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. The positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises at least three sublayers, the difference value m of the electronic conductivity multiple of the positive electrode active material of the two sublayers farthest apart in the positive electrode active material layer is not less than 1000, and the difference value n of the electronic conductivity multiple of the positive electrode active material of the two adjacent sublayers is less than 1000. The sublayer formed by the positive electrode active material with the electronic conductivity between the two is arranged between the two sublayers formed by the positive electrode active material with the electronic conductivity multiple difference value not less than 1000, so that the electronic conductivity multiple difference value between the sublayers is less than 1000, the probability of over-discharge of the positive electrode active material with small electronic conductivity at the interface between the sublayers is reduced, and the electric performance of the whole positive electrode sheet is improved.

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, even after the positive electrode sheets are arranged in layers, there is still a problem of poor electrical performance. 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 reduce the conductivity difference between sublayers of each positive electrode active material and improve the performance of electrical components.

[0004] In a first aspect, this application provides a positive electrode sheet, which includes a positive electrode active material layer, the positive electrode active material layer including at least three sub-layers, wherein the difference m between the electronic conductivity multiples of the positive electrode active materials of the two farthest sub-layers in the positive electrode active material layer is not less than 1000, and the difference n between the electronic conductivity multiples of the positive electrode active materials of the two adjacent sub-layers is less than 1000.

[0005] In the technical solution of this application embodiment, by setting a sublayer composed of a positive electrode active material with an electronic conductivity between two sublayers composed of two positive electrode active materials with an electronic conductivity difference of not less than 1000, the electronic conductivity difference between each sublayer is less than 1000. This reduces the probability of over-discharge of the positive electrode active material with lower electronic conductivity at the interface where the sublayers contact each other, thereby improving the electrical performance of the entire positive electrode sheet. At the same time, setting each positive electrode active material in layers can reduce the possibility of current unevenness between positive electrode active materials, thereby enabling the positive electrode sheet to have a higher capacity retention rate in the early stage of cycling.

[0006] In some embodiments, the ratio of the difference in electronic conductivity (n) between any of the middle sublayers in the positive electrode active material layer and its two adjacent sublayers does not exceed 10.

[0007] In the above implementation process, by controlling the ratio of the difference in electronic conductivity multiple n between the sublayer and the two adjacent sublayers to not exceed 10, the probability of over-discharge of the positive electrode active material with small electronic conductivity at the interface between each sublayer is further reduced, which is more beneficial to the electrical performance of the entire positive electrode sheet.

[0008] In some embodiments, the total thickness of the two farthest sublayers in the positive electrode active material layer accounts for at least 80% of the total thickness of the positive electrode active material layer.

[0009] In the above implementation process, by controlling the total thickness of the two farthest sublayers to be at least 80% of the positive electrode active material layer, the performance of the positive electrode active material in these two sublayers can be fully utilized, and the impact of the addition of the intermediate sublayer on the overall electrode performance can be reduced.

[0010] In some embodiments, the positive electrode sheet further includes a positive current collector, and a layer of positive active material is disposed on at least one side surface of the positive current collector, wherein the electronic conductivity of the positive active material is greater in the sublayer closer to the positive current collector.

[0011] In the above implementation process, by placing the positive electrode active material with higher electronic conductivity closer to the positive electrode current collector, the probability of polarization of the positive electrode sheet can be reduced, which is also beneficial to the rate performance and cycle performance of the positive electrode sheet.

[0012] In some embodiments, the positive electrode active material layer includes a first positive electrode active material sublayer, a second positive electrode active material sublayer, and a transition positive electrode active material sublayer disposed between the first positive electrode active material sublayer and the second positive electrode active material sublayer. The first positive electrode active material sublayer includes a first positive electrode active material, the second positive electrode active material sublayer includes a second positive electrode active material, and the transition positive electrode active material sublayer includes a transition positive electrode active material. The electronic conductivity a of the first positive electrode active material, the electronic conductivity b of the transition positive electrode active material, and the electronic conductivity c of the second positive electrode active material satisfy the following relationships: 30 < a: b < 1000, 30 < b: c < 1000.

[0013] In the above implementation process, it is usually only necessary to set a transition positive electrode active material sub-layer to reduce the difference in electronic conductivity multiple of the positive electrode active materials of each adjacent sub-layer to less than 1000, which can achieve a good improvement in the electrical performance of the positive electrode sheet with a relatively simple structure.

[0014] In some embodiments, the electronic conductivity α of the first positive electrode active material is 10. -2 ~10 -1 S / cm; and / or

[0015] The electronic conductivity b of the transition cathode active material is 10. -4 ~10 -2 S / cm; and / or

[0016] The electronic conductivity c of the second positive electrode active material is 10. -6 ~10 -4 S / cm.

[0017] In some embodiments, the first positive electrode active material includes at least one of a spinel structure positive electrode material, a layered structure positive electrode material, and a olivine structure phosphate positive electrode material; and / or

[0018] The second positive electrode active material includes at least one of the following: spinel structure positive electrode material, layered structure positive electrode material, and olivine structure phosphate positive electrode material.

[0019] In some embodiments, the first positive electrode active material includes Li a Ni b Mn c M1 2-b-c At least one of O4 and LiM2PO4, wherein 0.9≤a≤1.1, 0≤b≤2, 0≤c≤2, b+c=2, M1 includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and M2 includes Mn and non-Mn elements, wherein 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; and / or

[0020] The second positive electrode active material includes Li d Ni x Co y M3 1-x-y O 2+e M3 includes at least one of zLi2MnO3·(1-z)LiM4O2, wherein 0.2≤d<1.2, 0≤x≤1.0, 0≤y≤1.0, x+y≤1, -0.02≤e<0.02, M3 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M4 includes at least one of Co, Ni, and Mn.

[0021] In the above implementation process, Li a Ni b Mn c M1 2-b-c O4 and LiM2PO4 generally exhibit good safety performance, while Li d Ni x Co y M3 1-x-y O 2+e zLi₂MnO₃·(1-z)LiM₄O₂ typically exhibits higher energy density, and Li₂MnO₃·(1-z)LiM₄O₂ is used in this process. a Ni b Mn c M1 2-b-c Either O4 or LiM2PO4 can be used as the second positive electrode active material, Li d Ni x Co y M3 1-x-y O 2+eUsing either zLi2MnO3·(1-z)LiM4O2 as the first positive electrode active material can enable the positive electrode to have both high safety performance and high energy density.

[0022] Secondly, this application provides a positive electrode sheet, which includes a positive electrode active material layer, the positive electrode active material layer including a first positive electrode active material sublayer, a second positive electrode active material sublayer, and a transition positive electrode active material sublayer disposed between the first positive electrode active material sublayer and the second positive electrode active material sublayer, the thickness of the transition positive electrode active material sublayer being less than 20% of the thickness of the positive electrode active material layer; the first positive electrode active material sublayer includes a first positive electrode active material, the second positive electrode active material sublayer includes a second positive electrode active material, and the transition positive electrode active material sublayer includes a transition positive electrode active material; the electronic conductivity a of the first positive electrode active material, the electronic conductivity b of the transition positive electrode active material, and the electronic conductivity c of the second positive electrode active material satisfy the following relationships: a:c≥1000, 30<a:b<1000, 30<b:c<1000.

[0023] In the technical solution of this application embodiment, a transition positive electrode active material sublayer with an electronic conductivity between the first positive electrode active material sublayer composed of a first positive electrode active material with an electronic conductivity difference of not less than 1000 is provided between the second positive electrode active material sublayer composed of a second positive electrode active material and a first positive electrode active material sublayer composed of a first positive electrode active material with an electronic conductivity difference of not less than 1000. This reduces the probability of over-discharge of the positive electrode active material with a smaller electronic conductivity at the interface where the sublayers contact each other, thereby improving the electrical performance of the entire positive electrode sheet. Furthermore, by controlling the thickness of the transition positive electrode active material sublayer to be less than 20% of the positive electrode active material layer, its influence on the performance of the first and second positive electrode active materials is reduced, which is more beneficial to the performance of the positive electrode sheet. At the same time, the layering of each positive electrode active material can reduce the possibility of current unevenness between the positive electrode active materials, thereby enabling the positive electrode sheet to have a higher capacity retention rate in the early stage of cycling.

[0024] Thirdly, this application provides a battery cell, which includes the positive electrode provided in the first or second aspect.

[0025] Fourthly, this application provides a battery, which includes the battery cell provided in the third aspect.

[0026] 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

[0027] 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:

[0028] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0029] Figure 2 This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0030] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0031] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0032] Figure 5 This is a first structural schematic diagram of the positive electrode sheet provided in some embodiments of this application;

[0033] Figure 6 This is a schematic diagram of the second structure of the positive electrode sheet provided in some embodiments of this application;

[0034] Figure 7 A flowchart illustrating a method for preparing a positive electrode sheet according to some embodiments of this application.

[0035] The reference numerals in the detailed embodiments are as follows:

[0036] 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 sublayer; 2312b - Transitional positive active material sublayer; 2312c - Second positive active material sublayer; 24 - Current collector component; 25 - Insulation protection component. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] However, when a positive electrode active material with high energy density and a positive electrode active material with high safety performance are simultaneously incorporated 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 can lead to rapid decay of the positive electrode in the early stage of cycling, which has a significant impact on the cycle retention rate of the positive electrode.

[0048] 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, after the layers are set, the conductivity difference between the two positive electrode active material layers is large, which makes the positive electrode 231 still have the problem of poor electrical performance.

[0049] Based on the above considerations, in order to reduce the conductivity differences between the positive electrode active material layers and improve the electrical performance, this application proposes a positive electrode sheet. The positive electrode sheet includes a positive electrode active material layer, which includes at least three sub-layers. The difference in electronic conductivity (m) between the positive electrode active materials of the two sub-layers that are furthest apart (d) is not less than 1000, and the difference in electronic conductivity (n) between the positive electrode active materials of two adjacent sub-layers is less than 1000.

[0050] In this type of positive electrode, by setting a sublayer of positive active material with an electronic conductivity between two sublayers composed of positive active materials with an electronic conductivity difference of not less than 1000, the electronic conductivity difference between the sublayers is reduced to less than 1000. This reduces the probability of over-discharge of the positive active material with lower electronic conductivity at the interface between the sublayers, thereby improving the overall electrical performance of the positive electrode. Simultaneously, layering the positive active materials reduces the possibility of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0051] 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. The power system of such an electrical device can be composed of battery cells, secondary batteries, etc., disclosed in this application.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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 231, which includes a positive electrode active material layer 2312. The positive electrode active material layer 2312 includes at least three sub-layers. The difference m between the electronic conductivity multiples of the positive electrode active materials of the two sub-layers that are furthest apart in the positive electrode active material layer 2312 is not less than 1000, and the difference n between the electronic conductivity multiples of the positive electrode active materials of the two adjacent sub-layers is less than 1000.

[0071] 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 two farthest sublayers refer to the two sublayers closest to and furthest from the positive electrode current collector 2311; electronic conductivity refers to the conductivity of electrons in a material under the action of an electric field; the difference m in the electronic conductivity multiple of the positive electrode active materials of the two farthest sublayers is obtained by dividing the electronic conductivity of the larger positive electrode active material by the electronic conductivity of the smaller positive electrode active material; wherein, the sublayer composed of the positive electrode active material with the larger electronic conductivity can be in direct contact with the positive electrode current collector 2311, or the sublayer composed of the positive electrode active material with the smaller electronic conductivity can be in direct contact with the positive electrode current collector 2311. The difference n in the electronic conductivity multiple of the positive electrode active materials of two adjacent sublayers is obtained by dividing the electronic conductivity of the larger positive electrode active material by the electronic conductivity of the smaller positive electrode active material.

[0072] 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 5In one embodiment, a positive electrode active material layer 2312 is disposed on one surface of the positive electrode current collector 2311; please continue reading Figure 6 In another embodiment, a positive electrode active material layer 2312 is provided on both surfaces of the positive electrode current collector 2311.

[0073] For lithium-ion batteries, the positive electrode active material in each sublayer refers to the material that can insert and extract lithium ions.

[0074] The positive electrode 231 incorporates a sublayer of positive active material with intermediate electronic conductivity between two sublayers composed of positive active materials with a difference in electronic conductivity of not less than 1000. This reduces the probability of over-discharge of the positive active material with lower electronic conductivity at the interface between the sublayers, thereby improving the overall electrical performance of the positive electrode 231. Furthermore, the layered arrangement of the positive active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0075] In some embodiments of this application, the ratio of the difference in electronic conductivity (n) between any middle sublayer of the positive electrode active material layer 2312 and its two adjacent sublayers does not exceed 10.

[0076] In the positive electrode active material layer 2312, the middle sublayer refers to the sublayer located between the two farthest sublayers in the positive electrode active material layer 2312. The ratio of the electronic conductivity multiple difference n between any middle sublayer and its two adjacent sublayers does not exceed 10. This means that the ratio of the electronic conductivity multiple difference n1 between the middle sublayer and its adjacent sublayer and the electronic conductivity multiple difference n2 between the middle sublayer and its other adjacent sublayer does not exceed 10. This ratio is obtained by dividing the larger of n1 and n2 by the smaller of the two. That is, when n1 is greater than n2, the ratio is calculated as n1 / n2, and when n2 is greater than n2, the ratio is calculated as n2 / n1.

[0077] By controlling the ratio of the difference in electronic conductivity multiples n between two adjacent layers to not exceed 10, the probability of over-discharge of the positive electrode active material with smaller electronic conductivity at the interface of each sublayer is further reduced, which is more beneficial to the electrical performance of the entire positive electrode 231.

[0078] For example, the ratio of the difference in conductivity multiples n between two adjacent electrons can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, or any value within the range not exceeding 10.

[0079] In some embodiments of this application, the total thickness of the two farthest sublayers in the positive electrode active material layer 2312 is at least 80% of the positive electrode active material layer 2312.

[0080] The total thickness of the two farthest sublayers is at least 80% of the positive electrode active material layer 2312, which means that the total thickness of the sublayers closest to the positive electrode current collector 2311 and the sublayer furthest from the positive electrode current collector 2311 divided by the thickness of the positive electrode active material layer 2312 is more than 80%.

[0081] By controlling the total thickness of the two farthest sublayers to be at least 80% of the positive electrode active material layer 2312, the performance of the positive electrode active material in these two sublayers can be fully utilized, and the impact of the addition of the intermediate sublayer on the overall electrode performance can be reduced.

[0082] For example, the total thickness of the two furthest sublayers as a percentage of the positive electrode active material layer 2312 can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, or any value above 85%.

[0083] In some embodiments of this application, the positive electrode 231 further includes a positive current collector 2311, and a positive active material layer 2312 is disposed on at least one side surface of the positive current collector 2311. The electronic conductivity of the positive active material in the sublayer closer to the positive current collector 2311 is greater. By placing the positive active material with greater electronic conductivity closer to the positive current collector 2311, the probability of polarization of the positive electrode 231 can be reduced, which is also beneficial to the rate performance and cycle performance of the positive electrode 231.

[0084] In some embodiments of this application, the positive electrode active material layer 2312 includes a first positive electrode active material sublayer 2312a, a second positive electrode active material sublayer 2312c, and a transition positive electrode active material sublayer 2312b disposed between the first positive electrode active material sublayer 2312a and the second positive electrode active material sublayer 2312c. The first positive electrode active material sublayer 2312a includes a first positive electrode active material, the second positive electrode active material sublayer 2312c includes a second positive electrode active material, and the transition positive electrode active material sublayer 2312b includes a transition positive electrode active material. The electronic conductivity a of the first positive electrode active material, the electronic conductivity b of the transition positive electrode active material, and the electronic conductivity c of the second positive electrode active material satisfy the following relationships: 30 < a: b < 1000 and 30 < b: c < 1000. Typically, only one transition positive electrode active material sublayer 2312b needs to be set to reduce the difference in electronic conductivity multiple of the positive electrode active materials of each adjacent sublayer to less than 1000, which can achieve a good improvement in the electrical performance of the positive electrode 231 with a relatively simple structure.

[0085] For example, the ratio of the electronic conductivity 'a' of the first positive electrode active material to the electronic conductivity 'b' of the transition positive electrode active material can be 30, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000, or any value within the range of 30 to 1000. The ratio of the electronic conductivity b of the transition cathode active material to the electronic conductivity c of the second cathode active material can be 30, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 or 1000, or any value within the range of 30 to 1000.

[0086] In some embodiments of this application, the electronic conductivity α of the first positive electrode active material is 10. -2 ~10 - 1 S / cm; The electronic conductivity b of the transition cathode active material is 10. -4 ~10 -2 S / cm; The electronic conductivity c of the second positive electrode active material is 10. -6 ~10 -4 S / cm.

[0087] For example, the electronic conductivity α of the first positive electrode active material can be 0.01 S / cm, 0.02 S / cm, 0.03 S / cm, 0.04 S / cm, 0.05 S / cm, 0.06 S / cm, 0.07 S / cm, 0.08 S / cm, 0.09 S / cm, or 0.1 S / cm, etc., and it can also be 10. -2 ~10 -1 The electronic conductivity b of the transition cathode active material can be any value within the range of S / cm. It can be 0.0001 S / cm, 0.0005 S / cm, 0.001 S / cm, 0.0015 S / cm, 0.002 S / cm, 0.0025 S / cm, 0.003 S / cm, 0.0035 S / cm, 0.004 S / cm, 0.0045 S / cm, 0.005 S / cm, 0.0055 S / cm, 0.006 S / cm, 0.0065 S / cm, 0.007 S / cm, 0.0075 S / cm, 0.008 S / cm, 0.0085 S / cm, 0.009 S / cm, 0.0095 S / cm, or 0.01 S / cm, etc., and can also be 10. -4 ~10 -2 The electronic conductivity c of the second positive electrode active material can be any value within the range of S / cm. This can be 0.000001 S / cm, 0.000005 S / cm, 0.00001 S / cm, 0.000015 S / cm, 0.00002 S / cm, 0.000025 S / cm, 0.00003 S / cm, 0.000035 S / cm, 0.00004 S / cm, or 0.000045 S / cm. 0.00005S / cm, 0.000055S / cm, 0.00006S / cm, 0.000065S / cm, 0.00007S / cm, 0.000075S / cm, 0.00008S / cm, 0.000085S / cm, 0.00009S / cm, 0.000095S / cm, or 0.0001S / cm, etc., which can also be 10. -6 ~10 -4 Any value within the range of S / cm.

[0088] In some embodiments of this application, the first positive electrode active material includes at least one of a spinel structure positive electrode material, a layered structure positive electrode material, and an olivine structure phosphate positive electrode material; the second positive electrode active material includes at least one of a spinel structure positive electrode material, a layered structure positive electrode material, and an olivine structure phosphate positive electrode material.

[0089] Spinel-structured cathode materials refer to cathode active materials with a spinel structure, typically including lithium manganese oxide and lithium nickel oxide. Layered-structured cathode materials refer to cathode active materials with a layered structure, typically including ternary system materials and lithium-rich manganese-based materials. Olivine-structured phosphate cathode materials refer to cathode active materials with an olivine structure, typically including lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate, etc., which are polyanionic cathode materials. Among them, polyanionic cathode materials are a general term for a series of compounds containing tetrahedral or octahedral anionic structural units (XOm)n-, which 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-state method, sol-gel method, hydrothermal method, electrospinning method, etc. Ternary system materials typically include two types: NCA and NCM. Among them, NCA is widely used due to its long lifespan, large capacity, and high energy density, but its specific heat capacity is relatively low; NCM combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, exhibiting a significant ternary synergistic effect. NCM can usually be represented as LiNi x Co y Mn z O2.

[0090] In some embodiments of this application, the first positive electrode active material includes Li a Ni b Mn c M1 2-b-c At least one of O4 and LiM2PO4, wherein 0.9≤a≤1.1, 0≤b≤2, 0≤c≤2, b+c=2, M1 includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and M2 includes Mn and non-Mn elements, wherein 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; the second positive electrode active material includes Li d Ni x Co y M3 1-x-y O 2+e M3 includes at least one of zLi2MnO3·(1-z)LiM4O2, wherein 0.2≤d<1.2, 0≤x≤1.0, 0≤y≤1.0, x+y≤1, -0.02≤e<0.02, M3 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M4 includes at least one of Co, Ni, and Mn.

[0091] Lithium manganese oxide, lithium nickel oxide, and polyanionic cathode materials typically exhibit good safety performance, while lithium cobalt oxide, lithium-rich manganese-based materials, and ternary system materials typically exhibit high energy density. Using any one of lithium manganese oxide, lithium nickel oxide, and polyanionic cathode materials as the second cathode active material, or any one of lithium cobalt oxide, lithium-rich manganese-based materials, and ternary system materials as the first cathode active material, allows cathode sheet 231 to possess both high safety performance and high energy density.

[0092] It should be noted that the above LiM2PO4 is not a specific molecular structure formula, but a general expression of lithium manganese phosphate.

[0093] 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.

[0094] 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.

[0095] In some embodiments of this application, the first doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

[0096] In some embodiments of this application, the second doping element includes one or more elements selected from B, S, Si, and N.

[0097] In some embodiments of this application, the second positive electrode active material includes Li 1+x Mn 1-y A y 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.

[0098] In some embodiments of the technical solutions of this application, the compound Li 1+x Mn 1-y AyP1-z The preparation method of RzO4 may include the following steps:

[0099] (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.

[0100] (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;

[0101] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0102] (4) The particles obtained in step (3) are sintered to obtain the positive electrode active material.

[0103] 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.

[0104] 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.

[0105] In some embodiments of this application, 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.

[0106] It should be noted that Li h A iMn 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.

[0107] 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. 50 The 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 .

[0108] In some embodiments of this application, the first positive electrode active material further has a carbon-containing coating layer.

[0109] The conductivity of the first positive electrode active material is improved by introducing a carbon-containing coating layer. In this case, the structure of the first 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.

[0110] 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.

[0111] 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.

[0112] For example, the first positive electrode active material can be a ternary system material or LiFePO4, 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 0.6 PO4, 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 0.5In LiM2PO4, M2 includes Mn and non-Mn elements. The non-Mn elements include one or both of the first and second doping elements. The first doping element is manganese doping, and the second doping element is phosphorus doping. The first doping element includes one or more of 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 of B, S, Si, and N.

[0113] In some embodiments of this 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. The modified materials of nickel-cobalt-manganese ternary materials and nickel-cobalt-aluminum ternary materials refer to materials obtained by doping or coating nickel-cobalt-manganese ternary materials or nickel-cobalt-aluminum ternary materials, respectively. The coating layer can be selected as an oxide, nitrate, phosphate, or carbonate containing one or more elements selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P, specifically such as Al2O3, B2O3, TiO2, etc. For example, the chemical formula of the ternary system material is LiNi. x Co y Mn z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1. Specifically, it can be LiNi. 0.4 Co 0.2 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.3 O2 and LiNi 0.7 Co 0.15 Mn 0.15 O2, etc.

[0114] In some embodiments of this application, the lithium-rich manganese-based material can specifically be 0.5Li₂MnO₃·0.5LiNi. 0.5 Mn 0.3 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Mg 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Al 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Ca0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Ba 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 V 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Zn 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Ti 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Fe 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Co 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Cr 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Nb 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 W 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Mo 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Zr 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Ta 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Hf 0.2 O2, 0.1Li2MnO3·0.9LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.2Li2MnO3·0.8LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.3Li2MnO3·0.7LiNi 0.5Mn 0.3 Na 0.2 O2, 0.4Li2MnO3·0.6LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.6Li2MnO3·0.4LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.7Li2MnO3·0.3LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.8Li2MnO3·0.2LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.9Li2MnO3·0.1LiNi 0.5 Mn 0.3 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.1 Mn 0.7 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.2 Mn 0.6 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.3 Mn 0.5 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.4 Mn 0.4 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.6 Mn 0.2 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.7 Mn 0.1 Na 0.2 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Na 0.1 Mg 0.1 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Cr 0.1 W 0.1 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.3 Fe 0.1 Co 0.1 O2, 0.5Li2MnO3·0.5LiNi0.5 Mn 0.3 Zn 0.1 Ta 0.1 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.4 Na 0.1 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2.

[0115] It should be noted that the above enumeration of the first and second positive electrode active materials is merely an illustration of the feasibility of this solution and is not intended to limit the solution. The implementation of this solution only requires that the first and second positive electrode active materials meet the corresponding electronic conductivity requirements. In other embodiments, those skilled in the art can select specific substances for the first and second positive electrode active materials according to actual needs, such as the materials listed above and their modified forms. Modification includes doping or coating, or other materials that meet the electronic conductivity requirements of this application.

[0116] In some embodiments of this application, the transition positive electrode active material can be the same as the first positive electrode active material or the second positive electrode active material. When the transition positive electrode active material is the same as the first positive electrode active material, that is, when the transition positive electrode active material is selected from lithium manganese oxide, lithium nickel oxide, or polyanionic positive electrode material, the electronic conductivity can be reduced by decreasing the amount of carbon coating, thereby achieving a transition in electronic conductivity between the first positive electrode active material sublayer 2312a and the second positive electrode active material sublayer 2312c. When the transition positive electrode active material is the same as the second positive electrode active material, that is, when the transition positive electrode active material is selected from lithium cobalt oxide, lithium-rich manganese-based material, or ternary system material, the electronic conductivity can be increased by increasing the amount of carbon coating, thereby achieving a transition in electronic conductivity between the first positive electrode active material sublayer 2312a and the second positive electrode active material sublayer 2312c.

[0117] Having introduced the materials and structure of the positive electrode 231, the preparation method of the positive electrode 231 will be described in detail below.

[0118] The preparation method of the positive electrode 231 includes the following steps: preparing sub-layers layer by layer on the positive electrode current collector 2311 to form a positive electrode active material layer 2312. The positive electrode active material layer 2312 includes at least three sub-layers. The difference m between the electronic conductivity multiples of the positive electrode active materials of the two sub-layers that are furthest apart among the at least three sub-layers is not less than 1000, and the difference n between the electronic conductivity multiples of the positive electrode active materials of the two adjacent sub-layers is less than 1000.

[0119] This method involves placing a sublayer of positive electrode active material with an electronic conductivity between two sublayers composed of positive electrode active materials with an electronic conductivity difference of not less than 1000. This reduces the probability of over-discharge of the positive electrode active material with lower electronic conductivity at the interface between the sublayers, thereby improving the overall electrical performance of the positive electrode 231. Simultaneously, the layered arrangement of the positive electrode active materials reduces the possibility of current unevenness between them, resulting in higher capacity retention of the positive electrode 231 during the early stages of cycling.

[0120] The following example illustrates the preparation of a positive electrode sheet 231, which includes a first positive electrode material active layer, a transition positive electrode material active layer, and a second positive electrode active material layer 2312.

[0121] Figure 7 For flowcharts illustrating the preparation methods of the positive electrode 231 provided in some embodiments of this application, please refer to [link / reference]. Figure 7 This application provides a method for preparing a positive electrode 231, the method comprising:

[0122] 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 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.

[0123] For the specific selection of polyanionic cathode materials, please refer to the selection of polyanionic cathode materials in the first positive electrode active material sublayer 2312a in the aforementioned cathode sheet 231, which will not be repeated here.

[0124] 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.

[0125] S120, Preparation of transition positive electrode active slurry: The transition positive electrode active material, binder and conductive agent are dispersed in a solvent to form a transition positive electrode active slurry. The electronic conductivity of the transition positive electrode active material is between that of the first positive electrode active material and the second positive electrode active material.

[0126] S130, 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 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.

[0127] 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 transition 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 transition 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 transition positive electrode active material. Additionally, leveling agents, dispersants, etc., can also be added to the transition positive electrode active slurry; this application does not impose any limitations on this.

[0128] For the specific selection of ternary system materials, please refer to the selection of ternary system materials in the second positive electrode active material sublayer 2312c in the aforementioned positive electrode sheet 231, which will not be repeated here.

[0129] 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.

[0130] It should be noted that steps S120 and S130 can be interchanged or performed simultaneously, and this application does not impose any restrictions.

[0131] S140, Preparation of the first positive electrode active material sublayer 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 sublayer 2312a. During coating, it can be applied to one or both surfaces of the positive electrode current collector 2311 as needed.

[0132] The coating method can be, for example, scraping, roller coating, slot coating, etc., and this application does not limit the method. It should be noted that steps S120, S130 and S140 can be interchanged or performed simultaneously, and this application does not limit the method.

[0133] S150, Preparation of transition positive electrode active material sublayer 2312b: The transition positive electrode active slurry is coated onto the surface of the first positive electrode active material sublayer 2312a, and then dried to form the transition positive electrode active material sublayer 2312b. During coating, the transition positive electrode active material sublayer 2312b can be formed on the surface of the first positive electrode active material sublayer 2312a, depending on the condition of the first positive electrode active material sublayer 2312a.

[0134] It should be noted that steps S130 and S150 can be interchanged or performed simultaneously; this application does not impose any restrictions.

[0135] S160, Preparation of the second positive electrode active material sublayer 2312c: The second positive electrode active slurry is coated onto the surface of the transition positive electrode active material sublayer 2312b, and then dried to form the second positive electrode active material sublayer 2312c. During coating, the second positive electrode active material sublayer 2312c can be formed on the surface of the transition positive electrode active material sublayer 2312b, depending on the condition of the transition positive electrode active material sublayer 2312b.

[0136] S170, roll-press the second positive electrode active material sublayer 2312c to obtain the positive electrode sheet 231.

[0137] It should be noted that the above is only an example of sequentially setting a first positive electrode active material sublayer 2312a, a transition positive electrode active material sublayer 2312b, and a second positive electrode active material sublayer 2312c in the positive electrode current collector 2311. In other embodiments, the positions of the first positive electrode active material sublayer 2312a and the second positive electrode active material sublayer 2312c can be interchanged.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] Examples and Comparative Examples

[0142] [Preparation of the positive electrode plate]

[0143] Preparation of the first positive electrode active material sublayer: The first positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:2.5 and stirred and mixed evenly to obtain the first coating slurry; then the slurry is uniformly coated on the positive electrode current collector and dried to obtain the first positive electrode active material sublayer.

[0144] Preparation of transition positive electrode active material sublayer: The transition positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:2.5 and stirred to obtain a transition coating slurry. Then, the slurry is uniformly coated on the first positive electrode active material sublayer and dried to obtain the transition positive electrode active material sublayer.

[0145] Preparation of the second positive electrode active material sublayer: The second positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:2.5 and stirred to obtain a second coating slurry. Then, the slurry is uniformly coated on the transition positive electrode active material sublayer. The weight ratio of the first positive electrode active material and the second positive electrode active material is 1:1. After drying, the lithium-ion battery positive electrode sheet is obtained by rolling and die cutting.

[0146] [Preparation of the negative electrode]

[0147] 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.

[0148] Preparation of Electrolyte

[0149] 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% (w / w) fluoroethylene carbonate is dissolved in the above organic solvent and stirred evenly to obtain the electrolyte.

[0150]

Isolation Film

[0151] Polyethylene film is used as the separation membrane.

[0152] [Preparation of Lithium-ion Batteries]

[0153] The prepared positive electrode, negative electrode, and separator (polyethylene (PE) porous polymer film) are stacked in a Z-shaped structure to form the corresponding battery cell. The cell is vacuum dried at 90℃ for 12 hours, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs, and the negative electrode uses nickel tabs, with the tabs located on the same side of the cell. The cell with welded tabs is then placed into an aluminum-plastic film of appropriate size for top and side sealing at 145℃. Electrolyte is then injected and the cell is sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0154] The main parameter controls for Examples 1 to 11 and Comparative Examples 1 to 4 are shown in the table below:

[0155]

[0156]

[0157] It should be noted that no transition positive electrode active material sublayer was set in Comparative Examples 1 to 3.

[0158] In Comparative Example 1, the first positive electrode active material is (LiFePO4), with an electronic conductivity of (0.081), and the second positive electrode active material is (LiNi). 0.5 Co 0.2 Mn 0.3 Its electronic conductivity is (0.00009);

[0159] In Comparative Example 2, the first positive electrode active material is (LiFePO4), with an electronic conductivity of (0.081), and the second positive electrode active material is (LiNi). 0.5 Co 0.25 Mn 0.25 Its electronic conductivity is (0.000081);

[0160] In Comparative Example 3, the first positive electrode active material is (LiFePO4), with an electronic conductivity of (0.081), and the second positive electrode active material is (LiNi). 0.5 Co 0.2 Mn 0.3 Its electronic conductivity is (0.0000081);

[0161] In Comparative Example 4, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), the transition positive electrode active material is (LiMn2O4) with an electronic conductivity of (0.0405), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0162] In Example 1, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), the transition positive electrode active material is (LiCoO2) with an electronic conductivity of (0.00256), and the second positive electrode active material is (LiNi). 0.5 Co 0.2 Mn 0.3 Its electronic conductivity is (0.00009);

[0163] In Example 2, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.9 Mn 0.1 Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0164] In Example 3, the first positive electrode active material is (LiFePO4), with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.6 Co 0.3 Mg 0.1 Its electronic conductivity is (0.001013), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0165] In Example 4, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.6 Co 0.2 Mg 0.2 Its electronic conductivity is (0.00162), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0166] In Example 5, the first positive electrode active material is (LiFePO4), with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.6 Co 0.3 Al 0.1 Its electronic conductivity is (0.002025), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0167] In Example 6, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Mg 0.1 Its electronic conductivity is (0.002562), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0168] In Example 7, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.6 Co 0.2 Al 0.2 Its electronic conductivity is (0.00324), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0169] In Example 8, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Al 0.1 Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0170] In Example 9, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Al 0.1Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0171] In Example 10, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Al 0.1 Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0172] In Example 11, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Al 0.1 Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081);

[0173] In Example 12, the first positive electrode active material is (LiFePO4) with an electronic conductivity of (0.081), and the transition positive electrode active material is (LiNi). 0.8 Co 0.1 Al 0.1 Its electronic conductivity is (0.00081), and the second positive electrode active material is (LiNi). 0.6 Co 0.2 Mn 0.2 Its electronic conductivity is (0.0000081).

[0174] The performance of the batteries provided in each embodiment and comparative example was tested. The performance testing specifically included:

[0175] Capacity retention test: At room temperature (25℃), the lithium-ion secondary battery was first charged to 4.35V with a constant current of 1C, then further charged to 0.05C with a constant voltage of 4.35V, and finally discharged to 2V with a constant current of 1C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery was subjected to multiple charge-discharge cycles in the above manner, and the discharge capacity of the 1000th cycle was measured. The capacity retention rate of the battery after cycling was calculated by dividing the discharge capacity of the 1000th cycle by the discharge capacity of the first cycle.

[0176] The test results are shown in the table below:

[0177] Capacity retention rate after 1000 cycles / % Comparative Example 1 88.23 Comparative Example 2 86.55 Example 1 94.11 Comparative Example 3 82.59 Comparative Example 4 84.23 Example 2 92.15 Example 3 91.56 Example 4 90.98 Example 5 90.43 Example 6 90.11 Example 7 89.35 Example 8 88.55 Example 9 90.73 Example 10 91.67 Example 11 90.37 Example 12 89.11 Example 13 90.34

[0178] As can be seen from the table above, the battery made using the positive electrode sheet provided in the embodiments of this application has a better capacity retention rate.

[0179] By comparing the data from Examples 1 to 3, it can be seen that as the difference in electronic conductivity between the two sublayers of the positive electrode active material layer increases, the capacity retention rate of the battery shows a decreasing trend. When the difference in electronic conductivity between the two sublayers reaches more than 1000, the capacity retention rate of the battery drops to below 85%.

[0180] A comparison of the data from Example 1 and Comparative Example 2 shows that setting a transition positive electrode active material layer with an electronic conductivity in between two sub-layers with a difference of 1000 in electronic conductivity can significantly improve the battery capacity retention rate, increasing it to about 94%, an improvement of about 9%.

[0181] A comparison of data from Examples 2 to 7 and Comparative Examples 3 to 4 shows that placing a transition positive electrode active material layer with intermediate electronic conductivity between two sublayers exhibiting significant differences in electronic conductivity can significantly improve the battery's capacity retention. Furthermore, the smaller the ratio of the difference in electronic conductivity (n) between two adjacent sublayers, the higher the battery's cycle capacity retention. In particular, when the ratio of the difference in electronic conductivity (n) between two adjacent sublayers is less than 10, the battery's cycle capacity retention can reach over 90%.

[0182] By comparing the data from Examples 2 and 8 to 12, it can be seen that as the thickness of the transition positive electrode active material layer increases, the cycle capacity retention rate of the battery shows a trend of first increasing and then decreasing. When the thickness of the transition positive electrode active material layer is 5% to 20%, the cycle capacity retention rate of the battery is above 90%.

[0183] A comparison of the data from Examples 2 and 13 shows that placing the positive electrode active material with higher electronic conductivity closer to the positive electrode current collector results in a battery with better cycle capacity retention and energy density. This may be because placing the positive electrode active material with higher electronic conductivity closer to the positive electrode current collector can reduce the probability of polarization of the positive electrode, thereby benefiting the battery's cycle capacity retention and energy density.

[0184] 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 sheet includes a positive electrode active material layer, which includes at least three sub-layers. The difference m between the electronic conductivity multiples of the positive electrode active materials of the two sub-layers that are furthest apart is not less than 1000, and the difference n between the electronic conductivity multiples of the positive electrode active materials of the two adjacent sub-layers is less than 1000.

2. The positive electrode sheet according to claim 1, characterized in that, The ratio of the difference in electronic conductivity (n) between any of the middle sublayers in the positive electrode active material layer and its two adjacent sublayers does not exceed 10.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The total thickness of the two sub-layers that are furthest apart in the positive electrode active material layer is at least 80% of the total thickness of the positive electrode active material layer.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode sheet also includes a positive current collector, and the positive active material layer is disposed on at least one side surface of the positive current collector, and the electronic conductivity of the positive active material in the sub-layer closer to the positive current collector is greater.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The positive electrode active material layer includes a first positive electrode active material sublayer, a second positive electrode active material sublayer, and a transition positive electrode active material sublayer disposed between the first positive electrode active material sublayer and the second positive electrode active material sublayer. The first positive electrode active material sublayer includes a first positive electrode active material, the second positive electrode active material sublayer includes a second positive electrode active material, and the transition positive electrode active material sublayer includes a transition positive electrode active material. The electronic conductivity a of the first positive electrode active material, the electronic conductivity b of the transition positive electrode active material, and the electronic conductivity c of the second positive electrode active material satisfy the following relationships: 30 < a: b < 1000, 30 < b: c < 1000.

6. The positive electrode sheet according to claim 5, characterized in that, The electronic conductivity α of the first positive electrode active material is 10. -2 ~10 -1 S / cm; and / or The electronic conductivity b of the transition positive electrode active material is 10. -4 ~10 -2 S / cm; and / or The electronic conductivity c of the second positive electrode active material is 10. -6 ~10 -4 S / cm.

7. The positive electrode sheet according to any one of claims 5 to 6, characterized in that, The first positive electrode active material includes at least one of the following: spinel structure positive electrode material, layered structure positive electrode material, and olivine structure phosphate positive electrode material; and / or The second positive electrode active material includes at least one of the following: spinel structure positive electrode material, layered structure positive electrode material, and olivine structure phosphate positive electrode material.

8. The positive electrode sheet according to any one of claims 5 to 7, characterized in that, The first positive electrode active material includes Li a Ni b Mn c M1 2-b-c At least one of O4 and LiM2PO4, wherein 0.9≤a≤1.1, 0≤b≤2, 0≤c≤2, b+c=2, M1 includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and M2 includes Mn and non-Mn elements, wherein 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; and / or The second positive electrode active material includes Li d Ni x Co y M3 1-x-y O 2+e M3 includes at least one of zLi2MnO3·(1-z)LiM4O2, wherein 0.2≤d<1.2, 0≤x≤1.0, 0≤y≤1.0, x+y≤1, -0.02≤e<0.02, M3 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M4 includes at least one of Co, Ni, and Mn.

9. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive electrode active material layer, which includes a first positive electrode active material sublayer, a second positive electrode active material sublayer, and a transition positive electrode active material sublayer disposed between the first and second positive electrode active material sublayers. The thickness of the transition positive electrode active material sublayer is less than 20% of the thickness of the positive electrode active material layer. The first positive electrode active material sublayer includes a first positive electrode active material, the second positive electrode active material sublayer includes a second positive electrode active material, and the transition positive electrode active material sublayer includes a transition positive electrode active material. The electronic conductivity a of the first positive electrode active material, the electronic conductivity b of the second positive electrode active material, and the electronic conductivity c of the transition positive electrode active material satisfy the following relationships: a:c≥1000, 30<a:b<1000, and 30<b:c<1000.

10. A single battery cell, characterized in that, The battery cell includes the positive electrode sheet according to any one of claims 1 to 9.

11. A battery, characterized in that, The battery comprises the battery cell of claim 10.

12. An electrical appliance, characterized in that, The electrical device includes the battery cell of claim 10 or the battery of claim 11.

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