A positive electrode plate, a battery cell, a battery, and an electrical device.

Abstract

A positive electrode sheet, a battery cell, a battery, and an electrical device are disclosed, belonging to the field of battery technology. The positive electrode sheet includes a positive electrode active material layer, which 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 and a first conductive agent. The second positive electrode active material layer includes a second positive electrode active material. The electronic conductivity of the second positive electrode active material is greater than that of the first positive electrode active material. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship: This relationship can reduce the conductivity difference between the first and second positive electrode active material layers, thereby improving the overall electrical performance of the positive electrode sheet.

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 the positive electrode active material layers and improve the performance of electrical components.

[0004] In a first aspect, this application provides a 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 and a first conductive agent, the second positive electrode active material layer comprising a second positive electrode active material, the electronic conductivity of the second positive electrode active material being greater than that of the first positive electrode active material, and the powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfying the following relationship:

[0005] In the technical solution of this application embodiment, the addition amount C of the first conductive agent that cooperates with the first positive electrode active material with poor electronic conductivity and the powder resistivity F of the second positive electrode active material with good electronic conductivity at 8 MPa are controlled to satisfy... This reduces the conductivity difference between the first and second positive electrode active material layers, thereby improving the overall electrical performance of the positive electrode sheet. Simultaneously, layering the first and second positive electrode active materials reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling.

[0006] In some embodiments, the powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship:

[0007] In the above implementation process, by controlling the amount C of the first conductive agent added in combination with the first positive electrode active material with poor electronic conductivity and the powder resistivity F of the second positive electrode active material with good electronic conductivity at 8 MPa, the following conditions are met: This can further reduce the conductivity difference between the first and second positive electrode active material layers, thereby further improving the overall electrical performance of the positive electrode. Simultaneously, it can further reduce the amount of the first conductive agent required, minimizing its detrimental effect on gas production under high temperature and high voltage conditions.

[0008] In some embodiments, the powder resistivity of the second positive electrode active material at 8 MPa is 10–80 Ω·cm; and / or

[0009] The first conductive agent comprises 1.9% to 2.8% by weight in the first positive electrode active material layer; and / or

[0010] The powder resistivity of the first conductive agent at 8 MPa is ≤0.025 Ω·cm.

[0011] In the above implementation process, by controlling the powder resistivity of the second positive electrode active material, the content of the first conductive agent in the active layer of the first positive electrode material is kept within a suitable range, maintaining a high proportion of the first positive electrode active material, thereby reducing the decrease in the overall energy density of the positive electrode sheet. Simultaneously, the powder resistivity of the second positive electrode active material at 8 MPa, within the range of 10–80 Ω·cm, also ensures its own cycle performance.

[0012] In some embodiments, the first positive electrode active material includes a ternary material; and / or

[0013] The second positive electrode active material includes polyanion positive electrode material.

[0014] In the above implementation process, polyanionic cathode materials usually exhibit good safety performance, while ternary system materials usually exhibit high energy density. Using polyanionic cathode materials as the second cathode active material and ternary system materials as the first cathode active material can enable the cathode sheet to have both high safety performance and high energy density.

[0015] 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.

[0016] 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.

[0017] Optionally, the second doping element includes one or more elements selected from B, S, Si, and N.

[0018] 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.

[0019] 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.

[0020] In some embodiments, the polyanionic cathode material also has a carbon-containing coating layer.

[0021] In the above implementation process, the conductivity of the positive electrode active material is improved by introducing a carbon-containing coating layer. At this time, 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.

[0022] In some embodiments, the powder resistivity of the second positive electrode active material at 8 MPa is 20–50 Ω·cm.

[0023] In the above implementation process, the powder resistivity of the polyanionic cathode material such as LiMPO4 often shows a negative correlation with the surface carbon coating amount. The lower the powder resistivity, the higher the carbon coating amount. However, this surface carbon coating layer will also deteriorate the gas generation during storage under high-temperature and high-voltage conditions. Therefore, by controlling the powder resistivity of the second cathode active material to be 20 - 50 Ω·cm at 8 Mpa, the possibility of significantly deteriorating the gas generation can be reduced, and at the same time, its own cycle performance can be taken into account.

[0024] 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.

[0025] 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 the materials obtained by doping or coating the nickel-cobalt-manganese ternary material or the nickel-cobalt-aluminum ternary material.

[0026] In some embodiments, the molar content ratio of Ni in the ternary of the ternary system material is 0.4 - 0.7.

[0027] In the above implementation process, the ternary system material with a Ni molar content of 0.4 - 0.7 has good conductivity. It can reduce the conductivity difference between the first cathode active material layer and the second cathode active material layer with the addition of less conductive agent, thereby reducing the deterioration of gas generation under high-temperature and high-voltage conditions and the decrease in the energy density of the entire cathode sheet. At the same time, controlling the Ni molar content to be 0.4 - 0.7 can reduce the loss of the ternary system material during cycling. In addition, it can also reduce the possibility of performance deterioration when applied at high voltages, such as 2.5 - 4.4 V.

[0028] 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, 0.4 < b < 0.7, 0 < c < 1, 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.

[0029] In some embodiments, the thickness of the second cathode active material layer does not exceed 62% of the thickness of the entire cathode active material layer.

[0030] In the above implementation process, because the polyanionic cathode material has a large specific surface area, it is prone to water absorption. When used as a battery, it can easily cause a high hydrofluoric acid content in the battery, which deteriorates the electrical performance. Therefore, controlling the thickness of the second cathode active material layer to not exceed 62% of the thickness of the entire cathode active material layer can reduce its deterioration on the battery's electrical performance.

[0031] In some embodiments, the positive electrode active material layer further includes an intermediate layer disposed between the first positive electrode active material layer and the second positive electrode active material layer, and the intermediate layer includes a hydrophobic conductive polymer.

[0032] In the above implementation process, by setting a hydrophobic intermediate layer between the first positive electrode active material layer and the second positive electrode active material layer, the damage to the ternary system material caused by water absorption by the polyanionic positive electrode material can be reduced.

[0033] In some embodiments, the hydrophobic conductive polymer includes at least one of polypyrrole, polyaniline, polythiophene, and polyacetylene.

[0034] In some embodiments, the intermediate layer further includes a hydrophobic and conductive carbonaceous material.

[0035] In the above implementation process, by adding hydrophobic and conductive carbon materials, the intermediate layer has better conductivity, thereby reducing its impact on the electrical performance of the positive electrode active material layer.

[0036] In some embodiments, the hydrophobic conductive carbon material includes hydrophobic carbon nanotubes and / or hydrophobic carbon nanofibers.

[0037] Secondly, this application provides a positive electrode sheet, comprising a positive electrode active material layer, which includes a first positive electrode active material layer and a second positive electrode active material layer. The thickness of the second positive electrode active material layer does not exceed 62% of the total thickness of the positive electrode active material layer. The first positive electrode active material layer includes a first positive electrode active material and a first conductive agent. The second positive electrode active material layer includes a second positive electrode active material, the electronic conductivity of which is greater than that of the first positive electrode active material. The second positive electrode active 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. The first doping element is manganese site doping, and the second doping element is phosphorus site doping. The first positive electrode active material is a ternary material, wherein the molar content of Ni in the ternary material is 0.4–0.7%. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship:

[0038] In the technical solution of this application embodiment, the amount C of the first conductive agent added in combination with the ternary system material with poor electronic conductivity and the powder resistivity F of LiMPO4 with good electronic conductivity at 8 MPa are controlled to meet the following requirements. This reduces the conductivity difference between the first and second positive electrode active material layers, thereby improving the overall electrical performance of the positive electrode. Simultaneously, layering the ternary system material and LiMPO4 reduces the likelihood of current unevenness between them, resulting in higher capacity retention in the early stages of cycling. Furthermore, LiMPO4 typically exhibits good safety performance, while ternary system materials generally demonstrate high energy density. Using LiMPO4 as the second positive electrode active material and the ternary system material as the first positive electrode active material allows the positive electrode to possess both high safety performance and high energy density.

[0039] Thirdly, this application provides a battery cell, which includes the positive electrode provided in the first or second aspect.

[0040] Fourthly, this application provides a battery, which includes the battery cell provided in the third aspect.

[0041] 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

[0042] 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:

[0043] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0044] Figure 2 This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0045] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0046] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0047] Figure 5 This is a first structural schematic diagram of the positive electrode sheet provided in some embodiments of this application;

[0048] Figure 6 This is a schematic diagram of the second structure of the positive electrode sheet provided in some embodiments of this application;

[0049] Figure 7 A flowchart illustrating a method for preparing a positive electrode sheet according to some embodiments of this application.

[0050] The reference numerals in the detailed embodiments are as follows:

[0051] 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

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 2312, uneven current is likely to occur between the two positive electrode active materials in the positive electrode active material layer 2312. This phenomenon will cause the positive electrode 231 to decay rapidly in the early stage of cycling, which will have a significant impact on the cycle retention rate of the positive electrode 231.

[0063] 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.

[0064] 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 231 includes a positive electrode active material layer 2312, which includes a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b. The first positive electrode active material layer 2312a includes a first positive electrode active material and a first conductive agent. The second positive electrode active material layer 2312b includes a second positive electrode active material. The electronic conductivity of the second positive electrode active material is greater than that of the first positive electrode active material. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer 2312a satisfy the following relationship:

[0065] In such a positive electrode 231, by controlling the amount C of the first conductive agent added in combination with the first positive electrode active material with poor electronic conductivity and the powder resistivity F of the second positive electrode active material with good electronic conductivity at 8 MPa, the following conditions are met: This reduces the conductivity difference between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b, thereby improving the overall electrical performance of the positive electrode 231. Simultaneously, layering the first and second positive electrode active materials reduces the likelihood of current unevenness between them, thus enabling the positive electrode 231 to maintain a higher capacity retention rate during the early stages of cycling.

[0066] The positive electrode 231 can be used to prepare the electrode assembly 23, which can be used, but is not limited to, in electrical devices such as vehicles 1000, ships, or aircraft. The power system of this electrical device can be composed of the battery cell 20 and secondary battery 100 disclosed in this application. This is beneficial for fully utilizing the high-limit compaction density positive electrode material to improve the compaction density of the entire positive electrode active material layer 2312, achieving a significant increase in the compaction density of the entire positive electrode active material layer 2312, thereby increasing the energy density of the positive electrode 231 and improving the capacity of the battery cell 20.

[0067] 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.

[0068] 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.

[0069] Please refer to Figure 1 , Figure 1 This 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 2 As 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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 electrode tab and the negative electrode tab 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; 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b. The first positive electrode active material layer 2312a includes a first positive electrode active material and a first conductive agent. The second positive electrode active material layer 2312b includes a second positive electrode active material. The electronic conductivity of the second positive electrode active material is greater than that of the first positive electrode active material. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer 2312a satisfy the following relationship:

[0086] 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.

[0087] 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 first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be interchanged.

[0088] 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.

[0089] Conductive agents are added during electrode fabrication to ensure good charge-discharge performance. These conductive materials collect microcurrents between active materials and between the active materials and the current collector, reducing contact resistance and accelerating electron movement, thereby improving charge-discharge efficiency. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The first conductive agent refers to the conductive agent added to the first positive electrode active material layer 2312a. A conductive agent is often also added to the second positive electrode active material layer 2312b; for ease of description, this conductive agent is referred to as the second conductive agent in this application. The proportion of the second conductive agent in the second positive electrode active material layer 2312b is typically no more than 0.5%.

[0090] Powder resistivity, also known as powder resistivity, is the ratio between the actual resistance value and the theoretical resistance value. It is an indicator used to represent the ability of powder materials to conduct electric current.

[0091] By controlling the amount C of the first conductive agent (which has poor electronic conductivity) added in conjunction with the first positive electrode active material and the powder resistivity F of the second positive electrode active material (which has good electronic conductivity) at 8 MPa, the following conditions are met: This reduces the conductivity difference between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b, thereby improving the overall electrical performance of the positive electrode 231. Simultaneously, layering the first and second positive electrode active materials reduces the likelihood of current unevenness between them, thus enabling the positive electrode 231 to maintain a higher capacity retention rate during the early stages of cycling.

[0092] For example, the powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer 2312a satisfy the following relationship: The value can be 3.6, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42 or 42.1, etc., or it can be any value in the range of 3.5 to 42.1.

[0093] In some embodiments of this application, the powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight ratio C of the first conductive agent in the first positive electrode active material layer 2312a satisfy the following relationship: By controlling the amount C of the first conductive agent (which has poor electronic conductivity) added in conjunction with the first positive electrode active material and the powder resistivity F of the second positive electrode active material (which has good electronic conductivity) at 8 MPa, the following conditions are met: This can further reduce the conductivity difference between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b, and further improve the electrical performance of the entire positive electrode sheet 231. At the same time, it can further reduce the addition of the first conductive agent and reduce the deterioration of gas generation by the first conductive agent under high temperature and high voltage conditions.

[0094] In some embodiments of this application, the powder resistivity of the second positive electrode active material at 8 MPa is 10–80 Ω·cm; the weight percentage of the first conductive agent in the first positive electrode active material layer 2312a is 1.9%–2.8%; and the powder resistivity of the first conductive agent at 8 MPa is ≤0.025 Ω·cm. By controlling the powder resistivity of the second positive electrode active material, the content of the first conductive agent in the active layer of the first positive electrode material is kept within a suitable range, maintaining a high proportion of the first positive electrode active material, thereby reducing the decrease in the energy density of the entire positive electrode sheet 231. Simultaneously, the powder resistivity of the second positive electrode active material within the range of 10–80 Ω·cm at 8 MPa also ensures its own cycle performance.

[0095] For example, the powder resistivity of the second positive electrode active material at 8 MPa can be 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm, 55 Ω·cm, 60 Ω·cm, 65 Ω·cm, 70 Ω·cm, 75 Ω·cm and 80 Ω·cm, etc., or it can be any value in the range of 10 to 80 Ω·cm. The weight percentage of the first conductive agent in the first positive electrode active material layer 2312a can be 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, and 2.8%, or any value within the range of 1.9% to 2.8%. The powder resistivity of the first conductive agent at 8 MPa can be 0.005 Ω·cm, 0.010 Ω·cm, 0.015 Ω·cm, 0.020 Ω·cm, or 0.025 Ω·cm, or any value within the range of ≤0.025 Ω·cm.

[0096] In some embodiments of this application, the first positive electrode active material includes a ternary system material; the second positive electrode active material includes a polyanion positive electrode material.

[0097] 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.

[0098] Ternary cathode materials typically include two types: NCA and NCM. NCA is widely used due to its long lifetime, high 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.

[0099] Polyanionic cathode materials typically exhibit good safety performance, while ternary system materials typically exhibit high energy density. Using polyanionic cathode materials as the second cathode active material and ternary system materials as the first cathode active material enables cathode sheet 231 to have both high safety performance and high energy density.

[0100] 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.

[0101] It should be noted that the above LiMPO4 is not a specific molecular structure formula, but a general expression of lithium manganese phosphate.

[0102] 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.

[0103] 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.

[0104] In some embodiments of this application, the first doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

[0105] In some embodiments of this application, the second doping element includes one or more elements selected from B, S, Si, and N.

[0106] In some embodiments of this application, the second positive electrode active material includes Li 1+x Mn1-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.

[0107] 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:

[0108] (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.

[0109] (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;

[0110] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0111] (4) The particles obtained in step (3) are sintered to obtain the positive electrode active material.

[0112] 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.

[0113] 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.

[0114] In some embodiments of this application, the polyanion cathode material includes Li h A i Mn1-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.

[0115] 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.

[0116] 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 .

[0117] In some embodiments of this application, the second positive electrode active material further has a carbon-containing coating layer.

[0118] The conductivity of the second positive electrode active material is improved by introducing a carbon-containing coating layer. In this case, the structure of the second 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.

[0119] 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.

[0120] 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.

[0121] 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 Fe0.6 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 0.5 In LiMPO4, the M element includes both 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-site doping, and the second doping element is phosphorus-site 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.

[0122] In some embodiments of this application, the powder resistivity of the second positive electrode active material at 8 MPa is 20–50 Ω·cm. The powder resistivity of polyanionic positive electrode materials such as LiMPO4 often shows a negative correlation with the amount of carbon coating on the surface; the lower the powder resistivity, the higher the carbon coating. However, this surface carbon coating layer can deteriorate under high temperature and high voltage conditions, leading to gas generation. Therefore, by controlling the powder resistivity of the second positive electrode active material at 8 MPa to 20–50 Ω·cm, the possibility of significant deterioration in gas generation can be reduced, while maintaining its own cycle performance.

[0123] 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 Mnz O₂, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z = 1.

[0124] In the technical solutions of some embodiments of the present application, the molar content ratio of Ni in the ternary of the ternary system material is 0.4 - 0.7. The ternary of the ternary system material refers to the ternary of Ni, Co, and Mn or the ternary of Ni, Co, and Al. The molar content ratio of Ni in the ternary of the ternary system material being 0.4 - 0.7 means the proportion of the molar content of Ni in the total molar content of the ternary. For example, in NCM, the calculation method of this molar content ratio is the molar content of Ni / (the molar content of Ni + the molar content of Co + the molar content of Mn). If the ternary system material is doped at the Ni site, Co site, or Mn site, the molar content of the doping element is added to the denominator for calculation. The ternary system material with a molar content of Ni of 0.4 - 0.7 has good electrical conductivity, and can reduce the difference in electrical conductivity between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b with the addition of a smaller amount of conductive agent, thereby reducing the deterioration of gas generation under high temperature and high voltage conditions and reducing the decrease in the energy density of the entire positive electrode sheet 231. At the same time, controlling the molar content of Ni to be 0.4 - 0.7 can reduce the loss of the ternary system material during cycling. In addition, it can also reduce the possibility of performance deterioration when applied at high voltages, such as 2.5 - 4.4V.

[0125] Exemplarily, the molar content ratio of Ni in the ternary of the ternary system material can be 0.4, 0.5, 0.6, or 0.7, etc., and it can also be any value within the range of 0.4 - 0.7.

[0126] In the technical solutions of some embodiments of the present application, the ternary system material includes LiaNibCocM1dM2eOfRg, where 0.75 ≤ a ≤ 1.2, 0.4 < b < 0.7, 0 < c < 1, 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.

[0127] Exemplarily, the first positive electrode active material can be a ternary positive electrode material, specifically LiNi 0.4 Co 0.2 Mn 0.4 O₂, LiNi 0.5 Co 0.2 Mn 0.3 O₂ and LiNi 0.7 Co 0.15 Mn 0.15In O2, LiaNibCocM1dM2eOfRg, a can be any one or more values ​​in the range of 0.75 to 1.2, b can be any one or more values ​​in the range of 0.4 to 0.7, c can be any one or more values ​​in the range of 0 to 1, d can be any one or more values ​​in the range of 0 to 1, e can be any one or more values ​​in the range of 0 to 0.2, f can be any one or more values ​​in the range of 1 to 2.5, and g can be any one or more values ​​in the range of 0 to 1.

[0128] 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 the specific substances of 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 can be selected. For example, the first positive electrode active material can be a lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide.

[0129] In some embodiments of this application, the thickness of the second positive electrode active material layer 2312b does not exceed 62% of the total thickness of the positive electrode active material layer 2312. Because polyanionic positive electrode materials have a large specific surface area and are prone to water absorption, when used in batteries, they can easily lead to high hydrofluoric acid content and deteriorate electrical performance. Therefore, controlling the thickness of the second positive electrode active material layer 2312b to not exceed 62% of the total thickness of the positive electrode active material layer 2312 can mitigate its deterioration on battery electrical performance.

[0130] For example, the thickness of the second positive electrode active material layer 2312b can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 62% of the thickness of the entire positive electrode active material layer 2312, or it can be any value in the range of 0% to 62% (excluding 0% and including 62%).

[0131] In some embodiments of this application, the positive electrode active material layer 2312 further includes an intermediate layer disposed between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b. The intermediate layer comprises a hydrophobic conductive polymer. By providing a hydrophobic intermediate layer between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b, the damage to the ternary system material caused by water absorption by the polyanionic positive electrode material can be reduced.

[0132] The hydrophobic conductive polymer can be a polymer that inherently possesses both hydrophobicity and conductivity, or it can be a composite of a hydrophobic polymer and a conductive material. In some embodiments of this application, the hydrophobic conductive polymer includes at least one of polypyrrole, polyaniline, polythiophene, and polyacetylene. In other embodiments, the intermediate layer further includes a hydrophobic conductive carbon material. This hydrophobic conductive carbon material includes hydrophobic carbon nanotubes and / or hydrophobic carbon nanofibers. By adding this hydrophobic conductive carbon material, the intermediate layer acquires better conductivity, thereby reducing its impact on the electrical properties of the positive electrode active material layer 2312.

[0133] 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.

[0134] The method for preparing the positive electrode 231 includes the following steps: A positive electrode active material layer 2312 is sequentially prepared on the positive electrode current collector 2311. The preparation order 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: the first positive electrode active material layer 2312a is disposed on at least a portion of the surface of the positive electrode current collector 2311, and the second positive electrode active material layer 2312b is disposed on at least a portion of the surface of the first positive electrode active material layer away from the positive electrode current collector 2311; or it can be: the second positive electrode active material layer 2312b is disposed on the positive electrode current collector 2311... At least a portion of the surface of the second positive electrode active material layer 2312a is disposed on at least a portion 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 2312a includes a first positive electrode active material and a first conductive agent, the second positive electrode active material layer 2312b includes a second positive electrode active material, the electronic conductivity of the second positive electrode active material is greater than the electronic conductivity of the first positive electrode active material, and the powder resistivity F of the second positive electrode active material at 8 MPa in Ω·cm and the weight ratio C of the first conductive agent in the first positive electrode active material layer 2312a satisfy the following relationship:

[0135] This method achieves the desired results by controlling the addition amount C of the first conductive agent (which has poor electronic conductivity) and the powder resistivity F of the second positive electrode active material (which has good electronic conductivity) at 8 MPa. This reduces the conductivity difference between the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b, thereby improving the overall electrical performance of the positive electrode 231. Simultaneously, layering the first and second positive electrode active materials reduces the likelihood of current unevenness between them, thus enabling the positive electrode 231 to maintain a higher capacity retention rate during the early stages of cycling.

[0136] 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:

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] S150, roll-press the second positive electrode active material layer 2312b to obtain the positive electrode sheet 231.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] Examples and Comparative Examples

[0152] [Preparation of the positive electrode plate]

[0153] Preparation of the first positive electrode active material layer: The first positive electrode active material NCM, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP), wherein the mass ratio of the binder polyvinylidene fluoride (PVDF) was 2.5%. The mixture was stirred and mixed evenly to obtain the first coating slurry; then the slurry was prepared at a concentration of 30 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.

[0154] 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 70 mg / 1540.25 mm. 2 The material is uniformly coated onto the second positive electrode active material layer, dried, and then rolled and die-cut to obtain the positive electrode sheet for lithium-ion batteries.

[0155] [Preparation of the negative electrode]

[0156] 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.

[0157] Preparation of Electrolyte

[0158] 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.

[0159]

Isolation Film

[0160] Polyethylene film is used as the separation membrane.

[0161] [Preparation of Lithium-ion Batteries]

[0162] 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°C 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-side sealing at 145°C. 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.

[0163] The main parameter controls for each embodiment and comparative example are shown in the table below:

[0164]

[0165] In the table above, the chemical formula of NCM with a Ni content of 0.55% is LiNi. 0.55 Co 0.05 M 0.4 The chemical formula of NCM with an O4 and Ni content of 0.65% is LiNi. 0.65 Co 0.07 M 0.28 The chemical formula of NCM with an O4 and Ni content of 0.4% is LiNi. 0.4 Co 0.05 M 0.55 The chemical formula of NCM with an O4 and Ni content of 0.7% is LiNi. 0.7 Co 0.07 M 0.23 The chemical formula of NCM with an O4 and Ni content of 0.33% is LiNi. 0.33 Co 0.05 M 0.62 The chemical formula of NCM with an O4 and Ni content of 0.83% is LiNi. 0.83 Co 0.12 M 0.05 O4.

[0166] The carbon content (C) test of the first positive electrode active material layer includes: taking powder of the first positive electrode active material layer of the electrode sheet, with a weight of ≥100mg, placing it in a ceramic crucible and heating it to 1000℃ for 4h (this step can remove the influence of the binder in the first positive electrode active material layer on the carbon content and prepare the test sample at the same time). After the crucible and the residue therein have cooled to room temperature (25℃), they are placed in an HCS-140 high-frequency infrared carbon-sulfur analyzer for carbon content analysis.

[0167] The resistivity test of cathode material powder includes: the test equipment is the Yuaneng Technology PRCD2100 powder resistivity tester. First, 0.2g of sample is weighed and added into the sample cavity of the mold of the equipment. The mold is placed in the pre-vibration compactor. The pre-vibration compactor is turned on to vibrate and level the powder. Then, the equipment software is opened to start the test and obtain the test results.

[0168] The Ni content test for NCM materials includes: taking 0.4g of NCM material powder from the electrode layer into a 25ml beaker, adding 2ml-5ml of nitric acid, letting it stand overnight, then placing it on a hot plate and heating it at about 100℃ (using a voltage regulator to adjust the input voltage and control the temperature) until the powder is digested. Then adding 0.5ml of perchloric acid and heating it at about 140℃ until the white fumes are completely eliminated, the residue should be white. Otherwise, nitric acid and perchloric acid should be added again for repeated digestion. Finally, it is dissolved and extracted with 7% (referring to the volume percentage of acid, the same below) hydrochloric acid. After adjusting the volume to an appropriate level according to the content of the element to be tested, it is placed on an ICP-OES instrument to start testing the mass fraction of Ni, Co, Mn, and Li. Based on the powder mass and the mass fraction of different elements, the mass of different elements can be calculated, and then the molar amount can be calculated according to its molar mass. The Ni content can be confirmed by the ratio of the molar amounts of different elements.

[0169] Example 14

[0170] Except for the exchange of the order of the first positive electrode active layer and the second positive electrode active material layer, this embodiment is the same as embodiment 3.

[0171] The performance of the batteries provided in each embodiment and comparative example was tested. The performance testing specifically included:

[0172] 25℃ Cycling Test: The lithium-ion battery product prepared above was charged at 0.5C to 4.4V 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 at 1C to 2.5V. The capacity was recorded as Cn (n=1,2,3……). The above operation was repeated. The capacity retention rate was calculated according to the ratio of Cn / C3. When Cn / C3×100%=80%, the corresponding number of cycles was extracted as the evaluation index of cycle capability.

[0173] 25℃ Cyclic Internal Resistance Growth Test: ① Initial Internal Resistance Test: The prepared pouch cells were charged at 0.5C to 4.4V in a constant temperature environment of 25℃ and 2.5~4.4V. Then, they were charged at 4.4V with constant voltage until the current ≤0.05C. After standing for 30 minutes, the voltage U1 was recorded. Then, the cells were discharged at 1C for 30 seconds, and the voltage at 30 seconds was recorded as U2. The internal resistance 1 = (U1-U2) / 1C; ② Cyclic Internal Resistance Test: After testing the cycle performance of the cells with the initial internal resistance, the internal resistance 2 was tested again. The internal resistance growth rate = (internal resistance 2-internal resistance 1) / internal resistance 1.

[0174] High-temperature storage gas generation test: The length, width and height of the soft-pack stacked battery prepared above were measured in a constant temperature environment of 25℃ to calculate the battery volume V1 = length × width × height. Then the battery was placed in a constant temperature chamber of 60℃±2℃ for 50 days. On the 50th day, the battery was taken out and the length, width and height of the battery were measured immediately to obtain the volume V2 after high-temperature storage. The volume change rate was (V2-V1) / V1.

[0175] The test results are shown in the table below:

[0176]

[0177]

[0178] As can be seen from the table above, when the positive electrode provided in this application embodiment is used as a battery, the battery has better cycle performance and less internal resistance growth.

[0179] A comparison of the data from Examples 1 to 5 and Comparative Examples 1 to 2 shows that as the F / (C*100) ratio gradually increases, the number of cycles first increases and then decreases, while the growth rate of the cycle internal resistance first decreases and then increases. Furthermore, when the F / (C*100) ratio is between 3.6 and 42.1, the number of cycles is consistently above 1000, and the growth rate of the cycle internal resistance is below 32%. Therefore, the F / (C*100) ratio between 3.6 and 42.1 is considered an optimal range. In particular, when the F / (C*100) ratio is between 8 and 23.5, the number of cycles exceeds 1200.

[0180] A comparison of the data from Examples 3 and 6 to 10 shows that as the Ni content in NCM increases, the number of cycles first increases and then decreases, while the growth rate of the cycle resistance first decreases and then increases. Furthermore, when the Ni content in NCM is between 0.4 and 0.7%, the number of cycles is above 980, and the growth rate of the cycle resistance is below 41%. This indicates that a Ni content of 0.4 to 0.7% in NCM is a favorable range.

[0181] Comparison of data from Examples 3 and 11 to 12 shows that when the thickness of the second positive electrode active material layer is less than 62%, the number of cycles is above 1000 and the cycle resistance growth rate is within 42%. However, when the thickness is 70%, the cycle performance and the growth rate of internal resistance deteriorate significantly. Therefore, a thickness of less than 62% for the second positive electrode active material layer is a better range.

[0182] A comparison of the data from Examples 3 and 13 shows that placing an intermediate layer between the first and second positive electrode active material layers can further improve the number of cycle times. The inventors believe that this is because the hydrophobic intermediate layer can reduce the damage to the ternary system material caused by water absorption by the polyanionic positive electrode material, thereby achieving good cycle performance and a smaller increase in cycle resistance.

[0183] A comparison of the data from Examples 3 and 14 shows that placing the ternary material closer to the current collector is more conducive to maintaining cycle performance and controlling cycle resistance. The inventors believe that this is because placing the ternary material in the inner layer reduces side reactions with the electrolyte, thereby achieving good cycle performance and a smaller increase in cycle resistance.

[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 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 and a first conductive agent. The second positive electrode active material layer includes a second positive electrode active material. The electronic conductivity of the second positive electrode active material is greater than that of the first positive electrode active material. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship: .

2. The positive electrode sheet according to claim 1, characterized in that, The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight ratio C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship: .

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The second positive electrode active material has a powder resistivity of 10~80 Ω·cm at 8 MPa; and / or The first conductive agent accounts for 1.9% to 2.8% of the weight of the first positive electrode active material layer; and / or The powder resistivity of the first conductive agent at 8 MPa is ≤0.025 Ω·cm.

4. The positive electrode sheet according to claim 1, characterized in that, The first positive electrode active material includes a ternary system material; and / or The second positive electrode active material includes a polyanionic positive electrode material.

5. The positive electrode sheet according to claim 4, 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.

6. The positive electrode sheet according to claim 5, 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.

7. The positive electrode sheet according to claim 5, 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.

8. The positive electrode sheet according to claim 5, 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.

9. The positive electrode sheet according to claim 4, characterized in that, The polyanionic cathode material also has a carbon-containing coating layer.

10. The positive electrode sheet according to claim 9, characterized in that, The powder resistivity of the second positive electrode active material at 8 MPa is 20~50 Ω·cm.

11. The positive electrode sheet according to claim 5, characterized in that, The molar content of Ni in the ternary system material is 0.4~0.7%.

12. The positive electrode sheet according to claim 5, 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, 0.4 < b < 0.7, 0 < c < 1, 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.

13. The positive electrode sheet according to claim 4, characterized in that, The thickness of the second positive electrode active material layer does not exceed 62% of the total thickness of the positive electrode active material layer.

14. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material layer further includes an intermediate layer, which is disposed between the first positive electrode active material layer and the second positive electrode active material layer, and the intermediate layer includes a hydrophobic conductive polymer.

15. The positive electrode sheet according to claim 14, characterized in that, The hydrophobic conductive polymer includes at least one of polypyrrole, polyaniline, polythiophene, and polyacetylene.

16. The positive electrode sheet according to claim 14 or 15, characterized in that, The intermediate layer also includes hydrophobic and conductive carbonaceous materials.

17. The positive electrode sheet according to claim 16, characterized in that, The hydrophobic conductive carbon materials include hydrophobic carbon nanotubes and / or hydrophobic carbon nanofibers.

18. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive electrode active material layer, which comprises a first positive electrode active material layer and a second positive electrode active material layer. The thickness of the second positive electrode active material layer does not exceed 62% of the total thickness of the positive electrode active material layer. The first positive electrode active material layer comprises a first positive electrode active material and a first conductive agent. The second positive electrode active material layer comprises a second positive electrode active material. The electronic conductivity of the second positive electrode active material is greater than that of the first positive electrode active material. The second positive electrode active material comprises LiMPO4, where M includes Mn and non-Mn elements. The non-Mn element includes one or both of a first doping element and a second doping element. The first doping element is manganese site doping, and the second doping element is phosphorus site doping. The first positive electrode active material comprises a ternary material system, where the molar content of Ni in the ternary material system is 0.4~0.

7. The powder resistivity F of the second positive electrode active material at 8 MPa (in Ω·cm) and the weight percentage C of the first conductive agent in the first positive electrode active material layer satisfy the following relationship: .

19. A single battery cell, characterized in that, The battery cell includes the positive electrode sheet according to any one of claims 1 to 18.

20. A battery, characterized in that, The battery comprises the battery cell of claim 19.

21. An electrical appliance, characterized in that, The electrical device includes the battery cell of claim 19 or the battery of claim 20.

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