Positive electrode sheet, battery cell, battery and electric apparatus

Abstract

A positive electrode sheet, a battery cell, a battery and an electric apparatus, which belong to the technical field of batteries. In a first positive-electrode active material layer of the positive electrode sheet, a ternary material containing monocrystalline particles and a ternary material containing polycrystalline particles are used together, and the percent by weight wmono of the monocrystalline particles, the particle dimension Dmono of the monocrystalline particles, the percent by weight wpoly of the polycrystalline particles and the particle dimension Dpoly of the polycrystalline particles are controlled to satisfy formula (I), such that good particle composition is achieved between the relatively small monocrystalline particles and the relatively large polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing the energy density thereof. Moreover, a transport path of Li ions can be made within a relatively small range, and when the positive electrode sheet is applied to a battery, polarization of the battery and the increase of the internal resistance of the battery are reduced, thereby facilitating the performance of the battery.

Description

Positive electrode sheet, battery cell, battery and power-consuming device

[0001] Cross-references

[0002] This application claims priority to the Chinese invention patent application with application number 202310802214.X filed on June 30, 2023, entitled “A positive electrode sheet, a battery cell, a battery and an electrical device”, the contents of which are incorporated herein by reference. Technical Field

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

[0004] In positive electrode sheets that use multiple positive electrode active materials, in order to reduce the possibility of current unevenness between the positive electrode active materials, the positive electrode active materials are usually arranged in layers. Usually, the particle sizes of different positive electrode active materials are different. The layered arrangement cannot give full play to the grading advantages of the particles, and the compaction density of the entire positive electrode sheet needs to be improved.

[0005] Summary of the Invention

[0006] In view of the above problems, the present application provides a positive electrode sheet, a battery cell, a battery and an electrical device, which can improve the compaction density of the positive electrode sheet.

[0007] In a first aspect, the present application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer comprising a first positive electrode active material, the first positive electrode active material comprising a ternary system material, the ternary system material comprising single crystal particles and polycrystalline particles, the second positive electrode active material layer comprising a second positive electrode active material, the second positive electrode active material comprising a polyanion positive electrode material, the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

[0008] In the technical solution of the embodiment of the present application, a ternary system material of single crystal particles and polycrystalline particles is used in combination in the first positive electrode active material layer, and the mass proportion of the single crystal particles is controlled by w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多, the particle size D of polycrystalline particles 多 satisfy This creates a good particle gradation between smaller single crystal particles and larger polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing its energy density. It also reduces the Li ion transmission path within a smaller range, which, when used in a battery, reduces the increase in polarization and internal resistance of the battery, which is beneficial to battery performance. Furthermore, the layered arrangement of the first and second positive electrode active materials reduces the possibility of current unevenness between the first and second positive electrode active materials, thereby ensuring a higher capacity retention rate for the positive electrode sheet in the early stages of cycling.

[0009] In some embodiments, the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

[0010] In the above implementation process, by controlling the mass proportion of single crystal particles w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 satisfy It can further improve the compaction density of the entire positive electrode sheet and increase its energy density.

[0011] In some embodiments, the positive electrode sheet further includes a current collector, the first positive electrode active material layer is disposed on at least one surface of the current collector, and the second positive electrode active material layer is disposed on a surface of the first positive electrode active material layer away from the current collector.

[0012] In the above implementation, by placing the second positive electrode active material layer, which has weaker ion transport properties, on the surface of the first positive electrode active material layer, when used in a battery, the second positive electrode active material layer is closer to the negative electrode sheet, shortening its ion transport path, which helps to increase its ion transport rate and, in turn, its rate performance. This also reduces the possibility of side reactions in the ternary system materials, which is more beneficial to the electrochemical performance of the positive electrode sheet.

[0013] In some embodiments, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0014] The thickness H1 of the first positive electrode active material layer is 5 to 35 μm; and / or

[0015] The thickness H2 of the second positive electrode active material layer is 35 to 80 μm.

[0016] In the above implementation process, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is controlled to satisfy: The thickness H1 of the first positive electrode active material layer is 5 to 35 μm, and the thickness H2 of the second positive electrode active material layer is 35 to 80 μm. This allows the amount of the ternary system material to be within a relatively suitable range, thereby fully utilizing its performance, such as energy density and service life, while reducing the probability of its side reactions causing deterioration in battery performance and safety. At the same time, the average transmission distance of the entire second positive electrode active material layer is within a smaller range, which is beneficial to its own ion transmission rate and can reduce the weakening of the ion transmission capacity of the first positive electrode active material layer, thereby achieving better rate performance. In addition, the amount of the second positive electrode active material can be within a relatively suitable range, thereby fully utilizing its performance, such as safety performance.

[0017] In some embodiments, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0018] The thickness H1 of the first positive electrode active material layer is 10 to 30 μm; and / or

[0019] The thickness H2 of the second positive electrode active material layer is 40 to 70 μm.

[0020] In some embodiments, the relationship between the mass percentage wNi of the Ni element in the ternary system material, the mass percentage wMn of the Mn element in the ternary system material, the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0021] The mass percentage wNi of the Ni element in the ternary system material to all elements is 20% to 55%; and / or

[0022] The mass percentage wMn of the Mn element in the ternary system material to all elements is 5% to 25%.

[0023] During the above implementation process, the content of Ni in the ternary system material and the probability of its side reaction are positively correlated to a certain extent. The higher the Ni content, the more likely the side reaction is to occur. The content of Mn in the ternary system material and its structural stability are positively correlated to a certain extent. The higher the Mn content, the higher the structural stability. The thickness of the first positive electrode active material layer and the probability of its side reaction are positively correlated to a certain extent. The thicker the thickness, the more the corresponding content of the first positive electrode active material, and the more likely the side reaction is to occur. The thickness of the second positive electrode active material layer and the probability of the ternary system material side reaction are positively correlated to a certain extent. The thicker the second positive electrode active material layer, the more likely the ternary system material is to have a side reaction. By controlling the mass proportion of Ni wNi, the mass proportion of Mn wMn, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer, the relationship is satisfied: The mass percentage of Ni element in the ternary system material, wNi, of all elements is 20% to 55%, and the mass percentage of Mn element in the ternary system material, wMn, of all elements is 5% to 25%. This can reduce the probability of side reactions in the ternary system material, while making the positive electrode sheet have better safety and cycle stability, and can also take into account the energy density of the positive electrode sheet.

[0024] In some embodiments, the relationship between the mass percentage wNi of the Ni element in the ternary system material, the mass percentage wMn of the Mn element in the ternary system material, the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: and / or

[0025] The mass percentage wNi of the Ni element in the ternary system material to all elements is 30% to 45%; and / or

[0026] The mass percentage wMn of the Mn element in the ternary system material to all elements is 10% to 20%.

[0027] In some embodiments, the mass proportion of the single crystal particles in the ternary system material is 10% to 40%, and the mass proportion of the polycrystalline particles in the ternary system material is 60% to 90%; and / or

[0028] The volume median particle size of the single crystal particles is 2.5 to 4.5 μm; and / or

[0029] The volume median particle size of the polycrystalline particles is 8 to 10 μm.

[0030] In some embodiments, the polyanion positive electrode material includes LiMPO4, 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 doping, and the second doping element is phosphorus doping.

[0031] Optionally, the first doping element includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge.

[0032] Optionally, the second doping element includes one or more elements selected from the group consisting of B, S, Si and N.

[0033] Optionally, the polyanion cathode material includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein 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 the group consisting of 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 the group consisting of B, S, Si and N.

[0034] Optionally, the polyanion 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 the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from the group consisting of B, S, Si, and N; D includes one or more elements selected from the group consisting of 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 polyanion positive electrode material is electrically neutral.

[0035] In some embodiments, the polyanionic cathode material further comprises a carbon-containing coating layer.

[0036] 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.

[0037] In some embodiments, the ternary system material includes nickel-cobalt-manganese ternary materials and their modified materials, and nickel-cobalt-aluminum ternary materials and their modified materials.

[0038] In the above implementation process, the modified materials of the nickel-cobalt-manganese ternary material and the nickel-cobalt-aluminum ternary material respectively refer to materials obtained by doping or coating the nickel-cobalt-manganese ternary material or the nickel-cobalt-aluminum ternary material.

[0039] In some embodiments, the ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is selected from one or two elements of Mn or Al, M2 is selected from one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from one or more elements of N, F, S, Cl.

[0040] In a second aspect, the present application provides a positive electrode sheet, which includes a positive electrode active material layer and a current collector. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer is disposed on at least one surface of the current collector, and the second positive electrode active material layer is disposed on the surface of the first positive electrode active material layer away from the current collector; the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, the mass ratio w of the single crystal particles in the ternary system material 单 , the volume median diameter D of the single crystal particles in μm 单 , the mass ratio w of the polycrystalline particles in the ternary system material 多 and the volume median diameter D of the polycrystalline particles in μm 多 satisfy the following relationship:

[0041] In the technical solution of the embodiment of the present application, a ternary system material of single crystal particles and polycrystalline particles is used in combination in the first positive electrode active material layer, and the mass proportion of the single crystal particles is controlled by w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 satisfy This allows a good particle gradation to be formed between the smaller single crystal particles and the larger polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing its energy density. It also allows the Li ion transmission path to be within a smaller range, which, when used as a battery, reduces the polarization and increase in internal resistance of the battery, which is beneficial to the performance of the battery. At the same time, layering the first positive electrode active material and the second positive electrode active material can reduce the possibility of current unevenness between the first positive electrode active material and the second positive electrode active material, thereby allowing the positive electrode sheet to have a higher capacity retention rate in the early stages of the cycle. In addition, polyanion positive electrode materials generally exhibit better safety performance, and ternary system materials generally exhibit higher energy density. Using polyanion positive electrode materials as the second positive electrode active material and ternary system materials as the first positive electrode active material can enable the positive electrode sheet to have both higher safety performance and higher energy density. In addition, a second positive electrode active material layer with weaker ion transport performance is arranged on the surface of the first positive electrode active material layer. When used as a battery, the second positive electrode active material layer is closer to the negative electrode sheet, making its ion transport path shorter, which is beneficial to improving its ion transport rate and thus improving its rate performance.

[0042] In a third aspect, the present application provides a battery cell, which includes the positive electrode sheet provided in the first aspect or the second aspect.

[0043] In a fourth aspect, the present application provides a battery, which includes the battery cell provided in the third aspect.

[0044] In a fifth aspect, the present application provides an electrical device, which includes the battery cell provided in the third aspect or the battery provided in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0046] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application;

[0047] FIG2 is a schematic diagram of the exploded structure of a secondary battery provided in some embodiments of the present application;

[0048] FIG3 is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0049] FIG4 is an exploded view of a battery cell provided in some embodiments of the present application;

[0050] FIG5 is a schematic diagram of a first structure of a positive electrode sheet provided in some embodiments of the present application;

[0051] FIG6 is a second structural schematic diagram of a positive electrode sheet provided in some embodiments of the present application;

[0052] FIG7 is a flow chart of a method for preparing a positive electrode sheet provided in some embodiments of the present application.

[0053] The accompanying drawings in the specific implementation manner are as follows:

[0054] 1000-vehicle; 100-secondary battery; 200-motor; 300-controller; 10-housing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-housing; 211-opening; 22-end cover assembly; 221-end cover; 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 collecting member; 25-insulating protection member. DETAILED DESCRIPTION

[0055] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0057] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0058] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0059] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0060] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0061] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0062] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0063] Currently, market developments indicate that power batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As power battery applications continue to expand, market demand is also growing.

[0064] Power batteries can be lithium-ion batteries, which are widely used in portable electronic devices, electric vehicles, and other fields. In the production process of lithium-ion secondary battery electrode plates, a single-layer coating is usually adopted, in which the required active material is coated on the current collector. With the increasing requirements for energy density and safety performance, some people have proposed using a combination of positive electrode active materials with high energy density characteristics, such as ternary system materials, and positive electrode active materials with high safety performance characteristics, such as polyanion positive electrode materials, to achieve a balance between energy density and safety performance.

[0065] However, when a positive electrode active material with high energy density characteristics and a positive electrode active material with high safety performance characteristics are directly incorporated into a positive electrode active material layer, current unevenness is likely to occur between the two positive electrode active materials in the positive electrode active material layer. This phenomenon will cause the positive electrode sheet to decay rapidly in the early stage of the cycle, which will have a great impact on the capacity retention rate of the positive electrode sheet.

[0066] In order to further improve the problem of rapid attenuation of the electrode in the early stage of the cycle, the two active materials can be layered. However, the particle size of the ternary system material is often an order of magnitude larger than that of the polyanion positive electrode material. After the layered arrangement, the particle grading advantages of the two cannot be brought into play, resulting in the compaction density of the entire positive electrode sheet needs to be improved.

[0067] Based on the above considerations, in order to increase the compaction density of the positive electrode sheet and improve its energy density. The present application proposes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

[0068] In such a positive electrode sheet, a ternary system material of single crystal particles and polycrystalline particles is used in the first positive electrode active material layer, and the mass proportion of the single crystal particles is controlled. 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w多 , the particle size D of polycrystalline particles 多 satisfy This creates a good particle gradation between smaller single crystal particles and larger polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing its energy density. It also reduces the Li ion transmission path within a smaller range, which, when used in a battery, reduces the increase in polarization and internal resistance of the battery, which is beneficial to battery performance. Furthermore, the layered arrangement of the first and second positive electrode active materials reduces the possibility of current unevenness between the first and second positive electrode active materials, thereby ensuring a higher capacity retention rate for the positive electrode sheet in the early stages of cycling.

[0069] The positive electrode sheet can be used to prepare an electrode assembly, which can be used, but is not limited to, in electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the battery cells and secondary batteries disclosed herein can be used to form the electrical device. This facilitates fully leveraging the effect of the high ultimate compaction density positive electrode material on increasing the compaction density of the entire positive electrode active material layer, thereby significantly improving the compaction density of the entire positive electrode active material layer, thereby increasing the energy density of the positive electrode sheet and the capacity of the battery cell.

[0070] The present invention provides an electric device that uses a battery as a power source. The electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0071] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0072] Please refer to Figure 1, which is a structural schematic diagram of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A secondary battery 100 is provided inside the vehicle 1000, and the secondary battery 100 can be provided at the bottom, head or tail 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 an 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 power the motor 200, for example, for starting, navigating and driving the vehicle 1000.

[0073] In some embodiments of the present application, the secondary battery 100 can serve not only as an operating power source for the vehicle 1000 , but also as a driving power source for the vehicle 1000 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000 .

[0074] In this application, a secondary battery 100 refers to a single physical module that includes multiple battery cells 20 to provide higher voltage and capacity. It can be in the form of a battery pack, a battery module, etc. The secondary battery 100 can include a housing 10 for enclosing the multiple battery cells 20. The housing 10 can prevent liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0075] FIG2 is a schematic diagram of the exploded structure of a secondary battery 100 provided in some embodiments of the present application. Referring to FIG2 , the secondary battery 100 includes a housing 10 and a battery cell 20 , wherein the battery cell 20 is housed in the housing 10 .

[0076] The housing 10 is used to provide a storage space 11 for the battery cells 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap to define the storage space 11 for accommodating the battery cells 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a seal (not shown), such as a sealing ring, sealant, or the like.

[0077] The first portion 12 and the second portion 13 can have various shapes, such as a rectangular parallelepiped, a cylinder, etc. The first portion 12 can be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The second portion 13 can also be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The open side of the second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11. Of course, as shown in Figure 2, the first portion 12 can also be a hollow structure with an opening on one side, and the second portion 13 can be a plate-like structure. The second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11.

[0078] In the secondary battery 100, there are multiple battery cells 20. These multiple battery cells 20 can be connected in series, in parallel, or in a hybrid connection. Hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. Multiple battery cells 20 can be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can be first connected in series, in parallel, or in a hybrid connection to form a battery module, and then the multiple battery modules are further connected in series, in parallel, or in a hybrid connection to form an entire battery module, which is then housed within the housing 10. The battery cells 20 can be cylindrical, flat, rectangular, or in other shapes. Figure 2 exemplifies a case where the battery cells 20 are square.

[0079] In some embodiments, the secondary battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or hybrid connection of the multiple battery cells 20 .

[0080] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of the present application. Referring to Figures 3 and 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, and the electrode assembly 23 is accommodated within the housing 21. The end cap assembly 22 is used to seal the opening 211.

[0081] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a rectangular parallelepiped structure, the housing 21 can be a rectangular parallelepiped structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0082] The shell 21 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0083] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the outer shell 21 to form a sealed installation space (not shown), which is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 serves as a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to electrically connect to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0084] It should be noted that the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.

[0085] In some embodiments, as shown in FIG4 , the battery cell 20 may further include an insulating protective member 25 secured to the 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 a tape adhered to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is disposed around the periphery of the multiple electrode assemblies 23, forming the multiple electrode assemblies 23 into a single integrated structure to maintain structural stability.

[0086] The electrode assembly 23 includes a positive electrode sheet 231, a negative electrode sheet, and a separator. The positive electrode sheet 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 electrode collector 2311. The positive electrode collector 2311 not coated with the positive active material layer 2312 protrudes from the positive electrode collector 2311 coated with the positive active material layer 2312. The positive electrode collector 2311 not coated with the positive active material layer 2312 serves as a positive electrode tab.

[0087] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector. The negative electrode current collector not coated with the negative electrode active material layer protrudes from the negative electrode current collector coated with the negative electrode active material layer. The negative electrode current collector not coated with the negative electrode active material layer serves as a negative electrode tab. The material of the negative electrode current collector may be copper, and the negative electrode active material may be carbon or silicon, etc. In order to ensure that a large current passes without melting, the number of positive electrode tabs is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the isolation membrane may be PP (polypropylene, polypropylene) or PE (polyethylene, polyethylene), etc. In addition, the electrode assembly 23 may be a wound electrode assembly or a laminated electrode assembly, and the embodiments of the present application are not limited to this.

[0088] FIG5 is a schematic diagram of the first structure of a positive electrode sheet 231 provided in some embodiments of the present application, and FIG6 is a schematic diagram of the second structure of a positive electrode sheet 231 provided in some embodiments of the present application; please refer to FIG5 and FIG6, an embodiment of the present application provides a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, and the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

[0089] The positive electrode active material layer 2312 is attached to at least part of the surface of the positive electrode 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 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 collector 2311 can be: the first positive electrode active material layer 2312a is attached to the positive electrode 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 facing away from the positive electrode collector 2311; it can also be: the second positive electrode active material layer 2312b is attached to the positive electrode 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 facing away from the positive electrode collector 2311.

[0090] The material of the positive electrode current collector 2311 can be one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Continuing with 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. Continuing with Figure 6, in another embodiment, the first positive electrode active material layer 2312a and the 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 merely an example of how this solution can be implemented. In other embodiments, the positions of the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be interchanged.

[0091] For lithium-ion batteries, the first positive electrode active material and the second positive electrode active material refer to substances capable of intercalating and deintercalating lithium ions.

[0092] Ternary materials typically include two types: NCA and NCM. NCA is widely used due to its long lifespan, large capacity, and high energy density. NCM, on the other hand, combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide cathode materials, exhibiting a significant ternary synergistic effect.

[0093] A single crystal is a crystal in which the particles within it are arranged regularly and periodically in three-dimensional space. In other words, the entire crystal is composed of a uniform spatial lattice in three dimensions, and the arrangement of particles in the crystal is long-range ordered. A polycrystal is a collection of single crystals with numerous oriented grains. A particle is a geometric object with a specific shape within a certain size range.

[0094] The median particle size (Dv50) is the particle size corresponding to 50% of the cumulative amount in the volume particle size cumulative distribution diagram. The volume particle size cumulative distribution diagram, also known as the differential distribution diagram of the particle size, is a curve drawn with the particle size as the horizontal coordinate and the differential distribution of the content at different particle sizes as the vertical coordinate. It can more accurately reflect the particle size distribution characteristics of the material particles. Among them, a laser particle size analyzer can be used to measure the volume particle size distribution of the material and draw an interval particle size distribution curve. When the median particle size of the positive electrode active material in the active material layer of the electrode is measured, the positive electrode active material layer can be removed and immersed in the solvent NMP to wash out the binder in the positive electrode active material layer to obtain the powder material of the positive electrode active material layer. After the powder material is dried, it is detected using a laser particle size analyzer with the model number Mastersizer3000 to obtain a volume particle size cumulative distribution diagram. The median particle size of the polycrystalline particles and the single crystal particles can be obtained based on the peak in the volume particle size cumulative distribution diagram.

[0095] The median particle size (Dv50) of polycrystalline particles is the size of the polycrystalline particles accumulated from smallest to largest. When the accumulated volume accounts for 50%, the median particle size Dv50 of the polycrystalline particles is the median particle size Dv50. The median particle size (Dv50) of single crystal particles is the median particle size of the single crystal particles accumulated from smallest to largest. When the accumulated volume accounts for 50%, the median particle size Dv50 of the single crystal particles is the median particle size Dv50.

[0096] Polyanion positive electrode materials are a general term for a series of compounds containing tetrahedral or octahedral anion structural units (XOm)n-. They have the advantages of 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.

[0097] The mass ratio of single crystal particles and polycrystalline particles can be obtained by quantitatively distinguishing the distribution ratio of single crystal particles and polycrystalline particles using SEM test images.

[0098] By using a ternary system material of single crystal particles and polycrystalline particles in the first positive electrode active material layer, and by controlling the mass proportion of single crystal particles w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 satisfy This creates a good particle gradation between smaller single crystal particles and larger polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing its energy density. It also reduces the Li ion transmission path within a smaller range, which, when used in a battery, reduces the increase in polarization and internal resistance of the battery, which is beneficial to battery performance. Furthermore, the layered arrangement of the first and second positive electrode active materials reduces the possibility of current unevenness between the first and second positive electrode active materials, thereby ensuring a higher capacity retention rate for the positive electrode sheet in the early stages of cycling.

[0099] For example, the mass proportion of single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfied relationship: The value of can be 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44 or 0.45, etc. It can also be any value in the range of 0.02 to 0.45.

[0100] In the technical solutions of some embodiments of the present application, the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship: By controlling the mass proportion w of single crystal particles 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 satisfy It can further improve the compaction density of the entire positive electrode sheet and increase its energy density.

[0101] In the technical solutions of some embodiments of the present application, the positive electrode sheet 231 also includes a current collector. The first positive electrode active material layer is disposed on at least one surface of the current collector, and the second positive electrode active material layer 2312b is disposed on the surface of the first positive electrode active material layer 2312a away from the current collector. By disposing the second positive electrode active material layer 2312b, which has weaker ion transport performance, on the surface of the first positive electrode active material layer 2312a, when used in a battery, the second positive electrode active material layer 2312b is closer to the negative electrode sheet 232, shortening its ion transport path, which is beneficial for improving its ion transport rate and, in turn, its rate performance. At the same time, it can reduce the possibility of side reactions in the ternary system materials, which is more beneficial to the electrochemical performance of the positive electrode sheet.

[0102] In the technical solutions of some embodiments of the present application, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: The thickness H1 of the first positive electrode active material layer is 5 to 35 μm; the thickness H2 of the second positive electrode active material layer is 35 to 80 μm. The relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is controlled to satisfy: The thickness H1 of the first positive electrode active material layer is 5-35 μm, and the thickness H2 of the second positive electrode active material layer is 35-80 μm. This allows the ternary material to be used within a relatively suitable range, thereby fully utilizing its performance, such as energy density and service life, while also reducing the probability of side reactions that deteriorate battery performance and safety. Furthermore, the average transmission distance of the entire second positive electrode active material layer is kept within a relatively short range, which is beneficial to its own ion transmission rate while minimizing the reduction in the ion transmission capacity of the first positive electrode active material layer, thereby achieving better rate performance. Furthermore, the amount of the second positive electrode active material can be kept within a relatively suitable range, thereby fully utilizing its performance, such as safety.

[0103] For example, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfy the relationship The value of may be 0.8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 16, etc., and may be any value within the range of 0.8 to 16. The thickness H1 of the first positive electrode active material layer may be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 31 μm, 33 μm or 35 μm, etc., and may be any value within the range of 5 to 35 μm. The thickness H2 of the second positive electrode active material layer can be 35μm, 37μm, 39μm, 40μm, 43μm, 45μm, 47μm, 49μm, 51μm, 53μm, 55μm, 57μm, 59μm, 61μm, 63μm, 65μm, 67μm, 69μm, 71μm, 73μm, 75μm, 77μm, 79μm and 80μm, etc., and it can also be any value within the range of 35 to 80μm.

[0104] In the technical solutions of some embodiments of the present application, the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: The thickness H1 of the first positive electrode active material layer is 10 to 30 μm; the thickness H2 of the second positive electrode active material layer is 40 to 70 μm.

[0105] In the technical solutions of some embodiments of the present application, the relationship between the mass percentage wNi of the Ni element in the ternary system material, the mass percentage wMn of the Mn element in the ternary system material, the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: The mass percentage of Ni element in the ternary material to all elements, wNi, is 20% to 55%; the mass percentage of Mn element in the ternary material to all elements, wMn, is 5% to 25%. It should be noted that the values ​​of H1 and H2 are both in μm.

[0106] The content test of Ni and Mn in NCM materials can be as follows: take 0.4g of the electrode NCM material layer powder in a 25ml beaker, add 2ml~5ml nitric acid, leave it overnight, then place it on a hot plate and heat it at about 100℃ (use a voltage-regulating transformer to adjust the input voltage and temperature). After the powder is digested, add 0.5ml of perchloric acid and heat it at about 140℃ until the white smoke is gone. The residue should be white, otherwise nitric acid and perchloric acid should be added to repeat the digestion. Finally, use 7% (volume % of acid, the same below) hydrochloric acid to dissolve and extract. After the volume is adjusted to an appropriate volume depending on the content of the element to be tested, the mass fraction of Ni, Co, Mn, and Li can be tested on the ICP-OES test instrument. The mass of different elements can be calculated based on the mass of the powder and the mass fraction of different elements, and the Ni and Mn contents can be confirmed by different mass ratios.

[0107] The content of Ni in the ternary system material is positively correlated with the probability of its side reaction to a certain extent. The higher the Ni content, the more likely the side reaction will occur. The content of Mn in the ternary system material is positively correlated with its structural stability to a certain extent. The higher the Mn content, the higher the structural stability. The thickness of the first positive electrode active material layer is positively correlated with the probability of its side reaction to a certain extent. The thicker the thickness, the higher the content of the first positive electrode active material, and the more likely the side reaction will occur. The thickness of the second positive electrode active material layer is positively correlated with the probability of the side reaction of the ternary system material to a certain extent. The thicker the second positive electrode active material layer, the more likely the side reaction will occur in the ternary system material. By controlling the mass proportion of Ni wNi, the mass proportion of Mn wMn, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer, the relationship is satisfied: The mass percentage of Ni element in the ternary system material, wNi, of all elements is 20% to 55%, and the mass percentage of Mn element in the ternary system material, wMn, of all elements is 5% to 25%. This can reduce the probability of side reactions in the ternary system material, while making the positive electrode sheet have better safety and cycle stability, and can also take into account the energy density of the positive electrode sheet.

[0108] For example, the mass percentage of Ni element in the ternary system material to all elements wNi, the mass percentage of Mn element in the ternary system material to all elements wMn, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfy the relationship The value of can be 0.05, 0.5, 1, 1.5, 2, 2.5, 3 or 3.5, etc., and it can also be any value in the range of 0.05 to 3.5. The mass percentage of Ni element in the ternary system material to all elements wNi can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54% or 55%, etc., and it can also be any value in the range of 20% to 55%. The mass percentage of Mn element in the ternary system material to all elements wMn can be 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23% or 25%, etc., and it can also be any value in the range of 5% to 25%.

[0109] In the technical solutions of some embodiments of the present application, the relationship between the mass percentage wNi of the Ni element in the ternary system material, the mass percentage wMn of the Mn element in the ternary system material, the thickness H1 of the first positive electrode active material layer, and the thickness H2 of the second positive electrode active material layer satisfies: The mass percentage wNi of the Ni element in the ternary system material to all elements is 30% to 45%; the mass percentage wMn of the Mn element in the ternary system material to all elements is 10% to 20%.

[0110] In the technical solutions of some embodiments of the present application, the mass proportion of the single crystal particles in the ternary system material is 10% to 40%, and the mass proportion of the polycrystalline particles in the ternary system material is 60% to 90%; the volume median particle size of the single crystal particles is 2.5 to 4.5 μm; and the volume median particle size of the polycrystalline particles is 8 to 10 μm.

[0111] For example, the mass proportion of single crystal particles in the ternary material can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40%, etc., and can also be any value in the range of 10% to 40%. The mass proportion of polycrystalline particles in the ternary material can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%, etc., and can also be any value in the range of 60% to 90%. The volume median particle size of the single crystal particles may be 2.5 μm, 2.7 μm, 2.9 μm, 3.1 μm, 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.3 μm, or 4.5 μm, or any value within the range of 2.5 to 4.5 μm. The volume median particle size of the polycrystalline particles may be 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm, 9.0 μm, 9.2 μm, 9.4 μm, 9.6 μm, 9.8 μm, or 10 μm, or any value within the range of 8 to 10 μm.

[0112] In the technical solutions of some embodiments of the present application, the second positive electrode active material includes a polyanion positive electrode material. Optionally, the polyanion positive electrode material includes LiMPO4, and M includes Mn and non-Mn elements.

[0113] It should be noted that the above-mentioned LiMPO4 is not a specific molecular structure formula, but a general expression of lithium manganese phosphate.

[0114] In the technical solutions of some embodiments of the present application, the non-Mn element includes one or both of a first doping element and a second doping element, the first doping element is a manganese doping element, and the second doping element is a phosphorus doping element.

[0115] In the technical solutions of some embodiments of the present application, the first doping element includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0116] In the technical solutions of some embodiments of the present application, the first doping element includes at least two of Fe, Ti, V, Ni, Co and Mg.

[0117] In the technical solutions of some embodiments of the present application, the second doping element includes one or more elements selected from B, S, Si and N.

[0118] In the technical solutions of some embodiments of the present application, the second positive electrode active material includes Li 1+x Mn 1-y Ay P 1-z R z O4, Li 1+x Mn 1-y A y P 1-z R z In O4, x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from the group consisting of 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 the group consisting of B, S, Si and N.

[0119] In the technical solutions of some embodiments of the present application, the compound Li 1+x Mn 1-y AyP 1-z The preparation method of RzO4 may include the following steps:

[0120] (1) dissolving a manganese source, a source of element A to be doped at the manganese position, and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element A, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element A;

[0121] (2) adding a lithium source, a phosphorus source, an element R source, a solvent, and the manganese salt doped with element A obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry;

[0122] (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain granules;

[0123] (4) Sintering the particles obtained in step (3) to obtain a positive electrode active material.

[0124] 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. For example, the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

[0125] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, and may be, 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 a simple substance, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0126] In the technical solutions of some embodiments of the present application, the polyanion positive electrode material includes Li h A i Mn 1-j Bj P 1-k C k O 4-l D l , wherein A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from the group consisting of B, S, Si, and N; D includes one or more elements selected from the group consisting of 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 polyanion positive electrode material is electrically neutral.

[0127] 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 refer to Li 1+x Mn 1-y A y P 1-z R z O4, no limitation here.

[0128] Below is 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 are thoroughly mixed in a mixer for 6 hours. The mixture is transferred to a reactor, and 10 L of deionized water and 2 mol of dihydrated oxalic acid (calculated as oxalic acid) are added. The reactor is heated to 80°C and stirred at 600 rpm for 6 hours. The reaction is terminated (no bubbles are generated) to obtain an Fe-doped manganese oxalate suspension. The suspension is then filtered, and the filter cake is dried at 120°C and then ground to obtain a median particle size Dv 50Fe-doped manganese oxalate particles of about 100 nm. 2. Preparation of doped lithium manganese phosphate: Take 1 mol of the above-mentioned 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 and add them to 20L of deionized water. Transfer the mixture to a sand mill and grind and stir thoroughly for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C, dry for 4 hours, and obtain particles. In a protective atmosphere of nitrogen (90% volume) + hydrogen (10% volume), sinter the above powder at 700°C 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 .

[0129] In the technical solutions of some embodiments of the present application, the second positive electrode active material further has a carbon-containing coating layer.

[0130] The introduction of a carbon-containing coating layer improves the conductivity of the positive electrode active material. At this time, the structure of the positive electrode active material is actually a core-shell structure with LiMPO4 as the core and the surface of the core covered with the coating layer.

[0131] In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before adding the material. When the positive electrode material is used in a battery system, the molar content of Li will change after charge and discharge cycles.

[0132] In addition, the preparation process and conditions of the materials are different, and the molar content of the O element is usually not strictly the coefficient of the O element in the chemical formula, and there will be fluctuations, such as Li 1+x Mn 1-y A y P 1-z R z The molar content of the O element in O4 is not strictly 4.

[0133] For example, the second positive electrode active material may be LiFePO4, LiMn 0.1 Fe 0.9 PO4、LiMn 0.2 Fe 0.8 PO4、LiMn 0.3 Fe 0.7 PO4、LiMn 0.4 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 O4, etc. In LiMPO4, M includes Mn and non-Mn elements. The non-Mn elements include one or both of the first doping element and the second doping element. The first doping element is doping at the Mn site, and the second doping element is doping at the P site. The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; the second doping element includes one or more elements selected from B, S, Si, and N.

[0134] In the technical solutions of some embodiments of the present application, the ternary system material includes nickel-cobalt-manganese ternary material and its modified material, and nickel-cobalt-aluminum ternary material and its modified material. Among them, the ternary system material includes nickel-cobalt-manganese ternary material and its modified material, and nickel-cobalt-aluminum ternary material and its modified material.

[0135] In the technical solutions of some embodiments of the present application, the ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3. M1 is selected from one or both 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.

[0136] Exemplarily, the ternary system material can be LiNi 0.4 Co 0.2 Mn0.4 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2 and LiNi 0.7 Co 0.15 Mn 0.15 O2 etc. Li a Ni b Co c M1 d M2 e O f R g Where 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 0.3 to 1.0, c can be any one or more values ​​in the range of 0 to 0.4, 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 value in the range of 1 to 2.5, and g can be any one or more values ​​in the range of 0 to 1.

[0137] It should be noted that the above enumeration of the first positive electrode active material and the second positive electrode active material is merely an illustration of the feasibility of this solution and is not intended to limit this solution. In other embodiments, those skilled in the art may select specific materials for the first positive electrode active material and the second positive electrode active material according to actual needs, such as the materials listed above and their modified materials, including doping or coating.

[0138] After the above introduction to the material and structure of the positive electrode sheet 231 , the preparation method of the positive electrode sheet 231 will be specifically introduced below.

[0139] The preparation method of the positive electrode sheet 231 includes the following steps: preparing a positive electrode active material layer 2312 on a positive electrode current collector 2311, and 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 arranged 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 arranged on at least a portion of the surface of the first positive electrode active material away from the positive electrode current collector 2311; or: the second positive electrode active material layer 2312a is arranged on the positive electrode current collector 2311. 2b is arranged on at least a portion of the surface of the positive electrode collector 2311, and the first positive electrode active material layer 2312a is arranged on at least a portion of the surface of the second positive electrode active material layer 2312b away from the positive electrode collector 2311; the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, and the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

[0140] The method adopts a ternary system material of single crystal particles and polycrystalline particles in the first positive electrode active material layer, and controls the mass proportion of single crystal particles w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 satisfy This creates a good particle gradation between smaller single crystal particles and larger polycrystalline particles, thereby improving the compaction density of the entire positive electrode sheet and increasing its energy density. It also reduces the Li ion transmission path to a smaller range, reducing the polarization and internal resistance increase in the battery, which is beneficial to battery performance. Furthermore, the layered arrangement of the first and second positive electrode active materials reduces the possibility of current unevenness between the first and second positive electrode active materials, thereby ensuring a higher capacity retention rate in the early stages of the cycle.

[0141] FIG7 is a flow chart of a method for preparing a positive electrode sheet 231 provided in some embodiments of the present application. Referring to FIG7 , an embodiment of the present application provides a method for preparing a positive electrode sheet 231 , the method comprising:

[0142] S110, preparing a first positive electrode active slurry: dispersing a first positive electrode active material, a binder and a conductive agent in a solvent to form a first positive electrode active slurry. The first positive electrode active material can be the first positive electrode active material described above, for example: LiNi x Co y Mn z O2, (0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1) ternary system material, optionally a small amount of other positive electrode active materials can be added.

[0143] For the specific selection of the ternary system material, reference may be made to the selection of the ternary system material in the first positive electrode active material layer 2312 a in the aforementioned positive electrode sheet 231 , which will not be described in detail here.

[0144] The binder may be one or more of styrene-butadiene rubber, water-based acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polyvinyl butyral. The conductive agent may be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The solvent may be one or more of dimethyl glutarate and N-methylpyrrolidone. A leveling agent, dispersant, etc. may also be added to the first positive electrode active slurry.

[0145] S120, preparing a second positive electrode active slurry: dispersing a second positive electrode active material, a binder and a conductive agent in a solvent to form a second positive electrode active slurry. The second positive electrode active material can be the second positive electrode active material described above, for example: a material having a chemical formula of LiMn a Fe 1-a PO4, (0≤a≤1) polyanion positive electrode material, optionally a small amount of other positive electrode active materials can be added.

[0146] For the specific selection of the polyanion positive electrode material, reference may be made to the selection of the polyanion positive electrode material in the second positive electrode active material layer 2312 b in the aforementioned positive electrode sheet 231 , which will not be described in detail here.

[0147] The binder, conductive agent, and solvent may be the binder, conductive agent, and solvent in the first positive electrode active material slurry. The binder in the first positive electrode active material slurry may 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 material slurry may 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 material slurry may be the same as or different from the solvent in the second positive electrode active material. Furthermore, a leveling agent, dispersant, and the like may also be added to the second positive electrode active material slurry, but this application does not limit these.

[0148] S130, preparing the first positive electrode active material layer 2312a: coating the first positive electrode active slurry on the surface of the positive electrode current collector 2311, and then drying to form the first positive electrode active material layer 2312a. The coating can be applied to one or both surfaces of the positive electrode current collector 2311 as required.

[0149] The coating method may be: blade coating, roller coating, slit coating, etc., which is not limited in this application. It should be noted that step S120 and step S130 can be interchanged or performed simultaneously, which is not limited in this application.

[0150] S140, preparing the second positive electrode active material layer 2312b: The second positive electrode active material slurry is applied to the surface of the first positive electrode active material layer 2312a, and then dried to form the second positive electrode active material layer 2312b. The coating process can be based on the condition of the first positive electrode active material layer 2312a, so that the second positive electrode active material layer 2312b is formed on the surface of the first positive electrode active material layer 2312a.

[0151] S150 , rolling the second positive electrode active material layer 2312 b to obtain the positive electrode sheet 231 .

[0152] It should be noted that the above is only an example of sequentially arranging the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b on the positive electrode current collector 2311. In other embodiments, the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b can be swapped.

[0153] After the positive electrode sheet 231 is prepared, the first isolation film 233, the positive electrode sheet 231, the second isolation film 233 and the negative electrode sheet 232 are stacked in sequence, wound to form a wound flat structure, and then hot pressed to obtain a wound electrode assembly; or, after the positive electrode sheet 231 is prepared, the positive electrode sheet 231, the isolation film 233, the negative electrode sheet 232, the isolation film 233, and so on are stacked in sequence to form a laminated electrode assembly.

[0154] The electrode assembly 23 can be used to prepare a battery cell 20 , and the battery cell 20 can be used to prepare a secondary battery 100 and provide electrical energy to an electrical device.

[0155] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0156] Examples and Comparative Examples

[0157]

Preparation of positive electrode sheet

[0158] Preparation of the first positive electrode active material layer: the first positive electrode active material LiNi0.55 Co 0.12 Mn 0.33 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP), wherein the binder polyvinylidene fluoride (PVDF) accounts for 2.5% by mass, and stirred and mixed to obtain the first coating layer slurry; then the slurry is mixed at 90mg / 1540.25mm 2 The mass of the positive electrode active material is evenly coated on the positive electrode current collector and dried to obtain the first positive electrode active material layer.

[0159] 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) in a mass ratio of 96.5:1:2.5, and stirred to obtain a second coating slurry. The slurry was then added at a rate of 200 mg / 1540.25 mm 2 The mass of the positive electrode is evenly coated on the first positive electrode active material layer, and after drying, it is rolled and die-cut to obtain a lithium-ion battery positive electrode sheet.

[0160]

Preparation of negative electrode sheet

[0161] The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are dissolved in the solvent deionized water in a mass ratio of 90:5:3:2, and mixed evenly to prepare the negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0162] Preparation of electrolyte

[0163] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents ethylene carbonate (EC) / diethyl carbonate (DEC) / ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1 / 1 / 1, 1 mol / L LiPF6 lithium salt was added and dispersed evenly, and then 5% fluoroethylene carbonate was dissolved in the above organic solvents and stirred evenly to obtain an electrolyte.

[0164]

Isolation film

[0165] A polyethylene film was used as the separator, and its thickness was 7 μm.

[0166] Preparation of lithium-ion batteries

[0167] The prepared positive and negative electrodes and separator (polyethylene (PE) porous polymer film) are wound to form the corresponding battery cells. The battery cells are hot-pressed at 90°C and then ultrasonically welded to the positive and negative electrode tabs. The positive electrode uses aluminum tabs and the negative electrode uses copper tabs, and the positive and negative tabs are located on the same side of the battery cell. The battery cells with tab welding are placed in an aluminum shell of appropriate size for soft connection and top cover welding. The battery cells are vacuum-dried at 175°C for 24 hours, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes a series of processes such as static standing, formation, aging, exhaust, secondary sealing, and capacity testing to obtain a lithium-ion battery product.

[0168] The main parameters of each embodiment and comparative example are shown in the following table:

[0169] In the above table, the content test of Ni and Mn in NCM material can be as follows: take 0.4g of the electrode NCM material layer powder in a 25ml beaker, add 2ml~5ml nitric acid, leave it overnight, then place it on an electric hot plate, heat it at about 100℃ (use a voltage-regulating transformer to adjust the input voltage and temperature), add 0.5ml of perchloric acid after the powder is digested, and heat it at about 140℃ until the white smoke is gone. The residue should be white, otherwise nitric acid and perchloric acid should be added to repeat the digestion, and finally dissolved and extracted with 7% (volume % of acid, the same below) hydrochloric acid. After the volume is adjusted to an appropriate volume depending on the content of the element to be measured, the mass fraction of Ni, Co, Mn, and Li is tested on the ICP-OES test instrument. The mass of different elements can be calculated based on the mass of the powder and the mass fraction of different elements, and the Ni and Mn contents can be confirmed by different mass ratios.

[0170] Example 24

[0171] This embodiment is the same as Embodiment 2 except that the positions of the first positive electrode active material layer and the second positive electrode active material layer are swapped.

[0172] The performance test of the batteries provided in each embodiment and comparative example was performed, and the performance test specifically included:

[0173] The electrode compaction density test method is as follows: Based on the energy density design requirements, the electrode coating area density can be determined. After the electrode is dried and cold pressed, the total thickness of the electrode is measured using a micrometer. The coating thickness can be calculated by deducting the thickness of the current collector. Based on these two parameters, the electrode compaction density can be calculated.

[0174] The rate performance test method is as follows: in an environment of 25°C, charge and discharge are performed at a constant current of 0.33C (i.e., the current value that completely discharges the theoretical capacity within 3 hours) until the voltage reaches 2.5V. Then, constant current charge is performed at a charging current of 0.33C to a voltage of 4.4V, and constant voltage charge is continued to a current of 0.05C, at which point the battery is fully charged. After the fully charged cell is allowed to rest for 5 minutes, it is discharged at a constant current of 0.33C to 2.5V. The discharge capacity at this time is the actual capacity of the cell at 0.33C, recorded as C0. The cell is then charged at a constant current of 0.33C to 4.4V, then charged at a constant voltage to a current of 0.05C, allowed to rest for 5 minutes, and discharged at a constant current of 1C to 2.5V. The discharge capacity C1 is recorded as the 1C discharge capacity. 1C rate capacity retention rate = (1C discharge capacity / 0.33C discharge capacity) × 100%.

[0175] 25°C cycle test: The lithium-ion battery product prepared above was charged to 4.4V at 0.33C at 2.5-4.4V in a constant temperature environment of 25°C, then charged at a constant voltage at 4.4V to a current ≤ 0.05C, allowed to stand for 5 minutes, and then discharged to 2.5V at 0.33C. The capacity was recorded as Cn (n = 1, 2, 3...). The above operation was repeated for 500 cycles. The capacity retention rate was calculated according to the ratio of C500 / C3 as an examination indicator of the cycling ability.

[0176] 25℃ cyclic internal resistance growth test: ① Initial internal resistance test: The square shell battery prepared above was charged to 4.4V at 0.33C at 2.5~4.4V in a constant temperature environment of 25℃, and then charged at a constant voltage at 4.4V to a current ≤0.05C. After standing for 30min, the voltage U1 was recorded, and then discharged at 1C for 30s, and the voltage at 30s was recorded as U2. The internal resistance 1 = (U1-U2) / 1C; ② Internal resistance test after 500 cycles: After the battery with the initial internal resistance tested was tested for cycle performance according to the cycle test, the internal resistance 2 was tested again. The internal resistance growth rate = (internal resistance 2-internal resistance 1) / internal resistance 1.

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

[0178] It should be noted that the compaction density of Examples 1 to 7 and Comparative Examples 1 to 2 is the maximum compaction density that the electrode can achieve, while Examples 8 to 24 are compared and evaluated with Example 2, so their compaction density is a parameter that needs to be controlled, and is not the maximum compaction density of the electrode.

[0179] As can be seen from the above table, the positive electrode sheet provided by the present application has a high compaction density of up to 3g / cm 3Above, it has higher rate performance, which can reach more than 95%, higher capacity retention rate, which can reach more than 89% and lower cycle internal resistance growth rate, which does not exceed 80%.

[0180] By comparing Example 2, Examples 4 to 7 and Comparative Examples 1 to 2, it can be seen that as the mass proportion of single crystal particles w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 Satisfying relationship As the value of gradually increases, the compaction density, rate performance and capacity retention rate of the electrode all show a trend of first increasing and then decreasing, the cycle internal resistance growth rate of the electrode shows a trend of first decreasing and then increasing, and the mass proportion of single crystal particles w 单 , the particle size D of the single crystal particles 单 , the mass proportion of polycrystalline particles w 多 , the particle size D of polycrystalline particles 多 Satisfying relationship When the value is in the range of 0.02 to 0.45, the compaction density of the electrode can reach 3g / cm 3 The above results show that the rate performance can reach more than 98%, the capacity retention rate can reach more than 90%, and the cycle internal resistance growth rate does not exceed 60%. It can be seen that the relationship value of 0.02 to 0.45 is a better range. At the same time, when the relationship value is 0.15 to 0.3, the compaction density of the electrode can reach 3.1g / cm 3 The rate performance can reach about 99%, the capacity retention rate can reach about 94%, and the cycle internal resistance growth rate is about 40%. It can be seen that the relationship value of 0.15 to 0.3 is a better range.

[0181] By comparing Example 2 with Examples 8 to 11, it can be seen that as the thickness H1 of the first positive electrode active material layer gradually increases, the rate performance and capacity retention rate of the electrode sheet both show a trend of first increasing and then decreasing, and the cycle internal resistance growth rate of the electrode sheet shows a trend of first decreasing and then increasing. When the thickness H1 of the first positive electrode active material layer is in the range of 5 to 35 μm, the rate performance can reach more than 98.9%, the capacity retention rate can reach more than 93.2%, and the cycle internal resistance growth rate does not exceed 50%. It can be seen that the thickness H1 of the first positive electrode active material layer is in a better range of 5 to 35 μm.

[0182] By comparing Example 2 with Examples 12 to 15, it can be seen that as the thickness H2 of the second positive electrode active material layer gradually increases, the rate performance and capacity retention rate of the electrode sheet both show a trend of first increasing and then decreasing, and the cycle internal resistance growth rate of the electrode sheet shows a trend of first decreasing and then increasing. When the thickness H2 of the second positive electrode active material layer is in the range of 35 to 80 μm, the rate performance can reach more than 98.6%, the capacity retention rate can reach more than 92.9%, and the cycle internal resistance growth rate does not exceed 59%. It can be seen that the thickness H2 of the second positive electrode active material layer is in a better range of 35 to 80 μm.

[0183] By comparing Example 2 with Examples 16 to 19, it can be seen that the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is As the value of gradually increases, the rate performance and capacity retention rate of the electrode piece show a trend of first increasing and then decreasing, the cycle internal resistance growth rate of the electrode piece shows a trend of first decreasing and then increasing, and the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is When the value is in the range of 1 to 16, the rate performance can reach more than 98.2%, the capacity retention rate can reach more than 92.6%, and the cycle internal resistance growth rate does not exceed 59%. It can be seen that the relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer The value of is in the range of 1 to 16.

[0184] By comparing Example 2 with Examples 20 to 23, it can be seen that the relationship between the mass ratio of Ni wNi, the mass ratio of Mn wMn, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer is as follows: As the value of gradually increases, the rate performance and capacity retention rate of the electrode piece show a trend of first increasing and then decreasing, and the cycle internal resistance growth rate of the electrode piece shows a trend of first decreasing and then increasing, and the relationship between the mass proportion of Ni wNi, the mass proportion of Mn wMn, the thickness of the first positive electrode active material layer H1 and the thickness of the second positive electrode active material layer H2 When the value is in the range of 0.05 to 3.5, the rate performance can reach more than 98.1%, the capacity retention rate can reach more than 90.4%, and the cycle internal resistance growth rate does not exceed 53%. It can be seen that the relationship between the mass proportion of Ni wNi, the mass proportion of Mn wMn, the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer The value of is in the range of 0.05 to 3.5.

[0185] By comparing Example 2 and Example 24, it can be seen that when the ternary system material is arranged in the inner layer, it is more beneficial to the battery's rate performance, capacity retention rate and cycle internal resistance growth rate.

[0186] The above are merely specific embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes a ternary system material, the ternary system material includes single crystal particles and polycrystalline particles, the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes a polyanion positive electrode material, and the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

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

3. The positive electrode sheet according to any one of claims 1 to 2, characterized in that: The positive electrode sheet further includes a current collector. The first positive electrode active material layer is disposed on at least one surface of the current collector. The second positive electrode active material layer is disposed on a surface of the first positive electrode active material layer away from the current collector.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The relationship between the thickness H1 of the first positive electrode active material layer and the thickness H2 of the second positive electrode active material layer satisfies: and / or The thickness H1 of the first positive electrode active material layer is 5 to 35 μm; and / or The thickness H2 of the second positive electrode active material layer is 35 to 80 μm.

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

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

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

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The mass proportion of the single crystal particles in the ternary system material is 10% to 40%, and the mass proportion of the polycrystalline particles in the ternary system material is 60% to 90%; and / or The volume median particle size of the single crystal particles is 2.5 to 4.5 μm; and / or The volume median particle size of the polycrystalline particles is 8 to 10 μm.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The ternary system materials include nickel-cobalt-manganese ternary materials and modified materials thereof and nickel-cobalt-aluminum ternary materials and modified materials thereof; and / or The polyanion positive electrode material includes LiMPO4, 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 doping, and the second doping element is phosphorus doping.

10. The positive electrode sheet according to claim 9, characterized in that: The first doping element includes one or more elements selected from the group consisting of 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 the group consisting of B, S, Si and N.

11. The positive electrode sheet according to claim 9, characterized in that: The polyanion positive electrode material includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein 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 the group consisting of 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 the group consisting of B, S, Si and N.

12. The positive electrode sheet according to claim 9, characterized in that: The polyanion positive electrode 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 the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C includes one or more elements selected from the group consisting of B, S, Si and N; D includes one or more elements selected from the group consisting of 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 polyanion positive electrode material is electrically neutral.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The polyanion positive electrode material also has a coating layer containing carbon.

14. The positive electrode sheet according to any one of claims 1 to 13, characterized in that: The ternary system material includes Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0.3 < b < 1.0, 0 < c < 0.4, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is selected from one or two elements of Mn or Al, M2 is selected from one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from one or more elements of N, F, S, Cl.

15. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a positive electrode active material layer and a current collector, the positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer is arranged on at least one surface of the current collector, and the second positive electrode active material layer is arranged on a surface of the first positive electrode active material layer away from the current collector; the first positive electrode active material layer comprises a first positive electrode active material, the first positive electrode active material comprises a ternary system material, the ternary system material comprises single crystal particles and polycrystalline particles, the second positive electrode active material layer comprises a second positive electrode active material, the second positive electrode active material comprises a polyanion positive electrode material, and the mass proportion of the single crystal particles in the ternary system material is w 单 , the volume median particle size D of the single crystal particles in μm 单 , the mass proportion of the polycrystalline particles in the ternary system material w 多 and the volume median particle size D of the polycrystalline particles in μm 多 Satisfies the following relationship:

16. A battery cell, characterized in that: The battery cell comprises the positive electrode sheet according to any one of claims 1 to 15.

17. A battery, characterized in that: The battery comprises the battery cell according to claim 16.

18. An electrical device, characterized in that: The electrical device comprises the battery cell according to claim 16 or the battery according to claim 17.

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