A positive electrode sheet, a battery cell, a battery, and an electric device

Abstract

The application discloses a positive electrode sheet, a battery monomer, a battery and an electric device, and belongs to the technical field of batteries. 单 The mass ratio w of the single-crystal particles is controlled to be 0.1-10% of the total mass of the single-crystal particles and the polycrystal particles 单 The mass ratio w of the single-crystal particles is controlled to be 0.1-10% of the total mass of the single-crystal particles and the polycrystal particles 多 The mass ratio w of the single-crystal particles is controlled to be 0.1-10% of the total mass of the single-crystal particles and the polycrystal particles 多 The mass ratio w of the single-crystal particles is controlled to be 0.1-10% of the total mass of the single-crystal particles and the polycrystal particles

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a positive electrode, a battery cell, a battery, and an electrical device. Background Technology

[0002] In positive electrode sheets that use multiple positive electrode active materials, in order to reduce the possibility of uneven current between the positive electrode active materials, the positive electrode active materials are usually arranged in layers. However, different positive electrode active materials usually have different particle sizes, and the layered arrangement method cannot take advantage of the particle gradation. The compaction density of the entire positive electrode sheet needs to be improved. Summary of the Invention

[0003] In view of the above problems, this application provides a positive electrode sheet, a battery cell, a battery, and an electrical device, which can improve the compaction density of the positive electrode sheet.

[0004] In a first aspect, this application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer comprising a first positive electrode active material, the first positive electrode active material comprising a ternary system material, the ternary system material comprising single crystal particles and polycrystalline particles, the second positive electrode active material layer comprising a second positive electrode active material, the second positive electrode active material comprising a polyanionic positive electrode material, the single crystal particles comprising w of the ternary system material by mass. 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied:

[0005]

[0006] In the technical solution of this application embodiment, a ternary system material of single-crystal particles and polycrystalline particles is used in combination in the first positive electrode active material layer, and the mass ratio w of single-crystal particles is controlled. 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy This process creates a good particle size distribution between smaller single-crystal particles and larger polycrystalline particles, thereby improving the overall compaction density of the cathode sheet and increasing its energy density. It also narrows the Li ion transport path, reducing polarization and internal resistance when used in a battery, thus improving battery performance. Furthermore, separating the first and second cathode active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0007] In some embodiments, the mass percentage w of the single-crystal particles in the ternary material system 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied:

[0008] In the above implementation process, by controlling the mass ratio w of single crystal particles 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy It can further improve the compaction density of the entire positive electrode and increase its energy density.

[0009] In some embodiments, the positive electrode sheet further includes a current collector, a first positive electrode active material layer is disposed on at least one surface of the current collector, and a second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the current collector.

[0010] In the above implementation process, by placing a second positive electrode active material layer with weaker ion transport performance on the surface of the first positive electrode active material layer, when used as a battery, the second positive electrode active material layer is closer to the negative electrode, resulting in a shorter ion transport path, which is beneficial to improving its ion transport rate and thus enhancing its rate performance. Simultaneously, it reduces the possibility of side reactions in the ternary system materials, further benefiting the electrochemical performance of the positive electrode.

[0011] In some embodiments, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0012] The thickness H1 of the first positive electrode active material layer is 5–35 μm; and / or

[0013] The thickness H2 of the second positive electrode active material layer is 35–80 μm.

[0014] In the above implementation process, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is controlled to satisfy: The thickness H1 of the first positive electrode active material layer is 5–35 μm, and the thickness H2 of the second positive electrode active material layer is 35–80 μm. This allows for a suitable range of ternary material usage, maximizing the performance of the ternary system, such as energy density and lifespan, while reducing the probability of side reactions that could degrade battery performance and safety. Simultaneously, a shorter average transport distance for the entire second positive electrode active material layer is beneficial for its own ion transport rate and minimizes the weakening of the ion transport capability of the first positive electrode active material layer, thus achieving better rate performance. Furthermore, this allows for a suitable range of second positive electrode active material usage, further maximizing its performance, such as safety.

[0015] In some embodiments, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0016] The thickness H1 of the first positive electrode active material layer is 10–30 μm; and / or

[0017] The thickness H2 of the second positive electrode active material layer is 40–70 μm.

[0018] In some embodiments, the relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0019] In the ternary material, the mass percentage of Ni (wNi) among all elements is 20%–55%; and / or

[0020] In the ternary material, the mass percentage of Mn among all elements is 5% to 25%.

[0021] In the above implementation process, the Ni content in the ternary system material is positively correlated with the probability of its side reactions to a certain extent; the higher the Ni content, the more likely the side reactions are to occur. The Mn content in the ternary system material is positively correlated with its structural stability to a certain extent; the higher the Mn content, the higher the structural stability. The thickness of the first positive electrode active material layer is positively correlated with the probability of its side reactions to a certain extent; the thicker the layer, the higher the content of the first positive electrode active material, and the more likely the side reactions are to occur. The thickness of the second positive electrode active material layer is positively correlated with the probability of side reactions in the ternary system material to a certain extent; the thicker the second positive electrode active material layer, the more likely the ternary system material is to experience side reactions. By controlling the mass ratio of Ni (wNi), the mass ratio of Mn (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer, the following relationships are satisfied: In ternary materials, the mass percentage of Ni (wNi) is 20%–55% and the mass percentage of Mn (wMn) is 5%–25%. This reduces the probability of side reactions in ternary materials, while also giving the cathode good safety and cycle stability, and maintaining the energy density of the cathode.

[0022] In some embodiments, the relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0023] In the ternary material, the mass percentage of Ni (wNi) among all elements is 30%–45%; and / or

[0024] In the ternary material, the mass percentage of Mn among all elements is 10% to 20%.

[0025] In some embodiments, the single-crystal particles account for 10% to 40% of the mass of the ternary system material, and the polycrystalline particles account for 60% to 90% of the mass of the ternary system material; and / or

[0026] The median volumetric diameter of the single crystal particles is 2.5–4.5 μm; and / or

[0027] The median volumetric particle size of the polycrystalline particles is 8–10 μm.

[0028] In some embodiments, the polyanionic cathode material includes LiMPO4, where M includes Mn and non-Mn elements, and the non-Mn elements include one or both of a first doping element and a second doping element, wherein the first doping element is manganese site doping and the second doping element is phosphorus site doping.

[0029] Optionally, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0030] Optionally, the second doping element includes one or more elements selected from B, S, Si, and N.

[0031] Optionally, the polyanionic cathode material includes Li 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0032] Optionally, the polyanionic cathode material includes Li h A i Mn 1-j B j P 1-k C k O 4-l D l Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; h is selected from the range of 0.9 to 1.1, i is selected from the range of 0.001 to 0.1, j is selected from the range of 0.001 to 0.5, k is selected from the range of 0.001 to 0.1, l is selected from the range of 0.001 to 0.1, and the polyanionic cathode material is electrically neutral.

[0033] In some embodiments, the polyanionic cathode material also has a carbon-containing coating layer.

[0034] In the above implementation process, the introduction of a carbon-containing coating layer is used to improve the conductivity of the positive electrode active material. At this time, the structure of the positive electrode active material is actually a core-shell structure with LiMPO4 as the core and a coating layer covering the surface of the core.

[0035] In some embodiments, the ternary system material includes nickel-cobalt-manganese ternary material and its modified materials, and nickel-cobalt-aluminum ternary material and its modified materials.

[0036] In the above implementation process, the modified materials of the nickel-cobalt-manganese ternary material and the nickel-cobalt-aluminum ternary material respectively refer to materials obtained by doping or coating the nickel-cobalt-manganese ternary material or the nickel-cobalt-aluminum ternary material.

[0037] In some embodiments, the ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is selected from one or two elements of Mn or Al, M2 is selected from one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from one or more elements of N, F, S, Cl.

[0038] In a second aspect, the present application provides a positive electrode sheet. The positive electrode sheet includes a positive electrode active material layer and a current collector. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer is provided on at least one surface of the current collector, and the second positive electrode active material layer is provided on the surface of the first positive electrode active material layer away from the current collector; the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, the mass ratio w 单 of the single crystal particles in the ternary system material, the volume median diameter D 单 of the single crystal particles in μm, the mass ratio w 多 of the polycrystalline particles in the ternary system material, and the volume median diameter D 多 of the polycrystalline particles in μm satisfy the following relationship:

[0039] In the technical solution of this application embodiment, a ternary system material of single-crystal particles and polycrystalline particles is used in combination in the first positive electrode active material layer, and the mass ratio w of single-crystal particles is controlled. 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy This process creates a good particle size distribution between smaller single-crystal particles and larger polycrystalline particles, thereby improving the overall compaction density of the cathode sheet and increasing its energy density. It also narrows the Li-ion transport path, reducing polarization and internal resistance when used in a battery, thus improving battery performance. Furthermore, layering the first and second cathode active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention during the early stages of cycling. Additionally, polyanionic cathode materials typically exhibit better safety performance, while ternary systems generally demonstrate higher energy density. Using polyanionic cathode materials as the second cathode active material and ternary materials as the first cathode active material allows the cathode sheet to possess both high safety and high energy density. Furthermore, by placing a second positive electrode active material layer with weaker ion transport performance on the surface of the first positive electrode active material layer, when used as a battery, the second positive electrode active material layer is closer to the negative electrode, making its ion transport path shorter, which is beneficial to improving its ion transport rate and thus improving its rate performance.

[0040] Thirdly, this application provides a battery cell, which includes the positive electrode provided in the first or second aspect.

[0041] Fourthly, this application provides a battery, which includes the battery cell provided in the third aspect.

[0042] Fifthly, this application provides an electrical device, which includes a battery cell provided in the third aspect or a battery provided in the fourth aspect. Attached Figure Description

[0043] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0044] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0045] Figure 2This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0046] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0047] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0048] Figure 5 This is a first structural schematic diagram of the positive electrode sheet provided in some embodiments of this application;

[0049] Figure 6 This is a schematic diagram of the second structure of the positive electrode sheet provided in some embodiments of this application;

[0050] Figure 7 A flowchart illustrating a method for preparing a positive electrode sheet according to some embodiments of this application.

[0051] The reference numerals in the detailed embodiments are as follows:

[0052] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Shell; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Positive electrode sheet; 2311 - Positive current collector; 2312 - Positive active material layer; 2312a - First positive active material layer; 2312b - Second positive active material layer; 24 - Current collector component; 25 - Insulation protection component. Detailed Implementation

[0053] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0054] 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.

[0055] 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, "multiple" means two or more, unless otherwise explicitly defined.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0060] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0061] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0062] Power batteries can be lithium-ion batteries, which have a wide range of applications in portable electronic devices, electric vehicles, and other fields. In the manufacturing process of lithium-ion secondary battery electrode sheets, a single-layer coating is typically used, where the required active material is coated onto the current collector in a single layer. With increasing demands for energy density and safety, some researchers have proposed combining high-energy-density positive electrode active materials, such as ternary cathode materials, with high-safety-performance positive electrode active materials, such as polyanionic cathode materials, to achieve a balance between energy density and safety.

[0063] However, when a positive electrode active material with high energy density and a positive electrode active material with high safety performance are simultaneously doped into a single positive electrode active material layer, uneven current is likely to occur between the two positive electrode active materials in the positive electrode active material layer. This phenomenon will cause the positive electrode to decay rapidly in the early stage of cycling, which will have a significant impact on the capacity retention rate of the positive electrode.

[0064] To further improve the problem of rapid degradation of the electrode in the early stage of cycling, the two active materials can be set in layers. However, the particle size of the ternary system material is often an order of magnitude larger than that of the polyanionic cathode material. After layering, the advantages of the particle size distribution of the two materials cannot be brought into play, resulting in the need to improve the compaction density of the entire cathode.

[0065] Based on the above considerations, in order to improve the compaction density of the positive electrode and enhance its energy density, this application proposes a positive electrode, which includes a positive electrode active material layer. The positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer includes a first positive electrode active material, which is a ternary material system comprising single-crystal particles and polycrystalline particles. The second positive electrode active material layer includes a second positive electrode active material, which is a polyanionic positive electrode material. The mass percentage w of the single-crystal particles in the ternary material system is... 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied:

[0066] In such a cathode sheet, a ternary system of single-crystal and polycrystalline materials is used in combination in the first cathode active material layer, and the mass ratio w of the single-crystal particles is controlled. 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy This process creates a good particle size distribution between smaller single-crystal particles and larger polycrystalline particles, thereby improving the overall compaction density of the cathode sheet and increasing its energy density. It also narrows the Li ion transport path, reducing polarization and internal resistance when used in a battery, thus improving battery performance. Furthermore, separating the first and second cathode active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0067] This positive electrode sheet can be used to fabricate electrode assemblies, which can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system for this electrical device can be composed of battery cells, secondary batteries, etc., as disclosed in this application. This is beneficial for fully utilizing the high-limit compaction density positive electrode material's effect on improving the overall compaction density of the positive electrode active material layer, achieving a significant increase in the overall compaction density of the positive electrode active material layer, thereby increasing the energy density of the positive electrode sheet and improving the capacity of the battery cell.

[0068] This application provides an electrical device that uses a battery as a power source. 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. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0069] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0070] Please refer to Figure 1 , Figure 1This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The 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 secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0071] In some embodiments of this application, the secondary battery 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.

[0072] In this application, the secondary battery 100 refers to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which may be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating the multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0073] Figure 2 This is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Please refer to... Figure 2 The secondary battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0074] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0075] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0076] In the secondary battery 100, there are multiple battery cells 20. These multiple battery cells 20 can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. The battery cells 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0077] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0078] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... Figure 3 and Figure 4 The battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0079] The shape of the outer casing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the outer casing 21 can be a cuboid structure. Figure 3 and Figure 4 An example is shown where the housing 21 and electrode assembly 23 are square.

[0080] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0081] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0082] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used for electrical connection with the positive and negative electrode tabs of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used for electrical connection with the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used for electrical connection with the negative electrode plate of the electrode assembly 23.

[0083] In some embodiments, such as Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23.

[0084] The electrode assembly 23 includes a positive electrode 231, a negative electrode, and a separator. The positive electrode 231 includes a positive current collector 2311 and a positive active material layer 2312. The positive active material layer 2312 is coated on the surface of the positive current collector 2311. The positive current collector 2311 without the positive active material layer 2312 protrudes from the positive current collector 2311 with the positive active material layer 2312 coated. The positive current collector 2311 without the positive active material layer 2312 coated serves as a positive electrode tab.

[0085] The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector, and the negative current collector without the negative active material layer protrudes from the negative current collector with the negative active material layer. The negative current collector without the negative active material layer serves as the negative electrode tab. The material of the negative current collector can be copper, and the negative active material can be carbon or silicon, etc. To ensure that a large current can be passed without melting, there are multiple positive electrode tabs stacked together, and there are multiple negative electrode tabs stacked together. The material of the separator can be PP (polypropylene) or PE (polyethylene), etc. In addition, the electrode assembly 23 can be a wound electrode assembly or a stacked electrode assembly, and the embodiments of this application are not limited to this.

[0086] Figure 5 This is a first structural schematic diagram of the positive electrode 231 provided in some embodiments of this application. Figure 6 This is a schematic diagram of the second structure of the positive electrode 231 provided in some embodiments of this application; please refer to... Figure 5 and Figure 6 This application provides a positive electrode sheet, which includes a positive electrode active material layer. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer includes a first positive electrode active material, which is a ternary material system, comprising single-crystal particles and polycrystalline particles. The second positive electrode active material layer includes a second positive electrode active material, which is a polyanionic positive electrode material. The mass percentage w of the single-crystal particles in the ternary material system is... 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied:

[0087] The positive electrode active material layer 2312 is attached to at least a portion of the surface of the positive electrode current collector 2311. The first positive electrode active material layer 2312a and the second active material layer in the positive electrode active material layer 2312 can both be in direct contact with the positive electrode current collector 2311. In other words, the positional relationship between the first positive electrode active material layer 2312a, the second active material layer and the positive electrode current collector 2311 can be: the first positive electrode active material layer 2312a is attached to the positive electrode current collector 2311, and the second positive electrode active material layer 2312b is attached to the surface of the first positive electrode active material layer 2312a away from the surface of the positive electrode current collector 2311; or it can be: the second positive electrode active material layer 2312b is attached to the positive electrode current collector 2311, and the first positive electrode active material layer 2312a is attached to the surface of the second positive electrode active material layer 2312b away from the surface of the positive electrode current collector 2311.

[0088] The positive electrode current collector 2311 can be made of one or more of the following materials: aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Please continue reading. Figure 5 In one embodiment, a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b are sequentially disposed on one surface of the positive electrode current collector 2311; please continue reading Figure 6 In another embodiment, a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b are sequentially disposed on both surfaces of the positive electrode current collector 2311. It should be noted that this is only an example illustrating the feasibility of this solution; in other embodiments, the positions of the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be interchanged.

[0089] For lithium-ion batteries, the first positive electrode active material and the second positive electrode active material refer to substances that can insert and extract lithium ions.

[0090] Ternary materials typically include two types: NCA and NCM. NCA is widely used due to its long lifespan, large capacity, and high energy density; while NCM combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, exhibiting a significant ternary synergistic effect.

[0091] A single crystal refers to a crystal in which the particles within it are arranged in a regular and periodic manner in three-dimensional space; or, in other words, the entire crystal is composed of the same spatial lattice in three dimensions, and the arrangement of particles in space is long-range ordered. A polycrystalline material is a collection of single crystals with numerous oriented grains. A particle refers to a geometric body with a specific shape within a certain size range.

[0092] The median particle size (Dv50) is the particle size corresponding to 50% of the cumulative amount in the volumetric particle size distribution map. The volumetric particle size distribution map, also known as the differential particle size distribution map, is a curve plotted with particle size on the x-axis and the differential distribution of particle size at different dimensions on the y-axis. It can accurately reflect the particle size distribution characteristics of a material. A laser particle size analyzer can be used to determine the volumetric particle size distribution of the material and plot the interval particle size distribution curve. When measuring the median particle size of the positive electrode active material in the active material layer of the electrode sheet, the positive electrode active material layer can be removed, immersed in the solvent NMP, and the binder in the positive electrode active material layer can be washed out to obtain the powder material of the positive electrode active material layer. After drying the powder material, a Mastersizer3000 laser particle size analyzer is used to detect the volumetric particle size distribution map. The median particle size of polycrystalline and single-crystal particles can be obtained from the peaks in the volumetric particle size distribution map.

[0093] The median particle size (Dv50) of polycrystalline particles refers to the particle size that, when accumulated from smallest to largest, reaches 50% of the total volume. Similarly, the median particle size (Dv50) of single-crystal particles refers to the particle size that, when accumulated from smallest to largest, reaches 50% of the total volume.

[0094] Polyanionic cathode materials are a general term for a series of compounds containing tetrahedral or octahedral anionic structural units (XOm)n-. They have advantages such as high charge and discharge voltage, large energy storage capacity, fast charge and discharge capability and good cycle stability. Their synthesis methods mainly include: high temperature solid phase method, sol-gel method, hydrothermal method, electrospinning method, etc.

[0095] The mass ratio of single-crystal particles to polycrystalline particles can be obtained by using SEM test images to quantitatively distinguish the distribution ratio of single-crystal particles and polycrystalline particles.

[0096] By using a ternary system of single-crystal and polycrystalline materials in the first positive electrode active material layer, and by controlling the mass ratio w of the single-crystal particles... 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy This process creates a good particle size distribution between smaller single-crystal particles and larger polycrystalline particles, thereby improving the overall compaction density of the cathode sheet and increasing its energy density. It also narrows the Li ion transport path, reducing polarization and internal resistance when used in a battery, thus improving battery performance. Furthermore, separating the first and second cathode active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0097] For example, the mass percentage w of single-crystal particles in a ternary material system. 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 Satisfaction Relationship: The value can be 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, or 0.45, etc., or it can be any value in the range of 0.02 to 0.45.

[0098] In some embodiments of this application, the mass percentage w of the single-crystal particles in the ternary material system is... 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied: By controlling the mass ratio of single crystal particles w 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 satisfy It can further improve the compaction density of the entire positive electrode and increase its energy density.

[0099] In some embodiments of this application, the positive electrode 231 further includes a current collector. A first positive electrode active material layer is disposed on at least one surface of the current collector, and a second positive electrode active material layer 2312b is disposed on the surface of the first positive electrode active material layer 2312a away from the current collector. By disposing the second positive electrode active material layer 2312b, which has weaker ion transport performance, on the surface of the first positive electrode active material layer 2312a, when used as a battery, the second positive electrode active material layer 2312b is closer to the negative electrode, resulting in a shorter ion transport path, which is beneficial to improving its ion transport rate and thus enhancing its rate performance. Simultaneously, it can reduce the possibility of side reactions in the ternary system material, further improving the electrochemical performance of the positive electrode.

[0100] In some embodiments of this application, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: The thickness H1 of the first positive electrode active material layer is 5–35 μm; the thickness H2 of the second positive electrode active material layer is 35–80 μm. By controlling the relationship between the thicknesses H1 and H2 of the first and second positive electrode active material layers, the following conditions are met: The thickness H1 of the first positive electrode active material layer is 5–35 μm, and the thickness H2 of the second positive electrode active material layer is 35–80 μm. This allows for a suitable range of ternary material usage, maximizing the performance of the ternary system, such as energy density and lifespan, while reducing the probability of side reactions that could degrade battery performance and safety. Simultaneously, a shorter average transport distance for the entire second positive electrode active material layer is beneficial for its own ion transport rate and minimizes the weakening of the ion transport capability of the first positive electrode active material layer, thus achieving better rate performance. Furthermore, this allows for a suitable range of second positive electrode active material usage, further maximizing its performance, such as safety.

[0101] For example, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfy the following relationship: The value can be 0.8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, or any value within the range of 0.8 to 16. The thickness H1 of the first positive electrode active material layer can be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 31 μm, 33 μm, or 35 μm, or any value within the range of 5 to 35 μm. The thickness H2 of the second positive electrode active material layer can be 35μm, 37μm, 39μm, 40μm, 43μm, 45μm, 47μm, 49μm, 51μm, 53μm, 55μm, 57μm, 59μm, 61μm, 63μm, 65μm, 67μm, 69μm, 71μm, 73μm, 75μm, 77μm, 79μm, and 80μm, or any value within the range of 35 to 80μm.

[0102] In some embodiments of this application, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: The thickness H1 of the first positive electrode active material layer is 10–30 μm; the thickness H2 of the second positive electrode active material layer is 40–70 μm.

[0103] In some embodiments of this application, the relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: In the ternary material, the mass percentage of Ni (wNi) is 20%–55% of all elements; and the mass percentage of Mn (wMn) is 5%–25% of all elements. It should be noted that the values ​​of H1 and H2 are in μm.

[0104] The Ni and Mn content test of NCM material can be performed as follows: Take 0.4g of NCM material powder in a 25ml beaker, add 2ml-5ml of nitric acid, let it stand overnight, then place it on a hot plate and heat it at about 100℃ (using a voltage regulator to adjust the input voltage and control the temperature) until the powder is digested. Then add 0.5ml of perchloric acid and heat it at about 140℃ until the white fumes are exhausted. The residue should be white. Otherwise, nitric acid and perchloric acid should be added again for repeated digestion. Finally, dissolve and extract with 7% (volume percentage of acid, the same below) hydrochloric acid. Adjust the volume to an appropriate level according to the content of the element to be tested, and then test the mass fraction of Ni, Co, Mn and Li on an ICP-OES instrument. The mass of different elements can be calculated based on the powder mass and the mass fraction of different elements. The Ni and Mn content can be confirmed by different mass ratios.

[0105] In ternary cathode materials, the Ni content and the probability of side reactions are positively correlated to some extent; the higher the Ni content, the more likely side reactions are to occur. Similarly, the Mn content and structural stability are positively correlated to some extent; the higher the Mn content, the higher the structural stability. The thickness of the first cathode active material layer is also positively correlated to some extent with the probability of side reactions; a thicker layer corresponds to a higher content of the first cathode active material, making side reactions more likely. Likewise, the thickness of the second cathode active material layer is positively correlated to some extent with the probability of side reactions in the ternary cathode material; a thicker second cathode active material layer makes the ternary cathode material more prone to side reactions. By controlling the mass percentages of Ni (wNi), Mn (wMn), the thicknesses of the first and second cathode active material layers (H1 and H2), the following relationships are satisfied: In ternary materials, the mass percentage of Ni (wNi) is 20%–55% and the mass percentage of Mn (wMn) is 5%–25%. This reduces the probability of side reactions in ternary materials, while also giving the cathode good safety and cycle stability, and maintaining the energy density of the cathode.

[0106] For example, the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfy the following relationship: The value of can be 0.05, 0.5, 1, 1.5, 2, 2.5, 3, or 3.5, or any value within the range of 0.05 to 3.5. The mass percentage of Ni in the ternary material, wNi, can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, or 55%, or any value within the range of 20% to 55%. The mass percentage of Mn in the ternary material, wMn, can be 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, or 25%, or any value within the range of 5% to 25%.

[0107] In some embodiments of this application, the relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: In the ternary material, the mass percentage of Ni (wNi) is 30%–45% of all elements; and the mass percentage of Mn (wMn) is 10%–20% of all elements.

[0108] In some embodiments of this application, the single-crystal particles account for 10% to 40% of the mass of the ternary system material, and the polycrystalline particles account for 60% to 90% of the mass of the ternary system material; the median volumetric particle size of the single-crystal particles is 2.5 to 4.5 μm; and the median volumetric particle size of the polycrystalline particles is 8 to 10 μm.

[0109] For example, the mass percentage of single-crystal particles in the ternary system material can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40%, or any value within the range of 10% to 40%. The mass percentage of polycrystalline particles in the ternary system material can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%, or any value within the range of 60% to 90%. The median volumetric diameter of single-crystal particles can be 2.5 μm, 2.7 μm, 2.9 μm, 3.1 μm, 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.3 μm, or 4.5 μm, or any value within the range of 2.5 to 4.5 μm. The median volumetric diameter of polycrystalline particles can be 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm, 9.0 μm, 9.2 μm, 9.4 μm, 9.6 μm, 9.8 μm, or 10 μm, or any value within the range of 8 to 10 μm.

[0110] In some embodiments of this application, the second positive electrode active material includes a polyanionic positive electrode material. Optionally, the polyanionic positive electrode material includes LiMPO4, where M includes Mn and non-Mn elements.

[0111] It should be noted that the above LiMPO4 is not a specific molecular structure formula, but a general expression of lithium manganese phosphate.

[0112] In some embodiments of this application, the non-Mn element includes one or both of a first doping element and a second doping element, wherein the first doping element is manganese site doping and the second doping element is phosphorus site doping.

[0113] In some embodiments of this application, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0114] In some embodiments of this application, the first doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

[0115] In some embodiments of this application, the second doping element includes one or more elements selected from B, S, Si, and N.

[0116] In some embodiments of this application, the second positive electrode active material includes Li 1+x Mn 1-y Ay P 1-z R z O4, Li 1+x Mn 1-y A y P 1-z R z In O4, x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0117] In some embodiments of the technical solutions of this application, the compound Li 1+x Mn 1-y AyP 1-z The preparation method of RzO4 may include the following steps:

[0118] (1) Dissolve and stir the manganese source, the manganese-doped element A source and acid in a solvent to generate a suspension of manganese salt doped with element A. Filter the suspension and dry the filter cake to obtain manganese salt doped with element A.

[0119] (2) The lithium source, phosphorus source, element R source, solvent and manganese salt doped with element A obtained in step (1) are added to the reaction vessel, ground and mixed to obtain a slurry;

[0120] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0121] (4) The particles obtained in step (3) are sintered to obtain the positive electrode active material.

[0122] In any embodiment, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate, such as manganese source selected from one or a combination of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0123] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0124] In some embodiments of this application, the polyanionic cathode material includes Li h A i Mn 1-j Bj P 1-k C k O 4-l D l Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; h is selected from the range of 0.9 to 1.1, i is selected from the range of 0.001 to 0.1, j is selected from the range of 0.001 to 0.5, k is selected from the range of 0.001 to 0.1, l is selected from the range of 0.001 to 0.1, and the polyanionic cathode material is electrically neutral.

[0125] It should be noted that Li h A i Mn 1-j B j P 1-k C k O 4-l D l The compound is actually a specific LiMPO4 material. Its preparation method can be found in the Li... 1+x Mn 1-y A y P 1-z R z O4 is not specified here.

[0126] The following uses Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 The preparation process is further explained as follows: 1. Preparation of doped manganese oxalate: 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), resulting in a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain the median particle size Dv. 50The first step involves preparing Fe-doped manganese oxalate particles of approximately 100 nm. The second step involves preparing doped lithium manganese phosphate: 1 mol of the above manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose are added to 20 L of deionized water. The mixture is then transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry is then transferred to a spray drying equipment for spray drying and granulation. The drying temperature is set at 250℃, and the granules are dried for 4 hours to obtain particles. Under a nitrogen (90% by volume) + hydrogen (10% by volume) protective atmosphere, the above powder is sintered at 700℃ for 10 hours to obtain carbon-coated Li. 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0127] In some embodiments of this application, the second positive electrode active material further has a carbon-containing coating layer.

[0128] The conductivity of the positive electrode active material is improved by introducing a carbon-containing coating layer. In this case, the structure of the positive electrode active material is actually a core-shell structure with LiMPO4 as the core and the surface of the core coated with a coating layer.

[0129] In the examples of cathode materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0130] Furthermore, due to differences in material preparation processes and conditions, the molar content of oxygen is usually not strictly the same as the coefficient of oxygen in the chemical formula, and fluctuations may occur. For example, in Li... 1+x Mn 1-y A y P 1-z R z The molar content of O in O4 is not strictly 4.

[0131] For example, the second positive electrode active material can be LiFePO4 or LiMn. 0.1 Fe 0.9 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.9 Fe 0.1 PO4, LiMnPO4, LiMn 0.5 Al 0.5 P 0.5 B 0.5 O4, LiMn 0.5 Mg 0.5 P 0.5 S 0.5 O4, etc. In LiMPO4, M includes Mn and non - Mn elements. The non - Mn elements include one or two of the first doping element and the second doping element. The first doping element is doped at the Mn site, and the second doping element is doped at the P site. The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; the second doping element includes one or more elements selected from B, S, Si, and N.

[0132] In the technical solutions of some embodiments of the present application, the ternary system material includes nickel - cobalt - manganese ternary materials and their modified materials, and nickel - cobalt - aluminum ternary materials and their modified materials. Among them, the ternary system material includes nickel - cobalt - manganese ternary materials and their modified materials, and nickel - cobalt - aluminum ternary materials and their modified materials.

[0133] In the technical solutions of some embodiments of the present application, the ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3. M1 is selected from one or two elements of Mn or Al, M2 is selected from one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from one or more elements of N, F, S, Cl.

[0134] Exemplarily, the ternary system material can be LiNi 0.4 Co 0.2 Mn 0.4O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 and LiNi 0.7 Co 0.15 Mn 0.15 O2, etc. Li a Ni b Co c M1 d M2 e O f R g In the formula, a can be any one or more values within the range of 0.75 to 1.2, b can be any one or more values within the range of 0.3 to 1.0, c can be any one or more values within the range of 0 to 0.4, d can be any one or more values within the range of 0 to 1, e can be any one or more values within the range of 0 to 0.2, f can be any value within the range of 1 to 2.5, and g can be any one or more values within the range of 0 to 1.

[0135] It should be noted that the above enumeration of the first positive electrode active material and the second positive electrode active material is only for illustrative purposes to show that the present solution can be implemented, and is not intended to limit the present solution. In other embodiments, those skilled in the art can select specific substances of the first positive electrode active material and the second positive electrode active material according to actual needs, such as the materials listed above and their modified substances, and the modification includes doping or coating, etc.

[0136] After introducing the materials and structure of the positive electrode sheet 231 as described above, the preparation method of the positive electrode sheet 231 will be specifically introduced below.

[0137] The preparation method of the positive electrode sheet 231 includes the following steps: preparing a positive electrode active material layer 2312 on the positive electrode current collector 2311. The preparation sequence of the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b in the positive electrode active material layer 2312 is not limited. It can be: setting the first positive electrode active material layer 2312a on at least part of the surface of the positive electrode current collector 2311, and setting the second positive electrode active material layer 2312b on at least part of the surface of the first positive electrode active material away from the positive electrode current collector 2311; or it can be: setting the second positive electrode active material layer 2312b on at least part of the surface of the positive electrode current collector 2311, and setting the first positive electrode active material layer 2312a on at least part of the surface of the second positive electrode active material layer 2312b away from the positive electrode current collector 2311. The first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, and the mass fraction w 单 of the single crystal particles in the ternary system material, the volume median diameter D 单 in μm of the single crystal particles, the mass fraction w 多 of the polycrystalline particles in the ternary system material, and the volume median diameter D 多 in μm of the polycrystalline particles satisfy the following relationship:

[0138] By using a ternary system material of single crystal particles and polycrystalline particles in the first positive electrode active material layer in combination, and by controlling the mass fraction w 单 of the single crystal particles, the particle size D 单 of the single crystal particles, the mass fraction w 多 of the polycrystalline particles, and the particle size D 多 of the polycrystalline particles to satisfy a good particle size distribution is formed between the smaller single crystal particles and the larger polycrystalline particles, thereby improving the tap density of the entire positive electrode sheet and increasing its energy density. And it can make the transmission path of Li ions within a smaller range, weaken the polarization and the increase of internal resistance when used as a battery, which is beneficial to the performance of the battery. At the same time, by setting the first positive electrode active material and the second positive electrode active material in layers, the possibility of uneven current between the first positive electrode active material and the second positive electrode active material can be reduced, and thus the positive electrode sheet has a high capacity retention rate in the early stage of cycling.

[0139] Figure 7 The flowchart of the preparation method of the positive electrode sheet 231 provided by some embodiments of the present application is shown in Figure 7 . Embodiments of the present application provide a preparation method of a positive electrode sheet 231. The method includes:

[0140] S110, Preparation of the first positive electrode active slurry: The first positive electrode active material, binder, and conductive agent are dispersed in a solvent to form the first positive electrode active slurry. The first positive electrode active material can be the aforementioned first positive electrode active material, for example, a material with the chemical formula LiNi. x Co y Mn z O2, a ternary system material (0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), and optionally, a small amount of other positive electrode active materials can be added.

[0141] For the specific selection of ternary system materials, please refer to the selection of ternary system materials in the first positive electrode active material layer 2312a in the aforementioned positive electrode sheet 231, which will not be repeated here.

[0142] The binder can be one or more of styrene-butadiene rubber, waterborne acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polyvinyl butyral. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The solvent can be one or more of dimethyl glutarate and N-methylpyrrolidone. Leveling agents, dispersants, etc., can also be added to the first positive electrode active slurry.

[0143] S120, Preparation of the second positive electrode active slurry: The second positive electrode active material, binder, and conductive agent are dispersed in a solvent to form the second positive electrode active slurry. The second positive electrode active material can be the aforementioned second positive electrode active material, for example, a material with the chemical formula LiMn. a Fe 1-a PO4, (0≤a≤1) polyanionic cathode material, and optional small amounts of other cathode active materials may also be added.

[0144] For the specific selection of polyanionic cathode materials, please refer to the selection of polyanionic cathode materials in the second positive electrode active material layer 2312b of the aforementioned cathode sheet 231, which will not be repeated here.

[0145] The binder, conductive agent, and solvent can be the same as those in the first positive electrode active slurry. The binder in the first positive electrode active slurry can be the same as or different from the binder in the second positive electrode active material; the conductive agent in the first positive electrode active slurry can be the same as or different from the conductive agent in the second positive electrode active material; and the solvent in the first positive electrode active slurry can be the same as or different from the solvent in the second positive electrode active material. Furthermore, leveling agents, dispersants, etc., can also be added to the second positive electrode active slurry; this application does not impose any limitations on this.

[0146] S130, Preparation of the first positive electrode active material layer 2312a: The first positive electrode active slurry is coated on the surface of the positive electrode current collector 2311, and then dried to form the first positive electrode active material layer 2312a. During coating, it can be applied to one or both surfaces of the positive electrode current collector 2311 as needed.

[0147] The coating method can be, for example, scraping, roller coating, or slot coating; this application does not limit the method. It should be noted that steps S120 and S130 can be interchanged or performed simultaneously; this application does not limit the method.

[0148] S140, Preparation of the second positive electrode active material layer 2312b: The second positive electrode active slurry is coated onto the surface of the first positive electrode active material layer 2312a, and then dried to form the second positive electrode active material layer 2312b. During coating, the second positive electrode active material layer 2312b can be formed on the surface of the first positive electrode active material layer 2312a, depending on the condition of the first positive electrode active material layer 2312a.

[0149] S150, roll-press the second positive electrode active material layer 2312b to obtain the positive electrode sheet 231.

[0150] It should be noted that the above is only an example of sequentially setting the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b in the positive electrode current collector 2311. In other embodiments, the positions of the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b can be interchanged.

[0151] After preparing the positive electrode 231, the first separator, the positive electrode 231, the second separator, and the negative electrode are stacked in sequence, wound to form a wound flat structure, and then hot-pressed to obtain a wound electrode assembly; or, after preparing the positive electrode 231, the positive electrode 231, the separator, the negative electrode, the separator, and so on are stacked in sequence to form a stacked electrode assembly.

[0152] The electrode assembly 23 can be used to prepare a battery cell 20, which can be used to prepare a secondary battery 100 and provide electrical energy to the electrical device.

[0153] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0154] Examples and Comparative Examples

[0155] [Preparation of the positive electrode plate]

[0156] Preparation of the first positive electrode active material layer: The first positive electrode active material LiNi... 0.55 Co0.12 Mn 0.33 O2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP), with PVDF comprising 2.5% by mass. The mixture was stirred until homogeneous to obtain the first coating slurry. The slurry was then applied at a concentration of 90 mg / 1540.25 mm. 2 The material is uniformly coated onto the positive electrode current collector and dried to obtain the first positive electrode active material layer.

[0157] Preparation of the second positive electrode active material layer: The second positive electrode active material LiMn... 0.6 Fe 0.4 PO4, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:2.5 and stirred until homogeneous to obtain the second coating slurry; then the slurry was applied at a rate of 200 mg / 1540.25 mm. 2 The material is uniformly coated onto the first positive electrode active material layer, dried, and then rolled and die-cut to obtain the positive electrode sheet for lithium-ion batteries.

[0158] [Preparation of the negative electrode]

[0159] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 90:5:3:2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0160] Preparation of Electrolyte

[0161] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) / diethyl carbonate (DEC) / ethyl methyl carbonate (EMC) are mixed evenly in a volume ratio of 1 / 1 / 1. 1 mol / L LiPF6 lithium salt is added and dispersed evenly. Then, 5% fluoroethylene carbonate is dissolved in the above organic solvent and stirred evenly to obtain the electrolyte.

[0162]

Isolation Film

[0163] A polyethylene film with a thickness of 7 μm is used as the separator.

[0164] [Preparation of Lithium-ion Batteries]

[0165] The prepared positive electrode sheet, negative electrode sheet, and separator (polyethylene (PE) porous polymer film) are wound to form the corresponding battery cell. The battery cell is hot-pressed at 90°C, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs, and the negative electrode uses copper tabs, with the positive and negative electrode tabs located on the same side of the battery cell. The battery cell with welded tabs is then installed into an aluminum shell of appropriate size for flexible connection and top cover welding. The battery cell is vacuum dried at 175°C for 24 hours, then injected with electrolyte and sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, formation, aging, venting, re-sealing, and capacity testing to obtain the lithium-ion battery product.

[0166] The main parameter controls for each embodiment and comparative example are shown in the table below:

[0167]

[0168]

[0169] In the table above, the Ni and Mn content of NCM material can be tested as follows: Take 0.4g of NCM material powder from the electrode layer into a 25ml beaker, add 2ml-5ml of nitric acid, let it stand overnight, then place it on a hot plate and heat it at about 100℃ (using a voltage regulator to adjust the input voltage and control the temperature) until the powder is digested. Then add 0.5ml of perchloric acid and heat it at about 140℃ to digest until the white fumes are exhausted. The residue should be white. Otherwise, nitric acid and perchloric acid should be added again for repeated digestion. Finally, dissolve and extract with 7% (referring to the volume percentage of acid, the same below) hydrochloric acid. Adjust the volume to an appropriate level according to the content of the element to be tested, and then test the mass fraction of Ni, Co, Mn, and Li on an ICP-OES instrument. Based on the powder mass and the mass fraction of different elements, the mass of different elements can be calculated. The Ni and Mn content can be confirmed by different mass ratios.

[0170] Example 24

[0171] Except for the exchange of positions between the first positive electrode active material layer and the second positive electrode active material layer, this embodiment is the same as Embodiment 2.

[0172] The performance of the batteries provided in each embodiment and comparative example was tested. The performance testing specifically included:

[0173] The method for testing electrode compaction density is as follows: Based on the energy density design requirements, the electrode coating surface density can be determined. After the electrode is dried and cold-pressed, the total thickness of the electrode is measured using a micrometer screw gauge. Subtracting the thickness of the current collector, the coating thickness can be calculated. Based on the coating surface density and coating thickness, the electrode compaction density can be calculated.

[0174] The rate performance test method is as follows: In a 25℃ environment, a charge-discharge test is performed. Constant current discharge is applied at a discharge current of 0.33C (the current value required to completely discharge the theoretical capacity within 3 hours) until the voltage reaches 2.5V. Then, constant current charging is applied at a charging current of 0.33C until the voltage reaches 4.4V, followed by constant voltage charging until the current reaches 0.05C, at which point the battery is fully charged. After the fully charged cell is allowed to rest for 5 minutes, it is discharged at a constant current of 0.33C until 2.5V. The discharge capacity at this point is the actual capacity of the cell at 0.33C, denoted as C0. Then, the cell is charged at a constant current of 0.33C until 4.4V, followed by constant voltage charging until the current reaches 0.05C. After resting for 5 minutes, it is discharged at a constant current of 1C until 2.5V, and the discharge capacity C1 is recorded as the 1C discharge capacity. The 1C rate capacity retention rate = (1C discharge capacity / 0.33C discharge capacity) × 100%.

[0175] 25℃ Cycling Test: The lithium-ion battery product prepared above was charged to 4.4V at 0.33C in a constant temperature environment of 25℃ and 2.5~4.4V. Then, it was charged at 4.4V at a constant voltage until the current ≤0.05C. After standing for 5 minutes, it was discharged to 2.5V at 0.33C. The capacity was recorded as Cn (n=1,2,3……). The above operation was repeated. After 500 cycles, the capacity retention rate was calculated according to the ratio of C500 / C3, which was used as the evaluation index of cycle capability.

[0176] 25℃ Cyclic Internal Resistance Growth Test: ① Initial Internal Resistance Test: The prepared prismatic battery was charged at 0.33C to 4.4V in a constant temperature environment of 25℃ and 2.5~4.4V. Then, it was charged at a constant voltage of 4.4V until the current ≤0.05C. After standing for 30 minutes, the voltage U1 was recorded. Then, it was discharged at 1C for 30s, and the voltage at 30s was recorded as U2. Internal resistance 1=(U1-U2) / 1C; ② Internal Resistance Test after 500 Cycles: After testing the cycle performance of the battery after the initial internal resistance test, the internal resistance 2 was tested again. Internal resistance growth rate=(internal resistance 2-internal resistance 1) / internal resistance 1.

[0177] The test results are shown in the table below:

[0178]

[0179]

[0180] It should be noted that the compaction density of Examples 1 to 7 and Comparative Examples 1 to 2 is the maximum compaction density that the electrode can achieve, while Examples 8 to 24 are compared and evaluated with Example 2. Therefore, their compaction density is a parameter that needs to be controlled, and is not the maximum compaction density of the electrode.

[0181] As shown in the table above, the positive electrode sheet provided in this application has a high compaction density, reaching 3 g / cm³. 3 The above features high rate performance, reaching over 95%, high capacity retention, reaching over 89%, and low cycle resistance growth rate, not exceeding 80%.

[0182] A comparison of Examples 2, 4 to 7, and Comparative Examples 1 to 2 shows that as the mass percentage of single crystal particles w increases... 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 Satisfaction Relationship As the value gradually increases, the compaction density, rate performance, and capacity retention of the electrode all show a trend of first increasing and then decreasing, while the growth rate of the electrode's cycle resistance shows a trend of first decreasing and then increasing, and the mass proportion of single crystal particles w... 单 The particle size D of single crystal particles 单 The mass percentage of polycrystalline particles w 多 The particle size D of polycrystalline particles 多 Satisfaction Relationship When the value is in the range of 0.02 to 0.45, the compaction density of the electrode can reach 3 g / cm³. 3 The above results indicate that the rate performance can reach over 98%, the capacity retention rate can reach over 90%, and the cycle resistance growth rate does not exceed 60%. It is evident that a value between 0.02 and 0.45 represents an optimal range for this relationship. Furthermore, when this relationship is between 0.15 and 0.3, the electrode compaction density can reach 3.1 g / cm³. 3 With a rate performance of around 99%, a capacity retention of around 94%, and a cycle resistance growth rate of around 40%, it is evident that a value between 0.15 and 0.3 is a better range for this relationship.

[0183] A comparison of Examples 2 and 8 to 11 shows that as the thickness H1 of the first positive electrode active material layer gradually increases, the rate performance and capacity retention of the electrode both show a trend of first increasing and then decreasing, while the cycle resistance growth rate of the electrode shows a trend of first decreasing and then increasing. When the thickness H1 of the first positive electrode active material layer is in the range of 5 to 35 μm, the rate performance can reach more than 98.9%, the capacity retention rate can reach more than 93.2%, and the cycle resistance growth rate does not exceed 50%. It can be seen that the thickness H1 of the first positive electrode active material layer is in the range of 5 to 35 μm, which is a better range.

[0184] A comparison of Examples 2 and 12 to 15 shows that as the thickness H2 of the second positive electrode active material layer gradually increases, the rate performance and capacity retention of the electrode both show a trend of first increasing and then decreasing, while the cycle resistance growth rate of the electrode shows a trend of first decreasing and then increasing. When the thickness H2 of the second positive electrode active material layer is in the range of 35 to 80 μm, the rate performance can reach more than 98.6%, the capacity retention rate can reach more than 92.9%, and the cycle resistance growth rate does not exceed 59%. It can be seen that the thickness H2 of the second positive electrode active material layer is in the range of 35 to 80 μm, which is a better range.

[0185] By comparing Examples 2 and Examples 16 to 19, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer can be obtained. As the value gradually increases, the rate performance and capacity retention of the electrode both show a trend of first increasing and then decreasing, while the cycle resistance growth rate of the electrode shows a trend of first decreasing and then increasing. Furthermore, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is... When the value is in the range of 1 to 16, the rate performance can reach over 98.2%, the capacity retention rate can reach over 92.6%, and the cycle resistance growth rate does not exceed 59%. This demonstrates the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer. A value between 1 and 16 is considered optimal.

[0186] By comparing Examples 2 and Examples 20 to 23, the relationship between the mass percentage of Ni (wNi), the mass percentage of Mn (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer can be obtained. As the value gradually increases, the rate performance and capacity retention of the electrode both show a trend of first increasing and then decreasing, while the cycle resistance growth rate of the electrode shows a trend of first decreasing and then increasing. Furthermore, the relationships between the mass percentage of Ni (wNi), the mass percentage of Mn (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer are as follows: When the value is in the range of 0.05 to 3.5, the rate performance can reach over 98.1%, the capacity retention can reach over 90.4%, and the cycle resistance growth rate does not exceed 53%. This demonstrates the relationship between the mass ratio of Ni (wNi), the mass ratio of Mn (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer. A value between 0.05 and 3.5 is considered optimal.

[0187] A comparison of Examples 2 and 24 shows that when ternary materials are placed in the inner layer, it is more beneficial to the rate performance, capacity retention, and cycle resistance growth rate of the battery.

[0188] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a current collector and a positive electrode active material layer disposed on at least a portion of the surface of the current collector. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, which are located on one side of the current collector. The first positive electrode active material layer includes a first positive electrode active material, which is a ternary material system, comprising single-crystal particles and polycrystalline particles. The second positive electrode active material layer includes a second positive electrode active material, which is a polyanionic positive electrode material. The mass percentage w of the single-crystal particles in the ternary material system is... 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied: The relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: .

2. The positive electrode sheet according to claim 1, characterized in that, The mass percentage w of the single crystal particles in the ternary system material 单 The median volume diameter D of the single crystal particles, measured in μm. 单 The mass percentage w of the polycrystalline particles in the ternary material system 多 and the volume median particle size D of the polycrystalline particles in μm. 多 The following relationship must be satisfied: .

3. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet further includes a current collector, the first positive electrode active material layer is disposed on at least one surface of the current collector, and the second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the current collector.

4. The positive electrode sheet according to claim 1, characterized in that, The thickness H1 of the first positive electrode active material layer is 5~35μm; and / or The thickness H2 of the second positive electrode active material layer is 35~80μm.

5. The positive electrode sheet according to claim 4, characterized in that, The relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: ; and / or The thickness H1 of the first positive electrode active material layer is 10~30 μm; and / or The thickness H2 of the second positive electrode active material layer is 40~70μm.

6. The positive electrode sheet according to claim 1, characterized in that, The relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: ; and / or In the ternary material, the mass percentage of Ni (wNi) among all elements is 20%~55%; and / or In the ternary material, the mass percentage of Mn among all elements is 5% to 25%.

7. The positive electrode sheet according to claim 6, characterized in that, The relationship between the mass percentage of Ni in the ternary material (wNi), the mass percentage of Mn in the ternary material (wMn), the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: ; and / or In the ternary material, the mass percentage of Ni (wNi) among all elements is 30%~45%; and / or In the ternary material, the mass percentage of Mn among all elements is 10% to 20%.

8. The positive electrode sheet according to claim 1, characterized in that, The single-crystal particles account for 10% to 40% of the mass of the ternary material, and the polycrystalline particles account for 60% to 90% of the mass of the ternary material; and / or The median volumetric diameter of the single crystal particles is 2.5~4.5 μm; and / or The median volumetric diameter of the polycrystalline particles is 8~10 μm.

9. The positive electrode sheet according to claim 1, characterized in that, The ternary system materials include nickel-cobalt-manganese ternary materials and their modified materials, and nickel-cobalt-aluminum ternary materials and their modified materials; and / or The polyanionic cathode material includes LiMPO4, where M includes Mn and non-Mn elements. The non-Mn elements include one or both of a first doping element and a second doping element, wherein the first doping element is manganese site doping and the second doping element is phosphorus site doping.

10. The positive electrode sheet according to claim 9, characterized in that, The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or The second doping element includes one or more elements selected from B, S, Si, and N.

11. The positive electrode sheet according to claim 9, characterized in that, The polyanion cathode material includes Li 1+x Mn 1- y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

12. The positive electrode sheet according to claim 9, characterized in that, The polyanion cathode material includes Li h A i Mn 1-j B j P 1-k C k O 4-l D l The polyanionic cathode material is electrically neutral. Specifically, A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from B, S, Si, and N; D comprises one or more elements selected from S, F, Cl, and Br; h is selected from the range of 0.9 to 1.1; i is selected from the range of 0.001 to 0.1; j is selected from the range of 0.001 to 0.5; k is selected from the range of 0.001 to 0.1; l is selected from the range of 0.001 to 0.

1.

13. The positive electrode sheet according to claim 9, characterized in that, The polyanionic cathode material also has a carbon-containing coating layer.

14. The positive electrode sheet according to claim 9, characterized in that, The ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is selected from one or two elements of Mn or Al, M2 is selected from one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from one or more elements of N, F, S, Cl.

15. A single battery cell, characterized in that, The battery cell includes the positive electrode sheet according to any one of claims 1 to 14.

16. A battery, characterized in that, The battery comprises the battery cell of claim 15.

17. An electrical device, characterized in that, The electrical device includes the battery cell of claim 15 or the battery of claim 16.

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