mass percentage of the second active material in the second positive electrode active layer 233 can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc., or a range consisting of any two of the above values, for example, 90%-95% or 94%-97%.

[0137] In one embodiment, the first active material includes, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Optionally, the first active material may include materials with the general formula Li a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more of N, F, S, and Cl. Optionally, the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Optionally, the olivine-structured lithium phosphate may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. Optionally, the first active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05One or more of O2, LiFePO4 and LiMnPO4.

[0138] In one embodiment, the second active material includes, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Optionally, the second active material may include materials with the general formula Li a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more of N, F, S, and Cl. Optionally, the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Optionally, the olivine-structured lithium phosphate may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. Optionally, the second active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 A l0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0139] In one embodiment, the first active material is the same as the second active material.

[0140] By setting the first active material and the second active material to be the same, the same active material has similar electrochemical characteristics and reaction kinetics. The interface between the first positive electrode active layer 232 and the second positive electrode active layer 233 is relatively stable, maintaining a good electrochemical environment inside the positive electrode sheet and maintaining the stability of the battery cell performance.

[0141] In one embodiment, the first positive electrode active layer 232 includes a first conductive material, and the second positive electrode active layer 233 includes a second conductive material. The mass percentage of the first conductive material in the first positive electrode active layer 232 is greater than the mass percentage of the second conductive material in the second positive electrode active layer 233.

[0142] The mass percentage of the first conductive material in the first positive electrode active layer 232 refers to the ratio of the mass of the first conductive material to the total mass of the first positive electrode active layer 232 among all the substances constituting the first positive electrode active layer 232. The mass percentage of the second conductive material in the second positive electrode active layer 233 refers to the ratio of the mass of the second conductive material to the total mass of the second positive electrode active layer 233 among all the substances constituting the second positive electrode active layer 233.

[0143] By setting the mass ratio of the first conductive material in the first positive electrode active layer 232 and / or the mass ratio of the second conductive material in the second positive electrode active layer 233 as described above, the first positive electrode active layer 232, which is closer to the positive electrode composite current collector 231, contains a relatively larger amount of the first conductive material. This allows for the construction of a denser and more efficient electron conduction network, forming a good conductive channel between the active material and the positive electrode composite current collector 231. This reduces the internal resistance of electron transport, improves the conductivity of the positive electrode sheet, and is beneficial for enhancing the performance of the battery cell.

[0144] In one embodiment, the first conductive material accounts for 5%-20% of the mass of the first positive electrode active layer 232; and / or, the second conductive material accounts for 1%-10% of the mass of the second positive electrode active layer 233.

[0145] By setting the mass ratio of the first conductive material in the first positive electrode active layer 232 and / or the mass ratio of the second conductive material in the second positive electrode active layer 233 as described above, the first positive electrode active layer 232, which is closer to the positive electrode composite current collector 231, contains a relatively larger amount of the first conductive material. This allows for the construction of a denser and more efficient electron conduction network, forming a good conductive channel between the active material and the positive electrode composite current collector 231. This reduces the internal resistance of electron transport, improves the conductivity of the positive electrode sheet, and is beneficial for enhancing the performance of the battery cell.

[0146] The mass percentage of the first conductive material in the first positive electrode active layer 232 can be 5%, 8%, 10%, 13%, 15%, 18%, 20%, etc., or it can be a range of any two of the above values, such as 5%-13%, 10%-20%, etc. The mass percentage of the second conductive material in the second positive electrode active layer 233 can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., or it can be a range of any two of the above values, such as 1%-8%, 5%-10%, etc.

[0147] In one embodiment, the first conductive material includes one or more of superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, and carbon nanotubes.

[0148] In one embodiment, the second conductive material includes one or more of superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, and carbon nanotubes.

[0149] In one embodiment, the positive electrode composite current collector 231 includes a support layer and a conductive layer located on at least one side of the support layer.

[0150] The support layer provides the basic support structure, ensuring that the positive electrode composite current collector 231 maintains a stable shape during battery charging and discharging. The conductive layer has good conductivity, enabling it to efficiently collect and transport electrons generated inside the battery.

[0151] In one embodiment, the support layer includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE); the conductive layer includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0152] By designing the support layer using the aforementioned materials, which are polymer materials, the support layer possesses good flexibility and a certain strength. This allows the positive electrode composite current collector to withstand a certain degree of tensile, bending, and compressive forces during battery manufacturing and use, making it less prone to breakage or damage and contributing to the stability of the battery. By designing the conductive layer to include the aforementioned materials, which are metallic materials, the positive electrode current collector possesses excellent conductivity, enabling rapid and smooth electron transport within the battery. For example, the positive electrode composite current collector 231 can be formed by forming a metallic material on a polymer substrate.

[0153] In one specific embodiment, the positive electrode sheet includes a positive electrode composite current collector 231, a first positive electrode active layer 232, and a second positive electrode active layer 233. The first positive electrode active layer 232 is disposed on at least one side of the positive electrode composite current collector 231, and the second positive electrode active layer 233 is disposed on the side of the first positive electrode active layer 232 opposite to the positive electrode composite current collector 231. The positive electrode composite current collector 231 includes polyethylene terephthalate (PET) and aluminum foil layers disposed on opposite surfaces of the PET. The first positive electrode active layer 232 is a water-soluble film layer; specifically, the first positive electrode active layer 232 includes lithium iron phosphate, polyacrylic acid, and polyacrylamide. The second positive electrode active layer 233 is an oil-soluble film layer; specifically, the second positive electrode active layer 233 includes lithium iron phosphate, polyvinylidene fluoride, and polyacrylamide. The thickness of the first positive electrode active layer 232 is less than the thickness of the second positive electrode active layer 233. The lithium iron phosphate particle size of the first positive electrode active layer 232 is smaller than that of the lithium iron phosphate particle size of the second positive electrode active layer 233. The mass percentage of the aqueous binder in the first positive electrode active layer 232 is greater than that of the oily binder in the second positive electrode active layer 233. The mass percentage of the first conductive material in the first positive electrode active layer 232 is greater than that of the second conductive material in the second positive electrode active layer 233. The mass percentage of the first active material in the first positive electrode active layer 232 is less than that of the second active material in the second positive electrode active layer 233.

[0154] Layered coating effectively reduces the drying thickness of each coating layer. In the first positive electrode active layer 232, polyacrylic acid is used as a binder, and polyacrylamide is also introduced to reduce surface tension and thermal shrinkage stress. Simultaneously, it isolates the influence of the slurry in the second positive electrode active layer 233 on the positive electrode composite current collector 231. In the second positive electrode active layer 233, polyacrylamide is introduced as a dispersant, which has lower swelling than polyvinylidene fluoride, and the use of larger-particle-size lithium iron phosphate effectively reduces thermal shrinkage stress. Through the above-described configuration of the first and second positive electrode active layers 232 and 233, the safety performance of the battery cell is significantly improved, and the wrinkling phenomenon in the composite current collector coating is alleviated.

[0155] In one embodiment, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, a negative electrode binder, a negative electrode thickener, and a negative electrode conductive agent.

[0156] In one embodiment, the negative electrode current collector may be a metal foil or a composite negative electrode current collector. Optionally, copper foil may be used as the metal foil. Optionally, the composite negative electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite negative electrode current collector may be formed by forming a metal material on the polymer material substrate; the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0157] In one embodiment, the negative electrode active material includes, but is not limited to, at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0158] In one embodiment, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and polymethacrylic acid (PMAA).

[0159] In one embodiment, the negative electrode thickener includes at least one of sodium carboxymethyl cellulose (CMC-Na) and lithium carboxymethyl cellulose (CMC-Li).

[0160] In one embodiment, the negative electrode conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, and carbon nanotubes.

[0161] In one embodiment, the battery cell assembly 23 includes an electrolyte comprising a lithium salt and a solvent. Optionally, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, potassium difluorophosphate, lithium difluorooxalate borate (LiBF2(C2O4), LiDFOB), lithium bis(oxalate borate) (LiB(C2O4)2, LiBOB), potassium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate. Optionally, the solvent includes one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, 1,4-butylpropyl ester, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. Optionally, additives may be added to the electrolyte as needed. Electrolyte additives include, but are not limited to, one or more of fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VC), or 1,3-propanesulfonate lactone (PS).

[0162] Please refer to Figure 11, which is a schematic diagram of the structure of the battery device provided in the embodiment of this application.

[0163] The battery device 100 includes a housing 10 and battery cells 20, with the battery cells 20 housed within the housing 10. The battery cell 20 refers to the smallest unit that makes up the battery device 100.

[0164] The housing 10 provides a space for accommodating the battery cell 20, and can adopt various structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, which overlap each other, and together define a space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one open end, and the first part 11 may be a plate-like structure, covering the open side of the second part 12 so that the first part 11 and the second part 12 together define the space; alternatively, the first part 11 and the second part 12 may both be hollow structures with one open side, with the open side of the first part 11 covering the open side of the second part 12. Of course, the housing 10 formed by the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0165] In the battery device 100, there can be multiple battery cells 20. These multiple battery cells 20 can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, the battery device 100 can also be composed of multiple battery cells 20 first connected in series, in parallel, or in a mixed configuration to form a battery module, and then multiple battery modules are connected in series, in parallel, or in a mixed configuration to form a whole, which is then housed within the housing 10.

[0166] The battery device 100 may also include other structures, for example, the battery device 100 may also include a busbar for realizing electrical connection between multiple battery cells 20.

[0167] Each battery cell 20 can be a secondary battery. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0168] The battery device disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. The electrical device includes the battery device or the battery cell provided in the above embodiments. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0169] For ease of explanation, the following embodiments use a vehicle 1000 as an example of an electrical device according to an embodiment of this application. Please refer to Figure 12, which is a structural schematic diagram of the vehicle provided in an embodiment of this application.

[0170] Vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery device 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. The battery device 100 can be used to power vehicle 1000; for example, it can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the battery device 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0171] In some embodiments of this application, the battery device 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0172] This application also investigates the performance of the battery device provided using the embodiments of this application.

[0173] The preparation process of Example 1 is as follows:

[0174] (1) Preparation of positive electrode sheet:

[0175] (a) Obtain a positive electrode composite current collector, which includes polyethylene terephthalate (PET) and aluminum foil layers disposed on opposite surfaces of PET, wherein the thickness of PET is 6 μm and the thickness of aluminum foil layers is 1 μm.

[0176] (b) The first active material lithium iron phosphate (LiFePO4), the first conductive material carbon black, the water-based binder polyacrylic acid (PAA), and the first dispersant polyacrylamide (PAM) are dispersed in water at a mass percentage ratio of 70:16:13.9:0.1 and stirred until homogeneous to prepare the first positive electrode active slurry; wherein the particle size Dv50 of the first active material lithium iron phosphate is 0.9 micrometers. The first positive electrode active slurry is coated on both surfaces of the positive electrode composite current collector to form a first positive electrode active layer with a thickness of 20 μm.

[0177] (c) The second active material lithium iron phosphate (LiFePO4), the second conductive material carbon black, the oily binder polyvinylidene fluoride (PVDF), and the second dispersant polyacrylamide (PAM) are dispersed in the solvent N-methylpyrrolidone at a mass percentage ratio of 97:1:1.9:0.1 and stirred until homogeneous to prepare the second positive electrode active slurry; wherein the particle size Dv50 of the second active material lithium iron phosphate is 1.5 micrometers. The second positive electrode active slurry is coated on the surface of the first positive electrode active layer to form a second positive electrode active layer with a thickness of 70 μm.

[0178] (d) After cold pressing, a negative electrode sheet is obtained.

[0179] (2) Preparation of negative electrode sheet:

[0180] (a) Obtain a negative electrode current collector copper foil with a thickness of 6 μm.

[0181] (b) The negative electrode active material (natural graphite), conductive agent (carbon black (Super P), binder (carboxymethyl cellulose), and binder (styrene-butadiene rubber)) are mixed thoroughly in water at a weight percentage ratio of 95:2:1.5%:1.5%, and then dispersed uniformly in a degassing machine for 2 hours to prepare a negative electrode active slurry. The negative electrode active slurry is then coated onto the negative electrode current collector copper foil to form a negative electrode active material layer with a thickness of 136 μm.

[0182] (c) After cold pressing, a negative electrode sheet is obtained.

[0183] (3) Diaphragm:

[0184] A 13μm polyethylene film with a polycarbosilane coating (PCS coating) is used.

[0185] (4) Preparation of electrolyte:

[0186] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0187] (6) Assembly:

[0188] The prepared negative electrode and positive electrode are stacked in sequence, with the separator placed between the positive and negative electrode to act as a separator. The cells are then wound to obtain a bare cell, which is then inserted into the battery casing. After drying, electrolyte is injected, and the battery device (secondary battery) is obtained through vacuum sealing, settling, formation, and shaping processes.

[0189] The preparation process of the battery device in Examples 2 to 12 is similar to that in Example 1. The specific target components and proportions of Examples 2 to 12 are detailed in Table 1.

[0190] The difference between Comparative Example 1 and Example 1 is that in the positive electrode preparation process, in step (b) of forming the first positive electrode active layer, the water-based binder polyacrylic acid (PAA) is replaced with the oil-soluble binder polyvinylidene fluoride (PVDF).

[0191] The difference between Comparative Example 2 and Example 1 is that the positive electrode composite current collector is replaced with aluminum foil during the preparation of the positive electrode sheet.

[0192] The difference between Comparative Example 3 and Example 1 is that step (b) was omitted in the preparation of the positive electrode sheet, that is, the second positive electrode active layer was directly formed on the surface of the current collector.

[0193] The relevant parameter tests for each embodiment and comparative example are as follows:

[0194] 1. Particle size Dv50 test.

[0195] Particle size distribution can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0196] 2. Testing of film thickness.

[0197] Obtain the cross-section of the positive electrode and test it using a micrometer screw gauge.

[0198] 3. Safety testing method - needle prick test.

[0199] 1) At 25±5℃, discharge at 1C constant current to 2.5V, place for 1h, charge at 0.33C constant current to 3.65V, charge at 0.05C constant voltage, and place for 1h.

[0200] 2) At a speed of (25±5) mm / s, penetrate from a direction perpendicular to the battery plates. The penetration position should be close to the geometric center of the needle surface, and the steel needle should remain in the battery.

[0201] 3) Observe for 1 hour and record the fire situation.

[0202] 4) Repeat the above steps to perform the above test on 10 batteries with the same parameters, and record the number of fires of the 10 batteries.

[0203] 4. Wrinkle test.

[0204] The determination is made by visually observing the coating and curling state of the electrode sheets.

[0205] Table 1. Test data of relevant parameters for Examples 1-7 and Comparative Example 1

[0206]

[0207] By comparing Examples 1 to 12 with Comparative Examples 1 to 3, it can be seen that the positive electrode sheet provided in the embodiments of this application includes a positive electrode composite current collector, a first positive electrode active layer, and a second positive electrode active layer. The first positive electrode active layer is disposed on at least one side of the positive electrode composite current collector, and the second positive electrode active layer is disposed on the side of the first positive electrode active layer opposite to the positive electrode composite current collector. The first positive electrode active layer is a water-soluble film layer, and the second positive electrode active layer is an oil-soluble film layer, which can improve the safety performance of the battery cell and improve the coating wrinkling.

[0208] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A battery cell, wherein, It includes a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes: Positive electrode composite current collector; A first positive electrode active layer is disposed on at least one side of the positive electrode composite current collector; the first positive electrode active layer is a water-soluble film layer; The second positive electrode active layer is disposed on the side of the first positive electrode active layer away from the positive electrode composite current collector, and the second positive electrode active layer is an oil-soluble film layer.

2. The battery cell according to claim 1, wherein, The first positive electrode active layer includes a water-soluble binder; the second positive electrode active layer includes an oil-soluble binder.

3. The battery cell according to claim 2, wherein, The water-soluble binder accounts for a greater mass percentage in the first positive electrode active layer than the oil-soluble binder accounts for in the second positive electrode active layer.

4. The battery cell according to claim 3, wherein, The water-soluble binder accounts for 3.9%-19% of the mass of the first positive electrode active layer; and / or, The oil-soluble binder accounts for 1.5%-5% of the mass of the second positive electrode active layer.

5. The battery cell according to any one of claims 2 to 4, wherein, The water-soluble binder includes one or more of polyacrylic acid and its derivatives, polyvinyl alcohol and its derivatives; and / or, The oil-soluble binder includes one or more of polyvinylidene fluoride and its derivatives, and polyimide and its derivatives.

6. The battery cell according to any one of claims 1 to 5, wherein, The first positive electrode active layer includes a first dispersant, which includes one or more of polyacrylamide and its derivatives, carboxymethyl cellulose and its derivatives; and / or, The second positive electrode active layer includes a second dispersant, which includes one or more of polyacrylamide and its derivatives, and polyvinylpyrrolidone and its derivatives.

7. The battery cell according to any one of claims 1 to 6, wherein, The thickness of the first positive electrode active layer is less than the thickness of the second positive electrode active layer.

8. The battery cell according to any one of claims 1 to 7, wherein, The thickness of the first positive electrode active layer is 5 micrometers to 30 micrometers; and / or, The thickness of the second positive electrode active layer is 50 micrometers to 150 micrometers.

9. The battery cell according to claim 7 or 8, wherein, The first positive electrode active layer includes a first active material, and the second positive electrode active layer includes a second active material, wherein the particle size of the first active material is smaller than the particle size of the second active material.

10. The battery cell according to claim 9, wherein, The first active material comprises lithium iron phosphate, and the particle size Dv50 of the first active material is 0.5 μm to 1.1 μm; and / or, the second active material comprises lithium iron phosphate, and the particle size Dv50 of the second active material is 1.5 μm to 3 μm.

11. The battery cell according to claim 9 or 10, wherein, The mass percentage of the first active material in the first positive electrode active layer is less than the mass percentage of the second active material in the second positive electrode active layer.

12. The battery cell according to any one of claims 9 to 11, wherein, The first active material accounts for 70%-90% of the mass of the first positive electrode active layer; and / or, The second active material accounts for 90%-97% of the mass of the second positive electrode active layer.

13. The battery cell according to any one of claims 9 to 12, wherein, The first active material is the same as the second active material.

14. The battery cell according to any one of claims 1 to 13, wherein, The first positive electrode active layer includes a first conductive material, and the second positive electrode active layer includes a second conductive material. The mass percentage of the first conductive material in the first positive electrode active layer is greater than the mass percentage of the second conductive material in the second positive electrode active layer.

15. The battery cell according to claim 14, wherein, The first conductive material accounts for 5%-20% of the mass of the first positive electrode active layer; and / or, the second conductive material accounts for 1%-10% of the mass of the second positive electrode active layer.

16. The battery cell according to any one of claims 1 to 15, wherein, The positive electrode composite current collector includes a support layer and a conductive layer located on at least one side of the support layer.

17. The battery cell according to claim 16, wherein, The support layer comprises at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene; the conductive layer comprises at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

18. A battery device, wherein, Includes the battery cell as described in any one of claims 1 to 17.

19. An electrical appliance, wherein, Includes a battery cell as described in any one of claims 1 to 17 or a battery device as described in claim 18.

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