Positive pole piece, battery monomer, battery and electric device

Abstract

The invention provides a positive pole piece, a battery monomer, a battery and a power utilization device, and belongs to the technical field of batteries. The positive pole piece comprises a positive current collector, and a first positive active material layer and a second positive active material layer which are sequentially arranged on the surface of the current collector. The lattice volume shrinkage rate of the first positive electrode active material is greater than that of the second positive electrode active material, and the mass percentage of the binder in the first positive electrode active material layer is 0.8-1.5 wt%. According to the invention, the upper limit of the use amount of the binder in the first positive electrode active material layer is limited, so that the first positive electrode active material layer does not have more positive electrode active materials and other components, and the energy density and capacity exertion of the battery monomer or the whole battery are met; meanwhile, the lower limit of the use amount of the binder in the first positive electrode active material layer can be limited, the bonding performance of the first positive electrode active material layer with the positive electrode current collector and the second positive electrode active material layer can be improved, and the coating is prevented from falling off.

Description

Technical Field

[0001] 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

[0002] Positive electrode active materials with higher energy density, such as ternary materials, have the characteristics of low cost and long life, but insufficient safety performance and controllability of production process. Positive electrode active materials with lower energy density, such as lithium manganese phosphate, have the characteristic of high safety performance. The combination of positive electrode active materials with higher energy density and positive electrode active materials with lower energy density is conducive to the different positive electrode active materials to exert their advantageous properties.

[0003] 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, the battery cell or battery will rapidly decay in the early stage of the cycle. Separately coating the two positive electrode active materials to prepare two independent positive electrode active material layers requires consideration of the bonding effect between the different positive electrode active material layers. Summary of the invention

[0004] In view of the above problems, the present application provides a positive electrode plate, a battery cell, a battery and an electrical device, which can improve or avoid the shedding of positive electrode active materials and increase energy density.

[0005] In a first aspect, the present application provides a positive electrode sheet, comprising: a positive electrode current collector, and a first positive electrode active material layer and a second positive electrode active material layer sequentially disposed on the surface of the current collector, wherein the first positive electrode active material layer comprises a first positive electrode active material and a binder, and the second positive electrode active material layer comprises a second positive electrode active material. The lattice volume shrinkage rate of the first positive electrode active material is greater than the lattice volume shrinkage rate of the second positive electrode active material, and the mass percentage of the binder in the first positive electrode active material layer is 0.8wt% to 1.5wt%.

[0006] In the technical solution of the embodiment of the present application, the positive electrode sheet of the present application arranges the first positive electrode active material layer formed by the first positive electrode active material with a larger lattice volume shrinkage rate between the positive electrode current collector and the second positive electrode active material layer, which can reduce the risk of particle shedding caused by the large volume change of the first positive electrode active material during the battery cell or battery cycle deintercalation process, effectively reduce the probability of cycle diving, improve the battery cell or battery cycle capacity, and increase the cycle life. When the mass percentage of the binder in the first positive electrode active material layer is 0.8wt% to 1.5wt%, it can limit the upper limit of the amount of the binder in the first positive electrode active material layer, so that the first positive electrode active material layer can not have more positive electrode active materials and other components, meet the energy density and capacity of the battery cell or battery as a whole, and at the same time, it can also limit the lower limit of the amount of the binder in the first positive electrode active material layer, improve the bonding performance of the first positive electrode active material layer with the positive current collector and the second positive electrode active material layer, and prevent the coating from falling off.

[0007] In some embodiments, the first positive electrode active material layer includes 95.5 wt% to 97 wt% of the first positive electrode active material and 2.5 wt% to 3 wt% of the conductive agent. When the first positive electrode active material layer includes 95.5 wt% to 97 wt% of the first positive electrode active material and 2.5 wt% to 3 wt% of the conductive agent, the prepared battery or battery cell has a higher energy density and capacity.

[0008] In some embodiments, the positive electrode sheet satisfies the following conditions: Wherein, w1 = mass of the first positive electrode active material / (mass of the first positive electrode active material + mass of the second positive electrode active material), w2 = mass of the second positive electrode active material / (mass of the first positive electrode active material + mass of the second positive electrode active material), P1 is the particle compaction density of the first positive electrode active material at 3T, and P2 is the particle compaction density of the second positive electrode active material at 3T. When the positive electrode sheet meets the following conditions: When the compaction density of the two materials is different, the amount of the two materials can be limited to a certain range. It is necessary to select the first positive electrode active material and the second positive electrode active material with larger compaction density to improve the overall compaction level of the positive electrode sheet, and to maintain the content of the first positive electrode active material and the second positive electrode active material at a certain level to improve the electrical performance of the battery cell or battery, thereby effectively improving the energy density of the battery cell or battery.

[0009] In some embodiments, 0.5≤w1≤0.95, 0.05≤w2≤0.5. When 0.5≤w1≤0.95, 0.05≤w2≤0.5, the electrical performance of the battery cell or the battery can be improved.

[0010] In some embodiments, 3g / cc≤P1≤4g / cc, 2g / cc≤P2≤2.5g / cc. When 3g / cc≤P1≤4g / cc, 2g / cc≤P2≤2.5g / cc, the overall compaction level of the positive electrode sheet can be improved.

[0011] In some embodiments, the Dv50 of the first positive electrode active material is greater than the Dv50 of the second positive electrode active material. The first positive electrode active material layer formed by the first positive electrode active material with a larger particle size is combined with the positive electrode current collector, and the second positive electrode active material layer formed by the second positive electrode active material with a smaller particle size is combined with the first positive electrode active material layer. The second positive electrode active material layer can strengthen the adhesion effect of the first positive electrode active material layer, avoid or improve the shedding of the first positive electrode active material, and reduce the risk of battery cells or batteries diving.

[0012] In some embodiments, the first positive electrode active material contains Mn and Ni elements, and the positive electrode sheet satisfies the following conditions: Wherein, w(Mn) is the mass percentage of Mn element in the first positive electrode active material, w(Ni) is the mass percentage of Ni element in the first positive electrode active material, H1 is the thickness of the first positive electrode active material layer, and H2 is the thickness of the second positive electrode active material layer. Due to the synthesis process problems, some positive electrode active materials with lower energy density such as lithium manganese phosphate have a high water content and are difficult to completely remove. The thicker the second positive electrode active material layer and the higher the Ni content in the first positive electrode active material layer, the more likely the following side reaction will occur: the unremoved water in the positive electrode active materials with lower energy density such as lithium manganese phosphate reacts with the electrolyte to generate hydrogen fluoride, which will corrode the ternary materials with higher energy density, causing transition metal dissolution, affecting the service life and cycle stability of the battery cell or battery. When the positive electrode sheet meets the requirements of At the same time, it is possible to control the cost of the positive electrode sheet, as well as the safety and cycle stability of the battery cell or battery.

[0013] In some embodiments, the first positive electrode active material contains Ni and Co, 2wt%≤w(Co)≤15wt%, 20wt%≤w(Ni)≤55wt%. Wherein, w(Co) is the mass percentage of the Co element in the first positive electrode active material, and w(Ni) is the mass percentage of the Ni element in the first positive electrode active material. When 2wt%≤w(Co)≤15wt%, 20wt%≤w(Ni)≤55wt%, the first positive electrode active material can have both good energy density and rate cycle performance.

[0014] In some embodiments, the positive electrode sheet satisfies the following conditions: The performance differences of cathode active materials with different Ni contents are relatively large. Among the cathode active materials with the same Ni content, when the cathode electrode sheet meets the following conditions: it can not only reduce costs, improve low-temperature performance, but also improve the electrical conductivity and rate performance of the cathode active material.

[0015] In some embodiments, the chemical formula of the first cathode active material is Li a Ni b Co c M 1d M 2e O f R g . Among them, 0.75 ≤ a ≤ 1.2, 0.2 < b < 0.8, 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 Mn and / or Al, M2 is selected from any one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from any one or more of N, F, S, and Cl. The first cathode active material uses ternary materials and has a low Ni content. Using medium-low nickel ternary materials can improve safety performance when the energy meets the requirements.

[0016] In some embodiments, the first cathode active material is in single crystal form. In a high-voltage working environment, high-nickel polycrystals are prone to phase transformation during charge and discharge, causing anisotropic lattice changes, resulting in increased polarization, decreased cycle stability, capacity attenuation. At the same time, grain boundary cracking will occur in the material, microcracks or fragmentation will occur in secondary particles, and side reactions will occur between the farmer paintings and the electrolyte. Using the first cathode active material in single crystal form can slow down the impact of lithium ion insertion and extraction on particle fragmentation and cracking, and better exert the cycle stability and rate performance under high voltage. At the same time, the first cathode active material of medium-low nickel single crystal reduces the risk of side reactions with the electrolyte due to particle cracking, and effectively improves the gas generation risk of battery monomers or batteries.

[0017] In some embodiments, the chemical formula of the second cathode active material is Li 1+x Mn 1-y A y P 1-z E zO4. Wherein, -0.1≤x≤0.1, 0.001≤y≤0.5, 0.001≤z≤0.1. A is selected from any one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and E is selected from any one or more of B, Si, N, S, F, Cl and Br. The second positive electrode active material is a lithium manganese phosphate material, and when 0.001≤y≤0.5 is defined, the cycle stability of the battery cell or battery can be improved, and the voltage platform can be increased, thereby increasing the energy density of the battery cell or battery.

[0018] In a second aspect, the present application provides a battery cell, which includes the positive electrode plate in the above embodiment.

[0019] In a third aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

[0020] In a fourth aspect, the present application provides an electrical device, which includes the battery cell or battery in the above-mentioned embodiment, and the battery cell or battery is used to provide electrical energy.

[0021] 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

[0022] 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:

[0023] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0024] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0025] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0026] Figure 4 This is a cross-sectional view of the positive electrode sheet of some embodiments of the present application.

[0027] The reference numerals in the specific implementation manner are as follows:

[0028] 1000-Vehicle; 100-Battery; 200-Controller; 300-Motor;

[0029] 10-box; 11-first part; 12-second part;

[0030] 20 - battery cell; 21 - end cap; 22 - housing; 23 - electrode assembly;

[0031] 30 - positive electrode plate; 31 - positive electrode current collector; 32 - first positive electrode active material layer; 33 - second positive electrode active material layer. DETAILED DESCRIPTION

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Positive electrode active materials with higher energy density, such as ternary materials, have the characteristics of low cost and long life, but insufficient safety performance and controllability of production process. Positive electrode active materials with lower energy density, such as lithium manganese phosphate, have the characteristic of high safety performance. The combination of positive electrode active materials with higher energy density and positive electrode active materials with lower energy density is conducive to the different positive electrode active materials to exert their advantageous properties.

[0042] 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, the battery cell or battery will rapidly decay in the early stage of the cycle. Separately coating the two positive electrode active materials to prepare two independent positive electrode active material layers requires consideration of the bonding effect between the different positive electrode active material layers.

[0043] Based on the above considerations, in order to improve or avoid the problem of positive electrode active material shedding, the positive electrode sheet of the present application arranges the first positive electrode active material layer formed by the first positive electrode active material with a larger lattice volume shrinkage rate between the positive electrode current collector and the second positive electrode active material layer, which can reduce the risk of particle shedding of the first positive electrode active material due to large volume changes during the battery cell or battery cycle deintercalation process, effectively reduce the probability of cycle diving, improve the battery cell or battery cycle capacity, and increase the cycle life. At the same time, the mass percentage of the binder in the first positive electrode active material layer is selected to be 0.8wt% to 1.5wt%, which can limit the upper limit of the amount of the binder in the first positive electrode active material layer, so that the first positive electrode active material layer can not have more positive electrode active materials and other components, meet the energy density and capacity of the battery cell or battery as a whole, and at the same time, it can also limit the lower limit of the amount of the binder in the first positive electrode active material layer, improve the bonding performance of the first positive electrode active material layer with the positive current collector and the second positive electrode active material layer, and prevent the coating from shedding.

[0044] Moreover, there is a large difference in particle size between some positive electrode active materials with higher energy density such as ternary materials and positive electrode active materials with lower energy density such as lithium manganese phosphate. Among them, the particle size of positive electrode active materials with higher energy density such as ternary materials is one order of magnitude larger than the particle size of positive electrode active materials with lower energy density such as lithium manganese phosphate. The two positive electrode active materials are coated in layers, and the first positive electrode active material layer formed by the positive electrode active material with higher energy density such as the ternary material is combined with the positive electrode current collector, and the second positive electrode active material layer formed by the positive electrode active material with lower energy density such as lithium manganese phosphate is combined with the first positive electrode active material layer. The second positive electrode active material layer can have a coating effect on the large particles of positive electrode active material on the surface of the first positive electrode active material layer.

[0045] At the same time, the first positive electrode active material layer is combined with the positive electrode current collector, and the second positive electrode active material layer is combined with the first positive electrode active material layer. During the cold pressing process of the electrode sheet, the small particles of the second positive electrode active material directly contact the cold pressing roller, which avoids the direct action of the cold pressing roller on the large particles of the first positive electrode active material, reducing the risk of cold pressing damage to the large particles of the first positive electrode active material.

[0046] In addition, since the first positive electrode active material with a larger lattice volume shrinkage rate may be a ternary material, side reactions are likely to occur when the ternary material comes into contact with water, hydrogen fluoride and electrolyte. A layered coating method is adopted, and the first positive electrode active material layer formed by the positive electrode active material with a higher energy density such as the ternary material is combined with the positive electrode current collector, and the second positive electrode active material layer formed by the positive electrode active material with a lower energy density such as lithium manganese phosphate is combined with the first positive electrode active material layer. This can avoid large-area side reactions between the first positive electrode active material and water, hydrogen fluoride and electrolyte, thereby optimizing the electrochemical performance of the battery cell or battery.

[0047] 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 can be in the form of a battery module or a battery pack. The battery generally includes a battery box for encapsulating multiple battery cells, and the battery box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Please refer to Figure 3 , Figure 3 The first battery cell 20 is a schematic diagram of the exploded 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.

[0060] 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.

[0061] 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.

[0062] The electrode assembly 23 is a component in the battery cell 20 where electrochemical reactions occur. One or more electrode assemblies 23 may be included 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 lug. The positive and negative electrode lugs may be located together at one end of the main body or at both ends of the main body, respectively. During the charge and discharge process of the battery, the positive and negative electrode active materials react with the electrolyte, and the lugs connect the electrode terminals to form a current loop.

[0063] According to some embodiments of the present application, please refer to Figure 4 , Figure 4 It is a cross-sectional view of the positive electrode sheet 30 according to some embodiments of the present application.

[0064] The positive electrode sheet 30 includes: a positive electrode current collector 31, and a first positive electrode active material layer 32 and a second positive electrode active material layer 33 sequentially disposed on the surface of the current collector, the first positive electrode active material layer 32 includes a first positive electrode active material and a binder, and the second positive electrode active material layer 33 includes a second positive electrode active material. The lattice volume shrinkage rate of the first positive electrode active material is greater than the lattice volume shrinkage rate of the second positive electrode active material, and the mass percentage of the binder in the first positive electrode active material layer 32 is 0.8wt% to 1.5wt%.

[0065] The lattice volume shrinkage of the first positive electrode active material and the second positive electrode active material can be measured by the following method:

[0066] A soft-pack laminated battery is made by using the first positive electrode active material or the second positive electrode active material separately. The battery is charged to 4.4V at 0.5C0 at 2.5-4.4V at a constant temperature of 25°C, and then charged at a constant voltage of 4.4V to a current ≤0.05C0. The battery is then disassembled to remove the positive electrode sheet and an XRD test is performed. The a and c axis (material cell parameters) values ​​required for the material unit cell volume in the fully charged state can be obtained through XRD data and RietVeld software refinement. Vfull charge = a^2×c×sin120°. The same process is used to confirm the condition of the fresh positive electrode sheet to obtain Vfresh. The lattice volume shrinkage rate C1 = (Vfresh-Vfull charge) / Vfresh.

[0067] As an example, the mass percentage of the binder in the first positive active material layer 32 may be 0.8 wt %, 0.9 wt %, 1 wt %, 1.1 wt %, 1.2 wt %, 1.3 wt %, 1.4 wt % or 1.5 wt %.

[0068] When the first positive active material layer 32 includes a first positive active material, a conductive agent, and a binder, the mass percentage of the binder in the first positive active material layer 32 = m(binder) / (m(first positive active material)+m(conductive agent)+m(binder)).

[0069] Among them, m(binder) is the mass of the binder in the first positive electrode active material layer 32, m(first positive electrode active material) is the mass of the first positive electrode active material in the first positive electrode active material layer 32, and m(conductive agent) is the mass of the conductive agent in the first positive electrode active material layer 32.

[0070] The positive electrode sheet 30 of the present application arranges the first positive electrode active material layer 32 formed by the first positive electrode active material with a large lattice volume shrinkage rate between the positive electrode current collector 31 and the second positive electrode active material layer 33, which can reduce the risk of particle shedding caused by the large volume change of the first positive electrode active material during the battery cell or battery cycle deintercalation process, effectively reduce the probability of cycle diving, improve the battery cell or battery cycle capacity, and increase the cycle life. When the mass percentage of the binder in the first positive electrode active material layer 32 is 0.8wt% to 1.5wt%, it can limit the upper limit of the amount of the binder in the first positive electrode active material layer 32, so that the first positive electrode active material layer 32 can not only have more positive electrode active materials and other components, but also meet the energy density and capacity of the battery cell or battery as a whole, and at the same time, it can also limit the lower limit of the amount of the binder in the first positive electrode active material layer 32, improve the bonding performance of the first positive electrode active material layer 32 with the positive electrode current collector 31 and the second positive electrode active material layer 33, and prevent the coating from falling off.

[0071] Optionally, the lattice volume shrinkage rate of the first positive electrode active material is 2% to 4%, and the lattice volume shrinkage rate of the second positive electrode active material is 6% to 10%.

[0072] According to some embodiments of the present application, optionally, the first positive electrode active material layer 32 includes 95.5 wt % to 97 wt % of the first positive electrode active material and 2.5 wt % to 3 wt % of the conductive agent.

[0073] As an example, the first positive active material layer 32 may include 95.5wt%, 95.6wt%, 95.7wt%, 95.8wt%, 95.9wt%, 96wt%, 96.1wt%, 96.2wt%, 96.3wt%, 96.4wt%, 96.5wt%, 96.6wt%, 96.7wt%, 96.8wt%, 96.9wt% or 97wt% of the first positive active material, and 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3wt% of the conductive agent.

[0074] When the first positive active material layer 32 includes 95.5 wt % to 97 wt % of the first positive active material and 2.5 wt % to 3 wt % of the conductive agent, the prepared battery or battery cell has higher energy density and capacity.

[0075] According to some embodiments of the present application, optionally, the positive electrode plate 30 satisfies the following conditions: Wherein, w1=mass of the first positive electrode active material / (mass of the first positive electrode active material+mass of the second positive electrode active material), w2=mass of the second positive electrode active material / (mass of the first positive electrode active material+mass of the second positive electrode active material), P1 is the particle compaction density of the first positive electrode active material at 3T, and P2 is the particle compaction density of the second positive electrode active material at 3T.

[0076] As an example, The value of can be 0.32, 0.35, 0.38, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 16.5.

[0077] It should be noted that the present application does not limit the method for detecting the compacted density of particles. The present application embodiment provides a method for detecting the compacted density of particles:

[0078] Place a certain amount of powder in a special compaction mold, place the mold on a compaction density instrument, set the pressure to 4T, and read the thickness of the powder under a pressure of 4T on the device. Calculate the compaction density through density = mass / volume.

[0079] When the positive electrode sheet 30 meets the following conditions: When the amount of the two materials with different compaction densities can be limited to a certain range, it is necessary to select the first positive electrode active material and the second positive electrode active material with larger compaction density to improve the overall compaction level of the positive electrode plate 30, and to maintain the content of the first positive electrode active material and the second positive electrode active material at a certain level to improve the electrical performance of the battery cell or battery, thereby effectively improving the energy density of the battery cell or battery.

[0080] According to some embodiments of the present application, optionally, 0.5≤w1≤0.95, 0.05≤w2≤0.5.

[0081] As examples, the value of w1 may be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95.

[0082] The value of W2 can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.

[0083] When 0.5≤w1≤0.95 and 0.05≤w2≤0.5, the electrical performance of the battery cell or the battery can be improved.

[0084] Optionally, 0.6≤w1≤0.8, 0.2≤w2≤0.4.

[0085] According to some embodiments of the present application, optionally, 3g / cc≤P1≤4g / cc, 2g / cc≤P2≤2.5g / cc.

[0086] As an example, the value of P1 can be 3 g / cc, 3.1 g / cc, 3.2 g / cc, 3.3 g / cc, 3.4 g / cc, 3.5 g / cc, 3.6 g / cc, 3.7 g / cc, 3.8 g / cc, 3.9 g / cc or 4 g / cc.

[0087] The value of P2 may be 2 g / cc, 2.1 g / cc, 2.2 g / cc, 2.3 g / cc, 2.4 g / cc or 2.5 g / cc.

[0088] When 3 g / cc≤P1≤4 g / cc and 2 g / cc≤P2≤2.5 g / cc, the overall compaction level of the positive electrode sheet 30 can be improved.

[0089] According to some embodiments of the present application, optionally, Dv50 of the first positive electrode active material is greater than Dv50 of the second positive electrode active material.

[0090] The first positive electrode active material layer 32 formed by the first positive electrode active material with a larger particle size is combined with the positive electrode current collector 31, and the second positive electrode active material layer 33 formed by the second positive electrode active material with a smaller particle size is combined with the first positive electrode active material layer 32. The second positive electrode active material layer 33 can enhance the adhesion effect of the first positive electrode active material layer 32, avoid or improve the shedding of the first positive electrode active material, and reduce the risk of battery cells or batteries diving.

[0091] Optionally, the Dv50 of the first positive electrode active material is 3 μm to 5 μm, and the Dv50 of the second positive electrode active material is 0.5 μm to 1.2 μm.

[0092] According to some embodiments of the present application, optionally, the first positive electrode active material contains Mn element and Ni element, and the positive electrode plate 30 satisfies the following conditions:

[0093]

[0094] Wherein, w(Mn) is the mass percentage of the Mn element in the first positive electrode active material, w(Ni) is the mass percentage of the Ni element in the first positive electrode active material, H1 is the thickness of the first positive electrode active material layer 32 , and H2 is the thickness of the second positive electrode active material layer 33 .

[0095] As an example, The value of can be 0.025, 0.03, 0.05, 0.08, 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 17.5 or 17.8.

[0096] Since some positive electrode active materials with lower energy density, such as lithium manganese phosphate, have higher water content due to the synthesis process and are difficult to completely remove, the thicker the second positive electrode active material layer 33 is and the higher the Ni content in the first positive electrode active material layer 32 is, the more likely the following side reactions will occur: the unremoved water in the positive electrode active materials with lower energy density, such as lithium manganese phosphate, reacts with the electrolyte to generate hydrogen fluoride, which will corrode the ternary materials with higher energy density, causing transition metal dissolution and affecting the service life and cycle stability of the battery cell or battery. When the positive electrode sheet 30 meets When the positive electrode sheet 30 is reduced in size, the cost of the positive electrode sheet 30 and the safety and cycle stability of the battery cell or battery can be controlled.

[0097] Optionally, 5wt%≤w(Ni)≤25wt%, 20wt%≤w(Ni)≤55wt%.

[0098] Optionally, 20 μm≤H1≤70 μm, 5 μm≤H2≤60 μm.

[0099] Optionally, 25 μm≤H1≤55 μm, 20 μm≤H2≤50 μm.

[0100] Optionally, the thickness of the positive electrode current collector 31 is 10 μm to 15 μm.

[0101] Optionally, the thickness of the positive electrode current collector 31 is 13 μm.

[0102] According to some embodiments of the present application, optionally, the first positive electrode active material contains Ni and Co, 2wt%≤w(Co)≤15wt%, 20wt%≤w(Ni)≤55wt%, wherein w(Co) is the mass percentage of the Co element in the first positive electrode active material, and w(Ni) is the mass percentage of the Ni element in the first positive electrode active material.

[0103] As an example, the value of w(Co) can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0104] The value of w(Ni) can be 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%, 54wt% or 55wt%.

[0105] When 2wt%≤w(Co)≤15wt% and 20wt%≤w(Ni)≤55wt%, the first positive electrode active material can have both good energy density and rate cycle performance.

[0106] Optionally, 3wt%≤w(Co)≤12.5wt%, 25wt%≤w(Ni)≤50wt%.

[0107] Optionally, 30wt%≤w(Ni)≤45wt%.

[0108] Optionally, 30wt%≤w(Ni)≤40wt%.

[0109] According to some embodiments of the present application, optionally, the positive electrode plate 30 satisfies the following conditions:

[0110]

[0111] As an example, the value of w(Co) / w(Ni) may be 0.025, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.42, or 0.44.

[0112] The performance of positive electrode active materials with different Ni contents varies greatly. Among the positive electrode active materials with the same Ni content, when the positive electrode sheet 30 meets the following conditions: It can not only reduce costs and improve low-temperature performance, but also improve the conductivity and rate performance of the positive electrode active material.

[0113] Optionally,

[0114] Optionally,

[0115] According to some embodiments of the present application, optionally, the chemical formula of the first positive electrode active material is Li a Ni b Co c M 1d M 2e O f R g . Wherein, 0.75 ≤ a ≤ 1.2, 0.2 < b < 0.8, 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 Mn and / or Al, M2 is selected from any one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R is selected from any one or more of N, F, S, and Cl.

[0116] The first positive electrode active material is a ternary material with a low Ni content. Using a medium-low nickel ternary material can improve the safety performance while meeting the energy requirements.

[0117] According to some embodiments of the present application, optionally, the first positive electrode active material is in a single crystal form.

[0118] In a high-voltage working environment, high-nickel polycrystals are prone to phase transformation during charge and discharge, causing anisotropic lattice changes, resulting in increased polarization, decreased cycle stability, capacity attenuation, and at the same time, grain boundary cracking, microcracks or fragmentation of secondary particles will occur in the material, and side reactions will occur between the farmer painting and the electrolyte. Using the first positive electrode active material in a single crystal form can slow down the impact of lithium ion deintercalation on particle fragmentation and cracking, and better exert the cycle stability and rate performance at high voltages. At the same time, the first positive electrode active material of medium-low nickel single crystal reduces the risk of side reactions with the electrolyte due to particle cracking, and effectively improves the gas generation risk of the battery cell or the battery.

[0119] According to some embodiments of the present application, optionally, the chemical formula of the second positive electrode active material is Li 1+x Mn 1-y A y P 1- z E z O4. Wherein, -0.1 ≤ x ≤ 0.1, 0.001 ≤ y ≤ 0.5, 0.001 ≤ z ≤ 0.1. A is selected from any one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and E is selected from any one or more of B, Si, N, S, F, Cl, and Br.

[0120] When the second positive electrode active material is a lithium manganese phosphate material and is limited to 0.001≤y≤0.5, the cycle stability of the battery cell or battery can be improved, and the voltage platform can be increased, thereby improving the energy density of the battery cell or battery.

[0121] Optionally, 0.2≤y≤0.5.

[0122] Optionally, the second positive electrode active material has a coating layer on its surface, the coating layer is made of pyrophosphate, phosphate or carbon, and the number of coating layers is ≥1.

[0123] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. 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 feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0124] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0125] The following is a further detailed description of a positive electrode plate of the present application in conjunction with an embodiment.

[0126] The parameters of the positive electrode sheets of Examples 1 to 14 of the present application and Comparative Examples 1 to 2 are shown in Tables 1 to 3.

[0127] Table 1 Parameters of the first part of the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2

[0128]

[0129] Table 2 Second part parameters of positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2

[0130]

[0131]

[0132] Table 3 Parameters of the third part of the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2

[0133]

[0134] The first positive electrode active materials of Examples 1 to 14 and Comparative Examples 1 to 2 are all in single crystal form. The conductive agent in the first positive electrode active material layer of Examples 1 to 14 and Comparative Examples 1 to 2 is conductive carbon black, and the binder is polyvinylidene fluoride.

[0135] The positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 were prepared by the following method:

[0136] S1. Preparing the first positive electrode active material slurry

[0137] A first positive electrode active material, conductive carbon black and polyvinylidene fluoride are mixed to obtain a first mixture, N-methylpyrrolidone is added to the first mixture and stirred to obtain a first positive electrode active material slurry, wherein the viscosity of the first positive electrode active material slurry is 3000 mPa·S to 10000 mPa·S.

[0138] S2. Preparation of second positive electrode active material slurry

[0139] 96.7 wt % of the second positive electrode active material, 0.4 wt % of conductive carbon black and 2.9 wt % of polyvinylidene fluoride are mixed to prepare a second mixture, N-methylpyrrolidone is added to the second mixture and stirred to obtain a second positive electrode active material slurry, and the viscosity of the second positive electrode active material slurry is 3000 mPa·S to 10000 mPa·S.

[0140] S3. Preparation of positive electrode sheet

[0141] The first positive electrode active material slurry is coated on the surface of an aluminum foil with a thickness of 13 μm, the second positive electrode active material slurry is coated on the surface of the first positive electrode active material slurry, and the positive electrode sheet is obtained by drying and cold pressing.

[0142] Detection method of the content of the element to be tested:

[0143] Take about 0.4g of dry positive electrode sheet or about 1g of wet positive electrode sheet (both accurate to 0.0001g) in a 25ml beaker, add 2ml~5ml nitric acid, leave overnight, then place on a hot plate, heat at about 100℃ (use a voltage-regulating transformer to adjust the input voltage and temperature control) until the positive electrode sheet is digested, then add 0.5ml perchloric acid, heat and digest 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, and dilute to an appropriate volume depending on the content of the element to be measured, then start testing on the ICP-OES test instrument.

[0144] Test Example 1

[0145] The content of the elements to be measured in the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 was measured, and the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 were made into soft-pack laminated batteries. The positive electrode sheet bonding force, capacity retention rate after 500 cycles and battery cell capacity of the soft-pack laminated batteries were measured. The results are shown in Table 4.

[0146] The method for making the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 into soft-pack laminated batteries is as follows:

[0147] (1) Preparation of negative electrode sheet

[0148] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water, with the mass ratio of graphite: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent being 90:2:3:5, and stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·S. The slurry is coated on a copper foil and dried to form a negative electrode sheet.

[0149] (2) Preparation of soft-pack laminated batteries

[0150] The prepared positive electrode sheet, negative electrode sheet and separator (polyethylene (PE) porous polymer film) are made into corresponding battery cells according to the Z-shaped stacking structure, and the battery cells are vacuum dried at 170°C for 12 hours, and then the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses an aluminum tab and the negative electrode uses a copper tab. The positive and negative electrode tabs are located on the same side of the battery cell. The battery cell after the tab welding is placed in an aluminum-plastic film of a suitable size for top-side sealing packaging. The top-side sealing temperature is 145°C, and the electrolyte is injected (the electrolyte is 1mol / LLiPF6 / (ethylene carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC)) (volume ratio 1:1:1)+5wt.% fluoroethylene carbonate (FEC)), and the prepared soft-pack laminated battery is obtained by standing, forming, aging, exhausting, double sealing, and capacity testing.

[0151] Testing method for bonding strength of positive electrode sheet:

[0152] Take the electrode to be tested, use a blade to cut a sample with a width of 30mm and a length of 100-160mm, and stick the special double-sided tape on the steel plate, with a tape width of 20mm and a length of 90-150mm. Stick the cut electrode sample on the double-sided tape with the test side facing down. Insert a paper tape with a width equal to the electrode and a length greater than the length of the sample by 80-200mm under the electrode and fix it with wrinkle glue. Turn on the power of the Sansi tensile testing machine, the indicator light is on, and adjust the limit block to the appropriate position. Fix the end of the steel plate without the electrode with the lower clamp. Fold the paper tape upwards and fix it with the upper clamp. Use the "up" and "down" buttons on the manual controller attached to the tensile testing machine to adjust the position of the upper clamp and start the tensile test.

[0153] Detection method of capacity retention rate after 500 cycles:

[0154] The prepared soft-pack laminated battery is charged to 4.4V at 0.33C0 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 ≤ 0.05C0, left to stand for 5 minutes, and then discharged to 2.5V at 0.33C0. The capacity is recorded as Cn (n = 1, 2, 3 ...). The above operation is repeated. The capacity retention rate after 500 cycles = C 500 / C3, where C3 is the cell capacity at the 3rd cycle and C500 is the cell capacity at the 500th cycle.

[0155] Battery capacity detection method:

[0156] The cell capacity is the cell capacity of the third cycle, which is C3.

[0157] Table 4 Adhesion force of positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 and performance of the prepared soft-pack laminated batteries

[0158] project Adhesion force(N) Battery capacity (Ah) Capacity retention after 500 cycles Example 1 32.2 54.38 95.20％ Example 2 28.9 54.67 94.10％ Example 3 31.5 54.54 94.90％ Example 4 32.7 54.33 94.70％ Example 5 32.9 54.21 93.90％ Comparative Example 1 26.9 54.96 86.40％ Comparative Example 2 33.1 53.98 94.28％ Example 6 32.2 54.26 93.80％ Example 7 32.2 54.31 94.20％ Example 8 32.2 54.38 95.10％ Example 9 32.2 54.68 94.80％ Example 10 32.2 54.82 94.60％ Embodiment 11 32.2 54.91 94.50％ Example 12 32.2 54.38 94.10％ Embodiment 13 32.2 54.92 93.80％ Embodiment 14 32.2 54.76 91.32％

[0159] It can be seen from Table 4 that when the mass percentage of the binder in the first positive electrode active material layer is 0.8wt% to 1.5wt%, the bonding force of the positive electrode sheet is 28.9N to 32.9N, the capacity of the prepared soft-pack laminated battery is 54.21Ah to 54.92Ah, and the capacity retention rate after 500 cycles at 25°C is 91.32% to 95.2%; when the mass percentage of the binder in the first positive electrode active material layer is less than 0.8wt%, the bonding force of the positive electrode sheet is only 26.9N, and the capacity retention rate after 500 cycles at 25°C is only 86.4%; when the mass percentage of the binder in the second positive electrode active material layer is greater than 1.5wt%, the capacity of the prepared soft-pack laminated battery is only 53.98Ah.

[0160] 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, and a first positive electrode active material layer and a second positive electrode active material layer sequentially arranged on the surface of the current collector, wherein the first positive electrode active material layer comprises a first positive electrode active material and a binder, and the second positive electrode active material layer comprises a second positive electrode active material; The lattice volume shrinkage rate of the first positive electrode active material is greater than the lattice volume shrinkage rate of the second positive electrode active material, and the mass percentage of the binder in the first positive electrode active material layer is 0.8 wt % to 1.5 wt %.

2. The positive electrode sheet according to claim 1, characterized in that: The first positive electrode active material layer includes 95.5 wt % to 97 wt % of a first positive electrode active material and 2.5 wt % to 3 wt % of a conductive agent.

3. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet meets the following conditions: Wherein, w1=mass of the first positive electrode active material / (mass of the first positive electrode active material+mass of the second positive electrode active material), w2=mass of the second positive electrode active material / (mass of the first positive electrode active material+mass of the second positive electrode active material), P1 is the particle compaction density of the first positive electrode active material at 3T, and P2 is the particle compaction density of the second positive electrode active material at 3T.

4. The positive electrode sheet according to claim 3, characterized in that: 0.5≤w1≤0.95, 0.05≤w2≤0.

5.

5. The positive electrode sheet according to claim 3, characterized in that: 3g / cc≤P1≤4g / cc, 2g / cc≤P2≤2.5g / cc.

6. The positive electrode sheet according to claim 3, characterized in that: The Dv50 of the first positive electrode active material is greater than the Dv50 of the second positive electrode active material.

7. The positive electrode sheet according to claim 1, characterized in that: The first positive electrode active material contains Mn and Ni elements, and the positive electrode sheet meets the following conditions: Wherein, w(Mn) is the mass percentage of the Mn element in the first positive electrode active material, w(Ni) is the mass percentage of the Ni element in the first positive electrode active material, H1 is the thickness of the first positive electrode active material layer, and H2 is the thickness of the second positive electrode active material layer.

8. The positive electrode sheet according to claim 1, characterized in that: The first positive electrode active material contains Ni and Co, 2wt%≤w(Co)≤15wt%, 20wt%≤w(Ni)≤55wt%; Wherein, w(Co) is the mass percentage of the Co element in the first positive electrode active material, and w(Ni) is the mass percentage of the Ni element in the first positive electrode active material.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode sheet meets the following conditions:

10. The positive electrode sheet according to claim 1, characterized in that: The chemical formula of the first positive electrode active material is Li a Ni b Co c M 1d M 2e O f R g ; Among them, 0.75≤a≤1.2, 0.2<b<0.8, 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 Mn and / or Al, M2 is selected from any one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R is selected from any one or more of N, F, S, and Cl.

11. The positive electrode sheet according to claim 10, characterized in that: The first positive electrode active material is in a single crystal form.

12. The positive electrode sheet according to claim 1, characterized in that: The chemical formula of the second positive electrode active material is Li 1+x Mn 1-y A y P 1-z E z O4; Among them, -0.1≤x≤0.1, 0.001≤y≤0.5, 0.001≤z≤0.1; A is selected from any one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and E is selected from any one or more of B, Si, N, S, F, Cl and Br.

13. A battery cell, characterized in that: The battery cell comprises the positive electrode sheet as claimed in any one of claims 1 to 12.

14. A battery, characterized in that: The battery comprises the battery cell as claimed in claim 13.

15. An electrical device, characterized in that: The electrical device comprises the battery cell according to claim 13 or the battery according to claim 14, and the battery cell or the battery is used to provide electrical energy.

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