Positive pole piece and preparation method thereof, battery monomer, battery and power utilization device

Abstract

The invention provides a positive pole piece and a preparation method thereof, a battery monomer, a battery and a power utilization device, and belongs to the technical field of batteries. The positive electrode plate 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 the surface of at least one side of the positive electrode current collector, the second positive electrode active material layer coats the first positive electrode active material layer, and the volume expansion rate of the first positive electrode active material is greater than that of the second positive electrode active material. According to the positive electrode plate, the second positive electrode active material layer formed by the second positive electrode active material with a lower volume expansion rate is adopted, the first positive electrode active material layer formed by the first positive electrode active material with a higher volume expansion rate is coated, and the second positive electrode active material layer can be in contact with the positive electrode current collector and the first positive electrode active material layer; and the protective layer is formed, so that the overall rebound rate of the positive pole piece is reduced, the expansibility of the prepared battery monomer or battery is further reduced, and the cycle performance of the prepared battery monomer or battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode plate and a preparation method thereof, a battery cell, a battery and an electrical device. Background Art

[0002] Olivine structure positive electrode materials (including lithium iron phosphate, lithium manganese phosphate, etc.) have high structural stability, long material life, and excellent safety performance, but their gram capacity is low and the voltage platform is low. When used in power batteries, the battery energy density is low. Layered structure positive electrode materials (including lithium cobalt oxide, ternary materials, lithium-rich manganese-based materials, etc.) have poor structural stability, but their gram capacity is high and the voltage platform is high. When used in power batteries, the battery safety is poor. The positive electrode active material layer of the lithium-ion battery uses a combination of highly safe olivine structure positive electrode materials and high energy density layered structure positive electrode materials, so that the lithium-ion battery can have both high safety and high energy density.

[0003] The volume of layered positive electrode materials expands significantly before and after lithium is released. Excessive expansion force of battery cells or batteries will make it difficult for electrolyte to infiltrate. Lack of sufficient electrolyte infiltration during battery charging will lead to excessive polarization and serious lithium deposition on the negative electrode, affecting the battery's cycle performance. Summary of the invention

[0004] In view of the above problems, the present application provides a positive electrode plate and a preparation method thereof, a battery cell, a battery and an electrical device, which can improve the cycle performance of the battery cell or the battery.

[0005] In a first aspect, the present application provides a positive electrode sheet, which includes: a positive electrode current collector, a first positive electrode active material layer and a second positive electrode active material layer, wherein the first positive electrode active material layer is disposed on a surface of at least one side of the positive electrode current collector, and the second positive electrode active material layer covers the first positive electrode active material layer. The first positive electrode active material layer includes a first positive electrode active material, the second positive electrode active material layer includes a second positive electrode active material, and the volume expansion rate of the first positive electrode active material is greater than the volume expansion rate of the second positive electrode active material.

[0006] In the technical solution of the embodiment of the present application, the positive electrode plate of the present application adopts a second positive electrode active material layer formed by a second positive electrode active material with a lower volume expansion rate, which covers a first positive electrode active material layer formed by a first positive electrode active material with a higher volume expansion rate. The second positive electrode active material layer can contact the positive electrode collector and the first positive electrode active material layer to form a protective layer, thereby reducing the overall rebound rate of the positive electrode plate, thereby reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0007] In some embodiments, the positive electrode sheet includes a plurality of first positive electrode active material layers, and the plurality of first positive electrode active material layers are all disposed on the surface of at least one side of the positive electrode current collector. The first positive electrode active material layer is divided into a plurality of layers, and each first positive electrode active material layer is individually coated with a second positive electrode active material layer, which can further reduce the overall rebound rate of the positive electrode sheet, reduce the expansion force of the manufactured battery cell or battery, and improve the cycle performance of the manufactured battery cell or battery.

[0008] In some embodiments, multiple first positive electrode active material layers are spaced apart, the width of the gap between two adjacent first positive electrode active material layers is 5 μm to 15 μm, and the gap between two adjacent first positive electrode active material layers is filled with a second positive electrode active material layer. The two adjacent first positive electrode active material layers can be squeezed by the second positive electrode active material layer between them, thereby inhibiting their volume expansion, reducing the overall rebound rate of the positive electrode sheet, reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0009] In some embodiments, the volume expansion rate of the first positive electrode active material is 3% to 10%, and the volume expansion rate of the second positive electrode active material is 0.1 to 3%. Optionally, the volume expansion rate of the first positive electrode active material is 3% to 5%, and the volume expansion rate of the second positive electrode active material is 1 to 3%. The second positive electrode active material layer formed by the second positive electrode active material having a volume expansion rate of 0.1 to 3% is coated with the first positive electrode active material layer formed by the first positive electrode active material having a volume expansion rate of 3% to 10%. The second positive electrode active material layer can contact the positive electrode current collector and the first positive electrode active material layer to form a protective layer, reduce the overall rebound rate of the positive electrode sheet, and thereby reduce the expansion force of the manufactured battery cell or battery, and improve the cycle performance of the manufactured battery cell or battery.

[0010] In some embodiments, the first positive electrode active material includes a layered transition metal oxide and / or a spinel material. Optionally, the layered transition metal oxide includes LiCoO2, LiMnO2, LiNiO2, Li a’ Ni x Co y M 1 1-x-y O 2+d 、zLi2MnO3·(1-z)LiM 2 O2 at least one, wherein M 1 Including at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, La, M 2The layered transition metal oxide comprises at least one of Co, Ni and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a'<1.2, -0.02≤d<0.02, 0<z<1. Optionally, the layered transition metal oxide comprises Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1.15 O2、Li(Ni 0.5 Co 0.2 Mn 0.3 ) 1.07 At least one of O2. Optionally, the spinel material includes LiNi c Mn 2-c O4, wherein 0≤c<2. Optionally, the spinel material includes lithium manganate. A layered transition metal oxide and / or a spinel material is used as the first positive electrode active material, and the first positive electrode active material has the characteristics of high gram capacity and high voltage platform, which can improve the energy density of the prepared battery cell or battery. At the same time, the first positive electrode active material layer is made of a layered transition metal oxide, and the first positive electrode active material layer is placed close to the positive electrode current collector, which can effectively reduce the transmission path of lithium ions and give full play to the performance of the first positive electrode active material layer.

[0011] In some embodiments, the second positive electrode active material includes an olivine structure phosphate material. Optionally, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of the other metal elements except Fe, wherein 0≤a≤1.1, 0.3≤b≤1, 0≤m≤0.1, and 0≤n≤0.1. Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge. Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate. The olivine structure phosphate material is used as the second positive electrode active material, and the second positive electrode active material has the characteristics of long life and high safety, which can improve the safety of the prepared battery cell or battery.

[0012] In some embodiments, the first positive electrode active material layer has a thickness of 40 μm to 160 μm, and the second positive electrode active material layer coated on the surface of the first positive electrode active material layer has a thickness of 40 μm to 160 μm.

[0013] In a second aspect, the present application provides a method for preparing the positive electrode sheet in the above-mentioned embodiment, which comprises: coating a first positive electrode active material slurry on the surface of a positive electrode current collector, coating a second positive electrode active material slurry on the surface of the positive electrode current collector and the first positive electrode active material slurry, and drying and cold pressing to obtain a positive electrode sheet. The first positive electrode active material slurry comprises a first positive electrode active material, and the second positive electrode active material slurry comprises a second positive electrode active material.

[0014] In the technical solution of the embodiment of the present application, the preparation method of the positive electrode plate of the present application is simple, and the prepared positive electrode plate adopts a second positive electrode active material layer formed by a second positive electrode active material with a lower volume expansion rate, which covers a first positive electrode active material layer formed by a first positive electrode active material with a higher volume expansion rate. The second positive electrode active material layer can contact the positive electrode collector and the first positive electrode active material layer to form a protective layer, thereby reducing the overall rebound rate of the positive electrode plate, thereby reducing the expansion force of the prepared battery cell or battery, and improving the cycle performance of the prepared battery cell or battery.

[0015] In a third aspect, the present application provides a battery cell comprising the positive electrode plate in the above embodiment.

[0016] In a fourth aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

[0017] In a fifth aspect, the present application provides an electrical device, which includes the battery cell or battery in the above embodiment, and the battery cell or battery is used to provide electrical energy.

[0018] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0020] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0021] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0022] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0023] Figure 4 A perspective view of a first positive electrode sheet according to some embodiments of the present application;

[0024] Figure 5 A cross-sectional view of a first positive electrode sheet according to some embodiments of the present application;

[0025] Figure 6 A perspective view of a second positive electrode sheet according to some embodiments of the present application;

[0026] Figure 7 A cross-sectional view of a second positive electrode sheet according to some embodiments of the present application;

[0027] Figure 8 A cross-sectional view of the positive electrode sheet of Comparative Example 1 of the present application;

[0028] Fig. 9 This is a cross-sectional view of the positive electrode plate of comparative example 2 of the present application.

[0029] The reference numerals in the specific implementation manner are as follows:

[0030] 1000-Vehicle; 100-Battery; 200-Controller; 300-Motor;

[0031] 10-box; 11-first part; 12-second part;

[0032] 20 - battery cell; 21 - end cap; 22 - housing; 23 - electrode assembly;

[0033] 30 - positive electrode sheet; 31 - positive electrode current collector; 32 - first positive electrode active material layer; 321 - first side; 322 - second side; 323 - side surface; 33 - second positive electrode active material layer; 34 - positive electrode active material layer. DETAILED DESCRIPTION

[0034] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field 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" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0036] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0037] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0039] 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).

[0040] 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. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0041] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0042] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0043] Olivine structure positive electrode materials (including lithium iron phosphate, lithium manganese phosphate, etc.) have high structural stability, long material life, and excellent safety performance, but their gram capacity is low and the voltage platform is low. When used in power batteries, the battery energy density is low. Layered structure positive electrode materials (including lithium cobalt oxide, ternary materials, lithium-rich manganese-based materials, etc.) have poor structural stability, but their gram capacity is high and the voltage platform is high. When used in power batteries, the battery safety is poor. The positive electrode active material layer of the lithium-ion battery uses a combination of highly safe olivine structure positive electrode materials and high energy density layered structure positive electrode materials, so that the lithium-ion battery can have both high safety and high energy density.

[0044] However, due to the difference in electrochemical properties of the two positive electrode active materials, if the two positive electrode active materials are directly physically mixed to prepare the positive electrode active material layer, it will cause the battery cell or battery to decay rapidly in the early stage of the cycle.

[0045] If the two positive electrode active materials are coated separately to form two independent positive electrode active material layers, the mixing amount of the two positive electrode active materials can be reduced, thereby improving the problem of rapid attenuation of battery cells or batteries in the early stage of cycling.

[0046] However, the volume of the layered positive electrode material expands significantly before and after lithium is extracted and deintercalated, and its volume expansion rate is about 3% to 8%. At the same time, since the voltage range of the layered positive electrode material is 2.5V to 4.4V, the side reaction between the layered positive electrode material and the electrolyte is aggravated. When the battery cell or battery is cycled to the end of its life cycle, the volume expansion rate caused by the accumulation of reaction products is about 5% to 10%. Excessive expansion force of the battery cell or battery will make it difficult for the electrolyte to infiltrate. When the battery is charged without sufficient electrolyte infiltration, it will cause excessive polarization and serious lithium precipitation of the negative electrode, affecting the battery's cycle performance.

[0047] The volume change of the olivine structure positive electrode material before and after lithium deintercalation is not obvious, and its volume expansion rate before and after lithium deintercalation is about 0-0.5%. When the battery cell or battery is cycled to the end of its life cycle, the reaction products produced by the side reaction of the olivine structure positive electrode material with the electrolyte accumulate, resulting in a volume expansion rate of about 0.1-3%.

[0048] Based on the above considerations, in order to improve the cycle performance of the battery cell or battery, a second positive electrode active material layer formed by a second positive electrode active material with a lower volume expansion rate is used to cover the first positive electrode active material layer formed by a first positive electrode active material with a higher volume expansion rate. The second positive electrode active material layer can contact the positive electrode collector and the first positive electrode active material layer to form a protective layer, thereby reducing the overall rebound rate of the positive electrode sheet, thereby reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0049] The battery mentioned in the embodiments of the present application refers to a single physical module including multiple battery cells to provide higher voltage and capacity. The battery generally includes a battery box for packaging multiple battery cells, and the battery box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

[0050] Each battery cell is a secondary battery; it can be a lithium-ion battery or a lithium-sulfur battery, but is not limited thereto. The battery cell can be cylindrical, flat, rectangular or in other shapes. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells.

[0051] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The battery cell mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode collector. The positive electrode collector not coated with the positive electrode active material layer protrudes from the positive electrode collector coated with the positive electrode active material layer. The positive electrode collector not coated with the positive electrode active material layer serves as the positive electrode tab. Taking lithium-ion batteries as an example, the material of the positive electrode collector can be aluminum, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide. The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode collector. The negative electrode collector not coated with the negative electrode active material layer protrudes from the negative electrode collector coated with the negative electrode active material layer. The negative electrode collector not coated with the negative electrode active material layer serves as the negative electrode tab. The material of the negative electrode collector can be copper. In order to ensure that a large current does not melt, 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 film can be polypropylene (PP) or polyethylene (PE). In addition, the electrode assembly can be a winding structure or a laminated structure, and the embodiments of the present application are not limited thereto.

[0052] The battery cell also includes a current collecting component, which is used to electrically connect the tabs and electrode terminals of the battery cell to transmit electrical energy from the electrode assembly to the electrode terminals and then to the outside of the battery cell through the electrode terminals; multiple battery cells are electrically connected through a current collecting component to achieve series, parallel or mixed connection of multiple battery cells.

[0053] The battery also includes a sampling terminal and a battery management system. The sampling terminal is connected to the busbar to collect information about the battery cells, such as voltage or temperature, etc. The sampling terminal transmits the collected information about the battery cells to the battery management system. When the battery management system detects that the information about the battery cells exceeds the normal range, it will limit the output power of the battery to achieve safety protection.

[0054] It can be understood that the electrical devices used by the batteries described in the embodiments of the present application can be in various forms, for example, mobile phones, portable devices, laptops, battery vehicles, electric cars, ships, spacecraft, electric toys and electric tools, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers.

[0055] The battery cells and batteries described in the embodiments of the present application are not limited to the electrical devices described above, but can also be applied to all electrical devices using battery cells and batteries. However, for the sake of simplicity, the following embodiments are described using electric vehicles as examples.

[0056] See also Figure 1 , Figure 1 A schematic diagram of the structure of a vehicle provided for some embodiments of the present application. Vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000, for example, the battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0057] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve 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.

[0058] Please refer to Figure 2 , Figure 2 An exploded diagram of a battery provided for some embodiments of the present application. The battery 100 includes a housing 10 and a battery cell 20, and the battery cell 20 is contained in the housing 10. Among them, the housing 10 is used to provide a storage space for the battery cell 20, and the housing 10 can adopt a variety of structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, and the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the housing 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0059] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures, for example, the battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0060] Each battery cell 20 is a secondary battery, which may be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular or in other shapes.

[0061] Please refer to Figure 3 , Figure 3 The first battery cell 20 is a schematic diagram of the decomposed structure of some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23 and other functional components.

[0062] The end cap 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 22 to match the shell 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals can be provided on the end cap 21. The electrode terminal can be used to electrically connect to the electrode assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 21, and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0063] The shell 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, the electrolyte and other components. The shell 22 and the end cap 21 can be independent components, and an opening can be set on the shell 22, and the internal environment of the battery cell 20 is formed by covering the opening with the end cap 21 at the opening. Without limitation, the end cap 21 and the shell 22 can also be integrated. Specifically, the end cap 21 and the shell 22 can form a common connection surface before other components are put into the shell, and when the interior of the shell 22 needs to be encapsulated, the end cap 21 covers the shell 22. The shell 22 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0064] The electrode assembly 23 is a component in the battery cell 20 where electrochemical reactions occur. One or more electrode assemblies 23 may be contained in the housing 22. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The parts of the positive and negative electrode sheets with active materials constitute the main body of the electrode assembly, and the parts of the positive and negative electrode sheets without active materials each constitute a tab. The positive tab and the negative tab may be located together at one end of the main body or respectively at both ends of the main body. During the charge and discharge process of the battery, the positive active material and the negative active material react with the electrolyte, and the tabs connect the electrode terminals to form a current loop.

[0065] According to some embodiments of the present application, please refer to Figures 4-5 , Figure 4 This is a perspective view of a first positive electrode plate 30 of some embodiments of the present application. Figure 5 This is a cross-sectional view of a first positive electrode plate 30 according to some embodiments of the present application.

[0066] The present application provides a positive electrode sheet 30, which includes: a positive electrode current collector 31, a first positive electrode active material layer 32 and a second positive electrode active material layer 33, wherein the first positive electrode active material layer 32 is disposed on at least one side of the positive electrode current collector 31, and the second positive electrode active material layer 33 covers the first positive electrode active material layer 32. The first positive electrode active material layer 32 includes a first positive electrode active material, the second positive electrode active material layer 33 includes a second positive electrode active material, and the volume expansion rate of the first positive electrode active material is greater than the volume expansion rate of the second positive electrode active material.

[0067] The second positive electrode active material layer 33 coating the first positive electrode active material layer 32 means that the second positive electrode active material layer 33 coats at least a portion of the surface of the first positive electrode active material layer 32, so that after the first positive electrode active material layer 32 significantly expands in volume before and after lithium insertion and deintercalation, it can be subjected to the reaction force of the second positive electrode active material layer 33, thereby suppressing the volume expansion.

[0068] It should be noted that when the second positive electrode active material layer 33 covers at least part of the surface of the first positive electrode active material layer 32 , the second positive electrode active material layer 33 needs to be able to provide a reaction force to the first positive electrode active material layer 32 to suppress the volume expansion of the first positive electrode active material layer 32 .

[0069] For example, when the first positive electrode active material layer 32 is a layered structure, the first positive electrode active material layer 32 has a side surface 323 and a first surface 321 and a second surface 322 opposite to each other. The first positive electrode active material layer 32 is arranged on the surface of at least one side of the positive electrode current collector 31 with the first surface 321. The second positive electrode active material layer 33 cannot only cover the second surface 322 of the first positive electrode active material. In this way, the second positive electrode active material layer 33 needs to be able to provide a reaction force to the first positive electrode active material layer 32 to suppress the volume expansion of the first positive electrode active material layer 32, that is, the second positive electrode active material layer 33 can cover the second surface 322 and part of the side surface 323 of the first positive electrode active material.

[0070] Optionally, the second positive electrode active material layer 33 and the positive electrode current collector 31 together cover all surfaces of the first positive electrode active material layer 32 .

[0071] The volume expansion rate of the first positive electrode active material refers to the ratio of the difference between the volume of the first positive electrode active material after charge expansion and the uncharged volume to the uncharged volume.

[0072] The volume expansion rate of the first positive electrode active material is P1, the volume of the first positive electrode active material before charging is V1, and the volume of the first positive electrode active material after charging and expansion is V2.

[0073] P1 = (V2 - V1) / V1.

[0074] The volume expansion rate of the second positive electrode active material refers to the ratio of the difference between the volume of the second positive electrode active material after charge expansion and the uncharged volume to the uncharged volume.

[0075] The volume expansion rate of the second positive electrode active material is P2, the volume of the second positive electrode active material before charging is V3, and the volume of the second positive electrode active material after charging and expansion is V4.

[0076] P2 = (V4 - V3) / V3.

[0077] The positive electrode plate 30 of the present application adopts a second positive electrode active material layer 33 formed by a second positive electrode active material with a lower volume expansion rate, which covers a first positive electrode active material layer 32 formed by a first positive electrode active material with a higher volume expansion rate. The second positive electrode active material layer 33 can contact the positive electrode collector 31 and the first positive electrode active material layer 32 to form a protective layer, thereby reducing the overall rebound rate of the positive electrode plate 30, thereby reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0078] Alternatively, the first positive active material layer 32 includes 90 wt % to 99 wt % of the first positive active material, 0.1 wt % to 1 wt % of the first conductive agent, and 1 wt % to 2 wt % of the binder.

[0079] Wherein, the first conductive agent may be conductive carbon black.

[0080] Alternatively, the first positive active material layer 32 includes 96 wt % of the first positive active material, 2 wt % of the first conductive agent, and 2 wt % of the binder.

[0081] Alternatively, the second positive active material layer 33 includes 90 wt % to 99 wt % of the second positive active material, 0.2 wt % to 2 wt % of the second conductive agent, and 1 wt % to 2 wt % of the binder.

[0082] The second conductive agent may be conductive carbon black or carbon nanotubes.

[0083] Alternatively, the second positive active material layer 33 includes 96 wt % of the second positive active material, 2 wt % of the second conductive agent, and 2 wt % of the binder.

[0084] In such Figures 4-5 In the illustrated embodiment, the positive electrode plate 30 includes a first positive electrode active material layer 32 and a second positive electrode active material layer 33, the first positive electrode active material layer 32 having a side surface 323 and a first surface 321 and a second surface 322 opposite to each other, the first positive electrode active material layer 32 is bonded to the middle of the positive electrode collector 31 with the first surface 321, and the second positive electrode active material layer 33 is bonded to all side surfaces 323 and the second surface 322 of the first positive electrode active material layer 32, and the positive electrode collector 31, thereby cooperating with the positive electrode collector 31 to cover the entire first positive electrode active material layer 32.

[0085] According to some embodiments of the present application, optionally, refer to Figures 6-7 , Figure 6 This is a perspective view of a second positive electrode sheet 30 of some embodiments of the present application. Figure 7 It is a cross-sectional view of a second positive electrode sheet 30 according to some embodiments of the present application. The positive electrode sheet 30 includes a plurality of first positive electrode active material layers 32 , and the plurality of first positive electrode active material layers 32 are all combined with a positive electrode current collector 31 .

[0086] The plurality of first positive electrode active material layers 32 may be regularly or irregularly arranged on the surface of the positive electrode current collector 31 , and gaps are formed between the plurality of first positive electrode active material layers 32 , and the gaps can accommodate the second positive electrode active material layer 33 .

[0087] The first positive electrode active material layer 32 is divided into multiple layers, each of which is individually coated with the second positive electrode active material layer 33, which can further reduce the overall rebound rate of the positive electrode plate 30, reduce the expansion force of the manufactured battery cell or battery, and improve the cycle performance of the manufactured battery cell or battery.

[0088] It should be noted that the embodiment of the present application does not limit the number of the first positive electrode active material layers 32, which can be 2, 3, 4, 5 or more. The shapes of the multiple first positive electrode active material layers 32 can be the same or different, and the sizes of the multiple first positive electrode active material layers 32 can also be the same or different.

[0089] In such Figures 6-7 In the illustrated embodiment, the positive electrode plate 30 includes two first positive electrode active material layers 32 and one second positive electrode active material layer 33. The two first positive electrode active material layers 32 are combined side by side in the middle of the positive electrode current collector 31, and a gap is formed between the two first positive electrode active material layers 32. The second positive electrode active material layer 33 covers the two first positive electrode active material layers 32 and fills the gap. The two first positive electrode active material layers 32 have the same shape and size.

[0090] According to some embodiments of the present application, optionally, please continue to refer to Figures 4 to 7 , multiple first positive electrode active material layers 32 are distributed at intervals, the width (g) of the gap between two adjacent first positive electrode active material layers 32 is 5μm to 15μm, and the gap between two adjacent first positive electrode active material layers 32 is filled with the second positive electrode active material layer 33.

[0091] As an example, the width of the gap between two adjacent first positive electrode active material layers 32 may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm.

[0092] Two adjacent first positive electrode active material layers 32 can be squeezed by the second positive electrode active material layer 33 therebetween, thereby inhibiting their volume expansion, reducing the overall rebound rate of the positive electrode plate 30, reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0093] Optionally, the plurality of first positive electrode active material layers 32 are parallel to each other.

[0094] According to some embodiments of the present application, optionally, the volume expansion rate of the first positive electrode active material is 3% to 10%, and the volume expansion rate of the second positive electrode active material is 0.1 to 3%.

[0095] The volume expansion rate of the first positive electrode active material may be the volume expansion rate of the first positive electrode active material after lithium is deintercalated, or the volume expansion rate of the first positive electrode active material when the battery cell or battery is cycled to the end of its life cycle.

[0096] The volume expansion rate of the second positive electrode active material may be the volume expansion rate of the second positive electrode active material after lithium is deintercalated, or the volume expansion rate of the second positive electrode active material when the battery cell or battery is cycled to the end of its life cycle.

[0097] Optionally, the volume expansion rate of the first positive electrode active material is 3% to 5%, and the volume expansion rate of the second positive electrode active material is 1 to 3%.

[0098] The second positive electrode active material layer 33 formed by the second positive electrode active material with a volume expansion rate of 0.1-3% covers the first positive electrode active material layer 32 formed by the first positive electrode active material with a volume expansion rate of 3%-10%. The second positive electrode active material layer 33 can contact the positive electrode collector 31 and the first positive electrode active material layer 32 to form a protective layer, thereby reducing the overall rebound rate of the positive electrode plate 30, thereby reducing the expansion force of the manufactured battery cell or battery, and improving the cycle performance of the manufactured battery cell or battery.

[0099] According to some embodiments of the present application, optionally, the first positive electrode active material includes a layered transition metal oxide and / or a spinel material.

[0100] Optionally, the layered transition metal oxide includes LiCoO2, LiMnO2, LiNiO2, Li a’ Ni x Co y M 1 1-x-y O 2+d 、zLi2MnO3·(1-z)LiM 2 O2, wherein M 1 Including at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, La, M 2 The invention comprises at least one of Co, Ni and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a'<1.2, -0.02≤d<0.02, 0<z<1.

[0101] Optionally, the layered transition metal oxide comprises Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1.15 O2、Li(Ni 0.5 Co 0.2 Mn 0.3 ) 1.07 At least one of O2.

[0102] Optionally, the spinel material includes LiNi c Mn 2-c O4, where 0≤c<2.

[0103] Optionally, the spinel material comprises lithium manganate.

[0104] As an example, the first positive electrode active material may be lithium cobalt oxide, a ternary material, or a lithium-rich manganese-based material.

[0105] The layered transition metal oxide and / or spinel material is used as the first positive electrode active material. The first positive electrode active material has the characteristics of high specific capacity and high voltage platform, which can improve the energy density of the prepared battery cell or battery. At the same time, the first positive electrode active material layer 32 is made of layered transition metal oxide, and the first positive electrode active material layer 32 is close to the positive electrode current collector 31, which can effectively reduce the transmission path of lithium ions and give full play to the performance of the first positive electrode active material layer 32.

[0106] According to some embodiments of the present application, optionally, the second positive electrode active material includes an olivine structure phosphate material.

[0107] Optionally, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of other metal elements except Fe, wherein 0≤a≤1.1, 0.3≤b≤1, 0≤m≤0.1, and 0≤n≤0.1.

[0108] Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0109] Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0110] The olivine structure phosphate material is used as the second positive electrode active material. The second positive electrode active material has the characteristics of long life and high safety, and can improve the safety of the manufactured battery cell or battery.

[0111] According to some embodiments of the present application, optionally, please continue to refer to Figure 5 and 7 The thickness (t1) of the first positive electrode active material layer 32 is 40 μm to 160 μm, and the thickness (t2) of the second positive electrode active material layer 33 coated on the surface of the first positive electrode active material layer 32 is 40 μm to 160 μm.

[0112] As an example, the thickness of the first positive active material layer 32 may be 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, or 160 μm.

[0113] The thickness of the second positive electrode active material layer 33 coated on the surface of the first positive electrode active material layer 32 may be 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm or 160 μm.

[0114] According to some embodiments of the present application, optionally, the present application further provides a method for preparing the positive electrode sheet 30 in the above embodiment, which comprises: coating a first positive electrode active material slurry on the surface of the positive electrode collector 31, coating a second positive electrode active material slurry on the surface of the positive electrode collector 31 and the first positive electrode active material slurry, and drying and cold pressing to obtain the positive electrode sheet 30. The first positive electrode active material slurry comprises a first positive electrode active material, and the second positive electrode active material slurry comprises a second positive electrode active material.

[0115] The first positive electrode active material slurry is prepared by the following method:

[0116] The first positive electrode active material, the first conductive agent, the binder and the solvent are mixed according to a proportion and stirred to obtain a first positive electrode active material slurry.

[0117] The second positive electrode active material slurry is prepared by the following method:

[0118] The second positive electrode active material, the second conductive agent, the binder and the solvent are mixed according to a proportion and stirred to obtain a second positive electrode active material slurry.

[0119] Optionally, the coating width of the first positive electrode active material slurry is 10 μm to 80 μm.

[0120] As an example, the coating width of the first positive active material slurry may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm.

[0121] Optionally, the coating width of the second positive electrode active material slurry is 70 μm to 120 μm.

[0122] As an example, the coating width of the second positive active material slurry may be 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, or 120 μm.

[0123] The preparation method of the positive electrode plate 30 of the present application is simple. The prepared positive electrode plate 30 adopts a second positive electrode active material layer 33 formed by a second positive electrode active material with a lower volume expansion rate, which covers a first positive electrode active material layer 32 formed by a first positive electrode active material with a higher volume expansion rate. The second positive electrode active material layer 33 can contact the positive electrode collector 31 and the first positive electrode active material layer 32 to form a protective layer, thereby reducing the overall rebound rate of the positive electrode plate 30, thereby reducing the expansion force of the prepared battery cell or battery, and improving the cycle performance of the prepared battery cell or battery.

[0124] The following is a further detailed description of a positive electrode plate 30 and a preparation method thereof of the present application in conjunction with embodiments.

[0125] The parameters of the positive electrode sheets 30 of Examples 1 to 8 of the present application and Comparative Examples 1 to 2 are shown in Table 1.

[0126] Table 1 Parameters of the positive electrode sheet 30 of Examples 1 to 8 and Comparative Examples 1 to 2

[0127]

[0128]

[0129] The structure of the positive electrode sheet 30 of Examples 1 to 2 and 5 to 8 is as follows: Figures 4-5 As shown, the positive electrode sheet 30 includes a first positive active material layer 32 and a second positive active material layer 33, the first positive active material layer 32 has a side surface 323 and a first surface 321 and a second surface 322 opposite to each other, the first positive active material layer 32 is bonded to the middle of the positive current collector 31 with the first surface 321, and the second positive active material layer 33 is bonded to all the side surfaces 323 and the second surface 322 of the first positive active material layer 32, and the positive current collector 31, so as to cooperate with the positive current collector 31 to cover the entire first positive active material layer 32. The thickness of the positive current collector 31 is 13 μm, the coating width of the first positive active material layer 32 is 80 μm, and the coating width of the second positive active material slurry is 120 μm.

[0130] The structure of the positive electrode sheet 30 of Examples 4 to 5 is as follows: Figures 6-7As shown, the positive electrode sheet 30 includes two first positive active material layers 32 and one second positive active material layer 33. The two first positive active material layers 32 are combined side by side in the middle of the positive current collector 31, and a gap is formed between the two first positive active material layers 32. The second positive active material layer 33 covers the two first positive active material layers 32 and fills the gap. The two first positive active material layers 32 have the same shape and size. The thickness of the positive current collector 31 is 13 μm, the coating width of the first positive active material layer 32 is 40 μm, and the coating width of the second positive active material slurry is 120 μm.

[0131] The positive electrode sheets 30 of Examples 1 to 8 are prepared by the following method:

[0132] S1. Preparing the first positive electrode active material slurry

[0133] 96 wt % of a first positive electrode active material, 2 wt % of conductive carbon black and 2 wt % of polyvinylidene fluoride were mixed to prepare a first mixture, and N-methylpyrrolidone was added to the first mixture and stirred to prepare a first positive electrode active material slurry.

[0134] S2. Preparing the second positive electrode active material slurry

[0135] 96 wt % of the second positive electrode active material, 1 wt % of conductive carbon black, 1 wt % of carbon nanotubes and 2 wt % of polyvinylidene fluoride were mixed to prepare a second mixture, and N-methylpyrrolidone was added to the second mixture and stirred to prepare a second positive electrode active material slurry.

[0136] S3, prepare positive electrode sheet 30

[0137] The first positive electrode active material slurry is coated on the surface of the positive electrode collector 31 , and the second positive electrode active material slurry is coated on the surface of the positive electrode collector 31 and the first positive electrode active material slurry, and then dried and cold pressed to obtain the positive electrode sheet 30 .

[0138] The structure of the positive electrode plate 30 of Comparative Example 1 is as follows Figure 8 As shown, the positive electrode plate 30 includes only one positive electrode active material layer 34, which is bonded to the positive electrode current collector 31, and the positive electrode active material layer 34 includes 48 wt% of a first positive electrode active material, 48 wt% of a second positive electrode active material, 2 wt% of conductive carbon black and 2 wt% of polyvinylidene fluoride.

[0139] The structure of the positive electrode plate 30 of Comparative Example 2 is as follows: Fig. 9As shown, the positive electrode plate 30 includes a positive electrode collector 31, a first positive electrode active material layer 32 and a second positive electrode active material layer 33 which are stacked in sequence, the first positive electrode active material layer 32 includes 96wt% of a first positive electrode active material, 2wt% of conductive carbon black and 2wt% of polyvinylidene fluoride, and the second positive electrode active material layer 33 includes 96wt% of a second positive electrode active material, 1wt% of conductive carbon black, 1wt% of carbon nanotubes and 2wt% of polyvinylidene fluoride.

[0140] Test Example 1

[0141] The positive electrode sheets of Examples 1 to 8 and Comparative Examples 1 to 2 were made into batteries, and the thickness of the positive electrode active material layer before cycling, the actual thickness of the positive electrode active material layer after cycling, the actual rebound rate and the capacity retention rate after 500 cycles were measured. The results are shown in Table 2.

[0142] The steps of making the positive electrode sheets of Examples 1 to 8 and Comparative Examples 1 to 2 into batteries are as follows:

[0143] (1) Preparation of negative electrode sheet

[0144] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are mixed in a weight ratio of graphite: acetylene black: styrene butadiene rubber: sodium carboxymethyl cellulose = 95:2:2:1, and an appropriate amount of deionized water is added and stirred to form a uniform negative electrode slurry; after coating the slurry on the negative electrode current collector copper foil, it is dried and cold pressed to obtain a negative electrode sheet.

[0145] (2) Preparation of electrolyte

[0146] In an argon atmosphere glove box with a water content of <10ppm, one or more solvents 1 and one or more solvents 2 are mixed in a weight ratio to obtain a mixed solvent, a certain mass of fully dried lithium salt LiPF6 is dissolved in the mixed solvent, and then an inorganic lithium salt additive is added thereto, and after stirring evenly, an electrolyte is obtained.

[0147] (3) Preparation of batteries

[0148] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried battery, and then the battery is obtained after vacuum packaging, standing, forming, shaping and other processes.

[0149] The prepared battery was subjected to a 45°C cycle performance test, and the specific steps are as follows:

[0150] At 45°C, the lithium-ion secondary battery is first charged to 4.3V at a constant current of 1C, then further charged to a current of 0.05C at a constant voltage of 4.3V, and then discharged to 3V at a constant current of 1C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The battery is subjected to multiple cycle charge and discharge tests in the above manner, and the discharge capacity of the 500th cycle is detected, and the capacity retention rate of the battery after the cycle is calculated by the following formula.

[0151] Capacity retention rate (%) of the battery after 500 cycles = (discharge capacity at the 500th cycle / discharge capacity at the 1st cycle) × 100%.

[0152] Actual rebound rate = (actual thickness of positive electrode active material layer after cycle - thickness of positive electrode active material layer before cycle) / thickness of positive electrode active material layer before cycle * 100%;

[0153] The actual thickness of the positive electrode active material layer after cycling is the measured value. The test method is as follows: take 10 pole pieces from different regions after cycling, use liquid nitrogen brittle fracture to obtain the cross section, place them under an optical electron microscope, magnify them 500 times (the field of view includes the upper and lower layers of active materials and the current collector), take 2-3 photos, test the thickness of the upper and lower pole pieces (if it is a double-layer coating, it needs to be measured separately), and similarly magnify them 1000 times and 3000 times to measure, record the pole piece thickness and take the average value;

[0154] The thickness of the positive electrode active material layer before cycling = the thickness of the first positive electrode active material layer + the thickness of the second positive electrode active material layer.

[0155] Table 2 Battery performance of positive electrode sheets of Examples 1 to 8 and Comparative Examples 1 to 2

[0156]

[0157] It can be seen from Examples 1 to 8 that the actual rebound rate of the positive electrode sheet of the present application is ≤8.3%, and the capacity retention rate of the prepared battery after 500 cycles is ≥92.1%.

[0158] From the comparison between Examples 1 and 3, and between Examples 2 and 4, it can be seen that when the positive electrode sheet includes multiple first positive electrode active material layers, each first positive electrode active material layer is individually coated with a second positive electrode active material layer, the actual rebound rate of the positive electrode sheet is lower, and the capacity retention rate of the manufactured battery after 500 cycles is higher.

[0159] From the comparison between Examples 1 to 4 and Comparative Example 1, it can be seen that when the first positive electrode active material and the second positive electrode active material are mixed and coated into a layer, the actual rebound rate of the positive electrode sheet is as high as 10.8%, and the capacity retention rate of the prepared battery after 500 cycles is as low as only 88.3%.

[0160] From the comparison of Examples 1 and 3 and Comparative Example 2, it can be seen that when the first positive electrode active material and the second positive electrode active material are coated in sequence to form a stacked first positive electrode active material layer and a second positive electrode active material layer, the actual rebound rate of the positive electrode sheet is as high as 9.3%, and the capacity retention rate of the prepared battery after 500 cycles is as low as only 91%.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: a positive electrode current collector, a first positive electrode active material layer and a second positive electrode active material layer, wherein the first positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the second positive electrode active material layer covers the first positive electrode active material layer; The first positive electrode active material layer includes a first positive electrode active material, the second positive electrode active material layer includes a second positive electrode active material, and a volume expansion rate of the first positive electrode active material is greater than a volume expansion rate of the second positive electrode active material.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet includes a plurality of the first positive electrode active material layers, and the plurality of the first positive electrode active material layers are all disposed on the surface of at least one side of the positive electrode current collector.

3. The positive electrode sheet according to claim 2, characterized in that: The plurality of first positive electrode active material layers are distributed at intervals, the width of the gap between two adjacent first positive electrode active material layers is 5 μm to 15 μm, and the gap between two adjacent first positive electrode active material layers is filled with the second positive electrode active material layer.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The volume expansion rate of the first positive electrode active material is 3% to 10%, and the volume expansion rate of the second positive electrode active material is 0.1% to 3%; Optionally, the volume expansion rate of the first positive electrode active material is 3% to 5%, and the volume expansion rate of the second positive electrode active material is 1 to 3%.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first positive electrode active material comprises a layered transition metal oxide and / or a spinel material; Optionally, the layered transition metal oxide includes LiCoO2, LiMnO2, LiNiO2, Li a’ Ni x Co y M 1 1-x-y O 2+d 、zLi2MnO3·(1-z)LiM 2 O2, wherein M 1 Including at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, La, M 2 Including at least one of Co, Ni, and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a'<1.2, -0.02≤d<0.02, 0<z<1; Optionally, the layered transition metal oxide comprises Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1.15 O2、Li(Ni 0.5 Co 0.2 Mn 0.3 ) 1.07 At least one of O2; Optionally, the spinel material includes LiNi c Mn 2-c O4, where 0≤c<2; Optionally, the spinel material includes lithium manganese oxide.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The second positive electrode active material includes an olivine structure phosphate material; Optionally, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of other metal elements except Fe, wherein 0≤a≤1.1, 0.3≤b≤1, 0≤m≤0.1, 0≤n≤0.1; Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge; Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The thickness of the first positive electrode active material layer is 40 μm to 160 μm, and the thickness of the second positive electrode active material layer coated on the surface of the first positive electrode active material layer is 40 μm to 160 μm.

8. A method for preparing a positive electrode sheet according to any one of claims 1 to 7, characterized in that: The preparation method of the positive electrode sheet comprises: coating a first positive electrode active material slurry on the surface of the positive electrode current collector, coating a second positive electrode active material slurry on the surface of the positive electrode current collector and the first positive electrode active material slurry, and drying and cold pressing to obtain the positive electrode sheet; The first positive electrode active material slurry includes a first positive electrode active material, and the second positive electrode active material slurry includes a second positive electrode active material.

9. A battery cell, characterized in that: The battery cell comprises the positive electrode sheet according to any one of claims 1 to 7, or the positive electrode sheet prepared by the method for preparing the positive electrode sheet according to claim 8.

10. A battery, characterized in that: The battery comprises the battery cell as claimed in claim 9.

11. An electrical device, characterized in that: The electrical device comprises the battery cell according to claim 9 or the battery according to claim 10, and the battery cell or the battery is used to provide electrical energy.

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